EAB CONTROL COST MANUAL

(Third Edition)

EPA 450/5-87-001A

U.S. Environmental Protection Agency

Office of Air .and Radiation

Office of Air Qu~lity Planning and Standards

Economic Analysis Branch

Research Triangle Park, North Carolina 27711

February 1987

REPROOUCED BY

U.S. DEPARTMENTOFCOMMERCE

NATIONAL TECHNICAl

INFORMATION SERVICE

SPRINGFIELD, VA 22161

PB8? ·166583

1111111111111111111111111111111111111

1. REPORT NO.

EPA-450/5-87-001A

TECHNICAL REPORT DATA

(Please read Instructions on the reverse before completing)

3. RECIPIENT'S ACCESSION NO.

p:s87-166583/AS

4. TITLE AND SUBTITLE

EAB Control Cost Manual (Third Edition)

5. REPORT DATE

February 1987

6. PERFORMING ORGANIZATION CODE

11. CONTRACT/GRANT NO.

8. PERFORMING ORGANIZATION REPORT NO.

I

7,AUTHOR(S) W.M. Vatavuk (principal), R.E. Jenkins, V.S.

Katari','cW.L.· Kloti, J.D~ McKenna~ R.L.·,Stallings JH;f.

~~~~g~~fuJ bRgi~TI~1 ~N NAM'E AN 0 ADD RESS . - ----~·.......-1-:1-=-O.-;:P:-::R:-::O:-::G"=R~A-:-:M;-;E:-:-L-=E-:-:M:-:=E-:-:N':;'T'7N:-::O,.....------1

Office of Air and Radiation

Office of Air Quality Planning and Standards

Strategies and Air Standards Division

Economic Analysis Branch UI"\ ," " .,...., n .1. ..f' "~~11

13. TYPE OF REPORT AND PERIOD COVERED

14. SPONSORING AGENCY CODE

Same as box 9.

.. 15. 5,l..!PP.LEMENT./'R,¥ NqTES prlnClpal ~OntaCt : William M. Vatavuk (Comm'l #: 919-541-5309; FTS # 629-5309)

16. ABSTap..CT •• d d d f 1 d InlS report provldes deslgn proce ures an current cost ata or common y use

"add-on" air pollution control devices and auxiliary equipment. It supercedes two

EPA reports, both entitled Capital and Operatinq Costs of Selected Air Pollution

Control Systems: EPA-450/3-76-U14 tMay 1976) and ltS revlslon, EPA-450/5-8U-UU,

(December 1978). This issuance of the Manual contains five sections. Sections 1

("Introduction") and 2 ("Manual Estimating Methodology") present, respectively,

introductory material and a compr~hensive, general procedure for developing "study".

(+ 30% accurate) control cost estimates. Sections 3 to 5 discuss the applications,

design, and cost estimating procedures and data for thermal and catalytic incinerators,

carbon adsorbers, and fabric filters, respectively. This issuance of the Manual

will be followed by others as more sections are completed.

17. KEY WORDS AND DOCUMENT ANALYSIS

a. DESCRIPTORS

Costs

Manual

Fabric fi lters

Thermal incinerators

Catalytic incinerators

Carbon adsorbers

b.IDENTIFIERS/OPEN ENDED TERMS c. COSATI Field/Group

Cost estimation technique~

Capital costs

Annual costs

Control device design and

operation Air pollution control

systems

18. DISTRIBUTION STATEMENT

Un 1imited

19. SECURITY CLASS (This Report)

Unclassified

20. SECURITY CLASS (This page)

Unclassified

21. NO. OF PAGES

184

22. PRICE

EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION IS OBSOLETE

NOTE:

o A preliminary draft of this Manual was distributed in November 1986.

Since then, extensive revisions have been made to Section 5 ("Fabric

Filters") and minor changes to Sections 3 ("Thermal and Catalytic

Incinerators") and 4 ("Carbon Adsorbers"). No revisions were made to

Sections 1 and 2, however.

o The pages in this Manual have been fastened together. If desired,

they may be unfastened, hole-punched, and reassembled in a three-ring

binder. This will facilitate the addition of updates when they become

available.

OVERVIEW OF THE MANUAL*

Section

Completion

Date

Date To Be

Completed

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

INTRODUCTION

MANUAL ESTIMATING METHODOLOGY

THERMAL AND CATALYTIC INCINERATORS

CARBON ADSORBERS

FABRIC FILTERS

ELECTROSTATIC PRECIPITATORS

DUCTWORK

FANS

FLARES

REFRIGERATION UNITS

STACKS

PUMPS

GAS ABSORBERS

VENTURI SCRUBBERS

WASTEWATER TREATMENT FACILITIES**

CAPTURE HOODS

MECHANICAL COLLECTORS

PRECOOLERS (SPRAY CHAMBERS AND QUENCHERS)

SCREW CONVEYORS

COMPREHENSIVE SAMPLE COST-ESTIMATING PROBLEMS

ESCALATING COSTS

1/86

1/86

7/86

7/86

9/86

FY 87

FY 87

FY 87

FY 87

FY 87

FY 88

FY 88

FY 88

FY 88

FY 88

Not Established

Not Established

Not Established

Not Established

Not Established

Not Established

APPENDIX A COMPOUND INTEREST FACTORS

APPENDIX B EQUIPMENT COST INDICIES

APPENDIX C CONTROL EQUIPMENT VENDORS

Not Established

Not Established

Not Established

*For more information about the Manual, contact Albert Wehe, Robert PahelShort, or William Vatavuk (at FTS:629-5610).

**These are facilities that would be required to treat only the wastewater

generated by venturi scrubbers, quenchers, spray chambers, and gas absorbers.

TABLE OF CONTENTS

Section

1 INTRODUCTION

1.1 Role of Cost in the Setting of Regulations

1.2 Purpose of Manual

1.3 Organization of the Manual

1.4 "Uniqueness" of the Manual

References for Section 1

1-1

1-2

1-2

.1-5

1-7

2 MANUAL ESTIMATING METHODOLOGY

2.1 Types of Cost Estimates 2-1

2.2 Cost Categories Defined 2-3

2.2.1 Elements of Total Capital Investment 2-3

2.2.2 Elements of Total Annual Cost 2-7

2.3 Engineering Economy Concepts 2-9

2.3.1 Time Value of Money 2-9

2.3.2 Cash Flow 2-9

2.3.3 Annualization Methods 2-14

2.4 Estimating Procedure 2-15

2.4.1 Facility Parameters and Regulatory Options 2-15

2.4.2 Control System Design 2-17

2.4.3 Sizing the Control System 2-18

2.4.4 Estimating Total Capital Investment 2-20
TABLE OF CONTENTS

Section

2.4.5 Retrofit Cost Considerations

2.4.6 Estimating Annual Costs

References for Section 2

3 THERMAL AND CATALYIC INCINERATORS

3.1 Process Description

3.1.1 Elements of Combustion

3.1.2 Types of Incinerators

3.2 Design Procedure

3.2.1 Design and Operating Features

3.2.2 Design Cal cul ati ons

3.3 Estimating Total Capital Investment

3.3.1 Thermal Incinerator Equipment Costs

3.3.2 Catalytic Incinerator Equipment Costs

2-23

2-25

2-33

3-1

3-1

3-6

3-8

3-8

3-10

3-23

3-24

3-27

3.3.3 Total Capital Investment for Incinerators 3-29

3.4 Estimating Total Annual Cost

3.4.1 Direct Annual Costs

3.4.2 Indirect Annual Costs

References for Section 3

Appendi x 3A

Appendi x 3B

< ,

v

3-30

3-30

3-34

3-35
TABLE OF CONTENTS

Section Page

4 CARBON ADSORBERS

4.1 Process Description 4-1

4.1.1 Introduction 4-1

4.1.2 Types of Adsorbers 4-2

4.1.3 Adsorption Theory 4-6

4.2 Design Procedure 4-11

4.2.1 Sizing Parameters 4-11

4.2.2 Determining Adsorption and Desorption Times 4-13

4.2.3 Estimating Carbon Requirement 4-15

4.3 Estimating Total Capital Investment 4-20

4.3.1 Fixed-Bed Systems 4-21

4.3.2 Cannister Systems 4-26

4.4 Estimating Total Annual Cost 4-28

4.4.1 Direct Annual Costs 4-28

4.4.2 Indirect Annual Costs 4-34

4.4.3 Recovery Credits 4-35

4.4.4 Total Annual Cost 4-36

References for Section 4 4-37
TABLE OF CONTENTS

Section

5 FABRIC FILTERS

5.1 Process Description

5.1.1 Introduction

5.1.2 Types of Fabric Filters

5.1.3 Auxiliary Equipment

5.1.4 Fabric Filtration Theory

5.2 Design Procedures

5.2.1 Gas-to-Cloth Ratio

5.2.2 Pressure Drop

5.2.3 Particle Characteristics

5.2.4 Gas Stream Characteristics

5.2.5 Pressure or Suction Housings

5.2.6 Standard or Custom Construction

5.2.7 Filter Media

5.3 Estimating Total Capital Investment

5.3.1 Equipment Cost

5.3.2 Total Purchased Cost

5.3.3 Total Capital Investment

5.4 Estimating Total Annual Costs

5.4.1 Direct Annual Cost

5.4.2 Indirect Annual Cost

5.4.3 Recovery Credits

5.4.4 Total Annual Cost

5.4.5 Example Problem

References for Section 5

5-1

5-1

5-2

5-5

5-7

5-15

5-15

5-23

5-24

5-25

5-27

5-28

5-29

5-30

5-30

5-40

5-41

5-41

5-41

5-46

5-47

5-47

5-48

5-54
i-)

Section 1

INTRODUCTION

William M. Vatavuk

Economic Analysis Branch, OAQPS

1.1 Role of Cost in the Setting of Regulations

Cost has an important role in setting many state and federal ai r

pollution control regulations. The extent of this role varies with the

type of regulation. For some types of regulations, cost is explicitly used

in determining their stringency. This use may involve a balancing of costs

and environmental impacts. costs and dollar valuation of benefits, or

environmental impacts and economic consequences of control costs.

For other types of regulations cost analysis is used to choose among

alternative regulations with the same level of stringency. For these

regulations. the environmental goal is determined by some set of criteria

which do not include costs. However, cost-effectiveness analysis is employed

to determine the minimum cost way of achieving the goal.

For some regulations. cost influences enforcement procedures or

requirements for demonstration of progress towards compliance with an air

quality standard. For example. the size of any monetary penalty assessed

for noncompliance as part of an enforcement action needs to be set with

awareness of the magnitude of the control costs being postponed by the noncomplying facility. For regulations without a fixed compliance schedule,

demonstration of reasonable progress towards the goal is sometimes tied to

the cost of attaining the goal on different schedules.

Cost is a vital input into two other types of analyses that also

sometimes have a role in standard setting. Cost is needed for a benefit-cost

analysis that addresses the economic efficiency of alternative regulations.

1-2

Cost is also an input into any analysis of the economic impact of each

regulatory alternative. An economic impact analysis deals with the consequences

of the regulation for small businesses, employment, prices, and industry

structure.

1.2 Purpose of Manual

The pu rpose of thi s Manual is two-fol d: (l) to compil e up-to-date

capital costs, operating and maintenance expenses, and other costs for

"add-on" air pollution control systems and (2) to provide a comprehensive,

concise, consistent, and easy-to-use procedure for estimating and (where

appropriate) escalating these costs. (IlAdd-on" systems are those installed

downstream of an air pollution source to control its emissions.)

The Manual estimating procedure rests on the notion of the "factored" or

"study" estimate, nominally accurate to within + 30%. This type of estimate

is well suited to estimating control system costs intended for use in

regulatory development. Study estimates are sufficiently accurate, yet do

not requi re the detail ed, site-specifi c data inputs needed to make "defi ni t i veil

or other more accurate types of estimates.

1.3 Organization of the Manual

This Manual is a major revision of the 1978 edition of the EAB Control

Cost Manual,(1) which, in turn, was a revision of the original edition,

completed in 1976. This third edition of the Manual includes a more thorough

discussion of estimating methodology and more detailed design procedures

for an enlarged set of equipment types. The appendices have been revised

to delete some infrequently used material, and to include certain new and

more useful material.

The format of the Manual has been changed to one which will permit more

flexibility in its updating and expansion. To achieve this flexibility
1-3

this edition will be issued in self-contained sections. Each section will

address a logically separate topic, which can be either of a general nature

(e.g., this introduction) or of a more specific, equipment-oriented nature

(e.g., fabric filters). The sections which comprise this portion of the

Manual are listed in Table 1-1, alongside the sections in the 1978 Manual

they wi 11 repl ace.

Two changes in the 1978 Manual are indicated by Table 1-1. First,

the numbering scheme is different. In the third edition, each type of

equipment, background topic, etc., is given its own number, for ease of

identification and to reinforce the intent that each section should "stand

alonell

• Second, the auxiliary equipment items (e.g., ductwork), which were

collected into a single chapter in the previous Manuals, are now also standalone sections. This was mainly done to eliminate the confusion that arises

when classifying auxiliaries like mechanical collectors which can either

support a primary control device or be control devices in their own right.

The notion of a stand alone section is also new. Wherein the 1976

and 1978 Manuals, the various capital and annual cost factors were collected

in an introductory section (old Section 3), now they are dispersed among the

sections covering the equipment types. Each of these sections contains a:

o Process description, where the types, uses, and operating modes of

the equipment item and (if applicable) its auxiliaries are discussed;

o Design procedure, which enables one to use the parameters of the

pollution source (e.g., gas volumetric flowrate) to size the equipment

item(s) in question;

o ~apital and annual costs for the equipment and suggested factors to

use in estimating these costs from equipment design and operational
Table 1-1 Format of the EAB Control Cost Manual (Thi rd Edition)

New Section ! Old Section(s) Replaced

Number

1

2

3

4

5

Title

IIIntroduction li

IIManual Estimati ng Methodologyll

IIThermal and Catalyti c I nci neratorsll

IICarbon Adsorbersll

IIFabric Filtersll

(Other sections to be developed)

Number(s)

1

2,3

5.4

5.5

5.3

Titl e

III ntroducti on ll

IIApplication to Industryll; IICost Estimating

Procedu resII

IIThermal and Catalytic Incinerator Systemsll

IIAdsorbersli

IIFabric Filtersll

I-'

I

..j::>o
1-5

(e.g., operating hours) parameters. These costs are presented in

both graphical and equational forms wherever possible.

1.4 "Uniqueness" of the Manual

The Manual presents a different perspective on estimating air pollution

control system costs than other cost-oriented reports, such as:

o The Cost Digest: Cost Summaries of Selected Environmental Control

Technologies(2)

o A Standard Procedure for Cost Analysis of Pollution Control Operations(3)

o Evaluation of Control Technologies for Hazardous Air Pollutants(4)

Although these reports (as well as many of the NSPS Background

Information Documents) contain costs for add-on control systems, they do

not duplicate the Manual for one or more of the following reasons: (1)

their costs have been based either wholly or partly on data in the previous

Manuals; (2) they apply to specific source categories only, whereas the

Manual data may be applied generally; (3) their estimating procedures and

costs are of less than study estimate quality; or (4) they are not intended for

estimating costs used in regulatory development.

Reason (3) applies to the Cost Digest, for example, as this report,

designed for use by non-technical personnel, contains procedures for making

"order-of-magnitude" estimates (! 30% accuracy or worse). A Standard Procedure,

conversely, was primarily intended for estimating costs for R&D cases (e.g.,

demonstration projects), where some site-specific data are available. Further,

although the latter report contains a thorough list of equipment installation

factors, it contains few equipment costs. The report, Evaluation of Control

Technologies, used data and estimating procedures from the 1978 Manual to

provide sound generalized procedures for estimating thermal and catalytic
1-6

incinerator costs. The third edition of the Manual updates and expands

this information.

Finally, the second edition of the Manual (published December 1978),

was one of the earliest of its kind. It has been extensively used in

Agency regulatory development efforts. Accordingly, the Manual's role in

the speciality of air pollution control system cost estimating is both

unique and secure.
1-7

References for Section 1:

1. Neveril, R. B. (GARO, Inc.) Capital and Operati ng Costs for Sel ected

Air Pollution Control Systems, EPA, Office of Ai r Quality Planning

and Standaros, Economic Analysis Branch, December 1978 (EPA 450/5-

80-002).

2. DeWolf, Glenn, et al. (Radian, Inc.) The Cost Digest: Cost Summaries

of Selected Environmental Control Technologies. EPA, ORO, Office of

Environmental Engineering and Technology, October 1984 (EPA-600/884-010).

3. Vhl, Vincent W. Standaro Procedure for Cost Analysis of Pollution

Control Operations, Volumes I and II. EPA, ORO, Industrial Environmental

Research Laboratory, June 1979 (EPA-600/8-79-018a).

4. Katari, Vishnu (Pacific Environmental Services) Evaluation of Control

Technologies for Hazaroous Air Pollutants. EPA, Air and Energy Engineering

Research Laboratory, ORO, October 1985.
Secti on 2

MANUAL ESTIMATING METHODOLOGY

William M. Vatavuk

Economic Analysis Branch. OAQPS

This section presents a methodology that will enable the user. having

knowledge of the source being controlled. to produce study-level cost

estimates for a control system to control that source. The methodology.

which applies to each of the control systems included in this Manual. is

general enough to be used with other "add-on" systems as well. Further.

the methodology may also be applicable to estimating costs of fugitive

emission controls and of other nonstack abatement methods.

Before presenting this methodology in detail. we should first discuss

the various kinds of cost estimates and then define the cost categories and

engineering economy concepts employed in making the estimates.

2.1 Types of Cost Estimates

As noted above. the costs and estimating methodology in this Manual

are directed toward the "study" estimate. of.:!:. 30% accuracy. According to

Perry's Chemical Engineer's Handbook. a study estimate is "•••• used to

estimate the economic feasibility of a project before expending significant

funds for piloting. marketing. land surveys, and acquisition ••• [However]

it can be prepared at relatively low cost with minimum data."(1) Specifically,

to make a study estimate. the following must be known:

o Location of the source within the plant;

o Rough sketch of the process flow sheet (i .e., the relative locations

of the equipment in the system);

o Preliminary sizes of. and material specifications for, the system

equipment items;

2..2

o Approximate sizes and types of construction of any buildings required

to house the control system;

o Rough estimates of utility requirements (e.g.~ electricity);

o Preliminary flow sheet and specifications for ducting and piping;

o Approximate sizes of motors required.(l)

In addition~ an estimate of the labor hours required for engineering

and drafting is needed. as the accuracy of an estimate (study or otherwise)

is highly dependent on the amount of engineering work expended on the

project.

There are. however, four other types of estimates, three of which

are more accurate than the study estimate. These are:(l)

o 1I0 rder-of-magnitude llu "a rul e of-thumb procedure appl ied only to

repetitive types of plant installations for which there exists good

cost historyll. Its accuracy is >.:!:.30%. (However. according to

Perry's. 1I ••• no limits of accuracy can safely be applied to it. lI)

The sole input required for making this level of estimate is the

control system's capacity (often measured by the maximum volumetric

flowrate of the gas passing through the system). So-called IIsixtenths factorll estimates (not to be confused with factored

estimates) are examples of this type.

o IlS cope ll/IlBudget authorizationll;UPreliminari' • This estimate.

nominally of + 20% accuracy. requires more detailed knowledge than

the study estimate regarding the site, flow sheet. equipment.

buildings. etc. In addition. rough specifications for the insulation

and instrumentation are also needed.
2-3

o "Project controllll"Definitive" estimates. accurate to within 2:. 10%.

require yet more information than the scope estimates. especially

concerning the site. equipment. and electrical requirements.

o "FirmIlI"Contractor'sIlI"Detailed li

• This is the most accurate (..:!::. 5%)

of the estimate types. requiring complete drawings. specifications.

and site surveys. Further. II [t]ime seldom permits the preparati on

of such estimates prior to an approval to proceed with the project. II (1)

For the purposes of regulatory development. study estimates have been

found to be acceptable. as tney represent a compromise between the less

accurate 1I 0 rder-of-magnitude li and the more accurate estimate types. The

former are too imprecise to be of much value. while the latter are not only

very expensive to make. but require detailed site and process-specific

knowledge that most Manual users will not have available to them.

2.2 Cost Categories Defined

The names gi ven certai n II categori esll of costs and what they contai n

vary considerably throughout the 1iterature. Certain words 1ike II capital

costll can have vastly different meanings. which can often lead to confusion.

even among cost estimators. To avoid this confusion and. at the same time.

provide uniformity in the Manual. basic terms are defined in this Section

and will be used throughout. The terminology used is adapted from that of

the American Association of Cost Engineers(2). Although it has been

developed for general use. it is readily adaptable to air pollution control

system costing.

2.2.1 Elements of Total Capital Investment

First. two general kinds of costs are estimated. total capital investment

(TCI) and total annual cost (TAC). The total capital investment includes
2-4

all costs required to purchase equipment needed for the control system

(termed II purchased equipment ll costs), the costs of labor and materials for

install i ng that equi pment (termed lid i rect install ati on ll costs), site

preparation, building costs, and certain other costs which are termed

lIindirect installationll costs. Direct installation costs include costs for

foundations and supports, erecting and handling the equipment, electrical

work, piping, insulation, and painting. Indirect installation costs include

such costs as engineering costs; construction and field expenses (i .e.,

costs for construction supervisory personnel, office personnel, rental of

temporary offices, etc.); contractor fees (for construction and engineering

firms involved in the project); start-up and performance test costs (to get

the control system running and to verify that it meets performance guarantees);

and contingencies. Contingencies is a catch-all category that covers unforeseen costs that may arise, including (but certainly not limited to) II •••

possible redesign and modification of equipment, escalation increases in

cost of equipment, increases in field labor costs, and delays encountered

in start-up.II(2)

These elements of total capital investment are displayed in Figure

2-1. Note that the sum of the purchased equipment cost, direct and

indirect installation costs, site preparation, and buildings costs

comprise the battery limits estimate. By definition, this is the total

estimate II ••• for a specific job without regard to requi red supporting

facilities which are assumed to already exist••• 1I (2) at the plant. This

would mainly apply to control systems installed in existing plants, though

it could also apply to those systems installed in new plants when no special

facilities for supporting the control system would be required.
o Primary Control Device

o Auxiliary Equipment (including ductwork)

o Instrumentationa

o Sales Taxesa

o Freighta

Figure 2-1

Purchased

I Equipment

Cost

Elements of Total Capital Investment

Lande ]

Working Capital e

Total

Nondeprec1 ab1e

Investment

o Foundations and Supports

o Handling and Erection

o Electrical

o Piping

o Insulation

o Painting

Di rect

I Installation

Costb

Site Preparationc,d

Buildi ngsd

Total

Direct

Cost

"Battery

Limits"

Cost

Total

Capital

Investment N

I

U1

o Engineering

o Construction and Field

Expenses

o Contractor Fees

o Start-up

o Performance Test

o Contingencies

Indirect

Installation

Costb

Total

= Indirect

Cost

Off-Site

facilites e

Total

Depreciable

Investment

a These costs are factored from the sum of the control device and auxiliary equipment costs.

b . These costs are factored from the purchased equipment cost.

c Usually required only at "grass roots" installations.

d Unlike the other direct and indirect costs, costs for these items are not factored from the purchased equipment

cost. Rather, they are sized and costed separately. --- e Normally not required with add-on control systems.
2-6

Where required, these supporting facilities would encompass units to

produce steam, electricity, and treated water; laboratory buildings, railroad

spurs, roads, and the like. It is unusual, however, for a control system

to have one of these units (e.g., a power plant) dedicated to it. The

system needs are rarely that great. However, it may be necessary--especially

in the case of control systems installed in new or IIgrass rootsll plants--

for extra capacity to be built into the site generating plant to service

the system. (A venturi scrubber, which often requires large amounts of

electricity, is a good example of this.) It is customary for the utility costs

to be charged to the project as operating costs at a rate which covers both

the investment and operating costs for the utility.

As Figure 2-1 shows, there are two other costs which may be included

in the total capital investment for a control system. These are IIwo rk i ng

capital ll, and IIl andll• The first of these, working capital, is a fund set

aside to cover the initial costs of fuel, chemicals, and other materials,

as well as labor and maintenance. It usually does not apply to control

systems, for the quantities of utilities, materials, labor, etc., they

require are usually small. (An exception might be an oil-fired thermal

incinerator, where a small supply (e.g., 30-day) of distillate fuel would

have to be available during its initial period of operation.)

Land may also be required. But, since most add-on control systems

take up very little space (a quarter-acre or less) this cost would be

relatively small. (Certain control systems, such as those used for flue

gas desulfurization, require larger quantities of land for the process

equipment, chemicals storage, and waste disposal.)
2-7

Note also in Figure 2-1 that the working capital and land are

II nondepreci abl ell expenses. I n other words, these costs are II recovered II

when the control system reaches the end of its useful life (generally in 10

to 20 years). Conversely, the other capital costs are IIdepreciable ll , in

that they cannot be recovered and are included in the calculation of the

income tax credit and depreciation allowance, whenever such taxes are

considered in a cost analysis. (In the Manual methodology. however,

income taxes are not considered. See Section 2.3.)

Notice that when 100% of the system costs are depreciated, no salvage

value is taken for the system equipment at the conclusion of its useful life.

This is a reasonable assumption for add-on control systems, as most of the

equipment. which is designed for a specific source, cannot be used elsewhere

without modifications. Even if it were reusable, the cost of disassembling

the system into its components could be as high (or higher) than the salvage

val ue.

2.2.2 Elements of Total Annual Cost

The Total Annual Cost (TAC) for control systems is comprised of three

elements: IIdirectll costs, (DC) lIindirectll costs, (IC) and IIrecovery creditsll

(RC), which are related by the following equation:

TAC = DC + IC - RC (2-1 )

Clearly, the basis of these costs is one year, as this period allows for

seasonal variations in production (and emissions generation) and is directly

usable in profitability analyses. (See Section 2.3.)

Direct costs are those which tend to be proportional or partially

proportional to the quantity of exhaust gas processed by the control system

per unit time. These include costs for raw materials, utilities (steam.
2-8

electricity, process and cooling water, etc.), waste treatment and disposal,

maintenance materials, replacement parts, and operating, supervisory, and

maintenance labor. Of these direct costs, costs for raw materials, utilities,

and waste treatment and disposal are variable, in that they tend to be a

direct function of the exhaust flowrate. That is, when the flowrate is at

its maximum rate, these costs are highest. Conversely, when the flowrate

is zero, so are the costs.

Semivariable direct costs are only partly dependent upon the exhaust

flowrate. These include all kinds of labor, maintenance materials, and

replacement parts. Although these costs are a function of the gas flowrate,

they are not linear functions. Even while the control system is not

operating, some of the semivariable costs continue to be incurred.

Indirect, or "fixed", annual costs are those whose values are totally

independent of the exhaust flowrate and, in fact, would be incurred even if

the control system were shut down. They include such categories as overhead,

property taxes, insurance, and capital recovery.

Finally, the direct and indirect annual costs are offset by recovery

credits, taken for materials or energy recovered by the control system,

which may be sold, recycled to the process, or reused elsewhere at the

site. These credits, in turn, must be offset by the costs necessary for

their purification, storage, transportation, and any other costs required

to make them reusable or resalable. Great care and judgement must be

exercised in assigning values to recovery credits since materials recovered

may be of small quantity or of doubtful purity, resulting in their having less

value than virgin material.
2-9

The various annual costs and their interrelationships are displayed in

Figure 2-2. A more thorough description of these costs and how they may

be estimated is given in Section 2.4.

2.3 Engineering Economy Concepts

As mentioned previously, the estimating methodology presented in

Section 2.4 rests upon the notion of the IIfactored li or study estimate.

However, there are other concepts central to the cost analyses which must

be understood. These are (1) the time value of money, (2) cash flow, and

(3) annualization.

2.3.1 Time Value of Money

The IItime value of moneyll is based on the truism that 1I •••a dollar now

is worth more than the prospect of a dollar••• at some later date. II (3)

A measure of this value is the interest rate which 1I •••may be thought of as

the return obtainable by the productive investment of capital. II (3)

2.3.2 Cash Flow

During the lifetime of a project, various kinds of cash expenditures

are made and various incomes are received. The amounts and timing of these

expenditures and incomes constitute the cash flows for the project. In

control system costing it is normal to consider expenditures (negative cash

flows) and unusual to consider income (positive cash flows), except for

product or energy recovery income. By the simplifying convention recommended

by Grant, Ireson, and Leavenworth(4), each annual expenditure (or payment)

is considered to be incurred at the end of the year, even though the payment

will probably be made sometime during the year in question. (The error

introduced by this assumption is minimal, however.) Figure 2-3, which

shows three hypothetical cash flow IIdiagramsll , illustrates these end-ofyear payments. In these diagrams, IIpli represents the capital investment,
o Raw materials

o Utilities

- Electricity - Steam - Water - Others

Figure 2-2 Elements of Total Annual Cost

Variable

o Labor

- Operating - Supervisory - Mai ntenance 1---Semi vari abl e

o Maintenance materials

o Replacement parts

Oi rect

Annual

Costs

+

o Overhead

o Property Taxes

o Insurance

o Capital Recovery

Indirect

"- Annua1

Costs

= Total

Annual

Cost

o Materials

o Energy Recovery 1------Credits
Fi gure 2-3 Hypothetical Cash Flow Diagrams

1.

All Values Are Constant Year (Real) Dollars

o 1 2 3 4 5 6 7 8 9 10 Year

p1 Al A2t A3~ A4{ Asl Atil All Agt Agt AlO t

N( j I .

......

......

1- 2 3 4 5- 6 7 8 9- 10 Year

A A A A , A A , A A A , A

,

o

II. P

III.

o 1 2 3 4 5 6 . 7 8 9 10 Year

Al I All All AlI All· All At All All Al t
2-12

while the A's denote the end-of-year annual payments. Note that in all

diagrams, the cash flows are in "constant" (" real") dollars, meaning that

they do not reflect the effects of inflation. Also note that in the top

diagram (I), the annual payments are different for each year. {These

rep resent the cont rol system annual costs (excl usi ve of capital recove ry)

described in Section 2.2.) In reality, these payments would be different,

as labor and maintenance requirements, labor and utility costs, etc., would

vary from year to year. A generally upward trend in annual costs would be

seen, however.

In diagram II, these fluctuating annual payments have been converted

to equal payments. This can be done by calculating the sum of the present

values of each of the annual payments shown in diagram I and annualizing

the total net present value to equivalent equal annual payments via a capital

recovery factor. (See discussion in the following paragraphs and in Section

2.3.3.) Alternatively, it is adequate to choose a value of A equal to the

sum of the direct and indirect annual costs estimated for the first year.

This assumption is in keeping with the overall accuracy of study estimates

and allows for easi er cal cul ati ons.

Finally, notice diagram III. Here, the annual costs (AI) are again

equal, while the capital investment (P) is missing. Put simply, P has been

incorporated into Al so that Al reflects not only the various annual costs

but the investment as well. This was done by introducing another term, the

capital recovery factor (CRF), defined as follows: "when multiplied by a

present debt or investment, [the CRF] gives the uniform end-of-year payment

necessary to repay the debt or investment in n years with interest rate i."(5)

The product of the CRF and the investment (P) is the capital recovery cost (CRC):

CRC = CRF x P (2-2)
2-13

where:

CRF = i(1 + i) n

(l + i) 11_1

Therefore, Al is the sum of A and the CRC, or:

Al = A + CRF x P

(2-3 )

(2-4)

In this context, "n" is the control system economic life, which,

as stated above, typically varies from 10 to 20 years. The interest rate

("i") used in this Manual is a real rate of 10% (annual). This value is

used in most of the OAQPS cost analyses and is in keeping with current EAB

guidelines(6) and the Office of Management and Budget recommendation for use

in regul atory analyses.(7)

It may be helpful to illustrate the difference between II real II and

"nominal" interest rates. The mathematical relationship between them is

straightforward: (6)

(l + in) = (1 + i)(1 + r)

where:

in , i = the annual nominal and real interest rates, respectively

r =the annual inflation rate

(2-5 )

Clearly, the II real II rate does not consider inflation and is in keeping

with the expression of annual costs in constant (i.e., real) dollars.

EAB guidelines also recommend the exclusion of income tax considerations

from cost analyses.(6) Not only does this simplify the analysis, but it

also allows for the calculation of the "economic" costs of air pollution

control--i.e., the true cost to society. Income taxes generally represent

transfer payments from one segment of society to another and as such are not

properly part of the economic costs.
2-14

2.3.3 Annualization Methods

The above method of "smoothing out" the investment into equal end-ofyear payments, is termed the "equival ent uniform annual cash flow" (EUAC)

method.(8) In addition to its inherent simplicity, this method is very

useful when comparing the costs of two or more alternative control systems

(i.e., those which are designed to control the same source to an equivalent

degree). In fact, the EUAC's--or simply the total annual costs--of two

competing systems'may be compared even if both the systems have different

economic lives, say 10 and 20 years. We recommend that the EUAC method be

used for control cost work unless particular circumstances preclude its

use.

Comparisons of systems with differing economic lives cannot be made,

however, using the other two annualization (i.e., profitability analysis)

methods--"p resent worth" and "i nternal rate of retu rn" • The lip resent

worth" (or "discounted cash flow") method involves the "discounting" of all

cash flows occuri ng after year "0" (i .e., the system startup date) back to

year "0". These cash flows are discounted by multiplying each by a "discount

factor", 1 , where "mil is the number of years from year a to the year (1 + i)m

in which the cash flow is incurred. The sum of these discounted cash flows

is then added to the capital investment to yield the "present worth" of the

project. The alternative having the highest present worth would be selected

(in control system costing this is usually a negative number). But when

comparing the present worths of alternative systems, the system lifetimes

must be equal for the comparison to be valid.(9)
2-15

The third annualization method, "internal rate of return" (IRR). is

similar to the present worth method, in that it involves the discounting of

a series of unequal cash flows. However, where with the PW method the

interest rate, "i", is set beforehand, in the IRR method the interest rate

is solved for (usually via trial-and-error) after arbitrarily setting the

PW to zero. When comparing alternative systems, the one with the highest

IRR is selected.(10) But again, the alternative systems compared must have

equal economic lives.

2.4 Estimating Procedure

The estimating procedure used in the Manual consists of five steps:

(1) obtaining the IIfacil ity parameters" and "regul atory options" for a

given facility; (2) "roughing out" the control system design; (3) sizing

the control system components; (4) estimating the costs of these individual

components; and (5) estimating the costs (capital and annualized) of the

entire system.

2.4.1 Facility Parameters and Regulatory Options

Obtaining the facility parameters and regulatory options involves

not only assembling the parameters of the air pollution source (i .e., the

quantity, temperature, and composition of the emission stream(s)),

but also compiling data for the facility's operation. (Table 2-1 lists

examples of these.) Note that two kinds of facility parameters are identified -- "intensivell and lIextensive". The former are simply those variables

whose values are independent of quantity or dimensions -- i.e., the "extent"

of the system. Conversely, "extensivell parameters encompass all size-dependent

variables, such as the gas volumetric flowrate.
2-16

Table 2-1 Facility Parameters and Regulatory Options (11)

FACILITY PARAMETERS

o Intensive

- Facility status (new or existing, location)

- Gas characteristics (temperature, pressure, moisture content)

- Pollutant concentration(s) and/or particle size distribution

o Extensive

Facility capacity

- Faci 1ity 1ife

- Gas flow rate

Pollutant emission rate(s)

REGULATORY OPTIONS

o No control

o "Add-on" devices

Emi ssi on 1imits

- Opacity "

o Process modifications

- Raw material changes

- Fuel substitution

o Others

- Coal desulfurization
2-17

Like the facility parameters, the IIregulatory optionsll are usually

specified by others. These options are ways to achieve a predetermined

emission limit. They range from II no control II to maximum control technically

achievable. The option provided will depend, firstly, on whether the

emission source is a stack (point source), a process leak (llprocess fugitivesll

source) or an unenclosed (or partly closed) area, such as a storage pile

(ll area fugitivesll source). Stacks are normally controlled by lIadd-on ll

devices. As discussed above, this Manual will deal primarily with these

add-on devices. (However, some of these devices can be used to control

process fugitives in certain cases, such as a fabric filter used in conjunction

with a building evacuation system.) Add-ons are normally used to meet a

specified emission level, although in the case of particulate emissions,

they may also be required to meet an opacity level.

2.4.2 Control System Design

Step 2 -- roughing out the control system design -- first involves

deciding what kinds of systems will be priced (a decision that will depend

on the pollutants to be controlled, gas stream conditions, and other factors),

and what auxiliary equipment will be needed. When specifying the auxiliary

equipment, several questions need to be answered:

o What type of hood (if any) will be needed to capture the emissions

at the sou rce?

o Will a fan be needed to convey the exhaust through the system?

o Is a cyclone or another pre-cleaner needed to condition the exhaust

before it enters the control device?

o Will the captured pollutants be disposed of or recycled? How will

thi s be done?
2-18

o Can the on-site utility capacity (e.g., electricity) accomodate the

added requirements of the control system?

The kinds of auxiliary equipment selected will depend on the answers

to these and other site-specific questions. However, regardless of the

source being controlled, each system will likely contain, along with the

control device itself, the following auxiliaries:

o Hood, or other means for capturing the exhaust;

o Ductwork, to convey the exhaust from the source, to, through, and

from the control system;

o Fan system (fan, motor, starter, inlet/outlet dampers, etc.), to

move the exhaust through the system;

o Stack, for dispersing the cleaned gas into the atmosphere.

2.4.3 Sizing the Control System

Once the system components have been selected, they must be sized.

Sizing is probably the most critical step, because the assumptions made in

this step will more heavily influence the capital investment than any other.

Before discussing how to size equipment, we need to define the term. For

the purposes of this Manual, "sizing" is the calculation (or estimation) of

certain "critical" design parameters for a control device against which

the purchased cost of that device is most accurately correlated. For

instance, the purchased cost of an electrostatic precipitator (ESP) is most

often correlated with its collecting area. This, in turn, is a function

of the exhaust volumetric flowrate, the overall collection efficiency and

the empi ri cally-determi ned drift velocity, the ESP "critical" parameter.

(Table 2-2 lists examples of these parameters.)
2-19

Table 2-2 Examples of Typical Control Device Parameters(11)

GENERAL

- Material of construction: e.g., carbon steel

Insulated? Yes

Economic life: 20 yr

- Redundancya: none

DEVICE-SPECIFIC

- Air-to-cloth ratio (ll critical parameterll ): 7.5 to 1

- Pressure drop: 6.0 in w.g. (inches water gauge)

- Construction: suction (vs. pressurized)

- Duty: continuous (vs. intennittent)

- Other features: dilution air port (for exhaust temperature regulation)

a Refers to whether there are any extra equipment items installed (e.g.,

fans) to function in case the basic item becomes inoperative, so as to avoid

shutting down the entire system.
2-20

Also listed in Table 2-2 are "general" parameters which must also be

specified before the purchased cost of the system equipment can be estimated.

Note that, unlike the control device parameters, these may apply to

kind of control system. These include materials of construction (which may

range from carbon steel to various stainless steels to fiberglass-reinforced

polyester), presence or absence of insulation, and the economic or "useful"

life of the system. As indicated in Section 2.3.2, this last parameter is

required for estimating the annual capital recovery costs. The lifetime

not only varies according to the ty~e of the control system, but with the

severity of the environment in which it is installed. (Representative

values for this and the other control device parameters will be presented

in those Sections of the Manual covering them.)

2.4.4 Estimating Total Capital Investment

The fourth step is estimating the total purchased cost of the control

system equipment. These costs are available from this Manual for the most

commonly used add-on control devices and auxiliary equipment. Each type of

equipment is covered in a separate section. (See Table of Contents.)

Most of these costs, in turn, have been based on data obtained from

control equipment vendors. There are over one hundred of these firms, many

of whom fabricate and erect a variety of control systems.(12) They have

readily available, current price lists of their equipment, usually indexed

by model designation. If the items for which costs are requested are

fabricated, "off-the-shelf" equipment, then the vendor can provide a

written quotation listing their costs, model designations, date of quotation,

estimated shipment date, and other information. (See Figure 2-4 for a

sample quotation.) Moreover, the quote is usually "F.O.B. II ("free-on-board")
·2-·21 ..

Figure 2-4 Typical Vendor Quotation

.QUOTATION

xess EQuipment Plant (NOTE: Company name and address ha,.vebeen deleted.)

r MAIL DROP 1# 12 -,

QUOTATION NO. 85S23382

U.S. EPA'

RESEARCH TRIANGLE PARK DATE 9-23-85

DURHAM, NC 27711

REFERENCE VERBAL - BUDGET

ATTN: MR. BILL VATAVUK

L .-J

Thank you for your inQuiry. We are pleased to submit our Quotation as follows:

QUANTITY

1

1

DESCRIPTION

ITEM I#l PREHEATER .

MODEL 191-19 SIZE 1#9 IMPERVITE SHELL &TUBE HEAT EXCHANGER WITH'

55.8 SQ. FT. OF HEAT TRANSFER AREA AND CODE STAMPED

ITEM 1#2 CONDENS£R

MODEL 191-19 SIZE #12 IMPERVITE SHELL &TUBE HEAT EXCHANGER WITH

74.5 SQ. FT. OF HEAT TRANSFER AREA AND CODE STAMPED'

APPROVAL DWG'S 2 - 3 WEEKS AFTER RECEIPT OF ORDER.

THIS QUOTATION IS IN CONFIRMATION OF OUR PHONE CONVERSATION OF

9/18/85.

PRICE

$ 7,147.00 EA.

7,430.00 EAo

ESTIMATED SHIPMENT 6 to 8 WEEKS AFTER o RECEIPT OF ORDER o RECEIPT OF DRAWING APPROVAl.

Prices are F.O.B. >. Net 30 Days. ' •

Unless otherwise stated these prices are subject to acceptance within 30 days from date.

By_

lilY PURCHASE 01160 RESULnNG FROM THIS QUOTATION WILL IE SUBJECT TO THE CONTRACT TERMS AND CONIlITlONS PIIINTED ON THE REVERSE SIDE OF THIS PAGE.
2-22

the vendor, meaning that no taxes, freight, or other charges are included.

However, if the items are not off-the-shelf, they must be custom fabricated

or, in the case of very large systems, constructed on-site. In such cases,

the vendor can still give quotations--but will likely take much longer to

do so and may even charge for this service, to recoup the labor and overhead

expenses of his estimating department.

As discussed in Section 2.2 in this Manual, the total capital investment

is Ufactored ll from the IIpurchased equipment costll, which in turn, is the

sum of the base equipment cost (control device plus auxiliaries), freight,

instrumentation, and sales tax. The values of these installation factors

depend on the type of the control system installed and are, therefore,

listed in the individual Manual sections dedicated to them.

The costs of freight, instrumentation, and sales tax are calculated

differently from the direct and indirect installation costs. These items

are IIfactored ll also, but from the base equipment cost (F.O.B. the vendor(s)).

But unlike the installation factors, these factors are essentially equal

for all control systems. Values for these are as follows:

Cost Range Typical

Freight 0.01 - 0.10 0.05

Sales tax 0 - 0.08 0.03

Instrumentation 0.05 - 0.30 0.10

The range in freight costs reflects the distance between the vendor and the

site. The lower end is typical of major U.S. metropolitan areas, while the

latter would reflect freight charges to remote locations such as Alaska and

Hawaii.(ll) The sales tax factors simply reflect the range of local and

state tax rates currently in effect in the U.S.(13)
2-23

The range of i nstrumentati on factors is a1 so quite 1arge. For systems

requiring only simple continuous or manual control, the lower factor would

apply. However, if the control is intermittent and/or requires safety backup

instrumentation, the higher end of the range would be applicab1e.(ll)

Finally, some "package" control systems (e.g., incinerators covered in

Section 3) have built-in controls, whose cost is included in the base

equipment cost. In those cases, the factor to use would, of course, be zero.

2.4.5 Retrofit Cost Considerations

The installation factors listed elsewhere in the Manual apply primarily

to systems installed in new facilities. These factors must be adjusted

whenever a control system is sized for, and installed in (i.e, II retrofitted ")

an existing facility. However, because the size and number of auxiliaries

are usually the same in a retrofit situation, the total purchased cost of

the control system would probably not be different from the new plant

purchased cost. An exception is the ductwork cost, for in many retrofit

situations exceptionally long duct runs are required to tie the control

system into the existing process.

Each ret rofit install ati on is uni que; therefore, no general factors

can be developed. Nonetheless, some general information can be given

concerning the kinds of system modifications one might expect in a retrofit:

1. Auxiliaries. Again, the most important component to consider is

the ductwork cost. In addition, to requiring very long duct runs,

some retrofits require extra tees, elbows, dampers, and other

fitti ngs.

2. Handling and Erection. Because of a IItight fit", special care may

need to be taken when unloading, transporting, and placing the
2-24

equipment. This cost could increase significantly if special

means (i.e., helicopters) are needed to get the equipment on roofs

or to other inaccessible places.

3. Piping, Insulation, and Painting. Like ductwork, large amounts

of piping may be needed to tie in the control device to sources of

process and cooling water, steam, etc. Of course, the more piping

and ductwork required, the more insulation and painting will be

needed.

4. Site Preparation. Unlike the other categories, this cost may

actually decrease, for most of this work would have been done when

the original facility was built.

5. Facilities. Conceivably, retrofit costs for this category could

be the largest. For example, if the control system requires large

amounts of electricity (e.g., a venturi scrubber), the facility's

power plant may not be able to service it. In such cases, the

facility would have to purchase the additional power from a public

utility, expand its power plant, or build another one. In any

case, the cost of electricity supplied to that control system

would likely be higher than if the system were installed in

a new facility where adequate provision for its electrical needs

would have been made.

6. Engineering. Designing a control system to fit into an existing

plant normally requires extra engineering, especially when the

system is exceptionally large, heavy, or utility-consumptive. For

the same reasons, extra supervision may be needed when the

installation work is being done.
2-25

7. Lost Production. This cost is incurred whenever a retrofit control

system cannot be tied into the process during normally scheduled

maintenance periods. Then, part or all of the process may have to

be temporarily shut down. The revenue lost during this shutdown

period is a bonafide retrofit expense.

8. Contingency. Due to the uncertain nature of retrofit estimates,

the contingency (i.e., uncertainty) factor in the estimate should

be inc reased.

From the above points, it is apparent that some or most of these installation costs would increase in a retrofit situation. However, there may be

other cases where the retrofitted installation cost would be less than the

cost of installing the system in a new plant. This could occur when one

control device, sayan ESP, is being replaced by a more efficient unit--a

baghouse, for example. The ductwork, stack, and other auxiliaries for the

ESP may be adequate for the new system, as perhaps would the support

facilities (power plant, etc.).

2.4.6 Estimating Annual Costs

Determining the total annual cost is the last step in the estimating

procedure. As mentioned in Section 2.2 the TAC is comprised of three

components -- direct and indirect annual costs and recovery credits. Unlike

the installation costs, which are "factored" from the purchased equipment

cost, annual cost items are usually computed from known data on the

system size and operating mode, as well as from the facility and control

device parameters.

Following is a more detailed discussion of the items comprising the

total annual cost. (Values/factors for these costs are also given in the

sections for the individual devices.)
2-26

2.4.6.1 Raw Materials

Raw materials are generally not required with control systems. Exceptions

would be chemicals used in absorbers or venturi scrubbers as absorbents or

to neutralize acidic exhaust gases (e.g., hydrochloric acid). Chemicals

may al so be requi red to treat wastewater di scharged by scrubbers or absorbers

before releasing it to surface waters. But, these costs are only considered

when a wastewater treatment system is exclusively dedicated to the control

system. In most cases, a pro-rata waste treatment charge is applied. (See

section 2.4.6.5.)

Quantities of chemicals required are calculated via material balancies,

with an extra 10 to 20% added for miscellaneous losses. Costs for chemicals

are available from the Chemical Marketing Reporter and similar publications.

2.4.6.2 Operating Labor

The amount of labor required for a system depends on its size, complexity,

level of automation, and operating mode (i.e., batch or continuous). The

labor is usually figured on an hours-per-shift basis. As a rule, though,

data showing explicit correlations between the labor requirement and capacity

are hard to obtain. A typical correlation is logarithmic:

(2-6 )

where: ll' L2 =labor requirements for systems 1 and 2

Vl, V2 =capacities of systems 1 and 2 (as measured by the

gas flow rate, for instance)

y =0.2 to 0.25 (typically)(14)

The exponent in equation (2-6) can vary considerably, however. Conversely,

in many cases, the amount of operator labor required for a system will be

approximately the same regardless of its size.
2-27

A certain amount must be added to operating labor to cover supervisory

requirements. Fifteen per cent of the operating labor requirement is

representative. (15)

To obtain the annual labor cost, multiply the operating and supervisory

labor requirements by the respective wage rates (in $/hr) and the system

operating factor (number of hours per year the system is in operation).

The wage rates also vary widely, depending upon the source category,

geographical location, etc. These data are tabulated and periodically

updated by the U.S. Department of Labor, Bureau of Labor Statistics, in its

Monthly Labor Review and in other publications. Finally, note that these

are base labor rates, which do not include payroll and plant overhead.

(See overhead discussion below.)

2.4.6.3 Maintenance

Maintenance labor is calculated in the same way as operating labor

and is influenced by the same variables. The maintenance labor rate,

however, is normally higher than the operating labor rate, mainly because

more skilled personnel are required. A 10% wage rate premium is typical.(15)

Further, there are expenses for maintenance materials -- oil, other

lubricants, duct tape, etc., and a host of small tools. Costs for these

items can be figured individually, but since they are normally so small,

they are typically factored from the maintenance labor. Reference 15

suggests a factor of 100% of the maintenance labor.

2.4.6.4 Utilities

This cost category covers many different items, ranging from electricity

to compressed air. Of these, only electricity is common to all control

devices, where fuel oil and natural ~as are generally used only by
2-28

incinerators; water and water treatment, by venturi scrubbers, quenchers,

and spray chambers; steam, by carbon adsorbers; and compressed air, by

pulse-jet fabric filters.

Techniques and factors for estimating utility costs for specific devices

are presented in their respective sections. However, because nearly every

system requires a fan to convey the exhaust gases to and through it, a

general expression for computing the fan electricity cost (Ce ) is given

here:{ll)

Ce = 0.746 Q ~P s e Pe

6356

where:

Q = gas flowrate (actual ft3/min)

~P = pressure drop through system (inches of water, gauge)

(2-7)

(Values for are given in the sections covering the equipment

items.)

s = specific gravity of gas relative to air (1.000, for all practical

purposes)

e = operating factor (hr/yr)

= combined fan and motor efficiency (usually 0.60 to 0.70)

Pe = electricity cost ($/kwhr).

A similar expression can be developed for calculating motor electricity

requirements.

2.4.6.5 Water Treatment and Disposal

Though often overlooked, there can be a significant cost associated

with treating and/or disposing of waste material captured by a control system

that neither can be sold nor recycled to the process.

Liquid waste streams, such as the effluent from a venturi scrubber,

are usually processed before being released to surface waters. The type
2-29

and extent of this processing will, of course, depend on the characteristics

of the effluent. For example, the waste can first be sent to one (or more)

clarifiers, for coagulation and removal of suspended solids. The precipitate

from the clarifier is then conveyed to a rotary filter, where most of the

liquid is removed. The resulting filter cake is then disposed of, via land

filling, for example.

The annual cost of this treatment is relatively high--$1.00 to

$2.00/thousand gallons treated or more.(16) The solid waste disposal costs

(via land filling, for example) typically would add another $20 to $30/ton

disposed of-(lJ) This, however, would .not include transportation to the

disposal site. More information on these technologies and their costs is

found in References (16) and (17).

2.4.6.6 Replacement Parts

This cost is computed separately from maintenance, because it is a

large expenditure, incurred one or more times during the useful life of a

control system. This category includes such items as carbon (for carbon

adsorbers), bags (for fabric filters) and catalyst (for catalytic

incinerators), along with the labor for their installation.

The annual cost of the replacement materials is a function of the

initial parts cost, the parts replacement labor cost, the life of the

parts, and the interest rate, as follows:

CRC p = (C p + Cpl)CRFp (2-8)

where: CRCp = capital recovery cost of repl acement parts ($/yr)

Cp = initial cost of replacement parts, including taxes

and freight ($)

Cpl = cost of parts repl acement 1abor ($)

CRF p = capital recovery factor (defined in Section 2.3).
2-30

In the Manual methodology, replacement parts are treated the same as

any other investment, in that they are also considered an expenditure that

must be amortized over a certain period. Also, the useful life of the parts

(typically 2 to 5 years) is generally less than the useful life of the rest

of the control system.

Replacement part labor will vary, depending upon the amount of the

material, its workability, accessibility of the control device, and other

factors.

2.4.6.7 Overhead

This cost is easy to calculate, but often difficult to comprehend.

Much of the confusion surrounding overhead is due to the many different

ways it is computed and to the several costs it includes, some of which

may appear to be duplicative.

There are, generally, two categories of overhead, payroll and plant.

Payroll overhead includes expenses directly associated with operating,

supervisory, and maintenance labor, such as: workmen's compensation, Social

Security and pension fund contributions, vacations, group insurance, and

other fringe benefits. Some of these are fixed costs (i.e., they must be

paid regardless of how many hours per year an employee works). Payroll

overhead is traditionally computed as a percentage of the total annual

labor cost (operating, supervisory, and maintenance).

Conversely, pl ant (or IIfactoryll) overhead account for expenses not

necessarily tied to the operation and maintenance of the control system,

including: plant protection, control laboratories, employee amenities,

plant lighting, parking areas, and landscaping. Some estimators compute
2-31

plant overhead by taking a percentage of all labor plus maintenance materials(18)~

while others factor it from the total labor costs alone.(19)

For "study" estimates, it is sufficiently accurate to combine payroll

and plant overhead into a single indirect cost. This is done in this Manual.

Also, overhead will be factored from the sum of all labor (operating,

supervisory, and maintenance) maintenance materials, the approach

recommended in reference 18. The factors recommended therein range from 50

to 70% (18) An average value of 60% is used in this Manual.

2.4.6.8 Property Taxes, Insurance, and Administrative Charges

These three indirect o~erating costs are factored from the system total"

capital investment, and typically comprise 1,1, and 2% of it, respectively.

Taxes and insurance are self-explanatory. "Administrative charges" covers

sales, research and development, accounting, and other home office expenses.

(It should not be confused with plant overhead, however.) For simplicity,

the three items are usually combined into a single, 4% factor. This value,

incidentally, is standard in all OAQPS cost analyses.

2.4.6.9 Capital Recovery

As discussed in Section 2.3, the annualization method used in the Manual

is the equivalent uniform annualized cost method. Recall that the cornerstone

of this method is the capital recovery factor which, when multiplied by

the total capital investment, yields the capital recovery cost. (See

equation 2-2.)

However, whenever there are parts in the control system that must

be replaced before the end of its useful life, equation 2-2 must be adjusted,

to avoid double-counting.
(2-9)

2-32

That is:

CRCs = CRF s [TCI - (C p + Cpl) ]

where:

CRCs = capital recovery cost for control system ($/yr)

TCI = total capital investment for entire system ($).

CRF s = capital recovery factor for control system

The term (Cp+Cpl) accounts for the cost of those parts that would be

replaced during the useful life of the control system and the labor for

replacing them. Clearly, CRF s and CRF p will not be equal unless the control

system and replacement part lives are equal.
2-33

References for Section 2:

1. Perry, Robert H., and Chilton, Cecil H., Perry's Chemical Engineer's

Handbook (Fifth Edition). New York: McGraw-Hill, 1973, pp. 25-12 to

25-16.

2. Humphries, K. K. and Katell, S., Basic Cost Engineering, New York:

Marcel Dekker, 1981, pp. 17-33.

3. Grant, EeL., Ireson, W.G., Leavenworth, R.S., Principles of ~ngineering

Economy, ~ixth Edition. New York: John Wiley &Sons, 1976, p.25.

4. Ibid., p. 35.

5. I bi d ., p. 36.

6. EAB Guidel i ne Memo: "I nterest Rates for Regul atory Impact Analyses

(RIA)", May 27, 1982.

7. "l nterim Regul atory Impact Anal ysi s Guidance," Offi ce of Management

and Budget, June 5, 1981.

8. Grant, et al., Cit., p. 67.

9. rEid., p. 91.

10. Ibid., pp. 107-131.

11. Vatavuk, W. M. and Neveril, R. B., "Estimating Costs of Air-Pollution

Cont rol Systems--Part I: Parameters fo r Si zi ng Systems," Chemi cal

Engineering, October 6, 1980, pp. 165-168.

12. Pollution Equipment News, Pittsburgh: Rimbach Publishing, 1982, pp.

71-72.

13. Internal Revenue Service, Form 1040, 1985.

14. Peters, M. S. and Timmerhaus, K. D., Plant Design and Economics

for Chemical Engineers (Third Edition). New York: McGraw-Hill, 1980,

p. 195.

15. Vatavuk, W. M. and Neveril, R. B., "Estimating Costs of Air-Pollution

Control Systems--Part II: Factors for Estimating Capital and Operating

Costs," Chemical Engineering, November 3, 1980, pp. 157-162.

16. Ibid., "Part XVII: Particle Emissions Control," Chemical Engineering,

April 2, 1984, pp. 97-99.

17. The RCRA Risk-Cost Analysis Model: U.S. Environmental Protection Agency,

Office of Solid Waste, January 13, 1984.

18. Peters and Timmerhaus, Cit., p. 203.

19. Humphries and Katell, Cit., pp. 64-68.
Section 3

THERMAL AND CATALYTIC INCINERATORS

Vi shnu S. Katari

Pacific Environmental Services (Durham, NC 27707)

Willi am M. Vatavuk

Economic Analysis Branch, OAQPS .

3.1 Process Description

3.1.1 Elements of Combustion

Fume incineration, a controlled oxidation process, is a technique

used for destruction of vaporous volatile organic compound (VOG) emissions from industrial waste gases. In the process, the VOC content of

waste gases reacts at high temperatures with oxygen to form carbon

dioxide and water, while liberating heat. Three parameters: temperature,

residence time (also referred to as II retention time ll or IIdwell time ll

)

and turbul ence (the IIthree TsII) have an i nterrel ated effect upon the

final combustion performance. To achieve good oxidation rates and

obtain release of the full heat content of the combustion products,

emission effluents must be held for sufficient residence times at

combustion temperatures 100~ or more above reported ignition

temperatures. Further, turbulent flow conditions must be maintained in

the incinerator for good mixing of the fuel combustion products with

incoming effluents, so that a thorough homogeneity of combustion elements

(VaG and oxygen) may be achieved. The ignition temperature of a given

VaG is the minimum temperature at which the VaG reacts instantaneously

with oxygen. Below this temperature (if the supply of heat were interrupted) combustion would slow down and gradually stop.

Typically, the rudimentary combustion parameters for an incinerator

design are established empirically and no calculations are involved in

their estimation. Of the 3 Ts, time and turbulence are fixed by

3-2

incinerator design and air flow rate, and only temperature can be significantly controlled. The type of VOGs present in the waste gas usually

dictates the combustion temperature for a required VaG destruction

rate. Lower or higher combustion temperatures can be used to a limited

extent, with corresponding variations in the residence time (e.g., an

incinerator can be designed for a lower residence time but must operate

at a correspondingly higher combustion temperature). The possibilities

of varying these parameters are limited, because the combustion

temperature must always be above the ignition temperature. Moreover,

the cost savings realized from reducing the residence time (and, in

turn, the incinerator size) generally are not large enough to offset the

additional expenses (e.g., fuel) resulting from compensating increases

in the combustion temperature.

In general, the design of an incinerator system is based on

providing the required amounts of: (1) heat to bring the waste gas to

the oxidation temperature and (2) oxygen for complete combustion. The

waste gas heat and oxygen contents determine, respectively, the auxiliary

heat and oxygen requirements (i.e., the lower the waste gas heat and

oxygen contents, the higher are the auxiliary requirements). Either

natural gas or fuel oil can be used as an auxiliary heat source while

ambient air is the usual source of oxygen. Natural gas is preferred

and used in most incinerators. Oil-fired burners have limited turndown capabilities and require high maintenance. Depending upon the

fuel availability and geographic location, some incinerators are designed

for a dual fuel-burning capability (natural gas with standby oii). In

practice, a flue gas oxygen content of at least 3 percent (by volume)

is used empirically to insure that a sufficient amount of oxygen is

available for combustion.
3-3

The waste gas heat content measures the potential heat of VOG that

would be released as heat of combustion upon the oxidation of the VOG. The

heat and VOG contents of a waste gas are proportional to, and can provide

a measure of. each other. They are also inherently related to, and can

be expressed empirically, in terms of the VOG property "flammability."

Flammability is characterized by two limits: the lower explosive limit

(LEL) and the upper explosive limit (UEL). These limits represent,

respectively, the smallest and largest amounts of VOGs which, when

mixed with air, will burn without a continuous application of external

heat. Major reference books present VOG flammability (LEL and UEL)

data. Table 3A-1 in Appendix 3A presents the flammability data for

several VOGs commonly encountered in industrial waste gases. To avoid

potential explosions, the VOG content of industrial waste gases released

to the atmosphere is normally outside the flammability limits. The

majority of waste gases contain low concentrations of VQGs. For safety

reasons, their composition is typically limited to below 25 percent and

will seldom exceed 50 percent of the LEL level. It has been empirically

determined that, upon combustion, most VOCs release approximately 50

Btu/scf of waste gas, if their concentration is at 100 percent of the

LEL. Therefore, the VOC content of a waste gas at less than 25 percent

LEL, the safe upper limit for incineration, will have a potential heat

content of less than 13 BTU/scf.

The LEL and heat content values of a given waste gas can also be

related empirically to the temperature rise of the combustion flue

gases. Upon combustion, each one percent of LEL of the VaG (i.e., a

potential heat content of 0.50 BTU/scf of waste gas) can raise the

temperature of one ft3 of the waste gas by 27°F based on a heat capacity
3-4

of 0.018 BTU/ft3°F for dry ai r. These empi rical relations can sometimes

be used in making qualitative observations to determine if a given waste

gas can be incinerated. They can also be used to make quick and approximate estimates of the auxiliary fuel requirement.

Most industrial waste gases incinerated are dilute mixtures of

VaGs, air, and inert gas. Their VaG content is very low, and their

oxygen content exceeds that required for combustion of both the VaG and

the auxil iary fuel. If a waste gas with a VOG content over 25 percent

LEL is encountered, it is diluted to below 25 percent LEL prior to

incineration by adding outside air (thus increasing the waste gas

vol ume flow rate to be treated). However, a waste gas with a VaG content

from 25 to 50 percent LEL can be incinerated without adding dilution air,

provided the waste gas VaG levels in the system are continuously monitored

via LEL monitors, to satisfy fire protection regulations.

A low-oxygen content waste gas mixture of VaG, air, and inert gases

could disrupt the burner flame stability. Therefore, when a waste gas

with less than 13 to 16 percent oxygen content is incinerated, the portion

of such waste gas used for fuel combustion is augmented with ambient air.

In a few applications, the waste gas is an inert gas with a low VaG content

and negligible or zero oxygen content. In such cases ambient air is

provided for burning of both the waste gas VaG and aUXiliary fuel. In

rare cases, the waste gas is a rich VaG stream that can support combustion

without auxiliary fuel. Such a rich VaG waste gas is treated as a fuel

and burned, either premixed or oxygen free. This process is sometimes

referred to as "direct flame incineration." Figure 3-1 provides a flow

chart for categorizing a waste gas to determine its suitability for

incinerati.on. (For more information on waste gas characterization,

see Appendix 38.)
3-5

Hazardous, should ~----, not be ancounterad.

For majorrty of

IIOCs, waste gas is

OUlSide the

llammability limits if

0, < 10%

No

InappropriB1e for

incineration,

"-----'-="---' Dillpollilion dapends

on composition.

(NOI covered in tllia

lae:tion.)

No

No

OO'EGORV 4

No auxiliary fuel is

llIquirad for

~----, incineration,

Do nOl use incineration.

........._--' Use as fuel or

premix with ;

addrtional fuel.

CATEGORY 5

No auxUiary air ia

llIqUirad

OOEGORY 1·

'OO'EGORV 3

Incinerale, but

mull use LEL

,COnlfOIS and

monilDrs

Auxiliary air is

llIquirad

CATEGORV 2

Auxiliary fuel ia

llIquinld lor

incineration.

OO'EOORY 8

"The IllIjoriIy of-.. _ g.- "" inc_ ran inlll C8ISQarY 1. CaIculatJonl !Dr C8togory 1 "'" __in 1IIe _ and _lions !Dr

.. calIgOries (i.e. caIIgClries 1 tIlfoug/l 61 "'" _ in Appendi. 38.

Reproduced from

best available copy.

Figure 3-1. Flow chart for categorization of a waste

gas to determine its suitability for incineration

and need for auxiliaries.
3-6

3.1.2 Types of Incinerators

Two types of incinerators are in use: thermal and catalytic. The

combustion process, as well as equipment, design concept, and calculations,

are essentially the same with both incinerator types. The only exception

is that catalytic incineration is essentially a flameless combustion

process, wherein a catalyst bed is used to initiate the combustion reaction

at much lower temperatures.

HistoMcally, the greatest reason for using a catalytic incinerator

has been to reduce fuel consumption. However, because the application of

either a thermal or a catalytic incinerator system without a heat exchanger

(for recovery of flue gas heat) is now rare, the savings associated with

catalytic incinerators are less significant. Also, this fuel economy for

catalytic incinerators is partially offset by increased operating costs for

maintenance (i.e., periodic cleaning and replacement of catalyst). Catalysts

undergo a gradual loss of activity through thermal aging, fouling, and

erosion of their surfaces. Certain poisonous contaminants, such as phosphorus, arsenic, antimony, lead, and zinc, also cause catalyst deactivation.

Catalytic incineration is not recommended for waste gases containing significant concentrations of particulate matter (either organic or inorganic)

that cannot be vaporized.

The catalysts used in catalytic incinerator systems for gaseous

VOC control are usually precious or base metals or their salts, either

supported on inert carriers, such as alumina or porcelain, or unsupported.

Precious metal oxide catalysts are less brittle and more expensive than

base metal types, and are used in lesser amounts per unit of waste gas

volume. Of the precious metal oxide catalysts, platinum/palladium

oxides are preferred. Others include rhodium, nickel, and gold.
3-7

Manganese dioxide is the most commonly used base metal oxide catalyst.

The types of VOCs present in the waste gas determine the operating

temperature required in a catalytic unit. The more stable VOCs are

generally the least reactive and require higher inlet catalytic operating

temperatures. Methane is an example of a stable, low molecular weight

compound that requires a relatively high catalytic conversion temperature,

about 1,000°F. Hydrogen, on the other hand, is extremely reactive,

having a conversion temperature of about 200°F. To achieve a VOC

destruction efficiency of at least 90 percent, the catalytic ignition

temperature for most hydrocarbons must be between 400 and 500°F.

Higher temperatures are required to obtain higher VOC destruction

efficiencies. When methane is present along with other less stable

VOCs in a waste gas, preheat temperatures lower than 1,000°F can be

used, because the less stable VOCs burn first and generate heat.

The auxiliary fuel requirement is the most significant operating

expense of an incinerator. Further, the temperature rise of the

combustion products due to the VOC heat release can be substantial.

Therefore, to minimize auxiliary fuel expenses, a part of the heat from

the incinerator flue gases is recovered. This heat is usually recovered

in recuperative heat exchangers, in which the heat from the flue gases

is exchanged with the waste gas. Both countercurrent and cross-flow

types of heat exchangers are used for this purpose. When feasible,

heat may be recovered indirectly, by producing low-pressure steam in a

waste heat boiler. Further, heat recovery from the flue gases after

primary heat recovery (PHR) can be achieved by employing secondary heat

recovery (SHR) units. Of course, SHR can be economical, only if the

secondary heat can be consumed on-site and cheaper heat sources
3-8

are unavailable. The PHR and SHR combinations are most suitable for

large installations where recovered secondary heat may be used on-site

for water heating, ai r heating, and other purposes.

In general, a typical incinerator system may include the following

components: (1) a fan to move the waste gas; (2) a fan to supply

ambient ai r, if requi red; (3) a combustion unit (i .e., a refractory chamber

with burner for thermal units, and a preheat chamber with burner and

catalyst bed for catalytic units); (4) heat recovery equipment

(optional, but almost always used); (5) controls, instrumentation, and

control panel; (6) a stack; and (7) in the case of catalytic units, a

filter/mixer to assure flow distribution, protect the catdlyst bed from

flame impingement, and remove noncombustible particulate matter. In

addi t ion, auxil i ary equi pment. such as ductwork, may be requi red in the

system.

3.2 Desi gn Procedu re

3.2.1 Design and Operating Features

The minimum waste gas characteristics data needed to perform

incinerator design calculations are the waste volume flow rate

and temperature, and the VaG composition. The waste gas flow rate

primarily determines the quantity of combustion flue gases generated

which, in turn, dictates the size of an incinerator system. As discussed

in Section 3.1, the waste gas composition determines the combustion air

requirements. The waste gas and combustion temperatures, along with

the waste gas volume flow rate and VaG content, determine the auxiliary

heat requirement and the heat exchanger size. Finally, the types of

VaG present in the waste gas determine the combustion temperature

required in the incinerator for optimum oxidation.
3-9

In the incineration process, a waste gas is introduced to the

combustion chamber, (or "preheat chamber," in the case of a catalytic

incinerator), where the waste gas temperature is raised to the

appropriate combustion temperature by burning auxiliary fuel. Because

of the high combustion temperatures maintained, refractory chambers are

used in thermal incinerators, while stainless steel or carbon steel

chambers are used in catalytic incinerators. In thermal incinerators,

the waste gas is heated and retained for 0.3 to 1.0 seconds in the

combustion chamber at 100°F or more above the ignition temperature,

which ranges from 1,000 to l,400°F for most VOCs. At these temperatures,

95 to 99 percent of the VOCs in the waste gas are combusted. As discussed

in Section 3.1, the resulting flue gases are exhausted via a stack to

the atmosphere, after a part of their sensible heat is recovered via

direct exchange with the incoming waste gas.

In catalytic incinerators, the waste gas temperature is typically

raised in the preheat chamber to 500 to 600°F. This is above the

catalytic ignition temperature of 400 to 550°F theoretically required

for 90 percent destruction of most VOCs. (Thermal and catalytic ignition

temperature data for VOCs are well documented in the literature. Table

3A-2 in Appendix A presents catalytic ignition temperatures for several

common VOCs.) The thoroughly mixed gaseous effluents from the preheat

chamber (where partial oxidation may occur) are subsequently passed

through specially designed units containing catalyst elements, on the

surface of which oxidation occurs at an accelerated rate at temperatures

of 700-900°F--much lower than typical thermal incineration combustion

chamber temperatures. As the linear velocity through the catalyst bed

is high (600 to 1,200 ft/min.), the residence time is negligible.
3-10

For this reason residence time is rarely an important factor in the

design of catalytic incinerators. The heat of reaction from the oxidation

of the VOCs in the catalyst bed causes the gas temperature to increase as it

passes across the catalyst bed. The amount of VOCs present in the

waste gas determines the temperature increase in the catalyst bed.

The desired catalyst bed outlet temperature is typically 700 to

900°F. The maximum temperature to which the catalyst bed can be exposed

continuously is limited to about 1,200°F. Therefore, the heat released

from the combustion reaction and, accordingly, the vac content of the

waste gas are limited to about 20 percent LEL. (See Section 3.2.2. for

more detail s.)

Depending upon the catalyst bed temperature swings (i.e., the

frequency at which it is subjected to extreme temperature excursions),

the operating and maintenance practices, and the particulate matter and

specific catalyst poisons encountered, the catalyst would have an

effective life of 2 to 10 years. The amount of catalyst required

(measured by the standard hourly fl ue gas vol ume flow rate per unit

vol ume of catal yst or the "space velocity, II hr-1), depends on the type of

catalyst used, but increases with the required vac destruction efficiency.

The space velocity, incinerator gas velocity, and pressure drop used

in the system design are determined experimentally.

Finally, as in thermal incinerators, the flue gases exiting the

catalyst bed are exhausted to a stack, usually after heat exchange with

the incoming waste gas.

3.2.2 Design Calculations

This section presents calculations for designing an incineration

system to the level of detail requi red by a study cost estimate. Further,

these calculations only apply to dilute mixtures of vacs, air, and inert gas.
3-11

These mixtures are typical of most industrial waste gases (i.e., those

cases which require no outside air for dilution or for combustion

of fuel and waste gas VaC--Category 1 in Figure 3-1 and Table 3B-l,

Appendix 3B). Appendix 3B presents a general procedure applicable

to all types of waste gas compositions, including those requiring the

use of outside air for combustion or dilution purposes (i.e., Categories

1 through 6 in Figure 3-1 and Table 3B-l, Appendix 3B).

Figure 3-2 is a simplified schematic of an incinerator system. A

thermocouple in a thermal incinerator combustion chamber measures

temperature, and appropriate control circuitry alters the rate of

auxiliary fuel entering the incinerator to maintain the desired combustion

temperature. In catalytic incinerators, thermocouples installed in the

preheat chamber and catalytic bed perform the same function.

The incinerator design calculations for the waste gas cases where

no outside air is added for either combustion or dilution and where the

vac content is low (i.e., Category 1) can be summarized by the following

step-wise approach. The items that must be calculated or estimated

in the design of any emission control system are those which determine

the system size, performance, and capital and operating costs. In the

case of incinerators, these items are: (1) the auxiliary fuel requirement

and flue gas flow rate; (2) for catalytic incinerators, the amount of

catalyst required; and (3) the pressure drop across the system.

Item 1. Calculate Auxiliary Fuel Requirement and Flue Gas Flow Rate.

The calculations of the auxiliary fuel requirement and the flue gas flow

rate constitute an important incinerator design item. The flue gas flow rate

determines th~ incinerator system size and, consequently, its capital cost.

The auxiliary fuel can be a major operating cost for an incinerator system.
W

I

~, I-' ,"N

Flue Gas to

Vent/Stack!

Ambient (7)

Waste gas from the process

(0)

Heat Loss f------- DII." •• AIr' (0) (Hal -

t--

Combustion Catalyst Heat

ry Chamberb Exchanger Flue Bedc (6) (3) (Optional) Gas (5)

(2) j.

Auxflia

Fuel

Combustion

Air. (4)

Ca) When required.

Cb) Referred to as Preheat Chamber in

the case of catalytic incinerators.

Cc) Included only in catalytic incinerators.

Figure 3- 2. Schematic diagram of an incinerator system.
3-13

Identify the waste gas composition data. These

include: the volume flow rate (Ql), scfm; temperature

(Tl), of; VOC content, %LEL; and heat content (hI),

BTU/scf of waste gas. The heat content of the waste

gas is a function of the VOC content. (The waste gas

pressure is not a design consideration, because the

majority of waste gases enter the incinerator at

atmospheric pressure.)

For thermal incinerators, determine the combustion

temperature (T5) based on the desired VOC destruction

efficiency. Suggested combustion temperature (T5)

values for waste gases containing nonhalogenated VOCs

are 1,600°F and 1,800°F. respectively, for 98 and 99

percent VOC destruction efficiencies. These temperatures

correspond to a O.75-second residence time in the

incinerator. Higher temperatures of about 2,OOO°F

(and I-second residence time) are required for the

destruction of halogenated VOCs by 98 percent or

Step 2.

Calculations of the auxiliary fuel requirement and flue gas

flow rate are considered as one item, because they are interrelated.

The specified flue gas conditions determine the amount of auxiliary

fuel consumed which, in turn, becomes a part of the flue gas. The

necessary waste gas and combustion information to be compiled and

the calculations to be performed are presented in the following

steps:

Step 1.

more.
3-14

For catalytic incinerators, select the preheat

temperature (Ts) considering the amount and type of vacs

present in the waste gas. Upon oxidation in the catalyst

bed, the heat content of the waste gas vacs is released

in the bed. Consequently, the temperature of the bed and

waste gas increase, as explained in Section 3.1.1, by

about 27°F per each one percent of vac LEL. For most

vacs oxidized on precious metal catalysts, the suggested

preheat temperature (T5) is 60aoF. For a waste gas content

of 4 to 10 percent LEL, this results in an average catalyst

operating temperature of 7UU to 9UO°F (i.e., 60UoF + [4

to 10J% LEL x 27°F/%LEL = 70U to 9UO°F).

Less stable VOCs, such as monohydric alcohols,

aromatic hydrocarbons or propylene, can use lower catalyst

operating temperatures, on the order of 500°F.

In rare cases, where the vac content in the waste

gases is less than 2 percent LEL, higher preheat temperatures

(7aa-75aOF), or more catalyst than typically required, may

have to be used to obtain equivalent 700° to 900°F catalyst

operating temperature and VOC destruction. However, to

avoid this increase in fuel/catalyst costs, the vac content

of the waste gas is increased when possible by repeated

recycling of waste gases within the process being controlled,

before introducing them to the incinerator.

Waste gases with vac contents higher than 20 percent

LEL are not suitable for catalytic incineration, because
3-15

the vac heat content released increases the catalyst bed

temperature to beyond 1,200°F. the maximum permissible

temperature to which the catalyst bed can be exposed

continuously.

Conversely, for the destruction of more stable vacs.

such as methane, higher preheat temperatures (900-1.000°F)

are used. This, however, requires a lower maximum allowable

vac content--i.e., 7 to 11%.

Step 3. (Applies to only catalytic incinerators.) Calculate the

catalyst bed outlet temperature (T6). As indicated in

Step 2, T6 should not exceed 1,200°F. Further, as explained

in Section 3.1.1, the heat of combustion released by the

vac in the waste gas increases the waste gas temperature

by 27°F for each one percent of LEL. Because the average

heat capacity of air is approximately 0.018 BTU/scf-oF,

the waste gas heat content required to increase the waste

gas temperature by 27°F would be equivalent to 0.5 BTU/set.

(0.018 x 27). It foll ows that a waste gas vac heat content

of 1 BTU/scf would, when released through combustion,

increase the waste gas temperature by about 55°F upon

release (2 x 27°F). Therefore, we can write:

(3-1 )

where T5 = Preheat temperature, of, determi ned from

Step 2

hI = Waste gas heat content, (BTU/scf of waste

gas)

Q1/Q5 =Ratio of the waste gas flow rate at the

i nci nerator i nl et to the fl ue gas flow rate

at the preheat chamber exi t. For dil ute

waste gases consider the ratio to be equal

to 1, by neglecting the increase in flue

gas volume due to the fuel addition.

T6 < 1200°F
3-16

Step 4. Determine the waste gas temperature at the incinerator inlet

(T2) = the temperature at the heat exchanger outlet.

With thermal incineration, T2 must be no higher than

1,000 to 1,100°F, to avoid preignition of the waste gas

before it reaches the combustion chamber. T2 is also

limited by the heat VOC content of the inlet waste gas. As

eq. 3-1 indicates, the temperature rise realized in the

combustion chamber is proportional to this heat content.

For example, if a 20 percent LEL stream were incinerated,

the temperature rise would be about S40°F (20 x 27 0 ).

Subtracting this from a combustion temperature of IS00°F

yields a maximum T2 of about 9S0°F. For catalytic

incinerators, the waste gas temperature (T2) entering the

preheat chamber can be as high as the preferred preheat

temperature (TS), 600°F.

Broadly speaking, as T2 increases, the auxiliary fuel

requirement (and cost) decreases. But at the same time,

the size and cost of the recuperative heat exchanger

increases, driving up the total capital investment of the

system. Thus, there is a trade-off between capital and

operating costs, the extent of which depends upon the value

of T2 selected. However, as this selection depends

on the results of a process optimization analysis, no

firm guidance can be given for selecting T2--except that

it should not exceed the design limits noted above. The

discussion that follows may guide one in performing such an

optimization.
3-17

First of all, the waste gas temperature entering the

combustion chamber/preheat chamber is determined by the

heat exchanger heat transfer performance (denoted by

or HE) and the waste gas inlet temperature (T1).

For incinerator systems with heat exchangers

T2 = Tl (the temperature of the entering waste gas).

For incinerator systems with primary (recuperative)

heat exchangers, T2 is calculated from the known value of

the system1s heat exchanger heat transfer performance

(~) and the following expressions:

T2 = Tl + (TS Tl) for thermal incinerators

T2 = Tl + (T6 Tl) for catalytic incinerators

(Note: Use of a secondary heat exchanger has no affect

on the T2 value.)

Theoretically, a heat exchanger heat transfer performance

(0) approaching 100 percent is possible. However, as the heat

exchanger performance increases the required heat transfer

area, the heat exchanger cost increases enormously,

approaching infinity as approaches 100 percent.

Therefore, heat exchanger is selected based on economic

considerations, as well as the waste gas and flue gas data.

Included among the waste gas and flue gas data which impose

limitations on are: (1) the flue gas temperature at
3-18

the heat exchanger outlet (T7) in the case of either type

of incinerator and (2) t~e waste gas vac content in the

case of thermal incinerators.

Depending upon the flue gas constituents, mainly

moisture and corrosive elements, T7 should be about 5aO~,

due to possible equipment corrosion" and condensation

that may occur if it falls below this temperature.

The value of T7 is related to by the following

equati on:

= QsCps

Q2CP2

= Q6CP6

Q2CP2

TZ - Tl [1 - T5 _ T1 ] for thermal incinerators (3-4)

[1 - Tz - Tl] for catalytic incinerator (3-5) T6 - T1

where Q1, Q5, and Q6 = waste gas flow rate and flue gas flow rates

at the exit of combustion chamber and

catalyst bed respectively (scfm)

CP2, CP5, and CP6 =Mean heat capacities of waste gas and

of flue gas at the exit of the combustion

chamber3and catalyst bed, respectively (Btu/ft OF)

It is evident from the above equation that maximum

possible increases with the value of Tl. However, Tl can

never equal or exceed T7.

The following heat transfer performance (~) capabilities are commonly reported for typical modular heat exchangers:

35 to 40 percent for I-pass, 45 to 50 percent for 2-pass, and

65 to 70 percent for 3-pass units.

Step 5. Calculate the amount of auxiliary fuel required (Q3) based

on the following energy balance around the combustion chamber/

preheat chamber (see Figure 3-2):
Amount of

sensible heat

1eavi ng

3-19

Amount of

sensible heat = enteri ng

Amount of

heat of VOCs

rel eased

from . combusti on

Amount of

+ heat of fuel

released from

combustion

where

(H5 + HL) - (H2 + H3) = Q1 hI + Q3 h3 (for thermal incinerators) (3-6)

(H5 + HL) - (H2 + H3) = Q3 h3' (for catalytic incine- (3-7)

rators, because VOC heat

content is not released

in the preheat chamber).

H5 = Sensible heat of flue gas at the combustion

chamber/preheat chamber exit (BTU/min)

HL = Heat loss = 10% H5 (assumed)

H2 = Sensible heat of waste gas at the incinerator/

preheat chamber inlet (BTU/min)

H3 = Sensible heat of fuel used (BTU/min) = a (for fuel entering at ambient conditions)

Q1 = Waste gas flow rate (scfm)

Q3 = Auxiliary fuel flow rate (scfm)

hI = Waste gas heat content (BTU/scf of waste gas)

h3 = Lower heating value (LHV) of fuel (BTU/scf).

By substituting Hi = Qi CPi DoTi, where CPl represents the

mean heat capacity for the temperature difference of DoTi

(Ti-Tr, the reference temperature) the sensible heat

values of the gas streams leaving and entering the

chamber can be expressed by the following equations:

(3-8)

where = Mean heat capacity of the flue gas for the

temperature interval of DoT5) from the

reference temperature (70°F) to the combustion temperature (in the case of thermal

incinerators) or to the preheat temperature

(in the case of catalytic incinerators)3

CP5 =0.0194, 0.0196, and 0.0198 BTU/ft of

for thermal incinerator combustion

temperatures of 1,600, 1

j

800, 2,000°F, respect- ively, and 0.0183 BTU/ft of for a catalytic

incinerator preheat temperature of 600°F

(3-9 )
where

3-20

CP2 = Mean heat capacity of the waste gas for

the temperature interval &2 from the

reference temperature (70°F) to the

temperature at the inlet of the incinerat03

/

preheat chamber (T2). CP2 = 0.0181 BTU/ft of

for waste gas temperatures (Tl) up to 300°F

(3-10)

Substituting the above enthalpy values for H2 and HS

and Ql + Q3 = Q2 + Q3 for QS in eq. (3-6) or (3-7),

rearranging the resulting equation, and accounting for

the heat loss yields the following (see Appendix 3B for

details):

= Fuel used, ft3/std.ft3 of waste gas

= 1.1 Cps LlTS - CP2 LlT 2 - h1

h3 - 1.1 Cs LlT S

Step 6. Calculate the gas flow rate leaving the combustion

chamber/preheat chamber (QS). In the case of a thermal

incinerator, because the combustion takes place primarily in the combustion chamber, the resulting flue

gas consists of the products of combustion of the waste

gas VOCs and the auxiliary fuel. In the case of catalytic

incinerators, because fuel is added in the preheating

chamber to raise the waste gas temperature for subsequent

combustion in the catalyst bed, the gases exiting the

preheat chamber consist of the waste gas and the products

of fuel combustion.

In the incineration of dilute VOC waste gases the

flue gas flow rate is approximately equal to the total

of the waste gas flow rate and fuel flow rate used for
3-21

combustion, because no outside combustion air is used

(i .e., Q4 = 0). (This is because, in the case of thermal

incinerators, the increase in flow rate due to combustion

of the waste gas VOCs and fuel is negligible.) Therefore,

as indicated above:

where

Q5 = Q2 + Q3

Q5 =Flue gas flow rate (scfm)

Q2 =Waste gas flow rate (scfm)

Q3 = Auxiliary fuel burned (scfm)

Item 2. Establish the Amount of Catalyst Required.

(3-11)

The cost of catalyst consumed or replaced represents a significant

catalytic incinerator operating cost item. Therefore, the amount of

catalyst used and its expected life must be accurately determined in

the initial design of a catalytic incinerator system.

The amount of catalyst required usually depends upon the type and

age of catalyst used, types and amounts of VOCs encountered, the

destruction efficiency required, and the amounts of potential reactants

present that impair the catalyst activity, which is usually highest when

the catalyst is fresh. Because in most cases only limited information

is available about the potential reactants and noncombustible particulate

matter that may be present in the waste gas, most catalytic incinerator

systems are overdesigned to compensate for the unexpected. The amounts

of catalyst required for the destruction of various types of VOCs are

usually established by laboratory tests by catalyst manufacturers.

The amounts of precious metal catalysts commonly used are 1.5 and

2 ft3 per 1,000 scfm waste gas (equivalent to space velocities of

40,000 and 30,000 hr- 1) for 90 and 95 percent VOC destruction

efficiencies, respectively.(l) The corresponding amounts of base metal
3-22

catalysts used are 4 to 6 ft3j1,000 scfm (i .e., space velocities of

15,000 to 10,000 hr-1).(2)

Item 3. Determine the Pressure Drop Required Across the System.

The total pressure drop requi red across an incinerator system

determi nes the waste gas fan si ze and horsepower requi rements, whi ch,

in turn, determine the fan capital cost and electricity consumption.

The total pressure drop across an incinerator system depends on

the number and types of equipment included in the system and on

design considerations. The estimation of actual pressure drop requi rements involves complex calculations based on the specific system's

waste gas and flue gas conditions and equipment used. For the purposes

of this section, however, the following approximate values can be used:

Pressu~e drop (~p, in. H20) across

Thermal i nci nerators = 4

Catalytic incinerators = 6

Heat exchangers: 35% = 4

50% = 8

70% = 15

Once the total pressure drop required is estimated (as a summation

of the pressure drops across all pieces of equipment in the incinerator

system), the blower electricity requirements can be estimated from the

basic fan horsepower requirement equation. For example, at a combined

fan-motor efficiency of 62 percent, the fan horsepower equation dictates

that 0.19 kWh of electricity per hour is required for moving 1,000 acfm

of flow rate at a I-in. water pressure drop. Therefore. the fan

power requirement is estimated by multiplying the total pressure drop

(inches of water) by the total flue gas flow rate (thousand acfm) and

the 0.19 kWhjhr factor. For the cases where an additional fan is

3-24

carbon steel units at costs of 60 to 70 percent of that for stainless

steel units. Of course, the 1ife of such equi pment will be lower--

approximately 10 years. Catalytic incinerators will tolerate lower grade

material (e.g., carbon steel) better than thermal units because of thei r

lower operating temperatures. However, catalyst bed enclosures are mostly

fabricated of stainless steel.

3.3.1 Thermal Incinerator Equipment Costs

Figure 3-3 presents thermal incinerator equipment costs (April 1986

dollars) as a function of the waste gas volume flow rate at standard

conditions of 70°F and 0 psig. This figure was developed from cost

information received from three incinerator manufacturers for three

volume flow rates each.(3,4,5) Analytical equations for these equipment

cost curves are presented in Tabl e 3-1. (The tabl e al so presents

analytical equations for catalytic incinerators, the cost curves for

which are discussed in Section 3.3.2.) The equipment costs listed

represent all the equipment in an incinerator system including a combustion chamber with burner, waste gas fan, inlet and outlet plenums,

prepiping and prewiring, instrumentation and controls, a 10-ft stack,

and in the case of heat recovery, a primary heat exchanger. The cost

data apply to the cases of dilute vac content waste gases (to which no

outside air is added) containing up to 25 percent LEL vac and incinerated

at a 150aoF combustion temperature.

The Figure 3-3 (or Table 3-1) cost data can be applied to other cases

of waste gas compositions including those requiring slightly different

combustion temperatures without introducing significant errors to the costs.

When these data are applied to different combustion temperatures,
3-25

5 20 50 lOa

50~iiiiiii

3

l'OOO~~

-\0 500

co

en

- 400 --sa.

< 300

0

Q

0

•

...

-

• 200

en

Q

, , .j.,) )'

c

I;; i

0-

.... . , , , ;

c- 100 , I.! ';'i I t , .. I.LJ

Volume Flow Rate, 1,000 scfm

Figure 3-3. Thermal incinerator equipment; cost estimates
TABLE 3-1. EQUATIONS FOR INCINERATOR EQUIPMENT COSTSa

(APRIL 1986 DOLLARS)

~-=-=--==............,.. = ..... ~.= -::z .z=.=.::zo=.=: :C=Z:::=-':E-=-==~ ~-'--=--r ':=--='=-=:-:=: ·=_-=·=-=:a·~-_=-=_a:===-~~~=--.=·=..;:-~~..:--'_=.:~_==-~=~~-=-=:"==- -~=--==_=:;;.;:.,: ~;;:.:=

Extent of

heat Equipment cost equation for Equipment cost equation for

exchange thermal i nci nerators b catalytic incinerators

None 1n Eq = [14,402 - 992(lnQ)+ 70 (In Q)2] (10-3) In Eq = [24,086 - 3,252(ln Q)+ 205 (lnQ)2](10- 3

35% 1 n Eq = [16,175 - 1,262(1 nQ)+ 85 (1 n Q)2] (10-3) 1n Eq = [27,170 - 3,789(1 n Q)+ 231 (1 nQ)2](10-3

50% 1n Eq = [15,784 - 1,165(1 nQ)+ 81 (1 n Q)2] (10-3) In Eq = [26,497 - 3,650(1n Q)+ 225 (lnQ)2](10-3

70% 1n Eq = [20,608 - 2,119(1 nQ)+ 131 (1 n Q)2](l0-3) In Eq = [21,685 - 2,643(ln Q)+ 174 (lnQ)2](10-3

=,=,":z::..==-~~ ........... .=-_..:=:==: =- ~~='=~=~._::=C::.:-:_-:-~ -

aThese equations should not be extrapolated outside the flowrate range of 5,000 to 50,000 scfm.

b Eq - Equipment cost in April 1986 dollars, Q - Volume flow rate in scfm.

W

I

N

O'l
3-27

it is assumed that the system will tolerate minor adjustments

to the incinerator face velocity and residence time values resulting

from these temperatures. Even if the system size were adjusted to

compensate for these different temperatures,the resulting changes in

the equipment cost would be minor. For example, if a combustion chamber

were sized for a combustion temperature of 1,700°F instead of 1,500°F

the cost increase due to the increase in combustion chamber size would

be less than 5 percent.

The Figure 3-3 and Table 3-1 cost data can also be applied to

cases of waste gas compositions to which outside ambient air is added

for combustion. In these cases, the flue gas flow rate at standard

conditions must be substituted for the waste gas flow rate in the

figure.

3.3.2 Catalytic Incinerator Equipment Costs

Figure 3-4 presents catalytic incinerator equipment costs (April

1986 dollars) as a function of the waste gas volume flow rate at standard

conditions (70°F and 0 psi g), developed from cost information received

from five equipment manufacturers.(6-10) Analytical equations representing these cost data are presented in Table 3-1. The equipment

cost data represent all the equipment in an incinerator system, including

the burner, fan, housing, skid mounting, instrumentation and controls,

a lO-ft stack, catalyst, and where heat recovery is used, a primary

heat exchanger. The cost data apply to dilute vac waste gases requiring

a temperature of 60aoF at the preheat chamber exit/catalytic bed inlet.

The cost data can be applied to waste gases to which outside air is

added by substituting the fiue flow rate at standard conditions for

the waste gas flow rate in Figure 3-4.
3-28

100

., .

Exchange

20 50

,,,' :' 0 No HE"

I' , ' , ,'.

, 0 35% HE I I , II I I

" , I II I

" I:, " . 50~ HE I

I , :,:"."

0 70~ HE

5

5-. 100

LLJ

....

3

700

50011 400

--

s.

Q,

300

Q

0.

Volume Flow Rate, 1,000 scfm

. Figure 3-4. Catalytic incinerator equipment cost estimates
3-29

3.3.3 Total Capital Investment for Incinerators

The total incinerator capital investment as a percentage of equipment cost varies with the type of installation. i.e., whether custom or

package. The type of incinerator installation is an important consideration. For most nonchemical industry operations, such as drying ovens,

painting facilities, printing and coating operations and other processes

where incinerators are commonly used for VOC control, waste gas flow rates

generated are small. Modul ar i nci nerator units, prefabri cated and

preassembled, are most suitable for such flow rates. The size of

skid-mounted modular units is limited to handling flows up to about

20,000 cfm, .mainly because of limitations to the sizes of trucks carrying

them and access doors at the plant sites. Of course, larger units,

prefabricated and partially assembled, are possible for outdoor installations. Some incinerators handling up to 100,000 cfm, which are partly

field-fabricated and field-assembled, can be found in chemical plant

applications. Typically, heat exchangers can accommodate gas flows from

3,000 to 20,000 cfm. For larger flowrates, multiple heat exchangers

units are usually installed in parallel in a single incinerator system.

For incinerators, the total capital investment varies from a small

percentage (about 110 percent) to more than 200 percent of the total

equipment purchased cost. The custom installation charges of an incinerator

system, i ncl udi ng i nci nerator and heat exchanger units, ductwork, fans,

and a tall stack if required, may amount to 300 to 400 percent of the

total equipment purchased cost, depending upon the installation.

The skid-mounted units ready to be placed on a concrete pad at a

prepared site incur the lowest installation expenses. Roof top installations will require higher costs, field-assembled units even higher,
3-30

and field-fabricated and assembled units the highest costs.

For estimating purposes, the total capital investment (TCI) of a

skid-mounted modular unit can be calculated at .125 percent of the total

purchased equipment cost. Conversely, Table 3-2 presents typical

estimated capital cost factors applicable to custom installations of

both thermal and catalytic incinerator systems. No cost factor is

included for estimating ductwork cost in the table because the ductwork

size and length and, consequently, its cost will vary with the installation and the waste gas flowrate. For both packaged and custom incinerator units, the ductwork capital cost must be estimated separately.

Alternatively, in the case of custom units, the purchased cost of the

ductwork and other auxiliary equipment can be added to the total incinerator equipment cost prior to applying the Table 3-2 factors for estimating

the total capital investment. (Note: As Section 2 of the Manual

indicates, the TCI also includes costs for land, working capital, and

off-site facilities, which are not included in the direct/indirect

installation factor. However, as these items are rarely required with

incinerator systems, they will not be considered here. Further, no

factor has been provided for site preparation (S.P.), or buildings (Bldg.)

since these site-specific costs depend very little on the purchased equipment

cost. Lastly, for the incinerator cases in which outside air is added

for combustion or dilution, the cost of the fan used for this purpose

also must be estimated separately.)

3.4 Estimating Total Annual Cost

3.4.1 Direct Annual Costs

For incinerator systems with no heat exchanger, the cost of auxiliary

fuel is the major direct annual cost. Fuel costs are considerably
3-31

TABLE 3-2. CAPITAL COST FACTORS FOR CUSTOM THERMAL AND CATALYTIC INCINERATORS a

Cost Item Cost Factor (Fraction of Indicated Cost)

DIRECT COSTS

1) Purchased egui pment cost

Incinerator

Auxi 1i ary equi pmentb

I nstruments and control SC

Taxes

Frei ght

As requi red L

As requi red }1\

0.1 A

0.03 A

0.05 A

Total Purchased Equipment cost

2) Direct installation costs

B(=1.18A)

Foundations and supports

Erection and handli n9

El ect ri cal

Piping

Insul ation

Pai nti ng

Site preparation (S.P) Buildings

(Bldg. )

Total Installation Direct Costs

Total Di rect Cost

0.08 B

0.14 B

0.04 B

0.02 B

0.01 B

0.01 B

As regui red

0.30 B + S.P. + Bldg.

1.30 B + S.P. + Bldg.

INDIRECT COSTS

0.31 B

0.10 B

0.05 B

0.10 B

0.02 B

0.01 B

0.03 B

Engineering and supervlslon

Constructi on and fi eld expenses

Constructi on fee

Start-up

Perfonnance test

Conti ngency

Total Indi rect Costs

Total Di rect and Indi rect costs = Total Capital Investment ]1.61 B + S.P. + Bldg. L ~=-- -=o=o~ __..".",=--__I

:...-.z=o=o~ ,""""", ===-==_==o=o~~.~ -=

aReferenc"e 11.

bIncludes ductwork and any other equipment normally not included with unit furnished

by incinerator vendor.

cCost of instrumentation and controls often furnished by vendor.
(3-12)

3-32

lower for catalytic incinerators than for thermal units because of the

lower operating temperature. Besides the fuel, the utility requirements

for an incinerator include electricity for the waste gas fan and, if

used, the ambient air fan. Operating labor is usually small for both

types of incinerators--0.5 hr/shift.(ll)

Maintenance costs of well-designed and maintained thermal or catalytic

incinerators of either type are low, with a substantial portion required

for the heat exchanger maintenance. (Well-designed and fabricated heat

exchangers, i.e., stainless heat exchangers, usually have lower maintenance

expenses.) The incinerator unit maintenance requirements may include

repairs to the refractory lining and blowers, maintenance of control

instruments, and cleaning of flame rods, if used. Maintenance labor

may be estimated at 0.5 hr/shift. The maintenance materials may be assumed

to equal the maintenance labor cost.(ll)

Depending upon the incinerator and how it is operated, the life

of a given load of catalyst may be 2 to 10 years. A conservative

estimate of catalyst replacement cost can be based on the lower life

time--2 years. The initial costs of precious metal and base metal

(manganese dioxide) catalysts are $3,000/ft3(1) and $600/ft3 (2),

respectively. Item 2 of Section 3.2.2 showed how to estimate the

catalyst requirement (ft3). Finally, the catalyst replacement labor is

minimal compared to the catalyst cost.

Based on these values and the estimating procedure shown in Section 2,

the catalyst replacement cost (CRCcat) would be:

CRCcat = Ccat x 1.08 x CRFcat
3-33

TABLE 3-3. SUGGESTED FACTORS FOR ESTIMATING INCINERATOR ANNUAL COSTS

Item

Direct Operating Costs

Operating labora

Supervi sory 1abora

Maintenance labor

Maintenance materials a

Repl acement parts

Util iti es:

Fuel

£1 ectri ci tyb,c

Suggested Factor

0.5 hr/shi ft

15% of operating labor

0.5 hr/shift

100% of maintenance labor

Thermal incinerators: None

Catalytic incinerators: (See eq. 3-12)

The amount of fuel requi red is cal cul ated from

Step 5 (Q3) of Section 3.2.

Use the following P values in estimating electricity requirements:

Thermal incinerators = 4 in. water

Catalytic incinerators = 6 in. water

Heat exchange of

35%

50%

70%

Ductwork and stack

= 4 in. water

= 8 in. water = 15 in. water

= As requi red

Indirect Operating Costs

Overhead

Administrative charges

Property tax

Insurance

Capit~ recovery coste

60% of sum of operating, supervisory, and maintenance

labor and maintenance materials

2% XTCI d

1%XTCId

1%XTCI

CRFs X [TCI - 1.0~ x Ccat]

aReference 11.

bThe total P of an incinerator system is the sum of base (i.e., incinerator)

P + heat exchanger P.

CAn equation to calculate electricity requirements (kWh per hour) is given

in Item 3 of Section 3.2.2.

dTCI =Total capital investment.

€!The CRFs (system capital recovery factor) is a function of the equipment life

(10 years, typically) and the opportunity cost of the capital (i.e., interest

rate). For instance, for a 10-year 1ife and a 10% interest rate, CRF s = 0.1628.
3-34

where: Ccat = initial catalyst cost ($)

1.08 = factor accounting for taxes and freight

CRFcat = capital recovery factor for catalyst (e.g., for a

2-year life and a 10% interest rate, the factor would

be 0.5762).

3.4.2 Indirect Annual Costs

As Table 3-3 shows, the indirect (fixed) annual operating costs

include capital recovery; overhead; and property taxes, insurance, and

administrative charges. The last three costs can be estimated at 1

percent, 1 percent, and 2 percent of the total capital investment,

respectively. The system capital recovery cost is based on an estimated

10-year equipment life. (The incinerator system life varies from 5 to

15 years depending on the material of construction used and the durability

of the design.) However, as Section 2 indicates, the system capital

recovery cost is the product of the system capital recovery factor

(CRFs) and the total capital investment (TCI) less the purchased cost

of the catalyst (IICcat x 1.0811 ), Thi s offset is necessary to avoid

double-counting.

Finally, overhead may be estimated at 60% of the sum of operating,

supervisory, and maintenance labor and maintenance materials. (See

Section 2 of the Manual for a detailed discussion of the items comprising

the total annual cost.)
3-35

References for Section 3

1. Telephone conversation: Robert M. Yarrington (Engelhard Corporation, Union, NJ) with Vishnu S. Katari (Pacific Environmental Services,

Inc., Du rh am , NC), J une 2, 1986 •

2. Telephone conversation: Bob Campbell (Pillar Technologies, Inc.,

Hartland, WI) with Tom Rhoads (Pacific Environmental Services, Inc.,

Durham, NC), February 28, 1986.

3. Correspondence: Ralph N. Stettenbenz (C-E Air Preheater, Combustion

Engineering, Inc., Wellsville, NY), to Vishnu S. Katari, April 3,1986.

4. Correspondence: Ronald J. Baschiere (Hirt Combustion Engineers,

Montebello, CA) to Vishnu S. Katari, April 7,1986.

5. Correspondence: C.le Bumford (Peabody Engi neeri ng, Stamford, CT)

to Michael K. Sink (Pacific Environmental Services, Inc., Durham, NC),

Ma rch 24, 1986.

6. Correspondence: Robert M. Yarrington (Engelhard Corporation, Union,

NJ) to Vishnu S. Katari, April 30, 1986.

7. Correspondence: Kent Lewis (C-E Ai r Preheater, Combustion Engineering,

Inc., Well svill e, NY) and Vi shnu S. Katari, June 16, 1986.

8. Correspondence: Robert Hablewitze (Pillar Technologies, Inc., Hartland,

WI) to Vishnu S. Katari, March 3,1986.

9. Co rrespondence: Thomas Schmi dt (Energy Devel opmentAssoci ates, I tascon,

IL) to Michael K. Sink, March 7, 1986.

10. Correspondence: Ri chard J. Ihde (TEC Systems, DePere, WI) to Mi chael K.

Sink, March 11, 1986.

11. Vatavuk, William M. and Neveril, Robert. IIEstimating Costs of AirPollution Control Systems, Part II: Factors for Estimating Capital and

Operating Costs. 1I Chemical Engineering, November 3. 1980, pp. 157-162.
APPENDIX 3A. LOWER AND UPPER EXPLOSIVE LIMITS FOR VOCs
3A-2

TABLE 3A-1. FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE

ORGANIC COMPOUNDS IN AIRa,b

Mol. LEL,c UEL,d

wt. % vol. % vol.

Methane 16.04 5.0 15.0

Ethane 30.07 3.0 12.4

Propane 44.09 2.1 9.5

n-Butane 58.12 1.8 8.4

n-Pentane 72.15 1.4 7.8

n-Hexane 86.17 1.2 7.4

n-Heptane 100.20 1.05 6.7

n-Octane 114.23 0.95 3.2

n-Nonane 128.25 0.85 2.9

n-Decane 142.28 0.75 5.6

n-Undecane 156.30 0.68

n-Dodecane 170.33 0.60

n-Tridecane 184.36 0.55

n-Tetradecane 108.38 0.50

n-Pentadecane 212.41 0.46

n-Hexadecane 226.44 0.43

Ethyl ene 28.05 2.7 36

Propyl ene 42.08 2.4 11

Butene-1 56.10 1.7 9.7

cis-Butene-2 56.10 1.8 9.7

Isobutylene 56.10 1.8 9.6

3-Methyl-Butene-1 70.13 1.5 9.1

Propad iene 40.06 2.6

1,3-Butadiene 54.09 2.0 12

Acetylene 2.5 100

Methyl acetylene 1.7

Benzene 78.11 1.3 7.0

Toluene 92.13 1.2 7.1

Ethyl benzene 106.16 1.0 6.7

o-Xyl ene 106.16 1.1 6.4

m-Xyl ene 106.16 1.1 6.4

p-Xyl ene 106.16 1.1 6.6

Cumene 120.19 0.88 6.5

p-Cymene 134.21 0.85 6.5

Cyclopropane 42.08 2.4 10.4

Cyclobutane 56.10 1.8

Cyclopentane 70.13 1.5

Cyclohexane 84.16 1.3 7.8

Ethylcyclobutane 84.16 1.2 7.7
3A-3

TABLE 3A-l. FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE

ORGANIC COMPOUNDS IN AIRa,b

(concluded)

===-===:~.:a:===.:....::..:a .:::z....:= =~~==.:.~-::z:

Mol. LEL, UEL,

wt. % vol. % vol.

Cycloheptane 98.18 1.1 6.7

Methylcyclohexane 98.18 1.1 6.7

Ethylcyclopentane 98.18 1.1 6.7

Ethyl cycl ohexane 112.21 0.95 6.6

Methyl al cohol 32.04 6.7 36

Ethyl al cohol 46.07 3.3 19

n-P ropyl al cohol 60.09 2.2 14

n-Butyl al cohol 74.12 1.7 12

n-Amyl al cohol 88.15 1.4 10

n-Hexyl al cohol 102.17 1.2 7.9

Dimethyl ether 46.07 3.4 27

Di ethyl ether 74.12 1.9 36

Ethyl propyl ether 88.15 1.7 9

Diisopropyl ether 102.17 1.4 7.9

Acetaldehyde 44.05 4.0 36

Propi onal dehyde 58.08 2.9 14

Acetone 58.08 2.6 13

Methyl ethyl ketone 72.10 1.9 10

Methyl propyl ketone 86.13 1.6 8.2

Diethyl ketone 86.13 1.6

Methyl butyl ketone 100.16 1.4 8.0

~-~~~~===

aReference 1.

bMost common handbooks (e.g., Reference 2) provide

flammability information for VOCs.

cLEL - lower explosive limit

dUEL - upper explosive limit
3A-4

TABLE 3A-2. CATALYTIC IGNITION TEMPERATURE

FOR 90% CONVERSIONa

Component Temperature, of

Hyd rogen

Acetylene

Carbon monoxide

Propyne

Propadi ene

Propyl ene

Ethylene

.Q.-Heptane

Benzene

Toluene

Xylene

Ethanol

Methyl ethyl ketone

Methyl isobutyl ketone

Propane

Ethyl acetate

Dimethyl formamide

Ethane

Cyclopropane

Methane

aReference 3.

220

395

425

460

480

500

550

575

575

575

575

600

700

700

770

775

800

810

850

920
3A-5

References for Appendix 3A

1. Hilado, Carlos J., IIHow to Predict if Materials Burn," Chemical

Engineering, December 14, 1970, pp. 174-178.

2. Handbook Qf Chemistry and Physics, 54th Edition. Cleveland: The

Chemical Rubber Co., 1973-1974, pp. D85-D92.

3. Organic Chemical Manufacturin Volume!: Combustion Control Devices,

\EPA-450/3-80-026 • Research Tri angl e Park: U.S. Envi ronmental

Protection Agency, Emissions Standards and Engineering Division.

December 1980. Report 3, p. 1-2.
APPENDIX 3B

This appendix presents equations to estimate flue gas and fuel

requirements of incineration systems combusting all types of waste

gas compositions. These equations have been derived from energy and

material balances around the incinerator system. Figure 3B-1, a

reproduction of Figure 3-2, Section 3.2, is a schematic of an incinerator

system. {All streams shown in Figure 3B-1 are also identified by the

same subscripts in the energy and material balances}

lIe.t lou

(1\)

lIast. gas fr_ t'" proceu

(0)

"""u ",. ,OJ

lIast. Gil (I)

CoIIbustion

Afr' (4) ----.4

Auxn fary ---+f

Fu.l (3)

CoIIbustfon

Chuberb Flue

Gn (5)

(6)

Heat

Exch.nger

(Optfonal)

Flu. GiS to

Vent/Stackl

AIIbfent (7)

(.) IIhen required.

(b) Referred to as Pr.....t Chub.r hi

the c.se of c.t.lytfc fncfner.tors.

(c) Included only fn c.talytic IncfnerAtors. Reproduced from

best available copy.

Figure 3B-1. Schematic diagram of an incinerator system.

Energy Bal ance

The basic energy balance equation around the combustion chamber is:

sensib~e heat] rSensibl: heatl _ [Heat released] [Heat released J

leavlng - L enterlng J - from the + from the combustion , combustion of of fuel

VOCs

From Figure 3B-1, (HS + HL) - (H2 + H3 + H4) = Q1 hl + Q3 h3

where: H =Sensible heat of the stream identified by the

subscript, Btu/min

Q = Flow rate of the stream identified by the subscript, scfm
3B-2

hI = Waste gas heat content released upon combustion,

BTU/scf of waste gas

h3 = Lower heating value (LHV) of fuel (BTU/scf)

Assume

Therefore,

H3 = °for fuel at ambient temperature

H4 =°for ambient air

HL = 10% of H5

1.1 HS - H2 = Q1 hI + Q3 h3

Substituting the sensible heat expression H = Q Cp ~T in the above equation

yields:

(3B-1)

where Q = Flow rate (scfm)

Cp = Mean heat cap9city for the temperature interval

of ~T, BTU/ft3 of

~T = Temperature interval from TR (70°F) to T identified by the subscript

hI = Waste gas heat content (BTU/scf of waste gas)

h3 = Lower heating value (LHV) of natural gas

BTU/ft3

Material Balance (see Figure 3B-1)

An (approximate) material balance around the combustion chamber yields:*

(3B-2)

where Q5 = Flue gas flow rate (scfm)

Q2 = Waste gas flow rate entering the system (scfm)

Q3 = Auxiliary fuel burned (scfm)

Q4 = Ambient air used for combustion (scfm)

The quantities of Q2' Q3' and Q4 are estimated as follows:

1) Waste gas entering the combustion chamber (Q2)

= QO For cases of waste gases to which no dilution ai r

is added (i.e., Cases I, 2, and 4 through 6 in

Table 3B-1)

= QO (he/hd) For cases of waste gases to which dilution

air is added (i.e., Case 3 in Table 3B-1) (3B-3)

where he = Waste gas heat content before dilution, BTU/scf

hd = Waste gas heat content after dilution.

*Strictly speaking, equation 3B-2 is a mole balance, not a material balance.

However, because the moles (or volumesr-or the reactants (Vac, fuel, ai r,

etc.) entering the combustion chamber/catalyst bed approximately equal the

moles of products leaving (H20, C02, N2' etc.), equation 36-2 is accurate--

at least for purposes of this Manual.
3B-3

2) Ambient air used (Q4)

Q4 = 0 For dilute VOC waste gases (category 1 in

Tabl e 3B-1)

Q4 = Q4,VOC + Q4,Fuel (3B-4)

where Q4.VOC = Ambient air used for the combustion of the

VOC = Q2 [Lmi (X + Y/4 - Z/2)i - rna ] 4.79

2

where mi = Volume content of ith VOC component in the waste

gas

X, Y, Z = Atoms of C. H2, and 02 in the VOC

rna =Volume content of oxygen in the waste gas

2

Q4,Fuel = Ambient air used for the combustion of the fuel = 9.58 (base amount of fuel burned)(l + E)

where

where

E = Excess air used, %of total stoichiometric air

requi rement for fuel .Q!!.l.l

K = Excess amount used, %of base amount

The value of K can be determined as follows:

(Additional fuel used)

= [9.58 (base amount of fuel) E + Add iti onal fuel] CPS llTS ... h3*

Therefore.

Additional fuel used

K = Base amount of fuel

= 9.S8E/ [(h3/CPS llT5) - 1]

(3B-5)

= Constant for a given fuel and known values of E and TS

= a for dilute VOC waste gases.

*In other words, the "additional fuel" must heat both the excess ai r used

in combustion of the base fuel and itself, from the ambient (reference)

temperature to the combustion temperature (T5)'
38-4

Estimation of Combustion Flue Gases Generated

Substituting the values of Q2, Q3, and Q4 into the basic material

balance equation (Equation 38-2) yields the following expression:

Qs =Q2 + Q3 + Q2 [Imi (X + Y/4 - Z/2)i - m~ ] 4.79

+ 9.S8 (base amount of fuel)(l + E)

(3B-6)

so that:

Z/2)i - ma ] 4.79

2

However, the base amount of fuel = Q3/(1 + K),

Qs = Q2 + Q3 + Q2 [Imi (X + Y/4 -

+ 9.S8 Q3 (1 + E)/(l + K)

= Q2 + Q3 (for dilute vac waste gases)

(3B-7)

The above equation applies to the waste gases to which ambient air

is added for combustion purposes. However, in many cases, the waste gas

contains air sufficient to provide partial or complete combustion air

(38-8)

]

requirements. Table 38-1 identifies various waste gas types and their

ambient air and auxiliary fuel requirements. Table 3B-2 presents the

equations for estimating the flue gas (QS) flow rate from the combustion

of each type of waste gas.

Estimation of Actual Amount of Auxiliary Fuel Burned (Q3)

Substituting the material balance equation (Equation 3B-2) into the

energy balance equation (Equation 38-1) and solving for Q3/Q2 (i.e., the

amount of fuel required per unit of waste gas flow rate) yields the

following expression:

Q3 1.1 [1 +

Q2 =

_ 1.1 CPS flTS - CP2 flT2 - hI - h3 - 1.1 CPS flTS (for dilute waste gases)

The values of all items in the above equation are specific to the

waste gas composition and fuel type. Therefore, the equation can be further
3B-5

TABLE 3B-l. CATEGORIZATION OF WASTE GAS STREAMS

Category

1

2

3

4

5

6

Waste gas Composition

Mixture of VOC, air, and inert gas with >16% 02

and a VOC content <25% LEL (i.e., heat content

<13 Btu/ft3)

Mixture of VOC, air, and inert gas with >16% 02

and a VOC content between 25 and 50% LEL (i.e.,

heat content between 13 to 26 Btu/ft3)

Mixture of VOC, air, and inert gas with <16% 02

Mixture of VOC and inert gas with zero to

negligible amount of 02 (air) and <100 Btu/scf

heat content

Mixtu~e of VOC and inert gas with zero to

negligible amount of 02 (air) and >100 Btu/scf

heat

Mixture of VOC and inert gas with zero to negligible amount of 02 and heat content insufficient to

raise the waste gas to the combustion temperature

Auxiliaries and other requirements

Auxiliary fuel is required. No auxiliary

air is requ ired.

Dilution air is required to lower the heat

content to <13 Btu/ft3• (Alternative to

dilution air is installation of LEL monitors.)

Treat this waste stream the same as categories 1 and 2, except augment the portions

of the waste gas used for fuel burning with

outside air to bring its 02 content to above

16 percent.

Oxidize it directly with a sufficient amount

of air.

Premix and use it as a fuel.

Auxiliary fuel and combustion air for both

the waste gas VOC and fuel are required.
Waste gas

category

1

2

3

4

5

6

3B-6

TABLE 3B-2. EQUATIONS FOR ESTIMATING FLUE GAS QUANTITIES

Equations for flue gas flow rate (Q5). scfm

Q5 = Q2 + Q3. where Q2 = Qo

Q5 = Q2 + Q3. where Q2 = QO (he/hd)

Q5 = Q2 + Q3 + Q4.Fuel • where

Q4,Fuel = 9.58 (l+E) (Base amount of fuel used)

=9.58 Q3 (l+E)/(l+K)

Q5 = Q2 + Q2 [Dni (X + Y/4 - Z/2)i - rna ] 4.79 (l+E)

2

Assumes no auxiliary fuel except for pilot is needed

Premix and use it as a fuel.

Q5 = Q2 + Q3 + 9.58 Q3 (l+E)/(l+K) + Q2 [Dni (X + Y/4 - Z/2)i - mO ] 4.79

2
3B-7

simplified by substituting known values of these items.

The val ues of Cp and K are establ i shed based on the waste gas

temperature, flue gas combustion temperature, and the type of fuel used.

The overall Cp value of the flue gas is calculated more accurately from

the Cp values of the flue gas components, which include C02, H20, 02,

and N2. Alternatively, as an approximation, the Cp value of air can be

substituted for Cp values of the flue gas and the waste gas. The mean

heat capacity values for air are 0.0194,0.0196, and 0.0198 BTU/ft3°F

for combustion temperatures of 1,600, 1,800, and 2,OOO°F, respectively.

The mean heat capacity value of air, to use with a waste gas at 100°F,

is 0.018 BTU/ft3°F.

At a combustion temperature of l,600°F, K = 0.033 for a LHV of 900

BTU/ft3 for natural gas, an excess air of 10 percent, and a reference

temperature of 70°F. When this value of K and the values of Cps' and

~Ts' are substituted into equation 3B-8, assuming the waste gas

temperature to be 100°F, we obtain:

Table 3B-3 presents equations for estimating fuel requirements of

all types of waste gases.
3B-8

TABLE 3B-3. EQUATIONS FOR ESTIMATING FUEL REQUIREMENTS

Waste gas

category Gener~l e~uation for fuel,ft /ft of waste gas

1 1.1 CpS D.T5 - CP2 D.T2 - h)

h3 - 1.1 CP5 D.T5

1.1 CPSD.ts - CP2D.Tr - hI

h3 - 1.1 CP5D. 5

3b,c 1.1 CPSD.T S - CPZD.T Z - hI

(h3 - 1.1 CP5D.T5) - 10.54 CP5 D.T5 (l+El/(l+K)

4 ld.CpsD.Ts + 1.1 [l:mj (X + Y/4 - Z/2)jJ 4.79 (HE) CPSD.Ts - CP2t:.T2 - h)

h3

5

6

Waste gas is premixed and used as fuel.

Q3 = 1.1 [l + (l:mi (X + Y/4 - Z/2)i - mo~) 4.79J CPjt:.Ts - [CPZt:.T2 + hIJ

Q2 (h3 - 1.1 CP5t:.T5) - 10.54 ( +E) CP5t:.T5 (l+K)

aThe waste gas for this category must be adjusted for dilution (See Table 38-2).

bE - Excess air used

cK - Constant = 9.58E/[(h3/CP5t:.T5) - 1J.

- i

Sect ion 4

CARBON ADSORBERS

William M. Vatavuk

Economic Analysis Branch. OAQPS

William L. Klotz and Robert L. Stallings

Research Triangle Institute

(Research Triangle Park, NC 27709)

4.1 Process Description

4.1.1 Introduction

In air pollution control, adsorption is employed to remove volatile

organic compounds (VOC's) from low to medium concentration gas streams,

when a stringent outlet concentration must be met and/or recovery of the

VOC is desired. Adsorption itself is a phenomenon where gas molecules

passing through a bed of solid particles are selectively held there by

attractive forces which are weaker and less specific than those of

chemical bonds. During adsorption, a gas molecule migrates to the surface

of the solid where it is held by physical atttraction releasing energy--

the "heat of adsorption" , which approximately equals the heat of condensation.

Adsorptive capacity of the solid for the gas tends to increase with the

gas phase concentration.

Some gases form actual chemical bonds with the adsorbent surface

groups. This phenomenon is termed "chemisorption".

Most gases ("adsorbates") can be removed ("desorbed") from the

adsorbent by heating to a sufficiently high temperature, usually via

steam, or by reducing the pressure to a sufficiently low value (vacuum

desorption). The physically adsorbed species in the smallest pores of

the solid and the chemisorbed species may require rather high temperatures

to be removed, and for all practical purposes cannot be desorbed during

regeneration. For example, approximately 3 to 5 percent of organics

adsorbed on virgin activated carbon is either chemisorbed or very
4-2

strongly physically adsorbed and, for all intents, cannot be desorbed

during regeneration.(1)

Adsorbents in large scale use include activated carbon, silica gel,

activated alumina, synthetic zeolites, fuller's earth, and other clays.

This Section is oriented toward the use of activated carbon, a commonly

used adsorbent for vacs.

4.1.2 Types of Adsorbers

Five types of adsorption equipment are used in collecting gases: (1)

fixed regenerable beds; (2) disposable/rechargable cannisters; (3)

traveling bed adsorbers; (4) fluid bed adsorbers; and (5) chromatographic

baghouses.(2) Of these, the most commonly used in air pollution control are

the fixed bed and cannister types.

4.1.2.1 Fixed-bed Units

Fixed-bed units are normally used for controlling continuous, VOCcontaining streams over a wide range of flowrates, ranging from several

thousand to several hundred thousand cubic feet/minute (cfm). The VOC

concentration of streams treated by fixed-bed adsorbers can be as low as

several parts per billion (ppbv) by volume in the case of some toxic

chemicals or as high as 25% of the VOCs' lower explosive limit (LEL).

For most VOCs, this ranges from 25UO to 1U,UOU ppmv.(3) Fixed-bed adsorbers

may be operated in either intermittent or continuous modes. In intermittent

operation, the adsorber removes vac for a specified time (the "adsorption

time"), which corresponds to the time during which the controlled source

is emitting VOC. After the adsorber and the source are shut down (e.g.,

overnight), the unit begins the desorption cycle during which the captured

VOC is removed from the carbon. This cycle, in turn, consists of three
4-3

steps: (1) regeneration of the carbon by blowing steam through the bed

in the direction opposite to the gas flow; (2) drying of the bed, with

compressed air or a fan; and (3) cooling the bed to its operating temperature via a fan. (In some designs, the same fan can be used both for bed

drying and cooling.) At the end of the desorption cycle (which usually

lasts 1 to 1 1/2 hours), the unit sits idle until the source starts up

again.

In continuous operation a regenerated carbon bed is always available

for adsorption, so that the controlled source can operate continuously

without shut down. For example, two carbon beds can be provided: while

one is adsorbing, the second is desorbing/idled. As each bed must be

large enough to handle the entire gas flowrate while adsorbing, twice as

much carbon must be provided than an intermittent system handling the

same flowrate. If the desorption cycle is significantly shorter than the

adsorption cycle, it may be more economical to have three, four, or even

more beds operating in the system. This can reduce the amount of extra

carbon capacity needed or provide some additional benefits, relative to

maintaining a low vae content in the effluent. (See Section 4.2 for a more

thorough discussion of this.)

A typical two-bed, continuously operated adsorber system is shown in

Figure 4-1. One bed is adsorbing at all times, while the second is

desorbing/idled. As shown here, the VaC-laden gas enters vessel #1

through valve A, passes through the carbon bed (shown by the shading) and

exits through valve B, from whence it passes to the stack. Meanwhile,

vessel #2 is in the desorption cycle. Steam enters through valve C,

passes up through the bed and exits through D. The steam-VQe vapor
I

Decanter

Out In

,

Coo11ng

Water

Total

Condenser

'Water

(To Treatmentl

Sewer)

VOC

Condensate I

(To Storage, • Processing)

SteamVOC Vapor

I

Outlet

Gas

D

, ..' • (To Stack)

Vessel 11

(Drying/Cooling Air)

Steam

Waste Gas

(From

Source)

System Fan

(Dryingl Cooling Air) ~~I '

Figure 4-1. Typical Two-Bed, Continuously Operated Fixed-Bed Carbon Adsorber Syst~
4-5

mixture passes to a condenser, where cooling water condenses the entire

mixture. The condensate next passes to a decanter, where the VOC

and water layers are separated. The VOC layer is conveyed to storage.

If impure, it may receive additional processing, such as distillation.

Depending on its quality (i.e., quantity of dissolved organics), the

water layer is discharged either to a wastewater treatment facility or to

the sewer.

Once steaming is completed, valves C and D are closed and valve E is

opened, to allo~ air to enter to dry and cool the bed. After this is

done, the bed is placed on standby until vessel #1 reaches the end of its

adsorption cycle. At this time, the VQC-laden gas is valved to vessel #2,

while vessel #1 begins its desorption cycle, and the above process is

repeated.

In Figure 4-1, the system fan is shown installed ahead of the vessels,

though it could also be placed after them. Further, this figure does not

show the pumps needed to bring cooling water to the condenser. Nor does

it depict the solvent pump which conveys the VOC condensate to storage.

Also missing are preconditioning equipment used to cool, dehumidify, or

remove particulate from the inlet gases. Such equipment mayor may not

be needed, depending on the condition of the inlet gas. In any case,

preconditioning equipment will not be covered in this Section.

4.1.2.2 Cannister Units

Cannister-type adsorbers differ from fixed-bed units, in that they are

normally limited to controlling low-volume, (typically 100 ft 3/min, maximum)

intermittent gas streams, such as those emitted by storage tank vents, where

process economics dictate that toll regeneration or throw-away cannisters
4-6

are appropriate. The carbon cannisters may not be desorbed. Alternatively,

the carbon may be regenerated at a central facility. Once the carbon

reaches a certain VOC content, the unit is shut down, replaced with

another, and disposed of or regenerated by the central facility. Each

cannister unit consists of a vessel, activated carbon, inlet connection

and distributer leading to the carbon bed, and an outlet connection for

the purified gas stream.(4) In one design (Calgon1s Ventsorb®), 150 lbs

of carbon are installed on an 8-inch gravel bed, in a 55-gallon drum.

The type of carbon used depends on the nature of the VOC to be treated.

In theory, a cannister unit would remain in service no longer than a

regenerable unit would stay in its adsorption cycle. Doing so would

prevent the allowable outlet concentration from being exceeded. In

reality, however, poor operating practice may result in the cannister

remaining connected until the carbon is near saturation. This is because:

(1) the carbon (and often the vessel) will probably be disposed of, so

there is the temptation to operate it until the carbon is saturated; and

(2) unlike fixed-bed units, whose outlet VOC concentrations are monitored

continuously (via flame ionization detectors, typically), cannisters are

usually not monitored. Thus, the user can only guess at the outlet

loadiny,and could tend to leave a unit in place longer.

4.1.3 Adsorption Theory

At equilibrium, the quantity of gas that is adsorbed on activated

carbon is a function of the adsorption temperature and pressure, the

chemical species being adsorbed, and the carbon characteristics, such as

carbon particle size and pore structure. For a given adsorbent-VOC

combination at a given temperature, an adsorption isotherm can be constructed
4-7

which relates the mass of adsorbate per unit weight of adsorbent

("equilibrium adsorptivity") to the partial pressure of the VOG in the

gas stream. The adsorptivity increases with increasing VaG partial

pressure and decreases with increasing temperature.

A family of adsorption isotherms having the shape typical of adsorption

on activated carbon is plotted in Figure 4-2. This and other isotherms whose

shapes are convex upward throughout, are designated "Type I" isotherms. The

Freundlich isotherm can be fit to a Type I curve; and it is commonly used

in industrial design.(2)

where:

p

=

=

=

(4-1)

equilibrium adsorptivity (lb adsorbate/lb adsorbent)

partial pressure of VaG in gas

stream (psia)

k,m = empirical parameters

The treatment of adsorption from gas mixtures is complex and beyond

the scope of this Section. Except where the VaG in these mixtures have

nearly identical adsorption isotherms, one VaG in a mixture will tend

displace another on the carbon surface. Ge.nerally, VOGs with lower vapor

pressures will displace those with higher vapor pressures, resulting in

the former displacing the latter previously adsorbed. Thus, during the

course of the adsorption cycle the carbon's capacity for a higher vapor

pressure constituent decreases. This phenomonen should be considered

when sizing the adsorber. To be conservative, one would normally base

the adsorption cycle requirements on the least adsorbable component in a

mixture and the desorption cycle on the most adsorbable component.(1)

The equilibrium adsorptivity is the maximum amount of adsorbate the

carbon can hold at a given temperature and VaG partial pressure. In
....

>....

+d

c:L, '-,

o

lit

§

....

'-

.,g

....

-....

=' a'

Adsorbate Partial Pressure (psia)

Figure 4-2. Freundlich (Type I) Adsorption Isotherms

For Hypothetical Adsorbate
4-9

actual control systems, however, the carbon bed is never allowed to reach

equilibrium. Instead, once the outlet concentration reaches a preset

1imit (the IIbreakthrough concentrat i on ll

), the adsorber is shut down for

desorption or (in the case of cannister units) replacement and disposal.

At the point where the vessel is shut down, the bed vac concentration may

only be 50% or less of the equilibrium concentration.

As equation 4-1 indicates, the Freundlich isotherm is a power function

that plots as a straight line on log-log paper. Conveniently, for the

concentrations/partial pressures normally encountered in carbon adsorber

operation, most vac - activated carbon adsorption conforms to equation

4-1. At very low concentrations, typical of breakthrough concentrations,

a linear approximation to the Freundlich isotherm is adequate. However,

the Freundlich isotherm does not accurately represent the isotherm at

high gas concentrations and thus should be used with care as such concentrations are approached.

Adsorptivity data for several vacs were obtained from an activated

carbon vendor and fitted to the Freundlich equation.(S) These VOCs are

listed in Table 4-1. The adsorbates listed include aromatics (e.g.,

benzene, toluene), chlorinated aliphatics (dichloroethane), and one

ketone (acetone). However, the list is far from all-inclusive. Additional

isotherm data are available from the activated carbon vendors, handbooks

(such as Perry's Chemical Engineer's Handbook), and the literature.

Notice that a range of partial pressures is listed with each set of

parameters, IIkll and IImll. (Note: In one case (m-xylene) the isotherm was

so curvilinear that it had to be split into two parts, each with a different

set of parameters.) This is the range to which the parameters apply.
4-10

Table 4-1 Parameters for Selected Adsorption Isothermsa,b

Isotherm Range of

Adsorption Parameters isothermc

Adsorbate Temp. (OF) k m (psia)

(1) Benzene 77 0.597 0.176 0.0001-0.05

(2) Ch1orobenzene 77 1.05 0.188 0.0001-0.01

(3 ) Cyc1ohexane 100 0.508 0.210 0.0001-0.05

(4) Dich1oroethane 77 0.976 0.281 0.0001-0.04

( 5) Phenol 104 0.855 0.153 0.0001-0.03

(6 ) Trichloroethane 77 1.U6 0.161 0.0001-0.04

(7) Vinyl Chloride IOU 2.00 0.477 U.0001-0.0~

( 8) m-Xy1ene 77 0.708 0.113 0.0001-0.Ll01

77 0.527 0.0703 O.LlOl -0.05

(9) Acry1 onitril e 100 0.935 0.424 0.0001-0.015

(10) Acetone 100 0.412 0.389 0.0001-0.05

(11 ) Toluene 77 0.551 0.110 0.0001-0.05

a Reference 5.

b Each isotherm is of the form: w =kpm. (Set text for definition of terms)

Data are for adsorption on Ca1gon type IIBPLII carbon (4 x 10 mesh).

c Equations should not be extrapolated outside these ranges.
4-11

Extrapolation beyond this range--especially at the high end--can introduce

inaccuracy to the calculated adsorptivity.

But high-end extrapolation may not be necessary, as the following

will show. In most air pollution control applications, the system pressure

is approximately one atmosphere (14.696 psi a). The upper end of the

partial pressure ranges in Table 4-1 goes from 0.04 to 0.05 psia.

According to Oalton1s Law, at a total system pressure of one atmosphere

this corresponds to an adsorbate concentration in the waste gas of 2,720

to 3,400 ppmv. However, as discussed in Section 4.1.2, the adsorbate

concentration is usually kept at 25% of the lower explosive limit (LEL).

For many VOCs, the LEL ranges from 1 to 1.5 volume %, so that 25% of the

LEL would be 0.25 to 0.375% or 2,500 to 3,750 ppmv, which approximates

the high end of the partial pressure range~ in Table 4-1.

Finally, each set of parameters applies to a fixed adsorption

temperature, ranging from 77° to 104° F. These temperatures reflect

typical operating conditions, although adsorption can take place as low

as 32°F and even higher than 104°F. As the adsorption temperature increases

to much higher levels, however, the equilibrium adsorptivity decreases to

such an extent that VOC recovery by carbon adsorption may become economically

i mpr acti ca1•

4.2 Design Procedure

4.2.1 Sizing Parameters

Data received from adsorber vendors indicate that the size and purchase

cost of a fixed-bed or cannister carbon adsorber system primarily depend on

four parameters:
4-12

(1) The volumetric flowrate of the vae laden gas passing throu~h

the carbon bed(s);

(2) The inlet and outlet voe mass loadings of the gas stream;

(3) The adsorption time (i.e., the time a carbon bed remains on-line

to adsorb voe before being taken off-line for desorption of

the bed);

(4) The working capacity of the activated carbon.

In addition, the cost could also be affected by other stream conditions,

such as the presence/absence of excessive amounts of particula~e, moisture,

or other substances which would require the use of extensive pretreatment

and/or corrosive-resistant construction materials.

The purchased cost depends to a large extent on the volumetric

flowrate (usually measured in actual ft3/min). The flowrate, in turn,

determines the size of the vessels housing the carbon, the capacities of ttle

fan and motor needed to convey the waste gas through the system, and the

diameter of the internal ducting.

Also important are the vue inlet and outlet gas stream loadings,

the adsorption time, and the working capacity of the carbon. These

variables determine the amount and cost of carbon charged to the system

initially and, in turn, the cost of replacing that carbon after it is

exhausted (typically, five years after startup). Moreover, the amount of

the carbon charge affects the size and cost of the auxiliary equipment

(condenser, decanter, bed drying/cooling fan), because the sizes

of these items are tied to the amount of voe removed by the bed. The

amount of carbon also has a bearing on the size and cost of the vessels.

To illustrate this effect, for each of a range of flowrates, the vae

inlet concentration was increased ten-fold from 500 to 5000 ppm, while
4-13

the respective flowrates and adsorption times were held constant. The

resultiny purchased costs obtained from a vendor increased by an aver aye

of 27%.(6) Part of these increases was needed to pay for the additional

carbon required. However, some was also needed for enlarging the adsorber

vessels to accomodate the added carbon and for the additional structural

steel needed to support the larger vessels. Also, larger condensers,

decanters, cooling water pumps, etc., were necessary to treat the more

concentrated voe streams. (See Section 4.3.)

The vae inlet loading is set by the source parameters, while the

outlet loading is set by the voe emission limit. (For example, in many

states, the average vae outlet concentration from adsorbers may not

exceed 25 ppm.)

4.2.2 Determining Adsorption and Desorption Times

The relative times for adsorption and desorption and the adsorber

bed configuration (i.e., whether single or multiple and series or parallel

adsorption beds are used) establish the adsorption/desorption cycle

profile. The cycle profile is important in determining carbon and vessel

requirements and in establishing desorption auxiliary equipment and

utility requirements. An example will illustrate. In the simplest case,

an adsorber would be controlling a process which emits a relatively small

amount of voe intermittently--say, during one 8-hour shift per day.

During the remaining 16 hours the system would either be desorbing or on

stand-by. Such a system would only require a single bed, which would

contain enough carbon to treat eight hours worth of gas flow at the

specified inlet concentration, temperature, and pressure. Multiple beds,

operating in parallel, would be needed to treat large gas flows (>100,00U

std. ft 3/min, generally)(6), as there are practical limits to the sizes
4-14

to which adsorber vessels can be built. But, regardless of whether a

single bed or multiple beds were used, the system would only be on-line

for part of the day.

However, if the process were operating continuously, extra carbon

capacity would have to be built into the system. The amount of this

extra capacity would depend on the number of carbon beds that would be

adsorbing at anyone time, the length of the adsorption period relative

to the desorption period, and whether the beds were operating in parallel

or in series. If one bed were adsorbing, a second would be needed to

come on-line when the first was shut down for desorption. In this case,

100% extra capacity would be needed. Similarly, if five beds in parallel

were adsorbing at any given time, again only one extra bed would be

needed and the extra capacity would be 20% (i.e., 1/~)--provided, of

course, that the adsorption time were at least five times as long as the

desorption time. The relationship between adsorption time, regeneration

time, and the required extra capacity can be generalized.

Mc =McI x f (4-2)

where: Mc' McI =amounts of carbon required for continuous or intermittent

control of a given source, respectively (lbs)

f =extra capacity factor (dimensionless)

The factor, f, is related to the number of beds adsorbing (NA) and

desorbing (NO) in a continuous system as follows:

NO

f= 1 + INA (4-3)

(Note: NA is also the number of beds in an intermittent system that would be

adsorbing at any given time. The total number of beds in the system would

be NA + NO.)
4-15

It can be shown that the number of desorbing beds required in a continuous

system (NO) is related to the desorption time (00), adsorption time (OA), and;

the number of adsorbing beds, as follows:

(4-4)

(Note: 00 is the total time needed for bed regeneration, drying, and cooling.)

For instance, for an eight-hour adsorption time, in a continuously operated

system of seven beds (six adsorbing, one desorbing) 0 0 would have to be 1 1/3

hrs or 1ess (8 hrs/6 beds). Otherwi se, additi ona1 beds wou1 d have to be added to

provide suffi ci ent extra capacity. duri ng desorpti on.

4.2.3 Estimating Carbon Requirement

4.2.3.1 Carbon Estimation Procedures Developed

Obtaining the carbon requirement (Mc or Mc ) is not as straightforward as

I

determining the other adsorber design parameters. When estimating the carbon

charge, the depth of the approach used depends on the data and calculational

tools available. In preparing this Section of the Manual, we have developed

two procedures for estimati ng the carbon requi rement. The fi rst procedure,

descri bed in more detai 1 below, is based to a 1arge extent on ru1 es-of-thumb.

This procedure, sometimes employed by adsorber vendors, is relatively

simple and easy to use, though it normally yields results incorporating a

1arge safety margi n.

The second procedure yi elds a more accurate estimate of the carbon

requirement but requires additional input data. In addition, the procedure

is of such mathematical complexity that a microcomputer is needed to use

it. This procedure is centered on the IIBED-.?IZE II model, developed by

William L Klotz of Research Triangle Institute. The program 1I •••uses a

detailed mathematical description of the adsorption process to predict the

bed size needed to maintain the effluent [outlet] concentration below a
4-16

defined allowable maximum when the inlet concentration is constant over

the time period for operation. II {7} Inputs needed to run the program

include the inlet and desired outlet (llbreakthrough ll ) vac concentrations,

gas stream temperature, and the IIbreakthrough time,1I which is usually

equal to the adsorption time. Other inputs needed are the carbon particle

size and bed void fraction and the gas superficial velocity through the

bed. (Superficial velocity is discussed in Section 4.3.1.) As outputs,

the program provides the carbon equilibrium capacity, working capacity

(see below), the requiTed bed size (as measured by the bed depth) and

pressure drop, and the bed efficiency--lIthe percent removal of all adsorbate entering the bed up to the breakthrough time. 1I This efficiency

is calculated by integrating the ratio of vac removed to the vac inlet

rate over the entire adsorption cycle. (See Section 4.4.3. for more on

thi s.)

These BED_SIZE outputs, along with the bed superficial velocity and

other parameters, are input to a second model (IICARADS II ), developed by

the Economic Analysis Branch. This model is'used to determine the carbon

requirement, size the adsorber vessels. and estimate the system capital

and annual costs in a manner similar to the rule-of-thumb procedure

detailed in the next sections. However, where the rule-of-thumb procedure

may be done by hand, a microcomputer is needed to utilize the CARADS

model.

4.2.3.2. Carbon Estimation Procedure Used in Manual

The rule-of-thumb carbon esimation procedure is based on the II wo rking

capacityll (wc , lb VaC/lb carbon). This is the difference per unit mass

of carbon between the amount of vac on the carbon at the end of the
4-17

adsorption cycle and the amount remaining on the carbon at the end of the

desorption cycle. It should not be confused with the lIequilibrium capacityll (we)

defined above in Section 4.1.3. Recall that the equilibrium capacity

measures the capacity of virgin activated carbon when the VaG has been in

contact with it (at a constant temperature and partial pressure) long

enough to reach equilibrium. In adsorber design, it would not be feasible

to allow the bed to reach equilibrium. If it were, the outlet concentration

would rapidly increase beyond the allowable outlet (or IIbreakthrough ll)

concentration until the outlet concentration reached the inlet concentration.

During this period the adsorber would be violating the emission limit.

The working capacity is some fraction of the equilibrium capacity.

Table 4-2 com~iles working capacities for selected VOGs. These data were

obtai ned from an adsorber manufacturer. (8) . For compari son, Table 4-2 also

shows the equilibrium capacities for some of these VOGs, which were computed

from the parameters given above in Table 4-1 in Section 4.1. Note that

the working capacities range from 24 to 100% of the respective capacities

at equilibrium, with an average value of 48%. This average approximates

the rule-of-thumb used by adsorber vendors--that is, working capacity

equals 5a% of equilibrium capacity. Further, like the equilibrium adsorptivity, the working capacity depends upon the temperature, the VaG partial

pressure, and the vac composition. The working capacity also depends on

the flow rate and the carbon bed parameters.

The working capacity, along with the adsorption time and VOC inlet

loading, is used to compute the carbon requirement for a cannister adsorber

or for an intermittently operated fixed-bed adsorber as follows:
4-18

Table 4-2. Equilibrium vs. Working Carbon Capacity for

Selected VOCs(8)

Adsorption Partial Carbon Capacities C

Compound Temp. (OF)a Press. (psi a)b Equilibrium(We) Working(Wc) wc/we Ratio

(1) Acetone 100 0.0147 0.0798 0.08 1.0

(2) Benzene 77 0.000147 0.126 0.06 0.48

(3) Cyclohexane 100 0.00441 0.163 0.06 0.37

(4) Toluene 77 0.00294 0.290 U.U7 0.24

( 5) m-Xylened 77 0.00147 0.333 0.10 0.3U

Aver aye 0.48

a Temperature at which equilibrium capacity was measured.

b Oirectly proportional to the VOC concentration in the influent (ppmv).

Calculated as follows:

Partial pressure =Cone. (ppmv) x 14.696 psia x 10-6

c Measured as lb of VOC/lb. of carbon. Equilibrium capacities were calculated

using parameters in Table 4-1; working capacities were obtained from Reference

8.

d Actually, the compound listed in Reference 8 was "xylene." The precise

structure -- i.e., ortho, meta, or para -- was not given. However, as the

molecular weight of all three is the same, we have assumed that the working

capacity data would apply to m-xylene, as well as to the other two isomers.
4-19

(4-5)

where: mVOC = vac inlet loading (lb/hr)

Combining this with equations (4-2) and (4-3) yields the general equation for

estimating the system total carbon charge:

Mc

=mVOC 0A (1 + NO/NA)

Wc

(4-6)

Values for Wc may be obtained from Table 4-2 or similar data sources. If

no value for Wc is available for the VOC (or VOC mixture) in question,

the working capacity may be estimated at 5U% of the equilibrium capacity, as

foll ows:

(4-7)

where: we(max) = the equnibrium capacity (lb VOC/lb carbon) taken at

the adsorber inlet (i.e., the point of maximum voe

concentrati on).

(Note: To be conservative, this 50% figure should be lowered if short

desorption cycles, very high vapor pressure consituents, or difficultto-desorb VOCs are involved.)

* * *

Example: A source emitting 100 1b/hr toluene is to be collected in a

carbon adsorberc The system operates continuously, with two beds adsorbing

at all times. For convenience, adsorption and desorption times of 12 and

1.5 hours, respectively, have been chosen. The total gas flowrate is

35,000 ft3/min at 77°F and 1 atmosphere (or approximately 200 ppmv of VUC).

Assume negligible quantities of particulate and moisture. Calculate the

system carbon requirement. Solution: From Table 4-2, we find the working

capacity of toluene to be 0.07 lb/lb carbon. Since the regeneration time
4-20

(1.5 hrs) is less than 1/2 the adsorption time (see eq. 4-4), one extra bed

will be adequate. Substituting these values into equation 4-6 yields the

carbon requirement:

Mc = (100 lb VOC/hr)(12 hr) (1 + 1/2)

0.07 lb VOC/lb carbon

=approximately 25,700 lbs.

* * *

As equation 4-6 shows, the carbon requirement is directly proportional

to the adsorption time. This would tend to indicate that a system could

be designed with a shorter adsorption time to minimize the carbon requirement

(and purchased cost). There is a trade-off here not readily apparent from

equation 4-6, however. Certainly, a shorter adsorption time would require

less carbon. But, it would also mean that a carbon bed would have to be

desorbed more frequently. This would mean that the regeneration steam

would have to be supplied to the bed(s) more frequently to remove (in the

long run) the same amount of VOC. Further, each time the bed is regenerated

the steam supplied must heat the vessel and carbon, as well as drive off

the adsorbed VOC. And the bed must be dried and cooled after each desorption,

regardless of the amount of VOC removed. Thus, if the bed is regenerated

too frequently, the bed drying/cooling fan must operate more often, increasing

its power consumption. Also, more frequent regeneration tends to shorten

the carbon life. As a rule-of-thumb, the optimum regeneration frequency for

fixed-bed adsorbers treating streams with moderate to high VUC inlet

loadings is once every 8 to 12 hours.(l)

4.3 Estimating Total Capital Investment

An entirely different procedure should be used in estimating the
4-21

purchased costs of fixed-bed and cannister-type adsorbers. Therefore,

they will be discussed separately.

4.3.1 Fixed-Bed Systems

As indicated in the previous section, the purchased cost is a function

of the volumetric flowrate, VOC inlet and outlet loadings, the adsorption

time, and the working capacity of the activated carbon. As Figure 4-1

shows, the adsorber system is made up of several different items. Of

these, the adsorber vessels and the carbon comprise nearly 3/4 of the

purchased cost. There is also auxiliary equipment, such as fans, pumps,

condensers, decanters, and internal piping. But because these usually

comprise a small part of the total purchased cost, they may be "factored"

from the costs of the two major items without introducing significant

error. The costs of these major items will be considered separately.

4.3.1.1 Carbon Cost

This cost (Cc ,$) is simply the product of the initial carbon requirement (M c) and the current price of carbon. As adsorber vendors bUy carbon

in very large quantities (million-pound lots or larger), their cost is

somewhat lower than the list price. Current vendor costs typically

range from $1.60 to $2.00/lb (spring 1986 dollars). Taking the midpoint

of this range, we have:

Cc =1.S0 Mc (4-8)

4.3.1.2 Vessel Cost

The cost of an adsorber vessel is primarily determined by its dimensions which, in turn, depend upon the amount of carbon it must hold

and the superficial gas velocity through the bed that must be maintained

for optimum adsorption. The desired superficial velocity is used to calculate
4-22

the cross-sectional area of the bed perpendicular to the gas flow. An

acceptable superficial velocity is established empirically, considering

desired removal efficiency, the carbon particle size and bed porosity,

and other factors. For example, one adsorber vendor recommends a superficial

bed velocity of 85 ft/min(6), while an activated carbon manufacturer cautions

against exceeding 60 ft/min in systems operating at one atmosphere.(5)

Another vendor uses a 65 ft/min. superficial face velocity in sizing its

adsorber vessels.(9) Lastly, there are practical limits to vessel dimensions

which also influence their sizing. That is, due to shipping restrictions,

vessel diameters rarely exceed 12 feet, while their length is generally

limited to 50 feet.(9)

The cost of a vessel is usually correlated with its weight. However,

as the weight is often difficult to obtain or calculate, the cost may be

determined from the external surface area. This is true because the

vessel material cost -- and the cost of fabricating that material --

is directly proportional to its surface area. The surface area (5, ft 2)

of a vessel is a function of its length (L) and diameter (D), which in turn,

depend upon the superficial bed face velocity, the L/D ratio, and other

factors.

Most commonly, adsorber vessels are cylindrical in shape and erected

horizontally (as in Figure 4-1). In these cases, it can be shown that:

and:

where:

I

o = O.127~c vb

Q

L =~(Q'/Vb)2

Me

vb =bed superficial velocity (ft/min)

I

Mc=carbon requirement vessel (lbs)

(4-9)

(4-10)
4-23

QI = volumetric flowrate per adsorbing vessel (ft3/min)

Equations (4-9) and (4-10) also assume that the carbon occupies 1/3 of

the vessel volume(6,9) and that the carbon's bulk density is 30 lb/ft3•

Finally, for a cylinder:

S = 'If D(L + D/2) (4-11 )

(4-12)

Similar equations can be developed for other vessel shapes, configurations,

etc.

Based on vendor data, we developed a correlation between adsorber

vessel cost and surface area:(9)

Cv =exp [18.827 - 3.3945 lnS + 0.3090 (lnS)2]

where: Cv = vessel cost (spring 1986 $), F.U.B. vendor

and: 228 ~S~ 2,111 ft 2

These units would be made of 304 stainless steel, which is the most

common material used in fabricating adsorber vessels.(6,9) However, to obtain

the cost of a vessel fabricated of another material, multiply Cv by an

adjustment factor (Fm)• A few of these factors are listed below:

Material Fro Factor Reference(s)

Stainless steel, 316 1.3 6, 9, 10

Carpenter 20 CB-3 1.9 10

Monel-400 2.3 6, 10

Ni ckel-200 3.2 10

Titanium 4.5 10

4.3.1.3. Total Purchased Cost

As stated earlier, the costs of such items as the fans, pumps,

condenser, decanter, instrumentation, and internal piping can be factored

from the sum of the costs for the carbon and vessels. Based on four data
4-24

points derived from costs supplied by an equipment vendor (9), we found

that, depending on the total gas flowrate (Q), the cost of the carbon and

vessels together comprised from 50% to 85% of the total adsorber equipment cost.

These data points spanned a gas flowrate range of 4,000 to 500,000 scfm. The

average of these points was 72%, with a standard deviation of 16%. Taking the

reciprocal of this average (i.e., 1/0.72 =1.39), we can write:

CA = 1.39[Cc + CvJ (4-13)

where: Cc = cost of carbon

Cv = cost of vessel(s)

CA = cost of adsorber equipment

4.3.1.4. Total Capital Investment

As discussed in Section 2, in the methodology used in this Manual, the

total capital investment (TCl) is estimated from the total purchased cost via

an overall direct/indirect installation cost factor. A breakdown of that

factor for carbon adsorbers is shown in Table 4-3. As Section 2 indicates,

the TCl also includes costs for land, working capital, and off-site facilities,

which are not included in the direct/indirect installation factor. However,

as these items are rarely required with adsorber systems, they will not be

considered here. Further, no factors have been provided for site preparation

(S.P.) and buildings (l3ldg.), as these site-specific costs depend very

little on the purchased equipment cost.

Note that the installation factor is applied to the total purchased

equipment cost, which includes the cost of the stack and external ductwork

and such costs as freight and sales taxes (if applicable). ("External ductwork iti

is that ducting needed to convey the exhaust gas from the source to the

adsorber system, and then from the adsorber to the stack. Costs for ductwork
4-25

Table 4-3. Direct and Indirect Installation Factors for Carbon Adsorbers a

Cost Item

DIRECT COSTS

1) Purchased equipment cost

Adsorber

Auxi 1i ary equi pment b

Instruments and controls c

Taxes

Frei ght

Cost Factor (Fraction of Indicated Cost)

As requi red)

As requi redT A

0.1 A

0.03 A

0.05 A

Total Purchased Equipment cost

2) Installation direct costs

B( =1.18A)

Foundations and supports

Erection and handling

El ect ri cal

Piping

Insulation

Painting

Site preparation (S.P.), Buildings (Bldg.)

Total Installation Direct Costs

Total Direct Cost

INDIRECT COSTS

Engineering and supervision

Construction and field expenses

Construct; on fee

Start-up

Performance test

Contingency

0.08 B

0.14 B

0.04 B

0.02 B

0.01 B

0.01 B

As requi red

0.30 B + S.P. + Bldg.

1.30B + S.P. + Bldg.

0.10 B

0.05 B

0.10 B

0.02 B

0.01 B

0.03 B

Total Indirect Cost

Total Direct and Indirect Costs = Total Capital

Investment

0.31B

[[.61B + S.P. + Bldg.l

a Reference 11.

b I ncl udes external ductwork, stack, and any other equi pment normally

not i ncl uded with unit furni shed by adsorber vendor.

C Instrumentation cost usually included in cost of vendor-supplied adsorber

unit.
4-26

and stacks are shown elsewhere in this Manual.) Normally, the adjustment

would also cover the instrumentation cost, but this cost is usually included

with the adsorber purchased cost. Finally, note that these factors reflect

"average" installation conditions and could vary considerably, depending upon

the installation circumstances.

4.3.2 Cannister Systems

Once the carbon requirement is estimated using the above ~rocedure,

the number of cannisters is determined. This is done simply by dividing

the total carbon requirement (Mc) by the amount of carbon contained by each

cannister (typically, 150 lbs.). This quotient, rounded to the next

highest digit, yields the required number of cannisters to control the

vent in question.

Costs for a typical cannister (Calgon's Ventsorb®) are listed in

Table 4-4. These costs include the vessel, carbon, and connections,

but do not include freight or installation charges. Note that the cost

per unit decreases as the quantity purchased increases. Each cannister

contains Calgon's "BPL" carbon (4 x 10 mesh), which is commonly used in

industrial adsorption. However, to treat certain VOCs, more expensive

speciality carbons (e.g., "FCA 4 x 10") are needed. These carbons can

increase the equipment cost by 60% or more. (4)

As fewer installation materials and labor are required to install a

cannister unit than a fixed-bed system, the composite installation factor

is consequently lower. The only costs required are those needed to place

the cannisters at, and connect them to, the source. This involves a

small amount of piping only; little or no electrical work, painting,

foundations, or the like would be needed. Twenty percent of the sum of
4-27

Table 4-4 Equipment Costs (Spring 1986 $) for a Typical Cannister Adsorbera

Quantity

1-3

4-9

10-29

>30

Equipment Cost (each)b

$687

659

622

579

a Refe rence 4.

b These costs are F.O.B., Pittsburgh, PA. They do not include taxes and freight

charges.
4-28

the cannister(s) cost, freight charges, and applicable sales taxes would

cover this installation cost.

404. Estimating Total Annual Cost

As Section 2 of this Manual explains, the annual operating cost is

comprised of three components: direct costs, indirect costs, and

recovery credits. These will be considered separately.

4.4.1 Direct Annual Costs

These include the following expenditures: steam, cooling water,

electricity, carbon replacement, operating and supervisory labor, and

maintenance labor and materials. Of these, only electricity and solid

waste disposal would apply to the cannister-type adsorbers.

4.4.1.1 Steam:

As explained in Se~ion 4.1, steam is used during the desorption

cycle. The quantity of steam required will depend on the amount of

carbon in the vessel, the vessel dimensions, the type and amount of vac

adsorbed, and other variables. Experience has shown that the steam

requirement ranges from approximately l to i lbs of steam/lb of adsorbed

VQC.(6,9) Using the midpoint of this range, we can develop the following

expression for the annual steam cost:

Cs =3.5axla-3 mvac as ps (4-14)

where: Cs = steam cost ($/yr)

as =system operating hours (hr/yr)

mvac =vac inlet loading (lbs/hr)

ps =steam price ($/thous. lbs)

If steam price data are unavailable, one can estimate its cost at

120% of the fuel cost. For example, if the local price of natural gas
4-29

were $5.00/mi11ion BTU, the estimated steam price would be $6.00/mi11ion

BTU • $6.00/thousand 1bs. (The 20% factor covers the capital and annual

costs of producing the steam.)

4.4.1.2 Cooling Water:

Cooling water is consumed by the condenser in which the steam-VOC

mixture leaving the desorbed carbon bed is totally condensed. Most of

the condenser duty is comprised of the latent heat of vaporization (~Hv)

of the steam and VOC. As the VOC ~Hv are usually small compared to the

steam ~Hv (about 1000 BTU/1b), the VOC 6Hv may be ignored. So Inay the sensible

heat of cooling the water-VOC condensate from the condenser inlet temperature

(about 212°F) to the outlet temperature. Therefore, the coo1in9 water

requirement is essentially a function of the steam usage and the allowable

temperature rise in the coolant, which is typically 30° to 40°F(6). Using

the average temperature rise (35°F), we can write:

Ccw =3.43Cs Pcw

where: Ccw = cooling water cost ($/yr)

Pcw = cooling water price ($/thous. gal.)

(4-15)

If the cooling water price is unavailable, use $0.15 to $0.30/thousand

gallons.

4.4.1.3 Electricity:

In fixed-bed adsorbers, electricity is consumed by the system fan, bed

drying/cooling fan, cooling water pump, and solvent pump(s). Both the

system and bed fans must be sized to overcome the pressure drop through

the carbon beds. But, while the system fan must continuously convey the
(4-17)

4-30

total gas flow through the system, the bed cooling fan is only used during

a part of the desorption cycle (one-half hour or less).

For both fans, the horsepower needed depends both on the gas f10wrate

and the pressure drop through the carbon bed. The pressure drop through

the bed (A Pb) depends on several variables, such as the adsorption temperature,

bed velocity, bed characteristics (e.g., void fraction), and thickness.

But, for a given temperature and carbon, the pressure drop per unit thickness

depends solely on the gas velocity. For instance, for Ca1gon 1s "PCB"

carbon (4 x 10 mesh), the following relationship ho1ds:(5)

-4 2 APb/tb=0.03679 vb + 1.107 x 10 vb (4-16)

where: APb/tb = pressure drop through bed (inches of water/foot of

carbon)

vb = superficial bed velocity (ft/min)

The bed thickness (tb,ft) is the quotient of the bed volume (Vb) and the

bed cross-sectional area (Ab). For a 30 1b/ft3 carbon bed density, this

becomes:

I

t b = = 0.0333Mc

Ab Ab

(For instance, for horizontally-erected cylindrical vessels, Ab~LD.)

Once APb is known, the system fan horsepower requirement (hPsf) can be

ca1cul ated:

hPsf = 2.50 x 10-4 Q APs

where: Q = gas volumetric f10wrate through system (ft3/min)

AP S =total system pressure drop = APb + 1

(4-18)

(The extra inch accounts for miscellaneous pressure losses through

tne external ductwork and other parts of the system.(6))
4-31

This equation incorporates a fan efficiency of 70% and a motor

effi ciency of 90%, or 63% overan.

The horsepower requirement for the bed drying/cooling fan (hPcf)

is computed similarly. While the bed fan pressure drop would still

be ~Pb' the gas flowrate and operating times would be different. (For

example, to cool a bed from the regeneration temperature to the adsorption

temperature, would require from 3 to 3.5 SCFM/lb of carbon, based on a

30-minute cooling/drying time.)

The cooling water pump horsepower requirement (hpcwp) would be computed

as fonows:

(4-19)

where: qcw = cooling water flowrate (gal/min)

H = required head (normally 100 feet of water)

s =specific gravity of fluid relative to water at 60°F.

n =combined pump-motor efficiency

Equation 4-18 may also be used to compute the solvent pump horsepower

requirement. In the latter case, the flowrate (qs) would be different, of

course, although the same head--100 ft. of water--could be used. The specific

gravity would depend on the composition and temperature of the condensed

solvent. For example, the specific gravity of toluene at 100°F would be

approximately 0.86 at 70° F. (However, the solvent pump horsepower is usually

very small--usually <0.1 hpo--so its electricity consumption can usually

be negl ected.)

Once the various horsepowers are calculated, the electricity usage

(in kWh) is calculated, by multiplying each horsepower value by 0.746 (the

factor for converting hp to kilowatts) and the number of hours each fan or
4-32

pump operates annually. For the system fan and cooling water pump, the hours

would be the annual operating hours for the system (0S).

But for the bed drying/cooling fan, the time (Sb) would be much

shorter. This is dependent on the time the bed fan is run during a

desorption cycle, the number of desorption cycles per year, the adsorption

time (0A), and other factors. For instance, for a three-bed system, with

a 12-hour adsorption time and a U.5-hour bed cooling/drying time per

desorption cycle, the bed fan would operate 8.33 hrs. for every IOU hrs

of on-stream (system) time.

To obtain the annual electricity cost, simply multiply kWh by the

electricity price (in $/kWh) that applies to the facility being controlled

For cannister units, use equation 4-17 to calculate the fan horsepower

requirement. However, instead of 6Pb, use the following to compute the

total cannister pressure drop (6PC, inches of water):(4)

6PC = 0.0471Qc + 9.29 x 10-4Qc2

where: Qc = flowrate through the cannister (ft 3/min)

4.4.1.4. Carbon Replacement:

(4-20)

As discussed above, the carbon has a different economic life than

the rest of the adsorber system. Therefore, its replacement cost must be

calculated separately. Employing the procedure detailed in Section 2,

we have:

CRCc =CRFc (I.U8Cc + Cel)

where: CRFc = capital recovery factor for the carbon

1.08 = taxes and freight factor

(4-21)

Ce, Ccl =initial cost of carbon and carbon replacement

labor cost, respectively ($/yr) (F.O.B. vendor)
4-33

The replacement labor cost covers the labor cost for removing spent

carbon from vessels and replacing it with virgin or regenerated carbon.

The cost would vary with amount of carbon being replaced, the labor rates, and

other factors. For example, to remove and replace a 50,000 - pound charge

would require about 16 person-days, which, at typical wage rates, is equivalent

to approximately $0.05/lb replaced.(12)

A typical life for the carbon is five years. However, if the inlet

contains VOCs that are very difficult to desorb, tend to polymerize, or react

with other constituents, a shorter carbon lifetime--perhaps as low as two

years--would be likely.(l) For a five-year life and 10% interest rate, CRF c

= 0.2638.

4.4.1.5 Solid Waste disposal:

Disposal costs are rarely incurred with fixed-bed adsorbers, because

the carbon is almost always regenerated in place, not discarded. In certain

cases, the carbon in cannister units is also regenerated, either off-site

or at a central regeneration facility on-site. However, most cannister

adsorbers are disposed of once they become saturated. The entire

cannister--carbon. drum, connections, etc.--is shipped to a secure landfill.

The cost of landfill disposal could vary considerably, depending on the

number of cannisters disposed of, the location of the landfill, etc.

Based on data obtained from two large landfills, for instance, the

disposal cost would range from approximately $35 to $65 per cannister

excluding transportation costs.(13.14)

4.4.1.6 Operating and Supervisory Labor:

The operating labor for adsorbers is relatively low, as most systems

are automated and require little attention. One-half operator hour per
4-34

shift is typical.(ll) Add to this 15% to cover supervisory labor. as

Section 2 suggests. The annual labor cost would then be the product of

these labor requirements and their respective wage rates ($/hr) which.

naturally. would vary according to the facility location, type of industry,

etc.

4.4.1.7 Maintenance Labor and Materials:

Use 0.5 hours/shift for maintenance labor (11) and the applicable

maintenance wage rate. If the latter data are unavailable, estimate the

maintenance wage rate at 110% of the operating labor rate. as Section 2

suggests. Finally, for maintenance materials. add an amount equal to the

maintenance labor. also per Section 2.

4.4.2 Indirect Annual Costs

These include such costs as capital recovery. property taxes •. insurance.

overhead. and administrative costs (IiG&A Ii ). The capital recovery cost is

based on the equipment lifetime and the annual interest rate employed. (See

Section 2 for a thorough discussion of the capital recovery cost and the

variables that determine it.) For adsorbers. the system lifetime is typically

ten years. except for the carbon. which. as stated above. typically needs to

be replaced after five years. Therefore. when figuring the system capital

recovery cost. one should base it on the installed capital cost less the cost

of replacing the carbon (i.e •• the carbon cost plus the cost of labor necessary

to replact it). Substituting the initial carbon and replacement labor

costs from equation 4-21. we obtain:

CRCs = [TCI - (l.08Cc + Cel)] CRFs

where: CRCs = capital recovery cost for adsorber system ($/yr)

TCI = total capital investment ($)

(4-22)
Ccl

4-35

1.08 = taxes and freight factor

= initial carbon cost (F.O.B. vendor) and carbon re~acement

cost, respectively ($)

CRFs = capital recovery factor for adsorber system (defi ned ; n

Section 2).

For a ten-year life and a 10% annual interest rate, the CRF s would be

0.1628.

As Section 2 suggests, the suggested factor to use for property taxes,

insurance, and administrative charges is 4% of the TCL Finally, the overhead

is calculated as 60% of the sum of operating, supervisory, and maintence

labor, and maintenance materials.

* * *

The above procedure applies to cannister units as well, except that,

in most cases, the carbon is not replaced--the entire unit is. Cannisters

are generally used in specialized applications. The piping and ducting

cost can usually be considered a capital investment with a useful life of

ten years. However, whether the cannister itself would be treated as a

capital or an operating expense would depend on the particular application

and needs to be evaluated on a case-by-case basis.

4.4.3 Recovery Credits

These coul~ apply to the VOC which is adsorbed, then desorbed, condensed,

and separated from the steam condensate. However, if the vac layer contained

impurities or were a mixture of compoundS, it would require further treatment,

such as distillation. Purification and separation costs are beyond the scope

of this Section. Suffice it to say" that the costs of these operations could

offset and, if large enough, obliterate any recovery credits. In any case,

the following equation can be used to calculate these credits:
4-36

where: pvac = resale value of the captured vac ($/lb)

RC = recovery credit ($/yr)

E = adsorber vac control efficiency

By definition, the efficiency (E) is the difference between the inlet

and outlet vac mass loadings, divided by the inlet loading. However, during

an adsorption cycle the outlet vac loading will increase from essentially

zero at the start of the cycle to the breakthrough concentration at the end

of the cycle. Because the efficiency is a function of time, it should be

calculated via integration over the length of the adsorption cycle. To do

this would require knowledge of the temporal variation of the outlet loading

during the adsorption cycle. If this knowledge is not available to the

Manual user, a conservative approximation of the efficiency may be made by

setting the outlet loading equal to the breakthrough concentration.

4.4.4 Total Annual Cost

Finally, as explained in Section 2, the total annual cost (TAC) is

the sum of the direct and indirect annual costs, less any recovery credits,

or:

TAC = DC + IC - RC (4-24 )
4-37

References for Section 4

1. Correspondence: Robert L. Stallings and William Klotz (Research Triangle

Institute, Research Triangle Park, NC) to William M. Vatavuk (U.S.

Environmental Protection Agency, Office of Air Quality Planning and

Standards, Economic Analysis Branch, Research Triangle Park, NC),

June 24, 1986.

2. Calvert, Seymour and Englund, Harold M. (eds.). Handbook of Air Pollution

Control Technology. New York: John Wiley & Sons, 1984, pP: 135-192.

3. Handbook of Chemistry and Physics, 54th Edition. Cleveland: The Chemical

Rubber Company, 1973-74, pp. 085-092. .

4. IICalgon Ventsorb@ for Industrial Air Purification ll (Bulletin 23-56a).

Pittsburgh: Calgon Corporation, 1986.

5. Adsorption Handbook. Pittsburgh: Calgon Corporation, 1980.

6. Correspondence: Richard Selznick (Baron Blakeslee, Inc., Westfield, NJ)

to William M. Vatavuk, April 23, 1986.

7. Klotz, William L., 1I0ocumentation for Program IBed Size'll. Research

Triangle Institute (Research Triangle Park, NC), September 3, 1986.

8. Manzone, R.R. et al. IIprofitability of Recycling Solvents from Process

Systems. II Pollution Engineering, October 1973.

9. Correspondence: James Jessup (M&W Industries, Inc., Rural Hall, NC)

to William M. Vatavuk, May 16, 1986.

10. Matley, Jay (ed.). Modern Cost Engineering. New York: McGraw-Hill

Publications Co., 1984, p. 142.

11. Vatavuk, WilliamM. and Neveril, Robert. IIEstimating Costs of Air

Pollution Control Systems, Part II: Factors for Estimating Capital

and Operating Costs. 1I Chemical Engineering, November 3, 1980, pp. 157-

162.

12. Telephone conversation: Robert L. Stallings (Research Triangle Institute,

Research Triangle Park, NC) with William M. Vatavuk, September 11, 1986.

13. Correspondence: William Kitto (Chemwaste, Sulphur, LA) to William M.

Vatavuk, July 25, 1986.

14. Correspondence: Jerry Locklear (GSX, Pinewood, SC) to William M.

Vatavuk, July 25, 1986.

5--/

Section 5

FABRIC FILTERS

James H. Turner

Andrew S. Viner

Research Triangle Institute

(Research Triangle Park, N.C. 22709)

John D. McKenna

ETS, Inc.

Roanoke, VA 24018-4394

Richard E. Jenkins

William M. Vatavuk

Economic Analysis Branch, OAQPS

5.1 Process Description

5.1.1 Introduction

A fabric filter unit consists of one or more isolated compartments

containing rows of fabric filter bags or tubes. Particle-laden gas passes up

(usually) along the surface of the bags then radially through the fabric.

Particles are retained on the upstream face of the bags while the cleaned gas

stream is vented to the atmosphere. The filter is operated cyclically

alternating between relatively long periods of filtering and short periods of

cleaning. During cleaning, dust that has accumulated on the bags is removed

from the fabric surface and deposited in a hopper for subsequent disposal.

This device will collect particle sizes ranging from submicron to several

hundred microns in diameter at efficiencies generally in excess of 99 or 99.9

percent. The dust cake collected on the fabric is primarily responsible for

such high efficiency. Gas temperatures up to 500 of, with surges to 550 of

can be accommodated routinely. Most of the energy used to operate the system
5-2

appears as pressure drop across the bags and associated hardware and ducting.

Typical values range from 5 to 20 in. of water gauge. Fabric filters are used

where high-efficiency particle collection is required. Limitations are

imposed by gas characteristics (temperature and corrosivity) and particle

characteristics (primarily stickiness) that affect the fabric or its operation

and that cannot be accommodated economically.

Important process variables include particle characteristics, gas

characteristics, and fabric properties. The most important design parameter

is the air- or gas-to-cloth ratio (volumetric flow rate divided by fabric

area, (ft3/min)/ft2), and the usual operating parameter of interest is

pressure drop across the filter system. The major distinguishing operating

feature of fabric filters is the ability to renew the filtering surface

periodically by cleaning.

5.1.2 Types of Fabric Filters

Fabric filters can be categorized by several means, including type of

cleaning (shaker, reverse-air, pulse-jet), direction of gas flow (from inside

the bag towards the outside or vice versa), location of the system fan

(suction or pressure), or size (low, medium, or high gas flow quantity).

Cleaning methods are discussed more fully in this section, and the other

categories are described in Section 5.2.

5.1.2.1 Shaker Cleaning

For any type of cleaning, enough energy must be imparted to the fabric to

overcome the adhesion forces holding dust to the bag. In shaker cleaning,

used with inside to outside gas flow, this is accomplished by suspending the

bag from a motor-driven hook or framework that oscillates. Motion may be

imparted to the bag in several ways, but the general effect is to create a

sine wave along the fabric. As the fabric moves outward, accumulated dust on
5-3

the surface moves with the fabric. When the fabric reaches the limit of its

extension, the patches of dust have enough inertia to tear away from the

fabric and descend to the hopper.

For small, single-compartment baghouses, a lever attached to the shaker

mechanism may be operated manually at appropriate intervals, typically at the

end of a shift. In multicompartment baghouses, a timer or a pressure sensor

responding to system pressure drop initiates bag shaking automatically. The

compartments operate in sequence so that one compartment at a time is cleaned.

Forward gas flow to the compartment is stopped, dust is allowed to settle,

residual gas flow stops, and the shaker mechanism is switched on for several

seconds to a minute or more. The settling and shaking periods may be

repeated, then the compartment is brought back online for filtering. Many

large-scale shaker systems employ a small amount of reverse air during the

shaker cycle to assist cleaning by deflating the bags.

Parameters that affect cleaning include the amplitude and frequency of

the shaking motion and the tension of the mounted bag. The first two

parameters are part of the baghouse design and generally are not changed

easily. Typical values are about 4 Hz for frequency and 2 to 3 in. for

amplitude (half-stroke). (1) The tension is set to about 2 lb/in. of bag

circumference when bags are installed. Some installations allow easy

adjustment of bag tension, while others require that the bag be loosened and

reclamped to its attaching thimble.

The vigorous action of shaker systems tends to stress the bags and

requires heavier and more durable fabrics. In the United States, woven

fabrics are used almost exclusively(2) for shaker cleaning. European practice

allows the use of felted fabrics at somewhat higher filtering velocities.
5-4

5.1.2.2 Reverse-air Cleaning

When glass fiber fabrics were introduced, a gentler means of cleaning the

bags was needed to prevent premature degradation. Reverse-air cleaning was

developed as a less intensive way to impart energy to the bags. In this

method, gas flow to the bags is stopped in the compartment being cleaned, and

a reverse flow of air is directed through the bags. This reversal of gas flow

gently collapses the bags and dust is removed from the fabric surface by shear

forces developed between the dust and fabric as the latter changes its

contours. Another difference between reverse-air and shaker cleaning is the

installation of sewn-in rings to prevent complete collapse of the bag, which

may be greater than 30 ft long, during cleaning. Without these rings,

collected dust tends to choke the bag as the fabric collapses in on itself.

As with mu1ticompartment shaker baghouses, the same cycle takes place in

reverse-air baghouses of stopping forward gas flow and allowing dust to settle

before cleaning action begins.

The source of reverse air is generally a separate fan capable of

supplying air for one or two compartments at a gas-to-c10th ratio similar to

that of the forward gas flow.

5.1.2.3 Pulse-jet Cleaning

This form of cleaning uses compressed air to force a burst of air down

through the bag and expand it violently. As with shaker baghouses, the fabric

reaches its extension limit and the dust separates from the bag. In pulse

jets, however, gas flows are opposite in direction when compared with shaker

or reverse-air baghouses. Bags are mounted on wire cages to prevent collapse

while the dusty gas flows from outside the bag to the inside. I~stead of

attaching both ends of the bag to the baghouse structure, the bag and cage
5-5

assembly generally is attached only at the top. The bottom end of the

assembly tends to move in the turbulent gas flow and may contact other bags.

which accelerates wear.

Although some pulse-jet baghouses are compartmented. most are not. Bags

are cleaned by rows when a timer initiates the burst of cleaning air through a

quick-opening valve. Usually 10% of the collector is pulsed at a time by

zones. A pipe across each row of bags carries the compressed air. The pipe

is pierced above each bag so that cleaning air exits directly downward into

the bag. Some systems direct the air through a short venturi that is intended

to entrain additional cleaning air. The pulse interrupts forward gas flow

only for a few tenths of a second. However. the quick resumption of forward

flow redeposits most of the dust back on the clean bag or on adjacent bags.

An advantage of online pulse-jet cleaning is the reduction in baghouse size

allowed by not having to build an extra compartment for offline cleaning.

Pulse jets normally operate at two or more times the gas~to-cloth ratio of

reverse-air baghouses.

5.1.3 Auxiliary Equipment

The typical auxiliary equipment associated with fabric filter systems is

shown in Figure 5-1. Along with the fabric filter itself. a control system

typically includes the following auxiliary equipment: a capture device (i.e ••

hood or direct exhaust connection); ductwork; dust removal equipment (screw

conveyor. etc.); fans. motors. and starters; and a stack. In addition. spray

chambers. mechanical collectors. and dilution air ports may be needed to

precondition the gas before it reaches the fabric filter. Capture devices are

usually hoods that exhaust pollutants into the ductwork or direct exhaust

couplings attached to a process vessel. Hoods are more common, yet poorly
Fabric Filter

U1

I

0"1

Stack

Fan

Dust Removal

Dilution Air

Spray Cooler

Direct Exhaust

Hood

Mechanical Collector

Figure 5-10 Typical alternative auxiliary equipment items used with fabric filter control systems,
5-7

designed hoods will allow pollutants to escape. Direct exhaust couplings are

less common, requiring sweep air to be drawn through the process vessel, and

may not be feasible in some processes. Ductwork provides a means of moving

the exhaust stream to the control device. Spray chambers and dilution air

ports are used to decrease the temperature of the pollutant stream to protect

the filter fabric from excessive temperatures. When a substantial portion of

the pollutant loading consists of relatively large particles, mechanical

collectors such as cyclones are used to reduce the load on the fabric filter

itself. The fans provide motive power for air movement and can be mounted

before (pressure baghouse) or after (suction baghouse) the filter. A stack,

when used, vents the cleaned stream to the atmosphere. Screw conveyors are

often used to remove captured dust from the bottom of the hoppers. Air conveying systems and direct dumping into containers are also used.

5.1.4 Fabric Filtration Theory

The key to designing a baghouse is to determine the face velocity that

produces the optimum balance between pressure drop (operating cost) and

baghouse size (capital cost). Major factors that affect design face velocity

(or gas-to-cloth ratio), discussed in Section 5.2, include particle and fabric

characteristics and gas temperature. Although collection efficiency is

another important measure of baghouse performance, it is generally assumed

that a properly designed and well run baghouse will be highly efficient.

Therefore, the design process focuses on the pressure drop. There are several

contributions to the pressure drop across a baghouse including the pressure

drop from the flow through the inlet and outlet ducts, from flow through the

hopper regions, and from flow through the bags. The pressure drop through the

baghouse (excluding the pressure drop across the bags) depends largely on the
5-8

baghouse design and ranges from 1 to 2 inches of H20(3) in conventional

designs and up to 3 inches of H2

0 in designs having complicated gas flow

paths. This loss can be kept to a minimum (i.e., 1 inch of H20 or less) by

investing in a flow modeling study of the proposed design. A study of this

sort would cost on the order of $50,000 (in 1986). The pressure drop across

the bags (also called the tubesheet pressure drop) can be as high as 10 inches

of H20 or more. The duct and hopper losses are constant and can be minimized

effectively through proper design based on a knowledge of the flow through the

baghouse. (NQte: A procedure for estimating duct pressure losses is given in

the "Ductwork" section of this Manual.) The tubesheet pressure drop is a

complex function of the physical properties of the dust and fabric and the

manner in which the baghouse is designed and operated.

Fabric filtration is inherently a batch process that has been adapted to

continuous operation through clever engineering. One requirement for a

continuously operating baghouse is that the dust collected on the bags must be

removed periodically. Shaker and reverse-air baghouses are similar in the

sense that they both normally use woven fabric bags, run at relatively low

face velocities, and the filtration mechanism is cake filtration. That is,

the fabric merely serves as a substrate for the formation of a dust cake that

is the actual filtration medium. Pulse-jet baghouses generally use felt

fabrics and run with a high face velocity (about double that of shaker or

reverse-air baghouses). Some investigators feel that the felt fabric plays a

much more active role in the filtration process. This distinction between

cake filtration and fabric filtration has important implications for calculating the rate of pressure loss across the filter bags. The theoretical

description of cake filtration is quite different from that for fabric

filtration, and the design processes are quite different.
5-9

The general equations used to design a baghouse follow beginning with the

reverse air/shake deflate type of baghouse.

5.1.4.1 Reverse Air/Shake Deflate Baghouses

The construction of a baghouse begins with a set of specifications

including average pressure drop, total gas flow, and o~her requirements; a

maximum pressure drop is always specified. Given these specifications, the

designer must determine the maximum face velocity that can meet these

requirements. The standard way to relate baghouse pressure drop to face

velocity is given by the relation:

AP(8) = Ssys(8)Vave

where:

(5-1)

AP(8) =

Ssys(8) =

Vave =

the pressure drop across the filter, in. H

2

0 (a function of time, 8)

system drag, in. H20/(ft/min) (a function of time)

average (i.e., design) face velocity (ft/min) (essentially constant)

For a multicompartment baghouse, the system drag is determined as the sum of

several parallel resistances representative of several compartments. For the

typical case where the pressure drop through each compartment is the same, it

can be shown that:

SsYS(8) = [~ i= s. lin] -1 =-M~l_l- = . 1 1 1 t' 1= t.. f:f ;=1 5;(8)

where

M= number of compartments ;n the baghouse

S;(8) = drag across compartment;

M

1:

;=1

M (5-2)
5-10

The compartment drag is a function of the amount of dust collected on the bags

in that compartment. In general, the dust will be distributed in a very

nonuniform manner. That is, there will be a variation of dust load from one

bag to the next and within a given bag there will also be a variation of dust

load from one area to another. For a suffic1ently small area j within

compartment i, it can be assumed that the drag is a linear function of dust

load:

S. . (9) = S + K

2

W. . (9) 1,J e 1,J

where:

(5-3)

Se = drag of a dust-free (freshly cleaned) filter bag

K2 = dust cake flow resistance, [in. H2o/(ft/min)]/(lb/ft2)

w. .(9) = dust mass per unit area of area j in compartment i

1 ,J

If there are N different areas of equal size within compartment i , each with a

different drag Si,j' then the total drag for compartment i can be computed in

a manner analogous to equation (5-2):

Si (9) = N/l: [l/Si ,j (9)] (5-4)

The constants Se and K2 depend upon the fabric and the nature and size of the

dust. The relationships between these constants and the dust and fabric

properties are not understood well enough to permit accurate predictions and

so must be determined empirically, either from prior experience with the

dust/fabric combination or from laboratory measurements. The dust mass as a

function of time is defined as:

(5-5)
5-11

where:

Wr = dust mass per unit area remaining on a "clean" bag

Cin = dust concentration in the inlet gas (gr/ft3)

Vi (8) = face velocity in compartment i

It is assumed that the inlet dust concentration and the filter area are

constant. The face velocity through each compartment changes with time,

starting at a maximum value just after cleaning and steadily decreasing as

dust builds up on the bags. The individual compartment face velocities are

related to the average face velocity by the expression:

Vave

= E{V i (8)Ai}/E{Ai

} (5-6)

= E{Vi}/M (for Mcompartments with equal area)

Equations (5-1) through (5-6) reveal that there is no explicit relationship

between the design face velocity and the tubesheet pressure drop. On the

contrary, the pressure drop that results from a given design can only be

determined by the simultaneous solution of equations (5-1) through (5-5), with

equation (5-6) as a constraint on that solution. This conclusion has several

implications for the design process. The design requires an iterative

procedure: one must begin with a known target for the average pressure drop,

propose a baghouse design (number of compartments, length of filtration

period, etc.), assume a face velocity that will yield that pressure drop, and

solve the system of equations (5-1) through (5-6) to verify that the calculated pressure drop equals the target pressure drop. This procedure is

repeated until the specified face velocity yields an average pressure drop

(and maximum pressure drop, if applicable) that is sufficiently close to the

design specification.
5-12

5.1.4.2 Pulse-Jet Baghouses

The distinction between pulse-jet baghouses and reverse-air and shake

baghouses is basically the difference between cake filtration and composite

dust/fabric filtration (noncake filtration). This distinction is more a

matter of convenience than physics. In reality, pulse-jet baghouses have been

designed to operate in a variety of modes. Some pulse jets remain online at

all times and are cleaned frequently. Others are taken offline for cleaning

at relatively long intervals. Obviously, if a compartment remains online long

enough without being cleaned, then the filtration mechanism becomes that of

cake filtration. A complete model of pulse-jet filtration therefore must

account for the depth filtration occurring on a relatively clean pulse-jet

filter, the cake filtration that inevitably results from prolonged periods

online, and the transition period between the two regimes.

Besides the question of filtration mechanism, there is also the question

of cleaning method. If a compartment is taken off-line for cleaning, then the

dust that is removed from the bags will fall into the dust hopper before

forward gas flow resumes. If a compartment is cleaned while online, then only

a small fraction of the dust removed from the bag will fall to the hopper.

The remainder of the dislodged dust will be redeposited (i.e., "recycled") on

the bag by the forward gas flow. The redeposited dust layer has different

pressure drop characteristics than the freshly deposited dust. The modeling

work that has been done to date focuses on the online cleaning method. Dennis

and Klemm(4) proposed the following model of drag across a pulse-jet filter~

S = Se + (K2)cWc + K2Wo

where:

S = drag across the filter

(5-7)
5-13

Se = drag of a just-cleaned filter

(KZ)c = specific dust resistance of the recycling dust

Wc = areal density of the recycling dust

KZ = specific dust resistance of the freshly deposited dust

Wo = areal density of the freshly deposited dust

This model has the advantage that it can easily account for all three regimes

of filtration in a pulse-jet baghouse, i.e., cake filtration, depth filtration, and filtration in the transition region. As in equations (5-1) to

(5-6), the drag and areal densities are functions of time (8). However, for a

pulse-jet baghouse with online cleaning, the filtration velocity is relatively

constant. The pressure drop can thus be expressed as the sum of a relatively

constant term and a term that increases due to dust build-up:

bP = (PE)bW + KZWoV

where:

(5-8)

bP = pressure drop (in. HZO)

V = filtration velocity (ft/min)

(PE)bW = [Se + (KZ)cWc] V (5-9)

Equation (5-8) describes the pressure drop behavior of an individual bag. To

extend this single bag result to a multiple-bag compartment, equation (5-7)

would be used to determine the individual bag drag and the total baghouse drag

would then be computed as the sum of the parallel resistances as in equation

(5-2). Pressure drop would then be calculated as in equation (5-1). It seems

reasonable to extend this analysis to the case where the dust is distributed

unevenly on the bag and then apply equation (5-7) to each area on the bag,

followed by an equation analogous to (5-4) to compute the overall bag drag.

The difficulty in doing this is that one must assume values for Wc for each

different area to be modeled.
5-14

The disadvantage of the model represented by equations (5-7) and (5-8) is

that the constants, Se' K2, and Wc ' cannot be predicted at this time. Consequently, correlations of laboratory data must be used to determine the value

of (PE)AW. For the fabric-dust combination of Dacron felt and coal fly ash,

Dennis and Klemm(4) developed an empirical relationship between (PE)AW' the

face velocity, and the cleaning pulse pressure. This relationship (converted

from metric to English units) was as follows:

-0.65

(PE)Aw = 6.08 VPj

where:

(5-10)

v = face velocity (ft/min)

Pj =pressure of the cleaning pulse (usually 60 to 100 psig; see Section

5.4.1.8)

It is not known how well the constants in equation (5-10) would fit the data

for a different dust/fabric combination. ~ased on a limited amount of data,

it appears that the power law form of equation (5-10) may be a valid model for

(PE)Aw. However, equation (5-10) can be used as a first approximation to

estimate (PE)Aw for other fabric-dust combinations.

Another model that shows promise in the prediction of noncake filtration

pressure drop is that of Leith and Ellenbecker(5) as modified by Koehler and

Leith. (6) In this model, the tubesheet pressure drop is a function of the

clean fabric drag, the system hardware, and the cleaning energy.

Specifically:

(5-11)

where:

Ps = maximum static pressure achieved in the bag during cleaning
5-15

K1 = clean fabric resistance

Vf = face velocity

K2 = dust deposit flow resistance

K- = bag cleaning efficiency coefficient 3

. K

v = loss coefficient for the venturi at the inlet to the bag

Comparisons of laboratory data with pressure drops computed from equation

(5-11) (5,6) are in close agreement for a variety of dust/fabric combinations.

The disadvantage of equation (5-11) is that the constants K1, K2, and K3 must

be determined from laboratory measurements. The most difficult one to

determine is the K3 value, which can only be found by making measurements in a

pilot-scale pulse-jet baghouse.

5.2 Design Procedures

5.2.1 Gas-to-C1oth Ratio

The gas-to-c1oth ratio is difficult to estimate from first principles.

However, shortcut methods of varying complexity allow rapid estimation.

Descriptions of three methods of increasing difficulty follow. For shaker and

reverse-air baghouses, the third method is best performed with publicly

available computer model programs.

5.2.1.1 Gas-to-Cloth Ratio From Similar Aoplications

Net gas-to-c1oth ratio is equal to the total actual volumetric flow rate

in cubic feet per minute divided by the net cloth area in square feet. This

ratio reduces to units of feet per minute and affects pressure drop and bag

life. After a fabric has been selected, the gas-to-c10th ratio can be

determined using Table 5-1. Column 1 shows the type of dust; column 2 shows

the gas-to-cloth ratios for woven fabric; and column 3 shows gas-to-c1oth

ratios for felted fabrics. The net cloth area is determined by dividing the
5-16

Table ~-1 Gas-~-Cloth Ratiosa(7)

(ft /min)/(ft of cloth area)

Dust

Alumina

Asbestos

Bauxite

Carbon Black

Coal

Cocoa, Chocolate

Clay

Cement

Cosmetics

Enamel Frit

Feeds, Grain

Feldspar

. Fe rtil i zer

Flour

Fly Ash

Graphite

Gypsum .. Iron Ore

Iron Oxide

Iron Sulfate

Lead Oxide

Leather Dust

Lime

Limestone

Mica

Paint Pigments

Paper

Plastics

Quartz

Rock Dust

Sand

Sawdust (Wood)

Sil i ca

Slate

Soap, Detergents

Spices

Starch

Sugar

Talc

Tobacco

Zinc Oxide

Shaker/Woven

Reverse-Air/Woven

2.5

3.0

2.5

1.5

2.5

2.8

2.5

2.0

1.5

2.5

3.5

2.2

3.0

3.0

2.5

2.0

2.0

3.0

2.5

2.0

2.0

3.-5

2.5

2.7

2.7

2.5

3.5

2.5

2.8

3.0

2.5

3.5

2.5

3.5

2.0

2.7

3.0

2.0

2.5

3.5

2.0

Pulse Jet/Felt

8

10

8

5

8

12

9

8

10

9

14

9

8

12

5

5

10

11

7

6

6

12

10

8

9

7

10

7

9

9

10

12

7

12

5

10

8

7

10

13

5

aGenerally safe design values--application requires consideration of particle size and grain loading.
5-17

gas-to-cloth ratio into the actual cubic feet per minute flow of the exhaust

gas stream. For an intermittent-type baghouse that is shut down for cleaning,

this is the total, or gross, cloth area. However, for continuously operated

filters, the area must be increased to allow the shutting down of one or more

compartments for cleaning. Table 5-2 provides a guide for adjusting the net

area to the gross area, which determines the size of a continuously cleaned

filter.

5.2.1.2 Gas-to-Cloth Ratio From Manufacturer's Methods

Manufacturers have developed nomographs and charts that allow rapid

estimation of the gas-to-cloth ratio. Two examples are given below, one for

shaker-cleaned baghouses and the other for pulse-jet cleaned baghouses.

For shaker baghouses, Table 5-3 gives a factor method for estimating the

ratio. Ratios for several materials in different operations are presented,

but are modified by factors for particle size and dust load. Directions and

an example are included. Gas-to-cloth ratios for reverse-air baghouses would

be about the same or a little more conservative compared to the Table 5-3

values.

For pulse-jet baghouses, another factor method(9) has been modified with

equations to represent temperature, particle size, and dust load:

v = A x B x 2.647T-0.2335 x (0.7471 + 0.0853 ln D) x 1.0873 L-0.06021

(5-12)

where:

V = gas-to-cloth ratio, ft/min

A = material factor, from Table 5-4

B = application factor, from Table 5-4

T = temperature, of (between 50 and 275)
5-18

Table 5-2 Approximate Guide to Estimate Gross Cloth Area(8)

Net Cloth Area Gross Cloth Area

(tt2) (tt2)

1-4,000 Multiply by 2

4,001-12,000 " 1.5

12,001-24,000 " 1.25

24,001-36,000 " 1.17

36,001-48,000 " 1.125

48,001-60,000 " 1.11

60,001-72,000 " 1.10

72,001-84,000 " 1.09

84,001-96,000 " 1.08

96,001-108,000 " 1.07

108,001-132,000 " 1.06

132,001-180,000 " 1.05

above 180,001 " 1.04
Table 5-3 Manufacturer's Factor Method for Estimating Gas-to-Cloth

Ratios for Shaker Baghouses

10, II

-----2n-RATi<Y------ --Y:511 RATIO ----·-T-·---·-------_.-. -.----------------.---

MATERIAL ~!!AT!~ MATERIAL OPERATION

Ammonium Phos· Activated Charcoal 2.4.5.6.7

phate Perl. 2.3,4.5,6,7 Carbon Black II. 14

Diatomaceous Detergents 2,4.5,6. 7

Earth 4.5,6,7 Metal Fumes,

Dry Pelrochem. 2,3.4,5,6,7,14 Oxides and

D 2 3 4 5 6 7 olher Solid

yes , , , , , Dispersed

Fly Ash 10 Producls

Metal Powders 2,3,4,5,6,7, 14

Plashes 2,3,4,5.6,7. 14

Resins 2,3,4,5,6,7, 14

Silicales 2,3,4.5,6,7. 14

Starch 6,7

~oaps 3,4,5,6,7

RATlO_:_=--1 2..5/1 RATIO--~

OPERATION MATERIAL OPERATION

I Ashestos 1,7.8--- Alumina--- 2.T4.D

2.3,4,5,6,7 Aluminum Dust I. 7.8 Carbon Black 4,5,6,7

2,3.4,5,6,7 FiblOus Mal'l. 1,4.7,8 Cement 3,4,5,6,7

2,3,4, 5, 6, 7 CellulQse Mat'!. 1,4. 7,8 Coke 2,3,5,6

1,7,8 Gypsum 1,3.5.6.7 Ceramic P,gm. 4,5,6,7

1,4,6,7 Lime (Hydrated) 2,4,6.7 Clay& Brick Dusl 2,4,6,12

13 Pe,lite 2.4,5.6 Coal 2,3,6,7,12

1,6.7 Rubbe, Chem. 4.5,6,7.8 Kaolin 4,5,7

Sail 2, 3. 4.5, 6, 7 Limeslone 2, 3, 4, 5, 6, 7

Sand • 4,5.6,7.9. 15 Rock, Ore Dust 2,3,4,5,6,7

hon Scale 1,7.8 Silica 2,3,4,5,6,7

Soda Ash 4,6,7 Suga, 3,4,5,6,7

Talc 3, 4, 5,6, 7

Machining Operaho 1,8

Cardboard

Feeds

Flour

Grain

Leather Dust

Tobacco

Supply All

Wood, Dust. Chips

A[-~~l-:i!!£{X~t{~~a-~=~~~f~RI~~1

This information constitutes a guide for commonly en.countered situations and should not be considered a "hard-and-fast" rule. Air-to-cloth ratios are dependent on dust loading, size distribution.

particle shape and "cohesiveness" of the deposited dust. These conditions must be evaluated for

each application. The longer the interval between bag cleaning 'the lower the air-to-c1oth ratio

must be, Finely-divided, uniformly sized particles generally form more dense filter cakes and require lower air-to-cloth ratios than when larger particles are interspersed with the fines. Sticky,

oily particles, regardless of shape or size, form dense filler cakes and require lower air-to-cloth

ratios.

CUTTING - I

CRUSHINr:; - 2

PUl VERIZING - 3

B

I

MIXING - 4 CONVEYING - 7

SCREENI~G - 5 I GRINDING - 8

STORAGE - 6 SHAK EOUT - 9

FINENESS FACTOR

'MICRON SIZE FACTOR

-->.!QL --q 50· 100 1.1

10· 50' 1.0 - ---- --.

__.L!L f----~!..- I· 3 .8

<I .7

FURNACE FUME - 10

REACTION FUME- II

D~MPING - 12

INTAKE ClEANING - 13

PROCESS - 14

BLASTING - 15 U1

I

.......

1.0

C DUST LOAD FACTOR

Loading GR. CU. FT. Fodor

1 - 3 1.2 I EXAMPLE:

4 - 8 1.0

-- 9 - 17 .95

18 - 40 .90

> 40 .85 __L--.._

Foundry shakeout unit handling 26000 CFM and collecting 3500 # / hr. of sand. The

particle distribution shows 90"/. greater than 10 microns. The air is to exhaust to room

in winter, to atmosphere in summer.

3500 #1 -7- 60 MIN. -+- 26000 f!L!!.: X 7000 GIl = 15.7..Q..!.. . IH I liT MIN. 1# cu. FT•

·Chart A = 3/1 ratio, Chart B = Factor 1.0, Chart C "....., .95; 3 x.l x .95 =c 2.9 air

to cloth ratio. 26000-;-. 2.9 = 9,000 sq. fl.

Reprinted with permission from Buffalo Forge Company Bulletin AHD-29.
5-20

Table 5-4 Factors for Pulse-Jet Gas-to-Cloth Ratios(9)

A. Material Factor

ISa

Cake mix

Cardboard dust

Cocoa

Feeds

Flour

Grain

Leather dust

Sawdust

Tobacco

12

Asbestos

Buffing dust

Fibrous and

cellulosic

materi al

Foundry shakeout

Gypsum

Lime (hydrated) Perl ite

Rubber chemicals

Salt

Sand

Sandblast dust

Soda ash

Talc

10

Alumina

Aspirin

Carbon black

(finished)

Cement

Ceramic pigments

Clay and

brick dusts

Coal

Fluorspar

Gum, natural

Kaolin

Limestone

Perchlorates

Rock dust,

ores and

minerals

Sil ica

Sorbic acid

Sugar

9.0

Ammonium

phosphatefertilizer

Cake

Diatomaceous

earth

Dry petro- chemicals

Dyes

Fly ash

Metal powder Metal oxides

Pigments,

meta11 ic

and synthetic Plastics

Resins

Silicates

Starch

Stearates

Tannic acid

Activated

carbon

Carbon

black

(molecul ar)

Detergents

Fumes

and

other

dispersed

products

direct

from

reactions

Powdered

mil k

Soaps

B. Application Factor

Nuisance Venting Relief of transfer

points, conveyors, packing stations, etc.

Product Collection

Air conveying-venting mills flash driers

classifiers, etc.

Process Gas Filtration

Spray driers, kilns,

reactors, etc.

LO

0.9

0.8

a1n general physically and chemically stable materials.

bAlso includes those solids that are unstable in their physical or chemical

state due to hygroscopic nature, sublimation, and/or polymerization.
5-21

D = mass mean diameter of particle, pm (between 3 and 100)

L = inlet dust loading, gr/ft3 (between 0.05 and 100)

For temperatures below 50 of, use T = 50 but expect decreased accuracy;

for temperatures above 275 OF, use T = 275. For particle mass mean diameters

less than 3 pm, the value of D is 0.8, and for. diameters greater than 100 pm,

D is 1.2. For dust loading less than 0.05 gr/ft3, use L = 0.05; for dust

loading above 100 gr/ft3, use L = 100.

5.2.1.3 Gas-to-Cloth Ratio From Theoretical/Empirical Equations

5.2.1.3.1 Shaker and reverse-air baghouses--The system described by

equations (5-1) through (5-6) is complicated; however, numerical methods can

be used to obtain an accurate solution. A critical weakness in baghouse

modeling that has yet to be overcome is the lack of a fundamental description

of the bag cleaning process. That is, to solve equations (5-1) through (5-6),

the value of Wr (the dust load after cleaning) must be known. Clearly, there

must be a relationship between the amount and type of cleaning energy and the

degree of dust removal from a bag. Dennis et al. (10) have developed

correlations for the removal of coal fly ash from woven fiberglass bags by

shaker cleaning and by reverse air cleaning. These correlations have been

incorporated into a computer program that generates the solution to the above

system of equations. (10,11,12) If one were to apply the correlations

developed with coal ash and woven glass fabrics to other dust/fabric

combinations, the accuracy of the results would depend on how closely that

dust/fabric combination mimicked the coal ash/woven glass fabric system.

Physical factors that affect the correlation include the particle size

distribution, adhesion properties of the dust and fabric, and fabric weave, as

well as cleaning energy. More research is needed in this area of fabric

filtration.
5-22

The rtgorous design of a baghouse thus involves several steps. First,

the design goal for average pressure drop (and maximum pressure drop, if

necessary) must be specified along with total gas flow rate and other

parameters, such as Se and K2 (obtained either from field or laboratory

measurements). Second, a face velocity is assumed and the number of

compartments in the baghouse is computed based on the total gas flow, face

velocity, bag size, and number of bags per compartment (typical compartments

in the U.S. electric utility industry use bags 1 ft in diameter by 30 ft long

with 400 bags per compartment). Standard practice is to design a baghouse to

meet the specified pressure drop when one compartment is off-line for

maintenance and a second compartment off-line for cleaning. The third step is

to specify the operating characteristics of the baghouse (i.e., filtration

period, cleaning period, and cleaning mechanism). Fourth, the designer must

specify the cleaning efficiency so that the residual dust load can be

estimated. Finally, the specified baghouse design is used to establish the

details for equations (5-1) through (5-6), which are then solved numerically

to establish the pressure drop as a function of time. The average pressure

drop is then computed by integrating the instantaneous pressure drop over the

filtration cycle and dividing by the cycle time. If the computed average is

higher than the design specification, then the face velocity must be reduced

and the procedure repeated. If the computed average pressure drop is

significantly lower than the design specification, then the proposed baghouse

was oversized and should be made smaller by increasing the face velocity and

repeating the procedure. When the computed average pressure drop comes

sufficiently close to the assumed specified value, then the design has been

determined. A complete description of the modeling process can be found in
5-23

the reports by Dennis et al. (10,12) A critique on the accuracy of the.model

is presented by Viner et al. (13)

5.2.1.3.2 Pulse-jet baghouses--The overall process of designing a pulse

jet baghouse is actually simpler than that required for a reverse-air or

shaker baghouse if the baghouse remains online for cleaning. The first step

is to specify what the desired average tubesheet pressure drop should be.

Second, the operating characteristics of the baghouse must be established

(e.g.! online time, cleaning energy). Third, the designer must obtain values

for the coefficients in either equation (5-10) or equation (5-11) from field,

pilot plant, or laboratory measurements. Fourth, a value is estimated for the

face velocity and the appropriate equation [(8) or (11)] is solved for the

pressure drop as a function of time for the duration of the filtration cycle.

This information is used to calculate the cycle average pressure drop. If the

calculated pressure drop matches the specified pressure drop, then the

procedure is finished. If not, then the designer must adjust the face

velocity and repeat the procedure.

5.2.2 Pressure Drop

Pressure drop for the bags can be calculated rigorously from the

equations given in the preceding section if values for the various parameters

are known. Frequently they are not known. For quick estimation, a maximum

pressure drop of 5- to 10-in. H

2

0 across the baghouse and 10- to 20-in H

2

0

across the entire system can be assumed if it contains much ductwork.

A comparable form of equations (5-1) and (5-3) that may be used for

pressure drop across the fabric in a shaker or reverse-air baghouse is:

(5-13)
5-24

where:

AP = pressure drop (in. H20)

Se = effective residual drag of the fabric [in. H20/(ft/min)]

V = superficial face ve-locity or gas-to-cloth ratio (ft/min)

K2 = specific resistance 20efficient of the dust [in.

H20/(ft/min)]/(lb/ft )

Ci = inlet dust concentration (lb/ft3)

8 = filtration time, min

Although there is much variability, values for Se may range from about

0.2 to 2 in. H2

0/(ft/min) and for K2 from 1 or 2 to 30 or 40 [in. H20/(ftl

min)]/lb/ft. Typical values for coal fly ash are 1 to 4. Inlet concentrations vary from less than 0.05 gr/ft3 to more than 100 gr/ft3, but a more

nearly typical range is from 0.5 to 10 gr/ft3• Filtration times may range

from 20 minutes to 8 hours for continuous duty reverse-air and shaker baghouses, but 30 minutes to 4 hours is more frequently found. Filtration times

for pulse-jet baghouses range from 2 to 60 minutes, but 5 to 20 minutes is

typical. For pulse-jet baghouses, use equations (5-8) and (5-10) to estimate

AP, after substituting CiVt for Wo and (PE)Aw for Se V.

5.2.3 Particle Characteristics

Particle size distribution and adhesiveness are the most important

particle properties that affect design procedures. Smaller particle sizes can

form a denser cake, which increases pressure drop. As shown in Table 5-3 and

equation (5-12), the effect of decreasing average particle size is a lower

applicable gas-to-cloth ratio.

Sticky particles may require installing equipment that injects a

precoating material onto the bag surface, which acts as a buffer that traps
5-25

the particles and prevents them from blinding or permanently plugging the

fabric pores.

5.2.4 Gas Stream Characteristics

Moisture and corrosives content are the major gas stream characteristics

requiring design consideration. The baghouse and associated ductwork should

be insulated and possibly heated to avoid condensation. Both the structural

and fabric components must be considered, as either may be damaged. Where

structural corrosion is likely, stainless steel substitution for mild steel

may be required, provided that chlorides are not present. (Most austenitic

stainless steels are susceptible to chloride corrosion.)

5.2.4.1 Temperature

The temperature of the pollutant stream to be cleaned must be above and

remain above the dew point of any condensables in the stream. If the

temperature is high and it can be lowered without approaching the dew point,

spray coolers or dilution air can be used to drop the temperature so that

temperature limits of the fabric will not be exceeded. The additional cost of

a precoo1er will have to be weighed against the higher cost of bags with

greater temperature resistance. The use of dilution air to cool the stream

also constitutes a tradeoff between a less expensive fabric and a larger

filter necessary to accommodate the additional volume of the dilution air.

Generally, precooling would not be necessary if fabric that will handle the

temperature and the chemical action of the pollutant stream is available.

(Costs for spray chambers, quenchers, and other precoo1ers are found in the

"Precoo1ers" section of the Manual.) Table 5-5 lists several of the fabrics

in current use and provides information on temperature limits and chemical

resistance. The column labeled "Flex Abrasion" indicates the fabric's

suitability for cleaning by mechanical shakers.
5-26

Table 5-5 Properties of Leading Fabric Materials(14)

Fabric

Cotton

Creslanb

Dacronc

Fiberglasd

Filtrone

Gore-Texf

Polypropylene

Teflonc

Wool

180

250

275

160

500

270

Depends

on

backing

375

200

260

200

450

200

Acid

Resistance

Poor

Good in mineral

acids

Good in most

mineral acids;

disolves par- t i ally i n concentrated H2

S04

Little effect

even at high concentration

Fair to good

Good to

excellent

Depends on

backing

Fair

Fair

Good to excellent in mineral

acids

Excellent

Inert except

to fl uorine

Very good

Alkali

Resistance

Very good

Good in weak

alkali

Good in weak

a1ka1i ; fa i r

in strong alkali

little effect

even in high concentration

Fair to good

Good

Depends on

backing

Excellent at

low temperature

Excellent

Fair to good in weak alkali

Excellent

Inert except

to trifluoride,

chlorine, and

molten alkaline

metals

Poor

Flex

Abrasion

Very good

Good to

very good

Very good

Fair to

good

Fair

Good to

Very good

Fair

Excellent

Excellent

Good

Excellent

Fair

Fair to good

aMaximum continuous operating temperatures recommended by the Industrial Gas

Cleaning Institute.

bAmerican Cyanamid registered trademark.

cOu Pont registered trademark.

dOwens-corning Fiberglas registered trademark.

eW. W. Criswell Div. of \~heelabrator-Fry, Inc., trade name.

fw. L. Gore and Co., registered trademark.
5-27

5.2.4.2 Pressure

Standard fabric filters can be used in pressure or vacuum service but

only within the range of about +25 inches of water gauge. Because of the

sheet metal construction of the house, they are not generally suited for more

severe service. However, for special applications, high-pressure shells can

be built.

5.2.5 Pressure or Suction Housings

The location of the baghouse with respect to the fan in the gas stream

affects the capital cost. A suction-type baghouse, with the fan located on

the downstream side of the unit, must-withstand high negative pressures and

therefore must be more heavily constructed and reinforced than a baghouse

located downstream of the fan (pressure baghouse). The negative pressure in

the suction baghouse can result in outside air infiltration, which can result

in condensation, corrosion, or even explosions if combustible gases are being

handled. In the case of toxic gases, this inward leakage can have an advantage over the pressure-type baghouse, where leakage is outward. The main

advantage of the suction baghouse is that the fan handling the process stream

is located at the clean-gas side of the baghouse. This reduces the wear and

abrasion on the fan and permits the use of more efficient fans (backwardcurved blade design). However, because for some designs the exhaust gases

from each compartment are combined in the outlet manifold to the fan, locating

compartments with leaking bags may be difficult and adds to maintenance costs.

Pressure-type baghouses are generally less expensive because the housing

must only withstand the differential pressure across the fabric. In some

designs the baghouse has no external housing. Maintenance also is reduced

because the compartments can be entered and leaking bags can be observed while
5-28

the-compartment is in service. With a pressure baghouse, the housing acts as

the stack to contain the fumes with the subsequent discharge at the roof of

the structure, which makes it ea~er to locate leaking bags. The main disadvantage of the pressure-type baghouse is that the fan is exposed to the

dirty gases where abrasion and wear on the fan blades may become a problem.

Also, some applications require a stack for dispersion of gaseous pollutants,

negating some of the construction economics.

5.2.6 Standard or Custom Construction

The design and construction of baghouses are separated into two groups,

standard and custom, (8) which are further separated into low, medium, and high

capacity. Standard baghouses are predesigned and factory built as complete

off-the-shelf units that are shop-assembled and bagged for low-capacity units

(hundreds to thousands of acfm throughput). Medium-capacity units (thousands

to less than 100,000 acfm) have standard designs, are shop-assembled, mayor

may not be bagged, and have separate bag compartment and hopper sections.

High-capacity baghouses (larger than 50,000 or 100,000 acfm) can be designed

as shippable modules requiring only moderate field assembly. These modules

may have bags installed and can be shipped by truck or rail. Upon arrival,

they can be operated singly or combined to form units for larger-capacity

applications. Because they are preassembled, field labor for installation is

less costly.

The custom baghouse, also high capacity, is designed for a specific

application and is usually built to the specifications prescribed by the

customer. Generally, these units are much larger than standard baghouses.

For example, many are used on power plants. The cost of the custom baghouse

is much higher per square foot of fabric because it is not an off-the-shelf
5-29

item and requires special setups for manufacture and expensive field labor for.

'assembly upon arrival. The advantages of the custom baghouse are many and are

usually directed towards ease of maintenance, accessibility, and other

customer preferences. In some very small baghouses, a complete set of bags

must be replaced in a compartment at one time because of the difficulty in

locating and replacing single leaking bags, whereas in custom baghouses,

single bags are accessible and can be replaced one at a time as leaks develop.

5.2.7 Filter Media

The type of filter material used in baghouses is dependent on the

specific application in terms of chemical composition of the gas, operating

temperature, dust loading, and the physical and chemical characteristics of

the particulate. A variety of fabrics, either felted or woven, is available

and the selection of a specific material, weave, finish, or weight is based

primarily on past experience. The type of yarn (filament, spun, or staple),

the yarn diameter, and twist are also factors in the selection of suitable

fabrics for a specific application. For some difficult applications, Gorelex, a polytetrafluoroethylene (PTFE) membrane laminated to a substrate fabric

(felt or woven) or altered-surface fabrics may be used. Because of the

violent agitation of mechanical shakers, spun or heavy weight staple yarn

fabrics are commonly used with this type of cleaning, while lighter weight

filament yarn fabrics are used with reverse-air cleaning.

The type of material will limit the maximum operating gas temperature for

the baghouse. Cotton fabric has the least resistance to high temperatures

(about 180 OF), while fiberglass has the most (about 500 OF). The temperature

of the exhaust-gas stream must be well above the dew point of any of its

contained condensables as liquid particles will usually plug the fabric pores
5-30

quickly. However, the- temperature must be below the maximum limit of the

fabric in the bags. These maximum limits are given in Table 5-5~

5.3 Estimating Total Capital Investment

Total capital investment includes costs for the baghouse structure, the

initial complement of bags, auxiliary equipment, and the usual direct and

indirect costs associated with installing or erecting new structures. These

costs are described below.

5.3.1 Equipment Cost

5.3.1.1 Bare Baghouse Costs

Six types of baghouses will be considered:

Preassembled units

Intermittent

Continuous

Continuous

Continuous

Continuous

Continuous

Shaker

Shaker

Pulse-jet (commo~ housing)

Pulse-jet (modular)

Reverse-air

Field-assembled units

Any method

Figure 5-2

Figure 5-3

Figure 5-4

Figure 5-5

Figure 5-6

Figure 5-7

Each figure gives costs for the filter without bags and additional costs

for stainless steel construction and for insulation. All curves are based on

a number of actual quotes. A least squares line has been fitted to the quotes

and the line's equation is given. However, extrapolation should not be used.

The reader should not be surprised if he obtains quotes that differ from these

curves by as much as +25%. Significant savings can be obtained by soliciting

multiple quotes. All units include inlet and exhaust manifolds, supports,
5-31

platforms, handrails, and hopper discharge devices. The indicated prices are

flange to flange. Note that the scales on both axes change from one figure to

another to accommodate the differing gas flow ranges over which the various

types of baghouses operate.

The 304 stainless steel add-on cost is used when such construction is

necessary to prevent the exhaust gas stream from corroding the interior of the

baghouse. Stainless steel is substituted for all metal surfaces that are in

contact with the exhaust gas stream.

Insulation costs are for 3 inches of shop-installed glass fiber encased

in a metal skin. One exception is the custom baghouse, which has fieldinstalled insulation. Costs for insulation include only the flange-to-flange

baghouse structure on the outside of all areas in contact with the exhaust gas

stream. Insulation for ductwork, fan casings, and stacks must be calculated

separately as discussed later.

The first baghouse type is the intermittent service baghouse cleaned by a

mechanical shaker. This baghouse is shut down and cleaned at convenient

times, such as the end of the shift or end of the day. Although few units are

sold, they are applicable for operations that require infrequent cleaning.

Figure 5-2 presents the unit cost with price in dollars plotted against the

gross square feet of cloth required. 15 Because intermittent service baghouses

do not require an extra compartment for cleaning, gross and net fabric areas

are the same. The plot is linear because baghouses are made up of modular

compartments and thus have little economy of scale. Because of the modular

construction, the price line should not be extrapolated downward. Costs for

both types of shaker baghouse include the. shaker mechanism.
Cost wittlout bags: 10-

I--

..... I...d ",.• ...oIi "",.

'2.-1-- l.diIIllII'"

61~~ \\ l;i~" . ....I!!:I-- I--

~f.;>~be .:;.... ISI.alnless steel add on I--

~.... T2 ....... 06 "--

1-"ldI"1 660 +~............ ldIIIIII J;- $ ::::: ,\"\.

....... IJI"" ,...

$ = 1 875 + 0 450 ft 2 Insulation add on- 10-

". I II I· Iii- I . - I I I I n I I I I I I I I I I I I I

1;) 50

o

o

o 75 8

T""

EI7

-

<.n

i

W

N

6 8 10 12 14 16 18

Gross Cloth Area (1000 ft

Caution: Do not extrapolate.

42

100

125

150

.....

ffi 25 E

a. -s

.ff 0

o

<0

T""

L-

•. (J)

:::1

o

"E

--

Source: ETS, Inc.

figure 5-2. Equipment costs for intermittent shaker filters.
5-33

Figure 5-3 presents the same costs for a continuously operated baghouse

cleaned by mechanical shaker. 15 ,16 Again, price is plotted against the gross

cloth area in square feet. As in Figure 5-2, the units are modular in

construction. Costs for these units, on a square foot basis, are higher

because of increased complexity and generally heavier construction.

The third and fourth types are common-housing pulse jets and modular

pulse jets. The latter are constructed of separate modules that may be

arranged for offline cleaning, and the former have all bags within one

housing. The costs for these units are shown in Figures 5-4 and 5-5,

respectively.15 The cleaning system compressor is not included. Note that in

the single-unit (common-housing) pulse jet, for the range shown, the height

and width of the unit are constant and the length increases; thus, for a

different reason than that for the modular units discussed above, the cost

increases linearly with size. Because the common housing is relatively

inexpensive, the stainless steel add-on is proportionately higher than for

modular units. Added material costs and setup and labor charges associated

with the less workable stainless steel account for most of the added expense.

Figure 5-6 shows the costs for the reverse-air baghouses. 15 The construction

is modular and the reverse-air fan is included. The final type is the custom

baghouse which, because of its large size, must be field assembled. It is

often used on power plants, steel mills, or other applications too large for

the factory-assembled baghouses. Prices for these units are shown in

Figure 5_7. 15

5.3.1.2 Bag Costs

Table 5-6 gives the price per square foot of bags by type of fabric and

by type of cleaning system used. The prices represent about a 10% range. In

calculating the cost, the gross area as determined from Table 5-2 should be
Caution: Do not extrapolate.

! Cost without ba9s l..<IlIII

LdI

• . i!~

4Jj~~

l1!! Stainless steel add on- L.- tz,. .- 10-

'-I---:~P" 9\\- liiII l~~~~~ be~9 __ ... "'"

6c60 1-1- -jijIII

1·l4iIP".l· C501 ~_ ... >( tz,.be\ .... !Q':> ... .--.- ~~~~~~ ~~- .

10- i-- ~... 1...1I ....

.....

•Ill"~ 2 l~ 0.335 ft •. .1~s~I~~I~nla~~ fJ~ , • i I - i I" I I

co 600

m.,..

.... 500

as

:J

o

:e 400

t=.

-

8 300

.,..

o

EI:)-

-

1ii 200 o

o

-c

CD 100 E

a.

:J

aff 0

o 10 20 30 40 50 60

Gross Cloth Area (1000 ft2)

70 80 90

U1

w•

Source: ETS, Inc.; Fuller Co.

Figure 5-3. Equipment costs for continuous shaker filters.
Cost without bags =

I--

I4lIIld .....

. ~~--",.,. .-

'(l2 .-IIJIIIII"

.... ,S'f{o2 .... _-""'IIl -ii!!iI""" . ffO . od8III "'"" 6 ~~ Stainless steel add on.- $ .;::; 9" :;;a~ ~_,....... 2- - ...................... 4.54'\\\

..ollII IIJIIIII" 0489 --t; $ .;::; '\ '"1 I I

I I I I 2

$..: 1.428 + 0.931 ft

Insulation add on:I--

1 I I I I 1 I 1 I I--

125

100

Caution: Do not extrapolate.

U1

I

W

U1

6 8 10 12 14 16 18

Gross Cloth Area (1000 ft4

2 4

1i) 50

o

o

.....

55 25 E

a.

:J

tff 0

o

co 150

m

,...

....

i

:J

o

"E.-

f=... § 75

,...

fh

-

Source: ETS. Inc.

Figure 6-4. Equipment costs for pulse-jet filters (common housing).
I I I I I I I ~. _l . . . ...,..I! Cost without bags

;i~"""

~?,~ r::;; .... 11""'"

•

1· L.dIIII"'" IdIIIIl

Stainless steel add on f},.O L4'I I--

I..II8Il! be1~ I-- .... fl, IilP ~-~,... ~\\ ... ..... ~. 'tIZ ~~~ ~,... .....11II"""" ~-: liiiJII

III"'" Z~O~ ......... fl,be, ' 'III'"

~~jj.~

"..

9 ft2 I I 3000 + 2.01 $::: '--~ Insulation add on-I--

Caution: Do not extrapolate.

co

co

0)

orLa>

t::

«1

::J

0

"E.-..t:

I-

.. -0

8

or-

-

1i)

0

0

-c:

a>

E

a. .-::J

0-

... W

150

125

100

75

50

25

o

o 2 . 4 6 8 10 12

Gross Cloth Area (1000 ft

14 16 18

U'l

I

W

m

Source: ETS, Inc,

Figure 5-5. Equipment costs for pulse-jet filters (modular).
Caution: Do not extrapolate.

R=t:~~tti±£EffR+~~t6II-'Cost II I I without .-1 bags I r-tiWIII",'...dIlf..+I-+-W.....I

~l~~Ef~~~ft~~~!~~~Ej3jEEI3~~l~~~ti~~EI~3... IJflII§t;;lii ...jIII1l

w

M-"'-H-I--I-I--J-W,....J

iIJ1~~ _ :::t:I-ti-H--Hrl_... ~::J=IClJu .... tJ

p:ttttt+H-l+P=ntt'z; IiIll! """"Iii .. - o:::tt::r-H-H+I~UI. \'2.\\ J-~.-~ ,.....~~L...lf·+-t-H4-l-+::o:::t:l rt-r-H++-il-l--I-Uc;~- 19_~..,j~ Gi~ l

.....\\~ !-On Will ...~~St at..oll~iIIi'I~:t:~±-8~Ptt:tjjj I I I n~')-'" ~t:;.I~'" 'n1() "" a ness steel add on -.....

~.(;iIIi 1-1- 'E>.~ lildll'tl:t:~~±BlfJR=fR=ii=P:E H-+-~-1-..l-~ 7 6-ti~-- \ A' ..... w...~,.~:tt:t:t:BEI±8::t==t=~tt:t:t:fB3 ...-r-t-+-+-I-L-LLl::ii--

li1IIIIIP".....

'\';}\~W~1lI""1c±t3:t+t:l:J:E±Et!ft:1R::t=t:l:EEej3 n.~~ ~1odI~.±r:±:1=H~a:E:aEttf:t=t=HR=S:E:EI H-t--t-I-+,....s~U.l..allilll.J_ ..1-~~;_~..... 1:=E8j:t:1::f::t:t:lt81:Et!:f:t:1::f::t=SIEe~ H-+--f.....J-W L ....1ilIIII -....~all-±t:t:Et~=F~lEEtf!3:f:f:~=FEl:EEt33 1_...... .....-r+-+-I-lt.::.L...L $ = 1,130 + 0.000 ft 2 Insulation add on:::

_,. -. I

• I I I I • I

co 600

co

m.....

L..

500

as

::l

o

"E 400 .- .

-

§ 300

.....

(f.)-

-

00 200

o

o

.....

c:

Q) 100 E

a.

::l

aff 0

o 10 20 30 40 50 60

Gross Cloth Area (1000 ft

70 80 90

U1

,

W

'-l

Source: ETS, Inc.

Figure 5-60 Equipment costs for reverse-aiF filterso
Caution: Do not extrapolate.

()1

I

W

(Xl

200 300 400

Gross Cloth Area (1000 ft4

100

0)

Tm""I~IT1'

i- 2500 Cost without bags I I I I •

:l 1 ........... I I 1 II

o IIilIIiI!!t • I I --. I:iiiii !. I I I •

"E2000 .... 1111111 .... :c 1::1iIlIl!!I ., ~, -. .... r::;,jjjj'" [liE I I I I I. I I •

'/.. .. 11111111111\-' .....::. 1....Oll I • I I. I -.

8o 1500 ~.~'2-0~ I~"'" .. - • I • I : I I. I.

T- I_n.<\ ... • I I. I 1--'

U'!":I-::l -"".. I

1ii 1000 r'tll-b........ I Stainless steel add on

o C!IJIIII I

o .~ 2 ..... tI"'" 2 208 1\ . 1_ii~ 500$1 ::::: 90,000 + ., I 1 I I. I

E .' .1 I 1 I I' 2

a. . $ = 60 184 + 0.637 It I I. I I ._ _,,~ . I 1 I I • I I I

:l 1 II

aB" 0 J. 1 Insulation add on I I I I I

1~J. J.l~1~J.1J IT

o

Source: ETS8 Inc.

figure 6-7 Equipment costs for custom-built filters,
5-39

Table 5-6 Bag Price~

(3rd quarter 1986 $/ft )

Type of Material a

Bay Diameter

Type of Cleaning inches) PE PP NO HA FG CO TF

Pul se jet, TRb 4-1/2 to 5-1/8 0.59 0.61 1.88 0.92 1.29 NA 9.05

6 to 8 0.43 0.44 1.56 0.71 1.08 NA 6.80

Pulse jet, BBR 4-1/2 to 5-1/8 0.37 0.40 1.37 0.66 1.24 NA 8.78

6 to 8 0.32 0.33 1.18 0.58 0.95 NA 6.71

Shaker

Strap top 5 0.45 0.48 1.28 0.75 NA 0.44 NA

Loop top 5 0.43 0.45 1.17 0.66 NA 0.39 NA

Reverse air with 8 0.46 NA l.72 NA 0.99 NA NA

rings

11-1/2 0.47 NA 1.69 NA 0.76 NA NA

Re~ers~ air w/o 8 0.32 NA 1.20 NA 0.69 NA NA

rlngs 11-1/2 0.32 NA 1.16 NA 0.53 NA NA

but used in low pressure pulse applications.

NA = Not applicable.

aMaterials:

PE = 16-oz polyester PP = 16-oz polypropylene NO = 14-oz nomex

HA = 16-oz homopolymer acrylic

bBag removal methods:

TR = Top bag removal (snap in)

BBR = Bottom bag removal

cldentified as reverse-air bags,

FG = 16-oz fiberglass with 10% Teflon

CO = 9-oz cotton

TF = 22-oz Teflon felt

NOTE: For pulse-jet baghouses, all bags are felts except for the fiberglass, which is woven. For bottom access pulse jets, the cage price for one

cage can be calculated from the single-bag fabric area using:

In 50 cage lots

In 100 cage lots

In 500 cage lots

Mild steel cage

$ = 4.941 + 0.163 ft~ $ =4.441 + 0.163 ft2 $ = 3.941 + 0.163 ft

Stainless steel cage

$ _ 2 - 23.335 + 0.280 ft2 $ = 21.791 + 0.263 ft2 $ = 20.564 + 0.248 ft

These costs apply to 4-1/2-in. or 5-5/8-in diameter, 8-ft and 10-ft

cages made of 11 gauge mild steel and having 10 vertical wires and

"Roll Band" tops. For flanged tops, add $1 per cage. If flow control

venturis are used (as they are in about half of the pulse-jet manufacturers' designs), add $5 per cage.

For shakers and reverse air baghouses, all 6ags are woven. All prices are for

finished bags, and prices can vary from one supplier to another. For Gore-Tex

bag prices, multiply base fabric price by factors of 3 to 4.5.

Source: ETS, Inc. (15)
5-40

used. Gore-Tex fabric costs are a combination of the base fabric cost and a

premium for the PTFE laminate and its application. As fiber market conditions

change, the costs of fabrics relative to each other also change. The bag

prices are based on typical fabric weights, in ounces/square yard, for the

fabric being priced. Sewn-in snap rings are included in the price, but other

mounting hardware, such as clamps or cages, is an added cost.

5.3.1.3 Auxiliary Equipment

The auxiliary equipment depicted in Figure 5-1 is discussed elsewhere in

the Manual. Because hoods, precoolers, cyclones, fans, motors, and stacks are

common to many pollution control systems, they are given extended treatment in

the following tentatively numbered separate sections: capture hoods in

Section 16, ductwork in Section 7, precoolers (spray chambers and quenchers)

in Section 18, cyclones in Section 17, fans and motors in Section 8, and

stacks in Section 11. If dust-removal equipment is to be considered,

Section 19 discusses screw conveyors.

5.3.2 Total Purchased Cost

The total purchased cost of the fabric filter system is the sum of the

costs of the baghouse, bags, auxiliary equipment, instruments and controls;

and of taxes and freight. The last three items generally are taken as

percentages of the estimated total cost of the first three items. Typical

values, from Section 2 of the Manual, are 10% for instruments and controls, 3%

for taxes, and 5% for freight.

Bag costs can vary from less than 15% to more than 100% of bare baghouse

cost, depending on type of fabric required. This situation makes it inadvisable to estimate total purchased cost without considering both costs, and

prevents effective use of factors to estimate a single cost for the baghouse

and bags.
5-41

5.3.3 Total Capital Investment

Using the Section 2 methodology, the total capital investment (TCI) is

estimated from a series of factors applied to the purchased equipment cost to

obtain direct and indirect costs for installation. The TCI is the sum of

these three costs. The required factors are given in Table 5-7. Because bag

costs can have such a large effect on total purchased equipment cost, the

factors may cause overestimation of total capital investment when expensive

bags are used. Using stainless steel components may also cause overestimation. Because baghouses may vary from small units installed within existing

buildings to large, separate structures, specific factors for site preparation

or for buildings are not given. However, costs for buildings may be obtained

from such references as Means Square Foot Costs 1986. (17) Land, working

capital, and offsite facilities are excluded from the table, as they are not

normally required. For very large installations, however, they may be needed

and would be estimated on an as-needed basis.

Note that the factors given in Table 5-7 are for average installation

conditions. Considerable variation may be seen with other-than-average

installation circumstances.

5.4 Estimating Total Annual Costs

5.4.1 Direct Annual Cost

Direct annual costs include operating and supervisory labor, operating

materials, replacement bags, maintenance (labor and materials), utilities, and

dust disposal. Most of these costs are discussed individually below. They

vary considerably with location and time, and, for this reason, should be

obtained to suit the specific baghouse system being costed. For example,

current labor rates may be found in such publications as the Monthly Labor

Review, published by the U.S. Department of Labor, Bureau of Labor Statistics.
5-42

Table 5-7 Capital Cost Factors for Fabric Filters(8)

Direct Costs

Purchased equipment costs:

Fabri c fi Her

Bags

Auxiliary equipment

Instruments &controls

Taxes

Freight Total purchased equipment cost

Installation direct costs

Foundations &supports Erection &handling Electrical

Piping

Insulation for ductworka

Painting

Site preparation (S.P.) Buildings (Bldg.) Total installation direct costs

Total direct costs

Factor

As

estimated

A = Sum of As

estimated

As

estimated

0010 A

0.03 A

0.05 A

B = 1.18 A

0.04 B

0.50 B

0.08 B

0.01 B

0.07 B

0.02 B

As requi red

As reguired 0.72 +

S.P. +

Bldg.

1.72 B +

S.P. +

Bldg.

Indirect costs

Engineering &supervlslon Construction and field expense Construction fee

Startup fee

Performance test

Contingencies Total indirect costs

Total direct and indirect costs = Total capital investment

0.10 B

0020 B

0.10 B

0.01 B

0.01 B

0.03 B

0.45 B

2.17 B +

SoP. +

Bldg.

aIf ductwork dimensions have been established, cost may be estimated based on

$10-12/ft2 of surface for field application. Fan housings and stacks may also

be insulated. 15
5-43

5.4.1.1 Operating and Supervisory Labor

Typical operating labor requirements are 2 to 4 hours per shift for a

wide range of filter sizes. (8) Small or well-performing units may require

less time, while very large or troublesome units may require more.

Supervisory labor is taken as 15% of operating labor.

5.4.1.2 Operating Materials

Operating materials are generally not required for baghouses. An

exception is the use of precoat materials injected on the inlet side of the

baghouse to provide a protective dust layer on the bags when sticky or

corrosive particles might harm them. Adsorbents may be similarly injected

when the baghouse is used for simultaneous particle and gas removal. Costs

for these materials should be included on a dollars-per-mass basis (e.g.,

dollars per ton).

5.4.1.3 Maintenance

Maintenance labor varies from 1 to 2 hours per shift. (8) As with

operating labor, these values may be reduced or exceeded depending on the size

and operating difficulty of a particular unit. Maintenance materials costs

are assumed to be equal to maintenance labor costs. (8)

5.4.1.4 Replacement Parts

The major replacement part items are filter bags, which have a normal

operating life of 1 to 5 years with about 2 years being typical. The

following formula is used for computing the bag replacement cost:

CRCB = (CB + CL) x CRFB

where:

CRCB = bag capital recovery cost ($/year)

CB = initial bag cost including taxes and freight ($)

(5-14)
5-44

Cl = bag replacment labor ($)

CRFB =capital recovery factor whose value is a function of the annual

interest rate and the useful life of the bags. (For instance, for

a 10% interest rate and a 2-year life, CRFB = 0.5762.)

The bag replacement labor cost (Cl

) will depend on such factors as the

number, size, and type of the bags; their accessibility; how they are

connected to the baghouse tubesheet; etc. For example, in a reverse-air

baghouse it would probably take from 10 to 20 man-minutes to change an 8-in.

by 24-ft bag that is clamped in place. This bag has a filtering surface area

of approximately 50 ft2• If the replacement labor rate were $21.12/h

(including overhead), Cl would be from $0.07 to $0.14/ft2 of bag area. As

Table 5-6 shows, for some bags (e.g., cotton), this range of Cl would

constitute a significant fraction of the purchase cost. For pulse jets,

replacement time would be about 5 to 10 man-minutes for a 5-in. by 10-ft bag

in a top-access baghouse. These bag replacement times are based on changing a

minimum of an entire module and on having typical baghouse designs. Times

would be significantly longer if only a few bags were being replaced or if the

design for bag attachment or access were atypical.

This method treats the bags as an investment that is amortized over the

useful life of the bags, while the rest of the control system is amortized

over its useful life (typically 20 years; see Section 5.4.2). Values of CRFB

for bag lives different from 2 years can be calculated from equation (2-3) of

the Manual.

5.4.1.5 Electricity

Power is reqUired to operate system fans and cleaning equipment. Fan

power for primary gas movement can be calculated from equation (2-7) of the

Manual. After substituting into this equation a combined fan-motor efficiency
5-45

of 0.65 and a specific gravity of 1.000, we obtain:(18)

F.P. = 0.000181(Q) (AP) (8)

where:

(5-15)

(5-16)

F.P. = fan power requirement (kWh/yr)

Q = system flow rate (acfm)

AP = system pressure drop (in. H20)

8 = operating time (h/yr)

Cleaning energy for reverse-air systems can be calculated from the number

of compartments to be cleaned at one time (usually one, sometimes two), and

the reverse gas-to-cloth ratio (from about one to two times the forward gasto-cloth ratio). Reverse-air pressure drop varies up to 6 or 7 in. H2

0

depending on location of the fan pickup (before or after the main system

fan). (19) The reverse-air fan generally runs continuously.

Typical energy consumption in kWh/yr for a shaker cleaning system

operated 8,760 h/yr can be calculated from:(2)

P = 0.053A

where:

A = gross fabric area (ft2)

5.4.1.6 Fuel

If the baghouse or associated ductwork is heated to prevent condensation,

fuel costs should be calculated as required. These costs can be significant,

but may be difficult to predict. For methods of calculating heat transfer

requirements, see Perry. (20)

5;4.1.7 Water

Cooling process gases to acceptable temperatures for fabrics being used

can be done by dilution with air, evaporation with water, or heat exchange
5-46

with normal equipment. The last two cases require consumption of plant water,

although costs are not usually significant. Section 4.4 of the Manual

provides information on estimating cooling-water costs.

5.4.1.8 Compressed Air

Pulse-jet filters use compressed air at pressures of about 60 to

100 psig. Typical consumption is about 2 scfm/1,OOO cfm of gas filtered. (2)

For example, a unit filtering 20,000 cfm of gas uses about 40 scf of

compressed air for each minute the filter is operated.

5.4.1.9 Dust Disposal

If collected dust cannot be recycled or sold, it must be landfilled or

disposed of in some other manner. Disposal costs are site-specific, but they

may typically run $20 or $30 per ton exclusive of transportation (see Section 2.4) of the Manual.

5.4.2 Indirect Annual Cost

These include such costs as capital recovery, property tax, insurance,

administrative costs ("G&A"), and overhead. The capital recove~ cost is

based on the equipment lifetime and the annual interest rate employed. (See

Section 2 for a thorough discussion of the capital recovery cost and the

variables that determine it.) For fabric filters, the system lifetime varies

from 5 to 40 years, with 20 years being typical. However, this does not apply

to the bags, which usually have much shorter lives. (See Section 5.4.1.4)

Therefore, as Section 2 of the Manual suggests, when figuring the system

capital recovery cost, one should base it on the installed capital cost less

the cost of replacing the bags (i.e., the purchased cost of the bags plus the

cost of labor necessary to replace them). In other words:
5-47

where:

CRCs = capital recovery cost for fabric filter system ($/yr)

TCI = total capital investment ($)

= initial cost of bags including taxes and freight ($)

labor cost for replacing bags ($)

capital recovery factor for fabric filter system (defined in

Section 2).

For example, for a 20-year system life and a 10% annual interest rate, the

CRFs would be 0.1175.

The suggested factor to use for property taxes, insurance, and

administrative charges is 4% of the TCI. Finally, the overhead is calculated

as 60% of the sum of operating, supervisory, and maintenance labor, and

maintenance materials.

5.4.3 Recovery Credits

For processes that can reuse the dust collected in the baghouse or that

can sell the dust in a local market, such as fly ash sold as an extender for

paving mixes, a credit should be taken. As used below, this credit (RC)

appears as a negative cost.

5.4.4 Total Annual Cost

Total annual cost for owning and operating a fabric filter system is the

sum of the components listed in Sections 5.4.1 through 5.4.3, i.e.:

TAC = DC + IC - RC (5-18)

where:

TAC = total annual cost ($)

DC = direct annual cost ($)

IC = indirect annual cost ($)

RC = recovery credits (annual) ($)
5-48

5.4.5 Example Problem

Assume a baghouse is required for controlling fly ash emissions from a

coal-fired boiler. The flue gas stream is 50,000 acfm at 325 of and has an

ash loading of 4 gr/ft3• Analysis of the ash shows a mass median diameter of

7 pm. Assume the baghouse operates for 8,640 h/yr (360 d).

Design Gas-to-C10th Ratio

The gas-to-c10th ratio (G/C) can be taken from Table 5-1 as 2.5, for

woven fabrics in shaker or reverse-air baghouses, or 5, for felts used in

pulse-jet baghouses. If a factor method were used for estimating G/C,

Table 5-3 for shakers would yield the following values: A = 2, B = 0.9, and

C = 1.0. The gas-to-cloth ratio would be:

2 x 0.9 x 1.0 = 1.8.

This value could also be used for reverse-air cleaning. For a pulse-jet unit,

Table 5-4 gives a value of 9.0 for factor A and 0.8 for factor B. Equation

(5-12) becomes~

v = 9.0 x 0.8 x 2.647 (275)-0.2335 x (0.7471 + 0.0853 1n 7)

x 1.0873 (4)-0.06021

= 4.69

(5-19)

Because this value is so much greater than the shaker/reverse-air G/C, we

conclude that the pulse-jet baghousewou1d be the least costly design.*

*This conclusion is based on the inference that a much higher G/C would

yield lower capital and, in turn, annual costs. However, to make a more

rigorous selection, we would need to calculate and compare the total annual

costs of all three baghouse designs (assuming all three are technically acceptable). The reader is invited to make this comparison. Further

discussion of the effects of G/C increases, and accompanying pressure drop increases, on overall annual costs will be found in Reference 21.
5-49

Assume the use of online cleaning in a common housing structure and, due to

the high operating temperature, the use of glass filter bags (see Table 5-5).

At a gas-to-cloth ratio of 4.69, the fabric required is:

50,000 acfm/4.69 fpm = 10,661 ft2•

Baghouse Cost

From Figure 5-4, the cost of the baghouse ("common housing" design) is:

Cost = 9,688 + 5.552 (10,661)

= $68,878

(5-20)

(5-21)

Insulation is required. The insulation add-on cost from F.igure 5-4 is:

Cost = 1,428 + 0.931 (10,661)

= $11,353

Bag and Cage Cost

From Table 5-6, bag costs are $1.24/ft2 for 5-1/8-in diameter glass

fiber, bottom removal bags. Total bag cost is:

10,661 ft2 x $1.24/ft2 = $13,220.

For 10-ft long cages, fabric area per cage = 5-1/8 in./12 in. 1ft x x 10 ft =

13.42 ft2• The number of cages = 10,661 ft 2/13.42 ft2 = 795 cages. From

Table 5-6, individual cage cost is:

3.941 + 0.163 (13.42 ft2) = $6.128.

Total cage cost is:

795 cages x $6.128/cage = $4,872.

Costs of Auxiliaries

Assume the following auxiliary costs have been estimated from data in

other parts of the Manual:
5-50

Ductwork $16,000

Fan 16,000

Motor 7,500

Starter 4,000

Dampers 7,200

Screw conveyor 4,000

Stack 8,000

$62,700

Total Capital Investment

Direct costs for the fabric filter system, based on the factors in Table

5-7, are given in Table 5-8. (Again, we assume site preparation and buildings

costs to be negligible.) Total capital investment is $412,315.

Annual Costs--Bags

Table 5-9 gives the direct and indirect annual costs, as calculated from

the factors given in Section 5.4. For bag replacement labor, assume 10 min

per bag for each of the 795 bags. At a maintenance labor rate of $21.12

(including overhead), the labor cost is $2,809 for 133 h. The bags are

assumed to be replaced every 2 yr. The replacement cost is calculated using

equation (5-14).

Annual Costs--Pressure Drop

Pressure drop (for energy costs) can be calculated from equations (5-8)

through (5-10), with assumed values of 15 [in. H2

o/(ft/min)]/(lb/ft2) for K2,

100 psig for P

j , and a cleaning interval of 10 min. We further assume that

the G/C (4.69 ft/min) is a good estimate of the mean face velocity over the

duration of the filtering cycle.
5-51

Table 5-8 Example Costs-for Fabric Filter System

Purchased Equipment Costs

Fabric filter (with insulation)

Bags and cages Auxiliary equipment

Instruments and controls, O.lA

Taxes, 0.03A

Freight, 0.05A

Total purchased equipment cost

Installation Direct Costs

Foundation and supports, 0.04B

Erection and handling, 0.50B

Electrical, 0.08B

Piping, O.OlB

Insulation for ductwork, 0.07B

Painting, 0.02B

Site preparation Facilities and buildings Total installation direct costs

Total direct costs

Indirect Costs

Engineering and supervision, 0.10B

Construction and field expense, 0.20B

Construction fee, 0.10B

Startup fee, O.OlB

Performance test, O.OlB

Contingencies, 0.03B

Total indirect costs

Total capital investment

$ 80,231

18,092

62,700

$161, 023 = A

16,102

4,831

8,051

$190,007 = B

7,600

95,004

15,201

1,900

13,300

3,800

$136,805

$326,812

19,001

38,001

19,001

1,900

1,900

5,700

$85,503

$412,315
$25,920

3,888

5-52

Table 5-9 Example Annual Costs for Fabric Filter Systems

Direct Annual Costs

Operating labor

Operator, 6 h/day x 360 d/yr x $12/h = Supervisor, 15% of operator =

Operating materials

Maintenance

Labor, 3 h/day x 360 d/yr x $13.20/h = 14,256

Material, equal to labor costs 14,256

Replacement parts, bags, [2,809 + (13,220 x 1.08*)] x 0.5762 = 9,845

Utilities

Electricity, 0.000181 x 50,000 acfm x 10.3 in. H20

x 8,649 h/yr x $0.06/kWh = 48,323

Compressed air (dried and filtered), 2 scfm/1,OOO acfm

x 50,000 acfm x $0.16/1,000 scfm x 60 min/h x 8,640 h/yr = 8,294

Waste disposal, at $20/ton onsite for essentially 100%

collection efficiency:

4~ft

3 1 lb 50,000 ft x 60 min x 8,640 h x 1 ton $20 - 8 7,000 gr x mln h yr 2,000 16 x ton - 14 ,114

Total direct annual costs

Indirect Annual Costs

Overhead, 0.6 x (25,920 + 3,888 + 14,256 + 14,256) = Property tax, 0.01 x 412,315 = Insurance, 0.01 x 412,315=

Administration, 0.02 x 412,315=

Capital recovery cost, (412,315 - 2,809 - 13,220 x 1.08)

x 0.1175

Total indirect annual costs

Total annual cost

*The "1.08" accounts for freight and sales tax on the bags.

$272,896

34,992

4,123

4,123

8,246

46,439

97,923

$371,000

(rounded)
5-53

3 1 lb Wo = Ci V6 = 4 grift x 7,000 gr x 4.69 ft/min x 10 min = 0.0268 lb/ft2

(5-22)

-0.65

AP = 6.08 x 4.69 ft/min x [100 psi9J + 15 [in. H20/ft/min)]/(lb/ft2)

x 0.0268 lb/ft2 x 4.69 ft/min = 3.32 in. H20 across the fabric (when fully loaded).

Assume the baghouse structure and the ductwork contribute an additional 3 in.

H20 and 4 in. H

2

0, respectively. The total pressure drop is, therefore, 10.3

in.

Total Annual Cost

The total annual cost is $371,000, nearly half of which is for ash

disposal. If a market for the flyash could be found, the total annual cost

would be greatly reduced. For example, if $2/ton were received for the ash,

the total annual cost would drop to $208,000 ($370,819 - $148,114 - $14,811),

or 56% of the cost when no market exists. Clearly, the total annual cost is

extremely sensitve to the value chosen for the dust disposal cost in this

case. In this and in similar cases, this value should be selected with care.

5.4.6 Acknowledgment

We gratefully acknowledge the following companies for contributing data to

this section:

Aget

BACT

BHA

Dustex

Full er

Griff; n

W. W. Sly

Zurn
3.

.2.

5-54

References for Section 5

1. Turner, J. H., "Bag Filtration," in Handbook of Multiphase Systems, ed.

by G. Hetsroni, Hemisphere, 1982.

2. Turner, J. H., and J. D. McKenna, "Control of Particles by Filters," in

Handbook of Air Pollution Technology, ed. by S. Calvert and H. Englund, New York: John Wiley &Sons, 1984.

3. Donovan, R. P., Fabric Filtration For Combustion Sources, New York:

Marcel Dekker, Inc., 1985, p. 201.

4. Dennis, R., and H. A. Klemm, "Modeling Concepts for Pulse Jet

Filtration." JAPCA, 30(1), January 1980.

5. Leith, D. and M. J. Ellenbecker, "Theory for Pressure Drop in a Pulse Jet

Cleaned Fabric. Filter." Atm. Environment, 14, 1980, pp. 845-852.

6. Koehler, J. L. and D. Leith, "Model Calibration for Pressure Drop in a

Pulse-Jet Cleaned Fabric Filter," Atm. Environment, 17(10), 1983, pp. 1909-1913.

7. Northrop Services, Inc. Fabric Filter Workshop Reference Materials, 1977

Workshop. Air Pollution Tralnlng Institute.

8. Vatavuk, W. M., and R. B. Neveril, "Estimating Costs of Air-Pollution

Control Systems, Part II: Factors for Estimating Capital and Operating Costs," Chemical Engineering, November 3, 1980, pp. 157-162.

9. Frey, R. F., and To V. Reinauer, "New Filter Rate Guide," Air

Engineering, 30 April 1964. ---

lO. Dennis, R., et al. Filtration Model for Coal Fly Ash with Glass Fabrics,

August 1977 (EPA-600/7-77-084 (NTIS PB 276489]).

ll. Owen, M. K. and A. S. Viner, Microcomyuter Programs for Particulate

Control, June 1985 (EPA-600/8-85-025a •

Dennis, R. and H. A. Klemm. Fabric Filter Model ChaQge: Vol. I Detailed

Technical Report. February 1979 (EPA-600/7-79-043a [NTIS PB 293551).

Viner, A. S., et al. "Comparison of Baghouse Test Results with the

GCA/EPA Design Model." JAPCA, Vol. 34(8), August 1984 •

.4. Reigel, S. A. and R. P. Bundy. "Why the Swing to Baghouses?" Power,

121-1, pp. 68-73, January 1977 (modified) •

.5. ETS, Inc., Suite C-I03, 3140 Chaparral Dr. SW, Roanoke, VA 24018-4394.

6. Fuller Company, P.O. Box 2040, Bethlehem, PA 18001.
17.

18.

19.

20.

21.

5-55

R. S. Means Company, Inc., Means Square Foot Costs 1986, Kingston, MA.

Perry, Robert H., et al., perr1's Chemical En~ineers' Handbook (Fourth Edition), New York: McGraw-Ai I, 1963, p. 6- O.

Personal communication from Gary Greiner, ETS, Inc., to Jim Turner,

Research Triangle Institute, October 24, 1986.

Perry, Robert H., et al., perr1's Chemical Engineers' Handbook (Sixth Edition), New York: McGraw-Ai I, 1984.

McKenna, J. D., J. H. Turner, D. Furlong, and D. S. Beachler, Fabric

Filters-Baghouses, It Theory, Desi8n and Selection, in preparation, ETS,

Inc., Suite C-103, 3 40 Chaparral r. 5W, Roanoke, VA 24018-4394.