# Cement Kilns

Technical Support Document

for the NOx FIP

January 2001

EPA, OAR, OAQPS, AQSSD, OPSG

## CONTENTS

PAGE

INTRODUCTION

................................ ................................ ..................... 1

UNCONTROLLED EMISSIONS

................................ ............................ 3

EMISSION CONTROL TECHNIQUES

................................ .................. 7

COSTS/COST EFFECTIVENESS

................................ ......................... 131



# Introduction

In cement manufacturing, conditions favorable for formation of nitrogen oxides (NO
x ) are reached routinely because of high process temperatures. Essentially all NO
x emissions

associated with cement manufacturing are generated in cement kilns . In cement kilns, NO
x emissions are formed during fuel combustion by two primary mechanisms: Oxidation of molecular nitrogen present in the combustion air which is termed thermal NO
x formation, and oxidation of nitrogen compounds present in the fuel whi ch is termed fuel NO
x formation. Often the raw material feed to the kiln may also contain a significant amount of nitrogen compounds which may lead to feed

NO
x formation similar to fuel NO
x formation. Because of the high temperatures involved in the

burni ng or clinker formation step, thermal NO
x formation provides the dominant mechanism for

NO

x formation in cement manufacturing.

There are four different types of cement kilns used in the industry: long wet kilns, long dry kilns, kilns with a preheater, and kilns with a precalciner. The long wet and dry kilns and most preheater kilns have only one fuel combustion zone, whereas the newer precalciner kilns and preheater kilns with a riser duct have two fuel combustion zones. Since the typical temperatures in t he two types of combustion zones are different, the factors affecting NO
x formation are also somewhat different depending on the kiln type. In a primary combustion zone at the hot end of a kiln, the high temperatures lead to predominantly thermal NO

x forma tion; whereas in the secondary combustion zone lower gas

- phase temperatures suppress

thermal NO
x formation.

In addition, to the specific NO
x formation mechanisms, the energy efficiency of the

cement

- making process is also important as it determines the a mount of heat input needed to produce a unit quantity of cement. A high thermal efficiency would lead to less consumption of heat and fuel and would produce less NO

x emissions. Since the four types of cement kilns

exhibit different combustion characterist ics as well as energy efficiencies and heat requirements,

the available NO
x emissions data are grouped by these cement kiln types. The data indicate substantial spread in the reported NO
x emissions with large overlap for different kiln types. The

four diff erent cement kiln types, however, do appear to have different levels of NO
x emissions

and different characteristics influencing NO
x formation.

In the NO
x SIP Call final rule, EPA determined that NO
x emissions from large cement kilns (among other source categories) can be decreased by highly cost

- effective controls by an average 30 percent. 1 As defined in the NO
x SIP call rule, “large” is defined as a cemen t kiln which emitted, on average, greater than 1.0 ton/day during the ozone season. 1 “Highly cost

effective controls” are defined in the NO

x SIP call as controls which are less than $2,000/ton of

NO
x reduction in 1990 dollars during the ozone season. 1 In the final FIP rulemaking associated2

with this TSD, EPA is promulgating a rule applicable to large cement kilns to achieve the average 30% reduction called for by the final NO
x SIP call rule. In the October 27, 1998 final

NO
x SIP call rule, EPA identified about 90 large cement kilns. The EPA recently made

corrections in its final NO
x SIP call budget 2

.

A recent NESCAUM report estimates the control costs and NO
x emission reductions for large cement kilns. For four types of controls that achieve at least a 30% reduction, the report estimates the cost effectiveness for the ozone season to be less than $1,000 per ton. 3 ( For comparison to other recent EPA rule makings, the costs and cost effectiveness can be escalated to 1997$ using a factor of 1.21, resulti ng in $1,210/ton.)3



# Uncontrolled Emissions

In cement manufacturing, conditions favorable for formation of nitrogen oxides (NO
x ) are reached routinely because of high process temperatures. Essentially all NO
x emissions

associated with cement manufacturing are generated in cement kilns. In cement kilns, NO
x emissions are formed during fuel combustion by two primary mechanisms: Oxidation of molecular nitrogen present in the combustion air which is termed thermal NO
x formation, and

oxidation of nitrogen compounds present in the fuel which is termed fuel NO
x formation. Often the raw material feed to the kiln may also contain a significant amount of nitrogen compounds which may lead to feed NO
x formation similar to fuel NO
x formation. Because of the high temperatures involved in the burning or clinker formation step, thermal NO
x formation provides

the dominant mechanism for NO
x formation in cement manufacturing.

There are four different types of cement kilns used in the industry: long wet kilns, long dry kilns, kilns with a preheater, and kilns with a precalciner. The long wet and dry kilns and most preheater kilns have only one fuel combustion zone. The newer precalciner kilns and those preheater kilns which have a riser duct have two fuel combu stion zones. Since the typical temperatures in the two types of combustion zones are different, the factors affecting NO
x formation are also somewhat different depending on the kiln type. In a primary combustion zone

at the hot end of a kiln, the high temp eratures lead to predominantly thermal NO

x formation;

whereas in the secondary combustion zone lower gas

- phase temperatures suppress thermal NO
x formation.

In addition, to the specific NO
x formation mechanisms, the energy efficiency of the

cement

- making process is also important as it determines the amount of heat input needed to produce a unit quantity of cement. A high thermal efficiency would lead to less consumption of heat and fuel and would produce less NO
x emi ssions. Since the four types of cement kilns exhibit different combustion characteristics as well as energy efficiencies and heat requirements,

the available NO
x emissions data are grouped by these cement kiln types. The data indicate substantial spread i n the reported NO
x emissions with large overlap for different kiln types. The four different cement kiln types, however, do appear to have different levels of NO
x emissions

and different characteristics influencing NO
x formation.

For thermal NO
x , the primary source is fuel combustion in the kiln burning zone as the gas temperatures are well above 1,400 O C (2,550 F). In contrast, the fuel combustion temperature in a precalciner or in a kiln riser duct is well below 1,200 C (2,200 F), which

suppres ses thermal NO
x formation. Mainly fuel and feed NO
x may be formed in the secondary firing zone of preheater and precalciner kiln systems. Along with the combustion temperature, the gas

- phase residence time and the available oxygen concentration in the hi gh temperature kiln burning zone are important parameters. Longer residence times at the high temperatures will4

allow the NO to be formed in the equilibrium quantities. Greater amounts of oxygen in the combustion zone will of course lead to greater amoun ts of NO
x formation. Once formed, the decomposition of NO
x at lower temperatures, although thermodynamically favorable, is kinetically limited. Thus, strategies to reduce NO
x emissions need to be based upon reducing

formation of thermal NO
x which may be achieved by reducing combustion temperature, oxygen concentration in the high temperature combustion zone, and the gas residence time at high

temperatures.

Fuel NO
x is formed by the conversion of nitrogen present in the fuel used. A recent survey of the cement industry by Portland Cement Association indicates that almost 82 percent of the energy requirement of the cement industry is provided by coal. Natural gas contributed about 3 percent of the energy demand, oil about 1 percent, and other fuels such as waste solvents provided about 14 percent of the energy.

The amount of fuel NO
x formed is difficult to identify separately from thermal NO
x as measurements indicate the overall NO
x formed. In general, however, thermal NO
x is assumed

to be the dominant mechanism in cement kilns. Typically, natural gas burners produce more intense and hot flames compared to the less intense “lazy” flames produced by coal burners. Thus, gas

- fired kilns may be expected to produce greater thermal NO
x as compared to coal

- fired kilns. Coal, on the other hand, contains much greater amounts of fuel

- bound nitrogen than natural gas which has almost no fuel

- bound nitrogen. The coal

- fired kilns may thus be expected to produce more fuel NO
x than natural gas

- fired kilns. A stud y of natural gas

- and coal fired kilns, however, clearly indicated that natural gas

- fired, dry

- process kilns typically produce

almost three times more NO
x than the coal

- fired, dry

- process kilns. This fact indicated the

dominance of thermal NO
x in overall N O
x formation.

The four types of cement kilns have different combustion characteristics as well as energy efficiencies and heat requirements. For the 1994 ACT document, NO
x emissions data

were collected from 51 cement kilns. Uncontrolled emission data were obtained from 22 wet kilns, 10 long dry kilns, 10 preheater kilns and 9 precalciner kilns. Wet kilns were found to produce the highest NO
x emissions ranging from 3.6 to 19.5 lb NO
x /ton of clinker with an average of 9.7 lb NO
x /ton of clinker. The lon g dry kilns consume significantly less energy than wet kilns(about 4.5 MMBtu/ton on average) and produce less NO
x emissions that ranged from

6.1

- 10.5 lb NO
x /ton of clinker with an average of 8.6 lb NO
x /ton of clinker. 4

For preheater kilns, NO
x emissions ranged from 2.5 to 11.7 lb NO
x /ton of clinker with a average of 5.9 lb NO
x /ton of clinker. The highest values of 8.1 and 11.7 lb/ton were found in natural gas burning kilns. Energy consumption of preheater kilns was much lower, about 3.8

MM B tu/hr. In addition, combustion of a part of the fuel at a lower preheating temperature is expected to reduce the NO
x emissions as compared to burning all the fuel in the hot kiln burning

zone. These two factors account for the lower NO
x emissions in preh eater kilns as compared to wet or long dry kilns.

The precalciner kilns produced the least NO
x emissions ranging from 0.9 to 7.0 with an5

average of 3.8 lb NO
x /ton of clinker. These kilns are the most energy efficient with an average

energy cons umption of 3.3 MM Btu/ton of clinker. Precalciner kilns have lower NO
x emission rates because they burn more fuel at the calcining temperature.

Subsequent to the ACT document, EPA and members of the cement industry initiated an effort to update information on available techniques used to control NO
x emissions from cement kilns. In September 2000, EC/R completed a report for EPA which updates information in the

ACT document. 5 New uncontrolled emissions data were obtained from eight state air pol lution control agencies along with additional test data and industry literature. This data is summarized

below.

UNCONTROLLED NO X EMISSIONS

- STATE AIR AGENCIES

Cement kiln type Average rate(lb/ton

of clinker) Range(lb/ton of

clinker) Number of data

po ints

Wet kiln 6.2 1.9

- 13.4 10

Long dry kiln 4.5 2.5

- 7.1 6

Preheater kiln 1.7 0.4

- 3.7 6

Precalciner kiln 2.9 1.1

- 5.6 12

A comparison of these rates with the 1994 ACT document and the AP

- 42 section revised

in 1995 is shown on the next table.

UNCONTROLLED NO X EMISSIONS(LB NO X /TON OF CLINKER)

Kiln Type 1994 ACT AP

- 42 New Data

Wet 9.7 7.4 6.2

Long Dry 8.6 6.0 4.5

Preheater 5.9 4.8 1.7

Precalciner 3.8 4.2 2.9

As shown in this table, the four different cement kiln types appear to have different levels

of NO
x emissions. The rates calculated from the State data are generally lower than the 1994 ACT . The state data are not necessarily more representative than the 1994 ACT document.

The lower rates in the “New Data” probably result from the assumptions made regarding kiln production level and level of NO
x control. The lower emission rate in the new data for preheater kilns relative to precalciner kilns is contrary to expectations and could be due to the lack of data points for preheater kilns.

The AP

- 42 factors are also lower than the 1994 ACT document but are primarily based6

on short term tests, which do not reflect the inherent variability of kiln NO
x emissions. Also,

the data are all ov er 10 years old. Because the data used to calculate the 1994 ACT document are newer and include more CEMS data, the ACT rates are more representative of modern kilns. The uncontrolled emission rates in the ACT are used in calculating emission reduction s from

various NO
x controls and the cost effectiveness of these controls.7



# Emission Control Techniques

In the NO
x SIP call budget calculation, EPA divided cement kilns into 4 categories

– long wet, long dry, preheater, and preheater/precalciner

-- a nd assigned a 30 percent emissions decrease on average to each category based on information in EPA’s ACT document for cement kilns. As stated in the preamble to the proposed rule, the controls to achieve this 30 percent emissions

decrease are: low

- NOx bu rners(LNB), mid

- kiln firing, or equivalent controls. For all large cement kilns, EPA believes that 30% control is achievable on average and that NO
x controls are highly cost

- effective. Highly cost

- effective means that the cost

- effectiveness for the contr ol is less than $2,000/ton in 1990 dollars for the ozone season. This is demonstrated in the ACT

document for cement kilns. 4 In addition, the following sources provide supporting information (see docket A

- 96

- 56): * “Status Report on NO

x Controls”

- Decem ber 2000

- NESCAUM(Reference 3)

* “NO

x Control Technologies for the Cement Industry”

- September 2000

- EC/R (Reference 5) * “Assessment of Control Technologies for Reducing Nitrogen Oxide Emissions from

Non

- Utility Point Sources and Major Area Sources,” Final Ozone Transport Assessment Group (OTAG) Policy Paper, July 1996; Chapter 5, Appendix C, to the OTAG Final Report, http://www.epa.gov/ttn/rto/otag/index.html.

Based on information contained in the EC/R report and the NESCAUM, which were both comple ted after the FIP proposal, EPA believes that there are additional controls that achieve

30% NO
x reduction and that these controls are highly cost effective. These controls are

CemStar R , low

- NO
x precalciner, tire

- derived fuel at a preheater or precalcine r kiln, and selective

non

- catalytic reduction including biosolids injection.

1. Kiln Types

- NO
x Controls

A. Long Wet and Long Dry Kilns

The following control techniques are highly cost effective technologies applicable to long wet and long dry kilns and are capable of achieving on average at least a 30% reduction in NO
x emissions: mid

- kiln firing, LNB, and CemStar R

. 3

- 5 Mid

- kiln firing has been demonstrated to be effective at reducing NO
x emissions while recycling scrap tires at potential profit gene rating

rates. 5

Information on the required time for installation of NO
x controls was obtained from the Portland Cement Association(PCA), CemStar R , Cadence and from the NESCAUM Status Report. PCA estimates the total time required for NOx contr ols to range from 15

- 31 months. 6
This includes the times for engineering study, equipment design, permit application, permit review, manufacturing of the control technology, on

- site construction and equipment startup.8

For mid

- kiln firing, Cadence estima tes the engineering analysis to take 1 week; 1 month to prepare design; 4

- 6 months for completing the installation and a few days for startup. 7,8

CemStar R estimates that it takes 6 weeks to 3 months from the time a decision is made to install

the contr ol to the time the system is ready for operation. 9,10 In the NESCAUM 2000 Status Report, estimates are given for three plants. 3 At one plant, the total project time needed to

install low NO
x burners and mid kiln firing on a long dry kiln was 1 year. The kiln was shut down four weeks for installation. At another cement plant, two days of shutdown were required

to install CemStar R on a long wet kiln. At another cement plant that installed mid

- kiln firing on a long dry kiln, shutdown was one week. From the award of contract to startup took 28 weeks.

B. Preheater Kiln

The following control techniques are highly cost effective technologies applicable to preheater kilns and are capable of achieving a 30% reduction: low

- NO
x burners, low

- NO
x precalciners, CemStar R , tire

- derived fuel and selective non

- catalytic reduction including biosolids injection. 3

- 5

C. Preheater/Precalciner Kiln

The following control techniques are highly cost effective technologies applicable to preheater/precalciner ki lns and are capable of achieving a 30% reduction: low

- NO
x burners,

CemStar R , low NO
x precalciners, tire derived fuel and selective non

- catalytic reduction including biosolids injection. 3

- 5 Selective non

- catalytic reduction has been demonstrated in the U nited States and is operating at 18 kilns in Europe. 5

A summary of the various NO
x controls and their applicability to the several types of

kilns is shown on the next table.

TYPE OF CEMENT KILN

NOx Control Wet Long

- Dry Preheater Precalciner

Low NOx

Burners Yes Yes Yes Yes

Mid

- Kiln Firing Yes Yes No No

Tire

- Derived

Fuel Yes Yes Yes Yes

CemStar Yes Yes Yes Yes

SNCR No No Yes Yes

Low NO
x Precalciner No No Yes Yes9

2. SUMMARY OF NO
x CONTROLS

A. Low NO
x Burners(LNB)

For LNB as noted in the preamble to the proposed rule, the ACT document has one emission test with a reduction of 28% and experimental tests show 20

- 30% reductions. In January 2000, the Portland Cement Association provided results of a surv ey of 81% of the cement facilities that indicated that 14% of the operating kilns(22 kilns) have installed a LNB. Updated information including more recent emission test reports on LNB is contained in the EC/R report. This information is summarized i n the following table. For the 12 kilns tested,

the NO
x reduction ranged from 14

- 47% with an average of 29%.

LNB TEST RESULTS Kiln Type Uncontrolled(lb/ton) Controlled (lb/ton) Reduction (%)

50% coal added to

reduction zone

Precalciner kiln 2.8 1.9 31

100% coal

- reduction zone

Precalciner kiln 2.8 1.6 44

Unknown 970 ppm 650 ppm 33

“ Not Given Not Given 30

“ 650 ppm 460 ppm 29

“ 900 ppm 730 ppm 19

“ Not Given Not Given 15

Unknown 774 ppm 409 ppm 47

“ 865 ppm 664 ppm 23

“ 484 ppm 350 ppm 28

“ 487 ppm 336 ppm 31

Long wet kiln 277 ppm 239 ppm 14

B. Mid

- Kiln Firing

Mid

- kiln firing(MKF) is a type of staged combustion of fuels that injects solid fuel into the calcining zone of a rotating long kiln using a specially designed feed injection mechanism.10

MKF is applicable to conventional long wet and long dry kilns. The solid fuel which is often tires, burns at a temperature of 600 to 900 C(1,100 to 1,650F) which is much lower than the clinker burning temperature of 1,200 to 1,480C (2,200 to 2,700F). One facility uses baled industrial waste as a fuel and the use of energy waste materials from carpet scrap to pharmaceutical waste is bei ng studied.

By adding fuel in the main flame at mid

- kiln, MKF changes both the flame temperature and flame length. These changes may reduce thermal NO
x formation by burning part of the fuel at a lower temperature and by creating reducing conditions at th e solid waste injection point which may destroy some of the NO
x formed upstream in the kiln burning zone. MKF may also produce additional fuel NO
x depending upon the nitrogen content of the fuel. However as

discussed in the section on uncontrolled emissi ons, fuel NO
x is unimportant relative to thermal

NO
x emissions.

Waste

- derived fuels with high heating values represent an economical energy source for the cement industry and its consumption has been increasing during the past decade. MKF is a

proven te chnology and at least 21 cement kilns in the U.S. have been modified with MKF.

A summary of emission test data on the performance of MKF from the EC/R report

follows.

MKF

- EMISSION TEST RESULTS Emissions(lb NO
x /ton of clinker) Reductio n (%)

Dry Kilns

A NA 14

B NA 11

C NA 45, 55

D 2.7 NA

E 10.2 14

F NA 47, 50, 28

Average(Dry kilns) 6.4 33

Wet kilns

G NA 59

H NA 3511

I NA 28

Average(Wet kilns) NA 41

Average(Dry&Wet) 6.4 35

NA

- not available

C. CemStar R

CemStar R is a feed modification that was developed by and is patented by TXI Industries.

CemStar R is applicable to all types of kilns. This process adds a small amount of steel slag to the raw kiln feed. Steel slag has a low melting temperature and is chemically very similar to clinker. Since many of the chemical reactions required to convert steel slag to clinker have already taken place in a steel furnace, the fuel needed to convert steel slag into clinker is low. It

is estimated that CemStar R can increase production by 15 percent.

Kilns with lower initial baseline NO
x emissions would have less NO
x percent reductions

with CemStar R than those with higher baseline emissions. Wet and long dry kilns would have greater N O
x reductions with CemStar R because more energy is used per ton of clinker produced than preheater/precalciner kilns.

Wet kilns may achieve the greatest NO
x reductions with CemStar R because the addition of steel slag would reduce the amount of water nee ded to create the slurry and consequently decrease the amount of heat needed for drying.

Eleven facilities are using or in the process of incorporating CemStar R . CemStar R
requires little extra equipment and the addition of steel slag to the feed mix can result in a reduction or elimination of the need for some mineral sources, such as shale or clay.

A summary of emission test results data for CemStar R from the EC/R report follows.

CEMSTAR R

- EMISSION TEST RESULTS

Type of kiln Uncontrolled(lb

NO
x /ton of clinker) Controlled(lb NO
x /ton of clinker) Reduction(%)

Preheater/precalciner 5.6 3.9(normal feed rate) 30

“ ” 5.6 3.2(maximum feed rate) 44

Wet kiln (long term) 5.2 4.0 24

Wet kiln (short term) 17.5

- 24.7 11.2 36

- 5512

D. Selective non

- catalytic reduction(SNCR)

SNCR is the reduction of NO
x in the exhaust gases by ammonia or urea without the use of a catalyst. Ammonia or urea are injected into the kiln at a temperature between 870 to 1,090 C(1,600 to 2,000 F). For long dry and wet kilns, the appropriate location for reagent addition is the middle of the kiln. Because of the rotating nature of a long dry or wet kiln, continuous injection of reagents is not possible. Therefore, SNCR is not applica ble to long dry or wet

kilns.

In preheater/precalciner kilns, the temperatures at the cooler end of the rotating kiln, in the riser duct, and in the lower section of the cyclone preheater are likely to be in the SNCR temperature window. Such kilns are t herefore good candidates for application of SNCR.

In the US, SNCR has been tested in two kilns. NO
x Out(an SNCR process using aqueous urea) was tested under ten different operating conditions at a preheater/precalciner kiln. NO
x emissions were effectively reduced from 3.5 to 6.0 lb NO
x /ton of clinker. Another test showed

a NO
x reduction of 10 to 20 percent from a low baseline of 350 pounds NO
x /hour.

SNCR is presently being used in 18 cement suspension preheater or precalcine r kilns in Europe. 5 The most common reagent is 25% ammonia water. NO
x reduction rates vary from 10 to 50 percent. Two preheater/precalciner kilns achieved 80 to 85% reduction.

E. Biosolids Injection (BSI)

The BSI process was developed by the Cement Industry Environmental Consortium and is presently being used at one plant, Mitsubishi Cement, Lucerne Valley, California. BSI can

be considered to be a form of SNCR. The ammonia is contained in the dewatered biosolids

obtained from wastewater treatment plants. The biosolids are injected into the mixing chamber where the flue gas stream leaving the kiln and calciner mix. Emission test results indicate a 50 percent NO
x reduction from BSI going from 2.4 to 1.2 lb/ton of clinker.

F. Low

- NO
x Precalciner s

Low

- NO
x Precalciners typically consist of injecting a portion of the fuel into the feed end

of the kiln. This fuel is burned in a sub

- stoichiometric oxygen environment to create a strongly reducing atmosphere. This reducing atmosphere inhibits the for mation of fuel NO
x and destroys a portion of the NO
x formed in the kiln burning zone. Most of the major cement kiln suppliers are offering these systems for new kilns. Also, several precalciner kilns in the US have recently

been retrofitted with these c ontrols. NO
x reduction has been reported to be as much as 46

percent.

G. Tire

- Derived Fuel at a Preheater/Precalciner Kiln

Tire

- derived fuel can be added to the feed end of a preheater or precalciner kiln. One13

California plant has been adding whole was te tires to its precalciner kiln since 1993. From the EC/R report, emission test results indicate NO
x emissions were reduced by 30 to 40 percent. 514

COSTS/COST EFFECTIVENESS

The average cost effectiveness for large cement kilns using the above mentioned technologies has recently been estimated for EPA in the EC/R report. 5 The key variables in determining average cost effectiveness are the average uncontrolled emissions at the existing source, the projected level of controlled em issions, annualized costs of the controls, and number of hours of operation in the ozone season. The ACT document uses an average uncontrolled level which varies among the 4 types of kilns from 3.8

- 9.7 lb/ton of clinker and assumes nearly continuous opera tion in the ozone season. The EPA believes the ACT document provides a reasonable approach to calculating cost effectiveness for cement kilns. Further, EPA believes

the cost

- effectiveness analysis should use updated data as described in the EC/R report. The EPA acknowledges that specific values will vary from kiln to kiln.

1. LOW NO X BURNERS(LNB)

For LNB, cost information was obtained from a supplier of LNB for the EC/R report. The cost of a burner depends on the size or heat duty as well as the nu mber of different types of fuels that can be burned, e.g., only coal, or coal and gas or coal, waste

- derived liquid fuel and gas. The principal equipment cost of LNB using coal as the fuel is typically about $100,000 for a 200 MMBtu/hr heat duty. For a multi

- channel burner the cost is higher. The capital

cost of a multi

- channel retrofit LNB is about 100 percent greater than that for a single channel burner for the same heat duty. From the limited available data a linear correlation (R 2 =0.98)

was dev eloped for the approximate purchase cost for a retrofit application as a function of heat duty. This equation is:

PEC = 172,000 + 152 H where

PEC = Multi

- channel LNB purchase equipment cost

H = Burner heat duty in MM Btu/hr. The cost of a single cha nnel LNB is obtained by dividing the PEC of a multi

- channel burner by

2.

For LNB, indirect firing is required. Conversion of a direct

- fired kiln to an indirect

- fired kiln reduces the amount of primary air and increases the proportion of secondary air in put to the kiln. As shown in the EC/R report. the total cost to convert an existing dry process facility with two kilns, with a combined 100 tons/hr clinker capacity and a 225 Mm Btu/hr heat duty, was $5.6 million in 1998. The total installed cost is est imated to be $3.8 million (in 1997 dollars).

A summary of the capital and annual costs of LNB for various model kilns with existing

indirect

- fired kilns from the EC/R report is summarized below.

COSTS

- LNB

- INDIRECT

- FIRED KILNS

- 1997$15

Kiln type Capacity(tons/hr) Capital Costs Annual Costs

Wet 30 511,000 136,000

Wet 50 618,000 152,000

Long dry 25 473,000 130,000

Long dry 40 546,000 141,000

Preheater 40 538,000 140,000

Preheater 70 678,000 161,000

Precalciner 100 761,000 173,000

Precalciner 150 966,000 204,000

The capital and annual costs for existing direct

- fired kilns are summarized below.

COSTS

- DIRECT

- FIRED KILNS

- 1997 $

Kiln type Capacity(tons/hr) Capital Costs Annual costs

Wet 30 1,600,000 298,000

Wet 50 2,200,000 389,000

Long dry 25 1,210,000 241,000

Long dry 40 1,630,000 304,000

Preheater 40 1,490,000 282,000

Preheater 70 2,130,000 378,000

Precalciner 100 1,930,000 348,000

Precalciner 150 2,540,000 439,00016

In calculating cost effectiveness for LNB, an average cost effectiveness of 25 percent was used in the EC/R report. Cost effectiveness of LNB for an existing indirect

- fired kiln range from $330

- 620/ton of NO X removed. The cost effectiveness of LNB installed in an existing

direct

- fired kiln range from $760

- 1,200/ton of NO X removed. The next two tables present

cost effectiveness for LNB.

Cost effectiveness

- retrofit LNB

- Indirect fired kiln

- 1997$

Kiln type Capacity

(tons/hr) NOx Removed

(tons/yr) Annual costs Cost

effectiveness ($/ton)

Wet 30 320 136,000 430

Wet 50 500 152,000 300

Long dry 25 210 130,000 620

Long dry 40 400 141,000 350

Preheater 40 240 140,000 580

Preheater 70 500 161,000 320

Precalciner 100 400 173,000 430

Precalciner 150 400 204,000 510

Cost effectiveness

- Retrofit LNB

- direct

- fired kiln

- 1997 $

Kiln Type Capacity

(tons/hr) NOx Removed

(tons/year) Annual Costs Cost effectiveness($/ton)

Wet 30 320 298,000 930

Wet 50 500 389,000 780

Long dry 25 210 241,000 1,100

Long dry 40 400 304,000 760

Preheater 40 240 282,000 1,200

Preheater 70 500 378,000 760

Precalciner 100 400 348,000 870

Precalciner 150 400 439,000 1,10017

2. MID

- KILN FIRING (MKF)

For mid

- kiln firing of tires, the costs associated are those for kiln modifications necessary to facilitate secondary combustion of fuels as well as those for a conveying system required for the secondary fuel. For the EC/R report, costs were obtained from a vendor for four kilns

- two wet kilns and two dry kilns. The purchased equipment cost for each of the four kilns is approximately $1.5 million. The annual costs inclu de a fuel credit for the tire derived fuel(15% of the heat duty) as well as a tipping fee of $ 42 per ton of whole tires.

COSTS FOR MID

- KILN FIRING

- 1997 $

KILN TYPE CAPACITY

(TONS/HR) CAPITAL COSTS ANNUAL COSTS

Wet 30 3,170,000

- 15,000

Wet 50 3,240,000

- 370,000

Long Dry 25 3,150,000 190,000

Long dry 40 3,210,000

- 9,000

Cost effectiveness for mid

- kiln firing of tires is shown below. The NO
x reduction efficiency for wet kilns was 40% and for long dry kilns; 30%. The cost effectiveness includes a fuel credit for using waste

- derived fuel and a tipping fee for tires.

COST EFFECTIVENESS FOR MID

- KILN FIRING

- 1997 $

KILN TYPE CAPACITY

(TONS /HR) NOx REDUCTION

(TONS/YR) COST

EFFECTIVENESS ($/TON)

Wet 30 500

- 30

Wet 50 800

- 460

Long dry 25 260 730

long dry 40 440

- 20

3. CEMSTAR R

The costs associated with installing this process are primarily material handling18

equipment for the steel slag. TXI, the developer and patent holder of this process, estimates the cost of this equipment to range from $200,000 to $500,000. The annual costs for a 42 tons/hour, long, wet kiln are $220,000 which includes the cost of stee l slag, royalties, and credit for the reduction in raw materials. A credit for the increased production of clinker(approximately 3 tons/hour) is not included. Costs for other installations are not

available.

Costs for model plants could not be developed because the addition of steel slag is completely plant dependant. There is no set ratio of steel slag injection to kiln production rate. The amount of steel slag needed depends on the plant raw material and can vary from 5 to 10 percent addition of stee l slag, based on kiln production. The addition of steel slag results in a production increase. This is approximately an equal trade

- off; that is, one ton of steel slag is equal to one ton of clinker. Steel slag cost $5

- 15 per ton whereas clinker cost $72 per ton. Thus the average cost savings is $62/ton times the increase in production. In most plants, production is increased by 5 to 10% with the addition of the CemStar R process. Also, the addition of steel slag typically reduces the need for iron used in raw material feed. This can result in a savings of $.50 to $1.00 per ton of clinker produced. The facility installing the technology has to pay TXI $16 per ton of steel slag used.

In the EC/R report, cost effectiveness was determined for the 42 t ons clinker/hour; long, wet kiln. As mentioned above the annual costs are $220,000. Using an average emission
reduction of 30%, the NO
x emission reduction is 480 tons/year. The cost effectiveness for this facility is $550/ton of NO

x reduced.

4. BIOSO LIDS INJECTION

The costs associated with this technology include the sludge system and the sludge conveying system. For a 215 tons of clinker/hour preheater/precalciner, the purchased equipment cost is $240,000. Biosolids are added at a 20 tons/hour rat e. The total capital investment is $1,200,000. Annual costs are a savings of $320,000 which is based on a tipping fee of $5/ton.

Cost effectiveness for this 215 TPH precalciner is based on the annual cost of $

- 320,000

and a 50% NO
x reduction. Cost eff ectiveness is a credit of $

- 310/ton.

5. SELECTIVE NON

- CATALYTIC REDUCTION

Costs for this technology using NO
x Out were obtained from Nalco for two preheater/precalciner kilns for the EC/R report and are summarized in the table below.

COSTS

- SNCR

- NO
x OUT

- 1997 $

Kiln Production Rate(tons of clinker/hr) 92 13319

Capital Costs $1,060,000 $1,200,000

Annual Costs $560,000 $2,000,000

Cost effectiveness was calculated based on 40% efficiency and is $1,000/ton for the smaller kiln and $2,500/ton for the larger kiln.

6. Tire

- Derived Fuel

- Preheater/Precalciner

From the EC/R report, costs for a tire

- derived fuel system at a precalciner kiln with a capacity of 215 TPH were obtained from the facility. The annual costs for the system is $

- 1,600,000 which includes a fuel credit for using waste

- derived fuel and a tipping fee for tires($42.50/ton). Using a NO

x emission reduction of 30%, the cost effectiveness is $

- 1,900/

to n.



# Cost Factors

Monitoring costs

In the NO
x FIP proposed rulemaking, EPA assumed periodic emissions testing. The EPA now believes that CEMS may be an important part of the cement kiln’s successful operation. That is, such monitoring equipment may be necessary to assure stable operation and optimi zation of the kiln. 5 While EPA strongly encourages States and industry to consider CEMS as part of the overall operating system, it is one option in the FIP rule. Other monitoring options are annual emission testing or alternate monitoring approved by EPA

.

Experience with NOx Controls at Cement Kilns

Since the 1994 NO
x ACT was written, the industry has gained much experience in controlling NO
x emissions. This is particularly true with mid

- kiln firing, CemStar, selective catalytic reduction in Europe, an d low

- NO
x burners. Data available to EPA demonstrate that application of various NO
x control technologies can achieve an average of 30% reduction.

Time to Implement Controls for Cement Kilns Based on information primarily from manufacturers of control equipment, EPA believes the time between a request for cost proposal and field installation is less than 31 months. 3,6

- 10

Fuel Savings Implementation of mid

- kiln firing or other fuel replacement techniques to reduce NOx emissions can yield substantial co st benefits and fuel savings. Up to 15% of the fuel may be replaced in mid

- kiln firing by scrap tires. In addition, a fee may be collected by the cement kiln operator for collection and disposal of the tires, a revenue source.2021

REFERENCES

1. 63 FR 57356

- 10/27/98

2. 65 FR 11222

- 3/2/00

3. NESCAUM. Status Report on NO
x Controls for Gas Turbines, Cement Kilns, Industrial Boilers, Internal Combustion Engines. Boston, MA. December 2000.

4. U.S. Environmental Protection Agency. Alternative Control Techniques Document

- NO
x Emissions from Cement Manufacturing. EPA

- 453/R

- 94

- 004. Research Triangle Park, NC.

March 1994.

5. EC/R Incorporated. NO
x Control Technologies for the Cement Industry. Chapel Hill, NC. September 19, 2000.

6 . Email from Garth Hawkins, Portland Cement Association to Bill Neuffer, US EPA.

12/19/00.

7. Email from Kim Bramble, Cadence to Bill Neuffer, US EPA. 12/02/00

8. Email from Kim Bramble, Cadence to Bill Neuffer, US EPA. 11/30/00

9. Email from Greg Mayes, TXI to Bill Neuffer, US EPA. 12/01/00

10. Email from Greg Mayes, TXI to Bill Neuffer, US EPA. 12/01/00