# Emission Controls for

Small Wood

­ Fired Boilers

Prepared for:

United States Forest Service,

Western Forestry Leadership

Coalition



# February 2010

DATA  ANALYSIS  SOLUTIONS

## REPORT PREPARER

John Hinckley, Q.E.P.

Senior Project Consultant

Resource Systems Group, Inc.

55 Railroad Row

White River Junction, VT 05001

Email: jhinckley@rsginc.com

Voice: 802/295‐4999Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

19 October 2010 Page i 

# T ABLE OF 

# C ONTENTS

1.0 I NTRODUCTION 

# .......................................................................................1

2.0 S COPE OF 

# S TUDY 

# ......................................................................................3

3.0 E MISSIONS 

# O VERVIEW 

# ..............................................................................3

3.1 Vermont APCD Emission Study ................................................................................................................ 8

3.2 Hazardous Air Pollutant Information ....................................................................................................... 9

3.2.1 HAP Stack Emission Test Information................................................................................................. 9

3.2.2 Mercury Emissions...................................................................................................................... ......10



# 4.0 B EST 

# M ANAGEMENT 

# P RACTICES 

# (BMP S 

# )...................................................10

4.1 Fuel Quality ........................................................................................................................ ....................10

4.2 Operation and Maintenance Plan..........................................................................................................13

4.3 Boiler Operator Training ....................................................................................................................... .14

4.4 Equipment Sensors ........................................................................................................................ ........14

4.5 Automatic Ash Removal........................................................................................................................ .14

4.6 Raking Grates as Needed .......................................................................................................................14

4.7 Combustion Efficiency Testing...............................................................................................................14

4.8 Visual Plume Observations ................................................................................................................... .15

4.9 Recordkeeping .................................................................................................................. .....................15

4.10 Annual Tune Up ............................................................................................................................. ........16



# 5.0 A DD



# ‐ O N 

# P OLLUTION 

# C ONTROLS 

# ...............................................................16

5.1 Mechanical Collectors..................................................................................................................... .......16

5.1.1 Cyclones and Multicyclones..............................................................................................................17

5.1.2 High Efficiency Multicyclones ...........................................................................................................17

5.1.3 Core Separator ...................................................................................................................... ...........17

5.2 Dry Electrostatic Precipitators ...............................................................................................................18

5.3 Baghouses (Fabric Filters) ......................................................................................................................1 8



# 6.0 S UMMARY OF 

# E UROPEAN 

# E MISSION 

# C ONTROL 

# P RACTICES 

# ...........................19

7.0 C APITAL 

# C OSTS OF 

# E MISSION 

# C ONTROLS FOR 

# P ARTICULATE 

# M ATTER 

# .............20

8.0 C OST 

# E FFECTIVENESS OF 

# P ARTICULATE 

# M ATTER 

# E MISSION 

# C ONTROLS 

# ............22

9.0 O VERVIEW OF 

# E MISSION 

# C ONTROLS FOR 

# O THER 

# R ELEVANT 

# P OLLUTANTS 

# .......23

9.1 Nitrogen Oxides (NOx) .......................................................................................................................... .23

9.2 Sulfur Dioxide (SO

2 

### ).............................................................................................................................. ..24

9.3 Carbon Monoxide (CO) ..........................................................................................................................2 4

9.4 Volatile Organic Compounds (VOCs)......................................................................................................24

9.5 Hazardous Air Pollutants (HAPs) ............................................................................................................24



# 10.0 C ONCLUSIONS 

# .......................................................................................24Resource Systems Group, Inc. Project Name

23 February 2010 Page ii 

# 11.0 R ECOMMENDATIONS FOR 

# F UTURE 

# R ESEARCH 

# .............................................25

12.0 S UMMARY 

# ............................................................................................26

TERMS AND ACRONYMS

Total suspended particulate matter (TSP)

­ all sizes of filterable an d condensable particles.

PM10 ‐ particles equal to o r less than ten micrometers in aerodynami c diameter, also referred to as

“coarse particles” or “PM coarse”.

PM2.5

­ particles less than or equal to 2.5 micrometers in aerodynamic diameter, also re ferred to as “fine

particles” or “PM fine."

Filterable particulate matter – solid particles of all sizes (TSP, PM10, PM2.5, etc.) which can be

collected on a filter.

Condensible particulate matter – particles which form as vapors cool and condense into liquid

droplets.

CCG – close coupled gasifier or a c ombustion system which utilizes two separate combustion chambers in

series.

SA – a stoker combustor where the f uel is fed to the combustor wi th an auger.

SP – a stoker combustor where the f uel is fed to the combustor pn eumatically.

CS

­ core separator.

HEMC – high efficiency multicylone.

MC – conventional multicyclone.

FF – fabric filter or baghouse.

ESP – electrostatic precipitator.

Whole tree chips – wood chips created by chipping the entire tree (stem, top, l eaves, branches).

Bole tree chips – wood chips created by chipping the tree stem.

Mill chips – wood chips from sawmill residue, contain no bark.Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 1 

# 1.0 I NTRODUCTION

In 2001, Resource Systems Group, I nc. (RSG) produc ed an emissio n control report for a consortium of

northeastern government agencies called “An Evaluation of Air P ollution Control Technologies for Small

Wood‐Fired Boilers.” 1 

### While the study identified many ways to reduce emissions, it d id identify a single

add‐on control technology (the C ore Separator) as “BACT” or Bes t Available Contro l Technology for

controlling particulate matter em issions. While, the conclusion s of this report were accepted by the

consortium of northeastern state agencies, they did not transla te into a formal BACT determination at the

federal level.

According to the Environmental P rotection Agency (EPA), “BACT i s an emissions limi tation which is

based on the maximum degree of control that can be achieved. It is a case‐by‐case dec ision that considers

energy, environmental, and econom ic impact. BACT can be add‐on control equipment or modification of

the production processes or metho ds. This includes fuel cleanin g or treatment and innovative fuel

combustion techniques. BACT may b e a design, equipment, work pr actice, or operational standard if

imposition of an emissions standard is infeasible.” 2



### For the purposes of this report, the best available control tec hnology (BACT) may simply be defined as

the highest performing control technology for a specific pollut ant that is available commercially for a

general class and size of emissi on source. This is usually defi ned as resulting in the lowest emission rate

although differences in available fuel specifications may compl icate the issue. Other environmental,

health, safety and energy consump tion factors should be conside red in making the BACT determination.

The operation of a specific control technology applied to a com parable source anywhere in the US is

usually considered sufficient evi dence that the technology is B ACT. In principle, the search for BACT

should be worldwide, a lthough local conditio ns make comparabili ty complicated and in practice a control

technology usually needs a US based customer support system to make it truly available.

Costs are also a consideration in defining BACT for a specific application. Total cost per unit of pollutant

removed decline with increasing size of the facility; therefore , a technology may be BACT for a large plant

but not for a smaller one. Wood‐ fired boilers in the size range of 3 to 10 MMBtu/hour have not been

subject to formal federal BACT r eview for criteria pollutants g iven the comparatively high and therefore

challenging cost of control techn ologies in this size range. Ho wever, state air pollution control permits

are often required for this size range, which often require a n umber of technical analyses, including

emissions estimation, air qualit y modeling and some degree of i nformal economic ana lysis for pollution

control costs.

The EPA BACT process follows a top down procedure. It begins wi th the most effective control

technology available that will re sult in the lowest emission ra te and then reviewing that technology to

determine if there are technical , safety, health or other envir onmental factors which would make it

impractical or undesirable. If t he technology is not rejected b ecause of any of these factors, then a cost

analysis is conducted to determin e the absolute costs and per u nit costs of implementation. The cost

analysis follows guide lines established by EPA. If it is releva nt, the analysis may include special costs

associated with retrofitting the technology in an existing plan t. The cost analysis is then reviewed to

determine if the technology is e conomically feasible in the spe cific case. If the first technology choice is

rejected for technical, environm ental, safety or costs reasons, then the analysis pro ceeds to the second

best performing technology and s o on until a feasible technolog y is accepted or all available options are

1 An Evaluation of Air Pollution Control Technologies for Small Wood

‐ Fired Boilers.” Prepared for Vermont Department of Public Service;

Vermont Department of Environmental Conservation, Air pollution Control Division; New Hampshire Governor’s Office of Energy

Resources and Community Services; and the Massachusetts Division of Energy Resources. Resource Systems Group, Inc., White River

Junction, VT. Revised, September 2001.

2 US EPA. http://www.epa.gov/nsr/psd.htmlResource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 2 

### exhausted. This process may include not only add‐on technology but combustion pr ocess modifications

and changes in fuel specifications.

The study described by this repo rt builds upon the 2001 report, but differs in that its goal was not to

identify a single Best Available Control Technology (BACT). Rat her, its goal was to identify multiple

emission controls in order to pr ovide more flexibility in the d esign process for biomass combustion

systems. This is because there are many factors affecting the d egree of control due n ecessary to meet the

National Ambient Air Quality Standards (NAAQS), which were prom ulgated by EPA to protect human

health and welfare.

Regarding the NAAQS, we note EPA significantly strengthened the NAAQS for PM2.5 (ak a fine particulate

matter or particles less than 2.5 micrometers in aerodynamic di ameter) in 2006. PM2.5 consists of solid

particles and liquid d roplets less than 2.5 microns in aerodyna mic diameter and is widely held to be the

most critical pollutant resulting from biomass combustion. For comparison, the average period at the end

of a sentence is approximat ely 500 microns in diameter. 1 

### Concern for health impacts from PM2.5

exposure coupled with the strengthened PM2.5 NAAQS has led to a much greater emph asis on emission

control than in previous years.

The need to develop environmenta lly beneficial uses of low grad e timber, improve forest health, mitigate

climate change, offset rising fo ssil fuel oil prices and reduce foreign oil dependence have increased

demand for biomass energy system s. Given frequent budget limita tions, biomass developers are pressed

to find cost‐effective ways to re duce emissions of PM2.5 and ot her pollutants. In addition to being

affordable, emission controls must be practical and able to be easily implementable, otherwise they will

not be effective. This study was commissioned by the U.S. Fores t Service (USFS) to id entify and evaluate

such emission controls.

This report contains the following sections:

 Scope of study

 Emissions overview

 Best Management Practices (BMPs)

 Add‐on pollution controls

 Summary of European emission control practices

 Capital costs for particulate matter control

 Cost effectiveness of add‐on emission controls for particulate matter

 Overview of emission controls for other releva nt pollutants

 Summary

 Conclusion

 Recommendations

The use of trade or firm names i s for information only and does not imply endorsement by the authors or

this study’s sponsor.

1 “Health Effects of Wood Smoke.” Washington State Department of Ecology. http://www.ecy.wa.g ov/biblio/92046.htmlResource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 3 

# 2.0 S COPE OF 

# S TUDY

The scope of this study was to u pdate and expand the RSG 2001 r eport as follows:

1) Identify and Evaluate Best Management Practices (BMPs). BMPs, also called “work practice

standards” and “inherently lower emitting processes and practic es,” are used to control

emissions upstream of add‐on con trol technologies such as mecha nical collectors (cyclones,

multicyclones), baghouses (fabri c filters), electrostatic preci pitators (ESPs), etc. Attention is

typically directed toward add‐on emission control selection. Th ese solutions are typically more

costly. While not as effective as most add‐on controls BMPs can control substantial quantities of

emissions, improve system effici ency and improve system perform ance; therefore, this report

will focus on BMPs in addition to add‐on controls. This said, B MPs alone will not li kely satisfy the

requirements for “LAER” or lowes t achievable emission rate, whi ch is typically required in non‐

attainment areas. Non‐attainment areas are areas where one or m ore of the National Ambient

Air Quality Standards (NAAQS) are not met.

2) Expand the original size range evaluated from 3 MMBtu/hr

­ 10 MMBtu/hr to 3 MM Btu/hr

­ 30 MM Btu/hr (heat input). 1 

### This report will still focus on small (less than 10 MMBtu/hr)

wood boilers. However, there is new information available from recently constructed wood

boilers smaller than 3MMBtu/hr and larger than 10 MMBtu/hr that can be extrapolated to the 3

to 10 MMBtu/hr size range. This information was evaluated for t he purposes of this report.

3) Include emissions control information for PM2.5 and a number of hazardous air

pollutants (HAPs) including Mercury. This is primarily in response to EPA’s strengthening of

the PM2.5 NAAQS and due to recen t availability of stack emissio n test data for PM2.5 and HAPs.

4) Include pellet boiler emission information. Many new pellet boiler s and pellet production

plants (pellet mills) have been constructed in recent years in response to demand for this fuel. In

addition, a number of stack emis sion tests have been completed for pellet boilers in the United

States. This report will discuss this new information.



# 3.0 E MISSIONS 

# O VERVIEW

When evaluating emission control s for biomass boilers, it is im portant to first develop an understanding

of current actual emissions from biomass boilers. The most curr ent and descriptive emissions

information is obtained from exhaust stack emission tests perfo rmed according to EPA reference

methods. These tests are typica lly performed to fulfill air pol lution control permit requirements

requiring a demonstration that e mission limits are being met. I n addition to compliance emission tests,

many voluntary tests have been s ponsored by interested parties given the level of interest in knowing

actual emissions and effectiveness of emission controls. These tests were completed throughout the

United States, with dif ferent fuel characteristics, different f iring rates and differe nt emission controls.

This study focused on particulat e matter emissions. There are m any terms used to characterize

particulate matter. For the purp oses of this report, the term p articulate matter includes all sizes of solid

particles and liquid p articles (droplets). Solid particles are referred to as “filterable” particulate matter

because they can be removed from exhaust with a filter. Liquid particles are also c alled “condensable”

1 30 MMBtu/hr is the threshold level at which the federal PM emission limit drops to 0.030 lb/MMBtu. This emission limit cannot be

achieved with a mechanical collector. See 40 CFR Part 60, Subpart Dc.

– Standards of Performance for Small Industrial

‐ Commercial

‐

Institutional Steam Generating Units.Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 4 

### particulate matter because they are formed by vapors in exhaust which cool and condense into particles.

These vapors can also condense onto the solid particles.

Filterable and condens able particulate matter is grouped into t hree size classes. “Total suspended

particulate matter” (TSP) includ es all sizes of filterable and condensable particles. T he next smallest size

class is PM10 or filterable and condensable particles equal to or less than ten micrometers in

aerodynamic diameter. PM10 partic les are also ca lled “coarse pa rticles.” PM2.5 is the smallest particle

size class currently regulated. PM2.5 particles, also called “f ine particles,” includ e all filterable and

condensable particles l ess than or equal to 2.5 micrometers in aerodynamic diameter. For the purposes

of this report, it was assumed t hat all condensable particulate matter falls in the PM2.5 category.

Condensable particulate matter i s reported separately from filt erable PM2.5 because it is controlled

differently. Some of the “condens ables” will condense on filter able particles. Hence, anything controlling

filterable particulate matter wi ll inherently control some port ion of the total condensables. Good

combustion practices are typically used on small wood boilers t o control condensables.

Unless stated otherwise, the te rms PM10 and PM2.5 will refer to filterable particulate matter only. This is

because the methods used to meas ure the PM10 and PM2.5 emission s listed in this report measure

filterable particula te matter only.

RSG reviewed 24 recent stack emi ssion tests to develop an under standing of existi ng emissions (see

Appendix A for the supporting st ack test reports). All but one of these tests was completed after the 2001

RSG report. These stack tests we re performed in Idaho, Montana, New Hampshire, North Dakota, Rhode

Island and Vermont. Twenty‐two of the tests were performed on w ood chip boilers and two tests were

performed on wood pellet boilers. All tests measured some form of particulate matter emissions

(filterable PM10, filterable PM2. 5 and condensable PM). Some of the tests included other pollutants such

as carbon monoxide (CO) and a selected number of Hazardous Air Pollutants (HAPs). Fuels burned

included sawmill residue chips, b ole chips, whole tree chips, b ark chips, sawdust and municipal

vegetative waste combined with ground pallets. Add‐on emission controls included cyclones,

multicyclones, high efficiency m ulticyclones (HEMCs), core sepa rators and baghouses.

This study did not identify any stack emission data for ESPs on small wood‐fir ed boilers in the United

States. However, according to the EPA “RACT‐BACT‐LAER Clearingh ouse”, the lowest emission limit listed

for TSP and PM10 for large wood‐f ired boilers controlled with E SPs is 0.02 lb/MMBtu (PM2.5 was not

listed). 1 

### Given this limit is based on de monstrated technology, it is te chnically possible that small wood‐

fired boilers could meet this li mit. However, the economic anal ysis on which this lim it is based is for

significantly larger systems (100 MMBtu/hour or greater), where the total cost per ton of pollutant

removed is significantly lower. This is why the economic analy sis performed for this report was based on

outlet emissions not exceeding 0.045 lb/MMBtu of all filterable particulate matter.

It should also be noted that fac ilities subject to a limit of 0 .02 lb/MMBtu have the potential to emit more

than an order magnitude more emi ssions and theref ore must meet stringent emission limits in order to

meet federal ambient air quality requirements.

As shown below in Table 1, there is a large difference between the maximum and minimum values

measured. The difference was as m uch as three orders of magnitu de for PM10. The maximum PM10

value of 0.506 lb/MMBtu resulted from a facility burnin g a low quality fuel ‐ whole tr ee chips produced

by a grinder and having notable quantities of dirt and rock. Th e fuel was burned in a stoker combustor

with no add‐on emission control. The lowest PM10 value of 0.06 lb/MMBtu resulted from burning a high

quality mill chip (no bark and no soil/rock impurities) in a cl ose‐coupled gasifier controlled with a high

efficiency multicyclone (HEMC).

1 This emission limit applies to a utility sized boiler whose heat input exceeds 100 MMBtu/hour.Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 5 

### Table 1 summarizes the 24 partic ulate matter stack test results . Emissions are grouped into the three

categories: filterable PM10, fil terable PM2.5 and condensable P M. Table 2 through T able 4 summarize

emissions by the following heat input categories:

 Less than 30 MMBtu/hour and greater than 10 MMBtu/hour (based o n seven stack tests).

 Less than or equal to 10 MMBtu/hour (based on 18 stack tests).

 Less than or equal to 5 MMBtu/hour (based on nine stack tests).

A more detailed summary of all 24 tests is shown in Table 5.

As shown below in Table 1, there is a large difference between the maximum and minimum values

measured. The difference was as m uch as three orders of magnitu de for PM10. The maximum PM10

value of 0.506 lb/MMBtu resulted from a facility burnin g a low quality fuel ‐ whole tr ee chips produced

by a grinder and having notable quantities of dirt and rock. Th e fuel was burned in a stoker combustor

with no add‐on emission control. The lowest PM10 value of 0.06 lb/MMBtu resulted from burning a high

quality mill chip (no bark and no soil/rock impurities) in a cl ose‐coupled gasifier controlled with a high

efficiency multicyclone (HEMC). 1

Table 1: Summary of all Stack Emission Test Results

Category PM10 Emissions

(lb/MMBtu) PM2.5 Emissions

(lb/MMBtu) Condensable PM

(lb/MMBtu)

Average 2 0.178 0.111 0.021

Median 0.140 0.122 0.014

Maximum 0.506 0.267 0.039

Minimum 0.016 0.014 0.006

Table 2: Stack Test Summary for Heat Input Less than 30 MMBtu/hour and Greater than 10 MMBtu/hour

Category PM10 Emissions

(lb/MMBtu) PM2.5

Emissions

(lb/MMBtu) Condensable

PM Emissions

(lb/MMBtu)

Average 0.230 0.164 0.011

Median 0.101 0.188 0.014

Maximum 0.382 0.267 0.014

Minimum 0.019 0.062 0.006

Table 3: Stack Test Summary for Heat Input Less Than or Equal to 10 MMBtu/hr

Category PM10 Emissions

(lb/MMBtu) PM2.5

Emissions

(lb/MMBtu) Condensable

PM Emissions

(lb/MMBtu)

Average 0.175 0.107 0.018

Median 0.156 0.104 0.014

Maximum 0.506 0.179 0.039

Minimum 0.016 0.014 0.007

1 The HEMC was determined to be BACT for small wood

‐ fired boilers in Rhode Island in a 2006 BACT study completed by Resource

Systems Group. BACT for PM10 and PM2.5 were determined to be 0.20 lb/MMBtu and 0.18 lb/MMBtu respectively.

2 Average values represent the average of instances when both PM10 and PM2.5 were measured at the same site.Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 6 Table 4: Stack Test Summary for Heat Input Less Than or Equal to 5 MMBtu/hour

Category PM10 Emissions

(lb/MMBtu) PM2.5

Emissions

(lb/MMBtu) Condensable PM

Emissions

(lb/MMBtu)

Average 0.231 0.114 0.025

Median 0.161 0.110 0.026

Maximum 0.506 0.179 0.039

Minimum 0.016 0.014 0.009



### Table 5 provides more informatio n for each stack test than the tables above. Informat ion is provided in

ascending order of measured PM10 emissions. Table cells were le ft blank to represent instances when

PM2.5 and condensable PM data wer e not available. Also shown is the type of fuel burned and type of

emission control. The following combustion technologies are lis ted: close‐coupled gasifier), auger fed

stoker (SA), pneumatically fed stoker (SP).

Table 5: Stack Emission Test Summary for Particulate Matter

Location Design Heat

Input

(MMBtu/hr) Comb.

Type Fuel Burned Emission

Control PM10

Emissions

(lb/MMBtu) PM2.5

Emissions

(lb/MMBtu) Condens.

PM

Emissions

(lb/MMBtu)

Glocester, RI 4.6 CCG Mill chips HEMC 0.016 0.014

Middlebury, VT 29.0 CCG Bole chips MC + FF 0.019

Dillon, MT 19.0 CCG Bole chips MC 0.052

North Scituate,

RI 9.1 CCG Mill chips HEMC 0.058 0.054 0.007

North Scituate,

RI 9.1 CCG Mill chips HEMC 0.066 0.066

Thompson Falls,

MT 2.2 CCG Bole tree chips Cyclone 0.070

Brattleboro, VT 6.9 CCG Wood chips Core Sep. 0.078

Greenfield, NH 5.7 & 11.4 SA Bole chips MC + FF 0.078 0.062 0.014

Newport, VT 15.6 CCG Bole chips MC 0.101 0.006

Peterborough,

NH 2.8 SA Pellets MC 0.101

Bennington, VT 16.8 SP Whole tree

chips 2 MC 0.140

Darby, MT 3.3 SA Bole chips None 0.156

Victor, MT 2.6 SA Bole chips None 0.166 0.098 0.009

Springfield, NH 15.5 SA Sawdust None 0.168

Hinesburg, VT 6.5 SA Bole chips Cyclone 0.171 0.147 0.012

Brattleboro, VT 10.0 SA Mill chips Core Sep. 0.172 0.162 0.012

Burlington, VT 10.0 SA Mill chips MC 0.187 0.015

Darby, MT 3.3 SA Bole chips None 0.192 0.110 0.015

Bismarck, ND 1.0 SA Muni. veg. &

pallets None 0.199 0.151 0.077

Burlington, VT 10.0 SA Bole chips MC 0.257 0.017

Townsend, MT 0.75 SA Pellets None 0.305 0.133 0.036

Bennington, VT 16.8 SP Whole tree

chips 2 MC 0.382 0.267 0.014

Council, ID 1.9 SA Whole tree None 0.506 0.179 0.039Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 7 chips

Dillon, MT 19.0 CCG Bole chips MC 0.188



### The following observations of the tests were noted:

 Close‐coupled gasifiers emitted t he lowest levels of emissions.

 There is limited PM2.5 emissions data. This is partially becaus e PM2.5 is still not officially

enforced by most state air quality agencies; therefore, state a gencies are requiring compliance

stack testing PM10 only.

 The lowest PM10/PM2.5 emissions were produced by a close couple d gasifier burning a

relatively high qualit y wood chip, with emis sions controlled by a HEMC.

 PM10 emissions from baghouses were surprisingly not the lowest for all tests. They were the

third and eighth lowest emissions of all tests. The lower than expected control efficiency is

suspected to be due to a portion of the boiler e xhaust gases ci rcumventing the bag house via a

leaking damper in the bypass duct.

 PM10 emissions were equal to or l ess than 0.20 lb/MMBtu for 19 of the 24 tests (79%) and less

than 0.10 lb/MMBtu for 10 of the 24 tests (41%).

 All but one of the PM2.5 tests w ere less than 0.20 lb/MMBtu. Fi ve of the 13 PM2.5 tests were less

than 0.10 lb/MMBtu.

 The results suggest bark increase s PM emissions. In one example , the two results from

Burlington, Vermont, which was te sted with mill and bole chips, indicate bark can increase PM

emissions. In this case, PM10 em issions were 0.187 lb/MMBtu and 0.257 lb/MMBtu respectively.

 There are two stack test results for pellet fired systems. PM10 emissions from these systems

ranged from 0.101 lb/MMBtu to 0. 305 lb/MMBtu. However, the high er number corresponds to a

much older system with no add‐on emission contro ls. Conversely, the lower number

corresponds to a new system with a multicyclone. Average PM2.5 emissions from the older

system were 0.133 lb/MMBtu. PM2.5 emissions were not measured f or the newer system.

The EPA has developed emission factors for wood boilers. These emission factors are included in a

document called “AP 42”, which is a compilation of emission fac tors. 1 

### Comparable emission factors from

the AP 42 are summarized for ref erence below. Note these emissi on factors represent an average for a

group of emission tests. These e mission factors were published in September, 2003 and likely correspond

to systems larger than most of those considered for this report . The majority of the stack test data used to

develop these emission factors w as collected in the early to mi d 1990’s.

Table 6: Comparable EPA AP 42 Emission Factors

Fuel Type Control Device PM10 Emissions

(lb/MMBtu) PM2.5

Emissions

(lb/MMBtu) Condensable

PM Emissions

(lb/MMBtu)

Bark & wet wood None 0.50 0.43 0.017

Bark & wet wood Mechanical collector 0.32 0.19 0.017

Wet wood None 0.29 0.25 0.017

Wet wood Mechanical collector 0.20 0.12 0.017

All fuel types Fabric filter (baghouse) 0.074 0.065 0.017

All fuel types Electrostatic Precipitator (ESP) 0.04 0.035 0.017

1 Can be accessed at http://www.epa.gov/ttn/chi ef/ap42/ch01/index.htmlResource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 8 

# 3.1 Vermont APCD Emission Study

The Vermont Agency of Natural Re sources (ANR) recently complete d an emission stud y focusing on air

pollutant control efficiency for a number of add‐on pollution c ontrols. The study evaluated inlet and

outlet particulate matter emissi ons from five wood chip fired b oilers in the Northeas t. These boilers are

located at Crochet Mountain Reha bilitation Center (Greenfield, NH), Bennington College (Bennington,

VT), Brattleboro Union High Sch ool (Brattleboro, VT), Ponaganse t High School (North Scituate, RI) and

Champlain Valley Union High Sch ool (Hinesburg, VT). Emissions d ata and design heat inputs for these

boilers are provided pre viously in Table 5.

Table 7 shows the approximate PM 2.5, PM10 and TSP control effic iency for the five sites. 1 

### The control

efficiencies listed below refer to the percent of filterable pa rticulate matter removed by the add‐on

pollution control device. Control efficiencies for different ad d‐on pollution controls are further discussed

later in this report.

Table 7: Vermont ANR Emission Study Approximate Control Efficiencies



### Location PM Control PM2.5

Control

Efficiency PM10

Control

Efficiency TSP Control

Efficiency

Greenfield, NH Multicyclone +

baghouse 74% 74% 83%

Bennington, VT Two multicyclones in

series 14% 22% 61%

Brattleboro, VT Core separator (24”) 24% 32% 60%

North Scituate, RI High efficiency

multicyclone 15% 21% 23%

Hinesburg, VT Cyclone 3% 6% 4%

The following observations we re made from these results:

 Bennington and Brattleboro, VT. The overall control efficiencies are significantly higher than

the PM2.5 and PM10 efficiencies b ecause there were significant quantities of pa rticles larger

than PM10 particles (ten microns in aerodynamic diameter) emitt ed during the stack tests.

 Greenfield, NH. The control efficiency is rela tively low for a multicyclone f ollowed by a

baghouse. Baghouses are widely t hought to achieve 99% control e fficiency for PM2.5 and smaller

filterable particles. As mention ed, the low control efficiency is suspected to be due to a portion of

the boiler exhaust gases circumv enting the bag h ouse via a leak ing damper in the bypass duct.

 Bennington, VT. While this is the highest control efficiency value of all mecha nical collectors

tested, the actual emissions wer e higher than all other five si tes (0.382 for PM10 and 0.267

lb/MMBtu for PM2.5).  The higher emissions may be due to carry over of large particles from the

combustion chamber caused by pneumatic feeding of fuel into the combustion chamber.

It was discovered after this testing that some of the underfire air passages were obstructed by a

buildup of boiler bottom ash.  T his ash was subsequently cleane d out, the boiler combustion air

was adjusted and an improved ash management procedure was imple mented. The retesting

which occurred after these measure s were implement ed indicated the total PM emission rate

dropped to 0.14 lb/MMBtu (appr oximately a 63% reduction).

1 The PM2.5 and PM10 control efficiencies were calculated using the inlet and outlet emission factors (in lb/MMBtu) from the control

device. The TSP control efficiency was taken directly from the study report.Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 9 

###  Brattleboro, VT. The TSP collection efficiency w as nearly the same as at Bennin gton, but the

outlet emissions were lower (0.172 lb/MMBtu for PM10 and 0.162 for PM2.5). However, PM2.5

and PM10 control efficiencies wer e higher at Bennington. This s hows the core separator is more

effective at removing fine particles than conventional multicyc lones, even conventional

multicyclones in series.

The Core Separator operating at Brattleboro was designed for th e exhaust volume from a 400

horsepower (hp) boiler .  However, the boiler size was reduced t o 332 hp during project

development. So while a smaller “2‐core” unit would have worked , a “3 core” unit was operating.

The result is that during emissi on testing, the Core Separator was operating at half it's design

pressure drop. A higher collectio n efficiency would likely have resulted if it was operating at its

design pressure drop.

 North Scituate, RI. The outlet emissions were the l owest of all sites (0.0662 MMBt u/hr for

PM10 and 0.0660 MMBtu/hr for PM2.5) despite one of the lowest c ollection efficiencies

measured (23%). This is because t he system was operating at low capacity (30% load) which led

to a low pressure drop (approxima tely 0.7 inches of WC). The de sign pressure drop for this

system is 4” of WC. At this pre ssure drop it is quite conceivab le that the collection efficiency

would have been 75% or greater. Vendor calculations suggested a n TSP collection efficiency of

80% or greater at design load/pre ssure drop. It should also be noted that the vast majority of the

inlet loading was PM2.5 (88.7%). Therefore, the control efficie ncy is relatively high for a

mechanical collector operating at low pressure drop.

 Hinesburg, VT. Single cyclones have the lowest collection efficiency of all me chanical collectors.

This is evidenced by the collect ion efficiency measured, which is due to a cons iderably higher

portion of PM2.5 in the inlet exhaust. Despite the type of cont rol device, the outlet emissions

were relatively low (0.171 for PM10 and 0.147 lb/MMBtu for PM2. 5). Similar to North Scituat,

this boiler operated at relative ly low load and consequently th ere was relatively low pressure

drop across the cyclone.



# 3.2 Hazardous Air Pollutant Information

3.2.1 HAP S TACK 

# E MISSION 

# T EST 

# I NFORMATION

In addition to PM2.5, there is g rowing interest in Hazardous Ai r Pollutant (HAPs) emissions from wood

combustion. The EPA publishes HAP emission factors in Section 1 .6 of the AP 42, which was last updated

in September, 2001 and, as mentio ned, is based on emission test s conducted before that date. Since that

time, there have been advances in combustion technology and pra ctices, which suggest HAP emissions

have and will likely continu e to decline with time.

This study compared a number of AP 42 HAP emission factor value s with measured emissions from five

test sites. Both gaseous and par ticulate HAPs were evaluated. A full list of the HAPs e valuated is provided

in the appendix. HAP emissions were not weighted according to t heir respective toxicity level.

The information provided in this report is intended to establis h a starting point for understanding HAP

emissions. Firm conclusions shou ld not be drawn from the inform ation provided as it is based on a

limited number of stack emission tests.

Not all 188 federal HAPs were meas ured at each of the five test sites. Each HAP measured at each site was

compared with its AP 42 equivalent.

The comparisons made showed actu al emissions of individual HAPs were both higher and lower than AP

42 equivalents. They also showed the total HAPs measured at eac h site were lower than the total AP 42

HAP equivalent for all but one site. The average actual total H AP emission from all sites was 68% lower

than the AP 42 total HAP equival ent. The comparisons are summar ized below. Detail ed information is

provided in the appendix.Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 10 Table 8: Summary of HAP Test Sites

Location Design Heat

Input

(MMBtu/hr) Combustion

Type Emission

Control Emission

Test Date Number of

HAPs

Compared Total Measured

HAP Percent of

AP 42 Total HAP

North Scituate, RI 9.1 CCG HEMC 2009 24 13%

Glocester, RI 4.6 CCG HEMC 2009 24 8%

Council, ID 1.9 SA Uncontrolled 2007 22 23%

Green Acres, VT 2.2 SA Uncontrolled 1996 24 123%

Hazen Union, VT 2.8 CCG MC 1996 24 26%



# 3.2.2 M ERCURY 

# E MISSIONS

Mercury emissions have been mainl y considered with coal project s. Mercury emissions have been

considered for wood combustion projects, but to a lesser extent . There is much in formation about

mercury control from wood fired power plants via fuel and exhau st cleaning. Unlike NO 2 

### emissions,

Mercury emissions are a function of fuel mercury content. There fore, a fuel analysis provides a good

indication of potential mercury emissions.

Mentz et al, describes work perf ormed to measure mercury conten t of bark and stemwood in 30

locations throughout the country. 1 

### The average bark and stemwood c oncentrations at the 30 sites were

1.42 lb/10 12 

### Btu and 0.28 lb/10 12 

### Btu for bark and stemwood respec tively. The mean mercury conten t for

each of the 30 sites ranged from 0.57 lb/10 12 

### Btu to 3.14 lb/10 12 

### Btu in bark and from 0.12 lb/10 12 

### Btu to

0.46 lb/10 12 

### Btu in stemwood.

These numbers are based on the a ssumption that the entire quant ify of mercury is released from the fuel

into a vapor form and not does not combine with any other const ituents in the exhaust gas or be removed

by some form of emission control . For context, there is an EPA emission limit of 9 lb/10 12 

### Btu for existing

sources and 3 lb/10 12 

### Btu for new sources; therefore, actual mercury emissions are be low an established

limit. 2 

### Assuming that bark is a small po rtion of the fuel burned (e.g. bole tree or whole tree chip), the

weighted average of bark and ste mwood would be less than the li mit of 3 lb/10 12 

### Btu for new sources.

Pease et al, describes research performed to evaluate the poten tial for flue gas cooling, flue gas

humidification, pulsed energizat ion, and sorbent injection in w et and dry ESPs to reduce mercury

emissions. This study found that all of these measures are effe ctive. It also found that some mercury will

attach to fly ash thereby increa sing the potential for mercury removal.



# 4.0 B EST 

# M ANAGEMENT 

# P RACTICES 

# (BMP S 

# )

BMPs range from physical equipment such as oxygen sensors to op erational practices such as visual

observations of plume opacity. P roperly implemented, BMPs will optimize combustion conditions

thereby helping maximize energy efficiency and minimize emissio ns from any system.



# 4.1 Fuel Quality

The first step in implementing B MPs is to obtain the highest qu ality fuel possible. There are many factors

affecting fuel quality. Fuel quality is an important considerat ion as improved fuel quality improves

combustion conditions, increases efficiency and reduce emission s. Fuel quality is a function of fuel

1 Karen Mentz, John Pinkerton, and Jeff Louch.“Potential Mercury and Hydrochloric Acid Emissions from Wood Fuels.” Forest Products

Journal, 55(2): 46

‐ 50. Received for publication in August, 2004. Article No. 9919.

2 “National Emission Standards for Hazardous Air Pollutants for Industrial, Commercial and Institutional Boilers and Process Heaters; Final

Rule.” U.S. Environmental Protection Agency. Federal Register/Vol. 69, No. 176, September 13, 2004.Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 11 

### moisture content, bark content, uniformity, size, and purity. T hese factors are described in detail later in

this report.

There are no formally established grades of wood chips. However , there are four bas ic types of wood

chips, whose quality and corresp onding emissions are fairly wel l understood. For the purposes of this

report, the term “high quality” describes a chip which has mini mal ash content, is of uniform and proper

size and results in the le ast amount of emissions.

1. Sawmill residue chips (mill chips). This chip is thought to be the highest quality in that it

contains no bark. The availability of this chip is limited due to the decline in U.S. sawmills

coupled with the demand for higher value products from those ch ips such as pulp, wood

composite products and wood pellets.

2. Bole tree chips (bole chips). Are produced by chipping the tree trunk. This is a moderate to

high quality chip as it contains relatively minimal quantities of bark is relatively uniform in size.

3. Whole tree chips. Are produced by chipping the en tire tree and therefore include the tops,

leaves and branches in addition t o the trunk. This category wou ld also include municipal

vegetative waste in addition to trees removed in a given forest . These are a moderate to low

quality chip as they are less un iform in size/shape and have hi gher ash content than bole tree

chips.

4. Bark chips. These chips consist primarily of bark and are the lowest qualit y chip given the high

ash content of bark. In addition to its mineral content, bark c an have higher ash content because

it may have impurities adhered t o it from harvesting and transp ort.

Wood chips can be produced with c hippers and grinders. Grinders can handle more dirt and rocks and

therefore have greater potential for contaminating wood chips w ith those impurities. Grinders also

produce chips with greater size v ariation than chippers. As is discussed later in this section, fuel

homogeneity is important for effective fuel handling and combus tion.

In 2007, the Biomass Energy Resou rce Center (BERC) published a report for the South Dakota

Department of Agriculture, Resou rce Conservation & Forestry Div ision entitled “Woodchip Fuel

Specifications and Procurement S trategies for the Black Hills.” 1 

### While this document is intended for a

specific geographic area, the ov erall principles can be applied throughout the United States. This

document characterizes four grades of wood chip quality and pro vides guidelines for obtaining each of

those four grades.

The information in the BERC repo rt was combined with the author of this report’s wo rking knowledge to

develop the fuel quality BMPs su mmarized in the table below bel ow. Any number of these BMPs can be

applied to planned as well as existing facilities.

Table 9: Summary of Fuel Quality BMPs for Wood Chips



## BMP Category Description Fuel Quality

Improvement Combustion

Improvements / Emission

Reductions

Bark content Minimize bark content.

Mill chips and sawdust

based pellets do not

contain bark. Reduces ash content. Reduces clinker formation on

grates thereby maintaining proper

airflow through the grates.

Reduces emissions associated with

fly ash carry over. Increases

combustion efficiency.

1 Biomass Energy Resource Center (BERC). “Woodchip Fuel Specifications and Procurement Strategies for the Black Hills.” Prepared for the

South Dakota Department of Agriculture, Resource Conservation & Forestry Division. May 15, 2007. www.biomasscenter.orgResource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 12



## BMP Category Description Fuel Quality

Improvement Combustion

Improvements / Emission

Reductions

Moisture content Moisture content must

be within range

meeting combustion

system design

requirements. Ensures design fuel

heat content met. Energy loss occurs when excess

moisture is vaporized. Fugitive

dust and excess PM emissions

occur when fuel is excessively dry.

Storage surface Minimize/prevent

storage on ground

surfaces. Store on

concrete or other type

of clean paved surface. Prevents transfer of

soil, rocks, salts and

other impurities from

the ground surface to

the fuel. Improves combustion efficiency by

reducing clinker and ash

formation. Minimizes particulate

matter emissions.

Storage time for

trees with needles. When dry, needles fall

off tree when fallen

tree mechanically

shaken. Reduces ash content.

Increases fuel

uniformity. Lower ash content and reduced

potential for clinker formation

increases combustion efficiency.

Reduced PM emissions from

reduced fly ash carry over.

Storage Coverage Store in covered area. Ensures design

moisture content met.

Maximizes heat content

of fuel. Ensures design combustion

efficiency met by preventing

energy loss associated with excess

moisture vaporization. This

minimizes excess fuel

consumption.

Method of chip

production Sharp and properly

adjusted equipment is

critical for grinders and

chippers. Chipping

typically produces

better chip than

grinder. Maximizes wood chip

uniformity. "Stringer"

formation minimized. Promotes uniform combustion

thereby maximizing combustion

efficiency. Prevents system

interruptions (upset conditions)

caused by stringers in metering

bins.

Chipping/Grinding

Equipment

Operation and

Maintenance Manufacturer’s

operation and

maintenance

requirements should be

adhered to. Ensures chip

uniformity. Promotes uniform combustion

thereby maximizing combustion

efficiency.

Uniformity of fuel

input to chipper or

grinder Uniform size material

fed to chipper or

grinder. Increases chip

uniformity. Promotes uniform combustion

thereby maximizing combustion

efficiency.

Chip screening Mechanical screening

(sizing) of chips. Increases chip

uniformity, removes

oversized material and

removes fines. Has

potential to separate

and remove some

portion of bark from

raw chips. Promotes uniform combustion

thereby maximizing combustion

efficiency and reducing overall

emissions. PM emissions

potentially reduced as carry over

of fines into exhaust eliminated.

PM emissions reduced through

reduced bark content.

Long term fuel

supply contracts Encourages investment

in wood chip

production equipment

producing higher

quality chip. Optimal fuel

characteristics

developed. Promotes optimal combustion

conditions which maximizes

energy efficiency and minimizes

emissions.

Fuel supply testing Visually inspect fuel

geometry, uniformity,

moisture content prior Ensures design fuel

specifications are met. Ensures optimal combustion

conditions.Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 13



## BMP Category Description Fuel Quality

Improvement Combustion

Improvements / Emission

Reductions

to fuel being dumped

into storage bin. Retain

grab samples if need

for future fuel

measurements

anticipated.



### There are a number of grades of wood pellets defined by the Pel let Fuel Institute (PFI). They are super

premium, premium, standard and u tility. As shown in Table 10, g rades are a function of bulk density,

diameter, pellet durability index , percent of fines, inorganic ash content, length, moisture content,

chloride content, ash fusion and heating value. These categorie s are further described on the PFI Internet

Site. 1 

### There are no legal factors nece ssitating use of any particular grade of wood pellets. However, it is

useful to know the pellet grade for purposes of meeting air qua lity requirements for a given area.

Table 10: Values used for Classifying Residential Grades of Pellets according to the Pellet Fuels Institute

Fuel Property PFI Super Premium PFI Premium PFI Standard PFI Utility

Bulk Density, lb./cubic foot 40.0

‐ 46.0 40.0

‐ 46.0 38.0

‐ 46.0 38.0

‐ 46.0

Diameter, inches 0.250

‐ 0.285 0.250

‐ 0.285 0.250

‐ 0.285 0.250

‐ 0.285

Diameter, mm 6.35

‐ 7.25 6.35

‐ 7.25 6.35

‐ 7.25 6.35

‐ 7.25

Pellet Durability Index >97.5 >97.5 > 95.0 >95.0

Fines, % (at the mill gate) <0.50 <0.50 <0.50 <0.50

Inorganic Ash, %

‐ See Note 1 <0.50 < 1.0 <2.0 <6.0

Length, % greater than 1.50 inches < 1.0 < 1.0 < 1.0 < 1.0

Moisture, % <6.0 <8.0 <8.0 < 10.0

Chloride, ppm < 300 < 300 < 300 < 300

Ash Fusion NA NA NA NA

Heating Value As

‐ Rec

. ± 2SD As

‐ Rec. ± 2SD As

‐ Rec. ± 2SD As

‐ Rec. ± 2SD



# 4.2 Operation and Maintenance Plan

An operation and maintenance pla n (O&M Plan) is a document desc ribing the equipment and work

practices that will take place to ensure optimal combustion con ditions and complian ce with applicable

emission limits. These plans als o specify the frequency with wh ich all work p ractices will be completed.

Consequently, they may include d aily, weekly, monthly and annua l checklists to ensure all work p ractices

(BMPs) are completed. Facilities are oftentimes required to rec ord and maintain this information for a

period of time as part of a permit condition. O&M plans are dev eloped in concert by the boiler operator,

wood boiler equipment vendor and state regulatory office. O&M p lans should be fle xible to allow for

improved O&M measures if/when they are identified for a given f acility. Ideally, all O&M plans are

written and approved within a few months after start‐up.

Here is a sample list of O&M com ponents as speci fied in a Vermo nt air pollution control permit:

 Descriptions of routin e maintenance and inspection procedures.

 Description of procedure for and frequency of ash removal from the boiler and the particulate

matter emission control device.

1 http://www.pelletheat.org/3/instit ute/standards/PFI%20Standards.pdfResource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 14 

###  Provisions for maintaining recor ds of maintenance and inspectio n procedures, including both

routine activities and actions t aken in response to observation s of low combustion efficiency.

 Provisions for calibration and maintenance of any testing instr uments and/or equipment used to

measure the concentrations of CO 2 

### and CO in the boiler exhaust gases.



# 4.3 Boiler Operator Training

Boiler operator traini ng is essential to pro per operation and m aintenance. This is typically provided by

the vendor prior to and shortly after start‐up. There are curre ntly no standardized training programs for

acquiring boiler operator certification.

There are occasions when the boi ler operator who was trained by the vendor upon start‐up leaves for a

new job. In these situations, it is critical to ensure the repl acement operator has sufficient training and

experience.



# 4.4 Equipment Sensors

Many wood boilers are equipped wi th internal sensors that provi de real time information about some

aspect of the combustion process to an automated control system . The information from these sensors

helps the system self‐regulate with the intelligence they provi de. Sensors are freque ntly used to measure

pressure drop across a mechanical collector or baghouse, opacit y in the exhaust stack (with smoke

density meters), oxygen level in the combustion chamber and/or exhaust stack, and temperature in the

combustion chamber and/or exhaust stack.



# 4.5 Automatic Ash Removal

Bottom ash, or ash collected at the bottom of the combustion ch amber, can become re‐suspended and

carry over into the exhaust, ther eby increasing particulate mat ter emissions. Automatic ash removal can

ensure frequent bottom ash remov al. This may be especially usef ul if burning a high ash content fuel.



# 4.6 Raking Grates as Needed

In most direct burn combustion s ystems, biomass is combusted on grates. Ash will accumulate on these

grates. If left to accumulate, this can lead to clinker formati on and limit under‐fire airflow thereby

reducing combustion efficiency. Raking the grates reduces this problem.



# 4.7 Combustion Efficiency Testing

Combustion efficiency testing is a way to quantify the degree o f combustion completeness, not the overall

thermal efficiency (heat input d ivided by heat output). One met hod for measuring combustion efficiency

is by measuring carbon monoxide (CO) and carbon dioxide (CO 2 

### ) concentrations in the boiler exhaust

with a hand‐held portable analyzer.

CO is an indicator of the level of gaseous air toxics in boiler exhaust and therefore a good surrogate for

gaseous air toxics. The relation ship between CO and carbon diox ide (CO 2 

### ) concentrations provides an

indication of the degree combust ion completeness and is therefo re appropriate for the levels of all

emissions in boiler exhaust.

Vermont and Rhode Island impleme nted a permit condition requiri ng measurement of both CO and CO 2 

### in the exhaust gas to determine combustion efficiency. Combusti on efficiency is determined using this

equation, taken from a Vermont air pollution control permit:Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 15 Equation 1



# ( ) 100 %

2 2 

## ×

+ = CO CO CO CE

Where:

CE = Combustion efficiency,

CO 2 

### = % by volume of carbon dio xide in the flue gas, and

CO = % by volume of carbon monoxide in the flue gas.

Compliance is demonstrated when the combustion efficiency is ca lculated to be equal to or greater than

99%. A representative number of m easurements should be taken gi ven the broad range of operating

conditions that can occur in a given biomass boiler.



# 4.8 Visual Plume Observations

Visually observing the exhaust p lume is a way to confirm good c ombustion conditions are occurring. EPA

publishes two methods for visually evaluating plume opacity. Th e first one, Method 22, is mostly

qualitative and does not require formal training. 1 

### The second, Method 9, i s more quantitative and

requires the observer be re‐ certified every six months. 2 

### If the plume characteri stics pass a Method 22

test, then the observation is co mplete. If the M ethod 22 test i s not passed, then the observer can perform

a Method 9 test to quantify the plume characteristics, if neces sary. At minimum, steps should be taken to

correct combustion conditions if a Method 22 test is not passed

.



# 4.9 Recordkeeping

Consistent and thorough record k eeping is another means to ensu re optimal combustion conditions

occur continually. Record keeping is therefore considered a mea ns for demonstrating ongoing

compliance with pollutant emission limits. Record keeping is re quired in the areas of fuel use,

maintenance and monitoring. Reco rd keeping has been required fo r the items below. These requirements

listed are directly quoted or de rived from recent permits issue d in Vermont and New Hampshire.

 Track fuel use on a monthly basi s if heat input equal to or gre ater than 10 MMBtu/hr. Track fuel

use on an annual basis if heat input less than 10 MMBtu/hr.

 Measure and record oxygen in perc ent volume, in the exhaust gas and permanently record the

output in a log book.

 Maintain records of the results of the combustion efficiency te sting conducted on the Facility’s

boiler.  These records shall at l east include the test date, id entification of boiler tested, a

measurement of the load on the b oiler (such as fuel feed rate o r steam production rate), the

concentrations of oxygen, carbon monoxide and car bon dioxide in the exhaust gas as well as the

calculated combustion efficiency.

 Install and maintain a temperature sensor to measure the wood‐f ired boiler’s exhaust exit

temperature and permanently recor d the output in the log book.

 Observe visible emissions (via E PA Method 22) once a day on nor mal business days. Record the

date, time, duration of excursio n, and corrective actions taken if visible emissions are not typical

of good operation.

 Inspect the differential pressur e across the cyclone (once per shift).

1 More information can be accessed at http://www.epa.gov/ttn/emc/methods/method22.html

2 More information can be accessed at http://www.epa.gov/ttn/emc/methods/method9.htmlResource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 16 

###  Visually inspect the cyclone she ll, piping, and ducts for leaks ; inspect the ash collection

equipment and check for abnormal noise or hot spots (once per s hift).

 Clean the boiler grates once a day on normal business days.

 Inspect the cyclone/multicyclone at least once per year or if c onditions indicate it may need

maintenance. Clean the boot and vanes if possible on the annual inspection.

 Empty the cyclone/multicyclone a sh collection ve ssel as necessa ry, but not less than once per

week, in accordance with the manufacturer’s recommendations. 1



# 4.10 Annual Tune Up

Annual tune ups are typically pe rformed on wood boilers. The an nual tune up includes a comprehensive

inspection of the combustor, boiler and pollution control syste m components.

Adjustments/improvements to syst em components ar e performed as needed. Combustion efficiency is

typically measured when the annual tune up is performed.



# 5.0 A DD



# ‐ O N 

# P OLLUTION 

# C ONTROLS

Add‐on pollution controls are em ission control devices which re move pollutants from the exhaust gas

stream somewhere between the boi ler combustion chamber and the exhaust stack. They are installed

when the combustion equipment ca nnot reduce emi ssions to a desi red level. In the absence of a fixed

BACT requirement, 2 

### emission controls are determined on a case by case basis and a re a function of the

following: level of uncontrolled emissions, applicable state/fe deral emission limits, existing ambient

pollutant concentrations (backg round concentrations), stack hei ght and stack proximity of stack to

sensitive populations. Potential add‐on controls reviewed for t his study include cyclones, multicyclones,

high efficiency multicyclones (H EMCs), core separators, electro static precipitators (ESPs) and baghouses

(fabric filters). The core separator was d etermined in the 2001 emission control re port by Resource

Systems Group as the Best Availa ble Control Technology (BACT) f or small wood‐fired boilers burning a

wood chip type fuel and capable of limiting PM10 emissions to 0 .1 lb/MMBtu. 3 

### The core separator will be

discussed in further detail late r in this section. Again, the c onclusions of this report were accepted by a

consortium of New England states, they did not translate into a formal BACT determination at the federal

level.

This section will focus on add‐o n controls for reducing filtera ble particulate matter because for the boiler

size range considered in this study, combust ion controls are us ed to limit emissions of other pollutants

such as condensable particulate matter, nitrogen oxides (NOx), carbon monoxide (CO), volatile organic

compounds (VOCs) and most hazardous air pollutants (HAPs or “ai r toxics”). Add‐on controls are not

discussed for sulfur dioxide (SO 2 

### ) given the low sulfur content of biomass.



# 5.1 Mechanical Collectors

Mechanical collectors use centri fugal forces to separate partic ulate matter from an exhaust gas stream.

Mechanical collectors include si ngle cyclones, multicyclones, h igh efficiency multicyclones (HEMCs) and

1 This would also suffice for any other add

‐ on control device.

2 Massachusetts currently requires all wood boilers meeting the state permit applicability threshold meet a PM10 emission limit of 0.10

lb/MMBtu.

3 An Evaluation of Air Pollution Control Technologies for Small Wood

‐ Fired Boilers.” Prepared for Vermont Department of Public Service;

Vermont Department of Environmental Conservation, Air pollution Control Division; New Hampshire Governor’s Office of Energy

Resources and Community Services; and the Massachusetts Division of Energy Resources. Resource Systems Group, Inc., White River

Junction, VT. Revised, September 2001.Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 17 

### core separators. They are often used as exhaust gas pre‐cleaner s for other control devices, such as

baghouses or ESPs.

The exhaust gas flow rate is dir ectly proportional to the opera ting load of the boile r. Pressure drop, an

indicator of centrifugal separat ion force which removes particl es from exhaust, is dire ctly proportional to

the exhaust gas flow rate. Therefore, mechanical collectors wor k best when operating at their respective

design (maximum) pressure drop.



# 5.1.1 C YCLONES AND 

# M ULTICYCLONES

Single and multicyclones can rem ove a large percentage (approxi mately 90%) of large particles (PM10

and larger) and remove a small percentage (less than 10%) of fi ne particles (PM2.5). HEMCs and core

separators will collect higher pe rcentages of PM10 and PM2.5.



# 5.1.2 H IGH 

# E FFICIENCY 

# M ULTICYCLONES

The high efficiency multicyclone (HEMC) is simil ar to a convent ional multicyclone, but has a higher

collection efficiency due to use of a higher pressure drop. Con versely, the additiona l pressure drop has a

higher energy demand. The HEMC w as found to be the Best Availab le Control Technology (BACT) in a

2006 permit application to the Rho de Island Department of Envir onmental Management (RI DEM) for

new institutional wood boilers w ith heat input less than 10 MMB tu/hour. The BACT study translated into

emission limits of 0.20 lb/MMBtu and 0.18 lb/MMBtu for PM10 and PM2.5 respectively (these limits

include both filterable and cond ensable particulate matter).

Inlet‐outlet testing was perform ed for the Vermont APCD study a t the HEMC installed at the Ponaganset

Middle School in North Scituate, RI. Two, one‐hour tests were c ompleted for a single wood boiler. The

HEMC there is designed to operat e most effectively at four inch es of pressure drop. During testing, the

wood boiler operated a t low load (30% capaci ty) which created a pressure drop of approximately only

0.7 inches of water. The HEMC co llected 23% of the particulate matter in the boiler exhaust despite the

low pressure drop and a very high percentage of fine particles in the inlet exhaust gas stream

(approximately 90%).

A collection efficiency of 23% is a relatively low number in co mparison with other add‐on controls.

However, it is approximately 10% h igher than what a conventiona l multicyclone can achieve for PM2.5

removal under design (maximum) p ressure drop conditions. Furthe rmore, design calculations provided

by the vendor indicate the PM2.5 collection efficiency would ha ve been approximately four times higher

at design pressure drop.

HEMC’s can be designed to mainta in a high pressure drop at low loads. This can be achieved by using

valves to regulate the number of cyclones through which exhaust gas passes. For examp le, at high load, all

valves would open thereby allowi ng exhaust gas to distribute am ong all the cyclones. As load decreased,

valves would close causing exhaust gas to be distributed among a smaller number of cyclones.



# 5.1.3 C ORE 

# S EPARATOR

The core separator was previously determined to be BACT for par ticulate mater, in a 2001 report written

by Resource Systems Group. 1 

### This technology became commercia lly unavailable after the repo rt was

issued, when LSR Technologies we nt bankrupt. Since that time, t he rights to the pat ent were transferred

to Easom Corporation, from whom core separators can be purchase d.

Unlike conventional cyclone/multicyclones and the HEMCs in Rhod e Island, the core separator design

will maintain a relatively high p ressure drop at all operating loads. Therefore, this t echnology’s collection

efficiency will not deteriorate with reduced operating loads. S tack test results indicate it has a TSP

1 An Evaluation of Air Pollution Control Technologies for Small Wood

‐ Fired Boilers. Resource Systems Group, 55 Railroad Row, White River

Junction, Vermont 05001. September 2001.Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 18 

### collection efficiency of approxim ately 60% and outlet PM2.5 emi ssions of less than 0.1 lb/MMBtu with

close coupled gasifiers and appr oximately 0.15 lb/MMBtu with st oker combustors.



# 5.2 Dry Electrostatic Precipitators

Dry Electrostatic precipitators (ESPs) work on the principle of electrostatic attraction. In this, particles in

an exhaust gas stream are charged as they pass through the ESP and are pulled out of the exhaust gas

stream by oppositely charged pla tes on the side of the ESP.  Th is technology is widely used in Europe to

control particulate emissions fro m biomass systems. The control efficiency of PM10 and PM2.5 appears

to be 99% or greater, making this control technology very compe lling. 1 

### There no demonstrated

applications of ESPs on small w ood boilers in the United States . The pervasiveness of ESPs in Europe is

due to stricter emission limits and higher subsidies. 2 

### There is one demonstrated ESP on a small coal fired

boiler in North Carolina.

Until recently, it has been commo nly held that ESPs have signif icantly higher capital costs than

baghouses. Given changes in ESP design and recent cost analyses , it is now thought that ESPs have

comparable capital costs to bagho uses as they require less anci llary equipment (such as insulated

ductwork, multicyclone for exhaust pre‐cleaning) than baghouses . This combined with significantly lower

operating costs and smaller spat ial requirements than baghouses , make ESPs seem especially attractive

when advanced emission control is necessary.

Significant pressure drops do no t occur in ESPs; therefore, the y do not require the e xtra energy to run

fans to overcome the pressure dro p. This means ESPs potentially will have a lower energy demand than

all other add‐on controls.



# 5.3 Baghouses (Fabric Filters)

Baghouses utilize fabric filtrati on to remove particles from an exhaust gas stream. They are thought to

provide the highest degree of control of all add‐on controls. T hey are thought to be capable of removing

99%+ of filterable PM2.5 emissions. 3 

### This is higher than the control efficiency measured in Greenfi eld,

NH or 74%. Again, this lower value was likely due to tramp air flowing through a bypass during the stack

test there

Cyclone/multicyclones are used to pre‐clean exhaust gas upstrea m of baghouses to prevent partially

burned fly ash particles to reduce fire hazard. As with mechani cal collectors, there is pressure drop

across this control device caused by the exhaust gas passing th rough fabric. Therefore, energy is required

to draw exhaust through the fabric.

The 2001 RSG report determined ba ghouses were technically infea sible due to threat of fire. A 2006 RSG

BACT study also found them techn ically infeasible due to fire h azard and due to potential for filter bag

clogging, a condition which occur s when the exhaust gas cools t o the dew point causing moisture to

condense on the particulate “cake ” on the side of the bag walls . The end product is impermeable and can

cause bags to rupture.

Historically in New En gland, baghouses have not been selected f or systems with design inputs less than

10 MMBtu/hour because the faciliti es which they would serve did not have the financial or technical

resources to purchase and servic e them. For example, this size boiler would serve a small school, which

would not have a large and exper ienced facilities staff which c ould service the baghouse. In the absence

of a significant subsidy, a small school would not have the fin ancial resources to pu rchase a baghouse.

1 Compilation of Emission Factors, AP 42, Chapter 1.6. US EPA, revised September, 2003

2 Personal communication with Biomass Energy Resource Center. September, 2009.

3 Compilation of Emission Factors. AP 42 Chapter 1.6. Revised September, 2003Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 19 

### There are now three demonstrated applications of baghouses on r elatively small wood fired boilers in

New England. These installations are not experiencing filter ba g clogging problem because the vendors

developed a design to avoid this problem. However, there was on e fire which occurred in one of the

systems which required the bags to be replaced. A multicyclone was installed after the fire. No fires have

been reported since that time. T hese systems are described belo w:

 Mount Wachusett College, Gardiner , MA ‐ 10 MMBtu/hour wood chip boiler.

 Crochet Mountain Rehabilitation C enter, Greenfield, NH – 5.7 an d 11.4 MMBtu/hour wood chip

boilers.

 Middlebury College, Middlebury, VT – 29 MMBtu/hour wood chip bo iler.

These applications indicate baghouses are technically feasible, provided they are designed to avoid fire

and filter clogging.

Baghouses have the highest opera ting cost of all add on control s discussed in this report. This is largely

due to the cost of replacement bags and to the amount of time r equired to keep baghouses in proper

working order. At this time, it is not known exactly how freque ntly bags need to be replaced on small

wood boilers. The rule of thumb is to replace a given bag every three years, which means replacing one

third of all the bags every year. However, this may not be appl icable to wood boilers operating only

during the heating season.



# 6.0 S UMMARY OF 

# E UROPEAN 

# E MISSION 

# C ONTROL 

# P RACTICES

The Biomass Energy Resource Cent er (BERC) recently completed a research trip to Europe to learn more

about their biomass facilities. Here is a synopsis of their fin dings.

 There are larger economic incenti ves for bioenergy in Europe as compared to the US. For

example, electricity from biomas s power plants can be sold by u tilities for approximately 30 euro

cents/kwh. Utilities in Austria are purchasing electricity for 11 euro cents/kwh. For comparison,

in Vermont, biomass ele ctricity is sold to utilities for approx imately 12.5 cents/kwh and in turn

sold by utilities for approx imately 13 to 14 cents/kwh.

 Most of the biomass systems depl oy energy efficiency measures s uch as:

- High combustion temper ature 1013°C (1855 F);

- Low excess air (approx imately 50 to 75%);

- Continuous oxygen co ntent monitoring (%O 2 

### ) to achieve target content in flue of

approximately about 7 to 9%;

- Setting target CO 2 

### exhaust content.  T he target of the CO 2 

### in the flue gas is 13%. If less than

10%, the secondary air is adjuste d. Even for the small wood pel let boilers (residential scale)

the O 2 

### % in the flue gases is monitore d continuously and the excess a ir is modulated based

on the % O 2 

### content;

- Pre‐heating of both the primary and the secondary air using an economizer;

- A heat recovery system using the hot air from the upper level o f the boiler room is used to

dry the woodchips;

- Water preheated using the flue gas, cooling the flue gases from 900°C (1652 °F) to 180°C

(356°F) 1 

### before the ESP; and

- Variable speed drives on the h ot water distribution pumps.

 Emissions control equipment normally used is a multicyclone and ESP in series. ESP’s are

frequently installed ou tside of buildings.

1 This temperature is maintained to prevent condensation.Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 20 

###  Some projects have condensers to remove the moisture from the f lue gases simultaneously

recovering some addition al thermal energy.

 The average ash conten t is about 2‐5% of the biomass and reflec ts burning lower quality

biomass (in some cases). The ash streams are collected separate ly and utilized where

appropriate. The ash from the mu lti‐cyclone and the combustion chamber of the boiler may be

used as fertilizer in farm operations.  The ash from ESP (fine ash) is land filled, as it may contain

heavy metals. The plant pays for the removal of the ash from th e ESP. In some cases,

multicyclones are used upstream of ESPs to recover lower metal content ash which is therefore

less toxic and can be land applied.

 The capital cost of a typical ESP for a new power plant of 5 to 10 MW capacity range was

typically about 12‐14% of the cost of the project. This percent may be more for smaller capacity

plants producing only heat.

 The quality of woodchips is not considered to be very critical. This is likely attributable to the

widespread use of ESPs.



# 7.0 C APITAL 

# C OSTS OF 

# E MISSION 

# C ONTROLS FOR 

# P ARTICULATE



# M ATTER

Capital and operating costs were estimated with quotes from and personal communication with

equipment vendors as well as the equations and methods presente d in the “EPA Cost Control Manual.” 1



### Information used to generate cos ts is detailed in the appendix. In addition to the size of the biomass

combustor, there are a number of other factors which cause vari ability in the capital costs. Here is a

selected list of factors aff ecting price variability:

• Change in the price of steel. This change had a significant a ffect on the price of the Core

Separator and other mechanical collectors.

• Foreign exchange rates. For equipment purchased oversea s, specifically Europe, the cos t is

significantly affected by the ex change rate, which now increase s price. The two high efficiency

multicyclones featured in this r eport were purchased from a Eur opean vendor.

• Pollution control device design. Capital costs are also affect ed by the pollution control

equipment design. For example, t he price of electrostatic preci pitators is sensitive to the size of

the particle collectio n plates. Collection efficiency is relate d to collection plate size; therefore,

projects requiring relatively hi gh collection efficiency will r esult in larger collection plates and a

more expenive electrostatic prec ipitator than otherwise. As ano ther example, some baghouses

are designed with additional ce lls, to guard against filter clo gging which can significantly

increase the price of a standard baghouse.

• Space requirements. The amount of horizontal and vertical space required for a giv en control

can affect the installation cost. For examples, baghouses can r equire more space than

electrostatic precipitators. The additional spac e required can increase the footprint and/or

height of the building housing t he equipment, thereby increasin g construction costs.

• Ancillary equipment. For example, baghouses require more ancillary equipment, such as

insulated ductwork and a mechani cal collector (to reduce fire r isk), than a baghouse.

• Shipping costs. The proximity of the location to major transportation hubs as well as the

equipment production location can affect costs.

1 EPA Cost Control Manual, Sixth Edition. U.S EPA report # EPA/452/B

‐ 02

‐ 001. January, 2002. Available at:

http://www.epa.gov/ttn/c atc/dir1/c_allchs.pdf.Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 21 

### Estimated capital costs for add‐on particulate matter controls are shown below for a single cyclone,

multicyclone, high efficiency mu lticyclone (not valved), high e fficiency multic yclone (valved), 1 

### Core

Separator (with 24 inch diameter separators), Core Separator (w ith 12 inch diameter separators),

cyclone coupled with baghouse, an d an electrostatic precipitato r. Approximate costs are shown for

systems from approximately 2 MMBtu /hour to 34 MMBtu/hour heat i nput in Figure 1.

Figure 1: Particulate Matter Add

‐ On Emission Control Costs



### All capital costs shown above except those for “cyclone + bagho use” were derived exclusively with

vendor quotes. This ca tegory was calculated by inputting the co st of the bags into an equation listed in

Table 1.9 of the EPA Cost Contro l Manual, which calculated rema ining costs based on the price of the

bags. They are intended to repre sent all costs leading up to an d including installation.

1 As previously mentioned, the term “valved” refers to the use of valves to maintain pressure drop over a range of firing rates.Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 22 

# 8.0 C OST 

# E FFECTIVENESS OF 

# P ARTICULATE 

# M ATTER 

# E MISSION



# C ONTROLS

Cost effectiveness was estimated for the same particulate matte r add‐on controls. For the purposes of

this report, the term “cost effe ctiveness” refers to the dollar s spent to remove one to n of a given pollutant

in a given year and are a function of the capital and operating costs. Costs were estimated using the

methodology in the EPA Air Pollution Cost Control Manual and wi th price quotes and personal

communication with equipment vendors and other technology exper ts. 1 

### Cost effectiveness is linearly

related to the:

1) Design heat input of the system,

2) Annual fuel consumption rate (annual capacity factor),

3) Pollutant inlet loading of the pollution control device and

4) Size of particle being contr olled (PM10 and PM2.5).

This means the cost effectivenes s values listed later in this s ection can be scaled upward or downward,

given the linear relationship of the aforementioned factors wit h cost effectiveness,

Cost effectiveness was estimated for PM10 and PM2.5. Table 11 s ummarizes the assumed parameter

values used to model cost effect iveness. The values used are in tended to help portray a small inst itutional

wood boiler operating approximat ely half the year to provide he at and hot water. The inlet loading values

were taken from AP 42 and corresp ond to the “wet wood” category . These values wer e deemed as being

generally representative for a st oker combustion system. Actual numbers may be lower for “stokers” and

are likely lower for close coupled gasifiers.

Table 11: Assumed Parameter Values for Cost Effectiveness Analysis

Wood boiler design heat input 5.0 MMBtu/hour

PM10 Inlet loading 0.31 lb/MMBtu

PM2.5 inlet loading 0.25 lb/MMBtu

Operating hours per year 4380 (half the year)

Average daily operating capacity 50%

Annual capacity factor 25%

Fuel heat content at 40% MC 5,013 btu/lb

Annual fuel consumption 1,095 tons/year



### Table 12 and Table 13 show estim ated cost effectiveness PM10 an d PM2.5 removal respectively, from the

system summarized in Table 11. A best estimate h as been made to assign control efficiencies, capital

costs and operating costs. Contro l efficiencies were estimated with the emission test information

reviewed for this report, AP 42 uncontrolled and controlled emi ssion factors and “Controlling Emissions

from Wood Boilers,” the RSG 2001 BACT report, personal communic ation with equipment vendors, and a

1 EPA Air Pollution Control Cost Manual, Sixth Edition. EPA/452/B

‐ 02

‐ 001. United States Environmental Protection Agency, Office of Air

Quality Planning and Standards. Research Triangle Park, North Carolina. January, 2002Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 23 

### draft report written by the North east States for Coordinated Ai r Use Management (NESCAUM). 1



### “Assumed control efficiency value s reflect optimal operating co nditions are occurring for both the

combustor and the control equipment. It should be noted that th e HEMC’s ranking is based on vendor

calculations, not actual performance. Furthermore, actual contr ol efficiency will be lower for “un‐valved”

HEMC’s whose wood boiler is operating below full load.

As mentioned, there are many fac tors which cause variability in capital and operating costs. Therefore,

actual costs could vary considera bly than quoted below. Further more, these costs shou ld not be regarded

as exact costs.

Table 12: Cost Effectiveness for Removing PM10

Pollution Control Device Control

Efficiency Capital Cost of

Equipment Annual

Operating Costs Total Annual

Costs Total Cost per

Ton Removed

Cyclone 50% $2,243 $580 $791 $930

Multicyclone 75% $9,424 $580 $1,469 $1,151

HE Multicyclone 77% $62,878 $800 $6,980 $5,297

HE Multicyclone (valved) 77% $125,756 $800 $12,915 $9,802

Core Separator (12") 98% $63,337 $1,239 $7,784 $4,668

Core Separator (24") 98% $111,709 $1,459 $12,570 $7,537

Cyclone + Baghouse 99% $109,878 $3,920 $14,291 $8,483

ESP 95% $138,005 $1,867 $14,894 $9,213

Table 13: Cost Effectiveness for Removing PM2.5

Pollution Control Device Control

Efficiency Total Capital

Investment Annual

Operating Costs Total Annual

Costs Total Cost per

Ton Removed

Cyclone 5% $ 2,243 $580 $791 $11,534

Multicyclone 10% $9,424 $580 $1,469 $10,707

HE Multicyclone 77% $65,478 $800 $6,980 $6,569

HE Multicyclone (valved) 77% $128,356 $800 $12,915 $12,154

Core Separator (12") 75% $69,337 $1,239 $7,784 $7,563

Core Separator (24") 60% $117,709 $1,459 $12,570 $15,266

Cyclone + Baghouse 99% $109,878 $3,920 $14,291 $10,519

ESP 90% $138,005 $1,867 $14,894 $ 12,059



# 9.0 O VERVIEW OF 

# E MISSION 

# C ONTROLS FOR 

# O THER 

# R ELEVANT



# P OLLUTANTS



# 9.1 Nitrogen Oxides (NOx)

Minimizing excess air usage reduces thermal NOx emissions. Oxyg en concentration is an indicator of the

amount of excess air; therefore, monitoring oxygen concentratio n and linking oxygen measurements with

automated controls establish the appropriate quantity of excess air on a continual b asis and prevent

excess thermal NOx emissions.

1 “Controlling Emissions from Wood Boilers.” Northeast States for Coordinated Air Use Management (NESCAUM). October, 2008.

Available at: http://www.nescaum.org/topics/commercial

‐ wood

‐ boilers.Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 24 

# 9.2 Sulfur Dioxide (SO 2 

# )

SO 2 

### emissions from wood combustion ar e negligible given very low su lfur content in biomass.



# 9.3 Carbon Monoxide (CO)

Carbon monoxide emissions are mi nimized by good combustion cond itions, specifically, maintaining the

proper air to fuel ratio. Plume opacity observation, proper ope ration and maintenance, periodic

combustion efficiency testing, and in‐situ oxygen concentration monitoring are ways to ensure ongoing

good combustion condit ions. A combustion chamber designed with staged combustion increases the

degree of combustion completeness and is therefore useful for m inimizing CO emissions.



# 9.4 Volatile Organic Compounds (VOCs)

The same measures for minimizing CO emissions will minimize VOC emissions.



# 9.5 Hazardous Air Pollutants (HAPs)

Hazardous air pollutants include both gaseous and particulate b ased pollutants. The aforementioned

controls for CO and VOCs are also effective at controlling HAPs , but most effective at controlling gaseous

HAPs. Particulate HAPs are also controlled with an add‐on contr ol device.



# 10.0 C ONCLUSIONS

 There is new stack emission test information which provides som e additional insights into how

fuel characteristics and add‐on c ontrols affect levels of parti culate emissions.

 Limited information is available for pellet combustion emission s, high efficiency multicyclone

(HEMC) control efficiency, and electrostatic precipitator (ESPs ) control efficien cy for small wood

boilers only.

 While the quantity of emissions information for wood boilers ap proximately 10 MMBtu/hour

and smaller is growing to a level on which generally meaningful interpretations can be made, this

quantity of information is not available to make meaningful int erpretations for wood boilers

smaller than 5.0 MMBtu/hour.

 Fuel characteristics and fuel qu ality affect fuel handling and combustion conditions and

therefore levels of po llutant emissions.

 There are many measures which ca n be implemented to characteriz e, enhance, preserve and test

fuel quality. Implementing these measures will translate into i mproved combustion conditions

thereby increasing energy effici ency and reducing emissions.

 There are many Best Management P ractices (BMPs), also called wo rk practice standards which,

when implemented, promote combust ion completeness, minimize ene rgy loss and reduce

emissions.

 The increased combustion complet eness created by BMPs not only helps control particulate

matter emissions, but also helps control emissions of gaseous p ollutants, including carbon

monoxide, nitrogen oxides, volatile organic compounds (VOCs) an d hazardous air pollutants

(HAPs).

 BMPs help prevent combustion ups et conditions which will help e liminate nuisance episodes

such as excessive plume opacity.Resource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 25 

###  Particle size has a large affect on collection efficiency in co nventional mechanical collectors

(mechanical collectors with a relatively lo w pressure drop). Su bstantially smaller quantities of

fine particles (PM2.5) than coar se particles (PM10) can be coll ected in conventional mechanical

collectors.

 Pressure drop has a large affect on mechanical collector collec tion efficiency. Core separators

collect substantially larger quantities of fine particles than conventional mechanical collectors, at

all firing rates, as they are de signed to maintain a high press ure drop at all firing rates.

 New baghouse designs are safer a nd technically feasible. These conclusions are demonstrated by

three relatively new baghouse in stallations in the northeast.

 Potential exists for implementin g an HEMC design which maintain s a relatively high pressure

drop at a range of firing rates using valves.

 The core separator was commercia lly unavailable, but now has th e potential to emerge back into

the marketplace.

 ESPs and baghouses have comparable capital costs for some size systems. ESPs have lower

operating costs and have lower energy demand.

 Recent experience in Europe indi cates greater prevalence of ESP s due to greater financial

incentives and stricter emission limits.

 Baghouses and ESPs are the add‐o n controls providing the highes t degree of control of PM2.5 for

all firing rates.

 For small systems less than 2.0 MMBtu/hr, the annual operating cost of all add‐on emission

controls except cyclones, multicy clones and “non‐valved” high e fficiency mult icyclones may

likely exceed the annual fuel savings.



# 11.0 R ECOMMENDATIONS FOR 

# F UTURE 

# R ESEARCH

Based on the analysis completed for this project, it is clear t here are many variables which affect emission

rates (location of source, type of fuel burned, firing rate, ty pe of combustion technology, etc.).

Consequently, it would be benefi cial for more testing to be com pleted. It would be helpful for future tests

to be structured to further understandin g of the following:

 Particulate and gaseous emission s from pellet boilers (PM10, PM 2.5, CO and NOx).

 Inlet‐outlet testing of PM10 and PM2.5 for add‐on control devic es controlling pellet boiler

emissions. Particle size distrib ution should also be measured a t the inlet and outlet, in addition

to measuring mass emission rates.

 Inlet‐outlet testing at a range of firing rates for particulate emissions (PM10, PM2.5) controlled

by HEMCs. Particle size distribu tion should also be measured at the inlet and outlet, in addition

to measuring mass emission rates.

 Inlet‐outlet testing of PM10 and PM2.5 for ESPs o n small wood‐f ired boilers (there will likely be

a number constructed in 2010). Particle siz e distribution shoul d also be measured at the inlet

and outlet, in addition to mea suring mass emission rates.

 HAP emissions in concert with CO and PM2.5. Inlet and outlet te sting should be performed for

particulate HAPs. PM2.5 should b e tested because it is consider ed a surrogate for particulate

HAPs. CO should be tested (outlet testing only) because it is c onsidered a surrogate for gaseous

HAPs.

Stack testing for any given site should be expanded to include emissions from the following:

 Low, medium and high firing ratesResource Systems Group, Inc. Emission Control Technologies for Small Wood

‐ Fired Boilers

23 February 2010 Page 26 

###  At least two fuels, such as, woo d with bark (bole chips or whol e tree chips) and wood without

bark (mill chips).

The following are also recommended:

 Development of a voluntary unive rsal boiler operator training p rogram for obtaining boiler

operator certification.

 Further development of fuel qual ity specificatio ns to further e stablish grades of wood fuels.



# 12.0 S UMMARY

A number of emission controls for small wood‐fired boilers have been evaluated. This study evaluated a

number of Best Management Practices (BMPs – also called work pr actice standards) and add‐on controls.

While these controls a re focused on particulate matter control, their implementation will control

emissions of all types of polluta nts, including carbon monoxide , sulfur dioxide, nitrogen oxides, volatile

organic compounds and hazardous air pollutants. Maximizing fuel quality, optimizing combustion

conditions and selecting a well designed add‐on pollution contr ol are the three main categories for

controlling emissions. Control efficiency and cost varies by bo iler size and type of add‐on pollution

control.

### APPENDIX A

STACK TEST REPORTS

### APPENDIX B

EMISSION CALCULATIONSHazardousAirPollutantSynopsisPollutantCategorySystemInformation/PollutantPonagansetMSResult(lb/MMBtu)PonagansetHSResult(lb/MMBtu)CouncilResult(lb/MMBtu)GreenAcresResult(lb/MMBtu)HazenUnionResult(lb/MMBtu)OverallAverageResult(lb/MMBtu)AP42EmissionFactor(lb/MMBtu) %ofAP42Ponaganset%ofOthersDesignHeatInput 9.1 4.6 1.9 2.2 2.8Combustiontype CCG CCG SA SA CCGEmissioncontrol HEMC HEMC Uncontrolled Uncontrolled MulticycloneMetals Arsenic 1.54E‐06 8.40E‐07 4.54E‐06 2.66E‐06 5.71E‐07 2.03E‐06 2.20E‐05 9% 46%Cadmium 2.15E‐05 1.78E‐05 3.93E‐06 1.44E‐05 4.10E‐06 352%Chromium 2.34E‐05 2.64E‐05 6.51E‐06 1.88E‐05 2.10E‐05 89%ChromiumVI 4.83E‐06 1.31E‐06 1.31E‐06 8.37E‐07 2.07E‐06 3.50E‐06 59% 286%Nickel 9.87E‐06 3.29E‐06 2.20E‐05 2.11E‐05 3.57E‐06 1.20E‐05 3.30E‐05 36% 42%Manganese 9.58E‐05 8.66E‐05 9.12E‐05 1.60E‐03 6%Phosporus 1.00E‐04 1.29E‐04 1.15E‐04 2.70E‐05 425%Organics Formaldehyde 9.30E‐04 4.77E‐04 9.50E‐04 1.05E‐02 1.38E‐03 2.84E‐03 4.40E‐03 65% 16%Benzene 1.50E‐04 4.11E‐06 4.49E‐05 5.80E‐05 6.43E‐05 4.20E‐03 2% 150%PAHs Acenapthene 4.27E‐08 5.05E‐08 0.00E+00 7.53E‐07 4.65E‐07 2.62245E‐07 9.10E‐07 29% 11%Acenapthylene 4.80E‐06 4.81E‐06 0.00E+00 3.33E‐05 2.04E‐04 4.93813E‐05 5.00E‐06 988% 6%Anthracene 1.82E‐06 1.41E‐06 0.00E+00 2.44E‐06 1.42E‐05 3.97491E‐06 3.00E‐06 132% 29%Benz(a)anthracene 2.38E‐05 2.84E‐05 0.00E+00 1.54E‐06 1.63E‐05 1.40124E‐05 6.50E‐08 21,558% 439%Benzo(b)fluoranthene 2.18E‐05 1.83E‐05 0.00E+00 3.66E‐06 2.51E‐05 1.37725E‐05 1.00E‐07 13,772% 209%Benzo(ghi)perylene 2.82E‐06 2.57E‐06 2.52E‐07 1.93E‐06 1.44E‐05 4.39315E‐06 9.30E‐08 4,724% 49%Benzo(e)pyrene 1.50E‐05 9.65E‐06 0.00E+00 2.38E‐06 1.57E‐05 8.5388E‐06 2.60E‐09 328,416% 204%Benzo(a)pyrene 4.56E‐06 5.50E‐06 0.00E+00 9.91E‐07 1.34E‐05 4.88928E‐06 2.60E‐06 188% 105%Chrysene 4.91E‐05 4.46E‐05 0.00E+00 3.15E‐06 2.43E‐05 2.42272E‐05 3.80E‐08 63,756% 512%Dibenz(a,h)anthracene 3.73E‐07 4.15E‐07 0.00E+00 1.33E‐07 6.97E‐06 1.57829E‐06 9.10E‐09 17,344% 17%Fluoranthene 2.82E‐05 9.15E‐05 1.31E‐06 1.08E‐05 9.51E‐05 4.53915E‐05 1.60E‐06 2,837% 168%Fluorene 1.17E‐07 1.39E‐07 1.43E‐06 6.22E‐07 2.90E‐06 1.04166E‐06 3.40E‐06 31% 8%Ideno(1,2,3‐cd)pyrene 2.22E‐06 1.98E‐06 0.00E+00 1.28E‐06 2.77E‐06 1.65057E‐06 8.70E‐08 1,897% 156%2‐methylnapthalene 1.02E‐06 9.51E‐07 0.00E+00 1.32E‐05 1.32E‐05 5.67378E‐06 1.60E‐07 3,546% 11%Napthalene 2.85E‐05 2.57E‐05 6.55E‐06 1.26E‐04 7.47E‐05 5.2285E‐05 9.70E‐05 54% 39%Phenanthrene 2.46E‐05 2.05E‐05 3.17E‐06 2.67E‐05 2.64E‐04 6.77896E‐05 7.00E‐06 968% 23%Pyrene 3.05E‐05 3.22E‐05 4.69E‐06 9.38E‐06 8.12E‐05 3.15871E‐05 3.70E‐06 854% 99%AP42 PonagansetTotalHAPs 1.53E‐03 9.91E‐04 1.04E‐02Comparison Ponaganset%ofAP42 15% 10%CouncilTotalHAPs 1.04E‐03 4.60E‐03Council%ofAP42 23%GreenAcresTotalHAPs 1.08E‐02 8.81E‐03GreenAcres%ofAP42 123%HazenTotalHAPs2.32E‐03 8.81E‐03Hazen%ofAP4226%GreenAcres&HazenTotalHAPs3.29E‐03 8.81E‐03GreenAcres&Hazen%ofAP4237%

### APPENDIX C

OPERATING COST CALCULATIONS

# Operating Cost Calculation Values & References

GENERAL INPUTS

Category Value Notes

Interest rate (%) 0.07 Default value from EPA Cost Control Manua l

Economic life (years ) 20 Default value from EPA Cost Control Manua l

Capital Recovery Factor (CRF ) 9% Equation 2.8a from EPA Cost Control Manua l

CYCLONE / MULTICYCLONE OPERATING COSTS

Category Value Notes

total ash disposal cos t $0.00 all ash land applied for soil enhancemen t

electricity price ($/kwh ) 0.1 av'g commercial elec. cost in 2009 (http://www.eia.doe.gov/cneaf/electricity/epm/table5_3.html )

waste gas flow rate (acfm ) 2562 from review of recent stack test reports in Vermon t

static pressure drop (in wc ) 2 based on project experienc e

combined fan

‐ motor efficienc y 60% from EPA Cost Control Manual

hours per yea r 2,190 operating half the year at average operating capacity of 50% loa d

incremental electricity cos t $219.76 EPA Cost Control Manual, Equation 1.46.

labor hours per yea r 12 regular inspections, unexpected maintenance and annual inspection of the interio r

labor rate $30.00 personal communication with wood boiler vendo r

labor cost s $360.00

total annual costs $579.76

HIGH EFF MULTICYCLONE

Category Value Notes

total ash disposal cos t $0.00 all ash land applied for soil enhancemen t

electricity price ($/kwh) 0.1 av'g commercial elec. cost in 2009 (http://www.eia.doe.gov/cneaf/electricity/epm/table5_3.html)

waste gas flow rate (acfm) 2,562 from review of recent stack test reports in Vermont

static pressure drop (in wc ) 4 from vendor quot e

combined fan

‐ motor efficienc y 60% from EPA Cost Control Manual

hours per yea r 2,190 operating half the year at average operating capacity of 50% loa d

incremental electricity cos t $439.52 EPA Cost Control Manual, Equation 1.46.

labor hours per yea r 12 regular inspections, unexpected maintenance and annual inspection of the interio r

labor rate $30.00 personal communication with wood boiler vendor

labor cost s $360.00

total annual cost s $799.52

CORE SEPARATOR (24 INCH)

Category Value Notes

total ash disposal cost $0.00 all ash land applied for soil enhancement

electricity price ($/kwh) 0.1 av'g commercial elec. cost in 2009 (http://www.eia.doe.gov/cneaf/electricity/epm/table5_3.html)

waste gas flow rate (acfm ) 2,562 from review of recent stack test reports in Vermon t

static pressure drop (in wc ) 8 personal communication with vendo r

combined fan

‐ motor efficienc y 60% from EPA Cost Control Manual

hours per yea r 2,190 operating half the year at average operating capacity of 50% loa d

incremental electricity cos t $879.03 EPA Cost Control Manual, Equation 1.46.

labor hours per yea r 12 regular inspections, unexpected maintenance and annual inspection of the interio r

labor rate $30.00 personal communication with wood boiler vendo r

labor cost s $360.00

total annual cost s $1,239.03CORE SEPARATOR (12 INCH)

Category Value Notes

total ash disposal cos t $0.00 all ash land applied for soil enhancemen t

electricity price ($/kwh ) 0.1 av'g commercial elec. cost in 2009 (http://www.eia.doe.gov/cneaf/electricity/epm/table5_3.html )

waste gas flow rate (acfm ) 2,562 from review of recent stack test reports in Vermon t

static pressure drop (in wc ) 10 personal communication with vendo r

combined fan

‐ motor efficienc y 60% from EPA Cost Control Manual

hours per yea r 2,190 operating half the year at average operating capacity of 50% loa d

incremental electricity cos t $1,098.79 EPA Cost Control Manual, Equation 1.46.

labor hours per yea r 12 regular inspections, unexpected maintenance and annual inspection of the interio r

labor rate $30.00 personal communication with wood boiler vendo r

labor cost s $360.00

total annual cost s $1,458.79

BAGHOUSE OPERATING COSTS

Category Value Notes

total ash disposal cos t $0.00 all ash land applied for soil enhancemen t

total bag cos t $4,250.00 vendor quote for coated bag s

% of bags replaced annuall y 8% 1/12 of bags replaced every year assuming 50% annual capacity facto r

bag replacement cost ($/yr ) $350.63

electricity price ($/kwh ) 0.1 av'g commercial elec. cost in 2009 (http://www.eia.doe.gov/cneaf/electricity/epm/table5_3.html )

waste gas flow rate (acfm ) 2,562 from review of recent stack test reports in Vermon t

static pressure drop (in wc ) 5 from permit application for new wood boiler in central Massachusett s

combined fan

‐ motor efficienc y 60% from EPA Cost Control Manual

hours per yea r 2190 operating half the year at average operating capacity of 50% loa d

incremental electricity cos t $549.40 EPA Cost Control Manual, Equation 1.46.

labor rate $30.00 personal communication with wood boiler vendo r

labor hours per yea r 81 1 hr/wk general maint., 80 hours to replace all bags, 8 hours for black light testing at 2x per yea r

labor cost s $2,440.00

total annual cost s $3,340.02

ESP OPERATING COSTS

Category Value Notes

total ash disposal cos t

‐ $ all ash land applied for soil enhancemen t

pressure drop (in. water ) 0.04 page 3

‐ 34 in EPA Cost Control Manual

operating time (h/yr) 2,190 operating half the year at average operating capacity of 50% loa d

system flow rate (acfm ) 2,562 from review of recent stack test reports in Vermon t

fan power req. (kWh/yr ) 41 EPA Cost Control Manual, equation 3.4 6

electricity req. (kWh/yr ) 2431 personal communication with vendo r

electricity price ($/kwh ) 0.1 av'g commercial elec. cost in 2009 (http://www.eia.doe.gov/cneaf/electricity/epm/table5_3.html )

total electricity deman d 569.4 sum of fan and other electricity requirement s

total power cos t 247.20 $

labor hours per yea r 8 personal communication with vendor. Open, inspect and clean ESP

.

labor rate 30.00 $ personal communication with wood boiler vendo r

labor cost s 240.00 $

maintenance cost s 1,380.05 $ page of EPA Cost Control Manual, equation 3

‐ 4 5

total annual cost s 1,867.25 $