New York State Energy Research and Development Authority

Final Report

August 2010

Revised June 2012

No. 13-01

Evaluation of the Performance and 

Emission from Commercial Scale 

Advanced Wood Combustion Systems
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Evaluation of the Performance and Emissions

from Commercial Scale Advanced

Wood Combustion Systems

Final Report

Prepared for the

New York State

Energy Research and

Development Authority

Albany, NY

nyserda.ny.gov

Ellen Burkhard, Ph. D.

Senior Project Manager

and 

Nathan Russell

Assistant Project Manager 

Prepared by:

Clarkson University

Potsdam, NY

Philip K. Hopke, Ph.D. 

Thomas M. Holsen, Ph.D.

Principal Investigators

NYSERDA NYSERDA August 2012

Report 13-01 10672; 10668; 11166; 18127 Revised June 2012
ii

NOTICE

This report was prepared by Clarkson University in the course of performing work contracted for 

and sponsored by the New York State Energy Research and Development Authority (hereafter 

the "Sponsor"). The opinions expressed in this report do not necessarily reflect those of the 

Sponsor or the State of New York, and reference to any specific product, service, process, or 

method does not constitute an implied or expressed recommendation or endorsement of it. 

Further, the Sponsor and the State of New York make no warranties or representations, 

expressed or implied, as to the fitness for particular purpose or merchantability of any product, 

apparatus, or service, or the usefulness, completeness, or accuracy of any processes, methods, or 

other information contained, described, disclosed, or referred to in this report. The Sponsor, the 

State of New York, and the contractor make no representation that the use of any product, 

apparatus, process, method, or other information will not infringe privately owned rights and will 

assume no liability for any loss, injury, or damage resulting from, or occurring in connection 

with, the use of information contained, described, disclosed, or referred to in this report. 
iii

Table of Contents

NOTICE.......................................................................................................................................... ii

INTRODUCTION .......................................................................................................................... 1

Walker Center Boiler .................................................................................................................. 2

Cayuga Nature Center Boiler ..................................................................................................... 2

W!ld Center Boiler ..................................................................................................................... 3

Fuel Analysis .............................................................................................................................. 4

MEASUREMENT METHODS ..................................................................................................... 5

CTM-39 Dilution Sampling System ........................................................................................... 5

EPA Method 5 and OTM-28 ...................................................................................................... 5

Thermal Efficiency Measurement Methods ............................................................................... 6

MEASUREMENT RESULTS ....................................................................................................... 8

150 kW Hamont wood pellet boiler at the Walker Center ......................................................... 8

150 kW Hamont Wood Chip-Fired Boiler (Cayuga Nature Center) ........................................ 14

500kW ACT pellet boiler at the W!ld Center........................................................................... 20

Comparison of EPA Method 5, European EN303-5, and CTM–039 Measurements ............... 22

Carbon Monoxide as an Indicator of Polycyclic Organic Matter ............................................. 24

THERMAL EFFICIENCY RESULTS ........................................................................................ 25

Spring 2010 Measurements ...................................................................................................... 25

Additional Measurements during the 2010-11 Heating Season ............................................... 28

Comparison of Emissions from Other Wood Fired Boilers and Heating Equipment .............. 30

EVALUATION OF ADDITIONAL CONTROL TECHNOLOGY ............................................ 37

Introduction .............................................................................................................................. 37

Experimental Methods .............................................................................................................. 37

Results ...................................................................................................................................... 38

Cost Estimates for Adding ESPs to Full-Scale AWC Systems ................................................ 41

SUMMARY.................................................................................................................................. 41

REFERENCES ............................................................................................................................. 43
1 

INTRODUCTION

There is a renewed interest in the use of biomass fuel combustion for residential and small to 

moderate scale commercial heating because of the fluctuating price of fossil fuels and the desire 

to use renewable energy. However, conventional wood burning systems tend to have relatively 

low efficiency and high emissions of CO and particulate matter (Gammie and Snook 2009). In 

Europe, a number of advanced combustion systems have been developed that are reported to 

provide substantially higher thermal efficiency and lower emissions than conventional systems. 

These advanced systems use staged combustion that provide high thermal efficiency and also 

greatly reduced emissions of pollutants from the stack. 

In 2008, the New York State Energy Research and Development Authority (NYSERDA) 

initiated a series of studies on both conventional and high efficiency wood boiler systems. 

Clarkson University has evaluated three two-stage combustion systems that are described in the 

next section. Two of these units were made by Hamont and imported from Austria, while 

Advanced Climate Technologies Bioenergy LLC (ACT) manufactured the other in the U.S. One 

150 kW pellet-fired unit has been installed on the Clarkson campus to provide building heat for 

the Walker Center and has been subjected to continuous monitoring over multiple time periods. 

Clarkson has also conducted stack testing on the same model 150 kW wood chip boiler at the 

ACT facility in Schenectady, NY prior to its installation at the Cayuga Nature Center. In 

addition, Clarkson has organized the stack testing of a 500 kW pellet system with the same 

burner design but manufactured by ACT, that was installed at the W!ld Center in Tupper Lake, 

NY. Clarkson has also examined the potential problems that might be found with the use of 

conventional electrostatic precipitators (ESPs) on advanced wood burners given that these 

systems produce an ash that is essentially all inorganic salts. Such material could result in very 

high ash resistivity that could limit particle removal in an ESP. 

BOILER CONFIGURATIONS

The Hamont CATfire and ACT boilers (150 and 500 kW) utilize a triple air staging process that 

ensures complete combustion of the fuel. Figure 1 shows an illustration of the fuel feed auger, 

ash auger and combustion zones of the Hamont boiler. 

Air staging is accomplished by injecting primary air into the fuel bed at a low air to fuel ratio (λ) 

to devolatilize but not combust the fuel. Secondary and tertiary air streams are injected at higher 

λ values to burn the pyrolysis gases and achieve complete combustion. In order to ensure 

optimum excess air delivery into the different combustion stages, the boiler was equipped with 

an accurate process control system (CO/ λ control system) that varies the λ by measuring CO and 

λ using sensors in the combustion chamber.
2 

During the first stage, the fuel is heated to around 400oC (750oF), and in the second and third 

stages, air is tangentially injected into the combustion zone to reach temperatures up to 1100oC 

(2000oF). Because of good mixing of combustion air with pyrolysis gases, the boiler operates at 

low excess air levels, thus enabling the boiler to operate at higher temperatures in the combustion 

zone with high combustion efficiency (Nussbaumer, 2003). 

Figure 1. Detailed view of fuel feed auger, ash augers, and combustion zones of a Hamont Boiler. 

(Hamont European Operating Manual for CATfire 150-500 kW Wood Boilers).

tertiary zone

secondary zone 

primary zone 

fuel auger

ash augers

Walker Center Boiler

The 150 kW (514,000 BTU h-1) Hamont CATfire, installed at the Walker Center was 

unpressurized since it was not ASME certified. The boiler utilizes a triple air staging 

combustion process, which can lower NOx and PM emissions (Nussbaumer, 1998; Oser & 

Nussbaumer, 2004). The wood pellets used during testing had a calorific value of 8052 

BTU lb-1, a moisture content of 4.8% and an ash content of 0.6%. During the Walker 

measurements, the boiler was tested for different feed rates (45 lb h-1) between 260,000 BTU hr-1

and 630,000 BTU hr-1or 50% to 122% of rated nominal load.

Cayuga Nature Center Boiler

This 150 kW boiler was identical to that installed at the Walker Center except this boiler was

configured to burn wood chips with an operating range of 154,000-514,000 BTU hr-1 output or 

30% and 100% of full load. The fuel for the project was urban wood waste comprised primarily 

of chipped wood pallets. Unlike virgin wood chips, these chips had visible dirt and paint 

contamination. The chips had a 27% moisture content and a heat content of 6111 BTU lb-1

. 

The fuel feed rate was at 48 lb h-1

. 
3 

W!ld Center Boiler

The boiler installed at the W!ld Center is the first ACT boiler made in the U.S. It is an ASME

certified, 1.7 MMBTU hr-1, boiler integrated with a solar hot water system. This system is

expected to supply much of the energy required to heat the 54,000ft2 facility. The boiler used 

wood pellets supplied by Curran Renewable Energy, Massena, NY. Figure 2 is an illustration of 

a commercial size pellet boiler with solar thermal system at the W!ld Center. The average fuel 

feed rate (wood pellets) through the auger feed system ranged between 160 and 416 lb hr-1, and 

the heat input rate ranged between 1.3 and 3.4 MMBTU hr-1. Although loads of 25%, 50%, 75% 

and 100% were targeted, due to very little heat demand during the testing in April 2010 the 

boiler was run at 100% only by artificial manipulation. The measured gross calorific value of 

the pellet was 8059 BTU lb-1. 

Figure 2. Schematics of commercial size pellet boiler with solar thermal system at the W!ld Center. 

Obtained from www.wildcenter.org.
4 

All of these boilers were configured to operate with a CO/ λ control system to optimize 

combustion airflows. This control adjusts the combustion air fan speed based on measured CO 

and O2 levels in the flue gas. The target oxygen level was 8%. However, during the test of the 

150 kW wood chip boiler, the oxygen levels ranged from 10 to 12% indicating that lambda 

control may have not been operating optimally and excess air was flowing through the 

combustion chamber. The boilers were generally operated at 100% load with the inlet and outlet 

water temperatures varying depending on the heat demand from the facility. When the heat 

demand from the building was low, the boiler input and output water set temperatures were 

varied to artificially force the boiler load to 100%. 

Fuel Analysis

Table 1 summarizes the measured properties of fuel used in this work. Measurements were made 

using ASTM standard methods. Wood chips were slightly lower in terms of general fuel quality 

in comparison to wood pellets. Moisture content of wood pellets (about 5%) is much lower than 

the moisture content present in woodchips (about 27%). Sulfur content in woodchips is more 

than two times the sulfur present in wood pellets. Similarly, nitrogen content in chips, although 

low, is more than two times the value present in pellets. The calorific value of woodchips is 

slightly lower than pellets, while W!ld Center pellets show nearly the same heat content as the 

pellets used in the Walker measurements.

Table 1. Analysis of fuel used in emissions measurement in the three boilers tested in this work.

Fuel Property Wood Pellets 

(Walker) – 150 kw 

Wood Chips (ACT 

Bioenergy) – 150 kw 

Pellets 

(W!ld Center) – 500 kw 

Heat Content (MJ/lbs) 8047 6369 8060

Moisture (%) 4.8 27 5.1

Ash (d.w. %) 0.6 1.79 0.6

Carbon (d.w. %) 51.5 45 48.74

Nitrogen (d.w. %) 0.13 0.37 0.15

Sulfur (d.w. ppm) 70.1 175 67.1
5 

MEASUREMENT METHODS

CTM-39 Dilution Sampling System 

Gaseous and PM2.5 (particle matter <2.5 μm) concentrations were measured using a dilution 

tunnel sampling system obtained from Environmental Supply Co., Durham, NC conforming to 

Environmental Protection Agency's (EPA) conditional test method CTM–039. Stack gas was 

drawn isokinetically through an in-stack cyclone to remove particles larger than 2.5 μm and then 

into heated sample lines to prevent wall condensation. The heated sample gas was then mixed 

under turbulent conditions with dehumidified and HEPA filtered ambient air via a mixing cone. 

Dilution ratios of 20−60 were used. Sampling ports located at the end of the mixing chamber

allowed for continuous measurements of carbon monoxide (CO), nitrogen oxides (NOx), sulfur 

dioxide (SO2), PM2.5

Quartz filters, Telfon

, and ultrafine particle number concentrations and size distributions. 

® filters, and polyurethane foam plugs (PUFs) were collected for particle 

characterization and organic compound speciation. Continuous CO, NOx and SO2 measurements 

were taken using ambient gas monitors (Thermo Models 42i, 43i and 48i). Continuous PM2.5

The 142 mm quartz filters were analyzed for organic and elemental carbon (OC/EC) following 

the NIOSH 5040 method (Sunset Laboratories, Tigard, OR), and anions and cations by ion 

chromatography (IC). Organic artefacts from gas-phase adsorption onto quartz filters were 

corrected using a backup quartz filter. Teflon filters (47 mm) were analyzed for trace metals 

using inductively coupled plasma mass spectrometry (ICP-MS). 

mass was determined using TEOM Filter Dynamics Measurement System (FDMS) (R&P Model 

8500b), and ultrafine particle number concentrations and size distributions in the range from 5.6 

to 560 nm were measured using a Fast Mobility Particle Sizer Spectrometer (FMPS) (TSI Model 

3091). 

Quartz filters (142 mm) in series with PUFs were collected and analyzed for organic molecular 

markers, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated dibenzodioxin and 

dibenzofurans (PCDD/Fs) using gas chromatography-mass spectrometry (GC/MS). 

All emission factors and concentrations in this report are average emissions at full load during 

steady-state operation at dry gas standard state conditions (293.34 Kelvin temperature and 101.31 

kPa pressure).

EPA Method 5 and OTM-28 

At the W!ld Center, additional measurements for particulate matter according to the EPA 

Method 5 and OTM-28 were conducted by CK Environmental under contract to Clarkson 

University. Briefly, particulate matter (PM) was withdrawn isokinetically from the stack gas, 

using a sampling apparatus obtained from Environmental Supply Company, Durham, NC. PM 

was collected on an out-of-stack glass fiber filter maintained at a constant temperature (248 ± 
6 

25°F) inside a heating box. The filter was heated to prevent condensation of moisture and 

gaseous compounds. The collected PM mass includes any material that condenses at or above the 

filtration temperature, and is determined gravimetrically. There are no specific load requirements 

for EPA Method 5 testing. Usually, the testing is done at loads between 90 % and 100%, or the 

most probable boiler load. 

After the particulate matter was removed from stack gas using the sampling apparatus described 

above, the stack gas sample stream was passed through dry impingers for measurement of 

condensable particulate matter (organic and inorganic fraction). In this method (OTM-28), the 

stack sample gas passes through a water-jacketed coil condenser, a dry short stem moisture 

dropout impinger, and a dry regular impinger without a bubbler, and then through a Teflon CPM 

filter. The sample gas is maintained at less than 85°F throughout this portion of the sampling 

system. Upon completion of sampling, the sampling train is purged with nitrogen for one hour 

and the components of the sampling train are rinsed with water and organic solvents. The organic 

and inorganic fractions are extracted in the lab, dried and weighed. The sum of these fractions is 

used to calculate the condensable PM mass concentration. The reported emission factors are at 

dry gas standard state conditions (293.34 K temperature and 101.31 kPa pressure).

Thermal Efficiency Measurement Methods

Boiler efficiency was determined using the direct method of dividing the useful heat output of 

the boiler by the energy input of the fuel (equation 1). 

100*

fv

pw

mC

∆TcQ= ρ

η

(1)

Where:

η – Boiler Thermal Efficiency

Qw

ρ – Density of water (kg/L)

 – Volumetric pipe flowrate (L/min)

cp

ΔT – Water temperature difference (°C)

 – Specific heat capacity of water (MJ/kg°C)

Cv

m

 – Gross calorific value of fuel (MJ/kg)

f – Fuel feed rate (kg/min)

Heat input was calculated from the gross calorific value (or higher heating value that takes into 

account the latent heat of vaporization of water) of the fuel and the fuel feed rate into the boiler. 

Gross calorific values were determined using oxygen bomb calorimetry according to STM E711 

(Parr Oxygen Bomb Calorimeter and Calorimetric Thermometer Models 1341 and 6772). 
7 

Fuel feed rates into the 150 kW pellet and chip boilers were determined by hand feeding a 

known quantity of pellets into each boiler’s feed bin and recording the time of consumption. The 

boiler fuel feed system is equipped with a display system to indicate the level of the fuel in the 

feeding bin. The initial fuel level was noted from the display and a known mass of 

pellets/woodchips was fed into the feed bin. The time elapsed for the fuel level to reach the 

initial level was noted and used to calculate the fuel feed rate. Several trials were conducted to 

yield better confidence in the estimated values. The W!ld Center boiler had an automated 

reporting system where a binary value ‘1’ is reported every time the fuel feed system is activated 

and ‘0’ when the feeding system is inactive. Based on real-time measurements and fuel feed rate 

settings on the boiler control system, the fuel feed rate of the W!ld Center boiler was determined.

Heat output from the boiler was determined by the temperature differences and flow rate in the 

output and return water pipe. Temperature was measured with thermocouples connected to a 

portable handheld data logger (Omega DAQPRO-5300). A handheld ultrasonic flow meter with 

type M1 transducers (Shenitch STUF-200H) was used to measure the water flow rate at the 

Walker Center and at the W!ld Center. The water flow rate was not determined for the wood 

chip boiler, so the manufacturer reported flow rate of the pump was used. Figure 3 shows the 

boiler piping and the approximate positions of the thermocouple and flow meter used for direct 

thermal efficiency measurements

Figure 3. Illustration of boiler piping with approximate location of thermocouple and flowmeter.
8 

MEASUREMENT RESULTS

150 kW Hamont wood pellet boiler at the Walker Center 

The emission concentrations and emission factors of CO, NOx, SO2, PM2.5, and particle OC and 

EC from the 150 kW pellet boiler at the Walker Center while it was operating at steady state are 

summarized in Table 2. All measurements were taken while the boiler was running at 72% of 

thermal capacity. The uncertainty values in Table 2 are 95% confidence intervals for the mean 

values. Figure 6 (solid lines) shows the concentration of criteria pollutants emitted by the Walker 

Center boiler when burning wood pellets. 

The ultrafine particle number size distribution during steady state, in Figure 5, is lognormal with 

a peak in the accumulation mode. The geometric mean diameter (GMD) of the distribution was 

89.3 nm, and count median diameter 80.6 nm. The average ultrafine particle number 

concentration for steady state operation was 2.66x107 # cm-3. The emission factor was 1.71x1016

# MMBtu-1. 

NIOSH Method 5040 analyzed eight 142 mm quartz filters for OC and EC, and IC analyzed 

anions and cations. Four 47 mm Teflon filters were analyzed for trace metals by ICP-MS (Table 

3). The particles were found to be composed primarily of inorganic salts (K+ and SO 2-

4 ), which 

have been found to be much less toxic relative to organic based particles (Klippel and 

Nussbaumer, 2007). Potassium (K+) and sulfate (SO 2-

4 ) combined made up 61% of total mass, 

while organic carbon (OC) made up 8% and EC was negligible. Sodium (Na+), chloride (Cl-), 

nitrate (NO -

3 ), and zinc (Zn) were present at low levels. Figure 4 shows the fine PM composition 

of the Walker Center boiler stack emissions when burning wood pellets. 

Figure 4. Pie chart of fine PM composition from stack emission of the Walker Center boiler when 

burning wood pellets at 72% of thermal capacity. 

OC

EC

Na+

K+

Ca+

Mg+

SO 2- 4

ClNO3-

Zn

Unresolved 
9 

Particle and semi-volatile organic compounds were collected on the 142 mm quartz filter in 

series with a PUF plug. These samples were then analyzed by GC/MS. Eight quartz filters and 

six PUFs were collected (Table 4). Because of gas-phase adsorption of organic species onto the 

quartz filters, gas-particle partitioning could not be determined. Most of the n-alkane 

concentrations were low except for C29 and C30 compounds that had the highest concentrations 

of 240 μg m-3 and 160 μg m-3, respectively. Levoglucosan, which has been used as a tracer for 

wood smoke, had the third highest concentration of 80 μg m-3. Polychlorinated dioxins and 

dibenzofurans (PCDD/Fs) were below detection limits (<22 pg m-3).

Table 2. Emissions factors for a 150 kw Hamont staged combustion wood boiler during steady state operation 

at 72% thermal capacity using premium wood pellets tested at the Walker Center, Clarkson University.

Emission Species -3 mg m g/kg -1 lb MMBtu

CO 168 ± 1.76 2.16 0.27

NOx 25.7 ± 0.13 0.35 0.04

SO2 0.47 ± 0.00 6.46 0.001

PM2.5 37.2 ± 0.60 0.47 0.06

* OC 2.23 ± 0.62 0.02 0.004

* EC 0.10 ± 0.05 0.001 0.00

Note: Average emissions at steady state operation. Uncertainty indicated in this table represents the 95% confidence 

interval of the average value. Results are based on 8 aggregated filter samples.
10 

Table 3. Chemical Composition of PM2.5. for 150Kw pellet boiler at the Walker Center. 

Elemental and Organic Carbon (wt % of PM2.5)

NIOSH 5040 OC 7.67 ± 1.69

NIOSH 5040 EC 0.00 ± 0.00

Ionic Species (wt % of PM2.5)

IC + Na 0.18 ± 0.03

IC 4+ NH <0.05

IC + K 40.6 ± 7.22

IC + Mg 0.06 ± 0.04

IC + Ca 0.05 ± 0.07

IC 4- SO 20.0 ± 0.58

IC - Cl 0.44 ± 0.2

IC 3- NO 0.49 ± 0.07

Elemental Species (wt % of PM2.5)

ICP-MS Al -3 <8.57 x 10

ICP-MS As -4 <6.30 x 10

ICP-MS Ba 4.13 x 10-3 ± -5 5.15 x 10

ICP-MS Cd 1.07 x 10-3 ± -5 1.39 x 10

ICP-MS Co -4 <3.29 x 10

ICP-MS Cr 8.69 x 10-4 ± -5 1.57 x 10

ICP-MS Cu ± 0.00

ICP-MS Fe <0.07

ICP-MS Li 4.11 x 10-3 ± -5 2.53 x 10

ICP-MS Mn 0.04 ± 0.00

ICP-MS Ni -3 <1.98 x 10

ICP-MS Pb 0.01 ± 0.00

ICP-MS Rb 0.09 ± 0.00

ICP-MS Tl 1.27 x 10-4 ± -6 2.22 x 10

ICP-MS V 6.93 x 10-5 ± -6 3.06 x 10

ICP-MS Zn 0.15 ± 0.00

Note: Uncertainty values indicated are the 95% confidence intervals
11 

Table 5 shows the stack concentrations and emission factors for 27 polycyclic aromatic 

hydrocarbons (PAHs) when using wood pellets as fuel. Total PAH emissions (34 ng BTU-1

Electrical Mobility Diameter [nm]

1 10 100 1000

dN/dlogDp [cm-3] 

0

20x106

40x106

60x106

80x106

) 

were lower than previous measurements of residential pellet stoves and burners during good 

combustion conditions (Boman et al. 2005; Johansson et al. 2004). The compounds with the 

highest emissions were phenanthrene, pyrene, acenaphthene, fluoranthene, indeno (1,2,3-cd) 

pyrene, and acenaphthylene. 

Figure 5. Ultrafine particle number size distribution during steady state of the boiler at the Walker

Center, Clarkson University. Error bars are one standard deviation.
12 

Table 4. Emissions of total particle and semi-volatile organic functional groups and compounds when using 

wood pellets as fuel. The numbers in parentheses indicate the number of compounds analyzed in each 

functional group. 

Functional Groups/Compounds -3 Total (μg.m ) -1 Total (ng.BTU )

n-Alkanes (31) 539 398

PAHs (27) 48.6 33.7

Aromatic acids (5) 43.6 30.5

Alkanoic acids (22) 86.2 62.7

Dicarboxylic acids (12) 55.8 39.4

Pentacyclic triterpane (hopanes) (5) 64.4 41.3

Cholestane (sterols and cholestenes) (4) 0.64 0.48

Methyloxylated phenols (5) 23.6 16.5

Phytosterols (4) 0.52 0.37

Nonyl aldehyde 15.4 11.4

Squalene 3.44 2.20

cis-Pinonic acid 44.6 31.3

Levoglucosan 77.6 53.0

PCDD/Fs (17) <0.02 <0.02

Note: Numbers in the parentheses represent the number of compounds in each functional 

<b.d. – below detection limit.

* - Value reported is the sum of species measured on the filter and the PUF plug.

Data based on three PUF and three filter samples.

group.
13 

Table 5. Total semi-volatile and particle PAH emission concentrations and emission factors for 

boiler burning wood pellets at the Walker Center. 

a 150 kW 

PAHs Total -3 (μg.m ) -1 Total (ng.BTU )

Naphthalene 1.63 1.11

Acenaphthylene 4.87 3.41

Phenanthrene 8.62 5.75

Fluoranthene 5.24 3.53

Pyrene 5.50 3.68

Benzo[a]anthracene 0.55 0.38

Benzo[k]fluoranthene 1.09 0.75

Dibenz[a,h]+[a,c]anthracene N/F N/F

Benzo[ghi]perylene 0.90 0.64

Anthracene 1.59 1.06

Benzo[b]fluoranthene 0.81 0.57

Indeno[1,2,3-cd]pyrene 4.58 3.42

Chrysene&Triphenylene 1.10 0.76

1-Methylnaphthalene 0.76 0.51

2,6-Dimethylnaphthalene 1.10 0.76

2-Methylanthrancene 0.69 0.45

Retene 1.34 0.96

Benzo[a]pyrene 1.19 0.86

Coronene 0.00 0.00

Benzo[e]pyrene 0.38 0.26

1-Methylpyrene N/A N/A

3-Methylchrysene 0.11 0.07

Indeno[1,2,3-cd]fluoranthene N/F N/F

4-H-cyclopenta[def]phenanthrene 1.17 0.77

Acenaphthene 4.71 3.54

Fluorene 0.71 0.48

Picene N/F N/F
14 

 

150 kW Hamont Wood Chip-Fired Boiler (Cayuga Nature Center) 

Table 6 summarizes the measured average emission factors for NOx, SO2, CO, PM2.5, and total 

organic carbon (TOC). The uncertainty values in the table represent the 95% confidence interval 

of the average value. The CO/CO2 ratio indicative of the extent of combustion in the boiler was 

0.08%, this low percentage indicates that there was almost complete combustion of the fuel. 

Figure 6 (dashed lines) shows the concentrations of criteria pollutants measured during steady 

state operation at 60 and 75% load of boiler for 150 kW boiler burning wood chips and pellets 

respectively. The plot shows very stable concentration of the NOx, SO2, and PM2.5 emitted during 

steady state operating conditions for woodchips and pellets. Carbon monoxide concentrations 

were more variable than the other pollutants for the woodchip boiler. Oxygen concentration 

(percent by volume) ranged between 10 and 12 percent during this measurement. Additional axis 

on the right shows the CO concentration converted to 7% oxygen concentration (volume basis). 

The CO varied between 140 and 200 ppm at 7% oxygen, for the boiler, possibly as a result of the 

variability in the oxygen concentration during these measurements. 

Time (minutes) 

 00 10 20 30

) -3 O Concentration (mg.m

C

300

250

200

150

100

) -3 ncentration (mg.m oC

1000

100

10

1

0.1

) -3 mg. (m

2 O at 7% O

C

CO

400

350

300

250

200

150

NOx

SO2

 PM2.5

Figure 6. Concentration of criteria pollutants (CO, NOx, SO2 and PM2.5) during steady state operation of 150 

kW boiler (at full load). Dashed lines indicate data for wood pellets (Walker Center boiler) and solid line 

indicate data for wood chips (ACT Bioenergy boiler). 
15 

The NOx, and SO2 emission factors when using wood pellets were smaller than when burning 

wood chips. This result is likely because the pellets were a cleaner fuel with less fuel-bound 

nitrogen and sulfur. The PM2.5

Boiler shutdown operation was initiated at 17:30 hours by stopping the fuel feed (Figure 7). The 

PM

 emission factor was also lower when burning wood pellets 

compared with wood chips. This result may be due to the higher ash content of the wood chips, 

three times greater than the pellets. Previous studies have found that higher fuel ash content 

results in higher PM emissions (Johansson et al., 2004; Sippula et al., 2007; Wiinikka and 

Gebhart, 2005). 

2.5 and CO concentration increased during boiler shutdown, while NOx and SO2 decreased. 

CO concentrations remained high (~725 mg.m-3

In the particle phase, TOC is the sum of organic carbon (OC) and elemental carbon (EC). 

Measurements of OC and EC revealed that there were negligible amounts of EC on the filters. 

However, the EC concentration during shutdown operation was 5.8 mg m

) for about 15 minutes even after the boiler was 

completely shutdown. Emissions data during boiler shutdown is available only for the 150 kW 

wood chip boiler. 

-3, and the OC 

concentration was 20.3 mg m-3

Average ultrafine particle size distributions during two trials at steady-state operation and during 

shutdown are shown in Figure 8. During both steady-state periods, the particle size distributions 

were fairly similar with a much higher mean value than during shutdown. The number average 

particle diameter during steady-state operation was 80.2 nm, while the number average particle 

diameter during shutdown was 17.1 nm. 

. 

Of the PAHs measured, phenanthrene and retene had the largest concentrations (1.0 and 2.6 

μg/m3, respectively, Table 7). As indicated earlier, the larger concentrations may be due to the 

incidental amounts of wood chips coated with paint. Most linear alkane concentrations are low 

except for the alkanes with chain length C15 to C20 and especially n-C16 and n-C17 (128 and 

132 μg.m-3, respectively). Table 8 shows the average emission factors of major polycyclic 

aromatic hydrocarbons from the Cayuga wood chip-fired boiler.
16 

Table 6. Average emissions from a high efficiency 150 kW Hamont boiler using wood chips 

as fuel at 60% boiler load. 

Emission Emission Factor (Fuel: Wood Chips)

Species -3 -1 -1 mg m g kg lb MMBTU

CO 138 ± 20.1 (76.7 – 516) 2.13 ± 0.29 (1.08 – 7.77) 0.35 ± 0.05 (0.18 – 1.27)

CO2 (x 18.0 ± 0.72 (15.2 – 21.4) 0.06 ± 0.00 (0.05 – 0.07) 0.01 ± 0.00 (0.008 – 0.011)

104) 

NOx 119 ± 1.88 (106 – 155) 1.84 ± 0.05 (1.54 – 2.33) 0.30 ± 0.01 (0.25 – 0.38)

SO2 1.30 ± 0.02 (1.13 – 1.65) 0.02 ± 0.00 (0.01 – 0.02) 0.004 ± 0.00 (0.003 – 0.006)

PM2.5 38.4 ± 0.9 (35.8 – 41.3) 0.54 ± 0.05 (0.39 – 0.69) 0.11 ± 0.02 (0.06 – 0.16)

(0.003 – 0.002) 0.00 ± 0.003 (0.02 – 0.01) 0.00 ± (1.16 – 0.70) 0.17 ± 0.97 ٭TOC

Note: Average emissions at steady state operation. Uncertainty indicated in this table represents the 95% confidence 

interval of the average value. Data in parenthesis indicate the range (minimum - maximum) measured during full 

load operation.

٭- Data based on three aggregated filter samples. TOC is OC plus EC

Time

 16:54 17:04 17:14 17:24 17:34 17:44 17:54

CO Concentration (mg.m-3)

10

100

1000

10000

Concentration (mg.m-3) 0.001

0.01

0.1

1

10

100

1000

100

1000

10000

CO

NOx

SO2

 PM2.5

Figure 7. Concentration of criteria pollutants (CO, NOR

xR, SOR2R and PMR2.5R) during shutdown of Hamont 

boiler burning wood chips. Boiler shutdown was initiated at 17:30 hours.
17 

Figure 8. Average particle size distribution at full load during steady state operation and during boiler 

shutdown. Error bars in this figure are one standard deviation.

Electrical Mobility Diameter (nm)

5 10 50 100 500

dN/dlogDp [cm-3]

0

20x106

40x106

60x106

80x106

100x106

dN/dlogDp [cm-3] (Boiler Shutdown)

0.0

1.0x109

2.0x109

3.0x109

4.0x109

Steady State Trial 1

Steady State Trial 2

Boiler Shutdown
18 

Table 7. Full load average emissions of selected aromatic compounds from a high efficiency wood boiler using 

wood chips as fuel.

Compound Total -3 (μg m ) -1 Total (ng BTU )

n-Alkanes (31) 310 375

PAHs (27) 34.8 44.4

Aromatic acids (5) N/F N/F

Alkanoic acids (22) 41.3 49.6

Dicarboxylic acids (12) 5.06 6.07

Pentacyclic triterpane (hopanes) (5) 0.22 0.26

Cholestane (sterols and cholestenes) (4) 0.72 0.86

Methyloxylated phenols (5) 10.9 13.7

Phytosterols (4) 4.46 5.33

Nonyl aldehyde 0.01 0.02

Squalene 38.0 45.4

cis-Pinonic acid 0.13 0.15

Levoglucosan 38.0 45.4

PCDD/Fs (17) <b.d. <b.d.

<b.d. – below detection limit.

* - Value reported here is the sum of species 

three filter samples.

measured on the filter and the PUF plug. Data based on three PUF and 
19 

Table 8. Full load average emissions of selected aromatic compounds from a two-stagewood boiler 

using wood chips as fuel.

Compound Total* Total* Total*

Phenanthrene 1.01 0.02 2.78

Fluoranthrene 0.33 0.01 0.93

Pyrene 0.3 0.01 0.85

Benzo[a]anthracene 0.00 0.00 0.01

Benzo[k]fluoranthrene 0.04 0.00 0.15

Dibenz[a,h]+[a,c]anthracene 0.00 0.00 0.00

Benzo[ghi]perylene 0.03 0.00 0.08

Anthracene 0.14 0.00 0.37

Benzo[b]fluoranthrene 0.09 0.00 0.29

Indeno[1,2,3-cd]pyrene 0.00 0.00 0.00

Chrysene&Triphenylene 0.07 0.00 0.23

1-Methylnaphthalene 0.65 0.01 1.84

2,6-Dimethylnaphthalene 0.30 0.01 0.84

2-Methylanthracene 0.36 0.01 1.07

Retene 2.63 0.05 7.91

Benzo[a]pyrene 0.00 0.00 0.00

coronene 0.00 0.00 0.00

Benzo[e]pyrene 0.04 0.00 0.12

1-Methylpyrene 0.05 0.00 0.14

3-Methylchrysene < b.d. < b.d. < b.d.

Indeno[1,2,3-cd]fluoranthrene 0.00 0.00 0.00

4-H-cyclopenta[def]phenanthrene 0.05 0.00 0.12

<b.d. – below detection limit

* - Value reported here is the sum of species 

three filter samples.

measured on the filter and the PUF plug. Data based on three PUF and 
20 

500kW ACT pellet boiler at the W!ld Center 

Figure 9 shows the concentration of criteria pollutants measured during operation at 100% load 

of boiler for a 500 kW boiler burning wood pellets. Table 9 gives the full load average emission 

factors of the 500 kW boiler at the W!ld Center. Table 10 compares the measurements conducted 

using EPA Method 5 using a glass fiber filter and the CTM−039 using a dilution sampling 

system. Comparison of particulate matter measurements from these two methods indicate that 

the EPA Method 5 measurements are about 11% higher than the CTM−039 dilution sampling 

measurement with Teflon filters. 

Although loads of 25%, 50%, 75% and 100% were targeted, it was only possible to run the boiler 

at 100% by artificial manipulation because of the very low heat demand during April 2010. In 

order to force the system to operate, it was necessary to operate under non-steady state 

conditions. The boiler operates to meet a set output water temperature (usually 90°C). Once this 

temperature is attained, the boiler automatically modulates the fuel feed rate to maintain that 

temperature. For the higher fuel feed rates, the boiler was easily reaching the set temperature 

and then reducing the fuel feed rate. In order to maintain the boiler running at 100% of the set 

feed rate, the output water temperature setting was manipulated to ~60°C, which effectively shut 

off the boiler. Once the water temperature dropped to 60°C, the required water temperature was 

raised to 90°C, at which point the boiler started feeding pellets at 100% of the set fuel feed rate. 

The boiler then ran at 100% of the set fuel feed rate until the output water temperature reached 

90°C. The thermal efficiencies were estimated during this period of full feed rate operation.

Method 5 captures total particulate matter, while CTM−039 was sampled using an in-stack 2.5 

μm cyclone. The calorific value of the fuel obtained from the measurements at Clarkson was 

8060 Btulb-1

To quantify the mass of PM collected in the in-stack PM

 was used in the dilution method (CTM–039) and EPA Method 5 calculations. 

2.5 cyclone during the CTM–039 

measurements, the particles were dissolved in hexane, dried and weighed. The estimate PM 

concentration collected in the cyclone for the first measurement on April 20, 2010 between 9:23 

and 11:20 was 9.4 mg m-3. Thus, the total PM collected during this measurement was 118.41 mg 

m-3 from the Teflon filter measurement and 100.9 mg m-3

The boiler during our second and the third measurement (in Table 10) was mostly operating in an 

unsteady state. Since Method 5 is an aggregated filter measurement, the operator was unable to 

turn off the system during this unsteady boiler operation and, therefore, kept the measurement 

system running. The CTM−039 measurement system and the TEOM FDMS system were turned 

off temporarily to protect the instrument from these large fluctuations in the PM emissions. 

Therefore, the PM emissions during these fluctuations are not included in the reported values 

from the CTM−039 method, leading to the large discrepancy in the measured values.

from the TEOM FDMS measurement 

system. The difference in the result, therefore, is about 3.7 % and 17.9% from the Teflon filter 

and TEOM FDMS system, respectively. 
21 

Table 9. Full load average emissions from the ACT 500 kW wood boiler at W!ld Center using wood

pellets as fuel.

Emission Species -3 mg m -1 g kg -1 lb MMBTU

CO 1182 ± 64.11 7.63± 0.58 1.21 ± 0.09

CO2 96.74 ± 13.82 0.26±0.04 0.03 ± 0.00

NOx 72.06 ± 0.79 0.421±0.015 0.07 ± 0.00

SO2 0.92 ± 0.01 0.0049±0.0002 0.0007 ± 0.00

PM2.5 55.50 ± 5.55 0.473±0.051 0.06 ± 0.01

Condensable PM 5.22 ± 0.46 0.044±0.04 0.004 ± 0.00

0.00 ± 0.01 0.08±0.02 0.29 ± 2.27 ٭TOC

Note: Average emissions at steady state operation. Uncertainty indicated in this table represents the 95% confidence 

interval of the average value. Condensable PM was measured using EPA OTM -28.

٭- Data based on three aggregated 142 mm filter samples.

Table 10. Comparison of particulate 

Dilution Method CTM−039.

matter concentration measurements by EPA Method 5 and 

FPM PMR

2.5 FPM PMR2.5

Sampling Date/Time -3 (mg m ) -3 (mg m ) (lb MMBTU-1) (lb MMBTU-1) 

Method 5 CTM–039 Method 5 CTM–039 

4/20/10 09:23 – 11:20 123.0 109.01(1) 91.50(2) 0.07 0.07(1) 0.06(2)

4/20/10 13:23 – 14:29 121.6* 57.29(1) 45.30(2) 0.11 0.06(1) 0.05(2)

4/21/10 8:52 – 11:12 93.8 38.34(1) 58.04(2) 0.10 0.06(1) 0.08(2)

FPM – Filterable particulate matter, PMR

2.5R – particulate matter with particles less than 2.5μm aerodynamic

diameter.

*-Data collected using an in-stack PMR

2.5R cyclone.

Data collected using Teflon filter, averaging time was typically about one hour.

Data collected using TEOM FDMS system.

P P P P P P P P

P P P P

P P P P

P P P P
22 

Time

 09:20 09:30 09:40 09:50 10:00

CO Concentration (mg.m-3)

1000

10000

Concentration (mg.m-3) 0.001

0.01

0.1

1

10

100

1000

CO

NOx

SO2

 PM2.5

Figure 9. Concentration of criteria pollutants (CO, NOx, SO2 and PM2.5) during steady state 

operation of 500 kW boiler (at full load).

Comparison of EPA Method 5, European EN303-5, and CTM–039 Measurements

Table 11 compares previously reported European emissions measurement results with all the 

results of the EPA test methods (CTM–039 and EPA Method 5) measurements. The CTM−039 

is a dilution method, where the stack gas is diluted with HEPA filtered ambient air; whereas the 

EPA Method 5 does not dilute the stack gas. The EN303-5 measurement method is typically 

conducted for boilers up to 300 kW load using solid fuels such woodchips, pellets, coal and 

coke. EN303-5 prescribes a maximum water temperature of 212°F and a maximum water 

pressure of 5.9 atmospheres. EN303-5 method includes two tests at nominal load and one test at 

50% of nominal load. The EPA Method 5 measurements are typically done at 90% to 100% 

capacity of the boiler with no prescribed water temperature and pressure. 

The European measurement results show much lower emissions of PM (reported as dust) and 

emissions gases such as CO, NOx and CO2 in comparison to the emission measurement results 

from the EPA methods (CTM–039 and Method 5). The European emissions factors report dust 

as total PM (TSP).
23 

Several possible reasons can be hypothesized for the higher emission factors for certain species 

reported here, in comparison to the European measurements. There could be differences in fuel 

quality for both wood chips and pellets between the U.S. and Europe. Mill chips used in the 

European measurements did not include pine needles and wood bark that was present in the 

wood chips used in the ACT Bioenergy boiler tests. A small proportion of wood chips was found 

to be coated with paint. Moreover, measurements at the W!ld Center were conducted in midApril when there was little heat load on the system given relatively high ambient temperatures. 

In order to force the system to operate, it was necessary to operate under non-steady state 

conditions where the boiler load was modulating depending on the variability in the heat demand 

from the W!ld Center facility.

Table 11. Comparison of European measurements with dilution tunnel CTM–039 and EPA Method 5.

Pollutant

European Measurements 1 CTM–039 EPA 

2 Method 5 

150 kW 

(Pellets)

150 kW 

(Woodchips) 

500 kW 

(Pellets)

150 kW 

(Pellets)

150 kW 

(Woodchips) 

500 kW 

(Pellets)

500 kW 

(Pellets)

-3 PM (mg.m ) 25 44 13 37 38 56 108

PM (lb/mmBTU) _ _ _ 0.06 0.11 0.07 0.07 

CO -3 (mg.m ) 42 111 140 168 138 1182 -

CO @ 7% O2(ppm) 182 113 143 224 168 1015 _ 

NOx -3 (mg.m ) 136 153 135 26 119 72 -

ηeff (%) 85 83 87 72 72 80 -

Note: European measurements for PM indicated here was reported as dust by Hamont

O2 concentration (percent by volume) was 10% for European measurements and was between

CTM–039 and Method 5 measurements. 

CTM–039 measurements are averages of at least 8 hours of measurements.

EPM Method 5 are averages of about 2 hour aggregated filter measurements.

Efficiency measurements based on higher heating value at 100% load.

10 and 12% for 

The PM2.5 mass concentrations reported here include non-volatile and condensed volatile species 

because of the dilution with filtered air. Dilution sampling may slightly increase the reported 

PM2.5 concentration. However, based on the TEOM FDMS measurements (Raja et al., 2009), 

and the condensable fraction obtained from OTM-28 for W!ld Center boiler, this process is not 

expected to increase the reported value by more than 3%. The ash content in wood chips was 
24 

Figure 10. Relationship between seven selected POM compounds with CO 

in the stack emissions.

1.6% and the moisture content was 27%. The ash content and the moisture content in the wood 

pellets being combusted at Clarkson were 0.6% and 4.8%, respectively. The fly ash had an OC 

content of 0.09 gram per gram of ash, while the fuel had average OC content of 0.28 gram per 

gram of wood pellet. 

Carbon Monoxide as an Indicator of Polycyclic Organic Matter 

 As part of the US EPA’s proposed National Emission Standards for Hazardous Air Pollutants 

for Area Sources: Industrial, Commercial, and Institutional Boilers (EPA, 2010), EPA is trying 

to control mercury emissions from coal-fired area source boilers and the proposed emission 

standards for control of polycyclic organic matter (POM) emissions. The proposed emission 

standards for control of mercury emissions from biomass-fired and oil-fired area source boilers 

and for other hazardous air pollutants are based on EPA’s proposed determination as to what 

constitutes the generally available control technology or management practices. However, the 

rules actually do not require measurement of POM in the emissions. The EPA is proposing to 

regulate CO as a surrogate for the emission of POM based on seven specific POM species 

(benzo[a]anthracene, chrysene+triphenylene, benzo[b]fluoranthene, benzo[k]fluoranthene, 

indeno[1,2,3-cd]pyrene, dibenz[a,h]+[a,c]anthracene, benzo[a]pyrene) (EPA, 2010). 

Measurements on conventional boilers suggest there is a reasonable correlation between CO and 

POM. Figure 10 shows the correlation between the sums of the 7 POMs with CO for the three 

high efficiency boilers tested in this study. It can be seen that there is no significant relationship 

among these values for these boilers. 
25 

THERMAL EFFICIENCY RESULTS

Spring 2010 Measurements

Table 12 shows the type of fuel used, energy input rate, energy output rate (by direct method 

calculation), boiler load capacity as percent of the input rate, and the calculated thermal 

efficiency for the three boilers tested between spring 2009 and spring 2010. The results are 

plotted in Figures 11 and 12. 

The efficiency of the boilers at the three locations ranged from a low of 61% and a high of 91% 

over a boiler thermal capacity at 50% to 101% (Table 12). The lowest feed rate (57.1%) was the 

manufacturer’s recommended lowest feed rate. Efficiency ranged from 72−77% when the boiler 

was running at steady state at the Walker Center, and from 61−62% when the boiler was 

manipulated to run at 100% of the set fuel feed rate (Figures 11 and 12). 

Most of the W!ld Center tests were run by manipulating the run as described above. However, 

this approach may have resulted in lower efficiencies than operating under actual steady-state 

conditions. The one steady-state run did result in a higher thermal efficiency value. Additional 

tests are recommended during the next heating season when the ambient temperatures are lower 

and there is a real load on the boiler.

Similarly, for the three highest fuel loads at the Walker Center in the spring of 2010 (86%, 87% 

and 101% of boiler capacity), the boiler was also not operating at steady state and the procedure 

of manipulating the output water temperature setting outlined previously was employed. 

The average difference in inlet and outlet water temperatures (ΔT) were about 8°F during the 

Walker Center measurements, 10°F during the Cayuga boiler measurements, and 18°F during the 

W!ld Center measurements. Although the ΔT (in °F) during the W!ld Center measurements was 

nearly two times of the ΔT measured during the Walker Center measurements, the average 

estimated thermal efficiencies during these measurements were nearly the same (~ 64%). The 

larger ΔT in the W!ld Center boiler is most likely due to the larger capacity of the boiler (500 

kW) and a higher fuel intake rate.
26 

Table 12. Thermal efficiency of the 150 kW Hamont and 500 kW ACT 

with different fuels. 

boilers at different heat inputs and 

Test Period Fuel Input rate (kW) Output rate (kW) Boiler Capacity (%) ηthermal (%)

Spring 2011 pellets 182 125 36 68# ± 3

Spring 2011 pellets 202 152 40 75# ± 1

Spring 2011 pellets 271 212 54 78# ± 3

Spring 2011 pellets 330 279 66 84# ± 2

Spring 2011 pellets 404 360 81 89# ± 2

Spring 2011 pellets 459 420 92 91# ± 1

Spring 2011 pellets 88 77.1 59 73#± 4

Spring 2011 pellets 104 64 69 79# ± 3

Spring 2011 pellets 122 77 81 82# ± 3

Spring 2011 pellets 147 91 98 86# ± 2

Spring 2010 pellets 620 448 - 66* ± 2

Spring 2010 pellets 379 303 76 80*# ± 2

Spring 2010 pellets 694 458 - 66* ± 1

Spring 2010 pellets 476 309 95 65* ± 6

Spring 2010 pellets 107 77.1 71 72* ± 4

Spring 2010 pellets 129 80.1 86 62* ± 4

Spring 2010 pellets 131 81.7 87 62* ± 4

Spring 2010 pellets 152 92.8 101 61* ± 4

Spring 2009 chips 86 62.2 57 72# ± 5

Spring 2009 pellets 114 86.9 76 77# ± 7

Note: Uncertainties indicated here are the 95% confidence intervals.

* - Boiler manipulated to run at 100% of selected feed rate, non-steady state.

# - Boiler operated at steady state conditions. 
27 

Boiler Input (% full load)

40 60 80 100

Boiler Efficiency (%)

0

20

40

60

80

100

Walker 2010

Walker 2009

Cayuga 2009

Wild Center 2010

Walker 2011

Wild Center 2011

Figure 11. Thermal efficiency of the Walker Center, ACT Bioenergy and W!ld Center boilers using the 

gross calorific value with 95% confidence intervals. The data points with red edges indicate data when the 

boiler was manipulated to run at 100% of the selected feed rate.

Figure 12. Comparison of thermal energy input rate and output rate of the Walker Center, ACT Bioenergy 

and W!ld Center boilers (input rate calculated using the gross calorific value). The data points with red edges 

indicate data when the boiler was manipulated to run at 100% of the selected feed rate.

Output rate (kW)

0 100 200 300 400 500

Input rate (kW)

0

200

400

600

800

1000 Walker 2010

Walker 2009

Cayuga 2009

Wild Center 2010

Walker 2011

Wild Center 2011
28 

There could be several reasons to explain these estimated lower thermal efficiencies. The studies 

at the W!ld Center in mid-April were at a time when there was little heat load on the system 

given relatively high ambient temperatures. Based on the available information, the estimated 

lower thermal efficiencies at W!ld Center are expected to be most likely due to lower heat 

demand. Low heat demand from the W!ld Center facility may have also resulted in large 

fluctuations in boiler operations. Similar artificial manipulation of the boiler to run at 100% may 

be the most probable reason for lower estimated thermal efficiencies during the Walker Center 

measurements. Other factors that may have contributed to lower thermal efficiencies are 

currently being evaluated.

Additional Measurements during the 2010-11 Heating Season 

Over the 2010−2011 heating season, it was possible to collect additional thermal efficiency data 

on the Walker Center and W!ld Center boilers under normal operating conditions. The external 

heat exchanger for the boiler at the Walker Center was insulated to avoid the heat losses. 

Because of the continuous monitoring system at the W!ld Center, there was substantially more 

data available on hourly basis that was averaged for 24 hours, than was collected manually at the 

Walker Center which was an average of four hours at each load. Both the Walker Center 

(70−86%) and W!ld Center boilers (68%−91%) had similar thermal efficiency ranges at the 

various energy input rates (% full load) tested. Boiler input and output energy were linearly 

related (Figure 13) and efficiency increased with input rate (Figure 14). The maximum 

efficiency measured was about 86% for the 150 kW pellet boiler and 91% for the 500 kW pellet 

boiler (Figure 14). The measured efficiencies were in good agreement with European 

measurements of the same model boilers (Figure 14). 
29 

Input (kW)

0 100 200 300 400 500 600

Output (kW)

0

100

200

300

400

500

Input (kW)

0 20 40 60 80 100 120 140 160 180

Output (kW)

0

20

40

60

80

100

120

140

160

(a) Walker Center (b) Wild Center

Figure 13. Thermal energy input rate and output rate of (a) the 150 kW pellet-fired boiler by Hamont tested 

at the Walker Center and (b) 500 kW ACT pellet-fired boiler tested at the W!ld Center (input rate calculated 

using the gross calorific value). 

Figure 14. Thermal efficiency of (a) 150 kW Hamont pellet boiler tested at the Walker Center and (b) 500 kW 

ACT pellet boiler tested at the W!ld Center boilers for various energy inputs. 

Thus, when these systems are operating in a normal fashion during the heating season, they show 

a much more consistent pattern of thermal efficiencies with the two boilers behaving similarly. 
30 

Comparison of Emissions from Other Wood Fired Boilers and Heating Equipment

Emissions from residential wood fireplace and stoves, and other commercial boilers burning dry 

and wet wood residue are compared with the measurements from this study presented in Table 

13. Emission factors for commercial boilers listed here burned wood residue generally in the 

form of hogged wood, bark, sawdust, shavings, chips, mill rejects, sander dust, or wood trim 

(EPA, 2008). Emissions measured in this study are lower than other commercial boilers and 

burners. Data from NESCAUM, (2008) show that PM emissions from a U.S. conventional wood 

chip boiler equipped with a cyclone has an emission factor of 0.20 lb MMBTU-1 which is 

roughly 50% higher than the average PM2.5 emissions from the boiler in the present study (0.11 

lb MMBTU-1

Tables 14a and 14b compares the emissions factors from England, 2004 for oil-fired boilers and 

McDonald, 2009 for several pellet stoves, with the emissions determined in the present work. 

The wood stove studies from McDonald, 2009 is mostly residential scale appliances, which is 

smaller when compared to the current study. The PM

).

2.5 and NOx emission factors are higher 

than the emission factors reported in the measurements from the delta site reported by England, 

2009, and from pellet stove emissions reported by McDonald, 2009. However, the 150 kW 

boiler-burning pellets have somewhat similar NOx emissions as the pellet stove. The SO2

Table 14 also reports the thermal efficiencies of the boilers tested in the present work. These 

values were higher than the efficiency typically reported for other pellet stoves. In addition to the 

direct measurement of the efficiencies, it was possible to use an indirect method to assess the 

efficiency of the W!ld Center boiler. The indirect method (BEE, 2008) is a theoretical 

estimation where the efficiency is calculated from the estimated total losses resulting from (1) 

dry flue gas, (2) moisture content of the fuel, (3) radiation and convection, and (4) partial 

conversion of C to CO and subtracting from 100% efficiency. It is calculated as: 

emission factors, on the other hand, are lower from the present work in comparison to the oilfired boiler (England, 2009) and in pellet stoves (McDonald, 2009). 

(% efficiency)indirect = 100 – (loss due to Dry Flue gases + Loss due to Moisture in fuel + Loss 

due to Radiation and Convection + Loss due to Partial conversion of C to CO) 

There was good agreement between the direct and indirect method estimates of the W!ld Center 

500 kW boiler efficiency. 
31 

Table 15 compares the particulate matter emissions from the two 150 kW and 500 kW boilers 

tested in this work with five wood fired boilers operating in Vermont, New Hampshire and 

Rhode Island. The capacity of these boilers range between 5.7 and 16.8 MMBTU per hour, while 

the boilers tested here were two 0.5 and one 1.7 MMBTU per hour boilers. The particulate 

matter emission factors of the boilers tested in the present work are clearly lower than the high 

capacity boilers greater than 10 MMBTU per hour. The Ponaganset High School boiler (9.1 

MMBTU/hr) is a closely coupled gasifier system equipped with multiclones. It was the only 

boiler that had low emissions of PM compared to the other boilers tested in this work. 

The Walker Center boiler emissions of carbonaceous derived species (CO, OC, EC, PAHs, and 

organic compounds) during steady-state operation were all relatively low due to near complete 

combustion. The emissions of all of these species were comparable to testing when using wood 

chips, so fuel quality variability for the fuels used in this study does not seem to affect 

combustion conditions significantly. PM2.5 was found to be comprised primarily of inorganic 

salts (K+

 and SO4

2-), which have a lower toxicity than organic-based particles. NOx, SO2, and 

PM2.5 were lower using wood pellets than wood chips, which is most likely due to the better 

quality of the fuel.
3

2

Table 13. Criteria emissions from various types of wood-fired burners and boilers.

Emission 

Species

Residential: Commercial: This study: This study: This study:

Emission factors

(Deangelis et al., 1980) 

Emission factors

(EPA, 2008) 

150 kW Wood Chips 150 kW Pellets 500 kW Pellets 

Fireplace

(g/kg)

Wood Stove 

(g/kg)

Wet Wood

(lb/mmBTU)

Dry Wood 

(lb/mmBTU)

Wood 

Chips 

(g/kg)

Wood

Chips 

(lb/mmBTU)

Wood 

Pellets 

(g/kg)

Wood

Pellets 

(lb/mmBTU)

Wood 

Pellets 

(g/kg)

Wood

Pellets 

(lb/mmBTU)

PM ● 13 ● 9.1 ♦ 0.350 ♦ 0.300 * 0.54 * 0.112 0.47 * 0.060 0.47 * 0.06

SO2 0.2 0.2 0.025 0.025 0.02 0.004 0.0065 0.001 0.005 0.001

NOx 2.0 0.49 0.220 0.490 1.84 0.302 .35 0.040 0.42 0.07

CO 67 180 0.600 0.600 2.13 0.348 2.16 0.270 7.62 1.21

*

♦ 

●

– 

– 

– 

measurements include only particles with diameters less than 2.5μm, cyclone used for PM control

multiclones used in series for PM control

no controls for PM
3

3

Table 14a. Comparison of emission factors of criteria pollutants from No. 6 Oil fired boiler (England, 2004) and from advanced wood combustion 

systems (this work).

Emission Site: Delta (Oil) Pellet Stove (average) 150 kW 150 kW 500 kW

Species (England, 2004) (McDonald, 2009) (Wood Chips) (Pellets) (Pellets)

lb/MMBTU 3 mg/m lb/MMBTU ppm lb/MMBTU ppm lb/MMBTU ppm lb/MMBTU ppm

PM2.5 0.016 - 0.058 - 0.112 - 0.06 - 0.06 -

SO2 0.033 - 2 0.004 0.7 0.001 0.3 0.001 0.3

NOx 0.182 - 33 0.302 131 0.040 32 0.070 58

CO - 128 149 224 1015

Efficiency (%) 

(Direct method) - 69 72 72 80 

Efficiency (%)

(Indirect 

method) 

- -- - 82 
Table 14b. Comparison of emissions from residential wood stoves and commercial size wood boiler.

Appliance type Scale Over Feed Drop down Electric Gasification unit

feed ignition

lbs/MMBtu

* PM2.5 Emissions Stoves I Residential 0.065 0.09 0.056 -

* Stoves J 0.047 0.056 0.051 -

* Stoves K 0.056 0.052 0.049 -

CAT 150kW Commercial 0.06

CAT 500kW

*BNL -91286-2009, Roger. J. McDonald

0.06

3

4
35 

Table 15. Comparison of PM emissions from ACT Bioenergy boilers with five wood fired boilers operating in Vermont, 

New Hampshire and Rhode Island.

Boiler Location Boiler type

Particle Control 

Technology 

(removal %)

Fuel Type EPA Test 

Method

Capacity 

(MMBTU/hr)

Filterable PM

(lb MMBTU-1) 

Condensable PM

(lb MMBTU-1) 

ACT Bioenergy (this 

work)

Ithaca, New York

Hamont,

Gasification Cyclone Wood chip CTM – 039 0.5 * 0.11 - 

Walker Center (this 

work)

Potsdam, New York

Hamont,

Gasification Cyclone Wood 

Pellets CTM – 039 0.5 * 0.06 - 

W!ld Center Museum 

(this work)

Tupper Lake, New York 

ACT,

Gasification Cyclone Wood 

Pellets CTM – 039 1.7 * 0.06 - 

W!ld Center Museum 

(this work)

Tupper Lake, New York 

ACT,

Gasification Cyclone Wood 

Pellets

Method – 5 

OTM – 28 

1.7 0.09 0.004 

Bennington College

1 Bennington, Vermont 

AFS,

(stoker)

Two multicyclones

(61%) 

Whole tree

Hardwood 

chips 

Method – 5 

OTM – 28 

16.8 0.35 0.031 

Brattleboro High School

1 Brattleboro, Vermont 

Messersmit

h, 

Stoker

Core separator

(57%) 

Millend 

Wood chip 

Method – 5 

OTM – 28 

10.0 0.16 0.011 
Champlain Valley Union 

High School 

1 Hinesburg, Vermont 

Messersmit

h, 

Stoker

Single cyclone

(38) 

Millend 

Wood chip 

Method – 5 

OTM – 28 

6.5 0.17 0.012 

Crotched Mountain 

Rehab. Center Greenfield, 1 New Hampshire

Messersmit

h, 

Stoker

Baghouse and 

multi-cyclone 

(83%) 

Bolewood 

Wood chip 

Method – 5 

OTM – 28 

5.7 0.07 0.012 

Ponaganset High School

North Scituate, Rhode 1 Island

Chiptec 

closely-

coupled 

gasifier

High efficiency 

Multi-cyclone 

(23%) 

Millend

Hardwood 

chip 

Method – 5 

OTM - 28 

9.1 0.05 0.007 

* - 1

 – 

Particulate Matter less than 2.5 microns in size.

Data obtained from Gammie and Snook, 2009. 

36 
37 

EVALUATION OF ADDITIONAL CONTROL TECHNOLOGY

Introduction

Given the potential impact of wood combustion on local air quality and public health, it may be 

desirable to control emissions from advanced wood combustion (AWCs) systems using 

conventional electrostatic precipitator (ESP) particularly in applications such as schools and 

other facilities where susceptible populations are exposed to the boiler effluent. The process 

operating conditions significantly influences the performance of an ESP in terms of its collection 

efficiency. In particular, the resistivity of the fly ash to be collected, that is dependent on the 

chemical composition of the stack upstream of the ESP, is an important parameter that 

determines the ESP effectiveness. Ash resistivity is a measure of the resistance of the collected 

ash layer to the flow of electrical current. Particles with too high a resistivity (>1011 ohm-cm) 

cause problems in the ESP as they build a layer of insulation over the collection plates inhibiting 

the effective collection of particles. On the other hand, particles with too low a resistivity (<104

ohm-cm) may not get collected or quickly lose their charge after being collected and potentially 

re-entrain into the effluent stream. ESPs operate effectively when the particle resistivity is within 

the range of 107

 to 1011

Particles in the stack are reportedly inorganic salts with essentially no organic material; 

 ohm-cm. Ash resistivity may be problematic for ESPs installed on AWC 

boilers because: 

Inorganic salts possess very high resistivity if they are devoid of water. However, combustion of 

the biomass fuel could produce varying relative humidity in the stack gas depending on the stack 

temperature. The inorganic particles could then deliquesce into high ionic strength solutions (low 

resistivity). In addition, the presence of liquids on the collection plates would be problematic 

because it can cause short circuits and corrosion; and 

Wood pellets or wood chips used in AWC systems are typically low sulfur fuels. Although these 

fuels provide low SO2 emissions, the potential problem of high ash resistivity may be important 

since resistivity generally increases as the ratio of sulfur to ash content decreases.

Experimental Methods

The ESP used in this study is a two-stage device that was originally designed for the differential 

mass measurement of ambient particulate matter mass (Patashnick et al., 2001; Yi et al., 2004). 

The ESP unit was tested in the laboratory before installation on the wood pellet boiler. Stack gas 

sampling was performed using an EPA conditional test method (CTM–039) (EPA, 2004). 

Particle number concentrations and size distributions were measured using a scanning mobility 

particle sizer (SMPS) for particles with mobility diameters (dm) in the size range of 0.01–0.64 

μm. For particles with aerodynamic diameters (da) in the size range of 0.7–10 μm, an 

aerodynamic particle sizer (APS) was used. Different boiler load conditions representing high, 
38 

medium and low thermal inputs were tested. High, medium, and low thermal inputs represented 

input rates of 147, 103, and 76 kW. The thermal input was determined as a function of the fuelfeeding rate and the fuel quality. During all the tests, the average stack gas temperature was 126 

± 6oC while the exhaust gas temperature was 29.4 ± 2.5oC. The average moisture fraction of the 

stack gas was about 3.5 ± 1.2 % H2

The ESP was installed downstream of the dilution sampling train but before the particle 

measurement instruments. The ESP was alternately switched on (energized) and off (deenergized) to determine its collection efficiency. An estimate of the resistivity of the ash 

collected by the ESP was made based on the Bickelhaupt’s model.

O (by volume). 

5

 All test runs were conducted 

at an average exhaust relative humidity of about 7% and were repeated at least three times at 

each boiler load.

Results

Estimates of fly ash resistivity from the Bickelhaupt’s model (Bickelhaupt, 1979) revealed that 

the resistivity of the fly ash was about 3x1010 ohm-cm at 120o

C (Figure 13). The Bickelhaupt’s 

model predicts that the resistivity would be lower (~ 109 ohm-cm) at lower temperatures and 

highest (~ 2x1012 ohm-cm) at about 250o

C. The model results indicate that ash resistivity would 

not be a major problem for the ESP installed on the boiler, especially if the stack gas temperature 

is less than 200o

C.

Figure 13. Ash resistivity as predicted from the Bickelhaupt’s model

 

Temperature (oC)

100 200 300 400 500 600

Predicted Resistivity (ohm-cm)

1e+9

1e+10

1e+11

1e+12

1e+13
39 

Table 16 shows the total number concentrations, the geometric mean diameters and the total 

collection efficiencies based on the number concentrations measured by the SMPS and the APS. 

The average collection efficiency of the ESP was approximately 98% for particles < 0.7 μm and

99% for particles in the size range of 0.7–10 μm. The total number concentration of the 

particulate matter emitted from the boiler was about 3x107 #/Ncm3

Table 17 shows the total mass concentrations as estimated from the SMPS and APS data 

assuming spherical particles and an effective particle density of 2 g/cm

 at low load and increased by 

about 40% when the boiler load was increased from low to high. 

3

. The total mass 

concentration upstream of the ESP was between 160–285 mg/Nm3

Table 16. Total number concentrations, geometric mean diameters and number efficiencies for the ESP 

measured with the SMPS and APS instruments.

 with particles of size 0.7 – 10 

μm accounting for about 30–50% of the total mass. Downstream of the ESP (ESP energized), the 

particle mass was reduced by approximately 96–98% (particles < 0.7 μm) and 99% (particles > 

0.7 μm), demonstrating excellent particle removal characteristics for particles emitted from the 

AWC boiler. 

High Load Medium Load Low Load

SMPS (0.01 < dm

Total number concentration (#/Ncm

< 0.64 μm) 

3

)

ESP de-energized

a

4.81x107 ± 1.27x10 3.26x10 5 7 ± 1.27x10 2.93x10 5 7 ± 9.65x10

ESP energized

4

6.96x105 ± 2.43x10 6.53x10 3 5 ± 8.50x10 4.62x10 3 5 ± 1.40x10

Geometric mean 

diameter (μm) 

3

• ESP de-energized 0.1105 ± 0.0050 0.1292 ± 0.0022 0.1220 ± 0.0016

• ESP energized 0.0981 ± 0.0015 0.1015 ± 0.0018 0.1051 ± 0.0011

Total number collection 

efficiency (%)

98.555 ± 0.0013 97.998 ± 0.0361 98.424 ± 0.0004

APS (0.7 < da

Total number concentration (#/cm

< 10 μm) 

3

)

ESP de-energized

a

9.70x104 ± 1.34x10 9.14x10 3 4 ± 2.96*10 8.88x10 3 4 ± 0.96x10

ESP energized

3

71.90 ± 35.56 160.96 ± 37.25 105.49 ± 31.11
40 

Geometric mean 

diameter (μm)

• ESP de-energized 0.8347 ± 0.0104 0.8387 ± 0.0123 0.8393 ± 0.0251

• ESP energized 0.8503 ± 0.0131 0.8351 ± 0.0212 0.8503 ± 0.0181

Total number collection 

efficiency (%)

99.923 ± 0.0357 99.825 ± 0.0351 99.923 ± 0.0357

Table 17. Total mass concentrations and particle collection efficiencies calculated from SMPS and APS data 

at the different boiler load conditions.

High Load Medium Load Low Load

SMPS (0.01 < da

Total mass concentration (mg/m

< 0.64 μm)

3

)

b

ESP de-energized

 

184.70 ± 28.412 134.71 ± 33.102 83.90 ± 12.786

ESP energized 2.94 ± 0.995 3.46 ± 0.813 2.86 ± 0.618

Total mass collection 

efficiency (%)

98.454 ± 0.301 97.424 ± 0.029 96.625 ± 0.222

APS (0.7 < da

Total mass concentration (mg/m

< 10 μm)

3

)

b

ESP de-energized 

 

100.65 ± 9.30 88.21 ± 6.55 78.51 ± 1.23

ESP energized 0.454 ± 0.0212 0.634 ± 0.1652 0.416 ± 0.0198

Total mass collection 

efficiency (%)

99.566 ± 0.04 99.323 ± 0.165 99.471 ± 0.017
41 

Cost Estimates for Adding ESPs to Full-Scale AWC Systems 

The equipment cost of the ESP was estimated from the cost algorithm for ESPs as outlined in 

Chapter 6 of the OAQPS Control Cost Manual (EPA, 1996). For a boiler with a gas flow rate of 

0.2 m3

For small-to-medium ESPs with an installed cost of approximately $100,000 or less, the total 

cost of maintenance is approximately 5% of the total capital cost. That is approximately $4,700. 

The operating cost will depend on several factors including labor costs, waste disposal and/or 

treatment, total hours of operation in a year, etc. A good estimate would be about $10,000 

annually. 

/s (assuming a migration velocity of 10 cm/s and specific collection area ratio of 3), the 

equipment cost was estimated at $34,000. Estimates of direct and indirect costs showed a total 

capital cost of approximately $93,000 excluding site preparation costs. 

The operating power consumption in an ESP mainly comes from the corona power and pressure 

drop, with corona power being the main source. For an estimated total plate area of 600 ft2

, the 

ESP power consumption would be approximately 4,350 kWh assuming continuous operation for 

five months. 

SUMMARY

The Walker Center boiler emissions of carbonaceous derived species (CO, OC, EC, PAHs, and 

organic compounds) during steady-state operation were all relatively low due to near complete 

combustion. Although, PM2.5 and NOx emissions are higher than the emissions from oil fired 

boilers in comparison to the boilers tested in the present work, emissions of SO2 were lower in 

comparison to oil-fired boilers (England, 2004). The emissions of CO, OC, EC, PAHs and 

organic compounds were comparable to testing when using wood chips, so fuel quality does not 

seem to affect combustion conditions. PM2.5 was found to be comprised primarily of inorganic 

salts (K+ and SO4

2-), which have a lower toxicity than organic-based particles. NOx, SO2, and 

PM2.5

The CO/CO

 were lower using wood pellets than wood chips, which is most likely due to the better 

quality of the fuel. 

2

The slightly higher PM

 ratio of the ACT Bioenergy boiler tested in Schenectady, NY was about 0.08% 

indicating almost complete combustion of the fuel, while the W!ld Center boiler had higher ratio 

of 12% due to unsteady boiler operation. 

2.5 emissions from the ACT Bioenergy boiler burning wood chips, in 

comparison to the Walker boiler burning pellets, are mostly attributed to the quality of the fuels. 

Therefore, the wood chip boiler would be expected to have lower emissions, if wood pellets are 

used as they have lower moisture content and are a better fuel by quality and calorific heat value.
42 

PM2.5 and NOx emissions from the W!ld Center boiler were higher than the smaller boilers 

burning woodchips and wood pellets. However, the SO2

The thermal efficiencies during steady-state operation calculated were between 70−77%, for both 

the Walker Center and ACT Bioenergy boilers. The W!ld Center boiler efficiency ranged 

between 61% and 91%. These efficiencies are lower than might be expected based on the 

reported European values reported by the vendor. 

emissions were lower at the W!ld

Center in comparison to the two smaller boilers. The PM emission factors from Method 5 and 

CTM–039 for this boiler were in agreement, except when the boiler was operating in an unsteady 

manner.

Assessment of the collection characteristics of a model ESP installed on a high efficiency, low 

emissions wood pellet boiler showed that the ESP efficiently captured the particles at the typical

operating conditions. The estimated resistivity of the fly ash collected by the ESP was about 

3x1010 ohm-cm at 120o

C, indicating that ash resistivity was not a significant factor influencing 

the ESP performance. The ESP exhibited a high average collection efficiency of about 96–98% 

by mass at different boiler load conditions tested, reducing the total mass emissions to about 3.0 

mg/m3

The measurements made in this study of high efficiency, low emissions Europeandesigned wood boilers suggest that they represent a significant improvement over the stoker 

design wood boilers that have been previously used in the U.S. The stoker design represents the 

typically available commercial wood boiler in the U.S. If there is to be widespread use of 

renewable woody biofuels (pellets and chips obtained from sustainable forestry), then it is 

important that advanced gasification systems be used rather than conventional technologies. 

From the available European literature, the staged combustion units in this study may not 

represent the state of the art in boiler design. Thus, there are additional opportunities to improve 

combustion efficiency with the potential of lower emissions and higher thermal efficiencies. 

Such improved performance will be necessary to make such systems more competitive with oilfired boilers that currently represent boilers with similar efficiencies but lower emissions of 

pollutants particularly particulate matter. 

. The total capital cost for installing ESPs on full-scale advanced wood combustion 

systems was estimated at about $93,000, excluding site preparation costs. Annual operating and 

maintenance costs were estimated at about $15,000 while the ESP power consumption over a 

period of five months was estimated at approximately 4,350 kWh. 
43 

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Evaluation of the Performance and 

Emissions from Commercial Scale 

Advanced Wood Combustion Systems.

Final Report

August 2010

Revised June 2012

New York State Energy Research and Development Authority

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