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Gaseous, Particulate and Semi-volatile Emission Rates from a High Efficiency 

Wood Pellet Boiler using Wood Pellets

J. Laing, S. Raja, T.M. Holsen, P.K. Hopke

Introduction

There has been mounting concern over the health risks posed by pollutants emitted from biomass 

combustion, particularly fine PM. However, newer designs of fully automated, high efficiency wood 

boiler systems have been presented as a solution due to their low emissions. Continuous measurements of 

carbon monoxide, nitrogen oxides, sulfur dioxide, PM2.5, particle number concentration, and particle size 

distributions from a Hamont CATfire (Hamont Consulting and Engineering, Austria) gasification wood 

boiler (Figure 1) running at steady state were determined using wood pellets as fuel. Particle organic and 

elemental carbon fractions and particle and semi-volatile organic compounds were also quantified.

Results

Summary of Findings 

Selected two and a half hours of continuous gaseous and particle emission measurements are displayed in Figure 4. 

The temporal variations in emissions are seen collectively among all species, indicating that they are a function of in 

boiler variability. Emission factors for gaseous species, PM2.5, organic and elemental carbon, and particle number 

concentration are shown in Table 2. All criteria emissions were relatively low, comparable to other studies. Total 

carbon made up around 8.8 percent of PM2.5 mass, the rest being inorganic compounds derived from volatizing ash 

forming elements. The low organic fraction of PM2.5and the low CO emissions attest to nearly complete combustion 

in the boiler. The ultrafine particle distribution during steady state operation was unimodal with a geometric mean 

diameter of 89 nm (Figure 5). Particle number concentration was 1.50 x 10

13 particles/MJ. Particle and semivolatile organic compound emissions are presented in Table 3. Alkanes were the most prevalent group of 

compounds, peaking at C29. Levoglucosan was the second most prominent resolved compound. PAHs were 

dominated by phenanthrene, acenaphthylene, pyrene, and fluoranthene, with minor amounts of indeno[1,2,3-

cd]pyrene, naphthalene, anthracene, and retene. Hexadecanoic acid, octadecanoic acid, and nonanoic acid were the 

predominant alkanoic acids. 

Experimental Methods

Emissions characterizations were performed on the gasification wood boiler running at steady state using 

wood pellets. The boiler has a thermal capacity of 150kW and was run at 76% capacity during testing. A 

dilution stack sampling system (Figures 2 & 3) conforming to EPA’s conditional test method (CTM) 039 

was used to provide sample flue gas to ambient gas monitors, a TEOM with FDMS, and an FMPS. A 

switch valve prior to the gas monitors provided background ambient concentrations ten minutes out of 

every hour. Quartz fiber filters and polyurethane foam (PUF) samples were collected and analyzed for 

particulate organic and elemental carbon content by the NIOSH protocol as well as gaseous and 

particulate organic compounds using GC/MS. Organic compounds included polycyclic aromatic carbon 

(PAHs) compounds, n-alkanes, alkanoic acids, dicarboxylic acids, certain bio-markers and levoglucosan. 

Figure 3. Dilution Sampling System.

Figure 4. Gaseous and particle emission concentrations 

during steady state operation.

Figure 5. Particle size distribution during steady state 

operation for wood chips.

Table 1. Characteristics of the Fuel.

Fuel Analysis

The wood pellets used were manufactured by New England Wood Pellet, LLC. Samples were collected 

for every testing period from the boiler feed bin. Gross heating value, ash content, moisture content, 

sulfur content, and nitrogen content were determined (Table 1).

Fuel Characteristics Wood Pellets

heat content (MJ/lbs) 8.49

moisture (%) 4.80

ash (d.w. %) 0.60

carbon (d.w. %) 51.5

nitrogen (d.w. %) 0.13

sulfur (d.w. ppm) 70.1

Figure 1. Hamont CATfire Wood Boiler.

Table 2. Gaseous and particle emissions factors. All 

emissions are in mg/MJ unless otherwise noted.

Dilution Chamber

Dilution air

Sampling 

ports

142 mm 

quartz filter

PUF Exhaust

HEPA 

filter

PM2.5

cyclone 

& nozzle

Probe Hot box

Stack

FDMS & FMPS

TEOM

CO

NOx

SO2

CO2

in-line filter

Table 3. Particle and semi-volatile organic emissions.

Organic Compounds μg/MJ

Alkanes 377

PAHs 32.0

Aromatic acids 28.9

Alkanoic acids 59.4

Dicarboxylic acids 37.3

Pentacyclic triterpane (hopanes) 39.2

Cholestane (sterols and cholestenes) 0.45

Methyloxylated phenols 15.7

Sterols 0.35

Levoglucosan 50.2

Figure 2. Schematic of Dilution Sampling System.

Emission 

Species 

(mg/MJ)

This Study Other Studies

Hamont 

CATfire 

Old-type 

boilers*

Modern wood 

boilers*

CO 115 ± 1.21 7433 1324

NOx18.4 ± 0.10 61.2 91.7

SO20.26 ± 0.00

PM2.525.1 ± 0.34 566

a 35.7a

OC 2.15 ± 0.64

EC 0.07 ± 0.03

total particle 

x10

12

(#/MJ) 15.0 ± 0.10 559 45.7

GMD (nm) 89.3 ± 0.06 

*Johansson 2004

aTotal PM – in-stack filter

Acknowledgements

This study was funded by the New York State Energy Research and Development Authority (NYSERDA) under contract 10672. We want to thank David Dungate of ACT Bioenergy for his assistance in these studies.