Ultra-low Emissions, European-style 

Wood and Biomass Combustion Technology

Raymond J. Albrecht, P.E.

Buildings Research

NYSERDA

Albany, NY

Gasification and Staged Combustion - a path to lower emissions, 

higher efficiency and increased market success 
Firewood and wood

pellets account for 25 

percent of heating energy

in Austria

BLT is the leading

independent certification 

lab in Europe for biomassfired heating systems
Improved Energy and Environmental Performance

Of Wood and Biomass-fired Heating Systems in Austria

Decreasing emissions

Increasing CO2 in exhaust (less excess combustion air)
Wood and Biomass Emissions Standards and Actual Performance in Austria

Note: 10 mg/MJ is approximately 0.02 lb/MMBtu
Total Annual Emissions from Small Wood and Biomass Combustion

in Lower Austria

Note: Average PM values have continued to decrease with time 
Improved Energy and Environmental Performance

Of Small Wood and Biomass-fired Heating Systems in Austria

Increasing efficiency
Sales of Wood and Biomass Boilers in Lower Austria
Key Components of Clean Wood Combustion

Gasification with 20 to 40 percent of total air flow

to primary combustion chamber

Maintain approximately 1200 degrees F

Low air velocity to minimize fly ash
Key Components of Clean Wood Combustion

Pre-heated secondary combustion air and insulated secondary

combustion chamber

Significant residence time in secondary combustion chamber 
Key Components of Clean Wood Combustion

Forced combustion air supply Oxygen sensor 
Key Components of Clean Wood Combustion

Large water volume in boiler or secondary storage tank
Key Components of Clean Wood Combustion

Electrostatic filter-separator
Wood gasification-type boiler imported from Denmark

No emissions data directly available but European version (with 

electronic air fuel ratio control) shows clean combustion performance
KWB Wood American Oil-fired

NOx 0.08 0.10 lb/MMBtu

CO 10 to 60 10 - 30 ppm

PM 0.01 0.005 lb/MMBtu

Note: Secondary conversion of SO2 to sulfate 

aerosols from oilheat not addressed here
Gasification boiler manufactured in Czech Republic

More Examples of Gasification-type, Wood-fired Boilers
Swiss Research - Wood Combustion PM vs Diesel Soot

Poor wood combustion shows higher 

PAH levels than diesel soot

Clean wood combustion eliminates most 

PAH formation

Swiss Study of PM Emissions in Gasification Boilers vs. Percentage Air Flow

into Primary (Gasification) Combustion Chamber 

Optimal: about one-third of air flow into primary combustion chamber
Swiss Woodstove Emissions Research

790 mg/m3 approximately equal to 4 gm/hr
Swiss Research - Chemical Composition of PM from Wood Combustion

Poor combustion - PM carbon-based

Clean combustion - PM inorganic salt-based

Comparison of PM filters from diesel and 

clean wood combustion
Swiss Research on Health Effects - Clean Wood Combustion vs Diesel
Pellet Heating Systems

In Austria

New emissions standards implemented

in early 1990's led to development of

ultra-clean pellet combustion technology

Bulk delivery and storage of pellets 

Pellet heating system sales have skyrocketed

In Austria and several other European countries

Sales of pellet-fired systems now equal or exceed

oil-fired heating systems in several regions of Europe
Pellet Stove Testing at Brookhaven National Laboratory

USEPA CTM 39 Test Method - Dilution Tunnel Sampling

Stoves operated with automatic controls

American 

NOx 0.150 + lb/MMBtu

CO 300 + ppm

PM 2.5 0.07 - 0.2 lb/MMBtu

PM 2.5 emissions 10 - 20 times higher than for 

oil-fired heating systems
KWB American

NOx 0.14 0.15 lb/MMBtu 

CO 10 to 25 300 + ppm

PM 0.01 to 0.03 0.07 - 0.2 lb/MMBtu
Electrostatic Particle Filter for Clean Wood

Combustion Systems

Ruegg-Cheminee AG in Switzerland

75 - 90 percent removal efficiency
PM Emissions (lb/MMBtu) and Energy Efficiency vs Fuel Type

OWB standard - Phase I 0.44 input 30 - 40 % ?

OWB standard - Phase II 0.32 output

EPA certified woodstove (non-catalytic) 0.78 approx. 70 %

EPA certified woodstove (catalytic) 0.42 approx.

American pellet stoves 0.07 - 0.2 60 - 80 %

Austrian pellet stoves 0.01 - 0.02 80 - 90 %

Austrian wood-fired boilers 0.01 - 0.04 80 - 90 %

No. 2 oil-fired boilers 0.005 80 - 90 %

500 ppm S oil-fired boilers 0.001

500 ppm S - B20 oil-fired boilers 0.0008

15 ppm ULS oil-fired boilers 0.00002 - 0. 00004

Natural gas-fired boilers 0.00002 80 - 90 %

Crop-based Pellet Fuels

Ash and Sulfur Content

Crop-based solid biofuels show interesting 

potential but high (3 - 5 %) ash contents can 

cause operating challenges

Some crop-based pellets have 0.1 % sulfur 

content (equivalent to high sulfur heating oil)

SO2 emissions not thoroughly tested yet
Multi-biomass Fuel Boiler 

Manufacturer claims 

Capability to handle 

high ash content fuels
Thank You!