Final Report: Emission Suppression System for Outdoor Wood Boilers

EPA Contract Number: EPD11039
Title: Emission Suppression System for Outdoor Wood Boilers
Investigators: Gosau, Jan-Michael
Small Business: Adherent Technologies Inc.
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2011 through August 31, 2011
Project Amount: $80,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2011) RFA Text |  Recipients Lists
Research Category: SBIR - Air and Climate , Small Business Innovation Research (SBIR)


The purpose of this Phase I SBIR project was to design and test a catalytic combustor system that can be retrofitted into existing Outdoor Wood Boilers (OWB)s to reduce their emissions. Representative OWBs are shown in Figure 1.
The reticulated ceramic catalyst support structure used in the EPA-certified Clear Skies Unlimited, Inc. (CSUI) CS-200 catalytic combustor used in both woodstoves and woodburning fireplaces with a noble metal catalyst was the central design component. An OWB heats the home or business by burning wood in the firebox and transferring the heat from the fire into the water in the water jacket. That water is then circulated using electric pumps to a heat exchanger located in the home or business. That heat exchanger is linked to whatever kind of heating system is in the house, whether forced air, boiler, or radiant floor heating. The water in the water jacket is maintained at a temperature slightly below boiling, typically 185°F, plus or minus about 10°F. This is accomplished by setting that temperature into the electronic controller. The controller then opens and closes the draft door, which allows combustion air into the firebox, thereby controlling the rate of combustion. In the process, the OWBs emit a considerable amount of smoke containing particulates, carbon monoxide, and volatile organic compounds.

Summary/Accomplishments (Outputs/Outcomes):

Considerable testing was conducted in the Phase I program using a Central Boiler Model Classic 5036. The testing was divided into two phases. In the first phase, a retrofit unit containing the catalyst(s) was fabricated and tested through numerous modifications. Visual smoke appearance was used as the metric for reducing emissions. As the retrofit design improved over time, the visual smoke was greatly reduced as shown in Figure 2.
Figure 2 a and b. Heaviest smoke level during high burn No. 1
That testing led to a design for a prototype retrofit unit, which was fabricated by a fireplace manufacturer. The key to the prototype design was the use of a 12-inch diameter 1-inch thick catalyst support housed in a Venturi to bring in supplemental air below the catalyst (Figure 3).
Figure 3. Entire inner and outer sections of the OWB retrofit system
The prototype retrofit unit is 72 inches tall and interfaces with the 8-inch diameter exhaust stack commonly used on OWBs. The unit shown in Figure 3 was installed on the Classic 5036 and interfaced to a dilution tunnel for particulate sampling. The baseline value (without catalyst) for particulates was 0.49 pounds of particulate per million BTU input (wood burned). Particulate emissions were reduced by 47% with the standard palladium catalyst used in woodstoves and fireplaces (0.26 lb/million BTU) and 57% with a new nano-platinum catalyst (0.21 lb/ million BTU). Carbon monoxide was reduced by 64% with the palladium catalyst. A similar reduction in volatile organic compounds is expected. A summary of the test results is given in Table I.


A retrofit catalytic unit was successfully designed, fabricated, and tested for reducing emissions from OWBs. Particulate and carbon monoxide emissions were reduced 47-64% by the prototype unit. With further optimization in the Phase II program, additional emission reductions should result. The addition of these catalytic retrofit units to existing and new OWBs will substantially improve air quality in the air sheds where they are prevalent.
It is estimated that over 500,000 OWBs are in use in the northern United States. Thus, a very large market exists for the retrofit units to meet EPA clean air requirements. Sales of OWBs are increasing at a rapid rate (Figure 4).
Figure 4. Sales of outdoor woodfired boilers
At $1,000 each, there is a potential $500 billion market. We have contacted Central Boiler and will furnish them a prototype unit to evaluate.

SBIR Phase II:

Catalytic Emissions Reduction System for Outdoor Wood Boilers  | Final Report