This was taken from the article Ray suggested:
How a Combustor Functions
A combustor is usually made of ceramic or stainless steel with a wash coat of catalyst such as platinum or palladium applied.
During the initial firing of a catalytic woodstove, a by-pass, designed in the stove to allow gases to exit the stove without being forced through a combustor, is left in the open position.
The actual amount of time required for a combustor to become active varies based on stove design and combustor design. The total start-up time is based on thermal mass and conductivity of the substrate. As a rule of thumb, stainless steel combustors, which have thinner cell walls, become active more quickly and require less by-pass time.
After the by-pass mechanism is closed, smoke and gases are forced through the combustor.
Combustible gases in wood smoke are ignited as they pass through the cells of a catalytic combustor.
Wood smoke requires high temperatures to be consumed and there is a great deal of energy to be harvested in wood smoke. An active combustor greatly reduces and concentrates the temperatures needed to process and harvest wood smoke gases. It can burn smoke with lower firebox temperatures. This is a critical point.
In some non-catalytic wood stoves, very high temperatures are used and larger amounts of steel or stainless steel components are exposed to this excessive heat. Over time, much like a combustor, these steel components may require replacement to keep the stove functioning correctly and to keep it within EPA emission requirements for non-catalytic stoves. Most manufacturers design these parts, like the combustors, to be removed for replacement when needed.
As the gases pass through a combustor, the active temperature and total surface area burn these gases and return them as energy to heat the given living area. Most gases commonly considered to be harmful to the environment are burned within the combustor. Most encouraging is that a catalytic woodstove can in fact remove up to 65% of methane gases, something non-catalytic stoves have not established.
Properly functioning catalytic combustors destroy a large percentage of air toxics emitted during the combustion of wood.
Combustors can destroy up to 90% of the creosote associated with wood combustion and remove 90% or more of the harmful pollutants found in wood smoke. What a combustor can not do is tolerate ongoing or constant misuse or abuse. Catalytic wood stove manufacturers should always encourage stove purchasers to burn only well seasoned cord wood. Wet or green wood should not ever be burned in any wood stove, regardless of design. Affordable moisture meters are accurate enough to educate consumers as to the moisture content of the fuel they wish to burn.
Although a combustor can process gases and chemicals such as formaldehyde, building materials, printed materials and other items with glues, adhesives and metals should not be burned in any stove. Unfortunately, repeated burning of such materials results in the release of these agents which can then over-plate or fill up the pores and surface areas of the catalyst coated combustor; eventually leading to the combustor becoming plugged. These are not proven to be destroyed in the combustion of a non-catalytic stove and go up the stack.
To be certain, any individual who burns materials other than recognized fuels, i.e. cordwood or approved manufactured logs, in a catalytic wood stove for any period of time can shorten the lifespan of the combustor. These folks are quick to learn about proper burn techniques, especially since their stove will not function as well as when first purchased. Essentially, catalytic woodstoves discourage individuals from burning anything other than good quality fuel. Today when individuals purchase a catalytic woodstove they know about the level of commitment they will have to make to their burn habits, use and maintenance. Catalytic woodstove purchasers invest more money in a catalytic woodstove so as to receive maximum efficiency and clean burning, just as owners of quality made, more costly vehicles tend to take better care of their vehicles.
Today, catalytic woodstove owners know it is far less costly to replace a combustor than it is to purchase an additional 10-30% more cordwood each year.
Recently, Applied Ceramics, a leading combustor manufacturer, performed a comparison of the performance at different burn rates of various stove designs. We were told by Applied Ceramics that various manufacturers were contacted by Applied Ceramics and asked to supply burn data for their products. Data provided by both catalytic woodstove and non-catalytic woodstove manufacturers showed that catalytic woodstoves had exceptional performance numbers.
