a. Preheated secondary air supply. Since most of the intake oxygen is used up in the firebox burning, preheated secondary air must be supplied to the catalytic combustor. This air is mixed with the wood gases from the firebox and distributed across the intake face of the combustor. Air to fuel ratio is important. Too much air will cool the combustor and not allow it to work properly. To little air will starve the combustor of necessary oxygen needed for its operation.
b. By-pass system. (By-pass damper)
The by-pass system is used in an open position when starting the initial fire in the stove.
This allows the smoke to by-pass the combustor while the combustor is heating up and temperatures throughout the stove are stabilizing. This requires anywhere from 20 to 30 minutes of burning with the by-pass in an open position. After this period of time the combustor will light-off and the by-pass should be closed.
c. Flame shield.
The flame shield is designed to protect the combustor from direct flame impingement. It is located at the top of the firebox. Most flame shields are removable so that the combustor can be serviced or replaced if necessary. It is usually held in place with four brass nuts.
d. A Properly sized catalytic combustor.
This is determined by the manufacturer and the size stove being built. The flow rate going through the stove will have a lot to do in determining the correct combustor size and cell density to be use. Also the amount of room available where the combustor is to be positioned will help determine what combustor size to use.
Cell density determines the amount of open frontal area needed to control the flow rate and also the amount of surface area required to burn the gases received by the combustor.
Height of the combustor (distance through the cells) also plays a role in the residence time the gases have to burn within the combustor. 3” height combustors will create more residence time for the gases to burn, providing the stove has the available area for mounting the combustor.
Applied Ceramics carries a wide range of combustor in various shapes, sizes and cell densities to select from.
e. Stove must be airtight.
In the United States all catalytic stoves are required by law to be airtight. This allows the consumer control over the flames in the stove’s firebox.
f. Firebox must have primary adjustable air intakes.
The firebox air controls are used to control the amount air intake to the firebox. These controls can be adjusted by the stove’s operator to reduce or increase the amount of oxygen being supplied to the fire. Reducing the air intakes will lower the flames and create a longer burn rate. Reducing will also keep flames from wrapping the flame shield and burning directly into the combustor when the by-pass is in the closed position.