Encore Woodburning Stove
Appendix: Catalytic Combustor
In any chemical reaction, including the combustion process, there are certain conditions which must be met before the reaction can take place. For example, a reaction may require a certain temperature, or a certain concentration of the reactants (the combustion gases and oxygen), or a certain amount of time. Catalysts, though not changed themselves during the reaction, have the ability to act at a molecular level to change these requirements. In the Encore’s secondary com- bustion chamber the catalyst reduces the temperature at which secondary combustion can start from the 1000
-1200°F (540 - 650°C) range to the 500 - 600°F (260
-315°C) range, increasing efficiency, and reducing creosote and emissions.
The catalytic reaction does have some limitations of its own. Primary among these is that the reactants (the gases) come into close physical contact with the cata- lyst itself.
To ensure the necessary contact, the catalytic element in your Encore is composed of a ceramic base in the shape of a honeycomb. Each of the honeycomb’s many surfaces carries a coating of the catalyst (usually a noble metal such as platinum or palladium). The large surface area exposed in this form ensures that the com- bustion gases have the greatest opportunity to come in contact with the catalyst.
Loss of catalytic activity will be apparent in several ways. First you may notice an increase in fuel con- sumption. Second, there will be a visible increase in the rate at which creosote builds up in your chimney con- nector system. You may also notice a heavy discharge of smoke from the chimney. There are a number of catalytic problems which can cause loss of activity:
Blockage
While the honeycomb pattern ensures good contact, it also increases the resistance to flow of the combustion gases, and, because of the many surfaces, provides more places for creosote and fly ash to deposit. It is important to follow the operating instructions in order to minimize these deposits, and to periodically inspect your catalyst for signs of blockage.
Masking and Poisoning
While the catalyst itself does not enter into the combus- tion process, certain elements, such as lead and sulfur, can attach to the active sites on the surface of the hon- eycomb. Though the catalyst is still there, it is covered, or masked, by the contaminant, and cannot function. To avoid this situation, it is important not to burn anything in your Encore that is a source of these contaminants. Particularly avoid painted or treated wood, coal, house- hold trash, colored papers, metal foils, or plastics. Chemical chimney cleaners may also contain harmful elements. The safest approach is to burn only untreat- ed, natural wood.
Flame Impingement
The catalytic element is not designed for exposure to direct flame. If you continually overfire your Encore, the chemistry of the catalyst coating may be altered, inhibit- ing the combustion process.
Thermal degradation of the ceramic base may also oc- cur, causing the element to disintegrate. Stay within the recommended guidelines of the Operation section.
Mechanical Damage
If the element is mishandled, damage may occur. Always treat the element carefully. Remember the cata- lyst is made of a ceramic material; treat it as you would fine china. Hairline cracks will not affect the perfor- mance of the catalyst, as long as the steel sleeve holds the element in the proper position.
Peeling
The surface coat may peel if the catalytic element is frequently subjected to excessive temperatures. Follow the operating instructions carefully to avoid this type of damage.
General
Every Vermont Castings’ Encore is equipped with either a Corning
If you must ship your catalytic element for any reason, remember its fragile nature. Place the element in a plastic bag, and package it with a generous amount of shock absorbing material.
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