Vermont Casting 1990CE installation instructions Appendix Catalytic Combustor

Intrepid II 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 Intrepid II’s secondary combustion chamber the catalyst reduces the tempera- ture at which secondary combustion can start from the 540 - 650° C (1000 - 1200° F) range to the 260 - 315° C (500 - 600° F) range, increasing efficiency, and reduc- ing creosote and emissions.

The catalytic reaction, though advantageous, does have some limitations of its own. Primary among these it that the reactants (the gases) come into close physi- cal contact with the catalyst itself.

To ensure the necessary contact, the catalytic element in your Intrepid II is composed of a ceramic base in the shape of a honeycomb. On each of the honeycomb’s many surfaces a coating of the catalyst (usually a noble metal such as platinum or palladium) is applied. The large surface area exposed in this configuration ensures that the combustion 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. A number of catalytic problems which can cause loss of activity are described below:

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, it is possible for certain elements, such as lead and sulfur, to attach to the active sites on the surface of the honeycomb. 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 Intrepid II that is a source of these contaminants. Particularly avoid painted or treated wood, coal, household trash, colored papers, metal foils, or plastics. Chemical chimney cleaners may also contain harmful elements. The safest approach is to burn only untreated, natural wood.

Flame Impingement

The catalytic element is not designed for exposure to direct flame. If you continually overfire your Intrepid II, the chemistry of the catalyst coating may be altered, inhibiting the combustion process. A glowing stove part at the back of the firebox is a sign of over-firing.

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 catalyst is made of a ceramic material; treat it as you would fine china. Hairline cracks will not affect the performance of the catalyst, as long as the steel sleeve holds the element in the proper position.

Peeling

Peeling of the surface coat may occur if the catalytic element is frequently subjected to excessive tempera- tures. Follow the operating instructions carefully to avoid this type of damage.

Every CFM Corporation product is equipped with either a Corning “Long-Life”®or a Technical Glass Products “Honeycomb”®. The products are equivalent. If for any reason you must ship your catalytic element, remem- ber 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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