POSSIBLE PROBLEMS
Problems encountered with the operation of catalytic-combustor equipped wood heaters are usually the same as those experienced in the operation of traditional wood heaters. Our experience has shown that adoption of good operating practices will eliminate most of these problems. In addition, it should be noted that problems with catalytic combustors are rare-fewer than 1 percent of combustors are returned for any reason. Nonetheless, installers and retailers should make themselves aware of the nature, cause and solution to possible problems so as to serve their customers better.
Plugging-Plugging can occur if the combustor is operated improperly. It may occur if the wrong materials are burned. Evidence of these types of plugging is a coating of black soot, creosote or fly ash on the combustor. Burning materials that produce large flakes of char, such as Christmas wrapping paper or cardboard, can plug enough cells to cause smoke spillage.
Extreme Temperature-A combustor becomes extremely hot during operation. Temperatures between 1400o F and 1600o F (760o C - 870o C) are common, but operating temperatures between 1200o F and 1400o F (650o C - 760o C) are recommended. Most of this heat is transmitted to surrounding heater parts via thermal radiation.
Flow Restrictions-Because the combustor is mounted in the gas flow stream, it does offer resistance to draft. This restriction or resistance presents two problems:
If the bypass is not open when the fuel-loading door is opened, smoke rollout will occur.
Chimneys that produce marginal draft may prevent operation of a combustor-equipped device. A chimney that provides, on average, .02” of water draft in low-fire operation would probably not operate with a catalytic combustor appliance in the low-fire mode. In such a case, the combustor resistance would offset the remaining draft, resulting in a system that will not draft.
Creosote Build-up-Even though reduction of creosote is one of the primary advantages of a combustor-equipped device, some creosote-forming gases will escape unburned during normal operation. In the event the combustor ceases to function, creosote can be expected to accumulate. Consequently, flues and chimneys should be inspected regularly (every 2-3 months of operation) and any creosote build-up removed. Failure to do this could result in a chimney fire.
Chemical Deactivation-Deactivation can occur when the catalyst is attacked by materials such as compounds of sulphur, phosphorus, or lead and other heavy metals. Burning large quantities of trash, pressure-treated lumber or painted wood can deactivate the catalyst. The operator takes a chance when burning anything other than natural wood. The catalysts are durable and are not likely to be greatly affected by an occasional mistake, but burning large quantities of chemical-laden materials will appreciably shorten the life of the combustor. The catalyst can also be deactivated when it is coated with excessive creosote, carbon or fly ash. This build-up greatly reduces the amount of catalyst available to react with the smoke.
Excessive Handling-An older combustor, especially one that is “uncanned”, is susceptible to handling damage. Stress-relief cracks may develop in service but will not affect the performance of the combustor if it is not moved or handled. Handling a unit with these cracks, however, could result in it breaking apart. Excessive handling could also potentially remove some of the catalyst coating.
Condensation In Chimney-The burning that takes place in a combustor converts harmful hydrocarbons and carbon monoxide to heat, carbon dioxide and water. The additional water produced by this complete burning can lead to associated problems in the chimney.