Low Temperature Catalytic Heaters THE CATAHEAT RANGE OF FLAMELESS COMBUSTION SYSTEMS

The small radiant heaters that burn hydrocarbon fuels propane, butane, methane/natural gas and liquid hydrocarbon fuels are used widely because of their simple design, their portability, and the ready availability of fuels. The open flame heater presents obvious disadvantages as follows. An upset heater is a grave fire risk where the surroundings are flammable and this restricts usage in, for example, farm buildings. If there is incomplete combustion of the fuel then the flame tends to smoke and a build-up of soot occurs on the heater. And, most important, the temperature of the flame may exceed IOOO'C with much energy being wasted in heating the surrounding atmosphere and in the emission of visible light energy. To avoid these problems it is necessary to suppress the flame, to ensure efficient combustion and to reduce emission of useless energy. The solution is to use a catalyst that permits combustion of the hydrocarbon fuels at much lower temperatures. A suitable catalyst enables oxidation of the fuel to take place at a much lower energy level than would otherwise be possible. For example, using propane as fuel, combustion can take place on a catalyst at about 400"C, much lower than the 1000°C quoted above for a naked flame. The properties of the platinum group metals have led to their wide use as catalysts in oxidation reactions, including the oxidation of hydrocarbons. Technical staff in the Chemicals Division of Matthey Bishop have studied how these properties can best be adapted to construct low temperature catalytic heaters. They have developed a range of such platinum group metal catalysts, which are known as Cataheat, each of which is designed to operate with a specific type of fuel. Basically the Cataheat systems consist of platinum group metals supported on new and improved substrates to produce catalytic burning surfaces suitable for use with each fuel. The characteristics of three types of Cataheat unit are summarised in the table opposite. Cataheat L has been developed for the combustion of liquid fuel such as white gasoline, Cataheat P for the combustion of propane or butane, and Cataheat M for combustion of methane/natural gas. Cataheat systems reduce the temperature at which the oxidation reaction of combustion takes place to well below that at which combustion occurs in a flame. The reaction is still, of course, exothermic but the heat that is emitted is radiant. The infra-red radiation warms surfaces exposed to the catalytic heater whileleaving the air around the heater virtually unaffected. Thus the efficiency of heating is higher than where there is an open flame. Heat is directed only where it is wanted. Improved safety is an added bonus. There is 98.6 per cent conversion of hydro-