Space heaters, catalytic

Catalytic or flameless combustion of hydn en exhibits many advantages in comparison with flame combustion. It occurs at low temperatures (ambient - 800 K), is safe and leads to a very high conversion of the burning gas (99.9 %). The NOX formation which usually occurs in conventional combustion at temperatures of about 1700 K, is here almost completely suppressed. The catalytic combustion in diffusion burners (Fig. 7-2) occurs in the presence of small amounts of Pt or Pd catalysts. It is adequate, e.g., for kitchen appliances such as cooker, oven, water heater, space heater. Drawbacks are the possible non-uniformity of the temperature distribution at die catalyst surface, rapid changes in the operational state, and relatively small heat flux densities [47]. 

Oil seepages on the surface were the early sources of crude oil. Kerosene was initially used primarily for lamps. Today, it is generally used for heating as space heaters, where a catalytic surface maintains a hot radiating source of heat. In cotmtries where electricity is expensive, e.g., Japan and Israel, it is not uncommon to see such appliance heaters in homes and offices. Such open flames are sufficiently hot to produce NOx as well as some hydrocarbon products which are readily detected by their odor. The main characteristics of a domestic grade of kerosene, which bums on a catalytic surface, are low sulfur and controlled smoke point and volatility. 

System Preheating. - The thermal efficiency of a catalytic oxidation system may be enhanced by preheating the feed gas in air prior to catalytic combustion. Tichenor and Palazzolo [5] have determined the relative contribution of the pre-heater to the overall efficiency. A mixture of iso-propanol, methyl ethyl ketone, ethyl acetate, benzene and n-hexane was combusted at a space velocity of 50,000h" in the temperature range 300-450°C over a bi-metallic Pt-Pd catalyst supported on a ceramic monolith. The results are shown in figure 1. 

The stripper was operated with these two objectives in mind. However, the lab test showed the C5 component distribution. The stripper bottom contained 2mol% C5, which exceeds the targeted C5 removal from the bottom, which is undesirable. Two negative results were observed. Because C5 is not involved in the catalytic reforming reaction, C5 material not only occupied the space in the reactor and hence reduced reaction throughput, but also consumed extra heat in the feed heater for the reforming reactors. 

Natural-circulation recombiner. For some applications it may be desirable to have a catalytic recombiner which will operate satisfactorily without a pump or e aporator to circulate diluent to keep the gases below the explosive limit. The natural-circulation recombiner [40] was developed for such uses (Fig. 8-15b). Electric heaters or steam coils installed below the catalyst start the circulation of the diluent and keep the catalyst dry. A cooling coil located in the annular space around the top of the chimney completes the convective driving circuit. 

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