![]() These reactions take place first and are sometimes referred to as the decolorisation reactions. The first group of reactions involves the reaction of the fuel with oxygen and nitrogen dioxide, reducing the latter to nitric oxide. The reactions taking place on the catalyst surface can be divided into two groups. The bed is built up from slabs of the catalyst. Honeycat catalyst consists of platinum metals deposited on a ceramic honeycomb. The fuel gas is introduced into the gas stream and a homogeneous mixture of tail gas and fuel passed into a reactor containing a bed of catalyst as shown in Fig. Minimum inlet temperatures for good conversion efficiency and catalyst life are shown below for commonly used fuels with the Honeycat * catalyst specially developed by the Johnson Matthey Group. The tail gas from the absorption tower is pre-heated by heat exchange with the hot gases from the rhodium-platinum ammonia-oxidation gauze to a temperature which is dependent on the design of the plant and the fuel used. The reducing fuel chosen is generally determined by availability and price typical fuels are hydrogen (for example, ammonia synthesis-loop purge gas or refinery off-gas), light naphtha, methane (natural gas), or L.P.G. The catalytic method for removing the nitrogen oxides is based on the reaction of NO x with a fuel to give colourless and harmless nitrogen and water.
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