Combined power cycles are being developed in which low calorific value fuel gas is produced by a fluidised bed coal gasifier at high temperatures and pressures (up to 1000°C and 20 bar) to be burned and expanded through a gas turbine. The turbine specifications required the removal of all particulate material greater than 5 μm. To ensure adequate collection efficiencies it may be necessary to use filtering media such as granular beds or ceramic fibres. Filters, however, need to be replaced or regenerated at regular intervals in order to maintain the pressure differentials across them to within specified levels. This paper describes how fluidic valves (vortex amplifiers) can be used in the hostile conditions to provide the switching capability in a regenerative filtration system. A penalty is incurred in using the valves in that they require an extraneous control fluid to perform the switching function. Results of experiments at elevated temperatures together with an analysis of the system at high pressures show that in a practical system the dilution of the mainstream fuel gas by the control gas can be reduced to 0.35 percent. The fluidic switching circuit is shown to be a highly effective system for handling gas flows at elevated temperatures and pressures.

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