Solid fuel combustion technology for the Stirling engine

Abstract

The current status of fluidized bed combustion has been reviewed with emphasis on its potential application to industrial power or heating plants and to alternative fuels. This technology is ready for commercialization and there is strong evidence of its high adaptability to a large variety of fuels, including biomass and industrial wastes. Coal-oil slurry combustion also is being developed and has been demonstrated in small industrial boilers. The combustion tests to date indicate a need for improved fuel stability, fuel feed control and atomizer design. There is a tendency for the ash from the combustion process to accumulate on the boiler tubes or flow stagnation regions. The ash deposited was readily removed. In the tests conducted, the burning of coal-oil mixtures led to a 1 to 2 percent derating of the boilers. Longer life tests than those reported to date are required to determine ash build up, the frequency of boiler tube cleaning, and the corrosion of boiler tubes. The ash content in the combustion products may make direct heat transfer to the Stirling engine impractical. This is due to the high probability of ash deposition on the heat exchanger for the high temperature (expander side) of the engine with a marked decrease in heat transfer rate. In this case it would become necessary to add a heat exchanger between the combustor and the hot side of the engine. This could be a heat pipe, pressurized gas or other appropriate method. However, this leads to lower heat exchange rates to the heater head increasing its size and decreasing Stirling engine efficiency due to increased dead space. It also will add to system initial and maintenance costs.