Removal of Molten Slag Particles by a Packed Bed of Ceramic Balls under High Temperature

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In this research, a new concept of a filter for capturing coal slag particles under high temperature is proposed, where high temperature combustion gas of coal with molten slag particles is introduced into a packed bed of ceramic balls (pebbles). In the packed bed, molten slag particles are captured by the inertial impaction and are extracted as a liquid condensate.In order to demonstrate the technical feasibility of this high temperature filter concept, hot model experiments have been carried out. In these experiments, coal fly ash was injected into a high temperature combustion gas of natural gas to produce combustion gas with molten slag particles, and this combustion gas was introduced into a pebble bed filter composed of refractory materials. The experimental results have successfully demonstrated continuous capture and extraction of slag particles without clogging of the slag extraction hole. At the same time, it has been shown that capture efficiency as high as 97% is achievable, which well coincides with the cold model experiments performed under normal temperature using oil droplets instead of real molten slag particles.One of critical technical problems associated with commercialization of this filter concept is the durability of the pebble materials contacting with molten slag. Thus the durability test of pebble materials against molten slag was conducted using an electric furnace. This test has shown that high purity alumina pebbles show good resistance against molten slag if the operating temperature is 1600ﾟC or less.Finally, some new coal-fired power generation systems combining the pebble bed filter and the high temperature air combustion technologies are proposed, which are environmentally friendly high efficiency systems.