Slag/seed interaction in coal-fired MHD generators

Abstract

An analytical investigation of slag/seed interaction phenomena in coal-fired MHD generators is presented. A two-dimensional boundary-layer model, including potassium seed mass transfer to the slag layer, was developed. Work on the chemistry of the seeded plasma/slag system performed in conjunction with the modeling approach is also discussed. The model is used to study slag/seed interaction effects on a 275 MWth first-generation MHD power train. The simulations show that seed losses in the channel are small under normal operating conditions. The slag layer coating the walls, rather than the entrained droplets, is where most of the seed absorption takes place. I. Introduction A COAL-FIRED MHD open-cycle topping a conventional steam cycle can provide a way to achieve high efficiency in the production of electricity from the combustion of a fossil fuel. The combustion products of coal are rendered electrically conductive by seeding the flow with a readily ionizable material such as potassium. As a result of combustion, mineral matter in coal is converted to molten slag. A portion of the slag is carried over from the combustor into the MHD channel and a liquid slag layer develops on the generator walls. The presence of the slag layer induces effects that can reduce the overall efficiency of the MHD plant. Slag (being mostly silica and alumina) combines with the potassium in the gas phase forming a