Electrode system maintenance processes in slagging MHD generators. Final report

Utilization of coal slag as a protective wall coating material was investigated in this program. Its ability to function in the MHD topping cycle environment, protecting cooled wall structures and limiting heat loss from high temperature, high velocity flows was tested experimentally. Data on mineral deposition, slag coating growth mechanism and rate, and steady state coating properties was obtained, using a flow sytem which simulated MHD topping cycle flow conditions. Gas flow field, wall structure, slag and gas composition, and electrical current transport were varied over regimes projected for topping cycle operation. Results were in good agreement with predictions of the flow and transport models developed. Exposed refractory, integral with a cooled metal wall structure, with temperature well below the slag fusion temperature, functions as a bonding surface for development of a slag coating. This class of wall structure develops a stable equilibrium dlag coating without erosive or corrosive damage. This allows use of a cold structure, typically 400 to 1000 K, optimized to meet MHD flow and power extraction constraints. The slag coating equilibrates to a steady state condition in a period of tens of minutes, with a typical thickness of one to three millimeters in the regime investigated.more » Coating surface temperature, controlled by slag viscous flow, is in the range 1700 to 2000 K. This form of slag coating is found to be compatible with overall MHD cycle requirements, and capable of protecting all internal surfaces of the topping cycle components from erosive damage, while limiting heat loss. Limited measurements of slag coating interaction with electrical power extraction imply overall compatibility with the power extraction channel.« less