Status report on MHD electrical power generation–IAEA/ENEA International Liaison Group on MHD Electrical power generation

Abstract

The present status of commercial large-scale MHD electrical power generation is reviewed in the light of information presented at the Third International Symposium on MHD Electrical Power Generation (Salzburg, 1966) and of subsequent developments. Research and development activities, and the state of evaluation of engineering and economic factors are assessed in respect of open-cycle MHD power plant, closed-cycle MHD power plant, and the associated electromagnet.The MHD power generator is attractive in that energy is extracted directly from that of the flow of working fluid. The generator itself is of simple static construction, thus permitting high maximum cycle temperature, high specific power output and potentially much larger unit size than may ultimately be achievable with turbomachinety. In principle, these features should offer increased thermal efficiency and reduced capital cost compared with conventional plant.In the ‘open-cycle’ MHD system electrical energy is extracted directly from the flow of a plasma formed by the seeded products of combustion of a hydrocarbon fuel. The ‘closed-cycle’ MHD system similarly employs a working fluid which may be a seeded inert gas (helium, neon, argon) or a pure alkali metal. Operation may be based on the gas turbine or Brayton cycle, or incorporate steam plant (for the lower range of temperature) based on the condensing or Rankine cycle. In the case of the open-cycle MHD system, installations are being constructed or already operating successfully with hundreds of MW thermal input and tens of MW electrical output, and substantial effort has been devoted to other aspects of the plant. It is concluded that a pilot-scale power station is technically feasible but that the economics of MHD steam plant are not fully established.Research and development towards the closed-cycle MHD system is at an earlier stage, and there are fundamental aspects of plasma behaviour relating to instabilities and the feasibility of utilizing magnetically-induced non-equilibrium ionization which have to be resolved. Engineering and economic evaluation of system concepts requires attention. Closed-cycle systems operated on a condensing or Rankine cycle with liquid-metal MHD generators are also at an early stage of development. There is as yet insufficient information on the performance of various liquid acceleration schemes and MHD generators to allow assessment for commercial plant, although for special applications (e.g. space vehicle power systems) the concept is attractive.Superconducting electromagnets are technically and economically necessary for MHD power systems which, in almost all respects, derive benefit from operation at higher magnetic fields. Field levels of 5 – 7 T are attainable at present, and there are good prospects for further development to large size and higher fields.