A Critique of MHD Power Generation

Magnetohydrodynamic electrical power generation is a promising new technique for upgrading the efficiency of converting heat into electricity. The concept has been explored intensively but on a small scale during the past ten years, and the initial enthusiasm in it has been confirmed. Its utilization in base-load plants, in addition to increasing overall efficiency, can also lead to important reductions in the adverse environmental effects of thermal and air pollution. The projected efficiencies of large dual cycle systems are initially in the range of 47–50 percent, and improvements in technology could later increase this to 60 percent. In an MHD system, energy is extracted from a flowing electrically conducting fluid. The fluid may be either a seeded plasma or a liquid metal. Various MHD power cycles and systems are therefore under consideration. The status of these systems will be reviewed with emphasis on their application to large central-station commercial systems. The major technological problems and progress in the three major cycles (open cycle, closed-cycle plasma, and closed-cycle liquid metal) will be discussed in depth. In the open-cycle system, the engineering solutions that have been proposed for the major problems in the generator and auxiliary equipment will be detailed. In addition, the experience gained from the operation of a succession of generators will be summarized. In the case of the closed-cycle plasma system, the progress that has been made toward developing a generator with the requisite conversion efficiency will be cited. Recent cycle analyses that have established the conditions for matching these systems to current heat sources will also be reviewed and their implications noted. The potential of developing liquid-metal MHD systems for commercial application will be explored in the light of recently obtained experimental and analytical performance information. In particular, promising new techniques that can lead to improved efficiencies will be detailed.