OMACON liquid-metal MHD natural-gas-fired systems

The results of an assessment of liquid-metal MHD (magnetohydrodynamics) for high-pressure offshore natural gas fields are presented. The optimized magnetohydrodynamic conversion (OMACON) system was selected for this study. Preliminary screening analyses for five OMACON cycles were conducted by computer simulations employing a lumped-component model of the OMACON MHD conversion module. The analyses identified the most attractive cycles and the parameter ranges of interest. A detailed model of the OMACON module was developed and used for limited analysis of three selected cycles. Preliminary capital cost estimates were generated. Of the three cycles, the OMACON pass through Brayton cycle has an efficiency approaching 80% because the expansion of the gas occurs with a relatively low temperature drop, and no gas compression is required. The efficiencies of the other two cycles are essentially comparable at approximately 41% at a temperature of 1200°F. The efficiencies of all three cycles could be improved by raising the top cycle temperatures by changing to higher quality materials. The performance and costs indicate that a combination of the pass through cycle and a dual-turbine Rankine open cycle should be attractive. It has a projected efficiency of 51% at 70 MWe output. The total power output can range up to approximately 525 MWe, consuming a total gas flow of 10⁹ Sm³/yr, and the efficiency at that point is approximately 40%