Insertion of Shock Wave Compression Technology into Micro Turbines for Increased Efficiency and Reduced Costs

The following analysis is presented to serve as a preliminary design guide for micro turbine engine designers to consider the potential advantages of incorporating the Rampressor into their recuperated engine designs. It is shown that the increase in compressor efficiency and the shift in optimum pressure will increase the efficiency of the engine and lower the recuperator inlet temperature and specific cost. This also provides the opportunity to increase the turbine inlet temperature and specific power without incorporating more costly air-cooled metal or ceramic components into the turbine design. Ramgen Power Systems, Inc. (RPS) is developing a family of high performance supersonic compressor designs that combine many of the aspects of shock compression systems, commonly used in supersonic flight inlet design, with turbo-machinery design practices employed in conventional axial and centrifugal compressor design. The result is a high efficiency compressor that is capable of single stage pressure ratios in excess of those available in existing axial or centrifugal compressor designs. This technology provides a tremendous opportunity for replacement and/or de-staging of multi-stage centrifugal or axial compressors in gas turbines for greater efficiency, less cost, fewer parts, lower weight, and reduced footprint. A conceptual single-stage supersonic compressor has been defined for integration with a micro turbine in the 200 to 500 kWe class. This configuration offers the potential to achieve the DOE Advanced Micro Turbine Systems goals of greater than 40% LHV electric efficiency and $500 per kWe package selling price. INTRODUCTION Global electric power capacity additions over the next 20 years are projected to reach over 1500 GW, or approximately twice the present operating capacity. Aging and congested power grids, rising fuel costs and lower emissions requirements have all caused stationary power generation manufacturers to respond with aggressive and costly “distributed generation” (DG) technology development programs. In addition, DOE funded activities, such as the Advanced Turbine Systems and the Advanced Micro Turbine Systems programs, are further evidence of a newly developing age in electricity production, transmission, and distribution. Micro and mini gas turbines have been identified as part of the evolving DG resource technology portfolio. There is a great deal of interest in these products, although in recent years some of that interest has subsided due to shifting dynamics of DG concepts. This is largely a result of regulatory uncertainty, volatile and rising natural gas prices and the continued electric utility resistance to on-site generation, seen as a competitive threat. These are not new phenomena, but their impact has been magnified by the general inability of the equipment developers to meet their claimed efficiency and selling price targets. Today’s micro turbine at best is 28% LHV net electric efficiency and it appears that, as currently designed, the highest these units will achieve is 34% LHV net electric efficiency. This limits their practical application to CHP projects, and as a result, also limits the number of units sold. The basic problem is that these recuperated simple cycle designs cannot use the full turbine rotor inlet temperature Robert Steele, Peter Baldwin Ramgen Power Systems, Inc. Bellevue, WA James Kesseli Brayton Energy, LLC Greenland, NH