Cheng cycle

Abstract: In this work an overview of current and future sustainable gas turbine technologies is presented. In particular, the various gas turbine technologies are described and compared. Emphasis has been given to the various advance cycles involving heat recovery from the gas turbine exhaust, such as, the gas to gas recuperation cycle, the combined cycle, the chemical recuperation cycle, the Cheng cycle, the humid air turbine cycle, etc. The thermodynamic characteristics of the various cycles are considered in order to establish their relative importance to future power generation markets. The combined cycle technology is now well established and offers superior to any of the competing gas turbine based systems, which are likely to be available in the medium term for large-scale power generation applications. In small-scale generation, less than 50 MWe, it is more cost effective to install a less complex power plant, due to the adverse effect of the economics of scale. Combined cycle plants in this power output range normally have higher specific investment costs and lower electrical efficiencies but also offer robust and reliable performance. Mixed air steam turbines (MAST) technologies are among the possible ways to improve the performance of gas turbine based power plants at feasible costs (e.g. peak load gas turbine plants).

Abstract: The Cheng Cycle gas turbine has enjoyed its 25th anniversary since its conception. More than 100 sites around the world including the United States, Japan, Australia, Italy, Germany, and the Netherlands have used the Cheng Cycle. A chronology will be presented in this paper which will highlight the steps taken to develop the fully automated, load following power and cogeneration system. The Cheng cycle operates with a steam to air ratio trajectory that has its highest “peak efficiency” at the onset of a turbine’s operation. The peak efficiency point was coined as the Cheng point by Dr. Urbach [ref.1] of the US Navy’s David Taylor Research Center. Many thermodynamic and professional textbooks refer to the original Dual Fluid Cycle as the Cheng Cycle. Besides the high efficiency feature, the Cheng Cycle is mechanically simple and flexible in operation. It can put power on line faster than a combined cycle, and it has extremely clean emissions at low cost. The future performance of the Advanced Cheng Cycle will also be projected.Copyright © 2002 by ASME

Abstract: The planar solid oxide fuel cell (SOFC) with a Y 2 O 3 -stabilized ZrO 2 electrolyte is expected to be a candidate for distributed power sources in the next generation due to its high efficiency of power generation. In this study, we analyzed the system performance of a SOFC/gas turbine combined cycle of about 500 kW electrical output, using our two-dimensional simulation code for the planar SOFC with internal reformer. The effects of cell temperature, cell pressure, recirculation rations of fuel and air, utilization ratios of fuel and air, and average current density of SOFC on both the system efficiency and the cell temperature and current density distributions, were calculated under typical operating conditions taking account of realistic efficiencies and heat losses for auxiliary equipment. The addition of a Cheng cycle to the SOFC/gas turbine combined cycle improved system efficiency by 1-3%. The combined SOFC/gas turbine/Cheng cycle gave a high efficiency of 61.2% (based on a higher heating value) even under a small power generation scale of 500 kW class at 2.0 MPa SOFC pressure. We also discussed the possibility of carbon deposition at both external and internal reformers by calculating the chemical equilibrium carbon activities for estimated carbon deposition reactions.