Probabilistic Modeling and Optimization of Clean Coal Technologies: Case Studies of the Externally-Fired Combined Cycle (EFCC) System

INTRODUCTION The Externally Fired Combined Cycle (EFCC) is an advanced coal-fired power generation concept with a potential for higher thermal efficiency and lower cost than conventional coal-based systems. 1 The concept incorporates efficient gas turbine combined cycle technology for use with coal. Unlike "direct fired" combined cycles, the EFCC does not require any special fuel preparation. The EFCC concept has yet to be demonstrated commercially. The concept is under development by Hague International and the U.S Department of Energy (DOE). The main obstacle to the development of a viable EFCC system has been the unavailability of a suitable heat exchanger which would allow for a sufficiently high gas turbine inlet temperature. Recent developments in ceramic heat exchanger (CerHx) technology for use in the EFCC process have been promising enough to warrant further development of this system. This project involves development of engineering performance and cost models of the EFCC technology based on available performance and cost information. Since this technology is in the early stages of development, there are inherent uncertainties in the performance and cost parameter estimates. A probabilistic modeling capability has been incorporated to account for the uncertainties in the performance parameters. Details of previous work on probabilistic modeling can be found elsewhere. 2-5 The results obtained from the EFCC model simulation include the possible ranges of values for the performance, environmental emissions, and cost parameters, and information about the probability of obtaining these results. These results have been used to characterize key uncertainties; optimize the flowsheet configuration and parameter values; and identify priorities for further research. The model results provide insight into the risks and potential payoffs of the EFCC technology. A conceptual process model was developed by Hague International (HI) to estimate the performance of a 300 MW EFCC system. 6 A conceptual diagram is shown in Figure 1. Coal is combusted in an atmospheric pressure combustor. The combustor exhaust gases pass through a slag screen to remove large (> 12 micron) particles and enter a shell and tube ceramic heat exchanger. Filtered air is compressed before it enters the tube-side of the heat exchanger. In the heat exchanger, the thermal energy of the shell-side combustion flue gas is transferred to the tube-side high pressure air. The high pressure air is heated to the desired turbine inlet temperature and transported to the turbine via internally insulated piping. The hot pressurized air is expanded to provide shaft …