Cogeneration and Combined Cycle

In this chapter, we explore how the exergy concept can be used in the analysis of energy conversion processes. We provide a brief overview of commonly used technologies and analyze the thermodynamic efficiency of (1) coal and gas combustion, (2) a simple steam power plant, (3) gas turbine, and (4) combined cycle and cogeneration. At the end of this chapter, we summarize our findings with some concluding remarks. 

The majority of the electricity currently generated in the United States today is produced by facilities that employ steam turbine systems (Figure 15.1). Other power generation systems employ a combination of the aforementioned, such as combined-cycle and cogeneration systems (Figure 15.2). The numbers of these systems being built are increasing as a result of the demands placed on the industry to provide economic and efficient systems. 

The combined cycle and the combined cycle cogeneration plant showed that waste heat could be put to good use, thus generating less lost work. The process conditions used in the analysis of the combined cycle plant were chosen for illustrative purposes and were arbitrary. In practice, the conditions are generally chosen to increase power output (see, e.g., Chapter 5). 

Energy recovery, combined cycle technologies, cogeneration and others... 

Conventional fossil fuel-fired power plants, nuclear power faciUties, cogeneration systems, and combined-cycle faciUties all have one key feature in common some type of steam generator is employed to produce steam. Except for simple-cycle cogeneration faciUties, the steam is used to drive one or... 

Gas turbine-based power plants, particularly natural gas-fired cogeneration and combined-cycle faciUties, have proven to be highly rehable, efficient, and environmentally attractive. Advances in machine design, more efficient plant integration, and optimistic forecasts for the availabiUty of affordable natural gas worldwide have boosted the appeal of these systems for both base-load and peaking service. 

Boyce, M.P., Cogeneration and Combined Cycle Power Plants, Chapter 1, ASME Press 2001. 

Boyce, M.P., Gabriles, G.A., and Meher-Homji, C.B., Enhancing System Availability and Performance in Combined Cycle Power Plants by the Use of Condition Monitoring, European Conference and Exhibition Cogeneration of Heat and Power, Athens, Greece, November 3-5, 1993. 

Includes combined cycle plant (CCP) and combined heat and power plant (CHP or cogeneration plant). 

Between stacks networked in series, heat can be removed from the reactant streams to assist in controlling stack temperatures. The heat in a network reactant stream can be transferred to a cooler process stream in a heat exchanger or hot and cold reactant streams can be mixed directly. The recovered heat may be utilized in a combined cycle or for cogeneration. 

The cycles considered so far in this chapter are power cycles. However, there are applications in which Rankine cycles are used for the combined supply of power and process heat. The heat may be used as process steam for industrial processes, or steam to heat water for central or district heating. This type of combined heat and power plant is called cogeneration. A schematic cogeneration plant is illustrated in Fig. 5.19. A different schematic cogeneration plant is illustrated in Fig. 5.20. 

Figure 6.10 pictures the case of a natural gas-fired power station. The hot combustion gases drive a combined cycle consisting of a gas turbine and a steam power plant. The power station "cogenerates," or produces, electricity and heat. The produced heat and electricity are used to upgrade the quality... 

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