Utility systems combined cycle

Beyond the ATS program, the DOE is looking at several new initiatives to work on -with industry. One, Vision 21, aims to virtually eliminate environmental concerns associated with coal and fossil systems while achieving 60 percent efficiency for coal-based plants, 75 percent efficiency for gas-based plants, and 85 percent for coproduction facilities. Two additional fossil cycles have been proposed that can achieve 60 percent efficiency. One incorporates a gasifier and solid oxide fuel into a combined cycle the other adds a pyrolyzer with a pressurized fluidized bed combustor. Also under consideration is the development of a flexible midsize gas turbine. This initiative would reduce the gap between the utility-size turbines and industrial turbines that occurred during the DOE ATS program. 

Process Simplification VIP The process simplification VIP uses the value methodology and is a formal, rigorous process to search for opportunities to eliminate or combine process and utility system steps or equipment, ultimately resulting in the reduction of investment and operating costs. The focus is the reduction of installed costs and critical path schedule while balancing these value improvements with ejq)ected facility operability, flexibility, and over-alllife cycle costs. 

A similar opportunity exists for the public utility industry in the potential of LBG and MBG. The reduced environmental impact of a coal gasification plant which produces a perfectly clean fuel equivalent to natural gas, compared to direct combustion of coal may allow increased use of coal in areas where increased pollutant emission is barred. As these PSD areas increase in number, the advantages of coal gasification become more apparent. The potential of more efficient combined cycle generation systems which can be used with coal-derived gases is an added factor for implementing coal gasification. 

Another solution is given in Fig. 7.3 (Dimian, 1996). This time the heat integration considers a more global viewpoint based on site integration . Excess heat available at high temperature is exported to the utility system. The heat needed to drive the distillation columns is imported from the steam network, at a temperature level compatible with the site policy. Exported energy as high-pressure steam is more valuable, and can be used to produce electricity in a combined heat and power cycle. Therefore, heat recovery is more efficient if treated as a plantwide problem. 

The pressurized bed was developed in the late 1980s to further improve the efficiency levels in coal-fired plants. In this concept, the conventional combustion chamber of the gas turbine is replaced by a PFBC. The products of combustion pass through a hot gas cleaning system before entering the turbine. The heat of the exhaust gas from the gas turbine is utilized in the downstream steam turbine. This technology is called PFBC combined cycle (Figure 22.8). 

The proper design criteria for a modem utility plant should include both environmental and economic requirements. In other words, not only the capital and operating costs of a utility plant but also the corresponding utility wastes must be minimised. The paper presents a systematic multicriteria process synthesis approach for designing sustainable and economic utility systems. The proposed approach enables the design engineer to systematically derive optimal utility systems which are economically sustainable and economic by embedding Life Cycle Assessment (LCA) principles within a multiple objective optimisation framework. It combines the merits of total site analysis, LCA, and multi-objective optimisation techniques... 

The CAAA mandates the reduction of SO2 emissions from utility power plants in the United States to a maximum or "cap" of 8.9 million tons per year by January 1, 2000 and thereafter. Any expansion in capacity of coal-based power generation will be allowed to emit SO2 only if SO2 emissions are reduced elsewhere in the utility system. Since coal gasification combined cycle power plants can be designed for over 99% sulfur recovery, they can be built with minimum offsetting impact for SO2 control on other utility power plants. 

The CAAA also contains provisions to reduce utility NO, emissions by 2.0 million tons per year. Each utility will be given an annual NO, emission limit or "bubble" for its entire system. This allows utilities to over-control NO, on some units and thereby avoid NOx reduction on other units. Any repowering of existing units with coal gasification combined cycle will significantly reduce NO, emissions which may reduce the necessity to reduce NO, emissions at other utility units. 

A fuel cell power generation system consists of several components besides the fuel cell such as a fuel processor and a power conditioner/inverter. The fuel processor is the first step of the conversion of fuel into an electrical current Typically, a fuel processor utilizes a combination of steam reforming (SR) and partial oxidation (POX) methods to convert hydrocarbons (methane, natural gas) into the pure hydrogen necessary as input to the fuel processor. During this process, the fuel processor also should strip the input gas of its pollutants such as carbon and carbon monoxide. The fuel processor is one of the areas in which the greatest environmental threat can occur because of this. There are a number of other considerations to be taken into account when examining the environmental impact and life cycle assessment of fuel cell power generation system such as axillary equipment and their economic and environmental impact (Kordesch and Simader 1995 van Rooijen 2006 Tromp 2002). 

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