Efficiency power plants

Figure 2.7 Projected improvements ofIGCC power plant efficiency. 

The addition of H2O and CO2 to the fuel gas modifies the equilibrium gas composition so that the formation of CH4 is not favored. Carbon deposition can be reduced by increasing the partial pressure of H2O in the gas stream. The measurements (20) on 10 cm x 10 cm cells at 650°C using simulated gasified coal GF-1 (38% H2/56% CO/6% CO2) at 10 atm showed that only a small amount of CH4 is formed. At open circuit, 1.4 vol% CH4 (dry gas basis) was detected, and at fuel utilizations of 50 to 85%, 1.2 to 0.5% CH4 was measured. The experiments with a high CO fuel gas (GF-1) at 10 atmospheres and humidified at 163°C showed no indication of carbon deposition in a subscale MCFC. These studies indicated that CH4 formation and carbon deposition at the anodes in an MCFC operating on coal-derived fuels can be controlled, and under these conditions, the side reactions would have little influence on power plant efficiency. 

As shown in Table 1.57, if the heat generated by the fuel cell is also recovered, the FC-based power plant efficiency can be nearly twice that of sub-critical fossil power plants. In addition to the improvement in efficiency, FC-based power generation is also superior to fossil fuel-based power generation, because there are no expenses associated with carbon recapture the only emission is distilled water. 

Table 7. H2 for electricity generation by combined-cycle power plants (efficiency = 55%).a...

Another approach to increasing power plant efficiencies is to use a nonther-mal conversion method for power production, such as fuel cells. Fuel cells rely on electrochemical conversion of the chemical energy in the fuel to electric power. In the cogeneration mode, these systems have been reported to be operable at overall efficiencies as high as 85% (Schora, 1991). Large-scale power plants based on fuel cells have not been developed yet and are not expected to be available for generating central station power until well into the twenty-first century. 

The amount of land required depends on the tree yield, power plant efficiency, and the capacity factor. The average biomass yield was assumed to be 11.3 dry ton/hectare. The power plant efficiency is based on a dry higher heating value of 20,200 kj/kg. A power plant annual capacity factor of 86.3% was assumed. Power plant sizes of 25, 50, and 150 MW were considered. 

TABLE 14.11 Results of power plant efficiency calculations ... 

In a gasification-based power plant, the hot, high pressure coal gases from the gasifier turn a gas turbine. Hot exhaust from the gas turbine is then fed into a conventional steam turbine, producing a second source of power. This dual, or combined cycle arrangement of turbines is not possible with conventional coal combustion. It offers major improvements in power plant efficiencies. 

The process is detrimental to cell performance because it involves a considerable loss of reactant and thereby reduces power-plant efficiency. Moreover, the methane can, in turn, be decomposed to carbon. 

The major difficulty to limit the higher thermal efficiency of the indirect cycle is the lower core inlet temperature. For the direct cycle, the cold gas leaving the precooler can be extracted to cool the reactor pressure vessel (RPV) and the other steel structures. Therefore the core inlet temperature can be as higher as 500- 600°C. For the indirect cycles proposed before, such as MGR-GTI proposed by Yan and Lidskyl, the core inlet temperature is kept as lower as 310°C in order to cool RPV The plant busbar efficiency of MGR-GTI is about 42.1%. In order to achieve higher power plant efficiency, it seems special designs of RPV cooling should be provided for the indirect gas turbine cycle. 

Power recovery system High-pressure gases can be used to generate power Plant efficiency decreases, operating pressure settings need adjustment Turbine shall be compatible with corrosive gases... 

VII. AUXILIARY POWER CONSUMPTION AND OVERALL POWER PLANT EFFICIENCY... 

On the assumption of a thermal efficiency of 34% (similar to PWR plants), the overall tokamak power plant efficiency would be... 

The operating temperatures and acid concentrations of PAFCs have increased to achieve higher cell performance temperatures of about 200 °C (392 °F) and acid concentrations of 100 percent H3PO4 are commonly used today. Although the present practice is to operate at atmospheric pressure, the operating pressure of PAFCs surpassed 8 atm in the 11 MW electric utility demonstration plant, confirming an increase in power plant efficiency. However, a number of... 

The mercury process needs the most electrical energy, but no steam is required to concentrate the caustic solution. The overall primary energy needed (if a power plant efficiency of 40% is assumed) for the mercury and diaphragm process is about the same, whereas the membrane process is more efficient (Table 6.19.6). Today, 54% of all chlor-alkali plants are membrane plants (Table 6.19.7) in the last 20 years, all new plants utilize this technology (Behr, Agar, and Joerissen, 2010). 

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