Availability Analysis of Three Different Types of Combined Cycle Power Plants
Sammanfattning: The goal of power plants with higher efficiency and lower environmental risk than conventional power plants has produced three types of combined cycle power plants. These are: 1) the conventional combined cycle (CCC) power plant, 2) the pressurised fluidised bed combustion (PFBC) power plants, and 3) the integrated gasification combined cycle (IGCC) power plants.
The efficiency of the CCC power plant has been sufficiently improved so that it is higher than the conventional power plant. Due to high combustion temperature in the gas turbine, the problem of NOx arose. Different NOx reduction techniques were adopted, such as steam or water injection, and dry low-NOx combustors. Strict environmental regulations in various countries were still violated. Therefore, the selective catalytic reduction (SCR) was installed in the waste heat boiler. Due to design of the CCC power plant, there is still risk of high NOx emission with a simple-cycle operation of the gas turbine. If the simple-cycle operation is not permitted then the effectiveness (energy availability) of the plant deteriorates.
The PFBC and IGCC are new rival technologies. Both have a potential for higher efficiency and lower environmental risk than pulverized coal fired (PCF) power plants. These benefits will be lost if the effectiveness of these plants does not compete with the effectiveness of PCF power plants.
Backup fuel can be utilized to improve the effectiveness of an IGCC power plant. Improving the effectiveness by using backup fuel involves increased cost for the fuel. If the gas turbine is operated as a simple-cycle with a backup fuel, then the problem of high NOx emission arises, as for the CCC power plant.
Differently designed combined cycle power plants have been analysed to investigate the effects of reserve capacity (active redundancy) and repair policy. The Markov process has been used for the analysis and the following results were obtained.
1. The CCC power plant with an appropriate reserve capacity and a suitable repair policy can be chosen to obtain greater effectiveness of the plant with less NOx emission.
2. The effectiveness of PFBC power plants can potentially compete with the effectiveness of PCF plants. With an appropriate reserve capacity or double repair crew policy, the effectiveness of PFBC power plants can be even higher than that of the PCF power plants.
3. With an appropriate reserve capacity and with double repair crepolicy, the effectiveness of IGCC power plants can be improved to equal the effectiveness of PCF power plants.
4. The PFBC power plants have more potential for higher effectiventhan IGCC power plants without backup fuel.
5. The use of appropriate reserve capacity and a suitable repair minimize the use of backup fuel and NOx emissions and, at the same time, improve the effectiveness of integrated gasification combined cycle power plants.
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