97/01257 Life-cycle analysis of a fossil-fuel power plant with CO 2 recovery and a sequestering system

Abstract

It is very important to prevent global warming, and with regard to power-generation technology, there are two ways of achieving it. One way is to decrease greenhouse gas (mostly CO2) emission itself, and the other is to capture emitted greenhouse gas. Raising steam conditions such as inlet temperature and pressure is the most effective and fundamental method to decrease CO2 emission since cycle efficiency becomes higher. In this regard, advanced ultra-supercritical (A-USC) steam turbines having steam temperatures higher than 700°C and steam pressures higher than 30 MPa are very promising technology. Conversely, carbon capture and storage (CCS) is direct way to realize zero-emission, or at least decrease environmental impact by partly capturing carbon dioxide emitted from combustion process, either in boilers or combustors, in fossil-fueled power plants.There is no commercial A-USC plant yet: it is still in the research and development stage. However, thanks to the successful operation of recent ultra-supercritical (USC) plants, A-USC attracts the attention of both power-plant operators and governments all over the world. In many countries, it has recently become quite difficult to construct coal-fired power plants because of their carbon dioxide emissions, even though coal is the most economical fossil fuel and its amount of deposit is the biggest among fossil fuels. Therefore, if the two technologies, A-USC and CCS, are effectively combined together, they will realize very economical and environmentally friendly coal-fired power generation.Cutting-edge USC plants have steam temperatures of 600–620°C and steam pressures of 25 MPa. In order to expand these steam conditions to A-USC plants, whose temperature and pressure will be higher than 700°C and 35 MPa, improvements in many areas are necessary, such as material, steam path, cooling, sealing, evaluation of rotor dynamics, and optimization of bearing selection, etc. Combination of A-USC and CCS is a promising area in the future, though each technology started its research and development program independently. Both technologies affect each other when they are combined together; in particular, the design of the turbine must be adjusted depending on the selection of CCS technology because a large amount of heat is extracted before the low-pressure turbine. In any case of CCS technology, optimized combination is very important because there is a large amount of heat exchange between the two technologies. In this chapter, the combination of A-USC and CCS is discussed in detail.