Tham khảo tài liệu 'advanced gas turbine cycles episode 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 118 Advanced gas turbine cycles Within the steam plant 7Jl depends on several factors the boiler and condenser pressures the turbine and boiler feed pump efficiencies whether or not there is steam reheat whether or not there is feed heating and whether the steam is raised in one two or three stages. On the other hand rjB depends on some of the following features of the gas turbine plant the gas turbine final exit temperature the specific heat capacity of the exhaust gases and i the allowable final stack temperature. The interaction between the gas turbine plant and the steam cycle is complex and has been the subject of much detailed work by many authors 5-8 . A detailed account of some of these parametric studies can be found in Ref. 1 and hence they are not discussed here. Instead we first illustrate how the efficiency of the simplest CCGT plant may be calculated. Subsequently we summarise the important features of the more complex combined cycles. . A parametric calculation We describe a parametric point calculation of the efficiency of a simple CCGT plant firstly with no feed heating. It is supposed that the main parameters of the gas turbine upper plant pressure ratio maximum temperature and component efficiencies have been specified and its performance 7 o h determined Fig. shows the diagram for the two plants and the various state points . For the steam plant the condenser pressure the turbine and pump efficiencies are also specified there is also a single phase of water steam heating with no reheating. The feed pump work term for the relatively low pressure steam cycle is ignored so that ib ha. For the HRSG two temperature differences are prescribed a the upper temperature difference AT . T4 Te- and b the pinch point temperature difference ATfc Tf Tc. With the gas temperature at turbine exit known T4 the top temperature in the steam cycle Te is then obtained from a . It is assumed that this is less than the prescribed maximum steam temperature.
