Effects of High Pressure Heater Splitting to Heat Economy of Double Reheat Unit

Abstract

At present, mankind is faced with serious energy problems, as the energy-hungry, power energy saving is significant. Compared with the traditional single reheat unit, using secondary reheat to further improve the thermal efficiency of the unit, and meet the requirements of the unit low pressure cylinder exhaust steam eventually humidity. Double reheat power generation technology is the important technical direction to improve the efficiency of the power plant coal-fired generating units. In this paper, we researched the thermal economy calculation of double reheat units ,to single reheat unit economy calculation as the basis, adding the process of second reheat, calculated turbine internal work, boiler heat absorption and cycle thermal efficiency of double reheat units. Consider the case of the actual operation of the presence of high pressure splitting, according to the steam distribution unit matrix equation, calculated the steam distribution of different load after high pressure splitting, and calculated the corresponding cycle thermal efficiency. The results showed that in same conditions, double reheat cycle thermal efficiency was 2.26% higher than single reheat unit, after high pressure splitting, cycle thermal efficiency increased about 10%, and with load decreasing cycle thermal efficiency is declining, Effects of high pressure splitting is also reduced. Introduction China's energy structure determines the pattern in coal-based power generation ,and in China's coal consumption, coal consumption accounted for more than half of the total output of coal, Therefore, to reduce the energy consumption of coal-fired generating units of thermal power generation is an important task facing our country.[1] At present, the world faced with the lack of energy crisis. Mankind constantly searching for new energy sources, developing new energy sources, at the same time, we should make better use of existing valuable resources in our hands, The best use and maintain a greater level of human development, energy saving is imperative. With the increasing steam parameters, as one of ultra-supercritical units the role of double reheat unit is gradually improved . China has determined the double reheat supercritical unit to the Twelfth Five-Year Plan National Energy Development Project.[2] Using secondary reheat, then will further improve the efficiency of power stations, its economy as same as Integrated Gasification Combined Cycle (IGCC)and Pressurized Fluidized Bed Combusting Combined Cycle (PFBC-CC). China's double reheat technology in its infancy, and so far there is no secondary reheat operation, In discussing the second reheat economy, the theory has done by a lot of scholars[3]-[7].In this paper, calculates the economy of 2×660MW secondary reheat unit. Verify that the secondary reheat superiority in power generation efficiency, and discuss the influence of high pressure heater splitting on the double reheat unit cycle thermal efficiency in different conditions. Introductions of Secondary reheat economy calculation methods In this paper, in accordance with previous experience, add the second reheat process, as follows: International Power, Electronics and Materials Engineering Conference (IPEMEC 2015) © 2015. The authors Published by Atlantis Press 367 In accordance extraction location, the turbine is divided into several small turbines, for each small turbine to get the energy and mass balance equation, Then the calculated internal work and internal work of the various small turbine that is the whole unit turbine work, equation as follows: 1