Theoretical Analysis And Research Of Waste Heat Utilization Based On The Low Temperature Economizer

With the development of economy, the contradiction of energy supply and demand is more and more serious, and people start to pay more and more attention to the environment pollution, energy and environment problems become the main factor of the Chinese economy development, improving the energy efficiency is an important means to solve the two problems. Coal fired power plants hold dominant position in the power structure, and enhancing the efficiency of the coal fired plant has good effects on energy and environment. Setting the low temperature economizer becomes a general measure to improving the unit performance, so the theory analysis and studies of low temperature economizer has practical significance.In the optimum design of low temperature economizer, the multiple traffic connection mode is put forward, and the optimal design of low temperature economizer is established with the maximum of pure profit as the objective function. With the N200 unit as example, the results show:the heat can be used in high efficiency in the multiple traffic low temperature economizer, Compared with the single flow model, the coal consumption is reduced more 0.5g; and the difference of two connection model in different temperature of exhaust gas is analyzed,the result shows:the multiple traffic mode has better economic benefit than the single traffic mode, when the temperature of exhaust gas is higher than 140 "C.In the effect of low temperature economizer on the unit, considering the variable condition of the regenerative heater, the mathematical model for heat economy of unit is built. Used N300 units as a example, when the external heat is introduced into the heater, this means、the equivalent enthalpy drop method and the detailed calculation are used to calculated the economy difference of unit, the result shows:the result of the detailed calculation is consistent with that of this method, which verifies the rightness of this method, and the result of this method is bigger than that of equivalent enthalpy drop method in terms of incremental doing work and circulation heat.In the optimum distribution of enthalpy rise of regenerative system with low temperature economizer, the mathematical model of optimum distribution of enthalpy rise is built. Taking a N300 power unit with low temperature economizer as the example, genetic algorithm is applied to solve the feed-water heating allocation. The calculation result demonstrates that, compared with non-optimized unit, the enthalpy rise distribution is more reasonable, and the coal consumption reduces further 0.54g. when a large number of external heat are introduced to regenerative system, the optimum distribution of enthalpy rise should be optimized to obtain higher efficiency of the unit.In this paper, the research of low temperature economizer is classified into the optimum design, the influence of the unit economy and the optimum distribution of enthalpy rise. The multiple traffic connection mode is put forward, the mathematical model for heat economy of unit is built considering the variable condition of the regenerative heater, and the mathematical model of optimum distribution of enthalpy rise of regenerative system with low temperature economizer is built, which give directions for the design and theoretical analysis of low temperature economizer.