Research On Engineering Application Of Cascade Heating Technology With High Back-pressure

Combined heat and power generation is a major part of energy-saving measures and power production of China.In March 2016,the National Development and Reform Commission,the Energy Bureau and other jointly promulgated the "Cogeneration Management Approach".The Approach requires the rate of cogeneration district heating of northern large and medium-sized cities reaches 60% or more.It is expected that there will be a large number of coal-fired generating units retrofitted to cogeneration units or build new cogeneration units.Cascade heating technology with high back-pressure is the focus of attention in the cogeneration retrofitting engineering.Cascade heating unit with high back-pressure can reduce the loss of cold source,improve thermal efficiency,expand heating capacity,thus to achieve energy saving of cogeneration system.This paper is part of the research task of the National Key Technology Support Program," Research on Low-level Energy Cascade Heating Technology of Steam Turbine for Thermal Power Units",that is to provide feasible analysis for demonstrating unit application of cascade heating technology with high back-pressure.In this paper,the cascade heating technology with high back-pressure is discussed in detail,and the Ebsilon software is used to establish the variable condition calculation model of cascade heating unit with high back-pressure based on the boundary conditions of district heating.On this basis,the performance of cascade heating unit with high back-pressure is analyzed,In addition,the calculation method of the heat load distribution of cascade heating system with high back-pressure is described,and the heat distribution method is used to calculate the heat economy of high back-pressure heating unit.For the 2×350MW supercritical single extraction heating unit of the demonstration power plant,Unit 1 is retrofitted to cascade heating with high back-pressure,Unit 2 still used the original extraction heating method.The thermal economy of this plant before and after the retrofitting under design heat load and maximum heat load is analyzed combined with local actual heating parameters.The results show that the standard coal consumption rate of the whole plant is 205.46 g/kW·h and 199.07 g/ kW·h under design heat and maximum heat load load during heating season,which shows the application of cascade heating technology with high back-pressure has remarkable energy-saving effect.This paper studies the heat load distribution problem of direct exhaust steam and extraction steam coupling cascade heating system of steam turbine(DCK heating system),and proposes different heat load distribution schemes for DCK heating system for a practical heating network.The optimal heat load distribution scheme of DCK system is determined by calculating the annual profit under different heat load distribution schemes,taking overall economy of heat source and heat network as the evaluation index.