Abstract:Combined supply of heat and power can effectively improve the economy of large coal-fired power units and reduce carbon dioxide emissions.The electricity-heat ratio can help to measure the economy of such units.In the case of supplying heat to general thermal users,by comparing the electric ratio of subcritical,supercritical and ultra-supercritical units,and single-reheat and double-reheat units,it is concluded that the ultra-supercritical unit and double-reheat units are more economical and rational.According to the variable load operation of cogeneration units,the flexibility of the three kinds of units to adapt to load changes is analyzed,and it is concluded that the ultra-supercritical unit is more flexible.For high-pressure hot users heating,the double-reheat units are more economical,and the method of heat sources switching can be used to make the heating steam pressure to adapt to the unit load changes.