In order to find out the optimal applicable flue gas waste heat utilization scheme for utility boilers

based on the principle of energy cascade utilization

the waste heat recovery system has been idealized as a heat exchanger network composed of many temperature matching heaters according to the temperature distribution of hot and cold fluids. The optimization variables and constraints have been identified according to the system structure

the conservations of energy and mass. The mathematical optimization mode

that the maximum increase of power generation is the optimization target

has been built. Moreover

the optimization results have been calculated by using the fmincon function. The ideal waste heat recovery scheme for an ultra supercritical 1 000 MW unit has been achieved through the optimization model. The maximum increase of power generation of the ideal scheme is22.34 MW. By reducing the system complexity according to the project engineering needs

the project scheme has been obtained from the ideal scheme. Compared with the pre-existing waste heat recovery schemes

the project scheme is much simpler and more energy efficient

and its net coal consumption dropped by 5.05 g/(kW·h).