In order to construct a novel energy level composite curve

the energy level concept is calculated by the differential concept. The new composite curve is capable of providing total energy target for the whole system. An energy level grand composite curve is further proposed to realize the simultaneous integration of thermal and work. The thermal target

the work target and the process exergy loss can be obtained in the energy level grand composite curve. The methanol synthesis process was selected for case study. Through graphic analysis of the energy level composite curve and the energy level grand composite curve

the work demand is 28 MW

the cold utility is 137 MW

and the energy consumption is reduced by 71.1%. Electricity and circulating cold water were selected as the utility of the methanol process.