Abstract
Chemical industries consume most of the energy for heating and compression needs. This energy can be saved by synergizing the work and heat requirements of the processes. In this work, we propose a generalized framework for handling both heat and work integration simultaneously. A mixed-integer nonlinear programming (MINLP) model is developed for work-heat exchange network synthesis (WHENS). Stage-wise superstructure with fixed number of splits and isothermal mixing is used for heat integration. Work integration involves turbines and compressors on single shaft turbine compressor (SSTC). In this work, the individual streams are not classified as high or low-pressure streams. Hence, pressure changing streams can undergo either compression in compressor or expansion in turbine or valve depending upon the process needs and specified target operating conditions. Also, the pressure changing stream are not classified as hot or cold stream a priori in the heat integration. This provides more flexibility and generalization for work-heat integration. Starting with a set of streams with known inlet flows, temperatures and pressures, the network can be synthesized for any desired objective. The model can also handle unknown exit temperatures of some streams. Finally, we illustrate the applicability of this framework on a natural gas liquefaction process.
