Modeling of Multi-Stream Heat Exchangers with Phase Changes for Cryogenic Applications

A new equation-oriented process model for multi-stream heat exchangers (MHEX) is presented with a special emphasis on phase changes. The model internally uses the pinch concept to ensure the minimum driving force criteria. Streams capable of phase change are split into sub-streams corresponding to each of the phases. A novel disjunctive representation is proposed which identifies the phases traversed by a stream during heat exchange and assigns appropriate heat loads and temperatures for heat integration. Model is suitable for optimization studies particularly when the phases of the streams at the entry and exit of the MHEX are not known a priori. The capability of the model is illustrated using a case study on liquefaction of natural gas.