Use of sophisticated heat exchanger simulation models for investigation of possible design and operational pitfalls in LNG processes

The simulation rating programs S-FIN for PFHE and S-PLATE for PHE have been developed at SINTEF Energy Research. These tools can be incorporated in process simulation environments like PRO/II and Aspen HYSYS®, and thus be used as an integrated part when doing process energy simulation and optimization.Static flow instabilities that can occur in heat exchangers used in cryogenic services are discussed.Examples on how to perform, and how to interpret, a Ledinegg instability analysis, are shown using the developed programs.With the well-known single mixed refrigerant process as a case study, a thermally valid plate-fin heat exchanger was designed that was subjected to Ledinegg instability. Remedies to avoid this and the effect on the process energy consumption are discussed. For the selected case, the compressor power increased by 14% going from an unstable to a stable design/operation.The examples show that detailed heat exchanger simulations should be performed as a part of process optimization.