Energy and exergy analysis for cryogenic process design/retrofit

Abstract

Energy and Exergy analysis are one of alternative techniques to analyze chemical processes in term of energy quality parameters such as enthalpy, entropy and exergetic temperature. The exergetic temperature can conduct Exergy Composite Curves diagram (ECCs) (Marmolejo-Correa, 2012) which represents exergy targets: exergy requirement, exergy rejection and exergy destruction etc. In addition, these targets can be used for improving processes. The strength points of these analysis are to design the new process and to improve the utility performance. Therefore, these analysis methods have been applied to low-temperature process that requires a large amount of energy consumption. In this work, there are two approaches of energy minimization. First model, a combination with ECCs diagram and mathematical programing (Wechsung, 2011) can synthesize a better design of process to reduce utility usage. Second model, a synthesis of cascade refrigeration systems (Colmenares, 1989) can indicate a configuration of refrigeration systems with alternative working fluids for minimizing the energy used by condenser and compressor. Besides that, these models were applied to a liquefied natural gas (LNG) production as a case study which comes from the Pro/II’s tutorial (commercial engineering software). The results show that the Exergy and Energy analysis have an ability and potential to design new synthesis for cooling systems for sub-ambient processes and a combination of heat exchanger with compression and expansion processes.