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Title: Gas-phase refrigeration: A promising alternative to the conventional refrigeration processes for LNG
Authors: Shah, N.M.
Hoadley, A.F.A.
Rangaiah, G.P. 
Keywords: Gas-phase refrigeration
Genetic algorithm
LNG processes
Multiobjective optimization
Propane pre-cooling
Issue Date: 2009
Source: Shah, N.M.,Hoadley, A.F.A.,Rangaiah, G.P. (2009). Gas-phase refrigeration: A promising alternative to the conventional refrigeration processes for LNG. OPEC, Oil Prices and LNG : 443-468. ScholarBank@NUS Repository.
Abstract: The refrigeration and liquefaction units are key sections of an LNG processing plant and account for almost 40% of the total capital investment of the entire plant. In gasphase refrigeration processes the refrigerant always remains in the gas phase and this is the major difference and advantage over conventional refrigeration processes like the cascade process or the mixed-refrigerant process. Some of the advantages include the simplicity and flexibility of the gas-phase refrigeration process. Another advantage is the low hydrocarbon inventory compared with condensing refrigeration processes. Gas-phase refrigeration processes are based on the Reverse-Brayton refrigeration cycle. This refrigeration cycle employs turboexpanders to expand the refrigerant gas at high isentropic efficiency to provide cooling. A significant amount of shaftwork is recovered from the expansion of the gas and this is used in the recompression part of the cycle. One of the objectives in the design of any refrigeration process is to match the process cooling curve as closely as possible. Gas-phase systems are adaptable to a range of processing conditions and over this range are capable of providing very close heat transfer. Gas-phase refrigeration has been employed for a diverse range of cryogenic processes including the separation of air into oxygen and nitrogen and at the lowest temperatures, the separation of hydrogen and helium using the Claude cycle. In this chapter, the focus is on the use of gas-phase refrigeration for LNG. Results for an optimization study are presented for one of the most recent developments in efficient gasphase refrigeration processes. This is the dual independent expander process which uses two separate gas-phase refrigeration cycles. The introduction of propane pre-cooling to the dual independent expander process is presented in detail. A multi-objective optimization study has also been carried out for two objectives: the minimization of the major equipment cost and the minimization of the total shaftwork. It has been found that the propane pre-cooled dual independent expander process is more efficient than other gas-phase processes and also the conventional single mixed-refrigerant process. © 2009 by Nova Science Publishers, Inc. All rights reserved.
Source Title: OPEC, Oil Prices and LNG
ISBN: 9781606928974
Appears in Collections:Staff Publications

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