Effect of multi-stream heat exchanger on performance of natural gas liquefaction with mixed refrigerant |
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| Authors: | Ho-Myung Chang Hye Su Lim Kun Hyung Choe |
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| Affiliation: | 1. Hong Ik University, Seoul 121-791, South Korea;2. Korea Gas Corporation, Incheon 406-130, South Korea;1. Center for Environmental Energy Engineering, Department of Mechanical Engineering, University of Maryland, College Park, MD 20742, USA;2. Green Generation Solutions, Bethesda, MD 20814, USA;3. Department of Mechanical Engineering, King Saud University, PO Box 800, Riyadh 11421, Saudi Arabia;1. Process Systems Engineering Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA;2. Department of Energy and Process Engineering, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway |
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| Abstract: | A thermodynamic study is carried out to investigate the effect of multi-stream heat exchanger on the performance of natural gas (NG) liquefaction with mixed refrigerant (MR). A cold stream (low-pressure MR) is in thermal contact with opposite flow of two hot streams (high-pressure MR and NG feed) at the same time. In typical process simulation with commercial software (such as Aspen HYSYS®), the liquefaction performance is estimated with a method of minimum temperature approach, simply assuming that two hot streams have the same temperature. In this study, local energy balance equations are rigorously solved with temperature-dependent properties of MR and NG feed, and are linked to the thermodynamic cycle analysis. The figure of merit (FOM) is quantitatively examined in terms of UA (the product of overall heat transfer coefficient and heat exchange area) between respective streams. In a single-stage MR process, it is concluded that the temperature profile from HYSYS is difficult to realize in practice, and the FOM value from HYSYS is an over-estimate, but can be closely achieved with a proper heat-exchanger design. It is also demonstrated that there exists a unique optimal ratio in three UA’s, and no direct heat exchanger between hot streams is recommended. |
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