(571c) Optimal Design and Dynamic Operation of MR Refrigeration System for Natural Gas Liquefaction Process

Optimal Design and Dynamic Operation of MR Refrigeration System for Natural Gas
Liquefaction Process
Mozammel Mazumder, Qiang Xu*, and Srinivas Palanki
Dan F. Smith Department of Chemical Engineering
Lamar University, Beaumont, Texas 77710, USA

Abstract

The traditional liquefied natural gas (LNG) processes mainly include cascade (Jensen, et al.; 2006),
nitrogen expansion cycle (Remeljej, et al., 2006), and mixed refrigeration cycle (MRC) (Wang, et al.,
2007). Most of the optimization research on mixed refrigerant liquefaction process were based on
steady-state simulation. Only a few addressed the dynamic performance of mixed refrigerant LNG
processes. Thus, the main purpose of this study is to study the dynamic behaviors and economic
performance of mixed-refrigerant LNG liquefaction processes. The developed methodology in this
paper contains three major tasks: (i) modeling and simulation of an existing LNG process (base case);
(ii) thermodynamics and mathematical analysis for solution identification; and (iii) design the dynamic
model of mixed-refrigerant LNG liquefaction process and study its dynamic behaviors and economic
performance. First, the plant-wide steady-state modelling and analysis for an LNG liquefaction
process has been conducted, which combines turboexpansion, dual mixed refrigeration (DMR), Joule-
Thompson expansion targeting energy consumption minimization. The steady state optimization result
shows that 18,168 KW of total compressor brake power is saved compare with base case, accounting
for near 12.24% savings. It shows that the heat exchanger and chiller duties are also reduced 22,950
KW which accounts for about 5.22% heat exchanger and chiller duties consumption. The COP for
base case is 1.42. It increases to 1.56 after optimized, which also indicates the liquefaction process
efficiency is improved after optimization. Second, the energy consumption roadmap is explored
through thermodynamic analysis. In the third stage, a rigorous dynamic model for the mixedrefrigerant
LNG liquefaction process will be developed. Based on the dynamic model, various
variations from natural gas temperature, pressure, flow rate, composition, refrigerant flow rate,
compressor pressure are introduced as disturbances to study the dynamic responses of the studied
process. The dynamic responses of LNG temperature and total compressor energy consumption are
the major performance evaluation criteria under these disturbances, from which the best control
strategies are investigated to maintain the stable and economic operation of the mixed-refrigerant
liquefaction process.

References
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