Analysis of Optimal Power Reduction Schemes for An LNG Plant

In this work, a typical Mixed Refrigerant Cycle (MRC) for the production of liquefied
natural gas (LNG) has been selected for the analysis of potential power reduction
schemes. However, such analysis requires complete process data for the MRC
liquefaction process flowsheet. Unknown data were be subjected to rigorous simulation
and reconciliation. Data reconciliation approaches for the MRC flowsheet involved the
combination of structural decomposition of complex units and systematic estimations of
unknown variables. Simulations performed and the data obtained is validated against
published data. The errors in the data were reconciled by minimizing the sum of squared
error (SSE) between the simulated data and the published data. After five iterations, the
reconciliation trial with the smallest SSE of 0.002% was selected and considered as the
base case MRC process flowsheet. The base case flowsheet was then analyzed to
establish its thermodynamic performances using WORK software. The software also
optimized the mixed refrigerant compositions. Three power reductions schemes have
been proposed that include the process expander, the multistage compressions with
intercoolers, and the multistage compressions with intercoolers incorporating the process
expander. Each of the proposed schemes was compared, utilizing both the current and the
optimized mixed refrigerant compositions. As a result, six power reduction options were
generated. Each of the six options was then simulated on HYSYS.