Published December 2018
To enhance project returns on liquefaction of natural gas, producers of liquefied natural gas (LNG) have moved to higher plant capacities. LNG train capacity has been increasing from a typical 1.5 MMTPA (million metric tons per year) in the 1970s to a current installed range of 7–8 MMTPA. Air Products’ two-cycle refrigeration process, using propane and a mixed refrigerant, has been the dominant technology for baseload LNG production worldwide. Several other baseload LNG production technologies are also available, including those by Axens-IFP, ConocoPhillips, Shell, and Statoil-Linde.
However, these large plants are characterized by a high degree of complexity to maximize energy efficiency, enhance coproduct value realization and improve online availability. In addition to this, equipment supply for these plants are from very limited vendors. The lack of competition for large equipment further increases capital cost and project schedules. Also, to achieve project return from these mega-scale trains, a very large-scale gas reserve is required—possibly more than 20 trillion cubic feet to sustain multiple-train plants for at least up to 25 years. Therefore, in the present era of distressed energy prices, LNG producers are seeking means to monetize mid-/small-scale and stranded gas reserves with low cost schemes.
Various technologies exist to monetize mid/small-scale gas reserves, such as nitrogen expander cycles, single mixed refrigerant cycles, dual mixed refrigerant cycles, etc. In this review, we discuss a new dual-methane (DM) expander liquefaction technology developed by Gasconsult Ltd. This cycle offers a practical solution for mid- and small-scale trains as well for floating LNG.
Unlike other conventional processes, the DM cycle uses no external refrigerants, instead using natural gas feed as the refrigerant, which removes the storage requirement for external refrigerant and its associated equipment to extract refrigerant components from the feed gas, thereby reducing capital cost and operating cost.
This review presents a technical and economic evaluation of the Gasconsult DM expander liquefaction process, based on the production of 2.34 MMTPA of LNG at a 0.9 stream factor. Our design includes all units required for processing of raw natural gas to liquefied natural gas. The units included are feed pretreatment, acid gas removal, drying, liquefaction, sulfur recovery, and tail gas treatment.
The technoeconomic evaluation in this review includes estimated capital and production cost estimates, showing the details of important process cost parameters such as battery limits and offsites costs, variable cost, plant cash cost, plant gate cost, production cost, etc. This review is prepared using information derived from public domain information sources and nonconfidential information published by the licensor, Gasconsult Ltd. Process design was done primarily using the Bryan Research & Engineering (BR&E) ProMax® process simulator, version 4.0. Plant and process economics (CAPEX and OPEX) were worked out using IHS proprietary PEPCOST software, using in places our own design judgments based on operational experience.