1. A series of heat exchangers with each stage using a different refrigerant. Tailored to take advantage of different thermodynamic properties of the refrigerants to be used. Usually have high capital costs and can handle very large base loads. Takes advantage of the cooling ability of hydrocarbons available in the natural gas to help in the liquefaction process. Numerous expansion stages are required to achieve desired temperatures. Considered as a safer method because there are no external refrigerants needing storage. (*) This work was done as part of the capstone Chemical Engineering class at OU (**)Capstone Undergraduate Students Evaluation of LNG Production Technologies* Oluwaseun Harris**, Ayema Aduku**, Valerie Rivera**, Debora Faria, and Miguel J. Bagajewicz, Natural Gas Cooling Curve Temperature Heat We made an analysis of twelve natural gas liquefaction processes and determined fixed costs and operating efficiency as a function of capacity. Eight of the eleven processes are currently established in various parts of the world. The four remaining processes are in developmental stages. Economic Life of 20 years New train required at the documented maximum capacity of each specific process. Average cost of electricity and cooling water throughout the US used in analysis. Energy cost evaluated at a minimum capacity of 1.2 MTPA Cost and Capacity Relationship One refrigeration loop that cools the natural gas to its required temperature range. Usually requires fewer equipment and can only handle small base loads. Lower capital costs and a higher operating efficiency Contains two or more refrigeration cycles. Refrigerants involved could be a combination of mixed or pure component refrigerants. Some cycles are setup primarily to supplement cooling of the other refrigerants before cooling the natural gas. More equipment usually involved to handle larger base loads. Cascade Processes Self Refrigerated Cycles Multiple Refrigeration cycles Single Refrigeration cycle Mixed Refrigerant Linde ProcessAxens Liquefin ProcessDual Mixed RefrigerantExxonMobil Technip-TEALARC Black and Veatch Prico ProcessTechnip- SnamprogettiDual Multi-component Pure Refrigerant Conoco Philips Simple Cascade Both Mixed and Pure Refrigerants Air Products and Controls inc. C3MR ProcessAPCI. APX ProcessEnhanced Linde Process Other BP Self Refrigerated ProcessWilliams Field Services co. ABB Randall Turbo-ExpanderMustang Group T-Q Diagram Objective of each design: getting the curves closer. It reduces the amount of work needed Processes Conditions after each stage of refrigeration was noted Processes were translated into simple simulations After making simple simulations mimic real process, variables were transferred to real process simulation Optimization- Refrigerant composition Optimization- Compressor work Restriction- Heat transfer area o All cells in LNG HX must have equal area Restriction- Second law of thermodynamics o Check temperature of streams Utilities- Acquire water flow rate needed Simulation Method Natural Gas composition Methane: 0.98 Ethane: 0.01 Propane: 0.01 Inlet conditions Pressure: 750 psia Temperature: 100 0 F Outlet conditions Pressure: 14.7 psia Temperature: -260 o F Capacity: Common min. to max. capacity of process Common min. Capacity: 200,000 lbs/hr Beihai City, China Black and Veatchs PRICO ProcessConocoPhillips Simple Cascade BP Self Refrigerated ProcessAPCI. C3MR Process Simulation Techniques Each liquefaction process was successfully simulated using SIMSCI Pro II software Capital and Energy costs were determined using simulated values. Ranking systems were created based on cost, efficiency and capacity. Connections with existing market trends were identified, but not all results coincide with those trends Because information on operating conditions is scarce and therefore the process may not be at their global optimum, but rather at a local one, better identification of these optimums is required.