LNG (Liquefied Natural Gas) Basics Combustible mixture of hydrocarbons Dry VS. Wet NGL Extraction Dehydration/Scrubbing Liquefied Natural Gas Target temperature for Natural gas:-260°F Reduces volume by a factor 600
Objective Main Objectives Simulate Processes Optimize Processes Minimize compressor work Compare Processes based on Capital cost Energy cost Total cost per capacity(Ton)
* Italicized processes signify Patent searched processes. * Bolded processes signify processes not included in scope of project. Liquefaction Processes Mixed RefrigerantsPure RefrigerantsBothOther Linde ProcessCoP Simple CascadeAPCI C3 MR BP Self refrigerated process Axens Liquefin Process CoP Enhanced Cascade APCI AP-X ABB Randall Turbo- Expander Dual Mixed RefrigerantLinde 2006 Williams Field Services co. Technip-TEALARC Mustang Group ExxonMobil Dual Multi-component Black and Veatch Prico Process Technip- Snamprogetti
Black and Veatchs PRICO Process Axens Liquefin Process ExxonMobil Dual Multi-Component Cycle C3MR: Air Products and Chemical Inc
AP-X: Air Products and Chemical Inc. DMR- Dual Mixed Refrigerant Technip- TEALARC System BP- Self Refrigerated Process
Linde/Statoil -Mixed Fluid Cascade Process Linde- CO 2 MFCP ConocoPhilips Simple Cascade
Simulation Specifications Natural Gas composition Methane: 0.98 Ethane: 0.01 Propane: 0.01 Inlet conditions Pressure: 750 psia Temperature: 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
Liquefaction Techniques Different Liquefaction techniques include : Single Refrigeration cycle Multiple Refrigeration cycles Self Refrigerated cycles Cascade Processes The cooling of natural gas involves the use of refrigerants which could either be pure component refrigerants or mixed component refrigerants.
Liquefaction Techniques Schematic of a Simple Refrigeration Cycle Compressor Heat Exchanger Expander
Liquefaction Techniques Mixed refrigerants are mainly composed of hydrocarbons ranging from methane to pentane, Nitrogen and CO 2. Pure component Refrigerants Specific operating ranges for each component Mixed Refrigerants Modified to meet specific cooling demands. Helps improve the process efficiency
Liquefaction Techniques Natural gas cooling curve Area between curves represents work done by the system T-Q Diagrams
Liquefaction Techniques Single Refrigeration Cycle 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
Black and Veatch: PRICO Process Single mixed refrigerant loop and single compression system Limited capacity (1.3 MTPA) Low capital cost Great Pilot Process Inlet Gas LNG Cold Box Compressor Condenser Expander Residue 100 o C -260 o C
Inlet Gas LNG Cold Box Compressor Simple Refrigeration Cycle Refrigeration Cycles and Natural Gas Liquefaction Black and Veatch- PRICO Process
Liquefaction Techniques Multiple Refrigeration cycles 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.
Air Products and Chemical Inc: C3-MR APCI processes are used in almost 90% of the industry Good standard by which to judge the other processes Capacity of about 5 MTPA Utilizes Propane (C 3 ) and Mixed Refrigerants (MR) Inlet Gas LNG Mixed Refrigerant
Liquefaction Techniques Self Refrigerated Cycles 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.
BP Self Refrigerated Process Neither refrigerants, compressor, nor expanders present in setup. Cost include mainly capital costs and electricity. Low Production rate (51%) Capacities of over 1.3MTPA attainable. Inlet gas LNG Residue Gas
Liquefaction Techniques Cascade Processes 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.
ConocoPhilips Simple Cascade 3 stage pure refrigerant process Propane Ethylene Methane 5 MTPA Capacity Pre- Cooling Sub-Cooling Liquefaction Inlet Gas LNG Residue Gas Propane Ethylene Methane
Plate Fin Heat Exchanger
Spiral Wound Heat Exchanger
Equipment Comparison Plate-Fin-Heat-ExchangersCoil-Wound-Heat-Exchangers Characteristics Extremely compactCompact Multiple streams Single and two-phase streams Fluid Very cleanClean Flow-types Counter-flowCross counter-flow Cross-flow Heating-surface m²/m³ m²/m³ Materials Aluminum Stainless steel (SS) Carbon steel (CS) Special alloys Temperatures -269°C to +65 °C (150 °F)All Pressures Up to 115 bar (1660 psi)Up to 250 bar (3625 psi) Applications Cryogenic plantsAlso for corrosive fluids Non-corrosive fluidsAlso for thermal shocks Very limited installation spaceAlso for higher temperatures
Our Evaluation Methods Data on operating conditions (Temperatures, Pressures, Flowrates, etc) for all these processes is not widely available (Only some is reported). We decided to perform simulations using our best estimates. We used minimum compression work as guide. We identified non-improvable points
Details of methodology Conditions after each stage of refrigeration were noted After making simple simulations mimic real process, variables were transferred to real process simulation Optimization- Refrigerant composition Optimization- Compressor work Restriction needed- Heat transfer area All cells in LNG HX must have equal area Restriction needed- Second law of thermodynamics Check temperature of streams Utilities Obtain cooling water flow rate
Pre- Cooling Sub-Cooling Liquefaction High Pressure Low Pressure CO 2 Pre-cooled Linde Process Modification of the Mixed Fluid Cascade Process Three distinct stages using 3 mixed refrigerants with different compositions Carbon dioxide is sole refrigerant in pre-cooling stage Separate cycles and mixed refrigerants help in the flexibility and thermodynamic efficiency Process is safer because hydrocarbon inventory is less 8 MTPA Capacity Inlet Gas LNG 100 o C -70 o C -140 o C -260 o C
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 Basis
ProcessCost per ton ($)Max capacity (MTPA) Prico Liquefin ExxonMobil DMR APX MFCP MFCP(CO2) TEALARC C3MR Conoco
Analysis Our results may not match market trends Operating temperature and pressure range as well as flowrate information unavailable Precedents to compare results unavailable Information on cost to use process unavailable (licensing, proprietary production fees, etc.)
Analysis We may be trapped in local minima and failed to identify better conditions Work Temperature Global Minimum Local Minimum
Conclusions We successfully simulated several LNG production plants We obtained capital and operating costs and determined a ranking Some connection with existing trends were identified, but other results do not coincide with market trends We discussed why discrepancies may arise.
References "Overview: LNG Basics." Center for Liquefied Natural Gas Center for Liquefied Natural Gas. 3 Feb Fossil Energy Office of Communications. U.S. Department of Energy: Fossil Energy. 18 Dec U.S. Department of Energy. 3 Feb "Mustang receives U.S. patent for LNG liquefaction process." Scandanavian Oil and Gas Magazine. 14 Dec Feb Spilsbury, Chris; Yu-Nan Liu; et al. "Evolution of Liquefaction Technology for today's LNG business." Journees Scientifiques Et Techniques (2006) Process Selection is Critical to onshore LNG economics. World-Oil Magazine. February 2006 com Flynn, Thomas N. Cryogenic Engineering. Second edition. Marcel Dekker. New York- NY. 2005