Ayema Aduku Oluwaseun Harris Valerie Rivera Miguel Bagajewicz Evaluation of LNG Production Technologies Ayema Aduku Oluwaseun Harris Valerie Rivera Miguel Bagajewicz University of Oklahoma

Outline LNG Background Objective Simulation Specifications Liquefaction Techniques Heat Exchanger Types Simulation Method Results

Heavy Component Removal Natural Gas Liquefaction Flow Diagram for a Typical LNG Plant Natural Gas CO2/H2S Removal Dehydration Heavy Component Removal Natural Gas Liquefaction Transportation

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)

Liquefaction Processes Mixed Refrigerants Pure Refrigerants Both Other Linde Process CoP Simple Cascade APCI C3 MR BP Self refrigerated process Axens Liquefin Process CoP Enhanced Cascade APCI AP-X ABB Randall Turbo-Expander Dual Mixed Refrigerant Linde 2006 Williams Field Services co. Technip-TEALARC Mustang Group ExxonMobil Dual Multi-component Black and Veatch Prico Process Technip- Snamprogetti * Italicized processes signify Patent searched processes. * Bolded processes signify processes not included in scope of project.

Flow diagrams

Black and Veatch’s PRICO Process Axens Liquefin Process C3MR: Air Products and Chemical Inc ExxonMobil Dual Multi-Component Cycle

AP-X: Air Products and Chemical Inc. Technip- TEALARC System BP- Self Refrigerated Process DMR- Dual Mixed Refrigerant

Linde- CO2 MFCP Linde/Statoil -Mixed Fluid Cascade Process ConocoPhilips Simple Cascade

Simulation Specifications Natural Gas composition Methane: 0.98 Ethane: 0.01 Propane: 0.01 Inlet conditions Pressure: 750 psia Temperature: 1000F Outlet conditions Pressure: 14.7 psia Temperature: -260oF 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 Cooling Water Gas low Temperature No Pressure change High Temperature refrigerant High Temperature High Pressure Expander Compressor low Temperature low Pressure Heat Exchanger refrigerant High Temperature low Temperature No Pressure change

Liquefaction Techniques Mixed refrigerants are mainly composed of hydrocarbons ranging from methane to pentane, Nitrogen and CO2. Pure component Refrigerants Specific operating ranges for each component Mixed Refrigerants Modified to meet specific cooling demands. Helps improve the process efficiency

Liquefaction Techniques T-Q Diagrams Natural gas cooling curve The main goal is to reduce the distance between the two curves. This would signify a reduction in the work during the cooling process and an increase in efficiency. Area between curves represents work done by the system

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 Inlet Gas LNG Cold Box Compressor Condenser Single mixed refrigerant loop and single compression system Limited capacity (1.3 MTPA) Low capital cost Great Pilot Process 100oC Residue -260oC Expander

Refrigeration Cycles and Natural Gas Liquefaction Cooling Water Gas Inlet Gas LNG Cold Box Compressor Simple Refrigeration Cycle Black and Veatch- PRICO Process Liquefaction techniques take advantage of modified refrigeration cycles

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 Inlet Gas LNG Mixed Refrigerant 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 (C3) and Mixed Refrigerants (MR)

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 Inlet gas LNG 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 . 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 Methane Ethylene Propane Residue Gas Sub-Cooling Inlet Gas Pre- Cooling Liquefaction LNG

Equipment

Plate Fin Heat Exchanger Very compact design but limited in operating range

Spiral Wound Heat Exchanger Large operating range but robust design

Spiral Wound Heat Exchanger Tube bundles wrap around central hollow tube

Equipment Comparison Extremely compact Compact Multiple streams   Plate-Fin-Heat-Exchangers Coil-Wound-Heat-Exchangers Characteristics Extremely compact Compact Multiple streams Single and two-phase streams Fluid Very clean Clean Flow-types Counter-flow Cross counter-flow Cross-flow Heating-surface 300 - 1400 m²/m³ 20 - 300 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 plants Also for corrosive fluids Non-corrosive fluids Also for thermal shocks Very limited installation space Also 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

CO2 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 100oC Pre- Cooling -70oC Liquefaction High Pressure -140oC Low Pressure Sub-Cooling -260oC LNG

TQ diagrams from PRO II simulation

Results

Cost Basis 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

Results 10 Spikes in chart represent points at which new train of process is installed

Results 10 Energy cost includes electricity and cooling water cost

Results The Liquefin Process is reported as fast becoming a popular LNG technique. The Prico process results were expected. Numerous equipment usually leads to higher overall costs. Process Cost per ton ($) Max capacity (MTPA) Prico 5.12 1.20 Liquefin 3.41 6.00 ExxonMobil 4.83 4.80 DMR 12.58 APX 19.20 7.80 MFCP 31.73 7.20 MFCP(CO2) 24.77 TEALARC 25.35 C3MR 12.93 Conoco 20.15 5.00

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 Local Minimum Global 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.

Questions?

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