Cryogenic Expander Application in Cryogenic Expander Application
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Cryogenic Expander Application in Propane Liquefaction Process AIChE Spring Meeting Houston TX Houston, 3 April, 2012 T6A08 – LNG equipment and Cryogenic Expander Michael Cords Senior Mechanical Engineer Ebara International Corporation Submerged cryogenic liquid expanders have a field history of 10+ years Over 100 units in operation Majority are installed in LNG liquefaction trains. LIQUID EXPANDERS Cryogenic liquid expanders replace a conventional Joule-Thomson valve The purpose is to increase LNG production (~3-5%) by reducing the boil-off boil off losses In the LNG liquefaction process, expanders are placed in the LNG production stream and the refrigerant loop Expanders reduce the enthalpy of the liquid in a near isentropic expansion The resulting energy is exported as electrical energy via a generator A submerged generator design allows for operation in the two-phase liquid-vapor region Two-phase expanders combine a liquid expander and flashing valve into one machine resulting in lower liquid quality (i.e. less vapor) P1 Saturation Curve Pressurre P2 P3 Joule – Thomson Valve Expander Two Phase Expander w/Jet Exducer Two Phase Expander w/Condensation Cone Enthalpy Mixed refrigerant is comprised of mostly propane The MR loop is a standard refrigerant cycle Propane is a common refrigerant in many applications Energy removal equates to increase in condensate product kJ / s = m kJ / kg Methane: 1kW of removed electrical power produces 60 tons per year of additional LNG 2MW = 120,000 tpa Propane: 1kW of removed electrical power produces 72 tons per year of additional LPG 2MW = 144,000 144 000 tpa Example of an Existing Propane Refrigeration Cycle Sales Gas Dew Point Control Gas Plant Chiller Low Temperature Separator Vessel Feed Gas Refrigeration Unit Inlet Separator Vessel Liquids to Stabilizer LTS Liquids Li id to Stabilizer Sales Gas Dew Point Control Gas Plant Chiller Low Temperature Separator Vessel Feed Gas Refrigeration Unit Inlet Separator Vessel Liquids to Stabilizer LTS Liquids Li id to Stabilizer Refrigeration Loop Chiller Compressor Condenser JT Valve Refrigeration Loop Chiller Compressor Condenser Expander Application for Propane Two-Phase Expander LNG Regasification Process LNG is stored at receiving terminals in insulated tanks at atmospheric pressure and a temperature of 111 Kelvin For regasification and distribution the LNG is pumped to high pressure and then heated to vaporize into its gaseous state Power Recovery from LNG Regasification LNG regasification plants are large heat sinks and require large heat sources The temperature difference of 170°C 170 C between the heat source and the heat sink provides the pre-condition pre condition for an efficient power recovery Regasification Cycle High g Pressure LNG Vaporizer Natural N t lG Gas Pipeline Heater Pump Expander Pre essure (Mp pa) Propane 3 2 1 Enthalpy (kJ/kg) 4 Losses The electrical motor for the pump, and the generator for the expander, have losses due to inefficiencies Net Power Loss = m * P * (1/M - G) Combined Machine Turbine-Generator / Pump-Motor Net Generated Power = h h = (h3 – h4) – (h2 – h1) Turbine Power Pump Power The proposed working fluid is LPG The LPG is passed p through two separate g and a heat exchangers single machine which pump p and a combines a p two-phase expander Regasification Cycle Vaporizer High g Pressure LNG Natural N t lG Gas Pipeline 12 Pump 23 Heat input 4 Expander p 34 Expansion 3 41 Condensation Cooling 1 2 Pump H t Heater Summary Propane liquid expanders are proven equipment in existing LNG liquefaction trains The opportunity exists to apply this technology to other propane refrigerant applications Thank You
