High-pressure methane (LNG) cryogenic reciprocating piston pumps

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High-pressure methane cryogenic reciprocating piston pumps are positive-displacement machines designed for liquefied natural gas (LNG) applications, often reaching pressures up to 330 barg. These pumps use back-and-forth piston movement to deliver precise flow rates, featuring vacuum-jacketed cold ends to minimize heat leakage and prevent cavitation. Common applications include LCNG filling stations and high-pressure LNG storage.

Key Features and Specifications

• Operating Principle: Positive displacement ensures consistent flow rates regardless of discharge pressure.
• Pressure Capabilities: Typically designed for high-pressure applications, with models available up to 330 bar g (approx. 4786 psi) for LNG.
• Flow Rates: Flow rates often range from 1 up to 74.9 liters per minute (lpm) depending on model and pressure requirements.
• Design Configuration: Often slightly inclined from horizontal to optimize degassing and manage low Net Positive Suction Head (NPSH), reducing cavitation risk.
• Insulation: Cold ends are housed in vacuum-insulated jackets to handle cryogenic temperatures.

Key Technical Specifications

High-pressure cryogenic methane pumps, such as the RPNG Series by TS Italia, are engineered for demanding industrial environments:

• Delivery Pressure: Capable of reaching up to 330 barg (approx. 4,800 psi). Some heavy-duty models can generate over 1,000 bar.
• Flow Rates: Typically range from 22 l/min at maximum pressure to 75 l/min at lower pressures (~50 barg). Large-scale systems can reach up to 35,000 l/h.
• Drive Systems: Often feature oil-lubricated crank drives for reduced noise and longer maintenance intervals compared to grease-lubricated versions.
• Design Configuration: Frequently use a slightly inclined horizontal setup to optimize degassing and prevent cavitation.

Components of a High-Pressure Cryogenic Pump

• Cold-end Assembly: Includes the piston, cylinder, piston rings, and suction/discharge valves, usually constructed with materials optimized for cryogenic temperatures.
• Piston Rings: Often made of PTFE (polytetrafluoroethylene) or similar materials to withstand low temperatures, requiring careful cooling to prevent premature wear.
• Supercharger: Many models include a supercharger to increase pressure before the main compression, resulting in near-zero required NPSH.

Common Applications

• LCNG Filling Stations: Liquid-to-Compressed Natural Gas stations.
• High-Pressure LNG Storage: Transporting or storing methane at elevated pressures.
• Industrial Gases: Similar technologies are used for filling cylinders with liquid nitrogen, oxygen, and argon.
• Marine FGSS: Fuel Gas Supply Systems for LNG-fueled vessels, such as Nikkiso's MSP series, which provide high-pressure gas for ME-GI ship
• engines. 

Safety and Operation

• Cooldown: Proper cooling of the cold end is required to prevent overheating and maintain, particularly with PTFE piston rings.
• Safety Measures: Systems often include high-temperature trips on the discharge line to detect loss of prime and prevent damage.
• Control Systems: Automated control panels are often integrated for safety monitoring and consistent performance.

Main Features & Components

• Vacuum Jacketed Cold End: To minimize heat gain and prevent the liquid methane from vaporizing during the pumping cycle, the "cold end" is often housed in a super-insulated vacuum jacket.
• Piston Seals: Constructed from specialized materials like PTFE (Teflon) compounds to remain flexible and functional at cryogenic temperatures.
• Safety & Compliance: High-pressure units are typically ATEX-certified for use in explosive atmospheres and comply with the Pressure Equipment Directive (PED).

 Safety and Operation

• Cooldown: Proper cooling of the cold end is required to prevent overheating and maintain, particularly with PTFE piston rings.
• Safety Measures: Systems often include high-temperature trips on the discharge line to detect loss of prime and prevent damage.
• Control Systems: Automated control panels are often integrated for safety monitoring and consistent performance.

Leading Manufacturers and Solutions

• TS Italia Srl: RPNG series for LNG applications, offering both high pressure and reliable, low NPSH performance.
• Alfa Laval: Cryomec® reciprocating pumps for high-pressure cryogenic liquid transfer.
• Tecnocryo: Pump skids for high-pressure cryogenic liquid.