L-CNG automobile gas station is a vehicle gas station that converts LNG with low pressure (0 ～ 0.6MPa) and low temperature (- 162 ℃～ 145 ℃) into natural gas with normal temperature and high pressure (20 ～ 25MPa). The equipment of the gas station includes: LNG storage tank, LNG low-temperature and high-pressure pump, high-pressure vaporizer, CNG gas storage (well and bottle group), sequential control panel, gas vending machine, automatic control system, etc.
Process flow of gas station equipment:
LNG in the tank is sent to the high-pressure air heated vaporizer by the low-temperature high-pressure pump. In the air heated vaporizer, the liquid natural gas undergoes phase change after heat exchange with the air, and is converted into a gas state and raised to an appropriate temperature. There are two air heated vaporizers, one for use and one for standby. Manual and pneumatic shut-off valves are set at the inlets of the two groups of air heated vaporizers. During normal operation, the two groups of air heated vaporizers are switched manually or automatically through pneumatic valves, The switching cycle time varies according to the ambient temperature and gas consumption. When the temperature outlet is lower than 5 ℃, the low temperature alarm will be given, the air heated vaporizer will be automatically switched, and the frost on the vaporizer will be removed at the same time, so as to ensure that the used vaporizer can achieve better heat exchange effect. The outlet temperature after LNG vaporization should exceed 5 ℃, and the outlet pressure is 20MPa. When the temperature at the outlet of the air heated vaporizer is less than 5 ℃, the temperature of the air heated vaporizer can reach above 5 ℃ through the water bath reheater, and then it will enter the low, medium, and CNG dispensers take gas from the three gas storage wells from low to high to fuel the vehicles.
This process uses LNG cryogenic high-pressure pump to pressurize LNG to 25.0MPa to complete the process of low pressure to high pressure. During the process, the control of the LNG booster pump and the overpressure shutdown, low-pressure pump startup, fluid metering of the booster pump are automatically completed by the console; This process does not use natural gas compressor, only uses small power high-pressure cryogenic pump, without cooling water, which greatly reduces noise pollution and saves a lot of power.
(1) Unloading process:
Transfer LNG from tank car to LNG storage tank in gas station;
The pressure of the tank car arriving at the station is about 0.4MPa, and the pressure in the tank is 0.5-0.6MPa. The pressure of the tank car storage tank is given by the unloading booster, and LNG is sent to the LNG tank for storage by using the differential pressure.
(2) Pressure regulating process:
After unloading, the LNG in the LNG tank is pressurized to more than 20MPa by the LNG high-pressure pump, vaporized into CNG through the high-pressure vaporizer, and stored in the high-pressure gas storage well or high-pressure cylinder group;
(3) Gas filling process:
CNG in the gas storage well fills gas to the car through CNG dispenser. When the pressure in the gas storage well is too low to fill gas normally, the high-pressure pump restarts and gasifies to supply gas to the gas storage well and pressurize the car.
(4) Control system:
Monitor the status and operation of various equipment to make the gas station operate normally and realize automatic control, and form a complete control system solution together with the gas station management system, safety assurance system and video monitoring system.
(5) Safety considerations for gas station equipment
The daily evaporation rate of low temperature vacuum tank is generally 0.2%. If this part of vaporized gas is not discharged in time, the pressure in the upper gas phase space of the tank will gradually increase. In order to ensure the safety of the tank, the top filling gas (BOG) is automatically discharged through the pressure reducing regulating valve according to the pressure. This BOG gas is heated by BOG and then enters the civil pipe network or gas filling station for its own use. Or BOG is heated and pressurized to 20MPa by a small compressor, and then enters the gas storage well.
Each LNG tank is equipped with high and low liquid level alarm facilities and high pressure alarm. The storage tank and the system pipeline are equipped with safety vent valves to ensure the safety of the storage tank and pipeline. The safety vent gas is heated by the EAG vaporizer and then vented through the vent pipe.
The inlets of the two groups of air heated vaporizers are equipped with manual and pneumatic shut-off valves. During normal operation, the two groups of air heated vaporizers are automatically switched through manual or shut-off valves. The switching cycle time varies according to the ambient temperature and gas consumption. When the temperature outlet is lower than 5 ℃, the low temperature alarm will be given and the air heated vaporizer will be switched automatically.