（1）LNG skid-mounted filling stations.LNG skid-mounted filling station adopts integrated skid-mounted design:The storage tank and its related valves are combined together to form a single piece of equipment,which is arranged on the basis of the skid;The gasifier,LNG cryogenic submersible pump and related process pipelines are separately arranged on a skid-mounted base to become an independent skid-mounted equipment,which meets the safety distance;The filling machine is arranged on a separate filling island,so that the entire filling station is simple.
The electrical control system and related operating parameters of the filling station are displayed locally and in the control room,and the production process is monitored and controlled by the station control system。The main types of process parameters for monitoring include:pressure,liquid level,temperature,flow,gas leakage.Through the use of PLC system control to complete the gas filling,unloading,pressure regulating and other operations.
（2）LNG/L-CNG filling station.LNG/L-CNG filling stations have both LNG filling and CNG filling functions.The LNG/L-CNG filling station is mainly composed of four parts.The first is the LNG skid:consisting of an LNG storage tank,a dump truck,a pressure-controlled air-temperature gasifier,an LNG submersible pump,a process pipeline,an electrical system,and a control instrument system。The second is the CNG skid:CNG high pressure plunger pump,process pipeline,valve,electrical system,control system。The third is composed of a sequence control panel,a gas storage tank group,a CNG dispenser,an EAG heater,a pipeline part,an electrical system,and a control instrument system.Fourth,control devices such as instrument air source,control cabinet,and PLC are installed in a safe area(gas control station control room)。
The process of the LNG filling station is divided into four steps:the unloading process,the pressure adjustment process,the filling process,and the pressure relief process
1）Unloading process:Transfer the LNG in the container or car tanker to the storage tank of the LNG filling station.This process can be achieved in three ways.
（1）Unloading by unloading booster（2）Unloading by submerged filling pump（3）Unloading by booster and pump。This gas filling demonstration station adopts the third way.The selected equipment specifications are:unloading pressure is 200Nm3/h,submerged pump flow is 40-200l/min,pressure is 0.2-1.2mpa.The actual working time of unloading a standard container is about 1.8h.
The first of the three ways of unloading should be preferred,and the method of feeding liquid into the storage tank at the same time is adopted.The advantages of this method are:simplicity and no energy consumption.The disadvantage is that the unloading time is long,and the time for unloading a standard container is about 2.5 to 3.0 hours.It is recommended to increase the unloading supercharger when the filling station site permits.If a 300NmVh unloading supercharger is selected,the time required to unload a standard container is about 2.0 hours.The second method of unloading is not recommended.
2）Pressure regulation process:Because the on-board bottle in the car currently does not have a supercharger,the liquid in the on-board bottle must be a saturated liquid.For this reason,before filling the car with liquid,first adjust the pressure of the LNG in the storage tank to make it a saturated liquid before filling the car.There are also three ways to regulate the voltage.(1)Regulating pressure by tank pressure regulator(2)Regulating pressure by pump low-speed circulation（3）The tank pressure regulator is used in combination with the pump low-speed circulation to regulate the pressure.The first method has the advantages of simple process and equipment and no energy consumption.The disadvantage is that the pressure adjustment time is long.The storage tank pressure regulation of LNG gas filling station is different from that of LNG gasification station storage tank.The pressure regulation of storage tank of LNG gasification station adopts gas phase pressure regulation.The pressure regulation of the storage tank of the LNG filling station is to obtain a saturated liquid with a certain pressure,which can only be performed in the liquid phase.Therefore,the time required to adjust the same pressure in the same storage tank with a pressure regulator of the same specification is quite different.Measured during actual work:A 200Nm pressure regulator is used to adjust the saturated liquid pressure of a 50m3 storage tank.The time required to reach 0.5Mpa is 8-10 hours,which varies depending on the temperature of the external climate.This causes great inconvenience to automobile refueling.The third method of tank pressure regulation is more reasonable,and the pressure regulator should be backed up,and its size should be increased if possible.In this way,although the investment and energy consumption are increased,the pressure adjustment time is greatly shortened.Theoretically,the calculation can be realized in 3.0 to 4.0 hours,thereby ensuring the aeration time.If the second method is used alone,the pressure adjustment time is still too long.
3）Filling process:The saturated liquid LNG in the storage tank is pressurized by the pump to refill the car with a refilling gun.The refilling pressure is 1.6Mpa.Before refilling the car bottle,the car bottle should be depressurized first,and the car bottle should be recovered through the air return port Respiration.At present,this part of the gas is vented.It is recommended to add a return pipe from the car bottle to the gas phase of the storage tank in the future filling stations,and design a measuring device to facilitate the recovery and measurement of the remaining gas in the car bottle.
4）Pressure relief process:During the pressure adjustment process of the storage tank,the liquid in the storage tank is continuously evaporating and gasifying at the same time.If this part of the vaporized gas is not discharged in time,the pressure in the storage tank will become greater and greater.When the pressure of the storage tank is greater than the set value,the relevant valve opens,releasing the gas in the storage tank,reducing the pressure and ensuring the safety of the storage tank.At present,this part of the gas is vented.It is suggested that in the future filling stations,this part of the gas be sent to the nearby municipal pipe network system after pressure adjustment.