Low emission device and method for liquefied natural gas filling station with pump

Abstract

The present invention relates to a low-emission device and method for a liquefied natural gas filling station with a pump, comprising a low-temperature storage tank (10), a submersible pump (20) and a gas dispenser (30), and a BOG recovery skid (40). The BOG recovery skid is provided with a recovery skid liquid inlet (41), a recovery skid liquid outlet (42) and a recovery skid gas inlet (43). The recovery skid liquid inlet (41) is connected to the submersible pump outlet (21), the recovery skid liquid outlet (42) is connected to the gas dispenser liquid phase port (31), the recovery skid gas inlet (43) is connected to the gas phase port (11) of the low-temperature storage tank, the gas return port (12) of the low-temperature storage tank is connected to the gas phase port (32) of the gas dispenser, and the liquid phase port (13) of the low-temperature storage tank is connected to the submersible pump inlet (22). The present invention uses a BOG recovery skid with a BOG recovery function, which can reduce BOG emissions, reduce resource waste, and improve the economic benefits of the gas station. The BOG recovery skid is independently configured and installed, and can be easily connected to existing LNG filling station equipment. There is no need to upgrade or modify the original equipment, and it does not affect the operation and control methods of the original system. It is particularly suitable for small LNG filling stations with small gas volumes.

Description

Technical Field

[0001] The present invention relates to the field of liquefied natural gas filling, and in particular to a low-emission device and method for a liquefied natural gas filling station with a pump. Background Art

[0002] Many small LNG filling stations currently operate, but due to their small filling volumes, they emit BOG (liquefied natural gas boil-off gases), wasting energy and polluting the environment. Some current improvements utilize recovery tanks to mix BOG with cryogenic liquefied natural gas (LNG), re-liquefying the BOG and enabling BOG recycling. For example, the Chinese invention patent (publication number CN106287202A) discloses a "tank-based LNG refueling device and method for BOG recovery without emissions." However, this improvement requires the complete replacement of existing station equipment, including cryogenic storage tanks, submersible pumps, and dispensers. This high cost makes it difficult to scale up and apply to small LNG filling stations. Furthermore, the current proliferation of filling station equipment manufacturers and inconsistent manufacturing standards presents significant challenges for upgrading small LNG filling stations. Summary of the Invention

[0003] The purpose of the present invention is to propose a low-emission device and method for a liquefied natural gas filling station with a pump, and to provide a filling station renovation solution with simple technical connection, convenient renovation and low cost.

[0004] In order to achieve the above-mentioned purpose, the technical solution of the present invention is: a low-emission device for a liquefied natural gas filling station with a pump, comprising a low-temperature storage tank (10), a submersible pump (20) and a gas dispenser (30), and provided with a BOG recovery skid (40), wherein the BOG recovery skid is provided with a recovery skid liquid inlet (41), a recovery skid liquid outlet (42) and a recovery skid gas inlet (43), wherein the recovery skid liquid inlet (41) is connected to the submersible pump outlet (21), the recovery skid liquid outlet (42) is connected to the gas dispenser liquid phase port (31), the recovery skid gas inlet (43) is connected to the gas phase port (11) of the low-temperature storage tank, the gas return port (12) of the low-temperature storage tank is connected to the gas phase port (32) of the gas dispenser, and the liquid phase port (13) of the low-temperature storage tank is connected to the submersible pump inlet (22).

[0005] Furthermore, a preferred BOG recovery skid structure is that the BOG recovery skid is provided with a BOG recovery tank (50) and a compressor (60), the BOG recovery tank is provided with a recovery tank liquid inlet (51), a recovery tank liquid outlet (52), a recovery tank air inlet (53) and a recovery tank gas phase port (54), an upper spray pipe (55) and a lower spray pipe (56) are provided in the BOG recovery tank, the BOG recovery tank is further provided with a recovery tank pressure transmitter (57), a recovery tank temperature sensor (58) and a recovery tank liquid level sensor (59), the recovery tank liquid inlet (51) is connected to The upper spray pipe (55) and the recovery tank air inlet (53) are connected to the lower spray pipe (56), the recovery tank liquid inlet (51) is connected to the recovery skid liquid inlet (41), the recovery tank liquid outlet (52) is connected to the recovery skid liquid outlet (42), the recovery tank air inlet (53) and the recovery tank gas phase port (54) are respectively connected to the compressor output end (61), the compressor input end (62) is connected to the recovery skid air inlet (43), and the recovery skid liquid inlet (41) and the recovery skid liquid outlet (42) are connected through a liquid phase bypass pipe (44).

[0006] Furthermore, in order to realize the control function of the BOG recovery skid, the liquid phase bypass pipe (44) is provided with a first control valve (45), which is a normally open valve. A second control valve (46) is provided between the recovery tank liquid inlet (51) and the liquid phase bypass pipe (44), a third control valve (47) is provided between the recovery tank liquid outlet (52) and the liquid phase bypass pipe (44), a fourth control valve (48) is provided between the recovery tank gas inlet (53) and the output end (61) of the compressor, and a fifth control valve (49) is provided between the recovery tank gas phase port (54) and the output end (61) of the compressor. The recovery skid is provided with a control system, which controls the opening and closing of the first control valve (45), the second control valve (46), the third control valve (47), the fourth control valve (48) and the fifth control valve (49).

[0007] Furthermore, in order to keep the compressor in good working condition, the BOG recovery skid is provided with a heat exchanger (70), which is a heat exchanger for heat exchange between a heat absorbing medium and a heat dissipating medium. The heat exchanger is provided with a heat absorbing medium inlet (71), a heat absorbing medium outlet (72), a heat dissipating medium inlet (73) and a heat dissipating medium outlet (74). The heat absorbing medium inlet (71) is connected to the air inlet (43) of the recovery skid, the heat absorbing medium outlet (72) is connected to the input end (62) of the compressor, the heat dissipating medium inlet (73) is connected to the output end (61) of the compressor, and the heat dissipating medium outlet (74) is respectively connected to the air inlet (53) and the gas phase port (54) of the recovery tank.

[0008] Furthermore, in order to lower the temperature of the BOG recovery tank, an air-cooled radiator (80) is provided between the compressor (60) and the heat exchanger (70), the input end (81) of the air-cooled radiator is connected to the output end (61) of the compressor, the output end (82) of the air-cooled radiator is connected to the heat dissipation medium inlet (73) of the heat exchanger, the air-cooled radiator is provided with a bypass pipe (83), and a temperature sensor (63) is provided at the output end (61) of the compressor.

[0009] Furthermore, in order to effectively control the operation of the BOG recovery skid, a temperature sensor (4a) and a pressure transmitter (4b) are provided at the liquid inlet of the recovery skid, and the recovery skid is provided with a control system, which receives the detection values ​​of the temperature sensor (4a) and the pressure transmitter (4b) and controls the operation of the recovery skid.

[0010] A low-emission method for a liquefied natural gas filling station with a pump, comprising the device according to any one of claims 1 to 6, characterized in that the method comprises:

[0011] Step a. If the pressure value at the recovery skid liquid inlet (41) is lower than the starting pressure setting value, open the first control valve (45), close the second control valve (46) and the third control valve (47), and then proceed to step e. If the pressure value at the recovery skid liquid inlet (41) is not lower than the starting pressure setting value, proceed to step b.

[0012] Step b. If the liquid level in the BOG recovery tank is not lower than the upper limit, open the first control valve, close the second control valve, open the third control valve, start the compressor (60), close the fourth control valve (48), open the fifth control valve (49), and return to step a. If the liquid level in the BOG recovery tank is lower than the upper limit, proceed to step c.

[0013] Step c. If the temperature at the recovery skid liquid inlet (41) is not lower than the start-up temperature setting value, open the first control valve (45), close the second control valve (46) and the third control valve (47), and then proceed to step e. If the temperature at the recovery skid liquid inlet (41) is lower than the start-up temperature setting value, proceed to step d.

[0014] Step d. If the liquid level in the BOG recovery tank is not higher than the lower limit, close the first control valve (45), open the second control valve (46), close the third control valve (47), and return to step a. If the liquid level in the BOG recovery tank is higher than the lower limit, close the first control valve (45), open the second control valve (46) and the third control valve (47), and then proceed to step e.

[0015] Step e. If the liquid level in the BOG recovery tank is not lower than the upper limit or not higher than the lower limit, turn off the compressor (60), close the fourth control valve (48), close the fifth control valve (49), and return to step a. If the liquid level in the BOG recovery tank is lower than the upper limit and higher than the lower limit, proceed to step f.

[0016] Step f. If the temperature in the BOG recovery tank is not lower than the set recovery temperature, the compressor (60) is turned off, the fourth control valve (48) is closed, the fifth control valve (49) is closed, and the process returns to step a. If the temperature in the BOG recovery tank is lower than the set recovery temperature, the compressor is turned on, the fourth control valve is opened, the fifth control valve is closed, and the process returns to step a.

[0017] Furthermore, in order to obtain a good BOG recovery effect, in step d, if the liquid level in the BOG recovery tank is higher than the lower limit, the first control valve (45) is closed, the second control valve (46) and the third control valve (47) are opened, and then the process proceeds to step d1;

[0018] Step d1. If the BOG recovery tank liquid level is less than 50%, adjust the second control valve to increase the opening. If the BOG recovery tank liquid level is not less than 50%, adjust the second control valve to decrease the opening and proceed to step e.

[0019] Furthermore, in order to keep the BOG temperature as low as possible, when the BOG temperature at the output end of the compressor is higher than the ambient air temperature, the bypass pipe (83) of the air-cooled radiator is closed and the air-cooled radiator (80) is started; when the BOG temperature at the output end of the compressor is lower than the ambient air temperature, the bypass pipe (83) of the air-cooled radiator is opened and the air-cooled radiator (80) is closed.

[0020] Furthermore, in order to ensure the normal startup of the recovery skid and the safety of the recovery tank, the startup pressure setting value at the liquid inlet (41) of the recovery skid is greater than the pressure value when the submersible pump (20) is shut down, the upper limit of the liquid level in the BOG recovery tank is the liquid level at which the liquid in the BOG recovery tank is 90% of its volume, and the lower limit of the liquid level in the BOG recovery tank is the liquid level at which the liquid in the BOG recovery tank is 10% of its volume.

[0021] The beneficial effects of this invention are: using a BOG recovery skid with BOG recovery capabilities can reduce BOG emissions, minimize resource waste, and improve the economic efficiency of gas stations. The BOG recovery skid is independently designed and installed, and can be easily integrated with existing LNG station equipment, eliminating the need for upgrades and modifications to existing equipment and maintaining the existing system's operation and control methods. It is particularly suitable for small LNG stations with low gas volumes.

[0022] The present invention is described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a system diagram of the present invention;

[0024] Figure 2 This is a diagram of the BOG recovery skid system of the present invention;

[0025] Figure 3 This is a system status diagram of the BOG recovery skid of the present invention when it stops operating;

[0026] Figure 4 This is a schematic diagram of the system operation when the liquid level of the BOG recovery tank of the present invention is higher than the upper limit;

[0027] Figure 5 This is a schematic diagram of the system operation when the liquid level of the BOG recovery tank of the present invention is lower than the lower limit;

[0028] Figure 6 This is a schematic diagram of the system operation when the liquid temperature of the BOG recovery tank of the present invention is higher than the set value of the recovery temperature;

[0029] Figure 7 This is a schematic diagram of the system operation when the present invention is performing normal BOG recovery;

[0030] Figure 8 It is the basic flow chart of the control system of the present invention;

[0031] Figure 9 This is the basic flow chart of the system with BOG recovery tank level control of the present invention. DETAILED DESCRIPTION

[0032] Example 1:

[0033] like Figure 2 A BOG recovery skid is provided with a recovery skid liquid inlet (41), a recovery skid liquid outlet (42), and a recovery skid air inlet (43). The BOG recovery skid is provided with a BOG recovery tank (50), a compressor (60), a heat exchanger (70), and an air-cooled radiator (80).

[0034] The BOG recovery tank (50) is provided with a recovery tank liquid inlet (51), a recovery tank liquid outlet (52), a recovery tank air inlet (53) and a recovery tank gas phase outlet (54). An upper spray pipe (55) and a lower spray pipe (56) are provided in the BOG recovery tank. The upper spray pipe (55) is provided at the upper part of the BOG recovery tank and is located at a position not lower than 90% of the liquid level. The lower spray pipe (56) is provided at the lower part of the BOG recovery tank and is located at a position not higher than 10% of the liquid level. The recovery tank liquid inlet (51) is connected to the upper spray pipe (55) inside the BOG recovery tank. The recovery tank air inlet (53) is connected to the lower spray pipe (56) inside the BOG recovery tank. The recovery tank liquid outlet (52) is connected to the lower end of the BOG recovery tank and is in communication with the liquefied gas (liquid) inside the BOG recovery tank. The recovery tank gas phase outlet (54) is connected to the upper end of the BOG recovery tank and is in communication with the BOG inside the BOG recovery tank. The volume of the BOG recovery tank (50) is much smaller than that of the low-temperature storage tank at the gas station, and can usually be designed to be about 1 cubic meter.

[0035] The compressor (60) is a compressor for compressing BOG gas.

[0036] The heat exchanger (70) is a heat exchanger for heat exchange between a heat absorbing medium and a heat dissipating medium. The heat exchanger (70) of this embodiment is a shell and tube heat exchanger. The heat absorbing medium flows through the internal tube side and exchanges heat with the heat dissipating medium flowing through the shell side of the heat exchanger. The heat exchanger is provided with a heat absorbing medium inlet (71), a heat absorbing medium outlet (72), a heat dissipating medium inlet (73), and a heat dissipating medium outlet (74).

[0037] An air-cooled radiator (80) is provided between the compressor (60) and the heat exchanger (70), and the air-cooled radiator (80) is provided with a bypass pipe (83).

[0038] The recovery skid liquid inlet (41) is connected to the recovery tank liquid inlet (51), and the recovery tank liquid outlet (52) is connected to the recovery skid liquid outlet (42). The recovery skid liquid inlet (41) and the recovery skid liquid outlet (42) are connected via a liquid phase bypass pipe (44).

[0039] The air inlet (43) of the recovery skid is connected to the heat absorbing medium inlet (71) of the heat exchanger, the heat absorbing medium outlet (72) of the heat exchanger is connected to the input end (62) of the compressor, the output end (61) of the compressor is connected to the input end (81) of the air-cooled radiator, the output end (82) of the air-cooled radiator is connected to the heat dissipation medium inlet (73) of the heat exchanger, and the heat dissipation medium outlet (74) of the heat exchanger is respectively connected to the air inlet (53) and the gas phase port (54) of the recovery tank through a tee.

[0040] The recovery skid liquid inlet (41) and the recovery skid liquid outlet (42) are connected via a liquid phase bypass pipe (44).

[0041] The liquid phase bypass pipe (44) is provided with a first control valve (45), which is a normally open valve. A second control valve (46) is provided between the recovery tank liquid inlet (51) and the recovery skid liquid inlet (41), and a third control valve (47) is provided between the recovery tank liquid outlet (52) and the recovery skid liquid outlet (42). The second control valve (46) and the third control valve (47) are provided between the BOG recovery tank (50) and the liquid phase bypass pipe (44). The second control valve (46) can adjust the flow rate by adjusting the opening. A fourth control valve (48) is provided between the recovery tank air inlet (53) and the heat exchanger heat dissipation medium outlet (74), and a fifth control valve (49) is provided between the recovery tank gas phase port (54) and the heat exchanger heat dissipation medium outlet (74). The temperature of the BOG output from the compressor is higher than the temperature of the BOG from the low-temperature storage tank (10) (i.e., the BOG output from the compressor). The BOG output from the compressor and the BOG input are heat-exchanged in the heat exchanger (70). The heat exchanger is beneficial for the compressor to maintain a good working condition.

[0042] A temperature sensor (4a) and a pressure transmitter (4b) are provided at the liquid inlet (41) of the recovery skid. The BOG recovery tank is provided with a recovery tank pressure transmitter (57), a recovery tank temperature sensor (58), and a recovery tank liquid level sensor (59). A temperature sensor (63) is provided at the output end (61) of the compressor.

[0043] The recovery skid is equipped with a control system that detects various sensors and transmitters. The control system controls the opening and closing of the first control valve (45), the second control valve (46), the third control valve (47), the fourth control valve (48), and the fifth control valve (49), and controls the start and stop of the compressor (60) and the heat exchanger (70). In essence, the control system is used for system detection and control within the recovery skid, and does not detect or control system devices outside the recovery skid.

[0044] Example 2:

[0045] like Figure 1 A low-emission device for a liquefied natural gas filling station with a pump is provided, wherein a low-temperature storage tank (10), a submersible pump (20), and a gas dispenser (30) are provided in the liquefied natural gas filling station with a pump. The low-emission device for the liquefied natural gas filling station with a pump in this embodiment is provided with a BOG recovery skid (40). The BOG recovery skid (40) is the BOG recovery skid described in the first embodiment.

[0046] This embodiment uses a BOG recovery skid (40) to transform a liquefied natural gas filling station.

[0047] In the existing liquefied natural gas filling station, the liquid phase port (13) of the cryogenic storage tank is connected to the submersible pump input port (22), the submersible pump output port (21) is connected to the filling machine liquid phase port (31), and the return gas port (12) of the cryogenic storage tank is connected to the filling machine gas phase port (32).

[0048] During the renovation of the liquefied natural gas filling station, a BOG recovery skid (40) is installed. The recovery skid liquid inlet (41) of the BOG recovery skid (40) is connected to the submersible pump outlet (21), and the recovery skid liquid outlet (42) is connected to the filling machine liquid phase port (31). The recovery skid gas inlet (43) is connected to the low-temperature storage tank gas phase port (11) (If the low-temperature storage tank (10) does not have a spare gas phase port, a gas phase port can be connected in parallel to the return gas phase port of the low-temperature storage tank non-pump pool cold port). The entire renovation process is very simple and does not change the basic equipment and control system of the filling station, nor does it affect the original operation process of the filling station.

[0049] Example 3:

[0050] A low-emission method for a liquefied natural gas filling station with a pump adopts the apparatus described in the first and second embodiments to achieve BOG recovery and emission reduction at the liquefied natural gas filling station.

[0051] The control system of the BOG recovery skid (40) detects the temperature sensor (4a) and the pressure transmitter (4b) at the recovery skid liquid inlet (41), as well as the recovery tank temperature sensor (58) and the recovery tank liquid level sensor (59).

[0052] A start-up temperature setting value is set in the control system. The start-up temperature setting value is the temperature at the liquid inlet (41) of the recovery skid. When the liquefied natural gas (LNG) in the cryogenic storage tank (10) flows through the temperature sensor (4a), the temperature sensor (4a) can detect the temperature of the liquefied natural gas in the cryogenic storage tank (10). The start-up temperature setting value represents that the liquefied natural gas in the cryogenic storage tank (10) has a sufficiently low temperature to be mixed with the BOG and re-liquefy the BOG. ​​The start-up temperature setting value can usually be set to -130°C and can be appropriately adjusted according to factors such as the length of the gas pipeline, pipeline insulation, and ambient temperature.

[0053] A starting pressure setting value is set in the control system. The starting pressure setting value is the pressure at the recovery skid inlet (41). The starting pressure setting value is a parameter value used to detect whether the submersible pump (20) is started. Therefore, the starting pressure setting value should be greater than the pressure value at the recovery skid inlet when the submersible pump (20) is stopped. It is a pressure value that can be reached at the recovery skid inlet (41) after the submersible pump (20) is started. The pressure transmitter (4b) can detect the pressure at the recovery skid inlet (41). When the pressure at the recovery skid inlet exceeds the starting pressure setting value, it can be determined that the submersible pump (20) has been started. Furthermore, it can be indicated that the gas station has started the gas filling operation process. The working pressure of the submersible pump of different liquefied natural gas filling stations will be different. The starting pressure setting value can be set according to the specific working conditions of the gas filling station.

[0054] The control system is also provided with a recovery temperature set value, which is the temperature of the liquefied natural gas (LNG) in the BOG recovery skid (40). The recovery tank temperature sensor (58) can detect the temperature of the LNG in the BOG recovery skid. Usually, the recovery temperature set value is slightly higher than the start-up temperature set value at the recovery skid liquid inlet (41). In this embodiment, the set value of the liquid temperature in the BOG recovery tank is set to -120°C. It can be appropriately adjusted according to factors such as the length of the gas pipeline, pipeline insulation, and ambient temperature for different gas filling stations.

[0055] In addition, the control system also sets an upper limit and a lower limit of the liquid level in the BOG recovery tank. The recovery tank liquid level sensor (59) can detect the liquid level in the BOG recovery tank. The upper limit of the liquid level in the BOG recovery tank is the liquid level at which the liquid (LNG) in the BOG recovery tank is 90% of its volume, and the lower limit of the liquid level in the BOG recovery tank is the liquid level at which the liquid (LNG) in the BOG recovery tank is 10% of its volume.

[0056] The method of this embodiment includes:

[0057] Step a.

[0058] If the pressure value at the recovery skid inlet (41) is lower than the starting pressure setting value, the first control valve (45) is opened, the second control valve (46) and the third control valve (47) are closed, and then step e is entered. This state indicates that the submersible pump (20) is not started and the gas filling station stops working. Since the first control valve (45) remains normally open, the submersible pump output port (21) is connected to the gas filling machine liquid phase port (31) through the liquid phase bypass pipe (44), which is the same as the working state of the original gas filling station, and the gas filling station can operate as usual. Figure 3 However, since the recovery skid can recover BOG independently from the aeration process of the submersible pump, the control process must enter step e (BOG recovery step).

[0059] If the pressure value at the recovery skid inlet (41) is not lower than the starting pressure setting value, this state indicates that the submersible pump (20) has been started, and the process proceeds to step b, which is the operation after the submersible pump is started.

[0060] Step b.

[0061] If the liquid level in the BOG recovery tank is not lower than the upper limit, open the first control valve, close the second control valve, open the third control valve, start the compressor (60), close the fourth control valve (48), open the fifth control valve (49), and return to step a. This step is for the safety of the BOG recovery tank. It detects whether the liquid level in the BOG recovery tank exceeds the upper limit. If the liquid level in the recovery tank exceeds the upper limit, the liquid level needs to be lowered. At this time, it is necessary to close the second control valve to stop inputting LNG into the BOG recovery tank, open the first control valve to allow the submersible pump to directly transport LNG to the gas dispenser, and open the third control valve at the same time so that the LNG in the BOG recovery tank can flow to the gas dispenser (30). Start the compressor (60), and inject BOG from the recovery tank gas phase port (54) set at the upper end of the BOG recovery tank through the fifth control valve (49), press out the LNG in the BOG recovery tank, and transport it to the gas dispenser. Figure 4 Then return to step a and restart the control cycle. If the submersible pump stops, the operation can be interrupted in time.

[0062] If the liquid level in the BOG recovery tank is lower than the upper limit, proceed to step c;

[0063] Step c. If the temperature at the recovery skid inlet (41) is not lower than the start-up temperature setting value, open the first control valve (45), close the second control valve (46) and the third control valve (47), and then proceed to step e. In this state, the liquefied natural gas (LNG) in the cryogenic storage tank (10) is not sufficiently low, so BOG recovery cannot be performed and LNG cannot be delivered to the BOG recovery tank. As in step a, keep the first control valve (45) open, and connect the submersible pump outlet (21) to the gas dispenser liquid phase port (31) through the liquid phase bypass pipe (44).

[0064] If the temperature at the recovery skid inlet (41) is lower than the start-up temperature setting value, in this state, the liquefied natural gas (LNG) in the cryogenic storage tank (10) has a sufficiently low temperature, and the process proceeds to step d.

[0065] Step d. If the liquid level in the BOG recovery tank is not higher than the lower limit, close the first control valve (45), open the second control valve (46), close the third control valve (47), and return to step a. This step is also for the safety of the BOG recovery tank. It detects whether the liquid level in the BOG recovery tank has not reached the lower limit. If the liquid level in the BOG recovery tank has not reached the lower limit, it is necessary to increase the liquid level. At this time, it is necessary to inject LNG into the BOG recovery tank. After the first control valve (45) and the third control valve (47) are closed, the LNG from the submersible pump directly enters the BOG recovery tank through the second control valve (46), so that the liquid level is increased. Figure 5 As shown. Although this will temporarily interrupt the gas dispenser's operation, it will quickly restore the BOG recovery tank's liquid level to above the lower limit, ensuring recovery efficiency. Then, return to step a and restart the control cycle. If the submersible pump stops, the operation can be interrupted immediately.

[0066] If the liquid level in the BOG recovery tank is higher than the lower limit, the first control valve (45) is closed, the second control valve (46) and the third control valve (47) are opened, and then the process proceeds to step e. In this state, the liquid level in the BOG recovery tank is within the normal range, and LNG can continue to be injected into the BOG recovery tank.

[0067] Step e. This step is the step for starting BOG recovery. In the present invention, BOG recovery is performed independently of the working state of the submersible pump, that is, it is not directly controlled according to the state of the submersible pump. The conditions for BOG recovery are: the liquid level in the BOG recovery tank is within the normal range, and the temperature of the BOG recovery tank meets the low temperature required for recovery. In the control process, there are two situations for entering the BOG recovery step (step e): one is to enter from step d, at which time the liquid level in the BOG recovery tank is already within the normal range; the other is to enter from step a or step c, at which time it is not certain that the liquid level in the BOG recovery tank is within the normal range. Therefore, this step needs to determine again whether the liquid level in the BOG recovery tank is within the normal range. If the liquid level in the BOG recovery tank is not lower than the upper limit or not higher than the lower limit, that is, the liquid level is not within the normal range, the compressor (60) is turned off, the fourth control valve (48) is closed, the fifth control valve (49) is closed, the BOG recovery process is stopped, and the control process returns to step a to restart.

[0068] If the liquid level in the BOG recovery tank is lower than the upper limit and higher than the lower limit, that is, the liquid level is within the normal range, then proceed to step f.

[0069] Step f. If the BOG recovery tank temperature is not lower than the recovery temperature setting value, the compressor (60) is turned off, the fourth control valve (48) is closed, the fifth control valve (49) is closed, and the process returns to step a. In this state, since the LNG in the BOG recovery tank does not meet the low temperature conditions for recovering BOG, the BOG recovery process is stopped and the compressor is turned off to save energy. It is possible to wait for the low temperature LNG from the low temperature storage tank (10) to lower the LNG temperature in the BOG recovery tank, such as Figure 6 Then return to step a and restart the control process.

[0070] If the BOG recovery tank temperature is lower than the recovery temperature setting value, start the compressor, open the fourth control valve, and close the fifth control valve. Then return to step a. At this time, the conditions for BOG recovery are met and the BOG recovery process can be started. At this time, the recovery skid enters the normal BOG recovery process. The compressor (60) extracts the BOG from the low-temperature storage tank (10) and inputs the BOG from the lower spray pipe (56) to the BOG recovery tank (40) through the opened fourth control valve (48), so that the BOG is mixed with the low-temperature LNG in the BOG recovery tank and re-liquefied to achieve BOG recovery. Figure 7 Then return to step a to perform loop control.

[0071] The control system cycles through steps a to f to control the operation and safety of the recovery skid.

[0072] Control process such as Figure 8 shown.

[0073] The BOG output from the compressor (60) is transported to the BOG recovery tank (50) through the air-cooled radiator (80) and the heat exchanger (70). A temperature sensor (63) is provided at the output end (61) of the compressor. When the BOG temperature at the output end of the compressor is not higher than the ambient air temperature, the bypass pipe (83) of the air-cooled radiator is opened, the air-cooled radiator (80) is closed, and the BOG is output through the bypass pipe (83) of the air-cooled radiator. When the BOG temperature at the output end of the compressor is higher than the ambient air temperature, the bypass pipe (83) of the air-cooled radiator is closed, and the air-cooled radiator (80) is started. The air-cooled radiator (80) can cool the BOG, thereby appropriately reducing the temperature of the BOG recovery tank (50).

[0074] Example 4:

[0075] A low-emission method for a liquefied natural gas filling station with a pump. This embodiment is an improvement of the third embodiment.

[0076] The BOG recovery method of the present invention is to transport the BOG in the cryogenic storage tank to the BOG recovery tank, mix it with the cryogenic LNG, and utilize the cold energy in the BOG recovery tank to re-liquefy the BOG. ​​The liquid level of the LNG in the BOG recovery tank will affect the recovery effect. If the LNG in the BOG recovery tank is kept at a high liquid level, the LNG flow rate input from the cryogenic storage tank to the BOG recovery tank will be reduced, and the cold energy in the BOG recovery tank comes from the LNG in the cryogenic storage tank. Therefore, it is not advisable to maintain an excessively high liquid level in the BOG recovery tank. In addition, an excessively high liquid level will easily cause the liquid level in the BOG recovery tank to exceed the upper limit of the liquid level. On the other hand, during the BOG recovery process, the gaseous BOG pumped into the BOG recovery tank by the compressor enters the lower spray pipe (56) at the lower end of the BOG recovery tank, and is mixed with the liquid cryogenic LNG by bubbling and absorbed by the cryogenic LNG. Therefore, if the BOG recovery tank is kept at an excessively low liquid level, the bubbling stroke and the time for mixing the BOG and the cryogenic LNG will be reduced, thereby reducing the BOG recovery effect. Similarly, a too low liquid level may easily cause the liquid level in the BOG recovery tank to fall below the lower limit.

[0077] In order to control the liquid level of the BOG recovery tank within an optimal range, this embodiment adopts the following method:

[0078] In step d, if the liquid level in the BOG recovery tank is higher than the lower liquid level limit, the first control valve (45) is closed, the second control valve (46) and the third control valve (47) are opened, and then the process proceeds to step d1.

[0079] Step d1. If the BOG recovery tank liquid level is lower than 50%, adjust the second control valve to increase the opening. If the BOG recovery tank liquid level is not lower than 50%, adjust the second control valve to decrease the opening and proceed to step e.

[0080] Control process such as Figure 9 shown.

[0081] This embodiment adds step d1, which can control the LNG liquid level in the BOG recovery tank within a range of about 50%, thereby preventing the LNG liquid level in the BOG recovery tank from being too high or too low.

[0082] The control method of this embodiment differs from the upper and lower limits of the BOG recovery tank liquid level in steps b and d. The upper and lower limits of the BOG recovery tank liquid level control are safety controls performed in the event of a system anomaly. The liquid level control of this embodiment, on the other hand, is performed during normal system operation.

[0083] The control system of the present invention can realize the following functions:

[0084] 1. Recovery skid start control. The temperature sensor (4a), pressure transmitter (4b), recovery tank temperature sensor (58), and recovery tank liquid level sensor (59) installed in the recovery skid are used to determine whether the conditions for BOG recovery are met and control the start and stop of the BOG recovery skid, allowing the BOG recovery skid to operate independently of the original gas filling station.

[0085] 2. Recovery process control. The LNG temperature in the BOG recovery tank is detected by the recovery temperature setpoint, and the BOG recovery process is started at the appropriate time. BOG recovery can still be carried out when the submersible pump is not working, making the BOG recovery skid operate efficiently.

[0086] 3. Recovery tank safety control: By detecting the upper and lower liquid levels in the BOG recovery tank, the liquid (LNG) in the BOG recovery tank can be replenished or discharged in a timely manner to ensure the safety of the BOG recovery tank.

[0087] 4. Reasonable liquid level control: Control the liquid level in the BOG recovery tank within a reasonable range to improve the efficiency of the BOG recovery skid.

[0088] The low-emission device and method for a liquefied natural gas filling station with a pump of the present invention are independent of the system of the original natural gas filling station. A BOG recovery skid (40) can be used to transform the liquefied natural gas filling station. In the original liquefied natural gas filling station, the liquid phase port (13) of the low-temperature storage tank is connected to the submersible pump input port (22), the submersible pump output port (21) is connected to the filling machine liquid phase port (31), and the return gas port (12) of the low-temperature storage tank is connected to the filling machine gas phase port (32). In the transformation of the liquefied natural gas filling station, a BOG recovery skid (40) is installed. The recovery skid liquid inlet (41) of the BOG recovery skid (40) is connected to the submersible pump output port (21), and the recovery skid liquid outlet (42) is connected to the filling machine liquid phase port (31). The air inlet (43) of the recovery skid is connected to the gas phase port (11) of the cryogenic storage tank (if the cryogenic storage tank (10) does not have a spare gas phase port, a gas phase port can be connected in parallel to the return gas phase port of the cryogenic storage tank that is not in the pump pool). The entire modification process is very simple. The control system works independently without changing the original control system of the gas station, nor is it interconnected with the original control system of the gas station. The recovery skid is activated by the output pressure of the submersible pump of the gas station and the temperature of the output LNG, and has no effect on the original operating procedures of the gas station. It can be applied to gas station systems of various manufacturers, specifications and configurations.

Claims

1. A low-emission device for a liquefied natural gas filling station with a pump, comprising a cryogenic storage tank (10), a submersible pump (20) and a filling machine (30), characterized in that: A BOG recovery skid (40) is provided, wherein the BOG recovery skid is provided with a recovery skid liquid inlet (41), a recovery skid liquid outlet (42) and a recovery skid gas inlet (43); the recovery skid liquid inlet (41) is connected to the submersible pump outlet (21); the recovery skid liquid outlet (42) is connected to the gas filling machine liquid phase port (31); the recovery skid gas inlet (43) is connected to the gas phase port (11) of the low-temperature storage tank; the gas return port (12) of the low-temperature storage tank is connected to the gas phase port (32) of the gas filling machine; and the liquid phase port (13) of the low-temperature storage tank is connected to the submersible pump inlet (22); The BOG recovery skid is provided with a BOG recovery tank (50) and a compressor (60). The BOG recovery tank is provided with a recovery tank liquid inlet (51), a recovery tank liquid outlet (52), a recovery tank air inlet (53) and a recovery tank gas phase port (54). An upper spray pipe (55) and a lower spray pipe (56) are provided in the BOG recovery tank. The BOG recovery tank is also provided with a recovery tank pressure transmitter (57), a recovery tank temperature sensor (58) and a recovery tank liquid level sensor (59). The recovery tank liquid inlet (51) is connected to the upper spray pipe (55). The recovery tank air inlet (53) is connected to the lower spray pipe (56), the recovery tank liquid inlet (51) is connected to the recovery skid liquid inlet (41), the recovery tank liquid outlet (52) is connected to the recovery skid liquid outlet (42), the recovery tank air inlet (53) and the recovery tank gas phase port (54) are respectively connected to the compressor output end (61), the compressor input end (62) is connected to the recovery skid air inlet (43), and the recovery skid liquid inlet (41) and the recovery skid liquid outlet (42) are connected through a liquid phase bypass pipe (44); The liquid phase bypass pipe (44) is provided with a first control valve (45), which is a normally open valve. A second control valve (46) is provided between the liquid inlet (51) of the recovery tank and the liquid inlet (41) of the recovery skid. A third control valve (47) is provided between the liquid outlet (52) of the recovery tank and the liquid outlet (42) of the recovery skid. A fourth control valve (48) is provided between the air inlet (53) of the recovery tank and the output end (61) of the compressor. A fifth control valve (49) is provided between the gas phase port (54) of the recovery tank and the output end (61) of the compressor. The recovery skid is provided with a control system, which controls the opening and closing of the first control valve (45), the second control valve (46), the third control valve (47), the fourth control valve (48) and the fifth control valve (49). The BOG recovery skid is provided with a heat exchanger (70), which is a heat exchanger for heat exchange between a heat absorbing medium and a heat dissipating medium. The heat exchanger is provided with a heat absorbing medium inlet (71), a heat absorbing medium outlet (72), a heat dissipating medium inlet (73) and a heat dissipating medium outlet (74). The heat absorbing medium inlet (71) is connected to the air inlet (43) of the recovery skid, the heat absorbing medium outlet (72) is connected to the input end (62) of the compressor, the heat dissipating medium inlet (73) is connected to the output end (61) of the compressor, and the heat dissipating medium outlet (74) is respectively connected to the air inlet (53) and the gas phase port (54) of the recovery tank. A temperature sensor (4a) and a pressure transmitter (4b) are provided at the liquid inlet of the recovery skid, and the control system receives detection values ​​from the temperature sensor (4a) and the pressure transmitter (4b) and controls the operation of the recovery skid.

2. A low-emission device for a liquefied natural gas filling station with a pump according to claim 1, characterized in that: An air-cooled radiator (80) is provided between the compressor (60) and the heat exchanger (70), the input end (81) of the air-cooled radiator is connected to the output end (61) of the compressor, the output end (82) of the air-cooled radiator is connected to the heat dissipation medium inlet (73) of the heat exchanger, the air-cooled radiator is provided with a bypass pipe (83), and a temperature sensor (63) is provided at the output end (61) of the compressor.

3. A low-emission method for a liquefied natural gas filling station with a pump, comprising the device according to any one of claims 1 to 2, characterized in that: The method comprises: Step a. If the pressure value at the recovery skid liquid inlet (41) is lower than the starting pressure setting value, open the first control valve (45), close the second control valve (46) and the third control valve (47), and then proceed to step e. If the pressure value at the recovery skid liquid inlet (41) is not lower than the starting pressure setting value, proceed to step b. Step b. If the liquid level in the BOG recovery tank is not lower than the upper limit, open the first control valve, close the second control valve, open the third control valve, start the compressor (60), close the fourth control valve (48), open the fifth control valve (49), and return to step a. If the liquid level in the BOG recovery tank is lower than the upper limit, proceed to step c. Step c. If the temperature at the recovery skid liquid inlet (41) is not lower than the start-up temperature setting value, open the first control valve (45), close the second control valve (46) and the third control valve (47), and then proceed to step e. If the temperature at the recovery skid liquid inlet (41) is lower than the start-up temperature setting value, proceed to step d. Step d. If the liquid level in the BOG recovery tank is not higher than the lower limit, close the first control valve (45), open the second control valve (46), close the third control valve (47), and return to step a. If the liquid level in the BOG recovery tank is higher than the lower limit, close the first control valve (45), open the second control valve (46) and the third control valve (47), and then proceed to step e. Step e. If the liquid level in the BOG recovery tank is not lower than the upper limit or not higher than the lower limit, turn off the compressor (60), close the fourth control valve (48), close the fifth control valve (49), and return to step a. If the liquid level in the BOG recovery tank is lower than the upper limit and higher than the lower limit, proceed to step f. Step f. If the temperature in the BOG recovery tank is not lower than the set recovery temperature, the compressor (60) is turned off, the fourth control valve (48) is closed, the fifth control valve (49) is closed, and the process returns to step a. If the temperature in the BOG recovery tank is lower than the set recovery temperature, the compressor is turned on, the fourth control valve is opened, the fifth control valve is closed, and the process returns to step a.

4. The low-emission method for a liquefied natural gas filling station with a pump according to claim 3, characterized in that: In step d, if the liquid level in the BOG recovery tank is higher than the lower liquid level limit, the first control valve (45) is closed, the second control valve (46) and the third control valve (47) are opened, and then the process proceeds to step d1; Step d1. If the BOG recovery tank liquid level is lower than 50%, adjust the second control valve to increase the opening. If the BOG recovery tank liquid level is not lower than 50%, adjust the second control valve to decrease the opening and proceed to step e.

5. The low-emission method for a liquefied natural gas filling station with a pump according to claim 3, characterized in that: When the BOG temperature at the output end of the compressor is higher than the ambient air temperature, the bypass pipe (83) of the air-cooling radiator is closed and the air-cooling radiator (80) is started; when the BOG temperature at the output end of the compressor is lower than the ambient air temperature, the bypass pipe (83) of the air-cooling radiator is opened and the air-cooling radiator (80) is closed.

6. The low-emission method for a liquefied natural gas filling station with a pump according to claim 3, characterized in that: The starting pressure setting value at the recovery skid liquid inlet (41) is greater than the pressure value when the submersible pump (20) is shut down. The upper limit of the liquid level in the BOG recovery tank is the liquid level at which the liquid in the BOG recovery tank is 90% of its volume. The lower limit of the liquid level in the BOG recovery tank is the liquid level at which the liquid in the BOG recovery tank is 10% of its volume.

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