Low-temperature receiving station energy-saving system and working method thereof

Abstract

The application provides a low-temperature receiving station energy-saving system and a working method thereof, which has reasonable structure design and low operation and maintenance cost. A pre-cooling pipeline and a ship loading and unloading pipeline are connected in parallel, control valve one and control valve two are installed on the pre-cooling pipeline, and control valve three and control valve four are installed on the ship loading and unloading pipeline. A pre-cooling submersible pump is installed in a low-temperature storage tank. The outlet of the pre-cooling submersible pump is connected with a pre-cooling submersible pump external delivery pipeline and a pre-cooling submersible pump standby external delivery pipeline, the pre-cooling submersible pump external delivery pipeline is connected with the pre-cooling pipeline, the connection position is between the control valve one and the control valve two, and control valve five is installed on the pre-cooling submersible pump external delivery pipeline. The pre-cooling submersible pump standby external delivery pipeline is connected with an external delivery submersible pump outlet pipeline, and control valve six is installed on the pre-cooling submersible pump standby external delivery pipeline. One end of a recovery pipeline is connected with the ship loading and unloading pipeline, the connection position is between the control valve three and the control valve four, and the other end is connected with the low-temperature storage tank.

Description

Technical Field

[0001] This invention relates to an energy-saving system for a cryogenic receiving station and its operating method. Background Technology

[0002] To prevent pipeline deformation and cracking due to rapid cooling, which could lead to leaks, fires, and explosions, cryogenic materials require pre-cooling of pipelines before loading and unloading. The pre-cooled cryogenic liquid is typically returned to the cryogenic storage tank, as shown in Chinese Patent Application No. 201621471283.9. The BOG gas generated by heat absorption is cooled by a matching BOG reliquefaction and recovery system that consumes electrical energy. The cryogenic liquid circulation volume of the pre-cooled loading and unloading pipeline is generally designed based on a 5°C temperature increase. The longer the distance between the dock and the tank area, the larger the circulating liquid volume, and the greater the electricity consumption required for compressing and reliquefying the generated BOG gas, resulting in higher operating and maintenance costs. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned shortcomings in the prior art and to provide a low-temperature receiving station energy-saving system and its working method that has a reasonable structural design and low operation and maintenance costs.

[0004] The technical solution adopted by this invention to solve the above problems is: an energy-saving system for a cryogenic receiving station, comprising a loading and unloading system, a cryogenic storage system, and a pressurization and reheating system; the loading and unloading system includes a liquid delivery arm and a loading and unloading pipeline, the loading and unloading pipeline being connected to the liquid delivery arm; the cryogenic storage system includes a cryogenic storage tank, an external submersible pump, a BOG reliquefaction and recovery system, and an external submersible pump outlet pipeline; the BOG reliquefaction and recovery system is connected to the cryogenic storage tank; the external submersible pump is installed inside the cryogenic storage tank, and the outlet of the external submersible pump is connected to the external submersible pump outlet pipeline; the pressurization and reheating system includes a buffer tank, a booster pump, and a reheater; the external submersible pump outlet pipeline is connected to the inlet of the buffer tank, and the outlet of the buffer tank is connected to the reheater via the booster pump;

[0005] The system is characterized in that: the loading and unloading system further includes a precooling pipeline, which is connected in parallel with the loading and unloading pipeline; control valve one and control valve two are installed on the precooling pipeline, and control valve three and control valve four are installed on the loading and unloading pipeline; the cryogenic storage system further includes a precooling submersible pump, a backup export pipeline for the precooling submersible pump, an export pipeline for the precooling submersible pump, and a recovery pipeline; the precooling submersible pump is installed inside the cryogenic storage tank; the outlet of the precooling submersible pump is connected to the export pipeline for the precooling submersible pump and... The precooled submersible pump's standby external delivery pipeline is connected to the precooling pipeline, with the connection point located between control valve one and control valve two. Control valve five is installed on the precooled submersible pump's external delivery pipeline. The precooled submersible pump's standby external delivery pipeline is connected to the external submersible pump's outlet pipeline, with control valve six installed on the precooled submersible pump's standby external delivery pipeline. One end of the recovery pipeline is connected to the loading / unloading pipeline, with the connection point located between control valve three and control valve four, and the other end is connected to the cryogenic storage tank.

[0006] The precooling pipeline described in this invention has a diameter of DN80~DN250.

[0007] The diameter of the loading and unloading pipeline described in this invention is DN200~DN1000.

[0008] The precooling submersible pump described in this invention is of the variable frequency type.

[0009] A method for operating an energy-saving system for a cryogenic receiving station, characterized by the following steps:

[0010] (1) By opening control valve 1, control valve 3, control valve 4 and control valve 5 and closing control valve 2 and control valve 6, the precooling channel is connected; the precooling submersible pump sends the cryogenic liquid in the cryogenic storage tank to the precooling pipeline through the precooling submersible pump external pipeline, the cryogenic liquid enters the loading and unloading pipeline through the precooling pipeline, and the cryogenic liquid flows through the loading and unloading pipeline, absorbs the heat intruded by the environment and returns to the cryogenic storage tank through the recovery pipeline;

[0011] Considering cold energy recovery, the pre-cooled liquid is sent into the buffer tank by opening and closing the control valve. In the buffer tank, it is mixed with the liquid that is pressurized by the external submersible pump and then input through the outlet pipeline of the external submersible pump. The mixture is then pressurized by the booster pump and sent into the reheater. After reaching the required temperature downstream, it is sent out of the boundary area.

[0012] (2) By turning on the precooling submersible pump, opening control valve six and closing control valve five, the precooling liquid is sent to the buffer tank after passing through the precooling submersible pump standby external pipeline and the external submersible pump outlet pipeline. After being buffered by the buffer tank, it continues to flow through the booster pump and reheater before being sent out of the boundary area, thus realizing the function of the precooling submersible pump as an external submersible pump.

[0013] (3) When the external submersible pump is damaged, by opening control valve 1 and control valve 5 and closing control valve 2, control valve 3 and control valve 6, the outlet of the precooled submersible pump is connected to the loading and unloading pipeline, thereby transporting the liquid in the cryogenic storage tank to the dock, and using the liquid delivery arm to connect with the ocean-going vessel to realize the cryogenic liquid loading operation, thus realizing the function of the precooled submersible pump as a loading pump.

[0014] Compared with the prior art, the present invention has the following advantages and effects:

[0015] (1) It can realize the export of pre-cooled liquid, avoid high-temperature liquid from entering the cryogenic storage tank, and make the pressure of the cryogenic storage tank more stable;

[0016] (2) Pre-cooled liquid can be transported out, which can reduce the amount of heat source used and reduce costs;

[0017] (3) Pre-cooled liquid can reduce the frequency of operation and running time of BOG reliquefaction and recovery system, thereby reducing power consumption and operating costs.

[0018] (4) Using the cold energy of the external liquid to pre-cool the loading and unloading pipeline can not only maintain the low temperature of the pipeline and enable loading and unloading operations at any time, but also avoid large pressure fluctuations in the low temperature storage tank under storage conditions. At the same time, it reduces the running time of the supporting compressor and refrigeration unit, and reduces the consumption of heat source required for reheating, thereby achieving the goal of reducing operating costs. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of an embodiment of the present invention. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are explanations of the present invention, but the present invention is not limited to the following embodiments.

[0021] The embodiments of the present invention include a ship loading and unloading system, a cryogenic storage system, and a pressurization and reheating system.

[0022] The loading and unloading system includes a liquid transfer arm 1, a loading and unloading pipeline L1, and a precooling pipeline L2.

[0023] The loading / unloading pipeline L1 is connected to the liquid transfer arm 1. Ocean-going vessels are connected to the cryogenic storage system via the loading / unloading system. The loading / unloading system can handle the loading and unloading of media such as LNG, ethylene, ethane, propane, propylene, butane, and liquid ammonia. At the dock front, the loading / unloading pipeline L1 is connected to the vessel via the liquid transfer arm 1. The loading / unloading pipeline L1 is designed for bidirectional operation, allowing for both unloading and loading. The precooling pipeline L2 is connected in parallel with the loading / unloading pipeline L1. Control valves X1 and X2 are installed on the precooling pipeline L2, while control valves X3 and X4 are installed on the loading / unloading pipeline L1.

[0024] The cryogenic storage system includes a cryogenic storage tank 2, a pre-cooled submersible pump 3, an external submersible pump 4, a BOG reliquefaction and recovery system 5, a backup external submersible pump line L3, an external submersible pump outlet line L4, a pre-cooled submersible pump external line L5, and a recovery line L6.

[0025] The cryogenic storage tank 2 is a vertical, domed, double-walled tank. The tank can be a single-containment tank, a double-containment tank, a full-containment tank, or a membrane tank. The tank is designed to withstand a pressure of 10-30 kPa and a storage temperature of -165℃ to -30℃.

[0026] The BOG reliquefaction and recovery system 5 is connected to the cryogenic storage tank 2. The BOG reliquefaction and recovery system 5 is equipped with a compressor, water cooler, refrigeration unit and flash tank, etc., to maintain the normal working pressure of the storage tank and recover the evaporated gas generated by the system. The submersible pump is a vertical centrifugal pump, which is placed in a special pump well inside the tank to deliver the liquid in the tank.

[0027] The external submersible pump 4 is installed inside the cryogenic storage tank 2, and the outlet of the external submersible pump 4 is connected to the external submersible pump outlet pipeline L4.

[0028] The precooling submersible pump 3 is installed inside the cryogenic storage tank 2. The outlet of the precooling submersible pump 3 has two channels. One channel connects to the precooling submersible pump external delivery pipeline L5, which in turn connects to the precooling pipeline L2. The connection point is located between control valve X1 and control valve X2. Control valve X5 is installed on the precooling submersible pump external delivery pipeline L5. The other channel connects to the precooling submersible pump standby external delivery pipeline L3, which connects to the external submersible pump outlet pipeline L4. Control valve X6 is installed on the precooling submersible pump standby external delivery pipeline L3. During normal production, the precooling submersible pump 3 is used for precooling the loading / unloading pipeline L1. When the external submersible pump 4 fails, the precooling submersible pump 3 can be used as a standby pump for the external submersible pump 4.

[0029] One end of the recovery pipeline L6 is connected to the loading and unloading pipeline L1, with the connection point located between control valve three X3 and control valve four X4, and the other end is connected to the cryogenic storage tank 2.

[0030] The pressurization and reheating system includes a buffer tank 6, a booster pump 7, and a reheater 8. The outlet pipeline L4 of the external submersible pump is connected to the inlet of the buffer tank 6, and the outlet of the buffer tank 6 is connected to the reheater 8 through the booster pump 7.

[0031] The liquid in cryogenic storage tank 2 is pressurized by pre-cooling submersible pump 3 and sent to pre-cooling pipeline L2 in the loading and unloading system. It then connects to loading and unloading pipeline L1 in the dock area. After recovering heat from loading and unloading pipeline L1, the cryogenic liquid is driven by pressure differential to continue entering buffer tank 6. There, it mixes with the liquid output from external submersible pump 4 and is further pressurized by booster pump 7. Finally, it is reheated or vaporized before being sent out of the boundary area. The specific working method of this invention includes the following steps:

[0032] (1) The precooling channel is connected by opening control valves X1, X3, X4, and X5, and closing control valves X2 and X6. The precooling submersible pump 3 pressurizes the cryogenic liquid at atmospheric pressure and ≤-30℃ in the cryogenic storage tank 2 and sends it to the precooling pipeline L2 through the precooling submersible pump external pipeline L5. The outlet pressure of the precooling submersible pump 3 is the sum of the pressure of the external submersible pump 4 and the pressure head of the cryogenic liquid flowing through the tank area-dock-back to the tank area, which is generally around 6 barg~12 barg. The flow rate of the precooling submersible pump 3 is also adjusted according to the distance between the dock and the tank area, and is generally set between 10t and 120t. The pipe diameter of the precooling pipeline L2 is controlled according to the liquid flow rate, the flow resistance along the pipe, and the temperature rise of the loading and unloading pipeline L1, and is generally between DN80 and DN250. The cryogenic liquid is connected to the loading / unloading pipeline L1 in the dock area via the pre-cooling pipeline L2. The diameter of the loading / unloading pipeline L1 is selected according to the length of the dock from the tank area and the flow rate requirements for loading and unloading ships, and is generally between DN200 and DN1000. After flowing through the loading / unloading pipeline L1, the cryogenic liquid absorbs the heat intruded from the environment and returns to the cryogenic storage tank 2 through the recovery pipeline L6.

[0033] Considering cold energy recovery, the pre-cooled liquid is sent to the buffer tank 6 by opening control valve X4 and closing control valve X5. In the buffer tank 6, it is mixed with the liquid that is pressurized by the external submersible pump 4 and input through the external submersible pump outlet pipeline L4. The temperature of the mixed liquid is slightly higher, but the overall temperature is still controlled to be 10~15℃ lower than the liquefaction temperature at the corresponding pressure to avoid cavitation of the booster pump 7. The pressurized liquid pressure is 15~30 barg, and then it is sent to the reheater 8. After reaching the required downstream temperature, it is sent out of the boundary area.

[0034] (2) The precooling submersible pump 3 of the present invention adopts a frequency conversion type. Through frequency conversion, the precooling submersible pump 3 can also be used as an external submersible pump. By turning on the precooling submersible pump 3, opening control valve six X6 and closing control valve five X5, the precooled liquid is sent to the buffer tank 6 after passing through the precooling submersible pump standby external pipeline L3 and the external submersible pump outlet pipeline L4. After being buffered by the buffer tank 6, it continues to flow through the booster pump 7 and the reheater 8 before being sent out of the boundary area.

[0035] (3) The precooling submersible pump 3 of the present invention can also be used as a loading pump. When the external submersible pump 4 is damaged, the frequency of the precooling submersible pump 3 can be changed to reduce the external pressure. By opening the control valves control valve one X1 and control valve five X5, and closing the control valve two X2, control valve three X3 and control valve six X6, the outlet of the precooling submersible pump 3 can be connected to the loading and unloading pipeline L1 in the tank area, thereby transporting the liquid in the cryogenic storage tank 2 to the dock, and connecting it with the ocean-going vessel using the liquid transfer arm 1 to realize the cryogenic liquid loading operation.

[0036] Assuming the wharf is 4 kilometers from the tank farm, pipeline cooling loss is 30 W / m, and the stored medium is calculated as low-temperature ethylene at -102℃ (latent heat of vaporization is 482 kJ / kg), the heat generated by pre-cooling is: 30 x 4000 x 2 = 240 KW, resulting in BOG flash evaporation of:

[0037] 240*3600 / 482=1792kg / h≈1.8t / h. When using the propylene refrigeration process commonly used in receiving terminals to liquefy propylene, the system has 30% gas circulation. Therefore, a BOG reliquefaction and recovery system of 1.8*1.3=2.34t / h is required for pre-cooling. For a 2.5t / h reliquefaction and recovery system, the energy consumption is 500KW. At an electricity cost of 0.6 yuan / KW, the daily electricity cost is 7200 yuan. Considering a two-month unloading period per year, and a total of 10 months of pre-cooling required, the annual electricity cost for pre-cooling alone is approximately 50 million yuan.

[0038] Furthermore, it should be noted that the specific embodiments described in this specification may differ in the shape and name of their components, etc. The above description is merely illustrative of the structure of the present invention. All equivalent or simple variations made based on the structure, features, and principles described in this patent concept are included within the protection scope of this patent. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to substitute them, as long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims, all of which should fall within the protection scope of this invention.

Claims

1. An energy-saving system for a cryogenic receiving station, comprising a loading / unloading system, a cryogenic storage system, and a pressurization and reheating system; the loading / unloading system includes a liquid delivery arm and a loading / unloading pipeline, the loading / unloading pipeline being connected to the liquid delivery arm; the cryogenic storage system includes a cryogenic storage tank, an external submersible pump, a BOG reliquefaction and recovery system, and an external submersible pump outlet pipeline; the BOG reliquefaction and recovery system is connected to the cryogenic storage tank; the external submersible pump is installed inside the cryogenic storage tank, and the outlet of the external submersible pump is connected to the external submersible pump outlet pipeline; the pressurization and reheating system includes a buffer tank, a booster pump, and a reheater; the external submersible pump outlet pipeline is connected to the inlet of the buffer tank, and the outlet of the buffer tank is connected to the reheater via the booster pump; Its features are: The loading and unloading system also includes a precooling pipeline connected in parallel with the loading and unloading pipeline. Control valves one and two are installed on the precooling pipeline, and control valves three and four are installed on the loading and unloading pipeline. The cryogenic storage system also includes a precooling submersible pump, a backup export pipeline for the precooling submersible pump, an export pipeline for the precooling submersible pump, and a recovery pipeline. The precooling submersible pump is installed inside a cryogenic storage tank. The outlet of the precooling submersible pump is connected to both the export pipeline for the precooling submersible pump and the backup export pipeline for the precooling submersible pump. The precooled submersible pump's external delivery pipeline is connected to the precooling pipeline, with the connection point located between control valve one and control valve two. Control valve five is installed on the precooled submersible pump's external delivery pipeline. The precooled submersible pump's standby external delivery pipeline is connected to the external submersible pump's outlet pipeline, with control valve six installed on the precooled submersible pump's standby external delivery pipeline. One end of the recovery pipeline is connected to the loading / unloading pipeline, with the connection point located between control valve three and control valve four, and the other end is connected to the cryogenic storage tank. The loading / unloading pipeline is connected to the inlet of the buffer tank.

2. The energy-saving system for a cryogenic receiving station according to claim 1, characterized in that: The diameter of the precooling pipeline is DN80~DN250.

3. The energy-saving system for a cryogenic receiving station according to claim 1, characterized in that: The diameter of the loading and unloading pipeline is DN200~DN1000.

4. The energy-saving system for a cryogenic receiving station according to claim 1, characterized in that: The precooling submersible pump is a variable frequency type.

5. A method for operating the energy-saving system of a cryogenic receiving station as described in any one of claims 1-4, characterized in that: (1) By opening control valve 1, control valve 3, control valve 4 and control valve 5 and closing control valve 2 and control valve 6, the precooling channel is connected; the precooling submersible pump sends the cryogenic liquid in the cryogenic storage tank to the precooling pipeline through the precooling submersible pump external pipeline, the cryogenic liquid enters the loading and unloading pipeline through the precooling pipeline, and the cryogenic liquid flows through the loading and unloading pipeline, absorbs the heat intruded by the environment and returns to the cryogenic storage tank through the recovery pipeline; Considering cold energy recovery, the pre-cooled liquid is sent into the buffer tank by opening control valve four and closing control valve five. In the buffer tank, it is mixed with the liquid that is pressurized by the external submersible pump and then input through the outlet pipeline of the external submersible pump. The mixture is then pressurized by the booster pump and sent into the reheater. After reaching the required temperature downstream, it is sent out of the boundary area. (2) By turning on the precooling submersible pump, opening control valve six and closing control valve five, the precooling liquid is sent to the buffer tank after passing through the precooling submersible pump standby external pipeline and the external submersible pump outlet pipeline. After being buffered by the buffer tank, it continues to flow through the booster pump and reheater before being sent out of the boundary area, thus realizing the function of the precooling submersible pump as an external submersible pump. (3) When the external submersible pump is damaged, by opening control valve 1 and control valve 5 and closing control valve 2, control valve 3 and control valve 6, the outlet of the precooled submersible pump is connected to the loading and unloading pipeline, thereby transporting the liquid in the cryogenic storage tank to the dock, using the liquid delivery arm to connect with the ocean-going vessel, realizing the cryogenic liquid loading operation, and realizing the function of the precooled submersible pump as a loading pump.

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