A BOG recovery process scheme for LNG tank trucks in LNG plants

Abstract

The present invention discloses a BOG recovery process scheme for LNG tank trucks in an LNG plant, which includes three routes, namely a main process route, a backup process route, and an auxiliary process route; the main process route: the BOG of the LNG tank truck is heated by vaporizer 1 and vaporizer 2, then reheated by a water bath heater, buffered by buffer tank 1, and pressurized by compressor 1, and then enters the outlet buffer tank 2 for buffering, and then is pressure-regulated to 0.35MPa by pressure regulating and metering skid 1, and then enters the city's medium-pressure pipeline network; the backup process route: from the outlet of buffer tank 1 to the original factory BOG compression system, pressure-regulated to 15kPa by pressure regulating and metering skid 2, enters buffer tank 3, and then enters the inlet of compressor 2. The auxiliary process route: is drawn out from the outlet of buffer tank 2, extends to the outlet of buffer tank 1, and merges with the backup process route. The present invention adopts the above-mentioned BOG recovery process scheme for LNG tank trucks in an LNG plant, which can solve the problem of resource waste and environmental pollution caused by BOG emissions from LNG tank trucks.

Description

Technical Field

[0001] The present invention relates to the technical field of BOG recovery from LNG tank trucks, and in particular to BOG recovery from LNG tank trucks. Background Art

[0002] Liquefied natural gas produced by LNG plants is primarily transported and shipped via LNG tanker trucks. Based on LNG plant experience, the average entry pressure for LNG tanker trucks is 0.4 MPa, while the optimal filling pressure is 0.1 MPa. Therefore, before filling, LNG tanker trucks must discharge the BOG inside to reduce the pressure to 0.1 MPa. This means each truck releases nearly 350 cubic meters of natural gas. Statistics show that LNG plants sometimes fill up to 25 LNG tanker trucks per day. Based on an average of 15 tanker trucks per day, this results in a total daily discharge of 5,250 cubic meters of natural gas.

[0003] Currently, before filling at an LNG plant, LNG tankers are required to discharge BOG from their tanks outside the plant, reducing the tank pressure from 0.4 MPa to 0.1 MPa. This BOG discharge is a significant waste. External LNG tankers typically discharge BOG outside the plant, wasting resources, polluting the environment, and risking penalties. Summary of the Invention

[0004] The purpose of the present invention is to provide a BOG recovery process scheme for LNG tank trucks in an LNG plant to solve the problems raised in the above background technology.

[0005] To achieve the above objectives, the present invention provides a BOG recovery process scheme for LNG tank trucks in an LNG plant, which includes three routes: a main process route, a backup process route, and an auxiliary process route;

[0006] The main process route is as follows: BOG from the LNG tank truck is heated in vaporizers 1 and 2, then reheated in a water bath heater, buffered in buffer tank 1, pressurized in compressor 1, and then buffered in outlet buffer tank 2. After that, the pressure is adjusted to 0.35 MPa by pressure regulating and metering skid 1 before entering the city's medium-pressure pipeline network.

[0007] The backup process route is: from the outlet of buffer tank 1 to the original BOG compression system, the pressure is adjusted to 15kPa by pressure regulating and metering skid 2, then enters buffer tank 3, and then enters the inlet of compressor 2. The original BOG system inlet pressure of the LNG plant is 15kPa;

[0008] The auxiliary process route is: it is led out from the outlet of buffer tank 2, extends to the outlet of buffer tank 1 and merges with the backup process route.

[0009] Preferably, when the BOG pressure of the LNG tank truck is high, it enters the city's medium-pressure pipeline network through the main process route; when the BOG pressure of the LNG tank truck is low, it enters the original BOG system of the LNG plant through the backup process route.

[0010] Preferably, the main process route and the backup process route are main routes, and the auxiliary process route is an auxiliary loop of the main process route.

[0011] Preferably, solenoid valve five is provided on the route between vaporizer one and vaporizer two and the water bath heater, solenoid valve four and solenoid valve three are provided on the auxiliary process route, solenoid valve one is provided on the route between buffer tank one and compressor one, and solenoid valve two is provided on the route between buffer tank one and pressure regulating and metering skid one.

[0012] Preferably, solenoid valve 1, solenoid valve 2, solenoid valve 3, solenoid valve 4 and solenoid valve 5 are all provided with automatic switches and manual switches, and solenoid valve 1, solenoid valve 2, solenoid valve 3, solenoid valve 4 and solenoid valve 5 can recover all the gas in the pipeline equipment.

[0013] Preferably, the first gasifier and the second gasifier are in a standby relationship.

[0014] Therefore, the present invention adopts the above-mentioned LNG plant LNG tank truck BOG recovery process scheme, which has the following beneficial effects:

[0015] 1. Recover BOG from LNG tankers to the city’s medium-pressure pipeline network or the original BOG recovery system to prevent waste of resources;

[0016] 2. The present invention adopts the BOG recovery process scheme of LNG tank trucks in LNG plants, which avoids the pollution caused by direct discharge of BOG to the environment;

[0017] 3. The present invention adopts the BOG recovery process scheme of LNG tank trucks in LNG plants, and the recovered BOG creates considerable economic benefits for the plant area;

[0018] 4. The three-way process of the present invention is more energy-efficient than directly recovering BOG from LNG tankers to the original BOG system. This is because the pressure of the LNG tanker is close to the pressure of the urban medium-pressure pipeline network, while the inlet pressure of the original BOG system is 15kPa. If it is directly recovered to the original BOG system, the pressure must be reduced from 0.4MPa to 15kPa, which is energy-intensive.

[0019] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a process flow chart of an embodiment of a BOG recovery process scheme for an LNG tanker in an LNG plant according to the present invention;

[0021] Figure 2 This is a backup process route diagram for an embodiment of a BOG recovery process scheme for an LNG tanker in an LNG plant according to the present invention;

[0022] Figure 3 This is an auxiliary process roadmap for an embodiment of a BOG recovery process scheme for an LNG tanker in an LNG plant according to the present invention;

[0023] Figure 4 This is a schematic diagram of the structure of a vaporizer in an embodiment of a BOG recovery process for an LNG tanker in an LNG plant according to the present invention;

[0024] Figure 5 This is a schematic diagram of the structure of a water bath heater in an embodiment of a BOG recovery process solution for an LNG tanker in an LNG plant according to the present invention;

[0025] Figure 6 This is a schematic diagram of the buffer tank structure of an embodiment of a BOG recovery process solution for an LNG tanker in an LNG plant of the present invention;

[0026] Figure 7 This is a schematic diagram of the structure of a pressure regulating and metering skid in an embodiment of a BOG recovery process solution for an LNG tanker in an LNG plant according to the present invention;

[0027] Figure 8 This is a schematic diagram of the compressor structure of an embodiment of a BOG recovery process solution for an LNG tanker in an LNG plant of the present invention;

[0028] Figure 9 This is a schematic diagram of the solenoid valve structure of an embodiment of the BOG recovery process solution for LNG tank trucks in an LNG plant of the present invention.

[0029] Reference numerals

[0030] 1. Vaporizer 1; 2. Vaporizer 2; 3. Water bath heater; 4. Buffer tank 1; 5. Buffer tank 2; 6. Buffer tank 3; 7. Pressure regulating and metering skid 1; 8. Pressure regulating and metering skid 2; 9. Compressor 1; 10. Compressor 2; 11. Solenoid valve 1; 12. Solenoid valve 2; 13. Solenoid valve 3; 14. Solenoid valve 4; 15. Solenoid valve 5. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0032] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the ordinary meaning understood by persons of ordinary skill in the field to which the present invention belongs. The terms "first", "second" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. The terms "include" or "comprise" and similar terms mean that the elements or objects preceding the word include the elements or objects listed after the word and their equivalents, but do not exclude other elements or objects. The terms "set", "install" and "connect" should be understood in a broad sense. For example, they can be fixed connections, detachable connections, or integral connections; they can be mechanical connections or electrical connections; they can be direct connections or indirect connections through an intermediate medium, or they can be internal connections between two elements. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0033] Example

[0034] Figure 1 This is a process flow chart of an embodiment of a BOG recovery process scheme for an LNG tanker in an LNG plant according to the present invention; Figure 2 This is a backup process route diagram for an embodiment of a BOG recovery process scheme for an LNG tanker in an LNG plant according to the present invention; Figure 3 This is an auxiliary process roadmap for an embodiment of a BOG recovery process scheme for an LNG tanker in an LNG plant according to the present invention; Figure 4 This is a schematic diagram of the structure of a vaporizer in an embodiment of a BOG recovery process for an LNG tanker in an LNG plant according to the present invention; Figure 5 This is a schematic diagram of the structure of a water bath heater in an embodiment of a BOG recovery process solution for an LNG tanker in an LNG plant according to the present invention; Figure 6 This is a schematic diagram of the buffer tank structure of an embodiment of a BOG recovery process solution for an LNG tanker in an LNG plant of the present invention; Figure 7 This is a schematic diagram of the structure of a pressure regulating and metering skid in an embodiment of a BOG recovery process solution for an LNG tanker in an LNG plant according to the present invention; Figure 8 This is a schematic diagram of the compressor structure of an embodiment of a BOG recovery process solution for an LNG tanker in an LNG plant of the present invention; Figure 9 This is a schematic diagram of the solenoid valve structure of an embodiment of the BOG recovery process solution for LNG tank trucks in an LNG plant of the present invention.

[0035] As shown in the figure, the LNG plant BOG recovery process scheme for LNG tank trucks described in this invention includes three routes: a primary process route, a backup process route, and an auxiliary process route. The primary and backup process routes are the primary routes, while the auxiliary process route is a secondary loop to the primary process route. Within the primary process route, the primary process route is primary, while the backup process route is secondary. When the LNG tank truck's BOG pressure is high, it enters the city's medium-pressure pipeline network via the primary process route. When the LNG tank truck's BOG pressure is low, it enters the LNG plant's existing BOG system via the backup process route.

[0036] The main process route is as follows: BOG from the LNG tank truck is heated by Vaporizer 1 and Vaporizer 2 (Vaporizer 1 and Vaporizer 2 are in standby relationship), then reheated by water bath heater 3, buffered by buffer tank 4, pressurized by compressor 9, and then buffered by outlet buffer tank 25. After being pressure-regulated to 0.35MPa by pressure regulating and metering skid 7, it enters the city's medium-pressure pipeline network.

[0037] The alternative process route is: from the outlet of buffer tank 1 (4) to the original BOG compression system, the pressure is adjusted to 15kPa by pressure regulating and metering skid 2 (8), enters buffer tank 3 (6), and then enters the inlet of compressor 2 (10). The original BOG system inlet pressure of the LNG plant is 15kPa.

[0038] The auxiliary process route is: it is led out from the outlet of buffer tank 2 5, extends to the outlet of buffer tank 1 4 and merges with the backup process route.

[0039] Solenoid valve 5 15 is installed on the route between vaporizer 1 and vaporizer 2 and water bath heater 3. Solenoid valve 4 14 and solenoid valve 3 13 are installed on the auxiliary process route. Solenoid valve 11 is installed on the route between buffer tank 4 and compressor 9. Solenoid valve 2 12 is installed on the route between buffer tank 4 and pressure regulating and metering skid 7. Solenoid valve 1 11, solenoid valve 2 12, solenoid valve 3 13, solenoid valve 4 14, and solenoid valve 5 15 are all equipped with automatic and manual switches, all using existing switch structures. Solenoid valve 1 11, solenoid valve 2 12, solenoid valve 3 13, solenoid valve 4 14, and solenoid valve 5 15 can fully recover the gas in the pipeline equipment.

[0040] from Figure 1It can be seen that vaporizer 1 is E-101A, vaporizer 2 is E-101B, water bath heater 3 is E-102, buffer tank 1 is V-101, buffer tank 2 is V-102, buffer tank 3 is V-103, pressure regulating and metering skid 1 is X-101, pressure regulating and metering skid 2 is X-102, compressor 1 is C-101, compressor 2 is C-102, solenoid valve 1 is KV101, solenoid valve 2 is KV102, solenoid valve 3 is KV103, solenoid valve 4 is KV104, and solenoid valve 5 is KV105. Vaporizer 1 1, vaporizer 2 2, water bath heater 3, buffer tank 1 4, buffer tank 2 5, buffer tank 3 6, pressure regulating and metering skid 1 7, pressure regulating and metering skid 2 8, compressor 1 9, compressor 2 10, solenoid valve 1 11, solenoid valve 2 12, solenoid valve 3 13, solenoid valve 4 14, and solenoid valve 5 15 all adopt existing structures.

[0041] The solenoid valve KV105 is remotely opened on the loading platform, and the BOG from the LNG tanker passes through the vaporizer E-101A / B, the water bath heater E-102, and the buffer tank V-101. When the pressure detection point PT101 is ≥0.35MPa, the bypass solenoid valve KV102 of compressor C-101 is automatically opened, and the BOG of the LNG tank truck directly enters the buffer tank V-102 behind the compressor C-101, and is pressure-regulated to 0.35MPa by the pressure regulating and metering skid X-101 before being transmitted outward; when PT101 is less than 0.35MPa, the bypass solenoid valve KV102 of compressor C-101 is closed, KV101 is opened, and the compressor is started. The BOG of the LNG tank truck is pressurized to 0.5MPa and enters the buffer tank V-102, and is pressure-regulated to 0.35MPa by the pressure regulating and metering skid X-101 before being transmitted outward; when PT101 is less than 0.1MPa, the compressor C-101 is shut down, and the compressor inlet valve KV101, KV102, and KV104 are closed.

[0042] When the pressure in buffer tank V-102 drops from 0.5MPa to 0.35MPa, the pressure regulating and metering skid X-101 stops operating, and PT102 interlocks with KV103 to open. The BOG gas from the LNG tanker is then pressure-regulated to 15kPa via the pressure regulating and metering skid X-102 and enters the factory BOG compressor C-102. When the pressure in buffer tank V-102 drops to 0.1MPa, the PT102 interlock with KV103 closes, ensuring that both the buffer tank V-102 and the pipeline maintain a pressure of 0.1MPa. Once the pipeline pressure in the pressure regulating and metering skid X-102 drops to 0.1MPa, the pressure regulating and metering skid X-102 stops operating, ensuring a pressure of 0.1MPa in the pipeline between the buffer tank V-102 and the pressure regulating and metering skid X-102.

[0043] When there are many tanker trucks and gas needs to be continuously recovered, KV101 and KV104 can be remotely opened simultaneously to start the main and backup process routes, recovering and releasing air simultaneously. When gas demand in the city's medium-pressure pipeline network decreases and cannot accommodate BOG tank trucks, KV104 can be remotely opened to use the backup process route.

[0044] Interlock control instructions:

[0045] When TT101 is less than -15℃, alarm will be triggered; when TT101 is less than -19℃, KV105 will be closed;

[0046] When PT101≥0.35MPa, the interlocking solenoid valve KV102 opens and the compressor C-101 does not start;

[0047] When PT101<0.35MPa, the interlocking solenoid valve KV102 is closed and the compressor C-101 is started;

[0048] When PT102<0.35MPa, KV103 opens; when PT102<0.1MPa, KV103 closes;

[0049] The pressure regulating and metering skid X-101 will start when the pipeline pressure is greater than 0.35MPa and stop working when it is lower than 0.35MPa. The pressure regulating and metering skid X-102 will stop working when the pipeline pressure is lower than 0.1MPa.

[0050] Therefore, the present invention adopts the above-mentioned LNG plant LNG tank truck BOG recovery process solution to solve the problem of resource waste and environmental pollution caused by BOG discharge from LNG tank trucks.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A BOG recovery process for LNG tankers in an LNG plant, characterized by: It includes three routes, namely the main process route, the backup process route and the auxiliary process route; The main process route is as follows: BOG from the LNG tank truck is heated in vaporizers 1 and 2, then reheated in a water bath heater, buffered in buffer tank 1, pressurized in compressor 1, and then buffered in outlet buffer tank 2. After that, the pressure is adjusted to 0.35 MPa by pressure regulating and metering skid 1 before entering the city's medium-pressure pipeline network. The backup process route is: from the outlet of buffer tank 1 to the original BOG compression system, the pressure is adjusted to 15kPa by pressure regulating and metering skid 2, then enters buffer tank 3, and then enters the inlet of compressor 2. The original BOG system inlet pressure of the LNG plant is 15kPa; The auxiliary process route is: it is led out from the outlet of buffer tank 2, extends to the outlet of buffer tank 1 and merges with the backup process route; When the BOG pressure of the LNG tank truck is high, it enters the city's medium-pressure pipeline network through the main process route. When the BOG pressure of the LNG tank truck is low, it enters the original BOG system of the LNG plant through the backup process route. The main process route and the backup process route are the main routes, and the auxiliary process route is the auxiliary circuit of the main process route; Solenoid valve 5 is installed on the route between vaporizer 1 and vaporizer 2 and the water bath heater, solenoid valve 4 and solenoid valve 3 are installed on the auxiliary process route, solenoid valve 1 is installed on the route between buffer tank 1 and compressor 1, and solenoid valve 2 is installed on the route between buffer tank 1 and pressure regulating and metering skid 1; Solenoid valve 1, solenoid valve 2, solenoid valve 3, solenoid valve 4 and solenoid valve 5 are all equipped with automatic switches and manual switches. Solenoid valve 1, solenoid valve 2, solenoid valve 3, solenoid valve 4 and solenoid valve 5 can recover all the gas in the pipeline equipment; Vaporizer 1 and Vaporizer 2 are in a standby relationship; Vaporizer 1 is E-101A, vaporizer 2 is E-101B, water bath heater is E-102, buffer tank 1 is V-101, buffer tank 2 is V-102, buffer tank 3 is V-103, pressure regulating and metering skid 1 is X-101, pressure regulating and metering skid 2 is X-102, compressor 1 is C-101, compressor 2 is the original BOG compressor C-102, solenoid valve 1 is the compressor intake valve KV101, solenoid valve 2 is KV102, solenoid valve 3 is KV103, solenoid valve 4 is KV104, solenoid valve 5 is KV105; Remotely open the solenoid valve KV105 on the loading platform, and the BOG from the LNG tanker passes through the vaporizer E-101A / B, water bath heater E-102, and buffer tank V-101. When the pressure detection point PT101 is ≥0.35MPa, the bypass solenoid valve KV102 of the compressor C-101 is automatically opened, and the BOG from the LNG tanker directly enters the buffer tank V-102 after the compressor C-101, and is then output after the pressure is adjusted to 0.35MPa by the pressure regulating and metering skid X-101. When PT When PT101 is less than 0.35MPa, the bypass solenoid valve KV102 of compressor C-101 is closed, KV101 is opened, and compressor C-101 is started to pressurize the BOG of the LNG tank truck to 0.5MPa and enter the buffer tank V-102. After being pressure-regulated to 0.35MPa by the pressure regulating and metering skid X-101, it is then output. When PT101 is less than 0.1MPa, compressor C-101 is shut down, and the compressor inlet valve KV101, KV102, and KV104 are closed. When the pressure of buffer tank V-102 drops from 0.5MPa to 0.35MPa, the pressure regulating and metering skid X-101 stops working and is opened by the PT102 interlock KV103. The BOG gas from the LNG tank truck is pressure-regulated to 15KPa via the pressure regulating and metering skid X-102 and enters the original BOG compressor C-102. When the pressure of buffer tank V-102 drops to 0.1MPa, the PT102 interlock KV103 is closed. The pressure of buffer tank V-102 and the pipeline is 0.1MPa. After the pipeline pressure of pressure regulating and metering skid X-102 drops to 0.1MPa, pressure regulating and metering skid X-102 stops working and the pipeline between buffer tank V-102 and pressure regulating and metering skid X-102 is 0.1MPa. When there are many filling vehicles and gas needs to be continuously recovered, KV101 and KV104 are remotely opened at the same time to start the main process route and the backup process route, and to recover and release air at the same time; when the gas consumption of the urban medium-pressure pipeline network decreases and cannot accommodate the BOG of the tank truck, KV104 is remotely opened to use the backup process route; Interlock control instructions: When TT101 is less than -15℃, alarm will be triggered; when TT101 is less than -19℃, KV105 will be closed; When PT101≥0.35MPa, the interlocking solenoid valve KV102 opens and the compressor C-101 does not start; When PT101<0.35MPa, the interlocking solenoid valve KV102 is closed and the compressor C-101 is started; When PT102<0.35MPa, KV103 opens; when PT102<0.1MPa, KV103 closes; The pressure regulating and metering skid X-101 will start when the pipeline pressure is greater than 0.35MPa and stop working when it is lower than 0.35MPa. The pressure regulating and metering skid X-102 will stop working when the pipeline pressure is lower than 0.1MPa.

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