High integrity pressure protection system for LNG receiving station gasification and transmission pipeline

Abstract

The present invention relates to a high-integrity pressure protection system for an external transmission pipeline after gasification at an LNG receiving station, the system comprising a cut-off valve, a pressure transmitter and a logic processing controller; the cut-off valve and the pressure transmitter are sequentially arranged on a pipeline between an external transmission main pipe of a gasifier and a first station of the external transmission pipeline; the logic processing controller is electrically connected to the cut-off valve and the pressure transmitter, the logic processing controller performs a logic judgment on a pressure value detected by the pressure transmitter, and then controls the cut-off valve to be shut off according to a preset pressure alarm value lower than a design pressure of the first station of the external transmission pipeline, so as to control the gas that is constantly rising in the external transmission main pipe of the gasifier to be within the range of the external transmission main pipe of the gasifier and not to enter the first station of the external transmission pipeline.

Description

Technical Field

[0001] The present invention relates to a high integrity pressure protection system for an external transmission pipeline after gasification at an LNG receiving station, and relates to the technical field of liquefied natural gas (LNG). Background Art

[0002] LNG receiving stations are usually built in conjunction with or independently of the first station of the external transmission pipeline. The main function of the first station of the external transmission pipeline is to measure the trade of natural gas transported to the downstream. It is equipped with a pig launcher, a metering device and a pressure regulating device. Usually, the economical and feasible approach is to include the first station of the external transmission pipeline in the boundary area of ​​the LNG receiving station or to independently build it at a location close to the boundary area of ​​the LNG receiving station. The control system of the external transmission pipeline is usually independent of the control system of the LNG receiving station. However, the problem brought about by this is that the pressure and control of the gasification external transmission unit of the LNG receiving station and the external transmission pipeline project are difficult to effectively connect, and even become one of the important hidden dangers. In the gasification and export process of the LNG receiving station, generally there are three equipment and facility units including LNG high-pressure export pump, gasifier and gasification export main pipeline. Their design pressure is the same, that is, 1.25 times the maximum operating pressure of export and 1.1 times the sum of the suction pressure of the LNG high-pressure export pump, which is often above 10Mpa. However, after entering the boundary area of ​​the first station of the export pipeline, the design pressure is usually considered according to the maximum operating pressure of export plus a margin, which is often two pressure levels lower than the design pressure of the gasification and export unit of the LNG receiving station.

[0003] Under normal external transmission operation, the LNG high-pressure external transmission pump will not cause overpressure at the first station of the external transmission pipeline if it is within the normal working range. However, the external transmission system of the LNG receiving station has no pressure protection system. As long as the pressure of the downstream external transmission pipeline exceeds its maximum operating pressure, the three-choice two pressure sensor will alarm, and the downstream pressure signal can control and adjust the output of the LNG receiving station external transmission system to avoid overpressure at the first station of the external transmission pipeline. However, in the case of emergency shutdown, if the emergency shut-off valve downstream of the first station of the external transmission pipeline is closed, and the emergency shut-off valve at the outlet of the vaporizer in the LNG receiving station cannot be closed as soon as possible due to delayed logic or failure, it will cause overpressure at the first station of the external transmission pipeline. Because the design of the vaporizer is special, in order to protect its own pressure in the case of emergency shutdown, the emergency shut-off valve at the outlet will be shut down about 20 to 40 seconds later than the emergency shut-off valve at the inlet. During this period, the LNG gas in the vaporizer continues to gasify, causing the pressure of the vaporizer external transmission pipeline to greatly exceed the operating pressure. Assuming that five vaporizers are working simultaneously, emergency shutdown will cause the volume of LNG retained in the ORV transmission pipeline to expand by about 600 times. Based on an estimated shutdown delay of 40 seconds, the resulting pressure increase will reach more than 2 MPa.

[0004] There are three traditional solutions. The first is to logically associate the emergency shut-off valve of the first station of the external transmission pipeline with the emergency shut-off valve of the outlet of the vaporizer of the LNG receiving station. The emergency shut-off valve of the outlet of the vaporizer adopts a fast-closing valve, but the logical association of the instrument has unreliability problems; the second is to add a safety valve and vent between the emergency shut-off valve of the first station of the external transmission pipeline and the emergency shut-off valve of the outlet of the vaporizer, but it is necessary to greatly increase the processing capacity of the flare system of the LNG receiving station and the investment in the discharge pipeline, increase the equipment investment cost, and also require a larger site safety distance; the third is to increase the design pressure of the first station of the external transmission pipeline to the same as the design pressure of the external transmission system of the LNG receiving station, which will of course also bring about a large increase in investment. Therefore, the traditional solutions have various disadvantages, either insufficient safety and reliability, or a significant increase in related investment. Summary of the invention

[0005] In view of the above problems, the object of the present invention is to provide a high-integrity pressure protection system for the post-gasification transmission pipeline of an LNG receiving station with relatively small investment and high safety and reliability.

[0006] To achieve the above object, the present invention adopts the following technical scheme: a high integrity pressure protection system for an external transmission pipeline after gasification at an LNG receiving station, the system comprising a cut-off valve, a pressure transmitter and a logic processing controller;

[0007] The shut-off valve and the pressure transmitter are sequentially arranged on the pipeline between the gasifier external transmission main pipe and the first station of the external transmission pipeline;

[0008] The logic processing controller is electrically connected to the shut-off valve and the pressure transmitter. The logic processing controller performs a logic judgment on the pressure value detected by the pressure transmitter, and then controls the shut-off valve to be closed according to a preset pressure alarm value that is lower than the design pressure of the first station of the external transmission pipeline, so as to control the gas that is constantly rising in the gasifier external transmission main pipe within the range of the gasifier external transmission main pipe and prevent it from entering the first station of the external transmission pipeline.

[0009] In some embodiments of the present invention, the shut-off valve is an electric, electromagnetic or pneumatic shut-off valve with its own power source.

[0010] In some embodiments of the present invention, the number of the cut-off valves is two, and the two cut-off valves are connected in series.

[0011] In some embodiments of the present invention, the number of the pressure transmitters is three, and the three pressure transmitters are connected in series in sequence.

[0012] In some embodiments of the present invention, the logic processing controller performs a two-out-of-three logical judgment on the alarm pressure values ​​detected by the pressure transmitter, and issues an operation instruction to the two series-connected cut-off valves based on the detected pressure values, and when different preset values ​​of the maximum operating pressure of the first station of the external transmission pipeline are reached, the corresponding cut-off valves are started to cut off within the set time.

[0013] In some embodiments of the present invention, the logic processing controller adopts a Siemens or Mitsubishi programmable logic processing controller, so that the instrument safety integrity level is 3 or above.

[0014] The present invention adopts the above technical solution, and has the following characteristics:

[0015] 1. The present invention sets a high integrity pressure protection system on the external transmission main pipe of the vaporizer of the LNG receiving station, cancels the emergency shut-off valve of the conventional external transmission main pipe of the vaporizer, and does not require the emergency shut-off valve downstream of the first station of the external transmission pipeline to be logically interlocked with the emergency shut-off valves at the inlet and outlet of the vaporizer of the LNG receiving station, so as to fully ensure the pressure safety of the first station of the external transmission pipeline with fast response speed and high reliability;

[0016] 2. The high integrity pressure protection system of the present invention has a small investment and is sufficiently safe and reliable, and can effectively solve the pressure protection problem between the external transmission unit after gasification at the LNG receiving station and the first station of the external transmission pipeline. The effect is most prominent in the early design of the relevant LNG receiving station and the transformation stage during the operation period. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the high integrity pressure protection system of the LNG receiving station after gasification and transmission pipeline of the present invention. DETAILED DESCRIPTION

[0018] It should be understood that the terms used herein are only for the purpose of describing specific example embodiments and are not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms "one", "an" and "said" as used herein may also be meant to include plural forms. The terms "include", "comprise", "contain", and "have" are inclusive, and therefore specify the existence of stated features, steps, operations, elements and / or parts, but do not exclude the existence or addition of one or more other features, steps, operations, elements, parts, and / or combinations thereof. The method steps, processes, and operations described herein are not interpreted as necessarily requiring them to be performed in the specific order described or illustrated, unless the execution order is clearly indicated. It should also be understood that additional or alternative steps may be used.

[0019] Although the terms first, second, third, etc. can be used in the text to describe multiple elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms can only be used to distinguish an element, component, region, layer or section from another region, layer or section. Unless the context clearly indicates, terms such as "first", "second" and other numerical terms do not imply order or sequence when used in the text. Therefore, the first element, component, region, layer or section discussed below can be referred to as the second element, component, region, layer or section without departing from the teaching of the example embodiments.

[0020] For ease of description, spatially relative terms may be used herein to describe the relationship of one element or feature relative to another element or feature as shown in the figures, such as "inside", "outside", "inner side", "outer side", "below", "above", etc. Such spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation depicted in the figures.

[0021] like Figure 1 As shown, the high-integrity pressure protection system for the external transmission pipeline after gasification of the LNG receiving station provided in this embodiment includes a shut-off valve, a pressure transmitter and a logic processing controller. The shut-off valve and the pressure transmitter are sequentially arranged on the pipeline between the gasifier external transmission main pipe and the first station of the external transmission pipeline, and the logic processing controller is electrically connected to the shut-off valve and the pressure transmitter.

[0022] Specifically, the number of the cut-off valves may be two, and the two cut-off valves A1 and A2 are connected in series. Preferably, the cut-off valve may be an electric, electromagnetic or pneumatic cut-off valve with its own power source;

[0023] The number of pressure transmitters may be three, namely pressure transmitters B1 to B3;

[0024] The logic processing controller C may adopt a Siemens or Mitsubishi programmable logic processing controller (such as Mitsubishi QnU series, etc.), and adopt a control loop to make the instrument safety integrity level (SIL) 3 or above.

[0025] When in use, the emergency shutdown is initiated according to the working conditions to be dealt with, such as an accident in the downstream of the gasifier external transmission pipeline, and the emergency shutdown signal is usually not linked to the control system of the LNG receiving station. When the LNG receiving station gasifier external transmission main pipe detects a pressure alarm, because the design of the gasifier is special, in the case of emergency shutdown, in order to protect the pressure of the gasifier itself, the emergency shutdown valve at the outlet of the gasifier will be delayed by about 20 to 40 seconds compared with the emergency shutdown valve at the inlet. During this period, the LNG gas in the vaporizer continues to vaporize, and the pressure in the vaporizer external transmission main pipe increases. The three pressure transmitters B1~B3 set at the downstream of the high-integrity pressure protection system of this embodiment detect the alarm pressure value, and perform a three-choice two logic judgment through the logic processing controller C (that is, the alarm pressure values ​​detected by the pressure transmitters B1, B2, and B3 are selected. If any two of them reach the alarm, the pressure transmitter triggers the alarm and it is confirmed. If only one pressure transmitter triggers the alarm, it will not act), causing the two series-connected shut-off valves A1 and A2 to respond quickly according to the preset pressure alarm value lower than the design pressure of the first station of the external transmission pipeline, so as to shut down, so that the gas that is constantly rising in the external transmission main pipe of the vaporizer can be controlled within the range of the gasification external transmission main pipe of the LNG receiving station and does not enter the boundary area of ​​the first station of the external transmission pipeline.

[0026] As the last level of protection for the process system, the pressure relief valve (PSV) usually provided can have sufficient discharge capacity in the fault state to discharge all the fluids entering the system, so that the pressure of the process system will not exceed the design conditions, thereby ensuring the safety of the entire process system, but there is no safety condition in the entire system. The function of the high integrity pressure protection system provided in the embodiment is to ensure that the upstream pressure source can be effectively cut off in a very short time in the fault state, ensuring that the downstream system will not be affected by the upstream high pressure source, and the high integrity pressure protection system of this embodiment has a faster response speed and higher reliability than the existing emergency shut-off valve device.

[0027] The following is a detailed description of the process of pressure protection performed by the high integrity pressure protection system for the gasification transmission pipeline of the LNG receiving station in this embodiment in combination with a specific embodiment:

[0028] S1. In the event of an accident or other unexpected situation downstream of the first station 1 of the external transmission pipeline, the emergency shut-off valve 2 is activated, and the signal of the emergency shut-off valve 2 is usually not linked to the control system of the LNG receiving station.

[0029] The LNG gas in S2, vaporizers 3, 4 continues to vaporize, and the pressure in the vaporizer external transmission main pipe increases. The three pressure transmitters B1, B2, and B3 set downstream of the high-integrity pressure protection system 5 detect that the alarm pressure value has reached the maximum operating pressure of the first external transmission station.

[0030] S3, the logic processing controller C performs a three-choice two logic judgment, and sends an operation instruction to the two series-connected cut-off valves A1 and A2 according to the detected pressure signal.

[0031] S4, two series-connected cut-off valves A1 and A2, respond quickly according to the preset pressure alarm value lower than the design pressure of the first station of the external transmission pipeline, and start the cut-off valve A2 when the maximum operating pressure of the first station of the external transmission reaches 105%, and cut off within 2 to 5 seconds;

[0032] S5. When the maximum operating pressure of the first external transmission station reaches 108% to 110%, the shut-off valve A1 is activated and shut off within 2 to 5 seconds;

[0033] S6, the emergency shut-off valves 6 and 7 upstream of the vaporizers 3 and 4 are shut off, and the LNG high-pressure pumps 8 and 9 are shut off. In the pipeline downstream of the emergency shut-off valves 6 and 7, LNG flows through the flow control valves 10 and 11 into the vaporizers 3 and 4 to continue to be gasified, and passes through the one-way valves 12 and 13. The pressure in the pipeline further increases until 20 to 30 seconds later, when the emergency shut-off valves 14 and 15 downstream of the vaporizers 3 and 4 are shut off.

[0034] 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 its protection scope. Although the present application has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that after reading the present application, those skilled in the art can still make various changes, modifications or equivalent substitutions to the specific implementation methods of the application, but these changes, modifications or equivalent substitutions are all within the protection scope of the claims to be approved.

Claims

1. A high integrity pressure protection system for the gasification and transmission pipeline of an LNG receiving station, characterized in that: The system includes a cut-off valve, a pressure transmitter and a logic processing controller; the number of the pressure transmitters is three; the number of the cut-off valves is two, and the two cut-off valves are connected in series; the cut-off valve and the pressure transmitter are sequentially arranged on the pipeline between the gasifier external transmission main pipe and the first station of the external transmission pipeline; the logic processing controller is electrically connected to the cut-off valve and the pressure transmitter, and the logic processing controller performs a logic judgment on the pressure value detected by the pressure transmitter, and then controls the cut-off valve to be closed according to a preset pressure alarm value lower than the design pressure of the first station of the external transmission pipeline, so as to control the gas that is constantly rising in the gasifier external transmission main pipe to be within the range of the gasifier external transmission main pipe and not to enter the first station of the external transmission pipeline; The logic processing controller performs a two-out-of-three logic judgment on the alarm pressure values ​​detected by the pressure transmitter, and issues an operation instruction to the two series-connected cut-off valves according to the detected pressure values, and respectively starts the corresponding cut-off valves to cut off within the set time when the different preset values ​​of the maximum operating pressure of the first station of the external transmission pipeline are reached. The specific implementation process is as follows: S1. When an accident occurs downstream of the first station of the external transmission pipeline, the emergency shut-off valve downstream of the first station of the external transmission pipeline is activated, and the signal of the emergency shut-off valve will not be linked to the control system of the LNG receiving station; S2. The LNG gas in the vaporizer continues to vaporize, and the pressure in the vaporizer external transmission main pipe increases. The three pressure transmitters installed downstream of the high integrity pressure protection system detect the alarm pressure value reaching the maximum operating pressure of the first station of the external transmission pipeline; S3, the logic processing controller performs a three-choose-two logic judgment and issues an operation instruction to the two series-connected cut-off valves according to the detected pressure signal; S4, two cut-off valves connected in series, respond quickly according to the preset pressure alarm value lower than the design pressure of the first station of the external transmission pipeline, and start one of the cut-off valves when the maximum operating pressure of the first station of the external transmission pipeline reaches 105%, and cut off within 2 to 5 seconds; S5. When the maximum operating pressure of the first station of the external transmission pipeline reaches 108%~110%, start another shut-off valve and shut it off within 2~5 seconds; S6. The emergency shut-off valve upstream of the vaporizer is shut off, and the LNG high-pressure pump is shut off. In the pipeline downstream of the emergency shut-off valve, LNG flows through the flow control valve into the vaporizer to continue gasification, and passes through the one-way valve. The pressure in the pipeline further increases until the emergency shut-off valve downstream of the vaporizer is shut off after 20 to 30 seconds.

2. The high integrity pressure protection system according to claim 1, characterized in that: The cut-off valve is an electric, electromagnetic or pneumatic cut-off valve with its own power source.

3. According to the high integrity pressure protection system according to any one of claims 1 to 2, the logic processing controller adopts a Siemens or Mitsubishi programmable logic processing controller, so that the instrument safety integrity level is 3 or above.

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