A pretreatment system and method for offshore fixed liquefied natural gas platform

Abstract

The present invention discloses a pretreatment system and method for an offshore fixed liquefied natural gas platform, wherein the pretreatment system comprises an onshore raw gas receiving system, an onshore sea gas receiving system, an onshore slug flow capture system, an onshore commodity gas receiving system, an onshore and offshore pipeline system, and an offshore receiving system. The present invention integrates the technical and economic advantages of the offshore fixed natural gas liquefaction processing platform, further considers the problems of multiple gas sources, multiple gas qualities, flow assurance, pipeline landing, and large-scale slug flow capture on land and proposes a mode in which the onshore gas sources are centrally pretreated on land, the offshore gas sources are centrally collected on the platform and then introduced into the onshore pretreatment, and the onshore centralized treatment is then sent back to the offshore for deep treatment according to a dedicated medium line, thereby maximizing the acceptance of different gas sources of the offshore fixed liquefied natural gas processing platform, and fully considering the slug flow capture frequency of the slug flow catcher, the offshore construction cost, and the maximally reducing the landing pipeline density from the land to the platform.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquefied natural gas processing, and in particular relates to a pretreatment system and method for an offshore fixed liquefied natural gas platform. Background Art

[0002] As the proportion of clean energy consumption increases, the global sales system of fossil energy represented by natural gas is gradually improved, and the demand for liquefied natural gas processing in natural gas producing countries is increasingly strong to meet the economic requirements of ultra-long-distance transportation. The main component of liquefied natural gas is methane, which is recognized as the cleanest fossil energy on the earth. It is colorless, odorless, non-toxic and non-corrosive. Its volume is about 1 / 625 of the volume of the same amount of gaseous natural gas. At present, the construction mode of liquefied natural gas processing plants mainly depends on the location of gas sources, approval of land use and other issues. Generally, land-based gas sources choose to build plants near the coast and rivers to meet the needs of product shipment. The main problems are difficult site selection and long approval process; deep-water gas fields can consider transporting natural gas to land for processing and liquefaction or directly setting up floating natural gas liquefaction units for direct processing and loading. For the scheme of transporting back to land for processing, there are similar difficulties in building plants on land. For land-based liquefied natural gas plants, the best site selection conditions are close to the coast, sufficient upstream gas sources, convenient transportation, complete supporting facilities and low safety risks. Therefore, in recent years, a model for building offshore fixed liquefied natural gas platforms has emerged, which aims to move liquefied natural gas plants from onshore to offshore, solve problems such as large-scale land use approval, onshore site selection, and safety risk control, and vigorously promote a modular plant construction model.

[0003] At present, this mode mainly considers offshore pre-treatment, natural gas liquefaction, storage and transportation units, all of which are installed in a centralized manner using a platform + module. For a system with an offshore platform as the processing center, it needs to receive multiple gas sources such as onshore commodity gas, onshore raw gas, and offshore raw gas to achieve processing and external transportation. Therefore, it is inevitable to encounter the problem of slug flow capture and control and the problem of mode selection of onshore pipeline landing platform. For the problem of slug flow capture and control, the characteristics of pipeline liquid accumulation in onshore and offshore raw gas gathering pipelines should be fully considered to meet the slug flow caused by cleaning, production increase, and low-volume production. If a large slug flow catcher is directly set on the platform, the collector body will occupy a large area and the corresponding platform foundation cost will be high; at the same time, for the adaptability of onshore multi-gas source intake, it is advisable to consider setting up a manifold station near the coast on the adjacent land, and after the multiple gas sources merge, they will land on the platform through fewer pipelines to comprehensively improve the functional adaptability and economy of this type of offshore platform-type liquefied natural gas plant. However, current related studies and reports have not yet involved the aforementioned scheme, and it is necessary to conduct a full design and analysis. Summary of the invention

[0004] The purpose of the present invention is to provide a pretreatment system and method for an offshore fixed liquefied natural gas platform in order to further improve the functionality and integrity of the offshore fixed liquefied natural gas platform in view of the above-mentioned problems.

[0005] The main technical idea of ​​the present invention is based on the demand for onshore and offshore raw gas processing, and comprehensively considers the adaptability and economy of offshore fixed liquefied natural gas platforms. It is proposed to set up a pre-processing station on offshore land to realize the functions of receiving, gathering, slug flow capture, gas-liquid separation, etc. of onshore raw gas pipelines and submarine raw gas reverse transmission pipelines, and at the same time realize the receiving and gathering functions of onshore commercial gas pipelines; it is proposed to set up a receiving unit on the offshore platform to realize the receiving, gathering, and reverse transmission of submarine raw gas pipelines to land, and realize the functions of onshore separation of raw gas (including reverse transmission of sea gas) pipelines, onshore separation of liquid (including reverse transmission of sea gas) pipelines, and commercial gas pipelines, and also realize the functions of commercial gas dust removal. The overall goal of land function coupling, offshore dedicated processing, and construction cost leadership is achieved to reduce the receiving load of the offshore platform and broaden the functionality of the offshore platform.

[0006] The technical solution adopted by the present invention is: a pretreatment system for an offshore fixed liquefied natural gas platform, characterized by: comprising an onshore raw gas receiving system, an onshore marine gas receiving system, an onshore slug flow capture system, an onshore commercial gas receiving system, an onshore marine pipeline system and an offshore receiving system;

[0007] The onshore raw gas receiving system is used to receive the onshore raw gas and pass the received raw gas into the onshore slug flow capture system;

[0008] The offshore receiving system is used to receive offshore raw gas, upstream land and sea raw gas, upstream land and sea liquid phase and land and sea commodity gas;

[0009] The onshore sea gas receiving system is connected to the offshore receiving system through the onshore sea pipeline system, and the onshore sea gas receiving system is used to receive the offshore raw gas collected by the offshore receiving system, and to feed the received offshore raw gas into the onshore slug flow capture system;

[0010] The onshore slug flow capture system is used to receive media from an onshore raw gas receiving system and an onshore marine gas receiving system. The onshore slug flow capture system is connected to the marine receiving system through a land-sea pipeline system. The land-sea raw gas and land-sea liquid separated by the onshore slug flow capture system enter the marine receiving system through the land-sea pipeline system.

[0011] The onshore commodity gas receiving system is connected to the offshore receiving system through the land-sea pipeline system, and the onshore commodity gas receiving system is used to receive the onshore commodity gas and pass the received commodity gas into the offshore receiving system through the land-sea pipeline system;

[0012] The onshore raw gas receiving system, onshore marine gas receiving system, onshore slug flow capture system and onshore commodity gas receiving system are arranged on the coast, the offshore receiving system is arranged on an offshore natural gas liquefaction processing platform, and the onshore systems are connected to the offshore receiving system through a land-sea pipeline system.

[0013] The pretreatment system for an offshore fixed liquefied natural gas platform described in the present invention, wherein the onshore raw gas receiving system includes at least one onshore raw gas pipeline receiving channel and an onshore raw gas manifold, each onshore raw gas pipeline receiving channel is composed of an onshore raw gas inlet trunk line, an onshore raw gas branch main pipeline, an onshore raw gas ball collecting cylinder and an onshore raw gas cleaning and ball collecting branch, the onshore raw gas of each onshore raw gas pipeline receiving channel is collected into the onshore raw gas manifold, and the onshore raw gas manifold is connected to the onshore slug flow capture system through the onshore raw gas manifold outlet pipeline.

[0014] The pretreatment system for an offshore fixed liquefied natural gas platform of the present invention, wherein the land-sea pipeline system comprises a reverse feed gas pipeline, a land-sea feed gas pipeline, a land-sea liquid phase pipeline and a land-sea commodity gas pipeline;

[0015] The onshore marine gas receiving system is connected to the offshore receiving system via a reverse raw gas pipeline, and the reverse raw gas pipeline is used to reverse the offshore raw gas to the onshore marine gas receiving system;

[0016] The onshore slug flow capture system is connected to the offshore receiving system through an onshore and offshore raw gas pipeline and an onshore and offshore liquid phase pipeline, respectively. The onshore and offshore raw gas pipeline is used to transport the separated onshore and offshore raw gas, and the onshore and offshore liquid phase pipeline is used to transport the separated onshore and offshore liquid phase medium.

[0017] The onshore commodity gas receiving system is connected to the offshore receiving system via a land-sea commodity gas pipeline, and the land-sea commodity gas pipeline is used to transport the commodity gas collected onshore.

[0018] The pretreatment system for an offshore fixed liquefied natural gas platform described in the present invention, wherein the onshore sea gas receiving system is composed of a reverse feed gas pipeline end, a reverse feed gas branch main pipeline, a reverse feed gas ball collecting cylinder, and a reverse feed gas cleaning and ball collecting branch, and forms a complete reverse feed gas receiving channel. The onshore sea gas receiving system sends the received offshore raw gas to the onshore slug flow capture system together with the onshore raw gas through the onshore raw gas manifold outlet pipeline.

[0019] The pretreatment system for an offshore fixed liquefied natural gas platform of the present invention, wherein the onshore slug flow capture system comprises a slug flow capturer, a gas phase outlet pipeline, a gas phase pigging and launching branch, a gas phase launching barrel, a first section of an onshore and offshore raw gas pipeline, a liquid phase outlet pipeline, a liquid phase pigging and launching branch, a liquid phase launching barrel, and a first section of an onshore and offshore liquid phase pipeline;

[0020] The onshore raw gas manifold outlet pipeline of the onshore raw gas receiving system is connected to the slug flow catcher;

[0021] The gas phase outlet pipeline is connected from the top of the slug flow catcher and connected to the first section of the land-sea raw gas pipeline to form a normal transportation channel of the land-sea raw gas pipeline. The gas phase pigging and ball-launching branch is connected from the middle of the gas phase outlet pipeline and connected to the gas phase ball-launching cylinder to form a ball-launching and transportation channel of the land-sea raw gas channel.

[0022] The liquid phase outlet pipeline is connected from the bottom of the slug flow catcher and is connected to the first section of the land-sea liquid phase pipeline to form a normal transportation channel of the land-sea liquid phase pipeline. The liquid phase pipe cleaning and ball launching branch is connected from the middle part of the liquid phase outlet pipeline and is connected to the liquid phase ball launching cylinder to form a ball launching and transportation channel of the land-sea liquid phase channel.

[0023] The pretreatment system for an offshore fixed liquefied natural gas platform of the present invention, wherein the onshore commodity gas receiving system comprises at least one onshore commodity gas pipeline receiving channel, an onshore commodity gas manifold, an onshore commodity gas manifold outlet pipeline, an onshore commodity gas cleaning and ball launching branch, an onshore commodity gas ball launching cylinder and a first section of an onshore and offshore commodity gas pipeline;

[0024] Each onshore commodity gas pipeline receiving channel is composed of an onshore commodity gas inlet trunk line, an onshore commodity gas branch main pipeline, an onshore commodity gas ball receiving cylinder, and an onshore commodity gas cleaning ball receiving branch. The onshore commodity gas of each onshore commodity gas pipeline receiving channel is collected to the onshore commodity gas manifold, which is connected to the first section of the onshore and sea commodity gas pipeline through the onshore commodity gas manifold outlet pipeline to form a normal transportation channel for the onshore and sea commodity gas pipeline;

[0025] The onshore commercial gas cleaning pipe ball launching branch is connected from the middle of the onshore commercial gas manifold outlet pipeline and is connected to the onshore commercial gas ball launching cylinder to form a ball launching and conveying channel of the land-sea commercial gas channel.

[0026] The pretreatment system for an offshore fixed liquefied natural gas platform of the present invention, wherein the offshore receiving system comprises an offshore raw gas receiving system, an offshore raw gas reverse transmission subsystem, a land and sea raw gas receiving subsystem, a land and sea liquid phase receiving subsystem and a land and sea commodity gas receiving subsystem;

[0027] The offshore raw gas receiving system is connected to the offshore raw gas reverse transmission subsystem, and the offshore raw gas reverse transmission subsystem is connected to the onshore marine gas receiving system through a reverse transmission raw gas pipeline;

[0028] The onshore slug flow capture system is connected to the onshore and offshore raw gas receiving subsystem via an onshore and offshore raw gas pipeline;

[0029] The onshore slug flow capture system is connected to the onshore and offshore liquid phase receiving subsystem via an onshore and offshore liquid phase pipeline;

[0030] The onshore commodity gas receiving system is connected to the onshore commodity gas receiving subsystem via an onshore commodity gas pipeline.

[0031] The pretreatment system for an offshore fixed liquefied natural gas platform described in the present invention, wherein the offshore raw gas receiving system includes at least one offshore raw gas pipeline receiving channel and an offshore raw gas reverse transmission manifold, each offshore raw gas pipeline receiving channel is composed of an offshore raw gas trunk line, an offshore raw gas branch main pipeline, an offshore raw gas ball receiving cylinder and an offshore raw gas cleaning and ball receiving branch, the offshore raw gas of each offshore raw gas pipeline receiving channel is collected into the offshore raw gas reverse transmission manifold, and the offshore raw gas reverse transmission manifold is connected to the offshore raw gas reverse transmission subsystem through an offshore raw gas reverse transmission external transmission pipeline;

[0032] The offshore raw gas reverse transmission subsystem is composed of an offshore raw gas reverse transmission external transmission pipeline, an offshore raw gas cleaning and ball-serving branch, an offshore raw gas ball-serving cylinder, and a first section of the reverse transmission raw gas pipeline. The offshore raw gas reverse transmission manifold is connected to the first section of the reverse transmission raw gas pipeline through the offshore raw gas reverse transmission external transmission pipeline to form a normal transmission channel of the offshore raw gas reverse transmission pipeline. The offshore raw gas cleaning and ball-serving branch is connected from the middle of the offshore raw gas reverse transmission external transmission pipeline, connected to the offshore raw gas ball-serving cylinder, and forms a ball-serving transmission channel of the offshore raw gas reverse transmission channel.

[0033] The land-sea raw gas receiving subsystem is composed of the land-sea raw gas pipeline terminal section, the land-sea raw gas branch main pipeline, the land-sea raw gas ball receiving cylinder and the land-sea raw gas pigging and ball receiving branch. The land-sea raw gas pipeline terminal section is connected to the land-sea raw gas branch main pipeline to form a normal transportation channel for the land-sea raw gas.

[0034] The land-sea liquid phase receiving subsystem is composed of the land-sea liquid phase pipeline terminal section, the land-sea liquid phase branch main pipeline, the land-sea liquid phase ball receiving cylinder and the land-sea liquid phase pigging and ball receiving branch. The land-sea liquid phase pipeline terminal section is connected to the land-sea liquid phase branch main pipeline to form a normal transportation channel for the land-sea liquid phase medium.

[0035] The land and sea commercial gas receiving subsystem is composed of the end section of the land and sea commercial gas pipeline, the land and sea commercial gas branch main pipeline, the land and sea commercial gas ball receiving cylinder and the land and sea commercial gas cleaning and ball receiving branch. The end section of the land and sea commercial gas pipeline is connected to the land and sea commercial gas branch main pipeline to form a normal transportation channel for land and sea commercial gas.

[0036] A pretreatment method for an offshore fixed liquefied natural gas platform, characterized in that it includes the following specific treatment steps:

[0037] Step 1: Set up an onshore raw gas receiving system, an onshore sea gas receiving system, an onshore slug flow capture system and an onshore commodity gas receiving system on the onshore side of the coast; set up an offshore receiving system on the offshore natural gas liquefaction processing platform; set up a land-sea pipeline system connecting the onshore system and the offshore receiving system;

[0038] Step 2: The receiving of onshore raw gas is divided into pigging receiving and non-pigging receiving operation. When a certain onshore raw gas inlet is pigged, the pigging channel of the onshore raw gas pipeline receiving channel is opened; the main raw gas channel is opened for the other onshore raw gas inlets; the collected channels enter the onshore slug flow capture system;

[0039] Step 3: The reception of offshore raw gas is divided into pigging reception and non-pigging reception operation. When a certain offshore raw gas is pigged, the pigging channel of the offshore raw gas pipeline receiving channel is opened; the main raw gas channel is opened for the other offshore raw gas inlets; the reverse raw gas pipelines of the various routes entering the land-sea pipeline system after the confluence are kept open, and after merging with the onshore raw gas through the onshore sea gas receiving system, the reverse raw gas pipelines are connected to the onshore slug flow capture system;

[0040] Step 4: The reception of onshore commodity gas is divided into pigging reception and non-pigging reception operation. When a certain commodity gas is received through pigging reception, the pigging channel of the onshore commodity gas pipeline receiving channel is opened; the commodity gas main channel is opened for the other commodity gas inlets; the collected commodity gas pipelines enter the onshore and offshore commodity gas pipeline system and are sent to the onshore and offshore commodity gas receiving subsystem of the offshore receiving system;

[0041] Step 5: the slug flow catcher is turned on, and the onshore raw gas and the offshore raw gas are separated and slug flow is captured in the slug flow catcher;

[0042] The separated gas phase enters the land-sea raw gas pipeline through the gas phase outlet pipeline and is transported to the land-sea raw gas receiving subsystem of the offshore receiving system;

[0043] The separated and captured liquid phase enters the land-sea liquid phase pipeline through the liquid phase outlet pipeline and is transported to the land-sea liquid phase receiving subsystem of the offshore receiving system;

[0044] Step 6: Open the receiving pipelines of the land-sea raw gas pipeline, land-sea liquid pipeline and land-sea commercial gas pipeline of the offshore receiving system to realize the normal reception and cleaning reception of the above pipelines. The received media are sent to the downstream gas phase and liquid phase deep processing systems respectively.

[0045] The pretreatment method for an offshore fixed liquefied natural gas platform of the present invention, when the reverse feed gas pipeline needs to be cleaned, the ball-sending device of the offshore feed gas reverse feed subsystem is turned on, and the ball-receiving device of the onshore sea gas receiving system is turned on at the same time, so as to realize the cleaning;

[0046] When the onshore and offshore commodity gas pipeline needs to be cleaned, the ball-sending device of the onshore commodity gas receiving system is opened, and the ball-receiving device of the onshore and offshore commodity gas receiving subsystem is opened at the same time to realize the cleaning;

[0047] When the land-sea raw gas pipeline and the land-sea liquid phase pipeline need to be cleaned, the gas phase and liquid phase ball-sending devices in the onshore plug flow capture system are opened, and the ball-receiving devices of the land-sea raw gas receiving subsystem and the land-sea liquid phase receiving subsystem are opened at the same time to realize the cleaning;

[0048] The slug flow catcher maintains low liquid level control and maintains the slug flow capture capability by adjusting the liquid phase displacement.

[0049] The pretreatment system and method for an offshore fixed liquefied natural gas platform proposed in the present invention integrate the technical and economic advantages of the offshore fixed natural gas liquefaction processing platform, further consider the problems of multiple gas sources on land and sea, multiple gas qualities, flow assurance, pipeline landing, and large-scale slug flow capture, and propose a mode in which onshore gas sources are centrally pretreated on land, offshore gas sources are centrally collected on the platform and then introduced into onshore pretreatment, and after centralized onshore treatment, the gas is sent back to the sea for deep treatment via a dedicated medium line.

[0050] Compared with the prior art, the present invention has at least the following beneficial effects: the present invention maximizes the different gas source acceptance of the offshore fixed liquefied natural gas processing platform, fully considers the slug flow capture frequency of the slug flow catcher, the offshore construction cost and other issues, and greatly reduces the density of the landing pipeline from the land to the platform. Specifically, it is:

[0051] (1) Scientific setting

[0052] The present invention is based on the advanced offshore fixed liquefied natural gas platform production model, comprehensively considers the platform processing acceptance issues of onshore raw gas, onshore commercial gas and offshore raw gas, moves the onshore receiving system with relatively dense pipeline layout and the slug flow catcher with a large footprint and low slug flow capture frequency to the onshore side of the coast, and establishes an offshore raw gas reverse transmission pipeline to realize the functions of onshore pretreatment of land and sea raw gas and dedicated line access platform for land and sea media.

[0053] (2) Good economic performance

[0054] The present invention rationally utilizes the geographical advantages of offshore platforms, sets up an onshore gas source receiving system and a slug flow capture system on the nearshore land, and serves the pretreatment of offshore raw gas at the same time, thereby realizing the centralized collection and pretreatment of raw gas and commercial gas, avoiding the construction of slug flow catchers on offshore platforms that occupy a large area but are used less frequently, and also avoiding excessive connecting pipelines from land to sea, thereby realizing a dedicated line unified supply from land to platform, streamlining the construction of offshore platforms and foundations, and reducing construction costs overall. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The present invention will be described by way of specific embodiments with reference to the accompanying drawings, in which

[0056] Figure 1 It is a schematic diagram of a pretreatment system for an offshore fixed liquefied natural gas platform according to the present invention.

[0057] Markings in the figure: Ⅰ is the onshore raw gas receiving system, Ⅱ is the onshore marine gas receiving system, Ⅲ is the onshore slug flow capture system, Ⅳ is the onshore commercial gas receiving system, Ⅴ is the onshore and offshore pipeline system, and Ⅵ is the offshore receiving system;

[0058] 1 is the onshore raw gas inlet trunk line, 2 is the onshore raw gas branch main pipeline, 3 is the onshore raw gas ball receiving cylinder, 4 is the onshore raw gas pigging ball receiving branch, 5 is the onshore raw gas manifold, 6 is the onshore raw gas manifold outlet pipeline, 11 is the onshore commercial gas inlet trunk line, 12 is the onshore commercial gas branch main pipeline, 13 is the onshore commercial gas ball receiving cylinder, 14 is the onshore commercial gas pigging ball receiving branch, 15 is the onshore commercial gas manifold, 16 is the onshore commercial gas manifold outlet pipeline, 17 is the onshore commercial gas pigging ball delivery Branch, 18 is the onshore commercial gas ball launcher, 19 is the first section of the onshore and offshore commercial gas pipeline, 31 is the end of the reverse feed gas pipeline, 32 is the reverse feed gas branch main pipeline, 33 is the reverse feed gas ball receiver, 34 is the reverse feed gas pigging and ball receiver branch, 41 is a slug flow collector, 42 is the gas phase outlet pipeline, 43 is the gas phase pigging ball launcher branch, 44 is the gas phase ball launcher, 45 is the first section of the onshore and offshore raw gas pipeline, 46 is the liquid phase outlet pipeline, 47 is the liquid phase pigging ball launcher branch, 48 is the liquid phase ball launcher, 49 is the first section of the land-sea liquid phase pipeline, 51 is the offshore raw gas trunk line, 52 is the offshore raw gas branch main pipeline, 53 is the offshore raw gas ball receiving cylinder, 54 is the offshore raw gas cleaning ball receiving branch, 55 is the offshore raw gas reverse transmission manifold, 56 is the offshore raw gas reverse transmission external pipeline, 57 is the offshore raw gas cleaning ball launching branch, 58 is the offshore raw gas launching cylinder, 59 is the first section of the reverse transmission raw gas pipeline, 61 is the last section of the land-sea raw gas pipeline, 62 is the land-sea raw gas branch main pipeline, 63 is the land-sea raw gas The ball-collecting cylinder is 64, which is the land-sea raw gas cleaning and ball-collecting branch, 71 is the end section of the land-sea liquid phase pipeline, 72 is the land-sea liquid phase branch main pipeline, 73 is the land-sea liquid phase ball-collecting cylinder, 74 is the land-sea liquid phase cleaning and ball-collecting branch, 81 is the end section of the land-sea commercial gas pipeline, 82 is the land-sea commercial gas branch main pipeline, 83 is the land-sea commercial gas ball-collecting cylinder, 84 is the land-sea commercial gas cleaning and ball-collecting branch, 91 is the reverse raw gas pipeline, 92 is the land-sea raw gas pipeline, 93 is the land-sea liquid phase pipeline, and 94 is the land-sea commercial gas pipeline. DETAILED DESCRIPTION

[0059] All features disclosed in this specification, or steps in all methods or processes disclosed, except mutually exclusive features and / or steps, can be combined in any manner.

[0060] Any feature disclosed in this specification (including any additional claims and abstract), unless otherwise stated, may be replaced by other equivalent or alternative features having similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0061] like Figure 1 As shown, a pretreatment system for an offshore fixed liquefied natural gas platform includes an onshore raw gas receiving system I, an onshore sea gas receiving system II, an onshore slug flow capture system III, an onshore commodity gas receiving system IV, a land-sea pipeline system V and an offshore receiving system VI. The onshore raw gas receiving system I, the onshore sea gas receiving system II, the onshore slug flow capture system III and the onshore commodity gas receiving system IV are arranged on the coast, and the offshore receiving system VI is arranged on an offshore natural gas liquefaction processing platform. The onshore systems are connected to the offshore receiving system through the land-sea pipeline system V.

[0062] Among them, the onshore raw gas receiving system I is used to receive onshore raw gas, and the received raw gas enters the onshore slug flow capture system III to achieve slug flow capture and gas-liquid separation and transmission to the offshore receiving system; the offshore receiving system VI is responsible for receiving the offshore raw gas, and then collecting and transmitting it to the onshore sea gas receiving system, and is also responsible for receiving the separated raw gas and separated liquid phase at the outlet of the onshore slug flow capture system, and is also responsible for receiving the commercial gas collected onshore; the onshore sea gas receiving system II is connected to the offshore receiving system VI through the land-sea pipeline system V, and the onshore sea gas receiving system II is used to receive the offshore raw gas collected by the offshore receiving system VI, and the received offshore raw gas enters the onshore slug flow capture system III, The separation and slug flow capture of sea gas on land are realized; the onshore slug flow capture system III is used to receive the medium of the onshore raw gas receiving system I and the onshore sea gas receiving system II, and the separation and slug flow capture are performed by using a slug flow catcher. The onshore slug flow capture system III is connected to the offshore receiving system VI through the land-sea pipeline system V, and the land-sea raw gas and land-sea liquid phase separated by the onshore slug flow capture system III enter the offshore receiving system VI through the land-sea pipeline system V; the onshore commodity gas receiving system IV is connected to the offshore receiving system VI through the land-sea pipeline system V, and the onshore commodity gas receiving system IV is used to receive onshore commodity gas, and the received commodity gas enters the offshore receiving system VI through the land-sea pipeline system V.

[0063] In the system shown, the land-sea pipeline system V includes a reverse feed gas pipeline 91, a land-sea feed gas pipeline 92, a land-sea liquid phase pipeline 93 and a land-sea commodity gas pipeline 94; the land-sea gas receiving system II is connected to the offshore receiving system VI through the reverse feed gas pipeline 91, and the reverse feed gas pipeline 91 is used to reverse the offshore feed gas to the land-sea gas receiving system II. When the gas-liquid ratio of the offshore feed gas pipeline is low, the liquid output is large or other slug flows are caused, the offshore feed gas is reversed to the land for primary gas-liquid separation and slug flow capture; the onshore slug flow capture system III is connected to the offshore receiving system VI through the land-sea feed gas pipeline 92 and the land-sea liquid phase pipeline 93, respectively, and the land-sea feed gas pipeline 92 is used to transport the separated land-sea feed gas, that is, the land-sea feed gas pipeline 92 is connected to the land-sea gas receiving system VI. The upper slug flow capture system and the offshore receiving system are responsible for transporting the onshore raw gas and the offshore reverse raw gas after the first-stage separation to the offshore receiving system. The land-sea liquid phase pipeline 93 is used to transport the separated land-sea liquid phase medium, that is, the land-sea liquid phase pipeline 93 connects the onshore slug flow capture system and the offshore receiving system, and is responsible for transporting the liquid phase after the first-stage separation, and is also responsible for transporting the slug flow received and accumulated in the slug flow collector; the onshore commercial gas receiving system IV is connected to the offshore receiving system VI through the land-sea commercial gas pipeline 94, and the land-sea commercial gas pipeline 94 is used to transport the commercial gas collected on land, that is, the land-sea commercial gas pipeline 94 connects the onshore commercial gas receiving system and the offshore receiving system, and is responsible for directly transporting the commercial gas received and collected on land to the inlet of the offshore natural gas liquefaction system for deep processing.

[0064] Among them, the material of each pipeline is consistent with the corresponding upstream pipeline. All of them are buried on the seabed and equipped with concrete counterweights. Each pipeline has insulating joints at both ends to achieve cathodic protection current isolation.

[0065] like Figure 1As shown, the onshore raw gas receiving system I includes at least one onshore raw gas pipeline receiving channel and an onshore raw gas manifold 5. In actual cases, there may be multiple onshore raw gas pipeline receiving channels, which can receive and collect multiple onshore raw gases. Each onshore raw gas pipeline receiving channel is composed of an onshore raw gas inlet trunk line 1, an onshore raw gas branch main pipeline 2, an onshore raw gas ball collecting cylinder 3, and an onshore raw gas cleaning ball collecting branch 4. The onshore raw gas inlet trunk line 1 and the onshore raw gas branch main pipeline 2 are connected to form an onshore raw gas main channel for non-cleaning The single-channel raw gas is collected under the pipe working condition, and the onshore raw gas ball collecting cylinder 3, the cut-off valve, and the onshore raw gas cleaning ball collecting branch 4 are connected to form an onshore raw gas cleaning channel for collecting single-channel raw gas under the cleaning working condition, that is, the onshore raw gas receiving system is responsible for receiving the incoming gas from various onshore raw gas pipelines, providing two modes of normal reception and cleaning ball receiving. The onshore raw gas of various onshore raw gas pipeline receiving channels is collected to the onshore raw gas manifold 5, and the onshore raw gas manifold 5 is connected to the onshore plug flow capture system III through the onshore raw gas manifold outlet pipeline 6. The onshore raw gas receiving system is installed on land, and can be installed by on-site construction or modular overall installation.

[0066] In this embodiment, the material of the onshore raw gas inlet trunk line 1 is determined according to the gas quality parameters, and the onshore raw gas branch main pipeline 2 is connected from the end of the onshore raw gas inlet trunk line 1 through the asymmetric end of the baffle tee, which is used for a non-pipe cleaning process channel. The material is consistent with the onshore raw gas inlet trunk line 1, and the onshore raw gas ball collecting cylinder 3 is connected to the other outlet of the baffle tee, and forms a pipe cleaning process channel with the onshore raw gas pipe cleaning ball collecting branch 4, and is connected to the onshore raw gas branch main pipeline 2; the onshore raw gas ball collecting cylinder 3 meets the requirements of intelligent pipe cleaning, and is equipped with a pressure transmitter, a balancing pipe, and a replacement The non-pigging process and the pigging process are determined according to the specific operation and switched by the shut-off valve on the pipeline; the material of the onshore raw gas manifold 5 is selected according to the highest requirements for the material of the raw gas pipeline receiving channel; the inlets of the onshore raw gas manifold 5 are arranged symmetrically, and each inlet is at least 1.2m apart to ensure maintenance and installation; the onshore raw gas manifold outlet pipeline 6 is connected from the middle of the onshore raw gas manifold 5, and it is advisable to maintain the same pipe diameter as the onshore raw gas manifold 5, and is used to collect all the onshore raw gas and then transport it to the downstream slug flow catcher 41.

[0067] Among them, the onshore commodity gas receiving system IV includes at least one onshore commodity gas pipeline receiving channel, an onshore commodity gas manifold 15, an onshore commodity gas manifold outlet pipeline 16, an onshore commodity gas cleaning and launching branch 17, an onshore commodity gas launching cylinder 18, and an onshore and offshore commodity gas pipeline first section 19. In actual cases, there may be multiple onshore commodity gas pipeline receiving channels, which can receive and collect multiple onshore commodity gases. The onshore commodity gas receiving system is responsible for receiving and collecting multiple onshore commodity gases and sending them to offshore platforms for further processing. The onshore commodity gas receiving system is installed on land and can be installed on-site or modularly installed as a whole.

[0068] In the system shown, each onshore commercial gas pipeline receiving channel is composed of an onshore commercial gas inlet trunk line 11, an onshore commercial gas branch main pipeline 12, an onshore commercial gas ball receiving cylinder 13 and an onshore commercial gas cleaning ball receiving branch line 14, wherein the onshore commercial gas inlet trunk line 11 is connected to the onshore commercial gas branch main pipeline 12 to form an onshore commercial gas main channel for receiving single-channel commercial gas under non-cleaning conditions, the commercial gas inlet trunk line 11, the onshore commercial gas ball receiving cylinder 13 and the onshore commercial gas cleaning ball receiving branch line 14 are connected to form an onshore commercial gas cleaning channel for receiving single-channel commercial gas under cleaning conditions, and the onshore commercial gas of each onshore commercial gas pipeline receiving channel is collected into the onshore commercial gas manifold 15. In this embodiment, the onshore commercial gas inlet trunk line 11 is made of carbon steel, and the onshore commercial gas branch main pipeline 12 is connected from the end of the onshore commercial gas inlet trunk line 11 through the asymmetric end of the baffle tee, which is used for a non-pipe cleaning process channel, and the material is consistent with the onshore commercial gas inlet trunk line 11; the onshore commercial gas ball collecting cylinder 13 is connected to the other outlet of the baffle tee, and forms a pipe cleaning process channel with the onshore commercial gas pipe cleaning ball collecting branch 14, and is connected to the onshore commercial gas branch main pipeline 12; the onshore commercial gas ball collecting cylinder 13 meets the requirements of intelligent pipe cleaning, and is equipped with accessories such as pressure transmitters, balancing pipes, replacement ports, and drainage cleaning ports ; The non-pigging process and the pigging process are determined according to the specific operation and switched by the shut-off valve on the pipeline; the material of the onshore commercial gas manifold 15 is carbon steel, and the diameter of the onshore commercial gas manifold 15 shall not exceed the maximum steel pipe manufacturing diameter during implementation, otherwise the transmission capacity of the onshore commercial gas manifold 15 should be increased, and the number of downstream external transmission systems should also be increased accordingly; the inlets of the onshore commercial gas manifold 15 are arranged symmetrically, and each inlet is at least 1.2m apart to ensure maintenance and installation; the onshore commercial gas manifold outlet pipeline 16 is connected from the middle of the onshore commercial gas manifold 15, and it is advisable to maintain the same diameter as the onshore commercial gas manifold 15.

[0069] The onshore commodity gas manifold 15 is connected to the first section 19 of the onshore commodity gas pipeline through the onshore commodity gas manifold outlet pipeline 16, forming a normal transportation channel of the onshore commodity gas pipeline; the onshore commodity gas cleaning and launching branch 17 is connected from the middle of the onshore commodity gas manifold outlet pipeline 16, and connected to the onshore commodity gas launching cylinder 18, forming a launching and transmitting channel of the onshore commodity gas channel, which is used for pipeline cleaning and internal inspection. The onshore commodity gas launching cylinder 18 meets the requirements of intelligent cleaning and is equipped with accessories such as pressure transmitter, balance pipe, replacement port, and drainage cleaning port.

[0070] In the system shown, the onshore marine gas receiving system II is composed of a reverse feed gas pipeline terminal 31, a reverse feed gas branch main pipeline 32, a reverse feed gas ball collecting cylinder 33 and a reverse feed gas cleaning and ball collecting branch 34, and forms a complete reverse feed gas receiving channel. In actual cases, a process of a reverse feed gas receiving channel is preferably adopted to reduce investment; wherein, the reverse feed gas pipeline terminal 31 is connected to the reverse feed gas branch main pipeline 32 to form an offshore raw gas reverse transmission main channel, which is used for collecting offshore reverse feed gas under non-cleaning conditions, and the reverse feed gas pipeline terminal 31, the reverse feed gas ball collecting cylinder 33 and the reverse feed gas cleaning and ball collecting branch 34 are connected to form an offshore raw gas reverse transmission cleaning channel, which is used for the reverse feed gas pipeline body cleaning condition; the onshore marine gas receiving system sends the received offshore raw gas to the onshore slug flow capture system III through the onshore raw gas manifold outlet pipeline 6 together with the onshore raw gas. The onshore marine gas receiving system is responsible for receiving the gas from the reverse feed gas pipeline. The system is installed onshore and can be installed on-site or in a modularized overall manner.

[0071] In this embodiment, the material of the reverse raw gas pipeline end 31 is determined according to the gas quality parameters, and the reverse raw gas branch main pipeline 32 is connected from the end of the reverse raw gas pipeline end 31 through the asymmetric end of the baffle tee, which is used for the non-pipe cleaning process channel, and the material is consistent with the reverse raw gas pipeline end 31; the reverse raw gas ball collecting cylinder 33 is connected to the other outlet of the baffle tee, and forms a pipe cleaning process channel with the reverse raw gas pipe cleaning ball collecting branch 34, and is connected to the reverse raw gas branch main pipeline 32; the reverse raw gas ball collecting cylinder 33 meets the requirements of intelligent pipe cleaning, and is equipped with accessories such as pressure transmitter, balance pipe, replacement port, drainage and cleaning port; the non-pipe cleaning process and the pipe cleaning process are determined according to the specific operation, and are switched by the shut-off valve on the pipeline; the reverse raw gas branch main pipeline 32 is connected to the aforementioned onshore raw gas manifold outlet pipeline 6 to realize the confluence of offshore raw gas and onshore raw gas.

[0072] In the system shown, the onshore slug flow capture system III includes a slug flow capture device 41, a gas phase outlet pipeline 42, a gas phase pigging and launching branch 43, a gas phase launching barrel 44, a land-sea raw gas pipeline first section 45, a liquid phase outlet pipeline 46, a liquid phase pigging and launching branch 47, a liquid phase launching barrel 48 and a land-sea liquid phase pipeline first section 49, and the onshore raw gas manifold outlet pipeline 6 of the onshore raw gas receiving system I is connected to the slug flow capture device 41. The onshore slug flow capture system is responsible for the two-phase separation of onshore raw gas and offshore raw gas, the upstream pipeline slug flow capture and storage, and the gas-liquid transmission of the separated pipeline. This system is installed on land. Due to its large size, the slug flow capture device is preferably a multi-tube slug flow capture device, which is constructed and installed on site; the rest of the parts can be constructed and installed on site or installed as a whole in a modular manner.

[0073] In this embodiment, the material of the slug flow catcher 41 is consistent with the onshore raw gas manifold outlet pipeline 6, and the size is determined according to the onshore raw gas and offshore raw gas separation requirements and the slug flow load. It is preferably a multi-tube slug flow catcher, which adopts constant liquid level control, and the reserved slug flow capture capacity is 1.2 times the maximum slug flow load; the gas phase outlet pipeline 42 is connected from the top of the slug flow catcher 41, and is connected to the first section 45 of the onshore and offshore raw gas pipeline through a baffle tee to form a normal transportation channel of the onshore and offshore raw gas pipeline, which is responsible for the transportation of the separated raw gas; the liquid phase outlet pipeline 46 is connected from the bottom of the slug flow catcher 41, and is connected to the first section 49 of the onshore and offshore liquid phase pipeline through a baffle tee to form a normal transportation channel of the onshore and offshore liquid phase pipeline, which is responsible for the transportation of the separated liquid phase, and a regulating valve interlocked with the large slug flow catcher 41 liquid level transmitter is installed on the liquid phase outlet pipeline 46 to control the liquid phase displacement of the liquid phase outlet pipeline 46 according to the actual liquid level.

[0074] Among them, the gas phase cleaning ball-serving branch 43 is connected from the middle of the gas phase outlet pipeline 42, and is connected to the gas phase ball-serving cylinder 44, forming a ball-serving conveying channel of the land-sea raw gas channel, which is used for cleaning and internal detection of the pipeline. The gas phase ball-serving cylinder 44 meets the requirements of intelligent cleaning and is equipped with accessories such as pressure transmitter, balance pipe, replacement port, and drainage and cleaning port; the liquid phase cleaning ball-serving branch 47 is connected from the middle of the liquid phase outlet pipeline 46, and is connected to the liquid phase ball-serving cylinder 48, forming a ball-serving conveying channel of the land-sea liquid phase channel, which is used for cleaning and internal detection of the pipeline. The liquid phase ball-serving cylinder 48 meets the requirements of intelligent cleaning and is equipped with accessories such as pressure transmitter, balance pipe, replacement port, and drainage and cleaning port.

[0075] In the system shown, the offshore receiving system VI includes an offshore raw gas receiving system, an offshore raw gas reverse transmission subsystem, a land-sea raw gas receiving subsystem, a land-sea liquid phase receiving subsystem, and a land-sea commodity gas receiving subsystem. The offshore receiving system is responsible for receiving the incoming gas from various offshore raw gas pipelines, providing two modes of normal reception and pigging and receiving, and then entering the reverse transmission raw gas pipeline after collection; at the same time, it is responsible for receiving the gas from the upstream land-sea raw gas pipeline, land-sea liquid phase pipeline and land-sea commodity gas pipeline, and also provides two modes of normal reception and pigging and receiving. This system is installed on an offshore platform, preferably in the form of an integral module.

[0076] Among them, the offshore raw gas receiving system is connected to the offshore raw gas reverse transmission subsystem, and the offshore raw gas reverse transmission subsystem is connected to the onshore sea gas receiving system II through the reverse transmission raw gas pipeline 91; specifically, the offshore raw gas receiving system includes at least one offshore raw gas pipeline receiving channel and an offshore raw gas reverse transmission manifold 55. In actual cases, there may be multiple offshore raw gas pipeline receiving channels, which can receive and collect multiple offshore raw gases. Each offshore raw gas pipeline receiving channel consists of an offshore raw gas trunk line 51, an offshore raw gas branch main pipeline 52, an offshore raw gas ball collecting cylinder 53 and an offshore raw gas cleaning ball collecting branch pipe. The offshore raw gas trunk line 51 is connected with the offshore raw gas branch main pipeline 52 to form an offshore raw gas main channel, which is used for collecting single-channel raw gas under non-pigging conditions. The offshore raw gas trunk line 51, the offshore raw gas ball collecting cylinder 53 and the offshore raw gas pigging ball collecting branch line 54 are connected to form an offshore raw gas pigging channel, which is used for collecting single-channel raw gas under pigging conditions; the offshore raw gas of each offshore raw gas pipeline receiving channel is collected into the offshore raw gas reverse transmission manifold 55, and the offshore raw gas reverse transmission manifold 55 is connected to the offshore raw gas reverse transmission subsystem through the offshore raw gas reverse transmission external transmission pipeline 56.

[0077] In this embodiment, the material of the offshore raw gas trunk line 51 is determined according to the gas quality parameters, the offshore raw gas branch main pipeline 52 is connected from the end of the offshore raw gas trunk line 51 through the asymmetric end of the baffle tee, and is used for the non-pigging process channel, and the material is consistent with the offshore raw gas trunk line 51; the offshore raw gas ball collecting cylinder 53 is connected to the other outlet of the baffle tee, and forms a pigging process channel with the offshore raw gas pigging ball collecting branch 54, and is connected to the offshore raw gas branch main pipeline 52; the offshore raw gas ball collecting cylinder 53 meets the requirements of intelligent pigging, and is equipped with accessories such as pressure transmitters, balance pipes, replacement ports, and drainage and cleaning ports; the non-pigging process and the pigging process are determined according to specific operations and switched by the shut-off valve on the pipeline; the material of the offshore raw gas reverse transmission and convergence pipe 55 is selected according to the highest requirements for the material of the raw gas pipeline receiving channel; the inlets of the offshore raw gas reverse transmission and convergence pipe 55 are arranged symmetrically, and each inlet is at least 1.2m apart to ensure maintenance and installation.

[0078] Among them, the onshore slug flow capture system III is connected to the onshore and offshore raw gas receiving subsystem through the onshore and offshore raw gas pipeline 92; the onshore slug flow capture system III is connected to the onshore and offshore liquid phase receiving subsystem through the onshore and offshore liquid phase pipeline 93; the onshore commercial gas receiving system IV is connected to the onshore and offshore commercial gas receiving subsystem through the onshore and offshore commercial gas pipeline 94.

[0079] In the system shown in the figure, the offshore raw gas reverse transmission subsystem is composed of an offshore raw gas reverse transmission external transmission pipeline 56, an offshore raw gas cleaning and ball-feeding branch 57, an offshore raw gas ball-feeding cylinder 58 and a reverse transmission raw gas pipeline first section 59. The offshore raw gas reverse transmission external transmission pipeline 56 is connected from the middle of the offshore raw gas reverse transmission manifold 55, and it is preferable to keep the same pipe diameter as the offshore raw gas reverse transmission manifold 55, and is used to collect all the offshore raw gas and then transmit it to the downstream onshore marine gas receiving system; the offshore raw gas reverse transmission manifold 55 passes through the offshore raw gas reverse transmission manifold 55. The raw gas reverse transmission external transmission pipeline 56 is connected to the first section 59 of the reverse raw gas pipeline, forming a normal transmission channel of the offshore raw gas reverse transmission pipeline. The offshore raw gas cleaning and ball-launching branch 57 is connected from the middle part of the offshore raw gas reverse transmission external transmission pipeline 56, connected to the offshore raw gas ball-launching cylinder 58, and forms a ball-launching transmission channel of the offshore raw gas reverse transmission channel, which is used for pipeline cleaning and internal inspection. The offshore raw gas ball-launching cylinder 58 meets the requirements of intelligent cleaning and is equipped with accessories such as pressure transmitter, balance pipe, replacement port, and drainage cleaning port.

[0080] In the system shown, the land-sea raw gas receiving subsystem is composed of the land-sea raw gas pipeline end section 61, the land-sea raw gas branch main pipeline 62, the land-sea raw gas ball collecting cylinder 63 and the land-sea raw gas pigging and ball collecting branch 64. The land-sea raw gas pipeline end section 61 is connected to the land-sea raw gas branch main pipeline 62 to form a normal transportation channel for the land-sea raw gas. The land-sea raw gas receiving subsystem has the function of receiving the raw gas after upstream separation, and the connection method and function of its pipeline and ball collecting cylinder are consistent with other receiving systems.

[0081] In the system shown, the land-sea liquid phase receiving subsystem is composed of the land-sea liquid phase pipeline end section 71, the land-sea liquid phase branch main pipeline 72, the land-sea liquid phase ball collecting cylinder 73 and the land-sea liquid phase pigging and ball collecting branch 74. The land-sea liquid phase pipeline end section 71 is connected to the land-sea liquid phase branch main pipeline 72 to form a normal transportation channel for the land-sea liquid phase medium. The land-sea liquid phase receiving subsystem has the function of receiving the liquid phase fluid after upstream separation, and the connection method and function of its pipeline and ball collecting cylinder are consistent with other receiving systems.

[0082] In the system shown, the land and sea commodity gas receiving subsystem is composed of the land and sea commodity gas pipeline end section 81, the land and sea commodity gas branch main pipeline 82, the land and sea commodity gas ball receiving cylinder 83 and the land and sea commodity gas pigging and ball receiving branch 84. The land and sea commodity gas pipeline end section 81 is connected to the land and sea commodity gas branch main pipeline 82 to form a normal transportation channel for land and sea commodity gas. The land and sea commodity gas receiving subsystem has the function of receiving the land commodity gas collected from the upstream, and the connection method and function of its ball receiving cylinder are consistent with other receiving systems.

[0083] The working principle and working process of the present invention are:

[0084] (1) This system can provide a full range of required media including offshore raw gas, onshore raw gas and onshore commodity gas for offshore natural gas liquefaction processing platforms installed in shallow waters. The offshore raw gas receiving system installed on the offshore platform is used to collect multiple raw gas channels. However, in order to reduce the land use and investment of the slug flow catcher installed on the offshore platform, and taking into account the onshore raw gas processing and onshore construction convenience, a large slug flow catcher is installed onshore, and the offshore raw gas is transported to the land through a separate reverse raw gas pipeline, and the onshore raw gas is collected and processed together.

[0085] (2) The raw gas from various onshore routes is collected on the offshore side and separated into gas and liquid through a large slug flow collector, replacing the two-phase separation at sea; the slug flow is also stored and processed. The separated raw gas and liquid phases are transported to the offshore platform through separate pipelines and directly enter their respective deep processing processes.

[0086] (3) Commercial gases from various onshore sources are collected on the offshore side and transported to offshore platforms through a main pipeline, directly entering the deep processing process.

[0087] (4) The reverse feed gas pipeline, land-sea feed gas pipeline, land-sea liquid phase pipeline and land-sea commercial gas pipeline were set up respectively, which effectively realized the connection between land and sea, and through upstream convergence, greatly reduced the number of pipelines with the same medium in the same direction.

[0088] (5) Each medium pipeline is equipped with normal transportation and cleaning transportation processes.

[0089] The present invention also proposes a pretreatment method for an offshore fixed liquefied natural gas platform, comprising the following specific treatment steps:

[0090] Step 1: Set up an onshore raw gas receiving system, an onshore sea gas receiving system, an onshore slug flow capture system and an onshore commercial gas receiving system on the land side of the coast; set up an offshore receiving system on the offshore natural gas liquefaction processing platform; set up a land-sea pipeline system connecting the onshore system and the offshore receiving system.

[0091] Step 2: The reception of onshore raw gas is divided into pigging reception and non-pigging reception operation. When a certain onshore raw gas intake is pigging reception, the pigging channel of the onshore raw gas pipeline receiving channel is opened; the main raw gas channel is opened for the other onshore raw gas intakes; the collected channels enter the onshore plug flow capture system.

[0092] Step 3: The reception of offshore raw gas is divided into pigging reception and non-pigging reception operation. When a certain offshore raw gas is received through pigging, the pigging channel of the offshore raw gas pipeline receiving channel is opened; the main raw gas channel is opened for the other offshore raw gas inlets; the reverse raw gas pipelines entering the land-sea pipeline system after the convergence are kept open, and after merging with the onshore raw gas through the onshore sea gas receiving system, they are connected to the onshore plug flow capture system.

[0093] Step 4: The reception of onshore commodity gas is divided into pigging reception and non-pigging reception operation. When a certain commodity gas is received through pigging reception, the pigging channel of the onshore commodity gas pipeline receiving channel is opened; the commodity gas main channel is opened for the other commodity gas inlets; the collected commodity gas pipelines enter the onshore and offshore commodity gas pipeline system and are sent to the onshore and offshore commodity gas receiving subsystem of the offshore receiving system;

[0094] Step 5: Open the slug flow catcher, and the onshore raw gas and offshore raw gas are separated and slug flow captured in the slug flow catcher. The separated gas phase enters the onshore and offshore raw gas pipeline through the gas phase outlet pipeline and is transported to the onshore and offshore raw gas receiving subsystem of the offshore receiving system; the separated and captured liquid phase enters the onshore and offshore liquid phase pipeline through the liquid phase outlet pipeline and is transported to the onshore and offshore liquid phase receiving subsystem of the offshore receiving system.

[0095] Step 6: Open the receiving pipelines of the land-sea raw gas pipeline, land-sea liquid pipeline and land-sea commercial gas pipeline of the offshore receiving system to realize the normal reception and cleaning reception of the above pipelines. The received media are sent to the downstream gas phase and liquid phase deep processing systems respectively.

[0096] Among them, when the reverse raw gas pipeline needs to be cleaned, the ball-serving device of the offshore raw gas reverse transmission subsystem is opened, and the ball-receiving device of the onshore sea gas receiving system is opened at the same time to achieve cleaning; when the land and sea commodity gas pipeline needs to be cleaned, the ball-serving device of the onshore commodity gas receiving system is opened, and the ball-receiving device of the land and sea commodity gas receiving subsystem is opened at the same time to achieve cleaning; when the land and sea raw gas pipeline and the land and sea liquid phase pipeline need to be cleaned, the gas phase and liquid phase ball-serving devices of the onshore slug flow capture system are opened, and the ball-receiving devices of the land and sea raw gas receiving subsystem and the land and sea liquid phase receiving subsystem are opened at the same time to achieve cleaning; the slug flow catcher maintains low liquid level control, and the slug flow capture capacity is maintained by adjusting the liquid phase displacement.

[0097] The present invention is not limited to the above-mentioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A pretreatment system for an offshore fixed liquefied natural gas platform, characterized in that: It includes an onshore raw gas receiving system (I), an onshore marine gas receiving system (II), an onshore slug flow capture system (III), an onshore commercial gas receiving system (IV), an onshore and offshore pipeline system (V) and an offshore receiving system (VI); The onshore raw gas receiving system (I) is used to receive the onshore raw gas and pass the received raw gas into the onshore slug flow capture system (III); The offshore receiving system (VI) is used to receive offshore raw gas, upstream land and sea raw gas, upstream land and sea liquid phase and land and sea commodity gas; The onshore sea gas receiving system (II) is connected to the offshore receiving system (VI) through the onshore sea pipeline system (V), and the onshore sea gas receiving system (II) is used to receive the offshore raw gas collected by the offshore receiving system (VI), and to pass the received offshore raw gas into the onshore slug flow capture system (III); The onshore slug flow capture system (III) is used to receive the medium of the onshore raw gas receiving system (I) and the onshore sea gas receiving system (II). The onshore slug flow capture system (III) is connected to the sea receiving system (VI) through the land-sea pipeline system (V). The land-sea raw gas and land-sea liquid phase separated by the onshore slug flow capture system (III) enter the sea receiving system (VI) through the land-sea pipeline system (V). The onshore commodity gas receiving system (IV) is connected to the offshore receiving system (VI) through the land-sea pipeline system (V), and the onshore commodity gas receiving system (IV) is used to receive the onshore commodity gas and pass the received commodity gas into the offshore receiving system (VI) through the land-sea pipeline system (V); The onshore raw gas receiving system (I), the onshore marine gas receiving system (II), the onshore slug flow capture system (III) and the onshore commodity gas receiving system (IV) are arranged on the coast, the offshore receiving system (VI) is arranged on the offshore natural gas liquefaction processing platform, and the onshore systems are connected to the offshore receiving system via the land-sea pipeline system (V); The onshore raw gas receiving system (I) comprises at least one onshore raw gas pipeline receiving channel and an onshore raw gas manifold (5), and the inlets of the onshore raw gas manifold (5) are symmetrically arranged.

2. The pretreatment system for an offshore fixed liquefied natural gas platform according to claim 1, characterized in that: Each onshore raw gas pipeline receiving channel is composed of an onshore raw gas inlet trunk line (1), an onshore raw gas branch main pipeline (2), an onshore raw gas ball collecting cylinder (3) and an onshore raw gas cleaning and ball collecting branch line (4). The onshore raw gas in each onshore raw gas pipeline receiving channel is collected into an onshore raw gas manifold (5), and the onshore raw gas manifold (5) is connected to an onshore slug flow capture system (III) through an onshore raw gas manifold outlet pipeline (6).

3. The pretreatment system for an offshore fixed liquefied natural gas platform according to claim 2, characterized in that: The land-sea pipeline system (V) comprises a reverse feed gas pipeline (91), a land-sea feed gas pipeline (92), a land-sea liquid phase pipeline (93) and a land-sea commodity gas pipeline (94); The onshore marine gas receiving system (II) is connected to the offshore receiving system (VI) via a reverse raw gas pipeline (91), and the reverse raw gas pipeline (91) is used to reverse the offshore raw gas to the onshore marine gas receiving system (II); The onshore slug flow capture system (III) is connected to the offshore receiving system (VI) through an onshore and offshore raw gas pipeline (92) and an onshore and offshore liquid phase pipeline (93), respectively. The onshore and offshore raw gas pipeline (92) is used to transport the separated onshore and offshore raw gas, and the onshore and offshore liquid phase pipeline (93) is used to transport the separated onshore and offshore liquid phase medium. The onshore commodity gas receiving system (IV) is connected to the offshore receiving system (VI) via a land-sea commodity gas pipeline (94), and the land-sea commodity gas pipeline (94) is used to transport the commodity gas collected onshore.

4. The pretreatment system for an offshore fixed liquefied natural gas platform according to claim 3, characterized in that: The onshore sea gas receiving system (II) is composed of a reverse feed gas pipeline end (31), a reverse feed gas branch main pipeline (32), a reverse feed gas ball collecting cylinder (33) and a reverse feed gas cleaning ball collecting branch (34), and forms a complete reverse feed gas receiving channel. The onshore sea gas receiving system sends the received offshore raw gas to the onshore slug flow capture system (III) together with the onshore raw gas through an onshore raw gas manifold outlet pipeline (6).

5. The pretreatment system for an offshore fixed liquefied natural gas platform according to claim 3, characterized in that: The onshore slug flow capture system (III) comprises a slug flow capture device (41), a gas phase outlet pipeline (42), a gas phase pigging and launching branch (43), a gas phase launching barrel (44), a first section of an onshore and offshore raw gas pipeline (45), a liquid phase outlet pipeline (46), a liquid phase pigging and launching branch (47), a liquid phase launching barrel (48) and a first section of an onshore and offshore liquid phase pipeline (49); The onshore raw gas manifold outlet pipeline (6) of the onshore raw gas receiving system (I) is connected to the slug catcher (41); The gas phase outlet pipeline (42) is connected from the top of the slug flow catcher (41) and connected to the first section (45) of the land-sea raw gas pipeline to form a normal transportation channel of the land-sea raw gas pipeline. The gas phase cleaning and ball-launching branch (43) is connected from the middle of the gas phase outlet pipeline (42) and connected to the gas phase ball-launching cylinder (44) to form a ball-launching and transportation channel of the land-sea raw gas channel. The liquid phase outlet pipeline (46) is connected from the bottom of the slug flow catcher (41) and is connected to the first section (49) of the land-sea liquid phase pipeline to form a normal transportation channel of the land-sea liquid phase pipeline. The liquid phase cleaning and ball-launching branch (47) is connected from the middle of the liquid phase outlet pipeline (46) and is connected to the liquid phase ball-launching cylinder (48) to form a ball-launching and transportation channel of the land-sea liquid phase channel.

6. The pretreatment system for an offshore fixed liquefied natural gas platform according to claim 3, characterized in that: The onshore commodity gas receiving system (IV) comprises at least one onshore commodity gas pipeline receiving channel, an onshore commodity gas manifold (15), an onshore commodity gas manifold outlet pipeline (16), an onshore commodity gas cleaning and ball launching branch (17), an onshore commodity gas ball launching cylinder (18) and a first section of an onshore and offshore commodity gas pipeline (19); Each onshore commodity gas pipeline receiving channel is composed of an onshore commodity gas inlet trunk line (11), an onshore commodity gas branch main pipeline (12), an onshore commodity gas ball receiving cylinder (13) and an onshore commodity gas cleaning ball receiving branch line (14). The onshore commodity gas in each onshore commodity gas pipeline receiving channel is collected into an onshore commodity gas manifold (15). The onshore commodity gas manifold (15) is connected to the first section (19) of the onshore and sea commodity gas pipeline through an onshore commodity gas manifold outlet pipeline (16), thereby forming a normal transportation channel of the onshore and sea commodity gas pipeline. The onshore commodity gas cleaning pipe ball launching branch (17) is connected from the middle of the onshore commodity gas manifold outlet pipeline (16) and is connected to the onshore commodity gas ball launching cylinder (18) to form a ball launching and conveying channel of the onshore and offshore commodity gas channel.

7. The pretreatment system for an offshore fixed liquefied natural gas platform according to any one of claims 3 to 6, characterized in that: The offshore receiving system (VI) includes an offshore raw gas receiving system, an offshore raw gas reverse transmission subsystem, a land and sea raw gas receiving subsystem, a land and sea liquid phase receiving subsystem and a land and sea commodity gas receiving subsystem; The offshore raw gas receiving system is connected to the offshore raw gas reverse transmission subsystem, and the offshore raw gas reverse transmission subsystem is connected to the onshore marine gas receiving system (II) via a reverse transmission raw gas pipeline (91); The onshore slug flow capture system (III) is connected to the onshore and offshore raw gas receiving subsystem via an onshore and offshore raw gas pipeline (92); The onshore slug flow capture system (III) is connected to the onshore and offshore liquid phase receiving subsystem via an onshore and offshore liquid phase pipeline (93); The onshore commodity gas receiving system (IV) is connected to the onshore commodity gas receiving subsystem via an onshore commodity gas pipeline (94).

8. The pretreatment system for an offshore fixed liquefied natural gas platform according to claim 7, characterized in that: The offshore raw gas receiving system comprises at least one offshore raw gas pipeline receiving channel and an offshore raw gas reverse transmission manifold (55), each offshore raw gas pipeline receiving channel is composed of an offshore raw gas trunk line (51), an offshore raw gas branch main pipeline (52), an offshore raw gas ball collecting cylinder (53) and an offshore raw gas cleaning and ball collecting branch line (54), the offshore raw gas of each offshore raw gas pipeline receiving channel is collected in the offshore raw gas reverse transmission manifold (55), and the offshore raw gas reverse transmission manifold (55) is connected to the offshore raw gas reverse transmission subsystem through an offshore raw gas reverse transmission external transmission pipeline (56); The offshore raw gas reverse transmission subsystem is composed of an offshore raw gas reverse transmission external transmission pipeline (56), an offshore raw gas cleaning and ball-feeding branch (57), an offshore raw gas ball-feeding cylinder (58) and a first section (59) of the reverse transmission raw gas pipeline. The offshore raw gas reverse transmission manifold (55) is connected to the first section (59) of the reverse transmission raw gas pipeline through the offshore raw gas reverse transmission external transmission pipeline (56) to form a normal transmission channel of the offshore raw gas reverse transmission pipeline. The offshore raw gas cleaning and ball-feeding branch (57) is connected from the middle of the offshore raw gas reverse transmission external transmission pipeline (56), connected to the offshore raw gas ball-feeding cylinder (58), and forms a ball-feeding transmission channel of the offshore raw gas reverse transmission channel. The land-sea raw gas receiving subsystem is composed of the land-sea raw gas pipeline end section (61), the land-sea raw gas branch main pipeline (62), the land-sea raw gas ball receiving cylinder (63) and the land-sea raw gas pigging and ball receiving branch (64). The land-sea raw gas pipeline end section (61) is connected to the land-sea raw gas branch main pipeline (62) to form a normal transportation channel for the land-sea raw gas. The land-sea liquid phase receiving subsystem is composed of a land-sea liquid phase pipeline end section (71), a land-sea liquid phase branch main pipeline (72), a land-sea liquid phase ball receiving cylinder (73) and a land-sea liquid phase pigging ball receiving branch (74). The land-sea liquid phase pipeline end section (71) is connected to the land-sea liquid phase branch main pipeline (72) to form a normal transportation channel for the land-sea liquid phase medium. The land and sea commodity gas receiving subsystem is composed of a land and sea commodity gas pipeline end section (81), a land and sea commodity gas branch main pipeline (82), a land and sea commodity gas ball receiving cylinder (83) and a land and sea commodity gas cleaning ball receiving branch (84). The land and sea commodity gas pipeline end section (81) is connected to the land and sea commodity gas branch main pipeline (82) to form a normal transportation channel for the land and sea commodity gas.

9. A pretreatment method for an offshore fixed liquefied natural gas platform, characterized in that: The specific processing steps include: Step 1: Set up an onshore raw gas receiving system, an onshore sea gas receiving system, an onshore slug flow capture system and an onshore commodity gas receiving system on the onshore side of the coast; set up an offshore receiving system on the offshore natural gas liquefaction processing platform; set up a land-sea pipeline system connecting the onshore system and the offshore receiving system; Step 2: The receiving of onshore raw gas is divided into pigging receiving and non-pigging receiving operation. When a certain onshore raw gas inlet is pigged for receiving, the pigging channel of the onshore raw gas pipeline receiving channel is opened; The other onshore feed gas intakes open the feed gas main channel; the collected feed gas flows enter the onshore slug flow capture system; Step 3: The receiving of offshore raw gas is divided into pigging receiving and non-pigging receiving operation. When a certain offshore raw gas inlet is pigged for receiving, the pigging channel of the offshore raw gas pipeline receiving channel is opened; The remaining offshore raw gas intakes open the main raw gas channel; the converged channels enter the reverse raw gas pipelines of the land-sea pipeline system, keep the reverse raw gas pipelines open, and after merging with the onshore raw gas through the onshore sea gas receiving system, connect to the onshore slug flow capture system; Step 4: The reception of onshore commodity gas is divided into pigging reception and non-pigging reception operation. When a certain commodity gas is received through pigging reception, the pigging channel of the onshore commodity gas pipeline receiving channel is opened; the commodity gas main channel is opened for the other commodity gas inlets; the collected commodity gas pipelines enter the onshore and offshore commodity gas pipeline system and are sent to the onshore and offshore commodity gas receiving subsystem of the offshore receiving system; Step 5: the slug flow catcher is turned on, and the onshore raw gas and the offshore raw gas are separated and slug flow is caught in the slug flow catcher; The separated gas phase enters the land-sea raw gas pipeline through the gas phase outlet pipeline and is transported to the land-sea raw gas receiving subsystem of the offshore receiving system; The separated and captured liquid phase enters the land-sea liquid phase pipeline through the liquid phase outlet pipeline and is transported to the land-sea liquid phase receiving subsystem of the offshore receiving system; Step 6: Open the receiving pipelines of the land-sea raw gas pipeline, land-sea liquid pipeline and land-sea commercial gas pipeline of the offshore receiving system to realize the normal reception and cleaning reception of the above pipelines. The received media are sent to the downstream gas phase and liquid phase deep processing systems respectively.

10. The pretreatment method for an offshore fixed liquefied natural gas platform according to claim 9, characterized in that: When the reverse raw gas pipeline needs to be cleaned, the ball-sending device of the offshore raw gas reverse transmission subsystem is turned on, and the ball-receiving device of the onshore marine gas receiving system is turned on at the same time to achieve the cleaning; When the onshore and offshore commodity gas pipeline needs to be cleaned, the ball-sending device of the onshore commodity gas receiving system is opened, and the ball-receiving device of the onshore and offshore commodity gas receiving subsystem is opened at the same time to realize the cleaning; When the land-sea raw gas pipeline and the land-sea liquid phase pipeline need to be cleaned, the gas phase and liquid phase ball-sending devices in the onshore plug flow capture system are opened, and the ball-receiving devices of the land-sea raw gas receiving subsystem and the land-sea liquid phase receiving subsystem are opened at the same time to realize the cleaning; The slug flow catcher maintains low liquid level control and maintains the slug flow capture capability by adjusting the liquid phase displacement.

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