Differential pressure power generation system for natural gas transmission station

Abstract

The invention discloses a differential pressure power generation system for a natural gas transmission station, which comprises a regulating valve group used for completing depressurization transportation of natural gas in the gas transmission station through control of a DCS (Distributed Control System) and realizing smooth transportation of the natural gas in gathering and transportation pipelines with different pressure grades; the differential pressure power generation system is used for enabling a turbo expander to maintain operation at rated generation power through interaction of the differential pressure power generation module process control system and the DCS control system, generating electric power through pressure energy of natural gas in a gathering and transportation pipeline, and adjusting and controlling the energy relation between network power and differential pressure power generation through a grid-connected system. A power supply mode combining network power and differential pressure power generation is achieved, differential pressure power generation is adopted for supplying power to equipment in a gas transmission station, and the network power is adopted as a beneficial supplement. Pressure energy is effectively utilized to generate clean electric power; natural gas loss can be effectively reduced, zero emission of natural gas is realized, and green low-carbon production is realized; therefore, the invention is necessary and practical.

Description

Technical Field

[0001] The present invention belongs to the technical field of natural gas transmission and power generation, and in particular relates to a pressure difference power generation system for a natural gas transmission station. Background Art

[0002] Natural gas is a clean, high-quality energy source and chemical raw material, but most of the gas fields that produce natural gas are located in remote areas, far away from major gas-consuming cities. Therefore, continuous, closed, high-pressure long-distance pipelines are often used to transport natural gas from gas fields to gas-consuming cities in my country. However, due to limitations in pipeline materials, construction costs and other factors, the operating pressure of my country's high-pressure long-distance pipelines is mostly lower than 12MPa, but the wellhead pressure of natural gas extracted from ultra-deep gas fields in my country may be as high as 70MPa. Therefore, the gathering and transportation pipelines from the natural gas wellhead to the long-distance pipeline need to be pressure-regulated. In the past, throttle valves were often used to reduce the pressure during the pressure regulation process, and the pressure energy between the wellhead and the long-distance pipeline was not fully utilized, wasting a lot of energy.

[0003] In recent years, in order to make full use of the pressure energy in the natural gas transportation process, expansion power generation technology has been gradually developed and applied. The existing expansion power generation technologies mainly include the following three types: turbine expander technology, dual-rotor expander technology, and screw expander technology. Among them, the efficiency of turbine expander technology is generally greater than 80% when generating electricity, which is significantly higher than the other two technologies. However, there are still some disadvantages in turbine expander technology, such as the need to establish lubricating oil and cooling systems, and the need to replace wear parts more frequently. In response to the shortcomings of the turbine expander, Beijing Xingxuan Technology Co., Ltd. proposed a star-type starter motor technology that does not require a lubricating oil system and a cooling system. However, the application results show that due to the lack of a lubricating oil system, the wear of the star-type starter motor is more serious, and the wear parts need to be replaced every year, and maintenance is frequent. Therefore, the use of turbine expander technology to utilize the pressure energy of the gathering and transportation pipeline is still the preferred option.

[0004] At present, there are other systems and equipment in the energy field that use turbine expander technology for pressure difference power generation, such as a pressure difference power generation system and operation method, but it is only a connection diagram composed of several branch structures and has no practical application value; there is also a pressure difference power generation device and system for natural gas pipeline pressure energy recovery, but the disadvantage is that the temperature of the natural gas after power generation is relatively low, and additional heating equipment is required to heat the natural gas; another composite power generation system using pressure difference power generation can use the waste heat of the turbine cooling air and flue gas of the gas turbine power generation equipment to improve the efficiency of the pressure difference power generation equipment, and also use the cold energy of liquefied natural gas to improve the efficiency of the supercritical fluid power generation equipment, but the supercritical fluid power generation equipment and LNG production equipment used in it are not available in remote gas transmission stations in my country. It is not applicable and will face the problems of excessive investment costs and uncompetitive products; another kind of expander pressure difference power generation system and its control method are mainly aimed at the special situation of emergency shutdown of the expander; there is also a natural gas pressure regulating power generation device, which is just a simple parallel structure and does not consider the maintenance of the device and the need to vent natural gas during maintenance; the last natural gas expansion pressure difference power generation system can control 4 power generation modes according to the principle of highest economic benefit to produce electricity, compressed natural gas or liquefied natural gas to achieve maximum utilization of natural gas pressure energy. Although the entire power generation system of this scheme is relatively complete, it does not give priority to the problem of ensuring gas supply of gathering and transmission pipelines, nor does it consider the problem of gas emissions when the power generation system is shut down. It is also not suitable for remote gas transmission stations in my country. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a pressure difference power generation system for a natural gas transmission station in view of the deficiencies in the above-mentioned prior art, which is used to solve the technical problem of how to give priority to ensuring gas supply through gathering and transmission pipelines from the macro perspective of users (referring to gas transmission stations in remote areas), and to provide a turbine expander power generation system which is green and environmentally friendly, has stable and reliable equipment, relatively simple process, and is easy to maintain and upgrade.

[0006] The present invention adopts the following technical solutions:

[0007] A pressure difference power generation system for a natural gas transmission station, comprising:

[0008] The regulating valve group is used to complete the pressure reduction and transmission of natural gas in the gas transmission station through the control of the DCS control system, and realize the smooth transportation of natural gas in the gathering and transmission pipelines with different pressure levels;

[0009] The pressure difference power generation system is used to maintain the turbine expander at the rated power generation power through the interaction between the pressure difference power generation module process control system and the DCS control system, and to produce electricity by using the pressure energy of the natural gas in the gathering and transmission pipeline. The energy relationship between the grid power and the pressure difference power generation is adjusted and controlled by the grid connection system to realize the power supply mode of the combination of grid power and pressure difference power generation. The pressure difference power generation is used to power the equipment in the gas transmission station, and the grid power is used as a beneficial supplement.

[0010] Specifically, the regulating valve group includes a main line, one end of which is connected to the upstream valve chamber, and the other end is respectively connected to the pressure difference power generation system, the downstream long-distance pipeline and the vent air recovery device. The main line is provided with a valve group and a vent air recovery system, and the valve group and the vent air recovery system are respectively connected to the DCS control system.

[0011] Furthermore, the main pipeline includes an air intake manifold, one end of which is connected to the upstream valve chamber, and the other end is connected to the downstream long-distance pipeline via the first branch pipe, the fifth branch pipe and the air outlet manifold in sequence.

[0012] Furthermore, a first electric ball valve is arranged between the air intake manifold and the first branch pipe, a second electric ball valve and a third electric ball valve are arranged in sequence between the first branch pipe and the fifth branch pipe, an eighth electric ball valve, a second electric regulating valve and a ninth electric ball valve are arranged in sequence between the fifth branch pipe and the air outlet manifold, and a filtering device is arranged between the air outlet manifold and the downstream long-distance pipeline.

[0013] Furthermore, the main line is also connected to a bypass pipeline, which includes a second branch pipe, a third branch pipe, a fourth branch pipe, a reserved air outlet branch pipe, and a reserved air inlet branch pipe; one end of the second branch pipe is connected to the upstream valve chamber, and the other end is divided into two paths, one path is connected to the pressure difference power generation system through the reserved air outlet branch pipe, and the other path is respectively connected to the third branch pipe and the fourth branch pipe, the other end of the third branch pipe is connected to the stop valve, and the other end of the fourth branch pipe is respectively connected to the reserved air inlet branch pipe and the air outlet manifold; the second branch pipe is sequentially provided with a fourth electric ball valve and a fifth electric ball valve, one end of the reserved air outlet branch pipe is connected to the pipeline between the fourth electric ball valve and the fifth electric ball valve, and the other end is connected to the pressure difference power generation system through the second ball valve and the reserved port in front of the regulating valve group; the fourth branch pipe is sequentially provided with a sixth electric ball valve, a first electric regulating valve and a seventh electric ball valve; the other end of the reserved air inlet branch pipe is connected to the pressure difference power generation system through the third ball valve and the reserved port after the regulating valve group.

[0014] Furthermore, the vent air recovery device is connected to the first branch pipe via the vent air recovery main pipe, and a first ball valve is provided on the vent air recovery main pipe.

[0015] Specifically, the pressure difference power generation system includes a pressure difference generator skid, one end of the pressure difference generator skid is connected to the reserved port in front of the regulating valve group through the raw gas inlet branch pipe and the dry gas inlet manifold, and the other end of the pressure difference generator skid is connected to the reserved port behind the regulating valve group through the raw gas outlet branch pipe and the dry gas outlet manifold; the pressure difference generator skid is also connected to the sealing system, the venting air recovery system and the grid connection system respectively, the sealing system is used to connect the regulating valve group, the venting air recovery system is used to release flammable and explosive natural gas, and is connected to the venting air recovery device of the regulating valve group; the pressure difference power generation module process control system includes a first pressure observation and alarm, a second pressure observation and alarm, a second pressure observation and alarm, a first temperature observation and alarm and a second temperature observation and alarm; the first pressure observation and alarm, the second pressure observation and alarm and the first temperature observation and alarm are arranged on the raw gas inlet branch pipe, and the second pressure observation and alarm and the second temperature observation and alarm are arranged on the raw gas outlet branch pipe.

[0016] Furthermore, a first cylinder ball valve and a pneumatic regulating valve are provided on the raw gas inlet branch pipe, and a check valve and a second cylinder ball valve are provided on the raw gas outlet branch pipe.

[0017] Furthermore, the sealing system includes a dry gas sealing subsystem and a nitrogen sealing subsystem; the dry gas sealing subsystem includes a dry gas sealing intake branch pipe, one end of which is connected to the pressure difference generator skid, and the other end is connected to the raw gas intake branch pipe via a fourth ball valve; the nitrogen sealing subsystem includes a nitrogen generator skid, and the nitrogen generator skid is divided into four routes through the nitrogen intake manifold, the first route is connected to a cylinder ball valve via a first nitrogen branch pipe, the second route is connected to a pneumatic regulating valve via a second nitrogen branch pipe, the third route is connected to the pressure difference generator skid via a third nitrogen branch pipe, and the fourth route is connected to the second cylinder ball valve via a fourth nitrogen branch pipe.

[0018] Furthermore, the vent air recovery system includes a leakage air recovery branch pipe, one end of the leakage air recovery branch pipe is connected to the pressure difference generator skid, and the other end is connected to the vent air recovery device through the vent air recovery branch pipe and the reserved port D of the vent air main pipe. The vent air recovery branch pipe is also connected to the raw gas outlet branch pipe through the throttling stop vent valve and the fifth ball valve.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects:

[0020] A pressure differential power generation system for a natural gas transmission station can effectively utilize pressure energy to generate clean electricity while ensuring continuous and safe transportation of natural gas through the collaboration of a regulating valve group and a pressure differential power generation system, as well as the interaction between a DCS control system and a pressure differential power generation module process control system.

[0021] The differential pressure generator skid and nitrogen generator skid are skid-mounted and modular in configuration, and no additional heater is required. The process is relatively simple and the equipment has good stability, which is convenient for later maintenance and overhaul. In addition, three connection ports are reserved on the pressure regulating valve group to facilitate later upgrades and renovations, and it has stronger expandability.

[0022] By connecting the leakage gas and vented air of the pressure difference power generation system to the vented air recovery system of the regulating valve group, the natural gas loss can be effectively reduced, zero emission of natural gas can be achieved, and green and low-carbon production can be realized.

[0023] The pressure difference generator skid adopts two-stage series dry gas seal and nitrogen seal. The cylinder ball valve and pneumatic regulating valve are connected to nitrogen, which helps to improve the sealing and explosion-proof capabilities of the pressure difference generator skid and valve group.

[0024] The pressure difference power generation system is suitable for flexibly adjusting the natural gas flow entering the pressure difference generator skid. When the gas volume, pressure, temperature and other operating parameters of the gathering and transportation pipeline are relatively stable or fluctuate greatly, it can meet the requirements of safe and stable operation of the pressure difference generator. It is especially suitable for power generation for self-use at gas transmission stations on gathering and transportation trunk lines in remote areas.

[0025] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the structure of the pressure difference power generation system of the natural gas transmission station of the present invention;

[0027] Figure 2 A schematic diagram of a regulating valve group in a pressure difference power generation system of the present invention;

[0028] Figure 3 A schematic diagram of a pressure difference power generation system in the pressure difference power generation system of the present invention;

[0029] Figure 4 It is a structural schematic diagram of the grid-connected system in the pressure difference power generation system of the present invention.

[0030] Among them: 1. Upstream valve chamber; 2. Downstream long-distance pipeline; 3. Vent air recovery device; 4. First temporary blocking pipeline; 5. Second temporary blocking pipeline; 6. Inlet manifold; 7. First branch pipe; 8. Second branch pipe; 9. Reserved outlet branch pipe; 10. Third branch pipe; 11. Fourth branch pipe; 12. Fifth branch pipe; 13. Reserved inlet branch pipe; 14. Outlet manifold; 15. Dry gas inlet manifold; 16. Raw gas inlet branch pipe; 17. Dry gas seal Inlet branch pipe; 18. Raw gas outlet branch pipe 18; 19. Dry gas outlet manifold; 20. Leakage gas recovery branch pipe; 21. Vent air recovery branch pipe; 22. Vent air recovery main pipe; 23. Nitrogen inlet manifold; 24. First nitrogen branch pipe; 25. Second nitrogen branch pipe; 26. Third nitrogen branch pipe; 27. Fourth nitrogen branch pipe; 28. Pressure difference generator skid; 29. ​​Nitrogen generator skid; W1. Filter device; P1. First pressure observation and alarm device; P 2. Second pressure observation and alarm; P3. Third pressure observation and alarm; T1. First temperature observation and alarm; T2. Second temperature observation and alarm; M1. First electric ball valve; M2. Second electric ball valve; M3. Third electric ball valve; M4. Fourth electric ball valve; M5. Fifth electric ball valve; M6. Sixth electric ball valve; M7. First electric regulating valve; M8. Seventh electric ball valve; M9. Eighth electric ball valve; M10. Second Electric regulating valve; M11. The ninth electric ball valve; Q1. The first ball valve; Q2. The second ball valve; Q3. The third ball valve; Q4. The fourth ball valve; Q5. The fifth ball valve; J1. The stop valve; J2. The check valve; J3. The throttling stop and vent valve; N1. The first cylinder ball valve; N2. The pneumatic regulating valve; N3. The second cylinder ball valve; D1. The reserved port in front of the regulating valve group; D2. The reserved port for the air vent main; D3. The reserved port at the back of the regulating valve group. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "one side", "one end", "one side" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0033] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0035] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an" and "the" are intended to include plural forms unless the context clearly indicates otherwise.

[0036] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0037] Various structural schematic diagrams of the embodiments disclosed in the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0038] See also Figure 1 The present invention discloses a pressure difference power generation system for a natural gas transmission station, comprising a regulating valve group and a pressure difference power generation system.

[0039] The regulating valve group is used to: complete the pressure reduction and transmission of natural gas in the gas transmission station through the control of the DCS control system, so as to achieve the smooth transportation of natural gas in the gathering and transmission pipelines with different pressure levels, and provide guarantee for the continuous and stable supply of natural gas from the gathering and transmission pipelines of the gas transmission station to the long-distance transmission pipeline.

[0040] The pressure difference power generation system is used to: provide a stable and reliable process. Through the interaction between the pressure difference power generation module process control system and the DCS control system, the turbine expander is maintained at the rated power generation power as much as possible, so as to fully utilize the pressure energy of the natural gas in the gathering and transmission pipeline to produce electricity.

[0041] See also Figure 2 The regulating valve group includes the main line, bypass line, valve group, vent air recovery system and DCS control system.

[0042] The main pipeline refers to the main channel for the gas from the upstream valve chamber to enter the downstream long-distance pipeline after passing through the regulating valve group, including the inlet manifold 6, the first branch pipe 7, the fifth branch pipe 12 and the outlet manifold 14.

[0043] The bypass pipeline refers to other branches in the regulating valve group that are not the main line, including the second branch pipe 8, the third branch pipe 10, the fourth branch pipe 11, the reserved outlet branch pipe 9, the reserved inlet branch pipe 13, and the first temporarily blocked pipeline 4 and the second temporarily blocked pipeline 5.

[0044] The valve group includes a first electric ball valve M1, a second electric ball valve M2, a third electric ball valve M3, a fourth electric ball valve M4, a fifth electric ball valve M5, a sixth electric ball valve M6, a seventh electric ball valve M8, an eighth electric ball valve M9, a ninth electric ball valve M11, a first electric regulating valve M7, a second electric regulating valve M10, a second ball valve Q2 and a third ball valve Q3.

[0045] Among them, the first electric ball valve M1, the second electric ball valve M2, the third electric ball valve M3, the fourth electric ball valve M4, the fifth electric ball valve M5, the sixth electric ball valve M6, the seventh electric ball valve M8, the eighth electric ball valve M9 and the ninth electric ball valve M11 are used to adjust the flow, the first electric regulating valve M7 and the second electric regulating valve M10 are used to adjust the pressure. The second ball valve Q2 and the third ball valve Q3 are used to adjust the flow.

[0046] The vent air recovery system includes a first ball valve Q1 , a vent air recovery main pipe 22 and a vent air recovery device 3 .

[0047] The DCS control system mainly manages the equipment and valve groups in the gas transmission station, and performs decentralized control on the equipment and valve groups in the gas transmission station. The DCS control system can realize alarm and control functions based on the monitored pressure, flow, temperature and other data. Intuitively, the DCS control system can control the valve group.

[0048] In order to further explain the regulating valve group, the connection of the main line, bypass line, valve group and bleed air recovery system is introduced below.

[0049] The air intake manifold 6 is used to receive and transport the natural gas from the upstream valve chamber 1; the air intake manifold 6 is provided with a first electric ball valve M1; the first electric ball valve M1 is used to adjust the total flow of natural gas entering the regulating valve group;

[0050] The air inlet ends of the first branch pipe 7 and the second branch pipe 8 are respectively connected to the air inlet manifold 6;

[0051] The first branch pipe 7 is provided with a second electric ball valve M2 and a third electric ball valve M3; the second electric ball valve M2 is used to adjust the natural gas flow entering the first branch pipe 7; the third electric ball valve M3 is used to adjust the natural gas flow entering the intermediate manifold from the first branch pipe 7.

[0052] The exhaust air recovery main pipe 22 is connected to the first branch pipe 7, and the connection point is located between the second electric ball valve M2 and the third electric ball valve M3; after the exhaust air recovery main pipe 22 is connected to the first branch pipe 7, it then leads to the exhaust air recovery device 3.

[0053] A first ball valve Q1 is provided at the air inlet end of the vent air recovery main pipe 22 for regulating the flow of natural gas entering the vent air recovery main pipe 22 from the first branch pipe 7 .

[0054] The air inlet end of the second branch pipe 8 is connected to the air inlet manifold 6, and the air outlet end of the second branch pipe 8 is connected to the intermediate manifold.

[0055] The second branch pipe 8 is provided with a fourth electric ball valve M4 and a fifth electric ball valve M5 in sequence from the air inlet end to the air outlet end; the fourth electric ball valve M4 is used to adjust the natural gas flow entering the second branch pipe 8, and the fifth electric ball valve M5 is used to adjust the flow from the second branch pipe 8 to the intermediate manifold.

[0056] The first temporary plugging pipeline 4 is connected to the second branch pipe 8, and the connection point is located between the air inlet end of the second branch pipe 8 and the fourth electric ball valve M4; the second temporary plugging pipeline 5 is connected to the second branch pipe 8, and the connection point is located between the fifth electric ball valve M5 and the air outlet end of the second branch pipe 8.

[0057] The first temporarily blocked pipeline 4 and the second temporarily blocked pipeline 5 are pipelines temporarily blocked by baffles and are reserved pipeline interfaces for subsequent upgrading and reconstruction of the regulating valve group.

[0058] The reserved outlet branch pipe 9 is connected to the second branch pipe 8 , and the connection point is located between the fourth electric ball valve M4 and the fifth electric ball valve M5 .

[0059] After the reserved gas outlet branch pipe 9 is connected to the second branch pipe 8, a second ball valve Q2 is provided, and then leads to the reserved port D1 in front of the regulating valve group; the second ball valve Q2 is used to control the natural gas flow from the second branch pipe 8 into the pressure difference power generation system.

[0060] After the first branch pipe 7 is connected to the air outlet end of the second branch pipe 8, there is an intermediate manifold leading to the fourth branch pipe 11 and the fifth branch pipe 12; the third branch pipe 10 is connected to the intermediate manifold, and the connection point is located between the air outlet end of the first branch pipe 7 and the air inlet end of the fourth branch pipe 11; a stop valve J1 is provided at the end of the third branch pipe 10 for temporary blocking; the third branch pipe 10 is also a reserved pipeline interface for subsequent upgrading and transformation of the regulating valve group.

[0061] The air inlet ends of the fourth branch pipe 11 and the fifth branch pipe 12 are respectively connected to the intermediate manifold.

[0062] The fourth branch pipe 11 is provided with a sixth electric ball valve M6 , a first electric regulating valve M7 , and a seventh electric ball valve M8 in sequence from the air inlet end to the air outlet end.

[0063] The sixth electric ball valve M6 is used to adjust the natural gas flow entering the fourth branch pipe 11; the first electric regulating valve M7 is used to adjust the pressure of the natural gas on the fourth branch pipe 11, mainly for reducing the pressure; the seventh electric ball valve M8 is used to adjust the natural gas flow from the fourth branch pipe 11 into the gas outlet manifold 14.

[0064] The reserved air intake branch pipe 13 is connected to the fourth branch pipe 11, and the connection port is located between the first electric regulating valve M7 and the seventh electric ball valve M8; the other end of the reserved air intake branch pipe 13 is connected to the reserved port D3 behind the regulating valve group, and a third ball valve Q3 is provided on the reserved air intake branch pipe 13; the third ball valve Q3 is used to adjust the natural gas flow rate entering the fourth branch pipe 11 in the regulating valve group from the dry gas outlet manifold 19 in the pressure difference power generation system.

[0065] The fifth branch pipe 12 is provided with an eighth electric ball valve M9, a second electric regulating valve M10, and a ninth electric ball valve M11 in sequence from the air inlet end to the air outlet end; the eighth electric ball valve M9 is used to adjust the flow of natural gas entering the fifth branch pipe 12; the second electric regulating valve M10 is used to adjust the pressure of the natural gas on the fifth branch pipe 12, mainly for reducing the pressure; the ninth electric ball valve M11 is used to adjust the flow of natural gas from the fifth branch pipe 12 into the air outlet manifold 14.

[0066] The gas outlet ends of the fourth branch pipe 11 and the fifth branch pipe 12 are connected to the gas outlet manifold 14 ; the gas outlet manifold 14 leads to the downstream long-distance pipeline; the gas outlet manifold 14 is provided with a filter device W1 to remove impurities carried by the natural gas when it reaches the gas outlet manifold 14 .

[0067] See also Figure 3 The pressure difference power generation system includes a pressure difference generator skid 28, a sealing system, an air recovery system, a grid connection system, a pressure difference power generation module process control system and connecting pipelines.

[0068] The differential pressure generator skid 28 is a complete set of modular differential pressure power generation skid-mounted equipment, including a turbine expander, an asynchronous generator, a lubricating oil system, a cooling system, a control system, and ancillary equipment such as thermal resistors and pressure transmitters, as well as inter-skid wiring.

[0069] The turbine expander of the pressure difference generator skid 28 is designed based on the thermal calculation data of natural gas in the gas transmission station, according to the minimum flow and minimum pressure difference before and after the operation of the regulating valve group; the asynchronous generator needs to be combined with the application of the gas transmission station environment and the requirements of low maintenance, and adopts the generator set with wide application in the current market, mature technology and simple structure, with high reliability and not restricted by the place of use.

[0070] The lubricating oil system adopts three sets of oil pumps to supply oil, namely main oil pump MOP + auxiliary oil pump AOP + emergency oil pump EOP, and no high-level oil tank is set.

[0071] The cooling system adopts air cooling; the control system is a complete turbine expansion generator set control system, including system design, hardware manufacturing, cabinet integration, system configuration and testing, etc.

[0072] The function of the control system is to isolate the turbine expander when an accident occurs (such as overspeed, lack of lubricating oil, abnormal pressure increase, etc.), thereby ensuring the safety of the skid-mounted unit.

[0073] The sealing system includes a dry gas sealing subsystem and a nitrogen sealing subsystem.

[0074] The sealing system has five connection ports, A, B, C, D, and E, distributed in sequence at the shaft end of the pressure difference generator skid 28 from the flow medium side to the outside atmosphere side; among them, A, C, and E are air inlets, and B and D are air outlets.

[0075] The dry gas sealing subsystem mainly includes the dry gas sealing intake branch pipe 17 , the fourth ball valve Q4 and the shaft end seal in the pressure difference generator skid 28 .

[0076] The dry gas sealing subsystem adopts a two-stage tandem shaft end seal. The first-stage sealing gas inlet is port A, which flows to the flow medium side; the second-stage sealing gas inlet is port C; both the first-stage sealing gas and the second-stage sealing gas are natural gas dry gas, and the dry gas sealing gas comes from the dry gas sealing inlet branch pipe 17 upstream of the expander.

[0077] The pressure of the dry gas sealing subsystem is 0.2MPa higher than the pressure of the flowing medium, thereby preventing the leakage of natural gas working fluid; due to material and process limitations, a small amount of leakage gas passes through the primary seal and enters the outlet B of the shaft end seal together with the secondary sealing gas.

[0078] The nitrogen sealing subsystem includes a nitrogen generator skid 29 and a nitrogen inlet manifold 23, a first nitrogen branch pipe 24, a second nitrogen branch pipe 25, a third nitrogen branch pipe 26 and a fourth nitrogen branch pipe 27, which respectively provide nitrogen to the first cylinder ball valve N1, the pneumatic regulating valve N2, the shaft end seal of the pressure difference generator skid 28 and the second cylinder ball valve N3 to meet the isolation, explosion-proof and sealing requirements.

[0079] The nitrogen generated by the nitrogen sealing subsystem is used as the isolation gas, and the air inlet at the shaft end of the pressure difference generator skid 28 is port E.

[0080] Due to material and process limitations, a small amount of leakage gas passes through the secondary seal and enters the outlet D of the shaft end seal together with the nitrogen.

[0081] The air outlets B and D of the shaft end seal are connected to the leakage air recovery branch pipe 20 of the exhaust air recovery system.

[0082] The vent air recovery system includes a leakage gas recovery branch pipe 20, a fifth ball valve Q5, a throttling stop vent valve J3, and a vent air recovery branch pipe 21.

[0083] The functions of the venting air recovery branch pipe 21 are as follows:

[0084] It is used to release the flammable and explosive natural gas in the system when the pressure difference power generation system is shut down or overhauled urgently, so as to ensure the safety of the pressure difference power generation system; the released natural gas enters the vent air recovery branch pipe 21 after being depressurized, and leads to the vent air recovery system of the regulating valve group, so as to realize the recycling of vent air, which is green and environmentally friendly.

[0085] Function of the leakage gas recovery branch pipe 20: Although a strict sealing system has been adopted, due to the limitation of the technological level, a small amount of natural gas working fluid still leaks from the pressure difference generator skid 28. The leakage gas recovery branch pipe 20 is used to guide the leaked trace gas into the venting air recovery branch pipe 21, and then to the venting air recovery system of the regulating valve group, so as to achieve zero emission of natural gas.

[0086] See also Figure 4 The grid-connected system refers to the electricity generated by the differential pressure generator 28, which is transmitted to the high-voltage distribution room of the gas transmission station through high-voltage cables. Through the grid-connected system, the energy relationship between the grid power and the differential pressure power generation is automatically adjusted and controlled to realize the power supply mode of the grid power and the differential pressure power generation. The differential pressure power generation is used to supply power in the gas transmission station first, and the grid power is used as a beneficial supplement.

[0087] The grid-connected system should have the functions of self-regulation complementary to the grid power, anti-islanding protection, and emergency fault power-off.

[0088] Grid-electricity complementary self-regulation function: the phase sequence of the produced electric energy should be the same as the phase sequence of the grid power return bus; the effective value of the voltage of the produced electric energy should be close to or equal to the effective value of the voltage of the grid power, and the waveform should be the same; the frequency of the produced electric energy should be basically equal to the frequency of the power system; the voltage phase of the produced electric energy should be equal to the voltage phase of the power supply of the power system; according to the amount of produced electric energy, self-regulation with grid power can be achieved to supply power to the gas transmission station.

[0089] Grid-connected anti-islanding protection function: When overvoltage, low voltage, overfrequency, underfrequency, frequency mutation, reverse power, external tripping, system power failure, frequency mutation blocking low frequency, automatic closing with pressure, simulated tripping, etc. occur, the grid-connected system can automatically control, thereby realizing the separation and protection of grid power and pressure difference power generation.

[0090] Emergency fault power-off function: In order to ensure the safety and reliability of power supply, and to make the pressure difference generator set run reliably and stably after being connected to the grid, the unit should have a safety protection device. Once the unit has an overload fault, overspeed fault, pressure fault, temperature fault, power direction fault, emergency stop device and other faults, it should automatically trip, disconnect from the grid, and automatically shut down.

[0091] The high-voltage cables of the grid-connected system are laid directly underground, with power pipes for protection throughout the entire process, covered with sand and protected by protective plates. The connection between the cable and the pressure difference generator skid 28 uses an explosion-proof cable sealing head with a double-layer sealing structure.

[0092] The pressure difference power generation module process control system includes a pressure difference generator skid 28 control cabinet, a nitrogen generator skid control cabinet, a first pressure observation and alarm P1, a second pressure observation and alarm P2, a second pressure observation and alarm P3, a first temperature observation and alarm T1, and a second temperature observation and alarm T2.

[0093] The pressure difference power generation module process control system can be operated locally and can be remotely controlled; it can collect signals from the pressure difference generator skid 28, the nitrogen generator skid, the pressure observation and alarm, and the temperature observation and alarm, and transmit them to the control console in the central control room of the gas transmission station for status judgment; it can adjust the power generation of the generator and the nitrogen output of the nitrogen generator according to work needs; it can interact with the DCS control system for data coordination and management.

[0094] In order to further explain the pressure difference power generation system, the connection of the pressure difference generator skid 28, the sealing system, the venting air recovery system, and the grid connection system are introduced below.

[0095] See also Figure 3 The pressure difference power generation system refers to the pipelines, equipment, valve groups and instruments between the reserved port D1 in front of the regulating valve group and the reserved port D3 behind the regulating valve group.

[0096] The pressure difference power generation system is connected to the regulating valve group through the dry gas intake manifold 15, and the connection is located at the reserved port D1 in front of the regulating valve group; a first cylinder ball valve N1 is provided on the dry gas intake manifold 15 to regulate the natural gas flow entering the pressure difference power generation system.

[0097] The inlet end of the raw gas inlet branch pipe 16 and the inlet end of the dry gas sealed inlet branch pipe 17 are connected to the dry gas outlet manifold 19 .

[0098] On the raw gas inlet branch pipe 16, a first pressure observation and alarm device P1, a pneumatic regulating valve N2, a second pressure observation and alarm device P2, and a first temperature observation and alarm device T1 are sequentially provided from the inlet end to the outlet end; the outlet end of the raw gas inlet branch pipe 16 is connected to the expander inlet of the pressure difference generator skid 28.

[0099] The first pressure observation and alarm device P1 is used to observe and monitor the pressure before the pneumatic regulating valve N2 of the raw gas inlet branch pipe 16, and timely transmit the monitored pressure data to the pressure difference power generation module process control system, as well as the emergency alarm.

[0100] The second pressure observation and alarm device P2 is used to observe and monitor the pressure after the pneumatic regulating valve N2 of the raw gas inlet branch pipe 16 and before the raw gas inlet port of the pressure difference generator skid 28, and also has the functions of transmission and alarm.

[0101] The first temperature observation and alarm device T1 is used to observe and monitor the temperature after the pneumatic regulating valve N2 of the raw gas inlet branch pipe 16 and before the raw gas inlet port of the pressure difference generator skid 28, and has the functions of transmission and alarm.

[0102] The pneumatic regulating valve N2 is used to adjust the pressure of the raw gas entering the pressure difference generator skid 28 so that the raw gas entering the pressure difference generator skid 28 is lower than the pressure of the sealing dry gas by about 0.2 MPa.

[0103] Optionally, 0.2 MPa represents the pressure difference between the raw gas and the sealing gas of the pressure difference generator skid 28, and its value can be changed according to actual conditions.

[0104] The outlet end of the dry gas seal inlet branch pipe 17 is connected to the axial end seal inlet ports A and C of the pressure difference generator skid 28; a fourth ball valve Q4 is provided on the dry gas seal inlet branch pipe 17; the fourth ball valve Q4 is used to adjust the natural gas flow entering the dry gas seal subsystem.

[0105] The air inlet end of the raw gas outlet branch pipe 18 is connected to the raw gas outlet of the pressure difference generator skid 28; a second cylinder ball valve N3 is provided at the end of the raw gas outlet branch pipe 18; the second cylinder ball valve N3 is used to adjust the natural gas flow entering the dry gas outlet manifold 19.

[0106] The raw gas outlet branch pipe 18 is provided with a third pressure observation and alarm device P3, a second temperature observation and alarm device T2, and a check valve J2 from the air inlet end to the air outlet end in sequence; the third pressure observation and alarm device P3 is used to observe and monitor the pressure of the raw gas outlet branch pipe 18, and has a transmission and alarm function; the second temperature observation and alarm device T2 is used to observe and monitor the pressure of the raw gas outlet branch pipe 18, and also has a transmission and alarm function; the check valve J2 is used to prevent the backflow of natural gas.

[0107] The air inlet end of the dry gas outlet manifold 19 is connected to the air outlet end of the second cylinder ball valve N3; the air outlet end of the dry gas outlet manifold 19 is connected to the reserved port D3 behind the regulating valve group, so that the pressure difference power generation system and the regulating valve group form a closed loop to complete the transportation of natural gas and the utilization of pressure difference.

[0108] The vent air recovery branch pipe 21 is connected to the raw gas outlet branch pipe 18, and the connection port is located between the check valve J2 and the second cylinder ball valve N3; the outlet end of the vent air recovery branch pipe 21 is connected to the vent air recovery main pipe 22, and the connection port is located at the reserved port D2 of the vent air main pipe.

[0109] A fourth ball valve Q4 and a throttling stop vent valve J3 are provided at the air inlet end of the vent air recovery branch pipe 21; the main function of the throttling stop vent valve J3 is to adjust the valve opening according to the instructions of the pressure difference power generation module process control system to determine whether to allow the high-pressure gas of the raw gas outlet branch pipe 18 to enter the low-pressure vent air recovery branch pipe 21.

[0110] The air inlet end of the leakage gas recovery branch pipe 20 is connected to the axial end air outlets B and D of the pressure difference generator skid 28 , and the air outlet end of the leakage gas recovery branch pipe 20 is connected to the vent air recovery branch pipe 21 .

[0111] The inlet end of the nitrogen inlet manifold 23 is connected to the outlet of the nitrogen generator skid.

[0112] The air inlet ends of the first nitrogen branch pipe 24, the second nitrogen branch pipe 25, the third nitrogen branch pipe 26 and the fourth nitrogen branch pipe 27 are connected to the nitrogen air inlet manifold 23; the air outlet end of the first nitrogen branch pipe 24 is connected to the air inlet interface of the first cylinder ball valve N1; the air outlet end of the second nitrogen branch pipe 25 is connected to the air inlet interface of the pneumatic regulating valve N2; the air outlet end of the third nitrogen branch pipe 26 is connected to the isolation air inlet of the pressure difference generator skid 28; the air outlet end of the fourth nitrogen branch pipe 27 is connected to the air inlet interface of the second cylinder ball valve N3.

[0113] The electricity generated by the pressure difference generator skid 28 is pressurized by the boosting equipment, and then connected to the high-voltage distribution room of the gas transmission station through the underground high-voltage cable. Through the control of the grid-connected system, a combined power supply mode of grid power and pressure difference power generation is realized to meet the power demand of the gas transmission station itself.

[0114] The pressure difference power generation system for a natural gas transmission station of the present invention has three operating modes: normal operating condition, maintenance shutdown condition and emergency shutdown condition.

[0115] 1. Normal operating conditions:

[0116] When the pressure difference power generation system of the natural gas transmission station operates normally, under the coordinated action of the DCS control system and the pressure difference power generation module process control system, the regulating valve group and the pressure difference power generation system are put into use.

[0117] 1. The natural gas delivered from the upstream valve chamber enters the intake manifold, the electric first ball valve Q1 is fully opened, and the natural gas reaches the intake ends of the first branch pipe and the second branch pipe.

[0118] 2. When the natural gas reaches the air inlet end of the first branch pipe and the second branch pipe, the natural gas is divided into two parts by the first branch pipe and the second branch pipe: one part of the natural gas is normally transported through the regulating valve group, and the other part of the natural gas enters the pressure difference power generation system to produce electricity, and then merges into the reserved air inlet branch pipe.

[0119] 3. First, the situation when natural gas is normally transported through the regulating valve group is described:

[0120] (1) After the natural gas enters the first branch pipe, the second electric ball valve M2 and the third electric ball valve M3 on the first branch pipe are opened, and the opening degree depends on the adjustment instruction of the DCS control system; generally, the opening degree of the second electric ball valve M2 and the third electric ball valve M3 is fully open by default;

[0121] Generally, the opening degree of all electric valves on the regulating valve group, unless otherwise specified, depends on the DCS control system; non-electric valve groups need to be opened manually, and the opening degree depends on the instructions issued by the central control room of the gas transmission station;

[0122] The first ball valve Q1 on the vent air recovery main pipe 22 connected to the first branch pipe is completely closed;

[0123] (2) Natural gas flows from the first branch pipe into the intermediate manifold, and the throttle valve on the third branch pipe connected to the intermediate manifold is completely closed; then the natural gas reaches the inlet end of the fourth branch pipe and the fifth branch pipe;

[0124] (3) The electric ball valve 6 on the fourth branch pipe is fully closed by default, the electric regulating valve 1 is fully closed by default, and the seventh electric ball valve M8 is fully open by default;

[0125] Since the electric ball valve 6 is completely closed, the natural gas enters the fifth branch pipe from the middle manifold;

[0126] The electric ball valve 8 and the ninth electric ball valve M11 of the fifth branch pipe are fully opened by default, and the opening degree of the second electric regulating valve M10 is controlled by the DCS system to reduce the natural gas pressure in the pipeline to meet the inlet pressure requirements of the downstream long-distance pipeline;

[0127] The third ball valve Q3 on the reserved intake branch pipe is fully open by default;

[0128] (4) The natural gas reaches the gas outlet manifold through the fifth branch pipe, and together with the natural gas generated by the pressure difference power generation system, is filtered by the filter device and then flows to the downstream long-distance pipeline;

[0129] Optionally, the natural gas filtered by the filtering device can pass through the downstream long-distance pipeline or can be directed to the next gas transmission station, that is, the object to which it is directed is not limited to the downstream long-distance pipeline.

[0130] 4. Secondly, the situation in which natural gas enters the pressure difference power generation system to produce electricity and then flows into the reserved air intake branch pipe is described:

[0131] (1) After the natural gas enters the second branch pipe from the intake manifold, the fourth electric ball valve M4 on the second branch pipe is opened, and the opening degree is fully open by default; the fifth electric ball valve Q5 on the second branch pipe is fully closed by default;

[0132] (2) The second ball valve Q2 on the reserved outlet branch pipe is fully open by default; the natural gas passes through the reserved port D1 in front of the regulating valve group and enters the pressure difference power generation system from the regulating valve group;

[0133] (3) The first cylinder ball valve N1 is fully opened by default, and natural gas enters the intake ends of the raw gas intake branch pipe 16 and the dry gas sealed intake branch pipe 17 from the dry gas intake manifold 15;

[0134] Generally, the valve group of the pressure difference power generation system is adjusted by the pressure difference power generation module process control system; the basis of the adjustment is to interact with the DCS system based on the monitored pressure, temperature, flow and other data, adjust the sealing system of the pressure difference power generation system, meet the safety requirements of the pressure difference generator skid 28, and make the pressure difference generator skid 28 generate electricity at the rated power as much as possible;

[0135] (4) The pneumatic regulating valve N2 is partially closed, and the degree of closing is determined by the process control system of the pressure difference power generation module, so that the pressure of the raw gas entering the pressure difference generator skid 28 is about 0.2 MPa lower than the pressure of the sealing dry gas;

[0136] The first pressure observation and alarm device P1 can observe and monitor the pressure before the start-up regulating valve; the second pressure observation and alarm device P2 can observe the pressure of the natural gas before entering the pressure difference generator skid 28; the first temperature observation and alarm device T1 can observe the temperature of the natural gas before entering the pressure difference generator skid 28;

[0137] The fourth ball valve Q4 of the dry gas seal intake branch pipe 17 is partially opened, and the degree of opening is determined by the pressure difference power generation module process control system;

[0138] (5) The natural gas enters the pressure difference generator skid 28 through the raw gas inlet branch pipe 16, expands and reduces the pressure to generate electricity through the turbine expander, and then enters the raw gas outlet branch pipe 18 after subsequent processing by the unit;

[0139] The power of the pressure difference generator skid 28 is always kept at the rated power during normal operation to maximize economic benefits;

[0140] The pressure reduction of the natural gas by the pressure difference generator skid 28 is consistent with the pressure reduction of the second electric regulating valve M10; its value is exchanged between the pressure difference power generation module process control system and the DCS system;

[0141] The generated electricity is pressurized by the booster equipment and then transmitted to the high-voltage distribution room where the gas transmission station is located through high-voltage cables. It is coordinated and processed by the grid-connected system, so that the pressure difference power generation and grid power input can jointly supply the electricity demand of the gas transmission station.

[0142] (6) The check valve J2 and the second cylinder ball valve N3 on the raw gas outlet branch pipe 18 are fully open by default, and the natural gas enters the dry gas outlet manifold 19 from the raw gas outlet branch pipe 18; the check valve J2 can prevent the natural gas from flowing back;

[0143] The third pressure observation and alarm device P3 can observe the pressure of the natural gas when it comes out of the pressure difference generator pry 28; the second temperature observation and alarm device T2 can observe the temperature of the natural gas when it comes out of the pressure difference generator pry 28;

[0144] (7) The fifth ball valve Q5 and the throttling stop vent valve on the vent air recovery branch pipe 21 are completely closed by default;

[0145] A small amount of leaked gas from the pressure difference generator skid 28 enters the vent air recovery branch pipe 21 through the leaked gas recovery branch pipe 20 and leads to the vent air recovery system;

[0146] (8) Natural gas flows out from the dry gas outlet manifold 19, enters the reserved air inlet branch pipe through the reserved port D3 after the regulating valve group, passes through the electric regulating valve 7, and then flows into the outlet manifold, and after being filtered, it leads to the downstream long-distance pipeline;

[0147] (9) The nitrogen of the nitrogen sealing system comes from the nitrogen generator skid, and the operating parameters of the nitrogen generator skid, such as power, pressure, temperature and flow, are regulated by the pressure difference power generation module process control system;

[0148] The nitrogen produced by the nitrogen generator is led to the first cylinder ball valve N1, the second cylinder ball valve N3 and the pneumatic regulating valve N2, and also to the isolation gas inlet port E of the pressure difference generator skid 28.

[0149] In addition, when the pressure difference power generation system operates normally, there are two points to note:

[0150] (1) If the flow rate entering the dry gas outlet manifold 19 is too large, the pressure difference power generation module process control system will interact with the DCS system and preferentially open the fifth electric ball valve Q5, so that part of the natural gas entering the second branch pipe is diverted into the intermediate manifold;

[0151] (2) When the natural gas flow entering the fifth branch pipe approaches or exceeds the carrying capacity of the fifth branch pipe, the DCS system will open the electric ball valve 6, so that part of the natural gas from the middle manifold is diverted into the fourth branch pipe; at this time, the electric control valve 1 is partially closed, so that the pressure of the natural gas entering the fourth branch pipe is reduced, and the pressure reduction is consistent with the pressure reduction generated by the second electric control valve M10; the closing degree of the electric control valve 1 is determined by the DCS system.

[0152] Therefore, when the pressure difference power generation system operates normally, it can not only meet the requirements of continuous and safe transportation of natural gas, but also make full use of pressure energy to produce electricity.

[0153] 2. Maintenance and shutdown conditions

[0154] When the pressure difference power generation system of the natural gas transmission station is shut down for maintenance, the pressure difference power generation system is completely shut down, and only the regulating valve group is put into use. At this time, the grid-connected system cuts off the power input from the pressure difference power generation system, and uses all the grid power input to supply the power demand of the gas transmission station.

[0155] (1) The second ball valve Q2 on the reserved gas outlet branch pipe and the third ball valve Q3 on the reserved gas inlet branch pipe are both completely closed, so that the natural gas entering the regulating valve group does not enter the pressure difference power generation system;

[0156] (2) If the first branch pipe 7 can carry the natural gas from the intake manifold 6, then under the regulation of the DCS system, the fourth electric ball valve M4 and the fifth electric ball valve Q5 are closed, so that the second branch pipe 8 is not used; if the first branch pipe 7 cannot fully carry the natural gas flow from the intake manifold 6, then under the regulation of the DCS system, the fourth electric ball valve M4 and the fifth electric ball valve Q5 are opened, and the second branch pipe 8 is used;

[0157] (3) If the fifth branch pipe 12 is able to carry the natural gas from the intermediate manifold, then under the regulation of the DCS system, the seventh electric ball valve M8 on the fourth branch pipe 11 is also completely closed, that is, the fourth branch pipe 11 is not used;

[0158] (4) Other operating modes of the regulating valve group are consistent with normal operating conditions.

[0159] Therefore, when the pressure difference power generation system of the natural gas transmission station is shut down for maintenance, the regulating valve group can also ensure the continuous and safe transportation and pressure reduction of natural gas in the gas transmission station, and can also recover the released natural gas.

[0160] 3. Emergency parking conditions:

[0161] When the pressure differential power generation system of the natural gas transmission station stops urgently, at least one of the regulating valve group or the pressure differential power generation system has an emergency. At this time, the grid-connected system cuts off the power input from the pressure differential power generation system and uses all the grid power input to supply the power demand of the gas transmission station.

[0162] (1) If an emergency occurs in the regulating valve group, the pressure difference power generation module process control system will exchange data with the DCS system and immediately implement isolation protection measures to close the first cylinder ball valve N1 and the second cylinder ball valve N3; the pressure difference generator skid 28 and the nitrogen generator skid will be gradually shut down; the second ball valve Q2 and the third ball valve Q3 of the regulating valve group will be immediately closed to cut off the connection between the pressure difference power generation system and the DCS system; the electric first ball valve Q1 on the intake manifold will be closed to cut off the source of natural gas; the first ball valve Q1 on the vent air recovery main 22 will be opened to release the natural gas in the regulating valve group, and the released natural gas will be introduced into the vent air recovery system for treatment;

[0163] (2) If an emergency occurs in the differential pressure power generation system, the DCS system exchanges data with the differential pressure power generation module control system, immediately implements isolation protection measures, and the second ball valve Q2 and the third ball valve Q3 of the regulating valve group are immediately closed to cut off the connection between the differential pressure power generation system and the DCS system; the differential pressure power generation module control system adjusts the differential pressure generator skid 28 to stop urgently, the nitrogen generator skid gradually stops, and the pneumatic first ball valve Q1 and the pneumatic second ball valve Q2 are closed; the differential pressure power generation module control system adjusts the fifth ball valve Q5 and the throttle cut-off vent valve J3 to open, release the natural gas in the differential pressure power generation system, and the released natural gas enters the vent air recovery main pipe 22 through the vent air reserved port through the vent air recovery branch pipe 21, and then leads to the vent air recovery system; the DCS system adjusts the electric fifth ball valve Q5 to open, so that the natural gas originally entering the differential pressure power generation system is merged into the intermediate manifold; then the fifth branch pipe is used first for gas transmission and pressure reduction, and the DCS system decides whether to activate the fourth branch pipe for gas transmission and pressure reduction based on the monitored flow data; other operating modes of the regulating valve group are consistent with normal operating conditions;

[0164] (3) When an emergency occurs simultaneously in the regulating valve group and the pressure differential power generation system, the DCS system exchanges data with the pressure differential power generation module control system, and the first cylinder ball valve N1 and the second cylinder ball valve N3, the second ball valve Q2 and the third ball valve Q3 of the throttle valve group are immediately closed to cut off the connection between the regulating valve group and the pressure differential power generation system; the electric first ball valve Q1 is closed to cut off the natural gas source; the seventh electric ball valve M8 and the ninth electric ball valve M11 are closed so that the natural gas of the regulating valve group no longer enters the downstream pipeline; the first ball valve Q1 of the air recovery main pipe 22 is opened, and the fifth ball valve Q5 and the throttle stop vent valve J3 of the air recovery branch pipe 21 are opened so that all the natural gas in the pressure regulating valve group and the pressure differential generator skid 28 is released, and the released natural gas enters the air recovery system; the nitrogen generator skid and the pressure differential generator skid 28 are stopped urgently, and the power supply is cut off after stopping.

[0165] Therefore, when the pressure difference power generation system of the natural gas transmission station is shut down in an emergency, the DCS system and the pressure difference power generation module process control system can quickly cut off the upstream gas and the downstream gas supply, and can realize the emergency shutdown of the pressure difference generator skid 28 and the nitrogen generator skid, thereby ensuring the safety of pipelines and equipment in the gas transmission station. In addition, all the natural gas released due to the emergency shutdown enters the venting air recovery system, which can reduce the loss of natural gas and realize the recovery and utilization of venting air.

[0166] Generally speaking, the pressure difference power generation system of a natural gas transmission station is in normal operating conditions, while maintenance shutdown conditions and emergency shutdown conditions are two special conditions.

[0167] In summary, the present invention provides a pressure differential power generation system for a natural gas transmission station, including a regulating valve group and a pressure differential power generation system. Through the collaboration of the regulating valve group and the pressure differential power generation system, and the interaction between the DCS control system and the pressure differential power generation module process control system, it is possible to use pressure energy to generate clean electricity while ensuring the continuous and safe transportation of natural gas.

[0168] The system's pressure difference generator skid 28 and nitrogen generator skid are skid-mounted and modularized, and no additional heater is required. The process is relatively simple, the equipment has good stability, and is easy to maintain and overhaul later.

[0169] The system connects the leakage gas and vented air of the pressure difference power generation system to the vented air recovery system of the regulating valve group, which can effectively reduce natural gas loss, achieve zero natural gas emissions, and realize green and low-carbon production.

[0170] The system can flexibly adjust the natural gas flow entering the differential pressure generator skid 28. When the gas volume, pressure, temperature and other operating parameters of the gathering and transportation pipeline are relatively stable or fluctuate greatly, it can meet the requirements of safe and stable operation of the differential pressure generator. It is especially suitable for power generation for self-use at gas transmission stations on gathering and transportation trunk lines in remote areas of my country.

[0171] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings here can usually be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0172] Example

[0173] In order to make the content of the present invention more clear and easy to understand, the operation method of the pressure difference power generation system of the natural gas transmission station provided by the present invention is explained below with reference to a specific example.

[0174] It is known that the gas flow rate of the upstream valve chamber of a gas transmission station is 202,700 cubic meters per hour, and the density of natural gas is 122.45 kg / m 3 The constant pressure specific heat capacity of natural gas is 2.51 kJ / (kg·K).

[0175] S1. Set the system to normal operating conditions;

[0176] S2, the gas from the upstream valve chamber enters the gas intake manifold, and through the DCS system, the natural gas flow from the gas intake manifold to the first branch pipe is 142,000 cubic meters per hour; the natural gas flow from the gas intake manifold to the second branch pipe 8 is 106,100 cubic meters per hour;

[0177] S3, the natural gas diverted into the first branch pipe 7 passes smoothly through the second electric ball valve M2 and the third electric ball valve M3 and then enters the middle manifold, and then enters the fifth branch pipe from the middle manifold;

[0178] Through the pressure reducing effect of the second electric regulating valve M10 on the fifth branch pipe 12 , the natural gas pressure is reduced from 6.73 MPa to 4.14 MPa; the reduced-pressure natural gas enters the gas outlet manifold from the fifth branch pipe 12 .

[0179] S4, the natural gas diverted into the second branch pipe 8 passes smoothly through the fourth electric ball valve M4 and the second ball valve Q2, and then enters the pressure difference power generation system; on the raw gas inlet branch pipe 16, the pressure measured by the pressure observation and monitoring device 1 is 6.73MPa; the pressure difference power generation module process control system controls the pneumatic regulating valve N2 to reduce the pressure of the natural gas in the raw gas inlet branch pipe 16; the pressure observation and monitoring device 2 measures the pressure before the raw gas inlet of the pressure difference generator skid 28 to be 6.53MPa, and the temperature observation and monitoring device 1 measures the temperature before the raw gas inlet of the pressure difference generator skid 28 to be 39.27℃;

[0180] After being regulated by the fourth ball valve Q4, part of the natural gas dry gas enters the sealing system of the pressure difference generator skid 28, and the sealing gas pressure is about 0.2MPa higher than the raw gas.

[0181] The natural gas flow rate used by the pressure difference power generation system is 106,100 cubic meters per hour; after the natural gas enters the pressure difference generator skid 28 as raw gas, the outlet pressure of the turbine expander is 4.15 MPa, and the actual enthalpy drop of the turbine expander is 60.13 kJ / kg; the efficiency of the asynchronous generator included in the pressure difference generator skid 28 is 95%, and the power generation of the asynchronous generator is 600.05 kW·h;

[0182] The pressure of the raw gas outlet branch pipe 18 measured by the pressure observation and monitoring device 3 is 6.14 MPa, and the temperature of the raw gas outlet branch pipe 18 measured by the temperature observation and monitoring device 2 is 17.18°C;

[0183] The natural gas coming out of the pressure difference generator skid 28 passes through the check valve J2J2, the second cylinder ball valve N3 and the third ball valve Q3, enters the reserved air inlet branch pipe, and then enters the air outlet manifold through the fourth branch pipe 11.

[0184] S5. Due to the limitation of materials and process level, a small amount of leakage gas (about 3m 3 / h) enters the vent air recovery main pipe 22 of the regulating valve group through the leaked gas recovery branch pipe 20, and then leads to the vent air recovery system;

[0185] S6. The electricity generated by the differential pressure generator skid 28 passes through the booster equipment, and the output voltage becomes 10kV, and then is transmitted to the 10kV high-voltage distribution room of the gas transmission station through a 10kV high-voltage cable. The grid-connected system adjusts the power supply mode of grid power input and differential pressure power generation input;

[0186] S7, calculate the annual power consumption of the pressure difference generator skid 28 and the nitrogen generator skid, and calculate the annual power generation of the pressure difference generator skid 28. According to the load of the nitrogen generator skid and the pressure difference generator skid 28, the annual power consumption of the pressure difference generator skid 28 and the nitrogen generator skid is calculated to be approximately 29.75*10 4 kW·h; and the annual power generation of the differential pressure generator skid 28 is 520*10 4 kW·h, the electricity generated is consumed by the gas transmission station itself; therefore, after the electricity generated by the pressure energy is integrated into the high-voltage distribution room of the gas transmission station, the annual purchase of grid electricity can be reduced by about 490.25*10 4 kW·h;

[0187] If the industrial electricity price in the remote western region where the gas transmission station is located is 0.5 yuan / kWh (1 kWh = 1 kW·h), the pressure difference power generation system and operation method of the natural gas transmission station are applied to the gas transmission station, and the annual profit generated is about 2.4513 million yuan.

[0188] S8. Calculate the amount of leaked gas and vented air recovered. If the regulating valve group and the pressure difference power generation system are overhauled once a year, and the natural gas in the valve group or the pressure difference power generation system needs to be fully released each time, the estimated annual vented air volume is about 105,000 cubic meters; and the natural gas introduced into the vented air recovery system through the leaked gas recovery branch pipe 20 is about 3m 3 / h, the amount of leaked gas that can be recovered each year is about 26,000 cubic meters; the amount of natural gas recovered through the vented air recovery system each year is about 131,000 cubic meters.

[0189] If the unit price of natural gas industrial production is 1 yuan / m 3 According to calculation, the leaked gas and vented air recovered by the vented air recovery system can save 131,000 yuan each year.

[0190] In summary, the pressure difference power generation system for a natural gas transmission station of the present invention can effectively utilize pressure energy to generate clean electricity while ensuring the continuous and safe transmission of natural gas; it can effectively reduce natural gas loss, achieve zero emission of natural gas, and realize green and low-carbon production. Therefore, the present invention has its necessity and practicality.

[0191] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A pressure difference power generation system for a natural gas transmission station, characterized in that: include: The regulating valve group is used to complete the pressure reduction and transmission of natural gas in the gas transmission station through the control of the DCS control system, and realize the smooth transportation of natural gas in the gathering and transmission pipelines with different pressure levels; The pressure difference power generation system is used to maintain the turbine expander at the rated power generation power through the interaction between the pressure difference power generation module process control system and the DCS control system, and to produce electricity by using the pressure energy of the natural gas in the gathering and transmission pipeline. The energy relationship between the grid power and the pressure difference power generation is adjusted and controlled by the grid connection system to realize the power supply mode of the combination of grid power and pressure difference power generation. The pressure difference power generation is used to power the equipment in the gas transmission station, and the grid power is used as a beneficial supplement.

2. The pressure difference power generation system for a natural gas transmission station according to claim 1 is characterized in that: The regulating valve group comprises a main line, one end of which is connected to an upstream valve chamber (1), and the other end of which is respectively connected to a pressure difference power generation system, a downstream long-distance pipeline (2) and a vented air recovery device (3). A valve group and a vented air recovery system are arranged on the main line, and the valve group and the vented air recovery system are respectively connected to a DCS control system.

3. The pressure difference power generation system for a natural gas transmission station according to claim 2 is characterized in that: The main pipeline comprises an air intake manifold (6), one end of which is connected to an upstream valve chamber (1), and the other end of which is connected to a downstream long-distance pipeline (2) via a first branch pipe (7), a fifth branch pipe (12) and an air outlet manifold (14) in sequence.

4. The pressure difference power generation system for a natural gas transmission station according to claim 3 is characterized in that: A first electric ball valve (M1) is arranged between the air inlet manifold (6) and the first branch pipe (7), a second electric ball valve (M2) and a third electric ball valve (M3) are arranged in sequence between the first branch pipe (7) and the fifth branch pipe (12), an eighth electric ball valve (M9), a second electric regulating valve (M10) and a ninth electric ball valve (M11) are arranged in sequence between the fifth branch pipe (12) and the air outlet manifold (14), and a filtering device (W1) is arranged between the air outlet manifold (14) and the downstream long-distance pipeline (2).

5. The pressure difference power generation system for a natural gas transmission station according to claim 3 is characterized in that: The main pipeline is also connected to a bypass pipeline, which includes a second branch pipe (8), a third branch pipe (10), a fourth branch pipe (11), a reserved outlet branch pipe (9), and a reserved inlet branch pipe (13); one end of the second branch pipe (8) is connected to the upstream valve chamber (1), and the other end is divided into two paths, one of which is connected to the pressure difference power generation system through the reserved outlet branch pipe (9), and the other is respectively connected to the third branch pipe (10) and the fourth branch pipe (11); the other end of the third branch pipe (10) is connected to the stop valve (J1), and the other end of the fourth branch pipe (11) is respectively connected to the reserved inlet branch pipe (13) and the outlet manifold (14); the second branch pipe (8 ) are sequentially provided with a fourth electric ball valve (M4) and a fifth electric ball valve (M5); one end of the reserved air outlet branch pipe (9) is connected to the pipeline between the fourth electric ball valve (M4) and the fifth electric ball valve (M5), and the other end is connected to the pressure difference power generation system via the second ball valve (Q2) and the reserved port (D1) before the regulating valve group; the fourth branch pipe (11) is sequentially provided with a sixth electric ball valve (M6), a first electric regulating valve (M7) and a seventh electric ball valve (M8); the other end of the reserved air intake branch pipe (13) is connected to the pressure difference power generation system via the third ball valve (Q3) and the reserved port (D3) after the regulating valve group.

6. The pressure difference power generation system for a natural gas transmission station according to claim 3 is characterized in that: The vent air recovery device (3) is connected to the first branch pipe (7) via the vent air recovery main pipe (22), and a first ball valve (Q1) is provided on the vent air recovery main pipe (22).

7. The pressure difference power generation system for a natural gas transmission station according to claim 1 is characterized in that: The pressure difference power generation system comprises a pressure difference generator skid (28), one end of the pressure difference generator skid (28) is connected to a reserved port (D1) in front of a regulating valve group via a raw gas inlet branch pipe (16) and a dry gas inlet manifold (15), and the other end of the pressure difference generator skid (28) is connected to a reserved port (D3) in the rear of the regulating valve group via a raw gas outlet branch pipe (18) and a dry gas outlet manifold (19); the pressure difference generator skid (28) is also connected to a sealing system, an exhaust air recovery system and a grid connection system respectively, the sealing system is used to connect to the regulating valve group, the exhaust air recovery system is used to release inflammable and explosive natural gas, and is connected to an exhaust air recovery system of the regulating valve group. The pressure difference power generation module process control system comprises a first pressure observation and alarm device (P1), a second pressure observation and alarm device (P2), a second pressure observation and alarm device (P3), a first temperature observation and alarm device (T1) and a second temperature observation and alarm device (T2); the first pressure observation and alarm device (P1), the second pressure observation and alarm device (P2) and the first temperature observation and alarm device (T1) are arranged on the raw gas inlet branch pipe (16), and the second pressure observation and alarm device (P3) and the second temperature observation and alarm device (T2) are arranged on the raw gas outlet branch pipe (18).

8. The pressure difference power generation system for a natural gas transmission station according to claim 7 is characterized in that: A first cylinder ball valve (N1) and a pneumatic regulating valve (N2) are arranged on the raw gas inlet branch pipe (16), and a check valve (J2) and a second cylinder ball valve (N3) are arranged on the raw gas outlet branch pipe (18).

9. The pressure difference power generation system for a natural gas transmission station according to claim 8, characterized in that: The sealing system comprises a dry gas sealing subsystem and a nitrogen sealing subsystem; the dry gas sealing subsystem comprises a dry gas sealing air intake branch pipe (17), one end of the dry gas sealing air intake branch pipe (17) is connected to a pressure difference generator skid (28), and the other end is connected to a raw gas air intake branch pipe (16) via a fourth ball valve (Q4); the nitrogen sealing subsystem comprises a nitrogen generator skid (29), the nitrogen generator skid (29) is divided into four paths via a nitrogen intake manifold (23), the first path is connected to a cylinder ball valve (N1) via a first nitrogen branch pipe (24), the second path is connected to a pneumatic regulating valve (N2) via a second nitrogen branch pipe (25), the third path is connected to the pressure difference generator skid (28) via a third nitrogen branch pipe (26), and the fourth path is connected to the second cylinder ball valve (N3) via a fourth nitrogen branch pipe (27).

10. The pressure difference power generation system for a natural gas transmission station according to claim 7, characterized in that: The vent air recovery system comprises a leakage air recovery branch pipe (20), one end of which is connected to a pressure difference generator skid (28), and the other end of which is connected to a vent air recovery device (3) via a vent air recovery branch pipe (21) and a reserved port D (2) of a vent air main pipe. The vent air recovery branch pipe (21) is also connected to a raw gas outlet branch pipe (18) via a throttling stop vent valve (J3) and a fifth ball valve (Q5).

Images