Natural gas excess pressure differential pressure power generation method and system

Abstract

The invention belongs to the technical field of differential pressure energy utilization, and relates to a natural gas excess pressure differential pressure power generation method and system.The method comprises the steps that S1, liquefied natural gas is gasified to form natural gas with the pressure P1; s2, after the natural gas with the pressure P1 is subjected to heat exchange, expansion power generation and pressure stabilization in sequence, natural gas with the pressure P2 and the temperature of 5-15 DEG C is formed and conveyed to a gas supply pipe network, and P1 is larger than P2; and meanwhile, electric energy is generated in the expansion power generation acting process and is conveyed to a power generation system. Through heat exchange, expansion power generation and pressure stabilization, the pressure of natural gas is reduced, the temperature of the natural gas is reduced by 5-15 DEG C, the requirement of a gas supply pipe network is met, meanwhile, pressure difference energy is recycled and converted into electric energy, energy waste is avoided, and secondary utilization of energy is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of pressure difference energy utilization, and relates to a natural gas excess pressure pressure difference power generation method and system. Background Art

[0002] The liquefied natural gas (LNG) gasification device adopts a loading and unloading storage process that combines a booster and a pump to unload, a LNG pump to load, and non-pressurized storage. It uses a pressurized gasification process that first pressurizes and then gasifies through an SCV, and a BOG compression and direct output processing process. The pressure of the natural gas after gasification by the SCV device is about 4MPaG, which needs to be reduced to a pipeline gas supply pressure of 3.5~3.8MPaG.

[0003] In conventional processes, natural gas pressure reduction is achieved through large pressure reducing valves and other pressure regulating devices. However, a large amount of pressure difference energy is seriously wasted in this irreversible process, which also causes serious problems such as pipeline vibration and noise. Summary of the invention

[0004] In view of the technical problem of waste of pressure difference energy in the existing natural gas decompression process, the present invention provides a natural gas residual pressure pressure difference power generation method and system.

[0005] The present invention reduces the pressure of natural gas to 5°C to 15°C through heat exchange, expansion power generation and pressure stabilization. While meeting the needs of the gas supply network, the pressure difference energy is recovered and converted into electrical energy, avoiding energy waste and achieving secondary energy utilization.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A natural gas residual pressure differential power generation method comprises the following steps:

[0008] S1, liquefied natural gas is gasified to form natural gas with a pressure of P1;

[0009] S2, natural gas with a pressure of P1, undergoes heat exchange, expansion power generation and pressure stabilization in sequence to form natural gas with a pressure of P2 and a temperature of 5°C to 15°C and is transported to the gas supply network, P1>P2; at the same time, electrical energy is generated during the expansion power generation process and is transported to the power generation system.

[0010] It is further defined that in step S1, the molar fractions of the components in the natural gas at a pressure of P1 are: methane 94.10%, ethane 4.18%, propane 0.74%, isobutane 0.17%, n-butane 0.11%, isopentane 0.04%, n-pentane 0.02%, hexane 0.07%, and nitrogen 0.55%.

[0011] It is further defined that in step S2, the expansion power generation is single-stage expansion power generation or multi-stage expansion power generation.

[0012] It is further defined that in step S2, when multi-stage expansion power generation is performed, the natural gas needs to be supplemented with heat after each stage of expansion power generation.

[0013] Further defined, P1 = 4.0MpaG, P2 = 3.5MpaG ~ 3.8MpaG, the natural gas flow rate entering the expansion power generation is 300×10 4 m 3 / d~660×10 4 m 3 / d, with power generation ranging from 271.8KWh to 704.5KWh.

[0014] A natural gas excess pressure differential power generation system for realizing the natural gas excess pressure differential power generation method, the natural gas excess pressure differential power generation system comprising a gasifier, a gas supply main pipeline, a main pipeline pressure reducing valve, a heat exchange expansion work unit, a power generation unit and a gas supply network;

[0015] The gasifier is connected to the gas supply network via the main gas supply pipeline; the main pipe pressure reducing valve is placed on the main gas supply pipeline; one end of the thermal expansion working unit is located between the gasifier and the main pipe pressure reducing valve and is connected to the main gas supply pipeline, the other end of the thermal expansion working unit is located between the main pipe pressure reducing valve and the gas supply network and is connected to the main gas supply pipeline, and the other end of the thermal expansion working unit is also connected to the power generation unit.

[0016] It is further defined that the heat exchange expansion working unit includes an expander; one end of the expander is located between the gasifier and the main pipe pressure reducing valve and is connected to the main gas supply pipeline, and the other end of the expander is located between the main pipe pressure reducing valve and the gas supply network and is connected to the main gas supply pipeline;

[0017] It is further defined that the power generation unit includes a generator and a power distribution mechanism; the expander is connected to the power distribution mechanism via the generator.

[0018] It is further defined that the expander is one or more; a plurality of the expanders are connected in series in sequence;

[0019] The expander is a turbine expander, a rotor expander or a screw expander.

[0020] It is further defined that the heat exchange expansion working unit also includes an inlet connecting pipe and an outlet connecting pipe, the inlet connecting pipe is located between the gasifier and the main pipe pressure reducing valve, the main gas supply pipeline is connected to the expander through the inlet connecting pipe, the outlet connecting pipe is located between the main pipe pressure reducing valve and the gas supply network, and the expander is connected to the main gas supply pipeline through the outlet connecting pipe; an inlet control valve and an inlet interlock valve are sequentially arranged on the inlet connecting pipe along the airflow direction; the inlet interlock valve is arranged close to the expander.

[0021] It is further defined that the natural gas residual pressure differential power generation system also includes a gas supply branch pipeline and a gas supply bypass pipeline;

[0022] One end of the gas supply branch pipeline is connected to the inlet connecting pipe and is located between the inlet control valve and the inlet interlock valve; the other end of the gas supply branch pipeline is connected to the outlet connecting pipe and is located between the expander and the natural gas pressure stabilizer; a branch pipe regulating valve is provided on the gas supply branch pipeline;

[0023] One end of the gas supply bypass pipeline is connected to the inlet connecting pipe and is located between the gas supply branch pipeline and the inlet interlock valve; the other end of the gas supply bypass pipeline is connected to the outlet connecting pipe and is located between the gas supply branch pipeline and the expander; a bypass interlock valve and a bypass regulating valve are sequentially arranged on the gas supply bypass pipeline along the air flow direction.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention is provided with a gasifier, a main pipe pressure reducing valve, a gas supply network, an expander, a generator and a power distribution mechanism. The pressure difference energy generated by the gasification of natural gas is converted into mechanical energy through the expander and the generator, and then finally converted into electrical energy through the power generation system, thereby avoiding energy waste and realizing the recovery and secondary utilization of the pressure difference energy.

[0026] 2. In the present invention, the expansion power generation is single-stage expansion power generation or multi-stage expansion power generation, which can meet the reuse of pressure difference energy in different occasions; in the present invention, when multi-stage expansion power generation is adopted, the natural gas needs to be supplemented with heat after each stage of expansion power generation to ensure that the temperature of the natural gas after the pressure reduction meets the needs of the gas supply network, and can also ensure that all pipelines, instruments and other facilities do not produce condensation or ice blockage under various operating conditions, thereby ensuring the normal operation of the system.

[0027] 3. The present invention is provided with a gasifier, a main pipe pressure reducing valve, a gas supply network and an expander, and the expander and the main pipe pressure reducing valve are connected in parallel, one for use and one for backup, which greatly improves the reliability and safety of the pressure difference power generation device.

[0028] 4. In the present invention, by setting a main pipe pressure reducing valve, an inlet control valve and an inlet interlock valve, the flow of natural gas entering the gas supply network and the expander is controlled respectively, so as to achieve smooth switching of the device and ensure safe operation.

[0029] 5. In the present invention, by providing a gas supply branch pipeline and a gas supply bypass pipeline, when LNG production is shut down urgently, natural gas passes through the gas supply branch pipeline and the gas supply bypass pipeline to ensure the safe and stable operation of the entire system.

[0030] 6. The pressure difference power generation device provided by the present invention utilizes the pressure difference energy generated during the production or transportation of natural gas, recovers it and converts it into mechanical energy, drives the generator to generate electricity, realizes secondary energy recovery, and achieves the purpose of energy saving and carbon reduction. The whole device is not only simple in structure and low in cost, but also stable and reliable in operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a structural schematic diagram of the first natural gas residual pressure differential power generation system;

[0032] Figure 2 This is a structural schematic diagram of the second natural gas residual pressure differential power generation system;

[0033] Figure 3 This is a schematic diagram of the structure of the third natural gas residual pressure differential power generation system;

[0034] Figure 4 This is a schematic diagram of a natural gas heating device;

[0035] in:

[0036] 1-Gasifier; 2-Main gas supply pipeline; 3-Main pipeline pressure reducing valve; 4-Gas supply network; 5-Gas supply branch pipeline; 6-Inlet control valve; 7-Branch pipe regulating valve; 8-Gas supply bypass pipeline; 9-Bypass interlock valve; 10-Bypass regulating valve; 11-Inlet interlock valve; 12-Expander; 13-Generator; 14-Power distribution mechanism; 15-Lubricating oil unit; 16-Inlet connecting pipe; 17-Outlet connecting pipe; 18-Sealing unit; 19-Natural gas regulator; 20-Water bath box; 21-Blower; 22-Combustion chamber; 23-Smoke pipe; 24-Natural gas heat exchanger; 25-Bubbling hole; 26-Chimney. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0038] Example 1

[0039] This embodiment provides a natural gas residual pressure differential power generation method, comprising the following steps:

[0040] S1, liquefied natural gas is gasified to form natural gas with a pressure of P1;

[0041] S2, natural gas with a pressure of P1, undergoes heat exchange, expansion power generation and pressure stabilization in sequence to form natural gas with a pressure of P2 and a temperature of 5°C to 15°C and is transported to the gas supply network, P1>P2; at the same time, electrical energy is generated during the expansion power generation process and is transported to the power generation system.

[0042] In the present invention, the natural gas with a pressure of P1 is directly reduced to P2 through a pressure reducing valve and then transported to the gas supply network.

[0043] In this embodiment, after liquefied natural gas is gasified, it is formed into natural gas and transported to the gas supply network. However, the pressure of the gasified natural gas is P1, the pressure of the gas supply network is P2, and P1>P2. Therefore, it is necessary to reduce the pressure to make the natural gas meet the pressure requirement of the gas supply network. However, a pressure difference will be generated during the pressure reduction process. Therefore, heat exchange and expansion are used to generate electricity, which not only meets the pressure requirement of the gas supply network, but also uses the pressure difference to generate electricity, thereby realizing the recovery and reuse of pressure energy.

[0044] In this embodiment, in step S2, the expansion power generation is single-stage expansion power generation or multi-stage expansion power generation. The expansion power generation is two-stage expansion power generation, and can also be three-stage expansion power generation.

[0045] Single-stage expansion power generation: Natural gas flows through expansion to generate mechanical energy, which is transferred to the power generation unit for power generation. The expansion of natural gas can be regarded as an isentropic process, producing the Joule-Thomson effect, and the temperature of natural gas decreases after expansion.

[0046] Two-stage expansion power generation: After the natural gas is heated by the preheater, it enters the pre-pressure regulating valve and then enters the first expansion (high-pressure expansion). The expanded natural gas enters the intermediate heater for heating, and then enters the low-pressure stage for secondary expansion (low-pressure expansion). The outlet natural gas enters the rear heat exchanger for heating. The heated natural gas enters the gas supply network, and the expansion work transmits the electrical energy to the power generation unit for power generation. The two-stage expansion process outputs more technical work, with high power generation per hour and good economic efficiency.

[0047] Three-stage expansion power generation: The high-pressure natural gas flow is expanded in three stages in sequence, and the pressure is gradually reduced until the pressure drops to the pressure required by the gas supply network. At the same time, a heating device is set between two adjacent expansion power generation stages to increase the natural gas inlet temperature of each stage of the expander through intermediate heating, thereby increasing the power generation power and the outlet natural gas temperature. The technical power output of the three-stage expansion power generation is greater than that of the two-stage expansion.

[0048] In this embodiment, the multi-stage expansion process is between the isentropic expansion process and the isothermal expansion process, and as the expansion stage increases, the multi-stage expansion process is infinitely close to the isothermal process, the more technical work is output, and the more power generation is ultimately generated.

[0049] In step S2, when multi-stage expansion power generation is performed, the natural gas needs to be reheated after each stage of expansion power generation to ensure that the natural gas temperature in the gas supply network is between 5°C and 15°C, and to prevent condensation and ice blockage in the pipeline, ensuring safe operation.

[0050] Example 2

[0051] See also Figure 1The present embodiment also provides a natural gas residual pressure differential power generation system, including a gasifier 1, a gas supply main pipeline 2, a main pipeline pressure reducing valve 3, a heat exchange expansion working unit, a power generation unit and a gas supply network 4.

[0052] The gasifier 1 is connected to the gas supply network 4 via the main gas supply pipeline 2; the main pipe pressure reducing valve 3 is placed on the main gas supply pipeline 2; one end of the thermal expansion working unit is located between the gasifier 1 and the main pipe pressure reducing valve 3 and is connected to the main gas supply pipeline 2, the other end of the thermal expansion working unit is located between the main pipe pressure reducing valve 3 and the gas supply network 4 and is connected to the main gas supply pipeline 2, and the other end of the thermal expansion working unit is also connected to the power generation unit.

[0053] In this embodiment, the heat exchange expansion working unit includes an expander 12, one end of the expander 12 is located between the gasifier 1 and the main pipe pressure reducing valve 3, and is respectively connected to the gasifier 1 and the main pipe pressure reducing valve 3; the other end of the expander 12 is located between the main pipe pressure reducing valve 3 and the gas supply network 4, and is respectively connected to the main pipe pressure reducing valve 3 and the gas supply network 4.

[0054] In this embodiment, the main pipe pressure reducing valve 3 is located on the main gas supply pipeline 2, and the gasifier 1 is connected to the gas supply network 4 through the main gas supply pipeline 2; and then the two ends of the expander 12 are connected to the main gas supply pipeline 2 at both ends of the main pipe pressure reducing valve 3. That is, the inlet end of the expander 12 is connected to the main gas supply pipeline 2 between the gasifier 1 and the main pipe pressure reducing valve 3, and the outlet end of the expander 12 is connected to the main gas supply pipeline 2 between the main pipe pressure reducing valve 3 and the gas supply network 4; so that the expander 12 and the main pipe pressure reducing valve 3 are connected in parallel, one for use and one for backup, which greatly improves the reliability and safety of the pressure difference power generation device.

[0055] In this embodiment, the power generation unit includes a generator 13 and a power distribution mechanism 14 ; the expander 12 is connected to the power distribution mechanism 14 via the generator 13 .

[0056] In this embodiment, an inlet connecting pipe 16 and an outlet connecting pipe 17 are arranged in sequence along the gas supply direction on the gas supply main pipeline 2; one end of the expander 12 is connected to the gas supply main pipeline 2 through the inlet connecting pipe 16; the other end of the expander 12 is connected to the gas supply main pipeline 2 through the outlet connecting pipe 17. The main pipeline pressure reducing valve 3 is located between the inlet connecting pipe 16 and the outlet connecting pipe 17.

[0057] During implementation, the connection between the main gas supply pipeline 2 and the inlet end of the expander 12 is achieved through the inlet connecting pipe 16, and the connection between the main gas supply pipeline 2 and the outlet end of the expander 12 is achieved through the outlet connecting pipe 17, thereby improving the rapid and stable connection between the devices.

[0058] In this embodiment, an inlet control valve 6 and an inlet interlock valve 11 are sequentially arranged on the inlet connecting pipe 16 along the air flow direction; the inlet interlock valve 11 is arranged close to the expander 12 .

[0059] In this embodiment, a natural gas pressure stabilizer 19 is provided on the outlet connecting pipe 17 , and its function is to maintain a stable pressure of the natural gas during the process of being transported to the gas supply network 4 .

[0060] In this embodiment, the inlet control valve 6, the inlet interlock valve 11 and the main pipe pressure reducing valve 3 are used in combination. When the main pipe pressure reducing valve 3 is opened, the inlet control valve 6 and the inlet interlock valve 11 are closed, and the natural gas gasified by the gasifier 1 is decompressed by the main pipe pressure reducing valve 3 and then transported to the gas supply network 4; when the main pipe pressure reducing valve 3 is closed, the inlet control valve 6 and the inlet interlock valve 11 are both opened, and the natural gas gasified by the gasifier 1 is transported to the expander 12 through the inlet connecting pipe 16, and a part of the natural gas is directly transported to the gas supply network 4 after being stabilized by the outlet connecting pipe 17, and a part of the natural gas is converted into mechanical energy through expansion work to drive the generator 13 to generate electricity. In addition, when the equipment is overhauled, by reducing the valve opening of the inlet interlock valve 11 and increasing the valve opening of the main pipe pressure reducing valve 3, a smooth switching of the natural gas is achieved to ensure the safe operation of the device.

[0061] In this embodiment, there are one or more expanders 12; multiple expanders 12 are connected in series. In implementation, there are two or three expanders 12, which can be selected according to the size of the pressure difference. The more expanders 12 there are, the more output work done by expansion, and the more power generation is obtained.

[0062] In this embodiment, the output power of the generator 13 is 800KW, and the expander 12 is a turbine expander, a screw expander or a rotor expander.

[0063] Turbine expander: suitable for medium and high pressure (actual ≤8MPaG), expansion ratio (≤8) and large flow conditions; rotor expander: suitable for medium and low pressure (≤3MPaG), small and medium expansion ratio (≤2.3) and small flow conditions; screw expander: suitable for medium and low pressure (≤6MPaG), small and medium expansion ratio (≤6) and small and medium flow conditions.

[0064] Preferably, the expander 12 uses a turbine expander, which mainly uses high-pressure airflow to impact the impeller to achieve energy conversion. It has the characteristics of high speed and high isentropic efficiency, and is suitable for working conditions with large flow rate and stable pressure.

[0065] In this embodiment, after the liquefied natural gas passes through the gasifier 1, it is gasified from the liquid state to natural gas (pressure 4MPaG), and after being reduced in pressure to 3.5MPaG-3.8MPaG through the main pipe pressure reducing valve 3, it directly enters the gas supply network 4. During the natural gas pressure reduction and transportation, the pressure difference energy is released due to the pressure reduction. Therefore, the main pipe pressure reducing valve 3 can be closed, and the released pressure difference energy can be introduced into the expander 12. The pressure difference energy is converted into mechanical energy through the expander 12, and the generator 13 is used to generate electricity, and then the mechanical energy is converted into electrical energy for providing power distribution to the power distribution mechanism 14, so as to realize the recovery, conversion and secondary utilization of the pressure difference energy, thereby avoiding energy waste and achieving the purpose of energy saving and carbon reduction.

[0066] See also Figure 2 In this embodiment, the expander 12 needs to be supported by bearings to rotate. To ensure safe and reliable operation, lubricating oil needs to be provided to each bearing lubrication point. Therefore, lubricating oil is injected into the connection between the generator 13 and the expander 12 through the lubricating oil unit 15 to meet the lubricating oil supply under normal working conditions and accident conditions. The lubricating oil used in the lubricating oil unit 15 is the conventional lubricating oil for the expander 12 and the generator 13.

[0067] See also Figure 2 In this embodiment, the expansion medium of the expander 12 is natural gas. Since natural gas is dangerous, flammable and explosive, high design requirements are placed on the seal so that there is no leakage of natural gas during the entire expansion process. In this embodiment, the expander 12 is sealed by a sealing unit 18. Preferably, the sealing unit 18 adopts a mechanical seal, a labyrinth seal or a dry gas seal, and a mixed seal of a mechanical seal and a dry gas seal. The above seals are all existing conventional sealing structures. Preferably, mechanical seals and dry gas seals are used, which have good sealing effects and high sealing quality, ensuring the safe and stable operation of the expander 12 equipment.

[0068] See also Figure 3 On the basis of Example 1, the natural gas residual pressure differential power generation system provided in this embodiment also includes a gas supply branch pipeline 5; one end of the gas supply branch pipeline 5 is connected to the inlet connecting pipe 16 and is located between the inlet control valve 6 and the inlet interlock valve 11; the other end of the gas supply branch pipeline 5 is connected to the outlet connecting pipe 17 and is located between the expander 12 and the natural gas pressure stabilizer 19.

[0069] In order to facilitate the conduction and closing of the gas supply branch pipeline 5, a branch pipe regulating valve 7 is arranged on the gas supply branch pipeline 5; when an emergency occurs in the system, the inlet interlock valve 11 is closed to cut off the natural gas from entering the expander 12. After the natural gas passes through the inlet control valve 6, the branch pipe regulating valve 7 is opened, and the natural gas is introduced into the outlet connecting pipe 17 through the gas supply branch pipeline 5, and enters the gas supply network 4 after being stabilized by the natural gas pressure stabilizer 19, so that the natural gas passes through the bypass to ensure the safe and stable operation of the entire system.

[0070] See also Figure 3 In this embodiment, the natural gas residual pressure differential power generation system further includes a gas supply bypass pipeline 8; one end of the gas supply bypass pipeline 8 is connected to the inlet connecting pipe 16 and is located between the gas supply branch pipeline 5 and the inlet interlock valve 11; the other end of the gas supply bypass pipeline 8 is connected to the outlet connecting pipe 17 and is located between the gas supply branch pipeline 5 and the expander 12. A bypass interlock valve 9 and a bypass regulating valve 10 are sequentially arranged on the gas supply bypass pipeline 8 along the air flow direction to facilitate the cutting and conducting of the gas supply bypass pipeline 8, and to form an interlock with other valves for convenient control.

[0071] During implementation, the gas supply bypass pipeline 8 and the gas supply branch pipeline 5 are two bypasses, one for backup and the other for use, which are flexible and convenient to use.

[0072] In the present invention, in order to facilitate the control of each valve, the natural gas residual pressure differential power generation system also includes a DCS control system, which is respectively connected to the main pipe pressure reducing valve 3, the inlet control valve 6, the inlet interlock valve 11, the branch pipe regulating valve 7, the bypass interlock valve 9 and the bypass regulating valve 10. By connecting all the corresponding valves to the DCS control system, automatic variable load operation is achieved according to the gas supply.

[0073] Example 3

[0074] In this embodiment, the high-pressure natural gas (pressure is 4.0 MPaG) generated after the liquefied natural gas is gasified has a pressure of 3.5 MPaG-3.8 MPaG and a temperature of 15°C in the gas supply network.

[0075] The natural gas residual pressure differential power generation method provided in this embodiment includes the following steps:

[0076] S1. Liquid natural gas is gasified to form natural gas with a pressure of P1, where P1 is 4.0MPaG.

[0077] In this embodiment, the components of the natural gas after gasification are shown in Table 1.

[0078] Table 1 Natural gas composition

[0079] Components Mole fraction, % Methane 94.10 Ethane 4.18 Propane 0.74 Isobutane 0.17 n-Butane 0.11 Isopentane 0.04 n-Pentane 0.02 Hexane 0.07 Nitrogen 0.55

[0080] S2. At the same time, the natural gas with a pressure of P1 undergoes heat exchange, expansion power generation and pressure stabilization in sequence to form natural gas with a pressure of P2 and a temperature of 15°C, and is transported to the gas supply network. P2 is 3.5MPa G-3.8MPaG; the electric energy generated in the process of expansion and power generation is transported to the power generation system; in addition, the natural gas with a pressure of P1 is also directly reduced to P2 through a pressure reducing valve and then transported to the gas supply network.

[0081] The process parameters of expansion power generation are selected according to the pressure difference between P1 and P2 and the power generation.

[0082] In this embodiment, the expansion power generation adopts turbine expansion power generation, and the specific parameters are shown in Table 2.

[0083] Table 2 Turbine expansion performance parameters in this embodiment

[0084]

[0085]

[0086] In this embodiment, during stable operation, the opening degree of the main pipe pressure reducing valve 3 is adjusted to 5% or directly closed, and the gasifier 1 discharges 4.0MpaG natural gas into the gas supply main pipeline 2, and flows to the inlet connecting pipe 16 through the inlet control valve 6, and then enters the expander 12 through the inlet interlock valve 11. Since the expander 12 is a turbine expander, a nearly isentropic (ideal) expansion is achieved in the turbine expander, and the pressure difference energy is converted into mechanical energy, and the generator 13 is driven to generate electricity for providing power distribution to the power distribution mechanism 14; at the same time, the high-pressure natural gas (4.0MPaG) is reduced in pressure to about 3.5MPaG-3.8MPaG after expansion, and is discharged from the expander 12 to the outlet connecting pipe 17, and after being stabilized by the natural gas pressure stabilizer 19, it is merged into the gas supply main pipeline 2, and finally input into the downstream gas supply network 4.

[0087] In this embodiment, the gas supply time is from November to March of the next year, a total of 4 months, which is a heating season. The internal power of the turbo expander is 557KW. Excluding the power loss, the net output power of the turbo expander is 515.6kW. The efficiency of the generator is 94.8%, and the power generation of the generator in each heating season is 1.408 million degrees to 2.030 million degrees.

[0088] According to the "Study on Carbon Dioxide Emission Factors of Regional Power Grids in China (2023)", the average emission factor of the national power grid is 0.608t CO2 / MWh. In this embodiment, the annual CO2 emission reduction is 856.1t~1398.4t.

[0089] In this embodiment, the natural gas is supplemented with heat by gas preheating. The principle of gas preheating is to use an external heat source to exchange heat with the inlet airflow to increase the temperature of the turbine expander inlet, so as to prevent the expansion machine outlet temperature from being too low in winter and causing operating problems. Specifically, the gas preheating methods mainly include: gas hot water boiler heat exchange heating and air source heat pump heating. Preferably, a gas hot water boiler is used to preheat the natural gas intake.

[0090] See also Figure 4The heat supplement device provided in this embodiment includes a water bath box 20, a fan 21, a combustion chamber 22, a smoke pipe 23 and a natural gas heat exchanger 24. The fan 21 is placed outside the water bath box 20, the combustion chamber 22, the natural gas heat exchanger 24 and the smoke pipe 23 are all placed in the water bath box 20, the combustion chamber 22 is connected to the smoke pipe 23, a bubbling hole 25 is arranged on the smoke pipe 23, the smoke pipe 23 is located below the natural gas heat exchanger 24, and the bubbling hole 25 is directly opposite to the natural gas heat exchanger 24, the water bath box 20 is filled with desalted water, and a chimney 26 is connected to the top of the water bath box 20. During the heating process, the gas is mixed with air and blown into the combustion chamber 22 through the fan 21 to burn and generate high-temperature flue gas. The high-temperature flue gas then enters the water bath box 20 through the bubbling holes 25 on the smoke pipe 23, exchanges heat with the desalted water, and the temperature of the desalted water increases. The low-temperature flue gas after heat exchange is discharged upward through the chimney 26; the natural gas to be heated enters the natural gas heat exchanger 24, and absorbs the heat of the desalted water through the natural gas heat exchanger 24 in the water bath box 20, so that the heating temperature of the natural gas increases. The heated natural gas comes out of the water bath box 20 and enters the expander 12. The above method heats the natural gas to the required temperature, ensuring that all pipelines, instruments and other facilities do not produce condensation or ice blockage under various operating conditions, and ensuring the normal operation of the system in various environments.

[0091] In this embodiment, a pressure regulating device (pressure regulating valve) is added before the expander, thereby losing a part of the pressure energy, which is then expanded and cooled by the expander, thereby ensuring that the gas transmission temperature is appropriate.

[0092] Example 4

[0093] Different from Example 3, the design and specific parameters of turbine expansion power generation are different, see Table 3 for details.

[0094] Table 3 Turbine expansion performance parameters in this embodiment

[0095]

[0096]

[0097] In this embodiment, the gas supply time is from November to March of the following year, a total of 4 months, which is a heating season. The internal power of the turbo expander is 834KW. Excluding the power loss, the net output power of the turbo expander is 773.2kW. The efficiency of the generator is 94.8%, and the power generation of each heating generator is 2.111 million degrees to 3.046 million degrees.

[0098] According to the "Study on Carbon Dioxide Emission Factors of Regional Power Grids in China (2023)", the average emission factor of the national power grid is 0.608tCO2 / MWh. In this embodiment, the annual CO2 emission reduction is 2995t~4648.8t.

[0099] To sum up, the natural gas waste pressure power generation method provided by the present invention utilizes the pressure difference energy generated during the production or transportation of natural gas, recovers it and converts it into mechanical energy for power generation. It is a clean and environmentally friendly power generation technology that does not produce excess carbon emissions. It not only realizes the recovery and reuse of pressure difference energy, but also brings considerable carbon reduction benefits while generating electricity.

[0100] The above descriptions are merely embodiments of the present invention, and are not intended to limit the protection scope of the patent of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, are also included in the protection scope of the present invention.

Claims

1. A natural gas residual pressure differential power generation method, characterized in that: The following steps are involved: S1, liquefied natural gas is gasified to form natural gas with a pressure of P1; S2, natural gas with a pressure of P1, undergoes heat exchange, expansion power generation and pressure stabilization in sequence to form natural gas with a pressure of P2 and a temperature of 5°C to 15°C and is transported to the gas supply network, P1>P2; at the same time, electrical energy is generated during the expansion power generation process and is transported to the power generation system.

2. The natural gas residual pressure differential power generation method according to claim 1, characterized in that: In the step S2, the expansion power generation is single-stage expansion power generation or multi-stage expansion power generation.

3. The natural gas residual pressure differential power generation method according to claim 2, characterized in that: In step S2, when multi-stage expansion power generation is performed, the natural gas needs to be supplemented with heat after each stage of expansion power generation.

4. The natural gas residual pressure differential power generation method according to claim 1, characterized in that: In step S1, the molar fractions of the components in the natural gas at a pressure of P1 are: methane 94.10%, ethane 4.18%, propane 0.74%, isobutane 0.17%, normal butane 0.11%, isopentane 0.04%, normal pentane 0.02%, hexane 0.07% and nitrogen 0.55%.

5. The natural gas excess pressure differential power generation method according to claim 4, characterized in that: The P1 = 4.0MpaG, P2 = 3.5MpaG-3.8MpaG, and the natural gas flow rate entering the expansion power generation is 300×10 4 m 3 / d~660×10 4 m 3 / d, the power generation system generates 271.8KWh~704.5KWh of electricity.

6. A natural gas excess pressure differential power generation system for realizing the natural gas excess pressure differential power generation method according to claim 1, characterized in that: The natural gas residual pressure differential power generation system comprises a gasifier (1), a gas supply main pipeline (2), a main pipeline pressure reducing valve (3), a heat exchange expansion work unit, a power generation unit and a gas supply pipeline network (4); The gasifier (1) is connected to the gas supply network (4) via the gas supply main pipeline (2); the main pipeline pressure reducing valve (3) is placed on the gas supply main pipeline (2); one end of the thermal expansion working unit is located between the gasifier (1) and the main pipeline pressure reducing valve (3) and is connected to the gas supply main pipeline (2); the other end of the thermal expansion working unit is located between the main pipeline pressure reducing valve (3) and the gas supply network (4) and is connected to the gas supply main pipeline (2); and the other end of the thermal expansion working unit is also connected to the power generation unit.

7. The natural gas residual pressure differential power generation system according to claim 6, characterized in that: The heat exchange expansion work unit comprises an expander (12); One end of the expander (12) is in communication with the main gas supply pipeline (2), and the other end of the expander (12) is in communication with the main gas supply pipeline (2); The power generation unit comprises a generator (13) and a power distribution mechanism (14); the expander (12) is connected to the power distribution mechanism (14) via the generator (13).

8. The natural gas residual pressure differential power generation system according to claim 7, characterized in that: There are one or more expanders (12); the multiple expanders (12) are connected in series in sequence. When there are multiple expanders (12), a heat supplement device is also connected after the previous expander (12).

9. The natural gas residual pressure differential power generation system according to claim 7, characterized in that: The heat exchange expansion work unit further comprises an inlet connecting pipe (16) and an outlet connecting pipe (17); the inlet connecting pipe (16) is located between the gasifier (1) and the main pipe pressure reducing valve (3); the main gas supply pipeline (2) is connected to the expander (12) via the inlet connecting pipe (16); the outlet connecting pipe (17) is located between the main pipe pressure reducing valve (3) and the gas supply network (4); the expander (12) is connected to the main gas supply pipeline (2) via the outlet connecting pipe (17); an inlet control valve (6) and an inlet interlock valve (11) are sequentially arranged on the inlet connecting pipe (16) along the gas flow direction; the inlet interlock valve (11) is arranged close to the expander (12); and a natural gas pressure stabilizer (19) is arranged on the outlet connecting pipe (17).

10. The natural gas residual pressure differential power generation system according to claim 9, characterized in that: The natural gas residual pressure differential power generation system also includes a gas supply branch pipeline (5) and a gas supply bypass pipeline (8); One end of the gas supply branch pipeline (5) is connected to the inlet connecting pipe (16) and is located between the inlet control valve (6) and the inlet interlock valve (11); the other end of the gas supply branch pipeline (5) is connected to the outlet connecting pipe (17) and is located between the expander (12) and the natural gas pressure stabilizer (19); a branch pipe regulating valve (7) is provided on the gas supply branch pipeline (5); One end of the gas supply bypass pipeline (8) is connected to the inlet connecting pipe (16) and is located between the gas supply branch pipeline (5) and the inlet interlock valve (11); the other end of the gas supply bypass pipeline (8) is connected to the outlet connecting pipe (17) and is located between the gas supply branch pipeline (5) and the expander (12); a bypass interlock valve (9) and a bypass regulating valve (10) are sequentially arranged on the gas supply bypass pipeline (8) along the gas flow direction.

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