Natural gas wellhead heating and depressurization system and method

Abstract

The invention provides a natural gas wellhead heating depressurization system and method. The natural gas wellhead heating depressurization system comprises a water bath heating module, a turbo expander, a power generator and an electric heater. Natural gas from a natural gas wellhead enters the electric heater to be preheated, the preheated natural gas from the electric heater enters the water bath heating furnace to be heated, and high-temperature natural gas from the water bath heating furnace enters the turbo expander. Low-temperature natural gas discharged from the turbo expander is heated by an electric heater and then enters a gas collecting pipe network to be output; the turbo expander is connected with the power generator and drives the power generator to generate power; and the generator is electrically connected with the electric heater. The electric heater is driven by pressure difference to reheat, the influence of environment temperature is avoided, and the application range is wider; the invention relates to less equipment, simple process and high integration level.

Description

Technical Field

[0001] The present invention belongs to the field of ground engineering technology, relates to the field of energy conservation and carbon reduction in the carbon capture, utilization and storage (CCUS) technology system, and specifically relates to a natural gas wellhead heating and pressure reduction system and method. Background Art

[0002] During the process of natural gas collection, the underground pressure can reach more than 20 MPa. Considering safety and economic factors, the underground natural gas needs to be throttled and depressurized before it can be transported. When the natural gas flows through the throttling element after collection, the pressure in the pipeline drops sharply and the volume expands, and the temperature drops synchronously. The sudden drop in temperature can easily cause hydrate formation, causing ice blockage in the pipeline and increasing the burden on the pipeline. At present, two natural gas gathering and transportation processes are adopted at home and abroad to prevent the formation of hydrates: (1) the wellhead outlet gas flows through the heating furnace, and then is pre-treated after heating and transportation; (2) antifreeze inhibitors are injected into the natural gas to change the interaction between water molecules to reduce the dew point of the natural gas, thereby preventing freezing. Although these two processes can effectively control the formation of hydrates, they also consume a lot of energy, mainly concentrated in the pressure energy loss in the throttling process and the heat energy loss in the gas heating process. If appropriate waste energy utilization methods can be used to recover energy, it can not only generate huge economic benefits, but also reduce environmental pollution caused by the combustion loss of natural gas that cannot be recycled, which is of great significance in the field of energy conservation and carbon reduction.

[0003] CN104088605A discloses a natural gas wellhead heating and throttling system based on pressure energy power generation and heat pump heating, which belongs to the technical field of heat pump heating; see Figure 1 The system includes an expander, a generator, a heat pump unit, an electric motor, an air preheater, a reheater, a pressure regulating valve, a separator, and a throttle valve; after the natural gas is collected from the natural gas well, the natural gas well is connected to the separator through a pressure regulating valve, and the separator is provided with a throttle valve, through which the oil-water mixture separated by the separator can be discharged; the separator is connected to the expander, the expander is connected to the air preheater, and the air preheater is connected to the reheater; this system does not require additional energy supply: the expander generator unit converts the pressure energy of the high-pressure natural gas into electrical energy, which drives the heat pump unit to operate, and the remaining electrical energy can also be used for other equipment or grid-connected transmission; it does not involve natural gas combustion equipment, is green and environmentally friendly, easy to operate, and has a wide range of applications. However, this method uses the temperature difference between the natural gas after expansion and cooling and the environment to make the natural gas absorb part of the heat from the environment to partially restore its temperature, and then uses the reheater to restore the temperature to the required temperature of the gathering and transportation pipeline. If the external environment temperature is similar to the natural gas temperature, it may not be possible to achieve a good heat absorption effect, and the equipment is cumbersome. Summary of the invention

[0004] In order to solve the above-mentioned problems of the prior art, the present invention provides a natural gas wellhead heating and pressure reduction system and method, which utilizes the pressure difference to drive the electric heater to recover heat, is not affected by the ambient temperature, and has a wider range of applications; and the present invention involves less equipment, a simple process, and a high degree of integration.

[0005] The present invention is achieved through the following technical solutions:

[0006] A natural gas wellhead heating and pressure reduction system comprises a water bath heating module, a turbine expander, a generator and an electric heater;

[0007] The natural gas coming out of the natural gas wellhead enters the electric heater for preheating, the preheated natural gas coming out of the electric heater enters the water bath heating furnace for heating, the high-temperature natural gas coming out of the water bath heating furnace enters the turbine expander, and the low-temperature natural gas coming out of the turbine expander is heated by the electric heater and then enters the gas gathering network for external transmission;

[0008] The turbine expander is connected to a generator, and the turbine expander drives the generator to generate electricity; the generator is electrically connected to an electric heater.

[0009] Preferably, a bypass pressure stabilizing module is further included, and the turbine expander and the electric heater are connected in parallel with the bypass pressure stabilizing module.

[0010] Furthermore, it also includes a bypass pressure stabilization module; the high-temperature natural gas coming out of the water bath heating furnace is divided into two paths, one path of high-temperature natural gas enters the turbine expander, and the other path of high-temperature natural gas is divided into two paths of stabilized pressure gas after passing through the bypass pressure stabilization module, one path of stabilized pressure gas enters the gas gathering network for external transmission, and the other path of stabilized pressure gas provides fuel gas for the water bath heating furnace.

[0011] Furthermore, it also includes a pressure reducing gas supply module; another path of stabilized pressure gas enters the water bath heating furnace for heating, and the heated stabilized pressure gas is divided into three paths, the first path enters the turbine expander, the second path enters the bypass pressure stabilizing module, and the third path enters the pressure reducing gas supply module. The natural gas after the pressure reduction by the pressure reducing gas supply module enters the water bath heating furnace as fuel gas for combustion.

[0012] Furthermore, the pressure reducing air supply module is a throttle valve.

[0013] Furthermore, the bypass voltage stabilization module is a throttle valve.

[0014] A method for heating and reducing the pressure at a natural gas wellhead. Based on the system, the natural gas coming out of the natural gas wellhead is preheated by an electric heater and then transported to a water bath heating furnace for heating. The heated high-temperature natural gas enters a turbine expander for reducing the pressure. The pressure difference is converted into kinetic energy to drive the turbine expander to rotate. The rotation of the turbine expander drives the generator to generate electricity. The generator supplies power to the electric heater. The low-temperature natural gas discharged from the turbine expander is heated by the electric heater and then transported out through a gas gathering pipeline network.

[0015] A method for heating and reducing the pressure of a natural gas wellhead is characterized in that, based on the system, the natural gas coming out of the natural gas wellhead is preheated by an electric heater and then transported to a water bath heating furnace for heating. The heated high-temperature natural gas is divided into two paths. One path of high-temperature natural gas enters the turbine expander for reducing the pressure, and the pressure difference is converted into kinetic energy to drive the turbine expander to rotate. The rotation of the turbine expander drives the generator to generate electricity, and the generator supplies power to the electric heater. The low-temperature natural gas discharged from the turbine expander is heated by the electric heater and then transmitted to the outside through a gas gathering pipeline network; the other path of high-temperature natural gas enters a bypass pressure stabilization module, and the pressure-stabilized gas coming out of the bypass pressure stabilization module is transmitted to the outside through a gas gathering pipeline network.

[0016] A method for heating and reducing the pressure of a natural gas wellhead is characterized in that, based on the system, the natural gas coming out of the natural gas wellhead is preheated by an electric heater and then transported to a water bath heating furnace for heating. The heated high-temperature natural gas is divided into two paths. One path of high-temperature natural gas enters the turbine expander for reducing the pressure. The pressure difference is converted into kinetic energy to drive the turbine expander to rotate. The rotation of the turbine expander drives the generator to generate electricity. The generator supplies power to the electric heater. The low-temperature natural gas discharged from the turbine expander is heated by the electric heater and then transmitted to the outside through a gas collection network; the other path of high-temperature natural gas enters a bypass pressure stabilizing module. The pressure-stabilized gas coming out of the bypass pressure stabilizing module is divided into two paths. One path of pressure-stabilized gas enters the gas collection network for transmission, and the other path of pressure-stabilized gas provides fuel gas for the water bath heating furnace.

[0017] A method for heating and reducing pressure at a natural gas wellhead, characterized in that, based on the system, natural gas coming out of the natural gas wellhead is preheated by an electric heater and then transported to a water bath heating furnace for heating. The heated high-temperature natural gas is divided into two paths. One path of high-temperature natural gas enters the turbine expander for pressure reduction, and the pressure difference is converted into kinetic energy to drive the turbine expander to rotate. The rotation of the turbine expander drives the generator to generate electricity, and the generator supplies power to the electric heater. The low-temperature natural gas discharged from the turbine expander is heated by the electric heater and then transmitted to the outside through a gas collection network; the other path of high-temperature natural gas enters a bypass pressure stabilizing module, and the pressure-stabilized gas coming out of the bypass pressure stabilizing module is divided into two paths. One path of pressure-stabilized gas enters the gas collection network for transmission, and the other path of pressure-stabilized gas enters the water bath heating furnace for heating. The heated pressure-stabilized gas is divided into three paths. The first path enters the turbine expander, the second path enters the bypass pressure stabilizing module, and the third path enters the pressure-reducing gas supply module. The natural gas after pressure reduction by the pressure-reducing gas supply module enters the water bath heating furnace as fuel gas for combustion.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention uses a turbine expander generator set to convert the pressure energy of high-pressure natural gas into electrical energy, and then uses the electrical energy to provide heat energy to heat the natural gas. The front end and the rear end of the wellhead of the present invention are both heated by electric heaters, which are not affected by the ambient temperature, can meet the requirements of different ambient temperatures, and have a wider range of applications. The present invention has less equipment, a simple process, and a high degree of integration.

[0020] Furthermore, the bypass pressure stabilizing module of the present invention can control the pressure balance of the system when the incoming gas volume is different, and can adjust the system imbalance caused by significant fluctuations in the incoming gas volume.

[0021] Furthermore, the present invention supplies part of the pressure-stabilized gas as fuel gas to the water bath heating furnace, which can reduce the amount of natural gas directly supplied externally to the water bath heating furnace for combustion, and realizes energy utilization and recovery through electric-gas coupled heating without consuming external energy.

[0022] Another path of stabilized pressure gas enters the water bath heating furnace for heating. The heated stabilized pressure gas is divided into three paths. The first path enters the turbine expander, the second path enters the bypass pressure stabilizing module, and the third path enters the pressure reducing gas supply module. The natural gas after the pressure reduction by the pressure reducing gas supply module enters the water bath heating furnace as fuel gas for combustion. The secondary pressure reduction of the pressure reducing gas supply module is because there is a difference between the gas pressure required by the gathering and transportation pipeline and the pressure of the combustion gas. The gas pressure required by the gathering and transportation pipeline is 0.4Mpa, and the pressure required by the combustion gas is 0.3Mpa. The natural gas enters the expander after being heated by the water bath heating furnace, which can ensure anti-freezing before entering the expander. The secondary heating also ensures that the natural gas is below the water dew point before going to the gas gathering network, and will not be frozen. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of a natural gas wellhead heating and throttling system based on pressure energy power generation and heat pump heating in the prior art;

[0024] Figure 2 This is a schematic diagram of a natural gas wellhead heating and pressure reduction system of the present invention.

[0025] In the figure: 11 is an electric heater, 12 is a turbine expander, 13 is a generator, 14 is a water bath heating furnace, 15 is a first throttle valve, and 16 is a second throttle valve. DETAILED DESCRIPTION

[0026] In order to further understand the present invention, the present invention is described below in conjunction with embodiments. These descriptions are only to further explain the features and advantages of the present invention and are not intended to limit the claims of the present invention.

[0027] See also Figure 2The natural gas wellhead heating and pressure reduction system of the present invention comprises a water bath heating module, a differential pressure power generation module, a bypass pressure stabilizing module and a pressure reducing gas supply module. The water bath heating module is a water bath heating furnace 14, the differential pressure power generation module comprises a turbine expansion module and a preheating and reheating module, the turbine expansion module comprises a turbine expander 12 and a generator 13, the preheating and reheating module is an electric heater 11, the bypass pressure stabilizing module is a first throttle valve 15, and the pressure reducing gas supply module is a second throttle valve 16.

[0028] After being collected from the natural gas well, the natural gas enters the water bath heating furnace 14 after being preheated by the electric heater 11, and is further heated in the water bath heating furnace 14 and divided into two high-temperature natural gas paths. One high-temperature natural gas path enters the turbine expander 12, and the low-temperature natural gas coming out of the turbine expander 12 is heated by the electric heater 11 and then enters the gas collection network for external transmission; the other high-temperature natural gas path is divided into two stabilized pressure gas paths after passing through the first throttle valve 15, one stabilized pressure gas path enters the gas collection network for external transmission, and the other stabilized pressure gas path returns to the water bath heating furnace 1 4 is heated, and the heated stabilized pressure gas is divided into three paths, the first path enters the turbine expander 12, the second path enters the first throttle valve 15, and the third path enters the second throttle valve 16. The natural gas after secondary throttling and pressure reduction by the second throttle valve 16 enters the water bath heating furnace 14, and fuel gas is supplied to the water bath heating furnace 14; the turbine expander 12, the electric heater 11 and the first throttle valve 15 are connected in parallel; the first throttle valve 15 and the water bath heating furnace 14 are connected in series, and the second throttle valve 16 is connected in series at the rear end of the water bath heating furnace 14.

[0029] The turbine expander 12 is connected to a generator 13 , and the turbine expander 12 works to drive the generator 13 to generate electricity; the generator 13 is electrically connected to the electric heater 11 and supplies power to the electric heater 11 .

[0030] The method for heating and reducing the pressure of a natural gas wellhead of the present invention is specifically as follows: natural gas is collected from each wellhead and transported to an electric heater 11 through a transport pipeline, preheated by the electric heater 11 and then transported to a water bath heating furnace 14 for heating, and then part of the natural gas enters a turbine expander 12 for reducing the pressure, and the pressure difference is converted into kinetic energy to drive the turbine expander 12 to rotate and drive the generator 13 connected thereto to generate electricity, and the generated electricity is used to provide electric energy for the electric heater 11, and the low-temperature natural gas discharged from the turbine expander 12 after expansion and work is recovered to the required temperature of the gathering and transportation pipeline by the electric heater 11. After reaching the temperature, it is transported out through the gas gathering network; another part of the high-temperature natural gas separated out after being heated in the water bath heating furnace 14 is reduced in pressure and stabilized by the first throttle valve 15 connected in parallel with the turbine expander 12 and the electric heater 11. One part of the stabilized flow gas is transported out through the gas gathering network, and the other part enters the water bath heating furnace 14 for heating and is divided into three paths. The first path enters the turbine expander 12, the second path enters the first throttle valve 15, and the third path enters the second throttle valve 16. After throttling and reducing the pressure by the second throttle valve 16, it enters the water bath heating furnace 14 as fuel gas for combustion to provide heat.

[0031] Simulation experiment

[0032] The present invention has carried out a simulation experiment, assuming that the wellhead natural gas pressure is 20MPa and the temperature is 25°C. The wellhead natural gas performs external work in the turbine expander through the adiabatic expansion process. According to the isentropic process calculation, the natural gas pressure at the outlet of the turbine expander can be obtained to be 10MPa and the temperature is 23°C. Assuming that the efficiency of the turbine expander is 75%, the output power of the turbine expander is 25kW, and the electric heating power is 8kW. The system can operate normally, which is a technical indicator that can be fully achieved. According to the isentropic process calculation, the natural gas indicators at different positions are obtained as shown in Table 1. It can be seen that the final natural gas temperature of 27°C can meet the temperature requirements of the gathering and transportation pipeline.

[0033] Table 1 Natural gas indicators at each node in the embodiment

[0034]

[0035] Note: 1. The gas field production is 100,000 Nm at standard conditions (1 atm, 20°C) 3 / d, at which point the natural gas density is 0.79156 kg / m 3 ;

[0036] 2. The enthalpy value of natural gas at each state point is calculated based on relevant software.

[0037] Simple calculations show that 5×10 4 Nm 3 / d gas well, if the conventional throttling process is adopted (i.e. the pressure energy is lost after throttling, and the pressure difference is not used to drive the expander to do work, and the throttling and pressure reduction process is only to meet the pressure and temperature of the gas collection network, which is an invalid loss for natural gas), and then the natural gas is used to provide combustion energy, the heating power of the natural gas heating furnace is about 199.3kW, and the efficiency of the heating furnace is calculated as 80%, then the daily natural gas consumption is about 579Nm 3 In this process, part of the steady-flow gas is separated and fed into the water bath furnace for heating, followed by secondary throttling and pressure reduction. As the fuel gas for the water bath furnace, the daily consumption of natural gas is 529Nm 3 , can effectively save 50Nm 3 Natural gas volume, the annual gas saving is 15000Nm 3 , which can effectively reduce carbon dioxide emissions by 28,500kg and save 18,000 yuan per year.

[0038] Example

[0039] High-pressure natural gas (about 16.1 MPa, 24°C) is extracted from the wellhead of the gas well, preheated to 38°C by the electric heater 11, and then heated to 66°C by the water bath heating furnace 14. It then enters the turbine expander 12 to reduce the pressure to 9.5 MPa and the temperature to 21°C. The pressure energy is converted into kinetic energy and drives the generator 13 to generate electricity. It is then heated to 25°C by the electric heater 11 and mixed with another part of the stable flow gas with reduced pressure and stable flow before being transmitted externally.

[0040] Practical application shows that the system and method of the present invention can achieve heating and pressure reduction of natural gas at the wellhead of a gas well, can adapt to different ambient temperatures, ensure that the external transmission temperature meets the requirements, and has the characteristics of a wide range of applications.

[0041] The present invention has a high degree of integration and a simple process. The electric heater, water bath heating furnace 14, turbo expander 12, generator 13, bypass pressure reduction and flow stabilization module, bypass pressure stabilization module and pressure reduction gas supply module can be integrated into one. The pressure difference after natural gas expansion is used to drive the generator 13 to generate electricity. At the same time, the electric-gas coupling heat supply does not require other energy input; the bypass pressure stabilization module is connected in parallel with the differential pressure power generation module to effectively ensure the system's pressure stabilization and safe operation; the steady flow gas is used to separate part of the water bath furnace for heat exchange and then throttled and depressurized as the water bath furnace fuel gas, which effectively utilizes energy and reduces carbon dioxide emissions to achieve low-carbon and environmental protection. The present invention does not require the addition of any agents, saves a lot of resources, and reduces the operating costs of enterprises.

Claims

1. A natural gas wellhead heating and pressure reduction system, characterized in that: It comprises a water bath heating module, a turbine expander (12), a generator (13) and an electric heater (11); The natural gas coming out of the natural gas wellhead enters the electric heater (11) for preheating, the preheated natural gas coming out of the electric heater (11) enters the water bath heating furnace (14) for heating, the high-temperature natural gas coming out of the water bath heating furnace (14) enters the turbine expander (12), and the low-temperature natural gas coming out of the turbine expander (12) is heated by the electric heater (11) and then enters the gas gathering network for external transmission; The turbine expander (12) is connected to a generator (13), and the turbine expander (12) drives the generator (13) to generate electricity; the generator (13) is electrically connected to the electric heater (11).

2. The natural gas wellhead heating and pressure reduction system according to claim 1, characterized in that: It also includes a bypass pressure stabilizing module, and the turbine expander (12) and the electric heater (11) are connected in parallel to the bypass pressure stabilizing module.

3. The natural gas wellhead heating and pressure reduction system according to claim 2, characterized in that: It also includes a bypass pressure stabilization module; the high-temperature natural gas coming out of the water bath heating furnace (14) is divided into two paths, one path of the high-temperature natural gas enters the turbine expander (12), and the other path of the high-temperature natural gas is divided into two paths of stabilized pressure gas after passing through the bypass pressure stabilization module, one path of the stabilized pressure gas enters the gas gathering network for external transmission, and the other path of the stabilized pressure gas provides fuel gas for the water bath heating furnace (14).

4. The natural gas wellhead heating and pressure reduction system according to claim 3 is characterized in that: It also includes a pressure reducing gas supply module; another path of stabilized pressure gas enters the water bath heating furnace (14) for heating, and the heated stabilized pressure gas is divided into three paths, the first path enters the turbine expander (12), the second path enters the bypass pressure stabilizing module, and the third path enters the pressure reducing gas supply module. The natural gas after the pressure reduction of the pressure in the pressure reducing gas supply module enters the water bath heating furnace (14) as fuel gas for combustion.

5. The natural gas wellhead heating and pressure reduction system according to claim 4, characterized in that: The pressure reducing air supply module is a throttle valve.

6. The natural gas wellhead heating and pressure reduction system according to claim 2, characterized in that: The bypass voltage stabilizing module is a throttle valve.

7. A natural gas wellhead heating and pressure reduction method, characterized in that: Based on the system described in claim 1, the natural gas coming out of the natural gas wellhead is preheated by the electric heater (11) and then transported to the water bath heating furnace (14) for heating. The heated high-temperature natural gas enters the turbine expander (12) to reduce the pressure. The pressure difference is converted into kinetic energy to drive the turbine expander (12) to rotate. The rotation of the turbine expander (12) drives the generator (13) to generate electricity. The generator (13) supplies power to the electric heater (11). The low-temperature natural gas discharged from the turbine expander (12) is heated by the electric heater (11) and then transported out through the gas gathering pipeline network.

8. A natural gas wellhead heating and pressure reduction method, characterized in that: Based on the system described in claim 2, the natural gas coming out of the natural gas wellhead is preheated by the electric heater (11) and then transported to the water bath heating furnace (14) for heating. The heated high-temperature natural gas is divided into two paths. One path of the high-temperature natural gas enters the turbine expander (12) to reduce the pressure, and the pressure difference is converted into kinetic energy to drive the turbine expander (12) to rotate. The rotation of the turbine expander (12) drives the generator (13) to generate electricity. The generator (13) supplies power to the electric heater (11). The low-temperature natural gas discharged from the turbine expander (12) is heated by the electric heater (11) and then transported out through the gas gathering network; the other path of the high-temperature natural gas enters the bypass pressure stabilization module, and the pressure-stabilized gas coming out of the bypass pressure stabilization module is transported out through the gas gathering network.

9. A natural gas wellhead heating and pressure reduction method, characterized in that: Based on the system described in claim 3, the natural gas coming out of the natural gas wellhead is preheated by the electric heater (11) and then transported to the water bath heating furnace (14) for heating. The heated high-temperature natural gas is divided into two paths. One path of the high-temperature natural gas enters the turbine expander (12) to reduce the pressure, and the pressure difference is converted into kinetic energy to drive the turbine expander (12) to rotate. The rotation of the turbine expander (12) drives the generator (13) to generate electricity. The generator (13) supplies power to the electric heater (11). The low-temperature natural gas discharged from the turbine expander (12) is heated by the electric heater (11) and then transmitted to the outside through the gas collection network; the other path of the high-temperature natural gas enters the bypass pressure stabilizing module, and the stabilized gas coming out of the bypass pressure stabilizing module is divided into two paths. One path of the stabilized gas enters the gas collection network for transmission, and the other path of the stabilized gas provides fuel gas for the water bath heating furnace (14).

10. A natural gas wellhead heating and pressure reduction method, characterized in that: Based on the system described in claim 4, the natural gas coming out of the natural gas wellhead is preheated by the electric heater (11) and then transported to the water bath heating furnace (14) for heating. The heated high-temperature natural gas is divided into two paths. One path of the high-temperature natural gas enters the turbine expander (12) to reduce the pressure. The pressure difference is converted into kinetic energy to drive the turbine expander (12) to rotate. The rotation of the turbine expander (12) drives the generator (13) to generate electricity. The generator (13) supplies power to the electric heater (11). The low-temperature natural gas discharged from the turbine expander (12) is heated by the electric heater. The first path of high-temperature natural gas is heated by the gas collector (11) and then transported out through the gas collection network; the other path of high-temperature natural gas enters the bypass pressure stabilization module, and the pressure-stabilized gas coming out of the bypass pressure stabilization module is divided into two paths, one path of pressure-stabilized gas enters the gas collection network and then transported out, and the other path of pressure-stabilized gas enters the water bath heating furnace (14) for heating. The heated pressure-stabilized gas is divided into three paths, the first path enters the turbine expander (12), the second path enters the bypass pressure stabilization module, and the third path enters the pressure-reducing gas supply module. The natural gas reduced in pressure by the pressure-reducing gas supply module is used as fuel gas and enters the water bath heating furnace (14) for combustion.

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