Natural gas differential pressure power generation and cold energy recovery method

Abstract

The invention discloses a natural gas differential pressure power generation and cold energy recovery method which comprises the steps that the outlet pressure of an expansion machine is set according to user requirements, and after high-pressure natural gas expands in the expansion machine to do work, the pressure of output natural gas is reduced, and the temperature is lowered; the expansion machine is connected with the reduction gear box which is connected with the generator, so that the reduction gear box is driven to operate and the generator is driven to generate electricity; low-temperature natural gas output by the expansion machine exchanges heat with gaseous carbon dioxide captured by the carbon dioxide capture station in the heat exchanger, the carbon dioxide is condensed, and the condensed liquid carbon dioxide enters the low-temperature storage tank to be stored and then is transported out through a vehicle or a pipeline to be used for reinjection oil displacement or burying; and the reheated natural gas is conveyed to downstream users through a pipeline. According to the method, natural gas expansion power generation and carbon dioxide liquefaction in the CCUS are combined, pressure energy contained in high-pressure natural gas can be fully excavated, generated cold energy is utilized, and the energy utilization rate is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of emission reduction and efficiency improvement in oilfield surface engineering, and particularly relates to a method for natural gas pressure difference power generation and cold energy recovery. Background Technique

[0002] Natural gas is a high-quality fuel with high calorific value and less pollution, and is one of the main energy sources. In order to increase the pipeline transportation volume, it is mostly transported in the pipeline at a higher pressure. The high-pressure natural gas transported by the high-pressure gas transmission main line needs to be depressurized at the natural gas receiving gate stations and pressure regulating stations in each city according to the gas use pressure requirements of downstream users. The pressure reduction generally adopts the method of directly reducing the pressure and temperature of the gas through a throttle valve (Joule-Thomson effect), and the pressure energy is completely consumed in overcoming the flow resistance and does not drive any mechanical work, resulting in energy waste. By using an expander for pressure reduction, the expander can drive a generator to generate electricity, producing electric energy and a large amount of cold energy. Its electric energy can be self-used or sold to the grid. Its cold energy can be used for refrigeration (ice making, cooling water) and gas storage (LNG, liquid CO 2 )

[0003] Carbon capture, utilization and storage (CCUS) is an important channel to achieve carbon neutrality. Liquid carbon dioxide is more flexible in use and is not restricted by the pipeline network construction area, so it can better utilize the carbon dioxide captured at the station. However, the liquefaction of carbon dioxide requires a large amount of cold energy, and the energy consumption of traditional refrigeration machines is high. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for natural gas pressure difference power generation and cold energy recovery, which combines natural gas expansion power generation with carbon dioxide liquefaction in CCUS, can fully exploit the pressure energy contained in high-pressure natural gas, utilize the generated cold energy, and improve the energy utilization rate.

[0005] To achieve the above purpose, the technical solution of the present application is: A method for natural gas pressure difference power generation and cold energy recovery, including:

[0006] Natural gas pressure reduction: Set the outlet pressure of the expander according to user requirements. After the high-pressure natural gas expands and does work in the expander, the output natural gas pressure decreases and the temperature decreases. The depressurized natural gas contains rich cold energy;

[0007] Expansion power generation: The expander is connected to a reduction gearbox, and the reduction gearbox is connected to a generator, thereby driving the reduction gearbox to operate and the generator to generate electricity. The generator supplies power to the external power grid connected to it;

[0008] Cold energy recovery and utilization: The low-temperature natural gas output by the expander exchanges heat with the gaseous carbon dioxide captured by the carbon dioxide capture station in the heat exchanger to condense the carbon dioxide. The condensed liquid carbon dioxide enters the low-temperature storage tank through the carbon dioxide gas-liquid separator and is then transported by vehicle or through an external pipeline for reinjection into oil reservoirs or storage; the natural gas after reheating is transported by pipeline to downstream users.

[0009] Furthermore, a first SDV emergency cut-off valve is provided between the high-pressure natural gas inlet and the expander, and a bypass pressure regulating valve group is provided between the high-pressure natural gas inlet and the low-pressure natural gas outlet.

[0010] Furthermore, the first BDV electric operation valve is connected to the bypass pressure regulating valve group, and a second BDV electric operation valve is provided between the bypass pressure regulating valve group and the low-pressure natural gas outlet.

[0011] Furthermore, the expander is connected to the low-pressure natural gas outlet through the cold energy recovery and utilization section.

[0012] Furthermore, the carbon dioxide gas enters the heat exchanger after being precooled by the pre-cooler and exchanges heat with the low-temperature natural gas. At this time, the low-temperature natural gas is reheated and the carbon dioxide is liquefied.

[0013] Even further, the liquefied carbon dioxide enters the carbon dioxide gas-liquid separator after being regulated in pressure and cooled by the first throttle valve.

[0014] Even further, the gas coming out of the top of the carbon dioxide gas-liquid separator enters the pre-cooler to recover cold energy after being regulated in pressure and cooled by the second throttle valve.

[0015] Even further, the liquid coming out of the bottom of the carbon dioxide gas-liquid separator enters the low-temperature storage tank for liquid carbon dioxide through the operation valve.

[0016] Even further, the low-temperature storage tank for liquid carbon dioxide is stored in the station and is pressurized by a loading pump when needed and transported through a loading hose to the tanker for external transportation.

[0017] Due to the adoption of the above technical solutions, the present invention can achieve the following technical effects:

[0018] (1) A new technical solution for natural gas pressure regulation is proposed, solving the problem of energy waste in pressure regulation using throttle valves; taking the natural gas flow rate of 2.6 million cubic meters per day and the pressure adjusted from 1.9 MPa to 0.5 MPa as an example, the power generation capacity can reach 2500 kW.

[0019] (2) It is selected to reheat the natural gas by exchanging heat with carbon dioxide, avoiding the energy consumption of traditional heat exchange with hot water while meeting the subsequent long-distance transportation requirements.

[0020] (3) Using low-temperature natural gas to cool carbon dioxide saves the energy consumption of ice machines. Taking liquid carbon dioxide with an annual output of 40,000 tons as an example, 2.94 million kWh of electricity can be saved annually. Description of the Drawings

[0021] Figure 1 It is a schematic diagram of the partial process of expansion power generation;

[0022] Figure 2 It is a schematic diagram of the partial process of cold energy recovery and utilization;

[0023] Figure 3 It is a schematic diagram of the principle of the carbon dioxide storage part. Detailed Implementation Modes

[0024] The principles of the present disclosure will be described below with reference to several exemplary embodiments shown in the drawings. Although the preferred embodiments of the present disclosure are shown in the drawings, it should be understood that the description of these embodiments is only to enable those skilled in the art to better understand and thus implement the present disclosure, rather than limiting the scope of the present disclosure in any way.

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the specification of the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Usually, the components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0026] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the present application claimed, but merely represents the selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts fall within the scope of protection of the present application.

[0027] It should be noted that in this article, the term "including", "comprising", or any other variant thereof is intended to cover non-exclusive inclusion, so that an article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such a process, method, article, or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, method, article, or device including the element.

[0028] In the description of the present application, the orientation or positional relationship indicated by terms such as "upper", "lower", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of this application is customarily placed during use. It is only for the convenience of describing the present application 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 should not be construed as a limitation to the present application.

[0029] In the description of the present application, it should also be noted that unless otherwise clearly specified and defined, the terms "arranged" 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 directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0030] The term "including" and its variations are used to indicate open inclusion, that is, "including but not limited to". Unless otherwise stated specifically, the term "or" means "and / or". The term "based on" means "at least partially based on". The terms "an example embodiment" and "an embodiment" mean "at least one example embodiment". The term "another embodiment" means "at least one additional embodiment". The terms "first", "second", etc. can refer to different or the same objects. There may also be other explicit and implicit definitions below.

[0031] The following will, with reference to the drawings, elaborate on some embodiments of the present application. As Figures 1-3 shown, this embodiment provides a method for natural gas pressure difference power generation and cold energy recovery, including:

[0032] Natural gas at normal temperature and high pressure (taking 2 MPa as an example) is transported through the upstream pipeline network to the pressure regulating station, and then transported to the natural gas turbine expansion generator through the pipeline in the station. The high-pressure natural gas expands and does work in the turbine expander of the natural gas turbine expansion generator. The main work of the turbine expander is completed by the nozzles and impellers inside it. After passing through the expander nozzles, the velocity of the high-pressure gas rises rapidly and can reach the speed of sound. The high-speed gas impacts the impeller to make the impeller rotate. The rotation of the impeller drives power generation devices such as generators to generate electricity. When the impeller speed exceeds normal, the configured reduction gearbox can reduce the speed of the impeller to ensure the normal operation of the subsequent power generation devices such as generators. The expansion energy drives the reduction gearbox connected to the turbine expander to operate and the generator to generate electricity. At the same time, the natural gas pressure is reduced to 1.0 MPa and the temperature is reduced to -29 °C. The low-temperature and low-pressure natural gas after expansion power generation is transported to the cold energy recovery and utilization unit for heat exchange to recover cold energy. After heat exchange, the temperature of the natural gas rises above 0 °C, and the obtained normal-temperature and low-pressure natural gas enters the low-pressure natural gas pipeline and is transported downstream for users to use.

[0033] In an exemplary embodiment, a bypass pressure regulating valve group is provided between the high-pressure natural gas inlet and the low-pressure natural gas outlet. This bypass pressure regulating valve group is the currently common decompression system based on the J-T throttle valve for regulating high-pressure natural gas to low-pressure natural gas. The purpose of setting this bypass pressure regulating valve group is that once the turbine expansion unit and the heat exchanger are damaged and cannot perform normal expansion power generation and cold energy recovery, the SDV emergency cut-off valve closes, and at the same time, the first BDV electric operation valve and the second BDV electric operation valve are interlocked to open, and this bypass pressure regulating valve group is started to regulate high-pressure natural gas to low-pressure natural gas, which belongs to the standby pressure regulating valve group.

[0034] The 3.0 MPa carbon dioxide gas is precooled to 34 °C through a precooler and then enters the natural gas-carbon dioxide heat exchanger to exchange heat with the low-temperature natural gas. The natural gas is reheated to 0 °C. The carbon dioxide is cooled to -20 °C, and at this time, the carbon dioxide is in a liquid state. The liquefied carbon dioxide enters the carbon dioxide gas-liquid separator.

[0035] The liquefied carbon dioxide liquid contains some incompletely liquefied components and non-condensable gases. In order to separate the incompletely liquefied components and non-condensable gases in the carbon dioxide liquid, a carbon dioxide gas-liquid separator needs to be set up to separate the non-condensable gases contained in the liquid carbon dioxide. The pressure of the liquefied carbon dioxide liquid is 2.8 MPa. At this time, it cannot directly enter the liquid storage tank because the storage pressure of the carbon dioxide low-temperature liquid storage tank is 2.2 MPa. Therefore, a first throttle valve needs to be set up to throttle the liquefied carbon dioxide from 2.8 MPa to 2.2 MPa. The carbon dioxide liquid is throttled from 2.8 MPa to 2.2 MPa through the first throttle valve. At the same time, the temperature of the liquid carbon dioxide further decreases to -25 °C, making the carbon dioxide further fully liquefied, and then enters the carbon dioxide gas-liquid separator.

[0036] The non-condensable gas separated from the top of the carbon dioxide gas-liquid separator needs to be throttled from 2.2 MPa to 0.3 MPa through the second throttle valve. After throttling, the temperature is -52 °C. The cold energy is recovered through the pre-cooler and raised to 20 °C, and then returned to the carbon dioxide capture device to reduce carbon dioxide venting and increase the carbon dioxide recovery rate.

[0037] The separated carbon dioxide liquid at the bottom of the carbon dioxide gas-liquid separator enters the low-temperature storage tank for liquid carbon dioxide for storage. The liquefied carbon dioxide needs to be stored in the station and loaded and transported out by truck when needed. Two loading pumps are set up for loading operations. The liquid carbon dioxide is pressurized by the loading pump and transported to the tanker through the loading hose.

[0038] The development of this technology is based on the projects of "Natural Gas Pressure Difference Power Generation and Cold Energy Comprehensive Utilization in Shuguang Pressure Regulation Station" and "Pilot Surface Project for Carbon Dioxide Capture, Enhanced Oil Recovery and Emission Reduction in Huanxiling and Tahe Oilfields of Liaohe Oilfield". The annual power generation can reach 1695×10 4 kWh, saving 294×10 4 kWh of electricity for liquefied carbon dioxide refrigeration ice machines, and reducing carbon emissions by 13,126 t per year. This technology will be promoted and used in the future for emission reduction and efficiency improvement in oilfield surface engineering.

[0039] The above description is only an optional embodiment of the present disclosure and is not intended to limit the present disclosure. For those skilled in the art, various changes and modifications can be made to the present disclosure. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure shall be included within the protection scope of the present disclosure.

[0040] Although the claims in this application have been formulated for specific combinations of features, it should be understood that the scope of the present disclosure also includes any novel feature or any novel combination of features that are explicitly or implicitly disclosed herein or any generalization thereof, regardless of whether it relates to the same solution as any of the currently claimed claims.

Claims

1. A method for natural gas pressure difference power generation and cold energy recovery, characterized in that, it includes: Natural gas pressure reduction: Set the outlet pressure of the expander according to user requirements. After the high-pressure natural gas expands and does work in the expander, the output natural gas pressure decreases and the temperature drops. The decompressed natural gas contains rich cold energy; Expansion power generation: The expander is connected to a reduction gearbox, and the reduction gearbox is connected to a generator, thereby driving the reduction gearbox to operate and the generator to generate electricity. The generator supplies power to the external power grid connected to it; Cold energy recovery and utilization: The low-temperature natural gas output by the expander exchanges heat with the gaseous carbon dioxide captured by the carbon dioxide capture station in the heat exchanger to condense the carbon dioxide. The condensed liquid carbon dioxide enters the low-temperature storage tank through the carbon dioxide gas-liquid separator and is then transported by vehicle or piped out; The reheated natural gas is piped to downstream users.

2. The method for natural gas pressure difference power generation and cold energy recovery according to claim 1, characterized in that, A first SDV emergency cut-off valve is provided between the high-pressure natural gas inlet and the expander, and a bypass pressure regulating valve group is provided between the high-pressure natural gas inlet and the low-pressure natural gas outlet.

3. The method for natural gas pressure difference power generation and cold energy recovery according to claim 2, characterized in that, The first BDV electric operation valve is connected to the bypass pressure regulating valve group, and a second BDV electric operation valve is provided between the bypass pressure regulating valve group and the low-pressure natural gas outlet.

4. The method for natural gas pressure difference power generation and cold energy recovery according to claim 1, characterized in that, The expander is connected to the low-pressure natural gas outlet through the cold energy recovery and utilization part.

5. The method for natural gas pressure difference power generation and cold energy recovery according to claim 1, characterized in that, The carbon dioxide gas enters the heat exchanger after being precooled by a precooler and exchanges heat with the low-temperature natural gas. At this time, the low-temperature natural gas is reheated and the carbon dioxide is liquefied.

6. The method for natural gas pressure difference power generation and cold energy recovery according to claim 5, characterized in that, The liquefied carbon dioxide enters the carbon dioxide gas-liquid separator after being pressure-regulated and temperature-reduced by a first throttle valve.

7. The method for natural gas pressure difference power generation and cold energy recovery according to claim 6, characterized in that, The gas coming out of the top of the carbon dioxide gas-liquid separator enters the precooler to recover cold energy after being pressure-regulated and temperature-reduced by a second throttle valve.

8. The method for natural gas pressure difference power generation and cold energy recovery according to claim 6, characterized in that, The liquid coming out of the bottom of the carbon dioxide gas-liquid separator enters the low-temperature storage tank for liquid carbon dioxide through an operation valve.

9. The method for natural gas pressure difference power generation and cold energy recovery according to claim 8, characterized in that, The low-temperature storage tank for liquid carbon dioxide is stored in the station and is pressurized by a loading pump when needed and transported to the tanker through a loading hose for external transportation.

Images