A surplus energy power generation system and method for a natural gas transmission compressor station

Abstract

A kind of surplus energy power generation system for natural gas distribution pressurizing station, system includes: natural gas compression subsystem for providing compressed natural gas, its inlet is the natural gas inlet of system, i.e. upstream natural gas, its outlet is compressed high pressure natural gas, continue to be transported to remote city;Natural gas expansion subsystem for providing medium pressure natural gas and low pressure natural gas, its inlet is the natural gas inlet of system, i.e. upstream natural gas, its outlet is expanded medium pressure natural gas and low pressure natural gas, respectively transported to peripheral remote and peripheral close city;Organic rankine cycle subsystem, with the hot gas stream of the compressed natural gas output as heat inlet, carries out power generation.The present application can provide pressure suitable natural gas for close, medium, remote three places respectively, and effectively utilize the waste heat when natural gas distribution pressurizes, improve system energy utilization rate, make the whole system energy maximization utilization, reduce the consumption of fossil fuel and greenhouse gas, pollution gas emission.

Description

Technical Field

[0001] This invention belongs to the field of energy technology, and relates to the fields of natural gas distribution and pressurization and organic Rankine cycle, and particularly to a waste energy power generation system and method for natural gas distribution and pressurization stations. Background Technology

[0002] Natural gas distribution and pressurization, as an important energy transmission and storage technology, has a wide range of applications. It enables long-distance transmission and supply of natural gas, meeting energy demands in various sectors and promoting economic development and improved living standards. During the operation of natural gas distribution and pressurization stations, natural gas is pressurized or depressurized, allowing it to be transported downstream via pipelines or delivered to cities to supply gas, meeting the needs of residential and industrial users. Simultaneously, pressurized natural gas can be transported to industrial parks or factories for use as energy in industrial production. However, currently, the energy utilization methods of natural gas distribution and pressurization systems are relatively singular, still requiring the consumption of fossil fuels for supplementary combustion. This leads to increased carbon emissions alongside energy consumption. Summary of the Invention

[0003] In order to overcome the shortcomings of the prior art, the present invention aims to provide a waste energy power generation system and method for natural gas distribution and pressurization stations. By utilizing the heat generated during natural gas compression and pressurization and the cold energy generated during expansion and decompression, organic Rankine cycle power generation is carried out to improve the energy utilization rate of natural gas distribution and pressurization stations, minimize the energy loss of the entire system, and reduce energy loss and carbon emissions.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] 1. A waste energy power generation system for a natural gas distribution and pressurization station, characterized in that it comprises:

[0006] The natural gas compression subsystem is used to provide high-pressure natural gas and system heat source, and its natural gas source is a portion of the upstream natural gas input into the system;

[0007] The natural gas expansion subsystem is used to provide medium and low-pressure natural gas and system cooling source, and its natural gas source is a portion of the upstream natural gas input into the system;

[0008] The organic Rankine cycle subsystem generates electricity by circulating the heat and cold produced during the operation of the natural gas compression subsystem and the natural gas expansion subsystem.

[0009] 2. The waste energy power generation system for a natural gas distribution and pressurization station according to claim 1, characterized in that the natural gas compression subsystem is composed of a compressor assembly and a heat exchanger assembly, and the natural gas is compressed by multi-stage compression and inter-stage cooling, and the high-temperature natural gas obtained is used as the system heat source;

[0010] The natural gas expansion subsystem consists of an expander assembly and a heat exchanger assembly. It expands natural gas using a multi-stage expansion and inter-stage heating method, and the resulting low-temperature natural gas serves as the system's cold source.

[0011] 3. The waste energy power generation system for a natural gas distribution and pressurization station according to claim 2, characterized in that, in the natural gas compression subsystem, the compressor assembly consists of N compressors connected in series, the heat exchanger assembly consists of N heat exchangers connected in series, the outlet natural gas of each compressor is fed into the heat exchanger to release the heat of compression to the liquid organic working medium, heat and vaporize the liquid organic working medium, and the natural gas flowing out of the heat exchanger is fed into the next stage compressor until it is compressed to the target pressure;

[0012] In the natural gas expansion subsystem, the expander assembly consists of M expanders connected in series, and the heat exchanger assembly consists of M heat exchangers connected in series. The outlet natural gas of each expander is fed into the heat exchanger to condense the gaseous organic working fluid after work into a liquid state. The natural gas flowing out of the heat exchanger is fed into the next stage expander until the expansion pressure is reduced to the target pressure.

[0013] 4. The waste heat power generation system for a natural gas distribution and pressurization station according to claim 2, characterized in that the organic Rankine cycle subsystem includes a main organic Rankine cycle and several auxiliary organic Rankine cycles; the main organic Rankine cycle includes at least one expander and at least one working fluid pump, the preheater of the first K stage of the natural gas compression subsystem and the preheater of the first L stage of the natural gas expansion subsystem are connected to the main organic Rankine cycle, and the waste heat generated by the first K stage compressor is used for power generation in this cycle; the waste heat generated by the remaining compressors is used for power generation in each auxiliary organic Rankine cycle; the organic working fluid is vaporized and expanded to generate electricity in the organic Rankine cycle using the heat provided by the natural gas compression subsystem, and after the work is completed, it releases heat to the natural gas expansion subsystem and is liquefied again.

[0014] 5. The waste heat power generation system for a natural gas distribution and pressurization station according to claim 4, characterized in that, in the main organic Rankine cycle, a common regenerator is added between its expander and the L-stage preheater of the natural gas expansion subsystem, and between the working fluid pump and the K-stage preheater of the natural gas compression subsystem. The exhaust steam from the expander in the main organic Rankine cycle and the liquid organic working fluid pressurized by the working fluid pump are respectively introduced into both sides of the regenerator. The liquid organic working fluid is heated by the exhaust steam and enters the preheater of the natural gas compression subsystem. The exhaust steam is cooled by the liquid working fluid and enters the preheater of the natural gas expansion subsystem. The regenerator also exists in the auxiliary organic Rankine cycle.

[0015] 6. The waste heat power generation system for a natural gas distribution and pressurization station according to claim 5, characterized in that, in the natural gas compression subsystem, the first-stage heat exchanger is a preheater, and subsequent heat exchangers are evaporators; the heat source inlet of the preheater is high-temperature natural gas compressed by the first-stage compressor, and the cold source inlet is liquid organic working fluid pumped by the working fluid pump; the heat source inlet of the first-stage evaporator is high-temperature natural gas compressed by the second-stage compressor, and the cold source inlet is organic working fluid preheated by the preheater; the heat source inlet of subsequent evaporators is high-temperature natural gas compressed by the preceding stage compressor, and the cold source inlet is liquid organic working fluid pumped by the working fluid pump in the auxiliary organic Rankine cycle in which it is located.

[0016] 7. The waste heat power generation system for a natural gas distribution and pressurization station according to claim 6, characterized in that, in the natural gas expansion subsystem, the heat exchanger is a condenser, the heat source side inlet of the first-stage condenser is the gaseous organic working fluid after the work done by the expander in the main organic Rankine cycle, the cold source side inlet is the low-temperature natural gas after the work done by the first-stage expander in the natural gas expansion subsystem, the heat source side inlet of subsequent condensers is the gaseous organic working fluid after the work done by the expander in the auxiliary organic Rankine cycle in which it is located, and the cold source side inlet is the low-temperature natural gas after pre-cooling by the previous stage condenser.

[0017] 8. The waste heat power generation system for a natural gas distribution and pressurization station according to claim 7, characterized in that the natural gas after the last stage evaporator of the natural gas compression subsystem is high-pressure natural gas, which is continued to be transported downstream; the natural gas after the last stage condenser of the natural gas expansion subsystem is medium-pressure natural gas, which is transported to distant cities; and the natural gas after the pressure reduction of the last stage expander of the natural gas expansion subsystem is low-pressure natural gas, which is transported to nearby cities.

[0018] 9. The waste energy power generation system for a natural gas distribution and pressurization station according to claim 1, characterized in that each compressor and expander is selected to be coaxial or non-coaxial according to the spatial layout of the entire system, or the compressor and some expanders are coaxial and some are non-coaxial.

[0019] 10. A method for combined cooling and heating of natural gas in a waste heat power generation system for a natural gas distribution and pressurization station as described in claim 1, characterized in that the process is as follows:

[0020] A portion of the upstream natural gas is compressed using a natural gas compression subsystem to obtain high-temperature, high-pressure natural gas.

[0021] By using a natural gas expansion subsystem, a portion of the upstream natural gas is expanded to obtain low-temperature, medium-low-pressure natural gas;

[0022] The low-temperature, medium-low-pressure natural gas and high-temperature, high-pressure natural gas are used as the heat source and cold source for the organic Rankine cycle to generate electricity.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. This invention utilizes a tiered operation of a compression system and a natural gas expansion subsystem to convert upstream natural gas into natural gas at three pressures: high pressure, medium pressure, and low pressure, thereby enabling the transportation of natural gas to different destinations.

[0025] 2. This invention adopts the principle of high-efficiency utilization of low-grade energy, which efficiently utilizes the heat generated by compressed natural gas to provide heat for the organic Rankine cycle subsystem, drives the organic working fluid to be converted into a high-enthalpy gaseous state, and expands in the expander to do work, thereby driving the generator to generate electricity, thus realizing the collection and utilization of low-grade energy.

[0026] 3. This invention utilizes the cooling energy obtained from expanding upstream natural gas to condense the organic working fluid, thereby achieving the liquefaction and recirculation of the working fluid in the organic Rankine cycle while obtaining low-pressure natural gas, without the need for an additional cooling system, thus simplifying the system structure.

[0027] 4. The system of the present invention couples the vortex tube with the air compression system and the organic Rankine cycle subsystem, resulting in a compact structure. The diversity of choices in components and forms makes the whole system more adaptable, while the reasonable distribution of flow makes the system operation more flexible.

[0028] 5. The regenerator added in this invention realizes a single-stage regenerating organic Rankine cycle, which can reduce the heat source and cold source losses of the organic Rankine cycle subsystem, further increase the cycle efficiency, and optimize the outlet natural gas temperature status.

[0029] In summary, compared with conventional natural gas distribution and pressurization technologies, this invention has a high energy utilization rate, simplifies complex equipment, reduces energy consumption and carbon emissions, and can also solve users' electricity and gas problems. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of the present invention.

[0031] Wherein, 1 is compressor #1, 2 is compressor #2, 3 is preheater, 4 is evaporator #1, 5 is compressor #3, 6 is evaporator #2, 7 is working fluid pump #1, 8 is expander #1, 9 is working fluid pump #2, 10 is expander #2, 11 is condenser #1, 12 is condenser #2, 13 is expander #3, 14 is expander #4, 15 is natural gas inlet pipeline, 16 is high-pressure natural gas outlet pipeline, 17 is medium-pressure natural gas outlet pipeline, and 18 is low-pressure natural gas outlet pipeline. Detailed Implementation

[0032] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings and examples.

[0033] like Figure 1 As shown, the present invention is a waste energy power generation system for a natural gas distribution and pressurization station, mainly including a natural gas compression subsystem, a natural gas expansion subsystem, and an organic Rankine cycle subsystem. The natural gas compression subsystem provides high-pressure natural gas and system heat source, the natural gas compression subsystem provides low-pressure natural gas and system cold source, and the organic Rankine cycle subsystem utilizes the heat and cold generated during the compression and expansion of natural gas to perform cyclic work and generate electricity.

[0034] The above is the subject matter and technical route of the present invention. Based on this, the following details or further optimizations are provided.

[0035] 1. Natural gas compression subsystem.

[0036] In this invention, the natural gas compression subsystem primarily provides high-pressure natural gas and a system heat source, with the natural gas source being a portion of the upstream natural gas input into the system. To meet the requirements of obtaining high-pressure natural gas for continued downstream transport and efficiently utilizing the heat generated during natural gas compression, the natural gas compression subsystem can be constructed using a compressor assembly and a heat exchanger assembly. To fully utilize the heat generated during compression and reduce compressor power, the compressor assembly and heat exchanger assembly employ multi-stage compression and interstage cooling to compress the natural gas, with the resulting high-temperature natural gas serving as the system heat source. Specifically, the compressor assembly consists of N compressors connected in series, and the heat exchanger assembly consists of N heat exchangers connected in series. The outlet natural gas from each compressor is fed into a heat exchanger to release the heat of compression onto the liquid organic working fluid, heating and vaporizing it. The natural gas flowing out of the heat exchanger is then fed into the next stage compressor until the target pressure is reached.

[0037] In the natural gas compression subsystem of this invention, the first-stage heat exchanger is named a preheater, and subsequent heat exchangers are evaporators. The preheater's heat source inlet is high-temperature natural gas compressed by the first-stage compressor, and its cold source inlet is liquid organic working fluid drawn by the working fluid pump. The first-stage evaporator's heat source inlet is high-temperature natural gas compressed by the second-stage compressor, and its cold source inlet is organic working fluid preheated by the preheater. The subsequent evaporators' heat source inlets are high-temperature natural gas compressed by the preceding compressor, and their cold source inlets are liquid organic working fluid drawn by the working fluid pump in their respective auxiliary organic Rankine cycle. The natural gas after the last-stage evaporator in the natural gas compression subsystem is high-pressure natural gas, which continues to be transported downstream.

[0038] This invention is in Figure 1In the illustrated embodiment, a three-stage compression and three-stage cooling system is selected, i.e., N=3. The compressor assembly includes compressor 1 (1), compressor 2 (2), and compressor 5 (5) connected in series from the system's natural gas inlet to its outlet. The inlet gas of compressor 1 is the system's inlet natural gas, i.e., upstream natural gas, and the outlet gas of compressor 3 is the system's high-pressure natural gas outlet gas. The heat exchanger assembly includes a preheater 3, an evaporator 4 (1), and an evaporator 6 (2). The outlet of compressor 1 is connected to the heat source side inlet of preheater 3, the heat source side outlet of preheater 3 is connected to the inlet of compressor 2, the outlet of compressor 2 is connected to the heat source side inlet of evaporator 4, the heat source side outlet of evaporator 4 is connected to the inlet of compressor 5, the outlet of compressor 5 is connected to the heat source side inlet of evaporator 6, and the heat source side outlet of evaporator 6 is connected to the downstream high-pressure natural gas pipeline 16. The cold source side inlets of the preheater 3, evaporator 4 (1#), and evaporator 6 (2#) are all liquid organic working fluids pressurized by pumps. The liquid organic working fluids will be vaporized in the heat exchanger and then fed into the expander to drive the engine to do work, thereby realizing the utilization of waste heat.

[0039] 2. Natural gas expansion subsystem.

[0040] In this invention, the natural gas expansion subsystem is mainly used to provide medium- and low-pressure natural gas and system cooling. Its natural gas source is a portion of the upstream natural gas input into the system. To obtain natural gas for supply to cities at both distant and nearby locations and to provide cooling to the system, the natural gas expansion subsystem can be constructed using an expander assembly and a heat exchanger assembly. To obtain natural gas at different pressures for supplying distant and nearby cities respectively, the upstream natural gas needs to undergo expansion and decompression to different degrees. This invention employs multi-stage expansion and interstage heating to expand the natural gas, with the resulting low-temperature natural gas serving as the system cooling source. Specifically, the expander assembly consists of M expanders connected in series, and the heat exchanger assembly consists of M heat exchangers connected in series. The outlet natural gas from each expander is fed into the heat exchanger to condense the gaseous organic working fluid after work into a liquid state. The natural gas flowing out of the heat exchanger is fed into the next-stage expander until the expansion and decompression reach the target pressure. During the expansion and decompression process, this invention yields low-temperature natural gas, which provides cooling to the system, condensing the gaseous organic working fluid after work into a liquid state so that it can continue to circulate.

[0041] In the natural gas expansion subsystem of this invention, the heat exchanger is a condenser. The heat source inlet of the first-stage condenser is the gaseous organic working fluid after work done by the expander in the main organic Rankine cycle, and the cold source inlet is the low-temperature natural gas after work done by the first-stage expander in the natural gas expansion subsystem. The heat source inlets of subsequent condensers are the gaseous organic working fluid after work done by the expander in the auxiliary organic Rankine cycle in which they are located, and the cold source inlets are the low-temperature natural gas pre-cooled by the preceding condenser. The natural gas after the last-stage condenser of the natural gas expansion subsystem is medium-pressure natural gas, which is transported to distant cities. The natural gas after depressurization by the last-stage expander of the natural gas expansion subsystem is low-pressure natural gas, which is transported to nearby cities.

[0042] This invention is in Figure 1 In the illustrated embodiment, a two-stage expansion and two-stage cooling system is selected, i.e., M=2. The expander assembly includes expander #3 (13) and expander #4 (14) connected in series from the system's natural gas inlet to outlet. The inlet gas of expander #3 (13) is the system's inlet natural gas, i.e., upstream natural gas, and the outlet gas of expander #4 (14) is the system's low-pressure natural gas outlet gas. The heat exchanger assembly includes condenser #1 (11) and condenser #2 (12). The outlet of compressor #3 is connected to the inlet of condenser #1 (11). The outlet of condenser #1 (11) is medium-pressure natural gas, which is divided into two streams. One stream flows into condenser #2 (12) and exits from its outlet, then is transported to a more distant city via medium-pressure natural gas outlet pipeline 17. The other stream flows into expander #4 (14) for further expansion and decompression, and exits from its outlet, then is transported to a more nearby city via low-pressure natural gas outlet pipeline 18. The heat source side inlets of condenser #11 and condenser #22 are both gaseous organic working fluids after the work is completed. The gaseous organic working fluids will be liquefied in the heat exchanger and pressurized by the working fluid pump, requiring only circulation.

[0043] 3. Organic Rankine Cycle Subsystem.

[0044] The organic Rankine cycle subsystem is a key component of this invention. It utilizes the heat and cold provided by the natural gas compression and expansion subsystems to undergo phase change and continuously generate electricity. Specifically, the organic working fluid is heated to a high-temperature gaseous state, which is then used as a generator by an expander to generate electricity. The low-enthalpy gaseous organic working fluid after power generation is condensed, pressurized by a working fluid pump, and continues to enter the cycle.

[0045] The organic Rankine cycle subsystem of the present invention includes a main organic Rankine cycle and several auxiliary organic Rankine cycles; wherein the main organic Rankine cycle includes at least one expander and at least one working fluid pump, the preheater of the first K stage of the natural gas compression subsystem and the preheater of the first L stage of the natural gas expansion subsystem are connected to the main organic Rankine cycle, and the waste heat generated by the first K stage compressor is used for power generation in the main organic Rankine cycle; while the waste heat generated by the remaining compressors is used for power generation in each of the auxiliary organic Rankine cycles; the organic working fluid is vaporized and expanded to generate electricity in the organic Rankine cycle using the heat provided by the natural gas compression subsystem, and after the work is completed, it releases heat to the natural gas expansion subsystem and is liquefied again.

[0046] exist Figure 1 In the illustrated embodiment, there are two-stage organic Rankine cycle subsystems. The first-stage organic Rankine cycle subsystem utilizes the preheater 3 and evaporator 4 to collect the heat generated when compressors 1 and 2 compress natural gas, heating and vaporizing the working fluid. This vaporized fluid is then fed into expander 8 to drive a generator for power generation. After performing work, the enthalpy of the gaseous organic working fluid decreases, and it is fed into condenser 11, where it is condensed using the cooling energy generated by expander 3. The condensed liquid working fluid is then pressurized by pump 7 and enters the next cycle. The first-stage Rankine cycle is the main waste heat utilization cycle of the system, utilizing a large amount of waste heat and generating a large amount of electricity. Therefore, it requires a high amount of heat and cooling energy, and thus connects two sets of compression heat exchange devices and expander 3 (which expands a large amount of natural gas).

[0047] Currently, the standard pressure of natural gas transmission pipelines is 80 bar, and the pipeline can withstand a standard pressure of 114 bar. The outlet gas of evaporator 4 (No. 1) already has a relatively high pressure, requiring only one compression at most to meet the standards for downstream transportation. Therefore, only one high-temperature compressed natural gas provides heat for the secondary organic Rankine cycle. Furthermore, the outlet gas of condenser 11 (No. 1) needs to be split into two streams. One stream needs to be converted into low-pressure natural gas through expander 14 (No. 4) and transported to nearby cities. Therefore, only the other stream can provide cooling for the secondary organic Rankine cycle. Thus, the secondary organic Rankine cycle subsystem is a secondary organic Rankine cycle subsystem with a smaller work output but more efficient waste heat utilization.

[0048] In this invention, the organic Rankine cycle subsystem can use working fluids such as R245fa, R11, and R12, or a mixture of two or more organic working fluids that meet the operating conditions. Depending on the system's operating conditions and requirements, the organic working fluid can be replaced; this invention uses "organic working fluid" as a general term.

[0049] This invention allows for the addition of regenerators to a two-stage organic Rankine cycle to achieve a regenerative cycle. Specifically, in the main organic Rankine cycle, a shared regenerator is added between the expander and the L-stage preheater of the natural gas expansion subsystem, and between the working fluid pump and the K-stage preheater of the natural gas compression subsystem. The regenerator is fed with exhaust steam from the expander in the main organic Rankine cycle and pressurized liquid organic working fluid from the working fluid pump, respectively. The liquid organic working fluid is heated by the exhaust steam and then enters the preheater of the natural gas compression subsystem. The exhaust steam is cooled by the liquid working fluid and then enters the preheater of the natural gas expansion subsystem. A regenerator is also present in the auxiliary organic Rankine cycle. Taking a single-stage Rankine cycle as an example, a shared regenerator is added between the #1 expander 8 and the #1 condenser 11, and between the #1 working fluid pump 7 and the preheater 3. The regenerator is fed with exhaust steam from the #1 expander 8 and pressurized liquid organic working fluid from the #1 working fluid pump 7 on its two sides, respectively. The liquid working fluid is heated by the exhaust steam from the #1 expander 8 and then enters the preheater 3. The exhaust steam from the #1 expander 8 is cooled by the liquid working fluid and then enters the #1 condenser 11. The regenerator for a two-stage organic Rankine cycle is implemented similarly to that of the single-stage organic Rankine cycle.

[0050] Based on the above system, the workflow of the present invention is as follows:

[0051] In the primary and secondary organic Rankine cycle subsystems, the organic working fluid is first heated into a gaseous state using the hot natural gas generated by the compression system. This gas expands in expander 8 (1#) and expander 10 (2#), driving the engine to generate electricity. The cooled hot gas flow is then supplied to condenser 11 (1#) and condenser 12 (2#). In the organic Rankine cycle subsystem, the organic working fluid condenses from a gaseous state to a liquid state in condensers 11 (1#) and condenser 12 (2#). The heat released is absorbed by the low-temperature natural gas generated by the natural gas expansion subsystem. The condensed liquid working fluid is then pumped by pumps 7 (1#) and 9 (2#) to continue circulating in the primary and secondary organic Rankine cycle subsystems.

[0052] Specifically, firstly, compressors 1 and 2 pressurize a portion of the upstream natural gas (generally between 50 and 60 bar) to a higher pressure (generally around 70 bar). The heat generated from the two compressions is input into the first-stage organic Rankine cycle subsystem via preheater 3 and evaporator 4. In the first-stage Rankine cycle system, this heat is used to expand the gas through expander 8 to drive an engine for power generation. The gas is then condensed and pressurized through condenser 11 and working fluid pump 1, and the working fluid is reintroduced into the cycle. The higher-pressure natural gas after the two compressions is pressurized into high-pressure natural gas (generally around 85 bar) by compressor 5, and this heat is transferred to the second-stage organic Rankine cycle via evaporator 6 for power generation. The resulting high-pressure natural gas continues to be transported downstream over long distances. Another portion of the upstream medium-pressure natural gas is depressurized through expander 13. The resulting low-temperature natural gas provides cooling energy to the first-stage organic Rankine cycle through condenser 11, condensing the working fluid after its work is completed into a liquid state, ensuring smooth cycle operation and improving the cycle's power generation efficiency. Part of the outlet gas from condenser 11 passes through condenser 2 to provide cooling energy to the secondary organic Rankine cycle. The resulting medium-pressure natural gas (generally between 25 and 40 bar) enters the high-grade gas pipeline to supply natural gas to surrounding cities at a greater distance. The other part of the outlet gas from condenser 1 passes through expander 4 to reduce pressure and expand again. The resulting low-pressure natural gas (generally between 1 and 4 bar) can supply natural gas to nearby factories and cities around the distribution and booster station.

[0053] During the operation of the two-stage organic Rankine cycle subsystem, there are regenerators between the expander and condenser, and between the pump and evaporator, which can realize a regenerative cycle. By utilizing the heat exchange between the low-enthalpy gaseous working fluid after work and the low-pressure liquid working fluid after the pump, the working fluid after work is pre-cooled and the working fluid after the pump is preheated, thereby improving the thermal efficiency of the organic Rankine cycle.

[0054] In this invention, each compressor and expander is selected to be coaxial or non-coaxial according to the spatial layout of the entire system, or the compressor and some expanders are coaxial while some are non-coaxial. For example, in this embodiment, compressor 1, compressor 2, and compressor 5 are arranged coaxially, expander 13 and expander 14 are arranged coaxially, and expander 8 and expander 10 are respectively coaxially connected to their respective generator sets to generate electricity.

[0055] This invention features control valves at the inlet and between certain pipes in the system, all of which are electromagnetic and may include radio frequency control devices. The working fluid pump of this invention may be equipped with frequency converters and may be fitted with radio frequency control devices.

[0056] In summary, this invention utilizes the principle of energy cascading utilization to divert upstream natural gas, compressing and expanding it separately to obtain natural gas at three different pressures, which are then distributed to natural gas pipelines at different transport distances, achieving scientific natural gas distribution. Simultaneously, based on the principle of cascaded energy utilization, the heat of natural gas compression and the cold of natural gas expansion are effectively utilized to provide the necessary heat and cold for the organic Rankine cycle subsystem, enabling the organic Rankine cycle to operate without external energy input and fully and rationally utilizing waste heat and cold. The coupling of the natural gas compression subsystem, the natural gas expansion subsystem, and the two-stage organic Rankine cycle subsystem in this invention results in a simple and compact structure, alleviating system redundancy and improving system mechanical efficiency. Adding a regenerator to the organic Rankine cycle further improves its thermal efficiency. Furthermore, the diversity of compression stages in the natural gas compression subsystem and the diversity of the organic Rankine cycle subsystem form mean that the system can be flexible and adaptable. The energy supply method of the system can be adjusted according to actual needs by regulating the pressure regulating valve, the valve at the hot gas end of the vortex tube, and the water flow rate. The system described in this invention has a high energy utilization rate, using compressed and expanded natural gas as energy sources. It meets users' electricity and gas needs while reducing carbon emissions. The system configuration can be flexibly changed according to actual needs, and it is environmentally friendly, energy-saving and emission-reducing.

Claims

1. A waste energy power generation system for a natural gas distribution and pressurization station, characterized in that, include: The natural gas compression subsystem provides high-pressure natural gas and serves as the system heat source. The natural gas source is a portion of the upstream natural gas input into the system. The natural gas compression subsystem consists of a compressor assembly and a heat exchanger assembly. It employs multi-stage compression and interstage cooling to compress the natural gas, resulting in high-temperature natural gas, which serves as the system heat source. The compressor assembly comprises N compressors connected in series, and the heat exchanger assembly comprises N heat exchangers connected in series. The outlet natural gas from each compressor is fed into the heat exchanger to release the heat of compression onto the liquid organic working fluid, heating and vaporizing it. The natural gas flowing out of the heat exchanger is then fed into the next stage compressor until the target pressure is reached. The natural gas expansion subsystem is used to provide medium and low-pressure natural gas and system cold source. Its natural gas source is a portion of the upstream natural gas input into the system. The natural gas expansion subsystem consists of an expander assembly and a heat exchanger assembly. It uses a multi-stage expansion and interstage heating method to expand the natural gas. The resulting low-temperature natural gas serves as the system cold source. The expander assembly consists of M expanders connected in series, and the heat exchanger assembly consists of M heat exchangers connected in series. The outlet natural gas of each expander is fed into the heat exchanger to condense the gaseous organic working fluid after work into a liquid state. The natural gas flowing out of the heat exchanger is fed into the next stage expander until the expansion pressure is reduced to the target pressure. An organic Rankine cycle subsystem generates electricity by circulating the heat and cold generated during the operation of the natural gas compression subsystem and the natural gas expansion subsystem. The organic Rankine cycle subsystem includes a main organic Rankine cycle and several auxiliary organic Rankine cycles. The main organic Rankine cycle includes at least one expander and at least one working fluid pump. The first K-stage heat exchanger of the natural gas compression subsystem and the first L-stage heat exchanger of the natural gas expansion subsystem are connected to the main organic Rankine cycle. The waste heat generated by the first K-stage compressor is used for power generation in this cycle. The waste heat generated by the remaining compressors is used for power generation in each of the auxiliary organic Rankine cycles. The organic working fluid is vaporized and expanded to generate electricity in the organic Rankine cycle using the heat provided by the natural gas compression subsystem, and after the power generation is completed, it releases heat to the natural gas expansion subsystem and is liquefied again.

2. The waste energy power generation system for a natural gas distribution and pressurization station according to claim 1, characterized in that, In the primary organic Rankine cycle, a shared regenerator is added between the expander and the first L-stage heat exchanger of the natural gas expansion subsystem, and between the working fluid pump and the first K-stage heat exchanger of the natural gas compression subsystem. The exhaust steam from the expander in the primary organic Rankine cycle and the pressurized liquid organic working fluid from the working fluid pump are respectively introduced into the two sides of the regenerator. The liquid organic working fluid is heated by the exhaust steam and then enters the heat exchanger of the natural gas compression subsystem. The exhaust steam is cooled by the liquid working fluid and then enters the heat exchanger of the natural gas expansion subsystem. The same regenerator exists in the secondary organic Rankine cycle.

3. The waste energy power generation system for a natural gas distribution and pressurization station according to claim 2, characterized in that, In the natural gas compression subsystem, the first-stage heat exchanger is a preheater, and subsequent heat exchangers are evaporators. The heat source inlet of the preheater is high-temperature natural gas compressed by the first-stage compressor, and the cold source inlet is liquid organic working fluid drawn by the working fluid pump. The heat source inlet of the first-stage evaporator is high-temperature natural gas compressed by the second-stage compressor, and the cold source inlet is organic working fluid preheated by the preheater. The heat source inlet of subsequent evaporators is high-temperature natural gas compressed by the preceding stage compressor, and the cold source inlet is liquid organic working fluid drawn by the working fluid pump in the auxiliary organic Rankine cycle in which they are located.

4. The waste energy power generation system for a natural gas distribution and pressurization station according to claim 3, characterized in that, In the natural gas expansion subsystem, the heat exchanger is a condenser. The heat source inlet of the first-stage condenser is the gaseous organic working fluid after the work done by the expander in the main organic Rankine cycle, and the cold source inlet is the low-temperature natural gas after the work done by the first-stage expander in the natural gas expansion subsystem. The heat source inlets of subsequent condensers are the gaseous organic working fluid after the work done by the expander in the auxiliary organic Rankine cycle in which they are located, and the cold source inlets are the low-temperature natural gas after pre-cooling by the previous stage condenser.

5. The waste energy power generation system for a natural gas distribution and pressurization station according to claim 4, characterized in that, The natural gas after passing through the last stage evaporator of the natural gas compression subsystem is high-pressure natural gas, which continues to be transported downstream; the natural gas after passing through the last stage condenser of the natural gas expansion subsystem is medium-pressure natural gas, which is transported to distant cities; and the natural gas after being depressurized by the last stage expander of the natural gas expansion subsystem is low-pressure natural gas, which is transported to nearby cities.

6. A method for combined cooling and heating of natural gas in a waste heat power generation system for a natural gas distribution and pressurization station as described in claim 1, characterized in that, The process is as follows: A portion of the upstream natural gas is compressed using a natural gas compression subsystem to obtain high-temperature, high-pressure natural gas. By using a natural gas expansion subsystem, a portion of the upstream natural gas is expanded to obtain low-temperature, medium-low-pressure natural gas; The organic Rankine cycle subsystem is used to generate electricity by circulating the heat and cold generated during the operation of the natural gas compression subsystem and the natural gas expansion subsystem.

Images