Waste heat gradient utilization method for gas field development

Abstract

The invention discloses a waste heat gradient utilization method for gas field development, which comprises the following steps of: firstly, generating power for high-temperature section flue gas with the temperature of 500-200 DEG C in a gas field station yard by adopting a steam Rankine cycle power generation technology, and outputting electric energy to the outside or heating a heat-conducting oil medium to supply heat to the outside, so as to obtain low-temperature section flue gas with the temperature of below 200 DEG C; and secondly, for low-temperature section flue gas with the temperature below 200 DEG C, generating electricity by adopting an organic Rankine cycle technology, and outputting electric energy or heating a hot water medium to supply heat to the outside. According to the waste heat gradient utilization method for gas field development, medium-high-temperature flue gas waste heat resources of a gas field station yard are recovered in a graded mode according to the high-temperature section and the low-temperature section, and the waste heat recovery rate is increased; the high-temperature section and the low-temperature section are used for preparing hot products or electric products according to the actual requirements of a station yard, flexible selection and switching can be achieved, and higher recovery benefits are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of waste heat cascade utilization methods, and in particular relates to a waste heat cascade utilization method for gas field development. Background Art

[0002] Industrial waste heat generally refers to the heat energy that cannot be recycled and discharged during the process of production, also known as waste heat. A large amount of waste heat, as a secondary energy source, has become an effective means for developed countries to improve energy utilization. Waste heat resources are common in my country's high-energy-consuming industrial fields such as steel, petrochemicals, and cement. They can usually be divided into three categories according to temperature: high-temperature waste heat (above 555°C), medium-temperature waste heat (2552555°C), and low-temperature waste heat (below 255°C).

[0003] Gas-driven compression technology is widely used in ground engineering for gas field development for natural gas gathering and transportation. At present, 7 natural gas processing plants in Changqing Gas Field are using a total of 44 large gas-driven compressors, and more than 155 gas gathering stations are using more than 355 gas-driven compressors. The normal exhaust temperature of gas engines is about 4752555℃, which is not used in any form and is directly discharged into the atmosphere. Based on the annual gas consumption of the processing plant booster station alone, the waste heat that can be used in the high-temperature flue gas discharged each year is equivalent to more than 60,000 tons of standard coal, which can be said to have great utilization potential.

[0004] At present, the means of utilizing industrial waste heat mainly include heating (heat exchange), power generation (heat-to-work conversion) or combined heat and power processes. There are a large number of heat and electricity units in ground stations such as gas field processing plants, so the main products of the waste heat recovery system - heat energy and electricity usually have ideal consumption methods. By designing a waste heat recovery system, the present invention not only focuses on whether it has a higher waste heat recovery rate, that is, whether the waste heat resources can be fully recovered; it should also achieve as high a recovery income as possible, that is, whether the heat products and electricity products can be fully utilized. Summary of the invention

[0005] The purpose of the present invention is to provide a method for cascade utilization of waste heat for gas field development, which achieves a higher waste heat recovery rate and waste heat recovery benefit through graded recovery and segmented cascade utilization of medium and high temperature waste heat resources in gas field stations.

[0006] The technical solution adopted by the present invention is: a method for cascade utilization of waste heat for gas field development, firstly, for the high-temperature flue gas with a temperature of 5552255°C in the gas field station, steam Rankine cycle power generation technology is used to generate electricity and output electrical energy to the outside or heat the heat transfer oil medium to supply heat to the outside, so as to obtain a low-temperature flue gas with a temperature below 255°C; secondly, for the low-temperature flue gas with a temperature below 255°C, organic Rankine cycle technology is used to generate electricity and output electrical energy to the outside or heat the hot water medium to supply heat to the outside.

[0007] The present invention is also characterized in that:

[0008] The device used in the steam Rankine cycle power generation technology includes a waste heat boiler, which is connected to a steam turbine through a steam-water pipeline. The steam turbine is coaxially connected to a generator I. The end of the steam turbine away from the waste heat boiler is connected to a condenser, a condensate pump, a water heater and a thermal deaerator in sequence through a pipeline, and then connected to the waste heat boiler through a boiler feed water pump. One side of the steam turbine is connected to a water heater and a thermal deaerator through pipelines respectively, and the water heater is connected to the condenser through a pipeline and a water treatment device. The bottom end of the steam drum of the waste heat boiler is connected to a sewage expansion tank through a pipeline.

[0009] The method of generating electricity using steam Rankine cycle power generation technology is as follows: a high-temperature flue gas with a temperature of 5552255°C is introduced into a waste heat boiler to heat the feed water, and the high-temperature flue gas is cooled to obtain a low-temperature flue gas with a temperature below 255°C; the feed water is heated to superheated steam by the high-temperature flue gas in the waste heat boiler, and then enters the steam turbine to expand and do work, driving the generator I to work and output electrical energy to the outside, and the exhaust steam leaving the steam turbine is cooled and condensed into a liquid phase in the condenser, and then pressurized by the boiler feed water pump and enters the heating surface of the waste heat boiler to be heated and evaporated by the high-temperature flue gas.

[0010] The device used to heat the heat transfer oil medium for external heat supply includes a heat transfer oil heat exchanger. The heat transfer oil heat exchanger is connected to the high-temperature heat user end and the heat medium circulation pump in sequence through a pipeline and then returns to the heat transfer oil heat exchanger. The pipeline between the heat transfer oil heat exchanger and the high-temperature heat user end is connected to an expansion tank, and the expansion tank is connected to an oil storage tank and an oil injection pump that are interconnected through a pipeline.

[0011] The method of heating the heat transfer oil medium to supply heat to the outside is: the high-temperature flue gas with a temperature of 5552255℃ is passed into the heat transfer oil heat exchanger to heat the heat transfer oil medium, and the high-temperature flue gas is cooled to obtain the low-temperature flue gas with a temperature below 255℃; the heat transfer oil medium is heated by the high-temperature flue gas in the heat transfer oil heat exchanger and then sent to the high-temperature heat user end. The return oil of the heat transfer oil medium after heat exchange and cooling is pressurized by the heat medium circulation pump and sent to the heat transfer oil heat exchanger for reheating.

[0012] The device used in the organic Rankine cycle technology includes an ORC evaporator, the ORC evaporator is connected to an expander through a pipeline, the expander is coaxially connected to a generator II, and the end of the expander away from the ORC evaporator is connected to an air cooler and a liquid receiver in sequence through a pipeline and then connected to the ORC evaporator through a working fluid pump.

[0013] The method of generating electricity using organic Rankine cycle technology is as follows: low-temperature flue gas with a temperature below 255°C is passed into the ORC evaporator to heat the organic working fluid. The organic working fluid is heated by the low-temperature flue gas in the ORC evaporator, and the generated organic working fluid steam enters the expander to perform work, driving the generator II to work and output electrical energy to the outside. The organic working fluid exhaust steam leaving the expander is cooled and condensed into a liquid phase, and then pressurized by the working fluid pump and enters the ORC evaporator to be heated and evaporated.

[0014] The device used to heat the hot water medium for external heat supply includes a hot water heat exchanger. The hot water heat exchanger is connected to the low-temperature heat user end and the hot water circulation pump in sequence through a pipeline and then returns to the hot water heat exchanger. The pipeline between the low-temperature heat user end and the hot water circulation pump is connected with a water replenishment constant pressure device.

[0015] The method of heating hot water medium to supply heat to the outside is: the low-temperature flue gas with a temperature below 255°C is passed into the hot water heat exchanger to heat the hot water medium. The hot water medium is heated by the low-temperature flue gas in the hot water heat exchanger and then sent to the low-temperature heat user end. The return water after heat exchange and cooling is pressurized by the hot water circulation pump and sent to the hot water heat exchanger for reheating.

[0016] The beneficial effects of the present invention are as follows: the waste heat cascade utilization method for gas field development of the present invention recovers the medium and high temperature flue gas waste heat resources of the gas field station in a graded manner according to the high temperature section and the low temperature section, thereby improving the waste heat recovery rate; the high temperature section and the low temperature section respectively produce heat products or electrical products according to the actual needs of the station, and can be flexibly switched to achieve higher recovery benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the structure of the device used for high temperature section waste heat power generation in the waste heat cascade utilization method for gas field development of the present invention;

[0018] Figure 2 It is a schematic diagram of the structure of the device used for heating by the waste heat in the high temperature section in the waste heat cascade utilization method for gas field development of the present invention;

[0019] Figure 3 It is a schematic diagram of the structure of the device used for low temperature section waste heat power generation in the waste heat cascade utilization method for gas field development of the present invention;

[0020] Figure 4 It is a schematic diagram of the structure of the device used for heating with waste heat in the low temperature section in the waste heat cascade utilization method for gas field development of the present invention;

[0021] Figure 5 It is a schematic diagram of the device structure of the high and low temperature two-stage power generation process in the waste heat cascade utilization method for gas field development of the present invention;

[0022] Figure 6It is a schematic diagram of the device structure of the two-stage waste heat recovery process of first electricity and then heat in the waste heat cascade utilization method for gas field development of the present invention;

[0023] Figure 7 It is a schematic diagram of the device structure of the two-stage waste heat recovery process of heat recovery followed by electricity recovery in the waste heat cascade utilization method for gas field development of the present invention;

[0024] Figure 8 It is a schematic diagram of the device structure of the high and low temperature two-stage heating process in the waste heat cascade utilization method for gas field development of the present invention.

[0025] In the figure, 11-1. Waste heat boiler, 11-2. Steam turbine, 11-3. Generator I, 11-4. Condenser, 11-5. Water treatment device, 11-6. Condensate pump, 11-7. Water heater, 11-8. Thermal deaerator, 11-9. Boiler feed pump, 11-15. Blowdown expansion tank;

[0026] 12-1. Thermal oil heat exchanger, 12-2. High temperature heat user end, 12-3. Expansion tank, 12-4. Oil storage tank, 12-5. Oil injection pump, 12-6. Heat medium circulation pump;

[0027] 2-1. induced draft fan, 2-2. chimney;

[0028] 21-1.ORC evaporator, 21-2.expander, 21-3.generator II, 21-4.air cooler, 21-5.liquid storage tank, 21-6.working fluid pump;

[0029] 22-1. Hot water heat exchanger, 22-2. Low-temperature heat user end, 22-3. Water replenishment and constant pressure equipment, 22-4. Hot water circulation pump. DETAILED DESCRIPTION

[0030] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] The flue gas with a temperature of nearly 555℃ in the gas field station belongs to the medium and high temperature waste heat resource. With the continuous heat release of the flue gas during the recycling process, the flue gas temperature is also continuously decreasing. It can be divided into a high temperature section (5552255℃) and a low temperature section (below 255℃).

[0032] (1) High temperature section:

[0033] Taking the treatment plant as an example, the electricity load of the Changqing Gas Field Treatment Plant is relatively stable, and the high-temperature heat load usually uses thermal oil as the heating medium. Therefore, the high-temperature section of the flue gas waste heat resource can be recovered through power generation or heating.

[0034] ① High temperature waste heat power generation: For medium and high temperature flue gas waste heat recovery power generation, the steam Rankine cycle power generation technology is used. The steam Rankine cycle power generation system uses water vapor as the circulating working fluid. The system process is as shown in the attached figure. Figure 1 As shown, the high-temperature flue gas heats the feed water in the waste heat boiler 11-1, and enters the low-temperature section of the system after cooling. After the feed water is heated to superheated steam by the high-temperature flue gas in the waste heat boiler 11-1, it enters the steam turbine 11-2 to expand and do work, driving the generator I11-3 to work and output electrical energy to the outside. After the exhaust steam leaving the steam turbine 11-2 is cooled and condensed into a liquid phase, it is then pressurized by the boiler feed water pump 11-9 and enters the heating surface of the waste heat boiler 11-1 to be heated and evaporated by the heat source. The specific devices and methods used are:

[0035] The device includes a waste heat boiler 11-1, which is connected to a steam turbine 11-2 through a steam-water pipeline, and the steam turbine 11-2 is coaxially connected to a generator I 11-3. The end of the steam turbine 11-2 away from the waste heat boiler 11-1 is connected to a condenser 11-4, a condensate pump 11-6, a water heater 11-7 and a thermal deaerator 11-8 in sequence through a pipeline, and then connected to the waste heat boiler 11-1 through a boiler feed water pump 11-9. One side of the steam turbine 11-2 is connected to the water heater 11-7 and the thermal deaerator 11-8 through pipelines respectively, and the water heater 11-7 is connected to the condenser 11-4 through a pipeline and a water treatment device 11-5. The bottom end of the steam drum of the waste heat boiler 11-1 is connected to a sewage expansion tank 11-15 through a pipeline.

[0036] As a circulating medium, water is heated by high-temperature flue gas into superheated steam in the waste heat boiler 11-1, completing the isobaric heating process of the medium; then it enters the steam turbine 11-2 to expand and do work, driving the coaxial generator I 11-3 to work and generate electricity externally; the exhaust steam of the medium leaving the steam turbine 11-2 is cooled and condensed into liquid phase in the condenser 11-4, and then passes through the condensate pump 11-6 and the water heater 11-7 to complete the deoxidation process in the thermal deaerator 11-8; the liquid medium is pressurized by the boiler feed water pump 11-9 and enters the heating surface of the waste heat boiler 11-1 again to be heated and evaporated by high-temperature flue gas. The intermediate exhaust gas of the steam turbine is used as the heating source for the thermal deaerator 11-8 and the water heater 11-7, and the system is replenished with water through the water treatment device 11-5, and the waste water from the waste heat boiler 11-1 continuously and evenly enters the waste expansion tank 11-15. The working fluid continuously undergoes a working cycle of heating, evaporation, expansion, work, and cooling to release heat in various thermal equipment in the system to output electrical energy to the outside.

[0037] ② High temperature section waste heat heating: Use the high temperature section of flue gas waste heat to heat, that is, use the high temperature part of flue gas waste heat to heat the heat transfer oil heating medium. The system flow is as shown in the attached figure. Figure 2As shown, the high-temperature flue gas releases heat to the heat transfer oil medium in the heat transfer oil heat exchanger 12-1, and enters the low-temperature section of the system after cooling. The heat transfer oil is heated by the flue gas in the heat transfer oil heat exchanger 12-1 and sent to the high-temperature heat user end 12-2. The low-temperature return oil of the heat transfer oil after heat exchange is pressurized by the heat medium circulation pump 12-6 and sent to the heat transfer oil heat exchanger 12-1, and then heated again to enter the circulation. The specific device and method used are:

[0038] The device includes a thermal oil heat exchanger 12-1, which is connected to a high-temperature heat user end 12-2 and a heat medium circulation pump 12-6 in sequence through a pipeline and then returns to the thermal oil heat exchanger 12-1. An expansion tank 12-3 is connected to the pipeline between the thermal oil heat exchanger 12-1 and the high-temperature heat user end 12-2, and the expansion tank 12-3 is connected to an oil storage tank 12-4 and an oil injection pump 12-5 which are interconnected through a pipeline.

[0039] The high-temperature section waste heat heating method adopts a forced closed circulation system. The heat transfer oil medium is heated by the heat transfer oil heat exchanger 12-1 and distributed to the high-temperature heat user end 12-2. The low-temperature heat transfer oil after heat exchange is collected by the pipe network to the heat transfer medium circulation pump 12-6 for pressurization and then sent to the heat transfer oil heat exchanger 12-1 for reheating. The thermal expansion of the heat transfer medium in the system is absorbed by the expansion tank 12-3, and the supplementary heat transfer oil is pumped into the expansion tank 12-3 from the oil storage tank 12-4 or the oil barrel through the oil injection pump 12-5.

[0040] (2) Low temperature section:

[0041] ① Low temperature waste heat power generation: The recovery of low temperature flue gas for power generation is achieved through the organic Rankine cycle (ORC system) technology. Using low boiling point organic matter as the circulating working fluid can make full use of the low temperature waste heat. The system flow is as shown in the attached figure. Figure 3 As shown, the flue gas releases heat to the organic working medium in the ORC evaporator 21-1 and is discharged into the atmosphere through the chimney 2-2. The organic working medium is heated by the flue gas in the ORC evaporator 21-1, generating organic working medium steam which enters the expander 21-2 to do work, drives the generator II 21-3 to work, and outputs electrical energy to the outside. The organic working medium exhaust steam leaving the expander 21-2 is cooled and condensed, and then enters the ORC evaporator 21-1 again to be heated and evaporated. The device and method used are specifically as follows:

[0042] The device includes an ORC evaporator 21-1, the ORC evaporator 21-1 is connected to an expander 21-2 through a pipeline, the expander 21-2 is coaxially connected to a generator II 21-3, and the end of the expander 21-2 away from the ORC evaporator 21-1 is connected to an air cooler 21-4 and a liquid storage tank 21-5 in sequence through a pipeline and then connected to the ORC evaporator 21-1 through a working fluid pump 21-6.

[0043] After the flue gas releases heat to the organic working fluid in the ORC evaporator 21-1, it is discharged into the atmosphere through the induced draft fan 2-1 and the chimney 2-2. The organic circulating working fluid of the ORC system is heated into superheated steam by the flue gas in the ORC evaporator 21-1, and then enters the expander 21-2 to expand and do work, driving the coaxial generator II 21-3 to work and generate electricity externally; the working fluid exhaust steam that has completed the expansion work is cooled and condensed into a liquid phase in the air cooler 21-4, and then enters the working fluid pump 21-6 through the liquid storage 21-5 to increase the pressure and enter the ORC evaporator 21-1 again to be heated and evaporated by the high-temperature flue gas. The organic working fluid continuously performs the working cycle of heating, evaporation, expansion, work, cooling and heat release in each thermal equipment of the system to output electrical energy externally. The entire system can adopt a skid-mounted integrated device to save land.

[0044] ② Heating with waste heat from low temperature section: The waste heat from low temperature section of flue gas can be used to heat hot water for heating or insulation. The system flow is shown in the attached figure. Figure 4 As shown, the low-temperature flue gas releases heat to the hot water medium in the ORC evaporator 21-1 and is discharged into the atmosphere through the chimney 2-2. The hot water heated by the flue gas in the ORC evaporator 21-1 is heat-exchanged at the low-temperature heat user end 22-2 to produce low-temperature return water, which is pressurized by the hot water circulation pump 22-4 and sent to the heat exchanger for reheating and circulation. The device and method used are specifically as follows:

[0045] The device includes a hot water heat exchanger 22-1, which is connected to a low-temperature heat user end 22-2 and a hot water circulation pump 22-4 in sequence through a pipeline and then returns to the hot water heat exchanger 22-1. A water replenishment constant pressure device 22-3 is connected to the pipeline between the low-temperature heat user end 22-2 and the hot water circulation pump 22-4.

[0046] After releasing heat in the hot water heat exchanger 22-1, the flue gas is discharged into the atmosphere through the induced draft fan 2-1 and the chimney 2-2. The heating medium is heated by the hot water heat exchanger 22-1 and distributed to the low-temperature heat user end 22-2. The low-temperature return water after heat exchange is collected by the pipe network to the hot water circulation pump 22-4 for pressurization and then sent to the hot water heat exchanger 22-1 for reheating and circulation. The system water replenishment and pressure regulation are undertaken by the water replenishment and pressure regulation equipment 22-3.

[0047] Through the above-mentioned method, the waste heat cascade utilization method for gas field development of the present invention is suitable for the recovery and utilization of high-temperature flue gas waste heat resources in gas field ground stations, and has the advantages of high waste heat recovery rate, flexible system switching and high recovery efficiency.

[0048] 1) The present invention realizes the efficient utilization of flue gas waste heat resources in gas field stations through innovative recovery technology, and theoretically achieves full recovery of waste heat.

[0049] 2) The high and low temperature thermal products or electrical products in the system process of the present invention can be selected and freely combined according to the actual needs on site to adapt to different engineering application scenarios.

[0050] 3) The system operation mode of the present invention follows the energy utilization principle of "high energy and high use, low energy and low use", and can achieve higher system benefits compared with traditional waste heat recovery and utilization methods.

[0051] Example

[0052] Taking a treatment plant in Changqing Gas Field as an example, the annual gas consumption of the booster station is 3565×15 4 Nm 3 , the average exhaust temperature is 492℃. In actual engineering applications, according to different on-site process requirements, high and low temperature stages can adopt different recovery methods:

[0053] Example 1 - Two-stage power generation

[0054] like Figure 5 As shown, if a two-stage power generation process is adopted, the annual power generation in the high temperature section is 1524×15 4 kWh, annual power generation in low temperature stage 184×15 4 kWh, annual power generation of the system is 1758×15 4 kWh, the system does not need external power supply except for the startup phase. After deducting the self-used electricity, the annual net income of the system is 1545×15 4 kWh of electricity generated. The gap between the net power generation of the waste heat power generation system and the power consumption of the station can be filled by external power supply.

[0055] Example 2 - Electricity first, then heat

[0056] like Figure 6 As shown in the figure, if the combined power generation process of "high temperature section power generation + low temperature section heating" is adopted, the annual power generation of the high temperature section is 1524×15 4 kWh, annual heat supply in low temperature section 8.2×15 4 GJ. After deducting the self-used electricity, the annual net income of the system is 1356×15 4 kWh power generation and 8.2×15 4 GJ heat supply. The insufficient power supply can be provided by external electricity, and the insufficient heat supply can be supplemented by other heat sources.

[0057] Example 3 - Heat first then electricity

[0058] like Figure 7 As shown in the figure, if a two-stage heating process is adopted, the annual heating capacity of the high temperature section is 28.6×15 4 GJ, annual heat supply in low temperature section 8.2×15 4 GJ. The system's annual net income is 28.6×15 4GJ heating and 184×15 4 kWh of electricity generated. The shortfall in electricity supply can be provided by external electricity, and the shortfall in heat supply can be supplemented by other heat sources.

[0059] Example 4 - Two-stage heating

[0060] like Figure 8 As shown in the figure, if the combined supply process of "high temperature section heating + low temperature section power generation" is adopted, the annual heat supply of the high temperature section is 28.6×15 4 GJ, annual heat supply in low temperature section 8.2×15 4 GJ. The system's annual net income is 36.8×15 4 GJ heat supply. The insufficient heat supply can be supplemented by other heat sources.

Claims

1. A method for cascade utilization of waste heat for gas field development, characterized in that: Firstly, for the high-temperature flue gas with a temperature of 500-200°C in the gas field station, the steam Rankine cycle power generation technology is used to generate electricity and export electricity to the outside or heat the heat transfer oil medium to supply heat to the outside, so as to obtain the low-temperature flue gas with a temperature below 200°C; secondly, for the low-temperature flue gas with a temperature below 200°C, the organic Rankine cycle technology is used to generate electricity and export electricity to the outside or heat the hot water medium to supply heat to the outside.

2. The method for cascade utilization of waste heat for gas field development according to claim 1, characterized in that: The device used in the steam Rankine cycle power generation technology includes a waste heat boiler (11-1), the waste heat boiler (11-1) is connected to a steam turbine (11-2) through a steam-water pipeline, the steam turbine (11-2) is coaxially connected to a generator (11-3), and the end of the steam turbine (11-2) away from the waste heat boiler (11-1) is connected to a condenser (11-4), a condensate pump (11-6), a water heater (11-7) and a thermal deaerator (11-3) in sequence through a pipeline. The steam turbine (11-2) is connected to the water heater (11-7) and the thermal deaerator (11-8) through pipelines. The water heater (11-7) is connected to the condenser (11-4) through pipelines and the water treatment device (11-5). The bottom of the drum of the waste heat boiler (11-1) is connected to the blowdown expansion tank (11-10) through pipelines.

3. The method for cascade utilization of waste heat for gas field development according to claim 1, characterized in that: The method for generating electricity by using the steam Rankine cycle power generation technology is as follows: a high-temperature flue gas with a temperature of 500 to 200° C. is introduced into a waste heat boiler (11-1) to heat feed water, and the high-temperature flue gas is cooled to obtain a low-temperature flue gas with a temperature below 200° C.; the feed water is heated to superheated steam by the high-temperature flue gas in the waste heat boiler (11-1), and then enters a steam turbine (11-2) to expand and perform work, thereby driving a generator (11-3) to work and output electrical energy to the outside; the exhaust steam leaving the steam turbine (11-2) is cooled and condensed into a liquid phase in a condenser (11-4), and then is pressurized by a boiler feed water pump (11-9) and enters a heating surface of the waste heat boiler (11-1) to be heated and evaporated by the high-temperature flue gas.

4. The method for cascade utilization of waste heat for gas field development according to claim 1, characterized in that: The device used for heating the heat transfer oil medium for external heat supply comprises a heat transfer oil heat exchanger (12-1); the heat transfer oil heat exchanger (12-1) is connected to a high-temperature heat user end (12-2) and a heat medium circulation pump (12-6) in sequence through a pipeline and then returns to be connected to the heat transfer oil heat exchanger (12-1); an expansion tank (12-3) is connected to the pipeline between the heat transfer oil heat exchanger (12-1) and the high-temperature heat user end (12-2); and the expansion tank (12-3) is connected to an oil storage tank (12-4) and an oil injection pump (12-5) which are connected to each other through a pipeline.

5. The method for cascade utilization of waste heat for gas field development according to claim 1, characterized in that: The method for supplying heat to the outside by heating the heat transfer oil medium is as follows: a high-temperature flue gas with a temperature of 500 to 200°C is introduced into a heat transfer oil heat exchanger (12-1) to heat the heat transfer oil medium, and the high-temperature flue gas is cooled to obtain a low-temperature flue gas with a temperature below 200°C; the heat transfer oil medium is heated by the high-temperature flue gas in the heat transfer oil heat exchanger (12-1) and then sent to the high-temperature heat user end (12-2); the return oil of the heat transfer oil medium after heat exchange and cooling is pressurized by a heat medium circulation pump (12-6) and sent to the heat transfer oil heat exchanger (12-1) for reheating.

6. The method for cascade utilization of waste heat for gas field development according to claim 1, characterized in that: The device used in the organic Rankine cycle technology includes an ORC evaporator (21-1), the ORC evaporator (21-1) is connected to an expander (21-2) through a pipeline, the expander (21-2) is coaxially connected to a generator II (21-3), and the end of the expander (21-2) away from the ORC evaporator (21-1) is connected to an air cooler (21-4) and a liquid storage tank (21-5) in sequence through a pipeline, and then connected to the ORC evaporator (21-1) through a working fluid pump (21-6).

7. The method for cascade utilization of waste heat for gas field development according to claim 1, characterized in that: The method for generating electricity using the organic Rankine cycle technology is as follows: low-temperature flue gas with a temperature below 200°C is passed into an ORC evaporator (21-1) to heat an organic working fluid; the organic working fluid is heated by the low-temperature flue gas in the ORC evaporator (21-1); the generated organic working fluid steam enters an expander (21-2) to perform work, drives a generator II (21-3) to work and output electrical energy to the outside; the organic working fluid exhaust steam leaving the expander (21-2) is cooled and condensed into a liquid phase, and then is pressurized by a working fluid pump (21-6) and enters the ORC evaporator (21-1) to be heated and evaporated.

8. The method for cascade utilization of waste heat for gas field development according to claim 1, characterized in that: The device used for heating the hot water medium for external heat supply comprises a hot water heat exchanger (22-1), the hot water heat exchanger (22-1) is connected to a low-temperature heat user end (22-2) and a hot water circulation pump (22-4) in sequence through a pipeline and then returns to be connected to the hot water heat exchanger (22-1), and a water replenishment constant pressure device (22-3) is connected to the pipeline between the low-temperature heat user end (22-2) and the hot water circulation pump (22-4).

9. The method for cascade utilization of waste heat for gas field development according to claim 1, characterized in that: The method of using the heated hot water medium to supply heat to the outside is as follows: low-temperature flue gas with a temperature below 200°C is passed into a hot water heat exchanger (22-1) to heat the hot water medium; the hot water medium is heated by the low-temperature flue gas in the hot water heat exchanger (22-1) and then sent to a low-temperature heat user end (22-2); the return water after heat exchange and cooling is pressurized by a hot water circulation pump (22-4) and sent to the hot water heat exchanger (22-1) for reheating.

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