Coupling device and method for natural gas liquefaction through gas field gas pressure energy

Abstract

The invention relates to the technical field of natural gas pressure energy recycling, in particular to a coupling device and method for natural gas liquefaction through gas field gas pressure energy. Comprising a pressure energy power generation system and a liquefaction process cold supply system. The pressure energy power generation system comprises an inlet, a pressure regulating system, an expansion power generation system and an outlet, the pressure regulating system and the expansion power generation system are arranged in parallel, the inlet is connected with the pressure regulating system and the expansion power generation system, and the pressure regulating system and the expansion power generation system are connected with the outlet; the liquefaction process cold supply system comprises a precooling refrigerant circulation system, a mixed refrigerant circulation system and a natural gas liquefaction heat exchange system. The utilization efficiency of pressure energy is improved, and the technological adaptability to natural gas parameter changes is also improved.

Description

Technical Field

[0001] The invention relates to the field of natural gas pressure energy recovery and utilization, and in particular to a coupling device and method for using gas field gas pressure energy for natural gas liquefaction. Background Art

[0002] Natural gas refers to gases that exist naturally in nature, including gases formed by various natural processes in the atmosphere, hydrosphere and lithosphere, including oilfield gas, gas field gas, mud volcano gas, coalbed methane and biogas. The main use of natural gas is as fuel. It can be used to produce black carbon, chemicals and liquefied petroleum gas. Propane and butane produced from natural gas are important raw materials for modern industry. Using natural gas as an energy source can reduce the use of coal and oil, thereby greatly improving environmental pollution problems.

[0003] At present, large-scale land transportation of natural gas at home and abroad is mainly pipeline transportation. The use of high-pressure transportation in long-distance pipelines is a development trend in countries around the world. However, high-pressure natural gas cannot be used directly and needs to be regulated to medium or low pressure before entering the downstream pipeline network for use by users. The traditional pressure regulation method will waste a lot of pressure energy. After the natural gas is processed at the station, it is in a low-temperature state after expansion by the expander. If it is not processed in time, it may lead to the formation of natural gas hydrates or freeze the condensate water and cause freezing. Too low temperature will also increase the cold brittleness of the pipeline material and bring safety hazards. At the same time, this part of the cold energy is often ignored and not reasonably utilized. Therefore, the wasted pressure energy and cold energy are recovered and utilized, which will not only prevent energy waste, but also prevent safety accidents.

[0004] Prior art CN103791690B discloses a liquefied natural gas production device and method that utilizes pipeline pressure energy to generate electricity and refrigerate. The invention expands high-pressure natural gas, and uses the electricity generated by the generator during the expansion process for the compressor of the mixed refrigerant in the liquefied natural gas process, while the refrigeration of the expanded natural gas is used in the natural gas liquefaction process. Although the process flow of the invention is relatively simple and the investment cost is low, the above invention only considers the situation where the refrigeration capacity of the high-pressure natural gas is insufficient after expansion, and does not consider the treatment method when the refrigeration capacity of the high-pressure natural gas is large after expansion, and does not mention how to recover and utilize the excessive refrigeration capacity.

[0005] Prior art CN108386719B discloses a device and method for comprehensive utilization of pipeline natural gas pressure energy and cold energy. The invention generates electricity through natural gas pressure energy, and uses the generated electricity to produce liquefied natural gas, while recovering the cold energy generated during the expansion process for use in the natural gas liquefaction process system. However, the above invention does not mention the flow distribution and processing method of natural gas when the natural gas volume is too large or too small.

[0006] Therefore, there is an urgent need to provide a coupling device and method for gas field gas pressure energy to be used for natural gas liquefaction, which can improve the pressure energy utilization efficiency and enhance the process adaptability to changes in natural gas parameters compared with the existing technology. Summary of the invention

[0007] The present invention solves the technical problems existing in the prior art and provides a coupling device and method in which gas field gas pressure can be used for natural gas liquefaction.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] A coupling device for using gas field gas pressure energy for natural gas liquefaction, comprising a pressure energy power generation system and a liquefaction process cooling system;

[0010] The pressure energy power generation system comprises an inlet, a pressure regulating system, an expansion power generation system and an outlet, wherein the pressure regulating system and the expansion power generation system are arranged in parallel, the inlet is connected to the pressure regulating system and the expansion power generation system respectively, and the pressure regulating system and the expansion power generation system are connected to the outlet respectively;

[0011] The pressure regulating system is used to control the natural gas flow in the expansion power generation system;

[0012] The liquefaction process cooling system includes a pre-cooling refrigerant circulation system, a mixed refrigerant circulation system and a natural gas liquefaction heat exchange system. The pressure energy power generation system is used to provide cold energy for the pre-cooling refrigerant circulation system. The pre-cooling refrigerant circulation system is used to cool the raw materials required for the natural gas liquefaction heat exchange system. The mixed refrigerant circulation system is used to provide thermal energy to the pre-cooling refrigerant circulating in the pre-cooling refrigerant circulation system and to provide mixed refrigerant for the natural gas liquefaction heat exchange system.

[0013] Further, the input end of the voltage regulating system is connected to the input end of the expansion power generation system, the output end of the voltage regulating system is connected to the output end of the expansion power generation system, and the input end of the expansion power generation system is connected to the inlet;

[0014] The pressure energy power generation system also includes a temperature control output system, which includes a third pipeline and a fourth pipeline. The output end of the expansion power generation system is connected to the third pipeline and the fourth pipeline through a valve. The third pipeline and the fourth pipeline are connected in parallel. The output end of the third pipeline merges into the output end of the fourth pipeline, and the output end of the fourth pipeline is connected to the outlet. A first heat exchanger is connected in series to the third pipeline, and the first heat exchanger is also connected in series to the pipeline connecting the inlet and the input end of the expansion power generation system.

[0015] Furthermore, the third pipeline is provided with a first temperature sensor, the first temperature sensor is arranged between the first heat exchanger and the outlet, and the fourth pipeline is provided with a second temperature sensor.

[0016] Furthermore, the pre-cooling refrigerant circulation system includes a second heat exchanger and a fourth temperature sensor, the second heat exchanger is connected in series to the fourth pipe, the second temperature sensor is located between the second heat exchanger and the outlet, and the pre-cooling refrigerant circulation system is connected in series with the fourth temperature sensor.

[0017] Furthermore, the mixed refrigerant circulation system includes a third heat exchanger, a third condenser, and a third temperature sensor. The third heat exchanger and the third condenser are arranged in parallel. The mixed refrigerant circulation system sequentially connects the pipelines of the third heat exchanger and the third condenser in parallel and the third temperature sensor along the flow direction of the mixed refrigerant. The third heat exchanger is connected in series in the pre-cooling refrigerant circulation system.

[0018] Furthermore, a compressor and a second condenser are connected in series on the mixed refrigerant circulation pipeline, the second condenser is connected to the mixed refrigerant inlet end of the parallel pipeline between the third heat exchanger and the third condenser, and the compressor is connected to the end of the second condenser away from the third heat exchanger.

[0019] Furthermore, the expansion power generation system comprises a second pressure regulating valve and an expander, the second pressure regulating valve and the expander are connected in series, and one end of the expander away from the second pressure regulating valve is connected to a generator.

[0020] Furthermore, the pressure regulating system includes a first condenser and a first pressure regulating valve, and the first condenser and the first pressure regulating valve are connected in series.

[0021] Furthermore, the natural gas heat exchange liquefaction system is also connected to a first-stage electric compression refrigeration process, and the first-stage electric compression refrigeration process is used to supplement cold energy for the natural gas heat exchange liquefaction system.

[0022] A coupling method for gas field gas pressure to be used for natural gas liquefaction, comprising the following steps:

[0023] S1, detecting whether the temperatures monitored by the first temperature sensor and the second temperature sensor in the temperature control output system are all normal, if normal, proceed to step S2, if abnormal, proceed to step S101;

[0024] S101, analyzing the abnormal reasons of the temperature sensor in the temperature control output system according to different situations, and taking corresponding solutions, and then proceeding to step S1;

[0025] S2, detecting whether the temperatures monitored by all temperature sensors in the natural gas heat exchange liquefaction system are normal, if normal, proceeding to step S3, if abnormal, proceeding to step S201;

[0026] S201, analyzing the abnormal causes of the temperature sensor in the natural gas heat exchange liquefaction system according to different situations, taking corresponding solutions, and then proceeding to step S2;

[0027] S3, detecting whether the temperatures monitored by all temperature sensors in the pre-cooling refrigerant circulation system are normal, if normal, proceeding to step S4, if not normal, proceeding to step S301;

[0028] S301, analyzing the abnormal reasons of the temperature sensor in the pre-cooling refrigerant circulation system according to different situations, taking corresponding solutions, and then proceeding to step S3;

[0029] S4, detecting whether the temperatures monitored by all temperature sensors in the mixed refrigerant circulation system are normal, if normal, proceeding to step S5, if abnormal, proceeding to step S401;

[0030] S401, analyzing the abnormal causes of the temperature sensor in the mixed refrigerant circulation system according to different situations, taking corresponding solutions, and then proceeding to step S4;

[0031] S5. Carry out the next round of testing.

[0032] Furthermore, the normal monitoring range of the temperature sensor in step S1 is 5 to 10°C; the normal monitoring range of the temperature sensor in step S2 is -30 to 35°C; the normal monitoring range of the temperature sensor in step S3 is 20 to 25°C; and the normal monitoring range of the temperature sensor in step S4 is 30 to 40°C.

[0033] Furthermore, S101 specifically includes the following steps:

[0034] S1011, when the temperature of the first temperature sensor is too low and the temperature of the second temperature sensor is too high, increase the flow rate of the fourth pipeline; when the above situation is not correct, proceed to step S1012;

[0035] S1012, when the temperature of the first temperature sensor is too high and the temperature of the second temperature sensor is too low, increase the flow rate of the third pipeline; when the above situation is not correct, proceed to step S1013;

[0036] S1013. When any of the following conditions exists: "the first temperature sensor or the second temperature sensor is too low", "the first temperature sensor is too low and the second temperature sensor is normal", "the first temperature sensor is normal and the second temperature sensor is too low", increase the flow of the pressure regulating system; if none of the above conditions are correct, proceed to step S1014;

[0037] S1014, when the flow rate of the expansion power generation system can be increased, increase the flow rate of the expansion power generation system; when the flow rate of the expansion power generation system cannot be increased, proceed to step S1015;

[0038] S1015. Detect the temperatures monitored by all temperature sensors in the natural gas heat exchange liquefaction system. When one temperature sensor is too high, start the first-stage electric compression refrigeration process. If no temperature sensor is too high, increase the flow rate of the third condenser branch of the mixed refrigerant system.

[0039] Furthermore, step S201 specifically adopts the following method: when a temperature sensor in the natural gas heat exchange liquefaction system is too high, the first-stage electric compression refrigeration process is started; if no temperature sensor in the natural gas heat exchange liquefaction system is too high, the flow of the third heat exchanger branch of the mixed refrigerant system is increased.

[0040] Furthermore, step S301 specifically adopts the following method: when the temperature sensor in the pre-cooling refrigerant circulation system is too low, the flow of the third heat exchanger branch of the mixed refrigerant system is increased; when the temperature sensor in the pre-cooling refrigerant circulation system is too high or normal, the flow of the third condenser branch of the mixed refrigerant system is increased.

[0041] Furthermore, step S401 specifically adopts the following method: first increase the flow rate of the third condenser branch of the mixed refrigerant system, and then select one of the following two situations: when the temperature sensor in the mixed refrigerant circulation system is too low, reduce the load of the third condenser; when the temperature sensor in the mixed refrigerant circulation system is too high or normal, increase the load of the third condenser.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) The present invention not only recovers gas field pressure energy for power generation, but also uses the cold energy of the expanded natural gas for front-end natural gas dehydration and sewage treatment and liquefied natural gas process, replacing the electric compressor unit of the original liquefied natural gas process, reducing the energy consumption of the water-cooled condenser, and saving up to 20-25% of the electric power required for refrigeration. The pressure energy utilization rate can be as high as 85%-87%, which is much higher than other natural gas pressure energy for natural gas liquefaction process.

[0044] (2) The present invention can meet the processing capacity of 1.5 million Nm 3 / d of total electricity consumption of natural gas liquefaction process project; and the generated cold energy can replace the cold energy required by the original first-stage electric compression refrigeration process and the cold energy required for water cooling in the second-stage electric compression refrigeration process, saving up to 20-25% of the electric power required for refrigeration.

[0045] (3) The present invention is applicable to incoming gas pressures of 15 to 30 MPa and flow rates of 100,000 to 2800,000 Nm 3 / d of various gas field gases, automatically monitors and adjusts the process according to the changes in the incoming gas pressure and flow rate, and realizes automatic control; at the same time, the two systems can operate independently or together, with strong operability.

[0046] (4) The present invention uses a pre-cooling refrigerant to reheat a portion of the expanded natural gas, and another portion of the expanded natural gas is heat exchanged with gas from the gas field for reheating, thereby ensuring that the natural gas outlet temperature meets the downstream gas requirements and improving the safety of gas transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a process principle diagram of the device of the present invention.

[0048] Figure 2 It is a process flow chart of the device of the present invention.

[0049] Figure 3 It is a control flow chart of the method of the present invention.

[0050] Description of reference numerals:

[0051] 1. First separator; 2. First heat exchanger; 3. First regulating valve; 4. First condenser; 5. First pressure regulating valve; 6. Second pressure regulating valve; 7. Expander; 8. Generator; 9. Second separator; 10. Second regulating valve; 11. Second heat exchanger; 12. First temperature sensor; 13. Second temperature sensor; 14. Combiner; 15. Compressor; 16. Second condenser; 17. Third regulating valve; 18. Third heat exchanger; 19. Third condenser; 20. Third temperature sensor; 21. Fourth temperature sensor; 22. Fourth heat exchanger; 23. Fifth heat exchanger; 24. Fifth temperature sensor; 25. Sixth temperature sensor. DETAILED DESCRIPTION

[0052] The technical solution of the present invention will be clearly described below in conjunction with the accompanying drawings. Obviously, the described embodiments are not all embodiments of the present invention, and all other embodiments obtained by ordinary technicians in the field without making creative work are within the protection scope of the present invention.

[0053] Example 1

[0054] like Figure 1As shown, Example 1 of the present invention provides a coupling device in which gas field gas pressure energy can be used for natural gas liquefaction, including a pressure energy power generation system and a liquefaction process cooling system.

[0055] The pressure energy power generation system includes an inlet, a pressure regulating system, an expansion power generation system, a temperature regulating output system and an outlet. The inlet is connected to the gas field gas, and the outlet is connected to the next stage process. The pressure regulating system and the expansion power generation system are arranged in parallel. The temperature regulating output system includes a first heat exchanger 2, a first temperature sensor 12 and a second temperature sensor 13. The first heat exchanger 2 includes a first input port, a second input port, a first output port and a second output port. The first input port of the first heat exchanger 2 is connected to the inlet to input the gas field gas, the first output port of the first heat exchanger 2 is connected to the input port of the dehydration and sewage treatment process, and the output port of the dehydration and sewage treatment process is connected to the first regulating valve 3. The first regulating valve 3 is set as a three-way valve. The input end of the first regulating valve 3 is connected to the output port of the dehydration and sewage treatment process. The two output ends of the first regulating valve 3 are respectively connected to the first pipeline (① pipeline in the figure) and The second pipeline (pipeline ② in the figure), the pressure regulating system is connected in series on the first pipeline, the expansion power generation system is connected in series on the second pipeline, the output end of the second pipeline merges into the output end of the first pipeline, the output end of the first pipeline is connected to the second regulating valve 10, the second regulating valve 10 is provided with three interfaces, one of the interfaces of the second regulating valve 10 is connected to the output end of the first pipeline, the remaining two interfaces of the second regulating valve 10 are respectively connected to the third pipeline (pipeline ③ in the figure) and the fourth pipeline (pipeline ④ in the figure), the output end of the third pipeline is connected to the second input port of the first heat exchanger 2, the second output port of the first heat exchanger 2 is connected to the outlet, the first temperature sensor 12 is connected in series to the pipeline connecting the second output port of the first heat exchanger 2 and the outlet, the output end of the fourth pipeline is connected to the outlet, and the second temperature sensor 13 is connected in series to the pipeline connecting the output end of the fourth pipeline to the outlet.

[0056] The liquefaction process cooling system includes a pre-cooling refrigerant circulation system, a mixed refrigerant circulation system and a natural gas heat exchange liquefaction system. The pre-cooling refrigerant circulation system is connected to a pressure energy power generation system. The pressure energy power generation system is used to provide cold energy for the pre-cooling refrigerant circulating in the pre-cooling refrigerant circulation system. The pre-cooling refrigerant circulation system is connected to the natural gas heat exchange liquefaction system. The pre-cooling refrigerant circulation system is used to cool down the raw materials required for the natural gas heat exchange liquefaction system. The mixed refrigerant circulation system is used to provide heat energy for the pre-cooling refrigerant circulating in the pre-cooling refrigerant circulation system.

[0057] Specifically, the precooling refrigerant circulation system includes a second heat exchanger 11, a third heat exchanger 18 and a fourth temperature sensor 21. The second heat exchanger 11 and the third heat exchanger 18 both include a first input port, a second input port, a first output port and a second output port. The second heat exchanger 11 is connected in series to a pipeline connected between the output end of the fourth pipeline and the outlet. The first input port of the second heat exchanger 11 is connected to the output end of the fourth pipeline, the second input port of the second heat exchanger 11 is connected to the first output port of the third heat exchanger 18, and the first output port of the second heat exchanger 11 is connected to the natural gas heat exchanger. The pre-cooling refrigerant inlet of the liquefaction system is connected, and the second output port of the second heat exchanger 11 is connected to the second temperature sensor 13; the first input port of the third heat exchanger 18 is connected to the pre-cooling refrigerant outlet of the natural gas heat exchange liquefaction system, and the first output port of the third heat exchanger 18 is connected to the second input port of the second heat exchanger 11. The fourth temperature sensor 21 is connected in series to the pipeline connecting the first output port of the third heat exchanger 18 and the second input port of the second heat exchanger 11, and the second input port and the second output port of the third heat exchanger 18 are connected in series inside the mixed refrigerant circulation system.

[0058] The mixed refrigerant circulation system includes a third temperature sensor 20, a third regulating valve 17 and a third condenser 19. The outlet of the natural gas heat exchange liquefaction system is connected to the third regulating valve 17. The third regulating valve 17 is provided with three interfaces, one of which is connected to the outlet of the natural gas heat exchange liquefaction system, and the other two interfaces are respectively connected to the fifth pipeline (⑤ pipeline in the figure) and the sixth pipeline (⑥ pipeline in the figure). The fifth pipeline and the sixth pipeline are arranged in parallel. The third heat exchanger 18 is connected in series to the fifth pipeline. The third heat exchanger 18 is connected in series to the fifth pipeline through the second input port and the second output port. The third condenser 19 is connected in series to the sixth pipeline. The output end of the fifth pipeline merges into the output end of the sixth pipeline. The output end of the sixth pipeline is connected to the mixed refrigerant input end of the natural gas heat exchange liquefaction system. The third temperature sensor 20 is connected in series to the pipeline connected to the output end of the sixth pipeline and the mixed refrigerant input end of the natural gas heat exchange liquefaction system.

[0059] The natural gas liquefaction system includes a fourth heat exchanger 22, a fifth temperature sensor 24, a sixth temperature sensor 25 and a natural gas heat exchange liquefaction process, the fourth heat exchanger 22 includes a raw gas input port, a raw gas output port, a mixed refrigerant input port, a mixed refrigerant output port, a precooling refrigerant input port, and a precooling refrigerant output port, the raw gas input port of the fourth heat exchanger 22 inputs the raw gas, the raw gas output port of the fourth heat exchanger 22 is connected to the natural gas heat exchange liquefaction process, and the raw gas output port of the fourth heat exchanger 22 is connected to the natural gas heat exchange liquefaction process A fifth temperature sensor 24 is connected in series to the connected pipeline, the mixed refrigerant input port of the fourth heat exchanger 22 is connected to the output end of the mixed refrigerant circulation system, the mixed refrigerant output port of the fourth heat exchanger 22 is connected to the natural gas heat exchange liquefaction process, and the fourth heat exchanger 22 is connected in series in the precooling refrigerant circulation system through the precooling refrigerant input port and the precooling refrigerant output port; the output end of the natural gas heat exchange liquefaction process outputs liquefied natural gas and mixed refrigerant respectively, and the mixed refrigerant output by the natural gas heat exchange liquefaction process serves as the input of the mixed refrigerant circulation system.

[0060] The fourth heat exchanger 22 is also connected to a first-stage electric compression refrigeration process, which is used to perform supplementary cooling operation on the natural gas heat exchange liquefaction system when the cold energy generated by the pressure energy power generation system is less.

[0061] like Figure 2 As shown, the inlet of the pressure energy power generation system is connected to the first separator 1. The first separator 1 is a gas-liquid separator for gas-liquid separation of gas field gas. The gas from the natural gas field first enters the first separator 1 for gas-liquid separation, the gas enters the pressure energy power generation system, and the liquid enters the gas field produced water treatment device connected to the first separator 1; the expansion power generation system includes a second pressure regulating valve 6, an expander 7 and a generator 8. The second pipeline is connected in series with the second pressure regulating valve 6 and the expander 7 in sequence along the flow direction of the natural gas. The expander 7 expands the inflowing natural gas and drives the generator 8 to rotate. The pressure regulating system includes a first condenser 4 and a first pressure regulating valve 5. The first condenser 4 and the first pressure regulating valve 5 are connected in series on the first pipeline along the flow direction of the natural gas. The output end of the first pipeline is connected to the second separator 9. The natural gas enters the second separator 9 for low-temperature sewage treatment. The output end of the second separator 9 is connected to the second regulating valve 10.

[0062] The natural gas flowing out of the second output port of the second heat exchanger 11 and the natural gas flowing out of the second output port of the first heat exchanger 2 merge into the combiner 14, and after entering the combiner 14, it is adjusted to a suitable temperature and then flows into the next stage process from the outlet of the pressure energy power generation system.

[0063] The compressor 15 and the second condenser 16 are connected in series in sequence between the outlet of the natural gas liquefaction system and the third regulating valve 17 along the flow direction of the mixed refrigerant; the output end of the first-stage electric compression refrigeration process is connected to the fifth heat exchanger 23, and the fifth heat exchanger 23 includes a mixed refrigerant input port, a mixed refrigerant output port, a raw gas input port, a raw gas output port, a pre-cooling refrigerant input port, and a pre-cooling refrigerant output port. The mixed refrigerant is input into the mixed refrigerant input port of the fifth heat exchanger 23, and the mixed refrigerant output port of the fifth heat exchanger 23 merges into the mixed refrigerant output port of the fourth heat exchanger 22. The raw gas input port of the fifth heat exchanger 23 inputs raw gas, and the raw gas output port of the fifth heat exchanger 23 merges into the raw gas output port of the fourth heat exchanger 22. The fifth heat exchanger 23 is connected in series with the first-stage voltage refrigeration process through the pre-cooling refrigerant input port and the pre-cooling refrigerant output port.

[0064] The first regulating valve 3 , the second regulating valve 10 , and the third regulating valve 17 are all three-way valves for distributing fluid flow. The first regulating valve 3 , the second regulating valve 10 , and the third regulating valve 17 can be replaced with two flow regulating valves for joint control.

[0065] The first temperature sensor 12 and the second temperature sensor 13 are used to monitor the temperature of the expanded natural gas after heat exchange. The third pipeline and the fourth pipeline are regulated by the second regulating valve 10 so that the output natural gas reaches the gas transmission temperature. The third temperature sensor 20 is used to monitor the temperature of the mixed refrigerant. The fourth temperature sensor 21 is used to monitor the temperature of the pre-cooling refrigerant after heat exchange. The flow of the mixed refrigerant is adjusted by the third regulating valve 17. The fifth temperature sensor 24 and the sixth temperature sensor 25 are used to monitor the temperature of the mixed refrigerant and the raw gas after heat exchange with the pre-cooling refrigerant. When the natural gas volume is insufficient or the pressure is low, the cooling capacity of the expanded natural gas is insufficient to supply the mixed refrigerant, and the raw gas is reduced to the required temperature. At this time, the refrigeration process of the first-level voltage is started to ensure sufficient cooling capacity in turn.

[0066] The present invention is suitable for flow rates of 100,000 to 2800,000 Nm 3 / d, gas field gas with a pressure of 15-30MPa, coupled natural gas liquefaction volume of 500,000-1.5 million Nm 3 / d natural gas liquefaction process, the ratio of gas field gas flow rate to natural gas liquefaction volume is 2:1-18:1; the inlet pressure of the expander 7 is 8.0-20.0MPa, the outlet pressure is 4.5-6.0MPa, and the pressure ratio is between 1.8 and 4.4. The high-pressure natural gas drives the expander 7 to work and thus drives the generator 8 to generate electricity, and its pressure energy utilization rate can be as high as 85%-87%.

[0067] The working principle of the coupling device provided by the present invention that can be used for natural gas liquefaction by gas field gas pressure is as follows:

[0068] (1) Working principle of the pressure energy power generation system: The gas field gas enters the first heat exchanger 2 to exchange heat with the partially expanded natural gas, then enters the first pressure regulating valve 5 for pressure regulation, and then enters the expander 7 for expansion. Then the expanded natural gas is discharged through the second separator 9 at low temperature. The low-temperature natural gas after low-temperature discharge is divided into two paths through the second regulating valve 10. The third pipeline enters the first heat exchanger 2 to exchange heat with the gas field gas; the fourth pipeline low-temperature natural gas enters the second heat exchanger 11 to exchange heat with the pre-cooling refrigerant. At this time, the temperature rises, and then enters the combiner 14 to mix with the partially heat-exchanged natural gas, and then transmits the gas to the outside after reaching the output temperature.

[0069] (2) Working principle of the liquefaction process cooling system: The precooling refrigerant passes through the second heat exchanger 11 to exchange heat with part of the expanded low-temperature natural gas. After the temperature is reduced, it enters the fourth heat exchanger 22 to exchange heat with the raw gas and the mixed refrigerant, and transfers the cold energy to the raw gas and the mixed refrigerant for the natural gas liquefaction process. At this time, the temperature of the precooling refrigerant increases after heat exchange, and then enters the third heat exchanger 18 to exchange heat with the high-temperature mixed refrigerant compressed by the compressor 15. After the temperature increases, it is monitored by the fourth temperature sensor 21, and then enters the second heat exchanger 11 to complete the cycle; after the mixed refrigerant exchanges heat from the natural gas liquefaction process, it enters the compressor 15 for compression. After the temperature increases, it enters the second condenser 16 for condensation. After the temperature decreases, it is allocated to the fifth pipeline and the sixth pipeline through the third regulating valve 17. The fifth pipeline enters the third heat exchanger 18 to exchange heat with the precooling refrigerant, and the sixth pipeline enters the third condenser 19 to exchange heat, and the temperature decreases again. Then, the temperature is monitored by the third temperature sensor 20 and then enters the fourth heat exchanger 22 to complete the cycle.

[0070] The following is an explanation of the specific implementation case:

[0071] Taking the actual natural gas field scenario as an example, the natural gas flow in the pipeline is 28 million Nm 3 / d, the pressure is 18.0MPa, the temperature is 40-65℃; and the flow rate of the raw gas to be liquefied is 1.5 million Nm 3 / d, the temperature range is 35-45℃, and the pressure is 5MPa; the pre-cooling refrigerant is R410A as an example.

[0072] After dehydration, the natural gas from the natural gas field will enter the first heat exchanger 2 and the expanded part flow rate is 14 million Nm 3 / d, the natural gas with a temperature of -45 to -55°C and a pressure of 4.5 to 5.5MPa is heat exchanged, the temperature is reduced to 20 to 30°C, and then enters the dehydration and sewage discharge process for dehydration and sewage discharge, and then the second pressure regulating valve 6 stabilizes the pressure to 15MPa, and then enters the expander 7 for expansion, and after expansion, it becomes a low-temperature natural gas with a temperature of -45 to -55°C and a pressure of 5MPa. At the same time, during the expansion process, the expander 7 drives the generator 8 to generate electricity, and the power generation power is about 33613kW. Then the low-temperature natural gas is discharged through the second separator 9 at low temperature. The low-temperature natural gas after low-temperature sewage discharge is divided into the third pipeline and the fourth pipeline through the second regulating valve 10. The flow rate of the third pipeline is 14 million Nm 3 / d, and the natural gas in the third pipeline enters the first heat exchanger 2 to exchange heat with the natural gas originally from the gas field gas processing scene with a temperature of 18MPa and a temperature of 40-65°C. After the heat exchange, the natural gas temperature rises to -5-10°C and enters the combiner 14; the flow rate of the fourth pipeline is 14 million Nm 3 / d, the low-temperature natural gas flowing in the fourth pipeline enters the second heat exchanger 11 and exchanges heat with the pre-cooling refrigerant with a flow rate of 221.5t / h, a temperature of 20-35℃, and a pressure of 0.2MPa. At this time, the natural gas temperature rises to 10--5℃, and then enters the combiner 14 and the third pipeline with a flow rate of 14 million Nm 3 / d The natural gas after heat exchange is mixed and transmitted to the outside after reaching a temperature of 0-5℃.

[0073] The precooling refrigerant with a temperature of 20-35°C, a pressure of 0.2 MPa and a flow rate of 221.5 t / h passes through the second heat exchanger 11 and the fourth pipeline with a flow rate of 14 million Nm 3 / d, the temperature after expansion is -55~-65℃, the pressure is 5MPa natural gas for heat exchange, the temperature rises to -35~-45℃ and then enters the fourth heat exchanger 22 and 1.5 million Nm 3 / d, raw gas with a temperature of 35-45°C and a pressure of 5MPa, and a mixed refrigerant of 6585kmol / h are used for heat exchange, and the cold energy is respectively transferred to the raw gas and the mixed refrigerant for the liquefaction process of natural gas. At this time, the temperature of the pre-cooling refrigerant rises to -35--45°C after heat exchange, and then enters the third heat exchanger 18 for secondary heat exchange with the mixed refrigerant after the first heat exchange. After the temperature rises to 20-35°C, the temperature is monitored by the fourth temperature sensor 21 to avoid over-high temperature, and then enters the second heat exchanger 11 to complete the cycle.

[0074] Example 2

[0075] Embodiment 2 of the present invention provides a coupling device in which gas field gas pressure can be used for natural gas liquefaction. Embodiment 2 of the present invention is different from Embodiment 1 in that it belongs to a different actual natural gas field scenario from Embodiment 1.

[0076] The natural gas flow rate in the pipeline of the actual natural gas field scenario is 3 million Nm 3 / d, pressure is 20~21MPa, temperature is 40~65℃; and the flow rate of raw gas to be liquefied is 1.5 million Nm 3 / d, the temperature range is 35-45℃, and the pressure is 5MPa; the pre-cooling refrigerant is R410A as an example.

[0077] The natural gas from the natural gas field scene will enter the second heat exchanger 11 after dehydration and the expanded part flow rate is 1.5 million Nm 3 / d, the natural gas with a temperature of -45 to -55°C and a pressure of 5 to 5.5MPa is heat exchanged, the temperature is reduced to 20 to 30°C, and then enters the dehydration and sewage discharge process for dehydration and sewage discharge, and then the second pressure regulating valve 6 stabilizes the pressure to 15MPa, and then enters the expander 7 for expansion, and after expansion, it becomes a low-temperature natural gas with a temperature of -50 to -60°C and a pressure of 5MPa. At the same time, during the expansion process, it drives the generator 8 to generate electricity, and the power generation power is about 3601kW. Then, it is discharged at low temperature through the second separator 9. After the low-temperature sewage discharge, the low-temperature natural gas is divided into the third pipeline and the fourth pipeline through the second regulating valve 10. The flow rate of natural gas in the third pipeline is 1.5 million Nm 3 / d, and enters the second heat exchanger 11 to exchange heat with the natural gas originally from the gas field gas processing scene with a temperature of 20MPa and a temperature of 40-65°C. After the heat exchange, the natural gas temperature rises to -5-10°C and enters the combiner 14; the flow rate of the fourth pipeline is 1.5 million Nm 3 / d low-temperature natural gas enters the second heat exchanger 11 and exchanges heat with the pre-cooling refrigerant with a flow rate of 24t / h, a temperature of 20-35℃, and a pressure of 0.2MPa. At this time, the natural gas temperature rises to 10--5℃, and then enters the combiner 14 and the third pipeline with a flow rate of 1.5 million Nm 3 / d The natural gas after heat exchange is mixed and transmitted to the outside after reaching a temperature of 0-5℃.

[0078] The precooling refrigerant with a temperature of 20-35°C, a pressure of 0.2 MPa and a flow rate of 24 t / h passes through the second heat exchanger 11 and the fourth pipeline with a flow rate of 1.5 million Nm 3 / d, the natural gas with a temperature of -55 to -65°C and a pressure of 5MPa after expansion is heat exchanged, and the temperature rises to -35 to -45°C before entering the fourth heat exchanger 22 and 1.5 million Nm 3 / d, raw gas with a temperature of 35-45°C and a pressure of 5MPa, and a mixed refrigerant of 6585kmol / h are used for heat exchange, and the cold is transferred to the raw gas and the mixed refrigerant for the natural gas liquefaction process respectively. At this time, the temperature of the pre-cooling refrigerant rises after the heat exchange, and then enters the third heat exchanger 18 to perform secondary heat exchange with the mixed refrigerant after the primary heat exchange. After the temperature rises, the temperature is monitored by the fourth temperature sensor 21 to avoid the situation of excessive temperature, and then enters the second heat exchanger 11 to complete the cycle; and the mixed refrigerant flows out of the natural gas liquefaction process and enters the compressor 15 for compression. After the temperature rises, it enters the second condenser 16, and then after being adjusted by the third regulating valve 17, the mixed refrigerant is divided into two flows of the fifth pipeline and the sixth pipeline according to the temperature monitored by the fourth temperature sensor 21 of the pre-cooling refrigerant. According to the cooling requirement, the divided flow enters the third heat exchanger 18 and the third condenser 19 respectively for condensation, so that it reaches the required temperature and enters the natural gas liquefaction process to complete the cycle.

[0079] Example 3

[0080] like Figure 3 As shown, Embodiment 3 of the present invention provides a coupling method for gas field gas pressure to be used for natural gas liquefaction, comprising the following steps:

[0081] S1, detecting the temperature monitored by the first temperature sensor 12 and the second temperature sensor 13;

[0082] S2, when the temperature range monitored by the first temperature sensor 12 and the second temperature sensor 13 is not between 5 and 10°C, proceed to step S201; when the temperature range monitored by the first temperature sensor 12 and the second temperature sensor 13 is between 5 and 10°C, proceed to step S3;

[0083] S201, determining that the temperature monitored by the first temperature sensor 12 is too low and the temperature monitored by the second temperature sensor 13 is too high, if yes, proceed to step S202; if no, proceed to step S203;

[0084] S202, controlling the second regulating valve 10 to increase the flow of the fourth pipeline, and then performing step S1;

[0085] S203, determining whether the temperature monitored by the first temperature sensor 12 is too high and the temperature monitored by the second temperature sensor 13 is too low; if yes, proceed to step S204; if no, proceed to step S205;

[0086] S204, control the second regulating valve 10 to increase the flow of the third pipeline, and then proceed to step S1;

[0087] S205, judging that "the temperature monitored by the first temperature sensor 12 is too low or the temperature monitored by the second temperature sensor 13 is too low", "the temperature monitored by the first temperature sensor 12 is too low and the temperature monitored by the second temperature sensor 13 is normal", "the temperature monitored by the first temperature sensor 12 is normal and the temperature monitored by the second temperature sensor 13 is too low", if any of the above three situations is judged to be correct, proceed to step S206, if none of the above three situations is correct, proceed to step S207;

[0088] S206, controlling the second regulating valve 10 to increase the flow rate of the first pipeline, and then performing step S1;

[0089] S207, determining whether the flow rate of the second pipeline cannot be increased, if not, proceed to step S208, if yes, proceed to step S209;

[0090] S208, controlling the second regulating valve 10 to increase the flow rate of the second pipeline, and then performing step S1;

[0091] S209, monitoring the fifth temperature sensor 24 and the sixth temperature sensor 25;

[0092] S2010, judging the above two situations of "the temperature monitored by the fifth temperature sensor 24 is too high" and "the temperature monitored by the sixth temperature sensor 25 is too high", and performing step S2011 when either of the above two situations is correct, and performing step S2012 if neither of the above two situations is correct;

[0093] S2011, start the first-stage electric compression refrigeration process, and then proceed to step S1;

[0094] S2012, controlling the third regulating valve 17 to increase the flow rate of the sixth pipeline, and then performing step S1;

[0095] S3, detecting the temperatures monitored by the fifth temperature sensor 24 and the sixth temperature sensor 25;

[0096] S4, if the temperatures monitored by the fifth temperature sensor 24 and the sixth temperature sensor 25 are both normal, and the normal determination standard is that the temperature range is -30 to 35°C, then proceed to step S5; if one of the temperature sensors is abnormal, then proceed to step S401;

[0097] S401, judging the following two situations: "the temperature monitored by the fifth temperature sensor 24 is too high", "the temperature monitored by the sixth temperature sensor 25 is too high", when either of the above two situations is correct, proceed to step S401; when neither of the above two situations is correct, proceed to step S402;

[0098] S401, start the first-stage electric compression refrigeration process, and then proceed to step S3;

[0099] S402, controlling the third regulating valve 17 to increase the flow of the fifth pipeline, and then performing step S3;

[0100] S5, detecting the temperature monitored by the fourth temperature sensor 21;

[0101] S6. If the temperature monitored by the fourth temperature sensor 21 is normal, and the normal determination standard is that the temperature monitoring range is 20-25° C., then proceed to step S7; if it is abnormal, then proceed to step S601;

[0102] S601, when the temperature monitored by the fourth temperature sensor 21 is too low, the third regulating valve 17 is controlled to increase the flow rate of the fifth pipeline, and then the step S5 is performed; when the temperature monitored by the fourth temperature sensor 21 is not too low, the third regulating valve 17 is controlled to increase the flow rate of the sixth pipeline, and then the step S5 is performed;

[0103] S7, judging whether the temperature value monitored by the third temperature sensor 20 is normal, the normal judgment standard is that the temperature monitoring range is 30-40° C.; if normal, proceed to step S8; if abnormal, proceed to step S701;

[0104] S701, control the third regulating valve 17 to increase the flow rate of the sixth pipeline; then determine whether the temperature monitored by the third temperature sensor 20 is too low, if it is too low, proceed to step S702, if not too low, proceed to step S703;

[0105] S702, reducing the load of the third condenser 19, and then proceeding to step S7;

[0106] S703, increasing the load of the third condenser 19, and then performing step S7;

[0107] S8. Conduct the next round of monitoring.

[0108] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A coupling device for liquefying natural gas using gas field pressure, characterized in that: Including pressure energy power generation system and liquefaction process cooling system; The pressure energy power generation system comprises an inlet, a pressure regulating system, an expansion power generation system and an outlet, wherein the pressure regulating system and the expansion power generation system are arranged in parallel, the inlet is connected to the pressure regulating system and the expansion power generation system respectively, and the pressure regulating system and the expansion power generation system are connected to the outlet respectively; The pressure regulating system is used to control the natural gas flow in the expansion power generation system; The liquefaction process cooling system includes a pre-cooling refrigerant circulation system, a mixed refrigerant circulation system and a natural gas liquefaction heat exchange system. The pressure energy power generation system is used to provide cold energy for the pre-cooling refrigerant circulation system. The pre-cooling refrigerant circulation system is used to cool the raw materials required for the natural gas liquefaction heat exchange system. The mixed refrigerant circulation system is used to provide thermal energy to the pre-cooling refrigerant circulating in the pre-cooling refrigerant circulation system and to provide mixed refrigerant for the natural gas liquefaction heat exchange system.

2. A coupling device for liquefying natural gas using gas field pressure according to claim 1, characterized in that: The input end of the voltage regulating system is connected to the input end of the expansion power generation system, the output end of the voltage regulating system is connected to the output end of the expansion power generation system, and the input end of the expansion power generation system is connected to the inlet; The pressure energy power generation system also includes a temperature control output system, which includes a third pipeline and a fourth pipeline. The output end of the expansion power generation system is connected to the third pipeline and the fourth pipeline through a valve. The third pipeline and the fourth pipeline are connected in parallel. The output end of the third pipeline merges into the output end of the fourth pipeline, and the output end of the fourth pipeline is connected to the outlet. A first heat exchanger is connected in series to the third pipeline, and the first heat exchanger is also connected in series to the pipeline connecting the inlet and the input end of the expansion power generation system.

3. A coupling device for liquefying natural gas using gas field pressure according to claim 2, characterized in that: The third pipeline is provided with a first temperature sensor, and the first temperature sensor is arranged between the first heat exchanger and the outlet. The fourth pipeline is provided with a second temperature sensor.

4. A coupling device for liquefying natural gas using gas field pressure according to claim 3, characterized in that: The precooling refrigerant circulation system includes a second heat exchanger and a fourth temperature sensor. The second heat exchanger is connected in series to the fourth pipeline. The second temperature sensor is located between the second heat exchanger and the outlet. The precooling refrigerant circulation system is connected in series with the fourth temperature sensor.

5. A coupling device according to claim 4, wherein the gas field gas pressure can be used for natural gas liquefaction, characterized in that: The mixed refrigerant circulation system includes a third heat exchanger, a third condenser, and a third temperature sensor. The third heat exchanger and the third condenser are arranged in parallel. The mixed refrigerant circulation system sequentially connects the pipelines of the third heat exchanger and the third condenser in parallel and the third temperature sensor along the flow direction of the mixed refrigerant. The third heat exchanger is connected in series in the pre-cooling refrigerant circulation system.

6. A coupling device for liquefying natural gas using gas field pressure according to claim 5, characterized in that: A compressor and a second condenser are also connected in series on the mixed refrigerant circulation pipeline. The second condenser is connected to the mixed refrigerant inlet end of the parallel pipeline between the third heat exchanger and the third condenser. The compressor is connected to the end of the second condenser away from the third heat exchanger.

7. A coupling device according to claim 1, wherein the gas field gas pressure can be used for natural gas liquefaction, characterized in that: The expansion power generation system comprises a second pressure regulating valve and an expander, wherein the second pressure regulating valve and the expander are connected in series, and one end of the expander away from the second pressure regulating valve is connected to a generator.

8. A coupling device for liquefying natural gas using gas field pressure according to claim 1, characterized in that: The pressure regulating system comprises a first condenser and a first pressure regulating valve, and the first condenser and the first pressure regulating valve are connected in series.

9. A coupling device for liquefying natural gas using gas field pressure according to claim 1, characterized in that: The natural gas heat exchange liquefaction system is also connected to a first-stage electric compression refrigeration process, and the first-stage electric compression refrigeration process is used to supplement cold energy for the natural gas heat exchange liquefaction system.

10. A coupling method for gas field gas pressure to be used for natural gas liquefaction, characterized in that: The following steps are involved: S1, detecting whether the temperatures monitored by the first temperature sensor and the second temperature sensor in the temperature control output system are all normal, if normal, proceed to step S2, if abnormal, proceed to step S101; S101, analyzing the abnormal reasons of the temperature sensor in the temperature control output system according to different situations, and taking corresponding solutions, and then proceeding to step S1; S2, detecting whether the temperatures monitored by all temperature sensors in the natural gas heat exchange liquefaction system are normal, if normal, proceeding to step S3, if abnormal, proceeding to step S201; S201, analyzing the abnormal causes of the temperature sensor in the natural gas heat exchange liquefaction system according to different situations, taking corresponding solutions, and then proceeding to step S2; S3, detecting whether the temperatures monitored by all temperature sensors in the pre-cooling refrigerant circulation system are normal, if normal, proceeding to step S4, if not normal, proceeding to step S301; S301, analyzing the abnormal reasons of the temperature sensor in the pre-cooling refrigerant circulation system according to different situations, taking corresponding solutions, and then proceeding to step S3; S4, detecting whether the temperatures monitored by all temperature sensors in the mixed refrigerant circulation system are normal, if normal, proceeding to step S5, if abnormal, proceeding to step S401; S401, analyzing the abnormal causes of the temperature sensor in the mixed refrigerant circulation system according to different situations, taking corresponding solutions, and then proceeding to step S4; S5. Carry out the next round of testing.

11. A coupling method for using gas field gas pressure for natural gas liquefaction according to claim 10, characterized in that: The normal monitoring range of the temperature sensor in step S1 is 5 to 10°C; the normal monitoring range of the temperature sensor in step S2 is -30 to 35°C; the normal monitoring range of the temperature sensor in step S3 is 20 to 25°C; the normal monitoring range of the temperature sensor in step S4 is 30 to 40°C.

12. A coupling method for using gas field gas pressure for natural gas liquefaction according to claim 10, characterized in that: S101 specifically includes the following steps: S1011, when the temperature of the first temperature sensor is too low and the temperature of the second temperature sensor is too high, increase the flow rate of the fourth pipeline; when the above situation is not correct, proceed to step S1012; S1012, when the temperature of the first temperature sensor is too high and the temperature of the second temperature sensor is too low, increase the flow rate of the third pipeline; when the above situation is not correct, proceed to step S1013; S1013. When any of the following conditions exists: "the first temperature sensor or the second temperature sensor is too low", "the first temperature sensor is too low and the second temperature sensor is normal", "the first temperature sensor is normal and the second temperature sensor is too low", increase the flow of the pressure regulating system; if none of the above conditions are correct, proceed to step S1014; S1014, when the flow rate of the expansion power generation system can be increased, increase the flow rate of the expansion power generation system; when the flow rate of the expansion power generation system cannot be increased, proceed to step S1015; S1015. Detect the temperatures monitored by all temperature sensors in the natural gas heat exchange liquefaction system. When one temperature sensor is too high, start the first-stage electric compression refrigeration process. If no temperature sensor is too high, increase the flow rate of the third condenser branch of the mixed refrigerant system.

13. A coupling method for using gas field gas pressure for natural gas liquefaction according to claim 10, characterized in that: Step S201 specifically adopts the following method: when a temperature sensor in the natural gas heat exchange liquefaction system is too high, start the first-stage electric compression refrigeration process; if no temperature sensor in the natural gas heat exchange liquefaction system is too high, increase the flow of the third heat exchanger branch of the mixed refrigerant system.

14. A coupling method for using gas field gas pressure for natural gas liquefaction according to claim 10, characterized in that: Step S301 specifically adopts the following method: when the temperature sensor in the pre-cooling refrigerant circulation system is too low, the flow of the third heat exchanger branch of the mixed refrigerant system is increased; when the temperature sensor in the pre-cooling refrigerant circulation system is too high or normal, the flow of the third condenser branch of the mixed refrigerant system is increased.

15. A coupling method for using gas field gas pressure for natural gas liquefaction according to claim 10, characterized in that: Step S401 specifically adopts the following method: first increase the flow rate of the third condenser branch of the mixed refrigerant system, and then select one of the following two situations: when the temperature sensor in the mixed refrigerant circulation system is too low, reduce the load of the third condenser; when the temperature sensor in the mixed refrigerant circulation system is too high or normal, increase the load of the third condenser.

Images