LNG cold energy cascade utilization power generation system and method combined with space division unit

Abstract

The application provides a LNG cold energy cascade utilization power generation system and method combined with an air separation unit, and the system comprises: an LNG gas supply path, which comprises a first booster pump, the air separation unit and an LNG evaporator connected in sequence; an ethylene glycol water circulation unit, which comprises the air separation unit, a second booster pump and a first heater connected in circulation sequence; and a power generation circulation unit, which circulates a circulating working medium to generate power, and comprises the first heater, a first turbine expander, the LNG evaporator and a third booster pump. The application supplies the power generation circulation unit with the waste heat absorbed by the ethylene glycol water from the air separation unit, and the natural liquefied gas provided by the LNG gas supply path releases the remaining cold energy in the power generation circulation unit after releasing high-grade cold energy in the air separation unit, so that the cascade utilization of the LNG cold energy and the waste heat is realized, the power consumption of the air separation unit can be effectively reduced, the working efficiency of the power generation circulation unit can be significantly improved, and clean and efficient utilization of energy is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power generation systems, in particular to a LNG cold energy cascade utilization power generation system combined with an air separation unit and a method thereof. BACKGROUND

[0002] The LNG cold energy air separation system is a high-efficiency, energy-saving and environmentally friendly technology that utilizes the cold energy of LNG (liquefied natural gas) for air separation. In the air separation process, after air is filtered, compressed and purified, it enters the oxygen-nitrogen-argon rectification system and is separated into components such as oxygen, nitrogen and argon. The cold energy of LNG cools the air and nitrogen through a heat exchange system. Since the air separation process needs to be carried out at extremely low temperatures, compared with traditional air separation systems, the introduction of LNG cold energy can achieve external supply of cold energy, reduce the energy consumption of the self-refrigeration unit, thereby significantly reducing power consumption and improving system operating efficiency. In addition, due to the reduction in energy consumption, the heat generated by the system is also reduced, thereby reducing the amount of water used for heat dissipation and cooling. Typically, the LNG cold energy air separation system uses ethylene glycol as a circulating cooling medium, which is cooled by LNG in the LNG-ethylene glycol heat exchanger, serving as a cold source for the inter-stage and final-stage coolers of the compressor, the motor system, the lubricating oil system, etc., further reducing water consumption. In summary, the LNG cold energy air separation technology has broad application prospects and can be applied to gas separation, gas purification, gas liquefaction and other fields in petrochemical, chemical, pharmaceutical, electronic, food and other industries.

[0003] In a power generation cycle, the calculation of cycle efficiency follows the Carnot theorem, and the improvement of efficiency is subject to the highest temperature and condensing temperature of the cycle. In existing power cycles, such as the water vapor Rankine cycle, the highest temperature is the gaseous temperature of water vapor, and the lowest temperature is around the ambient temperature of the condensed water vapor in the condenser. The two temperature limits limit the work range of the working medium, resulting in a further improvement in efficiency. The LNG cold energy power generation system is a high-efficiency energy utilization method, and its technical principle is mainly based on the large amount of cold energy released by LNG (liquefied natural gas) during vaporization, which cools the working medium to a temperature much lower than normal temperature, thereby increasing the temperature difference between the hot end and the cold end of the working medium and improving the power generation power and operating efficiency. In this process, LNG itself absorbs heat to evaporate and vaporize, and at the same time, it also obtains energy, with the temperature rising above 0 degrees Celsius, and then it is introduced into the natural gas pipeline network.

[0004] However, in a conventional LNG cold energy air separation system, a portion of the cold energy of LNG is not fully utilized after being supplied, and a certain scale of cooling water is also required for cooling the waste heat of the compressor inter-stage, motor system, lubricating oil system, etc. in the air separation system, resulting in energy waste. In a conventional LNG cold energy power generation system, the hot end is usually heated by seawater or air, and the heating temperature is normal temperature, lacking a higher temperature heat source input, which limits the further improvement of the power cycle efficiency. SUMMARY

[0005] In view of the above problems, the application provides a LNG cold energy cascade utilization power generation system combined with an air separation unit and a method thereof.

[0006] The application provides a LNG cold energy cascade utilization power generation system combined with an air separation unit, comprising:

[0007] An LNG supply path, comprising a first booster pump, an air separation unit and an LNG evaporator connected in sequence;

[0008] A glycol water circulation unit, comprising the air separation unit, a second booster pump and a first heater connected in sequence in circulation;

[0009] A power generation circulation unit, circulating a circulating working medium to do work and generate power, comprising the first heater, a first turbine expander, the LNG evaporator and a third booster pump,

[0010] The LNG supply path circulates liquefied natural gas input from outside, and the liquefied natural gas absorbs heat in the air separation unit and the LNG evaporator in sequence,

[0011] The glycol water circulation unit circulates glycol water, and the glycol water absorbs heat in the air separation unit and releases heat in the first heater,

[0012] The circulating working medium in the power generation circulation unit exchanges heat with the glycol water in the first heater, and exchanges heat with the liquefied natural gas in the LNG evaporator.

[0013] According to the above technical scheme, the air separation unit can realize high-efficiency air separation function by receiving low-temperature circulating glycol water indirectly supplied by the glycol water circulation unit and high-grade cold energy of the liquefied natural gas supplied by the LNG supply path; meanwhile, the power generation circulation unit can realize power generation circulation and realize high-efficiency power generation by receiving high-temperature circulating glycol water indirectly supplied by the glycol water circulation unit and low-grade cold energy of the liquefied natural gas supplied by the LNG supply path.

[0014] Further, the application forms a glycol water circulation loop by constructing the glycol water circulation unit, the glycol water can absorb waste heat of the compressor interstage, the motor system and the lubricating oil system in the air separation unit and exchange heat in the first heater to supply the power generation circulation unit; meanwhile, LNG cold energy not fully utilized in the air separation unit is also collected by the LNG evaporator to supply the power generation circulation unit, realizing efficient utilization of LNG cold energy and waste heat, effectively reducing power consumption and water consumption of the air separation unit, and significantly improving the working efficiency of the power generation circulation unit, realizing clean and efficient utilization of energy.

[0015] Optionally, the power generation cycle unit is formed by nesting multiple power generation cycle loops in a cascade arrangement.

[0016] According to the above technical solution, the cascade arrangement of multiple power generation cycle loops further realizes the cascade utilization of heat and cold, effectively increases the operation efficiency of the entire cycle system, and improves the power generation capacity.

[0017] Optionally, the power generation cycle unit comprises a first power generation cycle loop and a second power generation cycle loop arranged in cascade,

[0018] The first power generation cycle loop comprises a first heater, a first turbo expander, a second heater and a third booster pump connected in sequence in circulation,

[0019] The second power generation cycle loop comprises a second heater, a second turbo expander, an LNG evaporator and a fourth booster pump connected in sequence in circulation.

[0020] Optionally, in the LNG supply path, the liquefied natural gas input into the air separation unit is lower than -150℃, and the liquefied natural gas input into the LNG evaporator is lower than 0℃.

[0021] According to the above technical solution, the LNG supply path can provide high-grade cold energy for the air separation unit, and at the same time, can provide the remaining low-grade cold energy for the power generation cycle unit to cool and liquefy the circulating working medium, realizing the efficient utilization of LNG cold energy.

[0022] Optionally, in the ethylene glycol water cycle unit, the ethylene glycol water input into the air separation unit is lower than the ambient temperature, and the ethylene glycol water input into the first heater is higher than the ambient temperature.

[0023] According to the above technical solution, the ethylene glycol water cycle unit can provide cold energy for the air separation unit, and after absorbing the waste heat of the air separation unit, can provide heat energy for the power generation cycle unit to heat and evaporate the circulating working medium, realizing the efficient utilization of waste heat in the air separation unit.

[0024] Optionally, in the power generation cycle unit, the circulating working medium has a temperature higher than the ambient temperature after flowing through the first heater, and has a temperature lower than the ambient temperature after flowing through the LNG evaporator.

[0025] According to the above technical solution, the circulating working medium in the power generation cycle unit can be heated by the ethylene glycol water absorbing the waste heat of the air separation unit in the first heater, and at the same time, can be cooled by the remaining cold energy of the natural liquefied gas in the LNG evaporator, so that the circulating working medium can circulate and flow to do work and generate electricity, realizing the clean and efficient utilization of energy.

[0026] Optionally, the LNG evaporator is further connected with a natural gas expander.

[0027] According to the above technical solution, by inputting the liquefied natural gas after sequentially absorbing heat in the air unit and the LNG evaporator into the natural gas expander to expand and do work, the heat absorbed by the liquefied natural gas in the LNG supply path can be converted into electric energy and output, and the power generation capacity is further improved.

[0028] The application further provides a power generation method applied to the LNG cold energy cascade utilization power generation system combined with the air separation unit.

[0029] The power generation cycle unit comprises:

[0030] The working medium pressurization step: the low-temperature circulating working medium in liquid form is pressurized by the third pressurizing pump;

[0031] The working medium heat exchange step: the pressurized low-temperature circulating working medium absorbs the heat of the ethylene glycol water circulating unit at the first heater, and is vaporized by itself;

[0032] The working medium work step: the temperature and pressure of the circulating working medium after being heated are lowered by the first turbine expander;

[0033] The working medium cooling step: the circulating working medium after work absorbs the low-temperature cold energy of the liquefied natural gas at the LNG evaporator, and is liquefied by itself to form a low-temperature circulating working medium, and then the working medium pressurization step, the working medium heat exchange step and the working medium work step are repeated to perform the power generation cycle;

[0034] The ethylene glycol water circulating unit comprises:

[0035] The heat absorption step: the ethylene glycol water absorbs the waste heat inside the air separation unit, and the temperature of the ethylene glycol water is raised;

[0036] The pressurization step: the ethylene glycol water passes through the second pressurizing pump, and the pressure of the ethylene glycol water is raised to maintain the flow stability of the ethylene glycol water circulating unit;

[0037] The cooling step: the ethylene glycol water heats the low-temperature circulating working medium in the power generation cycle unit at the first heater, and the temperature of the ethylene glycol water is lowered, and then the heat absorption step and the pressurization step are repeated to perform the ethylene glycol water circulation;

[0038] The LNG supply path comprises:

[0039] The LNG pressurization step: the liquefied natural gas from the external supply is pressurized by the first pressurizing pump to maintain the flow stability of the LNG supply path;

[0040] The heating step: the pressurized liquefied natural gas enters the air separation unit to cool the air, and the temperature of the liquefied natural gas is raised;

[0041] Reheating step: liquefied natural gas output from the air separation unit cools the circulating working medium in the power generation cycle unit at the LNG evaporator, and the liquefied natural gas itself is further raised in temperature and gasified.

[0042] In the power generation method provided by the present application, the LNG supply path further comprises a work step: the liquefied natural gas after the reheating step is introduced into the natural gas turbine expander to expand and do work, and the temperature and pressure of the liquefied natural gas itself are lowered, and then the liquefied natural gas is introduced into the external natural gas supply pipeline. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 Structure diagram of the LNG cold energy cascade utilization power generation system combined with the air separation unit in the first embodiment of the present application;

[0044] Figure 2 Structure diagram of the LNG cold energy cascade utilization power generation system combined with the air separation unit in the second embodiment of the present application;

[0045] Figure 3 Structure diagram of the LNG cold energy cascade utilization power generation system combined with the air separation unit in the third embodiment of the present application.

[0046] Reference signs: first booster pump 1, air separation unit 2, second booster pump 3, first heater 4, first turbine expander 5, LNG evaporator 6, third booster pump 7, second heater 41, second turbine expander 51, fourth booster pump 71, natural gas expander 8. DETAILED DESCRIPTION

[0047] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0048] <First embodiment>

[0049] Figure 1 Structure diagram of the LNG cold energy cascade utilization power generation system combined with the air separation unit in the first embodiment of the present application.

[0050] As shown in Figure 1 the LNG cold energy cascade utilization power generation system combined with the air separation unit in the present embodiment comprises a first booster pump 1, an air separation unit 2, a second booster pump 3, a first heater 4, a first turbine expander 5, an LNG evaporator 6, and a third booster pump 7.

[0051] In the embodiment, the air separation unit is an LNG cold energy air separation system, the air separation unit separates air by rectification, and receives cold energy indirectly supplied from the LNG supply path and the ethylene glycol water circulation unit, which are used for cooling before air rectification and cooling of the motor, lubricating oil system and compressor system in the air separation unit. The air separation unit is a prior art and is not described in detail here.

[0052] The LNG supply path comprises a first booster pump 1, the air separation unit 2 and an LNG evaporator 6 connected in sequence.

[0053] The ethylene glycol water circulation unit comprises the air separation unit 2, a second booster pump 3 and a first heater 4 connected in sequence.

[0054] The power generation cycle unit comprises the first heater 4, a first turbine expander 5, the LNG evaporator 6 and a third booster pump 7 connected in sequence.

[0055] The LNG supply path circulates liquefied natural gas input from outside, and the liquefied natural gas absorbs heat in the air separation unit 2 and the LNG evaporator 6 in sequence.

[0056] The ethylene glycol water circulation unit circulates ethylene glycol water, which absorbs heat in the air separation unit 2 and releases heat in the first heater 4.

[0057] The power generation cycle unit circulates a circulating working medium, which exchanges heat with the ethylene glycol water in the first heater 4 and exchanges heat with the liquefied natural gas in the LNG evaporator 6.

[0058] Specifically, the liquefied natural gas input into the air separation unit 2 is an ultralow-temperature liquid below -150°C and absorbs heat in the air separation unit 2, the ethylene glycol water input into the air separation unit 2 is below the ambient temperature and absorbs heat in the air separation unit 2, the air separation unit 2 receives low-temperature circulating ethylene glycol water indirectly supplied from the ethylene glycol water circulation unit and high-grade cold energy of LNG supplied from the LNG supply path, and can realize efficient air separation.

[0059] The ethylene glycol water input into the first heater 4 is above the ambient temperature and exchanges heat with the circulating working medium, so that the low-temperature circulating working medium is warmed and evaporated to enter the first turbine expander 5 to do work and generate electricity; the liquefied natural gas input into the LNG evaporator 6 is a low-temperature liquid below 0°C and exchanges heat with the circulating working medium, so that the working circulating working medium is liquefied and enters the third booster pump 7 to be pressurized, which can realize the circulation and repetition of the circulating working medium to do work and generate electricity, and realize efficient power generation.

[0060] In the embodiment, the waste heat of the compressor interstage, the motor system and the lubricating oil system in the air separation unit 2 is absorbed by the ethylene glycol water, and then exchanges heat with the circulating working medium in the first heater 4, so that the waste heat is supplied to the power generation cycle unit, and the waste heat in the air separation unit 2 is fully utilized.

[0061] At the same time, the liquefied natural gas (LNG) inputted from outside releases high-grade cold energy in the air separation unit 2, and then enters the LNG evaporator 6 to exchange heat with the circulating working medium in the power generation cycle unit to release the remaining cold energy, so that the LNG cold energy is fully utilized.

[0062] Therefore, the LNG cold energy cascade utilization power generation system combined with the air separation unit in the embodiment fully utilizes the waste heat in the air separation unit and the LNG cold energy, can effectively reduce the power consumption and water consumption of the air separation unit, and can significantly improve the working efficiency of the power generation cycle unit, so that clean and efficient use of energy is realized.

[0063] Further, the power generation method applied to the LNG cold energy cascade utilization power generation system combined with the air separation unit in the embodiment comprises the following steps:

[0064] The power generation cycle unit comprises:

[0065] The working medium pressurization step: the low-temperature circulating working medium is pressurized in liquid form by the third pressurizing pump 7.

[0066] The working medium heat exchange step: the pressurized low-temperature circulating working medium absorbs the heat of the ethylene glycol water circulating unit at the first heater 4, and is vaporized by itself.

[0067] The working medium work step: the temperature and pressure of the circulating working medium are lowered after the first turbine expander 5 expands and does work.

[0068] The working medium cooling step: the circulating working medium after work absorbs the low-temperature cold energy of the liquefied natural gas at the LNG evaporator 6, and is liquefied by itself to form a low-temperature circulating working medium, and then the working medium pressurization step, the working medium heat exchange step, and the working medium work step are repeated to perform power generation cycle.

[0069] The ethylene glycol water circulating unit comprises:

[0070] The heat absorption step: the ethylene glycol water absorbs the waste heat of the motor system, the lubricating oil system, and the inter-stage compressor in the air separation unit 2, and the temperature of the ethylene glycol water is raised.

[0071] The pressurization step: the ethylene glycol water flows through the second pressurizing pump 3, and the pressure of the ethylene glycol water is raised to maintain the flow stability of the ethylene glycol water circulating unit.

[0072] The cooling step: the ethylene glycol water heats the low-temperature circulating working medium in the power generation cycle unit at the first heater 4, and the temperature of the ethylene glycol water is lowered, and then the heat absorption step and the pressurization step are repeated to perform ethylene glycol water circulation.

[0073] The LNG supply path comprises:

[0074] LNG pressurization step: liquefied natural gas from external supply is pressurized by the first booster pump 1 to maintain the flow stability of the LNG supply line.

[0075] Heating step: the pressurized liquefied natural gas enters the air separation unit 2 to cool the air and increase its temperature.

[0076] Reheating step: the liquefied natural gas output from the air separation unit 2 cools the circulating working medium in the power generation cycle unit at the LNG evaporator 6, further increases its temperature and gasifies, and then enters the external natural gas supply pipeline.

[0077] <Second embodiment>

[0078] In this embodiment, the LNG supply line and the ethylene glycol water circulation unit are the same as in the first embodiment.

[0079] The power generation cycle unit is formed by nesting multiple power generation sub-cycle loops. In this embodiment, the nesting mode is a cascading arrangement, and the number of power generation sub-cycle loops is two, which are a first power generation sub-cycle loop and a second power generation sub-cycle loop.

[0080] Figure 2 Structure diagram of the LNG cold energy cascade utilization power generation system combined with an air separation unit in the second embodiment of the present application.

[0081] As shown in Figure 2 , the LNG cold energy cascade utilization power generation system combined with an air separation unit in this embodiment includes a first booster pump 1, an air separation unit 2, a second booster pump 3, a first heater 4, a first turbo expander 5, an LNG evaporator 6, a third booster pump 7, a second heater 41, a second turbo expander 51, and a fourth booster pump 71.

[0082] The LNG supply line includes the first booster pump 1, the air separation unit 2, and the LNG evaporator 6 connected in sequence.

[0083] The ethylene glycol water circulation unit includes the air separation unit 2, the second booster pump 3, and the first heater 4 connected in sequence.

[0084] The power generation cycle unit includes a first power generation sub-cycle loop and a second power generation sub-cycle loop arranged in cascade.

[0085] The first power generation sub-cycle loop includes the first heater 4, the first turbo expander 5, the second heater 41, and the third booster pump 7 connected in sequence.

[0086] The second power generation sub-cycle loop includes the second heater 41, the second turbo expander 51, the LNG evaporator 6, and the fourth booster pump 71 connected in sequence.

[0087] In the embodiment, the first power generation sub-cycle and the second power generation sub-cycle circulate the first cycle working medium and the second cycle working medium respectively. The first heater 4 of the ethylene glycol water cycle is used as the first heat source, and the heat from the first heater 4 is transferred to the second power generation sub-cycle through the first power generation sub-cycle. The LNG evaporator 6 is arranged in the second power generation sub-cycle, and the cold energy is transferred to the first power generation sub-cycle through the second power generation sub-cycle, so as to realize the cascade utilization of the LNG cold energy and the waste heat in the air separation unit.

[0088] In the embodiment, the first cycle working medium in the first power generation sub-cycle exchanges heat with the ethylene glycol water in the first heater 4, the first cycle working medium exchanges heat with the second cycle working medium in the second heater 41, and the second cycle working medium exchanges heat with the natural liquefied gas in the LNG evaporator 6.

[0089] Further, in the power generation method applied to the LNG cold energy cascade utilization power generation system combined with the air separation unit in the embodiment, the steps in the ethylene glycol water cycle unit and in the LNG gas supply path are the same as those in the first embodiment, and the power generation cycle unit includes the first power generation sub-cycle and the second power generation sub-cycle, and specifically includes the following steps.

[0090] In the first power generation sub-cycle:

[0091] The pressurization step: the low-temperature first cycle working medium is pressurized in liquid form by the third pressurizing pump 6.

[0092] The heat exchange step: the pressurized low-temperature first cycle working medium absorbs the heat of the ethylene glycol water cycle unit at the first heater 4, and is itself warmed and evaporated.

[0093] The work step: the warmed first cycle working medium is expanded to do work outside the first turbine expander 5, and the temperature and pressure of the first cycle working medium are lowered.

[0094] The cooling step: the first cycle working medium after doing work exchanges heat with the second low-temperature cycle working medium at the second heater 41, and is itself cooled and liquefied to form the low-temperature cycle working medium, and then the pressurization step, the heat exchange step, and the work step are repeated to perform the first power generation sub-cycle.

[0095] In the second power generation sub-cycle:

[0096] The pressurization step: the low-temperature second cycle working medium is pressurized in liquid form by the fourth pressurizing pump 71.

[0097] The heat exchange step: the pressurized low-temperature second cycle working medium absorbs the heat of the first cycle working medium at the second heater 41, and is itself warmed and evaporated.

[0098] Work step: the second cycle working medium after temperature rising expands outside in the second turbine expander 51 to do work, and its temperature and pressure decrease.

[0099] Cooling step: the second cycle working medium after work is heated in the LNG evaporator 6 with natural liquefied gas, and its temperature and pressure decrease, forming low-temperature second cycle working medium, and then repeating the pressurization step, heat exchange step, work step to carry out the second power generation cycle.

[0100] It can be understood that in some embodiments, the number of cascaded multiple power generation cycle loop arrangements exceeds two, the heat from the first heater 4 can be transmitted layer by layer downward through the cascaded multiple power generation cycle loop arrangements, the LNG evaporator 6 is arranged in the last power generation cycle loop, and the cold energy can be transmitted layer by layer upward through the cascaded multiple power generation cycle loop arrangements, so that the cascade utilization of LNG cold energy and waste heat in the air separation unit is realized through the cascade arrangement of multiple power generation cycle loops.

[0101] <Third embodiment>

[0102] Figure 3 The structure diagram of the LNG cold energy cascade utilization power generation system combined with the air separation unit in the third embodiment of the present application.

[0103] As Figure 3 shown, in the present embodiment, the ethylene glycol water circulation unit and the power generation cycle unit are the same as the first embodiment. In the LNG supply path, the LNG evaporator 6 is further connected with a natural gas expander 8.

[0104] The liquefied natural gas after absorbing heat in the air unit and the LNG evaporator 6 in turn is input into the natural gas expander 8 to expand and do work, which can convert the heat absorbed by the liquefied natural gas in the LNG supply path into electrical energy and output, further improving the power generation capacity and realizing efficient utilization of energy.

[0105] Further, the first pressurization pump 1 pressurizes the externally input liquefied natural gas to a pressure higher than the input pressure of the external natural gas supply pipeline network, and after the liquefied natural gas flows through the air separation unit, the LNG evaporator 6 and the natural gas expander 8 in turn, the pressure of the liquefied natural gas is the required input pressure of the external natural gas supply pipeline network, and the liquefied natural gas is input into the natural gas supply pipeline network.

[0106] In the power generation method applied to the LNG cold energy cascade utilization power generation system combined with the air separation unit in the present embodiment, the steps in the ethylene glycol water circulation unit and the power generation cycle unit are the same as the first embodiment, and the following steps are included in the LNG supply path:

[0107] LNG pressurization step: liquefied natural gas from external supply is pressurized by the first pressurization pump 1 to maintain the flow stability of the LNG supply line.

[0108] Heating step: the pressurized liquefied natural gas enters the air separation unit 2 to cool the air and increase its temperature.

[0109] Reheating step: the liquefied natural gas output from the air separation unit 2 cools the circulating working medium in the power generation cycle unit at the LNG evaporator 6, and the temperature of the liquefied natural gas is further increased and gasified.

[0110] Work step: after the liquefied natural gas is heated and gasified by the reheating step, it is first input into the natural gas turbine expander 8 to expand and do work outside, and then the temperature and pressure of the liquefied natural gas are reduced, and then it is input into the external natural gas supply pipeline network.

[0111] The above is only a preferred embodiment of the present application, and is not used to limit the present application, any modification, equivalent replacement and improvement within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. An LNG cold energy cascade utilization power generation system combined with an air separation unit, characterized in that, include: The LNG supply circuit includes a first booster pump, an air separation unit, and an LNG evaporator connected in sequence. The ethylene glycol water circulation unit includes the air separation unit, the second booster pump, and the first heater, which are connected in sequence. The power generation cycle unit, which circulates a working fluid to generate electricity, includes a first heater, a first turbine expander, an LNG evaporator, and a third booster pump. The LNG supply line carries externally input liquefied natural gas, which absorbs heat sequentially in the air separation unit and the LNG evaporator. Ethylene glycol water circulating in the ethylene glycol water circulation unit absorbs waste heat from the compressor stages, motor system, and lubrication oil system in the air separation unit, and then supplies it to the power generation circulation unit via heat exchange in the first heater. In the power generation cycle unit, the circulating working fluid exchanges heat with the ethylene glycol-water in the first heater, and the circulating working fluid exchanges heat with the liquefied natural gas in the LNG evaporator. The power generation cycle unit is formed by nesting multiple power generation cycle loops, and the nesting method is a cascaded arrangement. The power generation cycle unit includes a first power generation electronic circulation loop and a second power generation electronic circulation loop arranged in a cascaded manner. The first power generator circulation loop includes the first heater, the first turbine expander, the second heater, and the third booster pump, which are connected in sequence. The second power generator circuit includes the second heater, the second turbine expander, the LNG evaporator, and the fourth booster pump, which are connected in sequence.

2. The LNG cold energy cascade utilization power generation system combined with an air separation unit according to claim 1, characterized in that, In the LNG supply circuit, the liquefied natural gas input to the air separation unit is below -150°C, and the liquefied natural gas input to the LNG evaporator is below 0°C.

3. The LNG cold energy cascade utilization power generation system combined with an air separation unit according to claim 1, characterized in that, In the ethylene glycol water circulation unit, the ethylene glycol water input to the air separation unit is below the ambient temperature, while the ethylene glycol water input to the first heater is above the ambient temperature.

4. The LNG cold energy cascade utilization power generation system combined with an air separation unit according to claim 1, characterized in that, In the power generation cycle unit, the temperature of the circulating working fluid is higher than the ambient temperature after flowing through the first heater, and the temperature of the circulating working fluid is lower than the ambient temperature after flowing through the LNG evaporator.

5. The LNG cold energy cascade utilization power generation system combined with an air separation unit according to claim 1, characterized in that, The LNG evaporator is also connected to a natural gas expander.

6. A power generation method, applied to an LNG cold energy cascade utilization power generation system combined with an air separation unit as described in any one of claims 1-5, characterized in that, Includes the following steps: The power generation cycle unit includes: Working fluid pressurization step: The cryogenic circulating working fluid is pressurized in liquid form by the third booster pump; Working fluid heat exchange step: The pressurized low-temperature circulating working fluid absorbs heat from the ethylene glycol-water circulation unit at the first heater and heats up to evaporate; The working process of the working fluid is as follows: after being heated, the circulating working fluid expands and does work in the first turbine expander, while its own temperature and pressure decrease. Working fluid cooling step: The working fluid that has done work absorbs the low-temperature cold energy of liquefied natural gas at the LNG evaporator, cools down and liquefies to form a low-temperature circulating working fluid, and then repeats the working fluid pressurization step, the working fluid heat exchange step, and the working fluid work step to carry out the power generation cycle. The ethylene glycol water circulation unit includes: Heat absorption step: Ethylene glycol water flows through the air separation unit and absorbs residual heat, causing its own temperature to rise; Pressurization step: The ethylene glycol water flows through the second booster pump, its own pressure increases, and the flow rate of the ethylene glycol water circulation unit remains stable; Cooling step: Ethylene glycol water heats the low-temperature circulating working fluid in the power generation cycle unit at the first heater, and its own temperature drops. Then, the heat absorption step and the pressurization step are repeated to circulate ethylene glycol water. The LNG supply line includes: LNG pressurization step: The liquefied natural gas supplied from the outside is pressurized by the first pressurization pump to maintain a stable flow rate in the LNG supply line; Heating step: The pressurized liquefied natural gas enters the air separation unit to cool the air, and its own temperature rises; Reheating step: The liquefied natural gas output from the air separation unit cools the circulating working fluid in the power generation cycle unit at the LNG evaporator, further increasing the temperature of the liquefied natural gas and causing it to vaporize, and then it is introduced into the external natural gas supply network.

7. The power generation method according to claim 6, characterized in that, The LNG supply line also includes: Work steps: After the liquefied natural gas is heated and vaporized through the reheating step, first... The natural gas turbine expander is input to expand and do work, causing the temperature and pressure of the liquefied natural gas to drop, and then it is introduced into the external natural gas supply network.

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