A light hydrocarbon separation coupled cycle power generation system using LNG cold energy

Abstract

The present invention relates to the technical field of LNG cold energy utilization, and discloses a light hydrocarbon separation coupled cycle power generation system utilizing LNG cold energy, comprising an LNG light hydrocarbon separation system for recovering C2+ light hydrocarbon resources, and an organic Rankine cycle system, a Kalina cycle system, and a natural gas direct expansion system connected to the LNG light hydrocarbon separation system and used for power generation; the present invention effectively improves the thermal efficiency, efficiency and power generation efficiency of the system through the cascade integrated utilization of LNG cold energy; the overall system design of the present invention is reasonable and compact, and has the advantages of safe and flexible control, high efficiency and energy saving, strong practicality and low cost.

Description

Technical Field

[0001] The invention relates to the technical field of LNG cold energy utilization and discloses a light hydrocarbon separation coupled cycle power generation system utilizing LNG cold energy. Background Art

[0002] LNG needs to be gasified to room temperature before it can be supplied to users. During the gasification process, LNG will release about 830-860 kWh / kg of cold energy. If this part of cold energy can be utilized, it will generate huge economic benefits. The C2+ light hydrocarbon components rich in LNG are very high-quality chemical raw materials and can be used to produce many petrochemical products with high added value. Using LNG cold energy to separate its own light hydrocarbon components can achieve efficient utilization of LNG, but the utilization rate of LNG cold energy is not high.

[0003] The organic Rankine cycle using low-boiling-point hydrocarbons and their mixtures as working fluids has good application prospects in the field of medium and low-temperature thermal power generation; the Kalina cycle uses an ammonia-water mixture as a working fluid, and its endothermic evaporation process is a variable temperature process, which can better match the heat release process of the heat source with the heat absorption process curve of the mixed working fluid, thereby minimizing the irreversible loss in the heat release process and improving its thermal energy utilization efficiency. However, both of the above technologies require a refrigerant to complete the cycle. Using LNG as a cold source can further improve its power generation efficiency, but the utilization rate of LNG cold energy is not high. Natural gas direct expansion power generation technology has the advantages of simple process and low cost, but it can only utilize the pressure energy of LNG and also has the disadvantage of low cold energy utilization.

[0004] In summary, LNG light hydrocarbon separation, organic Rankine cycle and Kalina cycle are only single utilization of LNG cold energy, so there are problems such as insufficient utilization of LNG cold energy and mismatch between cold temperature and LNG temperature. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a light hydrocarbon separation coupled cycle power generation system utilizing LNG cold energy.

[0006] The technical solution of the present invention is: a light hydrocarbon separation coupled cycle power generation system utilizing LNG cold energy, comprising an LNG light hydrocarbon separation system for recovering C2+ light hydrocarbon resources, and an organic Rankine cycle system, a Kalina cycle system, and a natural gas direct expansion system connected to the LNG light hydrocarbon separation system and used for power generation;

[0007] The LNG light hydrocarbon separation system comprises an LNG pump, wherein the working medium outlet side of the LNG pump is connected to the inlet side of a tee, the first outlet side of the tee is connected to the cold flow inlet side of a first heat exchanger, the cold flow outlet side of the first heat exchanger is connected to the cold flow inlet side of a second heat exchanger, the cold flow outlet side of the second heat exchanger is connected to a first feed inlet of a flash tower, the second outlet side of the tee is connected to the cold flow inlet side of a third heat exchanger, the cold flow outlet side of the third heat exchanger is connected to a second feed inlet of the flash tower, the kettle liquid port of the flash tower is connected to the working medium inlet side of a kettle liquid pump, and the working medium of the kettle liquid pump is connected to the working medium of the kettle liquid pump. The outlet side of the flash tower is connected to the feed inlet of the demethanizer, and the bottom outlet of the demethanizer is connected to the feed inlet of the deethanizer; the top outlet of the flash tower is connected to the working fluid inlet side of the compressor, the working fluid outlet side of the compressor is connected to the heat flow inlet side of the second heat exchanger, and the heat flow outlet side of the second heat exchanger is connected to the first inlet side of the first mixer; the top outlet of the demethanizer is connected to the heat flow inlet side of the first heat exchanger, and the heat flow outlet side of the first heat exchanger is connected to the second inlet side of the first mixer; the top outlet of the deethanizer is connected to the first heat flow inlet side of the third heat exchanger;

[0008] The organic Rankine cycle system comprises an organic Rankine turbine expander, the outlet side of the organic Rankine turbine expander is connected to the second heat flow inlet side of the third heat exchanger, the second heat flow outlet side of the third heat exchanger is connected to the working fluid inlet side of the organic working fluid pump, the working fluid outlet side of the organic working fluid pump is connected to the working fluid inlet side of the first seawater heater, and the working fluid outlet side of the first seawater heater is connected to the working fluid inlet side of the organic Rankine turbine expander;

[0009] The Kalina circulation system includes a second mixer, the outlet side of the second mixer is connected to the working fluid inlet side of the ammonia water pump, the working fluid outlet side of the ammonia water pump is connected to the working fluid inlet side of the second seawater heater, the working fluid outlet side of the second seawater heater is connected to the feed inlet of the ammonia separator, the bottom discharge port of the ammonia separator is connected to the heat flow inlet side of the fifth heat exchanger, the heat flow outlet side of the fifth heat exchanger is connected to the first inlet side of the second mixer, the top discharge port of the ammonia separator is connected to the working fluid inlet side of the ammonia turbine expander, the working fluid outlet side of the ammonia turbine expander is connected to the heat flow inlet side of the fourth heat exchanger, and the heat flow outlet side of the fourth heat exchanger is connected to the second inlet side of the second mixer;

[0010] The natural gas direct expansion system includes a first mixer, the outlet side of the first mixer is connected to the cold flow inlet side of the fourth heat exchanger, the cold flow outlet side of the fourth heat exchanger is connected to the cold flow inlet side of the fifth heat exchanger, the cold flow outlet side of the fifth heat exchanger is connected to the working fluid inlet side of the third seawater heater, and the working fluid outlet side of the third seawater heater is connected to the working fluid inlet side of the natural gas turbine expander.

[0011] Furthermore, the working fluid at the inlet side of the LNG pump is liquefied natural gas; liquefied natural gas is rich in C2+ light hydrocarbon components and is a very high-quality chemical raw material that can be used to produce many petrochemical products with high added value.

[0012] Furthermore, the working fluid on the first hot flow outlet side of the third heat exchanger is liquid ethane; cooling and liquefying the ethane released from the deethanizer can facilitate the storage and transportation of ethane.

[0013] Furthermore, the working fluid of the bottom outlet of the deethanizer is liquefied petroleum gas; the liquefied petroleum gas is composed of high-purity ethane and rich propane, butane, etc. The produced liquefied petroleum gas can be used to produce and synthesize a variety of products.

[0014] Furthermore, the cold source medium in the organic Rankine cycle system is LNG; LNG releases about 830-860 kWh / kg of cold energy during the gasification process, which can generate huge economic benefits.

[0015] Furthermore, the working fluid in the organic Rankine cycle is R245fa pentafluoropropane or R365mfc pentafluorobutane or n-Nonane n-nonane or n-Octane n-octane or n-Pentane n-pentane; the fluorine-containing products have good stability and non-flammable properties, and n-Nonane n-nonane, n-Octane n-octane, and n-Pentane n-pentane can achieve good utilization effects in pressurized heating.

[0016] Furthermore, the cold source medium in the Kalina cycle system is liquefied natural gas; liquefied natural gas can release a large amount of cold energy during the gasification process, which can effectively improve the cooling efficiency.

[0017] Furthermore, the circulating medium in the Kalina cycle system is an ammonia-water mixture; the ammonia-water mixture can be cooled into ammonia water by liquefied natural gas in the fourth heat exchanger, and the Kalina cycle can be realized at a lower cost.

[0018] Furthermore, the outlet side of the natural gas turbine expander is connected to a user or an enterprise, and can directly provide electric energy to the user or the enterprise.

[0019] Compared with the prior art, the present invention has the following beneficial effects: the overall system design of the present invention is reasonable, and part of the cold energy of LNG is utilized to recover C2+ light hydrocarbon resources in LNG through light hydrocarbon separation; the cold energy of LNG is utilized as the cold source of the Rankine cycle, and the ethane released from the deethanizer can be cooled and liquefied, which is convenient for the storage and transportation of ethane; the methane-rich natural gas that has absorbed the cold energy of LNG after separation of light hydrocarbons is used as the cold source of the Kalina cycle, and the methane-rich natural gas after heat absorption can be used for expansion power generation; through the cascade integrated utilization of LNG cold energy, the thermal efficiency of the system is effectively improved, The overall system design of the present invention is reasonable and compact, and has the advantages of safe and flexible control, high efficiency and energy saving, strong practicality and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a system processing flow chart of the present invention;

[0021] Among them, 1-LNG pump, 2-tee, 3-first heat exchanger, 4-second heat exchanger, 5-flash tower, 6-kettle liquid pump, 7-demethanizer, 8-deethanizer, 9-third heat exchanger, 10-compressor, 11-organic working fluid pump, 12-first seawater heater, 13-organic Rankine turbine expander, 14-first mixer, 15-fourth heat exchanger, 16-second mixer, 17-ammonia pump, 18-second seawater heater, 19-ammonia separator, 20-fifth heat exchanger, 21-ammonia turbine expander, 22-third seawater heater, 23-natural gas turbine expander. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below in conjunction with specific implementation methods to better reflect the advantages of the present invention.

[0023] Example

[0024] like Figure 1 A light hydrocarbon separation coupled cycle power generation system utilizing LNG cold energy is shown, comprising an LNG light hydrocarbon separation system for recovering C2+ light hydrocarbon resources, and an organic Rankine cycle system, a Kalina cycle system, and a natural gas direct expansion system connected to the LNG light hydrocarbon separation system and used for power generation;

[0025] The LNG light hydrocarbon separation system includes an LNG pump 1, the working fluid outlet side of the LNG pump 1 is connected to the inlet side of the tee 2, the first outlet side of the tee 2 is connected to the cold flow inlet side of the first heat exchanger 3, the cold flow outlet side of the first heat exchanger 3 is connected to the cold flow inlet side of the second heat exchanger 4, the cold flow outlet side of the second heat exchanger 4 is connected to the first feed inlet of the flash tower 5, the second outlet side of the tee 2 is connected to the cold flow inlet side of the third heat exchanger 9, the cold flow outlet side of the third heat exchanger 9 is connected to the second feed inlet of the flash tower 5, the kettle liquid port of the flash tower 5 is connected to the working fluid inlet side of the kettle liquid pump 6, and the working fluid outlet of the kettle liquid pump 6 The side of the flash tower 5 is connected to the feed inlet of the demethanizer 7, and the bottom discharge port of the demethanizer 7 is connected to the feed inlet of the deethanizer 8; the top discharge port of the flash tower 5 is connected to the working fluid inlet side of the compressor 10, the working fluid outlet side of the compressor 10 is connected to the heat flow inlet side of the second heat exchanger 4, and the heat flow outlet side of the second heat exchanger 4 is connected to the first inlet side of the first mixer 14; the top discharge port of the demethanizer 7 is connected to the heat flow inlet side of the first heat exchanger 3, and the heat flow outlet side of the first heat exchanger 3 is connected to the second inlet side of the first mixer 14; the top discharge port of the deethanizer 8 is connected to the first heat flow inlet side of the third heat exchanger 9;

[0026] The working fluid at the inlet side of the LNG pump 1 is liquefied natural gas; the working fluid at the first hot flow outlet side of the third heat exchanger 9 is liquid ethane; the working fluid at the bottom outlet of the deethanizer 8 is liquefied petroleum gas;

[0027] The organic Rankine cycle system includes an organic Rankine turbine expander 13, the outlet side of the organic Rankine turbine expander 13 is connected to the second heat flow inlet side of the third heat exchanger 9, the second heat flow outlet side of the third heat exchanger 9 is connected to the working fluid inlet side of the organic working fluid pump 11, the working fluid outlet side of the organic working fluid pump 11 is connected to the working fluid inlet side of the first seawater heater 12, and the working fluid outlet side of the first seawater heater 12 is connected to the working fluid inlet side of the organic Rankine turbine expander 13;

[0028] The cold source medium in the organic Rankine cycle system is LNG; the organic working fluid in the organic Rankine cycle is organic working fluid A, and the organic working fluid A specifically uses R245fa pentafluoropropane;

[0029] The Kalina circulation system includes a second mixer 16, the outlet side of the second mixer 16 is connected to the working fluid inlet side of an ammonia water pump 17, the working fluid outlet side of the ammonia water pump 17 is connected to the working fluid inlet side of a second seawater heater 18, the working fluid outlet side of the second seawater heater 18 is connected to the feed inlet of an ammonia separator 19, the bottom discharge port of the ammonia separator 19 is connected to the heat flow inlet side of a fifth heat exchanger 20, the heat flow outlet side of the fifth heat exchanger 20 is connected to the first inlet side of the second mixer 16, the top discharge port of the ammonia separator 19 is connected to the working fluid inlet side of an ammonia turbine expander 21, the working fluid outlet side of the ammonia turbine expander 21 is connected to the heat flow inlet side of a fourth heat exchanger 15, and the heat flow outlet side of the fourth heat exchanger 15 is connected to the second inlet side of the second mixer 16;

[0030] The cold source medium in the Kalina circulation system is liquefied natural gas; the circulating medium in the Kalina circulation system is ammonia water mixture;

[0031] The natural gas direct expansion system includes a first mixer 14, the outlet side of the first mixer 14 is connected to the cold flow inlet side of the fourth heat exchanger 15, the cold flow outlet side of the fourth heat exchanger 15 is connected to the cold flow inlet side of the fifth heat exchanger 20, the cold flow outlet side of the fifth heat exchanger 20 is connected to the working fluid inlet side of the third seawater heater 22, the working fluid outlet side of the third seawater heater 22 is connected to the working fluid inlet side of the natural gas turbine expander 23; the outlet side of the natural gas turbine expander 23 is connected to a user or an enterprise.

[0032] The working principle of this embodiment is as follows: LNG raw material is pressurized and transported to the tee 2 by the LNG pump 1, and the tee 2 divides the raw material into two streams of different sizes. The larger stream is heated twice by the first heat exchanger 3 and the second heat exchanger 4, and then enters the first feed inlet of the flash tower 5 for preliminary separation of methane. The smaller stream is heated by the third heat exchanger 9 and then enters the second feed inlet of the flash tower 5 for preliminary separation of methane. The heated LNG raw material is separated into methane-rich natural gas and kettle liquid rich in C2+ light hydrocarbon resources in the flash tower 5. The methane-rich natural gas is separated from the flash tower 5 by the methane-rich natural gas. The top of tower 5 is discharged, and the kettle liquid of the flash tower flows into the kettle liquid pump 6 for pressurization and then flows into the demethanizer 7 for further separation of methane. The demethanizer 7 separates the kettle liquid of the flash tower 5 into natural gas containing high-purity methane and a stream rich in C2+ light hydrocarbons. The methane-rich natural gas is discharged from the top of the demethanizer 7, and the kettle liquid of the demethanizer 7 flows into the deethanizer 8. The deethanizer 8 separates the liquid into high-purity ethane and a liquefied petroleum gas product rich in propane, butane and other components. The separated gaseous ethane is cooled in the third heat exchanger 9 to become a liquid ethane product, completing the light hydrocarbon separation process of LNG.

[0033] The organic working fluid is pressurized by the organic working fluid pump 11 and enters the first seawater heater 12 to be heated by seawater into a gas state, and then enters the organic Rankine turbine expander 13 to generate power. After the power generation process is completed, the output exhaust gas is cooled into a liquid state in the third heat exchanger 9, completing the organic Rankine cycle process;

[0034] After being pressurized by the ammonia pump 17, the ammonia water is heated by seawater in the second seawater heater 18 to be gas-liquid two-state, and then enters the ammonia separator 19 for gas-liquid separation, and the gas phase enters the ammonia turbine expander 21 to generate electricity, and the liquid phase is cooled by the fifth heat exchanger 20. After the power generation process is completed, the ammonia water mixture is cooled by LNG in the fourth heat exchanger 15 to be ammonia water, and then mixed with the ammonia water flowing out of the fifth heat exchanger 20 in the second mixer 16 to complete the Kalina cycle;

[0035] The methane-rich natural gas discharged from the top of the flash tower is compressed by the compressor 10 and then passed into the second heat exchanger 4 to be cooled into a liquid state. The methane-rich natural gas discharged from the top of the demethanizer enters the first heat exchanger 3 to be cooled into a liquid state. The two streams of LNG are mixed in the first mixer 14, and release cold energy through the fourth heat exchanger 15 and the fifth heat exchanger 20 in turn. They are then heated into a gaseous state by the third seawater heater 22 and enter the natural gas turbine expander 23 to generate power, thereby completing the direct expansion process of natural gas.

Claims

1. A light hydrocarbon separation coupled cycle power generation system utilizing LNG cold energy, comprising an LNG light hydrocarbon separation system for recovering C2+ light hydrocarbon resources, and an organic Rankine cycle system, a Kalina cycle system, and a natural gas direct expansion system connected to the LNG light hydrocarbon separation system and used for power generation; The LNG light hydrocarbon separation system comprises an LNG pump (1), wherein the working fluid outlet side of the LNG pump (1) is connected to the inlet side of a tee (2), the first outlet side of the tee (2) is connected to the cold flow inlet side of a first heat exchanger (3), the cold flow outlet side of the first heat exchanger (3) is connected to the cold flow inlet side of a second heat exchanger (4), the cold flow outlet side of the second heat exchanger (4) is connected to a first feed inlet of a flash tower (5), the second outlet side of the tee (2) is connected to the cold flow inlet side of a third heat exchanger (9), the cold flow outlet side of the third heat exchanger (9) is connected to a second feed inlet of the flash tower (5), the kettle liquid port of the flash tower (5) is connected to the working fluid inlet side of a kettle liquid pump (6), and the working fluid of the kettle liquid pump (6) is connected to the working fluid of the kettle liquid pump (6). The outlet side is connected to the feed inlet of the demethanizer (7), and the bottom outlet of the demethanizer (7) is connected to the feed inlet of the deethanizer (8); the top outlet of the flash tower (5) is connected to the working fluid inlet side of the compressor (10), the working fluid outlet side of the compressor (10) is connected to the heat flow inlet side of the second heat exchanger (4), and the heat flow outlet side of the second heat exchanger (4) is connected to the first inlet side of the first mixer (14); the top outlet of the demethanizer (7) is connected to the heat flow inlet side of the first heat exchanger (3), and the heat flow outlet side of the first heat exchanger (3) is connected to the second inlet side of the first mixer (14); the top outlet of the deethanizer (8) is connected to the first heat flow inlet side of the third heat exchanger (9); The organic Rankine cycle system comprises an organic Rankine turbine expander (13), the outlet side of the organic Rankine turbine expander (13) being connected to the second heat flow inlet side of the third heat exchanger (9), the second heat flow outlet side of the third heat exchanger (9) being connected to the working fluid inlet side of the organic working fluid pump (11), the working fluid outlet side of the organic working fluid pump (11) being connected to the working fluid inlet side of the first seawater heater (12), and the working fluid outlet side of the first seawater heater (12) being connected to the working fluid inlet side of the organic Rankine turbine expander (13); The Kalina circulation system comprises a second mixer (16), the outlet side of the second mixer (16) is connected to the working fluid inlet side of an ammonia water pump (17), the working fluid outlet side of the ammonia water pump (17) is connected to the working fluid inlet side of a second seawater heater (18), the working fluid outlet side of the second seawater heater (18) is connected to the feed inlet of an ammonia separator (19), the bottom discharge port of the ammonia separator (19) is connected to the heat flow inlet side of a fifth heat exchanger (20), the heat flow outlet side of the fifth heat exchanger (20) is connected to the first inlet side of the second mixer (16), the top discharge port of the ammonia separator (19) is connected to the working fluid inlet side of an ammonia turbine expander (21), the working fluid outlet side of the ammonia turbine expander (21) is connected to the heat flow inlet side of a fourth heat exchanger (15), and the heat flow outlet side of the fourth heat exchanger (15) is connected to the second inlet side of the second mixer (16); The natural gas direct expansion system comprises a first mixer (14), the outlet side of the first mixer (14) is connected to the cold flow inlet side of a fourth heat exchanger (15), the cold flow outlet side of the fourth heat exchanger (15) is connected to the cold flow inlet side of a fifth heat exchanger (20), the cold flow outlet side of the fifth heat exchanger (20) is connected to the working fluid inlet side of a third seawater heater (22), and the working fluid outlet side of the third seawater heater (22) is connected to the working fluid inlet side of a natural gas turbine expander (23).

2. According to claim 1, a light hydrocarbon separation coupled cycle power generation system utilizing LNG cold energy, It is characterized in that The working fluid on the inlet side of the LNG pump (1) is liquefied natural gas.

3. According to claim 1, a light hydrocarbon separation coupled cycle power generation system utilizing LNG cold energy, It is characterized in that The working fluid on the first hot flow outlet side of the third heat exchanger (9) is liquid ethane.

4. According to claim 1, a light hydrocarbon separation coupled cycle power generation system utilizing LNG cold energy, It is characterized in that The working fluid at the bottom outlet of the deethanizer (8) is liquefied petroleum gas.

5. According to claim 1, a light hydrocarbon separation coupled cycle power generation system utilizing LNG cold energy, It is characterized in that The cold source medium in the organic Rankine cycle is LNG.

6. According to claim 1, a light hydrocarbon separation coupled cycle power generation system utilizing LNG cold energy, It is characterized in that The working fluid in the organic Rankine cycle is pentafluoropropane, pentafluorobutane, n-nonane, n-octane or n-pentane.

7. According to claim 1, a light hydrocarbon separation coupled cycle power generation system utilizing LNG cold energy, It is characterized in that The cold source medium in the Kalina cycle system is liquefied natural gas.

8. According to claim 1, a light hydrocarbon separation coupled cycle power generation system utilizing LNG cold energy, It is characterized in that The circulating medium in the Kalina circulation system is an ammonia-water mixture.

9. According to claim 1, a light hydrocarbon separation coupled cycle power generation system utilizing LNG cold energy, It is characterized in that The outlet side of the natural gas turboexpander (23) is connected to a user or an enterprise.

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