Natural gas denitrification liquefaction device

Abstract

The utility model discloses a natural gas denitrification liquefying device, which solves the technical problem that the nitrogen content in a product LNG (Liquefied Natural Gas) exceeds 1 percent due to higher nitrogen content in natural gas. The device comprises a main heat exchanger, a heavy hydrocarbon separator, a denitrification tower, a denitrification tower condenser, a denitrification tower reboiler, a high-temperature refrigerant liquid separation tank, a low-temperature refrigerant liquid separation tank and the like. Cold energy at the top of the denitrification tower comes from circulating nitrogen, and a heat source at the bottom of the tower comes from low-temperature natural gas from which heavy hydrocarbon is removed. The device disclosed by the utility model has the advantages of simple process, high denitrification efficiency, strong operability, safety, reliability, low energy consumption, capability of obtaining good environmental protection benefits and economic benefits and the like.

Description

TECHNICAL FIELD

[0001] The utility model relates to a natural gas liquefaction device, specifically to a natural gas denitrogenation liquefaction device. BACKGROUND

[0002] Globally, the demand for natural gas as a clean energy source continues to grow. As the demand for cleaner energy increases globally, the proportion of natural gas in primary energy consumption will become increasingly large. In particular, in the face of environmental pressure and the demand for energy transformation, natural gas as a clean and efficient energy source will develop more quickly.

[0003] With the continuous development and innovation of technology, solving the problems of high energy consumption and safety hazards encountered in the liquefaction process of high-nitrogen natural gas plays an increasingly important role in the energy field. High nitrogen content in liquefied natural gas products not only hinders product storage, but also hinders downstream product utilization. Therefore, natural gas liquefaction devices with high nitrogen content must be equipped with a denitrogenation process. In the production and application of liquefied natural gas (LNG), denitrogenation liquefaction technology innovation will further improve the production efficiency and safety of LNG, meeting the global demand for clean energy.

[0004] The application of natural gas denitrogenation liquefaction technology aims to improve the quality and utilization rate of natural gas and reduce energy consumption. Through denitrogenation treatment, the quality and safety of natural gas have been improved. The GB / T 38753-2020 standard requires that the molar fraction of nitrogen in liquefied natural gas quality requirements be ≤1%. Similarly, experience shows that the nitrogen content in LNG is less than 1%, and the monitoring of boil-off gas can effectively prevent the rolling phenomenon during LNG storage and transportation.

[0005] CN115638609A discloses a natural gas liquefaction denitrogenation device and its denitrogenation process, including raw material gas precooling, high-pressure tower (lower tower) rectification, low-pressure tower (upper tower) rectification, product gas reheating / mixed refrigerant circulation, etc. Although single-tower technology reduces the number of equipment, the method of denitrogenation of natural gas / liquefied natural gas from nitrogen-containing methane gas only uses mixed refrigerant to provide cold energy, which requires a large amount of mixed refrigerant circulation, resulting in increased cost of cold box, increased energy efficiency of mixed refrigerant compressor, and increased overall project investment.

[0006] CN103697659A discloses a device and method for preparing liquefied natural gas and hydrogen-rich product from methane-rich gas, the device comprising a mixed refrigerant compressor refrigeration system, a precooling system, a liquefaction cold box system, and a nitrogen compressor system; the method comprising a mixed refrigerant circulation process, a methane-rich gas liquefaction and separation process, and a nitrogen refrigerant circulation process. The low-temperature hydrogen-rich gas generated by the rectification tower, the low-temperature nitrogen gas evaporated from the external liquid nitrogen of the condenser, and the liquid nitrogen before the condenser evaporator are supercooled, which is different from the traditional supercooled liquefied natural gas. The heat exchange curve of the cold fluid and the hot fluid in the entire heat exchanger process is more matched, and the temperature difference at the cold end of the heat exchanger is smaller, so the heat exchange efficiency is higher and the energy consumption is lower. However, the number of equipment in this patent is large, and the overall project investment is high.

[0007] CN113865263A discloses a production system for extracting crude helium from natural gas and producing liquefied natural gas, which adopts a mixed refrigeration cycle and a nitrogen expansion throttling refrigeration cycle to meet the cold quantity required for helium extraction and liquefied natural gas production. The process mainly extracts crude helium from natural gas and produces liquefied natural gas. In the process design, there are first-stage, second-stage, and third-stage helium extraction units, each of which is designed with a heat exchanger, a rectification tower, a tower top condenser, and a tower bottom reboiler. The device process is very complex.

[0008] Therefore, it is necessary to provide a natural gas liquefaction denitrification device and process to solve the above problems. Utility model content

[0009] The utility model discloses a kind of natural gas denitrification liquefied device and process, to solve the problem that the nitrogen content of raw material natural gas is higher in prior art, leading to the nitrogen content of liquefied natural gas after natural gas liquefaction exceeds standard requirement, simultaneously, solve the problems of many equipment quantity, complex process, control loop is complicated, engineering investment is big in existing denitrification process, the utility model provides a kind of natural gas liquefaction denitrification device and process.

[0010] To achieve the above object, the utility model provides the following technical scheme:

[0011] The utility model provides a kind of natural gas denitrification liquefied device and process, including main heat exchanger, heavy hydrocarbon separator, denitrification tower, denitrification tower condenser, denitrification tower reboiler, high-temperature refrigerant separator tank and low-temperature refrigerant separator tank etc. Preferably, denitrification tower condenser, denitrification tower reboiler are integrated into denitrification tower interior, reduce process equipment quantity, reduce energy consumption, reduce engineering investment again, improve enterprise economic benefit.

[0012] The main heat exchanger is provided with a raw material natural gas passage I, a raw material natural gas passage II, a raw material natural gas passage III, a liquefied natural gas passage I, a circulating nitrogen gas passage I, a circulating nitrogen gas passage II, a nitrogen-rich tail gas passage I, a high-pressure gas-phase cold agent passage I, a high-pressure gas-phase cold agent counter-flow passage II, a high-pressure liquid-phase cold agent passage I and a backflow cold agent passage I.

[0013] The inlet end of the raw material natural gas passage I is connected with an external purified raw material gas pipeline, the outlet end of the raw material natural gas passage I is connected with the inlet of a heavy hydrocarbon separator, the liquid-phase outlet of the heavy hydrocarbon separator is connected with an external heavy hydrocarbon pipeline, the gas-phase outlet pipeline of the heavy hydrocarbon separator is connected with the inlet end of the raw material natural gas passage II, the outlet end of the raw material natural gas passage II is connected with the inlet of a denitrogenation tower reboiler, the outlet of the denitrogenation tower reboiler is connected with the inlet end of the raw material natural gas passage III, the outlet end of the raw material natural gas passage III is connected with the inlet of the denitrogenation tower, the bottom outlet of the denitrogenation tower is connected with the inlet end of the liquefied natural gas passage I, and the outlet end of the liquefied natural gas passage I is connected with an external LNG pipeline.

[0014] Preferably, the inlet end of the circulating nitrogen gas passage I is connected with an external circulating nitrogen gas inlet pipeline, the outlet end of the circulating nitrogen gas passage I is connected with the inlet of a denitrogenation tower condenser, the outlet of the denitrogenation tower condenser is connected with the inlet end of the circulating nitrogen gas passage II, and the outlet end of the circulating nitrogen gas passage II is connected with an external circulating nitrogen gas outlet pipeline.

[0015] Preferably, the inlet end of the high-pressure gas-phase cold agent passage I is connected with an external high-pressure cold agent gas-phase pipeline, the outlet end of the high-pressure gas-phase cold agent passage I is connected with the inlet of a low-temperature cold agent separation tank, the first (upper) outlet and the second (lower) outlet of the low-temperature cold agent separation tank are connected with the inlet end of the high-pressure gas-phase cold agent counter-flow passage II, the outlet end of the high-pressure gas-phase cold agent counter-flow passage II is connected with the inlet end of the backflow cold agent passage I after being discharged from the main heat exchanger and then returning, the inlet end of the high-pressure liquid-phase cold agent passage I is connected with an external high-pressure cold agent liquid-phase pipeline, the outlet end of the high-pressure liquid-phase cold agent passage I is connected with the inlet end of a high-temperature cold agent separation tank, the first (upper) outlet end and the second (lower) outlet of the high-temperature cold agent separation tank are connected with the inlet end of the backflow cold agent passage I, and the outlet end of the backflow cold agent passage I is connected with an external cold agent return pipeline.

[0016] Preferably, the main heat exchanger is a plate heat exchanger, and the denitrogenation tower condenser and the denitrogenation tower reboiler are shell-and-tube heat exchangers. The denitrogenation tower condenser and the denitrogenation tower reboiler are integrated into the denitrogenation tower, so that the number of process equipment is reduced.

[0017] Preferably, the first regulating valve is arranged on the connecting pipeline between the outlet end of the raw material gas passage III and the inlet of the denitrification tower; the second regulating valve is arranged on the connecting pipeline between the outlet end of the circulating nitrogen gas passage I and the inlet of the denitrification tower condenser; the third regulating valve is arranged on the connecting pipeline between the top outlet of the denitrification tower and the inlet end of the nitrogen-rich tail gas passage I; the fourth regulating valve is arranged on the connecting pipeline between the outlet end of the high-pressure liquid-phase refrigerant passage I and the inlet of the high-temperature refrigerant distribution tank; the fifth regulating valve is arranged on the connecting pipeline between the outlet end of the high-pressure gas-phase refrigerant passage I and the inlet of the low-temperature refrigerant distribution tank; and the sixth regulating valve is arranged on the connecting pipeline between the outlet end of the liquefied natural gas passage I and the LNG pipeline for external delivery.

[0018] The natural gas for denitrification treatment of the device comes from a raw gas pretreatment section, is pressurized to 5.5 MPaG by a raw gas compressor, and is then sent to a purification unit. After purification treatment (CO2 content ≤ 50 ppm, H2O content ≤ 1 ppm, and mercury content ≤ 0.01 μg / m3), the natural gas (natural gas CH4 content 80%~95%, nitrogen content 1%~10%) is sent to a cold box for denitrification and liquefaction.

[0019] The process features of the natural gas denitrification and liquefaction device provided by the utility model include the following aspects:

[0020] S1, natural gas treatment process

[0021] The purified natural gas CH4 content 80%~95%, nitrogen content 1%~10% after the pretreatment section pressurization (pressurized to 5.5MPa), purification (MDEA aqueous solution removes CO2, molecular sieve removes H2O) enters the raw material natural gas passage I of the main heat exchanger after being precooled to -40±2℃, enters the heavy hydrocarbon separator for gas-liquid separation, the bottom low-temperature liquid is connected with the external heavy hydrocarbon pipeline from the liquid phase outlet of the heavy hydrocarbon separator, the top low-temperature gas leaves from the gas phase outlet of the heavy hydrocarbon separator and returns to the raw material natural gas passage II of the main heat exchanger and is continuously cooled to about -66±2℃, then flows out from the raw material natural gas passage II outlet end, is sent to the inlet of the denitrogenation tower reboiler as the heat source of the reboiler, is cooled to about -92±3℃, then leaves from the outlet end of the denitrogenation tower reboiler, returns to the raw material natural gas passage III of the main heat exchanger and is continuously cooled to about -140±2℃, then is regulated to 3.0 ±0.2MpaG through the first regulating valve and is sent to the inlet of the denitrogenation tower for rectification, the product liquid at the bottom outlet of the denitrogenation tower is sent to the liquefied natural gas passage I of the main heat exchanger and is continuously supercooled to -162±1℃, then is reduced to 0.5 ±0.1MpaG through the sixth pressure regulating valve and is connected with the LNG pipeline for external delivery, and the nitrogen molar fraction of the denitrogenated natural gas is ≤1%. The low-temperature gas at the top outlet of the denitrogenation tower is regulated to 0.35±0.05 MpaG through the third regulating valve and is sent to the rich nitrogen tail gas passage I of the main heat exchanger, is heated to about 10±2℃ and is sent out of the cold box.

[0022] S2, circulating nitrogen treatment process

[0023] The circulating nitrogen after pressurization by the circulating nitrogen compressor enters the circulating nitrogen passage I of the main heat exchanger and is cooled to -165±1℃, then is regulated to 1.5 ±0.2MpaG through the second regulating valve and is sent to the inlet of the denitrogenation tower condenser as the cold source of the denitrogenation tower condenser, is heated to about -162±1℃ and leaves from the outlet end of the denitrogenation tower condenser, returns to the circulating nitrogen passage II of the main heat exchanger and is continuously reheated to about 9±2℃, and the outlet end of the circulating nitrogen passage II is connected with the external circulating nitrogen back gas pipeline and returns to the inlet of the circulating nitrogen compressor.

[0024] S3, mixed refrigerant treatment process

[0025] The high-pressure gas-phase refrigerant is sent to the high-pressure gas-phase refrigerant passage I of the main heat exchanger through a high-pressure refrigerant gas-phase pipeline, is cooled to -165±1℃, and then is sent to the inlet of the low-temperature refrigerant separation tank after being regulated to 0.38±0.02 MpaG by the fifth regulating valve, is separated into gas and liquid, and then is returned to the high-pressure gas-phase refrigerant counterflow passage II of the main heat exchanger from the first outlet and the second outlet of the low-temperature refrigerant separation tank to provide cold energy, is reheated to about -78±2℃, and is sent to the inlet of the counterflow refrigerant passage I. The high-pressure liquid-phase refrigerant is sent to the high-pressure liquid-phase refrigerant passage I of the main heat exchanger through a high-pressure refrigerant gas-liquid-phase pipeline, is cooled to -66±2℃, and then is sent to the inlet of the low-temperature refrigerant separation tank after being regulated to 0.36±0.02 MpaG by the fourth regulating valve, is separated into gas and liquid, and then is returned to the counterflow refrigerant passage I of the main heat exchanger from the first outlet and the second outlet of the low-temperature refrigerant separation tank to provide cold energy, the mixed refrigerant is reheated to about 9±2℃, and flows out from the outlet of the counterflow refrigerant passage I to the external refrigerant return pipeline.

[0026] The composition of the mixed refrigerant is methane, nitrogen, propane, ethylene and isopentane, and the specific component ratio is adjusted according to the component of the raw gas of an actual project.

[0027] Based on the technical scheme, compared with the prior art, the embodiment of the utility model can at least produce the following technical effects:

[0028] (1) In the liquefied cold box of the utility model, the mixed refrigerant and the circulating nitrogen jointly act to provide cold energy for the cold box and the denitrogenation tower. The mixed refrigerant single-cycle double-throttling refrigeration process is adopted, the gas-liquid two-phase separated after the refrigerant is pressurized enters the cold box, the liquid-phase refrigerant medium provides a shallow cold temperature field and a heat medium for heat exchange and heat absorption, and is gasified until the temperature is raised to normal temperature, the gas-phase refrigerant medium provides a shallow cold temperature field and a deep cold temperature field to provide cold energy for the natural gas, and the purpose of liquefied natural gas is achieved. In the whole heat exchange process, the latent heat and the sensible heat of different components in the refrigerant are fully utilized to complete the refrigeration of the natural gas. The heat transfer efficiency is high, the heat exchange effect of the deep cold section is good, and the control is relatively easy. The circulating nitrogen throttling refrigeration process is adopted, the circulating nitrogen pressurized by the circulating nitrogen compressor enters the cold box for heat exchange, is secondarily cooled after being discharged from the cold box, and provides cold energy for the denitrogenation tower, thereby reducing the load of the mixed refrigerant. The nitrogen removed from the top of the denitrogenation tower is returned to the cold box for heat recovery, thereby reducing the energy consumption.

[0029] (2) The utility model selects single tower technology, rectifies nitrogen and hydrogen gas simultaneously, designs a rectifying tower, a tower top condensation evaporimeter, a tower top gas liquid separator and a tower bottom reboiler, reduces the cold box cost, reduces the overall project investment, makes full use of mixed refrigerant and circulating nitrogen to provide cold energy together, integrates the denitrogenation tower condenser and the denitrogenation tower reboiler into the denitrogenation tower, reduces the number of process equipment, reduces energy consumption, reduces engineering investment, improves enterprise economic benefit, can effectively solve the problem of natural gas final nitrogen content exceeding the standard, recovers the cold energy of removed nitrogen, and reduces energy consumption.

[0030] (3) The utility model provides a kind of natural gas denitrogenation liquefaction process, by sequentially treating natural gas to be handled with heavy hydrocarbon removal treatment, nitrogen removal treatment continues cryogenic to product LNG, process equipment quantity is less, energy consumption is low, with the advantages of simple process, low production cost, strong operability, safe and reliable. BRIEF DESCRIPTION OF DRAWINGS

[0031] The technical solutions of the utility model will be further described below in combination with drawings and through specific embodiments.

[0032] Figure 1 It is a kind of natural gas denitrogenation liquefying device's structural schematic diagram described in the utility model.

[0033] Reference signs: 2-main heat exchanger;3-heavy hydrocarbon separator;3-A-heavy hydrocarbon separator inlet end;3-B-heavy hydrocarbon separator gas phase outlet;3-C-heavy hydrocarbon separator liquid phase outlet;4-denitrogenation tower;4-A-denitrogenation tower entrance;4-B-denitrogenation tower top outlet;4-C-denitrogenation tower bottom outlet;5-denitrogenation tower condenser;5-A-denitrogenation tower condenser entrance;5-B-denitrogenation tower condenser outlet;6-denitrogenation tower reboiler;7-high temperature cold agent separation tank;7-A-high temperature cold agent separation tank entrance;7-B-high temperature cold agent separation tank first outlet;7-C-high temperature cold agent separation tank second outlet;8-low temperature cold agent separation tank;8-A-low temperature cold agent separation tank entrance;8-B-low temperature cold agent separation tank first outlet;8-C-low temperature cold agent separation tank second outlet;

[0034] 101-raw material natural gas passage I, 102-raw material natural gas passage II, 103-raw material natural gas passage III, 104-liquefied natural gas passage I, 105-circulating nitrogen passage I, 106-circulating nitrogen passage II, 107-nitrogen-rich tail gas passage I, 108-high pressure gas phase cold agent passage I, 109-high pressure gas phase cold agent backflow passage II, 110-high pressure liquid phase cold agent passage I and 111-backflow cold agent passage I. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the utility model clearer, the technical scheme of the utility model will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the utility model, rather than all the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by those skilled in the art without creative labor belong to the scope protected by the utility model.

[0036] As shown in Figure 1 The utility model provides a natural gas denitrogenation liquefying device, including: main heat exchanger 2, heavy hydrocarbon separator 3, denitrogenation tower 4, denitrogenation tower condenser 5, denitrogenation tower reboiler 6, high temperature cold agent distribution tank 7, low temperature cold agent distribution tank 8, preferably, denitrogenation tower condenser 5, denitrogenation tower reboiler 6 are integrated into the inside of denitrogenation tower 4, reduce the number of process equipment, reduce energy consumption.

[0037] The main heat exchanger 2 is equipped with raw material natural gas passage I 101, raw material natural gas passage II 102, raw material natural gas passage III 103, liquefied natural gas passage I 104, circulating nitrogen gas passage I 105, circulating nitrogen gas passage II 106, nitrogen-rich tail gas passage I 107, high-pressure gas-phase cold agent passage I 108, high-pressure gas-phase cold agent backflow passage II 109, high-pressure liquid-phase cold agent passage I 110 and backflow cold agent passage I 111.

[0038] The inlet end of raw material natural gas passage I 101 is connected with the external purified raw material gas pipeline, the outlet end of raw material natural gas passage I 101 is connected with the inlet end 3-A of heavy hydrocarbon separator, the liquid-phase outlet 3-C of heavy hydrocarbon separator is connected with the external heavy hydrocarbon pipeline, the gas-phase outlet 3-B of heavy hydrocarbon separator is connected with the inlet end of raw material natural gas passage II 102 through the pipeline, the outlet end of raw material natural gas passage II 102 is connected with the inlet end 6-A of denitrogenation tower reboiler 6, the outlet end 6-B of denitrogenation tower reboiler 6 is connected with the inlet end of raw material natural gas passage III 103, the outlet end of raw material natural gas passage III 103 is connected with the inlet 4-A of denitrogenation tower (middle part), the bottom outlet 4-C of denitrogenation tower is connected with the inlet end of liquefied natural gas passage I 104, the outlet end of liquefied natural gas passage I 104 is connected with the external LNG pipeline, and the nitrogen molar fraction of denitrogenated natural gas is less than or equal to 1%. The top outlet 4-B of denitrogenation tower is connected with the inlet end of nitrogen-rich tail gas passage I 107, and the outlet end of nitrogen-rich tail gas passage I 107 is connected with the external nitrogen-rich tail gas emission pipeline.

[0039] The inlet end of the circulating nitrogen passage I 105 is connected with an external circulating nitrogen inlet pipeline, the outlet end of the circulating nitrogen passage I 105 is connected with the inlet end 5-A of the denitrogenation tower condenser, the outlet end 5-B of the denitrogenation tower condenser is connected with the inlet end of the circulating nitrogen passage II 106, and the outlet end of the circulating nitrogen passage II 106 is connected with an external circulating nitrogen outlet pipeline.

[0040] The inlet end of the high-pressure gas-phase refrigerant passage I 108 is connected with an external high-pressure refrigerant gas pipeline, the outlet end of the high-pressure gas-phase refrigerant passage I 108 is connected with the inlet end 8-A of the low-temperature refrigerant separator tank, the first outlet 8-B and the second outlet 8-C of the low-temperature refrigerant separator tank are connected with the inlet end of the high-pressure gas-phase refrigerant reflux passage II 109, the outlet end of the high-pressure gas-phase refrigerant reflux passage II 109 is connected with the inlet end of the reflux refrigerant passage I 111 after passing through the main heat exchanger, the inlet end of the high-pressure liquid-phase refrigerant passage I 110 is connected with an external high-pressure refrigerant liquid pipeline, the outlet end of the high-pressure liquid-phase refrigerant passage I 110 is connected with the inlet end 7-A of the high-temperature refrigerant separator tank, the first outlet 7-B and the second outlet 7-C of the high-temperature refrigerant separator tank are connected with the inlet end of the reflux refrigerant passage I 111, and the outlet end of the reflux refrigerant passage I 111 is connected with an external refrigerant return pipeline.

[0041] The main heat exchanger is a plate heat exchanger, and the denitrogenation tower condenser and the denitrogenation tower reboiler are shell-and-tube heat exchangers.

[0042] The connecting pipeline between the outlet end of the raw material natural gas passage III 103 and the inlet end 4-A of the denitrogenation tower is provided with a first regulating valve 11, the connecting pipeline between the outlet end of the circulating nitrogen passage I 105 and the inlet end 5-A of the denitrogenation tower condenser 5 is provided with a second regulating valve 12, the connecting pipeline between the top outlet 4-B of the denitrogenation tower and the inlet end of the nitrogen-rich tail gas passage I 107 is provided with a third regulating valve 13, the connecting pipeline between the outlet end of the high-pressure liquid-phase refrigerant passage I 110 and the inlet end 7-A of the high-temperature refrigerant separator tank is provided with a fourth regulating valve 14, the connecting pipeline between the outlet end of the high-pressure gas-phase refrigerant passage I 108 and the inlet end 8-A of the low-temperature refrigerant separator tank is provided with a fifth regulating valve 15, and the connecting pipeline between the outlet end of the liquefied natural gas passage I 104 and the external LNG pipeline is provided with a sixth regulating valve 16. Embodiment

[0043] The natural gas denitrogenation liquefaction process of the natural gas denitrogenation liquefaction device has the following steps:

[0044] S1, natural gas treatment process

[0045] The purified natural gas (natural gas CH4 content 80%~95%, nitrogen content 1%~10%) after the pretreatment section pressurization (to about 5.5 MPa), purification (MDEA aqueous solution removes CO2, molecular sieve removes H2O) enters the raw material natural gas passage I 101 of the main heat exchanger 2 through the purified raw material gas pipeline and is pre-cooled to about -40℃, then enters the heavy hydrocarbon separator 3 for gas-liquid separation, the bottom low-temperature liquid is connected with the external heavy hydrocarbon pipeline from the liquid phase outlet 3-C of the heavy hydrocarbon separator 3, the top low-temperature gas leaves from the gas phase outlet 3-B of the heavy hydrocarbon separator 3 and returns to the raw material natural gas passage II 102 of the main heat exchanger 2 and is continuously cooled to about -66℃, then flows out from the outlet end of the raw material natural gas passage II 102, is sent to the inlet 6-A of the denitrogenation tower reboiler 6 as the heat source of the reboiler, is cooled to about -92℃, then leaves from the outlet end 6-B of the denitrogenation tower reboiler 6, is continuously cooled to about -140℃ in the raw material natural gas passage III 103 of the main heat exchanger 2, then is sent to the inlet 4-A of the denitrogenation tower 4 after pressure regulation to 3.0 MPaG through the first regulating valve 11, the product liquid of the bottom outlet 4-C of the denitrogenation tower 4 is sent to the liquefied natural gas passage I 104 of the main heat exchanger 2 and is continuously supercooled to -162℃, then is connected with the external LNG pipeline after pressure reduction to 0.5 MPaG through the sixth pressure regulating valve 16. The low-temperature gas of the top outlet 4-B of the denitrogenation tower 4 is sent to the rich nitrogen tail gas passage I 107 of the main heat exchanger 2 after pressure regulation to 0.35 MPaG through the third regulating valve 13, is heated to about 10℃ after heat exchange in the cold box and is sent out.

[0046] S2, circulating nitrogen treatment process

[0047] The circulating nitrogen after pressurization (to about 3.4 MPaG pressure) by the circulating nitrogen compressor enters the circulating nitrogen passage I 105 of the main heat exchanger 2 through the circulating nitrogen pipeline and is cooled to about -165℃, then is sent to the denitrogenation tower condenser inlet 5-A after pressure regulation to 1.5 MPaG through the second regulating valve 12, is heated to about -162℃ as the cold source of the denitrogenation tower condenser, then leaves from the denitrogenation tower condenser outlet end 5-B, is continuously reheated to about 9℃ in the circulating nitrogen passage II 106 of the main heat exchanger 2, the outlet end of the circulating nitrogen passage II 106 is connected with the external circulating nitrogen return gas pipeline and returns to the inlet of the circulating nitrogen compressor.

[0048] S3, mixed refrigerant treatment process

[0049] The high-pressure gas-phase cold agent (temperature 12°C, pressure 2.4 MPaG) is sent to the high-pressure gas-phase cold agent passage I 108 of the main heat exchanger 2 through the high-pressure cold agent gas-phase pipeline, cooled to -165°C, then regulated to 0.38 MPaG through the fifth regulating valve 15, and then sent to the low-temperature cold agent separation tank inlet 8-A. After gas-liquid separation, the low-temperature cold agent separation tank first outlet 8-B and second outlet 8-C (gas-liquid separation, to ensure the liquid level of the separator, and the gas-liquid outlets are mixed again in the cold box to provide cold energy) return the high-pressure gas-phase cold agent counterflow passage II 109 of the main heat exchanger 2 to provide cold energy. The high-pressure gas-phase cold agent counterflow passage II 109 is reheated to about -78°C and sent to the inlet of the counterflow cold agent passage I 111. The high-pressure liquid-phase cold agent (temperature 12°C, pressure 2.4 MPaG) is sent to the high-pressure liquid-phase cold agent passage I 110 of the main heat exchanger 2 through the high-pressure cold agent gas-liquid phase pipeline, cooled to -66°C, then regulated to about 0.36 MPaG through the fourth regulating valve 14, and then sent to the low-temperature cold agent separation tank inlet 7-A. After gas-liquid separation (gas-liquid separation, to ensure the liquid level of the separator, and the gas-liquid outlets are mixed again in the cold box to provide cold energy), the low-temperature cold agent separation tank first outlet 7-B and second outlet 7-C return the counterflow cold agent passage I 111 of the main heat exchanger 2 to provide cold energy. The mixed cold agent is reheated to about 9°C and flows out from the counterflow cold agent passage I 111 outlet to the external cold agent return pipeline.

[0050] The above process uses mixed refrigerant and circulating nitrogen to provide cold energy for the cold box and the denitrogenation tower. The mixed refrigerant single-cycle double-jet refrigeration process is used. After the gas-liquid two-phase separation of the pressurized cold agent, the liquid-phase cold agent medium provides a shallow cold temperature field and a heat medium for heat exchange and heat absorption vaporization until the temperature rises to normal temperature. The gas-phase cold agent medium provides a shallow cold and deep cold temperature field to provide cold energy for natural gas to achieve the purpose of liquefied natural gas. In the entire heat exchange process, the latent heat and sensible heat of different components in the cold agent are fully utilized to complete the refrigeration of natural gas. The process has high heat transfer efficiency, good heat exchange effect in the deep cold stage, and relatively easy control. The circulating nitrogen jet refrigeration process is used. The pressurized circulating nitrogen enters the cold box for heat exchange, is cooled again by the regulating valve, and provides cold energy for the denitrogenation tower to reduce the load of the mixed refrigerant. The nitrogen removed at the top of the denitrogenation tower is reheated in the cold box to recover cold energy and reduce energy consumption. The mixed refrigerant and the circulating nitrogen are fully utilized to provide cold energy. The denitrogenation tower condenser and the denitrogenation tower reboiler are integrated into the denitrogenation tower to reduce the number of process equipment, reduce energy consumption, reduce engineering investment, improve enterprise economic benefits, effectively solve the problem of excessive nitrogen content in natural gas, recover the cold energy of the removed nitrogen, and reduce energy consumption. By sequentially treating the to-be-processed natural gas to remove heavy hydrocarbons and nitrogen, the product LNG is continuously deep-cooled. The process has the advantages of few process equipment, low energy consumption, simple process, low production cost, strong operability, safety, and reliability.

[0051] The above is only a preferred embodiment of the present application, and is not used to limit the present application, and the patent protection scope of the present application is subject to the claims, and any equivalent structural changes made by using the content of the specification and drawings of the present application should also be included in the protection scope of the present application.

Claims

1. A natural gas denitrogenation liquefaction apparatus, characterized by, It comprises: The main heat exchanger (2), heavy hydrocarbon separator (3), denitrogenation tower (4), denitrogenation tower condenser (5), denitrogenation tower reboiler (6), high-temperature cold agent separation tank (7), low-temperature cold agent separation tank (8), The main heat exchanger (2) is provided with raw material natural gas passage I (101), raw material natural gas passage II (102), raw material natural gas passage III (103), liquefied natural gas passage I (104), circulating nitrogen gas passage I (105), circulating nitrogen gas passage II (106), nitrogen-rich tail gas passage I (107), high-pressure gas-phase cold agent passage I (108), high-pressure gas-phase cold agent counterflow passage II (109), high-pressure liquid-phase cold agent passage I (110) and backflow cold agent passage I (111); The inlet end of the raw material natural gas passage I (101) is connected with the external purified raw material gas pipeline, the outlet end of the raw material natural gas passage I (101) is connected with the heavy hydrocarbon separator inlet (3-A), the heavy hydrocarbon separator liquid-phase outlet (3-C) is connected with the external heavy hydrocarbon pipeline, the pipeline of the heavy hydrocarbon separator gas-phase outlet (3-B) is connected with the inlet end of the raw material natural gas passage II (102), the outlet end of the raw material natural gas passage II (102) is connected with the denitrogenation tower reboiler inlet (6-A), the denitrogenation tower reboiler outlet (6-B) is connected with the inlet end of the raw material natural gas passage III (103), the outlet end of the raw material natural gas passage III (103) is connected with the denitrogenation tower inlet (4-A), the denitrogenation tower bottom outlet (4-C) is connected with the inlet end of the liquefied natural gas passage I (104), the outlet end of the liquefied natural gas passage I (104) is connected with the external LNG pipeline, the denitrogenation tower top outlet (4-B) is connected with the inlet end of the nitrogen-rich tail gas passage I (107), and the outlet end of the nitrogen-rich tail gas passage I (107) is connected with the external nitrogen-rich tail gas emission pipeline; The inlet end of the circulating nitrogen gas passage I (105) is connected with the external circulating nitrogen gas inlet pipeline, the outlet end of the circulating nitrogen gas passage I (105) is connected with the denitrogenation tower condenser inlet (5-A), the denitrogenation tower condenser outlet (5-B) is connected with the inlet end of the circulating nitrogen gas passage II (106), and the outlet end of the circulating nitrogen gas passage II (106) is connected with the external circulating nitrogen gas outlet pipeline; The inlet end of the high-pressure gas-phase refrigerant passage I (108) is connected with an external high-pressure refrigerant gas pipeline, the outlet end of the high-pressure gas-phase refrigerant passage I (108) is connected with the inlet of a low-temperature refrigerant separation tank (8-A), the first outlet (8-B) and the second outlet (8-C) of the low-temperature refrigerant separation tank are connected with the inlet end of a high-pressure gas-phase refrigerant counterflow passage II (109), the outlet end of the high-pressure gas-phase refrigerant counterflow passage II (109) is connected with the inlet end of a reflux refrigerant passage I (111) through a pipeline out of a main heat exchanger, the inlet end of a high-pressure liquid-phase refrigerant passage I (110) is connected with an external high-pressure refrigerant liquid pipeline, the outlet end of the high-pressure liquid-phase refrigerant passage I (110) is connected with the inlet of a high-temperature refrigerant separation tank (7-A), the first outlet (7-B) and the second outlet (7-C) of the high-temperature refrigerant separation tank are connected with the inlet end of the reflux refrigerant passage I (111), and the outlet end of the reflux refrigerant passage I (111) is connected with an external refrigerant return pipeline.

2. The natural gas denitrification liquefaction apparatus according to claim 1, characterized by: The denitrogenation tower condenser (5) and the denitrogenation tower reboiler (6) are integrated into the denitrogenation tower (4).

3. The natural gas denitrification liquefaction apparatus according to claim 1, characterized by: The main heat exchanger (2) is a plate-fin heat exchanger, and the denitrogenation tower condenser (5) and the denitrogenation tower reboiler (6) are shell-and-tube heat exchangers.

4. The natural gas denitrification liquefaction apparatus according to any one of claims 1 to 3, characterized by: A first regulating valve (11) is arranged on a connecting pipeline between the outlet end of the raw material natural gas passage III (103) and the inlet of the denitrogenation tower (4-A).

5. The natural gas denitrification liquefaction apparatus according to claim 4, characterized by: A second regulating valve (12) is arranged on a connecting pipeline between the outlet end of the circulating nitrogen gas passage I (105) and the inlet of the denitrogenation tower condenser (5-A).

6. The natural gas denitrification liquefaction apparatus according to claim 5, characterized by: A third regulating valve (13) is arranged on a connecting pipeline between the top outlet of the denitrogenation tower (4-B) and the inlet end of the nitrogen-rich tail gas passage I (107).

7. The natural gas denitrification liquefaction apparatus according to claim 6, characterized by: A fourth regulating valve (14) is arranged on a connecting pipeline between the outlet end of the high-pressure liquid-phase refrigerant passage I (110) and the inlet of the high-temperature refrigerant separation tank (7-A).

8. The natural gas denitrification liquefaction apparatus according to claim 7, characterized by: A fifth regulating valve (15) is arranged on a connecting pipeline between the outlet end of the high-pressure gas-phase refrigerant passage I (108) and the inlet of the low-temperature refrigerant separation tank (8-A).

9. The natural gas denitrification liquefaction apparatus according to claim 8, characterized by: A sixth regulating valve (16) is arranged on a connecting pipeline between the outlet end of the liquefied natural gas passage I (104) and an external LNG connecting pipeline.

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