An LNG cold energy utilization air separation unit system and its design method

Abstract

The present invention discloses an LNG cold energy utilization air separation device system, which comprises an LNG heating system (1) and an air separation device (2); the air separation device (2) comprises an air compressor (7), a precooler (5), a molecular sieve (8), a heat exchanger (4), and a cold box (3) connected in sequence by an air pipeline; the LNG heating system (1) comprises an LNG storage tank (14), an LNG liquid phase booster pump, and an LNG delivery pipeline; the LNG delivery pipeline sequentially connects the LNG storage tank (14), the LNG liquid phase booster pump, the heat exchanger (4), and the precooler (5); the LNG cold energy utilization air separation device system of the present invention utilizes free LNG cold source cold energy to compress and cool and liquefy air, thereby utilizing the LNG cold source on the one hand and reducing the comprehensive energy consumption of a deep cold compression air separation system on the other hand.

Description

Technical Field

[0001] The invention belongs to the field of liquefied natural gas (LNG) and cryogenic air separation devices, and specifically proposes an LNG cold energy utilization air separation device system and a design method thereof. Background Art

[0002] According to my country's medium- and long-term energy development plan, natural gas will become a highlight of my country's energy development strategy and one of the pillars of green energy. In the future, my country will import a large amount of natural gas, most of which will be transported to China in the form of liquefied natural gas (LNG). A large amount of imported LNG also carries a large amount of cold energy. If this cold energy cannot be effectively utilized, it will cause huge energy waste and environmental pollution. Therefore, how to effectively utilize this cold energy becomes extremely important and necessary.

[0003] On the other hand, large-scale air separation units are increasingly used in the steel, chemical and synthetic ammonia industries, and more and more new large-scale air separation unit projects are being implemented, and their energy consumption accounts for an increasing proportion of the total social energy consumption year by year. Air separation equipment is a device that uses air as raw material, converts air into liquid through compression cycle deep freezing, and then gradually separates and produces inert gases such as oxygen, nitrogen and argon from liquid air through distillation.

[0004] The current mainstream compression cycle deep freezing method consumes huge amounts of energy. Therefore, the high energy consumption of large air separation units has become an important bottleneck hindering the development of the air separation industry.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The purpose of the present invention is to provide an LNG cold energy utilization air separation device system to solve the above-mentioned existing problems of waste of LNG cold source and huge refrigeration energy consumption of deep cold air separation.

[0007] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical scheme:

[0008] An LNG cold energy utilization air separation unit system comprises an LNG heating system and an air separation unit; the air separation unit comprises an air compressor, a precooler, a molecular sieve, a heat exchanger, and a cold box connected in sequence by an air pipeline; the LNG heating system comprises an LNG storage tank, an LNG liquid phase booster pump, and an LNG delivery pipeline; the LNG delivery pipeline sequentially connects the LNG storage tank, the LNG liquid phase booster pump, the heat exchanger, and the precooler.

[0009] Preferably, the precooler is provided with a single-stage or multi-stage heat exchanger.

[0010] Preferably, the heat exchanger is a plate heat exchanger, a shell and tube heat exchanger, or a fin-tube heat exchanger.

[0011] Preferably, the heat exchanger is a single-stage or multi-stage heat exchanger.

[0012] Preferably, the air separation device includes at least one of an expander, a booster, an oxygen compressor, and a nitrogen compressor, and at least one of the air compressor, the expander, the booster, the oxygen compressor, and the nitrogen compressor is driven by an electric or steam turbine.

[0013] Preferably, the air separation products such as oxygen, nitrogen or argon produced by the air separation device are stored in high-pressure filling cylinders, liquid phase filling cylinders or liquid phase low-temperature storage tanks.

[0014] Preferably, the LNG cold source provides the required low temperature environment for the liquid phase cryogenic storage tank of the air separation gas product.

[0015] Preferably, one or more LNG liquid phase storage tanks are provided, and the empty storage tanks among the multiple LNG storage tanks can utilize their heat-insulating and low-temperature environment to store liquid phase air separation gas products.

[0016] A multi-stage heat exchange design method for an LNG cold energy utilization air separation unit, the multi-stage heat exchange design method for an LNG cold energy utilization air separation unit uses the above-mentioned LNG cold energy utilization air separation unit system, and the specific method is as follows:

[0017] S1: Calculate the total available LNG cooling capacity Q based on the LNG tank capacity and the temperature, pressure and flow parameters of the final output natural gas. LNG ;

[0018] S2: Based on the total cooling capacity of LNG cold source Q LNG Based on the final pressure and temperature of the desired air separation gas product, oxygen or nitrogen, the total air flow rate F of the suction air compressor that can be processed for air liquefaction is estimated. 空 ;

[0019] S3: Calculate the total air flow F according to the system equipment process 空 Under the condition of using LNG cold source, the total cooling capacity Q LNG The temperature drop values ​​that can be achieved in the heat exchanger (4) and the precooler (5) are T 降换热器 、T 降预冷 ;

[0020] S4: According to the system equipment process and T 降换热器 Value, set the number of heat exchanger stages in heat exchanger (4).

[0021] Preferably, the total cooling capacity Q of the cooling source is LNG The calculation formula is:

[0022] Q LNG =Q LNG潜热 +Q 气升温 =FLNG *q LNG潜热 +F LNG *(T 供 -T1)*C p气 =Q 换热器 +Q 预冷器 ;

[0023] in:

[0024] Q LNG is the available cold energy of LNG, kJ / h;

[0025] F LNG is the LNG flow rate kg / h;

[0026] q LNG潜热 is the latent heat of vaporization of LNG kJ / kg;

[0027] C p气 The unit is the specific heat capacity of gaseous LNG kJ / kg℃.

[0028] Beneficial Effects

[0029] 1. The present invention effectively utilizes LNG cold energy, avoiding the impact of local environmental temperature changes caused by the release of cold energy from LNG terminals or large LNG devices to the air, seawater or river water;

[0030] 2. The present invention can separate air without a large-scale booster and expander in a cryogenic air separation unit, thereby reducing the comprehensive energy consumption and project investment of the air separation unit;

[0031] 3. The present invention utilizes the low temperature environment created by LNG, which can greatly reduce the pipeline pressure level of the air separation unit, thereby reducing the investment amount related to the air pipeline of the air separation unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The overall structure of the LNG cold energy utilization air separation device system of the present invention is schematically shown;

[0033] Figure 2 The relationship curve between temperature and LNG cold energy in the LNG cold energy utilization air separation device system of the present invention.

[0034] Description of Reference Numerals

[0035] In order to further clearly illustrate the structure of the present invention and the connection relationship between the various components, the following figure numbers are given and explained.

[0036] LNG heating system 1, air separation unit 2, cold box 3, heat exchanger 4, precooler 5, three-stage LNG heat exchanger 6, air compressor 7, molecular sieve 8, first-stage plate heat exchanger 9, second-stage plate heat exchanger 10, oxygen compressor 11, nitrogen compressor 12, storage tank 13, LNG storage tank 14.

[0037] Through the above-mentioned description of the accompanying drawings, combined with the embodiments of the present invention, the technical solution of the present invention can be more clearly understood and explained. DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the scope of protection claimed in the present invention is not limited to the scope described in the specific embodiments. It should be noted that the embodiments in this application and the features in the embodiments can be combined with each other arbitrarily without conflict.

[0039] Embodiment 1

[0040] An LNG cold energy utilization air separation unit system, such as Figure 1-Figure 2 As shown, the LNG cold energy utilization air separation device system includes an LNG heating system 1 and an air separation device 2, and the LNG heating system 1 includes an LNG storage tank 14, an LNG transmission pipeline, an LNG liquid phase booster pump, and an LNG cold energy utilization air separation heat exchange device. The LNG cold energy utilization air separation heat exchange device includes a multi-stage LNG heat exchange device; the LNG cold energy utilization air separation heat exchange device includes a heat exchanger 4, a precooler 5 and a three-stage LNG heat exchange device 6. The LNG transmission pipeline is connected to the LNG storage tank 14, the LNG liquid phase booster pump, and the LNG cold energy utilization multi-stage air separation heat exchange device in sequence; that is, the LNG transmission pipeline is connected to the LNG storage tank 14, the LNG liquid phase booster pump, the heat exchanger 4, the precooler 5 and the three-stage LNG heat exchange device 6 in sequence, and the LNG in the three-stage LNG heat exchange device 6 is gasified into natural gas. The LNG in the LNG storage tank 14 is heated once by the heat exchanger 4, and then passes through the precooler 5 after the first heating, and then is heated twice by the precooler 5, and finally passes through the tertiary LNG heat exchange device 6, and then is gasified into natural gas after being heated three times by the tertiary LNG heat exchange device 6. That is, the temperatures of the LNG in the heat exchanger 4, the precooler 5, and the tertiary LNG heat exchange device 6 are increased in sequence.

[0041] The air separation unit 2 includes an air compressor 7, a precooler 5, a molecular sieve 8, a three-stage LNG heat exchange device 6, a cold box 3 and an air pipeline. The air pipeline is connected to the air compressor 7, the precooler 5, the molecular sieve 8, the heat exchanger 4, and the cold box 3 in sequence. The air passes through the precooler 5, the heat exchanger 4, and the cold box 3, and absorbs the cold energy of LNG to deep-cool and liquefy the air. The cold box 3 is connected to the product booster and the storage tank 13; the product booster includes an oxygen compressor 11 and a nitrogen compressor 12. The storage tank 13 or the storage tank low-temperature liquid phase storage device can store the final air separation products such as liquid nitrogen, liquid oxygen, and liquid argon obtained by the air separation unit. The cold box 3 is provided with a product output port; the oxygen compressor 11, the nitrogen compressor 12, and the storage tank 13 are connected to the product output port on the cold box 3 to compress the gas products separated by the air separation unit and obtain gas products stored in a high-pressure manner (gas products such as oxygen or nitrogen stored in high-pressure cylinders). Preferably, the air separation products such as oxygen, nitrogen or argon produced by the air separation device are stored or sold in the form of high-pressure filling cylinders, liquid-phase filling cylinders or liquid-phase low-temperature storage tanks.

[0042] The relationship table of LNG's saturation temperature, density, and latent heat of vaporization at different pressures shows that as the temperature of LNG increases, its latent heat of vaporization decreases, and its cooling effect decreases; on the contrary, as the temperature of LNG decreases, its latent heat of vaporization increases, and its cooling effect increases. Since the temperature of LNG in the precooler 5 and the heat exchanger 4 decreases successively, its cooling effect increases accordingly. The air passing through the air compressor 7 in the air separation device 2 passes through the precooler 5, the heat exchanger 4, and the cold box 3 in turn to be cooled step by step, and finally the air is deep-cooled to obtain an air separation product. Correspondingly, the LNG in the LNG heating system 1 passes through the heat exchanger 4 and the precooler 5 in turn to be heated step by step to be vaporized into natural gas.

[0043] The precooler 5 in the air separation device 2 precools the air, and the air precooled by the precooler 5 passes through the molecular sieve 8. The air treated by the molecular sieve 8 passes through the heat exchanger 4; the heat exchanger 4 performs secondary cooling on the air, and the air passes through the cold box 3 after the secondary cooling, and the cold box 3 performs tertiary cooling on the air; after passing through the cold box 3, the gas product obtained by the air separation device is obtained.

[0044] Preferably, the heat exchanger 4 is a plate heat exchanger, a shell and tube heat exchanger, or a fin-tube heat exchanger.

[0045] Preferably, the heat exchanger 4 comprises a multi-stage heat exchanger, that is, comprises at least one stage of plate heat exchanger 9 .

[0046] Preferably, the heat exchanger 4 is a single-stage heat exchanger, that is, the heat exchanger 4 is a single-stage plate heat exchanger 9 .

[0047] Preferably, the heat exchanger 4 includes a secondary plate heat exchanger 10 and a primary plate heat exchanger 9. At this time, when LNG passes through the heat exchanger 4, the LNG is heated twice and tertiary; correspondingly, when the air passes through the heat exchanger 4, the air is cooled twice and tertiary.

[0048] Preferably, the cold box 3 can supply a cold source for the liquid nitrogen, liquid oxygen, liquid argon or gas products in the storage tank 13 obtained through the cold box 3. That is, the low temperature environment required by the liquid phase cryogenic storage tank of the air separation gas product can utilize the LNG cold source.

[0049] Preferably, the precooler 5 is provided with a single-stage or multi-stage heat exchanger to precool the air, and the number of heat exchanger stages of the precooling system is reasonably set according to the air flow rate and the number of available LNG cold sources.

[0050] Preferably, the three-stage LNG heat exchange device 6 can absorb heat from air, surface water, seawater, etc., so as to heat the LNG three times.

[0051] Preferably, one or more LNG storage tanks 14 can be provided, and the empty storage tanks among the multiple LNG storage tanks can utilize their heat preservation and low temperature environment to store liquid phase air separation gas products. That is, the liquid nitrogen, liquid oxygen, liquid argon obtained by the air separation device 2 or the gas products in the storage tank 13 are connected and returned to the LNG storage tank 14.

[0052] Preferably, the liquid nitrogen, liquid oxygen, liquid argon obtained by the air separation unit 2 or the gas product in the storage tank 13 is connected to the next stage heat exchanger.

[0053] In this embodiment, the LNG cold energy utilizing air separation device system utilizes the free LNG cold source cold energy to compress and cool the air for liquefaction, which on the one hand utilizes the LNG cold source, and on the other hand reduces the comprehensive energy consumption of the cryogenic compression air separation system.

[0054] Embodiment 2

[0055] The principle of the second embodiment is the same as that of the first embodiment, except that the air separation device includes an expander and a booster, and the air compressor, expander, booster, oxygen compressor or nitrogen compressor and other equipment in the air separation device are driven by electric or steam turbines.

[0056] Specifically, the air separation unit is connected to the thermal power plant generator set system. The thermal power plant generator set includes a large steam turbine, a generator and a peak-shaving control module, and the peak-shaving control module receives the peak-shaving instruction from the power grid dispatching center; the air separation unit is connected to the steam pipeline of the generator and / or the thermal power plant generator set, and the peak-shaving control module can transfer the power of the generator and / or the steam of the thermal power plant set to the air separation unit to drive the air separation unit.

[0057] That is, the air separation unit is connected to the steam pipeline of the thermal power plant generator set on the one hand to be driven by the peak-shaving steam of the power plant; on the other hand, it can be connected to the generator to use the generator to power the air separation unit. The air separation unit is driven by electric and / or steam turbines. The above settings can effectively utilize the peak-shaving surplus electricity and thermal energy of the thermal power generator set to meet the equipment energy supply of the air separation unit, reduce the energy consumption of the external supplementary drive of the air separation unit, avoid energy waste, improve energy utilization, and transform modern thermal power plants into comprehensive factories for electricity, thermal energy, compressed air energy and various air separation gas products.

[0058] Embodiment 3

[0059] A multi-stage heat exchange design method for an LNG cold energy utilization air separation unit is disclosed. The multi-stage heat exchange design method for an LNG cold energy utilization air separation unit uses the LNG cold energy utilization air separation unit system described in the above embodiment.

[0060] The specific method is as follows:

[0061] S1: Calculate the total available LNG cooling capacity Q based on the LNG tank capacity and the temperature, pressure and flow parameters of the final output natural gas. LNG ;

[0062] S2: Based on the total cooling capacity of LNG cold source Q LNG Based on the final pressure and temperature of the desired air separation gas product, oxygen or nitrogen, the total air flow rate F of the suction air compressor that can be processed for air liquefaction is estimated. 空 ;

[0063] S3: According to the system equipment process, calculate the total air flow F in detail 空 Under the condition of using LNG cold source, the total cooling capacity Q LNG The temperature drop values ​​that can be achieved in the heat exchanger 4 and the precooler 5 are T 降换热器 、T 降预冷 ;

[0064] Where T 降换热器 =T 空2 -T 空3 ; T 降预冷 =T 空1 -T 空2 ; T 空1 is the temperature of the air before it enters the precooler, T 空2 is the temperature of the air leaving the precooler and the temperature of the air before entering the heat exchanger; T 空3 It is the temperature of the air when it leaves the heat exchanger;

[0065] S4: According to the system equipment process and T 降换热器 Value, reasonably set the number of heat exchanger stages in heat exchanger 4.

[0066] Among them, the total cooling capacity of the cold source Q LNG The calculation formula is:

[0067] Q LNG =Q LNG潜热 +Q 气升温 =F LNG *q LNG潜热 +F LNG *(T 供 -T1)*C p气 =Q 换热器 +Q 预冷器

[0068] Q LNG潜热 =F LNG *q LNG潜热

[0069] Q 气升温 =F LNG *(T 供 -T1)*C p气

[0070] Q 换热器 =F LNG *(T2-T1)*C p气 =F 空 *(T 空2 -T 空3 )*C p空

[0071] Q 预冷器 =F LNG *(T3-T2)*C p气 =F 空 *(T 空1 -T 空2 )*C p空

[0072] in:

[0073] Q LNG is the available cold energy of LNG, kJ / h;

[0074] F LNG is the LNG flow rate kg / h;

[0075] q LNG潜热 is the latent heat of vaporization of LNG kJ / kg, which is calculated by dividing the data in Table 1 by 4.18 kCal / kJ;

[0076] C p气 The unit is the specific heat capacity of gaseous LNG kJ / kg℃;

[0077] C p空 The unit is the specific heat capacity of gaseous air kJ / kg℃.

[0078] Table 1 Saturation temperature, density and latent heat of vaporization of LNG at different pressures

[0079] Saturation pressure(MPag) 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Saturation temperature℃ -162 -146 -138 -132 -126 -122 -118 -115 -112 <![CDATA[Density kg / m 3 > 424 400 386 374 365 356 348 340 333 Latent heat of vaporization kcal / kg 122 115 110 106 102 98 94 91 87

[0080] On the one hand, the present invention effectively utilizes LNG cold energy, avoiding the impact of local environmental temperature changes caused by the release of cold energy from LNG terminals or large LNG devices to the air, seawater or river water; on the other hand, it can perform air separation without large-scale boosters and expanders in deep-cold air separation devices, reducing the comprehensive energy consumption and project investment of the air separation device; furthermore, the low-temperature environment created by LNG can greatly reduce the pipeline pressure level of the air separation device, thereby reducing the investment amount related to the air pipeline of the air separation device.

[0081] In the description of this application, "install", "connect", "connect", "fix" and the like should be understood in a broad sense. For example, "connect" can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or a connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0082] In the description of this specification, the description of the terms "one embodiment", "some embodiments", "specific embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0083] Those skilled in the art should understand that although the embodiments disclosed in the embodiments of the invention are as above, the contents described are only embodiments adopted to facilitate understanding of the invention and are not intended to limit the embodiments of the invention. Any person skilled in the art of the embodiments of the invention may make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in the invention, but the scope of patent protection of the embodiments of the invention shall still be subject to the scope defined by the attached claims.

Claims

1. A design method for an LNG cold energy utilization air separation unit system, characterized in that: The LNG cold energy utilization air separation unit system comprises an LNG heating system (1) and an air separation unit (2); the air separation unit (2) comprises an air compressor (7), a precooler (5), a molecular sieve (8), a heat exchanger (4), and a cold box (3) connected in sequence by an air pipeline; the LNG heating system (1) comprises an LNG storage tank (14), an LNG liquid phase booster pump, and an LNG delivery pipeline; the LNG storage tank (14), the LNG liquid phase booster pump, the heat exchanger (4), and the precooler (5) connected in sequence by the LNG delivery pipeline are designed using the following method: S1: Calculate the total available LNG cooling capacity Q based on the LNG tank capacity and the temperature, pressure and flow parameters of the final output natural gas. LNG ; The total cooling capacity QLNG of the cold source is calculated as follows: LNG =Q LNG潜热 +Q 气升温 =F LNG *q LNG潜热 +F LNG *(T 供 -T1)*C p气 =Q 换热器 +Q 预冷器 Q LNG潜热 =F LNG *q LNG潜热 ; Q 气升温 =F LNG *(T 供 -T1)*C p气 ; Q 换热器 =F LNG *(T2-T1)*C p气 =F 空 *(T 空2 -T 空3 )*C p空 Q 预冷器 =F LNG *(T3-T2)*C p气 =F 空 *(T 空1 -T 空2 )*C p空 in: Q LNG is the available cold energy of LNG, kJ / h, F LNG is the LNG flow rate kg / h, q LNG潜热 is the latent heat of vaporization of LNG kJ / kg, C p气 The unit is the specific heat capacity of gaseous LNG kJ / kg℃, C p空 The unit is the specific heat capacity of gaseous air kJ / kg℃, T2 and T1 represent the temperature of LNG after and before heat exchange in the heat exchanger respectively; S2: Based on the total cooling capacity of LNG cold source Q LNG Based on the final pressure and temperature of the desired air separation gas product, oxygen or nitrogen, the total air flow rate F of the suction air compressor that can be processed for air liquefaction is estimated. 空 ; S3: Calculate the total air flow F according to the system equipment process 空 Under the condition of using LNG cold source, the total cooling capacity Q LNG The temperature drop values ​​that can be achieved in the heat exchanger (4) and the precooler (5) are T drop heat exchanger and T drop precooler respectively; Where T 降换热器 =T 空2 -T 空3 ; T 降预冷 =T 空1 -T 空2 ; T 空1 is the temperature of the air before it enters the precooler, T 空2 is the temperature of the air leaving the precooler and the temperature of the air before entering the heat exchanger; T 空3 It is the temperature of the air when it leaves the heat exchanger; S4: According to the system equipment flow and T drop heat exchanger value, the number of heat exchanger stages in the heat exchanger (4) is set.

2. The design method of the LNG cold energy utilization air separation unit system according to claim 1 is characterized by: The precooler (5) is provided with a single-stage or multi-stage heat exchanger.

3. The design method of the LNG cold energy utilization air separation unit system according to claim 1 is characterized by: The heat exchanger (4) is a plate heat exchanger, a shell and tube heat exchanger, or a fin-tube heat exchanger.

4. The design method of the LNG cold energy utilization air separation unit system according to claim 3 is characterized by: The heat exchanger (4) is configured as a single-stage or multi-stage heat exchanger.

5. The design method of the LNG cold energy utilization air separation unit system according to claim 1 is characterized by: The air separation device (2) comprises at least one of an expander, a booster, an oxygen compressor, and a nitrogen compressor, and at least one of the air compressor, the expander, the booster, the oxygen compressor, and the nitrogen compressor is driven by an electric motor or a steam turbine.

6. The design method of the LNG cold energy utilization air separation unit system according to claim 1 is characterized in that: The air separation products such as oxygen, nitrogen or argon produced by the air separation device (2) are stored in high-pressure filling cylinders, liquid-phase filling cylinders or liquid-phase low-temperature storage tanks.

7. The design method of the LNG cold energy utilization air separation unit system according to claim 1 or 6, characterized in that: The LNG cold source provides the required low temperature environment for the liquid phase cryogenic storage tanks of air separation gas products.

8. The design method of the LNG cold energy utilization air separation unit system according to claim 1 is characterized by: One or more LNG storage tanks (14) are provided, and the empty storage tanks among the multiple LNG storage tanks can utilize their heat-insulating and low-temperature environment to store liquid-phase air separation gas products.

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