Method for regenerating dehydration dryer using LNG flash steam and natural gas liquefaction process

Abstract

The present invention provides a method for regenerating a dehydration dryer using LNG flash steam and a natural gas liquefaction process. The LNG flash steam, serving as a dehydration medium, flows sequentially through an LNG processing unit, a natural gas pretreatment unit, a natural gas decarbonization unit, a natural gas purification unit, a natural gas dehydration and mercury removal unit, and a regeneration gas unit, and is ultimately transported to a natural gas purification unit and / or a natural gas pretreatment unit. The natural gas dehydration and mercury removal unit includes at least a dehydration dryer. The incoming gas processed by the natural gas purification unit enters the natural gas dehydration and mercury removal unit, desorbs the moisture in the dehydration dryer, and generates regeneration gas. The present invention uses the flash steam flashed from the LNG storage tank as a dehydration medium by modifying the process. Since the LNG flash steam composition is very clean and the carbon dioxide and water dew points meet the requirements, it can be used as a dehydration dryer regeneration medium. The amine liquid circulation and heating and dehydration dryer regeneration in the traditional process are carried out simultaneously, thereby shortening the natural gas dehydration time.

Description

Technical Field

[0001] The present invention belongs to the field of natural gas processing, and in particular relates to a method for regenerating a dehydration dryer by utilizing LNG flash steam and a natural gas liquefaction process. Background Art

[0002] The natural gas liquefaction process is to pre-treat, decarbonize and dehydrate the raw natural gas until it meets the requirements, and then liquefy it into LNG using a low-temperature method (mixed refrigerant SMRC refrigeration process). The qualified LNG product is then stored in LNG storage tanks, loaded onto trucks and transported to tank trucks via pumps for external transportation.

[0003] The traditional natural gas liquefaction process is as follows: utility → amine liquid circulation, temperature increase → natural gas introduction, decarbonization → dehydration dryer regeneration, natural gas dehydration → refrigerant compressor start-up → cold box pre-cooling → product output. In the above process, the specific start-up time required for each link is as follows:

[0004]

[0005] As can be seen from the table above, natural gas dehydration must use qualified decarbonized natural gas. In this case, according to the traditional start-up method, the dehydration time is relatively long (48 hours), which increases the overall time of natural gas liquefaction and affects the economic benefits of the product. Summary of the Invention

[0006] The object of the present invention is to provide a method for regenerating a dehydration dryer using LNG flash steam and a natural gas liquefaction process to overcome the above technical defects.

[0007] To solve the above technical problems, the present invention provides a method for regenerating a dehydration dryer using LNG flash steam, comprising:

[0008] LNG processing unit, where the evaporated LNG flash gas is used as the dehydration medium;

[0009] Natural gas pretreatment unit, LNG flash gas from the LNG processing unit enters the natural gas pretreatment unit;

[0010] The natural gas decarbonization unit receives LNG flash gas from the natural gas pretreatment unit and circulates amine liquid;

[0011] natural gas purification unit;

[0012] The natural gas dehydration and mercury removal unit includes at least a dehydration dryer. The incoming gas treated by the natural gas purification unit enters the natural gas dehydration and mercury removal unit, dehydrates the water in the dehydration dryer, and generates regenerated gas.

[0013] The regeneration gas unit receives the regeneration gas and cools, separates, and compresses it, and finally transmits it to the natural gas purification unit and / or natural gas pretreatment unit.

[0014] Furthermore, the LNG processing unit includes:

[0015] The LNG storage tank, liquefaction heat exchanger, pre-cooling heat exchanger, LNG flash gas compressor, and circulating LNG flash gas compressor are sequentially connected through pipelines.

[0016] Furthermore, the natural gas pre-processing unit includes:

[0017] A raw gas separator, a de-mist device, and a raw gas filter connected in sequence through pipelines;

[0018] The outlet of the circulating LNG flash gas compressor is connected to the inlet of the raw gas separator through a pipeline.

[0019] Furthermore, the natural gas decarbonization unit includes:

[0020] Raw gas heat exchanger and absorption tower connected by pipelines;

[0021] The outlet of the raw gas filter and the outlet of the absorption tower are connected to the inlet of the raw gas heat exchanger through pipelines. The outlet of the raw gas heat exchanger is connected to the inlet of the natural gas purification unit and the inlet of the absorption tower through two branch pipelines.

[0022] Furthermore, the natural gas purification unit comprises:

[0023] A purified gas separator and a purified gas filter connected through pipelines;

[0024] The outlet of the raw gas heat exchanger is connected to the inlet of the purified gas separator through a pipeline.

[0025] Furthermore, the natural gas dehydration and mercury removal unit includes:

[0026] A dehydration dryer, a dehydration dust filter, a demercuration adsorber, a demercuration dust filter, and a dehydration heating furnace connected through pipelines;

[0027] The outlet of the purified gas filter is connected to the inlet of the dehydration dryer through a pipeline equipped with valve No. 1, the outlet of the dehydration dryer is connected to the inlet of the dehydration dust filter through a pipeline equipped with valve No. 4, the outlet of the dehydration heating furnace is connected to the inlet of the dehydration dryer through a pipeline equipped with valve No. 3, and the outlet of the dehydration dryer is connected to the regeneration gas unit through a pipeline equipped with valve No. 2.

[0028] Furthermore, the regeneration gas unit comprises:

[0029] A regeneration gas air cooler, a regeneration gas water cooler, a regeneration gas separator, and a regeneration gas compressor connected through pipelines;

[0030] The outlet of the dehydration dryer is connected to the inlet of the regeneration gas air cooler through a pipeline equipped with valve No. 2;

[0031] The outlet of the regeneration gas compressor is connected to the purified gas separator and / or the raw gas separator through a pipeline.

[0032] The present invention also provides a natural gas liquefaction process, the specific process flow includes:

[0033] Step 100. Dehydration dryer regeneration

[0034] A method for starting a flash steam regeneration dehydration dryer until the dehydration dryer regeneration is completed;

[0035] Step 200: Natural gas liquefaction

[0036] Raw natural gas is introduced, and the raw natural gas flows through the natural gas pretreatment unit, the natural gas decarbonization unit, and the natural gas purification unit in sequence to generate purified natural gas;

[0037] The purified natural gas flows through the pipeline in sequence through the dehydration dryer, dehydration dust filter, mercury removal adsorber, mercury removal dust filter, pre-cooling heat exchanger, liquefaction heat exchanger, sub-cooling heat exchanger, and LNG storage tank;

[0038] The LNG flash gas flowing out of the LNG storage tank returns to the liquefaction heat exchanger, and then returns to the pre-cooling heat exchanger after passing through the liquefaction heat exchanger;

[0039] After passing through the pre-cooling heat exchanger, it enters the LNG flash gas compressor. The pressurized LNG flash gas is first transported to the fuel gas buffer tank, and the excess LNG flash gas is sent to the circulating LNG flash gas compressor. After being pressurized to the pressure of the raw natural gas by the circulating LNG flash gas compressor, it returns to the raw gas separator.

[0040] The beneficial effects of the present invention are as follows:

[0041] By modifying the process, the flash gas flashed from the LNG storage tank will be used as the dehydration medium. Since the LNG flash gas composition is very clean, and the carbon dioxide and water dew points meet the requirements, it can be used as the regeneration medium for the dehydration dryer. The amine liquid circulation and heating and dehydration dryer regeneration in the traditional process are carried out simultaneously, shortening the natural gas dehydration time.

[0042] In order to make the above contents of the present invention more clearly understood, preferred embodiments are given below with reference to the accompanying drawings for detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a flow chart of a method for regenerating a dehydration dryer using LNG flash steam.

[0044] Figure 2 This is a natural gas liquefaction process flow chart. DETAILED DESCRIPTION

[0045] The following describes the embodiments of the present invention through specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0046] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided so as to provide a thorough and complete disclosure of the present invention and fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments shown in the accompanying drawings is not intended to limit the present invention. In the accompanying drawings, identical elements are denoted by the same reference numerals.

[0047] Unless otherwise specified, the terms used herein (including technical terms) have the meanings commonly understood by those skilled in the art. In addition, it is understood that terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0048] This embodiment relates to a method for regenerating a dehydration dryer using LNG flash steam, see Figure 1 ,include:

[0049] The LNG processing unit is used to liquefy, pre-cool and pressurize the LNG flash vapor. The evaporated LNG flash vapor is used as the dehydration medium.

[0050] Natural gas pretreatment unit, LNG flash gas from the LNG processing unit enters the natural gas pretreatment unit;

[0051] The natural gas decarbonization unit receives LNG flash gas from the natural gas pretreatment unit and circulates amine liquid;

[0052] natural gas purification unit;

[0053] The natural gas dehydration and mercury removal unit includes at least a dehydration dryer. The incoming gas treated by the natural gas purification unit enters the natural gas dehydration and mercury removal unit, first dehydrates the water in the dehydration dryer, and then flows through other equipment in the natural gas dehydration and mercury removal unit to generate regenerated gas.

[0054] The regeneration gas unit receives the regeneration gas and cools, separates, and compresses it, and finally transmits it to the natural gas purification unit and / or natural gas pretreatment unit.

[0055] That is to say, in the dehydration dryer regeneration method, the LNG flash gas flows through the LNG processing unit, the natural gas pretreatment unit, the natural gas decarbonization unit, the natural gas purification unit, the natural gas dehydration and mercury removal unit, and the regeneration gas unit in sequence, and finally returns to the LNG processing unit and / or the natural gas purification unit. At this point, a regeneration loop is formed, and the regeneration gas continuously circulates in the above-mentioned processing units in sequence until the moisture in the dehydration dryer is precipitated and the performance of the dehydration dryer is restored.

[0056] In the above regeneration process, LNG flash gas is used as the regeneration medium of the dehydration dryer, and during the regeneration process, the amine liquid circulation and heating (natural gas decarbonization unit) are also carried out simultaneously, that is, the dehydration dryer regeneration and the amine liquid circulation and heating are carried out simultaneously. Therefore, using this regeneration method to improve the traditional natural gas liquefaction process can save dehydration time.

[0057] It should be noted that the reason why LNG flash gas is chosen as the regeneration medium is that the composition of LNG flash gas is very clean, and the dew points of carbon dioxide and water meet the requirements, so it can be used as the regeneration medium for the dehydration dryer.

[0058] See also Figure 1 , the above processing units are described in detail below:

[0059] 1) LNG processing unit includes:

[0060] The LNG storage tank, liquefaction heat exchanger, pre-cooling heat exchanger, LNG flash gas compressor, and circulating LNG flash gas compressor are sequentially connected through pipelines.

[0061] The LNG storage tanks are used to store LNG products. The liquefaction heat exchangers and pre-cooling heat exchangers are used to pre-cool natural gas. The LNG flash steam compressors and circulating LNG flash steam compressors are used to pressurize natural gas.

[0062] 2) Natural gas pretreatment unit includes:

[0063] The raw gas separator, demisting device and raw gas filter are connected in sequence through pipelines.

[0064] The outlet of the circulating LNG flash gas compressor is connected to the inlet of the raw gas separator through a pipeline.

[0065] 3) Natural gas decarbonization unit includes:

[0066] The raw gas heat exchanger and absorption tower are connected through pipelines.

[0067] The outlet of the raw gas filter and the outlet of the absorption tower are connected to the inlet of the raw gas heat exchanger through pipelines. The outlet of the raw gas heat exchanger is connected to the inlet of the natural gas purification unit and the inlet of the absorption tower through two branch pipelines.

[0068] It should be noted that the composition of LNG flash gas is very clean and does not contain any harmful impurities. It does not require decarbonization. The function of the absorption tower here is to heat the amine liquid cycle in advance in preparation for use in the subsequent natural gas main process.

[0069] 4) Natural gas purification unit includes:

[0070] A purified gas separator and a purified gas filter connected through pipelines.

[0071] The outlet of the raw gas heat exchanger is connected to the inlet of the purified gas separator through a pipeline.

[0072] 5) Natural gas dehydration and mercury removal unit includes:

[0073] A dehydration dryer, a dehydration dust filter, a demercuration adsorber, a demercuration dust filter, and a dehydration heating furnace are connected through pipelines.

[0074] The function of the dehydration heating furnace is: the regeneration gas used by the dryer is taken from the purified natural gas after the mercury removal system. The regeneration gas first enters the dehydration heating furnace F-01 and is heated to 280℃ before entering the dryer as regeneration gas.

[0075] The outlet of the purified gas filter is connected to the inlet of the dehydration dryer through a pipeline equipped with valve No. 1, the outlet of the dehydration dryer is connected to the inlet of the dehydration dust filter through a pipeline equipped with valve No. 4, the outlet of the dehydration heating furnace is connected to the inlet of the dehydration dryer through a pipeline equipped with valve No. 3, and the outlet of the dehydration dryer is connected to the regeneration gas unit through a pipeline equipped with valve No. 2.

[0076] It should be noted that Figure 1 Two dehydration dryers are shown only to show that the same dehydration dryer has two pipelines. In fact, there is one dehydration dryer with two different pipelines, namely the pipeline where valves No. 1 and No. 4 are located, and the pipeline where valves No. 3 and No. 2 are located. Specifically:

[0077] The purified LNG flash gas flowing out of the clean gas filter flows through valve No. 1 into the dehydration dryer to dehydrate the moisture in the desiccant, and then flows out from valve No. 4 at the outlet of the dehydration dryer, and then flows through the dehydration dust filter, demercuration adsorber, demercuration dust filter, and dehydration heating furnace in sequence. At this time, the gas flowing out of the dehydration heating furnace returns to the dehydration dryer through valve No. 3, dehydrates the moisture in the desiccant for a second time, and finally flows out from valve No. 2 of the dehydration dryer and enters the regeneration gas unit.

[0078] 6) Regeneration gas unit includes:

[0079] The regeneration gas air cooler, regeneration gas water cooler, regeneration gas separator and regeneration gas compressor are connected through pipelines.

[0080] The outlet of the dehydration dryer is connected to the inlet of the regeneration gas air cooler through a pipeline equipped with a No. 2 valve.

[0081] The outlet of the regeneration gas compressor is connected to the purified gas separator and / or the raw gas separator through a pipeline.

[0082] The functions of each device in the regeneration gas unit are as follows:

[0083] Regeneration gas air cooler: cools the regeneration gas to room temperature.

[0084] Regeneration gas water cooler: cools the regeneration gas to room temperature.

[0085] Regeneration gas separator: Separates water carried in the regeneration gas.

[0086] Regeneration gas compressor: The regeneration gas is pressurized by the compressor and returned to the raw gas separator and / or the purified gas separator.

[0087] In general, the process of regenerating a dehydration dryer using LNG flash steam is as follows:

[0088] First, connect the circulating LNG flash gas compressor to the raw gas separator, decarbonization, dehydration, demercurization, and regeneration gas unit process, then start the LNG flash gas compressor and the circulating LNG flash gas compressor, and pressurize the decarbonization and dehydration systems to 4.2Mpa. Then, pressurize the regeneration gas unit to 1.7Mpa, start the regeneration gas compressor to regenerate the dehydration dryer, and after the regeneration is completed (16h), finally carry out normal natural gas introduction, decarbonization, dehydration and other steps.

[0089] It can be seen that the regeneration of the dehydration dryer and the circulation and heating of the absorption tower are carried out simultaneously, thereby saving dehydration time.

[0090] The present invention also protects a natural gas liquefaction process, the specific process flow includes:

[0091] Step 100. Dehydration dryer regeneration

[0092] Start the method of regenerating the dehydration dryer using LNG flash steam until the dehydration dryer regeneration is completed; Step 200. Natural gas liquefaction

[0093] Directly introduce raw natural gas, which flows through the natural gas pretreatment unit, natural gas decarbonization unit, and natural gas purification unit in sequence to generate purified natural gas;

[0094] The purified natural gas flows through the pipeline in sequence through the dehydration dryer, dehydration dust filter, mercury removal adsorber, mercury removal dust filter, pre-cooling heat exchanger, liquefaction heat exchanger, sub-cooling heat exchanger, and LNG storage tank;

[0095] The LNG flash gas flowing out of the LNG storage tank returns to the liquefaction heat exchanger, and then returns to the pre-cooling heat exchanger after passing through the liquefaction heat exchanger;

[0096] After passing through the pre-cooling heat exchanger, it enters the LNG flash gas compressor. The pressurized LNG flash gas is first transported to the fuel gas buffer tank, and the excess LNG flash gas is sent to the circulating LNG flash gas compressor. After being pressurized to the pressure of the raw natural gas by the circulating LNG flash gas compressor, it returns to the raw gas separator.

[0097] In the above-mentioned natural gas liquefaction process, the functions of various equipment are as follows:

[0098] Raw gas separator, separating free water and oil from natural gas.

[0099] The de-mist device removes the mist carried in the upstream natural gas.

[0100] Raw gas filter removes mechanical impurities carried in natural gas.

[0101] The raw gas heat exchanger exchanges heat with the purified gas from the absorption tower, which is beneficial to the absorption of CO2 in the raw gas by the amine liquid.

[0102] Absorption tower, the raw natural gas entering the bottom of the absorption tower comes into countercurrent contact with the MDEA solution coming from the top of the tower, and the CO2 gas in the natural gas is absorbed by the MDEA solution.

[0103] Purified gas separator, separates and purifies the solution in natural gas.

[0104] Purified gas filter, separates and purifies impurities in natural gas.

[0105] Dehydration dust filter, removes dust from natural gas.

[0106] Mercury removal adsorber removes mercury from natural gas to prevent mercury from corroding aluminum heat exchangers.

[0107] Mercury removal dust filter, removes dust from natural gas.

[0108] Precooling heat exchanger: After natural gas enters the cold box, it is precooled to -50℃ by the mixed refrigerant in the precooling heat exchanger.

[0109] Liquefaction heat exchanger, where natural gas is pre-cooled to -125°C by the mixed refrigerant.

[0110] Subcooling heat exchanger, where natural gas is pre-cooled to -160.5℃ by the mixed refrigerant.

[0111] LNG storage tanks, LNG products are sent to LNG storage tanks for storage.

[0112] LNG flash gas compressor: LNG flash gas is pressurized by the compressor and then sent to the fuel gas system, and the excess is sent to the circulating LNG flash gas compressor through the LNG flash gas compressor.

[0113] The excess LNG flash gas is pressurized by the circulating LNG flash gas compressor to the pressure of the raw natural gas and then returned to the raw gas separator.

[0114] It is worth mentioning that the dehydration dryer has different functions in the regeneration gas process and the natural gas liquefaction process. In the regeneration gas process, the function of the dehydration dryer is to extract the H2O from the regeneration gas entering the dryer; in the natural gas liquefaction process, the dehydration dryer absorbs and removes moisture from the natural gas after regeneration is completed.

[0115] The natural gas liquefaction process consists of two processes: the dehydration dryer regeneration process and the natural gas liquefaction main process. The working sequence is to start the dehydration dryer regeneration process first and then switch to the natural gas liquefaction main process. The details are as follows:

[0116] See also Figure 1 , first start the regeneration gas process, LNG flash gas flows out of the LNG storage tank, and the LNG flash gas flows through the liquefaction heat exchanger, pre-cooling heat exchanger, LNG flash gas compressor, circulating LNG flash gas compressor, raw gas separator, demist device, raw gas filter, raw gas heat exchanger, and then flows through the purified gas separator, purified gas filter, dehydration dryer, dehydration dust filter, mercury removal adsorber, mercury removal dust filter, dehydration heating furnace, the gas coming out of the dehydration heating furnace enters the dehydration dryer again, and then regeneration gas flows out of the dehydration dryer, the regeneration gas flows through the regeneration gas air cooler, regeneration gas water cooler, regeneration gas separator, regeneration gas compressor, and finally flows into the purified gas separator and / or raw gas separator, and the cycle continues until the regeneration is completed;

[0117] Stop the regeneration process and switch to the natural gas liquefaction process;

[0118] See also Figure 2The raw natural gas flows through the raw gas separator, the demist device, and the raw gas filter in sequence, and then enters the bottom of the absorption tower through the raw gas heat exchanger, where it contacts the MDEA solution coming from the top of the tower in countercurrent. The purified gas exiting the absorption tower enters the raw gas heat exchanger, exchanges heat with the raw gas, and then flows out of the raw gas heat exchanger. It then flows through the purified gas separator, the purified gas filter, the dehydration dryer (the pipeline where valves No. 1 and No. 4 are located), the dehydration dust filter, the mercury removal adsorber, the mercury removal dust filter, the pre-cooling heat exchanger, the liquefaction heat exchanger, the sub-cooling heat exchanger, and the LNG storage tank in sequence. The LNG flash gas flowing out of the LNG storage tank returns to the liquefaction heat exchanger, then returns to the pre-cooling heat exchanger after passing through the liquefaction heat exchanger, and then enters the LNG flash gas compressor after passing through the pre-cooling heat exchanger. The pressurized LNG flash gas is first transported to the fuel gas buffer tank, and the excess LNG flash gas is sent to the circulating LNG flash gas compressor. After being pressurized to the pressure of the raw natural gas by the circulating LNG flash gas compressor, it returns to the raw gas separator.

[0119] It should be noted that Figure 1 、 Figure 2 In the diagram, the equipment with the same name is the same equipment. When using it, you only need to switch the pipeline to achieve different process flows.

[0120] In the present invention, the specific start-up time of the natural gas liquefaction process is as follows:

[0121]

[0122] Compared with the traditional natural gas liquefaction process, it can be concluded that using LNG flash steam as the dehydration medium can save natural gas dehydration time, saving 38 hours compared to the traditional process, and can increase economic benefits by approximately 3.0875 million yuan (assuming a station's LNG production of 600 tons / day, the average LNG sales price in 2022 is 5,820 yuan / ton, the break-even point is 2,570 yuan / ton, and the profit is 3,250 yuan / ton.)

[0123] The use of LNG flash steam as the regeneration medium for the dehydration dryer effectively solves the problem of long natural gas dehydration time during the traditional start-up of the natural gas liquefaction unit, thereby saving natural gas dehydration time, gaining time for the enterprise and creating benefits.

[0124] Those skilled in the art will appreciate that the above-mentioned embodiments are specific examples for implementing the present invention, and that in actual applications, various changes may be made thereto in form and detail without departing from the spirit and scope of the present invention.

Claims

1. A method for regenerating a dehydration dryer using LNG flash steam, characterized in that: include: LNG processing unit, where the evaporated LNG flash gas is used as the dehydration medium; a natural gas pre-processing unit, into which the LNG flash gas from the LNG processing unit enters; a natural gas decarbonization unit, receiving LNG flash gas from the natural gas pretreatment unit and circulating amine liquid; natural gas purification unit; The natural gas dehydration and mercury removal unit comprises at least a dehydration dryer. The incoming gas treated by the natural gas purification unit enters the natural gas dehydration and mercury removal unit, dehydrates the water in the dehydration dryer, and generates regenerated gas. The regeneration gas unit receives the regeneration gas and cools, separates, and compresses the regeneration gas, and finally transmits the regeneration gas to the natural gas purification unit and / or the natural gas pretreatment unit.

2. The method for regenerating a dehydration dryer using LNG flash steam according to claim 1, wherein: The LNG processing unit comprises: The LNG storage tank, liquefaction heat exchanger, pre-cooling heat exchanger, LNG flash gas compressor, and circulating LNG flash gas compressor are sequentially connected through pipelines.

3. The method for regenerating a dehydration dryer using LNG flash steam according to claim 2, wherein: The natural gas pretreatment unit comprises: A raw gas separator, a de-mist device, and a raw gas filter connected in sequence through pipelines; The outlet of the circulating LNG flash gas compressor is connected to the inlet of the raw gas separator through a pipeline.

4. The method for regenerating a dehydration dryer using LNG flash steam according to claim 3, wherein: The natural gas decarbonization unit comprises: Raw gas heat exchanger and absorption tower connected by pipelines; The outlet of the raw gas filter and the outlet of the absorption tower are both connected to the inlet of the raw gas heat exchanger through pipelines, and the outlet of the raw gas heat exchanger is respectively connected to the inlet of the natural gas purification unit and the inlet of the absorption tower through two branch pipelines.

5. The method for regenerating a dehydration dryer using LNG flash steam according to claim 4, characterized in that: The natural gas purification unit comprises: A purified gas separator and a purified gas filter connected through pipelines; The outlet of the raw gas heat exchanger is connected to the inlet of the purified gas separator through a pipeline.

6. The method for regenerating a dehydration dryer using LNG flash steam according to claim 5, characterized in that: The natural gas dehydration and mercury removal unit comprises: A dehydration dryer, a dehydration dust filter, a demercuration adsorber, a demercuration dust filter, and a dehydration heating furnace connected through pipelines; The outlet of the purified gas filter is connected to the inlet of the dehydration dryer through a pipeline equipped with valve No. 1, the outlet of the dehydration dryer is connected to the inlet of the dehydration dust filter through a pipeline equipped with valve No. 4, the outlet of the dehydration heating furnace is connected to the inlet of the dehydration dryer through a pipeline equipped with valve No. 3, and the outlet of the dehydration dryer is connected to the regeneration gas unit through a pipeline equipped with valve No.

2.

7. The method for regenerating a dehydration dryer using LNG flash steam according to claim 6, wherein: The regeneration gas unit comprises: A regeneration gas air cooler, a regeneration gas water cooler, a regeneration gas separator, and a regeneration gas compressor connected through pipelines; The outlet of the dehydration dryer is connected to the inlet of the regeneration gas air cooler through a pipeline equipped with a No. 2 valve; The outlet of the regeneration gas compressor is connected to the purified gas separator and / or the raw gas separator through a pipeline.

8. A natural gas liquefaction process, characterized in that: The specific process includes: Step 100. Dehydration dryer regeneration Starting the method for regenerating a dehydration dryer using LNG flash steam according to claim 6 or 7 until the regeneration of the dehydration dryer is completed; Step 200: Natural gas liquefaction Directly introducing raw natural gas, the raw natural gas sequentially flows through the natural gas pretreatment unit, the natural gas decarbonization unit, and the natural gas purification unit to generate purified natural gas; The purified natural gas flows sequentially through the dehydration dryer, the dehydration dust filter, the mercury removal adsorber, the mercury removal dust filter, the pre-cooling heat exchanger, the liquefaction heat exchanger, the sub-cooling heat exchanger, and the LNG storage tank via a pipeline; The LNG flash gas flowing out of the LNG storage tank returns to the liquefaction heat exchanger, and then returns to the pre-cooling heat exchanger after passing through the liquefaction heat exchanger; After passing through the pre-cooling heat exchanger, the LNG flash gas enters the LNG flash gas compressor. The pressurized LNG flash gas is first transported to the fuel gas buffer tank, and the excess LNG flash gas is sent to the circulating LNG flash gas compressor. After being pressurized to the pressure of the raw natural gas by the circulating LNG flash gas compressor, it returns to the raw gas separator.

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