A device and method for preparing high-purity methane by double-tower rectification purification
By combining dual-tower distillation with an external refrigeration cycle, the problems of high energy consumption and system complexity in existing technologies are solved, achieving efficient and flexible high-purity methane production and diversified storage, and simplifying heat exchanger design.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHEJIANG UNIV
- Filing Date
- 2022-09-30
- Publication Date
- 2026-07-03
AI Technical Summary
Existing technologies for producing high-purity methane suffer from high energy consumption, complex heat exchanger design, high system complexity, and poor adjustment flexibility, failing to meet practical needs.
The method employs a dual-tower distillation combined with an external refrigeration cycle. Through a simple three-channel heat exchanger design and refrigeration cycle system, it achieves efficient production of high-purity methane, including a primary distillation tower and a secondary distillation tower. It utilizes the cold and heat energy of the raw material LNG for energy optimization and provides flexible operating conditions.
It achieves low-energy consumption and high-efficiency production of high-purity methane, with a simple heat exchanger design, easy system adjustment, and provides diverse product storage methods to meet different needs.
Smart Images
Figure CN115560542B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of gas purification technology, and in particular relates to an apparatus and method for preparing high-purity methane using a double-tower distillation process. Background Technology
[0002] Methane is the simplest organic compound with the chemical formula CH4. It is widely distributed in nature and is the main component of natural gas, biogas, oilfield gas, and coal mine tunnel gas, commonly known as methane.
[0003] High-purity methane contains a methane volume fraction greater than 99.999%. With technological advancements, high-purity methane is widely used in chemical, metallurgical, electronics, petroleum, and aerospace industries, primarily as a standard gas, calibration gas, online instrument standard gas, and catalyst evaluation gas. High-purity methane gas is also increasingly being used as an auxiliary additive gas in the manufacture of amorphous silicon solar cells and in dry etching and plasma etching processes for large-scale integrated circuits.
[0004] Currently, most high-purity methane production methods employ a combination of dual-tower distillation and an additional refrigeration cycle. However, these methods generally suffer from drawbacks such as high energy consumption, complex heat exchanger design, high system complexity, and poor system adjustment flexibility.
[0005] For example, Chinese patent document CN105622321A discloses a process for preparing high-purity methane by distillation purification, which includes a raw material storage tank equipped with a moisture analysis device. The outlet of the raw material storage tank is divided into two paths, one of which is directly connected to a dehydration adsorption tower via a pipeline, and the other is directly connected to a CO2 adsorption tower via a pipeline. The outlet of the dehydration adsorption tower is connected to the inlet of the CO2 adsorption tower via a pipeline. The outlet of the CO2 adsorption tower is connected in sequence to a filter, a distillation tower, a product buffer tank, and a diaphragm compressor via a pipeline. The raw material storage tank is an LNG raw material storage tank, and the distillation tower consists of two distillation towers connected in series.
[0006] Chinese patent document CN102675021A discloses a method for purifying high-purity methane, which uses a combination of pressure swing adsorption and cryogenic distillation to separate liquefied natural gas, which is a gas mixture. Specifically, two-stage series adsorption is used to remove low-boiling-point organic and inorganic impurities in sequence, thereby removing some components that affect the distillation efficiency. Then, the adsorption-treated liquefied natural gas is subjected to cryogenic distillation to remove high-boiling-point organic impurities.
[0007] Therefore, there is a need to design a distillation and purification technology for producing high-purity methane that is energy-efficient, has a simple heat exchanger design, is easy to adjust, and is easy to regulate. Summary of the Invention
[0008] This invention provides an apparatus for preparing high-purity methane using a dual-tower distillation process. The equipment is simple, energy-efficient, easy to adjust, and flexible in operation. Furthermore, the obtained high-purity methane product can be stored in various ways to meet different needs.
[0009] An apparatus for preparing high-purity methane using a dual-tower distillation process includes a high-purity methane distillation system, which comprises a primary distillation column, a secondary distillation column, a precooler, and a first heater; the feed inlet of the primary distillation column is connected to the raw material LNG supply system via a raw material LNG supply pipe.
[0010] The first-stage distillation column is equipped with a first reboiler at its bottom; the liquid outlet at the bottom of the first-stage distillation column is connected to the cold end inlet of the first heater via a first heavy component discharge pipe, and the cold end outlet of the first heater is connected to the feed inlet of the second-stage distillation column; the gas outlet at the top of the first-stage distillation column is equipped with a first light component discharge pipe, which is connected to the second heavy component discharge pipe at the bottom of the second-stage distillation column via a second tee, and the outlet of the second tee is connected to a throttling valve via a pipe; the throttling valve is equipped with a distillation column waste pipe connected to a precooler, and the distillation column waste pipe is discharged through the discharge pipe after being reheated by the precooler.
[0011] The top of the secondary distillation column is equipped with a condenser and a reflux tank; the upper gas outlet of the secondary distillation column is connected to the gas inlet of the condenser, the gas outlet of the condenser is connected to the gas inlet of the reflux tank, and the bottom liquid outlet of the reflux tank is connected to the liquid return port of the secondary distillation column; the top of the reflux tank is equipped with a second light component discharge pipe, which is connected to the inlet end of a first tee, and the first outlet end of the first tee is connected to a high-purity methane product gas cylinder through a pipe;
[0012] The bottom of the secondary distillation column is equipped with a second reboiler, the heat medium inlet and outlet of which are connected to the second heat source input pipe and the first heat source input pipe, respectively; the heat medium inlet and outlet of the first reboiler are connected to the first heat source input pipe and the first heat source discharge pipe, respectively; the refrigerant inlet and outlet of the condenser are connected to the first cold source input pipe and the first cold source discharge pipe, respectively.
[0013] Furthermore, the high-purity methane distillation system also includes a high-purity methane condenser. The hot end inlet of the high-purity methane condenser is connected to the second outlet end of the first tee via a pipe, and the hot end outlet of the high-purity methane condenser is connected to a high-purity methane product storage tank via a pipe.
[0014] The high-purity methane distillation system also includes a refrigeration cycle system, which includes a compressor, a regenerator, and an expansion module.
[0015] The compressor's outlet pipe is connected to the hot-end inlet of the regenerator; the hot-end outlet of the regenerator is connected to the inlet of the second reboiler at the bottom of the secondary distillation column via a second heat source input pipe; the outlet of the second reboiler is connected to the inlet of the first reboiler at the bottom of the primary distillation column via a first heat source input pipe; the outlet of the first reboiler is connected to the hot-end inlet of the first heater via a first heat source discharge pipe; the hot-end outlet of the first heater is connected to the hot-end inlet of the precooler; the hot-end outlet of the precooler is connected to the expansion module; the outlet of the expansion module is connected to the third tee; the first outlet of the third tee is connected to the refrigerant inlet of the condenser at the top of the secondary distillation column via a first cold source input pipe; the condenser has a first cold source output pipe for discharging refrigerant; the first cold source output pipe is connected to the first inlet of the fourth tee; the second outlet of the third tee is connected to the cold-end inlet of the high-purity methane condenser; the cold-end outlet of the high-purity methane condenser is connected to the second inlet of the fourth tee; the outlet of the fourth tee is connected to the cold-end inlet of the regenerator, and the cold-end outlet of the regenerator is connected to the compressor via the compressor inlet pipe.
[0016] Alternatively, the expansion module of the refrigeration cycle system may include an expander and / or a throttle valve.
[0017] The device also includes a raw material LNG supply system, which includes an LNG storage tank, an LNG manifold, and a tail gas manifold. The LNG manifold is connected to the liquid phase outlet of the LNG storage tank, and the outlet of the LNG manifold is connected to the raw material LNG supply pipe. The tail gas manifold is connected to the gas phase outlet of the LNG storage tank, and a tail gas discharge pipe is connected to the tail gas manifold.
[0018] The apparatus further includes a high-purity methane product storage and filling system, which comprises a high-purity methane product storage tank, a product buffer tank, a high-purity methane product gas cylinder, a second heater, and a filling compressor. The high-purity methane product storage tank is used to store high-purity liquid methane produced by the high-purity methane distillation system, and the product buffer tank is used to store high-purity gas methane produced by the high-purity methane distillation system. The product buffer tank is connected to a filling pipe, which is sequentially connected to the second heater, the filling compressor, and the high-purity methane product cylinder along the high-purity methane conveying direction.
[0019] The present invention also provides a method for preparing high-purity methane by double-tower distillation purification, using the above-mentioned apparatus, comprising the following steps:
[0020] Step 1: The raw material LNG is stored in an LNG storage tank. After being pressurized by the LNG storage tank, the raw material LNG directly enters the top of the first-stage distillation column. Distillation is carried out in the first-stage distillation column to separate the light components from the heavy components. The separated light components accumulate at the top of the first-stage distillation column and are discharged through the first light component discharge pipe. The first light component discharge pipe is connected to the second heavy component discharge pipe at the bottom of the second-stage distillation column through the second tee. After mixing in the second tee, the mixture enters the precooler for reheating before being discharged. The liquid rich in heavy components accumulates at the bottom of the first-stage distillation column and enters the first heater through the first heavy component discharge pipe at the bottom of the column for heating. After partial vaporization, it enters the second-stage distillation column.
[0021] Step 2: In the secondary distillation column, heavy components are removed by distillation. The liquid rich in heavy components is separated and accumulates at the bottom of the column. It is discharged through the second heavy component discharge pipe at the bottom of the column and enters the second three-way valve. High-purity methane gas is obtained at the top of the column. After partial condensation by the condenser, the high-purity methane gas enters the reflux tank at the top of the secondary distillation column. The liquid in the reflux tank returns to the secondary distillation column through the return pipe to participate in the distillation. Most of the high-purity methane gas is discharged through the second light component discharge pipe at the top of the reflux tank.
[0022] Step 3: The discharged high-purity methane gas is split into two streams through the first three-way valve. One stream passes through the heating and pressurizing device and enters the high-purity methane product gas cylinder for storage. The other stream enters the high-purity methane condenser for liquefaction and subcooling, and then enters the high-purity methane product storage tank for storage.
[0023] In the above process, the cooling capacity required by the condenser of the secondary distillation column and the high-purity methane condenser is provided by an external refrigeration cycle; the external refrigeration cycle process is as follows:
[0024] The refrigerant is pressurized by the compressor and then enters the regenerator. After cooling, the refrigerant passes through the second reboiler of the secondary distillation column, the first reboiler of the primary distillation column, and the first heater to provide heat. After cooling in the precooler, it enters the expansion module for further depressurization and cooling. The refrigerant exiting the expansion module enters the third three-way valve and splits into two streams. One stream is cooled by the condenser of the secondary distillation column, and the other is cooled by the high-purity methane condenser. The two streams are then mixed through the fourth three-way valve. The refrigerant exiting the fourth three-way valve is reheated by the regenerator and then enters the compressor, thus achieving refrigerant cyclic refrigeration.
[0025] Compared with the prior art, the present invention has the following beneficial effects:
[0026] 1. Low design and manufacturing difficulty and high energy efficiency of heat exchangers: This invention uses heat exchangers with no more than three channels to achieve heat exchange between materials with matching temperatures. Each heat exchanger has high energy efficiency and low design and manufacturing difficulty.
[0027] 2. Flexible operation and easy adjustment: The heat exchanger in this invention has no more than three channels, which makes it easy to adjust the state of each material flow and thus facilitates the adjustment of system parameters. An external refrigeration cycle is used to provide cooling capacity for the process. The appropriate refrigerant and refrigerant flow rate can be selected according to the specific process. The refrigerant flow can also be allocated according to the cooling capacity requirements of each heat exchanger in the process, which improves the flexibility of system operation.
[0028] 3. The overall process has high energy efficiency: The feedstock LNG directly enters the top of the first-stage distillation column, serving as the reflux liquid of the first-stage distillation column, eliminating the need for a condenser at the top of the distillation column. At the same time, the cold energy of the feedstock LNG can be used to pre-cool the refrigerant after pressurization and heating in the reboiler at the bottom of the column; the pressurized and heated refrigerant can be used to provide a heat source for the reboiler of the second-stage distillation column; and the cold energy of the distillation column waste can be used to cool the refrigerant before it enters the throttling valve.
[0029] 4. This invention can directly obtain high-purity methane gas. After obtaining high-pressure, high-purity methane gas using a pressurization device, it can be filled into product gas cylinders for storage. Alternatively, high-purity methane gas can be liquefied using a high-purity methane condenser and then sent to a high-purity methane product storage tank for storage. The various storage methods for high-purity methane products can meet different needs. Attached Figure Description
[0030] Figure 1 This is a schematic diagram of the high-purity methane distillation system in this invention;
[0031] Figure 2 This is a schematic diagram of the LNG supply system in this invention.
[0032] Figure 3 This is a schematic diagram of the expansion module in this invention;
[0033] Figure 4 This is a schematic diagram of the high-purity methane product storage and filling system of the present invention. Detailed Implementation
[0034] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not constitute any limitation thereof.
[0035] like Figure 1 As shown, an apparatus for preparing high-purity methane using a dual-tower distillation process includes a high-purity methane distillation system, a raw material LNG supply system, and a high-purity methane product storage and filling system.
[0036] The high-purity methane distillation system includes a primary distillation column T-101, a secondary distillation column T-102, a precooler H-104, a heater H-107, a high-purity methane condenser H-105, and a refrigeration cycle system. The first-stage distillation column T-101 includes a first reboiler H-101 at the bottom and a vapor-liquid contact device in the middle of the column. The liquid outlet at the bottom of the first-stage distillation column T-101 has a first heavy component discharge pipe 102 connected to a heater H-107. After being heated by the heater H-107, the first heavy component discharge pipe 102 is connected to the feed inlet of the second-stage distillation column. The gas outlet at the top of the first-stage distillation column T-101 has a first light component discharge pipe 110. The first light component discharge pipe 110 is connected to the second heavy component discharge pipe 111 at the bottom of the second-stage distillation column T-102 through a second tee M-102. The outlet of the second tee M-102 is connected to a throttle valve V-101 through a pipe 112. The throttle valve V-101 has a distillation column waste pipe 113 connected to a precooler H-104. After being reheated by the precooler, the distillation column waste pipe 113 is discharged through a discharge pipe 114.
[0037] The upper outlet of the secondary distillation column T-102 has a pipe 103 connected to the inlet of the condenser H-103 at the top of the secondary distillation column. The outlet of the condenser H-103 has a pipe 104 connected to the inlet of the reflux tank R-101 at the top of the secondary distillation column. The bottom outlet of the reflux tank R-101 has a return pipe 105 connected to the return port of the secondary distillation column T-102. The top of the reflux tank R-101 has a second light component discharge pipe 106. The second light component discharge pipe 106 is divided into two pipes by the first tee M-101. Pipe 109 is connected to the high-purity methane product gas cylinder, and pipe 107 is connected to the high-purity methane condenser H-105. After the high-purity methane gas is liquefied and subcooled in the high-purity methane condenser H-105, it is connected to the high-purity methane product storage tank through pipe 108. The bottom of the secondary distillation column T-102 has a second heavy component discharge pipe 111, which is connected to the second tee M-102.
[0038] The refrigeration cycle system includes compressor C-101, regenerator H-106, and expansion module EP-101. Expansion module EP-101 may contain an expander and / or a throttling valve, such as... Figure 3 As shown in the figure, (a) indicates that the expansion module EP-101 uses a throttle valve V-102; (b) indicates that the expansion module EP-101 uses an expander C-102; (c) indicates that the expansion module EP-101 uses a throttle valve V-102 and an expander C-102. In this case, the throttle valve V-102 is connected to the first hot end outlet of the precooler H-104 through pipe 206, and the expander is connected to the second hot end outlet of the precooler H-104 through pipe 214. In this embodiment, the expansion module EP-101 uses... Figure 3A throttle valve V-102 is shown in (a) to close the valve on pipe 214.
[0039] The outlet of compressor C-101 is connected to regenerator H-106 via compressor outlet pipe 201. After being cooled by regenerator H-106, compressor outlet pipe 201 is connected to the inlet of second reboiler H-102 at the bottom of secondary distillation column via second heat source input pipe 202. The outlet of the second reboiler H-102 is connected to the inlet of the first reboiler H-101 at the bottom of the first-stage distillation column via the first heat source input pipe 203. The outlet of the first reboiler H-101 is connected to the hot end inlet of the first heater H-107 via the first heat source discharge pipe 204. The hot end outlet of the first heater H-107 is connected to the hot end inlet of the precooler H-104 via pipe 205. The hot end outlet of the precooler H-104 is connected to the throttle valve V-102 via pipe 206. The outlet of the throttle valve V-102 is connected to the third tee M-103 via pipe 207. The first outlet of the third tee M-103 is connected to the refrigerant inlet of the condenser H-103 at the top of the second-stage distillation column via the first cold source input pipe 212. The condenser H-103 has a first cold source output pipe 213 for discharging refrigerant. The first cold source output pipe 213 is connected to the first inlet of the fourth tee M-104. The second outlet of the third tee M-103 is connected to the cold end inlet of the high-purity methane condenser H-105 via pipe 208. The cold end outlet of the high-purity methane condenser H-105 is then connected to the second inlet of the fourth tee M-104 via pipe 209. The outlet of the fourth tee M-104 has a pipe 210 connecting to the regenerator H-106. After being reheated by the regenerator H-106, it is connected to the compressor C-101 via the compressor inlet pipe 211.
[0040] The raw LNG supply system includes an LNG storage tank TK-301, an LNG manifold 301, and a tail gas manifold 302. The LNG manifold 301 connects to the liquid phase outlets of the two LNG storage tanks, and its outlet is connected to the raw LNG supply pipe 101. The tail gas manifold 302 connects to the gas phase outlets of the two LNG storage tanks, and a tail gas discharge pipe 303 is connected to the tail gas manifold 302.
[0041] like Figure 2 The diagram shows the structure of the raw material LNG supply system, which includes multiple LNG manifolds 301. Each LNG manifold 301 is connected to a raw material LNG supply pipe 101. Each LNG manifold 301 is connected to two LNG storage tanks TK-301, which serve as raw material LNG. In this embodiment, the LNG storage tanks are equipped with self-pressurization devices to maintain the supply pressure. When the LNG in one storage tank is about to run out, the two storage tanks are switched.
[0042] The high-purity methane product storage and filling system includes a product buffer tank TK-401, a second heater H-401, a filling compressor P-401, two sets of high-purity methane product cylinders G-401, and two high-purity methane product storage tanks (TK-402 and TK-403). The product buffer tank TK-401 is connected to the product cylinders via a filling pipe 401. The filling pipe 401 connects sequentially to the second heater H-401, the filling compressor P-401, and the high-purity methane product cylinders G-401 along the flow direction of the high-purity methane.
[0043] like Figure 4 The diagram shows the structure of a high-purity methane product storage and filling system. Gaseous high-purity methane from the high-purity methane distillation system is heated and pressurized by heater H-401 and filling compressor P-401 before being directly filled into product cylinder G-401 for storage. The product cylinder is a seamless steel cylinder connected to the filling rack via a high-pressure stainless steel hose. The product cylinders are divided into two groups; when one group is full, the filling is transferred to the other group. Liquid high-purity methane from the high-purity methane distillation system enters storage tanks (TK-402 and TK-403). When one storage tank is about to be full, the filling is transferred between the two tanks. The storage tanks are equipped with self-pressurizing devices that can pressurize the liquid high-purity methane to the user's required pressure of 0.6 MPa.
[0044] In this embodiment, the method for producing high-purity methane using the above-described apparatus comprises the following steps:
[0045] (1) The raw material LNG is stored in an LNG storage tank. After being pressurized by the storage tank, the raw material LNG directly enters the top of the first-stage distillation column T-101. Distillation is carried out in the first-stage distillation column T-101 to separate light components such as nitrogen and oxygen from heavy components. The separated light components such as nitrogen and oxygen accumulate at the top of the first-stage distillation column T-101 and are discharged through the first light component discharge pipe 110 at the top of the first-stage distillation column T-101. The first light component discharge pipe 110 is connected to the second heavy component discharge pipe 111 at the bottom of the second-stage distillation column T-102 through the second three-way valve M-102. The components are mixed in the second three-way valve M-102, and after being throttled by the throttle valve V-102, they enter the precooler for reheating and are then discharged. The liquid rich in heavy components accumulates at the bottom of the first-stage distillation column T-101 and enters the heater H-107 through the first heavy component discharge pipe 102 at the bottom of the column for heating. After partial vaporization, it enters the second-stage distillation column T-102.
[0046] (2) In the secondary distillation column T-102, heavy components such as alkanes are removed by distillation. The liquid rich in heavy components accumulates at the bottom of the column and is discharged through the second heavy component discharge pipe 111 at the bottom of the column, entering the second three-way valve M-102. High-purity methane gas is obtained at the top of the column. After being partially condensed by the condenser H-103, the high-purity methane gas enters the reflux tank R-101 at the top of the secondary distillation column T-102. The liquid in the reflux tank R-101 returns to the secondary distillation column T-102 through the return pipe 105 to participate in distillation. Most of the high-purity methane gas is discharged through the second light component discharge pipe 106 at the top of the reflux tank.
[0047] (3) The discharged high-purity methane gas is divided into two streams through the first three-way valve M-101. One stream passes through the heating and pressurizing device and enters the product gas cylinder for storage. The other stream enters the high-purity methane condenser H-104 for liquefaction and subcooling, and then enters the product storage tank for storage.
[0048] In the above process, the cooling capacity required by the condenser H-103 of the secondary distillation column and the high-purity methane condenser H-105 is provided by an external refrigeration cycle. The refrigerant is pressurized by the compressor C-101 and then enters the regenerator H-106. The cooled refrigerant gas passes sequentially through the second reboiler H-102 of the secondary distillation column, the first reboiler H-101 of the primary distillation column, and the first heater H-107 to provide them with heat. After that, it enters the precooler H-104 for further cooling and then enters the throttle valve V-102 for depressurization and cooling. The refrigerant coming out of the throttle valve V-102 enters the third three-way valve M-103 and is divided into two streams. One stream enters the condenser H-103 of the secondary distillation column through pipe 212 to provide it with a cooling source, and the other stream enters the high-purity methane condenser H-105 through pipe 208 to provide it with a cooling source. Then the two streams of refrigerant are mixed through the fourth three-way valve M-104. The refrigerant coming out of the fourth three-way valve M-104 is reheated by the regenerator H-106 and then enters the compressor C-101, thus realizing the cyclic refrigeration of the refrigerant.
[0049] In the description of this invention, the positional or orientational terms "top," "bottom," "upper," "lower," etc., indicate only the positional or orientational relationship based on the drawings, and do not indicate that the device or element referred to must be installed in the described position or orientation.
[0050] In this invention, terms such as "Level 1" and "Level 2" are used only to distinguish them from each other and do not indicate their degree of importance.
[0051] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.
Claims
1. An apparatus for preparing high-purity methane using a double-tower distillation process, characterized in that, The system includes a high-purity methane distillation system, which comprises a primary distillation column (T-101), a secondary distillation column (T-102), a precooler (H-104), and a first heater (H-107). The feed inlet of the primary distillation column (T-101) is connected to the raw material LNG supply system via a raw material LNG supply pipe (101). Specifically, the raw material LNG is stored in an LNG storage tank, and the pressurized raw material LNG directly enters the top of the primary distillation column (T-101). The first-stage distillation column (T-101) is equipped with a first reboiler (H-101) at its bottom; the bottom outlet of the first-stage distillation column (T-101) is connected to the cold end inlet of the first heater (H-107) via a first heavy component discharge pipe (102), and the cold end outlet of the first heater (H-107) is connected to the feed inlet of the second-stage distillation column (T-102); the top outlet of the first-stage distillation column (T-101) is equipped with a first light component discharge pipe (110), the first light component... The component discharge pipe (110) is connected to the second heavy component discharge pipe (111) at the bottom of the secondary distillation column (T-102) via a second tee (M-102). The outlet of the second tee (M-102) is connected to the first throttle valve (V-101) via a pipe. The first throttle valve (V-101) is equipped with a distillation column waste pipe (113) connected to the precooler (H-104). The distillation column waste pipe (113) is discharged through the discharge pipe after being reheated by the precooler (H-104). The top of the secondary distillation column (T-102) is equipped with a condenser (H-103) and a reflux tank (R-101); the upper outlet of the secondary distillation column (T-102) is connected to the inlet of the condenser (H-103), the outlet of the condenser (H-103) is connected to the inlet of the reflux tank (R-101), and the bottom outlet of the reflux tank (R-101) is connected to the return outlet of the secondary distillation column (T-102); the top of the reflux tank (R-101) is equipped with a second light component discharge pipe (106), which is connected to the inlet end of the first tee (M-101), and the first outlet end of the first tee (M-101) is connected to a high-purity methane product gas cylinder through a pipe; The high-purity methane distillation system also includes a refrigeration cycle system, which includes a compressor (C-101), a regenerator (H-106), and an expansion module (EP-101). The outlet pipe of the compressor (C-101) is connected to the hot end inlet of the regenerator (H-106); the hot end outlet of the regenerator (H-106) is connected to the heat medium inlet of the second reboiler (H-102) at the bottom of the secondary distillation column via the second heat source input pipe (202); the heat medium outlet of the second reboiler (H-102) is connected to the heat medium inlet of the first reboiler (H-101) at the bottom of the primary distillation column via the first heat source input pipe (203); The heat medium outlet of the reboiler (H-101) is connected to the hot end inlet of the first heater (H-107) via the first heat source discharge pipe (204); the hot end outlet of the first heater (H-107) is connected to the hot end inlet of the precooler (H-104); the hot end outlet of the precooler (H-104) is connected to the expansion module (EP-101); the outlet of the expansion module (EP-101) is connected to the inlet of the third tee (M-103); the first outlet of the third tee (M-103) is connected to the refrigerant inlet of the top condenser (H-103) of the secondary distillation column via the first cold source input pipe (212); the condenser (H-103) has a first cold source output pipe (213) for discharging refrigerant, and the refrigerant outlet of the condenser (H-103) is connected to the first cold source output pipe (213); the first cold source output pipe (213) is connected to the first inlet of the fourth tee (M-104). Connect the second outlet of the third tee (M-103) to the cold end inlet of the high-purity methane condenser (H-105); connect the cold end outlet of the high-purity methane condenser (H-105) to the second inlet of the fourth tee (M-104); connect the outlet of the fourth tee (M-104) to the cold end inlet of the regenerator (H-106); and connect the cold end outlet of the regenerator (H-106) to the compressor (C-101) via the compressor inlet pipe.
2. The apparatus for preparing high-purity methane using double-tower distillation according to claim 1, characterized in that, The high-purity methane distillation system also includes a high-purity methane condenser (H-105). The hot end inlet of the high-purity methane condenser (H-105) is connected to the second outlet end of the first tee (M-101) via a pipeline, and the hot end outlet of the high-purity methane condenser (H-105) is connected to a high-purity methane product storage tank via a pipeline.
3. The apparatus for preparing high-purity methane using double-tower distillation according to claim 1, characterized in that, The expansion module (EP-101) of the refrigeration cycle system includes an expander and / or a second throttle valve (V-102).
4. The apparatus for preparing high-purity methane using double-tower distillation according to claim 1, characterized in that, The device also includes a raw material LNG supply system, which includes an LNG storage tank (TK-301), an LNG manifold (301), and a tail gas manifold (302). The LNG manifold (301) is connected to the liquid phase outlet of the LNG storage tank (TK-301), and the outlet of the LNG manifold (301) is connected to the raw material LNG supply pipe (101). The tail gas manifold (302) is connected to the gas phase outlet of the LNG storage tank (TK-301), and a tail gas discharge pipe (303) is connected to the tail gas manifold (302).
5. The apparatus for preparing high-purity methane using double-tower distillation according to claim 2, characterized in that, The device also includes a high-purity methane product storage and filling system, which includes a high-purity methane product storage tank, a product buffer tank (TK-401), a high-purity methane product gas cylinder (G-401), a second heater (H-401), and a filling compressor (P-401). The high-purity methane product storage tank is used to store high-purity methane liquid produced by the high-purity methane distillation system. The product buffer tank (TK-401) is used to store high-purity methane gas produced by the high-purity methane distillation system. The product buffer tank (TK-401) is connected to a filling pipe (401), which is connected sequentially to the second heater (H-401), the filling compressor (P-401), and the high-purity methane product cylinder (G-401) along the high-purity methane conveying direction.
6. A method for preparing high-purity methane using double-tower distillation, characterized in that, The apparatus according to any one of claims 2 to 5 comprises the following steps: Step 1: The raw material LNG is stored in an LNG storage tank. After being pressurized by the LNG storage tank, the raw material LNG directly enters the top of the primary distillation column (T-101). Distillation is carried out in the primary distillation column (T-101) to separate the light components from the heavy components. The separated light components accumulate at the top of the primary distillation column (T-101) and are discharged through the first light component discharge pipe (110). The first light component discharge pipe (110) is connected to the second heavy component discharge pipe (111) at the bottom of the secondary distillation column (T-102) through the second tee (M-102). After mixing in the second tee (M-102), the mixture enters the precooler (H-104) for reheating and is then discharged. The liquid rich in heavy components accumulates at the bottom of the primary distillation column (T-101) and enters the first heater (H-107) through the first heavy component discharge pipe (102) at the bottom of the column for heating. After partial vaporization, it enters the secondary distillation column (T-102). Step 2: In the secondary distillation column (T-102), heavy components are removed by distillation. The liquid rich in heavy components is separated and accumulates at the bottom of the column. It is discharged through the second heavy component discharge pipe (111) at the bottom of the column and enters the second three-way valve (M-102). High-purity methane gas is obtained at the top of the column. After being partially condensed by the condenser (H-103), the high-purity methane gas enters the reflux tank (R-101) at the top of the secondary distillation column (T-102). The liquid in the reflux tank (R-101) returns to the secondary distillation column (T-102) through the return pipe to participate in the distillation. Most of the high-purity methane gas is discharged through the second light component discharge pipe (106) at the top of the reflux tank (R-101). Step 3: The discharged high-purity methane gas is split into two streams through the first three-way valve (M-101). One stream passes through the heating and pressurizing device and enters the high-purity methane product gas cylinder for storage. The other stream enters the high-purity methane condenser (H-105) for liquefaction and subcooling, and then enters the high-purity methane product storage tank for storage.
7. The method for preparing high-purity methane by double-tower distillation according to claim 6, characterized in that, The cooling required for the condensers (H-103) and high-purity methane condensers (H-105) of the secondary distillation column is provided by an external refrigeration cycle; the external refrigeration cycle process is as follows: The refrigerant is pressurized by the compressor (C-101) and then enters the regenerator (H-106). After cooling, the refrigerant passes through the second reboiler (H-102) of the secondary distillation column, the first reboiler (H-101) of the primary distillation column, and the first heater (H-107) to provide heat. After cooling, it enters the precooler (H-104) and then enters the expansion module (EP-101) for depressurization and cooling. The refrigerant from the expansion module (EP-101) enters the third three-way valve (M-103) and is divided into two streams. One stream is cooled by the condenser (H-103) of the secondary distillation column, and the other stream is cooled by the high-purity methane condenser (H-105). The two streams of refrigerant are then mixed through the fourth three-way valve (M-104). The refrigerant from the fourth three-way valve (M-104) is reheated by the regenerator (H-106) and then enters the compressor (C-101), thus realizing the cyclic refrigeration of the refrigerant.