CN220552182U

CN220552182U - System capable of extracting coarse helium from helium-depleted natural gas

Info

Publication number: CN220552182U
Application number: CN202322179207.7U
Authority: CN
Inventors: 张宗衡; 李声强; 李云翰; 张勇
Original assignee: Guangdong Jiufeng Special Gas Co ltd
Current assignee: Guangdong Jiufeng Special Gas Co ltd
Priority date: 2023-08-14
Filing date: 2023-08-14
Publication date: 2024-03-01
Anticipated expiration: 2033-08-14

Abstract

The utility model relates to the technical field of natural gas liquefaction processing, in particular to a system capable of extracting crude helium from helium-depleted natural gas. The utility model is provided with a refrigerating unit for providing a cold source and having a refrigerating temperature of more than-165 ℃, a pretreatment unit for removing heavy hydrocarbon in feed gas, a helium extraction unit, a denitrification unit, a feed gas feed pipe for conveying feed gas with a helium mole fraction of less than or equal to 0.05% and a helium output pipe for conveying helium with a mole fraction of more than or equal to 60%. The beneficial effects of the utility model are as follows: 1. the utility model can complete helium extraction under the refrigeration unit used for liquefying conventional natural gas without consuming liquid nitrogen or adding other circulating refrigeration units; 2. the system can still obtain helium with the concentration of more than 60% under the condition that the concentration of helium in raw material gas is lower than 0.05%, so that the economic value is high.

Description

System capable of extracting coarse helium from helium-depleted natural gas

Technical Field

The utility model relates to the technical field of natural gas liquefaction processing, in particular to a system capable of extracting crude helium from helium-depleted natural gas.

Background

Although natural gas resources in China are rich in reserves, the mole fraction of helium in natural gas is low, so that the development of helium extraction technology is relatively lagged. At present, helium-rich natural gas (helium mole fraction is more than 0.05%) is mainly helium gas flow in a mode of multistage membrane separation and low-temperature BOG helium extraction by natural gas production and liquefaction enterprises in China. Advanced technology for recycling helium for helium-depleted natural gas (mole fraction below 0.05%) has not been developed, resulting in a portion of the helium resources being wasted.

Because of the influence of late development of helium extraction technology, low helium mole fraction (generally less than 200 ppm) in natural gas in China and other factors, most of the existing natural gas production and liquefaction factories in China adopt a system shown in the figure 1, and in the traditional system of the figure 1, raw natural gas enters a cold box, is precooled to-40 ℃ by an MRC (magnetic resonance imaging) refrigerant circulation system, and is subjected to heavy hydrocarbon removal by a heavy hydrocarbon separation tank (V-100). After the natural gas (the molar fraction of the heavy hydrocarbon C4+ is about 1.0%) after heavy hydrocarbon removal is used for providing a heat source for the denitrification tower reboiler E-106, the natural gas enters the cold box again to be cooled to-155 ℃ (316 flow), is decompressed to 1100kPa through a valve (JT-01), and enters the denitrification tower (T-1102) to remove nitrogen in LNG. The nitrogen (stream 321) at the top of the denitrogenation column has a mole fraction of about 75% and the balance methane, and during this process, most of the helium will be vented to the flare via this stream, thereby wasting helium. LNG (322 flow) coming out of the tower kettle is cooled to-163 ℃ by a cold box and then enters an LNG storage tank (324 flow) for sale.

The helium extracting device is not specially arranged in the design stage of the system, and when the helium extracting requirement is increased in the later stage, helium extracting equipment is added to collect helium on the basis of the original LNG liquefying device (natural gas liquefying device), and the existing process with more applications mainly comprises two types: the first is to extract coarse helium with concentration of more than 40% by adding a multi-stage membrane separation device; in the second type, in the original LNG liquefaction device, flash gas of a cold box or BOG of a storage tank is collected, pressurized and liquefied and enriched helium is sent to a special helium purification unit or factory to be purified to 99.999% of high purity helium, but both methods have disadvantages and shortcomings, and the method specifically comprises the following steps:

the first process has the following disadvantages and shortcomings:

1. the stability requirement on the helium mole fraction in the feed gas is high, and if the helium mole fraction in the feed gas fluctuates greatly, the product purity and yield will be greatly affected. Meanwhile, the method is difficult to ensure that the yield of the crude helium product is more than 95% while the purity of the crude helium product is more than 40%.

2. When the mole fraction of helium in the natural gas feed is less than 200ppm, the economic value of crude helium extraction by membrane separation techniques is not high.

3. The helium-extracted metal film has high price, short service life (usually less than 6 years), low localization rate, generally low localization metal film performance, high investment cost and risk of outage caused by international situation change due to monopoly of the technology abroad.

The second process has the following disadvantages and shortcomings:

1. according to the national standard of GB/T38753-2020 liquefied Natural gas, the mole fraction of nitrogen in liquefied natural gas is less than 1.0%, so when the mole fraction of nitrogen in raw natural gas is more than 1.0%, a denitrification unit is required to be arranged in the liquefaction process, and the denitrification unit usually adopts a low-temperature flash evaporation denitrification process, and helium is easier to gasify than nitrogen, so once the denitrification unit is arranged for flash evaporation, the helium is led to flash evaporation and discharge along with the flash evaporation, and the storage tank BOG has almost no helium.

2. The tank BOG pressure is generally low (less than 200 kPaA) and needs to be re-pressurized to above 1100kPaA before the re-liquefaction of enriched helium is met, thus consuming a significant amount of additional electrical energy.

3. When the denitrification unit is not arranged, the collected BOG contains a large amount of nitrogen, the concentration of helium is increased to be more than 40% by reliquefaction, and the nitrogen and methane in the raw material gas need to be removed by reliquefaction, such as the reliquefaction separation in consideration of re-pressurization to be more than 1100 kPaA. At this pressure, a minimum cold source below-170 ℃ is needed, but the minimum temperature of the mixed refrigerant cold source used for liquefying the conventional natural gas is generally not lower than-170 ℃, so that the refrigeration system of the conventional liquefying plant can only provide a cold source of about-170 ℃, for example, helium is concentrated by adopting the method, liquid nitrogen is generally needed to be used or other refrigeration systems are added to provide a low-temperature cold source, and the operation cost and investment for extracting crude helium are greatly increased by the methods.

The following patents currently belong to the second process:

the application number 20211107822.6 discloses a three-tower low Wen Dihai system suitable for low helium-containing natural gas, and the technology mainly comprises the steps of firstly extracting mixed gas of nitrogen and helium in the natural gas and then denitrifying the mixed gas under the condition that the He mole fraction is 300ppm, wherein the method has the defects of needing to additionally add a low-temperature cold source, ensuring that the tower top condensation temperature is less than-170 ℃ and having large investment and high energy consumption.

The application number 202222744330.4 discloses a BOG concentration helium extraction system, the raw material of the helium extraction method of the system is storage tank or cold box flash steam, the pressure is lower, and coarse helium extraction can be carried out only after secondary pressurization is needed. The essence of the process is that nitrogen and helium are firstly separated from LNG together, and then the nitrogen and the helium are separated by a cooling and liquefying method, so that a flash air compressor is additionally arranged, a cryogenic low-temperature cold source (lower than minus 170 ℃) is additionally arranged, and the defects of large investment and high energy consumption are overcome.

The application number 202221221820.X discloses a natural gas crude helium co-production LNG device adopting nitrogen expansion refrigeration, the device is a natural gas liquefaction process helium extraction device, but the whole liquefaction refrigeration process adopts nitrogen double-expansion machine refrigeration, the refrigeration temperature is even as low as-190 ℃, but not the current main stream mixed refrigerant refrigeration process, the refrigerant circulation quantity is large, the equipment investment cost is high, the device cannot be applied to the improvement of the domestic existing device, the device does not consider denitrification, and when the nitrogen mole fraction in the raw gas is higher than 1%, qualified LNG products cannot be produced, and the application range is smaller.

The application number 2202111239619.4 discloses a helium extraction device and a natural gas helium extraction method, a denitrification unit is additionally arranged in the patent, but the method of firstly removing methane and then separating nitrogen and helium is adopted in the patent, so that a low-temperature cold source of minus 185 ℃ to minus 190 ℃ is needed to be provided in the denitrification link, and a nitrogen expander is also used in the patent to achieve the above effects, so that investment and operation cost are high, and the original natural gas liquefaction device is difficult to reform.

In the global scope, the supply and demand condition of helium as a scarce resource is more and more intense, and China is one of the large countries for consuming helium, so that development and utilization of helium resources are required to be enhanced, and research and development strength of helium technology are enhanced.

Disclosure of Invention

The present utility model aims to avoid the disadvantages of the prior art and to provide a system for extracting crude helium from helium-depleted natural gas. The system can obtain helium with purity of more than or equal to 60% from the feed gas with the helium mole fraction concentration of less than 0.05% in the feed gas, and no additional cold source is needed.

The above object of the present utility model is achieved by the following technical measures:

the system is provided with a refrigerating unit for providing a cold source and refrigerating the raw helium from the natural gas lean in helium, a pretreatment unit for removing heavy hydrocarbon in the raw helium, a helium extraction unit, a denitrification unit, a raw helium feed pipe for conveying the raw helium with the mole fraction of less than or equal to 0.05% and a helium output pipe for conveying the raw helium with the mole fraction of more than or equal to 60%.

Preferably, the feed gas feed pipe is connected with the feed inlet of the pretreatment unit through a pipeline, the gas phase outlet of the pretreatment unit is connected with the feed inlet of the helium extraction unit through a pipeline, the gas phase outlet of the helium extraction unit is connected with the helium output pipe through a pipeline, the liquid phase outlet of the helium extraction unit is connected with the feed inlet of the denitrification unit through a pipeline, the gas phase outlet of the denitrification unit is connected with the nitrogen output pipe through a pipeline, and the liquid phase outlet of the denitrification unit is connected with an external LNG storage tank through a pipeline.

Preferably, the helium extracting unit is provided with a helium extracting rectifying tower and a helium extracting tower reboiler, a feeding port of the helium extracting rectifying tower is connected with a gas phase outlet of the pretreatment unit through a pipeline, a gas phase outlet of the helium extracting rectifying tower is connected with the helium output pipe through a pipeline, a liquid phase outlet of the helium extracting rectifying tower is connected with a feeding port of the helium extracting tower reboiler through a pipeline, a gas phase outlet of the helium extracting tower reboiler is connected with a feeding port of the helium extracting rectifying tower through a pipeline, and a liquid phase outlet of the helium extracting tower reboiler is connected with a feeding port of the denitrification unit through a pipeline.

Preferably, the pretreatment unit is provided with a heavy hydrocarbon separation tank and a heavy hydrocarbon secondary flash tank, wherein a feed inlet of the heavy hydrocarbon separation tank is connected with a feed gas feed pipe through a pipeline, a gas phase outlet of the heavy hydrocarbon separation tank is connected with a feed inlet of the helium rectifying tower through a pipeline, a liquid phase outlet of the heavy hydrocarbon separation tank is connected with a feed inlet of the heavy hydrocarbon secondary flash tank through a pipeline, a gas phase outlet of the heavy hydrocarbon secondary flash tank is connected with a feed inlet of the helium rectifying tower through a pipeline, and a liquid phase outlet of the heavy hydrocarbon secondary flash tank is connected with an external heavy hydrocarbon storage tank through a pipeline.

Preferably, the three feed inlets of the helium extraction rectifying tower are respectively defined as an A1 feed inlet, an A2 feed inlet and an A3 feed inlet, wherein the A1 feed inlet is connected with a gas phase outlet of the heavy hydrocarbon separation tank through a pipeline, the A2 feed inlet is connected with a gas phase outlet of the heavy hydrocarbon secondary flash tank through a pipeline, and the A3 feed inlet is connected with a gas phase outlet of the helium extraction tower reboiler through a pipeline.

Preferably, the denitrification unit is provided with a denitrification tower and a denitrification tower reboiler, wherein a feed inlet of the denitrification tower is connected with a liquid phase outlet of the helium extraction tower reboiler through a pipeline, a gas phase outlet of the denitrification tower is connected with a nitrogen output pipe through a pipeline, a liquid phase outlet of the denitrification tower is connected with a feed inlet of the denitrification tower reboiler through a pipeline, a gas phase outlet of the denitrification tower reboiler is connected with a feed inlet of the denitrification tower through a pipeline, and a liquid phase outlet of the denitrification tower reboiler is connected with an external LNG storage tank through a pipeline.

The pipeline that will be connected between the gas phase export of heavy hydrocarbon knockout drum with the A1 feed inlet is defined as the pretreatment pipeline, the pretreatment pipeline is being close the gas phase exit end of heavy hydrocarbon knockout drum is divided into two pipelines to two pipelines pass through respectively carry helium tower reboiler with the denitrogenation tower reboiler, this two pipelines follow carry helium tower reboiler with the denitrogenation tower reboiler is drawn forth the back and is joined into a pipeline, reentrant process the inside of refrigeration unit, then this pipeline with A1 feed inlet is connected.

Preferably, two feed inlets of the denitrification tower are respectively defined as a B1 feed inlet and a B2 feed inlet, the B1 feed inlet is connected with the nitrogen output pipe through a pipeline, and the B2 feed inlet is connected with a gas phase outlet of the denitrification tower reboiler through a pipeline.

Preferably, the helium extraction rectifying tower is provided with 10 tower plates, and the A1 feed inlet is positioned above the 1 st tower plate of the helium extraction rectifying tower from top to bottom.

Preferably, the denitrification tower is provided with 8 trays, the trays are sequentially arranged from top to bottom, the trays of the denitrification tower comprise 3 rectification trays and 5 rectification trays, and the B1 feed inlet is positioned above the 4 th tray of the denitrification tower from top to bottom.

Preferably, the denitrification unit is further provided with a denitrification tower top condenser, and a part of pipelines connected between the helium output pipe and the gas phase outlet of the denitrification tower passes through the denitrification tower top condenser.

Preferably, the pretreatment unit is further provided with a first pressure reducing valve and a second pressure reducing valve, and the first pressure reducing valve is located in a pipeline connected between the liquid phase outlet of the heavy hydrocarbon separation tank and the feed inlet of the heavy hydrocarbon secondary flash tank.

Preferably, the second pressure reducing valve is located in the pipeline between the liquid phase outlet of the heavy hydrocarbon secondary flash tank and the external heavy hydrocarbon storage tank.

The beneficial effects of the utility model are as follows:

1. the utility model can complete helium extraction under the refrigeration unit used for liquefying conventional natural gas without consuming liquid nitrogen or adding other circulating refrigeration units;

2. the system can still obtain helium with the concentration of more than 60% under the condition that the concentration of helium in raw material gas is lower than 0.05%, so that the economic value is high.

Drawings

The utility model is further illustrated by the accompanying drawings, which are not to be construed as limiting the utility model in any way.

Fig. 1 is a schematic diagram of a conventional system.

FIG. 2 is a schematic diagram of a system capable of extracting crude helium from helium-depleted natural gas in accordance with the present utility model.

Fig. 3 is a schematic diagram of a second embodiment in example 6.

Fig. 4 is a schematic diagram of a first embodiment in example 6.

In fig. 1 to 4, there are included:

helium extraction unit 100, nitrogen removal unit 200, pretreatment unit 300, and refrigeration unit 400.

Detailed Description

The technical scheme of the utility model is further described with reference to the following examples.

Example 1

A system for extracting crude helium from helium-depleted natural gas is provided with a refrigeration unit 400 for providing a cold source and having a refrigeration temperature of-165 ℃ or higher, a pretreatment unit 300 for removing heavy hydrocarbons in the raw gas, a helium extraction unit 100, a nitrogen removal unit 200, a raw gas feed pipe for feeding a raw gas with a helium mole fraction of 0.05% or less and a helium gas output pipe for feeding helium with a mole fraction of 60% or more, as shown in FIG. 2.

The feed gas feed pipe is connected with the feed inlet of the pretreatment unit 300 through a pipeline, the gas phase outlet of the pretreatment unit 300 is connected with the feed inlet of the helium extraction unit 100 through a pipeline, the gas phase outlet of the helium extraction unit 100 is connected with the helium output pipe through a pipeline, the liquid phase outlet of the helium extraction unit 100 is connected with the feed inlet of the denitrification unit 200 through a pipeline, the gas phase outlet of the denitrification unit 200 is connected with the nitrogen output pipe through a pipeline, and the liquid phase outlet of the denitrification unit 200 is connected with an external LNG storage tank through a pipeline.

The system carries out helium stripping and rectifying treatment on raw material gas to obtain helium gas flow and intermediate product flow, and then carries out denitrification treatment on the intermediate product flow to obtain nitrogen gas flow and finished product flow.

The helium extracting unit 100 is provided with a helium extracting rectifying tower and a helium extracting tower reboiler, a feeding port of the helium extracting rectifying tower is connected with a gas phase outlet of the pretreatment unit 300 through a pipeline, a gas phase outlet of the helium extracting rectifying tower is connected with the helium output pipe through a pipeline, a liquid phase outlet of the helium extracting rectifying tower is connected with a feeding port of the helium extracting tower reboiler through a pipeline, a gas phase outlet of the helium extracting tower reboiler is connected with a feeding port of the helium extracting rectifying tower through a pipeline, and a liquid phase outlet of the helium extracting tower reboiler is connected with a feeding port of the denitrification unit 200 through a pipeline.

The pretreatment unit 300 is provided with heavy hydrocarbon knockout drum and heavy hydrocarbon secondary flash tank, the feed inlet of heavy hydrocarbon knockout drum with feed gas inlet pipe is with pipe connection, the gaseous phase export of heavy hydrocarbon knockout drum with carry the feed inlet of helium rectifying column and use pipe connection, the liquid phase export of heavy hydrocarbon knockout drum with the feed inlet of heavy hydrocarbon secondary flash tank is with pipe connection, the gaseous phase export of heavy hydrocarbon secondary flash tank with carry the feed inlet of helium rectifying column and use pipe connection, the liquid phase export of heavy hydrocarbon secondary flash tank is with outside heavy hydrocarbon storage tank and use pipe connection.

The heavy hydrocarbon separation tank of the utility model is capable of removing the c4+ components to give a total c4+ mole fraction in the pretreated stream of less than 0.1%. The heavy hydrocarbon secondary flash tank is used for increasing the liquid phase light hydrocarbon recovery of the heavy hydrocarbon separation tank, thereby increasing the recovery rate of light hydrocarbon and helium in natural gas.

Wherein, carry the feed inlet of helium rectifying column and be provided with three, define as A1 feed inlet, A2 feed inlet and A3 feed inlet respectively, A1 feed inlet with the gaseous phase export of heavy hydrocarbon knockout drum is with the pipe connection, A2 feed inlet with the gaseous phase export of heavy hydrocarbon secondary flash tank is with the pipe connection, A3 feed inlet with carry the gaseous phase export of helium tower reboiler and with the pipe connection.

The denitrification unit 200 is provided with a denitrification tower and a denitrification tower reboiler, wherein a feed inlet of the denitrification tower is connected with a liquid phase outlet of the helium extraction tower reboiler through a pipeline, a gas phase outlet of the denitrification tower is connected with a nitrogen output pipe through a pipeline, a liquid phase outlet of the denitrification tower is connected with a feed inlet of the denitrification tower reboiler through a pipeline, a gas phase outlet of the denitrification tower reboiler is connected with a feed inlet of the denitrification tower through a pipeline, and a liquid phase outlet of the denitrification tower reboiler is connected with an external LNG storage tank through a pipeline. The feed inlets of the denitrification tower are two, namely a B1 feed inlet and a B2 feed inlet, wherein the B1 feed inlet is connected with the nitrogen output pipe through a pipeline, and the B2 feed inlet is connected with the gas phase outlet of the reboiler of the denitrification tower through a pipeline.

The helium extraction tower reboiler and the nitrogen removal tower reboiler of the utility model have the functions of increasing the temperature of the bottom of the helium extraction rectifying tower and the bottom of the nitrogen removal tower, so that the helium extraction rectifying tower and the nitrogen removal tower form temperature gradients, namely the temperature from the bottom to the top of the tower is lower and lower, and the light components in the stream are gasified at the bottom of the helium extraction rectifying tower and the bottom of the nitrogen removal tower. For helium extraction tower reboiler, denitrogenation tower reboiler, heavy hydrocarbon knockout drum and heavy hydrocarbon secondary flash drum all belong to the common equipment in this field, and the skilled person should know its theory of operation, and the skilled person can correspond to select specific model according to actual conditions, can only be applicable to helium extraction tower reboiler, denitrogenation tower reboiler, heavy hydrocarbon knockout drum and heavy hydrocarbon secondary flash drum of this utility model all fall into the protection scope of this utility model.

The denitrification unit 200 is also provided with a denitrification tower top condenser, and a part of pipelines connected between the helium output pipe and the gas phase outlet of the denitrification tower pass through the denitrification tower top condenser.

The pretreatment unit 300 is further provided with a first pressure reducing valve and a second pressure reducing valve, wherein the first pressure reducing valve is positioned on a pipeline connected between a liquid phase outlet of the heavy hydrocarbon separation tank and a feed inlet of the heavy hydrocarbon secondary flash tank; the second pressure reducing valve is positioned in a pipeline between a liquid phase outlet of the heavy hydrocarbon secondary flash tank and an external heavy hydrocarbon storage tank.

The pipeline that will be connected between the gas phase export of heavy hydrocarbon knockout drum with the A1 feed inlet is defined as the pretreatment pipeline, the pretreatment pipeline is being close the gas phase exit end of heavy hydrocarbon knockout drum is divided into two pipelines to two pipelines pass through respectively carry helium tower reboiler with the denitrogenation tower reboiler, this two pipelines follow carry helium tower reboiler with the denitrogenation tower reboiler is drawn forth the back and is joined into a pipeline, reentrant process the inside of refrigeration unit 400, then this pipeline with A1 feed inlet is connected.

The pretreatment pipeline is divided into two paths, and the two paths pass through the helium extraction tower reboiler and the denitrification tower reboiler to provide heat sources for the helium extraction tower reboiler and the denitrification tower reboiler.

Based on the system of the utility model, the extraction of crude helium is performed by the following steps:

step (1), removing heavy hydrocarbon from raw gas to obtain a pretreated flow;

controlling the pressure of a pretreatment flow to 1280 kPaA-1320 kPaA, conveying the pretreated flow to a helium extraction rectifying tower for helium extraction rectifying treatment, keeping the top temperature of the helium extraction rectifying tower at-150 ℃ to-165 ℃, discharging a helium flow from the top of the helium extraction rectifying tower, and discharging an intermediate flow from the bottom of the helium extraction rectifying tower;

And (3) conveying the intermediate product stream to a denitrification tower for denitrification treatment to obtain a nitrogen stream and a finished product stream.

Wherein the step (1) specifically comprises:

step (1.1), conveying raw gas through a raw gas feeding pipe, conveying the raw gas to a refrigeration unit 400, and precooling to-38 ℃ to-42 ℃;

step (1.2), a feed gas feed pipe conveys feed gas to a heavy hydrocarbon separation tank for heavy hydrocarbon removal pretreatment to obtain a first pretreatment flow and a pretreated heavy hydrocarbon flow, wherein the first pretreatment flow is discharged from a gas phase outlet of the heavy hydrocarbon separation tank, and the pretreated heavy hydrocarbon flow is discharged from a liquid phase outlet of the heavy hydrocarbon separation tank;

step (1.3), depressurizing the pretreated heavy hydrocarbon stream to 1280 kPaA-1320 kPaA through a first depressurizing valve, entering a heavy hydrocarbon secondary flash tank, and entering flash evaporation treatment to obtain a second pretreated stream and a final heavy hydrocarbon stream, wherein the second pretreated stream is discharged from a gas phase outlet of the heavy hydrocarbon secondary flash tank, and the heavy hydrocarbon stream is discharged from a liquid phase outlet of the heavy hydrocarbon secondary flash tank.

Wherein the step (2) specifically comprises:

step (2.1), the first pretreatment flow firstly provides heat sources for a helium extraction tower reboiler and a denitrification tower reboiler, the first pretreatment flow is cooled to minus 158 ℃ to minus 153 ℃ through a refrigeration unit 400 and is depressurized to 1280kPaA to 1320kPaA through a second depressurization valve;

Step (2.2), the first pretreatment flow enters the helium stripping rectifying tower from an A1 feed inlet of the helium stripping rectifying tower, the second pretreatment flow enters the helium stripping rectifying tower from an A1 feed inlet of the helium stripping rectifying tower, the first pretreatment flow and the second pretreatment flow are subjected to helium stripping rectifying treatment in the helium stripping rectifying tower, the tower top temperature of the helium stripping rectifying tower is kept between minus 150 ℃ and minus 165 ℃, the gas phase flow generated by the helium stripping rectifying tower is discharged from the tower top (gas phase outlet) and is obtained, the liquid phase flow generated by the helium stripping rectifying tower flows to a helium stripping tower reboiler for heating through the tower bottom (liquid phase outlet), the gas phase flow generated by the helium stripping tower reboiler returns to the helium stripping rectifying tower through an A3 feed inlet, the liquid phase flow generated by the helium stripping tower reboiler is discharged from the helium stripping tower reboiler and is obtained to obtain a finished product flow, the pressure of the helium flow is 1150 kPaA-1200 kPaA, and the helium flow enters an external treatment system through an output pipe.

Wherein the step (3) specifically comprises:

step (3.1), the intermediate product stream enters a denitrification tower from a B1 feed inlet of the denitrification tower and is subjected to denitrification treatment, a gas phase stream generated by the denitrification tower is discharged from a tower top (gas phase outlet) to obtain a nitrogen stream, the liquid phase stream generated by the denitrification tower flows to a denitrification tower reboiler for heating through a tower bottom (liquid phase outlet), the gas phase stream generated by the gas phase outlet of the denitrification tower reboiler returns to the denitrification tower through a B2 feed inlet, the liquid phase stream of the denitrification tower reboiler is discharged from the liquid phase outlet of the denitrification tower reboiler to obtain a finished product stream, and the nitrogen stream is discharged through a nitrogen output pipe;

And (3.2) cooling the finished product stream to-165 to-160 ℃ through a refrigeration unit 400 and conveying the finished product stream to an external LNG storage tank.

Wherein in FIG. 2T-1102 is a denitrogenation column, T-1101 is a helium extraction rectifying column, E-102 is a denitrogenation column top condenser, E-106 is a denitrogenation column reboiler, E-105 is a nitrogen extraction column reboiler, V-100 is a heavy hydrocarbon separation tank, V-101 is a primary outlet separator, V-102 is a secondary outlet separator, V-103 is an LNG product separation tank, V-104 is a heavy hydrocarbon secondary flash tank, LNG-100 is a cold box, C-101 is an MRC compressor, E-101 is a primary outlet cooler, E-102 is a secondary outlet cooler, and LNG-JT01 and VLV-101 are valves. In fig. 2 the feed gases are stream 301 and stream 302; the first pretreated stream is stream 303, stream 304, stream 305, stream 308, stream 312, stream 315, stream 316 and stream 317; pretreating the heavy hydrocarbon stream into stream 306 and stream 307; the second pretreated stream is stream 309; the final heavy hydrocarbon stream is stream 310 and stream 311; helium flow is flow 318; intermediate stream is stream 319; nitrogen stream 321 and stream 327; the finished stream is stream 322.

It should be noted that, according to the helium extracting unit of the present utility model, a condenser may be correspondingly added to the gas phase outlet of the helium extracting rectifying tower according to practical situations, so as to stably control the temperature control of the helium gas flow. When the temperature and pressure of the components entering the rectifying tower are determined, the components discharged from the rectifying tower are determined, but in actual operation, the temperature and pressure change is always linked, namely, when the temperature is increased, the pressure is always increased because of more gas phase in the rectifying tower, and the temperature gradient and the tower top temperature of the rectifying tower can be indirectly controlled by directly controlling the flow rate and the tower pressure of the extracted rectifying tower. The internal pressure of the helium extraction rectifying tower is between 1200kPaA and 1180kPaA, and the upper pressure and the lower pressure of the helium extraction rectifying tower are low.

Generally for a rectifying column, the gas phase is optimally fed at dew point temperature and the liquid phase at bubble point temperature. For the same material, the dew point temperature of the gas phase is higher than the bubble point temperature of the liquid phase, so the feed point temperature of the gas phase is generally higher, and therefore the feed point is lower, and even if the dew point bubble point feed is not completely observed, the high temperature material is generally fed from the bottom, the low temperature material is fed from the top, and the temperature gradient in the tower is prevented from reversing. In terms of mass transfer, the gas phase is fed near the bottom, and the liquid phase is fed near the top, so that the gas moves upwards, and the liquid moves downwards, thereby realizing better contact mass transfer effect in the tower. For the purposes of the present utility model, the product stream is flash distilled to a vapor phase and the first pretreated stream is cooled to a liquid phase, whereby the first pretreated stream of the present utility model enters from the upper portion of the helium stripping rectifying column and the second pretreated stream enters from the lower portion of the helium stripping rectifying column.

The beneficial effects of the system are as follows:

1. helium extraction can be completed under the condition of using a traditional refrigeration unit 400 and a mixed refrigerant cold source used for conventional natural gas liquefaction by extracting helium and then denitrifying, and liquid nitrogen is not required to be consumed or other circulating refrigeration units 400 are not required to be added;

2. Proved by verification, the system can collect and obtain helium with the concentration of more than 60% when the mole fraction of helium is less than or equal to 0.05%, the mole fraction of nitrogen is 1.0% -4.5%, and the mole fraction of methane is 80.0% -98.5%, and the extraction and collection rate of helium in the feed gas is as high as 99%, so that the economic value is high;

3. by adding the heavy hydrocarbon secondary flash tank, the recovery rate of light hydrocarbons in the natural gas is increased, the light hydrocarbon loss in the heavy hydrocarbon separation process during the natural gas liquefaction is reduced, and the LNG product yield is increased;

4. according to the utility model, only based on the traditional cold box design scheme, the process of extracting helium first and then denitrifying is adopted, the equipment is increased by modifying the existing natural gas liquefaction process, the crude helium extraction requirement is met, the original cold box runner design is not required to be changed, the original natural gas liquefaction energy consumption is not increased, only one helium extraction rectifying tower and one heavy hydrocarbon secondary flash tank are required to be added, and therefore, the investment is small and the operation cost is low.

Example 2

A system for extracting crude helium from helium-depleted natural gas, the other features being the same as in example 1, except that: in the embodiment, the mole fraction of helium in the feed gas is 0.005% -0.02%, the mole fraction of nitrogen is 1.0% -4.5%, the mole fraction of methane is 80.0% -98.5%, the mole fraction of ethane is 0.1% -5.0%, the mole fraction of propane is 0.1% -5.0%, the mole fraction of n-butane is less than 2.0%, the mole fraction of isobutane is less than 2.0%, the mole fraction of n-pentane is less than 2.0%, and the mole fraction of isopentane is less than 2.0%. And the total mole fraction of helium, nitrogen, methane, ethane, propane, n-butane, isobutane, n-pentane and isopentane in the feed gas was 100%.

The steps for extracting crude helium in this example are different from those in example 1 as follows:

in step (1.1), the feed gas is pre-cooled to-40 ℃. In step (1.3), the heavy hydrocarbon removal stream is depressurized to 1300kPaA.

In step (2.1), the first pretreated stream is cooled to-155 ℃ by a refrigeration unit and depressurized to 1300kPaA.

In step (2.2), the overhead temperature of the stripping helium rectifying column is maintained at-155 ℃ and the pressure of the helium stream is 1180kPaA.

In step (3.2), the finished stream is cooled to-163 ℃ and sent to LNG storage tanks. In step (1.2), the heavy hydrocarbon stream is depressurized to 1300kPaA.

The present utility model was simulated by chemical process simulation software ASPEN HYSYS V (using the Peng-Robinson physical package), and the results of this example were compared with the conventional system (fig. 1) and are shown in table 1:

comparison item	Feed gas flow	LNG production	Shaft power of refrigerant compressor	Product energy consumption kWh/N _m 3NG
					Legacy system	92.5t/h	81.0t/h	30370kW	0.2962
The utility model is that	92.5t/h	82.6t/h	30370kW	0.2900

From the above table, it can be seen that the present utility model can increase LNG production by about 2% and also can reduce natural gas liquefaction unit energy consumption, thereby enabling significant economic benefits.

Example 3

A system for extracting crude helium from helium-depleted natural gas is characterized in that the system is otherwise identical to that of the embodiment 1 or 2, the number of the tower plates of the helium-extracting rectifying tower is 10, and a first pretreatment flow enters from the upper part of the first tower plate above the helium-extracting rectifying tower. The specific column diameter of the helium extraction rectifying column of the embodiment is 1300mm, the height of a packing section is 4000mm, and the type of the packing is MELLAPAK 125Y.

The number of the tower plates of the denitrification tower is 8, wherein 3 rectifying sections are provided, 5 stripping sections are provided, and the middle product stream enters from the upper part of the denitrification tower to the upper part of the 4 th tower plate. The packing height of the rectifying section of the denitrification tower is 1200mm, and the packing type is MELLAPAK 750Y; the packing height of the rectifying section is 2000mm, and the packing type is MELLAPAK 125Y.

The A2 feed inlet and the A3 feed inlet of the embodiment are both positioned above a 10 th column plate of the helium extraction rectifying tower from top to bottom. And the B1 feeding port and the B2 feeding port are both positioned above an 8 th column plate of the denitrification tower from top to bottom.

Example 4

With the system of example 3, the molar fraction of the feed gas is specified in table 2 below, and the feed gas pressure is 8100kPaA; the flow rate of the raw material gas is 92.5t/h; the circulation amount of the refrigerant is 500t/h; the refrigerant compressor inlet pressure is 510kPaA; the refrigerant compressor outlet pressure is 4900kPaA; the shaft power of the refrigerant compressor is 30370kW, and the refrigerant composition and mole fraction are as follows: 18.0% nitrogen, 25.3% methane, 25.5% ethylene, 16.9% propane, 14.3% isopentane.

TABLE 2 composition of feed gas in this example

Component (A)	Nitrogen gas	Methane	Ethane (ethane)	Propane	Helium gas	N-butane	Isobutane	N-pentane	Isopentane	Totalizing
											Mole fraction (%)	4.50	88.035	3.80	2.00	0.015	0.50	0.50	0.55	0.10	100

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The data in tables 3 and 4 are simulated calculations (using the Peng-Robinson physical package) performed by chemical process simulation software ASPEN HYSYS V, and it can be seen from tables 3 and 4 that in this example, the temperature of 318 stream is-151.25 ℃ and far higher than the lowest temperature of MRC, and this example can provide a corresponding cold source using a conventional natural gas liquefaction process refrigeration system (MRC), and can extract 61% helium from a feed gas with a helium mole fraction of only 0.015% without consuming additional liquid nitrogen cold source or a circulation refrigeration system, and the helium extraction rate of the feed gas is greater than 99%.

Example 5

With the system of example 3, the molar fraction of the feed gas is specified in table 5 below, and the feed gas pressure is 8100kPaA; the flow rate of the raw material gas is 92.5t/h; the circulation amount of the refrigerant is 500t/h; the refrigerant compressor inlet pressure is 510kPaA; the refrigerant compressor outlet pressure is 4900kPaA; the shaft power of the refrigerant compressor is 30370kW, and the refrigerant composition and mole fraction are as follows: 18.0% nitrogen, 25.3% methane, 25.5% ethylene, 16.9% propane, 14.3% isopentane.

Table 5 composition of the raw gas in this example

Component (A)	Nitrogen gas	Methane	Ethane (ethane)	Propane	Helium gas	N-butane	Isobutane	N-pentane	Isopentane	Totalizing
											Mole fraction (%)	4.50	88.045	3.80	2.00	0.005	0.50	0.50	0.55	0.10	100

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The data in tables 6 and 7 are simulated calculations (using the Peng-Robinson physical package) performed by chemical process simulation software ASPEN HYSYS V, and it can be seen from tables 6 and 7 that in this example, the temperature of 318 stream is-151.25 ℃ and is far lower than the minimum temperature of MRC, so that a conventional natural gas liquefaction process refrigeration system (MRC) can be used to provide a corresponding cold source, and the helium with a molar fraction of helium of only 0.005% can be extracted from the feed gas without consuming additional liquid nitrogen cold source or circulating refrigeration system, and the helium extraction rate of the feed gas is greater than 99%.

Example 6

With the system of example 3, the molar fraction of the feed gas is specified in table 8 below, and the feed gas pressure is 8100kPaA; the flow rate of the raw material gas is 92.5t/h; the circulation amount of the refrigerant is 500t/h; the refrigerant compressor inlet pressure is 510kPaA; the refrigerant compressor outlet pressure is 4900kPaA; the shaft power of the refrigerant compressor is 30370kW, and the refrigerant composition and mole fraction are as follows: 18.0% nitrogen, 25.3% methane, 25.5% ethylene, 16.9% propane, 14.3% isopentane.

Table 8 composition of the raw gas in this example

Component (A)	Nitrogen gas	Methane	Ethane (ethane)	Propane	Helium gas	N-butane	Isobutane	N-pentane	Isopentane	Totalizing
											Mole fraction (%)	4.50	88.030	3.80	2.00	0.02	0.50	0.50	0.55	0.10	100

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The data in tables 9 and 10 are simulated calculations (using the Peng-Robinson physical package) performed by chemical process simulation software ASPEN HYSYS V, and it can be seen from tables 9 and 10 that in this example, the temperature of 318 stream is-151.25 ℃ and is far lower than the minimum temperature of MRC, so that a conventional natural gas liquefaction process refrigeration system (MRC) can be used to provide a corresponding cold source, and the helium with a molar fraction of helium of only 0.02% can be extracted from the feed gas without consuming additional liquid nitrogen cold sources or circulating refrigeration systems, and the helium extraction rate of the feed gas is greater than 99%.

Example 7

Table 11 composition of the raw gas in this example

Component (A)	Nitrogen gas	Methane	Ethane (ethane)	Propane	Helium gas	N-butane	Isobutane	N-pentane	Isopentane	Totalizing
											Mole fraction (%)	4.50	88.000	3.80	2.00	0.05	0.50	0.50	0.55	0.10	100

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The data in tables 12 and 13 are simulated calculations (using the Peng-Robinson physical packages) performed by chemical process simulation software ASPEN HYSYS V, and it can be seen from tables 12 and 13 that in this example, the temperature of 318 stream is-151.25 ℃ and is far lower than the minimum temperature of MRC, so that a conventional natural gas liquefaction process refrigeration system (MRC) can be used to provide a corresponding cold source, and the helium with a molar fraction of helium of only 0.05% can be extracted from a feed gas without consuming additional liquid nitrogen cold sources or a circulation refrigeration system to obtain about 61% helium, with a helium extraction rate of greater than 99% for the feed gas.

Example 8

This example demonstrates the applicability of the temperature at the top of the helium stripping and rectifying column according to the utility model by calculation.

To illustrate when N ₂ Under the condition of raw natural gas with relatively high mole fraction (about 5% mole fraction) and relatively low He mole fraction (0.05% set as follows),crude helium is first extracted from feed gas and then the remaining LNG is denitrified to N ₂ The mole fraction is below 1 percent, compared with the prior art that the nitrogen is firstly removed from the raw material gas to N ₂ The molar fraction is less than 1%, and crude helium gas with the same concentration is extracted from the removed nitrogen-rich gas, so that an ultralow-temperature cold source (-cold source below 170 ℃) at the top of the tower is not needed.

The following description is made by comparing two schemes:

scheme one: the scheme demonstrates that helium extraction unit 100 and nitrogen removal unit 200 in the present utility model specifically performs helium extraction and rectification treatment on raw material gas to obtain helium gas flow and intermediate product flow, and then performs nitrogen removal treatment on the intermediate product flow to obtain nitrogen gas flow and finished product flow. Specifically referring to fig. 3, in fig. 3, the raw material gas (stream 1) is separated into helium through a helium extraction rectifying tower T-101, crude helium product is directly extracted from the tower top, nitrogen and methane are separated from the tower bottom material through a denitrification tower T-102, and under the condition that the tower pressure of the helium extraction rectifying tower T-101 is 1200kPaA, the mole fraction of helium in the crude helium product (stream 3) at the tower top is required to be more than 60%; meanwhile, the methane mole fraction of the nitrogen (stream 4) at the top of the T-102 column is required to be less than 25%, N of stream 5 ₂ The mole fraction is less than or equal to 1 percent.

Scheme II: the prior art (such as publication No. CN20211107822.6, 202222744330.4) is to extract a mixed stream of nitrogen and helium from a feed gas, and then to re-denitrify the mixed stream. Specifically, as shown in fig. 4, the raw material gas (stream 6) is separated from the bottom of the rectifying tower T-103 to obtain qualified LNG product (nitrogen mole fraction is less than or equal to 1.0%), the top of the tower (stream 12) is separated to obtain a mixed stream of mixed stream nitrogen and helium (methane mole fraction is less than or equal to 25%), and at this time, the components of the top of the tower (stream 12) are set to be: 74% nitrogen; 25% methane; 1% helium, N of stream 8 ₂ The molar fraction is less than or equal to 1%, then stream 12 enters denitrification tower T-104 for denitrification, and crude helium (stream 9) with the concentration of 60% is required to be obtained.

1. The temperatures at the tops of the T-101 and T-104 were controlled at-165℃to demonstrate the possibility of extracting crude helium at 60% concentration at this temperature for both schemes

The present embodiment sets the following conditions for simplifying the calculation process:

(1) The feed gas consists of only the following components: 5% N ₂ ；94.95％CH ₄ ；0.05％He；

(2) The column pressures T-101 and T-104 were set at 1200kPaA and the pressure drop across the column was ignored;

(3) The vapor pressure is calculated by adopting an Antoine formula, wherein the Antoine formula is ln (P) =a+b/(T+c) +ln (T) ×d+e×T≡f, and P is vapor pressure (kPa);

(4) In order to improve the natural gas liquefaction yield, the molar fraction of CH4 in the nitrogen-rich gas removed from the top of the T-103 tower in the scheme II is less than or equal to 25 percent;

(5) Will CH ₄ 、N ₂ And He are all considered as ideal gases for calculation;

(6) Because the critical temperature of He is-268 ℃, the temperature is far higher than the critical temperature in the whole separation process, so the liquid phase three-component system can be regarded as He gas phase dissolution in N ₂ And CH (CH) ₄ Instead of the N in liquid state after He liquefaction ₂ And CH (CH) ₄ Mixing.

It should be emphasized that, because ternary mixed components also involve binary interactions, etc., in this embodiment, because all gases are taken as ideal gases by manual calculation, and binary interactions are not considered, there may be a small error in the actual calculation result, but this implementation is a basic rule capable of reflecting the rectification separation of this ternary mixed component.

The saturated vapor pressure of nitrogen and methane is calculated by using Antoine, and an Antoine equation with 6 constants is used by Aspen Hysys software, and compared with a common 3-constant equation, the accuracy of the 6-constant Antoine equation is higher, wherein the temperature T is Kelvin temperature, and the unit is K.

The coefficients of the corresponding gas application to the Antoine equation were retrieved from Aspen Hysys database, as shown in table 8:

table 14 coefficients of Antoine equation

Coefficients of	N ₂	CH ₄
			a	3.54113××10	3.13500×10
b	-9.66234×10 ²	-1.30752×10 ³
			c	0	0
d	-4.31849	-3.26134
			e	7.93190×10 ^-5	2.94180×10 ^-5
f	2.00000	2.00000
			Temperature application range (K)	62～226	91～190.4

According to the Antoine equation, when the column top temperature was-165 ℃ (127.15K), the vapor pressure of methane was 76.01Kpa and the vapor pressure of nitrogen was 1312Kpa. According to the design principle of the rectifying tower, the temperature of the tower top is the gas phase dew point temperature.

By Dalton's law of partial pressure, as shown in equation 1-1:

P _i ＝P·y _i … … formula 1-1;

and Raoult's law, as shown in equations 1-2:

x is obtained according to formula 1-1 and formula 1-2 _i The expression of (2) is as shown in the formulas 1-3:

since the sum of the components of the feed gas is 1, the following formulas 1 to 4 are shown:

∑x _i =1 … … formula 1-4;

formulas 1 to 5 are obtained according to formulas 1 to 3 and 1 to 4:

in formulas 1-1 to 1-5: p (P) _i ^s Saturated vapor pressure of pure substances is expressed as kPa; p (P) _i Is the partial pressure of component i in the gas phase, in kPa; x is x _i Is the mole fraction of component i in the liquid phase; y is _i Is the molar fraction of the i component in the gas phase.

It should be noted that, when the pressure is increased after the saturated vapor pressure is reached, the pure material gas starts to liquefy, and when the critical temperature of He is-268 ℃, the pure material gas does not start to liquefy no matter how much the pressure is higher than the critical temperature, and therefore the saturated vapor pressure of the pure material gas can be regarded as infinity (+infinity), and since the mole fraction of He is required to reach 60%, N ₂ CH (CH) ₄ The sum of the molar fractions is 40%.

Thus, formulas 1 to 6 are obtained, specifically as follows:

solving the equation of the formula 1-6, wherein the first term of the formula 1-6 is 0, and calculatingThus (2)The liquid phase component +.2 in the top of the column can be resolved according to the formulas 1-3>In addition, a small amount of helium is dissolved in the liquid phase.

When the He concentration in the gas phase is required to be 60%, the CH in the liquid phase at the top of the column is unchanged ₄ When the liquid phase mole fraction is less than 67.3% (for example, assuming the overhead liquid phase CH ₄ The molar fraction was 50%, i.e) From the formulae 1 to 3 +.>Substituted into formulas 1 to 6, specifically as follows:

because the result of formulas 1-6 is less than 1, N ₂ CH (CH) ₄ The gas phase mixture is now unsaturated, inWhen N ₂ Further gasifies, N ₂ CH (CH) ₄ The sum of the molar fractions will exceed 40%, in which case +.>It should be satisfied as follows:

Solving to obtainThe following was obtained:

then He concentration at this time is:

thus, at-165 ℃ when CH in the overhead liquid phase ₄ If the molar fraction of the liquid phase is less than 67.3%, he having a concentration of 60% cannot be obtained.

The column top temperature requirement for scheme one was-165 ℃, validation procedure to give 60% crude He:

the methane mole fraction in the feed to the rectification column was 94.95% and CH ₄ At He and N ₂ In CH ₄ Is the heaviest component of these three gases. Thus, in the rectifying column, CH ₄ The molar fraction in the overhead liquid phase component must be lower than in the feed liquid phase, since 67.3%<94.95%. Thus, in scheme one under the above-mentioned prescribed conditions, when the overhead temperature of T-101 was set to-165 ℃, crude helium gas at a concentration of 60% could be obtained.

The column top temperature requirement for scheme two was-165 ℃, validation procedure to obtain 60% crude He:

in the material entering the T-104 rectifying tower, the mole fraction of methane is about 24%, the mole fraction of methane in the liquid phase at the top of the tower is necessarily lower than 24%, and therefore, the mole fraction of methane in the liquid phase at the top of the tower is necessarily lower than 67.3% of the minimum mole fraction of methane calculated in the prior art, so that in scheme II under the specified condition, 60% of crude He cannot be obtained when the temperature at the top of the tower is-165 ℃.

2. Scheme II verification of the highest overhead temperature when 60% helium can be separated from the overhead

Further, the mole fraction of methane at the top of the T-104 column for scheme II must be lowAt 24%, in order to obtain the highest column top temperature at which 60% helium can be separated from the column top, the column top liquid phase methane mole fraction was set to the limit of 24%, and at this time, the column top liquid phase nitrogen mole fraction was about 75%. And the mole fractions of methane and nitrogen in the overhead gas phase can be determined by the formulae 1 to 3, whereinThe deformation from the Antoine equation is expressed as a function of temperature, and the introduction of this into equations 1-6 yields a complex unitary equation that, although solved, is difficult to directly lend, so this example uses trial and error to determine the maximum temperature range for 60% helium exiting the top of the column.

When the temperature of the tower top is minus 170 ℃, CH can be obtained by an Antoine equation ₄ Has a vapor pressure of 47.8kpa, N ₂ The vapor pressure of (2) was 959.74kpa, which was determined by the formulas 1 to 3The concentration of the crude He extracted at this time was 1-0.009559-0.599837 = 0.390604, because 0.390604<0.6, and thus 60% of crude He is not obtained.

When the temperature of the tower top is continuously reduced to-175 ℃, CH can be continuously calculated by an Antoine equation ₄ Has a saturated vapor pressure of 28.61kpa, N ₂ The saturated vapor pressure of (2) was 681.44kpa, which was obtained from the formulae 1 to 3The concentration of the crude He extracted at this time was 1-0.005721-0.425901 = 0.568378, because 0.568378<0.6, and therefore 60% of crude He is not obtained at a top temperature of-175 ℃.

When the temperature of the tower top is further reduced to minus 176 ℃, CH can be obtained continuously according to the Antoine equation ₄ Has a saturated vapor pressure of 25.64kpa, N ₂ The saturated vapor pressure of (2) was 633.72kpa, which was obtained from the formulae 1 to 3The concentration of the crude He extracted at this time is 1-0.005128-0.396076 = 0.5988, because 0.5988 ≡0.6, 60% of crude He can be obtained only when the temperature of the top of the column is-176 ℃ or lower.

It is known that, in the case of the second scheme, if the column pressure is the same, the temperature of the top of the column must be lower than-176 ℃ in order to extract 60% or more of crude helium, because the minimum temperature of the mixed refrigerant cold source used for conventional natural gas liquefaction is generally not lower than-170 ℃, it can be proved that the second scheme must additionally use an ultralow temperature cold source such as liquid nitrogen, and the top of the column is continuously condensed so that the temperature of the top of the column is lower than-176 ℃.

3. Demonstration of the highest concentration of helium in the overhead of a tower obtained at different overhead temperatures from-150 ℃ to-180 DEG C

Because the above processes are all fixed overhead temperatures, then the demonstration of overhead component requirements is deduced. The following is the difference between the tower top components according to scheme one and scheme two, and the highest concentration of the tower top helium gas obtained from the tower top temperature of-150 ℃ to-180 ℃ under the tower pressure of 1200kPa under the two tower top components is demonstrated according to calculation.

It should be noted that, because methane is a relatively heavy component, the methane concentration at the top of the column cannot be lower than that of the feed, and the higher the molar fraction of methane, the higher the helium concentration that can be obtained at the same top temperature, as previously verified, and therefore, for the calculation of the maximum value of the helium concentration that can be obtained at the top of the column, the feed component of the rectifying column can be directly taken as the top component.

For scheme one, CH in the overhead liquid phase ₄ Mole fraction 0.9495, N ₂ If 0.05% He dissolution is not considered, only CH is considered ₄ And N ₂ The liquid phase mole fraction of the two components is:

from formulas 1 to 3, formulas 1 to 8 are obtained, specifically as follows:

for the tower top temperatures of-150 ℃, -155 ℃, -160 ℃, -165 ℃, -170 ℃, -175 ℃, -180 ℃ and-185 ℃, CH is calculated according to the Antoine formula respectively ₄ N ₂ Saturated vapor pressures, giving the following table 9:

TABLE 15 CH at a top temperature of-150 to-185 DEG C ₄ And N ₂ Corresponding saturated vapor pressure

Substituting the data in table 15 into equations 1-8, respectively, to obtain maximum helium concentration values at each temperature point, as shown in table 16:

table 16, maximum helium concentration at-150-185℃tower top temperature

As is clear from Table 16, in scheme one, when the column top temperature was-150 ℃, crude helium with a concentration exceeding 60% was obtained, and the simulation results of the present utility model were confirmed.

Similarly, for scheme II, because the T-103 denitrification tower mainly removes nitrogen and helium, the mole fraction of methane in the nitrogen-enriched gas is lower, and according to the simulation result of Aspen Hysys, about 24% -25%, the mole fraction is setAnd->

Similarly, the calculated tower top temperatures at-150 ℃, -155 ℃, -160 ℃, -165 ℃, -170 ℃, -175 ℃ and-180 ℃ can obtain the maximum helium concentration values at all temperature points, as shown in table 17:

table 17, scheme II, maximum helium concentration at-150 ℃ to-185 ℃ tower top temperature

As can be seen from Table 17, when the overhead temperature is at-150 ℃, -155 ℃ and-160 ℃, the He mole fraction of the gas phase is negative, i.e., the feed will all gasify to gas, at which temperature helium cannot be extracted. When crude helium with a concentration of 60% is required, the overhead temperature is required to be below-175 ℃.

In summary, the calculation verification of this example demonstrates that when a mixed stream of nitrogen and helium is first co-extracted and then denitrified in the mixed stream (scheme two), under the condition of raw natural gas with a relatively low He mole fraction, an additional liquid nitrogen cold source or a circulating refrigeration system must be used to further reduce the overhead temperature to-175 ℃ and below when crude helium with a concentration of 60% is required to be extracted. The utility model firstly carries out helium stripping and rectifying treatment on raw material gas to obtain helium gas flow and intermediate product flow, then carries out denitrification treatment on the intermediate product flow to obtain nitrogen gas flow and finished product flow (scheme one), and when crude helium with the concentration of 60% is required to be extracted under the same condition, the tower top temperature is only-150 ℃, so that the traditional natural gas liquefaction process refrigeration system (MRC) is adopted.

Finally, it should be noted that the above embodiments are only for illustrating the technical solution of the present utility model and not for limiting the scope of the present utility model, and although the present utility model has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solution of the present utility model may be modified or substituted equally without departing from the spirit and scope of the technical solution of the present utility model.

Claims

1. A system for extracting crude helium from helium-depleted natural gas, provided with a refrigeration unit for providing a cold source and having a refrigeration temperature above-165 ℃, characterized in that: the device is also provided with a pretreatment unit, a helium extraction unit, a denitrification unit, a feed gas feed pipe and a helium output pipe, wherein the pretreatment unit is used for removing heavy hydrocarbon in the feed gas, the feed gas feed pipe is used for conveying feed gas with the helium mole fraction of less than or equal to 0.05%, and the helium output pipe is used for conveying helium with the helium mole fraction of more than or equal to 60%;

the feed gas feed pipe is connected with the feed inlet of the pretreatment unit through a pipeline, the gas phase outlet of the pretreatment unit is connected with the feed inlet of the helium extraction unit through a pipeline, the gas phase outlet of the helium extraction unit is connected with the helium output pipe through a pipeline, the liquid phase outlet of the helium extraction unit is connected with the feed inlet of the denitrification unit through a pipeline, the gas phase outlet of the denitrification unit is connected with the nitrogen output pipe through a pipeline, and the liquid phase outlet of the denitrification unit is connected with an external LNG storage tank through a pipeline.

2. The system for extracting crude helium from helium-depleted natural gas of claim 1, wherein: the helium extraction unit is provided with a helium extraction rectifying tower and a helium extraction tower reboiler, a feed inlet of the helium extraction rectifying tower is connected with a gas phase outlet of the pretreatment unit through a pipeline, a gas phase outlet of the helium extraction rectifying tower is connected with a helium output pipe through a pipeline, a liquid phase outlet of the helium extraction rectifying tower is connected with a feed inlet of the helium extraction tower reboiler through a pipeline, a gas phase outlet of the helium extraction tower reboiler is connected with a feed inlet of the helium extraction rectifying tower through a pipeline, and a liquid phase outlet of the helium extraction tower reboiler is connected with a feed inlet of the denitrification unit through a pipeline.

3. The system for extracting crude helium from helium-depleted natural gas of claim 2, wherein: the pretreatment unit is provided with heavy hydrocarbon knockout drum and heavy hydrocarbon secondary flash tank, the feed inlet of heavy hydrocarbon knockout drum with feed gas inlet pipe is with pipe connection, the gaseous phase export of heavy hydrocarbon knockout drum with carry the feed inlet of helium rectifying column and use pipe connection, the liquid phase export of heavy hydrocarbon knockout drum with the feed inlet of heavy hydrocarbon secondary flash tank is with pipe connection, the gaseous phase export of heavy hydrocarbon secondary flash tank with carry the feed inlet of helium rectifying column and use pipe connection, the liquid phase export of heavy hydrocarbon secondary flash tank is with outside heavy hydrocarbon storage tank and use pipe connection.

4. A system for enabling the extraction of crude helium from helium depleted natural gas according to claim 3, wherein: the feed inlet of carrying helium rectifying column is provided with three, defines as A1 feed inlet, A2 feed inlet and A3 feed inlet respectively, A1 feed inlet with the gaseous phase export of heavy hydrocarbon knockout drum is with the pipe connection, A2 feed inlet with the gaseous phase export of heavy hydrocarbon secondary flash tank is with the pipe connection, A3 feed inlet with carry helium tower reboiler's gaseous phase export is with the pipe connection.

5. The system for extracting raw helium from helium-depleted natural gas of claim 4, wherein: the nitrogen removal unit is provided with a nitrogen removal tower and a nitrogen removal tower reboiler, the feed inlet of the nitrogen removal tower is connected with the liquid phase outlet of the helium extraction tower reboiler through a pipeline, the gas phase outlet of the nitrogen removal tower is connected with the nitrogen output pipe through a pipeline, the liquid phase outlet of the nitrogen removal tower is connected with the feed inlet of the nitrogen removal tower reboiler through a pipeline, the gas phase outlet of the nitrogen removal tower reboiler is connected with the feed inlet of the nitrogen removal tower through a pipeline, and the liquid phase outlet of the nitrogen removal tower reboiler is connected with an external LNG storage tank through a pipeline.

6. The system for extracting raw helium from helium-depleted natural gas of claim 5, wherein: the pipeline that will be connected between the gas phase export of heavy hydrocarbon knockout drum with the A1 feed inlet is defined as the pretreatment pipeline, the pretreatment pipeline is being close the gas phase exit end of heavy hydrocarbon knockout drum is divided into two pipelines to two pipelines pass through respectively carry helium tower reboiler with the denitrogenation tower reboiler, this two pipelines follow carry helium tower reboiler with the denitrogenation tower reboiler is drawn forth the back and is joined into a pipeline, reentrant process the inside of refrigeration unit, then this pipeline with A1 feed inlet is connected.

7. The system for extracting raw helium from helium-depleted natural gas of claim 5, wherein: the nitrogen removal tower is characterized in that two feed inlets are arranged and respectively defined as a B1 feed inlet and a B2 feed inlet, the B1 feed inlet is connected with the nitrogen output pipe through a pipeline, and the B2 feed inlet is connected with a gas phase outlet of the reboiler of the nitrogen removal tower through a pipeline.

8. The system for extracting raw helium from helium-depleted natural gas of claim 7, wherein: the helium extraction rectifying tower is provided with 10 tower plates, and the A1 feed inlet is positioned above the 1 st tower plate of the helium extraction rectifying tower from top to bottom;

the denitrification tower is provided with 8 trays, the trays are sequentially arranged from top to bottom, the trays of the denitrification tower comprise 3 rectification trays and 5 rectification trays, and the B1 feed inlet is positioned above the 4 th tray of the denitrification tower from top to bottom.

9. The system for extracting raw helium from helium-depleted natural gas of claim 5, wherein: the denitrification unit is also provided with a denitrification tower top condenser, and a part of pipelines connected between the helium output pipe and the gas phase outlet of the denitrification tower pass through the denitrification tower top condenser.

10. A system for enabling the extraction of crude helium from helium depleted natural gas according to claim 3, wherein: the pretreatment unit is also provided with a first pressure reducing valve and a second pressure reducing valve, and the first pressure reducing valve is positioned on a pipeline connected between a liquid phase outlet of the heavy hydrocarbon separation tank and a feed inlet of the heavy hydrocarbon secondary flash tank;

the second pressure reducing valve is positioned in a pipeline between a liquid phase outlet of the heavy hydrocarbon secondary flash tank and an external heavy hydrocarbon storage tank.