阅读说明：本技术 一种双塔天然气氦回收方法 (Double-tower natural gas helium recovery method ) 是由 蒋洪 祝梦雪 于 2021-09-27 设计创作，主要内容包括：本发明公开了一种双塔天然气氦回收方法,涉及天然气加工工艺技术领域,该方法采用双塔提氦工艺,氦气提浓塔和氦气回收塔均采用具有温度梯度的多股进料方式,氦气提浓塔和氦气回收塔部分塔底出料分别在主冷箱和氦气回收冷箱中升温后回流；氦气回收塔塔顶气相在氦气回收冷箱中升温,作为粗氦产品进入后续提纯单元。氦气提浓塔采用提馏塔,利用塔顶物流温位来控制塔顶出料中氦气含量,提高了氦气回收塔进料中氦气浓度,减少了氦气回收塔塔顶所需冷量。本发明适合于不同氦气含量的含氦天然气氦气回收系统,当天然气中氦气含量较低(天然气中氦气含量低于0.5％)时,系统节能优势明显,具有系统热集成度高、能耗低、投资小、氦气回收率高等特点。(The invention discloses a double-tower natural gas helium recovery method, which relates to the technical field of natural gas processing technology, and adopts a double-tower helium extraction process, wherein a helium concentration tower and a helium recovery tower both adopt a multi-strand feeding mode with temperature gradient, and partial tower bottom discharge materials of the helium concentration tower and the helium recovery tower respectively reflux after being heated in a main cooling box and a helium recovery cooling box; and the gas phase at the top of the helium recovery tower is heated in a helium recovery cold box and enters a subsequent purification unit as a crude helium product. The helium concentration tower adopts a stripping tower, and the helium content in the discharged material at the top of the tower is controlled by utilizing the temperature level of the material flow at the top of the tower, so that the helium concentration in the fed material of the helium recovery tower is improved, and the cold quantity required by the top of the helium recovery tower is reduced. The invention is suitable for helium recovery systems of natural gas containing helium with different helium contents, has obvious energy saving advantage when the helium content in natural gas is lower (the helium content in natural gas is lower than 0.5 percent), and has the characteristics of high system heat integration level, low energy consumption, small investment, high helium recovery rate and the like.)

1. A method for recovering helium from natural gas in a double column, comprising the steps of:

(1) the pretreated raw gas is cooled by a main cooling box (E-101) and enters a heavy hydrocarbon separator (V-101) for gas-liquid separation;

(2) the gas phase separated by the heavy hydrocarbon separator (V-101) is cooled in a main cooling box (E-101) and then enters a low-temperature separator (V-102) for further gas-liquid separation, the liquid phase separated by the heavy hydrocarbon separator (V-101) exchanges heat in the main cooling box after throttling, the liquid phase enters a flash tank (V-104) after heating, the gas phase flashed out enters a fuel gas system, and the condensate flashed out enters a condensate tank; the gas phase separated by the low-temperature separator (V-102) is cooled and depressurized in the main cooling box and then enters the top of the helium concentration tower (T-101), and the liquid phase separated by the low-temperature separator (V-102) is depressurized and then enters the middle of the helium concentration tower (T-101);

(3) the bottom discharge of the helium concentrating tower (T-101) is divided into two streams, the first stream is subjected to heat exchange and temperature rise in a main cooling box (E-101) and then is fed from the bottom of the helium concentrating tower, the second stream is divided into two parts, one part is subjected to pressure reduction and then enters the main cooling box (E-101) for reheating and then enters a pressurizing unit for pressurizing, and the other part is subjected to pressure reduction and then enters the main cooling box for reheating and then enters the pressurizing unit for pressurizing and outputting;

(4) the gas phase discharged from the top of the helium concentrating tower (T-101) is cooled by a helium recovery cold box (E-101) and then enters the middle part of a helium recovery tower (T-102);

(5) the discharge material flow at the top of the helium recovery tower (T-102) is heated by a helium recovery cold box (E-102) to be used as a crude helium product; the refrigeration cycle adopts nitrogen gas for refrigeration;

(6) the tower bottom material flow of the helium recovery tower (T-102) is divided into two material flows, one material flow is fed from the bottom of the helium recovery tower (T-102) after being subjected to heat exchange and temperature rise through a helium recovery cold box (E-102), and the other material flow is subjected to pressure reduction, then enters the helium recovery cold box (E-102) and the main cold box (E-101) respectively, is subjected to heat exchange and temperature rise, and then enters a pressurizing unit for pressurization.

2. The method for extracting helium from natural gas as claimed in claim 1, wherein the main cooling box (E-101) and the helium recovery cooling box (E-102) both adopt a multi-strand plate-fin heat exchanger.

3. The method for extracting helium from natural gas according to claim 2, wherein the main cold box (E-101) integrates three hot streams with five cold streams, and the helium recovery cold box (E-102) integrates two hot streams with four cold streams.

4. The method for extracting helium from natural gas as claimed in claim 3, wherein the main cooling box (E-101) integrates three hot streams and five cold streams, wherein the three hot streams are respectively a raw gas, a heavy hydrocarbon separator (V-101) gas phase stream and a low temperature separator (V-102) gas phase stream, the five cold streams are respectively a heavy hydrocarbon separator liquid phase, a three split stream at the bottom of a helium concentrating tower (T-101) and a split stream at the bottom of a helium recovery tower (T-102), the helium recovery cooling box (E-102) integrates two hot streams and four cold streams, wherein the two hot streams are a high pressure nitrogen gas and a helium concentrating tower (T-101) overhead gas stream, and the four cold streams are respectively a helium recovery tower (T-102) bottom two streams, a crude helium gas and a low temperature low pressure nitrogen gas.

5. The method of claim 1, wherein the refrigeration cycle is primarily a nitrogen refrigeration cycle.

6. The method for extracting helium from natural gas as claimed in claim 4, wherein the refrigeration cycle is a nitrogen refrigeration cycle, the high-pressure nitrogen is cooled and depressurized by a helium recovery cold box (E-102) to provide cold for an overhead condenser (E-103) of a helium recovery tower (T-102), the low-pressure and low-temperature nitrogen enters the helium recovery cold box (E-102) after being heated again and then enters an absorption tank (V-103), and the gas phase of the nitrogen enters a nitrogen compressor (K-101) for pressurization and a helium recovery cold box (E-101) for cooling respectively, and then enters the next cycle.

7. The method for extracting helium from natural gas as claimed in claim 1, wherein the helium concentration column (T-101) and the helium recovery column (T-102) use high efficiency packing to improve separation efficiency.

8. The method for extracting helium from natural gas as claimed in claim 1, wherein the feed gas is subjected to a purification pretreatment before entering the device, so as to ensure that carbon dioxide solids and natural gas hydrates are not formed in the process.

Technical Field

The invention relates to the technical field of natural gas processing technology, in particular to a natural gas helium recovery method.

Background

Helium is one of indispensable rare strategic materials for national defense military industry and high-tech industry development. The helium resource in China is quite poor, the method basically depends on import, the content of helium in natural gas is low, the extraction difficulty is high, and the cost is high.

The inventor and the like in patent CN101975503A improved Natural gas helium extraction technology propose a natural gas helium extraction technology, which adopts a rectifying tower and has the main defects of low helium concentration in the process, incomplete helium extraction system and further need to separate and concentrate helium in natural gas.

In patent CN111578621A, "a switchable natural gas two-tower helium extraction device and process", the inventor proposes a two-tower helium extraction process, in which a primary helium extraction tower and a secondary helium extraction tower in the process adopt a traditional rectification tower, and are respectively provided with a condenser and a reboiler, the reboiler and the condenser are respectively placed in the tower and at the tower top in the two towers, so that the characteristics of low-temperature separation helium extraction are not fully understood, and the heat integration degree of cold and hot material flows in the process is low. The primary helium concentration tower has the main function of improving the helium concentration in the feed gas, the product composition of the material flow discharged from the top of the tower does not need to be controlled, the mode of a stripping tower can be directly adopted, and a condenser and a reflux tank at the top of the tower do not need to be arranged in the primary helium concentration tower. The cold source at the top of the helium recovery tower adopts nitrogen refrigeration cycle, all material flows of the nitrogen refrigeration cycle are positioned in the helium recovery cold box, the temperature difference between cold material flows and hot material flows is too large (40 ℃ to minus 180 ℃), and the loss of effective energy is large. The method has the main defects that a primary helium concentration tower does not need a condenser and a reflux tank, a stripping tower form is adopted, and more process equipment is needed. The nitrogen refrigeration cycle is arranged in a helium recovery cold box, the heat exchange temperature difference is large, and the heat integration level is low.

In patent CN112179048A "a co-production system and method for recovering and extracting helium from low-helium natural gas light hydrocarbon", the inventor et al proposed a co-production system for recovering and extracting helium from natural gas light hydrocarbon, although the co-production system improves the heat integration of the system, the helium extracting part adopts a flash separation method, and the flash separation method has low helium recovery rate and low helium purity (in the example, the helium concentration is 38.03%), which increases the difficulty and load of subsequent helium purification.

The existing helium extraction patent mainly has the problems of complex flow, more equipment, low helium recovery rate, unreasonable helium extraction tower arrangement and the like.

Disclosure of Invention

The invention provides a natural gas helium recovery method, which is suitable for helium recovery systems of natural gas containing helium with different helium contents, and has obvious energy saving advantages when the content of helium in raw gas is low (the content of helium in natural gas is lower than 0.5%). The process adopts double towers to provide helium, the concentration tower adopts a multi-strand feeding mode with temperature gradient, the efficiency loss of the concentration tower is greatly reduced, the helium concentration tower and the helium recovery tower adopt a mode of partial logistics reheating at the bottom of the tower to provide a heat source for the tower bottom, the cold quantity of the helium recovery tower and the heat source at the bottom of the two towers are respectively obtained through a logistics heat exchange mode, the heat integration degree of the process is greatly improved, and the total compression work of the system is reduced. The technological process of the double-tower helium recovery is shown in figure 1.

The invention provides a natural gas helium recovery method, which has the flow characteristic as follows:

(1) the process comprises a helium concentration tower (T-101) and a helium recovery tower (T-102), the pretreated natural gas enters a heavy hydrocarbon separator (V-101) after being precooled in a main cooling box (E-101), the gas phase of the heavy hydrocarbon separator enters a low-temperature separator (V-102) after being cooled in the main cooling box, the liquid phase of the heavy hydrocarbon separator enters the main cooling box (E-101) and is heated up, the liquid phase of the heavy hydrocarbon separator enters a flash tank (V-104) after being depressurized, gas and condensate are separated, and the gas phase enters a fuel gas system. The method comprises the steps that a gas phase of a heavy hydrocarbon separator (V-101) enters a low-temperature separator (V-102) for separation after being cooled by a main cooling box (E-101), a gas phase of the low-temperature separator enters the top of a helium concentrating tower (T-101) after being cooled by the main cooling box, a liquid phase of the low-temperature separator enters the middle of the helium concentrating tower (T-101) after being throttled and depressurized, a discharged material at the top of the helium concentrating tower (T-101) enters the middle of the helium recovering tower (T-102) after being cooled in the helium recovering cooling box (E-102), one part of discharged material at the bottom of the helium concentrating tower (T-101) is heated in the main cooling box (E-101) and enters the bottom of the concentrating tower, and the other part of discharged material is divided into two streams which are depressurized respectively and then enters a pressurizing unit after being heated by the main cooling box (E-101) for pressurization. The top discharge of the helium recovery tower (T-102) is heated by a helium recovery cold box (E-102) and then output, one part of the bottom discharge of the helium recovery tower (T-102) enters the helium recovery cold box (E-102) to be heated to the bottom of the helium recovery tower, the other part of the bottom discharge enters the helium recovery cold box (E-102) and a main cold box (E-101) in sequence to be heated after throttling and pressure reduction, and then enters a pressurizing unit to be pressurized and output.

(2) The two towers are multi-strand feeding low-temperature fractionating towers with larger temperature gradient, the helium concentration tower (T-101) is provided with three strands of feeding materials, the gas phase of the low-temperature separator (V-102) enters the main cooling box (E-101) for cooling, then the gas phase is decompressed and enters the top of the helium concentration tower (T-101), the liquid phase of the low-temperature separator (V-102) is decompressed and enters the middle part of the helium concentration tower (T-101), and the partial material flow at the bottom of the helium concentration tower (T-101) enters the bottom of the helium concentration tower (T-101) after heat exchange in the main cooling box (E-101). The helium recovery column (T-102) has two feeds: discharging from the top of the helium concentrating tower (T-101) into a helium recovery cold box (E-102), reducing the temperature, then reducing the pressure, feeding from the middle part of the helium recovery tower (T-102), exchanging heat and raising the temperature of partial material at the bottom of the helium recovery tower (T-102) in the helium recovery cold box (E-102), and then feeding into the bottom of the recovery tower.

(3) The refrigeration cycle adopts nitrogen refrigeration cycle, high-pressure nitrogen is throttled and reduced in pressure by a throttle valve after being cooled in a helium recovery cold box (E-102) and then is subjected to heat exchange in a top condenser (E-103) of a helium recovery tower to provide cold energy, the heated nitrogen enters the helium recovery cold box (E-102) for reheating and heating and then enters an absorption tank (V-103), the gas phase of the nitrogen enters the helium recovery cold box (E-102) again for cooling after being pressurized, and then enters the next round of refrigeration cycle.

(4) The main cold box (E-101) and the helium recovery cold box (E-102) both adopt a multi-strand plate-fin heat exchanger, and three hot flows and five cold flows, and two hot flows and four cold flows are respectively integrated in the main cold box (E-101) and the helium recovery cold box (E-102). The three heat flows of the main cooling box (E-101) are raw material gas, a heavy hydrocarbon separator (V-101) gas phase and a low temperature separator (V-102) gas phase; the five cold flows are respectively a liquid phase of the heavy hydrocarbon separator (V-101), three split flows at the bottom of the helium concentrating tower (T-101) and a split flow at the bottom of the helium recovery tower (T-102). The four cold flows of the helium recovery cold box (E-102) are two streams at the bottom of a helium recovery tower (T-102), crude helium and low-temperature low-pressure nitrogen; the two hot streams are the overhead streams of the high pressure nitrogen and helium concentrating column (T-101).

(5) The raw gas needs to be purified and pretreated before entering the device, so that the natural gas in the process can not form carbon dioxide solid and natural gas hydrate.

(6) When the content of pentane and heavy hydrocarbon above pentane in the feed gas is more than 70mg/m³And the aromatic hydrocarbon mole content in the raw material gas is greater than 10^-6The raw material gas is fed into the equipment and is required to be subjected to dealkylation treatment.

Compared with the prior art, the invention has the advantages that:

(1) the invention combines the processes of cryogenic rectification and helium recovery, applies the heat integration technology, and integrates a plurality of strands of cold and hot material flows into the cold box, thereby improving the heat integration level of the system and reducing the energy consumption of the system.

(2) The helium concentrating tower (T-101) and the helium recovering tower (T-102) adopt a multi-strand feeding mode with temperature gradient, and both towers adopt a mode that partial material flows at the bottom of the tower enter a cold box (a main cold box or a helium recovering cold box) for temperature rise and reheating and then enter the bottom of the tower as a heat source, so that the matching degree of a heat exchange curve of the cold and hot material flows in the system is improved, the process is simplified, and the engineering investment is reduced.

(3) In the process, nitrogen refrigeration cycle is adopted to provide cold energy for the top of a helium recovery tower (T-102), so that the refrigeration temperature is reduced, and the purity of crude helium is improved; the cold energy of the main cooling box is provided by two streams of material at the bottom of the helium concentration tower and one stream of material at the bottom of the helium recovery tower, and the three streams of material have different flow rates and temperature levels; the cold energy of the helium recovery cold box is provided by depressurization at the bottom of the helium recovery tower, low-temperature nitrogen and crude helium.

(4) The process omits a reboiler and a condenser, reduces the number of equipment and equipment investment, and has the advantages of high helium recovery rate, high crude helium purity, adjustable recovery rate and strong flow adaptability.

Advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.

Drawings

The invention is described in further detail in the following with reference to the figures and the detailed description of the invention

FIG. 1 is a flow diagram of a natural gas dual tower helium recovery process;

wherein, E-101-main cooling box; e-102-helium recovery cold box; e-103-a condenser at the top of the recovery tower; e-104-water cooler; a V-101-heavy hydrocarbon separator; v-102-cryogenic separator; v-103-suction canister; v-104-flash tank; a T-101-helium concentrating tower; a T-102-helium recovery column; k-101-nitrogen recycle compressor; a-101-air cooler.

Detailed Description

The present invention will now be described with reference to the following examples, which are provided for illustration and explanation and are not intended to limit the scope of the invention.

The pressure used in the examples is absolute pressure.

Example 1

Raw material gas composition and working conditions:

scale of raw material gas treatment: 100 x 10⁴m³/d

Raw material gas pressure: 4.5MPa

Temperature of raw material gas: 40 deg.C

External gas transmission pressure: greater than 4.2MPa

The feed gas composition is shown in table 1.

TABLE 1 feed gas molar composition

Natural gas component	Helium	Nitrogen	CO2	Methane	Ethane	Propane	i-Butane
								The composition of natural gas is mol%	0.25	10	0.001	87.699	1.331	0.406	0.021
Natural gas component	n-Butane	i-Pentane	n-Pentane	n-Hexane	n-Heptane	n-Octane	n-Nonane
								The composition of natural gas is mol%	0.062	0.062	0.062	0.03	0.02	0.019	0.016
Natural gas component	n-Decane	n-C11
								The composition of natural gas is mol%	0.012	0.01

The process flow of the natural gas double-tower helium recovery method in the embodiment 1 is shown in fig. 1, and the process flow is briefly described as follows:

(1) natural gas after membrane separation enters a main cooling box (E-101) after being pressurized and is cooled to-80 ℃ through pretreatment (decarburization and dehydration), then enters a heavy hydrocarbon separator (V-101), a gas phase of the heavy hydrocarbon separator enters a low-temperature separator (V-101) after being cooled to-88.4 ℃ in the main cooling box (E-101), and a liquid phase of the heavy hydrocarbon separator (V-101) enters a flash tank (V-104) for separation after being heated to 36 ℃ in the main cooling box (E-101) and then is depressurized. The gas phase of the low-temperature separator (V-102) is cooled to-120 ℃ by the main cooling box (E-101), then the gas phase is depressurized to 3.85MPa and enters the top of the helium concentration tower (T-101), and the liquid phase of the low-temperature separator (V-102) is throttled and depressurized to 3.9MPa and enters the middle of the helium concentration tower (T-101).

(2) The top discharge (3.8 MPa-111 ℃) of the helium concentrating tower (T-101) enters a helium recovery cold box (E-102) to be cooled and decompressed (2.5 MPa-154 ℃) and then enters the middle part of the helium recovery tower (T-102).

(3) The bottom discharge of the helium concentrating tower (T-101) is divided into two parts, the first part (with the molar flow percentage of 16.5%) is fed from the bottom of the helium concentrating tower after heat exchange and temperature rise in a main cooling box (E-101), the second part (with the molar flow percentage of 83.5%) is divided into two parts, one part (with the molar flow percentage of 83%) is throttled and depressurized to 2.7MPa, then enters the main cooling box (E-101) for reheating and then enters a pressurizing unit for pressurizing, and the other part (with the molar flow percentage of 17%) is throttled and depressurized to 1.3MPa, then enters the main cooling box for reheating and then enters the pressurizing unit for pressurizing and outputting.

(4) Crude helium (with the purity of 73.476%) discharged from the top of the helium recovery tower (T-102) passes through a helium recovery cold box (E-102) and is heated to 36 ℃ and then enters a subsequent purification unit.

(5) The discharge of the bottom of the helium recovery tower (T-102) is divided into two streams, the first stream (with the molar flow percentage of 25.5%) enters a helium recovery cold box (E-102) for heat exchange and temperature rise and then is fed from the bottom of the helium recovery tower (T-102), the second stream (with the molar flow percentage of 74.5%) is throttled and depressurized to 0.6MPa and then respectively enters the helium recovery cold box (E-102) and a main cold box (E-101) for providing cold energy for the two cold boxes, and the cold energy is heated to 36 ℃ and then is output together with two streams at the bottom of the helium concentration tower (T-101) after being pressurized to 4.3MPa by a pressurizing unit.

(6) The refrigeration cycle adopts nitrogen refrigeration cycle, nitrogen is cooled to-175 ℃ in a helium recovery cold box (E-102), then is depressurized to 0.35MPa, enters a helium recovery tower overhead condenser (E-103) for heat exchange to provide cold, the nitrogen after being heated enters the helium recovery cold box (E-102) for reheating, is heated to-100 ℃ again, enters a suction tank (V-103), and the separated gas phase is pressurized and then enters the helium recovery cold box (E-102) again to enter the next cycle.

The main parameters of the natural gas double-tower helium recovery process are shown in tables 2, 3 and 4, and the simulation results show that: the total compression work of natural gas double-tower helium recovery is 1096kW, and the total compression work comprises raw gas pressurization compression work, refrigeration compression work and external gas delivery compression work. Helium recovery was 98.95% and crude helium product purity was 73.48%.

TABLE 2 Natural gas twin tower helium recovery Process Main parameters

Item	Process parameters
		Scale of natural gas treatment, 104m3/d	100×104
Pressure of raw gas, MPa	4.5
		Temperature of raw material gas, DEG C	40
Helium recovery rate%	98.95
		Helium purity%	73.48
kW of compression work of nitrogen refrigeration cycle	16.34
		External gas delivery supercharging compression work, kW	1079
Total work of compression, kW	1096

TABLE 3 crude helium product gas composition and operating conditions

TABLE 4 gas composition and operating conditions of external gas delivery