Method and device for recycling hydrogen in mixed gas under variable working conditions

Abstract

The invention provides a method and device for recycling hydrogen in mixed gas under variable working conditions, and relates to the technical field of separation of hydrogen from hydrogen-containing mixed gas. The method comprises the following steps: carrying out multi-stage membrane separation on mixed gas, wherein the multi-stage membrane separation comprises initial-stage membrane separation, middle-stage membrane separation of any times including zero, and tail-stage membrane separation; performing PSA treatment on the permeable gas of the initial-stage membrane separation to obtain a product hydrogen, and feeding the permeable gas of the middle-stage membrane separation and the permeable gas of the tail-stage membrane separation to any stage of membrane separation or discharging; and adjusting the permeation side pressure of the initial-stage membrane separation so as to adjust the permeation gas concentration of the initial-stage membrane separation. The device comprises an initial-stage membrane separator, any number of intermediate-stage membrane separators including zero, and an end-stage membrane separator which are arranged in sequence, wherein a PSA unit is communicated with a permeation side pipeline of the initial-stage membrane separator. According to the invention, the high hydrogen recovery rate of the mixed gas with fluctuating flow and components is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of separating hydrogen from hydrogen-containing mixed gas, and in particular to a method and device for recovering hydrogen from the mixed gas under variable working conditions. Background Art

[0002] In the existing technology, hydrogen recovery from mixed nitrogen generally includes three processes: membrane separation, PSA (pressure swing adsorption), and membrane separation and PSA combination. Among them, the disadvantage of membrane separation is that the purity of the separated products, whether nitrogen or hydrogen, is difficult to achieve above 99.8% (V / V); the disadvantage of PSA is low yield and narrow application range. If the nitrogen content in the hydrogen exceeds 30%, then the hydrogen recovery rate is difficult to exceed 50% under normal operating conditions; the disadvantage of the combination of membrane separation and PSA is that it can only be applied to relatively fixed gas volumes and components, otherwise the output gas indicators will vary greatly.

[0003] Currently, replacement gas and pressure-regulated venting in chemical plants are unstable, with certain time periods and uncertainties. Taking polysilicon plants as an example, the vast majority of replacement gas and pressure-regulated venting are hydrogen and nitrogen. However, these gases exhibit varying volume and composition as they exit individual equipment or systems. For example, the venting volume in one polysilicon plant fluctuates rapidly between 1500 and 6000 Nm³ / h, with the hydrogen content fluctuating rapidly from 8% to 54% (V / V). The timing of multiple venting points throughout the plant is relatively irregular, and ultimately, when the replacement gas and pressure-regulated venting are released to the leaching unit, they exhibit rapid and irregular variations in volume and composition. Therefore, all three hydrogen recovery schemes described above suffer from poor adaptability to this type of gas. Even if some hydrogen can be recovered, the yield is low (below 60% or even lower). Summary of the Invention

[0004] The purpose of the present invention is to develop a method and device for recovering hydrogen from a mixed gas under variable working conditions, which can achieve a high hydrogen recovery rate for a mixed gas with fluctuating flow and components.

[0005] The present invention is achieved through the following technical solutions: A method for recovering hydrogen from a mixed gas under variable working conditions, comprising: Pre-treating the mixed gas to remove impurities; The pretreated mixed gas is subjected to multi-stage membrane separation, which includes initial-stage membrane separation, any number of intermediate-stage membrane separations including zero, and terminal-stage membrane separation; Among them, in multi-stage membrane separation, the non-permeate gas separated by the previous membrane stage is sent to the next membrane stage for separation, and the hydrogen content of the non-permeate gas separated by the terminal membrane stage is less than 2% and is discharged; The permeate gas from the initial membrane separation is subjected to PSA treatment to obtain product hydrogen. The permeate gas from the intermediate and final membrane separation can be pressurized and sent to the inlet of any membrane separation stage or discharged. The permeate side pressure of the initial membrane separation is adjusted to adjust the permeate gas concentration of the initial membrane separation so that the permeate gas concentration tends to be constant.

[0006] Optionally, the hydrogen content in the mixed gas fluctuates between 5% and 80%, the gas volume of the mixed gas varies between 10% and 100%, the pressure of the mixed gas after pretreatment is controlled to be 1.5 to 4 MPa, and the permeate side pressure in the initial stage membrane separation is 0.1 to 1 MPa.

[0007] Optionally, the adsorption columns of the PSA are switched sequentially using a gas flow accumulation method.

[0008] Optionally, before PSA treatment, the permeate gas from the initial membrane separation is pressurized to 0.8~2Mpa.

[0009] Optionally, in the direction from the initial stage membrane separation to the final stage membrane separation, the permeate side pressure of each stage membrane separation decreases step by step, and the hydrogen concentration of the permeate gas decreases step by step.

[0010] Optionally, the permeate side pressure of the terminal stage membrane separation is controlled at -0.05~0.05MPa, and the hydrogen content in the permeate gas is 10~50%.

[0011] Optionally, the gases generated by the regeneration of the PSA adsorption column, including reverse venting and sucked vacuum air, are recycled to become pre-treated mixed gas components, and then subjected to initial membrane separation.

[0012] A device for recovering hydrogen from mixed gas under variable working conditions, comprising: An initial stage membrane separator, any number of intermediate stage membrane separators including zero, and a terminal stage membrane separator are arranged in sequence; The PSA unit is connected to the permeate side pipeline of the initial stage membrane separator; Among them, the non-permeate side of the previous membrane separator is connected to the air inlet pipeline of the next membrane separator, and the permeate side gas of the intermediate membrane separator and the terminal membrane separator can be pressurized and sent to the air inlet pipeline of any membrane separator or discharged; A regulating valve is provided on the pipeline between the PSA unit and the initial-stage membrane separator, and the PSA unit is communicated with the air inlet pipeline of the initial-stage membrane separator.

[0013] Optionally, a first compressor is provided before the initial-stage membrane separator, and the first compressor regulates the pressure of the gas entering the initial-stage membrane separator.

[0014] Optionally, a hydrogen purity analyzer, a pressure monitoring device, a flow monitoring device and a second compressor are further provided on the pipeline between the PSA unit and the initial-stage membrane separator.

[0015] The beneficial effects of the present invention are: The present invention timely adjusts the permeate concentration by adjusting the pressure on the permeate side of the initial membrane separation to achieve a relatively constant permeate concentration. Even if the gas volume of the permeate separated by the initial membrane is unstable, its hydrogen content is high and the concentration is stable. By monitoring the cumulative flow of the permeate separated by the initial membrane entering the PSA, the PSA timing can be switched to maximize the hydrogen recovery rate in the PSA process. The subsequent multi-stage membrane separation further ensures the hydrogen recovery rate, so that the hydrogen content of the non-permeate gas separated by the terminal membrane is sufficiently low, thereby achieving a high hydrogen recovery rate. In addition, the reverse bleed gas discharged by the regeneration of the adsorption column is recycled for membrane separation, and the hydrogen in the reverse bleed gas is recovered to further improve the hydrogen recovery rate. Therefore, even for a mixed gas with an original hydrogen concentration of at least 10% and fluctuating flow and composition, a recovery rate of more than 80% can be met. Finally, in the hydrogen recovery process of the entire mixed gas, the only hydrogen lost is the non-permeate gas discharged from the terminal membrane separation, and the hydrogen content in this part of the non-permeate gas is between 0.2% and 2%. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0017] Figure 1 This is the device structure diagram when the number of intermediate-stage membrane separators is zero.

[0018] Figure numerals: 1. first compressor; 2. initial stage membrane separator; 3. final stage membrane separator; 4. hydrogen purity analyzer; 5. pressure monitoring equipment; 6. regulating valve; 7. second compressor; 8. flow monitoring equipment; 9. PSA unit. DETAILED DESCRIPTION

[0019] Hereinafter, only certain exemplary embodiments are briefly described. As will be appreciated by those skilled in the art, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and description are to be regarded as illustrative in nature and not restrictive.

[0020] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0021] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0022] The present invention discloses a method for recovering hydrogen from a mixed gas under variable operating conditions. The mixed gas mainly comprises nitrogen and hydrogen, and the mixed gas is pretreated to remove impurities. The pretreatment comprises pressurizing, condensing, and adsorbing the mixed gas to remove easily condensable substances such as chlorosilane and hydrogen chloride.

[0023] The hydrogen content in the mixed gas fluctuates rapidly between 5% and 80%, and the gas volume of the mixed gas changes rapidly between 10% and 100%. When the gas volume of the mixed gas is 100%, the maximum mixed gas processing capacity of the process is reached.

[0024] The pretreated mixed gas pressure is controlled at 1.5-4 MPa before undergoing initial membrane separation. The permeate-side pressure during this initial membrane separation is 0.1-1 MPa. The permeate gas (primarily hydrogen, similarly below) undergoes PSA (pressure swing adsorption) treatment, yielding product hydrogen with a purity exceeding 99.9%. The non-permeate gas (primarily nitrogen, similarly below) from the initial membrane separation is output and subjected to final membrane separation. The initial membrane separation process adjusts the permeate-side pressure to promptly adjust the permeate gas concentration, maintaining a relatively constant permeate gas concentration.

[0025] The permeate pressure of the final membrane separation process can be controlled between -0.05 and 0.05 MPa, and the hydrogen content of the permeate gas can vary between 10 and 50%. The permeate gas from the final membrane separation process is recycled to become a pretreated mixed gas component before undergoing the initial membrane separation process. The non-permeate gas from the final membrane separation process has a hydrogen content of less than 2% and is discharged. If the hydrogen concentration of the permeate gas from the final membrane separation process is low, it can also be discharged directly.

[0026] Before PSA treatment, the permeate gas of the initial membrane separation is first pressurized to 0.8~2Mpa. The adsorption column of PSA adopts the gas flow accumulation method for time switching, that is, the total gas flow is used to judge whether the adsorption column has reached the maximum capacity of nitrogen adsorption, so that the adsorption column can be regenerated and other adsorption columns can be switched to continue adsorption. The regenerated adsorption column is back-vented or the vacuum air is sucked back to become the pre-treated mixed gas component, and then the initial membrane separation is carried out.

[0027] One or more intermediate membrane separations can be performed between the initial membrane separation and the terminal membrane separation. The initial membrane separation, intermediate membrane separation, and terminal membrane separation are performed in sequence, and the pressure on the permeate side of each membrane separation is controlled to decrease step by step. The hydrogen concentration of the permeate gas decreases step by step. The non-permeate gas separated by the previous membrane separation is sent to the next membrane separation. The permeate gas from the intermediate membrane separation and the terminal membrane separation can be pressurized and sent to the inlet of any membrane separation or discharged.

[0028] like Figure 1 As shown, the present invention also discloses a device for recovering hydrogen from a mixed gas under variable working conditions, comprising a first compressor 1, an initial-stage membrane separator 2, and a terminal-stage membrane separator 3 connected in sequence. The first compressor 1 pressurizes the mixed gas of hydrogen and nitrogen and sends it into the air inlet pipeline of the initial-stage membrane separator 2. The non-permeation side of the initial-stage membrane separator 2 is connected to the air inlet pipeline of the terminal-stage membrane separator 3. The non-permeation side of the terminal-stage membrane separator 3 is connected to an external exhaust pipeline.

[0029] The permeate-side pipeline of the initial-stage membrane separator 2 is connected to a second compressor 7 , the second compressor 7 is connected to a PSA unit 9 , and the PSA unit 9 is also connected to the first compressor 1 .

[0030] The PSA unit 9 includes a plurality of adsorption columns connected in parallel, and adsorption fillers are provided in the adsorption columns.

[0031] The pipeline connecting the second compressor 7 and the PSA unit 9 is equipped with a flow monitoring device 8, which monitors the gas flow entering the PSA unit 9. The pipeline connecting the second compressor 7 and the initial-stage membrane separator 2 is equipped with a hydrogen purity analyzer 4, a pressure monitoring device 5, and a regulating valve 6.

[0032] The permeate side of the terminal membrane separator 3 is connected to the first compressor 1 pipeline. The permeate gas of the terminal membrane separator 3 is sent to the first compressor 1 for pressurization and then enters the air inlet pipeline of the initial membrane separator 2.

[0033] One or more intermediate-stage membrane separators can also be arranged between the initial-stage membrane separator 2 and the final-stage membrane separator 3. The initial-stage membrane separator 2, the intermediate-stage membrane separator, and the final-stage membrane separator 3 are arranged in sequence. The non-permeation side of the previous-stage membrane separator is connected to the air inlet pipeline of the next-stage membrane separator. The permeation sides of the intermediate-stage membrane separator and the final-stage membrane separator 3 are provided with permeation air pipes, which can be connected to the air inlet pipeline of any stage membrane separator or to the outside world.

[0034] The present invention timely adjusts the permeate concentration by adjusting the pressure on the permeate side of the initial membrane separation to achieve a relatively constant permeate concentration. Even if the gas volume of the permeate separated by the initial membrane is unstable, its hydrogen content is high and the concentration is stable. By monitoring the cumulative flow of the permeate separated by the initial membrane entering the PSA, the PSA timing can be switched to maximize the hydrogen recovery rate in the PSA process. The subsequent multi-stage membrane separation further ensures the hydrogen recovery rate, so that the hydrogen content of the non-permeate gas separated by the terminal membrane is sufficiently low, thereby achieving a high hydrogen recovery rate. In addition, the reverse bleed gas discharged by the regeneration of the adsorption column is recycled for membrane separation, and the hydrogen in the reverse bleed gas is recovered to further improve the hydrogen recovery rate. Therefore, even for a mixed gas with an original hydrogen concentration of at least 10% and fluctuating flow and composition, a recovery rate of more than 80% can be met. Finally, in the hydrogen recovery process of the entire mixed gas, the only hydrogen lost is the non-permeate gas discharged from the terminal membrane separation, and the hydrogen content in this part of the non-permeate gas is between 0.2% and 2%.

[0035] The above embodiments are only preferred embodiments of the present invention and are not limitations on the technical solutions of the present invention. Any technical solution that can be implemented on the basis of the above embodiments without creative work should be deemed to fall within the scope of protection of the patent of the present invention.

Claims

1. A method for recovering hydrogen from mixed gas under variable working conditions, characterized in that: include: Pre-treating the mixed gas to remove impurities; The pretreated mixed gas is subjected to multi-stage membrane separation, which includes initial-stage membrane separation, any number of intermediate-stage membrane separations including zero, and terminal-stage membrane separation; Among them, in multi-stage membrane separation, the non-permeate gas separated by the previous membrane stage is sent to the next membrane stage for separation, and the hydrogen content of the non-permeate gas separated by the terminal membrane stage is less than 2% and is discharged; The permeate gas from the initial membrane separation is subjected to PSA treatment to obtain product hydrogen. The permeate gas from the intermediate and final membrane separation can be pressurized and sent to the inlet of any membrane separation stage or discharged. The permeate side pressure of the initial membrane separation is adjusted to adjust the permeate gas concentration of the initial membrane separation so that the permeate gas concentration tends to be constant.

2. The method for recovering hydrogen from mixed gas under variable working conditions according to claim 1, characterized in that: The hydrogen content in the mixed gas fluctuates between 5% and 80%, the gas volume of the mixed gas varies between 10% and 100%, the pressure of the mixed gas after pretreatment is controlled at 1.5~4Mpa, and the permeate side pressure in the initial stage membrane separation is 0.1~1MPa.

3. The method for recovering hydrogen from mixed gas under variable working conditions according to claim 1, characterized in that: The adsorption columns of PSA are switched sequentially using the gas flow accumulation method.

4. The method for recovering hydrogen from mixed gas under variable working conditions according to claim 1, characterized in that: Before PSA treatment, the permeate gas from the initial membrane separation is pressurized to 0.8~2Mpa.

5. The method for recovering hydrogen from mixed gas under variable working conditions according to claim 1, characterized in that: From the initial membrane separation to the final membrane separation, the permeate side pressure of each membrane separation stage decreases step by step, and the hydrogen concentration of the permeate gas decreases step by step.

6. The method for recovering hydrogen from mixed gas under variable working conditions according to claim 1, characterized in that: The permeate side pressure of the terminal membrane separation is controlled at -0.05~0.05MPa, and the hydrogen content in the permeate gas is 10~50%.

7. The method for recovering hydrogen from mixed gas under variable working conditions according to any one of claims 1 to 6, characterized in that: The gases generated by the regeneration of the PSA adsorption column, including reverse venting and vacuum air, are returned to become pre-treated mixed gas components and then subjected to initial membrane separation.

8. A device for recovering hydrogen from mixed gas under variable working conditions, characterized in that: include: An initial stage membrane separator, any number of intermediate stage membrane separators including zero, and a terminal stage membrane separator are arranged in sequence; The PSA unit is connected to the permeate side pipeline of the initial stage membrane separator; Among them, the non-permeate side of the previous membrane separator is connected to the air inlet pipeline of the next membrane separator, and the permeate side gas of the intermediate membrane separator and the terminal membrane separator can be pressurized and sent to the air inlet pipeline of any membrane separator or discharged; A regulating valve is provided on the pipeline between the PSA unit and the initial-stage membrane separator, and the PSA unit is communicated with the air inlet pipeline of the initial-stage membrane separator.

9. The device for recovering hydrogen from mixed gas under variable working conditions according to claim 8, characterized in that: A first compressor is provided before the initial stage membrane separator, and the first compressor regulates the pressure of the gas entering the initial stage membrane separator.

10. The device for recovering hydrogen from mixed gas under variable working conditions according to claim 8, characterized in that: A hydrogen purity analyzer, a pressure monitoring device, a flow monitoring device and a second compressor are also provided on the pipeline between the PSA unit and the initial stage membrane separator.

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