WO2018108067A1

WO2018108067A1 - Pressure swing adsorption process comprising concentrated waste gas pre-adsorption step

Info

Publication number: WO2018108067A1
Application number: PCT/CN2017/115595
Authority: WO
Inventors: 张国瑞; 胡小鹏
Original assignee: 北京信诺海博石化科技发展有限公司
Priority date: 2016-12-13
Filing date: 2017-12-12
Publication date: 2018-06-21
Also published as: CN107158882B; CN107158882A

Abstract

A pressure swing adsorption process at least comprising a concentration step and a concentrated waste gas pre-adsorption step in a process flow. An adsorption bed subjected to an adsorption step and a reduced pressure equalization step is concentrated, less readily adsorbable components in the adsorption bed are exhausted, and concentrated waste gas that contains a certain quantity of more readily adsorbable components and is exhausted during the concentration procedure is discharged into the adsorption bed in the pre-adsorption step after a recovery step is completed, so that the more readily adsorbable components in the concentrated waste gas are recovered inside the present pressure swing adsorption unit. The more readily adsorbable components can be clearly separated from the less readily adsorbable components, and a high-purity product containing the more readily adsorbable components and the less readily adsorbable components can be obtained at a high recovery rate.

Description

Pressure swing adsorption process comprising a pre-adsorption step of concentrated exhaust gas

Technical field

The invention relates to the field of pressure swing adsorption gas separation, in particular to a pressure swing adsorption gas separation process capable of clearly separating an easily adsorbable component and a non-adsorbing component.

Background technique

Pressure swing adsorption is a gas separation process that utilizes the difference in intermolecular forces between a gas adsorbate and a solid adsorbent. In the pressure swing adsorption process, the raw material gas is usually a mixed gas containing two or more different components, and a gas component or a mixed gas component having a relatively strong adsorption force with the adsorbent is called an easy adsorption. The component, and the gas component or the mixed gas component which has a relatively weak adsorption force with the adsorbent is referred to as a non-adsorbable component. Generally, in the adsorption step of higher pressure, when the raw material gas passes through the adsorption bed, the easily adsorbable component is adsorbed by the adsorbent having a large specific surface area packed in the adsorption bed, and is not easily adsorbed from the outlet side of the adsorption bed. Component product gas stream; in the subsequent adsorbent regeneration process, the adsorbent component is desorbed from the adsorbent by reducing the pressure of the adsorbent bed or reducing the gas phase partial pressure of the easily adsorbable component, so that the adsorbent The regeneration is obtained, and at the same time, the product gas stream of the easily adsorbable component is obtained.

In the practice of pressure swing adsorption gas separation, it has been the most desirable goal to achieve clear separation of easily adsorbable components and non-adsorbed components. Because clear separation means that the concentration of the easily adsorbable component product gas and the non-adsorbable component product gas are higher, and the higher concentration product gas tends to have higher use value and wider use; It means that the easily adsorbable component product gas brings out less difficult-to-adsorbed components, and the less-adsorbable component product gas brings out less easily adsorbed components. Therefore, the easily adsorbable component and the non-adsorbable component are collected. The rate is higher.

However, it is not easy to achieve a clear separation of easily adsorbable components and difficult to adsorb components in the pressure swing adsorption process. It is often much more difficult to obtain a high concentration of easily adsorbable component gas in a pressure swing adsorption unit than to obtain a high concentration of a non-adsorbable component. For example, in the process of separating and recovering hydrogen by pressure swing adsorption, the concentration of hydrogen which is not easily adsorbed is up to 99.9v%, but the concentration of hydrogen in the product stream of the easily adsorbed component is also 15~30v%, so the recovery rate of hydrogen is usually Only about 85 to 93%. The difficulty lies in that a large amount of non-adsorbed components remain in the adsorption bed at the end of the adsorption operation. Some of these non-adsorbed components are adsorbed by the adsorbent, and some are residual in the dead space of the adsorbent bed and only in the adsorbent bed. The easily adsorbable components are fully exhausted and recovered, so that the easily adsorbable components are sufficiently concentrated in the adsorption bed to obtain a high concentration of easily adsorbable component product gas in the subsequent depressurization process. In most cases, when the adsorption bed is reduced to a certain pressure after the adsorption step, and further depressurized and discharged into the adsorption bed, the components are not easily adsorbed, and tend to be accompanied by the easy-adsorption component, which is often an easily adsorbable component. The higher the gas concentration of the product, the more readily adsorbable components are discharged.

The pressure equalization is one of the most effective methods for concentrating the readily adsorbable components in the adsorbent bed. That is, the pressure equalization step of the adsorption pressure step after the completion of the adsorption step is connected to the adsorption bed of the pressure equalization step after the completion of the pressure reduction regeneration step, so that the two suctions The bed is subjected to equal pressure, and the non-adsorbed component in the adsorption bed of the pressure equalization step is discharged from the outlet side of the adsorption bed into the adsorption bed of the pressure equalization step. The pressure equalization process not only enables the adsorption bed of the pressure equalization step to be concentrated, but also enables the non-adsorbed components and the easily adsorbable components in the exhaust gas of the pressure equalization step to be recovered in the adsorption bed of the pressure equalization step, and simultaneously recovered. The pressure energy of the adsorption bed in the pressure drop step. Therefore, the use of pressure equalization process, and even multiple pressure equalization processes are very common in the existing pressure swing adsorption practice. However, the use of a pressure equalization process to concentrate the adsorption bed also has its limitations. First, for each additional pressure equalization, an adsorption bed needs to be added. Therefore, the more the pressure equalization times, the more complicated the process flow and the greater the investment; secondly, with the number of pressure equalization times The increase in the pressure equalization pressure is getting smaller and smaller, so the more the pressure equalization times, the lower the process efficiency. Secondly, the concentration curve of the easily adsorbed components of the pressure equalization exhaust gas is relatively steep, which means that only the average The pressure drop is not easy to drain the components that are not easily adsorbed in the adsorption bed; in addition, sometimes the excessive pressure drop will cause too much easy-adsorbed components to be discharged into the outlet side of the adsorption bed where the pressure is raised, and the pressure equalization step The adsorption bed causes an increase in the content of the easily adsorbable component in the gas which is not easily adsorbed by the adsorption step, thereby reducing the recovery rate of the easily adsorbable component. This phenomenon is more pronounced when the adsorption capacity of the easily adsorbable component is strong.

A common process for concentrating the readily adsorbable components in the adsorbent bed is a carry-on step and a displacement step. The step of discharging is to depressurize the adsorption bed in the forward direction, and the gas discharged from the adsorption bed in the depressurization process is discharged as the exhaust gas. Similar to the pressure equalization step, it is also difficult to discharge the components that are not easily adsorbed in the adsorption bed in the step of discharging. The replacement step is to introduce a part of the easily adsorbable component product gas from the inlet side of the adsorption bed, and replace the adsorption bed with the easily adsorbable component product gas, and the adsorption force of the easily adsorbable component is stronger than that of the non-adsorbable component, so that the latecomer is not easy to occupy. The competitive adsorption principle of the adsorption site originally occupied by the adsorption component will make it difficult to displace the adsorbed component out of the adsorption bed, so the displacement process will also produce replacement exhaust gas. The exhaust gas generated by the step-by-step process and the replacement exhaust gas generated by the replacement process are collectively referred to as concentrated exhaust gas, which often contains a relatively large amount of easily adsorbable components, and the higher the concentration requirement of the adsorbent bed, the higher the concentration of the concentrated exhaust gas discharged. The concentration of easily adsorbable components in the large, concentrated exhaust gas is also higher. If the concentrated exhaust gas is not recovered, the recovery rate of the easily adsorbable components will be significantly affected.

U.S. Patent No. 7,740,688 B2 discloses a process for recovering CO ₂ which is an easily adsorbable component in a shift gas. The concentration method used in the patent is to continue to depressurize the adsorbent bed after the completion of the pressure equalization, and exhaust the exhaust gas in the adsorbent bed. It is difficult to adsorb the components, so that the CO _{2 in} the adsorption bed is concentrated, and the gas with a higher concentration of CO ₂ discharged during the discharge process is compressed and pressurized by the compressor, and then recycled to the raw material gas. Chinese Patent No. CN104740972A discloses a pressure swing adsorption process for recovering replacement exhaust gas and forward gas, and the replacement exhaust gas and the forward exhaust gas are all or partially pressurized by a compressor and returned to the fresh raw material gas. The above process not only increases the investment of the process gas, but also the operating cost, the floor space, etc. due to the increase of the gas discharge and the replacement of the exhaust gas compressor. Moreover, due to the mixing of the gas or the exhaust gas, the amount of the raw material gas increases, and the raw material gas is easily adsorbed. The partial pressure of the components is lowered, which causes an increase in the volume of the adsorbent bed and adversely affects the adsorption separation effect.

The Chinese patent CN100423811C uses a gas of the adsorbed phase component (that is, the easily adsorbable component of the present invention) to replace the adsorbent bed after the completion of the pressure equalization, in order to recover the easily adsorbed component in the displaced exhaust gas generated by the replacement process, The patent specifically sets up a pressure swing adsorption unit for recovering the exhaust gas, and further performs pressure swing adsorption separation on the replacement exhaust gas. This is not However, the process is complicated, resulting in a significant increase in investment, operating cost, floor space, etc. of the entire pressure swing adsorption device; and because the partial pressure of the easily adsorbed exhaust gas component tends to be low, it is more difficult to replace the exhaust gas pressure swing adsorption unit. A high concentration of the easily adsorbable component product is obtained; in addition, the replacement exhaust gas pressure swing adsorption unit itself also generates a replacement exhaust gas, and there is still a problem of how to discharge the exhaust gas. Therefore, the actual industrial device operation effect of the process is that the concentration of the easily adsorbable component product is only about 85v%, and the easily adsorbable component product contains 5-10% of the easily adsorbable component, and the recovery rate of the easily adsorbable component product is only 80~. About 85%.

It is precisely because of the lack of a pressure swing adsorption process that clearly separates the easily adsorbable components and the non-adsorbed components. At present, when a single pressure swing adsorption unit is used to recover the non-adsorbed components as the target product, the recovery rate of the less easily adsorbed components is often not high enough; When the easily adsorbable component is recovered as a target product, it is often difficult to obtain a high concentration of the easily adsorbable component product with high recovery rate; or a more complicated recycling process has to be used.

Summary of the invention

In view of the above problems in the prior art, the present invention provides a pressure swing adsorption process capable of clearly separating an easily adsorbable component and a non-adsorbing component in a pressure swing adsorption unit.

In order to achieve the above object, the present invention provides the following technical solution: a pressure swing adsorption process in which a feed gas is at least separated into an easily adsorbable component product gas and a non-adsorbable component product gas in a pressure swing adsorption unit. The pressure swing adsorption device is provided with at least two adsorption beds with internal adsorbents, and each adsorption bed is alternately operated according to a set sequence step, and each adsorption bed undergoes at least the following operation steps in sequence:

a. adsorption step: introducing a raw material gas from the inlet of the adsorption bed into the adsorption bed, and the raw material gas passes through the adsorption bed at the adsorption pressure and the adsorption temperature, wherein the easily adsorbable component is adsorbed by the adsorbent packed in the adsorption bed to remove The easily adsorbable component gas of the easily adsorbable component is discharged from the outlet of the adsorption bed, and part of it is returned to the adsorption bed as a final charge back to the final charge step, and the remaining part is discharged as a product of the non-adsorbable component, and the adsorption front of the adsorbent bed is easily adsorbed. When the penetrating adsorption bed is approached, the adsorption is stopped;

b. Pressure equalization step: the adsorption bed outlet is connected with other adsorption beds or other intermediate tanks in the pressure equalization step, so that the adsorption bed is gradually depressurized, and the adsorption bed contains a small amount of easily adsorbable components. The gas is discharged to a pressure equalization step adsorption bed or other intermediate tank to obtain a preliminary concentration of the adsorption bed;

c. Concentration step: the adsorption bed outlet is connected with the inlet of the adsorption bed in the pre-adsorption step, and the adsorption bed is not easily adsorbed, so that the adsorption bed is sufficiently concentrated, and the adsorbent bed contains the easily adsorbable component during the concentration process. The concentrated exhaust gas is discharged to the adsorption bed of the pre-adsorption step;

d. Recovery step: reverse-pressure reduction from the inlet side of the adsorption bed, the easily adsorbed component adsorbed on the adsorbent is gradually desorbed during the depressurization process, and the depressurization process obtains an easily adsorbable component gas or directly as an easily adsorbable component product. The gas is discharged, or a part of it is returned to the adsorption step of the concentration step as a replacement gas, and the rest is used as an easily adsorbable component product. row;

e. Pre-adsorption step: receiving the concentrated exhaust gas discharged from the adsorption bed in the concentration step from the inlet side of the adsorption bed, the easily adsorbed component in the concentrated exhaust gas is adsorbed by the adsorbent under the adsorption bed, and the component which is not easily adsorbed enters the adsorption bed layer, in the process The adsorption bed pressure is gradually increased to the pre-adsorption pressure;

f. Pressure equalization step: the adsorption bed is connected with the adsorption bed or other intermediate tank in the pressure equalization step, so that the adsorption bed is partially pressurized, and the easily adsorbed components and the non-adsorbed component gases are recovered;

g. Final charging step: introducing part of the non-adsorbable component gas obtained in the adsorption step as a final aeration from the outlet side of the adsorption bed into the adsorption bed, and charging the adsorption bed to the adsorption pressure;

h. Cycle steps a to g.

Further, the concentration step includes a sequential step, namely:

Stepping step: depressurizing from the outlet side of the adsorption bed, exhausting the non-adsorbing components in the adsorption bed, so that the easily adsorbable components in the adsorption bed are sufficiently concentrated, and the concentrated exhaust gas is discharged from the outlet side of the adsorption bed.

Further, the concentration step includes a replacement step, namely:

Displacement step: introducing a part of the easily adsorbable component gas from the inlet side of the adsorption bed as a replacement gas, and replacing the non-adsorbing component adsorbed on the adsorbent and the empty volume of the adsorbent bed with the easily adsorbable component having strong adsorption force, so that The easily adsorbable component in the adsorbent bed is sufficiently concentrated, and the concentrated exhaust gas is discharged from the outlet side of the adsorption bed during the replacement process.

Further, the step of concentrating comprises first stepping the steps and then replacing the steps, namely:

Stepping step: depressurizing the pressure from the outlet side of the adsorption bed, discharging the non-adsorbing components in the adsorption bed, so that the easily adsorbable components in the adsorption bed are further concentrated, and discharging the exhaust gas from the outlet side of the adsorption bed;

Displacement step: introducing a part of the easily adsorbable component gas from the inlet side of the adsorption bed as a replacement gas, and replacing the non-adsorbing component adsorbed on the adsorbent and the empty volume of the adsorbent bed with the easily adsorbable component having strong adsorption force, so that The easily adsorbable component in the adsorption bed is sufficiently concentrated, and the replacement exhaust gas is discharged from the outlet side of the adsorption bed during the replacement process;

Wherein, the exhaust gas generated by the sequential step and the replacement exhaust gas produced by the displacement step are separately or mixed as a concentrated exhaust gas and discharged into the adsorption bed of the pre-adsorption step.

Further, the recycling step includes a reverse step, namely:

The reverse reaction step: reversely depressurizes from the inlet side of the adsorption bed until the pressure of the adsorption bed is equal to or close to the atmospheric pressure, and the adsorbable component adsorbed on the adsorbent is desorbed to obtain an easily adsorbable component gas.

Further, the recycling step includes a vacuuming step, namely:

Vacuuming step: vacuuming the adsorption bed from the inlet side of the adsorption bed with a vacuuming device, and vacuuming the adsorption bed to a low level At the atmospheric pressure, the adsorbable component adsorbed on the adsorbent is desorbed, and the easily adsorbable component gas is obtained from the outlet of the vacuuming device.

Further, the recycling step includes the step of first depressing and then the step of vacuuming, namely:

Reverse reaction step: reverse pressure reduction from the inlet side of the adsorption bed until the pressure of the adsorption bed is equal to or close to atmospheric pressure, desorbing the adsorbable component adsorbed on the adsorbent, and obtaining the gas which is easy to adsorb and adsorb the component;

Vacuuming step: vacuuming the adsorption bed from the inlet side of the adsorption bed with a vacuuming device, vacuuming the adsorption bed to a vacuum pressure lower than atmospheric pressure, desorbing the adsorbable components adsorbed on the adsorbent, and pumping The vacuum equipment outlet obtains a vacuum-adsorbable component gas;

Wherein, the reverse-adsorbing component gas generated by the reverse-releasing step and the vacuum-adsorbable component gas generated by the vacuuming step are mixed as an easily adsorbable component gas.

Further, a reverse charging step is selectively provided between the vacuuming step and the pre-adsorption step, namely:

The reverse charging step: the adsorption bed outlet is connected to the adsorption bed outlet of the pre-adsorption step, and the adsorption bed is reversely pressurized by the gas discharged from the adsorption bed outlet in the pre-adsorption step.

Further, a step of 1 to 2 pressure equalization steps is selectively provided between the recovery step and the pre-adsorption step.

Further, optionally, a step 1 is set after the concentration step, namely:

Step 1 of the process: the adsorption bed outlet is connected with the cleaning gas tank or the outlet side of the adsorption bed of the vacuum cleaning step, and the gas discharged from the adsorption bed and the gas similar to the concentrated exhaust gas at the end of the concentration step is discharged as a cleaning gas to the cleaning gas tank or the vacuum cleaning step. Adsorbent bed

At the same time, a vacuum cleaning step is set after the vacuuming step, namely:

Vacuum cleaning step: while vacuuming the adsorption bed from the inlet side of the adsorption bed, the cleaning gas is introduced from the outlet side of the adsorption bed from the cleaning gas tank or the 1-step adsorption bed, and the total pressure and the cleaning gas are reduced in vacuuming. Under the combined action of pressure, the easily adsorbed components adsorbed on the adsorbent are further desorbed, and the vacuum-cleaning easily adsorbing component gas is obtained from the outlet of the vacuuming device, and the vacuum-cleaning easily adsorbing component gas is mixed into the easily adsorbable component gas.

Further, the step of selectively setting is performed selectively during the execution of the pressure equalization step or the pre-adsorption step, or before or after the pressure-equalization step or the pre-adsorption step, ie:

The step of discharging: the main component which is discharged from the outlet side of the adsorption bed is a gas which is not easily adsorbed, and the adsorbent bed is partially depressurized;

When the step of discharging is included, the raw material gas is separated to obtain a product gas which is not easily adsorbed, a product gas which is easy to adsorb, and a gas stream which is a gas of the gas.

Further, the adsorbent charged in the adsorption bed includes one or a combination of activated alumina, activated carbon, silica gel, molecular sieve, resin, and a functional adsorbent modified with these adsorbents as a carrier.

Further, the number of equalizations including the pressure equalization step and the pressure equalization step is 1 to 10 times.

Further, the adsorption pressure in the adsorption step is 0.1 to 6.0 MPa (g).

Further, the pre-adsorption pressure in the pre-adsorption step is 0.1 to 1.0 MPa (g).

Further, the evacuation pressure of the vacuuming step is -0.05 to -0.099 MPa (g).

As used herein, "shun" or "forward" refers to the direction along which the gas stream is adsorbed; "reverse" or "reverse" refers to the direction against the adsorbed gas stream.

The raw material gas suitable for the pressure swing adsorption separation process of the present invention is a mixed gas composed of two or more gas components, and contains at least one easily adsorbable component having a strong adsorption force with the adsorbent and at least one A kind of non-adsorbing component that has weak adsorption force with the adsorbent. When the raw material gas contains two or more gas components, the mixed component of the gas component having a relatively weak adsorption force with the adsorbent is called a non-adsorbing component, and the adsorption force with the adsorbent is relatively strong. The mixed component of the gas component is referred to as an easily adsorbable component. The object product of the process of the invention may be a product gas which is easy to adsorb component gas, or a product gas which is not easy to adsorb component gas, or a product gas which is easy to adsorb component gas and a product gas which is not easy to adsorb component; sometimes the situation may be more complicated, the purpose In addition to the easy adsorption of component gas, the product also includes some components of the component gas that are not easily adsorbed, and there is also a difference in adsorption between these components and other non-adsorbable components. There are many such gases in actual industrial production that need to be separated and recovered. For example, but not limited to, a hydrogen sulfide product gas and a non-hydrogen fuel gas product gas, or a carbon dioxide gas product and a hydrogen-containing gas, obtained by pressure swing adsorption separation in a synthetic ammonia or hydrogen-producing gas having a main component of hydrogen, carbon dioxide, and other fuel gas components. Product gas; pressure swing adsorption from refinery hydrocarbon-rich hydrogen-rich gas with major components of hydrogen, C ₂ + (hydrocarbon components of 2 or more carbon atoms), light hydrocarbon components and other fuel gas components Separating and obtaining C ₂ + product gas and hydrogen-containing fuel gas product gas, or hydrogen product gas and non-hydrogen fuel gas product gas; from main components are hydrogen, nitrogen, carbon monoxide, methane, carbon dioxide, and hydrocarbon components such as ethane Separation and recovery of carbon monoxide gas product gas and hydrogen-rich gas product gas from water gas after carbon dioxide removal by pressure swing adsorption separation in coke oven gas ; obtaining methane gas from the product gas and C chiefly methane and C ₂ + light hydrocarbons such as natural gas or oil gas in the pressure swing adsorption gas products + _2; from the main component The olefin gas product gas and the nitrogen product gas are obtained by the pressure swing adsorption separation of the gas and olefin components in the polyolefin tail gas; the methane gas product gas is obtained from the medium and low concentration coalbed methane, or the biogas, or the landfill exhaust gas by pressure swing adsorption separation. Most of the systems suitable for pressure swing adsorption separation.

The adsorbent used in the present invention is comprehensively determined according to factors such as the composition of the raw material gas, the requirements of the intended product, the specific process, and the operating conditions. The general selection principle is that the adsorbent component has a large dynamic adsorption capacity and is easy to adsorb components. It has a large separation factor with the non-adsorbable components, and has good mechanical properties and shape. These adsorbents include, but are not limited to, activated alumina, activated carbon, silica gel, molecular sieves, adsorption resins, and the like, or a combination of one or more of various types of functional adsorbents modified with these adsorbents as carriers. The adsorbent bed can be a single adsorbent bed or a composite bed layered with multiple adsorbents. It is not difficult for a technician familiar with the expertise in the field to propose an adsorbent solution suitable for the characteristics of the project according to the specific conditions of the project.

The adsorption pressure refers to the operating pressure of the adsorption bed in the adsorption step. The increase of adsorption pressure is beneficial to increase the gas phase partial pressure of the easily adsorbable components, so it is beneficial to increase the adsorption capacity of the adsorbent to the easily adsorbed components, and also to improve the concentration of the product components which are not easily adsorbed and to improve the easily adsorbed components. The concentration of product logistics. Under normal circumstances, the adsorption pressure is determined comprehensively according to factors such as gas source pressure, specific process requirements, and operating conditions. A suitable adsorption pressure for the present invention is 0.1 to 6.0 MPa (g).

The adsorption temperature refers to the operating temperature of the adsorption bed in the adsorption step, or the operating temperature of the feed gas. Generally, the decrease of the adsorption temperature is beneficial to increase the static adsorption capacity of the adsorbent, and is also slightly advantageous for increasing the dynamic adsorption capacity of the adsorbent. However, in the practice of pressure swing adsorption, there is rarely a practice of specifically lowering the operating temperature simply to increase the adsorption capacity of the adsorbent, because this tends to pay a higher price. A suitable adsorption temperature for the present invention is from 0 to 60 °C.

The pressure equalization step and the pressure equalization step are two interrelated process steps that are widely used in existing pressure swing adsorption techniques. That is, the adsorption bed in the pressure equalization step with higher pressure is connected with the adsorption bed in the pressure equalization step with lower pressure, and the pressure in the adsorption bed is equalized by the pressure difference between the two adsorption beds. A small amount of easily adsorbable component gas which is easy to adsorb component is discharged into the adsorption bed of the pressure equalization step, so that the adsorption front of the easily adsorbable component in the adsorption bed of the pressure equalization step is closer to or breaks through the outlet of the adsorption bed, thereby causing the pressure drop The step adsorption bed is initially concentrated, while recovering the gas discharged by the pressure drop and the pressure energy of the gas. In general, the pressure equalization step is preferably concentrated after the pre-adsorption step, which is advantageous for providing a space for the pre-adsorption step to absorb more concentrated exhaust gas, thereby facilitating the reduction of the adsorption bed pressure of the displacement step and the pre-adsorption step. Or reduce the displacement gas consumption. However, when there are multiple pressure equalization processes in the process, it is also possible to selectively set one or two pressure equalization steps between the recovery step and the pre-adsorption step. The pressure equalization form is not limited to the "upper and upper pressure equalization" of the two adsorption bed outlets. It can also selectively adopt various prior art pressure equalization methods according to specific conditions, such as the pressure equalization step adsorption bed outlet and pressure equalization. The "up and down pressure equalization" of the inlet of the adsorption bed is increased, the "lower and lower pressure equalization" of the inlet of the adsorption bed and the inlet of the adsorption bed of the pressure equalization step, and even the pressure equalization form of the pressure equalization in the middle of the adsorption bed. The pressure equalization method may adopt a direct pressure equalization method in which the adsorption bed is in communication with the adsorption bed, or an indirect pressure equalization method in which the adsorption bed of the pressure equalization step is connected to the intermediate tank. The number of equalization times needs to be determined comprehensively according to factors such as operating conditions and process requirements of the separation system. For the inventive process, the pressure equalization process including the pressure equalization step and the pressure equalization step (1 time pressure drop and 1 pressure equalization constitute a pressure equalization process) is 1 to 10 times.

The concentration step is an important step in obtaining a high concentration of easily adsorbable components. There are two main methods, one is the step by step, and the other is the replacement step, namely:

Stepping step: depressurizing from the outlet side of the adsorption bed, discharging the non-adsorbing components in the adsorption bed, further concentrating the adsorption bed, and discharging the concentrated exhaust gas from the outlet side of the adsorption bed.

Displacement step: introducing an easily adsorbable component product gas from the inlet side of the adsorption bed, and replacing the non-adsorbing component which is adsorbed on the adsorbent and has a weak adsorption force remaining in the empty volume of the adsorption bed by the easily adsorbable component having strong adsorption force The adsorption bed is further concentrated, and the concentrated exhaust gas is discharged from the outlet side of the adsorption bed during the replacement process.

Depending on the characteristics and requirements of the isolate, the concentration step can optionally employ the following preferred protocol:

The concentration step is a sequential step.

The concentration step is a replacement step.

The concentration step is to first arrange the steps and then replace the steps.

The sequential steps referred to in the present invention are similar to, but different from, the prior art sequential steps and the sequential steps of the present invention. The step of discharging and the step of discharging are all venting gas from the outlet side of the adsorption bed; however, the prior art step of discharging and the gas discharged by the step of the present invention are discharged from the pressure swing adsorption unit, and the gas discharged in the step of discharging is The concentrated exhaust gas is discharged into the adsorption bed of the pre-adsorption step in the pressure swing adsorption unit. In order to distinguish from the step of placing, the present invention is referred to as a "stepping step."

The main function of the recovery step is to recover the product gas of the easily adsorbable component. That is, after the concentration step, the easily adsorbable component product gas stream is obtained from the inlet side of the adsorption bed by lowering the adsorption bed pressure. When the adsorption bed pressure is higher than atmospheric pressure after the concentration step, the depressurization process can adopt a reverse displacement step, namely:

Reverse reaction step: reverse pressure reduction from the inlet side of the adsorption bed until the pressure of the adsorption bed is equal to or close to atmospheric pressure, and the adsorbable component adsorbed on the adsorbent is desorbed to obtain a gas which is easy to adsorb and adsorb.

When the adsorption bed pressure has reached or approached atmospheric pressure after the concentration step or the reverse reaction step, and the adsorption bed pressure needs to be further reduced, the pressure reduction process may adopt a vacuuming step, namely:

Vacuuming step: vacuuming the adsorption bed from the inlet side of the adsorption bed with a vacuuming device, vacuuming the adsorption bed to a vacuum pressure lower than atmospheric pressure, desorbing the adsorbable components adsorbed on the adsorbent, and pumping The vacuum equipment outlet obtains a vacuum-adsorbable component gas.

Therefore, the recycling step can selectively adopt the following preferred schemes:

The recycling step is a reverse step.

The recovery step is a vacuuming step.

The recovery step is a reverse step followed by a vacuum step.

The concentration step and the pre-adsorption step are two interrelated process steps and are the process steps of the present invention that are most different from the prior art. That is, the adsorption bed outlet of the concentration step is connected with the inlet of the adsorption bed of the pre-adsorption step, and the concentrated exhaust gas containing a certain amount of easily adsorbable components discharged from the adsorption bed in the concentration step is discharged into the adsorption bed of the pre-adsorption step. The easily adsorbable component in the adsorption bed of the concentration step is sufficiently concentrated so that the easily adsorbable component product obtained in the subsequent recovery step reaches a sufficiently high concentration. After the concentrated exhaust gas discharged from the concentration step is discharged into the adsorption bed of the pre-adsorption step, the easily adsorbable component is adsorbed by the lower adsorbent in the adsorption bed of the pre-adsorption step, and the adsorbent component is not easily adsorbed into the adsorption bed, and the pre-adsorption step is simultaneously performed. The adsorption bed pressure is increased.

The pre-adsorption step is substantially identical to the prior art adsorption step. In the adsorption step of the prior art, the mixed gas of the easily adsorbable component and the non-adsorbing component enters from the inlet side of the adsorption bed, wherein the easily adsorbable component is adsorbed by the adsorbent, and the non-adsorbed component passes through the adsorbent bed from the outlet. The side is discharged, and the adsorption pressure is substantially constant throughout the adsorption process. However, in the pre-adsorption step of the present invention, after the concentrated exhaust gas enters the adsorption bed from the inlet side, the easily adsorbable component is adsorbed by the lower adsorbent, and the non-adsorbing component may not necessarily be discharged from the outlet side of the adsorption bed, in most cases The partially or all of the non-adsorbing components remain in the adsorbent bed, so that the pressure of the adsorbent bed in the pre-adsorption step is gradually increased.

The reason why the inventors call "pre-adsorption" is because, for the easily adsorbed component, after the recovery step, the adsorption amount of the easily adsorbable component on the adsorbent reaches the lowest value, and the adsorption step in the next adsorption cycle is adsorbed. Before the adsorption amount of the easily adsorbable component reaches the highest value, the adsorption bed preliminarily adsorbs the easily adsorbable component in the concentrated exhaust gas. Corresponding to the easily adsorbed component in the concentrated exhaust gas, the partial dynamic adsorption capacity of the adsorbent is preempted.

It is because the adsorption bed of the pre-adsorption step absorbs all the concentrated exhaust gas of the concentration step, so that the concentrated exhaust gas does not discharge the pressure swing adsorption unit, thereby significantly increasing the yield of the easily adsorbable component product and the non-adsorbable component product. Since there is a pre-adsorption step to "concentrate" the concentrated exhaust gas, the concentration step may exhaust as much as possible of the non-adsorbed components in the adsorption bed, so that the easily adsorbable components in the adsorption bed are sufficiently concentrated, so that The recovery step yields a sufficiently high concentration of readily adsorbable component product gas. As long as each regeneration step can regenerate the adsorption bed sufficiently thoroughly, and at the same time, the adsorption front of the adsorption component is controlled to prevent the adsorption front from penetrating the adsorption bed, and a sufficiently high concentration of the product gas which is not easily adsorbed can be obtained in the adsorption step. Thereby achieving a clear division of the easily adsorbable component and the less susceptible component. Compared with the prior art, the process flow of the process of the invention is simpler, and the investment and operation cost are lower, since the replacement exhaust gas compressor is omitted or the separately arranged replacement waste pressure swing adsorption recovery unit is omitted.

In order to better reduce the adsorbent component entering the adsorbent bed and the pressure change of the adsorbent bed is more gentle, or let a small amount of easily adsorbed components adsorbed on the upper adsorbent bed move further downward to obtain a higher concentration in the adsorption step. It is difficult to adsorb the product gas of the component, and the reverse charging step can be selectively set before the pre-adsorption step, and the adsorption bed outlet is used by the pre-adsorption step. The non-adsorbed component gas discharged from the side is used to pressurize the adsorption bed, that is:

The reverse charging step: connecting the outlet of the adsorption bed with the outlet of the adsorption bed of the pre-adsorption step, and charging the adsorption bed with the gas which is not easily adsorbed by the outlet of the adsorption bed in the pre-adsorption step.

The reverse charging step is similar but different from the final charging steps of the prior art and the inventive process. The final charging step of the prior art is to introduce a portion of the non-adsorbable component gas from the outlet side of the adsorption bed to pressurize the adsorption bed to the adsorption pressure. The reverse charging step of the present invention is to introduce the pre-adsorption step adsorption bed outlet gas from the outlet side until the pressure equilibrium is achieved with the adsorption bed of the pre-adsorption step, so that the reverse charging step here is more like a pressure equalization step, but only then The pre-adsorption step associated with the reverse charging step may also be receiving concentrated exhaust gas at the same time.

Further studies of the process of the present invention have shown that the vacuum cleaning step is provided after the vacuuming step, which facilitates a clearer separation of the readily adsorbable component and the less readily adsorbable component. The vacuum cleaning step mentioned here is that in the later stage of the vacuuming step, a small amount of gas having a similar composition to the concentrated exhaust gas discharged at the end of the concentration step is introduced from the outlet side of the adsorption bed as a cleaning gas, and the concentration of the easily adsorbable component is not too high. The cleaning gas passes through the adsorption bed from top to bottom in a vacuum state, and the partial pressure of the adsorbent component in the gas phase of the adsorption bed is lowered by the cleaning gas, so that a part of the easily adsorbable component is further desorbed from the adsorbent.

From the viewpoint of simply improving the recovery rate of the easily adsorbable components, the cleaning gas used as the vacuum cleaning step may be a gas having a relatively low concentration of various easily adsorbable components in the process, such as a pressure equalization step exhaust gas, a smooth exhaust gas, By venting gas, etc., the concentration of easily adsorbable components in these gases is relatively low, so that the vacuum cleaning effect is better, which is advantageous for improving the recovery rate of easily adsorbed components. However, from the viewpoint of improving the recovery rate of the easily adsorbable component and increasing the gas concentration of the easily adsorbable component, it is more advantageous to use a gas having a composition similar to that of the replacement exhaust gas discharged at the end of the concentration step.

Therefore, it is possible to selectively set the 1 step after the concentration step, namely:

When the concentration of the easily adsorbable component in the raw material gas is relatively low, and the easily adsorbable component is the target product component, the non-adsorbing component is not the target product component, or the non-adsorbing component is not the target product component. Can be selectively Before or after the pressure drop step, or in the pre-adsorption step or after the pre-adsorption step, a downstream step is provided, and a certain amount of the non-adsorbable component is enriched from the outlet side of the adsorption bed, or is rich in non-target product components. Probable gas that is not easily adsorbed, ie:

The step of discharging: the main component which is discharged from the outlet side of the adsorption bed is a gas which is not easily adsorbed, and the adsorbent bed is partially depressurized.

When the step of discharging is included, the raw material gas is separated by pressure swing adsorption to obtain a product gas which is easy to adsorb component gas, a product gas which is not easily adsorbed, and a gas stream which is a gas product of the gas.

The step of setting the discharge step can effectively reduce the adsorption bed pressure of the replacement step and the pre-adsorption step or reduce the amount of replacement gas, thereby reducing the investment and operation cost, and also improving the flexibility of the process operation, although this may be somewhat reduced. Recovery of adsorbed components, but sometimes doing so may be economically cost effective.

According to the experimental research on the process of the present invention, the process of the invention can not only achieve the purpose of cleaning and separating the easily adsorbable components and the components which are not easily adsorbed, but also has better flexibility in practical operation. In general, reducing the feed amount or shortening the switching time is beneficial to increase the recovery rate of the easily adsorbable components, but it is not conducive to increasing the concentration of the easily adsorbable components; increasing the displacement gas volume or increasing the pre-adsorption pressure is beneficial to improving the easy adsorption group. The concentration of the product is divided, but it has an effect on improving the recovery rate of the easily adsorbable component. Therefore, in practice, according to the condition of the raw material gas, the quality and yield requirements of the easily adsorbable component product, and the quality and yield requirements of the non-adsorbable component can be flexibly adjusted, such as the feed amount, the switching time or the replacement gas amount.

The pressure swing adsorption process including the concentrated exhaust gas pre-adsorption step of the present invention will be further described below in conjunction with the verification test of the present invention and the flow thereof. It is to be understood that the following examples are only intended to facilitate a better understanding of the present invention, and are not to be construed as limiting the scope of the invention to the embodiments, the various alternatives and Variations are included within the scope of the invention.

DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing the process flow of a pressure swing adsorption process verification test comprising a concentrated exhaust gas pre-adsorption step of the present invention.

detailed description

The test device process flow is shown in Figure 1. There are 8 adsorption beds in the test device, numbered A, B, C, D, E, F, G, H. The adsorption bed size is Φ50*500mm, and a cleaning gas tank numbered D1. The on-off valve used in the test device is a solenoid valve. There are 5 sets of valves on the inlet side of each adsorption bed, numbered V1*~V5* (* represents the omitted adsorption bed number); there are 4 sets of valves on the outlet side of each adsorption bed. , numbered V6*~V9*. For the sake of simplicity, the measurement and control instruments such as pressure, flow, temperature, concentration, and regulating valve in the actual test device, as well as some auxiliary equipment and valves, are omitted in the flow chart.

Example 1

The test raw material gas is a mixed gas of hydrogen, nitrogen and ethylene, and the composition of the raw material gas is shown in Table 1-1.

Table 1-1 Example 1 composition gas composition

组成composition	氢气(v％)Hydrogen (v%)	氮气(v％)Nitrogen (v%)	乙烯(v％)Ethylene (v%)	合计(v％)Total (v%)
原料气Raw gas	45.1345.13	30.3730.37	24.524.5	100100

Ethylene in the feed gas is representative of the easily adsorbable component. Hydrogen and nitrogen are representative of the non-adsorbable component. The feed gas pressure is 800 KPa (g), the temperature is normal temperature, and the feed flow rate is 9 NL/min (L/min). The displacement gas flow rate was 1.4 NL/min.

The lower layer of the adsorption bed is filled with activated carbon 300mm, and the upper layer is filled with 5A molecular sieve 200mm.

The process sequence includes two equalization steps, the concentration step includes a sequential step and a displacement step; the recovery step includes a reverse step and a vacuum step; and a reverse charge step is provided prior to the pre-adsorption step.

Table 1-2 is a flow chart of the adsorption bed operation of Example 1.

In the table: A: adsorption step E1D: one step of equalization

E2D: two equalization steps PD: alignment steps

RP: replacement step D: reverse step

V: vacuuming step R: reverse charging step

A0: pre-adsorption step E2R: two-average step

I: vacant step E1R: one step up

FR: Final charging step

Table 1-2 Example 1 adsorption bed operation timing chart

Each pressure swing adsorption cycle is divided into 24 time periods, each time period is 50s, which is equivalent to 1200s per cycle. The following takes the A adsorption bed as an example to explain the operation of the entire device.

In the first to third periods, the adsorption bed (A) is in the adsorption step A. At this time, the inlet valve (V1A) and the outlet valve (V9A) of the adsorption bed (A) are opened, and the remaining valves are closed (the valve that is not opened is not shown below), and the feed gas is introduced into the adsorption bed from the inlet of the adsorption bed, and the adsorption bed The operating pressure was 800 KPa (g) and the operating temperature was 25 °C. During the process of passing through the adsorption bed, ethylene having a strong adsorption force in the raw material gas is adsorbed as an easily adsorbable component by the adsorbent, and hydrogen and nitrogen having a weak adsorption force pass through the adsorption bed as a hydrogen-rich product gas from the adsorption bed. (A) The outlet is discharged, and after being depressurized by a pressure control valve (not shown), the pressure swing adsorption unit is discharged in the direction indicated by the arrow (2). When the adsorption time of the adsorption bed (A) reaches 150 s, the operation is switched.

In the fourth period, the adsorption bed (A) is in a step of equalizing E1D. Open the valve (V7A) and the valve (V7C), and connect the adsorption bed (A) with the adsorption bed (C) in a uniform rise to achieve a uniform drop in the adsorption bed (A). A pressure equalization process is a complete pressure equalization process. After a uniform drop, the pressure of the adsorbent bed (A) drops to 630 KPa (g).

In the fifth period, the adsorption bed (A) is in the second equalization step E2D, and the valve (V7A) is continuously opened and the valve (V7D) is opened to connect the adsorption bed (A) with the adsorption bed (D) in the second homogenization step, so that The adsorption bed (A) achieves a two-average drop. The two pressure equalization process is a complete pressure equalization process, and the pressure of the adsorption bed (A) is reduced to 465 KPa (g).

After one equalization and two equalization, most of the hydrogen and nitrogen in the adsorption bed are discharged, and the ethylene adsorption front has broken through the outlet of the adsorption bed, and the adsorption bed (A) is initially concentrated.

In the sixth period, the adsorption bed (A) is in the sequential step PD. The valve (V6A) and the valve (V5E) are opened, and the outlet gas of the adsorption bed (A) is discharged through the replacement waste gas line (6) to the inlet of the adsorption bed (E) in the pre-adsorption step.

During the 7th to 9th periods, the adsorption bed (A) is in the replacement step RP. In the 7th period, open the valve (V4A), valve (V6A) and valve (V5E), open the valve (V4A), valve (V6A) and valve (V5F) during the 8th to 9th period, with the compressor (5 The pressurized ethylene product gas is substituted for the adsorption bed (A). Since the adsorption force between ethylene and the adsorbent is greater than the adsorption force of hydrogen and nitrogen, during the replacement process, the hydrogen and nitrogen adsorbed on the adsorbent in the adsorbent bed and the empty volume of the adsorbent bed are replaced together with a part of ethylene as a replacement. The exhaust gas is discharged into the adsorbent bed (E) in the pre-adsorption step at the 7th period via the line (6), and discharged into the adsorbent bed (F) in the pre-adsorption step at the 8th period. The amount of displacement gas in the displacement step and the pressure of the adsorption bed at the end of the displacement step are determined according to the concentration requirements of the adsorption bed. The displacement gas flow rate of this example was 1.3 NL/min, and the displacement pressure was 300 KPa (g).

During the 10th to 12th periods, the adsorption bed (A) is in the reverse step D. Open the valve (V3A) and gradually reduce the operating pressure of the adsorbent bed (A) to the atmospheric pressure near atmospheric pressure. During the depressurization and depressurization process, as the pressure is reduced, the ethylene component adsorbed on the adsorbent is gradually desorbed, and the ethylene product gas is reversed.

During the 13th to 15th periods, the adsorption bed (A) is in the vacuuming step V. Open the valve (V2A) and use the vacuum pump (4) The adsorption bed (A) was evacuated, and the pressure of the adsorption bed (A) was gradually evacuated to a vacuum pressure of -90 KPa (g). During the vacuuming process, as the pressure is reduced, the ethylene component adsorbed on the adsorbent is further desorbed, and the obtained vacuumed ethylene product gas is pressurized by the vacuum pump (4), and then mixed with the ethylene product gas after the reverse discharge step. A part of the adsorbent bed in the displacement step is returned as the replacement gas, and the remainder is discharged as the ethylene product gas in the direction indicated by the arrow (3).

In the 16th period, the adsorption bed (A) is in the reverse charging step R. Open the valve (V8A) and the valve (V8H), connect the adsorption bed (A) with the adsorption bed (H) in the pre-adsorption step, and pressurize the adsorption bed (A) with the outlet gas of the adsorption bed (H) in the pre-adsorption step. The adsorption bed (A) is gradually pressurized to a pressure of about 150 KPa (g).

During the 17th to 19th periods, the adsorption bed (A) is in the pre-adsorption step A0. Open the valve (V5A), open the valve (V4D) and (V6D) in the 17th to 18th period, and fill the displacement exhaust gas discharged from the adsorption bed (D) in the replacement step into the adsorption bed (A); The valves (V4E) and (V6E) are opened to discharge the displacement exhaust gas discharged from the adsorption bed (E) in the displacement step into the adsorption bed (A), and the pressure of the adsorption bed (A) is gradually increased to 300 KPa (g).

In fact, it is the pre-adsorption step of the 17th to 19th period and the reverse charging step of the 16th period that absorbs the concentrated exhaust gas discharged from the adsorption bed in the sequential step and the replacement step, so that the adsorption bed pressure is raised from -90 KPa (g) to At 300 KPa (g), the concentrated exhaust gas discharged from the sequential and replacement steps is absorbed in the pressure swing adsorption unit, which is the most prominent feature of the process of the present invention and the prior art.

In the 20th period, the adsorption bed (A) is in the second equalization step E2R. Open the valve (V7A) and the valve (V7F), connect the adsorption bed (A) with the adsorption bed (F) in the second equalization step, and make the adsorption bed (A) achieve two equal rises. After the second equalization step, the adsorption bed is completed. (A) The pressure rises to 465 KPa (g).

In the 21st period, the adsorption bed (A) is in the vacant step I. During this period, all inlet and outlet valves of the adsorption bed (A) are closed, and the adsorption bed maintains the original state.

In the 22nd period, the adsorption bed (A) is in a uniform rising step E1R. Open the valve (V7A) and the valve (V7G), connect the adsorption bed (A) with the adsorption bed (G) in a step of equalization, so that the adsorption bed (A) achieves a uniform rise, and the adsorption bed after the end of one equalization step (A) The pressure rises to 630 KPa (g).

During the 23rd to 24th periods, the adsorption bed (A) is in the final charging step FR. Open the valve (V8A) and the valve (11), and gradually pressurize the adsorption bed (A) with a hydrogen-rich product gas to an adsorption pressure of 800 KPa (g).

At this point, the adsorption bed (A) ends with one adsorption cycle and then circulates to the next adsorption cycle.

The adsorption bed (B), the adsorption bed (C), the adsorption bed (D), the adsorption bed (E), the adsorption bed (F), the adsorption bed (G), and the adsorption bed (H) are also in the same manner in the PLC Under the logic control, the operations are sequentially switched according to the timing steps shown in Table 1-2 to achieve the continuity of the entire adsorption desorption process.

After the raw material gas is separated by the above pressure swing adsorption process, a hydrogen-rich product gas and an ethylene product gas are obtained. Ethylene product gas The concentration is 93.42v%, the ethylene concentration in the hydrogen-rich product gas is 1.05v%, the recovery of ethylene component is 96.80%, and the recovery rate of hydrogen nitrogen is 97.68%. The composition, flow rate and component recovery rate of each stock are shown in Table 1-3.

Table 1-3 Example 1 raw material and product composition, flow rate, recovery data table

Example 2

The test raw material gas is a mixed gas of hydrogen, nitrogen and ethylene, and the composition of the raw material gas is shown in Table 2-1.

Table 2-1 Example 2 composition gas composition

组成composition	氢气(v％)Hydrogen (v%)	氮气(v％)Nitrogen (v%)	乙烯(v％)Ethylene (v%)	合计(v％)Total (v%)
原料气Raw gas	51.3251.32	29.0129.01	19.6719.67	100100

Ethylene in the feed gas is representative of the easily adsorbable component. Hydrogen and nitrogen are representative of the non-adsorbable components. The main components for recovery are ethylene and hydrogen. The feed gas pressure is 800 KPa (g), the temperature is normal temperature, and the feed flow rate is 9NL/min, displacement gas flow 0.7NL/min.

The process comprises a concentrated exhaust gas pre-adsorption step; comprising 2 pressure equalization; the concentration step comprises a displacement step; the recovery step comprises a reverse step and a vacuum step; and the reverse charging step is included. The biggest difference from Embodiment 1 is that a step of placing is provided between a step of equalizing and a step of equalizing the two.

Table 2-2 is a flow chart of the adsorption bed operation of Example 2.

In the table: A: adsorption step E1D: one step of equalization

PP: Follow-up step E2D: Two equal steps

RP: replacement step D: reverse step

V: vacuuming step R: reverse charging step

A0: pre-adsorption step I: vacant step

E2R: two equal steps E1R: one step up

FR: Final charging step

Table 2-2 Example 2 adsorption bed operation timing chart

Each pressure swing adsorption cycle is divided into 24 time periods, each time period is 50s, which is equivalent to 1200s per cycle. The following takes the A adsorption bed as an example to explain the operation of the entire device. Since the present embodiment is identical to the main process flow and most of the timing steps of Embodiment 1, the discussion of the same portions will be omitted for the sake of simplicity.

In the first to third periods, the adsorption bed (A) is in the adsorption step A. This step is the same as in the first embodiment.

In the fourth period, the adsorption bed (A) is in a step of equalizing E1D. This step is basically the same as Embodiment 1. The difference is that after one drop, the pressure on the adsorbent bed (A) drops to 520 KPa (g).

In the fifth period, the adsorption bed (A) is in the step of discharging PP. Open the valve (V7A) and open the valve (V10) to reduce the pressure of the adsorbent bed to 350KPa(g). Discharge the discharged gas in the direction indicated by the arrow (7).

In the sixth period, the adsorption bed (A) is in the second equalization step E2D. This step is basically the same as Embodiment 1. The difference is that the pressure of the adsorption bed (A) drops to 250 KPa (g) after the three-average drop.

During the 7th to 9th periods, the adsorption bed (A) is in the replacement step RP. This step is basically the same as Embodiment 1. The difference is replacement The displacement gas flow rate of the step was 0.7 NL/min, and the pressure of the adsorption bed (A) at the end of the displacement step was 150 KPa (g).

During the 10th to 12th periods, the adsorption bed (A) is in the reverse step D. This step is the same as in the first embodiment.

During the 13th to 15th periods, the adsorption bed (A) is in the vacuuming step V. This step is the same as in the first embodiment.

In the 16th period, the adsorption bed (A) is in the reverse charging step R. This step is basically the same as Embodiment 1. The difference is that the adsorption bed (A) is gradually boosted to 50 KPa (g) after the end of the reverse charging step.

During the 17th to 19th periods, the adsorption bed (A) is in the pre-adsorption step A0. This step is basically the same as Embodiment 1. The difference is that at the end of the pre-adsorption step, the pressure of the adsorbent bed (A) is gradually increased to 150 KPa (g).

In the 20th period, the adsorbent bed (A) is in the vacant step I. This step is the same as in the first embodiment.

In the 21st period, the adsorption bed (A) is in the second equalization step E2R. This step is basically the same as Embodiment 1. The difference is that at the end of the second homogenization step, the pressure of the adsorbent bed (A) is gradually increased to 250 KPa (g).

In the 22nd period, the adsorption bed (A) is in a uniform rising step E1R. This step is basically the same as Embodiment 1. The difference is that the adsorption bed (A) pressure rises to 520 KPa (g) after the end of the homogenization step.

During the 23rd to 24th periods, the adsorption bed (A) is in the final charging step FR. This step is the same as in the first embodiment.

The adsorption bed (B), the adsorption bed (C), the adsorption bed (D), the adsorption bed (E), the adsorption bed (F), the adsorption bed (G), and the adsorption bed (H) are also in the same manner in the PLC Under the logic control, the operations are sequentially switched according to the timing steps shown in Table 2-2 to achieve the continuity of the entire adsorption desorption process.

Since the discharge step is set in the pressure equalization stage, a part of the hydrogen-rich gas component is discharged as the gas, so that the pressure of the adsorption bed is lowered, and the displacement of the replacement gas and the replacement pressure are reduced, thereby achieving a reduction in investment and The effect of energy saving. A similar effect can be obtained if the step of setting is performed at the same time as the pre-adsorption step or after the pre-adsorption step.

After the raw material dry gas is separated by the above pressure swing adsorption process, an ethylene product gas, a hydrogen rich product gas and a three-stream gas are obtained. The concentration of ethylene component in the ethylene product gas recovered from the target product is 92.37v%, the concentration of ethylene component in the hydrogen-rich gas product gas and the gas in the purge gas is 1.32v% and 3.44v%, respectively, and the ethylene component recovery rate is 93.9%. The component recovery rate was 98.3%. The composition, flow rate and component recovery rate of each stock are shown in Table 2-3.

Table 2-3 Example 2 raw material and product composition, flow rate, recovery data table

Example 3

The test raw material gas is a mixed gas of hydrogen, nitrogen and ethylene, and the composition of the raw material gas is shown in Table 3-1.

Table 3-1 Example 3 composition of raw material gas

组成composition	氢气(v％)Hydrogen (v%)	氮气(v％)Nitrogen (v%)	乙烯(v％)Ethylene (v%)	合计(v％)Total (v%)
原料气Raw gas	47.3147.31	24.5524.55	28.1428.14	100100

Ethylene in the feed gas is representative of the easily adsorbable component. Hydrogen and nitrogen are representative of the non-adsorbable components. The main components for recovery are ethylene and hydrogen. The feed gas pressure is 800 KPa (g), the temperature is normal temperature, and the feed flow rate is 9 NL/min, displacement gas flow 1.2 NL / min.

The process comprises a concentrated exhaust gas pre-adsorption step; comprising 2 pressure equalization; the concentration step comprises a displacement step; the recovery step comprises a reverse step and a vacuum step; and the reverse charging step is included. The biggest difference from Example 1 is that the process includes a 1 step and a vacuum cleaning step.

Table 3-2 is a flow chart of the adsorption bed operation of Example 3.

In the table: A: adsorption step E1D: one step of equalization

E2D: two equalization steps PD: alignment steps

RP/PP1: Replacement/Shun 1 step D: Reverse step

V: vacuuming step VP: vacuum cleaning step

R: reverse charging step A0: pre-adsorption step

E2R: two equal steps Step I: vacant step

E1R: One step up FR: Final charge step

Table 3-2 Example 3 adsorption bed operation schedule

In the fourth period, the adsorption bed (A) is in a step of equalizing E1D. This step is the same as in the first embodiment.

In the fifth period, the adsorption bed (A) is in the second equalization step E2D. This step is the same as in the first embodiment.

In the sixth period, the adsorption bed (A) is in the sequential step PD. This step is the same as in the first embodiment.

In the 7th to 9th periods, the adsorption bed (A) is in the replacement step and the step 1 is RP/PP1. The replacement step in this period is the same as the replacement step in the first embodiment. However, by the end of the ninth period, the adsorbent bed is transferred to the first step of the discharge. Continue to open the valve (V4A) and valve (V6A), and at the same time open the valve (V12), discharge the gas discharged from the adsorption bed (A) into the cleaning gas tank (D1) as the cleaning gas, (the length of the execution step 1 step according to the upper The difference in the pressure of the cleaning tank in one cycle is automatically adjusted by the PLC control program. The amount of exhaust gas discharged by the first stage is adjusted by the hand valve (not shown).

During the 13th to 14th periods, the adsorption bed (A) is in the vacuuming step V. This step is basically the same as Embodiment 1. The difference is that the vacuuming step of this embodiment is carried out for 2 periods, and the vacuuming pressure is about -80 KPa (g).

In the 15th period, the adsorption bed (A) is in the vacuum cleaning step VP. Continue to open the valve (V2A), continue to vacuum the adsorption bed (A) with a vacuum pump, open the valve (V4) and valve (V7A), and purge the cleaning gas in the cleaning gas tank (D1) from the adsorption bed (A). The side is introduced into the adsorption bed (the purge gas flow rate is adjusted by the hand valve (not shown)), and the ethylene component adsorbed on the adsorbent is further desorbed under the combined action of the vacuum negative pressure and the purge gas lowering partial pressure. The pressure of the adsorption bed (A) is gradually evacuated to a vacuum pressure of about -0.09 MPa (g). The vacuum pump outlet was vacuum-cleaned and the C2+ component gas was also mixed into the mixed ethylene product gas, and the subsequent procedure was substantially the same as in Example 1.

In the 16th period, the adsorption bed (A) is in the reverse charging step R. This step is the same as in the first embodiment.

During the 17th to 19th periods, the adsorption bed (A) is in the pre-adsorption step A0. This step is the same as in the first embodiment.

In the 20th period, the adsorption bed (A) is in the second equalization step E2R. This step is the same as in the first embodiment.

In the 21st period, the adsorption bed (A) is in the vacant step I. This step is the same as in the first embodiment.

In the 22nd period, the adsorption bed (A) is in a uniform rising step E1R. This step is the same as in the first embodiment.

The adsorption bed (B), the adsorption bed (C), the adsorption bed (D), the adsorption bed (E), the adsorption bed (F), the adsorption bed (G), and the adsorption bed (H) are also in the same manner in the PLC Under the logic control, the operations are sequentially switched according to the timing steps shown in Table 3-2 to achieve the continuity of the entire adsorption desorption process.

Compared with Example 1, the ethylene component recovery rate and the ethylene product gas concentration in this example were both improved due to the provision of the purge 1 and vacuum cleaning steps.

After the raw material dry gas is separated by the above pressure swing adsorption process, two streams of ethylene product gas and hydrogen-rich product gas are obtained. The ethylene product concentration of the ethylene product gas recovered in the recovered product is 94.26 v%, the ethylene component concentration in the hydrogen-rich product gas is 0.92 v%, and the ethylene component recovery rate is 97.68%. The logistics composition, flow rate and component recovery rate of each stock are shown in Table 3-3.

Table 3-3 Example 3 raw material and product composition, flow rate, recovery data table

Claims

The pressure swing adsorption process is characterized in that: in a pressure swing adsorption unit, at least a raw material gas is separated into a product gas which is easy to adsorb component gas and a product gas which is not easy to adsorb component gas, and the pressure swing adsorption device is provided with At least two adsorbent beds filled with adsorbent, each adsorbent bed is alternately operated according to a set timing step, and each adsorbent bed is subjected to at least the following steps in sequence:

a. adsorption step: introducing a raw material gas from the inlet of the adsorption bed into the adsorption bed, and the raw material gas passes through the adsorption bed at the adsorption pressure and the adsorption temperature, wherein the easily adsorbable component is adsorbed by the adsorbent packed in the adsorption bed to remove The easily adsorbable component gas of the easily adsorbable component is discharged from the outlet of the adsorption bed, and part of it is returned to the adsorption bed as a final charge back to the final charge step, and the remaining part is discharged as a product of the non-adsorbable component, and the adsorption front of the adsorbent bed is easily adsorbed. When the penetrating adsorption bed is approached, the adsorption is stopped;

b. Pressure equalization step: the adsorption bed outlet is connected with other adsorption beds or other intermediate tanks in the pressure equalization step, so that the adsorption bed is gradually depressurized, and the adsorption bed contains a small amount of easily adsorbable components. The gas is discharged to a pressure equalization step adsorption bed or other intermediate tank to obtain a preliminary concentration of the adsorption bed;

c. Concentration step: the adsorption bed outlet is connected with the inlet of the adsorption bed in the pre-adsorption step, and the adsorption bed is not easily adsorbed, so that the adsorption bed is sufficiently concentrated, and the adsorbent bed contains the easily adsorbable component during the concentration process. The concentrated exhaust gas is discharged to the adsorption bed of the pre-adsorption step;

d. Recovery step: reverse-pressure reduction from the inlet side of the adsorption bed, the easily adsorbed component adsorbed on the adsorbent is gradually desorbed during the depressurization process, and the depressurization process obtains an easily adsorbable component gas or directly as an easily adsorbable component product. The gas is discharged, or a part of it is returned to the adsorption step of the concentration step as a replacement gas, and the remaining part is discharged as a product of the easily adsorbable component;

e. Pre-adsorption step: receiving the concentrated exhaust gas discharged from the adsorption bed in the concentration step from the inlet side of the adsorption bed, the easily adsorbed component in the concentrated exhaust gas is adsorbed by the adsorbent under the adsorption bed, and the component which is not easily adsorbed enters the adsorption bed layer, in the process The adsorption bed pressure is gradually increased to the pre-adsorption pressure;

f. Pressure equalization step: the adsorption bed is connected with the adsorption bed or other intermediate tank in the pressure equalization step, so that the adsorption bed is partially pressurized, and the easily adsorbed components and the non-adsorbed component gases are recovered;

g. Final charging step: introducing part of the non-adsorbable component gas obtained in the adsorption step as a final aeration from the outlet side of the adsorption bed into the adsorption bed, and charging the adsorption bed to the adsorption pressure;

h. Cycle steps a to g.
The process flow according to claim 1, wherein the concentration step comprises a step of aligning, namely:

Stepping step: depressurizing from the outlet side of the adsorption bed, exhausting the non-adsorbing components in the adsorption bed, so that the easily adsorbable components in the adsorption bed are sufficiently concentrated, and the concentrated exhaust gas is discharged from the outlet side of the adsorption bed.
The process flow according to claim 1 wherein the concentration step comprises a replacement step, namely:

Displacement step: introducing a part of the easily adsorbable component gas from the inlet side of the adsorption bed as a replacement gas, and replacing the non-adsorbing component adsorbed on the adsorbent and the empty volume of the adsorbent bed with the easily adsorbable component having strong adsorption force, so that The easily adsorbable component in the adsorbent bed is sufficiently concentrated, and the concentrated exhaust gas is discharged from the outlet side of the adsorption bed during the replacement process.
The process according to claim 1, wherein the concentrating step comprises the steps of aligning and then replacing, ie:

Stepping step: depressurizing the pressure from the outlet side of the adsorption bed, discharging the non-adsorbing components in the adsorption bed, so that the easily adsorbable components in the adsorption bed are further concentrated, and discharging the exhaust gas from the outlet side of the adsorption bed;

Displacement step: introducing a part of the easily adsorbable component gas from the inlet side of the adsorption bed as a replacement gas, and replacing the non-adsorbing component adsorbed on the adsorbent and the empty volume of the adsorbent bed with the easily adsorbable component having strong adsorption force, so that The easily adsorbable component in the adsorption bed is sufficiently concentrated, and the replacement exhaust gas is discharged from the outlet side of the adsorption bed during the replacement process;

Wherein, the exhaust gas generated by the sequential step and the replacement exhaust gas produced by the displacement step are separately or mixed as a concentrated exhaust gas and discharged into the adsorption bed of the pre-adsorption step.
The process of claim 1 wherein the recycling step comprises a reverse step, namely:

The reverse reaction step: reversely depressurizes from the inlet side of the adsorption bed until the pressure of the adsorption bed is equal to or close to the atmospheric pressure, and the adsorbable component adsorbed on the adsorbent is desorbed to obtain an easily adsorbable component gas.
The process of claim 1 wherein the recovering step comprises a vacuuming step, namely:

Vacuuming step: vacuuming the adsorption bed from the inlet side of the adsorption bed with a vacuuming device, vacuuming the adsorption bed to a vacuum pressure lower than atmospheric pressure, desorbing the adsorbable components adsorbed on the adsorbent, and pumping The vacuum equipment outlet obtains an easily adsorbable component gas.
The process of claim 1 wherein the recovering step comprises the step of first depressing and then the step of evacuating, ie:

Reverse reaction step: reverse pressure reduction from the inlet side of the adsorption bed until the pressure of the adsorption bed is equal to or close to atmospheric pressure, desorbing the adsorbable component adsorbed on the adsorbent, and obtaining the gas which is easy to adsorb and adsorb the component;

Vacuuming step: vacuuming the adsorption bed from the inlet side of the adsorption bed with a vacuuming device, vacuuming the adsorption bed to a vacuum pressure lower than atmospheric pressure, desorbing the adsorbable components adsorbed on the adsorbent, and pumping The vacuum equipment outlet obtains a vacuum-adsorbable component gas;

Wherein, the reverse-adsorbing component gas generated by the reverse-releasing step and the vacuum-adsorbable component gas generated by the vacuuming step are mixed as an easily adsorbable component gas.
The process according to claim 1, wherein a reverse charging step is provided between the vacuuming step and the pre-adsorption step, namely:

The reverse charging step: the adsorption bed outlet is connected to the adsorption bed outlet of the pre-adsorption step, and the adsorption bed is reversely pressurized by the gas discharged from the adsorption bed outlet in the pre-adsorption step.
The process according to claim 1, wherein a step of averaging one to two times is provided between the recovery step and the pre-adsorption step.
The process according to claim 1 or 6 or 7, wherein the step of setting is performed after the concentration step, namely:

Step 1 of the process: the adsorption bed outlet is connected with the cleaning gas tank or the outlet side of the adsorption bed of the vacuum cleaning step, and the gas discharged from the adsorption bed and the gas similar to the concentrated exhaust gas at the end of the concentration step is discharged as a cleaning gas to the cleaning gas tank or the vacuum cleaning step. Adsorbent bed

At the same time, a vacuum cleaning step is set after the vacuuming step, namely:

Vacuum cleaning step: while vacuuming the adsorption bed from the inlet side of the adsorption bed, the cleaning gas is introduced from the outlet side of the adsorption bed from the cleaning gas tank or the 1-step adsorption bed, and the total pressure and the cleaning gas are reduced in vacuuming. Under the combined action of pressure, the easily adsorbed components adsorbed on the adsorbent are further desorbed, and the vacuum-cleaning easily adsorbing component gas is obtained from the outlet of the vacuuming device, and the vacuum-cleaning easily adsorbing component gas is mixed into the easily adsorbable component gas.
The process flow according to claim 1, characterized in that the step of setting is performed before or after the completion of the pressure equalization step or the pre-adsorption step, or before or after the pressure-equalization step or the pre-adsorption step, namely:

The step of discharging: the main component which is discharged from the outlet side of the adsorption bed is a gas which is not easily adsorbed, and the adsorbent bed is partially depressurized;

When the step of discharging is included, the raw material gas is separated to obtain a product gas which is not easily adsorbed, a product gas which is easy to adsorb, and a gas stream which is a gas of the gas.
The process according to claim 1, wherein the adsorbent packed in the adsorbent bed comprises activated alumina, activated carbon, silica gel, molecular sieve, resin, and functional adsorbent modified by using the adsorbent as a carrier. One or a combination thereof.
The process according to claim 1 or 9, wherein the number of equalizations including the pressure equalization step and the pressure equalization step is 1 to 10 times.
The process according to claim 1, wherein the adsorption pressure in the adsorption step is from 0.1 to 6.0 MPa (g).
The process according to claim 1, wherein the pre-adsorption pressure in the pre-adsorption step is 0.1 to 1.0 MPa (g).
The process according to claim 6 or 7, wherein the vacuuming pressure of the vacuuming step is -0.05 to -0.099 MPa (g).