JPH0583286B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is based on the pressure swing adsorption method (hereinafter referred to as PSA
It is called. The present invention relates to a method and apparatus for extracting a target component gas from a source gas and recovering it with high purity by using the following method. [Conventional technology] Conventionally, target component gas is extracted from raw material gas,
As a means of recovery, PSA, which utilizes the ability of an adsorbent to adsorb a specific gas, is widely known. This PSA is suitable for concentrating and recovering carbon monoxide from converter gas whose main components are carbon monoxide and nitrogen, and when concentrating and recovering carbon dioxide from combustion exhaust gas whose main components are carbon dioxide and nitrogen. It is used for. FIG. 8 shows an example of a conventional device for performing this PSA. This device includes a raw material gas blower 80, adsorbers 82, 82, and a vacuum pump 8.
4. A product gas storage tank 86 and the like are provided, and automatic valves 87 to 97 are provided at appropriate positions in each passage. In this apparatus, the product gas is purified by sequentially performing and repeating the four steps described below. Here, as an example, one of the adsorbers 81
The steps performed in this section will be explained. Adsorption process Automatic valve 87 is activated by the operation of raw material gas blower 80.
The raw material gas is supplied into the adsorber 81 through the adsorbent. The gas that is not adsorbed here is disposed of outside the apparatus through an automatic valve 95. Cleaning (Purge) Step A part of the product gas stored in the product gas storage tank 86 is supplied to the adsorber 81 through the cleaning gas supply pipe 98 and the automatic valve 91, and with this gas,
Non-target components in the adsorber 81, specifically non-target component gases staying in dead spaces such as the outer surface of the adsorbent, are expelled. In this cleaning process, the main adsorber 81
Since the cleaning exhaust gas discharged from the source gas is rich in target components compared to the raw material gas, it is recovered again, that is, returned to the upstream side of the raw material gas blower 80 through the automatic valve 93 and the cleaning exhaust gas recovery pipe 99, and is used for other adsorption. It is used for adsorption in the vessel 82. Desorption step The vacuum pump 84 is activated to suck the gas inside the adsorber 81 through the automatic valve 89 and reduce the pressure inside the adsorber 81 . As a result, the target component gas adsorbed by the adsorbent is desorbed and recovered as a product gas. Pressure increase process By opening the automatic valves 95 and 96 and sending the gas in the adsorber 82 into the adsorber 81, the adsorber 8
Increase the pressure inside 1. The above shows the processes generally performed in PSA,
Furthermore, JP-A-62-61616 discloses a method for separating high-purity gases, in which the desorption process is divided into an initial process, a middle process, and a final process, and only the gas desorbed in the middle process is recovered as a product gas. is disclosed. According to this method, the recovered gas at the early and final stages of desorption, which has relatively low purity, is used for cleaning, and only the recovered gas at the middle stage of desorption, which has relatively high purity, is recovered as product gas. Purification can be achieved. [Problem to be solved by the invention] The conventional method explained based on FIG.
There are the following problems. (1) In the above method, in order to increase the purity of the recovered gas, a cleaning process is performed to expel non-target gas from the outer surface of the adsorbent, etc., but in this cleaning process, a part of the product gas (actually Because more than half of the recovered amount must be circulated within the device, the power cost for the entire device is more than double that of a case where no cleaning step is performed. (2) If the cleaning process has not been performed yet, each main adsorber 81, 82 contains many non-target components, so it is difficult to obtain high-purity product gas immediately from the start of the device. In reality, it is necessary to gradually increase the purity of the gas by repeatedly performing adsorption/desorption cycles. Therefore, it takes a relatively long time to obtain high-purity gas, and it is also difficult to reduce power costs. (3) In the above method, part of the product gas is circulated to the adsorber as cleaning gas, while the exhaust gas from this cleaning process is recovered and supplied to the adsorber. Even if this is done, it is impossible to extract 100% of the target components contained in this re-recovered gas, and a decrease in product recovery rate is inevitable. On the other hand, according to the method disclosed in JP-A No. 62-61616, it is possible to improve the purity of the product by extracting only the recovered gas in the middle stage of desorption, when the purity of the desorbed gas is highest, as product gas. You can, but
The gas recovered during the initial and final stages of desorption also
Compared to the raw material gas, it is rich in target component gas,
Discarding such recovered gas without taking it out as a product or circulating it as a cleaning gas will lead to a decrease in product recovery rate and impair economic efficiency. In view of these circumstances, the present invention maintains the purity of the recovered product gas at a high level while reducing or eliminating the cleaning process, thereby reducing power costs and improving the product recovery rate. An object of the present invention is to provide a method and apparatus for purifying high-purity gas. [Means for Solving the Problems] The present invention includes an adsorption step in which a raw material gas is passed through a main adsorber having an adsorbent and a target component in the raw material gas is selectively adsorbed, and the pressure inside the main adsorber is reduced. In a high-purity gas purification method that sequentially performs a desorption step of desorbing the gas adsorbed on the adsorbent and recovers the desorbed gas, in the early stage of the desorption step, the desorption step of desorbing the gas adsorbed on the adsorbent is performed. The target components in the gas are adsorbed by introducing the desorbed gas into a sub-adsorber having an adsorbent, and during the period from the end of the initial desorption process to the end of the desorption process, the gas desorbed from the main adsorption unit is used as product gas. collected as
After the desorption step, the pressure inside the sub-adsorber is reduced to desorb the gas adsorbed by the adsorbent in the sub-adsorber, and this gas is recovered as a product gas (Claim 1). Here, during the period from the initial end of the desorption process to the end of the desorption process, the gas desorbed from the main adsorber may be directly recovered as product gas, or the gas may be passed through the sub-adsorber. It may be collected later. The present invention also provides an apparatus for carrying out the above method, including a main adsorber having an adsorbent that selectively adsorbs target components in the raw material gas, and a raw material gas supply means for supplying the raw material gas to the main adsorber. and a desorption means for depressurizing the inside of the main adsorber to desorb the gas, which is connected to the outlet side of the main adsorption device, and is connected to the outlet side of the main adsorber, and the gas desorbed from the main adsorption device is A sub-adsorber having an adsorbent that selectively adsorbs the target component, a sub-desorption means for depressurizing the inside of the sub-adsorber to desorb the gas, and a passage on the outlet side of the sub-adsorber for desorbing the gas. The present invention is provided with passage means for selectively switching between a passage for sending the gas discharged from the container to the recovery side and a passage for sending it to the disposal side (claim 2). [Function] According to the above configuration, in the early stage of the desorption process, the gas desorbed from the main adsorption device is directly guided to the sub adsorption device, and the target component in the gas is adsorbed. Thereafter, as the desorption process progresses and the purity of the desorbed gas from the main adsorber becomes high, this gas is recovered as a product gas either directly or through a sub-adsorber or the like. After this desorption step is completed, the sub-adsorber is depressurized, whereby the gas adsorbed by the sub-adsorber is desorbed and recovered as a product gas. [Embodiment] FIGS. 1 to 6 show the overall configuration of an embodiment of an apparatus for carrying out the method of the present invention. This device includes a raw material gas blower (raw material gas supply means) 10, main adsorbers 11 and 12, a vacuum pump (also used as a desorption means and a sub-desorption means) 14, and a product gas storage tank 16. 1
2 contains an adsorbent that selectively adsorbs target components in the raw material gas. The raw material gas blower 10 is connected to the inlets of the main adsorbers 11 and 12 via automatic valves 19 and 20, respectively, and the vacuum pump 14 is also connected to the inlets of the main adsorbers 11 and 12 via automatic valves 23 and 24, respectively. has been done. The outlet of each main adsorber 11, 12 is connected to an automatic valve 2.
7 and 28, respectively, and is connected to the upstream side of the source gas blower 10 via automatic valves 31 and 32 and a cleaning exhaust gas recovery pipe . The product gas storage tank 16 is
Located downstream of the vacuum pump 14, the cleaning gas supply pipe 36 and automatic valves 37, 38
It is connected to the inlet side of each main adsorber 11, 12 via. Furthermore, as a feature of this device, a sub-adsorption device 4 is provided between the vacuum pump 14 and the product gas storage tank 16.
0 is set. Similar to the main adsorbers 11 and 12, this sub-adsorber 40 also contains an adsorbent that selectively adsorbs only the target component in the raw material gas. Automatic valves 42 to 44 are disposed between the sub-adsorber 40 and the vacuum pump 14. The outlet side passage pipe of the sub-adsorber 40 branches into a product gas recovery pipe 46 connected to the product gas storage tank 16 and a waste pipe 47 connected to the waste side, and each pipe 46, 47 has a passage switching pipe. Automatic valve (passage switching means) 50,
51 are arranged. In addition, the vacuum pump 1
4 and the product gas storage tank 16 are directly connected by a bypass pipe 54, and an automatic valve 56 is also disposed in the middle of this bypass pipe 54. Next, a process of purifying product gas (high purity gas) performed by this apparatus will be explained. With this device,
As shown in FIG. 7, each main adsorber 11, 12
High-purity gas is purified by sequentially performing four steps with different phases from each other, and by alternately performing adsorption and desorption steps in the sub-adsorber 40. The explanation will mainly focus on the process involved. Adsorption step (FIG. 1) The automatic valve 19 is opened, the raw material gas blower 10 is operated, and the raw material gas is supplied into the main adsorber 11. As a result, the target component in the raw material gas is transferred to the main adsorber 11.
The gas that is adsorbed by the adsorbent inside and not adsorbed is disposed of outside the apparatus from the waste gas discharge pipe 30 through the automatic valve 27. Cleaning process (Fig. 2) Open the automatic valve 37 and use the product gas stored in the product gas storage tank 16 as cleaning gas to the main adsorber 11.
into the tank under approximately atmospheric pressure. With this cleaning gas, non-target component gases staying in dead spaces such as on the outer surface of the adsorbent are expelled. At this time, the main adsorber 1
The cleaning exhaust gas discharged from 1 is recovered again by being returned to the upstream side of the raw material gas blower 10 through the automatic valve 31 and the cleaning exhaust gas recovery pipe 34,
It is again subjected to adsorption in the main adsorber 12. Desorption process (Figures 3 and 4) Initial stage (Figure 3) Open the automatic valve 23, operate the vacuum pump 14 to reduce the pressure inside the main adsorber 11, perform desorption, and open the automatic valves 42 and 44. Open, main adsorber 11
The gas desorbed from the adsorbent is fed into the sub-adsorber 40. This sub-adsorber 40 adsorbs the target component gas contained in the desorption gas. At the initial stage of this desorption process, the main adsorber 1
Since the desorption gas discharged from the adsorbent 1 still contains a large amount of non-target gas, the remaining gas that has not been adsorbed even in the sub-adsorber 40 does not have sufficient purity as a product gas. Therefore, at this initial stage, automatic valve 50 is closed and automatic valve 51 is closed.
By opening only the sub-adsorber 40, the gas discharged from the sub-adsorber 40 is disposed of to the outside of the apparatus through the waste pipe 47. After the initial completion (FIG. 4) When the initial stage of the desorption process is completed and desorption progresses, the amount of non-target components contained in the desorption gas becomes small, and the desorption gas has sufficient purity. Therefore, the gas not adsorbed by the sub-adsorber 40, that is, the gas discharged from the sub-adsorber 40, also has a purity sufficient to be used as a product gas. Therefore, during this period, the automatic valve 51
By closing the automatic valve 51 and opening only the automatic valve 51, the gas discharged from the sub-adsorber 40 is recovered as product gas. In this way, after the initial stage of the desorption process is completed, the product gas can be recovered even if the target component is not adsorbed in the sub-adsorber 40, so that the adsorbent in the sub-adsorber 40 is in a breakthrough state. It doesn't matter if you get old. Therefore, the adsorbent in the sub-adsorber 40 only needs to have an adsorption amount sufficient to perform good adsorption at least in the initial stage of the desorption process. Desorption process of the sub-adsorber 40 (Fig. 5) The pressure inside the sub-adsorber 40 is reduced by opening the automatic valves 42 and 43 and operating the vacuum pump 14,
Desorbs the adsorbed gas. At the same time, by opening the automatic valve 56, the gas desorbed from the sub-adsorber 40 is sent through the bypass pipe 54 to the product gas recovery pipe 46, and the desorbed gas is recovered as product gas. Note that while the desorption process of the sub-adsorber 40 is being performed, the automatic valves 27 and 28 are opened and the gas in the main adsorber 12 is supplied into the main adsorber 11, so that the main adsorber 11 is The pressure is increased, and then the process returns to the adsorption step. As described above, in this device, the main adsorber 11,
A sub-adsorber 40 is provided on the outlet side of the 12, and this sub-adsorber 40 also adsorbs the target component, so there is no need to rely on the washing process as in the past, and without reducing the product recovery rate. High purity gas can be purified. Therefore, the above-mentioned cleaning process can be eliminated, and in some cases, the cleaning process can be abolished. When the cleaning process is abolished, the elements indicated by broken lines in FIGS. 1 to 5, namely the cleaning gas supply pipe 36, the cleaning gas recovery pipe 34,
And each automatic valve 31, 32, 37, 38 can be omitted. Moreover, in this method, from the time when the initial stage of the adsorption process is completed, that is, from the time when the purity of the desorption gas sucked from the main adsorber 11 becomes sufficiently high,
The gas passing through the sub-adsorber 40 is also recovered as a product gas, and the product gas is recovered in both the latter stages of the desorption process of the main adsorber 11 and the desorption process of the sub-adsorber 40. Since the product gas is recovered in the desorption step 11, the amount of gas that must be recovered through desorption in the sub-adsorber 40 can be reduced. Therefore, by reducing the power required for desorption of the sub-adsorber 40 as much as possible, it is possible to significantly reduce power costs compared to the conventional method of purifying the product gas by performing a cleaning process. can be achieved. Next, experimental data will be shown. The conventional apparatus shown in FIG. 8 was operated under the conditions shown in Table 1 on the next page, and carbon monoxide was recovered approximately 2.75 hours after the start of operation. Product gas with a purity of 98.7% could be stably obtained with a product recovery rate of 67%.

[Table] Here, the amount of gas during cleaning is equivalent to 1/2 of the total amount of product gas recovered, but in reality, a larger amount of cleaning gas is required to achieve high purity products. become. In contrast, the apparatus of the present invention shown in Figures 1 to 5 is operated under the conditions shown in Table 2 on the next page, and the timing of passage switching is adjusted so that the purity of carbon monoxide gas is 98.7%. As a result, we achieved a recovery rate of 73% for product gas with the above purity within one hour of starting operation.
I was able to get it.

【table】

〔Effect of the invention〕

As described above, in the present invention, at the initial stage of the desorption process in the main adsorber, the desorbed gas is further guided to the sub-adsorber, where the target component is adsorbed, and after this initial stage of the desorption process is completed, the desorbed gas is This system recovers the desorbed gas as product gas, and then desorbs the sub-adsorber after the desorption process and recovers the desorbed gas as product gas. The purity of the product can be maintained at a high level, which has the effect of reducing power costs and improving the product recovery rate.

[Brief explanation of the drawing]

Fig. 1 is an overall configuration diagram showing the flow of gas during the adsorption process in the main adsorber in a high-purity gas purification apparatus according to an embodiment of the present invention, and Fig. 2 shows the gas flow during the cleaning process in the main adsorber in the same apparatus. Figure 3 is an overall configuration diagram showing the flow of gas at the beginning of the desorption process in the main adsorber in the same equipment, and Figure 4 is a diagram showing the gas flow after the initial desorption process in the main adsorber in the same equipment. Figure 5 is an overall configuration diagram showing the gas flow during the pressure increase process of the main adsorber and the desorption process of the sub-adsorber in the same equipment, and Figure 6 is an overall configuration diagram showing the gas flow during the pressure increase process of the main adsorber and the desorption process of the sub-adsorber in the same equipment. Figure 7 is a process diagram showing the steps performed in each main adsorber and sub-adsorber of the same device, and Figure 8 is a conventional high-purity adsorption system. FIG. 1 is an overall configuration diagram showing an example of a purification device. 10... Raw material gas blower (raw material gas supply means),
11, 12...Main adsorption device, 14...Vacuum pump (desorption means and sub-desorption means), 40...Sub-adsorption device, 46...Product gas recovery pipe, 47...Disposal pipe,
50, 51... Automatic valve (passage switching means).

Claims (1)

[Scope of Claims] 1. An adsorption step in which a raw material gas is passed into a main adsorber having an adsorbent to selectively adsorb a target component in this material gas, and an adsorption step in which the target component in the material gas is selectively adsorbed, and the adsorbent is absorbed by reducing the pressure inside the main adsorber. In a high-purity gas purification method that sequentially performs a desorption step in which the adsorbed gas is desorbed and then recovers the desorbed gas, in the early stage of the desorption step, the desorbed gas is removed from the adsorbent in the main adsorber. During the period from the end of the initial desorption process to the end of the desorption process, the gas desorbed from the main adsorption unit is recovered as a product gas, and the target component in the gas is adsorbed. After the process, the pressure inside the sub-adsorber is reduced to desorb the gas adsorbed by the adsorbent in this sub-adsorber, and this gas is recovered as a product gas. Purification of high-purity gas using an adsorption method. Method. 2. A main adsorber having an adsorbent that selectively adsorbs target components in the raw material gas, a raw material gas supply means for supplying the raw material gas to this main adsorber, and a method for depressurizing the inside of the main adsorber to desorb the gas. A high-purity gas purification apparatus equipped with a desorption means for desorbing the gas, the apparatus having an adsorbent connected to the outlet side of the main adsorption device to selectively adsorb the target component in the gas desorbed from the main adsorption device. A sub-adsorber, a sub-desorption means that depressurizes the inside of the sub-adsorber to desorb the gas, and a passage on the outlet side of the sub-adsorber as a passage for transporting the gas discharged from the sub-adsorber to the recovery side and disposal. 1. An apparatus for purifying high-purity gas using an adsorption method, characterized in that it is equipped with a passage switching means for selectively switching between a passage to the side and a passage to the other side.