JPS6297622A - Pressure swing adsorbing method - Google Patents

Abstract

PURPOSE:To conserve washing gas, by comparing the concn. of the specific component in washing gas introduced into a tower with that of the specific component in the washing waste gas passed through the tower and stopping washing when the ratio of both of them or the difference therebetween reached a tolerance value. CONSTITUTION:Stock gas is made to flow to adsorbing towers 3a, 3b to adsorb CO. Product CO-gas is introduced into the adsorbing towers 3a, 3b to perform the washing of both towers but, at this time, the concn. of CO in washing gas before introduced into the adsorbing towers is measured by an analyser 10a an the concn. of CO in washing waster gas passed through the adsorbing towers is measured by the analyser 21 provided between adsorbing tower connection pipes 8a, 8b. At the point of time when the concn. of CO obtained by the analysers 21, 10a became equal, a valve 11 or a valve 12 is closed through a control apparatus 31 to stop the supply of the washing gas. By this method, the washing gas is conserved and the recovery ratio of the product gas is en hanced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a pressure swing adsorption method for concentrating and recovering easily adsorbable components as useful components, and in particular, a method for rationally performing the washing step in the pressure swing adsorption method. The present invention relates to a pressure swing adsorption method that saves cleaning gas, increases the product gas recovery rate, and increases the effective adsorption capacity of the useful components to efficiently recover the product.

[Prior Art] A cryogenic separation method is widely used industrially as a method for concentrating and recovering carbon monoxide gas (CO), nitrogen gas (N2), and the like. However, if this separation method were to be carried out, the equipment would be expensive, so there is a tendency to use the pressure swing adsorption method, which requires relatively simple equipment.

FIG. 2 is a piping explanatory diagram showing a typical example of a pressure swing adsorption device (PSA device). Now, a method of concentrating and recovering CO from converter gas using a two-column type adsorption tower will be taken up as a representative method, and will be explained below focusing on the adsorption/desorption pattern of the adsorption tower 3a. In this example, zeolite is used as the adsorbent. The raw material gas, which has been adjusted to a three-component mixed gas of Co, N2, and N2 through pretreatment, is taken into the line 1 by the compressor 2 in the direction of the arrow, and after being pressurized by the compressor 2, it passes through the valve 13. (valve 14 is closed) adsorption tower 3
supplied to a. Among Co, N2, and N2, Co, which has the highest adsorption to the adsorbent, is adsorbed to the adsorbent in the largest amount, while N2 and N, which have lower adsorption,
2 passes through the valve 19 and is discharged from the exhaust gas exhaust pipe 7. When the above adsorption step continues and the co adsorption capacity in the adsorption tower 3a decreases, the CO adsorption capacity at the outlet of the adsorption tower 3a decreases.
The O concentration begins to rise and eventually becomes the same as the concentration on the population side (reaching the breakthrough point of adsorption), so before that, the supply of raw material to the adsorption tower 3a is stopped and the adsorption process is completed.

While the adsorption tower 3a is performing the adsorption step, the adsorption tower 3b is performing a desorption step in parallel, in which the co adsorbed by the adsorbent in the previous step is desorbed by reducing the pressure inside the tower 3b. The completion of the adsorption process in the adsorption tower 3a and the completion of the desorption process in the adsorption tower 3b proceed almost synchronously, and after the completion of both processes, the adsorption towers 3a and 3b are directly connected by the connecting pipe 8a, and the high pressure gas in the adsorption tower 3a is released. It is moved to the adsorption tower 3b and the pressure is equalized. At this time, the N2 and N2 remaining in the adsorption tower 3a
(including those existing in a non-adsorbed state in the space of the column 3a and those adsorbed by the adsorbent) are the adsorption column 3b.
However, some N2 and N2 components remain in gaps between adsorbent particles in the adsorption tower 3a, inside the pipes, etc. Therefore, if the desorption process of the adsorption tower 3a is started to recover CO, the concentration of the recovered product (CO) will decrease. Therefore, in order to avoid this, the product CO gas is introduced from the product storage tank 5 into the adsorption tower 3a via the adsorption tower cleaning pipe 10 and the valve 11. The introduced cleaning gas (product Co) is sent to the adsorption tower 3b through the connecting pipe 8a after purging the remaining impurity components in the adsorption tower 3a.
CO in the cleaning waste gas is adsorbed again by the adsorbent in the adsorption tower 3b, and other N2 and N2 components are discharged from the gas waste pipe 7 through the valve 20.

When the above washing step is completed, the adsorption tower 3a is depressurized by the vacuum pump 4, and the adsorbed co is desorbed and recovered. The recovered CO product gas is stored in a product gas storage tank 5.
As mentioned above, a part of the gas is used as a cleaning gas to clean each adsorption tower 3a, 3b, and a part of it is also used as a cleaning gas in the product recovery pipe 6.
will be collected and used from After the desorption process in the adsorption tower 3a is completed, the adsorption process is repeated again, and the cycle of adsorption and desorption is continuously repeated. On the other hand, the adsorption/desorption cycle is similarly repeated in the adsorption tower 3b, but the process is shifted by % cycles from the cycle in the adsorption tower 3a. Table 1 shows cycle examples of the adsorption towers 3a and 3b.

[Problems to be solved by the invention] As described in the previous section, in the adsorption tower after the adsorption process,
Cleaning with product gas is performed to remove impurity components present in the gaps between adsorbent particles. The success or failure of the cleaning process has a large impact on the recovered product gas concentration.
Insufficient cleaning may cause problems such as a decrease in product gas concentration. Therefore, when supplying cleaning gas, it is necessary to supply a little more than the minimum amount required for cleaning, and the minimum amount required for cleaning also varies depending on the adsorption temperature and fluctuations in the composition of the source gas. Because of the need to anticipate each of these cases, it has become common practice to use a significantly larger amount of cleaning gas. The (equal pressure + cleaning) process time T2 (same as T4) shown in Table 1 is set taking into consideration these margins, and the cleaning process is performed intermittently based on the process time (T2 or T4). It will be held in

In addition, if the cleaning waste gas is disposed of as is, the product recovery rate will drop significantly, so as mentioned above, the cleaning waste gas is passed to another adsorption tower and adsorbed again. However, if the amount of cleaning waste gas becomes too large, the actual amount of adsorption (the amount of adsorption from the raw material gas) in other adsorption towers will decrease. That is, the total amount of useful components supplied to each adsorption tower is
It is the sum of the useful components in the raw material gas, the useful components in the cleaning waste gas, and the useful components in the cleaning gas. Unless it is kept to a minimum within a range that does not fall below the net adsorption amount, product purity and product recovery rate will decrease. Therefore, if the amount of cleaning gas is too large, useful components will be supplied to the adsorption tower in excess of the effective adsorption amount, and the gas discarded from the adsorption tower will contain many useful components, resulting in product recovery. There is also the inconvenience that the rate decreases.

Therefore, the inventor of the present invention has completed the present invention as a result of repeated research into various ways to increase the product recovery rate by suppressing the excessive supply of product gas in the cleaning process while maintaining a high level of product purity. Ta.

[Means for solving the problem] The method of the present invention for suppressing excessive supply of cleaning gas in the adsorption tower cleaning process is based on the concentration of specific components in the cleaning gas introduced into the tower and the cleaning gas that has passed through the tower. The gist of this method is to compare the concentrations of specific components in the waste gas, and to stop the supply of cleaning gas when the ratio or difference between the two reaches an allowable ratio or difference.

[Operation] The cleaning step is a step in which the recovered useful components are supplied as a cleaning gas to the adsorption tower where the adsorption step has been completed, and impurity components remaining in the gaps between the adsorbent particles are removed.

Therefore, in the early stages of cleaning, the composition of the cleaning gas and the composition of the cleaning waste gas differ widely, but in the later stages of cleaning, the compositions of the two become similar.

From this point of view, as a method to prevent oversupply of cleaning gas, the concentration of specific components (product gas, impure gas, etc.) in °C1 cleaning waste gas is measured, and when the concentration reaches a certain level, the cleaning gas is It is also possible to stop the supply of product gas, but this method will only work if various conditions are kept constant, such as the product gas concentration in the product gas storage tank being always constant and the adsorption concentration also being constant. Under circumstances where these conditions are fluctuating, for example, the concentration of product gas in the product gas storage tank 5 is low at the beginning of operation, so if product gas is selected as the specific component, the cleaning gas It is not even possible to determine whether the supply has been interrupted. Another problem is that the time required for cleaning becomes long, leading to loss of product gas.

In contrast, according to the present invention, the concentration of a specific component in the cleaning gas and the concentration of a specific component in the cleaning waste gas are compared to determine the ratio or difference between the two, and when these reach a preset tolerance value, the cleaning gas If the supply is stopped, the time until the supply of cleaning gas is stopped can be accurately controlled at any time during operation, and problems such as wasted supply of cleaning gas can be prevented.

[Example] Fig. 1 shows a pressure swing adsorption device used for carrying out the present invention. The difference from the apparatus shown in Fig. 2 is that an analyzer 21 is provided in the adsorption tower connecting pipes 8a and 8b. C
A case will be described below by way of example in which CO is concentrated and recovered using a converter gas composed of o, N2, and N2 gas as a raw material.

Each adsorption tower 3a.

The adsorption/desorption pattern in 3b is almost the same as that explained in the conventional example section, but in the conventional example, the supply of cleaning gas must be continued for the entire set process time (set time for cleaning). In contrast, in the present invention, the analyzer 21 and the analyzer 10 installed in the adsorption tower cleaning pipe 10
By comparing the measurement results of a, it is possible to accurately determine when to stop the supply of cleaning gas. In this embodiment, a CO concentration analyzer is provided in the analyzers 21 and 10a, and the CO concentration in the cleaning gas before being introduced into the adsorption tower is measured by the analyzer 10a.
The CO concentration in the cleaning waste gas that has passed through the adsorption tower is measured using an analyzer 21 installed in the adsorption tower connection pipes 8a and 8b. For example, co obtained with two analyzers 21 and 10a;
When the degrees become equal, it means that the cleaning has been performed to the maximum, so at this point, the valve 11 or 12 is immediately closed via the control device 31 to stop the supply of cleaning gas. In the above example, co? in the cleaning gas? A method is shown in which the cleaning gas supply is stopped when the IA degree and the COf14 degree in the cleaning waste gas become equal, but the ratio or difference between the two is not limited to this example. Alternatively, the supply of the cleaning gas may be stopped when the cleaning gas reaches the maximum temperature. Further, the gas component to be measured may be CO, which is a useful component, or may be N2 or N2, which is an impure component. Furthermore, it can be used not only for the above-mentioned CO concentration and recovery method, but also for separating and recovering N2 from the air, and there are no limitations on the application of gas separation.

FIG. 3 is an explanatory diagram showing details of an example of the analyzer 21. Automatic opening/closing valve 2 from adsorption tower connecting pipes 8a and 8b
2.23, 24.25 via analyzer 29. Compressor 30
．． Control valves 26 to 28 are provided, and valves 22.24 are opened when sampling the gas in the adsorption tower connecting pipe 8a, and valves 23.25 are opened when sampling the gas in the connecting pipe 8b. The analyzer 29 is preferably a non-dispersive infrared analyzer that has high responsiveness and accuracy even when the amount of sampling gas is small. code 2
6 is a secondary pressure control valve, and 27 is a flow control valve, these are provided to quantitatively send the sampling gas to the analyzer 29 at a constant pressure, and the compressor 30 is connected to the analyzer 29.
These are provided to prevent the pressure of the gas that has passed through the connecting pipes 8a and 8b from dropping below that of the connecting pipes 8a and 8b. Note that a primary pressure control well 28 may be provided in order to prevent pressure fluctuations within the analyzer 29 when the compressor 30 is operated.

When the cleaning process is started, valve 22.24 or valve 23.25
Either set is opened, and the cleaning waste gas flowing through either the connecting pipes 8a or 8b is sampled and its concentration is measured by the analyzer 29. The analyzer 29 is connected to a control device (not shown) along the dashed line, and when the measured value of the analyzer 29 reaches a permissible set value with respect to the measured value of the cleaning gas analyzer 10a. Then, it is determined that the cleaning purpose has been achieved and one of the valves 12 is closed and the supply of cleaning gas is stopped. At this time, either of the valves 15 and 16 provided in the connecting pipes 8a and 8b is also closed in accordance with the above-mentioned valve operation.

(Example 1) An experiment was conducted to concentrate and recover CO from a raw material gas composed of Co and N2 using the pressure swing adsorption apparatus shown in FIG. 1 under the following conditions.

(a) Raw material gas composition: CO80%, N20% (b) Adsorbent = 5A type synthetic zeolite (2-3 mm spherical product) (c) Adsorbent filling amount: φ3.9cm x 200cm,
Two-column type (d) Adsorption and desorption pressure crab 1.8kg/cm
2G, 150Torr (e) Adsorption temperature: 25°C (f) Process setting time: Process T1 = T2 in Table 1
=73 =74 =3 minutes (g) Cleaning gas flow rate: 6N 111 minutes (h) A non-dispersive infrared analyzer was used as the analyzer 29, and the 82 Co amphoteric acid component was measured using a gas chromatograph.

(i) Cleaning gas supply is cleaning waste gas and cleaning waste gas C
It was stopped when the O concentrations were equal.

As a result, product c was produced approximately 180 minutes after the start of operation.

When the concentration reached 99.9% or more, the supply of cleaning gas was stopped between 2 minutes 27 seconds and 2 minutes 32 seconds in the cleaning process. At this time, the product recovery rate was 81.7%, and the recovery rate when the present invention was not adopted and the cleaning gas was supplied for 3 minutes was 74.4%, and the method of the present invention improved the recovery rate by about 10%. .

(Example 2) Under the same conditions as in Example 1, the raw material gas composition in (a) was increased from 80% to 90%, and the conventional method and the method of the present invention were compared.

As a result, the amount of N2 remaining in the adsorption tower at the end of the adsorption process should have been smaller than in Example 1, but since the amount of cleaning gas is not controlled in the conventional method, the recovery rate was 69.7%.
It became low. - In the power wood invention method, the cleaning gas is stopped 2 times.
Runs between minutes 12 seconds and 2 minutes 19 seconds, product purity 99
．． While maintaining 9%, the recovery rate was 76.3%, demonstrating that it is superior to the conventional method.

[Effects of the Invention] The method of the present invention succeeded in improving the recovery rate of useful components without reducing the purity of the useful components to be recovered. It has also become possible to increase the effective adsorption capacity, making it possible to efficiently process the raw material gas.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the pressure swing adsorption device used in the present invention, FIG. 2 is an explanatory diagram showing the pressure swing adsorption device used in the conventional method, and FIG. 3 is an explanatory diagram showing the analyzer 2 shown in FIG. 1.
FIG. 1 is an explanatory diagram showing details of FIG. 1... Raw material gas supply pipe 2... Raw material gas compressor 3a
, 3b...Adsorption tower 4...Pump for product gas recovery 5...Product gas storage tank 6...Product gas supply pipe 7.
...Waste gas disposal pipes 8a, 8b...Adsorption tower connection pipe 9
・・・Product gas extraction pipe

Claims (1)

[Claims] When concentrating and recovering easily adsorbable components using a pressure swing adsorption tower, a part of the recovered easily adsorbable components is introduced into the adsorption tower after the adsorption process has been completed, and the inside of the tower is cleaned.Cleaning gas introduced into the tower The cleaning gas supply is stopped when the ratio or difference between the two reaches an allowable ratio or difference by comparing the concentration of a specific component in the column and the concentration of a specific component in the cleaning waste gas that has passed through the tower. Pressure swing adsorption method.