JP2686349B2 - Pressure swing hydrogen purification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] Hydrogen gas such as steam reforming gas by a steam reforming furnace such as an ammonia plant, a city gas plant, a hydrogen production plant or a coke oven of gas and its accompanying CO, The present invention relates to a pressure swing type hydrogen purification method from a gas such as CO ₂ .

[Conventional technology]

Coke oven, oil refinery off-gas, natural gas,
In liquefied petroleum gas, steam reforming furnaces that use naphtha as raw material, etc.
It produces a gas containing H ₂ , CO, CO ₂ , H ₂ O, etc. as its main components. The selective enrichment of H ₂ from this gas mixture is extremely significant and important given the wide range of applications for H ₂ .

H ₂ is conventionally used in a hydrogenation reaction in which a higher hydrocarbon is brought into contact with a higher hydrocarbon under coexisting conditions to lower the hydrogen, and is also widely used as a basic substance in the chemical industry such as methanol synthesis and ammonia synthesis.

As another application, since a large amount of energy is instantly generated by the combustion reaction of H ₂ with O ₂ , it has been attracting attention as a fuel for rocket fuels such as fuel cells and hydrogen engines.

An outline of a typical method for purifying conventional H ₂ is as follows. The apparatus is composed of three or four or more adsorption columns, an on-off valve, and a flow control valve.

The high-pressure mixed gas containing H ₂ , CO, CO ₂ , H ₂ O, etc., as the main components, which was supplied to one tower in this device, was sequentially fed from the inlet side to H ₂ O,
CO ₂ and CO are adsorbed in order from the strongly adsorbed component to the difficultly adsorbed component.

Usually, an adsorbent suitable for adsorbing strongly adsorbing components such as alumina and activated carbon is arranged near the inlet of the adsorption tower, and a zeolite adsorbent for weakly adsorbing components is arranged in the downstream.

Since H ₂ does not have an adsorbing ability for most adsorbents, it flows through as it is at a high pressure from the outlet. If this step is continued, gas other than H ₂ will start to flow from the outlet of the tower, so the supply of the raw material gas is terminated before that. (End of adsorption step) At this time, in the other columns, the column internal pressure is reduced to atmospheric pressure, and the adsorbent has already been regenerated as described later. (End of regeneration process) Since a large amount of H ₂ still remains in the tower at the end of the adsorption process, connecting the towers at the end of the regeneration process causes H ₂ to flow out from the high pressure column and the low pressure column. And the pressure in each tower becomes equal. (Inter-column pressure equalization process) After that, if the front of the column is further opened and the pressure is reduced in countercurrent, the pressure inside the adsorption column will decrease, and the adsorbed CO, CO ₂ , H ₂ O, etc. will separate from the adsorbent and the system will be released. Released to the outside.

(Depressurization process) Since only this process is insufficient, the product H ₂
When a part of the adsorbent gas is caused to flow countercurrently, the adsorbed gas is more thoroughly desorbed from the adsorbent and regenerated. By performing shifting the cycle the same operation in (product H ₂ purge) a plurality of columns, it can be recovered continuously H _2.

In the above hydrogen purification method, in general, the more the number of columns is increased and the pressure between the columns is increased, the higher the H ₂ recovery rate is, but the lower the H ₂ purification amount per unit adsorbent and unit time is. To do.

Due to high pressure adsorption and atmospheric pressure regeneration, it becomes difficult to secure H ₂ for product H ₂ purging when the pressure drops, and the adsorption pressure is
10atm or more is desirable.

It is said that.

For this reason, efforts have been made to improve the recovery rate of the product H ₂ which is mainly due to the pressure equalization between the towers, but the maximum H ₂ recovery rate is 85%.

Regarding H ₂ concentration, high-purity H ₂ can be easily obtained, and the maximum attainable concentration reaches 99.999%.

[Problems to be solved by the invention]

In the above-mentioned conventional method, in order to recover unadsorbed hydrogen, a method of sequentially performing inter-column pressure equalization between the high pressure column after completion of adsorption and the low pressure column after completion of decompression regeneration is adopted. in this way,
Although hydrogen will be recovered without using a utility such as electric power, it has the following drawbacks.

In order to measure the high recovery rate of hydrogen, it is necessary to increase the number of towers and operate the pressure equalization between towers in multiple stages. This requires complex sequences and multiple valves.

In order to measure the high recovery rate of hydrogen, it is necessary to set a high adsorption pressure because a multistage pressure equalization operation between columns is required.

As an example of purifying hydrogen from a steam reformer, the case of purifying 99.9vol% hydrogen from 70vol% CO ₂ 25vol% gas and 5vol% CO gas in the downstream of the shift reactor, the pressure is 20a.
It is said that the tm4 tower type adsorption tower has a hydrogen recovery rate of 70% and the 10 tower type has a hydrogen recovery rate of 85%, and the 10 atm four tower type has a hydrogen recovery rate of less than 60%.

The cause of this decrease in the hydrogen recovery rate is, first of all, because the adsorption zone (adsorption zone) for weakly adsorbing components below CO is long, so high-purity hydrogen remains between the adsorbents and in the voids inside the adsorbents. ,
This is because it is not collected.

The present invention is intended to solve the above-mentioned drawbacks of the conventional pressure swing hydrogen purification method.

[Means for solving the problem]

The present invention, CO is associated hydrogen thereto under pressure, the components that accompany the hydrogen in the source gas consisting of CO _2, etc. is adsorbed by the adsorbent and purified high-purity hydrogen, leaving the adsorbed components in vacuo A plurality of systems for regenerating the adsorbent are provided, and in each of the pressure swing type hydrogen purification methods in which the adsorption and desorption are alternately repeated in each system, the first adsorbent that adsorbs a strongly adsorbed component of CO ₂ or more is used. The pressurized raw material gas is introduced into the adsorption stage and then into the second adsorption stage filled with an adsorbent that adsorbs weakly adsorbed components of CO or less, and CO ₂ is introduced in the first adsorption stage from the raw material gas first. After adsorbing the above strongly adsorbed components, and then adsorbing weakly adsorbed components of CO or less at the second adsorption stage to obtain high-purity hydrogen, the strongly adsorbed components adsorbed at the first adsorption stage are removed. It is released under reduced pressure, released outside the system, and adsorbed in the second adsorption stage above. After desorbing the weakly adsorbed components under reduced pressure, they are introduced into the shift converter together with the hydrogen remaining in the second adsorption stage to react CO with H ₂ O to generate hydrogen, and then to the above adsorption stage. It is characterized in that it is purified again.

[Action]

In the present invention, CO ₂ in the raw material gas, CO, etc. are respectively adsorbed in the first adsorption stage and the second adsorption stage in the adsorption tower, high-purity hydrogen passes through the first and second adsorption stages. Recovered,
This is sequentially performed in a plurality of systems to continuously collect hydrogen.

Looking at the adsorption stage of each system, when the above adsorption process is completed, the first adsorption stage filled with the adsorbent that has adsorbed the strongly adsorbed component of CO ₂ or more is decompressed, and the strongly adsorbed component is the adsorbent. The adsorbent is regenerated by being separated from the adsorbent, and the strongly adsorbed component of CO ₂ or more separated from the adsorbent is discharged out of the system.

On the other hand, in the second adsorption stage that adsorbs weakly adsorbed components rather than CO, the weakly adsorbed components are adsorbed by the adsorbent at the stage when the adsorption step is completed, and high-purity hydrogen remains in the voids at high pressure.
The second adsorption stage is decompressed, weakly adsorbed components of CO or less are separated from the adsorbent, and the adsorbent is regenerated. In addition, CO and components having a weaker adsorption force than CO are desorbed from the adsorbent and introduced into the shift converter together with the remaining hydrogen. In the shift converter, CO shifts to CO + H ₂ O → H ₂ + CO ₂ As a result, the raw material gas, which has been converted to hydrogen, joins and reaches the first and second adsorption stages again to purify hydrogen.

As described above, in the present invention, the hydrogen remaining in the second adsorption stage is recovered, and the CO adsorbed in the second adsorption stage is desorbed from the adsorbent, whereby hydrogen is obtained by the shift converter. Therefore, a high hydrogen recovery rate can be achieved even if the pressure during adsorption is lowered.

〔Example〕

FIG. 1 shows an embodiment of the present invention that realizes a high hydrogen recovery rate.

In FIG. 1, 100 Nm ³ / h of steam reformed gas of 70 vol% hydrogen, 20 vol% CO ₂ and 10 vol% CO at a pressure of 7 atm on the basis of dry gas discharged from the steam reforming furnace 1, the flow path 2 and the heat exchange 3 Through 250 ℃
The temperature is lowered to the shift converter 4. The shift converter 4 is filled with the shift catalyst 5, and CO + H ₂ O → H ₂
CO is reduced to 5 vol% by the reaction of + CO ₂ , and the flow path 6 and valve 7
CO ₂ or more strongly adsorbed component adsorption stages arranged in parallel via a
One of the strong adsorption components 8a and 8b reaches the adsorption stage 8a. The strongly adsorbing component adsorption stage 8a has alumina 9 for adsorbing water in the front
It is filled with (Na-X) 10 as a CO ₂ adsorbent and contains water, C
Strongly adsorbed components such as O ₂ are adsorbed and removed, and after passing through the valve 11a,
The weaker adsorbent component of CO or less on the downstream side reaches the adsorption stage 12a. The weak adsorption component adsorption stage 12a is filled with (Ca-X) 13 as a CO adsorbent to adsorb weak adsorption components such as CO, and high concentration hydrogen of 99.9 vol% or more reaches the product hydrogen holder 15 through the valve 14a.
At this time, the other strong adsorption component adsorption stage 8b and the weak adsorption component adsorption stage 12b, which are arranged in parallel with the adsorption stages 8a and 12a and are filled with the same adsorbent, reach a reduced pressure of 0.5 atm by the vacuum pump 16. However, the adsorbent is being regenerated.

When the regeneration of the adsorption stages 8b, 12b is completed, 11a, 17a, 17b,
When 11b is opened and the other valves are closed, hydrogen remaining behind the adsorption stage 12a is recovered by the low-pressure adsorption stage 12b, and the adsorption stage 8a, 12a of 7atm after the adsorption is reduced to 3.75atm, while the regeneration is performed. The pressure of the adsorption stages 8b and 12b of 0.5 atm which has been completed is increased to 3.75 atm and the pressure between the adsorption stages becomes equal.

Focusing on the adsorption stage reduced to 3.75 atm, in the strong adsorption component adsorption stage 8a, the valves 18a and 19 are first opened to reduce the pressure to atmospheric pressure, and below the atmospheric pressure, the valve 19 is closed and the vacuum pump 16 is used outside the system.
Strongly adsorbed components such as CO ₂ are desorbed. On the other hand, weakly adsorbed component stage 12a
Then, the valve 20a is opened and the gas having CO as a main component and hydrogen remaining in the adsorption stage 12a in the recirculation compressor 21 is recirculated from the flow path 22 to the upstream side of the shift converter 4. When the pressure of the weakly adsorbed component stage 12a becomes atmospheric pressure, the valve 2
0a is closed and valve 11a is left open.
It is evacuated as in a.

After that, the adsorption stages 8a, 12a, 8b, 12b arranged in parallel are exchanged and the same operation is performed.

In the adsorption process, when the pressure is increased from 3.75 atm to 7 atm, the valves 23 and 17a are opened to flow the product hydrogen from the holder 15 in a countercurrent direction to increase the pressure to cause the pressure fluctuation of the adsorption stage in the steam reforming furnace 1. Is taken into consideration so that it will not be transmitted.

The high-purity hydrogen of 99.9 vol% reaching the product hydrogen holder 15 is taken out from the flow path 24 under high pressure. Vacuum pump
The strongly adsorbed component such as CO ₂ released from 16 is supplied as fuel for the steam reforming furnace 1 from the flow path 25.

Further, the high-pressure weakly adsorbed components of CO and hydrogen supplied from the flow path 22 are combined with the raw material gas in the shift converter 4 to carry out the above-mentioned hydrogen purification.

As described above, in this embodiment, the CO adsorbed from the adsorption stages 12a and 12b that absorbs weakly adsorbed components is introduced into the shift converter 4 together with the hydrogen remaining in the adsorption stages, and the CO reacts there. To generate hydrogen, which are then adsorbed to the adsorption stage 8
By introducing into a, 12a; 8b, 12b, the recovery rate of hydrogen can be significantly increased.

In order to confirm the effect of the embodiment shown in FIG. 1, the inventor has a raw material dry gas amount of 100 Nm ₃ / h. Component H ₂ 70vol% CO ₂ 25vol%, CO5vo
The gas at the shift converter outlet with l% and pressure of 7 atm is
The hydrogen purification performance of the present invention was confirmed by introducing the hydrogen purification apparatus shown in the figure.

Fig. 2 shows the relationship between the adsorption column pressure (atm) and product hydrogen recovery rate (vol%) at a product hydrogen concentration of 99.9 vol% in this equipment. The solid line, the example, and the alternate long and short dash line show the hydrogen purification performance (recovery rate) of the conventional 4-column high-pressure adsorption atmospheric pressure regeneration. Conventional method
It was confirmed that the maximum hydrogen recovery rate at 20 atm was less than 85% and that at 5 atm was less than 40%, whereas in the present example, the hydrogen recovery rate was almost 95% at 3 atm or more.

Further, Fig. 3 shows the relationship between the adsorption tower pressure (atm) at a product hydrogen concentration of 99.9 vol% and the hydrogen purification amount with 1 Ton of adsorbent. In this embodiment, a value of 80 to 200 Nm ₃ / h / Ton is shown, which is 30% higher than that of the conventional method. This is because, in this example, since there is no pressure equalization between multiple columns (adsorption stage), a larger adsorption capacity can be maintained.

As shown in the above embodiment, this embodiment can obtain a high hydrogen recovery rate even at a low pressure, and therefore, it is not necessary to depressurize hydrogen at the time of use. Suitable for supplying hydrogen to. Further, for the same reason, it is suitable for purifying and recovering hydrogen from a low-pressure hydrogen-containing gas such as off-gas of a coke oven.

〔The invention's effect〕

As described above, the present invention is, in each system of the pressure swing type hydrogen purifier, a first adsorption stage for adsorbing strongly adsorbed components of CO ₂ or more and a _second adsorption stage for adsorbing weakly adsorbed components of CO or less. By adsorbing in a stage and repeating this alternately in a plurality of systems, a high concentration of hydrogen can be continuously recovered.

In addition, CO, which is a strongly adsorbed component separated from the first adsorption stage,
₂ , H ₂ O, etc. are released to the outside of the system, and CO desorbed from the second adsorption stage and hydrogen remaining in the same adsorption stage are introduced into the shift converter to generate hydrogen by CO, and these are adsorbed again. By introducing the hydrogen into the stage, the recovery rate of hydrogen can be significantly increased.

Furthermore, according to the present invention, a high hydrogen recovery rate can be obtained even when the pressure of the adsorption stage is low.

[Brief description of the drawings]

FIG. 1 is a system diagram of one embodiment of the present invention, FIG. 2 is a graph showing the relationship between pressure and product hydrogen recovery rate regarding the effect of the same embodiment, and FIG. 3 is an adsorbent amount regarding the effect of the same embodiment. It is a graph which shows the relationship of product hydrogen amount. 1 ... Steam reforming furnace, 4 ... Shift converter, 8a, 8b ... Strong adsorption component adsorption stage, 9 ... Alumina, 12a, 12b ... Weak adsorption component adsorption stage, 1
5… Product hydrogen holder, 16… Vacuum pump, 21… Recirculation compressor.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Seiichi Tanabe 2-5-1, Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Heavy Industries, Ltd. (72) Inventor Shozo Kaneko 1-1-1, Atunoura-cho, Nagasaki-shi, Nagasaki Mitsubishi Heavy Industrial Co., Ltd. Nagasaki Shipbuilding Co., Ltd. (72) Inventor, Nagao Kurume, Nagano Prefecture Nagasaki City, No. 1-1 Atsunoura-machi Mitsubishi Heavy Industries, Ltd. Nagasaki Shipyard (56) Reference JP-A-1-242120 (JP, A) JP Sho 60-103002 (JP, A)

Claims (1)

(57) [Claims] 1. A high-purity hydrogen is purified by adsorbing a component of hydrogen and a component of hydrogen in a raw material gas, such as CO and CO ₂ which accompanies it under pressure, by an adsorbent to purify high-purity hydrogen. In a pressure swing type hydrogen purification method that has multiple systems for desorbing and regenerating the adsorbent, and repeating the adsorption and desorption alternately in each system, fill the adsorbent that adsorbs strongly adsorbed components of CO ₂ or more. To the first adsorption stage, and then to the second adsorption stage filled with an adsorbent that adsorbs weakly adsorbed components below CO,
Introducing a pressurized raw material gas, adsorbing strongly adsorbed components of CO ₂ or more in the first adsorption stage from the raw material gas,
Then, in the second adsorption stage, weakly adsorbed components of CO or less are adsorbed to obtain high-purity hydrogen, and then the strongly adsorbed components adsorbed in the first adsorption stage are desorbed under reduced pressure to the outside of the system. At the same time as releasing the weakly adsorbed components adsorbed in the second adsorption stage under reduced pressure, they are introduced into the shift converter together with the hydrogen remaining in the second adsorption stage and reacted with CO and H ₂ O to produce hydrogen. Is generated and further introduced into the adsorption stage for re-purification, and a pressure swing-type hydrogen purification method is characterized.