JPH0465302A - Pressure-swing hydrogen purification method - Google Patents

Abstract

PURPOSE:To obtain high-purity hydrogen in good yield by providing a first adsorption stage packed with an adsorbent capable of adsorbing a strongly adsorptive component such as CO2 and a second adsorption stage packed with an adsorbent capable of adsorbing a weakly adsorptive component such as CO. CONSTITUTION:The steam-reformed gas 2 from a steam reforming furnace 1 is introduced into a shift converter 4 to reduce the CO content. The gas is then introduced into the first adsorption stage 8a or 8b packed with an adsorbent capable of adsorbing a strongly adsorptive component such as CO2 to adsorb CO2, etc., The gas is further introduced into the second adsorption stage 12a or 12b packed with an adsorbent capable of adsorbing a weakly adsorptive component such as CO to adsorb CO, etc., to obtain high-purity hydrogen 24. The strongly adsorptive components adsorbed by the first adsorption stage 8a or 8b are desorbed under reduced pressure and discharged outside the system. Meanwhile, the weakly adsorptive components adsorbed by the second stage 12a or 12b are desorbed under reduced pressure, introduced into the converter 4 along with the hydrogen remaining in the second adsorption state 12a or 12b, and CO reacts with H2O therein to generate hydrogen.

Description

[Detailed Description of the Invention] [Industrial Application Field] Hydrogen gas such as water-stalk-gas reformed gas from a water-based air-to-air reformer in an ammonia plant, city gas plant, hydrogen production plant, etc. or coke oven gas, and accompanying hydrogen gas. co, c
A pressure swing type hydrogen purification method from a gas such as O2 is used.

[Conventional technology]

H2 in coke ovens, oil refining plant off-gas, natural gas, liquefied petroleum gas, water vapor reforming furnaces used as raw materials for naphtha, etc.
, Co, Co, , H2O, etc. are produced as main components. Selective enrichment of H2 from this gas mixture is
This is extremely meaningful and important considering the wide range of uses of 2.

H7 is conventionally used in hydrogenation reactions in which higher hydrocarbons are lowered by contacting them in the presence of a catalyst, and is also used as a basis for chemical industry applications such as methanol synthesis and ammonia synthesis! It is widely used as 1171 quality.

As for other uses, since a large amount of energy is instantaneously generated by the combustion reaction of H2 with 02, it is being used as a fuel with rocket fuel in fuel cells, hydrogen engines, etc.

To give an overview of a typical conventional H2 purification method, the apparatus is composed of three or four or more adsorption towers, an on-off valve, and a flow rate control valve.

In this device, f(z, CO, C
A high-pressure mixed gas containing 0zH20 etc. as a main component is sequentially released from the population side) 120. CO2 and Co are adsorbed in the order of strongly adsorbed components to poorly adsorbed components.

An adsorbent suitable for adsorbing strongly adsorbed components, such as alumina or activated carbon, is usually arranged near the entrance of the adsorption tower, and a zeolite-based adsorbent is arranged downstream for weakly adsorbed components.

Since H2 does not exhibit adsorption ability for most adsorbents, it flows under high pressure from the outlet. If this process is continued, gases other than H2 will begin to flow from the tower outlet, so the supply of raw material gas is terminated before that. (Adsorption step completed) In this Shisen Tower, the internal pressure has reached atmospheric pressure and the adsorbent has already been regenerated as described below. (Completion of regeneration process) Since a large amount of H2 still remains in the column at the end of the adsorption process, if the column at the end of the regeneration process is tied at the rear, H2 will flow out from the high pressure column and be collected in the low pressure column. The pressures in both towers become equal. (Pressure equalization process between columns) After this, the front of the column is further opened and the pressure is reduced in a countercurrent flow, the pressure inside the adsorption column decreases, and the adsorbed Co, CO2H, O, etc. are separated from the adsorbent and released outside the system. be done.

(Depressurization process) Since this process alone is insufficient, the product H2 under atmospheric pressure
When a portion of the adsorbent is flowed countercurrently, the adsorbed gas is more thoroughly removed from the adsorbent and regenerated. (Product H purge) H2 can be continuously recovered by performing the same operation in a plurality of towers at different times.

In the above hydrogen purification method, the recovery rate of +2 increases as the number of columns increases and the pressure is equalized between the columns, but the amount of H2 purified per unit adsorbent and unit time increases. descend.

(2) Since high-pressure adsorption and atmospheric pressure regeneration are used, if the pressure decreases, it becomes difficult to secure H2 for the product H2 barge, so it is desirable that the adsorption pressure be 10 atm or more.

It is said that

For this reason, efforts have been made to improve the recovery rate of the product lI2, which mainly involves pressure equalization between columns, but the recovery rate of H2 is only 85%.
is the best.

At 824 degrees, highly pure H2 is easily obtained and the maximum concentration reaches 99.999%.

(One problem to be solved by the invention) In the above conventional method, in order to recover unadsorbed hydrogen, inter-column pressure equalization is performed successively between the high pressure column after dyeing is finished and the low pressure column after vacuum regeneration is finished. A method is being taken. This method recovers hydrogen without using utilities such as electricity, but it has the following drawbacks.

■ In order to achieve a high hydrogen recovery rate, it is necessary to increase the number of columns and perform multi-stage pressure equalization operations. This requires a complex soaking system and a large number of valves.

■ In order to achieve a high hydrogen recovery rate, a multi-stage pressure equalization operation is required, so the adsorption pressure must be set high.

As an example of hydrogen purification from a steam reformer, hydrogen 70 vol 1% COz 25 vol 1% downstream of a soft reactor.

In the case of purifying 99.9vo1% hydrogen from gas with CO5ν01%, it is said that the hydrogen recovery rate is 70% in a four-column adsorption tower with a pressure of 2Qatm, and 85% in a ■00 column. The hydrogen recovery rate will drop below 60%.

The reason for this decrease in hydrogen recovery rate is firstly that the adsorption zone (adsorbed zone) of weakly adsorbed components below CO is long, resulting in high-purity hydrogen remaining between the adsorbents and in the voids inside the adsorbent. ,
This is due to the fact that it is not collected.

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

[Means to solve the problem]

The present invention purifies high-purity hydrogen by adsorbing components accompanying hydrogen in a raw material gas such as hydrogen and accompanying COCO2 with an adsorbent under pressure, and then removes the adsorbed components under reduced pressure and adsorbs them. In the pressure swing type hydrogen purification method, which is equipped with a plurality of systems for regenerating the agent and alternately repeats the above adsorption and desorption in each prefecture, the first adsorption stage is filled with an adsorbent that adsorbs strongly adsorbed components of CO2 or more. Next, the pressurized raw material gas is introduced into a second adsorption stage filled with an adsorbent that adsorbs weakly adsorbed components below CO, and from the raw gas, the first adsorption stage first adsorbs strongly adsorbed components above CO□. After adsorbing the components and then adsorbing weakly adsorbed components below CO in the second adsorption stage to obtain highly pure hydrogen, the strongly adsorbed components adsorbed in the first adsorption stage are removed under reduced pressure. At the same time, the weakly adsorbed components adsorbed in the second adsorption stage are removed under reduced pressure, and then introduced into the shift converter together with the hydrogen remaining in the second adsorption stage, where CO and H, It is characterized in that it reacts with O to generate hydrogen, and then introduces it into the adsorption stage for repurification.

[Function] In the present invention, co, co, etc. in the raw material gas are adsorbed in the first and second adsorption stages in the adsorption tower, and high-purity hydrogen passes through the first and second adsorption stages. 3M is passed through and recovered, and this is carried out sequentially in a plurality of systems to continuously recover hydrogen.

Looking at the adsorption stages in each prefecture, when the above adsorption process is completed, the first adsorption stage filled with adsorbent that has adsorbed strongly adsorbed components of CO2 or more is depressurized, and the strongly adsorbed components are removed from the adsorbent. The adsorbent is desorbed and regenerated, and strongly adsorbed components of CO2 or more desorbed from the adsorbent are discharged to the outside of the system.

On the other hand, in the second adsorption stage, which adsorbs a component weaker than CO, at the end of the adsorption step, the weakly adsorbed component is adsorbed on the adsorbent, and high-purity hydrogen remains in the void under high pressure. This second adsorption stage is depressurized, weakly adsorbed components below CO are removed from the adsorbent, and the adsorbent is regenerated. In addition, adsorbed CO and components with weaker adsorption power than CO are separated from the adsorbent and introduced into the soft converter together with the remaining hydrogen. In the shift converter, CO is converted into CO+I□0-t(2+ CO It is converted into hydrogen as □, joins with the raw material gas, and reaches the above-mentioned first and second adsorption stages to be purified.

In this way, in the present invention, hydrogen remaining in the second adsorption stage is recovered, CO adsorbed in the second adsorption stage is released from the adsorbent, and hydrogen is thereby obtained in the shift converter. As a result, a high recovery rate of hydrogen can be achieved even if the pressure during adsorption is lowered.

〔Example〕

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

In Figure 1, hydrogen is 70vo1% and COz is 20vo1% Co 10v based on the dry gas that exited the water vapor reformer I.
O1% pressure cuff at- steam reformed gas 10100N/
h passes through the flow path 2 and the heat exchanger 3, cools down to 250°C, and reaches the shift converter 4. The shift converter 4 is filled with a shift catalyst 5, and CO+H, O→H2+CO□
Through this reaction, CO is reduced to 5νo1%, and passes through the flow path 5 and the valve 7a to the strongly adsorbed component adsorption stage 8a, one of the strongly adsorbed component adsorption stages 8a8b arranged in parallel with COz or more.

The strongly adsorbed component adsorption stage 8a is filled with alumina 9 at the front for moisture adsorption and (Na-X) 10 at the rear as a CO□ adsorbent, so that strongly adsorbed components such as water and CO□ are adsorbed and removed. The gas then passes through valve lla and reaches a downstream adsorption stage 12a for weakly adsorbed components below CO. c in the weakly adsorbed component adsorption stage 12a.

Filled with adsorbent (Ca4N3), weakly adsorbed components such as CO are adsorbed, and highly concentrated hydrogen of 99.9vol.1% or more reaches the product hydrogen holder 15 through the valve 14a. The other strongly adsorbed component adsorption stage 8b is placed at
, the weakly adsorbed component adsorption stage 1.2b is operated by the vacuum pump 16,
A vacuum of 0.5 ats has been reached and the adsorbent is being regenerated.

When the regeneration of the adsorption stages 8b and 12b is completed, 1la
17a, 17b, and llb are opened and other valves are closed, the hydrogen remaining behind the adsorption stage 12a is recovered to the low-pressure adsorption stage 12b, and the adsorption stage 8812a at 7 atm, which has completed adsorption, is depressurized to 3.75 atm. On the other hand, adsorption stages 8b and 12b at 05atm, which have completed regeneration, are 3.75
The pressure is increased to ATM, and the pressures between the adsorption stages become equal.

Focusing on the adsorption stage where the pressure has been reduced to 3.75 atm, in the strongly adsorbed component adsorption stage 8a, valves 18a and 19 are first opened to reduce the pressure above atmospheric pressure, and when it is below atmospheric pressure, valve 19 is closed and the vacuum pump I6 is used to drain the system out of the system. Strongly adsorbed components such as C02 are desorbed. On the other hand, in the weakly adsorbed component stage 12a, the valve 20a is opened, and the CO released from the adsorbent is transferred to the adsorption stage 1 by the recirculation compressor 21.
Gas containing hydrogen as a main component remaining in 2a is recirculated from the flow path 22 to the upstream side of the shift converter 4. When the pressure in the weakly adsorbed component stage 12a becomes atmospheric pressure, the valve 20a is closed and the valve lla is opened, and the remaining gas is evacuated in the same manner as in the strongly adsorbed component stage 8a.

After this, the bite stages 8a and 12a8b arranged in parallel
, 12b and perform the same operation.

In addition, in the above adsorption step, from 3.75at to 7a
When increasing the pressure to tm, the valve 23.17a is opened to allow product hydrogen to flow countercurrently from the holder 15 to increase the pressure. There is.

The high purity hydrogen of 99.9v01% that has reached the product hydrogen holder 15 is taken out from the flow path 24 under high pressure.

Strongly adsorbed components such as CO2 released from the vacuum pump 16 are supplied from the flow path 25 as fuel to the steam reforming reactor I.

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, and the above-mentioned hydrogen purification is performed.

As explained above, in this embodiment, the CO adsorbed from the adsorption stages 12a and 12b that absorb weakly adsorbed components is introduced into the soft converter 4 together with the hydrogen remaining in the adsorption stages, where the CO reacts. By generating hydrogen and reintroducing it into the adsorption stages 8a, 12a; 8b, +2b, the hydrogen recovery rate can be significantly increased.

In order to confirm the effect of the example shown in FIG.
The hydrogen purification performance of the present invention was confirmed by introducing gas at the outlet of a shift converter of a pressure cuff ATM containing 225 vol 1% and Co 5 vol % into the hydrogen purification apparatus shown in FIG.

Figure 2 shows the relationship between the adsorption tower pressure (atm) and the product hydrogen recovery rate (v01%) at a product hydrogen concentration of 99.9vol% in this device. The solid line shows the example, and the dashed-dotted line shows the hydrogen purification performance (recovery rate) of the conventional four-column high-pressure adsorption atmospheric pressure regeneration.

The conventional method has a maximum of 85% at 20 atm and 4 at 5 atm.
It was confirmed that in this example, the hydrogen recovery rate was approximately 95% at 3a Lm or higher, whereas the hydrogen recovery rate was 0%.

In addition, the third panel shows the relationship between the adsorption tower pressure (atm) and the amount of hydrogen purified by the 1 Ton adsorbent at a product hydrogen concentration of 99.9 vol%. In this example, 80 to 20 ONm'/h
/Ton, which is 30% higher than the conventional method. this is,
This is because, in this example, there is no pressure equalization between the multi-stage columns (adsorption stages), so a larger adsorption capacity can be maintained.

In addition, as shown in the above example, this example can obtain a high hydrogen recovery rate even at low pressure, and therefore,
Since there is no need to reduce the pressure of hydrogen during use, it is suitable for supplying hydrogen to fuel cells, etc., which have low pressure resistance. For the same reason, it is also suitable for purifying and recovering hydrogen from low-pressure hydrogen-containing gas such as off-gas from a coke oven.

〔Effect of the invention〕

As explained above, the present invention is a pressure swing type hydrogen seismic device! 8! In the main thread of the device, adsorption is performed in a first adsorption stage that adsorbs strongly adsorbed components of CO and above, and a second adsorption stage that adsorbs weakly adsorbed components of CO and below, and this is sequentially and alternately carried out in multiple systems. By repeating this process, high concentration hydrogen can be continuously recovered.

In addition, co, which is a strongly adsorbed component separated from the first adsorption stage,
. The hydrogen recovery rate can be significantly increased by introducing hydrogen into the hydrogen.

Furthermore, the present invention can obtain a high hydrogen recovery rate even if the adsorption stage is at a low pressure.

[Brief explanation of drawings]

Fig. 1 is a system diagram of an 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 the third review is a graph showing the effect of the embodiment as a function of adsorbent amount. It is a graph showing the relationship between product hydrogen amounts. ■...Water stem gas reforming furnace, 4...Soft converter 8a, 8b...Strongly adsorbed component adsorption stage 9...Alumina 12a, 12b...Weakly adsorbed component adsorption stage 15...Product hydrogen holder , 16...vacuum pump. 21... Recirculating compressor. Figure 1

Claims (1)

[Claims] High-purity hydrogen is purified by adsorbing components accompanying hydrogen in the raw material gas, such as hydrogen and accompanying CO, CO_2, etc., with an adsorbent under pressure, and then removing the adsorbed components under reduced pressure to remove the adsorbent. In a pressure swing hydrogen purification method that has multiple regenerating systems and alternately repeats the above adsorption and desorption in each system, the first adsorption stage is filled with an adsorbent that adsorbs strongly adsorbed components of CO_2 or more. Next, the pressurized raw material gas is introduced into a second adsorption stage filled with an adsorbent that adsorbs weakly adsorbed components of CO or less, and the first adsorption stage first adsorbs strongly adsorbed components of CO_2 or more from the raw gas. After adsorbing the adsorbed components and then adsorbing weakly adsorbed components below CO in the second adsorption stage to obtain highly pure hydrogen, the strongly adsorbed components adsorbed in the first adsorption stage are removed under reduced pressure. At the same time, the weakly adsorbed components adsorbed in the second adsorption stage are removed under reduced pressure and then introduced into the shift converter together with the hydrogen remaining in the second adsorption stage to generate CO and H_2O. A pressure swing type hydrogen purification method characterized by reacting to generate hydrogen and further introducing the hydrogen into the above-mentioned adsorption stage for repurification.