JPS60819A - Method for separating and removing carbon dioxide in gaseous mixture containing carbon monoxide by using adsorption method - Google Patents

Abstract

PURPOSE:To remove CO2 from a mixed gas contg. easily adsoprtive components such as CO with a variable-pressure adsorption method by carrying out the purging with the product gas after a reduced-pressure evacuation stage during vacuum evacuation. CONSTITUTION:Adsorption towers A and B contg. an adsorbent such as zeolite are evacuated under reduced pressure by a vacuum pump 16. The waste gas from a steel making plant contg. CO is introduced into the adsorption tower A under pressure by opening a valve 2. A part of easily adsorptive components such as CO2, CO, and N2 is adsorbed, and the remainder is recovered from a valve 5 as the product gas. After finishing the adsorption stage, the valves 2 and 5 are closed, and a valve 3 is opened to release the pressure inside the adsorption tower A to the atmospheric pressure. Then the valve 3 is closed, a valve 4 is opened, and the tower is evacuated under reduced pressure by a vacuum pump to desorb remaining CO2. Then the valves 6 and 4 are opened to introduce the product gas, and the remaining CO2 is desorbed while evacuating under vacuum. After the product gas is purged, the valves 4 and 6 are closed, a valve 7 is opened to introduce the product gas, and the internal pressure of the tower A is increased to the adsorption pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes a pressure fluctuation type adsorption separation method (hereinafter referred to as PSA method) to remove mainly carbon dioxide, -carbon oxide, nitrogen and hydrogen gas from steelworks exhaust gas, mainly converter or blast furnace gas. Several 1 o o o p of carbon dioxide from the mixed gas containing
This relates to a method for removing even prn.

Traditional methods for removing carbon dioxide from gas include a wet dissolution method in which it is dissolved in a solvent, and an adsorption method that uses an adsorbent that has the ability to adsorb carbon dioxide, such as synthetic zeolite. has been adopted. Although the method of dissolving carbon dioxide in a solvent has a high efficiency in removing carbon dioxide, the gas becomes saturated with moisture, etc., and the product gas needs to be dried, and maintenance is troublesome.

In addition, to remove carbon dioxide by adsorption method, temperature fluctuation adsorption method (TS
There are two methods: method A) and pressure fluctuation adsorption method (PSA method) using a pressure difference in the atmospheric gas of the adsorbent.

The temperature fluctuation type adsorption method requires energy to heat and cool the adsorption tower, and has disadvantages such as a long adsorption tower switching time and a large amount of adsorbent. In comparison, the pressure fluctuation type adsorption method has advantages such as not requiring energy for heating and cooling, and requiring a shorter adsorption tower switching time (as it is possible to do so, the amount of adsorbent required is small. Up until now, the purpose of the adsorption method has been to remove carbon dioxide in the air, or carbon dioxide in the adsorbed gas component by adsorbents such as hydrogen and helium.

An attempt was made to remove carbon dioxide from steelworks exhaust gas, mainly converter or blast furnace gas, which mainly contains carbon monoxide, carbon dioxide, nitrogen, and hydrogen gas, using the PSA method. It was found that high concentration oxygen gas could not be obtained due to insufficient regeneration. This is-
Since carbon oxide, carbon dioxide, and nitrogen are gas components that are easily adsorbed to zeolite adsorbents, they are co-adsorbed and desorbed from the adsorbent in the order of nitrogen, carbon oxide, and carbon dioxide. This is because the adsorption rate and desorption rate are different, and desorption of carbon dioxide cannot be regenerated by normal pressure purge.

The object of the present invention is to provide a pressure fluctuation type adsorption method capable of removing carbon dioxide in easily adsorbed gas components or co-adsorbed gas components to an adsorbent to several 100 PP''.

It is difficult to use the pressure fluctuation adsorption method to remove carbon dioxide gas from a mixed gas such as steelwork exhaust gas containing carbon monoxide, but it is difficult to regenerate the product gas for regeneration.
%, it is uneconomical and is not put to practical use. However, as a result of experiments and research, the present inventors discovered a method for removing carbon dioxide to several tens of pprn from a mixed gas containing -carbon oxide, and completed the present invention.

The present invention will be explained in detail below.

When separating and removing carbon dioxide from steelworks exhaust gas using the adsorption method, two or more adsorption towers filled with zeolite-based adsorbents are used. An adsorption step in which gas is introduced and the adsorbent mainly adsorbs carbon dioxide until the end point or near the end point of the adsorption step to obtain a product gas; 11) After the adsorption step, the pressure of the adsorption tower is increased, preferably in the countercurrent direction. 111) After the completion of depressurization and depressurization, a production reduction exhausting step in which the gas inside the tower is exhausted to near vacuum using an exhaust pump, preferably in the countercurrent direction, lv ) An exhaust purge step in which the product gas or nitrogen gas is introduced countercurrently into the adsorption tower that has been depressurized and exhausted, and ■) Product gas is preferably flowed countercurrently into the tower after exhaust purging. A product pressurizing step of pressurizing the product, and the above operation is repeated in all the adsorption towers by periodically changing the flow between the adsorption towers.

Step (1) of the present invention is an adsorption step in which the mixed gas is introduced into the adsorption tower and the adsorbent adsorbs easily adsorbable gases such as carbon dioxide under pressure. The mixed gas is introduced from the bottom of the tank, and the purified gas exits from the top as a product gas.

Step (11) is a pressure reduction step in which the introduction of raw material gas into the column is stopped, the pressure is reduced in the column, the gas flows out in the countercurrent direction, and the reduced pressure gas release valve is closed at or near atmospheric pressure.

■Progress Qii) is the exhaust process. Since the depressurization step alone is not enough to desorb adsorbed components such as carbon dioxide, residual carbon dioxide is desorbed by evacuation in the countercurrent direction. In this case, the degree of vacuum in the adsorption tower may be kept close to the partial pressure of carbon dioxide contained in the target product gas.

With this vacuum evacuation and the conventional PSA method of removing carbon dioxide using the above-mentioned depressurization or depressurization step and purge at normal pressure, desorption may not be sufficiently performed, or even if regeneration is possible, the purified product 40 to 50% of the gas should be used as purge gas to improve the recovery rate since the product gas recovery rate is poor, and to allow the adsorbent to fully control the desorption effect of carbon dioxide. Various processes such as evacuation As a result of careful consideration of the adsorption and desorption speed in the mixed gas where co-adsorption is performed, we found that by performing evacuation and purging in vacuum evacuation after the evacuation process, It was found that good results were obtained.

Step (1v) is an exhaust purge step. Product gas or nitrogen gas is introduced countercurrently into the adsorption tower that has been evacuated to reduce pressure, and the remaining carbon dioxide that has not been desorbed by the adsorbent is removed by the entrainment-desorption effect by the partial pressure of carbon dioxide in the product gas or nitrogen gas. , which attempts to desorb carbon dioxide from an adsorbent.

Step (v) is a product gas pressurization step. This is a step in which the product gas is introduced into the tower after the exhaust purging step and the adsorption tower is pressurized with the product gas in order to make the gas concentration distribution of the adsorbent in the adsorption tower uniform.

As the adsorbent used in the present invention, activated alumina is used to remove moisture in the mixed gas, and zeolite main adsorbent and activated carbon adsorbent are used to adsorb and remove carbon dioxide in the mixed gas. The concentration of carbon dioxide in the product gas can be changed by selecting different adsorbents depending on the concentration of carbon dioxide.

The following is a converter exhaust gas that is a typical example of the present invention.

A method for removing carbon dioxide therein will be explained in detail, but the method of the present invention is not limited to these specific examples.

Adsorbents that can be used in the present invention include natural or synthetic zeolites, activated carbon, silica gel, and the like.

A combination of an activated alumina layer and a zeolite adsorbent layer, a combination of an activated alumina layer and an activated carbon adsorbent layer, or a combination of an activated alumina layer, an activated carbon adsorbent, and a zeolite adsorbent is preferable. These layers are applied in the order listed.

Figure 1 is a flow sheet for continuously removing carbon dioxide from converter flue gas by adsorption method.

Adsorption towers A and B house adsorbents that selectively adsorb easily adsorbable components such as carbon dioxide. Adsorption towers A and B are depressurized and evacuated to 100 Torr or less, preferably 6 oTorr or less, using a vacuum pump (16), and now the raw material gas is introduced into adsorption tower A under pressure, and a valve is used to increase the pressure from the vacuum state to the adsorption pressure. (2) This is done by opening. At this time, all valves other than valve (2) are closed. Adsorption tower B still maintains a vacuum state at this step.

After increasing the pressure of adsorption tower A to the adsorption pressure, the adsorption pressure is 0.0, 1
From kg/am2G to 3, Okg/am2G preferred L <k'r, 0.5 k+1? /c+a2G Cara 1, valve (to maintain Okg/cTLG adsorption pressure)
5) is opened, and a portion of carbon dioxide, carbon monoxide, and nitrogen, which are easily adsorbed gas components, are adsorbed by the adsorbent, and the rest is recovered as product gas. After completion of the adsorption process for a certain period of time or a certain amount, the mixed gas introduced pulp (2) and the output robulp (5
) opens the closing valve (3) and releases the internal pressure of the adsorption tower A to near atmospheric pressure. When the adsorption tower A reaches near atmospheric pressure, the valve (3) is closed, and the valve (4) is opened from the bottom of the adsorption tower to perform reduced pressure exhaust using a vacuum pump to remove carbon dioxide, an easily adsorbed gas component adsorbed on the adsorbent. Attach and detach. The exhaust pressure at this time is 100 Torr or less, preferably 60 TOrr or less. After the evacuation is completed, the valves (6) and (4) are opened and the product gas is introduced while evacuation is performed and carbon dioxide remaining in the adsorbent is desorbed. At this time, the valve (4) is opened by an amount relative to the purge amount.

After completing the product gas purging process for a certain period of time or a certain amount, the valves (4) and (6) are closed, the valve (forced) is closed, and the product gas is introduced into the adsorption tower, and the pressure inside the tower is increased to the adsorption pressure.

By sequentially repeating the above operations in each adsorption tower, carbon dioxide is continuously adsorbed onto the adsorbent and removed.

Example (1) To further specifically explain the present invention, co-C02
This is the result of separating and removing carbon dioxide using a mixed gas.

As described above, the separation/removal step was carried out based on the purification cycle of "raw material pressurization - depressurization, exhaust, exhaust purging, product pressurization".

Activated Zeo Herb 1/8 "0.
After a steel adsorption tower (IBXlm) filled with 5 kg was evacuated and maintained at 6Q Torr, Go2 = 3.8% GO.
= 96.2% was introduced from the bottom of the column at a linear velocity of 6.6 cm/sec to conduct a carbon dioxide removal experiment.

Experimental conditions Adsorbent filling amount Zeoherb ZE-501500g Operating temperature 25U Adsorption pressure 1.0kg/cIn2G raw material supply amount 291 Exhaust purge gas amount 3.41 Purge vacuum degree 150 TO7-r Product N, x, C○2 concentration 400 ppm Product Gas amount 2
2.611 In the conventional normal pressure purge method, the amount of purge gas used for regeneration after carbon dioxide adsorption is 40 to 40% of the purified product gas.
In the case of only the vacuum evacuation method, the throughput was 1/3 to 1/4 of that of the exhaust purge method.

Example (2) These are the results of separation and removal using the same apparatus as in Example (1) under the following experimental conditions.

Experimental conditions Gas composition C0 = 96.6% Go2 = 3.7% Adsorbent filling amount Shirasagi G Filter 00U Operating temperature 25, C Adsorption pressure 1.0 kg/CTL2G Adsorption rate 6.5 Excel/sec Raw material supply amount 31. i Exhaust purge amount 6.51 Purge vacuum degree 135'forr Product gas CO2 concentration Filtration 30 PPm Product gas amount 21.7A' Example (3) Separation and removal was carried out under the following experimental conditions using the same equipment as Example (1). This is the result.

Experimental conditions Gas composition GO = 96.3% CO2 = 6.7% Adsorbent filling amount Activated carbon Shirasagi G 200. ! 7 Zeohers ZE-501130, 9' Operating temperature 25C Adsorption pressure 1. OI'vcIIL2G adsorption speed 6.5 cm/
Se' Raw material supply amount 30.31 Exhaust purge amount. 6.6 Nopurge vacuum degree 200 Torr Product gas concentration 380 ppm Product gas amount 20.7 # Example (4) The activated adsorbent was transferred to a steel adsorption tower (12 B x 2.7 m)
Two towers were filled and an experiment was conducted to separate and remove carbon dioxide using converter exhaust gas.

Experimental conditions Gas composition C0-85%, N2=4%, C02=4%,
H, Near% Adsorbent filling amount Iono 1-bu ZE-50166kfil
Column adsorption rate 6.6crrv'se' Raw material supply amount 48.9M3/H Exhaust purge amount 4.4M3/H Purge vacuum degree 100TOrr Product gas concentration Go2=400ppm C0=87.5
5% N2 = 4.3% H2 = 8.0% Product gas amount 42.9M37H was obtained.

As described above, according to the present invention, it has been possible to separate and remove carbon dioxide down to several hundred ppm by the pressure fluctuation adsorption method, which has been difficult with gas compositions in which co-adsorption exists. .

[Brief explanation of drawings]

The figure shows a flowsheet implementing the invention. Patent applicant: Kawasaki Steel Corporation Osaka Sanso Kogyo Co., Ltd. (4 other people)

Claims (1)

[Scope of Claims] (α) The mixed gas is introduced into one tower that has completed regeneration, and the adsorbent mainly adsorbs carbon dioxide at the adsorption pressure until the end point or near the end point of the adsorption process, thereby producing a product gas. (b) a depressurization and release step in which the pressure of the adsorption tower is lowered to atmospheric pressure or near atmospheric pressure after the adsorption step is completed; (C) an exhaust step in which the inside of the tower is evacuated to near vacuum below atmospheric pressure; (d) Exhaust purge step in which carbon dioxide adsorbed on the adsorbent is purged while exhausting while introducing the product gas, a gas with low carbon dioxide close to the product gas, or crab gas in a countercurrent flow into the adsorption tower that has been exhausted under reduced pressure. , (e) A product pressurization step in which the product gas is passed through the tower after the exhaust/ξ-di step and the tower is pressurized, and the flow between the adsorption towers is periodically changed to ensure that all adsorption towers A method characterized by repeating the above operations.