JPH0693968B2 - Pressure swing adsorption device for carbon dioxide recovery from source gas containing nitrogen oxides - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a carbon dioxide recovery pressure for adsorbing and recovering carbon dioxide from a nitrogen-based raw material gas by an adsorbent. More particularly, it relates to a pressure swing adsorption device for separating carbon dioxide from a raw material gas containing nitrogen oxides as impurities, such as combustion exhaust gas discharged from a converter exhaust gas boiler.

<Prior Art> Various techniques for separating, recovering and utilizing carbon dioxide from a nitrogen-based source gas have been conventionally known.

For example, a raw material gas that has been subjected to a pretreatment such as dust removal or dehumidification is passed under normal pressure or pressure to an adsorption tower filled with an adsorbent to adsorb carbon dioxide, and a carbon dioxide is adsorbed by a vacuum pump or the like. There is a pressure swing adsorption device that recovers carbon. Using this device, carbon dioxide can be efficiently recovered from the raw material gas.

<Problems to be Solved by the Invention> As a raw material gas of the pressure swing adsorption device, it is possible to use combustion exhaust gas from a converter exhaust gas boiler that uses converter exhaust gas because it contains a large amount of carbon dioxide. Conceivable.

However, the exhaust gas from the converter exhaust gas boiler contains a certain amount of nitrogen oxides (NO _X ), and this nitrogen oxide is adsorbed by the adsorbent and accumulates, thereby increasing the adsorption capacity of the adsorbent. It is known to gradually decrease.

Therefore, in order to remove nitrogen oxides from the combustion exhaust gas of the converter exhaust gas boiler in advance, a nitrogen oxide removal tower filled with another adsorbent for adsorbing nitrogen oxides inside, and ammonia (NH ₃ ) and It is conceivable to install a nitrogen oxide catalytic cracking device that reduces nitrogen oxides with a catalytic reduction catalyst before the pressure swing adsorption device, but the equipment is relatively large and the amount of chemicals used is large. Therefore, a huge cost is required. In addition, there is a problem that the removal efficiency of nitrogen monoxide (NO) is particularly poor in the nitrogen oxide removal tower using the adsorbent. There is also a problem that a device for suppressing the possibility that the gas remains in the raw material gas is additionally required.

Then, as the adsorbent of the pressure swing adsorption device as described above, for example, when using an adsorbent made of activated carbon,
The present inventors have found that when a gas containing a predetermined concentration of nitrogen oxides is continuously passed through the adsorbent, the nitrogen oxides are not adsorbed by the adsorbent at a certain point. Further, when recovering carbon dioxide from the raw material gas as described above,
The main purpose is to separate nitrogen and carbon dioxide,
As will be described later, the adsorption capacity of the adsorbent is such that the selective adsorption of carbon dioxide is rather high because the adsorption amount of nitrogen is much lower than that of carbon dioxide due to the accumulation of nitrogen oxides. Found by others.

In view of such problems of the conventional technology and the findings of the present inventors, the main object of the present invention is to always produce carbon dioxide at a high yield from a raw material gas containing carbon dioxide even when it contains nitrogen oxides as impurities. An object is to provide a low-cost pressure swing adsorption device for carbon dioxide recovery that can be separated and recovered.

[Means for Solving the Problems] <Means for Solving the Problems> Therefore, according to the present invention, the above-mentioned object is to provide the carbon dioxide in a adsorption tower from a source gas containing nitrogen, carbon dioxide and nitrogen oxides as impurities. A pressure swing adsorption device for carbon dioxide recovery for adsorbing and separating the adsorbent in a packed state, wherein the amount of the adsorbent filled in the adsorption tower is adsorbed by nitrogen oxide in the raw material gas. This is achieved by providing a pressure swing adsorption device for carbon dioxide recovery from a raw material gas containing nitrogen oxide, which is characterized by being overfilled according to the saturated accumulation amount of nitrogen oxide accumulated in the agent.

<Operation> As described above, compared with the case where the adsorbent made of, for example, activated carbon is used in a state where the adsorbent does not deteriorate due to the accumulation of nitrogen oxides, the adsorbent is used only in a slightly larger amount, that is, deteriorated by the nitrogen oxide in the raw material gas. The carbon dioxide can always be separated and recovered in a high yield only by using an adsorbent in an amount that allows for the carbon dioxide separation capability. In addition, this concept is widely applicable not only to the combustion exhaust gas of the converter exhaust gas boiler but also to the recovery of carbon dioxide from other raw material gas containing nitrogen oxides.

<Embodiment> Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a pressure swing adsorption device (hereinafter referred to as PSA) for separating and recovering carbon dioxide from combustion exhaust gas from a converter exhaust gas boiler to which the present invention is applied, and a raw material gas and a product gas supplied to the PSA. It is a flow chart showing the flow of.

The fuel exhaust gas discharged from a converter exhaust gas boiler (not shown) (hereinafter referred to as an LDG boiler) is cooled as a raw material gas by a raw material gas cooler 3 and dust is removed by a cooling tower 4. Then, after being dried by the source gas dehumidifier 5, the pre-filter 6
At, the sulfur content is removed and stored in the source gas holder 7. Here, the LDG boiler fuel exhaust gas is carbon dioxide (C
It contains 30.0 vol% to 34.0 vol% as O ₂ ), 100 ppm to 150 ppm as impurity nitrogen oxides, and most of the rest consists of nitrogen (N ₂ ).

The raw material gas holder 7 is connected to a blower 9 via an open / close valve 8, the blower 9 is connected to an adsorption tower 13 via an open / close valve 11, and an open / close valve to an adsorption tower 14 provided in parallel with the adsorption tower 13.
Connected via 12. The adsorption towers 13 and 14 are filled with a predetermined amount of an adsorbent mainly composed of activated carbon. On the side of the adsorption towers 13, 14 opposite to the on-off valves 11, 12 is an on-off valve 1 for releasing the exhaust gas after adsorbing carbon dioxide to the outside.
5 and 16 are provided. Further, an opening / closing valve 17 is connected to the adsorption tower 13 on the same side as the opening / closing valve 11 to collect the product gas adsorbed by the adsorbent, and an opening / closing valve 18 is connected to the adsorption tower 14 on the same side as the opening / closing valve 12. The on-off valves 17 and 18 are connected to each other and are connected in parallel to the vacuum pump 19. Vacuum pump 19
Is connected to the product gas holder 20.

Here, the operation of the blower 9, the on-off valves 11, 12, 15 to 18 and the vacuum pump 19 will be described. As shown in FIG. While the process and the washing process are being carried out, the other tower carries out the desorption process, and the operation is carried out while repeating this process.

Explaining each step, the adsorption tower 13 in FIG.
At this time, only the on-off valve 15 is opened, and the atmosphere is introduced into the tower, which had been in a vacuum in the desorption process before that, and the pressure is increased to normal pressure. Next, the opening / closing valves 8 and 11 are opened, and the adsorption process is performed in which the raw material gas is introduced from the holder 7 into the adsorption tower 13 by the blower 9. Here, in the tower of the adsorption tower 13, carbon dioxide and a small amount of nitrogen in the raw material gas are adsorbed by the filled adsorbent,
The remaining gas is discharged to the outside of the system via the opening / closing valve 15. Next, when the opening / closing valve 8 is closed and 21 is opened, a part of the product CO ₂ gas stored in the holder 20 is introduced into the adsorption tower 13 by the blower 9 in a cleaning step. Here, the nitrogen adsorbed in small amounts in the adsorbent filled in the adsorption tower 13, via an on-off valve 15 by substitution of CO ₂ is discharged out of the system, CO in the tower ₂
Purity increases. Next, the opening / closing valves 11 and 15 are closed and 17 is opened, the CO ₂ adsorbed in the tower of the adsorption tower 13 is decompressed and desorbed by the vacuum pump 19, and the recovered CO ₂ is stored in the product gas holder 20. .

On the other hand, as shown in FIG. 2, while the adsorption tower 13 is performing the pressurizing step, the desorption step, and the washing step, the adsorption tower 14 is performing the desorption step, and then the cycle in which this is reversed is repeated. Incidentally, FIG. 3 shows a schematic component distribution of the adsorption tower in each step.

Due to the structure as described above, this PSA has high purity (97-9
Of CO ₂ 9 vol%) allows recovery. Further, it has been confirmed by the present inventors that when this CO ₂ gas is applied to a liquefaction facility which is an existing process, it can be recovered as liquefied CO _{2 with} higher purity (99.99 vol% or more).

In this embodiment, the case where the adsorption tower is of the two-column type has been shown, but the operation and effect of the present invention will not change if the PSA has a plurality of types such as three-column type and four-column type.

Here, in order to supplement the operation of the present invention, a detailed description will be given with reference to FIG.

As described above, an adsorbent mainly composed of activated carbon is used as the adsorbent filled in the adsorption towers 13 and 14, and nitrogen oxide is adsorbed to the adsorbent, and the oxide against the weight change due to accumulation is accumulated. The adsorbed amount of carbon and the adsorbed amount of nitrogen were measured, and the relationship is shown as a graph in FIG. The adsorbent used for this measurement is one in which a predetermined amount of nitrogen oxide is adsorbed in advance. The gases passed through the adsorbent are substantially pure carbon dioxide gas and nitrogen gas.

In the adsorbents filled in the PSA adsorption towers 13 and 14, as shown in FIG. 4, when nitrogen oxides are accumulated in the adsorbent, the adsorbed amount of carbon dioxide gradually increases. (Solid line A) and the adsorption amount of nitrogen (solid line B) decrease. However, the rate at which the amount of carbon dioxide adsorbed decreases is lower than the rate at which the amount of nitrogen absorbed decreases. That is, the selectivity of carbon dioxide adsorption on the adsorbent is rather improved by the accumulation of nitrogen oxides. This means that the adsorbent in which nitrogen oxides are not accumulated adsorbs a large amount of both nitrogen and carbon dioxide, but when nitrogen oxides are accumulated, the adsorption amount decreases but the purity of the adsorbed carbon dioxide is rather high. Means to become. Therefore, it is the main purpose of PSA to separate nitrogen and carbon dioxide of the source gas,
If the amount of carbon dioxide produced using an adsorbent with no accumulated nitrogen oxides is set to 1.0, the amount of carbon dioxide produced will gradually decrease with the accumulation of nitrogen oxides in the adsorbent (solid line E) Actually, it is about 0.9 when the weight increase of the adsorbent is about 13%, that is, when the accumulation of nitrogen oxides reaches a saturation state, and PSA has no accumulation of nitrogen oxides at all. It was confirmed by experiments that the decrease was only about 10% as compared to when the adsorbent was used (broken line F).

In addition, for the adsorbent that does not accumulate nitrogen oxides at all, the source gas of the composition in charge of exhaust gas from the converter exhaust gas boiler is
The change in the weight of the adsorbent with respect to the adsorption time when the nitrogen oxide was continuously accumulated by passing through the PSA facility was measured, and the relationship is shown as a solid line G in the graph of FIG. Also,
The weight change was measured in the same manner as above for the adsorbent in which the nitrogen oxide was excessively accumulated to increase the weight by 15%, and it is shown as a solid line H in the graph of FIG. As can be seen from FIG. 5, when this raw material gas is used, the amount of nitrogen oxides accumulated in the adsorbent becomes saturated with a weight increase of about 13%. In addition, when the raw material gas is continuously passed through the adsorbent whose weight has been increased by 15% in advance, the weight of the adsorbent, that is, the amount of accumulated nitrogen oxides, gradually decreases, and the solid adsorbent has about the same weight as the solid line G. The amount of accumulated nitrogen oxides increased by 13%.

From the above two graphs, if the adsorbent mainly consisting of activated carbon is used in a slightly larger amount than when it is used in a situation where it does not deteriorate due to the accumulation of nitrogen oxides, nitrogen oxidation is performed before the raw material gas is passed through the PSA. It can be seen that carbon dioxide is always obtained as a product gas in a high yield without removing the substance.

Further, for example, carbon dioxide can be obtained as a product gas in a desired yield from the initial stage of PSA operation by using an adsorbent in which nitrogen oxides are accumulated so that the weight of the carbon dioxide will increase by approximately 13% in advance.

Further, even when another adsorbent is used, if the adsorbent is overfilled with the adsorbent according to the saturated accumulation amount of nitrogen oxides in the adsorbent as described above, Similar actions and effects can be obtained.

[Effects of the Invention] As described above, according to the present invention, as compared with the case where an adsorbent mainly composed of activated carbon is used in a state where it does not deteriorate due to the accumulation of nitrogen oxides, the adsorbent is used in a slightly larger amount, and the product gas As a result, not only is it possible to recover carbon dioxide as a high yield at all times, but it is also possible to reduce the production cost because equipment for removing nitrogen oxides can be downsized or omitted. . In addition, if nitrogen oxides are accumulated in the adsorbent in advance, the yield of carbon dioxide will be PSA.
It does not decrease from the beginning of operation, and management is easy.
From the above, the effect of the present invention is extremely large.

Further, this idea is not limited to the case where the combustion exhaust gas of the converter exhaust gas boiler is used as the raw material gas, and is widely applicable to the recovery of carbon dioxide from the raw material gas containing other nitrogen oxides.

[Brief description of drawings]

FIG. 1 shows the structure and gas flow of a two-column PSA to which the present invention is applied. FIG. 2 shows the operation flow of the double tower PSA. FIG. 3 shows a time schedule of each process in the operation flow of FIG. FIG. 4 is a graph showing the relationship between the weight change of the adsorbent due to the accumulation of nitrogen oxides and the decreasing rate of the carbon dioxide adsorption amount, the nitrogen adsorption amount and the carbon dioxide production amount. FIG. 5 is a graph showing the relationship between the adsorption time of the adsorbent and the weight change of the adsorbent due to the accumulation of nitrogen oxides. 3 ... Raw material gas cooler, 4 ... Cooling tower 5 ... Raw material gas dehumidifier, 6 ... Pre-filter 7 ... Raw material gas holder, 8 ... Open / close valve 9 ... Blower, 11, 12 ... Open / close valve 13, 14 …… Adsorption tower, 15-18 …… Open / close valve 19 …… Vacuum pump, 20 …… Product gas holder 21 …… Open / close valve

Claims (1)

[Claims] 1. A pressure swing for carbon dioxide recovery for adsorbing and separating the carbon dioxide from a raw material gas containing nitrogen, carbon dioxide, and nitrogen oxides as impurities in an adsorbent filled in an adsorption tower. An adsorption device, wherein the amount of the adsorbent filled in the adsorption tower is overfilled according to the saturated accumulation amount of nitrogen oxides accumulated in the adsorbent by the nitrogen oxides in the raw material gas, Pressure swing adsorption device for carbon dioxide recovery from raw material gas containing nitrogen oxides.