JPS5924654B2 - Pressure difference adsorption gas purification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure adsorption gas purification method, and more particularly to a pressure difference adsorption gas purification method and apparatus suitable for separating and removing carbon dioxide and moisture from the air.

When using gases such as air or nitrogen for control, purging, or cryogenic separation, or when producing oxygen-enriched gas or nitrogen-enriched gas using air as a raw material, impurities may be present in the raw material gas. Contained carbon dioxide gas (hereinafter referred to as Co2
It is written as

) and moisture (hereinafter referred to as H2O).

) is important to remove from air, etc., and adsorption treatment is generally performed.

The gas purification method by absorption and monitoring treatment involves regeneration of the adsorbent that has adsorbed the adsorbed substance, and purging of heated gas.
SA (temperature difference adsorption
Abbreviation for gAdsorption.

same as below. ) formula and E"plj, from 8 o'clock] PSA (pressure differential suction! PressureSwing Adsorpt) performed by gas purge without heating at low pressure
Abbreviation for ion.

same as below. ) expressions.

Conventionally, the TSA method using CaA type or NaX type synthetic zeolite as an adsorbent has been adopted, but this method requires heating and cooling, and therefore the switching time between adsorption and desorption is 4 to 8 hours. It had the disadvantage of being long.

Therefore, in recent years, the PSA method has been applied, which, compared to TSAi, does not require heating means or cooling means and can reduce the adsorbent filling capacity by shortening the switching time of the adsorption tower. .

The PSA method involves an adsorption operation that selectively adsorbs and removes specific components in the raw material gas to obtain a purified gas, and an adsorbent is desorbed from the adsorbent used for this adsorption operation in an atmosphere at a lower pressure than the adsorption operation. This is a waste purification method in which a desorption operation for regenerating the adsorbent and a desorption operation are performed alternately.

The apparatus for performing psA2 consists of an adsorption tower containing an adsorption layer, and a first gas passage system that communicates with one end of this tower and is used alternately for supplying raw material gas and exhausting exhaust gas. and a second gas passage system that also communicates with the other end of the base and is used alternately for exhausting purified gas and supplying desorption gas, and a second gas passage system provided in the first or second gas passage system. It has a differential pressure generating means such as a compressor or a vacuum pump.

In order to continuously obtain purified gas, one or more adsorption towers each equipped with the above two types of flow path systems are used.

However, compared to the TSA method, the PSA method has a new problem in that the concentration of a specific component to be adsorbed and removed in the purified gas increases as adsorption and desorption are alternately repeated.

According to the studies of the present inventors, this problem is caused by the fact that an adsorption layer that exhibits strong selective adsorption for a specific component that is to be adsorbed and removed from the source gas inevitably absorbs other coexisting components in the source gas. The reason is that it gets absorbed.

The selective adsorption ability of an adsorbent largely depends on the pore diameter, as will be described later.

The smaller the pore diameter (of course, it must be larger than the molecular diameter of the adsorbed material), the more likely it is that the adsorbed material is a specific component to be adsorbed and removed or a coexisting component that should be the main component of the purified gas. be.

Regardless of the crab force, the adsorption force is generally a dog. In the process in which the raw material gas flows through an adsorption layer that exhibits strong selective adsorption for specific components, a region with a high concentration of the specific component on the first gas flow path system side and a region with high concentration of the specific component on the second gas flow path system side are formed in the layer. A specific component low concentration region is generated.

In the high concentration region, specific components are selectively and actively adsorbed, so coexisting components are hardly adsorbed.

However, in a low concentration region, the adsorption amount of a specific component is small, so a relatively large amount of coexisting components is adsorbed.

In particular, co-adsorption of coexisting components takes place actively during adsorption, since the atmosphere is at a higher pressure than during desorption.

Next, each adsorbed component is gradually separated from the adsorbent under reduced pressure during desorption, but at this time, coexisting components for which the adsorbent does not exhibit selectivity are first desorbed.

As is well known, desorption heat is generated during desorption.

Therefore, the temperature of the adsorbent decreases due to the heat of desorption of the coexisting components.

As is well known, heat of adsorption is generated during adsorption, so the lower the temperature, the stronger the adsorption force becomes.

Therefore, due to the desorption of the covalent component, the adsorption power of the specific component to the cooled adsorbent becomes stronger.

Therefore, the desorption performance deteriorates, and the desorbed portion of the specific component is accumulated in the adsorbent.

While repeating adsorption and desorption in this way, the above-mentioned PSA
New legal problems arise.

The purpose of the present invention is to provide a PSA that can reduce the adsorbent filling capacity.
To provide a pressure difference adsorption gas purification method that does not increase the unadsorbed amount of specific components contained in purified gas that should have been adsorbed and removed by alternately repeating adsorption and de-N when adopting this method. There is something to do.

The present invention is designed to suppress co-formed Nf as a coexisting component so that desorption is not insufficient due to a temperature drop during desorption.

In other words, by using the optimal adsorbent for each of the high and low concentration regions of a specific component that occurs within the adsorption layer, the specific component can be exclusively absorbed in the high concentration region to the extent that almost no co-adsorption of coexisting components occurs. In the low concentration region, the adsorption of N is made to exclusively adsorb residual specific components without adsorbing coexisting components as much as possible.

There is no adsorbent that exhibits no adsorption for coexisting components and also exhibits strong selective adsorption for specific components.

Therefore, if stratification treatment is to be performed with one adsorption layer, the adsorption layer must be either (1) an adsorbent that exhibits strong selective adsorption for a given component, or (2) an adsorbent that exhibits adsorption for coexisting components. It is formed using either an adsorbent that does not exhibit the following or (3) a mixed system of the adsorbents described in (IX2) above.

In the adsorption layer according to (1), coexisting components are also actively adsorbed in a low concentration region, which causes the above-mentioned problem.

Since the adsorption layer according to (2) does not exhibit strong selective adsorption for specific components, the amount of adsorbent filling increases, and the advantages of the PSA method disappear.

In the adsorption layer according to (3), the above problem (2) occurs in a high concentration region of a specific component, and the above problem (1) occurs in a low concentration region of a specific component.

Furthermore, as seen in JP-A-52-122273, if the lamination relationship is reversed, that is, the adsorption layer according to (2) above is placed on the first gas flow path system side, and the adsorption layer according to above (1) is placed on the second side.
If it is placed on the gas flow path system side, adsorption of a specific component in a high concentration region will be insufficient during adsorption, and conversely, co-adsorption of coexisting components will occur in a low concentration region.

In addition, at the time of re-stratification, the gas flow may drive out specific components remaining in the adsorption layer on the second gas flow path system side, which may even reduce the purified gas purity.

The present inventors arrived at the present invention after confirming these facts.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 explains one embodiment of the present invention.

A gas passage system 2 is provided downstream of the compressor 1 into which air flows.

The gas flow path system 2 is connected to a gas flow path system 4 through a Kirimata valve 3, and to a gas flow path system 6 through a switching valve 5.

The gas flow path system 4 is connected to a gas flow path system 8 via a switching valve 7 separately from the gas flow path system 2.

Similarly, the gas flow path system 5 is connected to the gas flow path system 8 via a switching valve 9.

The gas passage system a is finally open to the atmosphere.

The gas passage column 4 opens at the bottom of the adsorption tower 10, and the gas passage system 6 opens at the bottom of the adsorption tower 11.

The adsorption tower 10 and the adsorption tower 11 have the same structure, and inside each group are provided radially porous partition plates 12 and 13 that are impermeable to adsorbent particles.

The adsorption tower 10 is partitioned by a partition plate 12, and an adsorption layer 14 is provided on the gas flow path system 4 side, and an adsorption layer 15 is provided on the opposite side.

On the other hand, the adsorption tower 11 is partitioned by a partition plate 13, and an adsorption layer 16 is provided on the gas flow path system 6 side, and an adsorption layer 17 is provided on the opposite side.

The adsorbent forming the adsorption layer 14°16 has an average pore diameter of 5 to 1
0 people's synthetic zeolite.

On the other hand, the adsorbent forming the adsorption layer 15.17 is activated alumina prepared by pickling and having an average pore diameter of 30 to 70A.

The filling rate of activated alumina in each adsorption tower is 50% of the total adsorption bed.
It is.

A gas passage system 18 is provided at the top of the adsorption tower 10, and an adsorption tower 110
A gas passage system 19 opens at the top.

The other end of the gas passage system 18 is connected to a gas passage system 21 via a switching valve 20 and to a gas passage system 23 via a switching valve 22.

Similarly, the other end of the gas flow path system 19 is connected to the gas flow path system 21 via the switching valve 24 and to the gas flow path system 23 via the switching valve 25.
is connected to.

The gas flow path system 21 and the gas flow path system 23 are connected to a switching valve 26.
．． It is connected via 27.

By adopting the above configuration, while one column is engaged in adsorption, the other columns are engaged in desorption.

First, air passes through the compressor 1, is pressurized, passes through the gas flow path system 2, the switching valve 3, and the gas flow path system 4 in this order and reaches the bottom of the adsorption tower 10.

At this time, the switching valve 7 is closed and communication with the gas flow path system 8 is cut off.

Further, the switching valve 5 is also closed, and pressurized air cannot flow into the adsorption tower 11.

However, as will be described later, the adsorption tower 11 and the gas passage system 8 are in communication with each other.

Pressurized air introduced from the seat of the adsorption tower 10 first passes through the adsorption layer 14, and in this process most of the C02 and N20 in the air are adsorbed and removed.

Then, it passes through the adsorption layer 15 via the partition plate 12.

During the process of passing through the adsorption layer 14, the remainder of CO2 and N20 in the air is replaced with nitrogen (hereinafter referred to as N2), which is a coexisting component.

) and nitrogen (hereinafter referred to as 0□) are adsorbed and removed without co-adsorption.

The obtained purified gas is recovered via a flow path system 18, a switching valve 20, and a gas flow path system 21.

At this time, the switching valve 22 is closed and communication with the gas flow path system 23 is cut off.

A portion of the purified gas flows into the gas flow system 23 via the switching valves 26,27.

The gas flow path system 23 is a flow path system for desorption gas, and is opened to the atmosphere through a gas flow path system 8, as will be described later.

The gas flow path system 23 reaches the top of the adsorption tower 110 via the switching valve 25 and the gas flow path system 19 in this order.

At this time, the switching valve 24 is closed, and the flow paths between the gas flow path system 19 and the gas flow path system 21 are cut off.

Further, the switching valve 22 is also closed, so that the desorption gas cannot flow into the adsorption tower 10 during adsorption operation.

The vacuum purified gas introduced from the top of the adsorption tower 110 first passes through the adsorption layer 17, and in this process, only a small amount of adsorbed matter is desorbed.

The gas flow further passes through the partition plate &3 and the adsorption layer 16 in order, performs a desorption action, and reaches the bottom of the adsorption tower 11.

The exhaust gas discharged from the bottom of the adsorption tower 11 is exhausted through the gas passage system 6, the switching valve 9, and the gas passage system 8 in this order.

At this time, the switching valve 5 is closed and pressurized air cannot flow in.

Further, the switching valve 7 is closed, and the communication between the gas flow path system 4 and the gas flow path system 8 is cut off.

As mentioned above, the switching valve 3,9°20.25 is in the open state,
Then, when the switching valves 5, 7, 22, 24 are closed, the interior of the adsorption tower 10 is in an adsorption operation, and the interior of the adsorption tower 11 is in a desorption operation.

By appropriately reversing this relationship, purified gas can be obtained continuously.

In other words, to make the inside of the adsorption tower 10 during the desorption operation and the inside of the adsorption tower 11 during the adsorption operation, the switching valves 3 and 9° 20.25 are closed, and the switching valves 5 and 7° 22.24 are opened. state.

By employing the above configuration and operation, the present embodiment provides the following effects.

The synthetic zeolin layer exclusively adsorbs CO2 and N20.
Since the activated alumina layer adsorbs residual CO2 and residual H20 while minimizing adsorption of N2 and O2, co-adsorption of N2 can be prevented.

Furthermore, CO2 and N20 can be removed to a high degree.

In addition, since the amount of N2 adsorbed, which is easily desorbed and becomes a source of desorption heat, is small, the temperature drop during desorption can be suppressed.

Therefore, even if adsorption and deN removal are repeated alternately, the C contained in the purified gas, although it should be removed by adsorption, remains
This has the effect of preventing an increase in the amount of unsorbed O2 and N20.

FIG. 2 shows the tendency of adsorption strength with respect to the pore diameter of the adsorbent constituting the adsorption layer when pressurized air is introduced into the adsorption layer.

Curve 1 shows the trend for N20, curve 11 for CO□, and curve ii1 for N2.

The other line segments are operating lines for explanation, and the fulcrum of each of the above-mentioned curves and each operating line indicates the adsorption strength of the component in the adsorption tower.

The operating line a relates to a synthetic zeolite with a pore diameter of 1ON, the operating line A relates to a method-prepared activated alumina with a pore diameter of 50A, and the operating line C relates to an alkaline method-prepared activated alumina with a pore diameter of 50A.

The two-layer adsorption layer of this example is indicated by the operating line d.

The operating line e shown for comparison relates to the case where an inverted two-layer adsorption layer, that is, an activated alumina layer with a pore diameter of 50 mm, is provided on the first channel system side, and the operating line f relates to the case where an activated alumina layer with a pore diameter of 50 mm is provided on the first flow path system side. The ratio of synthetic zeolite and activated alumina with a pore size of 50:1:
This relates to a mixed adsorbent having an average pore diameter of 201 mixed in Example 1.

As shown in this figure, the method of this example applies to N20 and C
Despite its excellent O2 adsorption and removal ability,
It is clear that the co-formed adhesion force of N2 is very small and is the best among the adsorption layer configurations shown in this figure.

Incidentally, FIG. 3 shows the change in temperature within the adsorption layer at the time of switching between adsorption and desorption when the above-mentioned synthetic zeolite and the method-prepared activated alumina are used individually.

In the figure, curve 1 ■ shows the tendency of synthetic zeolite, and curve 1 shows the tendency of activated alumina.

As is clear from this figure, the temperature change of synthetic zeolite is much more drastic than that of activated alumina.

It is therefore clear that when used alone in synthetic zeolite t-, a desorption loss occurs upon desorption.

By the way, in this example, the volume of activated alumina that occupies 50% of the total adsorption layer is clear from Figure 4, which shows the relationship between the filling ratio of activated alumina and the CO2 concentration in purified gas. Moreover, this is the best filling ratio in terms of removing CO2 from the air.

According to the studies of the present inventors, when removing CO2 from the air, it is desirable to reduce the filling ratio of activated alumina from 25% to 80% in order to suppress the CO2 concentration in the refining scum to f20 ppm or less.

Furthermore, in this embodiment, since a part of the purified gas obtained by the adsorption treatment is used as the desorption gas, there is an effect that the amount of the separate desorption gas used can be eliminated.

Although this embodiment deals with gas purification to separate and remove CO2 and N20 from air, the present invention is of course not limited to this.

Specific examples of purifying air or nitrogen-enriched gas using the same apparatus as in the above embodiment except for the adsorption layer in the adsorption tower will be shown below.

Each adsorption tower has an inner diameter of 200mm and a height of 1000mm.

Example 1: Air sheath 1 by removing N20 and CO2
) Adsorption layers 15 and 17 were filled with manufactured activated alumina having a pore diameter of 50 ck, and adsorption layers 14 and 16 were filled with synthetic zeolite having a pore diameter of 10X.

The filling ratio of activated alumina was 60%.

The operating conditions were an adsorption pressure of 8 kg/crAQ, a desorption pressure of atmospheric pressure, an air flow rate of 100 Ni/h-Fl), and a purified gas flow rate of 4 ONd/h.

The N20 and CO2 concentrations in pressurized air are each 1600
and 330 ppm.

The switching time of the adsorption tower is 15 times per half cycle.

As a result, the N20 and CO2 concentrations in the purified gas were both below 1 ppm.

Specific example 2 Air quality R2 by removing N20 and C02
) The filling ratio of activated alumina was set to 30%, and the operation was performed using the same equipment and the same conditions as in Example 1. As a result, the N20 and CO2 concentrations in the purified gas were 2 ppm and 5 pI)m, respectively. Natsu fko.

Comparative Example 1: Purification of air by removal of N20 and CO2 (
1) The above synthetic zeolite 1-+ was filled alone in the adsorption tower, and the other equipment was the same as in Example 1, and the operation was carried out under the same conditions.1 As a result, the N20 and CO□ concentrations in the purified gas were 5 and 30, respectively.
ppm and one summer.

Comparison fI12: Purification of air by removing H20 and CO2 (2) The above activated alumina was filled alone in the adsorption tower, and the other equipment was the same as that of Example 1, and was operated under the same conditions. N20 and CO2 concentrations were 4 and 25 pp, respectively.
M and Natsu 1 child.

Specific example 3: Purification of N2 gas by removing N20 and CO2 N20 and CO2 concentrations are 1600 ppm and 1200, respectively. N2 enriched gas with a beating pressure of 8 kg/cr A G is used as the raw material gas, and N20 and CO2 ev are 10 ppm each. and 0. 1ppm of N2 gas was used as the desorption gas, and the other equipment was the same as in Example 1, and the operation was carried out under the same conditions.
The O2 concentrations were 3 pI)m and 5 ppm, respectively.

Specific example 4: Purification adsorption layer 1 of N2 gas by removing NH3
In 5.17, activated alumina with a pore diameter of 50X was added to the adsorption layer 1.
4 and 16 are filled with synthetic olide having a pore diameter of 10'A.

The filling ratio of activated alumina is 50%.

The operating conditions were an adsorption pressure of 5 kg/cat G, a desorption pressure of atmospheric pressure, a raw material gas flow rate of 15 on/h, and a regeneration purified gas flow rate of 3 on/h.

The source gas was a N2-enriched gas containing 1000 ppm of NH3f.

The switching time of the adsorption tower is 15 mm per half cycle.

As a result, the NH3 concentration in the purified gas was 5 ppm or less.

Comparative Example 3: Purification of N2 gas by removal of NH3 The above synthetic zeolite was filled alone in the adsorption tower, and as a result of operation using the same equipment and under the same conditions as in Specific Example 4, NH3 in the purified gas was
3 concentration is 45 ppm and Natsu 1.

Specific example 5: Purification of N2 gas by removing N20, CO2 and NO Raw material gas kH201600ppm, CO21200
ppm.

The same apparatus and operation as in Example 1 were performed under the same conditions except that the N2-enriched gas containing 300pp of NNO was used.
The N20, CO2 and NO concentrations in the enriched gas are each 3
ppm, 15 ppm.

Comparative Example 4: Purification of N2 gas by removal of N20, CO2 and NO. The above synthetic zeolite f was filled alone in the adsorption tower, and as a result of operation using the same apparatus and the same conditions as in Specific Example 6, purified N2
The N20, CO2 and NO concentrations in the enriched gas are each 5
ppm, 41 ppm, and 120 ppm.

Specific example 6: Air dry adsorption layers 15 and 17 contain activated alumina prepared by alkaline method with a pore diameter of 100X, adsorption layers 14 and 16 contain pore diameter of 10X,
filled with synthetic zeolite.

The filling ratio of activated alumina was 60%.

The operating conditions were an adsorption pressure of 8 kg/crAG, a desorption pressure of atmospheric pressure, an air flow rate of 100 Ni/h, and an amount of drying air for regeneration of 4 ON/h.

N20 concentration in pressurized air is 2050 ppm and 1
child.

The switching time of the adsorption tower is 15 mm per half cycle.

As a result, as explained above, according to the present invention, even if adsorption and desorption are repeated alternately, N20 in dry air is contained in purified gas even though it should be adsorbed and removed. This has the effect of preventing an increase in the amount of unadsorbed specific components.

Therefore, by adopting the present invention, high-level gas purification is possible even with a small amount of adsorbent.

゛

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a gas purification device according to an embodiment of the present invention, Fig. 2 is a characteristic diagram showing the relationship between the pore diameter of the adsorbent and the adsorption strength during pressurized adsorption, and Fig. 3 is an adsorption/desorption diagram. FIG. 4 is a characteristic diagram showing the temperature change of the adsorbent at the time of switching. FIG. 4 is a characteristic diagram showing the relationship between the filling ratio of activated alumina and the CO2 concentration in the purified gas for the embodiment shown in FIG. 1... Compressor, 2, 4, 6, 18, 19, 21
. 23... Gas flow path system, 3, 5, 7, 9, 20. 22, 24, 25, 26, 27... switching valve, 10. 11... Adsorption tower, 12, 13... Switching plate, 14. 15, 15.17... Adsorption layer.

Claims (1)

[Claims] 1 A first adsorption layer made of synthetic zeolite and a second adsorption layer made of activated alumina, which accounts for 25-80% of the total adsorbent capacity.
an adsorption step of arranging adsorption layers in series and supplying the raw material sludge from the side of the first adsorption layer to obtain a nitrogen- or oxygen-enriched sludge, and a desorption gas having a lower pressure than the gas pressure during the adsorption step. A pressure difference adsorption type gas purification method, characterized in that a desorption step of desorbing the adsorbate by flowing from the second adsorption layer side is performed alternately.