JPH09267016A - Improved pressure swing adsorption method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the purity and the yield of a product in at least one stage by using an adsorptive component described under negative presser from an adsorbed in the regeneration process during the same step under the same pressure as that of mixed gas to be treated as a reflux to the other adsorber. SOLUTION: In a pressure swing adsorption method by which an adsorptive component is separated from mixed gas containing the adsorptive component having atmospheric pressure or more in at least one stage, the adsorptive component described under negative pressure from an adsorber in the regeneration process during the same step under the same pressure as that of mixed gas to be treated is used as a reflux to the other adsorber. For example, ammonia is taken as an adsorptive component. In a adsorptive product reflux process, gas of high ammonia concentration obtained in the previous process is made to have almost the same pressure as that of a line 1 and is introduced into an adsorber A and an adsorber B just before adsorption equilibrium is attained. In a between-columns pressure equalizing process, gas of high ammonia concentration is introduced into one adsorber to make one adsorber to have the same pressure as operating pressure of the other adsorber, that is, almost the same pressure as pressure of the line 1.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an improved pressure swing adsorption method (hereinafter referred to as PSA method) for the purpose of increasing the purity and yield of an adsorption product in at least one stage.

[0002]

2. Description of the Related Art An adsorbate component is adsorbed from a mixed gas consisting of an adsorbate component adsorbed on a filler and a component not adsorbed on the adsorbent, and the adsorbate component is recovered as a product (hereinafter referred to as adsorbate PSA). Alternatively, it is well known to recover the non-adsorbate component as a product (hereinafter referred to as non-adsorbate PSA).

Examples of the former include recovery of a small amount of ammonia contained in the ammonia purge gas, recovery of unreacted chlorine in an aluminum chloride plant, and the like.

An example of the latter is recovery of hydrogen from a mixed gas containing nitrogen, hydrogen, carbon monoxide, hydrogen and the like.

However, there are few known examples in which the adsorbate component and the non-adsorbate component are simultaneously recovered as a product. Applicants, as an example from such a viewpoint,
As one of the technologies for dividing a mixed gas containing at least ammonia, nitrogen, and hydrogen (for example, nitrogen, hydrogen, argon, methane, etc.) into ammonia and a gas other than ammonia,
Previously, the pressure swing separation device for ammonia separation and the ammonia separation method disclosed in JP-A-6-296819 were proposed. Japanese Unexamined Patent Publication No. 6-296819 discloses that a reactor outlet gas of an ammonia synthesis process, which conventionally consumes a large amount of energy, uses synthetic ammonia and unreacted nitrogen.
It is a technology that separates hydrogen and other gases with high energy consumption and low energy consumption. Furthermore, it is a technology that can separate the unreacted separated nitrogen / hydrogen to keep the same ratio as before separation and supply it to the ammonia synthesis reactor as it is. Was proposed as a technology for recovering ammonia that can be used for flue gas denitration. The purpose of this proposal is to combine one or more stages of adsorbate PSA and one or more stages of non-adsorbate PSA and to simultaneously recover the adsorbate component and the non-adsorbate component as a product. An example showing one embodiment of the apparatus is shown in FIG. In addition, it is free to choose whether or not to collect the collected product.

Now, referring to FIG. 3, when the adsorbate is used as a product gas to increase its purity and yield,
Table 1 shows the operation state of the adsorption tower corresponding to 6 steps, each cycle consisting of one adsorption step and returning to the adsorption step again. The time required for each step shows an example thereof. It goes without saying that if the adsorbate component is used as the product gas and its purity and yield are increased, the purity and the yield of the non-adsorbate component will also be increased as the product gas as a result.

[0007]

[Table 1]

In Table 1, the adsorption step time, adsorption product gas reflux step, inter-column pressure equalization step time, and regeneration step time in the adsorption tower B are the regeneration step (θ ₁₁ ) and the adsorption product gas reflux step in the adsorption tower A, respectively. Time (θ ₁₂ , θ ₂₂ ),
It is equal to the pressure equalizing step time between towers (θ ₁₃ , θ ₂₃ ), and the regeneration step time (θ ₂₁ ).

Each step shown in Table 1 will be described with reference to FIG. In step 1 (θ ₁₁ ), the adsorption tower B is in the adsorption step and the adsorption tower A is in the regeneration step. The details are the same as step 1 of the present invention described later.

In step 2 (θ ₁₂ ), the adsorption tower A and the adsorption tower B are in the adsorbed product reflux step (Q). Adsorption tower A
Is under a negative pressure because ammonia is desorbed by the pump P in the regeneration process of the previous process. In the regeneration process of step 1, the line 28 branched from the line 38, the flow rate control valve RN, the lines 27, 24, 23, 6, 7, the adsorption tower B,
The gas having a high ammonia concentration obtained in the previous step is introduced into the adsorption tower A through the lines 8, 13, 14, 70.

In step 3 (θ ₁₃ ), the adsorption tower A is under a negative pressure as described above, and in the pressure equalization step (T) between the towers, the adsorption tower A depends on the volume of all lines in step 2. And the pressure in the adsorption tower B is approximately 1/2 of the pressure in step 1.
Becomes

Step 4 (θ ₂₁ ) and step 5 (θ ₂₂ )
And step 6 (θ ₂₃ ) includes steps 1 to 3
Basically, the same operation is repeated except that the lines are different from. The relationship between the above operation time and pressure is shown in FIG.

[0013]

The above-mentioned conventional techniques have the following problems to be further improved.

In the above adsorbate PSA, one-stage PSA
According to the results of the equipment, ammonia can only be concentrated to about 55 vol%, and if higher separation performance is required, we propose a technology to combine multiple PSA equipment and recycle the gas separated by each PSA equipment. It had been.

An object of the present invention is to provide an improved pressure swing adsorption method for the purpose of increasing the purity and yield of a product in at least one stage in the PSA method.

[0016]

The present inventors have found that when the amount of adsorbent adsorbed reaches a certain pressure or higher, saturation is reached, but high pressure is advantageous for adsorption until saturation is reached,
That is, as a result of the conventional technique having undergone the product recirculation process and the inter-column pressure equalization process as shown in FIG.
Based on this finding, the inventors have studied the apparatus and method for increasing the pressure, and have completed the present invention.

That is, the present invention is a pressure swing adsorption method for separating an adsorbed component from a mixed gas containing an adsorbed component having a pressure equal to or higher than normal pressure in at least one stage under the same pressure as that of the mixed gas to be treated. The improved pressure swing adsorption method is characterized in that the adsorption component desorbed from the adsorption tower in the regeneration step under negative pressure is used for the reflux of another adsorption tower during the step (1).

The present invention can be carried out in an arbitrary plurality of towers such as two towers and four towers, but usually two towers or four towers are selected because the operation is simple.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a mixed gas containing ammonia, chlorine, carbon monoxide or the like as an adsorbing component is to be treated, and the mixed gas containing ammonia as an adsorbing component means ammonia and nitrogen. , A gas containing hydrogen, argon, methane and the like. The mixed gas containing chlorine as an adsorbing component means a gas containing chlorine, nitrogen, oxygen and the like. Further, the mixed gas containing oxygen monoxide as an adsorbing component means a gas containing nitrogen, hydrogen, and carbon monoxide. There is no particular upper limit to the concentration of the adsorbed component in these mixed gases, but in order to make the effect of the present invention more remarkable,
It is usually selected from the range of 2.0 vol% to 10.0 vol%.

In the present invention, the adsorbent filled in the PSA device has a pore size of 5 when the adsorbing component is ammonia.
It is possible to use a zeolite having a size of less than angstrom, preferably one having a size of around 3 angstrom. When chlorine is used as the adsorbing component, commercially available activated carbon, molecular sieving carbon, synthetic and natural zeolite and the like can be selected. When the adsorbing component is carbon monoxide, zeolite having a pore size of 5 Å, molecular sieving carbon or the like can be selected.

As described above, as the adsorbent to be filled in the PSA device in the present invention, an optimum adsorbent may be used depending on the type of adsorbing component, and a commercially available adsorbent may be used as it is.

To clarify the characteristics of the present invention,
Taking ammonia as an example of the adsorption component,
The operation of the two towers B and B will be described. Needless to say, the present invention is not limited to ammonia.

In the adsorbate PSA, one cycle of the adsorption tower after returning to the adsorption step after the adsorption step is regarded as one cycle, and the operation state of the adsorption tower corresponding to six steps is shown in Table 2 for the present invention. Show. The time required for each step shows an example thereof.

[0024]

[Table 2]

In Table 2, the adsorption step time, adsorption product gas reflux step, inter-column pressure equalization step time and regeneration step time in the adsorption tower B are the regeneration step time (θ ₁₁ ) and regeneration step time ( θ ₁₂ ), inter-column pressure equalization step time (θ ₁₃ , θ ₂₃ ), adsorption step time (θ ₂₁ ), adsorption product gas recirculation step (θ ₂₂ ).

First, each step described in Table 2 of the present invention will be described with reference to FIG. 1 and the pressure change of the system with reference to FIG. In step 1 (θ ₁₁ ), the adsorption tower B is in the adsorption step and the adsorption tower A is in the regeneration step. The pressure of the adsorption tower B is almost the same as that of the mixed gas containing ammonia, and the adsorption tower A is under reduced pressure. In this step, the mixed gas containing ammonia is fed into lines 1, 2, 3, 4, 5, 6,
It is introduced into the adsorption tower B through 7 and ammonia is adsorbed. The gas after the ammonia has been adsorbed and removed is discharged through lines 8, 9, 10, and 11. On the other hand, adsorption tower A
In line 7 to discharge the adsorbed ammonia.
0, 60, 50, 36, 35, 37, sucked by the pump P, the flow rate is adjusted by the flow rate control valve PN through the lines 38, 29, and the ammonia concentration in the line 1 from the line 12 to the adsorbed product tank E. Higher concentration gas is introduced.

In step 2 (θ ₁₂ ), the adsorption tower B is in the adsorbed product reflux step (Q), and the adsorption tower A is in the regeneration step following the previous step. The pressure of the adsorption tower B is almost the same as that of the mixed gas containing ammonia, and the adsorption tower A is under reduced pressure. In this step, the line 28 branched from the line 38 in the regeneration process of step 1, the flow rate control valve R
The gas having a high ammonia concentration obtained in the previous step is introduced into the adsorption tower B through N, lines 27, 24, 23, 6, and 7 just before reaching the adsorption equilibrium. Ammonia is adsorbed in the adsorption tower B, and the gas after the ammonia is adsorbed and removed is discharged through lines 8, 9, 10, and 11.

In step 3 (θ ₁₃ ), the inter-column pressure equalizing step (T) is performed, the valve is switched, and a gas having a high ammonia concentration is introduced into the absorption column A through lines 8, ₁₃ , 14, 70. In the absorption tower A, a negative pressure was used in the regeneration step, which is the previous step, but in this step, a gas having a high ammonia concentration was introduced, and the pressure was the same as the operating pressure of the adsorption tower B, that is, approximately 1/2 of line 1. Become.

In step 4 (θ ₂₁ ), the adsorption tower B is in the regeneration step and the adsorption tower A is in the adsorption step. The pressure of the adsorption tower A is almost the same as that of the mixed gas containing ammonia, and the adsorption tower B is under reduced pressure. In this step, the mixed gas containing ammonia is supplied to the lines 1, 2, 30, 40, 5 and 5.
It is introduced into the adsorption tower A through 0, 60 and 70, and ammonia is adsorbed there. The gas after the ammonia is adsorbed and removed is discharged through lines 80, 90, 100, and 11. On the other hand, the adsorption tower B passes through the lines 7, 6, 5, 33, 34 and 37, is sucked by the pump P, passes through the lines 38 and 29, and flows through the flow control valve PN to discharge the adsorbed ammonia. Is adjusted so that a gas having a higher concentration than the ammonia concentration in the line 1 is introduced into the adsorbed product tank E from the line 12.

In step 5 (θ ₂₂ ), the adsorption tower A is in the adsorption product gas reflux step (Q), and the adsorption tower B is in the regeneration step following the previous step. The pressure of the adsorption tower A is almost the same as that of the mixed gas containing ammonia, and the adsorption tower B is under reduced pressure. In this step, the gas having a high ammonia concentration obtained in the previous step is passed through the line 28 branched from the line 38, the flow rate control valve RN, the lines 27, 25, 26, 60, 70 in the regeneration step of Step 4 to the adsorption tower A. Is introduced just before reaching the adsorption equilibrium. Ammonia is adsorbed in the adsorption tower A, and the gas after the ammonia is adsorbed and removed is discharged through lines 80, 90, 100 and 11.

In step 6 (θ ₂₃ ), in the inter-column pressure equalizing step (T), the valve is switched and a gas having a high ammonia concentration is introduced into the adsorption column B through lines 80, 15, 16 and 7. In the adsorption tower B, a negative pressure was used in the regeneration step, which is the previous step, but in this step, a gas having a high ammonia concentration is introduced and the same pressure as the operating pressure of the adsorption tower A,
The pressure is about half that of line 1.

The operations described above are repeated. Table 3 shows the procedure of the valve switching operation at this time.

[0033]

[Table 3]

In the present invention, as is clear from FIG. 1 which is an embodiment of the present invention and FIG. 3 which is an example of the prior art, the number of valves is increased by two places as compared with the prior art, and the adsorbed product recirculation step (Q ) And the inter-column pressure equalizing step (T) are improved as described below to improve the product purity. (1) In the adsorption product recirculation process, the gas having a high ammonia concentration obtained in the previous step is introduced into the adsorption tower A and the adsorption tower B at a pressure almost equal to the line 1 and is introduced just before reaching the adsorption equilibrium. (2) In the pressure equalization step between towers, a gas having a high ammonia concentration is introduced into one of the adsorption towers, and the pressure is the same as the operating pressure of the other adsorption tower, that is, almost the pressure of line 1.

The reason why the product purity can be improved by the method of the present invention is as follows.

That is, for example, when a product gas having an extremely high ammonia concentration and a low non-adsorbate gas concentration is fed into the adsorption tower A after the adsorption step and under the same pressure as in the adsorption step, the adsorption is performed. The adsorbent in the tower A has already adsorbed ammonia in the previous step, but since a gas with a high partial pressure of ammonia flows in, it adsorbs more ammonia and the adsorption zone increases. On the other hand, since the adsorbent in the adsorption tower does not adsorb gases other than ammonia, the concentration of the non-adsorbate gas is extremely lower than the state before the reflux step due to equilibrium.

[0037]

The present invention will be described in more detail with reference to the following examples. Needless to say, the present invention is not limited to the examples described below.

Examples 1 to 3 As shown in FIG. 1, two adsorption towers A and B having an internal volume of 74 cc were prepared. As an adsorbent, 55 g of zeolite having a pore size of 3 Å was packed in the tower.

As a mixed gas containing ammonia, a raw material gas containing 5.5 vol% ammonia (NH ₃ ), 49.2 vol% nitrogen (N ₂ ) and 45.3 vol% hydrogen (H ₂ ) was prepared. The valve switching procedure shown in Table 3 was performed. The required time and pressure for each step were as shown in Table 4. The results are shown in Table 4.

Example 4 The ammonia concentration in the raw material gas of Examples 1 to 3 was set to 5.5 vol%.
Was changed to 2.0 vol%, and the treatment was carried out by the same procedure as in the above-mentioned example. The required time and pressure for each step were as shown in Table 4. The results are shown in Table 4.

Reference Example 1 Table 4 also shows the results of treatment using the same adsorbent and source gas as in Example 1 according to the conventional technique of FIG.

[0042]

[Table 4]

Example 5 The same apparatus as in Example 1 was used. As an adsorbent, 33 g of activated carbon PCB for gas adsorption (manufactured by Toyo Calgon Co., Ltd.) was packed in the tower.

As a mixed gas containing chlorine, nitrogen 75.1
vol%, oxygen 20.0 vol%, chlorine 5.0 vol%
A raw material gas containing was prepared. Table 5 shows operating conditions and results
Shown in

[0045]

[Table 5]

Example 6 The same apparatus as in Example 1 was used. As an adsorbent, 55 g of zeolite having a pore size of 5 Å was packed in the tower.

As a mixed gas containing carbon monoxide, nitrogen 1
A raw material gas containing 5.0 vol%, hydrogen 80.0 vol%, and carbon monoxide 5.0 vol% was prepared. Table 6 shows the operating conditions and the results.

[0048]

[Table 6]

[0049]

According to the improved pressure swing adsorption method of the present invention, the following effects can be obtained. (1) Recovery of ammonia and a gas other than ammonia from a mixed gas containing ammonia, recovery of chlorine and a gas other than chlorine from a mixed gas containing chlorine, separation of carbon monoxide from a mixed gas containing carbon monoxide Etc., the purity and yield of both products can be increased in at least one stage regardless of the adsorbate component and the non-adsorbate component.

Further, ammonia will be described below as a representative. (2) Conventionally, when a mixed gas containing about 5 vol% ammonia was concentrated with a PSA device, the maximum amount was about 55 vol% in one stage. In the invention, one step is 90
It was possible to achieve more than vol%. (3) Conventionally, when a mixed gas containing about 5 vol% ammonia was concentrated by a PSA apparatus to obtain 90 vol% or more ammonia, a multi-step treatment was required.
It became possible with steps. Along with this, it has become possible to omit the steps and save energy in the prior art.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between operation time and pressure in the present invention (a) and the prior art (b).

FIG. 3 is a schematic diagram showing an example of a conventional technique.

[Explanation of symbols]

A, B adsorption tower E adsorption product tank P pump FN, RN, PN flow control valve V1-V10 valve (automatic valve) 1-16, 20, 23-30, 33-38, 40, 5
0, 60, 70, 80, 90, 100 lines

Claims (4)

[Claims] 1. In a pressure swing adsorption method for separating an adsorbed component in at least one stage from a mixed gas containing an adsorbed component having a pressure equal to or higher than normal pressure, under the same pressure as that of the mixed gas to be treated and during the same step. An improved pressure swing adsorption method characterized in that the adsorption component desorbed from the adsorption tower in the regeneration step under negative pressure is used for the reflux of another adsorption tower. 2. The pressure swing adsorption method according to claim 1, wherein the adsorbing component is ammonia. 3. The pressure swing adsorption method according to claim 1, wherein the adsorbing component is chlorine. 4. The pressure swing adsorption method according to claim 1, wherein the adsorbing component is carbon monoxide.