JPH0559379A - Method for separating carbon dioxide gas and water content in gas in city gas purification process - Google Patents

Abstract

(57) [Summary] (Modified) [Objective] To provide a suitable and economical method for separating carbon dioxide and water in a city gas refining process. [Structure] The following steps are cycled using four adsorption towers in which an adsorbent is filled with molecular sieving carbon. In the adsorption process, the temperature behavior is detected, the adsorption time is automatically adjusted, and the purified gas of highly pure combustible components is constantly taken out. In the over-adsorption process, the recovered gas of the desorption tower is transferred to the adsorbent that has once adsorbed CO ₂ in the adsorption process, and the CO
Over-adsorb ₂ and take out the combustible component with high concentration. In the desorption process, after all the combustible components in the desorption tower have flowed out, moisture and high-purity CO ₂ are desorbed by suction and taken out. In the pressurizing process, only C in the pressure equalizing gas is present in the lower part of the pressurizing tower.
Primary pressurization for adsorbing the O ₂ component is performed, and the secondary pressurization operation in which a combustible component (purified gas) having a high purity is fed at a constant flow rate from the top of the tower raises the adsorption pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refining process for continuously separating carbon dioxide gas and water contained in a raw material gas generated in the production process of SNG, which is a high-calorie city gas, and more specifically to a PSA method. The present invention relates to a method for obtaining high purity (99%) and high recovery rate (99%) of both gases separated and split.

[0002]

[Prior art and its problems] The method of separating the carbon dioxide gas in the gas in the city gas refining process in a continuous flow with a purification purity and a recovery rate of about 99% is the conventional technique. There is a liquid absorption method in which the liquid is absorbed and separated.

On the other hand, the PSA method uses
It is easy to perform operations such as stopping and changing loads, and it is possible to dehydrate gas at the same time, which is advantageous for high-purity purification, but its low recovery rate is a drawback, and it is not generally adopted for regeneration treatment. Also, the adsorption process needs to be devised.

The PSA method is a decompression regeneration which requires no heat source for regeneration, and the above low recovery rate is due to consumption of a product gas as a purge gas during regeneration. The product recovery rate and the product purity differ depending on whether or not this regeneration process is effectively performed and how the adsorption process is carried out accordingly.

For example, it is advisable to carry out the adsorption operation until just before the adsorbed component in the raw material gas breaks through. However, since it is difficult to completely divide the adsorption front and the purified gas at the outlet at the end of the adsorption operation, for example, JP-A-59-147620 and JP-A-59-147620.
According to 61-146317, the adsorption process is performed in two towers, and the raw material gas is introduced into the second tower before cutting through the first tower to the second tower.

Further, according to JP-A-1-176417, two adsorption towers, which have been prepressurized in the adsorption step, are connected in series to completely pass through the adsorbed components in the first tower and the second tower in the next step. The product recovery rate is stabilized by setting it as the first adsorption tower.
According to a method different from this, for example, Japanese Examined Patent Publication (Kokoku) No. 45-20082, the adsorption operation is terminated in a state where the adsorption front is completely present in the adsorption bed, and the gas decompressed by cocurrent depressurization is immediately transferred to the second adsorption column. The adsorbent bed is regenerated by countercurrent flow pressure equalization, further pressure reduction and other column purge, and then countercurrent pressure reduction. In this case, highly purified hydrogen was obtained as a purified product, and the recovery rate was described as 76.5%. When the product purity is emphasized and improved as described above, the product recovery rate is lowered unless an ultrahigh selective adsorbent is used.

Japanese Patent Laid-Open No. 2-281096 discloses, for example, those which aim at an economic efficiency of about 99% both in terms of purity and recovery rate. This is because the upper and lower parts of the tower where the over-adsorption process is completed and the process is completed and the upper and lower parts of the tower for which the pressurizing process is performed are combined to equalize the pressure, and the flow rates of the upper and lower parts are adjusted to control the inside of the tower. The component distribution is adjusted, and the decompressed gas up to the atmospheric pressure and the initial depressurized decompressed gas are adsorbed to the adsorbent that has completed the adsorption process in the over-adsorption process, and the combustible component is taken out to improve the recovery rate. There is.

One of the significant limitations of the conventional PSA method is described above.
It is an active ingredient of city gas
It is the loss of combustible components. This loss is due to adsorption during the desorption process
It was co-adsorbed with the non-adsorbed combustible component in the tower void and the adsorbent,
Carbon dioxide gas, which is a desorption gas, which is co-desorbed when combustible components are desorbed
It is caused by mixing in the stream. This solution is in desorption gas
Can be reduced by recovering the combustible components of. That one
High-purity CO before desorption₂The reflux of
is there. This is a strongly adsorbed component, CO₂Adsorbed by gas
The co-adsorption component (flammable component) of the layer is replaced and CO adsorption ₂only
And CO in the adsorption tower₂In the process of filling the
This is referred to as “desorption or displacement desorption or washing”.
-A part of the waste gas is recovered in the next vacuum desorption operation,
CO₂May be required in several times. Therefore high purity
Degree CO₂Aborting the purge before it appears at the exit of the tower
It is considered economical.

On the other hand, the co-adsorbed component (combustible component) desorbed at the outlet of the tower is recovered by using it as a pressurized gas in another tower, or in another method, it is recovered by mixing it with the raw material gas in the adsorption step. It

However, these conventionally proposed methods require high-purity (99% or more) CO ₂ gas, and for that purpose, it is necessary to operate under high selective conditions with a highly selective adsorbent. Depending on the agent, the adsorption layer temperature may be 150 to 300.
It is preferable that the temperature of the raw material gas to be kept at 0 ° C. is not higher than room temperature and the water content must be removed as a pretreatment. Further, in order to perform cleaning or recovery more effectively, the tank volume for storing high-purity CO ₂ gas increases, and the power for gas transfer increases accordingly, which is accompanied by severe economic disadvantage.

[0011]

The raw material gas for high-calorie city gas such as SNG is a continuous flow gas at room temperature generated from a hydrocarbon material such as butane, propane, naphtha and methanol in a methanation process. From the chemical reaction formula, the main components are approximately H ₂ 2 to 3%, CH ₄ 65 to 70%, CO
It is in the range of 0 to 0.1%, CO ₂ 20 to 25%, and H ₂ O 5 to 6%.

As described above, in the conventional liquid absorption method, CO ₂ is removed from the gas having the above component ratio by the highly selective absorption liquid, and the combustible component purity is 99% and the recovery rate thereof is 99%. Therefore, even in this PSA method, if it does not have the same performance under the same use condition, it remains difficult to adopt. However, the purity of combustible components, which is an advantage of the PSA method, is 9
The ability to achieve ultra-high purity up to 9.9999% is necessary for the purpose of use. Therefore, it is an object of the present invention to provide the most economical PSA method by the most suitable adsorption / overadsorption / desorption / pressurizing operation under the above conditions.

[0013]

To achieve the above object, the technical means of the present invention is H ₂ , CH ₄ , CO, CO ₂ , H ₂ O obtained by catalytic decomposition reaction in the process of producing SNG. Carbon dioxide and water in the raw material gas, which is a mixture of
The method for separating a continuous stream by method A, once CO ₂
An over-adsorption step for adsorbing a high concentration of CO ₂ again to the adsorbent that has adsorbed is set, the advance position of the over-adsorption zone of the adsorption layer at the end of that step is set in advance, and the intermediate pressure at the beginning of the next desorption step is set. After the pressure equalization between the two towers is performed by cocurrent depressurization and cocurrent pressurization, the CH ₄ rich CO ₂ gas in the decompression tower is moved to the inlet side of the pressurization tower, and the subsequent operation of the decompression tower is performed up to atmospheric pressure. Co-current decompression and subsequent initial suction decompression below atmospheric pressure are carried out in both co-current and counter-current directions, and the flow rate ratio of and is adjusted according to the position of the super-adsorption zone adjusted and set in the over-adsorption step, and is in the void in the tower, etc. The CH4 component is removed on average,
C co-adsorbed in the adsorbent after decompression with suction in both countercurrent directions
The H ₄ component is removed and only CO ₂ is used as the adsorbent.

On the other hand, after passing through the water-containing gas holder, the gases (1) and (2) are introduced into the adsorption tower of the above-mentioned over-adsorption step and CH
₄ components are passed through and collected. Specifically, a mixture of process raw material gas and raw CH ₄ recovery gas is sent to one of the 4 adsorption towers at the adsorption pressure (reaction pressure) from the bottom of the tower. , CO ₂ and H ₂ O are selectively adsorbed, and high-purity combustible components such as H ₂ · CH ₄ · CO are taken out from the upper part of the tower,

Process Among the desorption gas of the process, the upper decompression gas, the lower decompression gas and the suction decompression gas are mixed by a water-containing gas holder to make the components uniform,
₂ Increase the temperature of the recovered gas with a high concentration by the adsorption pressure (reaction pressure) and send it from the bottom of the tower at a constant flow rate to selectively re-adsorb (over-adsorb) CO ₂ and H ₂ O in the recovered gas, After the raw CH ₄ recovery gas with a high CH ₄ concentration is taken out from the upper part of the tower, it is mixed with the raw material gas of the process,

The upper part of the column which has completed the over-adsorption of the process and the lower part of the other column which has completed the process are connected to each other, and CH ₄ rich gas at the upper part of the column is moved to the lower part of the other column to equalize both columns. (Equal pressure gas) to an intermediate pressure, then the upper part of the tower and the water-containing gas holder are connected, and the CH ₄ mixed gas (upper depressurized gas) at the upper part of the tower is discharged under its own pressure. It is also connected to the lower part and flows out in both directions including the CH ₄ mixed gas (lower decompressed gas) in the lower part of the tower under its own pressure to make the inside of the tower to the atmospheric pressure, and then to below the atmospheric pressure in both directions via the suction pump. By suction decompression (suction decompression gas), mixed CH ₄ components are collected (recovered gas) in the water-containing gas holder for both the upper decompression gas, the lower decompression gas, and the suction decompression gas, and then from the lower part of the tower.
Further, CO ₂ and H ₂ O having high purity are desorbed (suction desorption gas) by suction desorption at atmospheric pressure or less through a suction pump, and taken out.

Process: The pressure-equalized gas of the process of the other column is received from the lower part of the column to an intermediate pressure, and at the same time, a part of the high-purity combustible component gas taken out in the adsorption process of the process is fed from the upper part of the column at a constant flow rate. At the end, pressurize to the adsorption pressure (reaction pressure), and cycle operation of 4 steps of adsorption, over-adsorption, desorption (decompression) and pressurization, and CH ₄ component that comes out with CO ₂ at the time of desorption Are collected as much as possible to increase the yield of the combustible component, and in the pressurizing step, the CO ₂ component is shifted to the inlet side to distribute the component to improve the purity of the purified combustible component in the adsorption step.

[0018]

DETAILED DESCRIPTION OF THE INVENTION The refining process for separating CO ₂ and H ₂ O by the continuous flow PSA method of the present invention will be specifically described below with reference to the process flow shown in FIG.

A mixture of H ₂ , CH ₄ , CO, CO ₂ , H ₂ O, etc. is continuously generated at a reaction pressure (9 kg / cm ² G) at a constant pressure / constant flow / constant component and is recovered at room temperature. Nearby temperature (40
C.) and sent to the present refining process as a raw material gas and divided into a combustible component gas stream and a CO ₂ gas stream, and both are taken out as product gas (refined gas and CO ₂ ).

In this device, the adsorbent was filled with molecular sieving carbon having an average pore size of 3 Å.
The adsorption towers A, B, C, and D of the tower and the desorption gas suction pump 31 for vacuum desorption of the gas adsorbed in the adsorbent and a part of the desorption gas are collected, and the pressure / flow rate of the recovered gas / pressure regulation of the components A water-containing gas holder 32 for rectifying and homogenizing, and a recovery gas compressor 33 and a recovery gas surge tank that raise the temperature of the recovery gas stored in the water-containing gas holder to the over-adsorption tower and send it at a constant pressure / constant flow. 34, purified gas surge tank 35 for stabilizing purified gas pressure, and switching valve group 1 for operating each process
~ 11 and a device comprising a constant flow control valve 20 for quantitatively feeding the purified gas into the adsorption tower by pressurization operation, a control valve 21 for controlling the desorption gas suction flow rate, and a control valve 22 for controlling the recovery gas flow rate. It is a composition.

As shown in FIG. 2, the operation of this adsorption tower is carried out according to a sequence program of adsorption / over-adsorption / desorption / adsorption.
Each pressurizing process is cycled by four adsorption towers. When the A tower is the adsorption step, the B tower is an over-adsorption step, the C tower is a desorption step, and the D tower is a depressurization step. Is equalized
Upper self pressure decompression, lower self pressure decompression, suction decompression, suction desorption 5
It consists of steps and is a 4-cycle 20-step method. The cycle time and step time are set by selecting the optimum time according to the component ratio of the raw material gas, the adsorbent selection performance, and the required purity and recovery rate of both product gases.

The switching valve for performing the above operation is opened and closed according to a sequence program for performing each step of each process as shown in FIG. 3. The desorption gas suction pump 31, the water-containing gas holder 32, and the recovered gas compressor. Since it also works with 33, an interlock mechanism for safety during this time is also incorporated. The operation control of the water-containing gas holder 32 is disclosed in Japanese Patent Laid-Open No. 3-1276
According to the device of 05, rectification, pressure regulation, and homogenization are performed simultaneously and continuously, and a method of operating the constant flow rate control valve 20 to control the flow rate of the pressurized gas is the method of JP-A-3-31317. By

Regarding the operation and the operating principle in which the above-described purification process obtains both the combustible component purity of 99% and the combustible component recovery rate of 99%, based on the operating principle flow shown in FIG. ₂ concentration of 25% step development of the a CO ₂ concentration of 10% demonstration plant in the case of the prime recovery gas (over adsorption tower outlet gas) (FIG. 5) temperature behavior Found in the operation process of the adsorbent (6) An example of actually measured CO ₂ concentration behavior in the tower during the operation process (FIG. 7) will be described according to the process. Adsorption process

The wet source gas containing 25% CO ₂ and 75% combustible components is 10% CO _{2 in the} lower pipe of the tower as shown in FIGS. 4 and 5.
After merging with the element recovery gas coming from the outlet of the over-adsorption column, the pre-treatment gas is fed at a pressure of 9 Kg / cm ² G from the lower part of the column and flows in the column in parallel flow to adsorb CO ₂ and moisture. At this time, the CO ₂ concentration distribution in the tower was 24% of the combined gas concentration upstream of the adsorption zone (bottom of the tower) and 1% downstream of it (upper tower), and at the outlet of the tower top, purified (product) gas containing 99% of combustible components. Spill out.

When this is seen from the measured value of the temperature behavior in the tower, at the beginning of the process, as shown in FIG. 6, the thermometer installed at the lowermost position of the tower has already adsorbed CO ₂ in the pressurization process of the previous process, As the adsorption zone progresses in the upper direction, the lower part of the tower,
The temperature rises rapidly in the order that it passes through the center of the tower, then there is no change at a certain temperature and then it becomes a constant temperature. At the end of the process, the temperature rises rapidly in the order that the adsorption zone reaches the upper part of the tower as shown in FIGS. The adsorption process is terminated when the temperature of the thermometer installed at the top begins to rise. That is, the operation of the adsorption process is to detect the behavior of the thermometer and automatically adjust the process time (cycle time). This ends the process with the adsorption front completely within the adsorption bed.

Over-adsorption step Among the desorption gas whose main component in the desorption step of the next step is CO ₂ , a gas containing a combustible component (mainly CH ₄ ), that is, an upper decompression gas, a lower decompression gas and a suction decompression gas is used. As shown in Fig. 4, the recovered gas mixed with the water-containing gas holder 32 to make the components uniform is collected gas compressor 33 with the water-containing gas holder pressure of 0.02 Kg / cm ² G to the adsorption pressure of 9.0 Kg / cm ² After raising the pressure to G or higher and the gas temperature to 100 ° C. or higher, the gas is fed from the lower part of the column where the adsorption process is completed.

As shown in FIG. 5, the raw material gas CO fed in the adsorption step is passed by passing the gas in a parallel flow in the tower.
Over-adsorption (re-adsorption) of moisture and CO _{2 in} the 90% concentration of the recovered gas, which is several steps higher than the ₂ concentration (25%), causes an over-adsorption zone in the lower part of the tower at the beginning of the process and also in the upper part of the tower. At the same time, an adsorption zone similar to the previous step is generated. At this time, the CO ₂ concentration distribution in the tower was 90% CO ₂ due to the recovered gas upstream of the over-adsorption zone (bottom of the tower).
The concentration is 24% CO ₂ concentration due to the combined gas in the adsorption process in the downstream of the over-adsorption zone (the central part of the tower), there is an adsorption zone in the downstream (upper part of the tower), and the downstream of the adsorption zone (the tower) As a result of the adsorption of 24% of CO _{2 on} the upper part, 1% of C
It has an O ₂ concentration, and this gas flows out from the tower outlet.

As shown in FIG. 6, the temperature measurement in the tower shows that the temperature of the thermometer installed in the lower part of the tower rises rapidly in the order of excessive adsorption of CO _{2 in} the recovered gas as shown in FIG. After that, there is no change at a certain temperature, and then the temperature becomes constant.

At the end of the process, the over-adsorption zone and the adsorption zone
It moves to the upper part of the tower and the adsorption zone
As it starts to pass through the upper outlet of the tower,
CO ₂Concentrated gas flows out. Gas leaked during this process
The gas is referred to as elementary recovery gas, and as described in the adsorption process above.
It joins the raw material gas and becomes the pre-treatment gas. This operation process
CO in the tower₂Looking at the actual measurement value of the concentration behavior, the figure in the middle of the process
Gas sampling hole installed at the top of the tower as shown in 7.
The concentration of the gas detected at the position increases rapidly in the order of
24% CO₂No change when it becomes
Continue with. At the end of the process, the super adsorption zone passes through the center of the tower.
The gas detected at the gas sampling hole at the position
Is CO₂Ingredients soar from 24% to near 90%.

As described above, if the position of the over-adsorption zone at the end of the over-adsorption step is adjusted to a position downstream of the central part of the column and does not reach the uppermost part of the column to adjust the CO ₂ concentration distribution in the column, it will be described later. Since the amount of recovered gas in the desorption process is stable, excessive equipment and power consumption are reduced, and the adsorption process time is also stable, so there is no need to increase the amount of adsorbent. It is a point that brings about the improvement of. The control elements for the breakthrough position of the over-adsorption zone are the CO ₂ component concentration of the recovered gas fed into the over-adsorption column, the gas flow rate and the gas temperature, which are related to the operation of the desorption process and will be described later.

Desorption process The upper part of the column after the over-adsorption process and the lower part of the column after the desorption process are connected, and both columns are pressure-equalized (STEP-11
) Do. In this case, since the adsorption zone described above is present in the upper part of the high pressure side column (pressure reducing column), the combustible component concentration is 99 to 76% (CO ₂ 1 to 24% in the upper part of the column as shown in FIG. ), Which means that a gas having a CO ₂ concentration of 1 to 24% flows out in parallel flow from the upper part of the tower as a pressure-equalizing gas, whereby the internal pressure of the tower is 9.0 Kg / cm ² G to 3.3 Kg. / cm ² G down to equalize pressure. On the other hand, this effluent gas is fed from the lower part of the low pressure side column (pressure column) to the above-mentioned C
O ₂ is adsorbed and the pressure rises from 60 Torr to 3.3 Kg / cm ² G and the pressure equalization is completed.

When the adsorption / desorption phenomenon in this pressure equalization operation is seen from the measured value of the temperature behavior in the tower, as shown in FIG. 6, the thermometer installed in the upper part of the tower shows that the temperature rises at the same time as the pressure equalization starts and then the pressure is reduced. To descend. This is the result of the CO ₂ gas having a concentration of 24% existing in the upper half of the tower at the end of the over-adsorption step, moved to the upper part of the tower, adsorbed to the adsorbent at the upper part of the tower, and then desorbed by depressurization. In the process, the temperature at the bottom of the pressurizing tower rises at the same time as the pressure is equalized. This is 99 at the bottom of the pressure tower
When moving combustible components in pressure-equalized gas of ~ 76% concentration, 1
This is a result of adsorption because CO ₂ ˜24% concentration also moves.

The purpose of the parallel flow outflow equalization step in this desorption process is to discharge as much as possible the combustible components existing in the upper part of the desorption column, and to use this gas and the column for pressurizing the pressure of this gas. It is to collect.

The position of the over-adsorption zone at the end of the above-mentioned over-adsorption step is important for the discharge amount of the combustible components of the desorbing column and the adsorption amount of CO ₂ of the above-mentioned pressurizing column, and changes depending on this position. The total amount of gas to be pressure-equalized is almost fixed, but the amount of combustible components remains in the desorption column, and the amount of recovered gas described later increases, and conversely CO ₂ component is great when increases the CO ₂ adsorption pressure pressure column, thereby decreasing the adsorption of CO ₂ during the adsorption step result, the cycle time is shortened, resulting in adsorption also becomes shorter adsorbent regeneration time The ability of the agent is reduced.

In view of the above-mentioned conventional techniques and problems, JP-A-2-2810
Although 96 is explained, one of the important differences from the present invention is that
This is a pressure equalization method that adjusts the position of the over-adsorption zone at the end of over-adsorption, and flows out of the desorption tower in parallel and out of the pressure tower, and moves the CO ₂ component in the pressure-equalized gas only to the lower part of the pressure tower. That is, it is limited to CO ₂ having a concentration of 24% existing in the upper part of the desorption column, and there is no CO ₂ component in the central part and the upper part of the pressure column.

[0036] Downstream of the adsorbent from the adsorption front during the adsorption step as this effect, only the adsorption of CO ₂ traces the pressurizing gas in the purified gas, the adsorption tower bottom of the CO ₂ to be moved in a pressure equalizing Since there is no other means, desorption of this is eliminated, and the purity of the purified gas (combustible component) obtained in the adsorption step is improved.
In addition, since the CO ₂ concentration in the gas that moves at a uniform pressure is low, the decrease in the effective adsorption amount due to the adsorption of the CO ₂ is reduced, and the overall (including excessive adsorption) adsorption capacity is improved, resulting in an increase in equipment capacity.

Next, the upper part of the tower and the water-containing gas holder 32 are connected to each other, and the remaining combustible component mixed gas (upper decompressed gas) at the upper part of the tower is discharged under its own pressure.
EP-12). In this case, the gas flowing out from the top of the tower is 24
% CO ₂ concentration, and as shown in FIG. 5, the decompressible CO ₂ active ingredient in the adsorbent decreased from the uniform pressure of 3.3 Kg / cm ² G to 2 Kg / cm ² G due to the cocurrent depressurization in the tower. The amount is about 74%.

Subsequently, both the lower part of the tower were connected to the water-containing gas holder 32, and the CO _{2 of} 90% concentration fed in the over-adsorption step at the lower part of the tower.
(Lower decompression gas) and 24% CO remaining in the upper part of the tower
₂ (Upper depressurization gas) flows out together Perform the upper and lower self-pressure depressurization operation (STEP-13) shown in Fig. 4. In this case, as shown in FIG. 5, the upper part of the tower becomes a parallel flow, and the lower part of the tower becomes a countercurrent flow, and the pressure is also
2.0Kg / cm ² G to 0.1Kg / cm, which is about the pressure of a water-containing gas holder
^The amount of CO ₂ active ingredient that can be desorbed in the adsorbent is reduced to ² G
It will be about 56%.

Then, as shown in FIG. 4, a desorption gas suction pump 31 is connected in the suction pipe to suck the combustible component mixed gas remaining in the tower from below and above the tower in the same manner as above. Perform suction decompression operation (STEP-14). In this case, as shown in FIG. 5, as in the previous operation, the upper part of the column was in parallel flow, and the lower part of the column was in countercurrent flow, and the CO ₂ concentration of the gas flowing out from the upper part of the column was 24 to 90% at the beginning of the operation as the pressure decreased. And it will rise to 99% at the end of the period. On the other hand, the CO ₂ concentration of the gas flowing out from the lower part of the tower rises from 90% to 99%. This means that the concentration of combustible components in the tower has dropped to around 1%,
The components of this outflow gas are detected and confirmed with a gas analyzer, and the suction decompression operation time is set with the pressure (650 Torr) at that time. This setting is for adjusting the gas amount of the suction depressurizing gas collected in the water-containing gas holder 32 and also for setting the purity of the product carbon dioxide gas obtained in the subsequent operation.

The upper decompression gas, the lower decompression gas, and the suction decompression gas except for the pressure equalization operation in the desorption process so far are sent to the water-containing gas holder 32 and homogenized in the water-containing gas holder 32. After being mixed and homogenized by the device, it is stored as the above-mentioned recovered gas.

One of the important differences of the present invention is that the preceding step of the desorption step is an over-adsorption step, and the main purpose is over-adsorption of CO _{2 in} the recovered gas. Has not been done. Therefore, a considerable amount of combustible components remains in the desorption tower at the beginning of the desorption process. The method is characterized by removing this combustible component from the inside of the tower.

This is the pressure equalizing method of STEP-11 and STEP-1.
2 to 14 three-stage combustible component outflow method, STEP-11
At the top of the tower, press the high concentration combustible component from the top
At -12, the remaining combustible components with high concentration in the upper part of the tower are pressurized by themselves from above, at STEP-13 the combustible components such as voids in the tower are at their own pressure from above and below, and at STEP-14 by suction below atmospheric pressure. Combustible components in the adsorbent are removed from the top and bottom. As an effect of this, it is possible to discharge the combustible components in the desorption column to the same extent as in the conventional high-purity CO ₂ reflux purge (described above), so that high-purity CO ₂ can be discharged.
₂ (99% or more) Cleaning and the requirement for using highly selective adsorbent to obtain this gas are relaxed, which is very economically advantageous.

Further, compared with JP-A-2-281096 (described above), STEP
At -11, most of the high-concentration combustible components in the upper part of the tower flow out in parallel flow and are collected in the pressurizing tower, so the total amount of combustible components going to the recovered gas is small, and not only the combustible component recovery rate is improved. As a result, the amount of recovered gas also decreases, and the related equipment and power also decrease, resulting in a large economic effect.

When the above operation is completed, the amount of combustible components in the tower is very small. Therefore, in order to obtain the product carbon dioxide gas from the inside of the tower, the suction pipe so far is connected to the carbon dioxide from the water-containing gas holder. Switch to the gas storage tank line and perform suction / desorption operation (STEP-15) to desorb CO ₂ and water in the adsorbent by countercurrent suction only in the lower part of the tower. In this case, CO ₂ having a purity of 99% is obtained, but the operating time thereof is related to the regeneration level of the adsorbent because the cycle time in the adsorption step becomes rate-determining. Therefore, it is necessary to select the capacity of the desorption gas suction pump in the most economical manner and set the selectivity and amount of the adsorbent so that the final pressure in the column will be the embodiment of 60 Torr or more shown in FIGS.

In this example, since it is necessary to separate water saturated in the raw material gas at the same time and the adsorption temperature is room temperature, the adsorbent which can be used is molecular sieving carbon having an average pore size of 3 Å. used.

Pressurizing Step As shown in FIG. 4, in the above-mentioned pressure equalizing operation in the initial stage of the desorption step, the pressure equalizing gas that has flowed out is received from the lower part of the column into the column (primary pressurized gas), and at the same time the upper part of the column is increased. The product purified gas (combustible component gas flow) is fed in at a constant flow (secondary pressurization), and the pressure is adjusted to 9.0 kg / cm ² G adsorption pressure at the end of the process. In this case, as shown in FIG. 5, in the initial stage of the operation, the CO ₂ was adsorbed by the pressure-equalized gas having a CO ₂ concentration of 24% in the adsorbent in the lower part of the tower, and the adsorbent in the upper part of the column was purified with a CO ₂ concentration of 1%. The CO ₂ is adsorbed by the gas.

Looking at this with the temperature motion shown in FIG. 6, the temperature of the thermometer installed at the bottom of the board suddenly rises to a certain temperature, there is no change, and the temperature becomes constant thereafter. The temperature of the thermometer rises slightly, reaches a certain temperature, and there is no change. CO ₂ of 90% concentration of CO ₂ 24% concentration that existed desorption搭上part from this it is present in the lower part moves will be remaining in the desorption column.

[0048]

EXAMPLES Regarding the method for separating carbon dioxide gas and water in the gas in this refining process, each numerical value used in the above specific description is an actual measurement value in a demonstration plant. The process flow of this operation example is shown in FIG. 1, and the numerical values of the respective stream numbers are shown in Table-1.

[0049]

[Table 1]

[0050]

The present invention has the following advantages because of the above-mentioned configuration. (1) Since the temperature behavior when the adsorption front is completely present in the adsorption bed is detected and the process time is automatically adjusted,
A highly pure flammable component is constantly obtained. (2) After adjusting the CO ₂ concentration distribution in the tower by setting the position of the over-adsorption zone at the end of the over-adsorption step, most of the high-concentration combustible components in the upper part of the desorption tower are added in parallel flow (equal pressure). Since it is collected by the pressure tower, the adsorption process time and the amount of collected gas are stable,
The combustible component recovery rate is 99% or more. Further, the amount of collected gas collected in the water-containing gas holder is also reduced. (3) The combustible component (co-adsorbed component) of the desorption tower is discharged by the parallel flow outflow and pressure equalization means and the three-stage combustible component outflow means, and the conventional high-purity CO ₂ reflux purge (washing) is performed. Since the same effect of cleaning the inside of the tower is obtained, excessive equipment, power and operation are simplified compared to the cleaning method, and the economical efficiency is greatly improved. (4) SNG purification performance is 99% in both purity and recovery rate
Since the above combustible components are PSA that can be obtained continuously and economically in a continuous flow, by using them, the performance of immediate start, immediate load change, and simultaneous dehydration, which cannot be obtained by the conventional liquid absorption method, is added. ..

[Brief description of drawings]

FIG. 1 is a purification process flow chart.

FIG. 2 is a diagram showing an operation development of an adsorption tower.

FIG. 3 is a diagram showing an opening / closing operation of a switching valve.

FIG. 4 is a flowchart for explaining the operating principle.

FIG. 5 is a diagram showing an example of process development in a demonstration plant.

FIG. 6 is an actual measurement diagram of temperature behavior in the tower during each operation process.

FIG. 7 is an actual measurement diagram of CO ₂ concentration behavior in the tower during adsorption and overadsorption operation processes.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Natsuo Kinoshita 1-17-1 Chiyo, Hakata-ku, Fukuoka-shi, Fukuoka Within Seibu Gas Co., Ltd. (72) Kei Ota 1-1-17 Chiyo, Hakata-ku, Fukuoka No. 1 West Gas Co., Ltd. (72) Inventor Haruji Kawasaki 1-17-1 Chiyo, Hakata-ku, Fukuoka-shi, Fukuoka Prefecture West Gas Co., Ltd. (72) Inventor Kon Nishino 22-64 Kotobuki, Abiko-shi, Chiba

Claims (6)

[Claims] 1. H ₂ .CH ₄ .CO .CO ₂ .H obtained by catalytic cracking in the process of producing alternative natural gas (SNG)
_In the refining process that separates carbon dioxide gas and water in the mixed generated gas (raw material gas) such as ₂ O in a continuous flow by the pressure swing method (PSA), the process of the wet raw material gas and the raw CH ₄ recovery gas The mixture is sent to one of the four adsorption towers from the lower part of the tower at an adsorption pressure (reaction pressure) to selectively adsorb CO ₂ and H ₂ O and to produce highly pure combustible components such as H ₂ CH ₄ CO. It was taken out from the upper part of the column, and among the desorption gases of the process steps, the upper decompression gas, the lower decompression gas and the suction decompression gas were mixed in a water-containing gas holder to make the components uniform, and the CO ₂ concentration became higher than that of the raw material gas. The temperature of the recovered gas is raised by the adsorption pressure (reaction pressure) and sent from the lower part of the tower at a constant flow rate, and CO ₂ and H ₂ O in the recovering gas are selectively adsorbed again (overadsorption) to increase the CH ₄ concentration. preparative upper portion of the column of containing CH ₄ recovery gas After being extracted, it is mixed with the raw material gas for the process, and the upper part of the column where the process is over-adsorbed is connected to the lower part of the other column where the process is finished, and the CH ₄ rich gas at the upper part of the column is connected to the other column. After moving to the lower part to equalize the pressure of both columns (equalizing pressure gas) to an intermediate pressure, then connect the upper part of the column and the water-containing gas holder, and mix CH ₄ gas at the upper part of the column (upper decompressed gas) Of the mixed gas containing CH ₄ mixed gas in the lower part of the tower (lower decompressed gas) and flowing out of the tower under its own pressure in order to bring the inside of the tower to about atmospheric pressure, and then suction Suction decompression (suction decompression gas) in both directions below the atmospheric pressure via a pump, and mixed CH ₄ components are collected (collected) in the water-containing gas holder for both the upper decompression gas, the lower decompression gas, and the suction decompression gas. Gas), and then from the bottom of the tower, through a suction pump, by suction and desorption at atmospheric pressure or lower to obtain high purity. CO ₂ and H ₂ O are desorbed (sucked desorption gas) and taken out, and the pressure-equalized gas of the process of other towers is received from the lower part of the tower to an intermediate pressure and the high-purity combustible gas taken out in the adsorption process of the process A part of the component gas is sent from the upper part of the tower at a constant flow rate, and pressure is applied so that the adsorption pressure (reaction pressure) is reached at the end of the process. Cycle operation of the four processes of adsorption, over-adsorption, desorption and pressurization. A method for separating carbon dioxide gas and water in a gas in a city gas refining process, characterized by: 2. The raw material gas fed into the refining process is split into only two passages, a high-purity combustible component gas stream and a high-purity carbon dioxide gas stream, which are free of outflow gases such as cleaning gas and purge gas. The method according to claim 1, wherein 3. The method according to claim 1, wherein the high-purity combustible component flow is a constant pressure / constant flow / constant component continuous flow. 4. In the column of the over-adsorption step of the step,
Part of the adsorption band generated in the previous process and the lower part generated in the process
There is an over-adsorption zone, and both adsorption zones follow as the over-adsorption process progresses.
Both move to the upper direction, the position at the end of the process
CO in the tower ₂Breakthrough position (process time) and process delivery
It is a special feature that it is controlled by the composition and flow rate of the recovered gas.
The method of claim 1, which is a trait. 5. The distribution amount of the upper decompression gas and the lower decompression gas to be collected in the desorption process of the process is adjusted by the position of the over-adsorption zone at the end of the process, and the suction amount of the suction decompression gas (suction time) 2. The method according to claim 1, wherein the gas is controlled by the amount of decrease in the CH ₄ component of the gas. 6. A molecular sieving carbon having an average pore size of 3 Å is used as an adsorbent.
the method of.