JP2012016680A - Gas treatment method and gas treatment facility - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent moisture adsorption to an adsorption part at low cost, in a pressure swing adsorption method that supplies raw gas to the intermediate part of an adsorption column.SOLUTION: The gas treatment method uses two adsorption columns each having adsorption parts at one and the other ends. In one adsorption column, raw gas is supplied from the intermediate part between the one and the other ends and discharged from the one end so that components in the raw gas are adsorbed by the adsorption part 1a at the one end. In the other adsorption column 2, the components adsorbed by the adsorption parts 2a and 2b are desorbed by desorption gas supplied from the one end and are discharged from the other end. The discharged desorption gas is cooled so that part of the components are separated, and the remaining desorption gas is supplied from the other end of the one adsorption column 1 so that the components in the remaining desorption gas are adsorbed by the adsorption part 1b at the other end. The adsorption/desorption operations in the adsorption columns 1 and 2 are alternated to recover the components in the raw gas. In the gas treatment method, the remaining desorption gas from which a part of the components has been separated is heated and supplied to the one adsorption column 1 from the other end.

Description

  The present invention relates to a gas processing method for removing and recovering VOC from a raw gas containing, for example, a volatile organic compound (VOC) using a pressure swing adsorption method (PSA method) using a plurality of adsorption towers, and The present invention relates to a gas processing facility used for this.

  As a method for recovering and removing components in the raw gas such as VOC in the atmosphere, as described in Patent Documents 1 and 2, for example, the column is filled with an adsorbent such as activated carbon, zeolite, or silica gel. In general, at least two adsorption towers having an adsorbing portion are used, and in some of the adsorption towers, the raw gas is introduced to adsorb the above components under elevated pressure or normal pressure, while in the other adsorption towers, the desorption gas is introduced. A PSA method is known in which components previously adsorbed under normal pressure or reduced pressure are desorbed, and such adsorption / desorption operations are alternately switched between these adsorption towers.

  Further, in such a PSA method, as described in, for example, Patent Document 3 and Non-Patent Document 1, an adsorbing portion in which an adsorbent is packed on one end side and the other end side in the adsorption tower. There is known a pressure swing type adsorption method in which the raw gas is supplied to an intermediate portion between both ends of the adsorption tower. In such a pressure swing type adsorption method, when the VOC concentration in the raw gas is low However, it can be concentrated at a high magnification and recovered as a condensate that does not require post-treatment, which is efficient.

JP 2007-240967 A JP 2009-050378 A JP 2009-078257 A

Wakasugi, Recovery of Volatile Organic Solvents by Dual Recirculation Pressure Swing Adsorption “Adsorption News vol. 20 No. 2 (June 2006)” p. 10-14

  By the way, in the PSA method, the desorbed gas from which the components such as VOC are desorbed is cooled to a predetermined set temperature in the condenser to condense the VOC components and moisture and separate as the condensate, and the remaining desorbed gas. Is discharged at a concentration corresponding to the saturated vapor pressure at the set temperature of the condenser. In the PSA method described in Patent Documents 1 and 2, the remaining desorbed gas discharged in this manner is returned to the raw gas to reduce its humidity.

  However, in the pressure swing adsorption method in which the raw gas described in Patent Document 3 and Non-Patent Document 1 is supplied to the intermediate part of the adsorption tower, the remaining desorbed gas thus discharged is transferred to the partial adsorption tower. The VOC component and the like are adsorbed by the adsorbing portion on the one end side supplied from the one end side. At the same time as the adsorption of the VOC component, the moisture contained in the remaining desorption gas is also adsorbed to the adsorption part in a saturated state.

  However, if moisture in a saturated state is adsorbed in the adsorption part in this way, water droplets adhere to the adsorbent due to recondensation of the moisture and block the pores, so that the adsorption performance is significantly reduced. Therefore, the frequency of exchanging the adsorbent is increased, and accordingly, the frequency of stopping the gas processing facility is increased and the cost of the adsorbent to be replaced is increased, resulting in an inefficient and uneconomical result. . In order to prevent such adsorption of water, for example, a water removal tower may be provided. However, if such an expensive device is provided, the cost of the equipment is increased and the economy is impaired. Inevitable.

  The present invention has been made under such a background, and the adsorption of moisture to the adsorption part in the pressure swing type adsorption method in which the raw gas as described above is supplied to the intermediate part of the adsorption tower is relatively low cost. Gas treatment method capable of continuously performing gas treatment by adsorption of a stable VOC component, etc. over a long period of time, and gas therefor The purpose is to provide treatment facilities.

  In order to solve the above problems and achieve such an object, the gas treatment method of the present invention provides at least two adsorption towers in which adsorption portions are formed on one end side and the other end side in the tower. In some of these adsorption towers, the raw gas is supplied from the intermediate portion between the one end and the other end and discharged from the one end, thereby the one on the one end. While the component in the raw gas is adsorbed by the adsorption unit, in the other adsorption tower, the component adsorbed on the adsorption unit is desorbed by the desorption gas supplied from the one end side, and the other end side is used. The exhausted desorbed gas is cooled and part of the components in the desorbed gas is separated, and the remaining desorbed gas is supplied to the partial adsorption tower from the other end side. By doing this, the suction part on the other end side A gas treatment method for adsorbing the above components in the desorption gas and recovering the components in the raw gas by alternately switching the adsorption / desorption operations of these partial adsorption towers and other adsorption towers, The remaining desorption gas from which a part of the components has been separated is heated and supplied to the partial adsorption tower from the other end side.

  Moreover, the gas treatment facility of the present invention is a gas treatment facility used in such a gas treatment method, and the adsorption of at least two towers in which adsorption portions are formed on one end side and the other end side in the tower. The raw gas supply path is connected to an intermediate portion between one end and the other end of these adsorption towers, and the above components are adsorbed on one end of the adsorption tower. The raw gas discharge path and the desorption gas supply path are connected, while the other end of the adsorption tower is connected to the desorption gas discharge path and the discharged desorption gas by cooling. A supply means for supplying the remaining desorption gas, comprising a cooling means for separating a part of the component in the desorption gas and connected to a supply path for supplying the remaining desorption gas from which a part of the component has been separated. The passage is provided with heating means for heating the remaining desorption gas. That.

  In such a gas processing facility, heating that heats the remaining gas to a supply path that supplies the remaining desorption gas from which a part of the above components such as VOC has been separated by the cooling means to the other end side of the adsorption tower. In the gas processing method of the present invention using such equipment, the remaining desorption gas is heated by the heating means and supplied to the partial adsorption tower from the other end side. The Therefore, the remaining desorption gas supplied to the adsorption tower increases in saturated vapor pressure and reduces the relative humidity.

  For example, if the temperature of the remaining desorption gas after cooling and separation of a part of the above components is 10 ° C., the saturated water vapor pressure is 1.2 kPa (9 mmHg), which is just before the dew condensation. When heated to 30 ° C., the saturated water vapor pressure is 4.2 kPa (31.7 mmHg), the relative humidity is reduced to 28%, and no condensation or recondensation occurs in the adsorption section. For this reason, it is possible to prevent moisture in the remaining desorption gas from recondensing and adhering to the adsorbent, and it is possible to efficiently adsorb only components such as VOC in the remaining desorption gas. Become.

  On the other hand, the heating means for heating the remaining desorption gas only needs to be able to heat the desorption gas at 10 ° C. to about 30 ° C. as described above. It is only necessary to use a heat exchanger of the type, or to wind an electric heater (heating wire) around the piping of the supply path or to perform steam tracing, so that expensive equipment such as a moisture removal tower is not required. For this reason, it is possible to reliably prevent the performance of the adsorbent from being lowered at a relatively low cost.

  Moreover, in the gas processing equipment which is not provided with the heating means of the remaining desorption gas like patent document 3, the remaining desorption gas cooled by the cooling means (coagulator) is the other end part side of another adsorption tower. Since the heat balance in the facility becomes unbalanced, the supply temperature to the adsorbent on the other end side of the other adsorption tower decreases with time, and the adsorbent is cooled excessively. become. In general, it is considered that the lower temperature is preferable for the adsorption, but if the temperature is excessively low, the desorption operation becomes difficult. Supplying to the other end side of the adsorption tower is an effective means from the viewpoint of preventing excessive cooling.

  Here, with regard to the heating temperature for heating the remaining desorbed gas in this way, for example, the desorbed gas discharged from the other end by desorbing the above components in the other adsorption tower is cooled to 20 ° C. or lower. In the case of separating a part of the above components, the remaining desorption gas from which a part of the components has been separated is heated so as to have a high temperature in the range of 15 ° C. to 40 ° C. with respect to the temperature after cooling. It is desirable to supply the partial adsorption tower from the other end side. If the heating temperature is lower than this, it may not be possible to reliably prevent adhesion of moisture to the adsorbent, but even if the heating temperature is higher than this, the recondensation prevention effect may change so much. Absent.

  According to the knowledge of the inventors of the present invention, the desorption gas immediately after the start of the desorption process does not contain much moisture, and the amount of moisture in the gas tends to increase as the process proceeds. Therefore, in the gas processing facility, the heating means includes a control means for controlling the heating temperature of the remaining desorption gas. After switching between the adsorption and desorption operations, the heating temperature is increased by increasing the heating amount of the remaining desorption gas from which a part of the components have been separated after a certain period of time, and the next adsorption / desorption operation is performed. It is desirable to end the heating of the remaining desorption gas before switching in order to reduce the heating energy required for the heating means and save energy.

  As described above, according to the present invention, in the pressure swing type adsorption method in which the raw gas is supplied to the intermediate part of the adsorption tower, when the remaining desorption gas from which components such as VOC are separated is supplied to the adsorption tower, It is possible to reliably prevent a decrease in adsorption performance due to moisture adhering to the adsorbent in the adsorption section of the adsorption tower at a relatively low cost. As a result, stable gas treatment can be achieved without replacing the adsorbent over a long period of time.

It is the schematic which shows one Embodiment of the gas processing equipment of this invention. It is a figure which shows the temperature dependence of the humidity of desorption gas, and the adsorption amount of a VOC component.

  FIG. 1 shows one embodiment of the gas processing facility of the present invention. The gas processing facility of the present embodiment performs adsorption / desorption operation of the VOC component in the raw gas (air) alternately by the two adsorption towers 1 and 2, and FIG. 1 shows one adsorption tower on the left side in the figure. This shows a case where (partial adsorption tower) 1 adsorbs the VOC component in the raw gas, and the other adsorption tower (other adsorption tower) 2 on the right side desorbs the adsorbed component.

  Adsorption towers 1 and 2 are each filled with an adsorbent such as activated carbon, zeolite, or silica gel on one end side (upper side in FIG. 1) and the other end side (lower side in FIG. 1). The parts 1a, 1b, 2a, 2b are formed, and an intermediate part of these adsorbing parts 1a, 1b, 2a, 2b is connected to the supply path 3 of the raw gas via switching valves 3a, 3b, respectively. Yes. Further, on one end side of each adsorption tower 1 and 2, there are provided switching valves 4 a and 4 b, a discharge path 4 through which the raw gas having the above components adsorbed is discharged as exhaust gas, and switching valves 5 a and 5 b. The desorption gas supply path 5 is connected.

  Further, a desorption gas discharge path 6 provided with switching valves 6 a and 6 b and connected to a vacuum pump 7 is connected to the other end side of the adsorption towers 1 and 2, and the discharge path 6 is connected to the vacuum pump 7. The desorption gas is cooled by the condenser 8, and a part of the VOC component is condensed and separated, and is recovered in the recovery tank 9. On the other hand, the remaining desorbed gas containing the VOC component that could not be separated is supplied to the adsorption tower via the return path 10 provided with the switching valves 10a and 10b and connected to the other ends of the adsorption towers 1 and 2, respectively. It can be returned within 1 and 2, and is circulated.

  In the gas processing facility of the present embodiment, the return path 10 is provided with a heating unit 11, and the remaining desorbed gas cooled by the condenser 8 is heated by the heating unit 11 to be absorbed in the adsorption tower 1. 2 can be supplied to the other end side. Here, the heating means 11 is a multi-tube or jacket-type heat exchanger in the present embodiment, and the remaining desorption gas and a heat medium having a temperature higher than that exchange heat inside and outside these tubes and jackets. By performing, the remaining desorption gas is heated. The heating means 11 may be a heating means using an electric heater (heating wire) in addition to the heat exchanger.

  By the way, although not shown, the raw gas supply path 3 is preferably provided with a condenser. It is possible to improve the adsorption efficiency by condensing and separating the moisture in the raw gas in advance by cooling with this condenser. More preferably, by providing a heater on the downstream side of the condenser in the raw gas supply path 3, the relative humidity can be reduced and condensation of the cooled raw gas can be prevented.

  Here, when the same heat exchanger as the heating means 11 in the return path 10 is used as the heater, the heater and the heating means 11 in the return path 10 are connected to each other. It is more preferable that the heating medium in which the raw gas is heated is supplied to the heating means 11 so that the remaining desorption gas can be heated by the waste heat.

  An embodiment of the gas processing method of the present invention using the gas processing facility having such a configuration will be described. In the state of FIG. 1, the switching valve 3a on the one adsorption tower 1 side of the raw gas supply path 3 is opened, while the other The switching valve 3b on the adsorption tower 2 side is closed, and similarly, the switching valve 4a of the exhaust gas discharge path 4 is opened, the switching valve 4b is closed, the switching valve 5a of the desorption gas supply path 5 is closed, and the switching valve. 5b is opened, the switching valve 6a of the desorption gas discharge path 6 is closed, the switching valve 6b is opened, the switching valve 10a of the concentrated gas return path 10 is opened, and the switching valve 10b is closed.

  Accordingly, the raw gas supplied from the supply path 3 is introduced into the tower from the middle part of the one adsorption tower 1 and flows to the one end side while being pressurized or under normal pressure by the adsorption part 1a on the one end side. Thus, a component such as VOC is adsorbed and a part of the purified exhaust gas is discharged. On the other hand, the remaining exhaust gas is supplied to one end portion side of the other adsorption tower 2 through the switching valve 5b, and the above components adsorbed by the adsorption portions 2a and 2b are desorbed under reduced pressure by the vacuum pump 11 to remove the components. Accordingly, the gas is discharged from the desorption gas discharge path 6 on the other end side of the adsorption tower 2.

  If the raw gas contains oxygen, the desorption gas supplied to the one end of the other adsorption tower 2 may contain nitrogen or the like in order to avoid dangers such as explosion due to VOC concentration. It is preferable to use an inert gas.

  Next, the desorption gas with the above components is supplied to the condenser 8 through the vacuum pump 7 and cooled to, for example, 20 ° C. or less, preferably 0 ° C. to 20 ° C., more preferably 5 ° C. to 15 ° C. Thus, a part of the components is condensed and moisture remaining in the raw gas is condensed and separated, and the separated components and moisture are collected in the recovery tank 9 as a condensate. In addition, there exists a possibility that a water | moisture content may freeze when cooling temperature is less than 0 degreeC. On the other hand, the remaining desorption gas from which the flocculated liquid has been separated in this way is supplied from the other end side to the one adsorption tower 1 via the return path 7 together with the remaining components and moisture that have not been condensed. The remaining components are adsorbed in the adsorption section 1b in the side tower.

  The return path 10 to which the remaining desorption gas is returned and supplied from the other end of one adsorption tower 1 is provided with the heating means 11, and thus the remaining desorption supplied to the adsorption tower 1. By heating the gas, the saturated vapor pressure can be increased and the relative humidity can be reduced. For this reason, the water in the remaining desorption gas that has just reached the dew condensation state after being cooled by the condenser 8 is condensed in the adsorption portions 1b, 1a of the one adsorption tower 1 to form water droplets. This can prevent the adsorption performance of the one adsorption tower 1 from being deteriorated.

  Specifically, as shown in FIG. 2, when the temperature of the remaining desorption gas cooled in the condenser 8 is 10 ° C., the saturated water vapor pressure is 1.2 kPa (9 mmHg), and dew condensation occurs as described above. For example, if this is heated to 30 ° C, the saturated water vapor pressure will be 4.2 kPa (31.7 mmHg) and the relative humidity will be reduced to 28%. The relative humidity is reduced to about 20%. On the other hand, the saturated adsorption amount of the VOC component (toluene in FIG. 2) decreases only about 10% even when heated from 10 ° C. to 30 ° C., and decreases only about 20% even when heated to 50 ° C. For this reason, the moisture of the remaining desorption gas is not recondensed in the adsorption sections 1b and 1a of the adsorption tower 1, and thus the water droplets of the recondensed water are prevented from adhering to the adsorbent as described above. Thus, only the above-mentioned components such as VOC in the remaining desorption gas can be efficiently adsorbed by one adsorption tower 1.

  In addition, the heating means 11 only needs to heat the remaining desorption gas to about 25 ° C. to 60 ° C. as will be described later, so that the heat exchanger, electric heater, or steam trace as in this embodiment is used. A relatively low-cost means such as Moreover, since the heating medium when the heating means 11 is a heat exchanger can be used, a heating medium such as warm water, warm air, and steam, which is relatively inexpensive and easy to supply with gas processing equipment, can be used efficiently and economically. In addition, adhesion of moisture to the adsorbent in the adsorption tower 1 can be prevented.

  Here, as a result of further earnest research on the gas treatment method using such a gas treatment facility, the inventors of the present invention do not contain much moisture in the product gas (exhaust gas) immediately after the start of the desorption process, It came to the knowledge that there exists a tendency for the moisture content in gas to increase as a process progresses. Therefore, in the heating means 11, it is preferable that the exchange heat amount (heating amount) is reduced at the start of the desorption process and the exchange heat amount is increased after a predetermined time has elapsed. By performing such control, the heating energy required for the heating means 11 can be reduced, leading to energy saving.

  Specifically, when the heating means 11 is a heat exchanger as in this embodiment, the heat medium supply amount may be reduced at the beginning of desorption and the heat medium supply amount may be increased after a lapse of a certain time. The adjustment of the heating medium supply amount can be performed by performing time control using, for example, a timer. Further, as shown in FIG. 1, a temperature control mechanism 12 is provided on the gas outlet side of the heating means 11 of the return path 10, and the heat medium (FIG. 1) is supplied to the heating means 11 according to the temperature of the remaining desorbed gas to be returned. In this case, the supply amount of the deficient steam) may be controlled. Furthermore, when the heating means is an electric heater, the temperature can be controlled by controlling the heat generation amount (heating amount).

  The heating temperature of the remaining desorption gas by the heating means 11 is such that the desorption gas discharged by desorbing the above components in the other adsorption tower 2 is cooled to 20 ° C. or less in the condenser 8 as described above. When a part of the above components is separated, it is desirable to heat so that the temperature becomes higher in the range of 15 to 40 ° C. than the temperature after cooling. That is, if the temperature of the remaining heated desorption gas is below the above range, there is almost no difference from the temperature of the desorption gas after cooling, and the humidity is not sufficiently reduced as shown in FIG. 1 may not be able to prevent recondensation of moisture, but even if the heating temperature is higher than the above range, the recondensation preventing effect does not change so much as shown in FIG. Inefficient because it requires a high-temperature heat source. The range of temperature change of the desorption gas to be cooled and heated is desirably 0 ° C. to 60 ° C., and the difference between the cooling temperature and the heating temperature is within the above range in order to prevent moisture recondensation more reliably. It is preferable that the temperature of the desorption gas after heating is in the range of 25 ° C to 60 ° C, more preferably in the range of 30 ° C to 45 ° C.

  Further, in the gas processing facility of the present embodiment, the heating means 11 for heating the remaining desorbed gas is a heat exchanger, and a similar heat exchanger is used as a heater in the raw gas supply path 3 as described above. Is used, the heat exchanger as the heater and the heat exchanger as the heating means 11 are connected, so that the heating medium that has heated the raw gas in the supply path 3 is supplied to the heating means 14 and remains. The desorption gas can be heated. That is, since the remaining desorption gas can be heated using the waste heat of the heater of the raw gas, it is possible to prevent the adsorption performance in the adsorption tower 1 from being lowered more efficiently and economically.

  When the adsorption of the component in the raw gas in one adsorption tower 1 and the desorption of the component in the other adsorption tower 2 are completed in the state shown in FIG. 1, the switching valves 3a to 6a, 10a, 3b to Switching between 6b and 10b is reversed, and desorption is performed in one adsorption tower 1 and adsorption is performed in the other adsorption tower 2. At this time, the return path 10 to be connected from the condenser 8 through the switching valve 10b to the other end of the other adsorption tower 2 is provided with a heating means 11, and the other Since the remaining desorption gas supplied to the adsorption tower 2 can be heated, it is possible to prevent moisture from adhering to the adsorbent in the other adsorption tower 2, and without excessively cooling the adsorbent, Efficient gas processing can be performed economically.

DESCRIPTION OF SYMBOLS 1, 2 Adsorption tower 1a, 1b, 2a, 2b Adsorption part 3 Source gas supply path 4 Exhaust gas discharge path 5 Desorption gas supply path 6 Desorption gas discharge path 7 Vacuum pump 8 Condenser (cooling means)
DESCRIPTION OF SYMBOLS 9 Recovery tank 10 Return path of remaining desorption gas 11 Heating means 3a-6a, 10a, 3b-6b, 10b Switching valve

Claims (5)

Using at least two adsorption towers in which adsorption parts are formed on one end side and the other end side in the tower, and in some of these adsorption towers, there is a gap between the one end part and the other end part. While supplying the raw gas from the intermediate part and discharging it from the one end part side, the component in the raw gas is adsorbed by the adsorption part on the one end part side,
In other adsorption towers, the desorbed gas supplied from the one end side desorbs the components adsorbed on the adsorption section and discharges them from the other end side,
By cooling the discharged desorption gas, a part of the component in the desorption gas is separated, and the remaining desorption gas is supplied to the partial adsorption tower from the other end side, By adsorbing the components in the remaining desorption gas by the adsorption part on the other end side,
A gas processing method for recovering components in the raw gas by alternately switching the adsorption / desorption operation between these partial adsorption towers and other adsorption towers,
A gas treatment method, wherein the remaining desorption gas from which a part of the components has been separated is heated and supplied to the partial adsorption tower from the other end side.   In the other adsorption tower, the component is desorbed and the desorption gas discharged from the other end side is cooled to 20 ° C. or lower to separate part of the component, and part of the component is separated. The remaining desorption gas is heated so as to have a high temperature in the range of 15 ° C to 40 ° C with respect to the temperature after cooling, and is supplied to the partial adsorption tower from the other end side. Item 4. The gas treatment method according to Item 1.   After switching the adsorption / desorption operation between the partial adsorption tower and the other adsorption tower, the heating amount of the remaining desorption gas from which a part of the component is separated is increased, and the next adsorption / desorption operation is performed. 3. The gas processing method according to claim 1, wherein heating of the remaining desorption gas is terminated before switching.   It is a gas processing equipment used for the gas processing method according to any one of claims 1 to 3, and at least two towers in which adsorption parts are formed on one end side and the other end side in the tower. The adsorbing tower is provided, and the raw gas supply path is connected to an intermediate portion between one end and the other end of the adsorbing tower, and the component is disposed on one end of the adsorbing tower. The adsorbed raw gas discharge path and the desorption gas supply path are connected, and the desorption gas discharge path and the discharged desorption gas are cooled at the other end of the adsorption tower. A cooling means for separating a part of the component in the desorption gas is connected to a supply path for supplying the remaining desorption gas from which a part of the component has been separated. The supply passage is provided with a heating means for heating the remaining desorption gas. Gas processing facilities to be.   The gas processing facility according to claim 4, wherein the heating means includes a control means for controlling a heating temperature of the remaining desorption gas.

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