JP5846546B2 - Apparatus and method for treating exhaust gas containing volatile organic compound - Google Patents

Description

  The present invention relates to an apparatus and method for treating exhaust gas containing hydrocarbons such as volatile organic compounds, and in particular, volatilization in exhaust gas discharged from facilities handling paints, adhesives, inks, petrochemical products, gasoline, etc. The present invention relates to a removal / decomposition apparatus and a removal / decomposition method for volatile organic compounds.

  In recent years, air pollution related to suspended particulate matter (SPM) and photochemical oxidants has become a problem, and suppression of emission of hydrocarbons such as volatile organic compounds, which are one of the causative substances, has been demanded. In general, combustion methods, membrane separation methods, adsorption methods, absorption methods and the like are known as hydrocarbon removal methods.

  Among these volatile organic compound removal methods, an adsorption method using an adsorbent such as activated carbon or zeolite is known as a method applicable when treating exhaust gas containing a relatively low concentration of volatile organic compounds. . As an example of the adsorption method, adsorbent removes volatile organic compounds from the exhaust gas, and when the adsorbent is saturated with volatile organic compounds, the volatile organic compounds are desorbed from the adsorbent using heat or pressure. It is known that the concentrated gas containing the desorbed volatile organic compound is treated by a combustion method. Thereby, the quantity and combustion time of the auxiliary agent used for a combustion method can be reduced, and an operating cost can be reduced.

  As a method of heating and regenerating the adsorbent, a method of performing heat regeneration using the adsorption level of the adsorbent as an index has been proposed (Patent Document 1). However, the method of Patent Document 1 has a problem in that volatile organic compounds are concentrated, so that the concentration of organic compounds in the exhaust gas becomes high and falls within the explosion limit range, which may generate detonation. Therefore, as a method of avoiding detonation, nitrogen is circulated as a purge gas for desorbing volatile organic compounds from the adsorbent (Patent Document 2), or a method for reducing the oxygen concentration during desorption (Patent Document 3). Has been proposed.

JP-A-9-206557 Japanese Patent No. 3068272 JP 2007-83238 A

  However, in the methods of Patent Document 2 and Patent Document 3, it is necessary to provide a nitrogen generating facility, to prepare nitrogen, or to reduce the oxygen concentration, both of which increase the cost of facility costs and operating costs. Occurs.

  The present invention has been made in view of these problems, and is an exhaust gas treatment apparatus and treatment method containing a volatile organic compound that is mixed with air and sucked. It is an object of the present invention to provide a safe processing apparatus and processing method that is free from the risk of explosion of volatile organic compound gas in the gas.

<First invention>
An apparatus for treating exhaust gas containing a volatile organic compound according to the first invention houses an adsorbent that adsorbs a volatile organic compound, receives the exhaust gas, and converts the volatile organic compound in the exhaust gas to the adsorbent. An adsorbed state in which clean exhaust gas is discharged by adsorption removal, and a purge gas is received, and a volatile organic compound adsorbed on the adsorbent is desorbed by the purge gas, and a desorbed gas that is a purge gas containing the volatile organic compound is removed. An adsorption tower that can operate in a desorbed state to be discharged, and an oxidation that accepts the desorbed gas from the desorbed adsorption tower, oxidatively decomposes volatile organic compounds in the desorbed gas, and discharges the decomposed purge gas A decomposition apparatus and the decomposed purge gas that has been heated by oxidation and decomposition in the oxidative decomposition apparatus, and the temperature of at least a part of the purge gas supplied to the desorbed adsorption tower is increased. A heat exchanger that is heated by heat exchange with the decomposed purge gas, a concentration meter that measures a volatile organic compound concentration in the desorbed gas discharged from the desorbed adsorption tower, and the volatile organic compound Based on the volatile organic compound concentration measured by the densitometer so that the concentration is lower than the lower limit value of the predetermined explosion concentration range of the desorbed gas, the desorption is the atmospheric temperature in the desorbed adsorption tower. It has a desorption temperature control device for controlling the desorption temperature.

  According to the present invention having such a configuration, the desorption gas is always controlled by controlling the desorption temperature in the adsorption tower in accordance with the volatile organic compound concentration of the desorption gas discharged from the desorption state adsorption tower. Safe operation can be performed while keeping the volatile organic compound concentration below the lower limit of the explosion concentration range. Therefore, unlike conventional methods, it is not necessary to lower the oxygen concentration in the purge gas or to use a separate inert gas as the purge gas, and it is possible to remove and decompose volatile organic compounds at low cost and safely. Become.

  In the present invention, a plurality of adsorption towers are provided, and some of the adsorption towers adsorb and remove volatile organic compounds in the exhaust gas in an adsorption state to discharge clean exhaust gas, and the remaining adsorption towers are In order to desorb volatile organic compounds already adsorbed in a desorbed state, a portion of the clean exhaust gas is received as a purge gas from the partial adsorption tower, and the heat exchanger absorbs the remaining portion. A part of the purge gas supplied to the tower is heated by heat exchange with the heated decomposed purge gas, and the desorption temperature control device controls the supply amount of the partial purge gas and the remaining purge gas. By adjusting the supply amount, the desorption temperature in the remaining adsorption tower in the desorption state may be controlled. In this way, by using the clean exhaust gas of the partial adsorption tower as the purge gas for desorbing the volatile organic compounds in the remaining adsorption tower, it is not necessary to separately provide a purge gas generation facility. In addition, volatile organic compounds are adsorbed and removed in some adsorption towers, and volatile organic compounds are desorbed in the remaining adsorption towers, so that the exhaust gas can be treated efficiently and the adsorbent can be regenerated. it can.

  In the present invention, the adsorption tower is configured to receive the atmosphere as a purge gas in a desorbed state, and the heat exchanger decomposes a part of the purge gas supplied to the adsorption tower by raising the temperature. The desorption temperature control device is heated by heat exchange with the spent purge gas, and the desorption temperature control device adjusts the supply amount of the partial purge gas and the supply amount of the remaining purge gas, thereby desorbing the desorption temperature in the adsorption tower in the desorption state. It may be configured to control. Thus, by using the atmosphere as a purge gas for desorption of volatile organic compounds, it is not necessary to separately provide a purge gas generation facility.

  In the present invention, the apparatus further includes a high-temperature gas generator that generates a high-temperature gas by heating gas, and a plurality of adsorption towers are provided, and some of the adsorption towers are in an adsorbed state in the exhaust gas. Volatile organic compounds are adsorbed and removed to discharge clean exhaust gas, and the remaining adsorption tower is in a desorbed state, and the clean exhaust gas is removed from some of the adsorption towers in order to desorb already adsorbed volatile organic compounds. The high temperature gas generated by the high temperature gas generator is mixed in the purge gas, and the heat exchanger raises the temperature of the purge gas supplied to the remaining adsorption tower. The desorption temperature control device is brought into a desorption state by adjusting at least one of the amount and temperature of the high temperature gas generated by the high temperature gas generator. That may be adapted to control the desorption temperature in the adsorption tower of the remainder.

  In this way, by using the clean exhaust gas of the partial adsorption tower as the purge gas for desorbing the volatile organic compounds in the remaining adsorption tower, it is not necessary to separately provide a purge gas generation facility. Further, by mixing the high temperature gas into the purge gas, the desorption temperature in the remaining adsorption tower can be adjusted in a higher temperature range, and the desorption of the volatile organic compound is promoted and required for desorption. Time can be shortened. In addition, volatile organic compounds are adsorbed and removed in some adsorption towers, and volatile organic compounds are desorbed in the remaining adsorption towers, so that exhaust gas can be treated efficiently and adsorbents can be regenerated. it can.

  In the present invention, it further includes a heating device for heating the adsorbent of the adsorption tower, the adsorption tower is configured to receive the atmosphere as a purge gas in a desorbed state, and the heat exchanger includes the above adsorption tower And the desorption temperature control device adjusts the heating temperature by the heating device so that the adsorption tower is in the desorption state. It is good also as controlling the desorption temperature in.

  Thus, by using the atmosphere as a purge gas for desorption of volatile organic compounds, it is not necessary to separately provide a purge gas generation facility. In addition, by heating the adsorbent of the adsorption tower with a heating device, the desorption temperature in the adsorption tower can be adjusted in a higher temperature range, promoting the desorption of volatile organic compounds and desorption. Can be shortened.

  In the present invention, the adsorbent of the adsorption tower is formed as a detachable adsorbent cartridge having a plurality of plate-like adsorbent packed layers arranged at predetermined intervals, and the adsorbent cartridge is the above adsorbent cartridge. A flow of exhaust gas is formed such that the exhaust gas supplied to one side of the adsorbent packed bed passes through the adsorbent packed bed toward the other side, and the exhaust gas supplied to the adsorbent cartridge is It is preferable that the plurality of adsorbent packed beds be distributed and flow.

  By using the adsorbent cartridge having the above-described configuration as the adsorbent, the exhaust gas and the adsorbent packed bed come into contact with each other in a side flow manner, and the area of the adsorbent packed bed in contact with the exhaust gas can be increased. Therefore, the amount of adsorbent used can be reduced, and the installation area in the adsorption tower can be reduced, which is economical. Further, since the adsorbent packed layer is formed in a flat plate shape and is thin, the pressure loss can be reduced accordingly.

<Second invention>
According to a second aspect of the present invention, there is provided a method for treating an exhaust gas containing a volatile organic compound, wherein the exhaust gas is received by some of the adsorption towers among a plurality of adsorption towers containing an adsorbent that adsorbs the volatile organic compound. The volatile organic compound in the exhaust gas is adsorbed and removed by the adsorbent to discharge the clean exhaust gas, and the remaining adsorption tower accepts the purge gas and desorbs the already adsorbed volatile organic compound by the purge gas. The desorption gas, which is a purge gas containing a volatile organic compound, is discharged, and the volatile organic compound in the desorption gas discharged from the remaining adsorption tower is oxidatively decomposed to generate a decomposed purge gas. At least a part of the purge gas supplied to the adsorption tower is heated by heat exchange with the decomposed purge gas heated by oxidation and decomposed, and the residue is removed when the volatile organic compound is desorbed. The concentration of the volatile organic compound in the desorbed gas discharged from the adsorption tower was measured so that the concentration of the volatile organic compound was lower than the lower limit of the predetermined explosion concentration range of the desorbed gas. Based on the volatile organic compound concentration, the desorption temperature in the adsorption tower, which is the atmospheric temperature in the adsorption tower during the desorption, is controlled.

  Also in the present invention, similarly to the first invention, the volatile organic compound concentration in the desorption gas can be safely operated while keeping the lower concentration value of the explosion concentration range lower than the lower limit value of the explosion concentration range, and the volatile organic compound can be safely and inexpensively. Can be removed and disassembled. In addition, volatile organic compounds are adsorbed and removed in some adsorption towers, and volatile organic compounds are desorbed in the remaining adsorption towers, so that the exhaust gas can be treated efficiently and the adsorbent can be regenerated. it can.

  According to the exhaust gas treatment apparatus and treatment method of the present invention, by controlling the desorption temperature in the adsorption tower according to the concentration of the volatile organic compound of the desorption gas discharged from the desorption state adsorption tower, Safe operation can always be performed while maintaining the concentration of the volatile organic compound in the desorption gas lower than the lower limit of the explosion concentration range. Therefore, unlike conventional methods, it is not necessary to lower the oxygen concentration in the purge gas or to use a separate inert gas as the purge gas, and it is possible to remove and decompose volatile organic compounds at low cost and safely. Become.

It is the schematic which shows the structure of the exhaust gas processing apparatus which concerns on 1st embodiment of this invention. It is the schematic which shows the structure of the exhaust gas processing apparatus which concerns on 2nd embodiment of this invention. It is the schematic which shows the structure of the exhaust gas processing apparatus which concerns on 3rd embodiment of this invention. It is the schematic which shows the structure of the exhaust gas processing apparatus which concerns on 4th embodiment of this invention. It is a figure which shows the structure of the adsorbent cartridge provided in an adsorption tower. It is a figure which shows the other example of the installation form of the adsorption agent cartridge in an adsorption tower. It is a figure which shows the further another example of the installation form of the adsorption agent cartridge in an adsorption tower. It is II sectional drawing of FIG. 3 is a graph showing changes in benzene concentration in desorbed gas in Example 1. 6 is a graph showing changes in toluene concentration in desorbed gas in Example 2. It is a graph which shows the relationship between the frequency | count of adsorption | suction in Example 2, and time until activated carbon becomes unable to exhibit performance in an adsorption removal process.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

<First embodiment>
FIG. 1 is a schematic diagram illustrating a configuration of an exhaust gas treatment apparatus according to the present embodiment. The exhaust gas treatment apparatus has two adsorption towers A and B which have the same configuration and are connected to each other by a purge gas pipe 1 which will be described later. As seen in FIG. 1, the adsorption towers A and B are provided with a packed bed of an adsorbent such as activated carbon. In the present embodiment, as will be described later, as a preferable embodiment, the adsorbent is configured as an adsorbent cartridge 2 that can be attached to and detached from the adsorption tower (see FIG. 5).

  The adsorption tower A and the adsorption tower B include an adsorption state in which the volatile organic compound in the exhaust gas containing the volatile organic compound is adsorbed and removed by the adsorbent, and the volatile organic compound adsorbed on the adsorbent by the purge gas. Any state of desorption state of desorption is possible. The adsorption tower A and the adsorption tower B alternately perform a process in the adsorption state (hereinafter referred to as “adsorption removal process”) and a process in the desorption state (hereinafter referred to as “desorption process”). To do.

  In FIG. 1, it is shown in a simplified manner that the adsorption removal process is performed in the adsorption tower A and the desorption process is performed in the adsorption tower B, and only the minimum necessary piping is illustrated. However, actually, a pipe (not shown) is also connected to the adsorption towers A and B. By switching valves provided in the pipes, the desorption process is performed in the adsorption tower A and the adsorption removal process is performed in the adsorption tower B. Can also be done selectively.

  As seen in FIG. 1, the upper part of the adsorption tower A and the upper part of the adsorption tower B are connected by a purge gas pipe 1 for supplying a purge gas. The adsorption tower A in the adsorption state performing the adsorption removal process in FIG. 1 receives exhaust gas containing a volatile organic compound from the lower part, adsorbs and removes the volatile organic compound in the exhaust gas with an adsorbent, and produces clean exhaust gas. Drain from the top. A part of the clean exhaust gas flows through the purge gas pipe 1 and is supplied as purge gas from above to the adsorption tower B in the desorption state in which the desorption step is performed in FIG. The adsorption tower B desorbs the volatile organic compound adsorbed by the adsorbent with the purge gas, and discharges the desorbed gas, which is a purge gas containing the volatile organic compound, from below.

  In addition to the adsorption towers A and B, the exhaust gas treatment apparatus according to the present embodiment includes a blower 3 provided in the purge gas pipe 1 that sends the purge gas from the adsorption tower A toward the adsorption tower B, and one of the purge gases. A heat exchanger 4 that heats the part by heat exchange with a decomposed purge gas described later, an oxidative decomposition apparatus 5 that oxidatively decomposes volatile organic compounds in the desorbed gas from the adsorption tower B, and a desorption from the adsorption tower B. A concentration meter 6 for measuring the concentration of a volatile organic compound in the separated gas, and a desorption temperature control device for controlling the desorption temperature in the adsorption tower B based on the concentration of the volatile organic compound measured by the concentration meter 6 7.

  The blower 3 is connected to the purge gas pipe 1 on the downstream side of the adsorption tower A, and sends a part of the clean exhaust gas from the adsorption tower A toward the adsorption tower B as a purge gas. Thus, in this embodiment, since the clean exhaust gas from the adsorption tower A is used as the purge gas for desorption of the volatile organic compound in the adsorption tower B, it is not necessary to separately provide a facility for generating the purge gas. It can be downsized.

  The purge gas pipe 1 is branched downstream of the blower 3 into two purge gas branch pipes 1A and 1B. One purge gas branch pipe 1A has a valve 8 and the other purge gas branch pipe 1B has a valve. 9 is provided, and the flow rate of the purge gas flowing through the purge gas branch pipes 1A and 1B can be adjusted by adjusting the opening of the valves 8 and 9.

  The heat exchanger 4 is provided in the purge gas branch pipe 1A on the downstream side of the valve 8, and as will be described later, in the heat exchanger 4, the purge gas flowing in the purge gas branch pipe 1A is Heating is performed by heat exchange with a decomposed purge gas whose temperature has been raised from an oxidative decomposition apparatus 5 described later. The purge gas branch pipe 1A and the purge gas branch pipe 1B are connected to the downstream side of the heat exchanger 4, and an unheated purge gas (hereinafter referred to as “non-heated purge gas” flowing through the purge gas branch pipe 1B). )) Flows through the purge gas branch pipe 1A and is mixed with the purge gas heated by the heat exchanger 4 (hereinafter also referred to as “heated purge gas”) and mixed, and the mixed purge gas enters the adsorption tower B It comes to be supplied. As described above, the flow rate of the heated purge gas and the flow rate of the non-heated purge gas are adjusted by the opening degree of the valves 8 and 9, respectively, so that the temperature of the purge gas supplied to the adsorption tower B and the desorption state are thereby adjusted. The desorption temperature, which is the atmospheric temperature in the adsorption tower B, can be adjusted.

  The oxidative decomposition apparatus 5 is provided on the downstream side of the adsorption tower B, oxidatively decomposes volatile organic compounds in the desorbed gas discharged from the adsorption tower B, and discharges the decomposed purge gas. The oxidative decomposition apparatus 5 is loaded with, for example, a catalyst for oxidative decomposition of a volatile organic compound, and has an arrangement in which the atmospheric temperature is maintained at an appropriate temperature by heating a burner (not shown). When the desorbed gas is supplied from the adsorption tower B to the oxidative decomposition apparatus 5, the volatile organic compound in the desorbed gas is oxidatively decomposed, and the decomposed purge gas is heated by the heat generated by the oxidative decomposition, and the oxidation is performed. It is discharged from the decomposition device 5. In this embodiment, burner heating is performed in the oxidative decomposition apparatus 5 in order to maintain the atmospheric temperature. However, the burner is not essential when sufficient heat is generated by the oxidative decomposition reaction itself. Further, the oxidative decomposition apparatus is not limited to the configuration of the present embodiment, and may be configured of, for example, a direct combustion apparatus, a heat storage combustion apparatus, or the like. Hereinafter, the desorption process in the adsorption tower and the oxidative decomposition process in the oxidative decomposition apparatus are collectively referred to as “desorption and decomposition process”.

  As shown in FIG. 1, the above-described heat exchanger 4 provided in the purge gas branch pipe 1 </ b> A is located downstream of the oxidative decomposition apparatus 5. In the heat exchanger 4, the purge gas flowing in the purge gas branch pipe 1 </ b> A of the purge gas pipe 1 is heated by heat exchange with the decomposed purge gas whose temperature has been raised in the oxidative decomposition apparatus 5. The decomposed purge gas that has been subjected to heat exchange with the purge gas passes through the heat exchanger 4, is subjected to appropriate processing, and is discharged to the outside.

  The densitometer 6 measures the concentration of the volatile organic compound in the desorbed gas discharged from the adsorption tower B at a position between the adsorption tower B and the oxidative decomposition apparatus 5. The desorption temperature control device 7 is configured such that the volatile organic compound concentration measured by the densitometer 6 is such that the volatile organic compound concentration in the desorption gas is lower than the lower limit value of the predetermined explosion concentration range of the desorption gas. Based on the above, by adjusting the opening degree of each of the valves 8 and 9, the flow rate of the purge gas flowing through the purge gas branch pipe 1A and the flow rate of the purge gas flowing through the purge gas branch pipe 1B are adjusted. As a result, the temperature of the purge gas supplied to the adsorption tower B and the desorption temperature in the adsorption tower B are controlled. Specifically, when the temperature of the purge gas supplied to the adsorption tower B rises and the desorption temperature in the adsorption tower B rises, the volatile organic compound adsorbed by the adsorbent in the adsorption tower B Desorption is promoted, and the concentration of volatile organic compounds in the desorption gas increases.

  Here, the setting of the lower limit of the explosion concentration range of the desorbed gas will be described. For example, when the volatile organic compound is benzene, its theoretical explosion concentration lower limit is 1.3%, but it may be set to 0.5 times the lower limit of the explosion concentration range for safety reasons. Thus, when the explosion concentration range is defined, the lower limit of the explosion concentration of benzene is 0.65%. Therefore, in the method of the present invention, the desorption temperature is controlled so that the concentration of benzene in the desorption gas is lower than 0.65%. However, if the concentration of the volatile organic compound in the desorption gas after desorption is too low, the time required for desorption becomes long, and efficient desorption cannot be performed. Therefore, it is preferable to control the desorption temperature so that the benzene concentration is in the range of 0.55% to 0.65% until a predetermined time so that benzene can be desorbed in a short time.

  When a predetermined time elapses after the start of the desorption decomposition step, the concentration of benzene in the desorption gas decreases, but the concentration of benzene in the desorption gas measured by a densitometer falls below 0.55%. At this point, the benzene concentration falls within the range of 0.55% to 0.65% by gradually increasing the desorption temperature by a predetermined temperature. By repeating this, it becomes possible to continue desorbing benzene at a certain concentration or more while avoiding the explosion limit of benzene. Finally, it is made constant at a predetermined temperature, and when the benzene concentration in the desorbed gas is less than 0.1%, the desorbing and decomposing process is finished.

When the volatile organic compound contained in the desorption gas is a mixed gas, the explosion limit is determined using the following formula (1) (Le Chatelier's formula) as follows.
[Equation 1]
_{V = 100 / {N 1 /} V 1 + N 2 / V 2 + ... N I / V I + ...} (1)
Where V: Explosive limit concentration of mixed gas
V _I : Explosive limit concentration of I component
N _I : Concentration of I component For example, when the volatile organic compound is a mixed gas of 50% benzene and 50% toluene, the lower explosion limit is 1.3% for benzene, and the explosion limit for toluene. Since 1.27%, it is 1.285%. For safety reasons, it is set to 0.5 times, which is 0.64%.

  Thus, by controlling the desorption temperature when desorbing the volatile organic compound from the adsorbent according to the concentration of the volatile organic compound in the desorbed gas discharged from the adsorption tower B, the desorbed gas is always obtained. Operation can be performed while keeping the volatile organic compound concentration below the lower limit of the explosion concentration range. Therefore, it is possible to remove and decompose volatile organic compounds inexpensively and safely without lowering the oxygen concentration in the purge gas or using an inert gas as the purge gas as in the prior art.

  In addition, the relationship between the type of adsorbent, the purge gas flow rate, the desorption temperature in the adsorption tower, and the concentration of the volatile organic compound in the desorption gas is obtained in advance, and an appropriate desorption temperature is set based on these relationships. You may control to.

  Next, an exhaust gas treatment operation by the exhaust gas treatment apparatus according to the present embodiment will be described.

<Adsorption removal process in adsorption tower B>
In the present embodiment, first, at the start of operation, the supply pipe for the volatile organic compound-containing exhaust gas is connected to the lower part of the adsorption tower B by switching a valve (not shown), and the exhaust pipe for the clean exhaust gas is connected to the upper part. Thus, the adsorption tower B is in an adsorption state. In this adsorption state, the volatile organic compound-containing exhaust gas is supplied to the adsorption tower B, and the adsorption removal process is performed in the adsorption tower B. The volatile organic compound of the volatile organic compound-containing exhaust gas is adsorbed and removed by the adsorbent. At the same time, clean exhaust gas is discharged. Further, the adsorption tower A is left unattended at the start of operation.

<Adsorption removal process in adsorption tower A>
Next, at the stage where the adsorption removal process in the adsorption tower B is completed, the adsorption tower A is switched to a lower part of the adsorption tower A with the volatile organic compound-containing exhaust gas as shown in FIG. In addition to connecting the supply pipe, the exhaust gas exhaust pipe and the purge gas pipe 1 are connected to the upper part, and the adsorption tower A is in an adsorption state. In this adsorption state, the volatile organic compound-containing exhaust gas is supplied to the adsorption tower A, and an adsorption removal step is performed. The volatile organic compound of the volatile organic compound-containing exhaust gas is adsorbed and removed by the adsorbent, and is cleaned. Exhaust gas is discharged.

<Desorption step in adsorption tower B>
On the other hand, when the adsorption removal process in the adsorption tower B is completed, the supply of the volatile organic compound-containing gas is stopped for the adsorption tower B, and the adsorption state of the adsorption tower A is changed by switching a valve (not shown). Simultaneously with the switching, as shown in FIG. 1, the purge gas pipe 1 is connected to the upper part of the adsorption tower B and the desorption gas discharge pipe is connected to the lower part, so that the adsorption tower B is switched to the desorption state of FIG. In this desorption state, a part of the clean exhaust gas discharged from the adsorption tower A in the adsorption state flows through the purge gas pipe 1 by the blower 3 as a purge gas for desorption in the adsorption tower B and is supplied to the adsorption tower B. The

  In the present embodiment, the purge gas flowing through the purge gas branch pipe 1A out of the purge gas branch pipes 1A and 1B of the purge gas pipe 1 is heated in the heat exchanger 4 by heat exchange with the heated and decomposed purge gas. Then, it is supplied to the adsorption tower B. On the other hand, the purge gas flowing through the purge gas branch pipe 1B is mixed with the purge gas heated by the heat exchanger 4 without being heated.

  The flow rate of the heated purge gas flowing through the purge gas branch pipe 1A of the purge gas pipe 1 and the flow rate of the non-heated purge gas flowing through the purge gas branch pipe 1B of the purge gas pipe 1 are the volatile organics in the desorbed gas measured by the densitometer 6. The desorption temperature control device 7 is controlled by adjusting the opening degree of the valves 8 and 9 based on the compound concentration. As a result of adjusting the temperature of the purge gas flowing into the adsorption tower B in this way, the desorption temperature in the adsorption tower B is such that the volatile organic compound concentration in the desorption gas is lower than the explosive concentration range of the desorption gas. Controlled to be lower than the value.

  The purge gas supplied to the adsorption tower B is generated from the adsorbent in the adsorption tower B under the desorption temperature controlled by the desorption temperature control device 7, that is, the adsorbent that has already adsorbed the volatile organic compound. The volatile organic compound is desorbed and discharged from the adsorption tower B as a desorbed gas containing the volatile organic compound. The desorbed gas is supplied to the oxidative decomposition apparatus 5.

<Oxidative decomposition process in the oxidative decomposition apparatus 5>
In the oxidative decomposition apparatus 5, an oxidative decomposition process is performed, and the volatile organic compound in the desorbed gas from the adsorption tower B is oxidatively decomposed, and the heated purged purge gas is discharged. The heated and decomposed purge gas is heated in the heat exchanger 4 by heat exchange with the purge gas flowing in the purge gas branch pipe 1A, and then subjected to appropriate processing and released to the outside. .

  When the desorption / decomposition process is completed in the adsorption tower B and the oxidative decomposition apparatus 5, while the adsorption / removal process is completed in the adsorption tower A, the adsorption tower A and the adsorption tower B are switched by switching valves (not shown). Then, the desorption decomposition process is performed in the adsorption tower A and the oxidative decomposition apparatus 5, and the adsorption removal process is performed again in the adsorption tower B. Thereafter, the steps of both adsorption towers A and B are switched by the valve switching and repeated.

  As described above, by using two adsorption towers, the adsorption removal process and the desorption decomposition process can be performed simultaneously, so that the amount of exhaust gas treated per unit time can be increased. Further, the adsorption removal process and the desorption decomposition process do not always have to be performed at the same time. Since the desorption / decomposition process is usually completed in about several hours to 1 day, the adsorption tower B that has completed the desorption / decomposition process is put in a standby state, and when the adsorption tower A can no longer exhibit a predetermined adsorption removal performance, that is, When the adsorbent breaks through, the operation may be continued by switching the adsorption tower A to the desorption decomposition process and the adsorption tower B to the adsorption removal process. By performing such an operation, it is easy to switch between the adsorption removal process and the desorption decomposition process, and the entire system can be simplified.

<Second embodiment>
In the first embodiment, the clean exhaust gas discharged from one adsorption tower is supplied as a purge gas to the other adsorption tower. However, the present embodiment shown in FIG. 2 supplies the atmosphere (air) as the purge gas. In this respect, the configuration is different from that of the first embodiment. The following description will focus on portions that differ in configuration from the first embodiment, and portions having the same configuration will be assigned the same reference numerals and description thereof will be omitted.

  FIG. 2 is a schematic diagram showing the configuration of the exhaust gas treatment apparatus according to the present embodiment, and shows a state where the adsorption tower A performs an adsorption removal process and the adsorption tower B performs a desorption process. In the exhaust gas treatment apparatus according to this embodiment, the purge gas pipe 1 is not connected to the adsorption tower A, and the blower 3 provided in the purge gas pipe 1 sucks air (air) from the outside, and this air is purged with the purge gas. Is supplied to the adsorption tower B. Thus, by using the atmosphere as the purge gas, it is not necessary to separately provide a purge gas generation facility, so that the facility can be miniaturized.

<Third embodiment>
In the first embodiment, a part of the purge gas is heated by the heat exchanger 4 and the remaining purge gas is not heated but mixed into the heated part of the purge gas. This embodiment is different from the first embodiment in that all of the purge gas is heated by a heat exchanger and a high-temperature gas generated by a separately provided high-temperature gas generator is mixed into the purge gas. . The following description will focus on portions that differ in configuration from the first embodiment, and portions having the same configuration will be assigned the same reference numerals and description thereof will be omitted.

  FIG. 3 is a schematic diagram showing the configuration of the exhaust gas treatment apparatus according to the present embodiment, and shows a state in which the adsorption tower A performs the adsorption removal process and the adsorption tower B performs the desorption process. In the exhaust gas treatment apparatus according to the present embodiment, the purge gas pipe 1 connecting the adsorption tower A and the adsorption tower B is not branched, and all of the clean exhaust gas as the purge gas from the adsorption tower A is in the heat exchanger 4. Heated.

  Further, in the present embodiment, for example, a high temperature gas generator 10 configured to burn fuel and generate combustion gas as high temperature gas is provided. The hot gas generated by the hot gas generator 10 is mixed with the heated purge gas flowing in the purge gas pipe 1 on the downstream side of the heat exchanger 4.

  The desorption temperature control device 7 volatilizes in the desorption gas measured by the densitometer 6 so that the concentration of the volatile organic compound in the desorption gas is lower than the lower limit value of the predetermined desorption concentration range of the desorption gas. Based on the concentration of the organic compound, the opening degree of the valve 8 provided in the purge gas pipe 1 is adjusted, and the amount and temperature of the high-temperature gas generated by the high-temperature gas generator 10 are also adjusted. As a result, the temperature of the purge gas supplied to the adsorption tower B and the desorption temperature in the adsorption tower B are controlled. Further, the desorption temperature control device 7 may adjust only one of the amount and temperature of the hot gas generated by the hot gas generator 10.

  In this embodiment, by mixing high temperature gas into the purge gas, the desorption temperature in the adsorption tower for performing the desorption step can be adjusted in a higher temperature range, and the desorption of volatile organic compounds is promoted. The time required for desorption can be shortened.

<Fourth embodiment>
In the second embodiment described above, a part of the purge gas in the atmosphere is heated by the heat exchanger 4, and the remaining purge gas is not heated, but mixed into the heated part of the purge gas. It was. In contrast, in the present embodiment shown in FIG. 4, all of the purge gas that is the atmosphere is heated by a heat exchanger, and the adsorbent atmosphere temperature of the adsorption tower that performs the desorption process is set by a separately provided heating device. This is different from the second embodiment in that the temperature is raised. The following description will focus on portions that differ in configuration from those of the second embodiment, and portions having the same configuration will be assigned the same reference numerals and description thereof will be omitted.

  FIG. 4 is a schematic view showing the configuration of the exhaust gas treatment apparatus according to the present embodiment, and shows a state where the adsorption tower A performs the adsorption removal process and the adsorption tower B performs the desorption process. In the exhaust gas treatment apparatus according to this embodiment, the purge gas pipe 1 connected to the adsorption tower B and supplying the atmosphere as the purge gas to the adsorption tower B is not branched, and all of the purge gas is transferred to the heat exchanger 4. Is heated.

  Further, the adsorption tower B is provided with a heating device 11 composed of, for example, an electric heater, and the adsorbent atmosphere temperature of the adsorption tower B is raised. The desorption temperature control device 7 volatilizes in the desorption gas measured by the densitometer 6 so that the concentration of the volatile organic compound in the desorption gas is lower than the lower limit value of the predetermined desorption concentration range of the desorption gas. The desorption temperature in the adsorption tower B is controlled by adjusting the heating temperature by the heating device 11 based on the concentration of the volatile organic compound. In addition, the said heating apparatus 11 may heat an adsorbent directly, and may heat it indirectly.

  According to the present embodiment, by increasing the adsorbent atmosphere temperature of the adsorption tower for performing the desorption step with the heating device 11, the desorption temperature in the adsorption tower can be adjusted in a higher temperature range, The time required for the detachment can be shortened by promoting the detachment of the volatile organic compound.

  In the exhaust gas treatment apparatus according to the first to fourth embodiments, two adsorption towers are provided. Instead, three or more adsorption towers are provided, and some of these adsorption towers are provided. The adsorption removal process may be performed in the adsorption tower, and the desorption decomposition process may be performed in the remaining adsorption tower.

  Next, the adsorption tower used in the exhaust gas treatment apparatus in the first to fourth embodiments and the adsorbent filled in the adsorption tower will be described.

<Adsorption tower>
In the first to fourth embodiments, the adsorption tower is provided with a packed bed of adsorbent by installing the removable adsorbent cartridge 2 shown in FIG. 5 in one stage. As a method of providing the packed bed, it is possible to fill the adsorption tower with the adsorbent as it is, but considering the adsorption efficiency of volatile organic compounds, replacement of the filler, maintenance, etc., the adsorbent is packed in the cartridge. The cartridge is preferably installed in the adsorption tower. Further, the adsorbent cartridge 2 may be installed in a plurality of stages in the adsorption tower as shown in FIG.

<Adsorbent cartridge>
FIG. 5 is a view showing the structure of the adsorbent cartridge 2 provided in the adsorption towers A and B. As shown in FIG. A gas inlet 21 and an upstream lid portion 22 are alternately provided on the upstream end surface of the adsorbent cartridge 2. Further, on the downstream end surface of the adsorbent cartridge 2, a downstream lid portion 23 is provided at a portion corresponding to the gas inlet 21 on the upstream end surface, and a gas outlet 24 is disposed on a portion corresponding to the upstream lid portion 22 on the upstream end surface. Is provided.

  In the adsorbent cartridge 2, as shown in FIG. 5, a plurality of flat adsorbent layers 25 are arranged substantially in parallel at a predetermined interval, and one of the adsorbent layers 25 is disposed through the gas inlet 21. A gas flow is formed such that the gas supplied to the side surface passes through the adsorbent layer 25 and escapes to the other side surface, and the gas sent to the adsorbent cartridge 2 is a plurality of adsorbent layers 25. Then, it is distributed and removed by adsorption.

  The adsorbent cartridge 2 shown in FIG. 5 has a structure in which the exhaust gas and the adsorbent layer 25 are in contact with each other in a side flow manner, and the area of the adsorbent layer 25 in contact with the gas can be increased. It is economical because the installation area of the adsorption towers A and B can be made small and compact. Moreover, since the adsorbent layer 25 is usually very thin, about several centimeters, the pressure loss can be reduced, and the blower is downsized and economical.

  Further, the adsorbent layer 25 is arranged substantially parallel to each other and symmetrical with respect to the surface, and the adsorbent is compactly packed so that no gap is formed between the upstream lid portion 22 and the downstream lid portion 23. Therefore, it is possible to make the gas flow uniform, which is essential for exhibiting high adsorption performance, to prevent a short pass (blow-through) of the gas, and the contact efficiency between the adsorbent layer 25 and the gas is high. High performance is exhibited in Further, since the adsorbent cartridge 2 has a cartridge structure, the adsorbent cartridge 2 can be easily attached and detached from the adsorption towers A and B, and maintenance such as replacement of the adsorbent and inspection of the apparatus is facilitated. Can be done.

In addition, if the size of each adsorbent cartridge 2 is increased, the detachment workability from the adsorption towers A and B at the time of maintenance deteriorates. For example, a large amount of gas such as tens of thousands to several hundred thousand m ³ / h. In the case of processing, it is preferable to use a plurality of adsorbent cartridges 2 arranged in parallel in the adsorption towers A and B and installed in a plurality of stages in series. For example, in the example shown in FIG. 8 which is a cross-sectional view taken along the line I-I in FIGS. 7 and 7, an example is shown in which four adsorbent cartridges 2 are arranged in parallel and installed in two stages in series. Thus, by using the adsorbent cartridge 2, the arrangement of the adsorbent cartridge 2 can be combined in parallel and in series according to the use conditions, and can be used in an optimum arrangement.

  As the adsorbent, inorganic adsorbents such as silica gel and zeolite, activated carbon and the like can be used, and adsorbents excellent in adsorption and desorption performance are preferable. The smaller the particle size of the adsorbent used, the higher the adsorption rate and desorption rate. However, when the particle size is too small, the pressure loss in the packed bed becomes large. In addition, it is difficult or practical to produce a gas permeable surface having sufficiently small holes that can hold an adsorbent with a smaller particle size while ensuring the necessary strength as a gas inflow side and a gas outflow side in the storage case. It ’s not right. Therefore, the particle size of the adsorbent is preferably about 0.5 to 2.4 mm.

(Example 1)
The air containing 150 ppm of benzene as the volatile organic compound-containing gas was treated using the exhaust gas treatment apparatus of FIG. The adsorption tower was filled with activated carbon as an adsorbent, and 10 Nm ³ / h exhaust gas was supplied to the adsorption tower by a blower as an adsorption removal step. After performing the adsorption removal process, switching to the desorption decomposition process, heating with a burner so that the atmospheric temperature of the oxidative decomposition apparatus is always 400 ° C, heating the purge gas with a heat exchanger and supplying it to the adsorption tower Measure the benzene concentration of the desorbed gas discharged from the adsorption tower with a densitometer, and keep the benzene concentration below 0.65%, which is 0.5 times the lower limit of 1.3% of the explosion concentration range. The desorption temperature was controlled. The situation in which the benzene concentration of the desorbed gas is controlled by adjusting the desorption temperature is shown in FIG. 9 showing the time variation of the benzene concentration in the desorbed gas and the time variation of the desorption temperature.

  In this example, the operation was performed while gradually increasing the desorption temperature as much as possible. Specifically, the desorption temperature was controlled to be increased by 5 ° C. when the benzene concentration in the desorption gas fell below 0.55%. FIG. 9 shows that the desorption temperature is maintained at 180 ° C. after the desorption time of 80 minutes has elapsed, and after 80 minutes, the concentration of benzene in the desorption gas has decreased and desorption of benzene from the adsorbent has started to end. It shows that. In addition, benzene was decomposed by supplying the desorbed gas to an oxidative decomposition apparatus. After desorption decomposition treatment of the adsorption tower, the operation was switched again to the adsorption step, and this operation was repeated.

  During the adsorption removal process, the benzene concentration in the clean gas at the outlet of the adsorption tower was always maintained at 4 ppm or less. In addition, the time until the activated carbon can no longer exhibit performance in the adsorption removal process was about 9 hours, and the time required for desorption decomposition and regeneration in the desorption decomposition process was always within 5 hours.

(Example 2)
Air containing 180 ppm of toluene as a volatile organic compound-containing gas was treated using the exhaust gas treatment apparatus of FIG. The adsorption tower was filled with activated carbon as an adsorbent, and 10 Nm ³ / h exhaust gas was supplied to the adsorption tower by a blower as an adsorption removal step. After performing the adsorption removal process, switching to the desorption decomposition process, heating with a burner so that the atmospheric temperature of the oxidative decomposition apparatus is always 400 ° C, heating the purge gas with a heat exchanger and supplying it to the adsorption tower , The toluene concentration of the desorbed gas discharged from the adsorption tower is measured with a densitometer, and the desorption temperature is maintained so that the toluene concentration is 0.63% or less, which is 0.5 times the lower limit value of the explosion concentration range. Controlled. The situation in which the toluene concentration of the desorbed gas is controlled by adjusting the desorption temperature is shown in FIG. 10 showing the time variation of the toluene concentration in the desorbed gas and the time variation of the desorption temperature.

  Also in this example, as in Example 1, the operation was performed while increasing the desorption temperature stepwise so that the toluene could be desorbed in a short time. Specifically, the desorption temperature was controlled to increase by 5 ° C. when the toluene concentration in the desorption gas fell below 0.5%. FIG. 10 shows that the desorption temperature is maintained at 180 ° C. after 220 minutes elapses, and the toluene concentration in the desorption gas decreases and the desorption of toluene from the adsorbent begins after 220 minutes elapses. It shows that. Further, desorption gas was supplied to the oxidative decomposition apparatus to decompose toluene. After desorption decomposition treatment of the adsorption tower, the operation was switched again to the adsorption step, and this operation was repeated.

  During the adsorption removal step, the toluene concentration in the clean gas at the adsorption tower outlet was always maintained at 5 ppm or less. In addition, the time until the activated carbon can no longer exhibit its performance in the first adsorption removal process was about 9 hours, and the time required for desorption decomposition and regeneration was always within 5 hours. Further, when the adsorbent after the desorption / decomposition process was further adsorbed by the adsorption tower, the time until the activated carbon could not exhibit its performance was 7 to 8 hours.

  FIG. 11 shows the relationship between the number of repetitions of the adsorption removal step and the desorption decomposition step and the time until the activated carbon can no longer exhibit performance in the adsorption removal step in this example. All the time until performance could not be exhibited was 6 hours or more. As a result, it was confirmed that toluene was desorbed from the adsorbent with certainty and regeneration of the adsorbent was performed effectively.

A, B Adsorption tower 4 Heat exchanger 5 Oxidation decomposition device 6 Densitometer 7 Desorption temperature control device 10 High temperature gas generator 11 Heating device

Claims (5)

An apparatus for treating exhaust gas containing volatile organic compounds,
Contains an adsorbent that adsorbs volatile organic compounds, accepts the exhaust gas, adsorbs and removes volatile organic compounds in the exhaust gas by adsorbing and exhausts clean exhaust gas, and accepts a purge gas and adsorbs the adsorbent. An adsorption tower operable in a desorbed state in which a volatile organic compound adsorbed on the agent is desorbed by the purge gas and a desorbed gas that is a purge gas containing the volatile organic compound is discharged;
An oxidative decomposition apparatus that receives the desorbed gas from the desorbed adsorption tower, oxidatively decomposes volatile organic compounds in the desorbed gas, and discharges the purged purge gas;
Are oxidatively decomposed by oxidation-decomposition device accepts heating the above decomposed already purge gas, a part of the purge gas supplied to the adsorption tower of the desorption state by heat exchange with the decomposition already purge gas is heated A heat exchanger for heating;
A densitometer that measures the concentration of a volatile organic compound in the desorbed gas discharged from the desorbed adsorption tower;
Based on the concentration of the volatile organic compound measured by the densitometer so that the concentration of the volatile organic compound is lower than the lower limit value of the predetermined explosion concentration range of the desorbed gas, A desorption temperature control device for controlling the desorption temperature, which is the atmospheric temperature ,
A plurality of adsorption towers are provided, and some of the adsorption towers adsorb and remove volatile organic compounds in the exhaust gas in an adsorption state to discharge clean exhaust gas, and the remaining adsorption tower is in a desorption state. In order to desorb volatile organic compounds that have already been adsorbed, a part of the clean exhaust gas is accepted as a purge gas from the partial adsorption tower.
The desorption temperature control device adjusts the supply amount of a part of the purge gas supplied to the heat exchanger and the supply amount of the remaining purge gas supplied to the adsorption tower in the desorption state without going through the heat exchanger, An apparatus for treating an exhaust gas containing a volatile organic compound, wherein the desorption temperature in the remaining adsorption tower in the desorption state is controlled . An apparatus for treating exhaust gas containing volatile organic compounds,
Contains an adsorbent that adsorbs volatile organic compounds, accepts the exhaust gas, adsorbs and removes volatile organic compounds in the exhaust gas by adsorbing and exhausts clean exhaust gas, and accepts a purge gas and adsorbs the adsorbent. An adsorption tower operable in a desorbed state in which a volatile organic compound adsorbed on the agent is desorbed by the purge gas and a desorbed gas that is a purge gas containing the volatile organic compound is discharged;
An oxidative decomposition apparatus that receives the desorbed gas from the desorbed adsorption tower, oxidatively decomposes volatile organic compounds in the desorbed gas, and discharges the purged purge gas;
The decomposed purge gas that has been oxidatively decomposed and heated by the oxidative decomposition apparatus is received, and all of the purge gas supplied to the adsorption tower in the desorbed state is heated by heat exchange with the heated decomposed purge gas. A heat exchanger to
A densitometer that measures the concentration of a volatile organic compound in the desorbed gas discharged from the desorbed adsorption tower;
Based on the concentration of the volatile organic compound measured by the densitometer so that the concentration of the volatile organic compound is lower than the lower limit value of the predetermined explosion concentration range of the desorbed gas, A desorption temperature control device for controlling the desorption temperature, which is the atmospheric temperature,
A high-temperature gas generator that heats the gas and generates a high-temperature gas;
A plurality of adsorption towers are provided, and some of the adsorption towers adsorb and remove volatile organic compounds in the exhaust gas in an adsorption state to discharge clean exhaust gas, and the remaining adsorption tower is in a desorption state. In order to desorb volatile organic compounds that have already been adsorbed, a part of the clean exhaust gas is accepted as a purge gas from the partial adsorption tower.
The high temperature gas generated by the high temperature gas generator is mixed into the purge gas heated by the heat exchanger,
The desorption temperature control device controls the desorption temperature in the remaining adsorption tower in the desorption state by adjusting at least one of the amount and temperature of the high temperature gas generated by the high temperature gas generator. An exhaust gas treatment apparatus containing a volatile organic compound. The adsorbent of the adsorption tower is formed as a detachable adsorbent cartridge having a plurality of plate-like adsorbent packed layers arranged at predetermined intervals,
In the adsorbent cartridge, an exhaust gas flow is formed such that the exhaust gas supplied to one side of the adsorbent packed bed passes through the adsorbent packed bed toward the other side, and the adsorption cartridge The apparatus for treating exhaust gas containing a volatile organic compound according to claim 1 or 2 , wherein the exhaust gas supplied to the adsorbent cartridge is distributed and flows to the plurality of adsorbent packed beds. . A method for treating exhaust gas containing volatile organic compounds,
Among the plurality of adsorption towers containing adsorbents that adsorb volatile organic compounds, some of the adsorption towers receive the exhaust gas, and the volatile organic compounds in the exhaust gas are adsorbed and removed by the adsorbent to be cleaned. The exhaust gas is discharged, and the remaining adsorption tower accepts a part of the clean exhaust gas from the partial adsorption tower as a purge gas, desorbs the already adsorbed volatile organic compound by the purge gas, and the volatile organic compound. The desorption gas, which is a purge gas containing
A volatile organic compound in the desorbed gas discharged from the remaining adsorption tower is oxidized and decomposed to produce a decomposed purge gas,
The part of the purge gas supplied to the adsorption tower of the remainder, is oxidized and decomposed by heating by heat exchange with the heating the above decomposition already purge gas,
Measure the concentration of volatile organic compounds in the desorbed gas discharged from the remaining adsorption tower when desorbing volatile organic compounds,
Supply of a part of the purge gas heated by the heat exchange based on the measured volatile organic compound concentration so that the volatile organic compound concentration is lower than a lower limit value of a predetermined explosion concentration range of the desorbed gas. Containing a volatile organic compound characterized by controlling the desorption temperature, which is the atmospheric temperature in the remaining adsorption tower during the desorption , by adjusting the amount and the supply amount of the remaining purge gas that is not heated Exhaust gas treatment method. A method for treating exhaust gas containing volatile organic compounds,
Among the plurality of adsorption towers containing adsorbents that adsorb volatile organic compounds, some of the adsorption towers receive the exhaust gas, and the volatile organic compounds in the exhaust gas are adsorbed and removed by the adsorbent to be cleaned. The exhaust gas is discharged, and the remaining adsorption tower accepts a part of the clean exhaust gas from the partial adsorption tower as a purge gas, desorbs the already adsorbed volatile organic compound by the purge gas, and the volatile organic compound. The desorbed gas, which is a purge gas containing gas, is discharged, and the decomposed purge gas is generated by oxidizing and decomposing volatile organic compounds in the desorbed gas discharged from the remaining adsorption tower,
All of the purge gas supplied to the remaining adsorption tower is heated by heat exchange with the decomposed purge gas that has been oxidatively decomposed and heated up,
A high temperature gas is mixed in the purge gas heated by the heat exchange,
Measure the concentration of volatile organic compounds in the desorbed gas discharged from the remaining adsorption tower when desorbing volatile organic compounds,
Based on the measured volatile organic compound concentration, adjust at least one of the amount and the temperature of the high-temperature gas so that the concentration of the volatile organic compound is lower than a lower limit value of a predetermined explosion concentration range of the desorbed gas. Thus, a method for treating an exhaust gas containing a volatile organic compound, wherein a desorption temperature, which is an atmospheric temperature in the adsorption tower of the remaining portion at the time of the desorption, is controlled.

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