JPS5824319A - Treating device for waste gas of fumigation - Google Patents

Abstract

PURPOSE:To regenerate activated carbon and to desorb and recover methyl bromide with good efficiency without using a large amt. of a heating gas during desorption and regeneration by circulating the heating gas to an activated carbon adsorption tower and sucking the gas with a vacuum pump thereafter. CONSTITUTION:To desorb and regenerate the activated carbon adsorbed with CH3Br in the waste gas 21 contg. CH3Br from a fumigating plant 15 by passage of said gas therethrough, valves 10, 12 are closed, a valve 13 is opened and the heater of a heating device 3 is turned on, then the heating gas is circulated into an activated carbon adsorption tower 1. The pressure in the tower 1 which increases with a rise in the temp. of the active carbon is controlled to a prescribed value by operating a control valve 8 with a pressure controller 9 and sucking part thereof with a vacuum pump. When the activated carbon layers attain a prescribed temp., the valves 11, 13 are closed, the pressure controller is stopped, and the inside of the tower 1 is evacuated with a vacuum pump 4. The desorbed CH3Br is recovered through a valve 8, a cooler 5 and a mist filter 7 then through a line 22. Almost pure CH3Br contg. a small proportion of air and the like is recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fumigation exhaust gas detoxification treatment apparatus using an activated carbon adsorption tower having a desorption and regeneration function.

Conventionally, this type of equipment detoxifies the fumigated exhaust gas by passing it through a cylindrical tower or capsule filled with activated carbon to adsorb the methyl bromide used in the fumigation. To desorb the methyl bromide adsorbed on the activated carbon and regenerate the activated carbon, a heating method is used to desorb the activated carbon by passing combustion gas, high-temperature air, steam, etc. into a tower or capsule, or by creating a vacuum inside the activated carbon layer. A vacuum desorption method was used to desorb methyl bromide.

However, these conventional attachment/detachment methods have the following drawbacks. First, with the heating method, the desorbed methyl bromide is recovered mixed with a large amount of gas, making it difficult to reuse the methyl bromide, and with the vacuum method, the heat required for desorption is supplied by indirect heating. Therefore, in order to heat activated carbon, which has low thermal conductivity, an extremely large heat transfer area is required, and the heating time is also long.゛An object of the present invention is to overcome the drawbacks of the prior art, to adsorb methyl bromide in fumigated exhaust gas using an activated carbon adsorption tower, and to efficiently regenerate and regenerate activated carbon without using a large amount of heating gas during desorption and regeneration. The object of the present invention is to provide a fumigation exhaust gas treatment device capable of recovering methyl bromide.

In the activated carbon adsorption tower, when methyl bromide is adsorbed and then desorbed using a vacuum, the gas in the diseased carbon layer is circulated while being heated before the inside of the activated carbon adsorption tower is evacuated. Focusing on the fact that the desorption speed of activated carbon can be accelerated by starting vacuum desorption after the inside of the bed reaches a certain temperature, we installed a circulation line connecting the exhaust side and the inlet side during activated carbon adsorption. A heater is installed in the circulation line, and a vacuum desorption line is provided to evacuate the inside of the activated carbon adsorption tower.

That is, the present invention provides a fumigation exhaust gas treatment device in which exhaust gas from fumigation equipment is introduced into an activated carbon adsorption tower and methyl bromide in the exhaust gas is adsorbed, in which heated gas is circulated through the activated carbon adsorption tower to remove methyl bromide. The present invention is characterized by being provided with a heated gas circulation piping system for desorption and a gas recovery piping system for reducing the pressure in the activated carbon adsorption tower and recovering methyl bromide.

Hereinafter, the present invention will be explained in more detail using the drawings.

FIG. 1 is a system diagram of a fumigation exhaust gas treatment apparatus showing a typical embodiment of the present invention. This device is fumigation equipment 1
5 and an activated carbon adsorption tower 1 installed between the exhaust fan 2;
The dust filter 6 and valve 10 installed between the activated carbon adsorption tower 1 and the fumigation equipment 150, the valve 11 installed between the activated carbon adsorption tower 1 and the exhaust fan 2, and the exhaust fan 2 and the inlet of the activated carbon adsorption tower 1 A circulating heating line 16 connecting the circulating heating line 16, a heater 3 consisting of an electric heater installed in the circulating heating line 16, and a gas recovery line 17 connected to the activated carbon adsorption tower 1 for recovering mainly methyl bromide desorbed. , the control valve 8, the cooler 5, the vacuum pump 4, and the mist filter 7 arranged in sequence in the gas recovery line 17, and the circulation heating line 16 between the exhaust fan 2 and the stack 14; A valve] 2 provided closer to the stack 14 than the point, a valve 13 disposed between the heater 3 in the circulation heating line 16 and the activated carbon adsorption tower l, and a detection end on the activated carbon adsorption tower 1, It mainly consists of a pressure control device 9 installed to control a regulating valve 8.

In the above configuration, the exhaust gas 21 containing methyl bromide leaving the fumigation equipment 15 is introduced into the activated carbon adsorption chamber 1 through the dust filter 6 and the valve IO. exhaust 21
The concentration of methyl bromide in the fumigation facility varies depending on the object to be fumigated, the structure of the equipment, etc., but is, for example, about 5000 ppm at the outlet of the fumigation equipment 15 at the start of exhaust, and about 1100 ppm or less after about 100 minutes. When adsorbing activated carbon, the valves 10, 11, and 12 are opened, and the JJ gas 21 is guided to the activated carbon adsorption tower 1 through the dust filter 6 as described above, and passes through the activated carbon bed to undergo detoxification treatment. After that, the air is discharged from the stack 14 to the atmosphere by the exhaust fan 2. When the exhaust gas passes through the activated carbon layer, methyl bromide molecules in the exhaust gas are adsorbed by the activated carbon. Various types of activated carbon such as coal-based, petroleum-based, and wood-based activated carbon (for example, lump coal-based activated carbon of 2 to 3 particle sizes) are used as the activated carbon.

For example, if the concentration of methyl bromide at the outlet of the adsorption tower is 1
The design conditions of the adsorption tower, ie, the lacrimal overrate, the bed height of activated carbon, etc., are determined so that the amount of water is 00 pprn or less.

When the exhaust inside the fumigation equipment 15 is finished, the activated carbon adsorption tower l
The detoxification process is completed, and the valves 10 and 12
is closed.

Next, the activated carbon that has adsorbed methyl bromide needs to be desorbed and regenerated, but in the present invention, a heating step is provided before the direct air desorption step, and the activated carbon is heated while circulating gas in the adsorption tower. It was decided to raise the total amount. That is, in the heating step, the valve 13 is opened, the heater 3 is turned on, and gas (for example, steam, combustion gas, steam, etc.) is circulated within the activated carbon adsorption tower 1 by an exhaust fan. The activated carbon in the activated carbon adsorption tower 1 is heated by this gas circulation and heating, and its temperature rises. In addition to the above-mentioned self-heater 3, a heater may be installed around the activated carbon adsorption tower 1, or a heating jacket may be provided to promote heating. Some of the methyl bromide adsorbed on the activated carbon begins to desorb when the temperature of the activated carbon increases. The pressure inside the adsorption tower increases as the temperature rises, so normally the pressure inside the adsorption tower 1 is detected and the pressure control device 9 is used to operate the control valve 8 in the gas recovery line] the vacuum pump 4
is driven to suck and control to a predetermined value.

Therefore, the pressure inside the system will not increase due to heating and will not leak to the outside. As time passes, the circulating gas is gradually replaced with methyl bromide, increasing the concentration of methyl bromide in the circulating gas. Note that this change in composition does not cause any problems in the heating operation.
In fact, some methyl bromide is desorbed because the average molecular weight of the gas is higher than the originally existing air, but as it circulates, much methyl bromide is still adsorbed on the activated carbon. Therefore, when the temperature of the activated carbon layer reaches approximately 50° C., the next vacuum desorption step is performed.

In the vacuum desorption step, the pulp 11 and the pulp 13 are closed, the activated carbon adsorption tower 11d is in a sealed state, and the pressure control device 9 is also stopped. When the vacuum pump 4 is operated in this state to reduce the pressure inside the adsorption tower, the methyl bromide adsorbed on the activated carbon breaks the equilibrium with the methyl bromide in the gas and is desorbed, and the vacuum pump 4 desorbs the methyl bromide into the pulp 8. , cooler 5, line 17 and mist filter 7 and is recovered from line 22. The cooler 5 in line 17 is for cooling the gas entering the vacuum pump 4 and for protecting the vacuum pump. Note that heat is taken away when methyl bromide is desorbed from the activated carbon, but since the activated carbon is already heated, it is not cooled down to the lower part.

The methyl bromide recovered by the above operation can be reused for fumigation as it is because it has a small proportion of air mixed in, but liquefied methyl bromide may also be produced using a refrigerator etc. . In this case, since the gas is nearly pure, less electricity is required. On the other hand, since the activated carbon used in the adsorption tower is regenerated to nearly its original state, the ability to detoxify fumigated exhaust gas can always be maintained at a high level.

As described above, according to the present invention, by circulating heated gas through the activated carbon adsorption tower and then suctioning it with a vacuum pump, it is possible to efficiently desorb methyl bromide adsorbed on activated carbon and to regenerate activated carbon. .

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a fumigation exhaust gas treatment apparatus showing an embodiment of the present invention. l...Activated carbon adsorption tower, 3... Heater, 4...
Vacuum pump, 16...Circulation heating line. Figure 1

Claims (2)

[Claims] (1) Introducing the exhaust gas from the fumigation equipment into an activated carbon adsorption tower,
The exhaust gas treatment device for adsorbing methyl bromide in the exhaust gas includes a heated gas circulation piping system that circulates heated gas through the activated carbon adsorption tower to desorb methyl bromide, and a heated gas circulation piping system that depressurizes the activated carbon adsorption tower to remove methyl bromide. A fumigated exhaust gas processing device characterized by being provided with a gas recovery piping system for recovering fumigated exhaust gas. (2) The fumigated exhaust gas processing device according to claim 1, characterized in that the gas recovery piping system is provided with a pressure control device.