JPH0325208B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of cooling an activated carbon adsorption tank after desorption, and more particularly to a method of cooling when stopping operation for safe operation of adsorption and desorption processes using activated carbon.

Many methods and devices have been proposed for adsorbing the solvent in the raw gas using an activated carbon adsorption tank consisting of two or multiple fixed beds, and then passing steam through an activated carbon-filled tank to desorb and recover the solvent adsorbed on the activated carbon. has been done. However, with the progress of industry, the solvents used for adsorption treatment have become increasingly diverse, and accordingly, various problems have been posed in adsorption/desorption treatment. One of these is the ignition of the activated carbon layer during the adsorption process.

For example, cyclohexanone is a solvent that is discharged out of the system along with air in the drying process of magnetic tape manufacturing. In order to recover this, a mixed gas of air and cyclohexanone vapor is passed through an adsorption tank filled with activated carbon, so that the cyclohexanone is adsorbed on the activated carbon layer, and only the air is released into the atmosphere. After a certain amount of cyclohexanone is adsorbed on the activated carbon layer, water vapor is blown into the adsorption tank to desorb the adsorbed cyclohexanone, cyclohexanone and water vapor are condensed, and then cyclohexanone and water are separated to recover cyclohexanone. At this time, many ketone solvents such as cyclohexanone tend to be oxidized on activated carbon during the adsorption process to produce peroxides, and also tend to produce dimers and trimers upon heating during the desorption process. These peroxides and polymers have high boiling points and are not easily separated from activated carbon by water vapor in the desorption process, and accumulate in the pores of activated carbon, gradually causing a decline in activated carbon adsorption performance. In addition, the accumulation of peroxides often causes coal bed ignition due to the heat generated by its decomposition.

In order to suppress the formation of such peroxides and polymers, it is necessary to reduce the amount of adsorbed cyclohexanone remaining in the activated carbon as much as possible by desorption each time without allowing it to remain in the activated carbon for a long time. To achieve this, it is necessary to perform desorption using sufficient water vapor, which consumes a large amount of water vapor. Therefore, from the perspective of improving the economic efficiency of solvent recovery, desorption vapor latent heat recovery using a water vapor compression method has been adopted. The law is used as an advantageous method.

On the other hand, the cause of ignition of the activated carbon layer based on peroxide formation-decomposition of cyclohexanone is usually formed during shutdown, and ignition occurs early in the next adsorption step when the air and solvent mixture gas is passed into the adsorption tank. There is. The reason for this is thought to be as follows. In other words, even if heat generation occurs due to the decomposition of peroxide generated during the adsorption process and the oxidation of charcoal and organic matter, or heat generation due to adsorption, the heat is removed by the passing gas and ignition does not occur, and during the desorption process Even if heat generation occurs due to a similar phenomenon, the heat is removed by the passing water vapor, and furthermore, since there is almost no oxygen other than the oxygen caused by peroxide in the adsorption atmosphere, no ignition phenomenon occurs. However, when the operation is stopped, air exists in the activated carbon layer, and the heat of adsorption based on the diffusion movement of cyclohexanone remaining in the activated carbon, the heat of decomposition of peroxides, and the heat of oxidation of carbon and organic matter are prevented from venting. Therefore, heat removal does not occur, and the generated heat that causes ignition accumulates, and this heat accumulation is thought to be accelerated by the air in the raw gas containing the solvent at the beginning of the next adsorption process, forming an ignition point. It will be done.

An object of the present invention is to provide a method for cooling an adsorption tank to prevent coal bed ignition in the above-mentioned adsorption tank.

The structure of the present invention includes an adsorption/desorption device using a vapor compression method;
An inert gas supply device equipped with a separately attached pressure control valve and pressure regulator, a bypass circuit that bypasses the evaporator, and a circuit that guides the non-condensable gas of the desorbed vapor after exiting the vent condenser to the suction side of the vapor compressor. The inert gas is circulated through the adsorption tank to the vent condenser, and at the end of the desorption process, the supply of desorption steam is stopped and the remaining water vapor is condensed and separated in the vent condenser, and the pressure is adjusted according to the depressurization of the adsorption tank. Inert gas is passed through the adsorption tank using a meter,
This consists of keeping the pressure in the adsorption tank at normal pressure or slightly positive pressure, condensing and separating the entrained water vapor in a decanter, and circulating cooled inert gas through the adsorption tank and vent condenser to cool the adsorption tank.

By cooling the adsorption tank after the completion of desorption using an inert gas according to the present invention, the cause of coal seam ignition is effectively eliminated.

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart showing an embodiment of the present invention, and FIG. 3 shows the temperature drop and the amount of ventilation in the activated carbon layer.

In FIG. 1, the adsorption/desorption circuit using the water vapor compression method, which is the premise of the present invention, shows adsorption tanks 4-1 and 4-4.
2. Evaporator 5 for generating steam for desorption;
A vapor compressor 6 and an evaporator 5 for generating water vapor for desorption and supplying it to adsorption tanks 4-1 and 4-2.
It consists of a vent condenser 7 that cools the non-condensable gas passing through the heat exchanger, an evaporative water supply line to the evaporator 5, and conduits and valves that connect these devices. In this invention, the desorbed material vapor from the adsorption tank 4-2 bypasses the evaporator 5 and passes through the bypass circuit 10 and the vent condenser 7, which are directly connected to the vent condenser 7. A circuit 11 leading to the suction side is provided, and a pressure indicating controller PIC and a pressure regulating valve V-6 are installed in the gas circulation circuit formed between the adsorption tank 4-2 and the vent condenser 7 by the vapor compressor 6.
It is constructed with an attached inert gas supply device consisting of. This inert supply device is usually provided on the suction side of the vapor compressor, but it can also be provided at any other location in the circulation line.

In FIG. 1, adsorption tank 4-1 is in the adsorption process, and adsorption tank 4-2 is in the desorption process. Most of the desorption steam is condensed in the pipe of the evaporator 5 along with the desorbed cyclohexanone-containing solvent from the discharge side of the vapor compressor 6 through the activated carbon layer 3-2 of the adsorption tank 4-2 by the steam control valve V-7. The condensate enters decanter 8. The non-condensable content in the evaporator 5 is condensed in the vent condenser 7 and transferred to the decanter 8.
to go into. The remaining non-condensable gas is released by the non-condensable gas release valve V.
-5 is released into the atmosphere. The water for evaporation outside the tube of the evaporator 5 is reduced to a pressure such that the boiling point of the water is lower than the condensation temperature of the desorption vapor inside the tube by the vapor compressor 6. Steam generated by boiling and evaporating due to the heat of condensation is sent to the adsorption tank 4-2 by the vapor compressor 6. After performing this operation for a predetermined period of time, the desorption process is completed. At this point, the steam replenishment amount control valve V-7 and the evaporated water amount control valve V-
8. Close all of the desorption steam evaporator inlet valve V-1, evaporator steam discharge valve V-3, and non-condensable gas release valve V-5, and desorption steam vent condenser inlet valve V-2 and vent condenser. By opening the vent return valve V-4 and continuing the operation of the vapor compressor 6 while the PIC for inert gas supply is started, the water vapor in the system is condensed in the vent condenser 7, and the pressure in the system is gradually reduced. . In response to this, the pressure regulator PIC installed in the circulation line of the system opens the pressure regulating valve V-6 as the pressure decreases, and inert gas is introduced into the system from the inert gas line 9. The inert gas and water vapor enter the vent condenser 7, where the water vapor is condensed and the inert gas is cooled and sent to the adsorption tank 4-2 again for circulation.

By this operation, the inside of the system is filled with inert gas, and the activated carbon layer 3-2 of the adsorption tank 4-2 is gradually cooled. After the temperature of the activated carbon layer 3-2 drops to 40° C. or lower, the operation of the decompression blower is stopped, and all external connection valves of the adsorption tank 4-2 are closed, and the operation is suspended. As a result, the activated carbon layer is exposed to 40%
Because the temperature is below °C, the production of peroxide during shutdown is suppressed, and even if heat is generated due to decomposition of residual peroxide, diffusion of residual solvent, and re-adsorption, ignition of the coal seam is not possible. No.

Similar operations are performed on the adsorption tank 4-1 before stopping.

In the above operation, the pressure of the inert gas to be added to the adsorption tank 4-2 is selected from normal pressure to 0.5 kg/cm ² G. Negative pressure should be avoided because air is inhaled, and the maximum pressure is 0.5Kg/cm ² G due to the pressure resistance of the adsorption tank.
is desirable.

In addition, a gas holder (not shown) is installed in the inert gas supply line, and a non-condensable gas release valve V is installed in the inert gas supply line.
-5 with a conduit, the inert gas remaining in the adsorption tank can be recovered at the start of the next adsorption step. At this time, the residual inert gas is sent to the gas holder using steam. That is, to prevent ignition, steam is passed from the steam replenishment amount control valve V-7 to the adsorption tank 4-2 before starting the next adsorption step. At this time, the desorption steam vent condenser inlet valve V
-2. Open the non-condensable gas feed valve V-5 and send the inert gas to the gas holder using steam. Switching between inert gas and water vapor is performed by a temperature controller (not shown) set at the outlet of adsorption tank 4-2. In this case, an oxygen concentration meter (not shown) may be provided in the circuit from the non-condensable gas release valve V-5 to the gas holder. After extruding the inert gas and passing the water vapor for a certain period of time, the adsorption process begins. No particular cooling step is provided, and adsorption proceeds while being cooled by the raw gas. Furthermore, simply connecting an inert gas supply pipe to the adsorption tank after desorption without cooling by forced circulation of inert gas is effective to some extent as a safety measure, but with this method, the activated carbon packed bed The solvent remaining and retained in the activated carbon under high temperature conditions may be oxidized by the oxidation catalytic action of the activated carbon and by any oxygen that may be present, and may form heat-generating spots in the activated carbon layer.
As in the present invention, it is preferable to cool to 40° C. or lower by forced circulation of an inert gas. Furthermore, after cooling to below 40°C using the method of the present invention, the pressure regulator PIC is activated to automatically supply inert gas to the adsorption tank throughout the suspension of operation until the start of the next adsorption process. It is further advantageous to keep the vessel under positive pressure with an inert gas.

Further, an embodiment different from that shown in FIG. 1 is shown in FIG. The vapor compressor 6 compresses the desorbed material vapor leaving the adsorption tank 4-2 and uses it as a heating source for the evaporator. It is steam below ℃.
The only difference between the two is the installation position of the vapor compressor 6, and the rest is the same as the explanation of FIG. 1, and it is possible to obtain exactly the same effect as the embodiment of FIG. 1.

Example Recovery device for solvents containing cyclohexanone Adsorption tank 2200〓× _6500L Cylindrical horizontal type 2 units Activated carbon amount 4300Kg/unit Inert gas flow rate to keep the activated carbon layer below 40℃ is 5400Nm ³ /Basic method according to the invention Inert gas consumption: 28 Nm ³ /Basic According to the method of the present invention, by installing a relatively simple device, it is possible to cool the adsorption tank and eliminate oxidizing gas with a relatively small amount of inert gas, and water vapor compression Combined with the reduction in the amount of adsorbed residue due to desorption by the method, it is extremely effective in preventing ignition of the activated carbon layer.

[Brief explanation of the drawing]

FIGS. 1 and 2 are flowcharts showing different embodiments of the present invention, and FIG. 3 is a graph showing the relationship between the temperature conditions of the activated carbon layer and the amount of ventilation gas for cooling. 1...Solvent-containing gas, 2...Gas blower, 3...
...Activated carbon layer, 4...Adsorption tank, 5...Evaporator, 6...
...Vapor compressor, 7...Vent condenser, 8...
...Decanter, 9...Inert gas line, 10...
...Bypass circuit, 11...Cooling gas return pipe, V-
1... Desorption steam evaporator inlet valve, V-2... Desorption steam vent condenser inlet valve, V-3... Evaporator steam discharge valve, V-4... Vent condenser vent return valve, V-5... ...Noncondensable gas release valve, V-
6...Pressure control valve, V-7...Steam replenishment amount control valve, V-8...Evaporated water amount control valve.

Claims (1)

[Claims] 1. Consists of an activated carbon adsorption tank, an evaporator, a vapor compressor installed before or after the evaporator, a vent condenser, and a conduit, which absorbs the desorbed material vapor discharged from the adsorption tank during the vapor desorption of the adsorbed solvent and the retained heat of the water vapor. In an adsorption device in which desorption is carried out by newly generated water vapor using an adsorption device, the desorbed material vapor from the adsorption tank bypasses the evaporator and passes through a bypass circuit directly connected to the vent condenser and the vent condenser. A circuit is provided for guiding the remaining non-condensable content to the suction side of the vapor compressor, and a pressure indicating regulator is provided in the gas circulation circuit formed by the vapor compressor between the adsorption tank and the vent condenser. An inert gas supply device consisting of a pressure regulating valve is installed, and at the end of the desorption process, the supply of water vapor to the adsorption tank is stopped, and at the same time, the circulation circuit for the desorption material vapor is switched to the bypass circuit of the evaporator. At the same time, the inert gas supply device is started, and the residual vapor in the adsorption tank is separated from the condensate through the vent condenser by the vapor compressor, and the pressure in the adsorption tank is subsequently reduced. The activated carbon tank is cooled by circulating an inert gas supplied so as to maintain the pressure at normal pressure or slightly positive pressure through the adsorption tank while cooling and separating the condensate using the vent condenser. A method for cooling an activated carbon adsorption tank characterized by: