JPH0476724B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to a method for desorbing adsorbed matter such as an organic solvent adsorbed onto an adsorbent such as powdered or granular activated carbon or fibrous activated carbon using a heated air stream. (Prior Art) Adsorption devices using powdered or granular activated carbon, fibrous activated carbon, etc. have been used in many fields for a long time, and in recent years have been particularly active in the recovery and use of organic solvents for the purpose of resource conservation. These adsorption devices are basically equipped with two or more adsorption tanks and alternately repeat adsorption and desorption, and usually use heated airflow such as water vapor, heated air, or heated nitrogen for the adsorption and desorption. be. On the other hand, since a large part of the running cost of an adsorption device is dominated by the heated airflow for desorption, the key point in the design and operation of the adsorption device is how to use as little heated airflow as possible to achieve efficient desorption. A conventional adsorption/desorption method in an adsorption device will be explained with reference to FIG. That is, air containing substances to be adsorbed and removed is sucked by the fan 6 and sent to the adsorption tanks 1, 1a, and 1b. For example, when adsorbing in the adsorption tank 1a, valves 2a and 3a are opened and valves 2b and 3b are closed. Adsorption tank 1a
While the adsorption is progressing, the adsorption tank 1b is desorbed with water vapor 8, for example. Water vapor is introduced by opening the valve 4b, heats the adsorbent, desorbs the adsorbate, and then passes through the valve 5b to the condenser 7.
It flows into the air, where it is cooled and condensed. In this case, the flow rate of water vapor is a constant flow rate determined by the resistance determined by piping, valves, and in some cases appropriate throttles.
The flow rate usually does not change during the desorption time. (Problems to be Solved by the Invention) As described above, in the conventional technology, when performing desorption, a constant amount of heated air flow is always flowed during the desorption time, but this cannot be said to be an efficient means due to the following points. That is, if we look at the desorption process in detail, it is as follows. The adsorbent is heated from the surface by a heated air stream. As the temperature of the adsorbent increases, the vapor pressure of the adsorbate trapped in the pores of the adsorbent increases. Eventually, the adsorbate gains energy to overcome the adsorption force and leaves the pore, but the flow at this time is diffusion-controlled, and the lower the partial pressure outside the pore, the faster the desorption proceeds. Looking at it this way, there are two main roles for the heated airflow used for desorption. One is to heat the adsorbent to increase the vapor pressure of the adsorbate to make it easier to leave the pores, and the other is to diffuse the adsorbate molecules that have left the pores and carry them out of the system. Therefore, if the adsorbent is not sufficiently heated, the efficiency of desorption cannot be improved no matter how much desorption fluid is flowed. For these reasons, desorption efficiency was poor when a fixed amount of heated airflow was simply flowed without considering the role of the heated airflow, as in the past. As a result of intensive study by the present inventors on a desorption method that fully takes into account the role of such heated airflow,
We have discovered that by changing the flow rate of the airflow for desorption over time rather than keeping it at a constant flow rate, more efficient desorption can be performed, thereby significantly reducing the amount of airflow used for desorption, and have arrived at the present invention. . (Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides the following steps: Flowing the heated inert gas stream or heated steam at an average flow rate of 1/2 or less of the flow rate of the heated air stream from t ₁ (minutes) to t ₂ (minutes) until t ₁ (minutes),
A desorption method in an adsorption apparatus, characterized in that the amount of heated airflow flowing between t ₁ (minutes) and t ₂ (minutes) is 25 to 50% of the amount of adsorbent used. Here, t ₁ : Time (minutes) until the adsorbent is heated to 98° C. t ₂ : Time required for desorption (minutes) Technical means are employed. In order to carry out the desorption method of the present invention, the adsorption and desorption system shown in FIG. 1 described above can be used as is.
The important point is to vary the heated air flow 8 over time. There are no particular restrictions on the mode of change as long as the above-described role of the heated airflow can be fulfilled as is, but the following method is preferred. That is, let the time required for attachment and detachment be t ₂ (minutes), and t ₁
Until (t ₂ > t ₁ ), the heated air flow is flowed at an average flow rate that is less than half of the flow rate of the heated air flow flowed from t ₁ to t ₂ until (t 2 > t 1 ). _t1 may be tested in advance and set by a timer when the adsorbent temperature reaches 98°C, or may be switched by detecting the temperature. Also, from t ₁ (minutes) to t ₂ (minutes)
The amount of heated air flow during this period is 25 times the amount of adsorbent used.
Choose from ~50%. It may be selected from this range as appropriate depending on the type of solvent being adsorbed. Examples of the heated air stream used in the desorption method of the present invention include water vapor, heated air, heated nitrogen, and the like. Further, as the adsorbent, powdered activated carbon, granular activated carbon, fibrous activated carbon, etc. can be used. (Examples) Examples of the present invention will be described below, but the present invention is not limited in any way by these Examples. Example 1 A container with a diameter of 52.9 mm was filled with 8.26 g of activated carbon fibers, and N ₂ containing 1200 ppm of methyl ethyl ketone (MEK) was flowed for saturation adsorption, and then N ₂ at 150° C. was flowed in the opposite direction for desorption. Figure 2 shows the desorption rate determined by measuring the concentration of MEK being desorbed.
The broken line A in Figure 2 shows the case of desorption by flowing heated nitrogen at a constant flow rate of 4/min from beginning to end (comparative example), and the solid line B shows the case of desorption by flowing heated nitrogen at a constant flow rate of 4/min until 12.5 minutes and 4/min thereafter.
The figure shows the desorption rate when converted to /min.
After 25 minutes, almost the same desorption rate was reached, and after that, there was a tendency for the desorption rate to be better when the flow rate was initially lowered. Example 2 1700 ppm of trichlorethylene was processed at 15 m ² /min in an adsorption device using activated carbon fibers. A comparison was made between a normal desorption method in which the flow rate of water vapor is not changed and the method of the present invention in which the flow rate is reduced to half of the normal flow rate during the first half of the desorption time and returned to the normal flow rate during the second half.
Table 1 shows the concentration at the outlet of the adsorption device and the amount of water vapor used.

[Table] According to the method of the present invention, the water vapor flow rate could be reduced by 25%. (Effects of the Invention) By changing the flow rate of the heated air flow for desorption over time in this way, it has become possible to perform desorption with extremely high efficiency.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet of an adsorption/desorption system using an adsorption device, and FIG. 2 shows desorption rate curves in the present invention and a comparative example.

Claims (1)

[Scope of Claims] 1. When desorbing adsorbed substances by spraying a heated inert gas stream or heated steam onto an adsorbent containing an activated carbon material as a main component, the amount of the heated inert gas stream or heated steam is set to t. From t ₁ (minute) to ₁ (minute)
Flow at an average flow rate of 1/2 or less of the flow rate of the heated air flow flowing up to t ₂ (minutes), and set the amount of heated air flow flowing between t ₁ (minutes) and t ₂ (minutes) to 25% of the amount of adsorbent used. ~50% desorption method in an adsorption device. Here, t ₁ : Time (minutes) until the adsorbent is heated to 98°C. t ₂ : Time required for desorption (minutes).