JP4608685B2 - Volatile organic compound recovery unit - Google Patents

Description

  The present invention relates to a unit for separating and recovering VOC from a gas containing a volatile organic compound (hereinafter referred to as “VOC”).

In order to prevent air pollution caused by suspended particulate matter and photochemical oxidants, part of the Air Pollution Control Act was established in 2004 to suppress emissions from VOC, one of these causative substances, from factories and business establishments. Was amended.
VOC removal devices are roughly classified into a combustion method and an adsorption method. In the adsorption method, exhaust gas is introduced from an inlet of a tank filled with activated carbon, VOC is adsorbed on the activated carbon, and purified gas is discharged from the outlet. Then, the adsorbed VOC is recovered by heating and evaporation together with the carrier gas introduced from the outlet. Therefore, the adsorption method has advantages not found in the combustion method such that VOC can be recovered and reused, and it does not accompany global warming because it does not involve the generation of CO ₂ . Moreover, since activated carbon as an adsorbent has microwave absorption, it also has an advantage that activated carbon can be directly and efficiently heated by irradiating it with microwaves during recovery.

Conventionally, activated carbon used in adsorption-type VOC removal devices has been mainly in the form of particles for reasons such as low cost, but the granular activated carbon filled in the adsorption tank is likely to spontaneously ignite due to accumulation of adsorption heat. is there. Therefore, water vapor must be used as a carrier gas for recovery, and therefore, the removable VOC is limited to a low boiling point and water insoluble. Therefore, in recent years, it has been proposed to form activated carbon into a honeycomb-shaped block that allows gas to flow easily and has excellent heat dissipation, and loads this into an adsorption tank instead of granular activated carbon (Patent Document 1). As a result, there is no risk of ignition, and various VOCs can be recovered using a dry gas such as nitrogen as the carrier gas.
JP 2006-187767 A

However, the depth at which microwaves penetrate into the activated carbon is finite. Therefore, even if the activated carbon is formed to a thickness exceeding the penetration depth, or a plurality of blocks are laminated so as to have such a thickness, the portion where the microwave does not reach is not heated. VOCs adsorbed on the surface cannot be recovered. On the other hand, if the thickness is about the same as the penetration depth, the amount of VOC that passes without being adsorbed is too large, and the practicality becomes poor. In any case, honeycomb-shaped activated carbon has a high molding cost and is inferior in profitability.
Therefore, an object of the present invention is to provide a recovery unit that is excellent in both the adsorption rate and desorption rate of VOC at low cost.

In order to solve the problem, the recovery unit of the present invention is:
A plurality of tubes made of dense glass or ceramics that are transparent to microwaves and arranged in the radial direction;
A sheet made of microwave-permeable glass wool or ceramic wool and covering the outer peripheral surface of each cylinder;
A large number of pellets made of activated carbon and filled in the cylinder;
A shaped container made of a microwave permeable and gas impermeable material, containing the plurality of tubes and hermetically sealing the space around each tube, while allowing the inside of the tube to communicate with the outside It is characterized by providing.

  According to this recovery unit, VOC-containing exhaust gas passes through each cylinder and is sent from one of the cylinders to the other, while VOC is adsorbed on the pellets. Since the container hermetically seals the space around each cylinder, the exhaust gas does not pass outside the cylinder. Since the cylinder penetrates, the heat of adsorption is quickly released together with the purified gas. Therefore, it does not ignite spontaneously. The number of pellets is determined so that the exhaust gas is sufficiently purified according to the amount and concentration of the exhaust gas to be treated. And since the cylinder and the sheet are made of a microwave permeable material, even when a plurality of cylinders are arranged, the microwaves penetrate into the cylinder through the cylinder, the sheet or the space between the cylinders at the time of collection, Heat the pellet directly. Therefore, most of the VOC adsorbed on each pellet is desorbed. Moreover, since the cylinder and the sheet are made of a microwave transparent material, they are not heated and most of the microwave energy is efficiently consumed for desorption. Moreover, since a sheet | seat consists of wool, while absorbing the thermal expansion and impact of a pipe | tube, it heat-insulates adjacent pipe | tubes.

It is preferable that an inner diameter of the cylinder is larger than a depth at which the microwave can penetrate and not more than twice the depth. As described above, since the cylinder and the sheet are made of a microwave permeable material, the microwave can enter from the entire outer peripheral surface of the cylinder. This is because the adsorption amount per cylinder can be increased by making the inner diameter larger than the depth at which microwaves can penetrate. Although the microwave penetration depth varies depending on the microwave frequency, it can be obtained from the position where the temperature rises when the microwave is irradiated with the temperature sensor inserted into the cylinder. In the case of 2.45 GHz microwave, it is 20 mm.
As the material constituting the cylinder, PEEK, PTFE, glass, quartz, and ceramics can be used. However, since heat resistance is required, glass, quartz, ceramics, and PEEK are optimal.

  The microwave transmissive material applied to the container may be an inorganic material such as glass, quartz, ceramics, but polyester, polypropylene, nylon, polyethylene, polystyrene, fluororesin, PEEK, phenol resin, epoxy in terms of moldability. Resins such as resin, xylene resin, diallyl phthalate resin, polycarbonate, melamine resin, and furan resin are preferable. Further, these materials may be reinforced by containing fibers.

  The pellet is preferably in the form of a Lessing ring. This is because the pressure loss is smaller than the granular shape, the molding cost is lower than that of the honeycomb shape, and sufficient strength is secured by the partition plate. In this case, when the inner diameter of the cylinder is D, the diameter of the lessing ring is d, and the axial length of the lessing ring is L, the ranges of d = D / 6 to D / 2 and L = d / 2 to 2d are preferable.

  In the present invention, the housing for holding the container and fixing the microwave waveguide is not limited. However, in a preferable configuration, the cooling chamber that holds the container in an airtight manner and surrounds the container is provided between the container and the outer peripheral surface. A housing to be formed; and a microwave waveguide fixed to a portion of the housing facing the outer peripheral surface of the container with the cooling chamber interposed therebetween. Thereby, the heat of adsorption of VOC and the heat accompanying microwave irradiation are dissipated into the cooling chamber, thereby preventing deformation of the container. Furthermore, it is preferable to provide a cooling pipe that penetrates the lower part of the housing and the container from an external cooling gas source and reaches the cooling chamber. This is because the lower part of the container is susceptible to thermal deformation due to the gravity of the cylinder, and thermal deformation can be prevented by preventing heat storage in this part at an early stage. The cooling gas may be a purified gas that has passed through the cylinder.

  Since the recovery unit of the present invention does not ignite spontaneously even if the carrier gas at the time of recovery is not water vapor, various VOCs can be recovered with a carrier gas suitable for it. In addition, the adsorption rate can be increased by combining cylinders of the number and size necessary for purification of exhaust gas. Even in this case, since microwaves enter each cylinder, the desorption rate is also high. Therefore, the VOC can be reused efficiently. Moreover, since the shape of the filled pellet is not limited, it can be manufactured at low cost.

  Embodiments of the present invention will be described with reference to the drawings. 1 is a vertical cross-sectional view of a recovery unit according to the embodiment, FIG. 2 is a horizontal cross-sectional view of the same, FIG. 3 is a partially enlarged view of FIG. 1, and FIG. 5 (a) is a plan view showing pellets filled in the cylinder of the recovery unit, and FIG. 5 (b) is a perspective view of the same.

  The recovery unit 1 includes a stainless steel housing 2. The housing 2 has a rectangular parallelepiped shape surrounded by the four outer walls 21, the top plate 22, and the floor plate 23. A microwave waveguide 3 is attached to each outer wall 21. The top plate 22 and the floor plate 23 each have an opening at the center and serve as processing gas entrances 24 and 25. A container 4 made of fiber reinforced resin is installed in the housing 2. Both the fiber and the resin in the fiber reinforced resin have microwave permeability, and a preferred example of the resin is PEEK. A frame-like space serving as the cooling chamber 9 is provided between the inner peripheral surface of the outer wall 21 and the outer peripheral surface of the container 4. A cooling gas outlet 26 is provided near the upper end on one side of the outer wall 21.

The container 4 includes four side walls 41 extending from the top plate 22 to the floor plate 23, an upper plate 42 fixed to the side wall 41 at a position lower than the top plate 22, and a lower plate fixed to the side wall 41 at a position higher than the floor plate 23. The space surrounded by the side wall 41, the upper plate 42, and the lower plate 43 has a rectangular parallelepiped shape. The thickness of the side wall 41 varies depending on the amount of exhaust gas to be treated, and is 5 to 20 mm when the amount of treated gas is 5 m ³ / min, and 10 to 50 mm when 50 m ³ / min. The top plate 22, the floor plate 23, the upper plate 42, the lower plate 43, and the side wall 41 are joined while maintaining airtightness.

  A large number (64 in the figure) of cylinders 5 made of borate glass are accommodated in the container 4 so as to be arranged in 8 rows × 8 columns. The inner diameter D of each cylinder 5 is usually 20 to 50 mm, preferably 30 to 40 mm. The outer peripheral surface of each cylinder 5 is wound around a sheet 6 made of microwave permeable glass wool and having a thickness of 1 to 10 mm to be insulated from each other. Yes. The sheet 6 also functions to absorb an impact with the adjacent cylinder 5. The total thickness of the cylinder 5 and the sheet 6 is 5 to 20 mm. As shown in FIG. 3, the upper and lower ends of each cylinder 5 penetrate the upper plate 42 and the lower plate 43 in an airtight manner, respectively. Further, the entire array of 64 cylinders 5 is covered with a 10 mm sheet 7 and insulated from the side wall 41.

A cooling gas source (not shown) is disposed outside the housing 2, and a cooling pipe 8 is connected to the cooling gas source. The cooling pipe 8 passes through the outer wall 21 in an airtight manner, meanders in the lower plate 43 to reach the cooling chamber 9, and the cooling gas absorbs the heat of the lower plate 43, and then enters the cooling chamber 9. Yes.
Each cylinder 5 is filled with a large number of pellets 10 made of activated carbon. As shown in FIG. 5, the pellet 10 has a so-called Lessing ring shape having a partition plate integrally in the center of a cylinder, and is obtained by extruding and firing a mixture of powdered activated carbon and a binder. The diameter of the pellet 10 is 6-8 mm.

  When the VOC is removed from the exhaust gas using the recovery unit 1, the exhaust gas flows from the inlet 24 to the outlet 25 of the recovery unit 1. At the same time, a cooling gas is passed through the cooling pipe 8. VOC in the exhaust gas is adsorbed on the surface of the pellet 10 while passing through the cylinder 5. As a result, the purified gas is discharged from the recovery unit 1. Since the pellet 10 is in the shape of a recessing ring, there is little pressure loss and deformation is difficult. Further, since the cooling gas cools the lower plate 43 and the side wall 41, the heat of adsorption is not accumulated in the cylinder 5, and it is safe and the lower plate 43 is not deformed. A cooled purified gas may be used as the cooling gas.

  Next, when recovering the adsorbed VOC, the supply of the exhaust gas is stopped, and the carrier gas that is inert and dry with respect to both the activated carbon such as nitrogen and the VOC is opposite to the exhaust gas, that is, from the outlet 25 to the inlet 24. The microwave of 2.45 GHz is irradiated from the waveguide 3 to the container 4 while flowing in the direction of. At the same time, a cooling gas is caused to flow through the cooling pipe 8. The microwave passes through the side wall 41, the sheet 6, the sheet 7, and the cylinder 5 and is absorbed by the pellet 10. Since the penetration depth of this microwave into the activated carbon is 20 mm and the inner diameter D of each cylinder 5 is 20 to 50 mm, all the pellets 10 in the cylinder 5 are heated by the microwave that has entered from the periphery of the cylinder 5. The The VOC evaporated by receiving the heat is collected from the recovery unit 1 together with the carrier gas. Also at this time, since the cooling gas cools the lower plate 43 and the side wall 41, the heat generated by the activated carbon is not accumulated in the cylinder 5 and is safe.

It is a vertical direction sectional view of the recovery unit concerning an embodiment. It is a horizontal direction sectional view similarly. FIG. 2 is a partially enlarged view of FIG. 1. It is a perspective view which shows the principal part of the collection unit. (A) is a top view which shows the pellet with which the cylinder of a collection | recovery unit is filled, (b) is a perspective view similarly.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Recovery unit 2 Housing 3 Microwave waveguide 4 Container 5 Cylinder 6, 7 Sheet 8 Cooling tube 9 Cooling chamber 10 Pellet

Claims (7)

A plurality of tubes made of dense glass or ceramics that are transparent to microwaves and arranged in the radial direction;
A sheet made of microwave-permeable glass wool or ceramic wool and covering the outer peripheral surface of each cylinder;
A large number of pellets made of activated carbon and filled in the cylinder;
A shaped container made of a microwave permeable and gas impermeable material, containing the plurality of tubes and hermetically sealing the space around each tube, while allowing the inside of the tube to communicate with the outside A volatile organic compound recovery unit comprising:   2. The recovery unit according to claim 1, wherein an inner diameter of the cylinder is larger than a depth at which the microwave can enter and is not more than twice the depth.   The collection unit according to claim 1 or 2, wherein the microwave permeable and gas impermeable material constituting the container is a fiber reinforced resin.   The collection unit according to any one of claims 1 to 3, wherein the pellet has a shape of a ringing ring. And a housing that holds the container in an airtight manner and forms a cooling chamber that surrounds the container with the outer peripheral surface of the container;
The recovery unit according to claim 1, further comprising: a microwave waveguide fixed to a portion of the housing facing the outer peripheral surface of the container with the cooling chamber interposed therebetween.   Furthermore, the collection | recovery unit of Claim 5 provided with the cooling pipe which penetrates the lower part of the said housing and the said container from an external cooling gas source, and reaches a cooling chamber.   The recovery unit according to claim 6, wherein the cooling gas is a purified gas that has passed through the cylinder.

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