Mist recovery apparatus with twisted strip inserted pipes

Abstract: A mist recovery apparatus recovers the mist of water, oil and the like from the fumy or gassy exhaust produced in the rolling operation of aluminum plates. The apparatus has a shell (5) provided with a pair of upper and lower pipe plates (14) and a plurality of exhaust passing pipes (2) extending between the upper and lower pipe plates (14) and each having a twisted strip (1) therein. The shell has a upper casing (3) and a lower casing (4), which are placed above the upper plate (14) and beneath the lower plate (14). The exhaust containing mist flows through the upper casing (3), respective exhaust passing pipes (2), and the lower casing (4) sequentially. These exhaust passing pipes (2) are cooled by a coolant passing through and around the pipes, so that the mist are removed from the exhaust and recovered. The experimentally suitable ratio of the length (L) of the exhaust passing pipe and the twisting half pitch (P) of the twisting strip is 8 - 35.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for recovering mist from an exhaust gas containing a mist of water, oil, etc. 2. Description of the Prior Art Heretofore, an exhaust gas containing a mist of steam, rolling oil and the like, which was produced from a roll coolant when, for example, aluminum plates are rolled, has been treated through, for example, a filter installation as shown in FIG. 5 so as to remove the mist. In detail, the exhaust G containing the mist is supplied through an exhaust line 21 and respectively passes through a coarse mesh filter 23, a middle function filter 24, and a high function filter 25, in the filtering chamber 22 and is discharged to the atmosphere from an outlet 26. Flowing through such filters of the filtering chamber 22, the mist is held or kept in respective filters and removed from the exhaust. According to other filtering mechanisms of the prior art, one type has a plurality of corrugated plates arranged in parallel, through which plates an exhaust gas passes and another type is of a cyclone type. In a conventional filtering apparatus as shown in FIG. 5, the mist is held and deposited on the meshes of the filters, which gradually deteriorates the recovery of the mist. As a result, when the filter mesh is clogged with the mist, the old and clogged filter must be replaced by a new one. It is apparent that the maintenance cost is high, because the filter is high in price and the work replacing it is laborious. In many cases, since the mist content of the exhaust gas is supersaturated and passes through the filter mesh, there is a risk that the mist is discharged as it is to the atmosphere. The size of the conventional mist recovery installation must be large in order to lessen the draught resistance or pressure of air. Other apparatuses of the corrugated plate type and cyclone type, respectively have little or poor recovery of the mist. A mist recovery apparatus as acknowledged in the preamble of claim 1 is known from US-A-4 382 807 and comprises a shell, a pair of an upper pipe plate and a lower pipe plate respectively arranged in said shell, a twisted strip having the form of a helix and disposed in each exhaust passing pipe, wherein the fumy exhaust gas containing the mist is flowing downward through said exhaust passing pipe so as to separate and recover said mist from said exhaust gas. In this known mist recovery apparatus the twisted strips are secured to the exhaust passing pipes. Specific dimensions for the twisted strips are not mentioned. SUMMARY OF THE INVENTION It is the object of the invention to provide a mist recovery apparatus of the type known from US-A 4 382 807 which has a small size and a good recovery efficiency and is easy to handle. This object is solved by the features of the characterizing part of claim 1. A suitable embodiment is defined by the features of claim 2. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of the vertical section of the exhaust passing pipe to be used in the mist recovery apparatus according to the present invention; FIG. 2 shows an example of the mist recovery system containing the mist recovery apparatus of the present invention; FIGS. 3 and 4 are graphs depicting the relationship between diameters of the particles to be removed and L/P; and FIG. 5 is a section of the conventional filter apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First the construction of the exhaust passing pipes according to the present invention will be explained. As shown in FIG. 1 (vertical section), a twisted strip 1 is placed within the exhaust passing pipe 2. A number of exhaust passing pipes 2 is arranged between the upper and the lower pipe plates 14 within the shell 5 and both ends of each passing pipe 2 pass or penetrate through the pipe plates so as to open to the interiors of an upper casing 3 and a lower casing 4, respectively. Exhaust gas containing a mist is supplied to the upper casing 3 through a blower B and then the exhaust gas flows into the exhaust passing pipes 2 which are open to the interior of the upper casing 3. Flowing through the exhaust passing pipes, the exhaust gas contacts the twisted strips 1 and the inner walls of the exhaust passing pipes 2 and flows down vertically within the passageway formed by the twisted strip 1 and the inner wall of the exhaust passing pipe 2. The mist is separated from the exhaust gas and deposited on the outer surface of the twisted strip 1 and the inner wall of the exhaust passing pipes 2. The remaining exhaust gas enters the lower casing 4 and flows through a louver 6. After that, the remaining gas is sucked by a blower B and forced into a filter 8 through a conduit connecting the lower casing 4 and the filter 8. In the filter 8, fine mist of, for example, 10 µm or less, is separated from the remaining exhaust gas and then the exhaust gas is discharged to the atmosphere through a chimney or a discharging column 10. Coolant, which is cooled by radiating heat in a cooling tower 7, circulates through the shell 5 in a space provided inside the shell 5 and around the pipes 2 in order to cool the exhaust passing pipes 2 through their outer walls. Mist deposited or liquid condensed onto the inner wall of the exhaust passing pipes 2 and the surface of the twisted strips 1 within the exhaust passing pipes 2 falls into the lower casing 4 and is recovered. The recovered mist 11 is collected in an oil separator 9 through a drain outlet 12 and a U-shaped tube 13. Because the exhaust passing pipes 2 of the present invention each have a twisted strip 1 therein and the flow of the exhaust gas becomes a vertical flow while descending through the exhaust passing pipes 2, mist of several µm or more in diameter is effectively removed and saturated stream in the exhaust gas is effectively liquefied and recovered due to the heat transfer acceleration effect of the twisted strip 1. The twisted strips 1 are made of a metal, such as stainless steel and aluminum alloy or the like, and their outer diameters are a little smaller than the inner diameter of the exhaust passing pipes 2. The twisted strips 1 may be a suspension type so that the twisted strips 1 can be easily removed after a lid of the upper casing 3 is dismantled. The inner diameter of the exhaust passing pipe 2 and the twisting half pitch P of the twisted strip 1 are important in improving the mist arresting efficiency. First, preferably, the inner diameter of the exhaust passing pipes 2 is 25 - 60 mm. If the diameter is less than 25 mm, the resistance to the flow of the mist and the pressure loss increases, so that the number of the exhaust passing pipes 2 to be installed or used in the shell 5 has to be increased, resulting disadvantageously in the enlargement of the shell 5 and the mist recovery apparatus. Also, if the inner diameter of the exhaust passing pipes exceeds 60 mm, it is necessary to lengthen the exhaust passing pipes 2 in order to attain sufficient intimate contact of the mist with the inner wall of the pipe 2, which results in a large size of the mist recovery apparatus. Therefore, the preferable size of the inner diameter of the pipes 2 is 25 - 60 mm. The twisting half pitch P of the twisted strip 1 will be explained with reference to FIG. 3 and FIG. 4. The exhaust passing pipes of 25 mm and 60 mm in inner diameter are prepared and exhaust gas is passed through them at a speed of 8 m/s. FIG. 3 and FIG. 4 show the relationship between the particle diameter of the mist removed and L/P (the length L of the exhaust passing pipe 2 and a twisting half pitch P of the twisted strip 1). FIG. 3 is for a mist of kerosine and FIG. 4 is for a mist of water. As is apparent from the graphs, an L/P of 20 - 35 is preferable when the mist is kerosine and an L/P of 8 - 16 is suitable when the mist is water. In general, an L/P of 8 - 35 is preferable. As described above, the technical effects to be obtained by embodying the present invention are summarized as follows: 1. The mist contained in the exhaust gas can be recovered effectively at, for example, about a 95% removal effiency, so that a great pollution prevention effect can be obtained. 2. It is possible to remove elements of the mist and reuse them. From the recovery of kerosine, it is possible to repay the cost of the mist recovery installation in about 1.7 years. 3. The heat transfer efficiency of the exhaust passing pipes is improved and the gas cooling effect increases so that liquifaction of steam in the exhaust is accelerated. 4. Because outer surfaces of the twisted strip are smooth, liquid flows down smoothly and rapidly. 5. Any pollution and dirt sticking on the inner wall of the exhaust passing pipe are washed off. (i) Due to the vertical flow on the twisted strip, a great washing effect is obtained. (ii) The twisted strips are not secured to the exhaust passing pipes, so that they are easily taken out of the exhaust passing pipes for inspecting and cleaning them.

Claims: A mist recovery apparatus comprising a) a shell (5), b) a pair of an upper pipe plate (14) and a lower pipe plate (14) respectively arranged in said shell (5), and a plurality of exhaust passing pipes (2) arranged in said shell (5) between the upper and the lower pipe plates, c) a twisted strip (1) having the form of a helix and disposed in each exhaust passing pipe (2), d) wherein the fumy exhaust gas containing the mist can flow downwardly through said exhaust passing pipes (2) so as to separate and recover said mist from said exhaust gas, characterized in that e) the exhaust passing pipes (2) have an inner diameter of 25 - 60 mm, that f) for each twisted strip (1) the ratio L/P of the length L of said exhaust passing pipe (2) to the distance P between two adjacent nodes of the helix formed by twisting the strip (1) is in the range from 8 to 35, and that g) the twisted strips (1) are not secured to the exhaust passing pipes (2). A mist recovery apparatus according to claim 1, characterized by a cooling tower (7) adapted to cool the coolant to be circulated through said shell (5) so as to cool said exhaust passing pipes (2).

Inventors: KISARAGI TAKAYASU, SHIRASAKA YUICHI, KISARAGI, TAKAYASU, SHIRASAKA, YUICHI
Applicants: SUMITOMO LIGHT METAL IND, SUMITOMO LIGHT METAL INDUSTRIES LIMITED
Application year: 1990
Main classification: B01D45
IPC codes: H01T19, B04C3, G03G15, B01D5, B01D45, B01D50, B24D15