Tunnel dust collecting system

Abstract: Typically, in a tunnel dust collecting system comprising: a dust collecting chamber (2) formed in the upper space of a tunnel (1) with a ceiling board; electric dust collectors (3) arranged in the dust collecting chamber in such a manner that the dust collectors are shifted both longitudinally and laterally of the dust collecting chamber; and air blowers (4) provided in said dust collecting chamber at the air supplying end, the dust collectors except the first one closest to the air sucking end of the dust collecting chamber are set obliquely with respect to the longitudinal direction of the dust collecting chamber as if partially overlapped with one another when viewed from the air sucking end, whereby the contaminated air led in the dust collecting chamber is distributed uniformly to the dust collectors.

Description: BACKGROUND OF THE INVENTION (Field of the Invention) This invention relates to a tunnel dust collecting system, according to the preamble of claim 1 in which an electrical dust collector is used to remove dust and smoke from the contaminated air in a tunnel thereby to use the air again, and more particularly to a tunnel dust collecting system which is installed on the ceiling of a tunnel which is provided mainly for automobiles. (Prior Art) There are available a variety of tunnel dust collecting systems. Typical ones of the systems, are a tunnel dust collecting system of bypass tunnel type as shown in Fig.4 (A), and a tunnel dust collecting system of ceiling installation type as shown in Fig. 4(B) and Figs. 5(A) and 5(B). Figs. 5 (A) and 5 (B) are a plan view and a sectional view of the tunnel dust collecting system shown in Fig. 4(B). In the tunnel dust collecting system of bypass tunnel type as shown in Fig. 4(A), a bypass tunnel is connected, as a dust collecting chamber 2, to the main tunnel 1 provided for automobiles, so that the air contaminated in the tunnel 1 is led into the dust collecting chamber at one end opened in the side wall of the main tunnel 1, where it is decontaminated with an electrical dust collector 3 (hereinafter referred to merely as "a dust collector 3", when applicable). The air thus processed is supplied into the main tunnel 1 with an air blower 4 through the other end of the dust collecting chamber 2. On the other hand, in the tunnel dust collecting system of ceiling installation type, a ceiling board 5 is installed in such a manner as to form a dust collecting chamber 2 in the upper portion of a tunnel. The dust collecting chamber 2 has one end 2a which is used to suck air from the tunnel (hereinafter referred to as "an air sucking end 2a", when applicable), and the other end 2b which is used to supply decontaminated air into the tunnel (hereinafter referred to as "an air supplying end 2b", when applicable). The contaminated air sucked into the dust collecting chamber 2 through the air sucking end 2a is decontaminated with dust collectors 3, and the air thus decontaminated is supplied into the tunnel with air blowers 4 provided near the air supplying end 2b. When compared with the tunnel dust collecting system of bypass tunnel type, the tunnel dust collecting system of ceiling installation type is advantageous in that its installation cost is lower because it is unnecessary to form the bypass tunnel. In the tunnel dust collecting system of ceiling installation type, as shown in Fig.5 , two dust collectors 3 are provided in the dust collecting chamber 2 in such a manner that they are separated from each other with a partition board 6. More specifically, the dust collecting chamber is divided by the partition board 6 into two parts,in which the two dust collectors are provided, respectively. Two axial flow type air blowers 4 with cylindrical casings 4b are provided at the air supplying end 2b of the dust collecting chamber 2, and air sucking inlets 7 are provided at the air sucking end of the dust collecting chamber 2. The air in the upper portion of the tunnel is sucked through the air sucking inlets 7 linearly along the central axis of the tunnel into the dust collecting chamber and decontaminated with the dust collectors 3, and the air thus decontaminated is linearly supplied into the tunnel with the air blowers 4 through air supplying outlets 4a. The ceiling board 5 serves as a base board which supports the dust collectors 3 etc. Generally, the ceiling board 5 is extended to the air supplying outlets 4a of the air blowers 4, being utilized as means for making access to the air blowers for inspection or maintenance. In the case of Fig. 5, only two dust collectors 3 are provided. However, in the case where more than two dust collectors are employed, they are arranged staggered in the dust collecting chambers from the air sucking end 2a towards the air supplying end 2b. In the tunnel dust collecting system shown in Fig. 5, the air sucking end 2a of the dust collecting chamber 2 is employed as the air sucking inlets 7. On the other hand, there is available a tunnel dust collecting system of ceiling installation type in which, as shown in Fig. 6 , the end of the dust collecting chamber corresponding to the above-described air sucking end is closed, and instead an air sucking inlet is opened in the end portion of the ceiling board 5 (hereinafter referred to as "a tunnel dust collecting system of upward suction type", when applicable). In the tunnel dust collecting system of upward suction type, as shown in Fig. 6 , the air sucking end 2a of the dust collecting chamber 2 defined by the ceiling board 5 is closed with a closing board 8, and instead a rectangular-window-shaped air sucking inlet 9 is formed in the ceiling board 5 near the closing board 8. The contaminated air in the tunnel is led through the air sucking inlet 9 into the dust collecting chamber as indicated by the arrows, and decontaminated with the dust collectors 3. The air thus decontaminated is supplied into the tunnel with the air blowers 4. The above-described conventional tunnel dust collecting system of ceiling installation type is disadvantageous in the following points lowering its dust collection efficiency. In the conventional tunnel dust collecting system, as shown in Fig. 5, the air decontaminated by the dust collectors 3 is blown along the central axis of the tunnel 1 into the upper portion of the latter as it is. Therefore, when compared with the tunnel dust collecting system of bypass tunnel type, the decontaminated air is difficult to mix with the contaminated air in the driveway space la of the tunnel 1. In general, in order to completely mix the decontaminated air with the contaminated air, there must be a distance of about 100 m. That is, the interval of installation of the dust collecting systems is limited. Therefore, the conventional system cannot decontaminate air sufficiently in the area where the engine load of an automobile is increased to increase the contamination of air as in an up- grade driveway of an undersea tunnel. The interval of installation of dust collecting systems is determined with the distance taken into consideration with which decontaminated air is completely mixed with contaminated air. In the conventional tunnel dust collecting system, the ceiling board 5 is provided below the air blowers 4. Therefore, as shown in Fig. 5(B), the stream of air blown by the air blowers 4 is not smoothly met with the stream of air around it, thus forming eddies 12. As a result, energy loss is caused, and accordingly it is necessary to use high electric power to supply decontaminated air at a predetermined flow rate. On the other hand, the space for installation of a dust collecting system is limited because of limitations in public engineering works. It is desirable to increase the flow rate of decontaminated air as much as possible with the installation space per station decreased as much as possible. From JP-A-63-319072, a tunnel dust collecting system of ceiling installation type is known comprising an electrosatic precipitator and a blower in a housing unit wherein a discharge port is opened downward. From FR-A-2 253 877, a fresh air ventilation system for a road tunnel is known in which a top portion of the tunnel is separated by boards from a bottom portion where the exhaust fumes are produced. The boards comprise louvers positioned near the tunnel side walls for releasing the fresh air such as to flow from the board downward along the tunnel side wall. Since the system is designed for providing fresh air from outside the tunnel, the cleaning of the contaminated air produced in the tunnel is not addressed. From DE-A-25 09 279, a system for ventilating the interior of an artificial road cover is described, showing one or two blowers for exhaling fresh air into the tunnel with the blowers being arranged along the top board portion of the tunnel offset from the apex position. The blowers serve for distributing fresh air in the tunnel and thus do not contain any means for collecting dust from the air passing therethrough. SUMMARY OF THE INVENTION It is an object of this invention to provide an improved tunnel dust collecting system capable of improving the purifying efficiency of the dust collecting system and thus improving the cleanliness of the air in the tunnel. The foregoing objects and other objects of the invention have been achieved in tunnel dust collecting systems according to claim 1. In the conventional tunnel dust collecting system, the dust collectors are, in general, arranged in parallel with the longitudinal direction of the tunnel so as to lead the air stream straightly to the air sucking surfaces of the dust collectors. In the tunnel dust collecting system, according to claim 1 of the invention, all of the dust collectors except the first one as viewed from the air sucking end of the dust collecting chamber are set obliquely with respect to the longitudinal direction of the dust collecting chamber as if partially overlapped one another when viewed from the air sucking end, thus achieving the object of the invention. In this connection, in order to uniformly distribute the air stream to the dust collector, it is preferable that the first dust collector is smaller in air stream projection area than those of the remaining, and the distance between the first and second dust collectors is longer than those between the second and third dust collectors, between the third and fourth dust collectors, and so forth. Furthermore, in the system, each electric dust collector has outlet dampers, the degrees of opening of which are adjusted to control the flow rate of air therein. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Fig. 1 (A) is a plan view showing a dust collecting chamber in a tunnel dust collecting system according to a third aspect of the invention; Fig. 1 (B) is a cross sectional view taken along line B-B in Fig. 1 (A); Fig. 2 is a horizontal sectional view showing the arrangement of a dust collector in the system; Fig. 3 is a plan view showing essential components of the dust collecting chamber shown in Fig. 4, for a description of air streams therein; Fig. 4 (A) is a perspective view showing a typical example of a conventional tunnel dust collecting system of bypass tunnel type; Fig. 4 (B) is a perspective view showing an example of a conventional tunnel dust collecting system of ceiling installation type; Figs. 5 (A) and 5(B) is a plan view and a longitudinal sectional view of the tunnel dust collecting system of ceiling installation type shown in Fig. 4 (B), respectively; and Fig. 6 is a longitudinal sectional view showing a typical example of a tunnel dust collecting system of upward suction type. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS When a plurality of dust collectors are arranged in the dust collecting chamber in such a manner that they are shifted from one another both longitudinally and laterally of the dust collecting chamber, the effective air flow area for the dust collectors is increased when compared with the air flow area provided for the dust collecting chamber. However, if, in this case, the dust collectors are positioned as if they were partially overlapped with one another when viewed from the air sucking end of the dust collecting chamber, then the air stream to a dust collector is disturbed by the preceding dust collector. It has been found through experiments that, when all of the dust collectors except the first one as viewed from the air sucking end of the dust collecting chamber are arranged obliquely with respect to the longitudinal direction of the dust collecting chamber, then the air stream of a dust collector will not be disturbed by the preceding dust collector even if they are overlapped more. If, in this case, the dust collectors form an excessively large angle with the longitudinal direction of the dust collecting, then the contaminated air is not uniformly distributed to the dust collectors. In this connection, it has been found through experiments that, when the angle is not more than 12°, and the distance between adjacent dust collectors is at least twice the width of the dust collector, then the contaminated air is uniformly distributed to the dust collectors. Even in this case, the air flow area occupied by the first dust collector as viewed from the air sucking end of the dust collecting chamber is large when compared with the whole air flow area of the dust collecting chamber, so that the first dust collector adversely affects the flow rate of air in the second dust collector, at worst that in the third dust collector or in the fourth dust collector. This is due to the fact that the air flow area of the dust collecting chamber is greatly contracted by the top dust collector, thus forming contraction flows, as a result of which the air stream leaving the ceiling board in front of the second dust collector is allowed to flow over the second dust collector to the third or fourth dust collector. In order to overcome this difficulty, according to the invention, the first dust collector is made smaller in air stream projection area than the others, and the distance between the first and second dust collectors is made longer than the distance between the second and third dust collector, the distance between the third and fourth dust collectors, and so forth. Preferably the distance between the first and second dust collectors is least 1.5 times the diameter of the air stream in the dust collecting chamber at the air sucking end. The flow rate of air in each dust collector is controlled by adjusting the degrees of opening of dampers provided at the air outlet. When the degrees of opening of the dampers of a dust collector are decreased, the flow rate of air in the dust collector is decreased, and the air stream is distributed to the other dust collectors as much. The same dampers are provided at the air inlet of each dust collector. However, if the dampers at the air inlet are adjusted, then the air stream flowing through the electrode boards is deflected, so that the dust collection efficiency is lowered. Thus, preferably only the degrees of opening of the outlet dampers are controlled. Figs. 1 and 2 show an embodiment of the invention. In the tunnel dust collecting system, as shown in Fig. 1 (A), six dust collectors 3A through 3F are provided in the dust collecting chamber 2 in such a manner that they are arranged longitudinally of the dust collecting chamber 2 and shifted from one another laterally of the dust collecting chamber (from one side wall (left side wall) of the dust collecting chamber towards the other side wall (right side wall)) in the stated order. Partition boards 15 are extended between the dust collectors 3A through 3F. The top dust collector 3A is connected through a partition board 16 to the one side wall of the dust collecting chamber 2, and similarly the last dust collector 3F is connected through another partition board 16 to the other side wall of the dust collecting chamber 2. That is, these partition boards 15 and 16 are to separate the contaminated air to be processed by the dust collectors 3A through 3F from the air decontaminated by the latter. A guide board 17 is connected between the last dust collector 3F and to the other side wall of the dust collecting chamber 2, so as to lead the contaminated air to the dust collector 3F. Of the six dust collectors 3, the first dust collector 3F closest to the air sucking end 2a of the dust collecting chamber 2 is smaller in the area of projection to air stream than the others and is set in parallel with the longitudinal direction (right-to-left direction in Fig. 1 (A) of the dust collecting chamber. The remaining dust collectors 3B through 3F are arranged in such a manner that they form angles (described later) with the longitudinal direction of the dust collecting chamber 2, and they are partly overlapped one another as viewed from the end of the dust collecting chamber 2. The dust collectors 3B through 3E form an inclination angle (α) of 10°, and only last dust collector 3F 5°. The partition board 15 between the first and second dust collectors 3A and 3B includes a part S which is in parallel with the central axis of the dust collecting chamber 2, so that the distance D between the first and second dust collectors 3A and 3B is longer than the distance d between the second and third dust collectors 3B and 3C, the third and fourth dust collectors 3C and 3D, and so forth. In the tunnel dust collecting system thus constructed, the contaminated air in the tunnel is led into the dust collecting chamber through an air sucking inlet 7 at the air sucking end 2a. The contaminated air thus led is distributed uniformly to the dust collectors 3 as indicated by the solid line arrows, where it is decontaminated. The decontaminated air outputted by the dust collectors 3 is supplied into the driveway space la by the air blowers 4 as indicated by the broken line arrows. In the tunnel dust collecting system shown in Fig. 1, the effective air flow area is the sum of the areas of the air inlets of the dust collectors 3, and it is larger about 20% than that in the conventional dust collecting system, because the dust collectors 3 are arranged as if overlapped as was described before; that is, the flow rate of air processed per station is increased as much. Furthermore, since the second to last dust collectors 3B through 3F are so arranged as to form angles with the central axis of the dust collecting chamber as was described before, the contaminated air is distributed along the partition boards 15 substantially uniformly to the dust collectors 3B through 3F although the latter are arranged as if overlapped as viewed from the end of the dust collecting chamber. The area occupied by the first dust collector 3A in the air flow path in the dust collecting chamber 2 is larger than those occupied by the other dust collectors. Therefore, if the first dust collector 3A is equal in the area of projection to air stream to the remaining dust collectors 3B through 3F, then as shown in Fig. 3 contraction flows occur, as a result of which the air stream leaves the partition board 15 to flow over the second dust collector 3B to the third dust collector 3C. This difficulty is eliminated as follows: A relatively small dust collector is employed as the first dust collector 3A to suppress the possibility of occurrence of contraction flows. In addition, the distance D is increased so that the air stream flows to the second dust collector 3B. It has been confirmed through experiments that the distance D should be at least 1.5 times the diameter of the air stream at the air sucking end 2a of the dust collecting. In the dust collecting chamber thus constructed, the distribution of air stream to the dust collectors 3 may be precisely controlled by adjusting the degrees of opening of the outlet dampers of the dust collectors 3 as described below. Fig. 2 is a sectional plan view showing the arrangement of each of the dust collectors 3. The dust collector 3 comprises: inlet dampers 18; a charging section 19; a dust collecting section 20; and outlet dampers 21. The particles such as dust and smoke particles in the contaminated air led into the dust collector 3 through the inlet dampers 18 are charged by the charging section 19, so that they are caught by the dust collecting section 20 to which high voltage is applied by a high voltage generator 22; that is, the air is decontaminated. The air thus decontaminated is allowed to flow out of the dust collector through the outlet dampers 19. When the particles are deposited in the charging section 19 and the dust collecting section 20, compressed air is jetted to remove them therefrom. The inlet dampers 18 and the outlet dampers 21 are mounted on vertical shafts 18a and 21a, respectively, and are turned to open and close the air inlet and the air outlet of the dust collector. When the degrees of opening of the dampers 18 and 21 are decreased, the resistance of the dust collector to the air stream is increased, so that the flow rate of air stream is decreased, and accordingly the air stream is distributed to the other dust collectors as much as the flow rate of air stream has been decreased in the above-described manner. In this case, with the inlet dampers 18 fully opened, the degrees of opening of the outlet dampers 21 are so adjusted that all the dust collectors are uniform in the flow rate of air. If the degrees of opening of the inlet dampers 18 are decreased, then when flowing through the electrode boards in the dust collecting section 20, the decontaminated air stream may be deflected, with the result that the dust collection efficiency is lowered. Thus, it is preferable that only the outlet dampers is adjusted. In the dust collecting chamber, the air stream may be distributed uniformly to the dust collectors by providing guide vanes 26 as shown in Fig. 3. However, it is rather difficult to design the guide vanes most suitably because the guide vanes delicately affect one another depending on the positional relationships between the dust collectors 3. In addition, the provision of the guide vanes may excessively increases the loads of the air blowers 4 (Fig. 1). On the other hand, adjustment of the flow rate of air with the outlet dampers 21 in each dust collector 3 is advantageous in that it will not affect the flow rate of air in the other dust collectors 3. In the tunnel dust collecting system shown in Fig. 1 , a plurality of dust collectors are provided in the dust collecting chamber in such a manner that they are arranged longitudinally of the dust collecting chamber and shifted from one another laterally of the dust collecting chamber (from one side wall of the dust collecting chamber towards the other side wall) as if they were overlapped when viewed from one end of the dust collecting chamber. In the system, the effective air flow area is increased, so that the flow rate of air to be processed per dust collecting system can be increased without increasing its dust collector installation space. Furthermore in the system, the top dust collector is selected to be smaller than the remaining dust collectors, and the distance between the top and second dust collectors is made longer than those between the second and third dust collectors, between the third and fourth dust collector, and so forth, whereby the contaminated air led into the dust collecting chamber can be distributed uniformly to the dust collectors. In addition, the degrees of opening of the outlet dampers at each of the dust collectors are adjusted to finely control the flow rate of air therein.

Claims: A tunnel dust collecting system comprising: a dust collecting chamber (2) formed in the upper space of a tunnel (1) with a ceiling board (5) in such a manner that said dust collecting chamber (2) has one end serving as an air sucking end (2a) and the other end serving as an air supplying end (26); a plurality of electric dust collectors (3A, 3B, 3C, 3D, 3E, 3F); and air blowers (4) in said dust collecting chamber at the air supplying end (23), characterized in that said plurality of electric dust collectors are arranged in said dust collecting chamber (2) in such a manner that said dust collectors are shifted both longitudinally and laterally along said dust collecting chamber; and that all of said dust collectors (3B, 3C, 3D, 3F) except the first one (3A) as viewed from said air sucking end (2a) of said dust collecting chamber (2) are set obliquely with respect to the longitudinal direction of said dust collecting chamber (2) as if partially overlapping one another when viewed from said air sucking end (2b). A tunnel dust collecting system as claimed in claim 1, in which said first dust collector (3A) is smaller in air stream projection area than those of the remaining, and the distance between said first (3A) and second (3B) dust collectors is longer than those between said second (3B) and third (3C) dust collectors, between said third (3C) and fourth (3D) dust collectors, and so forth. A tunnel dust collecting system as claimed in claims 1 or 2, in which each electric dust collector (3A, 3B, 3C, 3D, 3E, 3F) has outlet dampers (21), the degrees of opening of which are adjusted to control the flow rate of air therein.

Inventors: MINOWA YOSHIHIRO, NAKAMURA SHOGO, SASAMOTO TOSHIHARU, MINOWA, YOSHIHIRO, NAKAMURA, SHOGO, SASAMOTO, TOSHIHARU, MINOWA, YOSHIHIRO, C/O FUJI ELECTRIC CO. LTD., NAKAMURA, SHOGO, C/O FUJI ELECTRIC CO. LTD., SASAMOTO, TOSHIHARU, C/O FUJI ELECTRIC CO. LTD.
Applicants: FUJI ELECTRIC CO LTD, FUJI ELECTRIC CO., LTD.
Application year: 1990
Main classification: E21F1
IPC codes: E21F5, E21F1