Abstract:
A apparatus for crushing waste metal products includes a rotor having a crushing device on a periphery thereof and a casing enclosing the rotor. The casing has an inlet and an outlet for products to be crushed. An exhaust gas from the casing is partly returned to the inlet of the casing by a circulator. The rest of the exhaust gas is ventilated and processed by an exhaust processor. An oxygen concentration is monitored in a gas pathway of the circulator to control the gas concentration in the casing. If the oxygen concentration is high, a water shower sprays into the casing.

Description:
[0001]    This application is a Divisional of Ser. No. 09/538,895, filed Mar. 30, 2000. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a rotary crusher for crushing waste metal products such as, for example, compressors, air conditioners or refrigerators, particularly those containing combustibles. More particularly, the invention relates to the rotary crusher in which exhausted smoke can easily be treated and in which gas concentration can be precisely monitored to prevent an explosion.  
           [0004]    2. Description of the Prior Art  
           [0005]    [0005] 
           [0006]    In the conventional recycling of wasted metal products including iron and copper, the products are broken into adequate size and then the iron and copper materials are separated therefrom by, for example, a magnetic separation technique. In crushing the waste metal products, a rotary crusher is generally used to facilitate the subsequent separation process. The rotary crusher has a rotor with hammers mounted on its periphery so that the waste products can be crushed while being compressed by the hammers.  
           [0007]    If the crusher breaks oil-containing metal wastes such as compressors, smoke arises in the crusher. The smoke travels having ridden on an airflow generated by rotation of the rotor and then emerges from an outlet of the crusher together with crushed pieces. Therefore, an exhaust processor having a ventilation fan is generally placed near the outlet of the crusher in order to collect the smoke.  
           [0008]    When metal wastes containing a flammable material such as oil is crushed, explosion may occur. Accordingly, the crusher needs an explosion-proof system. Hitherto, the explosion-proof system is implemented by, for example, blowing inert gas or water vapor into the crusher according to the concentration of oxygen in the crusher that is detected by an oxygen sensor to maintain the oxygen concentration under the explosion limit. Such an explosion-proof system is disclosed in, for instance, Japanese laid-open patent publication H6-226137.  
           [0009]    However, the conventional rotary crusher has the following drawbacks:  
           [0010]    (1) In order to vent the exhausted smoke from the crusher completely, the inlet capacity of the ventilation fan must be greater than the exhaust capacity of the crusher. Accordingly, increase of the exhaust capacity of the crusher by, for example, increasing the speed of rotation of the rotor results in necessity of use of the suction ventilation fan having a higher inlet capacity. This in turn increases the size of the exhaust processor. Also, the exhaust processor with such a high inlet capacity fan may draw in light-weight pieces such as, for example, insulating paper or copper together with the smoke. The pieces caught by the fan do not only bring about clogging of the fan, but also reduce the waste recycling efficiency.  
           [0011]    (2) The concentration of oxygen or flammable gas near a crushing point should be precisely monitored by, for example, an oxygen sensor to prevent explosion from taking place during crushing. When the oxygen sensor is placed in the crusher, the sensor should be disposed in a recess or protected with a cover to avoid its breakdown by collision with the crushed pieces. However, since the air stream is apt to stay in the recess or in the cover, the gas concentration tends to become uneven. Therefore, in the conventional crusher, an accurate measurement of the oxygen concentration has been difficult to achieve.  
           [0012]    (3) When the explosion-proof means such as introduction of inert gas or water vapor is employed, pipes and nozzles must be installed in the crusher to introduce the gas. This complicates the construction of the crusher.  
         SUMMARY OF THE INVENTION  
         [0013]    It is accordingly an object of the present invention to provide an apparatus, and a method of operating such apparatus, for crushing products containing flammable material, in which an exhausted smoke can easily be processed and in which gas concentration can be precisely monitored to prevent an explosion.  
           [0014]    Another object of the present invention is to provide a recycling system that has a high recycling efficiency and that is safely operable.  
           [0015]    In accordance with a first aspect of the present invention, a crushing apparatus comprises:  
           [0016]    a rotor having a crushing means on a periphery thereof;  
           [0017]    a casing for enclosing said rotor, the casing having an inlet and an outlet for materials to be crushed;  
           [0018]    exhaust-circulating means for returning a part of exhaust gas from the outlet to the inlet of said casing; and  
           [0019]    exhaust-processing means for ventilating and processing the exhaust gas exhausted from said casing.  
           [0020]    The advantage of this invention is the ability to reduce the exhaust capacity of the crusher casing. This downsizes the exhaust-processing section of the apparatus and prevents the exhaust-processing section from sucking light-weight crushed pieces, thereby allowing a smooth operation of the crushing apparatus.  
           [0021]    Preferably, the crushing apparatus comprises a gas sensor disposed in a gas pathway of said exhaust-circulating means. This arrangement makes it possible to measure accurately a gas concentration in the crusher casing.  
           [0022]    Further, the crushing apparatus preferably comprises water-supply means for supplying water according to an output signal from said gas sensor in the gas pathway or near a terminal of the gas pathway of said exhaust-circulating means. By arranging the water supplier in such a manner, an explosion during crushing can be prevented with simple construction.  
           [0023]    More preferably, the crushing apparatus comprises a crushed-piece sensor for detecting pieces sucked by said exhaust-processing means, an outlet smoke sensor for detecting leaked smoke without being sucked by said exhaust-processing means, and an inlet smoke sensor for detecting leaked smoke from the inlet of said casing of the apparatus. These sensors facilitate smooth operation of the crushing apparatus.  
           [0024]    In accordance with another aspect of the present invention, method of operating the crushing apparatus is characterized in that:  
           [0025]    if the crushed-piece sensor detects the crushed pieces, an inlet capacity of said exhaust-processing means is reduced until said crushed-piece sensor does not detect the pieces, but;  
           [0026]    if the outlet-smoke sensor detects the smoke, a circulating capacity of said exhaust-circulating means is increased to within a range in which said inlet-smoke sensor does not detect the smoke.  
           [0027]    In this manner, the smoke leakage from the inlet and outlet of the crusher casing is minimized, so that suction of the crushed pieces by the exhaust-processing means is prevented.  
           [0028]    Preferably, if the gas concentration measured by the gas sensor is higher than a predetermined value, the water-supply means operates. This infallibly prevents an explosion which would otherwise occur in the crusher.  
           [0029]    More preferably, if the gas concentration measured by the gas sensor is still higher than the predetermined value after a predetermined period from the start of operation of the water-supply means, the crushing apparatus stops operating. This further lowers the possibility of occurrence of the explosion.  
           [0030]    In accordance with still another aspect of the present invention, a waste-recycling system comprises:  
           [0031]    a crushing apparatus of the present invention;  
           [0032]    a transport means for transporting crushed pieces exhausted from said crushing apparatus; and  
           [0033]    a magnetic separator disposed above said transport means to collect ferrous components from the crushed pieces. In the waste-recycling system, suction of the crushed pieces by the exhaust-processing means is prevented. Accordingly, the waste-recycling system is smoothly operative and has a high recycling efficiency. Also, since a precise forecast of an explosion is possible, the system can be operated safely. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]    The above and other object and features of the present invention will become more apparent from the following description of a preferred embodiment thereof with reference to the accompanying drawings, throughout which like parts are designated by like reference numerals, and wherein:  
         [0035]    [0035]FIG. 1 is a schematic diagram of a waste-recycling system including a rotary crusher of the present invention;  
         [0036]    [0036]FIG. 2 is a block diagram showing a control system for controlling ventilating fan and an exhaust-circulating fan;  
         [0037]    [0037]FIG. 3 is a flowchart showing a controlling procedure of the exhaust-ventilation fan and the exhaust-circulating fan;  
         [0038]    [0038]FIG. 4 is a block diagram showing a control system for controlling a water-shower device; and  
         [0039]    [0039]FIG. 5 is a flowchart showing a controlling procedure of the water-shower device. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0040]    The application is based on an application No. 11-281378 filed in Japan, the content of which is incorporated herein by reference.  
         [0041]    Referring to FIG. 1, a waste-recycling system  1  includes a feeder  4 , a rotary crusher  10 , a transporter  34  which is, for example, a vibrating conveyer, magnetic separators  36  and  37 , and a receiving box  38 . The waste-recycling system  1  operates as follows. First, the feeder  4  supplies metal wastes  32  such as compressors to the rotary crusher  10 , in which the wastes  32  are crushed into pieces  40 . The transporter  34  transports the crushed pieces  40  discharged from the crusher  10 , and the magnetic separators  36  and  37  magnetically separate the pieces  40  into ferrous and non-ferrous elements. The box  38  receives the non-ferrous pieces that are not salvaged by the magnetic separators  36  and  37 .  
         [0042]    The crusher  10  includes a rapidly rotating rotor  12  having breaking means  14  such as hammers or cutters on its periphery; a casing  16  enclosing the rotary crusher  10 ; an exhaust processor  18 ; and an exhaust circulator  25 . The metal wastes  32  supplied from an inlet  16   a  travel through an injection chute  16   b  towards the rotor  12 . The wastes  32  are compressed and shorn into pieces  40  between the rotating hammers  14  and fixed cutters (not shown) that are arranged on the casing  16  around the rotor  12 . The crushed pieces  40  pass through a gate  16   c  and an ejection chute  16   d  and then emerge from the outlet  16   e.    
         [0043]    When the metal wastes (e.g. a compressor)  32  are oil-loaded products such as compressors, oil in the wastes  32  must be removed before they are thrown into the crusher  10 . However, the oil sticking to and/or wetting inner wall surfaces of the metal wastes is difficult to remove completely, and therefore, a small quantity of oil usually remains in the compressor  32  when the latter is supplied to the crusher  10 .  
         [0044]    If the wastes include oil even in a small quantity, smoke is generated by impact and friction that occur during crushing. In the rotary crusher  10 , a high-speed rotation of the rotor  12  carrying the hammers  14  produces an air stream flowing from inlet  16   a  to outlet  16   e . By the air stream, the generated smoke is exhausted from outlet  16   e  together with the crushed pieces  40 .  
         [0045]    In order to vent and process the smoke, the exhaust-processor  18  is installed near the outlet  16   e . The exhaust processor  18  draws in the smoke via a duct  19  with a ventilation fan  20  to process the smoke in an exhaust processing section  22  by, for example, adsorption. To absorb the smoke completely, an inlet capacity of the ventilation fan  20  must be greater than an exhaust capacity of the crusher  10 . However, excessive increase of the inlet capacity of the exhaust processor  18  results in inhaling of light-weight pieces such as insulated papers or cupric scraps by the processor  18 . If a large amount of light-weight pieces are drawn in, a filter  21  in the exhaust processor is quickly clogged and, as a result, requires frequent replacement or cleaning. This prevents smooth operating of the crusher  10  and lowers its recycling efficiency.  
         [0046]    In order to substantially eliminate such an unfavorable influence, it is preferable to lower the exhaust capacity of the crusher  10 . However, the exhaust capacity of the crusher  10  depends on a rotating rate of the hammer  14 , which rate relates to a crushing ability of the crusher  10 . Therefore, the exhaust capacity cannot be simply decreased. According to the present invention, a part of the exhaust from the casing  16  is returned to the inlet side of the rotor in the casing  16  by an exhaust (circulator an exhaust-circulating means)  25 , so that the exhausting capacity of the crusher  10  is reduced while keeping its crushing ability. For example, a circulation duct  24  having circulation fan  26  is connected to the ejection chute  16   d  and the injection chute  16   b . The circulation duct  24  returns a part of the exhaust from the ejection chute  16   d  to the injection chute  16   b . This reduces the exhaust capacity of the crusher  10 .  
         [0047]    The circulation duct  24  is preferably placed above the gate  16   c  so that the crushed pieces do not irrupt into the duct  24 . If the circulation duct  24  and the inhalation duct  24  are disposed so as to cooperate with each other in inhaling the exhausted smoke, different arrangements from that in FIG. 1 may be employed. For example, the circulation duct  24  may be connected to the inhalation duct  19  before the ventilation fan  20  instead of being connected to the ejection chute  16   d . Further, the inhalation duct  19  may be connected directly to the ejection chute  16   d  instead of being placed adjacent to the outlet  16   e.    
         [0048]    In order to prevent an explosion that may occur while crushing wastes including flammable material such as oil, the crusher  10  of this embodiment has an oxygen sensor (a gas sensor)  28  in the gas pathway of the circulation duct  24  to monitor an oxygen concentration in the circulation duct  24 . Alternatively, a gas sensor sensing a concentration of flammable material may be used. The oxygen sensor  28  can measure an accurate concentration of the oxygen, because the airflow does not stay in the circulation duct  24  and the oxygen sensor does not have a protecting cover on it. Since the air passing through the circulation duct  24  is blown into the casing  16 , the oxygen concentration in the duct  24  reflects that in the casing  16 . Preferably, the circulation duct  24  is connected near the point where the hammers  14  initially contact with the fixed cutter so that the oxygen concentration in the circulation duct  24  truly reflects the oxygen concentration near the first impacting point of the hammers  14 . Since the explosion is apt to occur at that first impacting point, the explosion occurrence may be precisely predicted by monitoring the oxygen concentration at that point. When the oxygen concentration in the circulation duct  24  increases over a limit value that is predetermined in reference to the lowest possible concentration oxygen at which the flammable material may explode, a water-shower device (a water-supply means)  30  starts to spray water. The wind generated by the circulation fan  26  carry the sprayed water into the casing  16  to rise the water concentration. Increase of the water concentration in the casing  16  lowers the oxygen concentration therein. If the oxygen concentration is lowered under the limit value corresponding to the lowest possible concentration oxygen at which the flammable material may explode, the explosion will not occur. As long as the wind by the fan  26  can carry the water into the casing  16 , the water shower  30  may be disposed at different places. For example, the shower  30  may be placed near the terminal of the circulation duct  24 . By using the water shower  30 , the water concentration in the casing  16  can be controlled without installing pipes and nozzles for introducing the water vapor in the casing  16 .  
         [0049]    Hereinafter, an example of an operating method of the rotary crusher  10  according to the present invention will now be described. First, the controlling method of the ventilation fan  20  and the circulation fan  26  to minimize a smoke leak from the outlet  16   e  is described. FIG. 2 is a block diagram showing a controlling system for controlling the ventilation fan  20  and the circulation fan  26 . A controller  46  is electrically connected to a crushed-piece sensor  23  for detecting pieces stuck on the filter  21  in the exhaust processor  18 ; an inlet-smoke sensor  42  for detecting leaked smoke from the inlet  16   a  of the casing  16 ; and an outlet-smoke sensor  44  for detecting smoke leaked from the outlet  16   e  of the casing  16  that has not been inhaled by the exhaust processor  18 . For example, a photo sensor may be utilized as the crushed-piece sensor  23 , the inlet-smoke sensor  42  or the outlet-smoke sensor  44 .  
         [0050]    [0050]FIG. 3 is a flowchart showing the controlling method of the ventilation fan  20  and the circulation fan  26 . At step S 1 , the crusher  10  starts operating, and the crushed-piece sensor  23 , the inlet-smoke sensor  42  and the outlet-smoke sensor  44  are activated. At step S 2  and step S 3 , the circulation fan  26  and the ventilation fan  20  start operating, respectively. At step S 4 , the determination is made whether the smoke leaks or not from the outlet  16   e  by signals from the outlet-smoke sensor  44 . If the smoke has not been detected, the procedure advances to step S 7 , and if the smoke has been detected, the procedure advances to step S 5  at which the rotation speed of the ventilation fan  20  is increased by a predetermined value. At subsequent step S 6 , if the smoke is still detected, the procedure returns to step S 5 , while if the smoke is no longer detected, the procedure advances to step S 7 .  
         [0051]    At step S 7 , in order to prevent the exhaust processor  18  from inhaling light-weight crushed pieces such as insulation sheets and cupric scraps, the determination is made whether crushed pieces are stuck or not on the filter  21  in the exhaust processor  18 . If no crushed piece is detected, the procedure advances to step S 9 . In contrast, if the crushed piece has been detected, the procedure advances to step S 8  at which the rotation speed of the ventilation fan  20  is reduced by a predetermined value. The step S 7  and the step S 8  are repeated until new sticking of the crushed pieces is no longer detected.  
         [0052]    At step S 9 , the determination is made again whether the smoke leaks or not from the outlet  16   e . If the smoke has not been detected, the procedure returns to step S 4 , while if the smoke has been detected, the procedure advances to steps S 10 ˜S 14  at which the smoke leakage from the outlet  16   e  is suppressed by adjusting the rotation speed of the circulation fan  26 .  
         [0053]    Steps S 10 ˜S 14  will be described in detail. First, at step S 10 , the rotation speed of the circulation fan  26  is increased by a predetermined value. At subsequent step S 11 , if the smoke leakage from the outlet  16   e  is still detected, the procedure returns to step S 10 , while if the smoke leakage is no longer detected, the procedure advances to step S 12 . At step S 12 , the determination is made whether the smoke leaks or not from the inlet  16   a  by the inlet-smoke sensor  42 . If the smoke is not detected, the procedure returns to step S 4 , while if the smoke is detected, the procedure advances to step S 13  at which the rotation speed of the circulation fan  26  is reduced by a predetermined value. At subsequent step S 14 , if the smoke leakage from the inlet  16   a  is still detected, the procedure returns to step S 13 , while if the smoke leakage is not detected the procedure returns to step S 4 . The reason why judgement is made of the presence of the smoke leakage from the inlet  16   a  is that excess returning of the exhaust to the inlet side of the casing  16  may cause a backflow in the casing  16   a  which results in smoke leakage from the inlet  16   a.    
         [0054]    By operating the crusher  10  in this manner, the smoke leakage from the inlet  16   a  and the outlet  16   e  can be minimized while preventing the inhaling of the light-weight pieces by the exhaust processor  18 .  
         [0055]    The controlling method of the water-shower device for preventing an explosion in the rotary crusher  10  will be described. FIG. 4 is a block diagram showing a control system for controlling the water-shower device and other devices. A controller  46  is electrically connected to the oxygen sensor  28 , the crusher  10 , an alarm  29  and the water-shower device  30 . A power supplier  45  supplies electric power to all of these devices.  
         [0056]    [0056]FIG. 5 is a flowchart showing the controlling method of the water-shower device  30  and other devices. First, at step S 21 , the rotary crusher  10  starts operating and the oxygen sensor  28  is activated. At step S 22 , the oxygen concentration in the circulation duct is determined. If the oxygen concentration is less than 5%, monitoring of the oxygen concentration is continued. In contrast, if the oxygen concentration is over 5%, the procedure advances to step S 23 , at which the alarm  29  is activated, and subsequently advances to step S 24  at which the water-shower device  30  starts spraying. The spraying of the water increases the water concentration in the crusher  10  to reduce the oxygen concentration therein relatively.  
         [0057]    When a predetermined time has passed from the operation start of the water-shower  30 , the procedure advances to step S 25 . At step S 25 , if the oxygen concentration in the circulation duct  24  has been reduced under 5%, the procedure advances to step S 26  at which the water-shower device stops spraying and further advances to step S 27  at which the alarm  29  stops. Then, the procedure returns to step S 22  at which the monitoring of the oxygen concentration is continued. In contrast, if the oxygen concentration has not been reduced under 5% at step S 25 , the procedure advances to step S 28  at which the crusher  10  stops operating because the possibility of explosion is quite high.  
         [0058]    In this manner, the oxygen concentration in the circulation duct  10  is kept under 5%, so that the atmosphere in the crusher  10  is kept out of an explosion region of the flammable gas generated from oil. The explosion threshold of the oxygen concentration depends on the kind of the flammable gas. Accordingly, the limit value of the oxygen concentration (in this example, 5%) must be adjusted according to the kind of oil in the wastes  32 . When a flammable gas sensor is employed instead of the oxygen sensor  28 , a similar control method can be applied. In such a case, the limit value of the flammable gas concentration is determined according to the explosion limit of the flammable gas.  
       EXAMPLE  
       [0059]    In the rotary crusher shown in FIG. 1, an inverter-driven fan having a capacity of 130 M 3 /min and a head 630 mmAq was adopted as the ventilation fan  20 . Varying the specification of the circulation fan  26 , the change of gas capacity at the inlet  16   a  and the outlet  16   e  was measured. Also, the change of the driving frequency of the ventilation fan  20  required to inhale all of the smoke exhausted from the outlet  16   e  was measured.  
       Comparative Example  
       [0060]    When the circulation fan  26  was stopped and the circulation duct  24  was closed, the gas capacity at the inlet  16   a  and the outlet  16   e  was 16 M 3 /min and 59 M 3 /min, respectively. The inverter frequency of the ventilation fan  20  required to inhale all the smoke was 50 Hz.  
       Example 1  
       [0061]    When the capacity and head of the circulation fan was 70 M 3 /min and 50 mmAq, the gas capacity at the inlet  16   a  and the outlet  16   e  was reduced to 13.6 M 3 /min and 44 M 3 /min, respectively. The inverter frequency of the ventilation fan to inhale all the smoke was reduced to 45 Hz.  
       Example 2  
       [0062]    When the capacity and head of the circulation fan was 125 M 3 /min and 35 mmAq, the gas capacity at the inlet  16   a  and the outlet  16   e  was reduced to 12 M 3 /min and 39 M 3 /min, respectively. The inverter frequency of the ventilation fan to inhale all the smoke was reduced to 35 Hz.  
         [0063]    These results are summarized in Table 1. In Table 1, the parenthesized values indicate a percentage expression of the gas capacity and the inverter frequency when those in the comparative example are taken as 100%.  
                                                         TABLE 1                                               Inverter                       Freq. of           Specification of   Gas Capacity   Gas Capacity   Inhalation           Circulation Fan   at Inlet   at Outlet   Fan                                    Comparative    0 M 3 /min     16 M 3 /min   59 M 3 /min   50 Hz       Example    0 mmAq   (100%)   (100%)   (100%)       Example 1    70 M 3 /min   13.6 M 3 /min   44 M 3 /min   45 Hz           50 mmAq    (85%)    (75%)    (90%)       Example 2   125 M 3 /min     12 M 3 /min   39 M 3 /min   35 Hz           35 mmAq    (75%)    (60%)    (70%)                  
 
         [0064]    Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted here that various changes and modifications will be apparent to those skilled in the art. Therefore, unless such changes and modifications otherwise depart from the spirit and scope of the present invention, they should be construed as being included therein.