Abstract:
For conversion of harmful compound in contaminated liquid into harmless compound by use of reactant, a plurality of agitators are arranged in a vertical superposition within a closed agitation chamber and, after the contaminated liquid is charged into the agitation chamber, the agitators are driven for rotation at a high speed in a rage from 10,000 to 18,000 rpm in order to create a field of super critical conditions in which free radicals are liberated from the harmful compound and coupled by the reactant. Neither high temperature heating nor high level pressurization is needed for processing of the contaminated liquid.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to method and unit for processing a contaminated liquid, and more particularly relates to formation of a field of super critical conditions within an agitation chamber containing a liquid contaminated with a harmful compound or compounds such as polychlorinated biphenyl (PCB) unsuited for any chemical reactions under normal conditions for the purpose of liberation and removal of such a compound or compounds. 
     In this specification, the term “a harmful compound” refers to a compound which poses malign influences, in any forms, on healthy human life and is unsuited for any chemical reactions under normal conditions. 
     Further, the term “perforated” encompasses a substantially planar construction which is provided with one or more holes opening in both surfaces of an agitator and/or one or more recesses formed in at least one of both surfaces of an agitator. 
     Conventionally, the following expedients have been generally employed in order to convert a harmful compound, which is unsuited for chemical reactions by use of reactants under normal conditions, into a harmless compound via reactions. 
     One of such expedients is called “separation of super critical water by oxidation”. Here the term “super critical water” refers to a kind of water placed under a condition in which the temperature is 374° C. or higher and the pressure exceeds 22 MPa. Such a water has a property to move actively just like gases to separate a target, i.e. a harmful compound. In practice it is required that the temperature is about 600° C. and the pressure is about 22 MPa. 
     Another of such expedients is called “separation by alkali catalyst”. In the case of this process, hydrogen provider, carbon type catalyst and alkali such as potassium hydroxide are added to a harmful compound, and the mixture is heated at a temperature in a range from 300 to 350° C. under presence of nitrogen in order to eliminate a part of the harmful compound, for example chlorine in the case of PCB. 
     In the case of such conventional expedients, however, it is necessary to carry out the process within a closed environment under high temperature and high-pressure conditions and/or under presence of nitrogen gas. This entails use of a reaction device well resistant to corrosions by high temperature, high pressure and reaction gas. In addition, high level of process control and maintenance of the device are required. For these reasons, the conventional expedients are suited for only batch-type processing but not for continuous processing. Consequently, all of the conventional expedients were not feasible in practice from the viewpoint of economic efficiency. 
     SUMMARY OF THE INVENTION 
     It is thus the primary object of the present invention to enable rapid conversion of a harmful compound into a harmless compound such as dechlorination of PCB under normal temperatures and normal pressures in a continuous mode. 
     In accordance with one aspect of the present invention, an agitation chamber is provided which incorporates two or more horizontal perforated agitators arranged in a vertically spaced superposed positions, a mixed solution of contaminated liquid containing harmful compounds and reactant capable of coupling to free radicals from the compounds is prepared, the mixed solution is charged into the agitation chamber, the agitators are driven for rotation at a speed in a range from 10,000 to 18,000 rpm, and a processed solution is discharged from the agitation chamber. 
     In accordance with another aspect of the present invention, a vertical-type agitation chamber is formed in a substantially closed construction, two or more horizontal perforated agitators are incorporated in the agitation chamber in a vertically spaced superposed arrangement, means are provided for charging into the agitation chamber a mixed solution of a contaminated liquid containing harmful compounds and a reactant capable of coupling to free radicals from the compounds, means are provided for driving the agitators for rotation at a speed in a range from 10,000 to 18,000 rpm, and means are provided for discharging a processed solution from the agitation chamber. 
     The agitator may take the form of either a circular disc or a branched disc. 
     In the system of the present invention of the above-described aspects, high-speed rotation of the agitators causes intense and dynamic frictional contact of the mixed solution with the surfaces of the agitators. This frictional contact generates heat of high temperature (from 230 to 300° C.). In addition, centrifugal force caused by the frictional contact strongly compresses the mixed solution within the holes and/or recesses in the agitators and the mixed solution in the region near the side wall of the agitation chamber, thereby creating a high pressure condition of 22 MPa or higher. Further, due to Bernoulli effect, high speed rotation of the agitators causes a large pressure drop in the mixed solution and such pressure drop causes generation of lots of fine bubbles via cavitation. These fine bubbles are destroyed by shearing force created by the high-speed rotation of the agitators. 
     Combination of the high temperature with the high pressure creates a field of super critical conditions within the agitation chamber. Such conditions induce a radical reaction by which a part of the contaminated liquid is liberated in the form of free radicals. In addition, destruction of the fine bubbles generates super sonic which promotes the above-described radical reaction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional side view of one embodiment of the unit for processing a contaminated liquid in accordance with the present invention, 
     FIG. 2 is a sectional plan view of the unit shown in FIG. 1, 
     FIG. 3 is a plan view of one embodiment of the agitator used for the unit shown in FIGS. 1 and 2, 
     FIG. 4 is a plan view of another embodiment of the agitator used for the unit shown in FIGS. 1 and 2, 
     FIG. 5 is a sectional side view of the other embodiment of the agitator used for the unit shown in FIGS. 1 and 2, 
     FIG. 6 is a plan view of a further embodiment of the agitator used for the unit shown in FIGS. 1 and 2, 
     FIG. 7 is a plan view of a still other embodiment of the agitator used for the unit shown in FIGS. 1 and 2, 
     FIG. 8 is a sectional side view of another embodiment of the unit for processing a contaminated liquid in accordance with the present invention, 
     FIG. 9 is a plan view of the hood usable for said unit, and 
     FIG. 10 is a schematic side view of one example of a plant incorporating the unit of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     One embodiment of the unit for processing a contaminated liquid in accordance with the present invention is shown in FIGS. 1 and 2, in which circular discs are used for the agitators. 
     The unit includes a processing unit  1  of a substantially closed construction and of an octagonal cross-sectional profile. Connections to later described conduits and partition are all sealed properly in a known manner. The interior of the processing unit  1  is divided into an upper cooling chamber  20  and a lower agitation chamber  10  by a horizontal partition  2 . 
     The cooling chamber  20  is used for suppressing rise in temperature within the agitation chamber  10  to be caused by the radical reaction. To this end, the cooling chamber  20  is associated with supply and exhaust conduits  21 ,  22  and the supply conduit  21  is connected to a proper supply source of cooling water not shown. A proper cooling device may be provided between the supply and exhaust conduits  21 ,  22  for constant circulation of the cooling water. 
     A rotary shaft  3  extends vertically thorough the center of the agitation chamber  10  in connection to an outside drive motor  5  via a bearing case  4  arranged in the cooling chamber  20 . The drive motor  5  is properly mounted atop the processing unit  1 . The drive motor  5  is designed to drive the rotary shaft  3  for rotation at a speed from 10,000 to 18,000 rpm. 
     Three sets of circular discs  16  are horizontally and concentrically secured to the rotary shaft  3  in a vertically spaced superposed arrangement. Each circular disc  16  is provided with one or more vertical through holes or one or more recesses  19  formed in at least one surface thereof. In the following description, however, it is assumed that the through holes are formed in the circular disc  16 . The superposed circular discs  16  may be different in diameter. 
     A supply conduit  11  of the mixed solution opens in the agitation chamber  10  near the bottom end thereof. The supply conduit  11  is connected, via a pump  12  and a control valve  13  to a supply source (not shown) of the mixed solution. The supply source contains the contaminated liquid containing a harmful compound and a reactant capable of coupling to free radicals to be liberated from the compound. As an alternative, the supply source may be accompanied with a separate reservoir for such a reactant. 
     An exhaust conduit  17  associated with a control valve  18  opens in the agitation chamber  10  near the top end thereof. A plurality of supply and exhaust conduits  11 ,  17  may be connected to the agitation chamber  10 . 
     A plurality of baffle pieces  14  are secured to the side wall of the agitation chamber  10  with circumferential distribution near the top and bottom ends of the agitation chamber  10 . As best seen in FIG. 2, each baffle pieces  14  is triangular in shape and projects toward the center of the agitation chamber  10 . 
     At positions between adjacent circular discs  16 , deflector rings  15  are secured to the sidewall of the agitation chamber  10 . As shown in FIG. 2, the inner edge of each deflector ring  15  extends toward the center of the agitation chamber  10  beyond the outer edge of the associated circular discs  16 . 
     In operation, the mixed solution is charged into the agitation chamber  10  via the supply conduit  11 . As the circular discs  16  are driven for high speed rotation, the mixed solution first tends to flow upwards from the bottom region in the chamber while convoluting about the center of the agitation chamber  10 . The upward flow of the mixed solution is, however, hampered by the lowest deflector ring  15  and directed inwards along the surface of the lowest circular disc  16 . This deflection of flow results in increased dynamic contact between the mixed solution and the adjacent circular discs  16 . 
     Next, the mixed solution changes its flow direction outwards due to centrifugal force generated by the high-speed rotation of the circular discs  16 . On collision against the sidewall of the chamber, the mixed solution again tends to flow upwards. This upward flow is hampered by the next deflector ring  15  and the mixed solution again flows towards the center of the chamber. 
     While repeating this process, the mixed solution gradually flows upwards within the agitation chamber  10  while convoluting. During this process, the convoluting mixed solution is directed towards the center of the chamber by the baffle pieces  14  to further increase its dynamic contact with the circular discs  16 . 
     When the agitation chamber  10  is provided with neither the baffle pieces nor the deflector rings, the mixed solution charged into the agitation chamber  10  would flow directly upwards while convoluting along the side wall of the chamber due to the centrifugal force, thereby reducing dynamic contact with the circular discs  16 . The baffle pieces  14  and the deflector rigs  15  are used to avoid such an undesirable situation. 
     As the circular discs  16  rotate at a high speed under increased dynamic contact with the mixed solution, dynamic friction between the mixed solution and the circular discs generates heat of high temperature from 230 to 300° C. or higher. Concurrently with this process, the centrifugal force generated by the high-speed rotation of the circular discs strongly compresses the mixed solution against the sidewall of the agitation chamber  10 , thereby resulting in significant rise in pressure of the mixed solution (higher than 22 Mpa). Such rise in pressure occurs also in the holes  19  in the circular discs  16 . That is, the mixed solution within each hole  19  is strongly compressed against the sidewall of the hole  19  remote from the center of the chamber. In addition, the pressure of the mixed solution drops greatly due to Bernoulli effect following the high-speed rotation of the circular discs  16  and lots of fine bubbles arm generated via cavitation. These bubbles are destroyed by the shearing force generated by the high-speed rotation of the circular discs  16  to generate super sonic speed which promotes rise in pressure of the mixed solution. 
     Due to the combined effect of the high temperature caused by frictional heat and the high pressure caused by centrifugal force, a field of super critical conditions is created within the agitation chamber  10  and the radical reaction occurs to liberate a part of the harmful compounds contained in the contaminated liquid in the form of free radicals. The free radicals are coupled to the reactant to convert the harmful compounds into harmless compounds. Destruction of the fine bubbles generates super sonic speed which well promotes the above-described radical reaction. 
     Thus, processing of the mixed solution is completed and processed solution flows upwards near the top end of the agitation chamber  10  while convoluting so as to be discharged outside the processing unit  1  via the exhaust conduit  17 . 
     One example of the design of the processing unit is shown in Table 1. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Specification of a processing unit 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 capacity of agitation chamber 
                 20 liters 
               
               
                   
                 diameter of circular disc 
                 280 mm 
               
               
                   
                 thickness of circular disc 
                 8 mm 
               
               
                   
                 number of circular disc 
                 4 
               
               
                   
                 gap between discs 
                 25 mm 
               
               
                   
                 diameter of hole 
                 10˜20 mm 
               
               
                   
                 number of hole 
                 56 
               
               
                   
                 surface percentage of holes 
                 24% 
               
               
                   
                 arrangment of holes 
                 12 radical directions 
               
               
                   
                 center angle 
                 30 degrees 
               
               
                   
                   
               
             
          
         
       
     
     The system of this invention is applicable to processing of contaminated liquids containing various harmful compounds. Most typically, the system is well suited for processing of a contaminated liquid containing PCB (polychlorinated biphenyl). In this case, a solid sodium is used for the reactant. As stated above, the radical reaction liberates chlorine in PCB as free radicals which reacts with sodium to produce sodium chloride. That is, harmful PCB is converted into harmless sodium chloride. Thus, the processed solution contains biphenyl and sodium chloride can be discharged outside the system without any detriment to healthy human life. 
     The system of the present invention is additionally applicable to processing of industrial wastes such as liquid isolation oils for capacitors and exhaust oils. In the case of contaminated soils, proper liquidation is employed for processing by the system of the present invention. 
     Another embodiment of the circular disc usable for the processing unit of the present invention is shown in FIG. 3, in which a circular disc  16  is provided with a plurality of vanes  161  secured onto at least one of its upper and lower surfaces near the outer edge. Each vane  161  is arranged with some bias with respect to the radial direction of the disc. As the circular discs  16  rotate at a high speed, the vanes  161  force the mixed solution near the surface or surfaces of the disc to flow radially outwards to enhance the centrifugal effect and the shearing effect on the fine bubbles. 
     The other embodiment of the circular disc  16  is shown in FIG. 4, in which a plurality of annular vanes  162  are secured onto at least one of its upper and lower surfaces. The annular vanes  162  have different diameters and arranged concentrically around the rotary shaft  3 . As the circular discs  16  rotate, the mixed solution is compressed against the inner wall of each annular vane  162  on the side remote from the center of the disc to promote its pressure rise. Shearing of the fine bubbles generated by cavitation is also reinforced. 
     The other embodiment of the circular disc  16  is shown in FIG. 5, in which the circular disc  16  has a hollow construction. More specifically, the circular disc  16  is internally provided an annular chamber  163  formed around the center thereof, which communicates with outside via holes  19 . As the disc  16  rotates at a high speed, the mixed solution outside the disc flows into the annular chamber  163  and strongly compressed against inner wall on a side remote from the center of the disc to promote rise in pressure. 
     Although circular discs are used for the agitator in the foregoing embodiments of the present invention, various different types of agitators are usable for the present invention. FIG. 6 shows a three-branched disc  36  whereas FIG. 7 shows an eight-branched disc  37 . Since the disc as the agitator is subjected to high speed rotation, the shapes and the arrangement of the branches need to be designed carefully so as to assure good dynamic balance during rotation. 
     As the discs rotate at a high speed, the branches strongly agitate the mixed solution within the agitation chamber  10  for increased pressure rise and, concurrently, furiously destroy the fine bubbles by shearing effect for promoted liberation of free radicals. 
     Another embodiment of the unit for processing contaminated liquid in accordance with the present invention is shown in FIG. 8, which provides increased cooling effect of the agitation chamber. Parts substantially same as those in the embodiment show in FIG. 1 are indicated with same reference numerals. 
     A processing unit  1  is divided by a horizontal partition  2  into upper and lower cooling chambers  20   a ,  20   b . Like the embodiment in FIG. 1, the cooling chambers are associated with supply and exhaust conduits  21 ,  22  of cooling water. The two cooling chambers may communicate each other. 
     A hollow cylindrical case  6  extends into the lower cooling chamber  20   b  to internally define an agitation chamber  10 . This agitation chamber  10  is mostly embraced by the lower cooling chamber  20   b  for increased cooling effect. A supply conduit  11  of mixed solution opens in the bottom section of the agitation chamber  10  while an exhaust conduit  17  of processed solution opens near the top end of the agitation chamber  10 . 
     A bearing case  4  secured to the processing unit  1  rotatably holds a rotary shaft  40  projecting centrally into the agitation chamber  10 . The rotary shaft  40  has a hollow construction and provided with an axial hole  41  opening at the upper end. The rotary shaft  40  is connected in operation to a drive motor  5  secured atop the processing unit  1 . 
     In the agitation chamber  10 , the lower section of the rotary shaft  40  holds circular discs  16  in an arrangement same as that in the embodiment shown in FIG.  1 . The bottom end of the rotary shaft  40  securely holds a conical hood  44  which converges downwards. As shown in FIG. 9, the inner surface of this hood  44  is provided with a plurality of vanes  45  which are somewhat biased in arrangement from the radial direction of the hood  44 . 
     A supplementary cooling chamber  20   c  is defied by a hollow case  7  whilst surrounding the top end of the rotary shaft  40 . Within the cooling chamber  20   c , the top end of the rotary shaft  40  securely holds a conical hood  46  which converges upwards. A supply conduit  42  of cooling water connected to a given supply source (not shown) extends downwards through the axial hole  41  in the rotary shaft  40  and opens at the bottom end into the axial hole  41 . The cooling chamber  20   c  is associated with one or more exhaust conduit  43  of the cooling water. 
     In operation, cooling water charged into the cooling chambers  20   a ,  20   b  is discharged outside the system via the exhaust conduits  22  while cooling the agitation chamber  10  and the bearing case  4 . Cooling water introduced into the axial hole  41  of the rotary shaft  40  flows upwards while cooling the rotary shaft  40 . At the top end of the axial hole  41 , it overflows into the supplementary cooling chamber  20   c  and is spattered radially outwards so as to be discharged outside the system through the exhaust conduit  43 . The mode of flow of the mixed solution charged into the agitation chamber is substantially same as that in the embodiment shown in FIG.  1 . 
     One example of a batch-type plant incorporating the processing unit of the present invention is shown in FIG.  10 . The processing unit  101  is connected on the upstream side to a reservoir tank  102  of contaminated liquid via a mixing unit  104  for addition of reactant. On the downstream side, the processing unit  101  is connected to a reservoir tank  108  of processed solution via a cooling unit  107 . The processing unit  101  is further connected to an activated carbon unit  110  via a cooling unit  109 . 
     In accordance with the preset invention, successful creation of the field of super critical conditions enables continuous processing of contaminated liquid under normal temperature and pressure conditions. It is not required for the processing to utilize burning steps and to employ advanced preparation of high temperature and/or pressure conditions. The system accompanies no production of undesirable arisings, harmful ashes thereby assuring safe operation of the system. 
     Possibility of continuous processing at high operation efficiency allows large scale processing at a small plant, thereby reducing the operation and installation costs greatly. Since the system is an entirely closed construction, it produces substantially no harmful substances to be discharged outside the system.