MXPA98004070A - Ventilation system for electrolytic cell - Google Patents

Abstract

An electrowinning cell comprised of a tank;an electrolytic solution within the tank defining a solution surface at a predetermined level within the tank;a plurality of flat metallic electrode plates, each of the plates having a support beam along an edge thereof;a support assembly disposed outside the tank for supporting a plurality of the electrodes by the support beams, the support assembly dimensioned to position the electrodes in side-by-side, spaced apart, parallel relationship with a lower portion of the electrodes immersed in the electrolytic solution and an upper portion disposed above the solution surface, the upper portions of the electrodes and the solution surface forming parallel channels extending from one side of the tank to a second side of the tank;a plurality of apertures formed in the tank wall along the one side of the tank, the apertures being disposed above the solution surface and positioned wherein at least one of the plurality of apertures is located between an adjacent pair of the electrodes;a blower and manifold assembly connected to the plurality of apertures for creating gas flow through the plurality of apertures, the blower and manifold assembly dimensioned to create a stream of gas through the channels across the solution surface;an elongated slot formed in the tank wall along the second side of the tank, the slot disposed above the solution surface;and an exhaust blower and manifold assembly for creating a suction through the slot to create a drop in gas pressure opposite the apertures.

Description

* VENTILATION SYSTEM FOR AN ELECTROLYTIC CELL Field of the Invention The present invention relates generally to ventilation systems and, more particularly, to a ventilation system for an electrolytic cell for copper electrolytic extraction. BACKGROUND OF THE INVENTION It is well known that an exceptionally pure form of copper can be obtained from copper dissolved in a sulfuric acid solution through an electrolytic extraction process. An electrolytic extraction process uses the known technique of metallic electrodeposition from an electrolytic solution on a cathode. Modern electrolytic extraction typically takes place in large nonconducting tanks containing copper sulfate dissolved in a sulfuric acid solution. A plurality of anodic and cathodic plates parallel and together are ™ 20 are suspended in the sulfuric acid solution, where a portion of the plates extend above the upper surface of the acid solution. The cathodes and anodes are alternately arranged such that each cathode is disposed between two anodes. The anodes and cathodes are connected to a source of sufficient electrical energy to cause electrodeposition to occur. HE is well aware of the use of said process to form either copper plates or copper powder based on the concentration of the copper in the solution and the current densities applied to the plates. During the electrodeposition process, oxygen is released on the surface of the anodic plates. The gas forms small bubbles that rise to the top of the acid solution. On the upper surface of the acid solution the * gas bubbles burst and create an acid mist above the tank. This acid mist represents not only a danger to the health of the workers in the area, but also creates a corrosive environment for the electrical equipment and connections necessary to electrically energize the plates, as well as for the mechanical aerial equipment that is required to insert and remove the cathodes to recover the deposited copper. In this regard, due to the structural material required to insert and remove the cathode plates, conventional air ventilation hoods are not practical for removing acid mist. In this regard, any type of cover that interferes with access to the cells to remove or replace the cathodes is not desirable. * The use of large mass ventilation systems has been known to remove and circulate air through the building structure, conventionally referred to as the tank building, in which said electrolytic extraction cells are located. As will be appreciated, extremely large and expensive ventilation systems are required to remove and circulate sufficient air to meet environmental standards. Even then, the workers inside the tank building are still exposed to acid mist, although at lower levels, and such systems do not prevent the mist from depositing on the 20 surfaces that exist within the structure before it can be removed from the installation. In this regard, such ventilation systems do not really solve the problem of acid mist, but simply reduce their levels within a facility. The suppression of this mist has also been known using foam or floating balls of coalescence, which float on the surface of the acid bath. Foam and floating balls theoretically prevent air bubbles from bursting when they reach the surface of the acid bath, thus reducing the mist generated by the tank. Although these systems reduce acid mist, they do not completely eliminate the problem and present problems in their own right. same. In this regard, when copper powder is formed, the particulate copper formed inside the tank has a tendency to adhere to the foam and the coalescence balls, forming possible short circuits between the adjacent anode and the cathode plates. In addition, the collection of gaseous fog within the foam and balls creates the potential for gas explosions. It is therefore desirable to provide a method for the venting of an electrolysis tank, which overcomes the above disadvantages, also eliminating the environmental and corrosive hazard of the acid mist without undue expense and without interfering with tank operations. The present invention therefore provides a ventilation system for an electrolytic cell, which suppresses and removes acid mist on the surface of the tank without obstructing access to the tank and without the use of foams or coalescence balls. In addition, no foreign objects or impurities such as those mentioned above are added to the acid solution. Objects of the Invention According to the present invention, a ventilation system is provided for an electrolytic extraction cell having a tank containing an electrolytic solution and a plurality of parallel electrodes in plate, partially submerged in the solution. The ventilation system comprises a first conduit extending along a first side of the tank and a blower fan for forcing air into the first conduit. A plurality of separate openings are found in the conduit. The openings are aligned at the top and are directed through the surface of the electrolytic solution. Each adjacent opening has an electrode plate disposed therein in the middle, wherein each of the openings directs a current of air along the surface of the electrolytic solution and the side of at least one electrode plate. A second conduit is provided which extends along a second side of the tank and is parallel to the first conduit. An elongated slot extends along the second conduit. The slot faces the apertures and is parallel to the surface of the electrolyte solution and is at a predetermined distance there above. An exhaust fan is provided to create a suction in the second duct to extract air through the slot. In accordance with another aspect of the present invention, a cell of electrolytic extraction comprising a tank containing an electrolytic solution at a predetermined level within the tank. A plurality of flat electrode metal plates is provided. Each of the plates has a support beam along one edge thereof. A support assembly is arranged outside the tank to support a plurality of the electrodes on the support beams. The support assembly is sized to place the electrodes in an adjacent, separate and parallel relationship, with a lower portion of the electrodes submerged within the electrolyte solution and an upper portion disposed above the surface of the solution. The upper portions of the electrodes and the surface of the solution form parallel channels that extend from one side of the tank to a second tank. A plurality of openings is formed in the wall of the tank along one side of the tank. The openings are disposed above the surface of the solution and are positioned where at least one of the plurality of openings is located between an adjacent pair of electrodes. A multiple blower and manifold assembly is connected to the plurality of openings to create a gas flow through the plurality of openings. The manifold and blower assembly is sized to create a gas stream through the channels through the surface of the solution. An elongated slot is formed in the wall of the tank along the second side of the tank. The slot is arranged above the surface of the solution. A manifold assembly and exhaust blower is provided to create a suction through the groove to create a drop in gas pressure opposite the openings. It is an object of the present invention to provide a ventilation system for the removal of gases and mists from an electrodeposition cell.

Another object of the present invention is to provide a ventilation system as described above for the removal of gases and mists from an electrolytic plating cell, parallel, which provides the suppression and improved removal of mists above the equivalent systems that they know each other until now. Still a further object of the present invention is to provide a ventilation system such as that described above and which does not obstruct access to the electrolytic cell. Still another object of the present invention is to provide a ventilation system such as that described above and which does not require surfactants, coalescence balls or other materials on the surface of the electrolytic solution. t Still A further object of the present invention is to provide a ventilation system such as that described above and which does not introduce foreign materials or objects into the electrolytic solution. Still another object of the present invention is to provide a ventilation system such as that described above and which is less expensive and more efficient than the ventilation systems known up to now. These and other objects and advantages will become clearer from the following description of a preferred embodiment of the invention., taken in conjunction with the accompanying drawings.

Brief Description of the Drawings. The invention may take form in certain parts and arrangement of elements, preferred embodiments of which will be described in detail in the specification and are illustrated in the accompanying drawings, wherein: Figure 1 is a perspective view of a cell of electrolytic extraction having parallel electrodes and which has a ventilation system in accordance with a preferred embodiment of the present invention; Figure 2 is an elevation view, partly cut away, illustrating the electrolytic extraction cell shown in Figure 1; Figure 3 is a top plan view of the cell shown in Figure 1; Figure 4 is a sectional view along lines 4-4 of Figure 3; Figure 5 is an enlarged sectional view of the ventilation system • • "push / pull", in accordance with the present invention; Figure 6 is an enlarged, perspective view of a part of the electrolytic extraction cell shown in Figure 1, illustrating the position and configuration of the push / pull ventilation system in relation to the anode / cathode plates and the solution acid; * Figure 7 is a computer generated representation, which shows the pattern of air flow created above the surface of the acid solution by the push / pull ventilation system of the present invention; and Figure 8 is a computer generated representation, which shows the air flow pattern created on top of the surface of the acid solution by an alternative embodiment of the present invention.

Detailed Description of Preferred Modes * 20 Referring now to the drawings in which the disclosure is for the purpose of illustrating a preferred embodiment of the invention only and is not intended to limit it, Figure 1 is a perspective view of a cell of electrolytic extraction 10 to produce metal extracted from an electrolytic solution containing the metal. The present invention will be described with respect to an electrolytic extraction cell that produces copper, although it should be appreciated that said cell can also be used to extract other metals, such as zinc. Said in a broad sense, cell 0 is composed of a tank 20 containing an electrolytic solution 12. In the embodiment shown, tank 20 is of generally rectangular shape and includes vertical side walls 22, 24, 26 and 28, and a bottom wall 32. The side wall 28 has an opening 34 formed therein to define an overflow and establish a predetermined level for the electrolytic solution 12 contained within of the tank 20. A trough 36, best seen in Figures 1 and 2, is formed along the side wall 28 to collect electrolytic solution flowing through the opening 34. The trough 36 has a drain 38 formed in the lower part of the same to remove electrolytic solution that is collected there. Tanks of electrolytic extraction cells of this type are typically formed of a corrosion resistant and acid-resistant material, such as plastics or inert metals, and the drain and feed lines are typically provided on the tank to facilitate the recirculation, re-filling and cooling of the electrolytic solution. Said drainage and recirculation systems do not form part of the present invention and, therefore, are not shown in the drawings. The tank 20 is sized to receive a plurality of parallel and together 40 electrodes. The electrodes 40 are generally flat plates adapted to be supported within the tank 20 in a separate and adjacent relationship. In the embodiment shown, the electrodes 40 are rectangular in shape and held in place by beams 42 which are secured to the upper edge of the electrodes 40. The beams 42 are sized to extend through the tank 20 and to be supported by supports 52 and 54 which are shown schematically in Figures 1 and 4. The electrodes 40 are individually connected to electrical power sources (not shown) to create anodes and cathodes. The electrodes 40 are electrically energized so that the electrodes 40 alternate between cathode and anode. In the modality shown, the anodic plates are slightly larger in length (that is, in length through the tank 20 from the wall 22 the tank towards the wall 26 of the tank) than the cathode plates. In the drawings, the electrodes 40 that are charged as anodes are designated 40A and the electrodes charged as cathodes are designated 40C.

The structural supports 52 and 54 are disposed outside the tank 20 to support the beams 42 with the electrodes 40A and 40C suspended within the tank 20. The supports 52 and 54 are dimensioned so that the lower portion 44 of each electrode 40 is disposed within the tank and is submerged inside the electrolyte solution contained there. Because the beams 42 extend across the upper edge of the tank, an upper portion 46 of each electrode 40 is disposed above the surface of the electrolytic solution. In accordance with the present invention, a ventilation system is provided with the cell 10 for collecting the mist and vapors generated by the electrolytic extraction process. In the embodiment shown, the ventilation system is comprised of a blower assembly 60 disposed along the upper edge of the tank wall 22 and an exhaust assembly 90 disposed along the upper edge of the tank wall 26. The blower assembly 60 is comprised of a blower fan 62, illustrated schematically in Figure 1, and a first duct 64 extending along the upper edge of the tank wall 22. In the embodiment shown, the conduit 64 is of generally rectangular shape and has an intake pipe 66 connecting the conduit 64 with the fan 62 of the blower. The conduit 64 defines an interior chamber 68, which is best seen in Figure 5, in communication with the internal passageway defined through the pipe 66.

As best seen in Figure 5, in the embodiment shown, a part of the conduit 64 is defined by the wall 22 of the tank. A plurality of openings 72 are provided in the wall 22 of the tank to communicate the inner chamber 68 with the side of the tank 20. The openings 72 are aligned along the upper edge of the tank wall 22 and are arranged at a predetermined distance above the upper surface of the electrolytic solution. A flat plate 74 is fixed to the tank wall 22 by conventional fasteners 76. The plate 74 is attached to the tank wall 22 in a fluid-tight manner. The plate 74 is provided with a plurality of threaded holes 78 arranged to be registered with the openings 72 that are found in wall 22 of the tank. The threaded holes 78 are sized to receive a tubular nozzle 80 having a threaded end 82.

* The tubular nozzle 80 defines an interior passageway 84 that is in communication (through the opening 72 in the wall 22 of the tank) with the interior chamber 68 of the conduit 64. The nozzle 80 is dimensioned in such a way that the free end 5 it extends near the plane of the edges of the electrodes 40A. Referring now to Figures 4 and 5, the exhaust assembly 90 is best appreciated. The exhaust assembly 90 is generally composed of a rectangular conduit 92 formed along the upper edge of the tank wall 26. The conduit 92 is arranged to be opposite the conduit 64. In the embodiment shown, the conduit 92 includes two branch conduits 94a and 94b that are *. connected to an exhaust blower 96, which is shown schematically in Figure 1. The duct 92 defines an internal plenum chamber 98 in communication with the passages defined in the branch ducts 94a and 94b. As seen, in Figure 5, in the embodiment shown, a part of the conduit 92 is defined by the wall 26 of the tank. A slot 100 is defined in the wall 26 of the tank such that the plenum 98 is in communication with the interior of the tank 20. The slot 100 is disposed at a predetermined distance above the surface of the electrolytic solution. In this respect, the slot 100 extends in a generally parallel to the surface of the electrolyte solution, and is disposed at approximately the same elevation as the nozzle 80. A rectangular plate 104 is fixed to the tank wall 26 by conventional threaded fasteners. The plate 104 is operable to reduce the size of the aperture defined by the slot 100. The blower assembly 60 and the exhaust assembly 90 are sized to provide a push / pull type ventilation system., through the surface of the electrolytic solution to suppress and collect fog and fumes generated by cell 10. Referring now to the operation of the ventilation system, reference is made to Figure 6, which is a perspective view of a part from the cell showing the positions of the nozzles 80 and the slot 100 in relation to the anodic and cathodic plates 40A and 40C. As illustrated in Figure 6, the nozzles * 80 are arranged and extend along an axis that is equidistant between adjacent plates 40A and 40C. The upper portion 44 of the anodic and cathodic plates 40A and 40C and the surface of the electrolytic solution define passages or parallel channels 110 that extend across the surface of the electrolytic tank. The blower fan 62 is sized to create a flow; air is passed through each nozzle 80. In this regard, an air stream is directed through the surface of the electrolyte solution between upper portions 44 of adjacent electrodes 40A and 40C. The exhaust blower 96 is sized to produce a predetermined air flow through the slot 100. In this regard, the exhaust blower 100 is dimensioned to create a greater air flow through the slot 100 than the total flow of air through the nozzles 80. When the nozzles 80 create an air jet through the channels 110, a "Venturi" effect is created along the surface of the electrolytic solution. The rapidly moving air stream which is created by the nozzles 80 along the surface of the electrolytic solution has a lower pressure than the air furthest from the surface of the electrolytic solution. In other words, the initially stationary air on the upper edges of the electrodes 40 is at a higher pressure than the air that is displaced through the electrolytic solution. This creates a pressure gradient that forces the air that is above the cell down to the surface of the electrolyte solution where it is drawn by the air stream that is being jetted by the nozzles 80 through the surface of the electrolyte. the electrolytic solution captured by the air that moves in a descending manner and which acts under the influence of the slot 100 by the exhaust fan 96. Figure 7 is a computer generated air flow profile for the ventilation system previously described. In Figure 7 the solid lines 200 represent ambient air, while the dotted lines 210 represent air provided by the blower assembly 60. Figure 7 illustrates how the exhausted air The jet out of a nozzle 80 travels through the surface of the electrolyte solution and is collected within the slot 100. In this regard, the jet of * Air created through the surface of the electrolyte solution lows the pressure at this location causing the air that is above the upper edge of the electrodes 40 (that is, above the cell), air that is at a higher pressure elevated to be brought down into the air stream as a result of the pressure gradient that exists on the surface of the electrolyte solution and at points above the cell. This downward movement of air coming from the area above the cell basically forces the mist and fumes illustrated as bubbles in Figure 7 to leave the region of the tank, and allows the exhaust fan 96 to collect these. In the context of the present invention, flr * 'it is believed that the parallel electrodes 40A and 40C also form an important part in the operation of the present invention since the confined channels 110 defined by adjacent electrodes create a restrictive path for the flow of air and in this way helps the creation of the downward flow illustrated in Figure 7. A computer simulation model of the operation of the preceding assembly was made. The computer simulation is based on a tank and a ventilation structure that has the following dimensions and that will be better understood with reference to Figure 5. * 20"a" (tank width) = 39 inches "b" (anode length) = 33 inches "c" (height of the tank wall above the surface of the solution) = 6 inches 25"d" (nozzle height 80 above the surface of the solution) = 3 inches "e" (nozzle internal diameter) = 0.25 inches go »(length of nozzle 80) = 3 inches "g" (height of slot 100 above 30 of solution surface) = 2.25 inches "h" (height of slot 100) = 1.5 inches II j »(space between adjacent electrodes) ) = 1.25 inches For the prototype cell of electrolytic extraction the following% limit conditions were considered. Acid mist release ratio = 1600 mg / min per complete cell Electrolytic surface temperature = 120 ° F Ambient building temperature = 60 ° F For purposes of computer simulation, the operation and effects of the ventilation system along a single channel 110 are evaluated, assuming that similar characteristics and results would be presented by the other channels 110. ío Based on the computer simulation, it was found that the air velocity (V0) in the nozzle as well as the air flow (Q0) through the slot 100 are important for the operation of the ventilation system. In this regard, the parameter Q0V0 of the jet (flow ratio multiplied by the velocity) is a determining factor in the performance of this ventilation system. It was found that a particular range of ejected jet Q0V0 values produces an optimum performance based on the given structural dimensions. In this regard, if the parameter of Q0V0 is too high, then the ejected jet will also draw too much air from the environment, which causes the exhaust assembly to be "overloaded" by the driven jet due to the fixed capacity of the exhaust system. * 20 escape. If the Q0V0 parameter of the jet is too low, the rising acid mist will push through the weak air curtain. In addition, a higher jet flow rate (V0) creates greater turbulence between the electrodes 40 resulting in a greater dispersion of the acid mist over the electrodes 40. With respect to the position of the nozzle 80, if the nozzle 80 of the Expelled jet is positioned too close to the electrolytic surface, it is very possible to increase the turbulence along the surface of the electrolyte solution and the dispersion of the acid mist will be further increased. Conversely, if the nozzle 80 is positioned too high, the buoyancy created by the acid heated below the air jet will increase the "bubble" characteristic in the flow stream and 3"raise" more acid mist above the plates of the liquid. electrode. Therefore, the position of the nozzle 80 as well as the air flow through the nozzle 80 are * critics. According to the present invention, the position of the nozzle 80 and the flow ratio are preferably selected wherein a smooth jet of air is created through the channel 110 without causing turbulence along the surface of the electrolytic solution, and wherein the air flow from the nozzle 80 will draw ambient air into the jet stream. Similarly, the flow rate through the slot 100 is selected so that it is capable of withdrawing the jetted air from the nozzle 80 together with the ambient air entrained and collected by the air flow coming from the nozzle 80 according to the moves through channel 110.% For the test of the model described above, computer simulations indicated that for a nozzle 80 of 3 inches in length, with an internal diameter of 0.25 inches, a jet velocity (V0) of 3,100 feet per minute (fpm) and a flow rate (Q0) of 1 cubic foot per minute (cfm) in slot 100, 15 yields a Q0V0 value of 31, 165 ft4 / min2 per cell foot Under these operating conditions , the computer simulation indicates that 100% of the mist generated by cell 10 is captured by the ventilation system, Referring now to Figure 8, an alternative embodiment of the present invention is shown. air flow diagram generated by the computer for a ventilation system of the type and size as previously described, but where nozzles 80 are not used on the thrust side of the ventilation system. In place of the nozzles 80 apertures with a diameter of 0.25 inches are provided on the tank wall 22. Figure 8 illustrates the computer generated air flow profile for such an arrangement when they are created operating conditions that were previously described. As shown in Figure 8, a flow of air from the side of the push towards the pull side of the ventilation system draws air from above the cell, creating a downward movement of air as a result of the low pressure created by the air jet. As with the previous configuration, when using nozzles 80, the air coming from above the cell is forced down towards the surface of the electrolytic solution, thus dragging mist and vapors from the electrolytic cell into the exhaust slot. The present invention therefore provides a ventilation system for an electrolytic extraction cell, which is highly efficient in the removal and confinement of mists and vapors from the surface of the electrolytic cell, and at the same time provides a ventilation system that does not obstruct the aerial use of the cell. The foregoing description is a specific embodiment of the present invention. It should be appreciated that this modality is described for purposes of illustration only and that numerous alterations and modifications may be. practiced by those skilled in the art, without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they fall within the scope of the invention as claimed or in equivalents thereof. fifteen ^ 20

Claims (8)

1. Novelty of the Invention 1. A ventilation system for an electrolytic extraction cell having a tank containing an electrolytic solution and a plurality of parallel plates of electrodes partially submerged in said solution, the ventilation system is composed of: a first conduit which extends along one side of said tank perpendicular to the electrode plates; a blower fan for forcing air into said first conduit; a plurality of spaced openings formed in said duct, said openings being aligned above and confronting the surface of said solution ^ electrolytic mir, each adjacent aperture having an electrode plate disposed therein in the middle, wherein each of said apertures directs a stream of air along the surface of said electrolytic solution and the side of at least one electrode plate; 15 a second conduit extending along one side of said tank parallel to said first conduit; an elongated slot and extending along said second conduit, the slot facing said openings and being parallel to the surface of said electrolytic solution and at a predetermined distance above; and an exhaust fan to create a suction in said second conduit for drawing air through said slot.
2. 2. A ventilation system as described in claim 1, wherein said conduit includes nozzles extending from there, the nozzles 25 forming said openings.
3. 3. An electrolytic extraction cell, which comprises: a tank; an electrolytic solution within said tank and defining a solution surface at a predetermined level within said tank; a plurality of metallic and flat electrode plates, each of said plates having a supporting beam along one end thereof; a support assembly disposed outside said tank to support a plurality of said electrodes by said support beams, said support assembly is sized to place the electrodes in a parallel, separate and adjacent relationship, with a lower portion of said electrodes submerged in said electrolytic solution and an upper portion disposed above the surface of the solution, the upper portions of said electrodes and the surface of the solution forming parallel channels extending from one side of the tank to a second side of the tank; a plurality of openings formed in the wall of the tank along one side of the tank, said openings disposed above the surface of the solution and arranged where at least one of said plurality of openings is located between an adjacent pair of said electrodes; a blower and manifold assembly connected to said plurality of openings to create a gas flow through said plurality of openings, the blower and manifold assembly is dimensioned to create a gas stream through said channels through the surface of the solution; an elongated slot formed in said wall of the tank along said second side of the tank, the slot being disposed above the surface of the solution; and an exhaust and manifold blower assembly to create a suction through said slot to create a drop in gas pressure opposite said openings.
4. 4. A cell as defined in claim 3, wherein said openings are aligned along an axis parallel to said surface of the solution, and said groove extends parallel to the surface of the solution.
5. 5. A cell as defined in claim 3, wherein the dimensions of said slot are adjustable to vary the aperture defined by it.
6. 6. A cell as defined in claim 3, wherein said blower and manifold assembly comprises a first conduit formed along one side of said tank, the first conduit having an internal chamber in communication with the plurality of openings, and a blower fan in communication with said inner chamber in said first conduit.
7. 7. A cell as defined in claim 6, wherein said blower and manifold assembly comprises a second conduit formed along said second flange of said tank, the second conduit having an internal chamber in communication with the slot, and at least an exhaust fan in communication with said inner chamber in said second conduit.
8. 8. A cell as defined in claim 3, wherein a plurality of tubular members have an internal passageway extending within said tank from said first side of the tank, said internal passageways defining said openings. Extract of the Description * An electrolytic extraction cell composed of a tank; an electrolytic solution within said tank and defining a solution surface at a predetermined level within the tank; a plurality of metallic and flat electrode plates, each of the plates having a support beam along one end thereof; a support assembly disposed outside said tank to support a plurality of said electrodes by said support beams, the support assembly is sized to place the electrodes in a parallel, separate and adjacent relationship, with a lower portion of said electrodes 10 submerged in said electrolytic solution and an upper portion disposed above the surface of the solution, the upper portions of said electrodes and the surface of the solution forming parallel channels extending from one side of the tank to a second side of the tank; a plurality of openings formed in the wall of the tank along one side of the tank, said openings are arranged above the surface of the solution and placed where at least one of said plurality of openings is located between an adjacent pair of said electrodes; a blower and manifold assembly connected to said plurality of openings to create a gas flow through said plurality of openings, the ~ ^ * blower and manifold assembly is sized to create a gas stream to 20 through said channels through the surface of the solution; an elongated slot formed in said wall of the tank along said second side of the tank, the slot being disposed above the surface of the solution; and an exhaust and manifold blower assembly to create a suction through said slot to create a drop in gas pressure opposite said openings. 25