Abstract:
An autonomous pushed liquid recirculation system (APLRS) is installed in a vessel, such as an electroplating tank. It situates around the interior perimeter and adjusts to changes in the level of liquid, maintaining the same location and orientation respective to the liquid&#39;s surface. It establishes a current near the surface that pushes liquid across the narrow horizontal dimension of the tank from a front wall to a rear wall. The current serves to push any bubbles resultant from operations within the tank to the rear wall. Over the rear wall is mounted an abbreviated exhaust hood covering only a short width of the surface of the tank along the rear wall. Because the exhaust system has to scavenge only a portion of the surface since all bubbles now burst along the rear wall, a much smaller air handling apparatus may be specified with an attendant savings in energy costs.

Description:
RELATED INVENTIONS  
       [0001]    This is a Continuation in Part of prior co-pending U.S. patent application Ser. No. 09/689,686, A Pushed Liquid Recirculation Method and System for an Electroplating Apparatus, by Hay et al., filed Oct. 13, 2000, and incorporated herein by reference. 
     
    
     STATEMENT OF GOVERNMENT INTEREST  
       [0002] The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
     
    
     
       FIELD OF THE INVENTION  
         [0003]    The field is fugitive emissions control. In particular, an autonomous system and method of its deployment is provided for minimizing fugitive airborne emissions of harmful products emitted by industrial operations, such as electroplating.  
         BACKGROUND  
         [0004]    Some electroplating processes, such as those used to chrome plate metal, are highly inefficient. U.S. patents cover some of these processes. U.S. Pat. No. 2,862,863, Apparatus for Electrolytic Production of a Metal Product from Fused Salts, to Griffith, Dec. 2, 1958, details a method for producing a metal derived from an electrolyte such as halides of the target metals. U.S. Pat. No. 3,104,221, Self Circulation Solution Anode for Chromium Plating Vessels, to Hill, Sep. 17, 1963 provides a method for chrome plating the interior of an article that may have one end completely enclosed. U.S. Pat. No. 4,933,061, Electroplating Tank, to Kulkarni et al., Jun. 12, 1990 describes an electroplating tank with a sparger system in the bottom of the tank for directing solution upward and a cathode rack for holding items to be plated intermediate anode plates.  
           [0005]    These plating systems create byproduct gases that rise as bubbles and burst, emitting a mist of chromic acid to the atmosphere. These emissions must be addressed to meet federal pollution standards since hexavalent chrome is a carcinogen.  
           [0006]    In chrome plating solutions, these chromic acid-forming bubbles rise and disperse uniformly on the surface of the electroplating solution, away from the plating process. To treat the particulates thus generated requires a sufficient ventilation flow to insure they are forwarded to and captured by scrubbing filters. A typically required ventilation flow is 200-250 ft 3 /min. of air per ft 2  of plating tank surface (cfm/sf). Conventional large ventilation systems remove the mist to an area of treatment removed from the plating tanks. These systems include large hoods, connecting ductwork, and at least one blower. The remote treatment technology may be a composite mesh pad unit or a packed bed scrubber. The large ventilation system incurs a large part of the energy costs to treat the mist as well as-requiring initial capital for installation and consuming valuable space in a work area.  
           [0007]    One somewhat unconventional treatment system is the Venturi/Vortex scrubber described in U.S. Pat. No. 5,149,411, Toxic Fumes Removal Apparatus for Plating Tank, to Castle, Sep. 22, 1992. This system, designed to replace larger more conventional systems, captures plating bubbles using a vortex drain operating by gravity. It was designed to separate the liquid and gas phases, re-circulate the liquid and treat the gas before exhausting the treated gas to the atmosphere. Although a patent was granted on this system and method, it had practical limitations that prevented it from being adopted commercially. Hay, K. J. et al.,  Venturi/Vortex Scrubber Technology for Controlling/Recycling Chromium Electroplating Emissions , ESTCP Demonstration Project Final Report, Technical Report 99/43, U.S. Army Construction Engineering Research Laboratory (CERL), March 1999.  
           [0008]    U.S. Pat. No. 5,766,428, Chromium Plating Solution, Solution Waste from Chromium Plating and Closed Recycling System for Chromic Acid Cleaning Water in Chromium Plating, to lida, Jun. 16, 1998 describes a large complex system for cleaning the mists emitted that uses a final treatment means preferably located underground.  
           [0009]    U.S. Pat. No. 3,985,628, Pollution Control in Electroplating Systems, to Myers, Oct. 12, 1976, provides a bulky complex means to scrub the emitted mist using plating rinsing water, claiming a transfer of “chemical values” to the water and water to the air. The resultant chemically enriched water is returned to the plating solution while no auxiliary air is added other than that required to “sweep over” the plating baths.  
           [0010]    Another concern with conventional electroplating tanks is their use of air circulation lines. Agitating (sparging) the plating solution with air bubbles near the plating activity ensures constant mixing of the solution thus yielding a uniform coating or plating. However, air bubbles thus generated increase surface emissions.  
           [0011]    In view of the drawbacks associated with conventional plating systems, there is a need for a system and method that reduces costs associated with controlling fugitive emissions. A system and method of its use are provided for reducing the size of the costly, energy robbing ventilation system mandated to be installed over any open vessel emitting airborne hazards.  
         SUMMARY  
         [0012]    To minimize the energy burden in treating fugitive emissions from open vessels that contain material that may volatilize and escape, an autonomous system, termed an autonomous pushed liquid recirculation system (APLRS), and method of its use are provided. The APLRS includes a fluid intake to a conduit connected to a pump, the intake positioned in the vessel along a portion of a wall of the vessel and a fluid exhaust from a conduit connected to an opposite side of the pump, the exhaust positioned in the vessel along a portion of a wall of the vessel approximately opposite the position of the intake. In a preferred embodiment, this configuration provides an equal path within the vessel from the pump to the intake and the pump to the exhaust. Because the APLRS depends on its location within the vessel in relation to fluid therein, it also incorporates a novel multi-part float that enables the APLRS to maintain an adequate geometry and position for fulfilling its function.  
           [0013]    The dimensions of the vessel in which a preferred embodiment of the present invention may be employed include a tank having a length longer than its width, but also may include square, round, oval or polygonal shapes other than rectangular.  
           [0014]    As compared to existing conventional fugitive emissions control systems and methods, an embodiment of the APLRS reduces ventilation requirements for electroplating tanks, thus reducing both capital equipment and operating (energy) costs.  
           [0015]    The reduction in size and energy cost is effected through a reduction in the bubbles that arise to the surface of the vessel during industrial operations, such as electroplating. Fewer bubbles bursting on the surface reduce the amount of required forced ventilation.  
           [0016]    A preferred embodiment of the APLRS meets the above goals by using jets of liquid to produce a uniform cross flow, i.e., a “push,” near and across the surface of liquid in a vessel such as an electroplating tank. This pushes any bubbles arising to the surface of the vessel to one side of the vessel. These bubbles then cluster at a wall of the vessel due to not being able to resist the induced flow of the jets of liquid originating from an opposite wall.  
           [0017]    This results in an effective reduction in the vessel&#39;s surface area since all of the bubbles are no longer dispersed over the entire surface but rather “pushed” to one side. In a preferred embodiment this side is a long side of the vessel-because of the advantages of exploiting the physics of inducing the flow across the narrowest part of the vessel.  
           [0018]    While controlling the location and area in which bubbles may burst, another advantage of the APLRS is the inducing of a natural recirculation of solution within the vessel. This leads to more efficient and uniform plating in those vessels employed in plating operations, for example. This may eliminate or reduce the need for a separate air sparger to achieve this function.  
           [0019]    Further, in a preferred embodiment of the APLRS, the bubbles are “pushed” to a controlled collection point prior to becoming a fugitive emission, unlike existing emissions control systems that capture resultant mist in a “push-pull” air system only after a bubble has burst and become a fugitive emission anywhere on the surface of liquid in the vessel.  
           [0020]    Thus, provided is an autonomous pushed liquid recirculation system for use with open systems containing hazardous materials that may be volatized. A preferred embodiment of the present invention will operate independently of the fluid level maintained in a vessel in which it is installed. This capability is enabled by a novel float system incorporated in the design of the APLRS.  
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0021]    [0021]FIG. 1 is a view of one side of a prior art system that uses some of the elements of a preferred embodiment of the present invention.  
         [0022]    [0022]FIG. 2 is a view of a prior art system, that of the side opposite that of FIG. 1.  
         [0023]    [0023]FIG. 3 is an end view of the prior art system of FIGS. 1 and 2, the depicted end being the one closest to a submersible pump.  
         [0024]    [0024]FIG. 4 is a top view of the topmost located components comprising a preferred embodiment of the present invention.  
         [0025]    [0025]FIG. 5 details an end view of the vertical part of one of multiple float support assemblies used with a preferred embodiment of the present invention.  
         [0026]    [0026]FIG. 6 is a detail of components of the float support assembly of FIG. 5 as shown in a profile view.  
         [0027]    [0027]FIG. 7 depicts a front side view of a preferred embodiment of the present invention emplaced within a rectangular vessel.  
         [0028]    [0028]FIG. 8 shows an end view of the system as emplaced in FIG. 7, the end containing a submersible pump.  
         [0029]    [0029]FIG. 9 is a cross section through  4 - 4 ′ of FIG. 4 showing the activity of a preferred embodiment of the present invention in operation.  
         [0030]    [0030]FIG. 10 is a graph showing surface velocity versus depth of the exhaust ports in piping used with a preferred embodiment of the present invention.  
         [0031]    [0031]FIG. 11 depicts a view taken from the side opposite the view of FIG. 7.  
     
    
     DETAILED DESCRIPTION  
       [0032]    A predecessor of the present invention was conceived to work with a system required to maintain a level of fluid in an open vessel to very close tolerances. This predecessor system is described fully in a related application, U.S. patent application Ser. No. 09/689,686, A Pushed Liquid Recirculation Method and System for an Electroplating Apparatus, to Hay et al., filed Oct. 13, 2000, and incorporated herein by reference. See also Hay (1999).  
         [0033]    Refer to FIG. 1. First conceived by the inventors of the present invention as a non-autonomous pushed liquid recirculation system (PLRS), the piping and connections used to effect the flow of liquid to push bubbles  903  (not separately shown in FIG. 1 but shown in FIG. 9) to one side of a rectangular open tank  101  are shown in profile. This piping is connected to the exhaust side of a pump  301  (not separately shown in FIG. 1 but shown in FIG. 3) via a pipe  104  (shown in end view only in FIG. 1). These components are installed very close to a first long side  302  (labeled in FIG. 3), or front wall, of the tank  101  and just below the surface  102  of the liquid in the tank  101 . At first  103  and second  111  ends of the tank  101  are fixed connection plates  109  to which connectors  110  from the distribution lines  107  are affixed. The piping itself may be comprised of a feed line  105  from an origination line  104  fed by the pump  301  to one or more feed arrangements  106  such as one or more Tees having multiple risers that provide an approximately equal flow of liquid to one or more distribution lines  107  incorporating holes  108  that are spaced and of a number and geometry to be in accordance with proper engineering design to effect a uniform current flow across the surface  102 . These holes  108  are angled away from the first long side, or front wall  302 , upward at an optimum angle, y, (not separately shown in FIG. 1 but shown in FIG. 9) and the distribution lines  107  are located at an optimum distance, x, just under the surface  102 .  
         [0034]    Refer to FIG. 2. Shown is the profile view of the collection, or intake piping of the prior art PLRS, installed in like manner to the exhaust piping of FIG. 1, but on the opposite  303  long side (labeled in FIG. 3), or rear wall, of the tank  101 . This piping is connected to the intake side of the pump  301  (not separately shown in FIG. 2 but shown in FIG. 3) via a pipe  201  (shown in end view only in FIG. 2). As with the exhaust/distribution components of FIG. 1, these components are installed very close to the rear wall  303  of the tank  101  and just below the surface  102  of the liquid in the tank  101 . At first  103  and second  111  ends of the tank  101  are fixed connection plates  209  to which connectors  210  from the distribution lines  207  are affixed. The piping itself may be comprised of a collection arrangement  206  that may comprise multiple risers arranged in a Tee configuration similar to that shown in FIG. 1, a return line  205  connected to an intake line  201  to the pump  301 . This “collection half” of the prior art PLRS collects an approximately equal flow of liquid from collection lines  207  incorporating appropriately sized and aligned holes  208 . These holes  208 , are oriented towards the back wall and preferably angled upward with respect to the horizontal at an angle of between 30° and 60° but most preferably at an angle of approximately 45°, collect fluid to be returned to the pump  301 . The collection lines  207  are located at an optimum distance, z, under the surface  102 , where z is greater in magnitude than x, i.e., the collection lines  207  are located deeper in the tank than the distribution lines  107 . The depth, z, is chosen as close to the surface  102  as possible, generally less than about 250 mm (10 in.) and optimally about 150 mm (6 in.), so that it may effect an efficient return of fluid from the current generated from the distribution lines  107  while avoiding development of a vortex (not separately shown) that may entrain the bubbles  903  or air (not separately shown) from above the surface  102 .  
         [0035]    Refer to FIG. 3. A view of the prior art PLRS from the second end  111  of the rectangular tank  101  is shown. Here is it evident from the positions of the connectors  110 ,  210  that z&gt;x. It is also evident that both z and x are fixed with respect to the tank  101 . Note, to simplify FIG. 3, no power source is shown, nor means for transferring power, to the pump, although it is to be implied. As well, the pump may be connected to a throttle valve (not separately shown) and an inline flow meter (not separately shown) for purposes of controlling and monitoring flow. The operation of the pump may be controlled to operate only when operations are being conducted in the tank, such as electroplating. Further, the pump  301  may be one used with an existing system within a tank, such as a sparger (not separately shown).  
         [0036]    Refer to FIG. 4 showing a top view highlighting salient features of a preferred embodiment of the present invention, i.e., the APLRS, that may be viewed by looking directly down upon the top of the sides of a tank  101  and the surface  102  of liquid in the tank  101  in which a preferred embodiment of the APLRS is installed. At each of the narrow ends  103 ,  111  of the tank  101  are located “floats”  401 ,  403  to which the distribution  107  and collection  207  lines of the APLRS are connected via their respective connectors  110 ,  210 . These floats  401 ,  403  are of a size, strength, and durability to support the APLRS in its expected installed environment and are designed according to accepted engineering practices. To support the distribution  107  and collection  207  lines piping along their long dimension, “supports”  402  are provided on the long sides  302 ,  303  of the tank  101 . In one embodiment a submersible pump  301  is used and must be supported. To support the pump  301  and intake  201  and exhaust  104  lines, another set of identical supports  402  is shown overhanging the edge of the tank  101 . These supports  402  are further described in the profile and side views of FIGS. 5 and 6, respectively.  
         [0037]    [0037]FIG. 5 depicts one of the supports  402  of FIG. 4 as shown looking down one of the sides  111 ,  302 ,  303  of the tank  101  on which it is mounted. In its humblest form, it comprises a configuration of CPVC pipe components, e.g., CPVC of 3.8 cm (1½ in.) inside diameter. At the top is a straight horizontal piece  508  that provides some overhang of the side  111 ,  302 ,  311  of the tank  101  to insure the support  402  does not fall into the tank  101 . To effect a right angle an elbow  502  is attached to the straight piece  508 . A vertical piece  505  is attached to the elbow  502  to effect a length necessary to accommodate expected fluctuation of the level of the surface  102  of the liquid in the tank  101  with some safety measure thrown in. Encircling this vertical piece  505  is a T-collar  506 , e.g., CPVC reducing Tee connector of inside diameter of 5.0 cm (2 in.) with a reducing connection on the leg of the Tee to 3.8 cm (1½ in.) CPVC. This T-collar  506  acts to slide up and down the vertical piece  505  as the surface  102  of the liquid changes. To the reducing connection is affixed a “tab”  503 , e.g., a short section of CPVC of inside diameter 3.8 cm (1½ in.). For the shown embodiment, each of the vertical supports  402 , this tab  503  will support the applicable distribution  107  or return  207  lines along the long sides  302 ,  303  of the tank  101  and the intake  201  and exhaust  104  lines along the pump end  111  of the tank  101 . At the base of the vertical piece  505  is an elbow  504  that provides a change in direction perpendicular to both the tab  503  and the top horizontal straight piece  508 . This elbow  504  allows two vertical supports  402  to be connected via a straight horizontal pipe  507  as shown in FIG. 6. The configuration  601  is used with the floats  401 ,  403  and connectors  110 ,  210  thereto to provide an autonomous PLRS, i.e., an APLRS, an efficient emissions control system that is independent of the system for which it is controlling fugitive emissions.  
         [0038]    Refer to FIG. 7. Shown is a view of a front wall  302  of a rectangular tank  101  in which an embodiment of the APLRS has been installed. Note that the vertical piece  505  (not labeled in FIG. 7) is quite long so that, as depicted, the level of fluid in the tank  101  may be varied substantially. Although this is not a preferred embodiment if installed in a conventional electroplating tank, it may be useful in other applications in which deep tanks may be used with minimal loading for other than their main purpose: Thus, this may be useful when a small batch or smaller pieces are being processed and it is not necessary to use the whole depth of the tank  101 . This gives the operator increased flexibility, especially if the hood  901  (not separately shown in FIG. 7 but shown in FIG. 9) is able to be run down the inside of the tank  101  to accommodate fluid level changes.  
         [0039]    Refer to FIG. 8 depicting a view of the support  601  installed at the pump end  111  of the tank. Note the different relative positions of the connectors  110 ,  210  shown in end view. The collection lines  207  (as shown in FIG. 2) must always be below that of the distribution lines  107  (as shown in FIG. 1) and the depth, x, of the distribution lines  107  below the surface  102  should be optimized to effect a uniform strong current across the surface for pushing the bubbles  903  (as shown in FIG. 9).  
         [0040]    Refer to FIG. 9, a vertical cross section through the tank  101  of FIG. 4 at  4 - 4 ′ such that one is viewing the tank  101  from the end  103  with the front side  302  to the viewer&#39;s right. With respect to the distribution and collection of liquid, the APLRS operates in the same manner as the PLRS described in U.S. patent application Ser. No. 09/689,686, but will be reiterated here for convenience. Fluid is pumped from the pump  301  up to a distribution lines  107  where it exits through holes  108  oriented toward the back wall  303  at a pre-specified angle, y. This establishes a “current” in the direction of the single large arrow  902 . A nominal time of passage for liquid in this current to flow from a front wall  302  to a rear wall  303  of an average electroplating tank  101  is two seconds. Preferably, this may be accomplished with a flow rate of from 40-200 liters/min./m 2  (1.0-5.0 gallons/min./ft 2 ) of liquid surface  102  area and most preferably with a flow rate of about 120 lpm/m 2  (three gpm/ft 2 ) of liquid surface  102  area. As bubbles  903  are initiated by some operational action within the tank  101 , e.g., electroplating, they rise to the surface  102  and meet this current and are deflected to the rear wall  303  of the tank  101 . The rear wall  303  has an exhaust hood  901  placed over it for collecting any emissions occurring as a result of these bubbles  903  bursting as indicated by the arrows  904 . Note that the exhaust hood  901  extends only a portion of the way over the tank  101 , requiring a fraction of the surface  102  area of the tank to be exhausted, thus reducing the size of the equipment as well as the amount of energy needed to operate it. Further, since the exhaust hood need not cover the entire surface  102 , it may be located closer to the portion of the surface  102  that it does cover, thus requiring less energy to “pull” any fugitive emissions from the bursting bubbles  903  along the rear wall  303 . Further, access above the tank  101  is facilitated since no large ventilation hood covers most of the surface  102 , thus enabling use of devices such as overhead cranes (not separately shown) to move items for treatment in the tank  101 . Near the rear wall  303  are the collection lines  207  that return fluid to the pump  301  through holes  208  in the collection lines  207 . The collection lines  207  and holes  208  therein are arranged near the rear wall  303  to take advantage of the rebound effect (as indicated by the arrow  905 ) induced by the current terminating at the rear wall  303 . In an optimum configuration to minimize adverse components of rebound from the rear wall  303  due to cross flow at the surface  102 , these holes  208  are oriented toward the rear wall  303  at approximately 45° from the horizontal, although they may be oriented from 30° to 60° upward from the horizontal in other embodiments. Note that if this rebound effect is not present, bubbles  903  will drift from the location of the back wall  303  and perhaps burst in a location not under the exhaust hood  901 .  
         [0041]    Refer to FIG. 10. Shown are test results taken from a tank  101  in which the angle, y, of the holes  108  in the distribution lines  107  were varied with respect to the horizontal and with the depth, x. An optimum value of z had been determined previously. The angle, y, was investigated at three values: 0°, 15°, and 30° for depths, x, varied in half-inch increments from 0.5 in (12.5 mm) to 2.5 in. (63.5 mm). Results show the maximum flow is available in a very narrow depth range of 12.5-25 mm (0.5-1.0 in.) at an angle, y, of 15°. However, for values of x less than 1.0 in., splashing occurs, exacerbating the emissions problem. This demonstrates the critical need for maintaining the value of x within a preferable narrow range of 1.0-2.0 in., and more preferably between about 1.0-1.5 in., to not only optimize flow but also minimize unintended emissions. This is accomplished via the unique capability provided by the APLRS to adjust depth with change in the level of the liquid surface  102  instantaneously and simply, with no need for active control devices. This capability also facilitates installing the APLRS in any existing system without in-tank retrofit of controls. It also permits a significant reduction in the size of the emissions control system required. The burden imposed is a small increase in energy to run the pump  301  and a reduction in available tank capacity due to installation of the lines  104 - 107 ,  201 ,  205 - 207  and pump  301  along three edges  111 ,  302 ,  303  and floats  401 ,  403  along the ends  103 ,  111 . For new designs, this could be accommodated by a slight increase in the dimensions of a tank  101 , for example. However, existing tank designs equipped with in-tank spargers may no longer need them upon installing an APLRS, thus recouping some lost energy and volume in this manner.  
         [0042]    Refer to FIG. 11. Shown is a view of an APLRS installation that is the mirror image of FIG. 7 as installed on the rear wall  303  of the tank  101 . Note that the collection lines  207  are installed deeper, i.e., z&gt;x, along the back wall  303 .  
         [0043]    Although specific types, geometry and orientations of piping, floats, and pumps are discussed, other similar types, geometry and orientations of piping, floats, and pumps, including those that may have only some of the constituents used in the above described examples, may be suitable for reducing fugitive emissions using a structure or method that falls within the ambit of a preferred embodiment of the present invention as provided in the claims herein. For example, the vertical risers of the support configuration  601  may comprise flexible hose and the pump  301  may be affixed near the bottom of the tank  101  so that a support configuration  601  is not required on an end  111  of the tank  101 .