Abstract:
An apparatus to dispense water soluble compositions into a process stream involves recirculating water through the water soluble chemical held in a tank. The recirculating water is heated to establish a defined temperature and repeatedly recirculated through the bed of chemical to achieve relative saturation concentration of the recirculating water. The water is dispensed from the recirculating unit thereby achieving a consistent concentration of chemical in the dispensed water.

Description:
FIELD OF THE INVENTION 
     Chemicals are added to processing streams to accomplish a wide variety of goals. These chemicals may be detergents, surfactants, bleaching agents, biocides as well as a variety of other chemicals. A commonly used method to dispense chemicals into a process stream is to start with a solid material and dissolve a portion of the solid material and then inject the formed solution into the process stream. This is a relatively simple way of adding a soluble solid chemical to a liquid stream. 
     In actuality, this dispensing method has many different problems. Typically the water is added to one end of a holding tank and passes through the solid and is recovered from the opposite end of the holding tank. Because of the nature of water flow, it tends to channel through the bed of solid material providing limited contact between the water and the solid. 
     Further, solubility changes dramatically with temperature. As a result, the concentration of the liquid added to the process stream is extremely inconsistent. Variations of 50% to 60% are common. Variations in concentration is at best wasteful. More likely it can lead to much worse consequences. With biocide treatment concentration variation can cause dramatic increases in bacteria levels. This can damage equipment and products. 
     The apparatus typically used in these dispensing systems is also problematic. Generally the tanks are pressurized. Pressurization forces the water through the tank into the process stream. A pressurized tank of dissolved processing chemicals is inherently dangerous. Further, the tank generally must be relatively tall, otherwise there will not be adequate physical contact between the liquid and the solid. Frequently these need to be fifteen feet or taller which requires a special room. The tank height and its pressurization also makes it more difficult to load the tank with additional solid chemical. The system generally must be shut down and at least partially drained to add additional solid chemical. Draining concentration and liquid solutions to cover is problematic. It can cause environmental damage and can harm bacteria used in waste water treatment facilities. 
     SUMMARY OF THE INVENTION 
     The present invention is premised on the realization that a uniformed concentration of dissolved chemical can be obtained in an aqueous stream by recirculating an aqueous stream through a tank holding the solid chemical. By passing the solution repeatedly through the tank, a uniform concentration can be achieved at atmospheric pressure. Further, a heater is employed within the recirculation loop of the apparatus to establish a desired temperature. This stabilizes the concentration of the solute in the solution, again improving the consistency of the concentration. 
     In a preferred embodiment, the tank employs a gravel bed or other water dispersion system at the base of the tank. The water is injected through the gravel bed distributing the water evenly across the diameter of the bed. The solution is recovered from the top of the bed after passing through the solid material. This provides for even distribution and avoids the channeling incurred with prior art apparatus. 
     Further, the apparatus of the present invention, since it uses a recirculation loop, employs a separate pump allowing the tank to be maintained at atmospheric pressure. This eliminates the inherent safety problem associated with maintaining a pressurized tank of dissolved chemicals. 
     The objects and advantages of the present invention will be further appreciated in light of the following detailed description and drawings in which: 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a diagrammatic depiction of the present invention. 
     FIG. 2 is a diagrammatic depiction of an alternate embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     The present invention is a method and apparatus for dispensing water soluble chemicals into a process stream. For purposes of the present invention, process stream refers to a wide variety of different applications and include basically any aqueous based systems. Exemplary systems would include paper processing, cooling towers, boiler water treatment, drinking water treatment, waste water treatment, food manufacture and warewashing. 
     The present invention describes as a preferred embodiment which is the application of biocides to a paper processing operation. However, this is merely exemplary and the present invention should no,t be limited to this particular application. 
     The water soluble composition used in the present invention can be a wide variety of different chemical compositions. These could include detergents, minerals, surfactants, biocides, flocculents various mixtures and 
     Typical biocides include halohydantoins, such as bromomethyl halohydantoin, chloromethylhalohydantoin, and other biocides such as calcium hypochlorite, dibromonitylpropylamine, glutaraldehyde salts as well as many other well known biocides. These can be applied at various well-known locations in the process stream and the particular point of application forms no part of the present invention. 
     Shown more particularly in FIG. 1, the present invention includes a water tank  12  which includes an inlet  14 , a primary outlet  16  which leads to injection pumps  18  and  22 . The discharge line  24  from outlet  16  also leads to a recirculating pump  26  which pumps fluid through a heater  28  back to the tank inlet  14 . 
     The tank  12  is made from any chemically resistant material. It can be metal or a plastic material or can be lined as desired depending upon the material being distributed. The base  32  of the tank  12  is an inverted truncated cone which is designed to provide for even distribution of the injected water throughout the base of the tank  12 . More particularly water inlet  14  has a dispersing head  34  which includes a cap  36  with multiple water outlets  38  which direct the incoming water downwardly. Also, the lower portion  32  of tank  12  is designed to disperse the water throughout the base of the tank. 
     As shown, a gravel bed  33  is used. Other means to disperse water include baffles or a series of plates with water distribution holes drilled throughout. These simply provides for even water flow throughout the base of the tank. 
     Above the gravel bed  33  is a bed of the water soluble material  42  preferably in the form of briquettes, pellets or tablets. A pool of water  44  above the bed  42  of briquettes. An air space  45  is at the top of the tank  12 . The tank includes high and lower water sensors  46  and  48  and an emergency sensor  49  to provide a warning emergency and/or shut down. The top of the tank also includes an inlet or hatch  82  to allow the operator to manually place additional briquettes into the tank  12 . 
     Water is directed through outlet  16  and valve  52  through line  24 . This water flow is continuous and maintained by recirculating water pump  26 . A magnetic drive centrifuge pump or an air driven double diaphram pump is suitable for this application. 
     Pump  26  directs the water through line  54  through heater  28  which, as shown, is a steam mixing valve and then back through line  14  to the base  32  of tank  12 . A temperature sensor  56  is used to control the operation of heater  28 . 
     Heater  28  includes a steam source  58  which directs steam as needed through needle valve  62  to the heater  28  to maintain constant temperature of the inlet water. This steam is mixed with the recirculating water to maintain the desired temperature. 
     When the pool water  44  is below sensor  48 , water is added through line  64  controlled by air valve  68 . The water flows through valve  68  into line  14  into the bottom  32  of tank  12 . Again, as the inlet water is being fed through valve  68 , steam can be added from heater  28  through valve  68  to establish a desired temperature for the inlet water if desired. If the water temperature in tank  12  needs to be increased, needle valve  69  can be opened along with valve  62  to heat the liquid in tank  12 . 
     Pumps  30  and  31 , when needed, direct the recirculating solution from line  24  to injection ports upstream as indicated by arrows  72  and  74 . The amount can be determined through flow meters  76  and  78 . Pumps  30  and  31  are preferably variable speed diaphram pumps or air operated double diaphram pumps to provide uniform flow. 
     In order to provide maximum efficiency, the diameter of tank  12  relative to the height of the briquette bed should be greater than 1:1 and generally 1.5 to 1 to about 2 to 1. This provides for optimum distribution of the water through the bed of briquettes and therefore optimum dissolution of the material. 
     The temperature of the water within tank  12  can be maintained at any desired level. Generally it can be anything above 0 up to boiling. However, for practical applications it will be above room temperature and up to about 110° F. with about 70-110 being preferred with 80-95 the most preferred range. This depends upon the material being dissolved. These optimum ranges are for the halohydantoins. 
     The chemical is obviously a solid and is preferably a briquette, tablet or pellet. Granules can also be used. The term briquette is considered exemplary of the physical form of the chemical. The briquettes can be added to the tank  12  during operation because the tank itself is at atmospheric pressure and there is an airspace  45  above the water level  44 . Thus, to add additional material, one simply opens port  82  and pours additional briquettes into the tank  12 . This can also be done with a conveyor system if desired. 
     In the operation of the present invention, it is preferred that on average the water makes at least two passes through tank  12  prior to being drawn off by pumps  30  and  31 . In other words, there is a recirculation to discharge ratio of at least 2:1 and preferably about 4 to 1 in order to ensure product saturation in the liquid discharged into the process stream at the defined temperature. This may change depending on the particular chemical being dispensed as well as the temperature. 
     Further, in order to maintain its optimum concentration, it is important that the incoming water should be limited to 10%-25% greater than discharge flow. Additional water is added to the system when pumps  30  and  31  are in operation. 
     FIG. 2 shows an alternate embodiment  100  of the present invention designed to dispense a larger amount of treatment chemical. Two tanks  102  and  104  are used, both with bottom water inlets  106  and  108  respectively. Again, these will utilize water outlets  110  and  112  with outlet  110  leading to a recirculation pump  114 . Outlet  112  leads to line  140  and into tank  102 . 
     Pump  114  directs water past a temperature sensor  116  through an electric heater  118  which then directs water back through line  108 . Additional inlet water can be provided through line  120  from either hot or cold water inlets  119 ,  121  through tempering valve  123 . This system employs four separate discharge pumps  122 ,  124 ,  126  and  128 . In this embodiment there are three discharge ports  130 , 132  and  134 . Pump  128  acts as a backup pump in the event any of pumps  122 ,  124  or  126  is disabled. 
     Again system  100  operates in the same manner as the apparatus  10  disclosed in FIG. 1 with the exception that the water is injected through both ports  106 - 108  into tanks  102  and  104 . Liquid from tank  102  flows through line  110  and is directed to recirculating pump  114  which directs the water through heater  118  to inlet  108 . Discharged water from tank  104  flows via outlet  112  back through line  140  and directly back into the first tank  102  through line  106 . Line  140  acts to equalize the water level in the two tanks. 
     Anytime solution is required for dispensing into the process flow, pumps  122 - 126  can be selectively operated. Whenever temperature sensor  116  detects a low temperature in the recirculating water, heater  118  is activated to establish a constant temperature. Additional temperature probes as well as sample ports can be employed throughout the system and can be employed for example in tank  104 ,  102  or in any of the process streams. Additional tanks, pumps and heaters can be added as needed to increase capacity. This in turn can all be controlled by a outside controller using a PLC controller ORP meter, total chlorine meter or a DCS system. 
     The present invention provides many different advantages. The use of a flow distribution medium bed at the base of the tank provides even distribution of water and uniform flow through the briquettes. This reduces or eliminates channeling and improves product concentration and dissolution efficiency. This in turn allows a shallower briquette bed to be used. 
     The recirculation system providing multiple passes of the water through the briquette bed ensures product saturation at the established temperature and thus uniform concentration in the discharge stream. Recirculating the water at least twice through the briquette bed prior to discharge further ensures saturation. 
     The use of the heater which maintains the temperature of the recirculating water establishes a consistent known concentration. Thus, by recirculating the water and controlling the temperature one can control the concentration of the solute in the recirculating stream. In turn, by controlling the amount of liquid added to the processing stream, one provides a reliable application rate of the particular chemical. 
     The present invention operates at atmospheric pressure which is significantly safer than a system using a pressurized tank of process chemicals. The system also allows for multiple bags of product to be charged into the unit in a single operation. Thus, the present invention significantly improves efficiency, reduces costs and improves safety. 
     This has been a description of the present invention along with the preferred method of practicing the invention. The invention itself should only be defined by the appended claims whereby we claim: