Liquid purification or separation – Processes – Chemical treatment
Reexamination Certificate
2001-06-26
2003-02-11
Hoey, Betsey Morrison (Department: 1724)
Liquid purification or separation
Processes
Chemical treatment
C210S167150, C422S028000, C137S014000
Reexamination Certificate
active
06517727
ABSTRACT:
DESCRIPTION OF THE INVENTION
The present invention is directed to a method of operating automatic chemical feeders useful for preparing a liquid solution, e.g., an aqueous solution, of a chemical material, such as a sanitizing chemical, wherein the chemical material is contacted with a fluid in which the chemical material is soluble, i.e., a solvating fluid. The resultant liquid solution is discharged from the feeder and forwarded to the point of application, e.g., a body of water, where it is to be used. In particular, the present invention is directed to method of operating a pressurized chemical feeder so that the feeder automatically dispenses controlled amounts of a solution of a chemical material, e.g., a sanitizing chemical such as calcium hypochlorite, in a reliable, efficient and cost effective manner. Examples of systems that can be treated with aqueous solutions produced by the method of the present invention include water treatment plants, potable water supplies, water for industrial or process usage, waste water systems, water systems for cooling towers, run-off water, swimming pools, hot tubs and the like.
More particularly, the present invention is directed to a novel method of operating pressurized chemical feeders, i.e., feeders that operate under positive pressure, so that only a desired portion of the chemical material charged to the feeder is contacted with solvating fluid. Still more particularly, the novel method comprises establishing and maintaining an atmosphere of substantially inert gas, e.g., air, in the chemical feeder above the soluble chemical material, e.g., a solid chemical material such as calcium hypochlorite tablets, while the feeder is operating, thereby to control the level of solvating fluid within the feeder and hence the amount of chemical material contacted by the solvating fluid. As used herein and as later more definitively defined, the term “substantially inert gas” or “inert gas” means a gas that is substantially chemically inert with respect to the soluble chemical material within the feeder.
Chemical feeders for producing solutions of chemical materials are known. Particularly well known are chemical feeders for producing aqueous solutions of chemical materials such as sanitizing agents, e.g., calcium hypochlorite, that are used for the treatment of water and water systems. Typically, such feeders operate by providing a solid composition, which contains a soluble chemical material of a suitable shape, e.g., tablets, pellets or granules, within a suitable chamber and controllably contacting the chemical material (solute) with a solvating fluid, e.g., water or other suitable solvent, thereby to dissolve the chemical material and produce a solution of the chemical material in the solvating fluid or liquid. The solution of chemical material so produced is removed from the feeder and forwarded, directly or indirectly and with or without further treatment (physical or chemical), to the point of application or use. Aqueous solutions of sanitizing agents produced by such feeders have been utilized in various applications, e.g., to disinfect effluent from sewage treatment plants, for sanitizing water used in swimming pools and hot tubs, for the treatment of food supplies and surfaces used in connection with the preparation or treatment of food, e.g., tables, sinks, tanks, walls and floors, and for the treatment of other aqueous streams and water systems. Such feeders have been used also for preparing water-soluble chemicals other than sanitizing agents.
Chlorine, hypochlorous acid and other sanitizing chemicals are used in swimming pool and hot tub applications to control the growth of algae and other organisms in the water. The concentration of the sanitizing chemical in the water, e.g., swimming pool, must be kept between a concentration that is effective to eliminate algae and other objectionable organisms and below a higher concentration that is harmful to the user. Consequently, chemical feeders which produce aqueous solutions of sanitizing agents that are used in the treatment of recreational water for bathing, swimming and hot tubs, have been designed to alleviate the shortcomings that typically accompany periodic manual additions, e.g., by broadcasting of the sanitizing agent over the surface of the recreational water, e.g., a variation in the amount of sanitizing agent added. Examples of chemical feeders are described in U.S. Pat. Nos. 3,595,786; 3,595,395; 4,584,106; 4,732,689; 4,759,907; 4,842,729; 5,089,127; 5,427,748; 5,441,711; 5,447,641; 5,932,093; and 6,077,484.
A feature associated with many chemical feeder installations, such as those described in the above-cited U.S. Pat. Nos. 5,089,127, 5,384,102 and 5,427,748, is that the feeder, when used in a closed system, is installed in close liquid communication with the suction side of a recirculation pump, which results in the feeder operating at or slightly below atmospheric pressure. Such an installation avoids the build-up of pressurized air within the feeder and also the requirements for a feeder design and materials of construction that will withstand positive pressures that are encountered during operation of a feeder at above atmospheric pressures.
Notwithstanding the aforementioned advantages of operating a chemical feeder at atmospheric pressure, there are applications where operating a chemical feeder under positive pressures, i.e., at pressures above atmospheric pressure, e.g., at pressures from just above atmospheric, e.g., 1 pound per square inch gage (psig) (6.9 kPa) to 50 (psig) (345 kPa), is desirable and even required by the particular installation.
Such installations include those where the feeder is located below the level at which the body of water, e.g., the swimming pool, to be treated is situated, e.g., below grade, or where the feeder is in association with a pressurized pipe line, or anytime the pressure at the outlet of the feeder is above ambient pressure. In such installations, the feeder is usually installed in close liquid communication with the outlet side of the recirculation pump, which then must develop at least sufficient force to overcome the static head of pressure represented by the difference in height between the pump and the level of the body of water. For example, water withdrawn from a swimming pool for treatment is forwarded by gravity to a filter and then pumped sequentially to a heater (if used) and the chemical feeder before being returned to the pool. Other arrangements place the filter after the recirculation pump, or position the feeder in a bypass conduit parallel to the main flow line but located on the discharge side of the recirculation pump. A further example is when a feeder is used for the treatment of a potable water supply and the feeder is placed in series with an elevated potable water tank, which is used to supply a water distribution system.
Typically, such pressure feeders are operated in a manner wherein the dissolving or solvating fluid (solvent) introduced into the feeder contacts most or substantially all of the chemical material within the feeder, i.e., the solvating fluid floods the chamber containing the dissolvable chemical material. Such feeders are sometimes referred to as soaker feeders. Further, in the absence of means to allow the solvating fluid to drain out of the soaker feeder when it is not operating, the chemical material in the feeder continues to soak (and dissolve) in the solvating fluid. When “soaking” of the chemical material occurs during periods of feeder inoperation, the concentration of the chemical in the solution within the feeder increases above that desired for normal operating levels, results in premature depletion of the chemical material, and the possible occlusion of contiguous openings by partially dissolved and re-crystallized chemical material. In, for example pressure feeders used to sanitize swimming pools, “soaking” of the chemical material, e.g., calcium hypochlorite, causes delivery to the pool (when the feeder is subsequently placed in an operating mode) of a solution h
Ferguson Richard H.
Pickens Stanley R.
Hoey Betsey Morrison
Millman Dennis G.
PPG Industries Ohio Inc.
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