Liquid purification or separation – Constituent mixture variation responsive
Reexamination Certificate
2001-06-12
2003-06-24
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Constituent mixture variation responsive
C204S228100, C204S230200, C204S240000, C204S269000, C204S661000, C204S665000, C204S672000, C210S120000, C210S143000, C210S149000, C210S180000, C210S181000, C210S192000, C210S199000, C210S205000, C210S512100
Reexamination Certificate
active
06582592
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to fluid treatment methods and apparatus for precipitation of metal ions, such as copper, nickel, cadmium, lead, zinc, and chromium, from fluids by chemical oxidation-reduction processes produced by electrolysis, commonly referred to as electrocoagulation (EC), and more particularly to electrocoagulation apparatus for dissolving replacement metals, such as iron and aluminum, by electrolysis to initiate the precipitation process and force the reactions to completion.
2. Description of Related Art
Organic compounds produced or used in industrial processes can contaminate the water used in the processes. Many industrial plants, such as petrochemical refineries and gas plants destroy the organic compounds in biological reactors before discharging the wastewater into public streams. Metals used in the processes, e.g. catalysts, and metals corroded from the stainless steel piping can also contaminate the wastewater. Wastewater contaminated with certain heavy metals cannot be introduced into the biological reactors because the metals kill the microorganisms that feed on the organic compounds. Thus, the metals must be precipitated and removed from the wastewater before the water is introduced into the biological reactors or discharged directly into public streams.
Governmental regulations restrict to very low levels the amount of contamination that can be discharged. Some of those low discharge levels dictated by regulation can be extremely difficult to reach using current systems. If the low limits of the regulations are exceeded, the fines for not complying with the discharge regulations can be substantial. Further, when the wastewater cannot be decontaminated in a timely fashion on the plant site to comply with the regulations, the water is hauled off to facilities specializing in wastewater processing or pumped down approved hazardous wastewater disposal wells. The regulations become even more restrictive if the hazardous wastewater is transported off the plant site where it is generated. The cost and accountability of transporting the wastewater off-site can become cost prohibitive. Some plants discharge hundreds and others even thousands of gallons per minute on a continuous 24-hours per day, 365-days per year basis. Similar wastewater issues are prevalent in other plants such as electric power plants or electroplating plants.
Electrical means have been used for some time to treat water and to reduce problems of encrustation or scaling due to mineral deposits. For instance, the present inventor invented such a system for treating water in an open re-circulating system as disclosed in U.S. Pat. No. 4,235,698, issued on Nov. 25, 1980. For that application, electrodes of the most inactive metals practical were selected for the apparatus on the basis of effectively treating the water only with the electrical signals without the electrodes going into solution.
Many attempts using various methods have been made to process wastewater on the sites where it is generated. Previous attempts to remove metals from wastewater have included electrocoagulation (a process where iron or aluminum plates, configured as sets of cascaded electrodes, are consumed by electrolysis as waste water passes over them) systems. It is known that typical electrocoagulation reactors employ electrodes of non-hazardous metals, such as iron (Fe
+++
) and aluminum (Al
+++
), that go into solution. Wastewater having hazardous metals is passed between the electrodes and a current is applied to the electrodes. The electrodes then form positive ions that can replace the ions of hazardous metals in compounds that keep them in-solution, so both the hazardous and non-hazardous metals can precipitate together (known as adsorption and co-precipitation). In this way, the metals are separated from the wastewater as solids.
The selection of the non-hazardous metals for the electrodes is based on several factors: availability and cost; their chemical activity relative to the hazardous metals to be removed indicated by their position in the chemical oxidation potential tables; the ease at which they can be ionized by electrical means in accordance with Faraday's Law; the ability to concentrate them and increase the reaction potentials due to concentration in accordance with the Nernst equation; the ease at which they can be removed from solution following the removal of the other metals either by precipitation or plating out of solution; and the ability of the apparatus used to affect and contain the reactions.
The present electrocoagulation systems have been deficient in a number of ways. For instance, with present EC systems, the amount of metal contamination cannot be reduced to the regulated discharge limits. Further, present EC reactors require relatively large electrode surface areas. To provide the large surface areas needed from material generally available on the market, rectangular or square plates are used for the electrodes in many units. Those EC reactors are typically enclosed on all six sides by six exterior insulating plates of plastic.
These plastic plates bow and the units become visibly deformed when subjected to even moderate pressures on the inside of the plates. Because of this distortion, the plastic plates are difficult to seal. The larger the plates the more difficult it is to seal them. Many of the units may not withstand the pressures needed to operate at the stated flowrate. These units then leak the electrically-charged wastewater. Thus, those units are typically restricted to relatively small sizes with relatively small side panels and low flow rates.
Present electrocoagulation reactors generate large amounts of oxygen and hydrogen gases, by decomposition of water. In general in many industries, potential sources of electrical ignition are carefully protected by sealing them with explosion proof housings. However, the existing electrocoagulation units are typically not explosion proof. Thus, present EC reactors may leak leading to a potential safety hazard for the people immediately around the units.
Pure iron is not generally available for the electrode plates, so the iron needed for the EC reactor is obtained from steel plates. Steel electrodes have imperfections that cause the electrical erosion of the plate not to be uniform. As a result, small chips fall off the plates. The chips are conductive and can short the electrodes if they are lodged between the plates. Current EC systems are susceptible to this shorting problem.
For instance, U.S. Pat. No. 5,928,493 to Morkovsky et al. discloses mounting the plates horizontally. Large plates mounted horizontally sag as they erode to go into solution. The erosion is not uniform and the plates touch each other electrically shorting out the EC reactor. Morkovsky also discloses an EC reactor with electrode plates alternately unsupported at one end. Wastewater flows around the unsupported ends of the electrical plates in the apparatus disclosed as it zigzags through the reactor. The unsupported ends of the plates are exposed to the larger areas of adjacent plates during the treating action. Further, being exposed to a larger cathode area (from both sides) causes an anode to deteriorate faster. Faster erosion of the smaller area only causes the deficiency to become worse. This action has the adverse consequence of accelerating the sagging of the unsupported end of the plate and shorting the life of the entire plate assembly.
Further, the Morkovsky system utilizes costly clarifiers and a de-foam tank, both of which increase the costs of removing the heavy metals from wastewater. These limitations may also limit the capacity of the electrocoagulation system.
German Patent Application DE 3641365A1, published Aug. 25, 1988, discloses an apparatus for the cleaning and treatment of contaminated water using the electrocoagulation process. Again, this process utilizes the disadvantageous horizontal electrodes and clarifiers.
Manzione et. al describe using adso
Howrey Simon Arnold & White , LLP
Hruskoci Peter A.
Hydrotreat, Inc.
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