US20190330086A1

US20190330086A1 - Electrocoagulation Unit and a Method for Operating the Same

Info

Publication number: US20190330086A1
Application number: US16/476,099
Authority: US
Inventors: Robert John Stephenson; Michael Stephen GARDNER; Peter Douglas Jack
Original assignee: MUDDY RIVER TECHNOLOGIES Inc
Current assignee: MUDDY RIVER TECHNOLOGIES Inc
Priority date: 2017-01-05
Filing date: 2018-01-03
Publication date: 2019-10-31
Also published as: CA3049270A1; CA2953591A1; US11377374B2; CA3049269A1; WO2018126311A1; US20190352195A1; WO2018126312A1

Abstract

An electrocoagulation unit for removing one or more dissolved constituents from an untreated feedstock comprises a non-electrically conductive housing having a fluid inlet, a fluid outlet and an interior surface; a cathode and anode arranged within the housing, the cathode and anode each having an ionizing surface, the ionizing surfaces of the anode and cathode in opposed facing relation so as to define a gap having a separation distance therebetween; the cathode and the anode configured to be electrically coupled to a DC power supply in a DC electrical circuit so as to ionize and dissolve the ionizing surface of the anode; and a controller configured to maintain the separation distance at a set value as the ionizing surface of the anode dissolves. A method for using a plurality of electrocoagulation units in series is also provided.

Description

RELATED APPLICATIONS

This Patent Cooperation Treaty patent application claims priority to U.S. Provisional Patent Application No. 62/442,603 filed on Jan. 5, 2017 and Canadian Patent Application No. 2,953,591 filed on Jan. 5, 2017, each of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to electrocoagulation (EC) units for treating wastewater, otherwise referred to herein as a feedstock, and methods for operating same; in particular, the present disclosure relates to improved EC units for removing targeted constituents in a feedstock.

BACKGROUND

Various methods and processes for treatment of feedstock are known. The term “feedstock”, as used herein, includes various types of water or wastewater, including but not limited to waste water from hydraulic fracturing; so called fracking, oily water, mining water, brine, industrial wastewater, municipal wastewater, anaerobic digester effluent, landfill leachate, and groundwater. The feedstock is therefore an aqueous mixture which may contain or include one or more contaminants, constituents or components (hereinafter, referred to by the term “constituent”), which one or more constituents need to be removed from the feedstock.
Feedstock may need to be treated to remove one or more constituents from the feedstock for the following reasons: (a) for feedstock obtained from or produced by an industrial process, it may be desirable to re-use that feedstock in the same industrial process so as to conserve water resources and/or prevent discharge of contaminated feedstock to the environment. However, one or more constituents may need to be removed from the feedstock prior to re-using the feedstock in the industrial process; (b) to remove constituents from the feedstock so as to reduce potential harm to people or the air, water, land environment when the feedstock is discharged to the environment; or (c) so constituents, such as metals, nutrients, algae or other materials can be removed and recovered or harvested for other uses.
Amongst the various known processes and methods for treating feedstocks to remove targeted constituents, are conventional EC units. A conventional EC unit typically includes multiple pairs of anodes and cathodes, with a gap provided between each anode and cathode. The feedstock to be treated is forced to flow through the series of gaps between the multiple anode/cathode pairs, which electrodes are typically contained within a non-conductive cell housing with a feedstock influent connection and a treated feedstock outlet connection. An electrical power supply is connected to the pairs of anodes and cathodes by electrical cables. The electrical power requirement is relatively small to treat feedstocks at relatively low flow rates, requiring relatively long total hydraulic residence times of the influent feedstock stream within the gaps between the electrodes. The current density (electric current per total electrode area) of a conventional EC is relatively small.
Conventional EC units may either use direct current (DC), where the anodes and the cathodes are unchanging, or alternating current (AC), where the plates that serve as anodes and cathodes change their function when the polarity of the current is reversed.
Feedstock is introduced into an EC unit, otherwise referred to interchangeably herein as an EC cell, so as to flow through the gaps between multiple pairs of metallic anodes and cathodes. Typically, the anodes are constructed from carbon steel or aluminum plates, however, the anodes may also be constructed from magnesium, stainless steel, titanium, copper, or zinc, or other materials such as graphite. The anodes and cathodes are each electrically connected to either an AC or DC power supply. In use, electrical current flows from the anode through the influent feedstock to the cathode, gradually causing the anode to dissolve into the feedstock. The dissolved metallic anode ions, which are positively charged, serve to coagulate negatively charged constituents of the feedstock, increasing the constituents' particle size. Electrocoagulation also causes hydrolysis of water, whereby hydrogen (H₂) and oxygen (O₂) gas bubbles and hydroxide (OH⁻) ions are produced as by-products. The produced oxygen may oxidize feedstock constituents, which may result in the destruction of those constituents as their oxidation to other species (for example, Fe²⁺ is oxidized to Fe³⁺, which is less soluble), and their subsequent removal through solid-liquid separation techniques. The produced hydrogen and oxygen escape as gas bubbles from the feedstock. These gas bubbles may be used to separate coagulated solids by gas flotation. The produced hydroxide may increase the pH of the treated feedstock, depending on the feedstock composition and the anode material.
A conventional EC unit includes multiple pairs of anodes and cathodes, typically configured as sets of parallel metal plates having fixed positions relative to each other. A gap between each anode and cathode set is provided so feedstock can only flow through the gap. This requires that the side edges of each anode and cathode be sealed against the cell housing so the feedstock flows between each anode and cathode pair without by-passing the gap, the feedstock then exiting the EC unit through a treated feedstock outlet connection.
Electrical current dissolves the anodes. Therefore, the magnitude of electrical current controls the rate of feedstock treatment by EC. For typical EC cell configurations, as the supply of electrical current dissolves the metal anodes to treat the feedstock, the gaps between the anodes and cathodes eventually increase over time as the surface of the anode facing the cathode gradually dissolves. Where feedstock conductivity and DC current power supply remain constant, as the size of the gap between electrodes increases, the voltage increases linearly. However, because voltage increase does not result in an increase of the rate of feedstock treatment by EC, in order to minimize electrical power cost (the product of current and voltage), the electrode gap would ideally be maintained at a relatively small and constant distance. Once the anode is consumed to a significant extent, the electrode plates may therefore need to be re-positioned so as to maintain the gap between the anode and the cathode at the small and substantially constant distance.
Typical EC cells use multiple sets of anodes and cathodes configured as parallel plates, each plate having a thickness of approximately one inch or less, and positioned so as to have an initial gap of approximately one inch or less between the anode and cathode of each set of electrodes. As each anode is dissolved by EC treatment, the gap between each anode and cathode pair gradually increases.
Typically, the edges of each anode and cathode plate are sealed against the cell housing so the feedstock flows between each anode and cathode pair without flow by-pass. Therefore, when the voltage becomes too high, indicating excessive electrode gaps, or when the electrodes become plugged, or when the anodes are dissolved to the extent that they cannot prevent by-pass and direct flow of feedstock between the anodes and the cathodes, EC cell maintenance is required.
Performing maintenance on the multiple sets of electrodes in a conventional EC unit involves removing the electrodes from the cell so they may be cleaned of fouled material, replaced, and/or mechanically reset so as to adjust the distance of the gap between the anodes and the cathodes. Such maintenance is labour intensive and costly, resulting in a loss of productivity as the EC unit is taken out of service during maintenance.

SUMMARY

In some embodiments of the present disclosure, an improved EC unit includes one anode and one cathode. One small and nearly constant gap between the anode and cathode is maintained by one or more spacers positioned between the anode and cathode, or in other embodiments, the nearly constant gap distance may be maintained by controls which trigger the adjustment of the anode relative to the cathode, based on measured voltage, or alternatively, based on current or treatment time.
Feedstock flows through one or more holes in the cathode to enter into the gap between the cathode and the anode. Feedstock may flow upwardly through the EC cell so the gas bubbles that are by-products of the electrochemical reactions rise with the flowing feedstock to exit the EC cell along with treated feedstock, rather than accumulating inside the cell where the gas bubbles may decrease conductivity of the liquid feedstock within the gap between the anode and cathode and risk explosion. In some embodiments, the cathode may be stationary and sealed against the cell housing. In one embodiment, treated feedstock exits the gap at the periphery of the anode and flows up around the outside cylindrical wall surface of the anode towards the EC cell treated feedstock discharge connection. The anode is not sealed against the cell housing, but is configured to be translated within the cell housing either towards or away from the fixed cathode, thereby enabling for periodic adjustment of the distance of the gap between the anode and the cathode as the anode slowly dissolves. Typically, the EC cell housing may be constructed from PVC pipe, rubber lined steel, or other suitable materials which are non electrically-conductive and resistant to corrosion; ideally, the EC cell housing may be constructed of materials that are relatively inexpensive and which are capable of accommodating a small pressure drop.
Although in some embodiments the electrodes may be constructed of sections of a round bar enclosed within a cylindrical EC cell housing, it will be appreciated that such geometry is not intended to be limiting, provided the one anode is configured to be translatable within the cell housing so as to enable adjustment of the distance of the gap between the anode and cathode. Furthermore, the anode may be a single anode, or, in other embodiments, the anode may be a plurality of anodes, provided that the plurality of anodes are in electrical communication with each other and connected to the power supply. In the embodiments described herein, the cathode is held in a fixed position within the EC cell housing and the anode is configured so as to be translatable within the cell housing, such that the anode may be moved towards or away from the fixed cathode. However, the Applicant notes that other embodiments providing for relative motion between the anode and cathode; for example, in which the anode is held in a fixed position within the cell housing and the cathode is configured so as to be translatable towards or away from the fixed anode, for maintaining a substantially constant gap distance G between the anode and cathode, one also intended to be included within the scope of the present disclosure.
An electrical power supply is connected to the translatable anode and stationary cathode by electrical cables. The electrical cable connected to the anode may be of sufficient length so as to maintain an electrical connection between the power supply and the anode until the anode is entirely dissolved. Advantageously, by maintaining a substantially constant distance between the anode and cathode within the EC cell, the electrical power requirement is relatively large but consistent to treat feedstock at a relatively high flow rate, thereby enabling a hydraulic residence time in the gap of approximately one second. With the high flow rate, small EC cell disclosed herein, the current density (current per electrode area) of embodiments of the EC unit disclosed herein is high compared to conventional EC units, although the electrical current requirement per mass of targeted constituent to be removed is similar to that of conventional EC cells. For example, without intending to be limiting, the EC unit embodiments disclosed herein may have a current density in substantially the range of 0.1 A/cm²to 1 A/cm², and the flow velocity of the feedstock through the EC cell gap may be in the range of 1 cm/s to 10 cm/s. In one example of an EC unit according to the present disclosure, the EC unit's electrodes have a current density of substantially 0.24 A/cm²and operate at a feedstock flow velocity through the EC cell gap of substantially 2.3 cm/s.
Electrical power supplies are rated according to their capacity to deliver electrical current at a specified voltage. In addition to lowering operating costs, minimizing voltage requirements minimizes the capital cost of power supplies. Consequently, the distance across the electrode gap needs to be maintained substantially constant and relatively small so as to reduce power costs.
Using EC to treat feedstocks that have only small electrical conductivity requires high voltage in order to provide enough electrical current to dissolve the anode. Minimizing the gap between the electrodes minimizes voltage requirements and lowers the capital cost of the power supply.
Furthermore, maintaining a substantially constant gap distance helps to ensure that consistent treatment of feedstock is achieved. Because increasing the gap distance increases the voltage across the gap and thus, may decrease current, EC treatment will decrease. Thus, a small and constant gap between the electrodes is desirable.
Maintaining a small gap maximizes fluid turbulence as feedstock flows through the gap between the anode and the cathode. Maximizing turbulence maximizes contact between the feedstock and the anode surface, so the dissolved metal efficiently contacts feedstock constituents for their effective coagulation.
For a given flow rate, a small electrode gap maximizes turbulent contact and scouring by the feedstock with the anode surface, thus minimizing fouling of the anode surface.
A small and constant electrode gap minimizes voltage and thus enables high current to be delivered from a power supply, thus providing high current density that helps prevent electrode fouling.
In an aspect of the present disclosure, an electrocoagulation unit for removing one or more dissolved constituents from an untreated feedstock comprises a non-electrically conductive housing having a fluid inlet, a fluid outlet and an interior surface; a cathode and an anode arranged within the housing, the cathode and anode each having an ionizing surface, the ionizing surfaces of the anode and cathode in opposed facing relation so as to define a gap having a separation distance therebetween; the cathode and the anode configured to be electrically coupled to a direct current (DC) power supply in a DC electrical circuit so as to ionize and dissolve the ionizing surface of the anode; and a controller configured to maintain the separation distance at a set value as the ionizing surface of the anode dissolves. In some embodiments, the electrocoagulation unit's cathode includes an inlet surface opposite the cathode's ionizing surface and at least one aperture extending through the cathode from the inlet surface to the ionizing surface, the cathode mounted to and sealed against the interior surface of the housing so as to orient the inlet surface towards the fluid inlet, and the at least one aperture defines a flow path for the untreated feedstock to flow from the fluid inlet to the gap. In some embodiments, the anode may be replaceable.
In another aspect of the present disclosure, the controller of the electrocoagulation unit may comprise at least one non electrically-conductive spacer, the at least one spacer sandwiched between the cathode and the anode so as to simultaneously contact the ionizing surface of the cathode and the ionizing surface of the anode. In some embodiments, the anode may be weighted so as to maintain contact between the ionizing surface of the anode and the at least one spacer.
In another aspect of the present disclosure, the cathode may be mounted to and sealed against the interior surface of the housing and the controller comprises an actuator operatively coupled to cause relative movement between the anode and cathode. In some embodiments, the actuator is actuated when a measurable parameter attains a threshold value, and the measurable parameter may be selected from a group comprising: unit operation time, voltage, current. In some embodiments, when actuated, the actuator is configured to translate the anode towards the cathode so as to contact the ionizing surfaces of the anode and the cathode and then translate the anode away from the cathode so as to separate the ionizing surfaces of the anode and cathode by the separation distance.
In some embodiments, the one or more constituents of the untreated feedstock includes at least dissolved metal ions and the anode comprises magnesium so as to facilitate removal of the at least dissolved metal ions from the untreated feedstock.
In another aspect of the present disclosure, a method of treating an untreated feedstock using the electrocoagulation units comprises the steps of:

- providing a plurality of EC units, such as those described above,
- connecting each EC unit of the plurality of EC units in series by connecting the fluid outlet of one EC unit of the plurality of EC units to the fluid inlet of an adjacent unit of the plurality of EC units, wherein a first unit of the plurality of EC units has a free fluid inlet and a last unit of the plurality of EC units has a free fluid outlet,
- operatively connecting at least one DC power supply to the anode and cathode of each EC unit of the plurality of EC units,
- flowing a volume of the untreated feedstock into the free fluid inlet,
- wherein a coagulated amount of at least one dissolved constituent of the volume of untreated feedstock increases within each EC unit of the plurality of EC units as the volume of untreated feedstock flows from the first unit to the last unit.

In another aspect of the present disclosure, providing the controller of each EC unit of the plurality of EC units includes providing an actuator operatively coupled to the anode so as to selectively translate the anode relative to the cathode; detecting when a measurable parameter of any unit of the plurality of EC units attains a threshold value; identifying the EC unit of the plurality of EC units in which the parameter has attained the threshold value; and actuating the actuator so as to adjust the separation distance of the identified EC unit so as to optimize the separation distance.
In some embodiments, the step of actuating the actuator may further include translating the anode towards the cathode so as to contact the ionizing surface of the anode against the ionizing surface of the cathode and then translating the anode away from the cathode until the separation distance is optimized. In some embodiments, the measurable parameter may be selected from a group comprising: unit operation time, voltage, current.
In another aspect of the present disclosure, the plurality of EC units connected in series may include a conduit for conducting an intermediate feedstock from the fluid outlet of one unit to the fluid inlet of an adjacent unit, wherein the method further comprises the step of adding an anionic polymer to the intermediate feedstock as the intermediate feedstock flows through the conduit so as to flocculate the intermediate feedstock. In some embodiments, the one or more constituents of the untreated feedstock includes at least dissolved metal ions and the anode comprises magnesium so as to facilitate removal of the at least dissolved metal ions from the untreated feedstock.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cut-away view of an embodiment of an EC unit in accordance with the present disclosure.

FIG. 2 is a cut-away view of an embodiment of an EC unit in accordance with the present disclosure.

FIG. 3 is a flow diagram of an embodiment of a method for maintaining a gap distance within an EC unit in accordance with the present disclosure.

FIG. 4 is a flow diagram of an embodiment of a method for maintaining a gap distance within an EC unit in accordance with the present disclosure.

FIG. 5 is a schematic illustrating an embodiment of a method for using a plurality of EC units in series in accordance with the present disclosure.

DETAILED DESCRIPTION

In some embodiments of the present disclosure, the improved EC unit includes one anode and one cathode. The anode and cathode are contained in a non electrically-conductive cell housing with a feedstock influent connection and a treated feedstock outlet connection. Typically, the cell housing may be constructed from PVC pipe or rubber lined steel pipe. The diameter or inside dimensions of the cell housing is sized to accommodate flow of the feedstock between the typically cylindrical anode and the cell housing.
In some embodiments, such as illustrated in FIG. 1, the anode 130 consists of a metal round bar, which may typically range from three to 12 inches diameter D, or larger. The length L of a new anode, prior to use, may typically be in the range of 24 inches, but could be as small or as large as needed, taking into consideration the factors of treatment requirements, anode weight and interior volume of the housing. Because the anode 130 dissolves over time while the EC unit 198 is operating, a larger diameter D or longer length L of anode 130 would allow the heavier anode to be in service for a longer period of time before requiring replacement. The diameter D of the anode is selected to provide treatment while maintaining a high current density and a high flow velocity of the untreated feedstock as it flows through the gap 111 between the anode 130 and the cathode 124, so as to provide efficient mass transfer and to minimize electrode fouling by fluid turbulence. The shape of the active area between the anode and cathode may be selected so as to provide a constant pressure drop between the one or more inlet apertures 126 in the cathode and the periphery of the electrode gap 111.
The anode 130 may be manufactured of aluminum, carbon steel, magnesium, copper, zinc, or any other suitable material which releases positively charged ions upon dissolution wherein the positively charged ions are suitable for coagulation of dissolved constituents in the feedstock. The time to dissolve the entire anode for EC treatment of feedstock is directly proportional to the electrical current, the duration of treatment operation, and the mass of the anode. The cathode 124 is made of electrically conductive material that is resistant to chemical degradation under the conditions of treating the feedstock. For example, not intended to be limiting, the cathode may be constructed from aluminum, stainless steel, carbon steel, titanium, or graphite.
In some embodiments, a pipe connection is attached to the base of the cathode to serve as the fluid inlet 116 to the EC cell 198. The cathode 124, which may be in the form of a plate, is sized such that the ionizing surface 125 of the cathode, facing the ionizing surface 129 of the anode, and the inlet surface 123 of the cathode opposite the ionizing surface 125, substantially occupies the entire cross-sectional area of the cell housing 110, and the cathode 124 is mounted to an interior surface 109 of the cell housing 110, such that all incoming feedstock flows through the gap 111 between the anode and the cathode. Feedstock flows through a flow path, whereby untreated feedstock enters the EC unit 198 through the fluid inlet 116 and through one or more apertures 126 which extend through the cathode 124 from the inlet surface 123 of the cathode to the ionizing surface 125 of the cathode, the one or more apertures 126 typically located near the center of the inlet and ionizing surfaces 123, 125 of the cathode, so as to enter the gap 111 between the cathode and the anode. The number of apertures, and the total surface area of those apertures, is preferably selected to create a pressure drop across each aperture to minimize risk of plugging the one or more apertures during operation of the EC unit. Feedstock then flows through the gap in a radial direction to exit the gap at the perimeter of the anode and the cathode 160.
After feedstock exits the gap 111 between the anode and the cathode, it flows between the perimeter 160 between the anode 130 and the interior surface 109 of the EC cell housing and then exits out the top of the EC cell housing through a fluid outlet connection 122.
An electrical cable 151 may be attached to an outlet surface of the anode 131, the outlet surface positioned opposite the ionizing surface of the anode and facing towards the fluid outlet of the EC unit, and the electrical cable is configured to connect to a direct current (DC) power source 150. The length of the electrical cable may be selected so as to accommodate the complete dissolution of the anode, as the ionizing surface of the anode will gradually dissolve over time while the EC unit is operating, thereby causing the outlet surface 131 of the anode to gradually move towards the cathode 124 as the ionizing surface 129 of the anode dissolves. An electrical cable 152 is also attached to the cathode 124 so as to supply DC electrical current from the DC power source 150 to the cathode; for example in some embodiments, the electrical cable 152 may be attached to the edge of the cathode and is configured to be connected to the DC power source 150.
In one embodiment of the EC unit 198, illustrated in FIG. 1, during operation the anode 130 rests loosely on top of one or more non-conductive spacers 128 that are mounted on the cathode 124 to provide a gap 111 between the anode 130 and the cathode 124, the gap 111 having a set distance G. As the ionizing surface 129 of anode 130 is dissolved into the feedstock that flows through the electrode gap 111, the weight of the anode 130 causes the anode to continue to rest on the spacers and thus maintain a gap 111 having a substantially constant distance G between the ionizing surfaces 129, 125 of the anode and cathode respectively. In general, maintenance of the EC cell 198 may not be required until the anode 130 is fully dissolved, at which time a replacement anode 130 may be connected to the electrical cable 151 and dropped into place on the spacers 128.
In a preferred embodiment of the present disclosure, such as illustrated in FIG. 1, the cathode 124 remains in a fixed position within the cell housing 110, such as by mounting the cathode to the interior surface 109 of the cell housing 110, whereas the anode 130 is not affixed to the cell housing 110 and is therefore free to move within the cell housing 110. Optionally, so as to ensure the anode 130 remains in contact with the spacers 128 during dissolution of the ionizing surface 129 of the anode, a weight 134 may be positioned so as to apply a downward force in direction X to the outlet surface 131 of the anode 130.
Spacers can be made from any non-fragile and non-conductive material, such as plastic or nylon or hardened rubber, for example, which materials do not degrade in the environmental conditions within the EC cell and which materials are capable of supporting the weight of the anode 130 without significant deformation. The spacers are preferably narrow, for example having a width W in the range of not more than 0.5 inches, so as to reduce the impact of the shadow effect, whereby non-conductive materials in the gap between the anode and the cathode result in localized increased electrical resistance, and thus less electrical current, in the area 115 of the ionizing surface 129 of the anode which is proximate to the one or more spacers 128. In areas in the gap where the electrical current is less, the rate of anode dissolution is correspondingly less. Consequently, non-conductive materials such as spacers result in unequal anode consumption on the ionizing surface 129 of the anode. Therefore, using narrow spacers 128 reduces the impact of the shadow effect on the consumption of anode 130.
When a new anode 130 is initially put into service, the ionizing surface 129 is substantially flat and the ionizing surface 129 will be preferentially dissolved in the areas not contacted by the spacers 128, and the anode surface area 115 which is in contact with or proximate to the spacers 128 will dissolve at a slower rate compared to the rest of the ionizing surface 129. However, over time, because the anode surface 115 that contacts or is proximate to each spacer 128 forms the smallest local distance to the cathode 124, depending on the current density and the width dimension W of each spacer 128, the shadow effect of the spacers may eventually be overcome, so the localized electrical resistance in the localized area 115 becomes approximately equal to the electrical resistance where the spacers 128 do not contact the ionizing surface 129. The factors of higher current density and smaller width W of each spacer 128 reduces the shadow effect, thereby producing a smaller and shallower raised area on the ionizing surface 129 of anode 130. Although the anode surface is uneven, the Applicant observes the wear pattern is generally steady during routine operations until the anode 130 is almost completely dissolved.
The spacers 128 may take various shapes and geometries; for example, without intending to be limiting, the one or more spacers 128 may include plates, rods, nubs, balls, spirals or any combination thereof. Preferably, the spacers 128 are held in place by attaching them to the cathode through screws, mating slots or any other suitable means, such that the spacers 128 do not shift position during flow of the feedstock through the gap 111. The spacers 128 are ideally configured so as to enable approximately uniform flow of feedstock through the electrode gap 111 from the inlet apertures 126 to the periphery 160 of the anode 130. The gap 111 between the anode and cathode is preferably configured to have a set distance G of substantially ⅛ of an inch or less, although this is not intended to be limiting, as in other EC cell configurations the set distance G may range up to substantially one inch.
In other embodiments, the EC unit may include a controller for moving the anode towards the cathode, so as to maintain the distance of the gap between the anode and the cathode at a set value, upon detecting a parameter of the EC unit attaining a specified value. In such embodiments, the anode may be mounted on a vertically movable platform, such as a piston, inside the EC cell housing. Moving the platform may be accomplished by actuating an actuator operatively connected to the platform. Examples of actuators may include, for example, a hydraulic or pneumatic piston, a mechanical screw, or a lifting jack. Actuating the actuators may be accomplished by electromechanical means, or in the alternative, actuation may occur by an operator manually actuating the actuator. As one example of a parameter of the EC unit, changes in voltage may be monitored. As operation of the EC unit dissolves the anode, thereby increasing the distance of the gap between the anode and cathode, the voltage required to treat the feedstock increases. Once the parameter of the voltage supplied to the electrodes is detected to reach a set value, thereby indicating the distance between the anode and cathode has become too large, an actuator operatively connected to the movable platform moves the anode towards the cathode until a lower, desired voltage is reached.
In another embodiment, a set period of operation for the EC unit may be used as a parameter to trigger the actuation of the platform so as to move the anode closer to the cathode. The set period of operation may be selected based on the electric current and thus the approximate rate of dissolution of the ionizing surface of the anode. In some embodiments, upon reaching the set period of operation of the EC unit, the DC power supply is turned off, and then the actuator is actuated so as to lift the anode until it comes into contact with the cathode. Then, the anode is lowered until the distance of the gap between the anode and cathode reaches the set value. The DC power supply is then resumed.
FIG. 2 depicts further embodiments of an EC unit 298, which maintains the distance G of the gap 211 between a cathode 224 and an anode 230 at a relatively constant value, utilizing a hydraulic piston and hydraulic pump as the actuator for moving the anode towards the cathode, as described above. However, it will be appreciated by a person skilled in the art that the following description of the embodiment depicted in FIG. 2 is not intended to be limiting, and that, for example, other types of actuators, whether manually or mechanically or electromechanically actuated, are intended to be included within the scope of the present disclosure.
The EC unit 298 comprises a housing 210, two end flanges 212, 214, the cathode 224, the anode 230, a platform such as a hydraulic piston 217 and an actuator such as a hydraulic pump 234. The housing 210 and two end flanges 212, 214 may define a substantially fluid tight plenum that houses the cathode 224, the anode 230 and the hydraulic piston 217. Fluid inlet 216 conducts a volume of untreated feedstock into the EC unit 298, for example through end flange 214 proximal to the cathode 224. Fluid outlet 222 conducts treated feedstock from the EC unit 298. The volume of feedstock within EC cell 298 may be drained via a drain including a valve 221 and conduit 218, for example when servicing the EC cell 298.
The housing 210, the end flanges 212, 214, the cathode 224 and anode 230 may be manufactured from the same materials as described above for the corresponding components of the EC unit 198. The hydraulic piston 217 can be made from similar non-conductive and thermally resistant materials as the end flanges 212, 214. The cathode 224 also comprises at least one aperture 226, which is similar to the at least one aperture 126 described above in relation to EC cell 198. Furthermore, the anode 230 includes an ionizing surface 229 and the cathode includes an ionizing surface 225, oriented towards the ionizing surface 229 of the anode 230.
The hydraulic piston 217 is contained within the housing 210 and positioned adjacent a piston surface 231 of the anode 230, opposite the ionizing surface 229 of the anode. The hydraulic piston 217 is in fluid communication with the hydraulic pump 234 via manifold 238. The end flange 212 includes one or more inlet ports 212′. The inlet ports 212′ provide fluid communication between the manifold 238 and the interior of the housing 210. The hydraulic pump 234 is in fluid communication with a supply reservoir 236 of hydraulic fluid. In one example, the hydraulic fluid may include the untreated feedstock. Optionally, the drain 218, 221 may be in fluid communication with the supply reservoir 236 via conduit 218 for providing fluid to the supply reservoir 236. The hydraulic pump 234 may comprise one or more of a fixed or variable displacement pump. For example, the hydraulic pump 234 may be one or more of a gear pump, a peristaltic pump, an axial pump with or without a swash plate, a screw pump or a rotating vane pump.
The hydraulic piston 217 further comprises annular seals 201 that are positioned between a circumferential edge of the hydraulic piston 217 and the inner surface 209 of the housing 210. The annular seals 201 form a fluid tight seal, such that as the hydraulic pump 234 introduces and removes hydraulic fluid into the housing 210 via the manifold 238, the hydraulic fluid will push or pull the hydraulic piston 217 towards or away from the anode 230. Alternatively, the hydraulic pump 234 may only introduce hydraulic fluid to move the hydraulic piston 217 towards the anode 230. A valve 221 of the drain may be activated to drain hydraulic fluid and allow the hydraulic piston 217 to move away from the anode 230, for example by gravity. Optionally, the valve 221 may be an electrically controlled solenoid.
During operation of the EC unit 298 a direct electrical current is provided by a direct current (DC) power source 250, resulting in the dissolution of the ionizing surface 229 of anode 230 and delivering highly reactive, positively charged ions; for example, not intending to be limiting, the positively charged ions may be Al³⁺, Fe³⁺ or Mg²⁺, depending on whether the anode is constructed of aluminum, iron or magnesium respectively. The positively charged ions are released into the gap 211 where they come into contact with the influent feedstock, causing coagulation of negatively charged constituents in the feedstock. Negatively charged constituents may include, for example, petroleum hydrocarbons, suspended solids, or phosphate; although it will be appreciated by persons skilled in the art that such examples of negatively charged constituents in a volume of untreated feedstock are not intended to be limiting, and may include any type of negatively charged constituent which is desired to be removed from the volume of untreated feedstock. Operation of the EC unit also causes hydrolysis of the water in the untreated feedstock, to produce O₂(oxygen) gas, H₂(hydrogen) gas and dissolved OH⁻ (hydroxide). For volumes of untreated feedstock containing dissolved chloride, operation of the EC unit on the untreated feedstock also produces Cl₂(chlorine) gas. The anode/cathode electrode pair(s) may be positioned in any orientation as long as the entire volume of untreated feedstock flows through the gap 211 between the anode and cathode, and the above gaseous by-products produced within the EC unit during operation will flow through the fluid outlet 222 rather than accumulate within the cell housing 210.
The controller, consisting of an actuator such as the hydraulic pump 234 and piston 217 as shown in FIG. 2, may maintain a substantially constant distance G of the gap 211 between the anode 230 and the cathode 224, for example by one or more of the processes described in FIGS. 3 and 4, by which a parameter of the EC cell 298 is monitored and the actuator is actuated upon detection of the parameter reaching a set value. For example, as illustrated in FIGS. 2 and 3, process 1100 comprises the steps of setting a time interval at step 1110 which is a time interval during which the EC unit 298 is operated prior to moving the anode towards the cathode; attaining the set time interval, at step 1113; interrupting the DC power supply to the electrodes, at step 1115; actuating the actuator at step 1120, such as by pumping the hydraulic fluid, so as to move the anode 230 in direction X towards the cathode 224; at step 1130, contacting the ionizing surface 229 of the anode 230 with the ionizing surface 225 of the cathode 224; at step 1150, actuating the actuator so as to move the anode in direction Y away from the cathode, such as by releasing hydraulic fluid, until the distance G of the gap 211 reaches the set value.
The step 1110 of setting a time interval is based upon the expected rate of anode consumption; for example, the time interval may be set to an EC unit operation time of 30 minutes, or any other suitable time interval. For example, a higher rate of anode consumption would result in the distance G of the gap 211 increasing at a faster rate, thereby requiring a lower set time interval for triggering actuation of the anode so as to decrease the distance G of the gap 211; and conversely, a lower rate of anode consumption would result in the distance G of the gap 211 increasing at a slower rate, in which case the selected set time interval may be longer before actuating the actuator so as to decrease the distance G of the gap 211. Upon detecting that the set time interval has been attained, the actuator, which may be a hydraulic pump 234, is actuated so as to pump hydraulic fluid to move the hydraulic piston 217 and the anode 230 in direction X until the anode 230 briefly contacts the cathode 224. While various hydraulic fluids may be used, untreated feedstock or other aqueous fluids are preferred because minor leaks past the seals 201 and into the volume of untreated feedstock contained within the other portions of the EC unit 298 are of minimal consequence. The contact between the anode 230 and the cathode 224 causes the DC current to momentarily spike and the voltage to decrease to near zero. Creating a current spike at step 1130 may, in some embodiments, result in activating the valve 221 and releasing hydraulic fluid from below the hydraulic piston 217 for moving the anode 230 out of contact with the cathode 1150, thereby re-establishing the gap 211 at a set distance G between the anode 230 and the cathode 224. Advantageously, utilizing the unit operation time as the parameter for actuating the actuator so as to adjust the distance G of the gap 211 may be used to establish a relatively constant distance G between the anode and cathode, even where the conductivity of the influent, untreated feedstock is variable.
FIGS. 2 and 4 depict a further embodiment of controlling the distance G of the gap 211. Process 1200 comprises the steps of setting a threshold value of voltage or current, at step 1210; detecting when the threshold value is attained, at step 1215, for example by monitoring the DC power source 250; actuating the actuator, at step 1220, for example by pumping hydraulic fluid so as to move the piston and the anode 230 towards the cathode 224; and reducing the distance G of the gap 211 to the set value of distance G, at step 1230. For example, with reference to FIG. 2, during operation of the EC unit 289, if the direct current source 250 operating voltage exceeds a threshold voltage, for example 10 volts, hydraulic fluid is pumped from below the hydraulic piston 217 in housing 210 to move up the hydraulic piston 217. This causes the anode 230 to move closer to the cathode 224 and reduce the distance G of gap 211. The reduced gap reduces the operating voltage of the DC power source 250. Pumping continues until the operating voltage of the DC power source 250 reduces to less than the threshold voltage and then the pumping stops. This approach for controlling the distance G of the gap 211 may preferably be used when the conductivity of the influent feedstock is relatively constant.
In some embodiments, either one of the processes 1100 and 1200 may be automated. For example, the controller may be configured to monitor the EC unit 298 and control the hydraulic pump 234 by the set time interval (as in process 1100) or by monitoring the voltage or current output of the DC power source 250 (as in process 1200). The processes 1100, 1200 maintain a relatively constant gap distance G, advantageously enabling the EC unit 298 to operate without intervention or maintenance until the entire anode 230 is dissolved. In some embodiments, when the anode 230 is entirely dissolved, the voltage or current cannot be reduced when the actuator is actuated, in which case the controller may include a high voltage or high current alarm, signaling to the operator that a replacement anode 230 is required.
Optionally, the EC units 198 or 298 may further comprise a removable cap 132 or 232. A removable cap 132 or 232 may be positioned above the anode 130 or proximate the anode 230 to provide access so the anode 130 or 230 may be placed inside the housing 110 or 210 and one or more electrical cables may be connected between the anode 130 or 230 and the DC power source 150 or 250.
The use of spacers 128 in the EC unit 198 and the processes 1100, 1200 in the EC unit 298, as described above, are preferred approaches. There are other ways to adjust the gap G in response to detected changes in current, voltage, and/or pressure drop across the EC units 198, 298. Such means of automated electrode positioning may include: a hydraulic piston, ram or jack; a pneumatic piston, ram or jack; or a mechanical screw or a range of mechanical jack configurations.
The smallest practical gap distance G is limited by pressure drop as feedstock flows through the EC unit 198 or 298. As G decreases, the pressure drop increases. This effect is more pronounced at elevated flow rates. As the pressure drop across the EC units 198, 298 increases, more energy is required to pump the feedstock through the EC units 198, 298. The preferred gap distance G is one where a target flow rate of feedstock is achieved while the sum of the energy input for the direct current source 150, 250 and for pumping water through the EC units 198, 298 is minimized.
The anode 230 may be replaced following these steps: turning off the direct current power source 250; stopping the flow of feedstock into the EC unit 298; releasing the volume of feedstock that may be trapped within the EC unit 298, for example by opening drain 231 in cap 232; removing cap 232; removing any remnants of the used anode 230; disconnecting the electrical connection between the anode 230 and the direct current source 250; placing a replacement anode 230 upon the hydraulic piston 217; connecting the replacement anode 230 to the direct current source 250; opening drain 218, 221 to release hydraulic fluid trapped between the hydraulic piston 217 and the end flange 212; replacing cap 232 and closing drain 231 therethrough; closing drain 218; resuming the flow of feedstock into the EC unit 298; turning the current source 250 back on; activating the hydraulic pump 234 to re-establish the set gap distance G, which may be in response to a current spike or a threshold voltage value, for example, depending on the embodiment of a controller utilized to maintain the distance G at the set value.
In another aspect of the present disclosure, as EC units operate to dissolve, for example, an aluminum or carbon steel anode to deliver positively charged aluminum or iron ions for coagulating constituents in the feedstock, the dissolved hydroxide (OH—) that is also produced as a by-product of hydrolysis reacts with the dissolved metal ions, thus removing hydroxide from the feedstock and resulting in only a minor change of pH levels in the feedstock. With their hydroxide-consuming properties, aluminum and iron are acid-producing metals.
In contrast with aluminum and iron, using a magnesium anode within an EC unit delivers dissolved magnesium and a surplus of hydroxide ions, resulting in significant pH increase. Compared with steel or aluminum anodes, magnesium anodes consume far less of the produced dissolved hydroxide. Advantageously, this increase in the pH level may therefore facilitate removal of dissolved metal constituents in the feedstock, through formation of insoluble metal hydroxides between the dissolved metal constituents and the surplus dissolved hydroxide, in addition to removal of negatively charged constituents in the feedstock.
Treating feedstock with EC produces both positive and negative charges. Dissolved metals may be positively charged but dissolved metal hydroxides are negatively charged. EC introduces positively charged dissolved metal ions which coagulate negatively charged feedstock constituents. Therefore, following treatment of feedstock in an EC unit with flocculation using anionic polymer produces negative charges that attach to positive charges, resulting in agglomeration of constituents to increase the size of the formed particles. Repeating this cycle of EC unit treatment and flocculation one or more times may remove both negatively and positively charged constituents to form agglomerations of larger particle sizes. As these agglomerated particles become larger, they are more readily separated by liquid: solid separation techniques such as flotation, sedimentation, or filtration.
For feedstock constituents such as with iron, manganese, or sulphide where oxygen reacts with these constituents to render them less soluble, multiple stages of EC units in series may advantageously improve treatment performance. Initially, the constituents are oxidized to form less soluble solids that are then subsequently separated by coagulation, flocculation, and flotation.
The EC units disclosed herein also deliver dissolved hydroxide that reacts with dissolved metals to form insoluble metal hydroxides. Multiple stages of EC units in series can improve removal of these metal hydroxides that carry a negative charge. By each cycle of EC unit treatment and flocculation, the constituents form metal hydroxides (negative charge), and subsequently they are coagulated by EC (positive charge), and flocculated (negative charge). This cycle is repeated until the concentration of soluble metals meets treatment objectives and the agglomerated particles are large enough to favour their separation from the treated feedstock. The on-going production of excess hydroxide in EC units, particularly when using magnesium anodes, helps to provide a chemical environment that favours insolubility of the formed metal hydroxides.
Employing multiple stages of EC and flocculation is more than just additive. For each of these mechanisms, employing multiple stages of EC and flocculation may result in performance synergies to remove constituents from feedstock. Operating EC and flocculation in series may be performed when the solubility of constituents is decreased by changes in pH or by oxidation due to EC, to remove dissolved constituents that are present in small concentrations, or where constituents need to be removed until they are present in reduced concentrations, depending on the desired parameters for the treated feedstock.
This approach of multiple stages of EC and flocculation in series may either be employed utilizing the EC units disclosed herein, or by using conventional EC units. However, with conventional EC unit designs which employ low flow rates and low current density, electrode fouling by agglomerated insoluble particles formed by EC and flocculation is more likely to occur, whereas such electrode fouling is reduced or eliminated by the EC units disclosed herein, due to the increased efficiency of the EC units described above which enable higher flow rates for the influent untreated feedstock.
In addition to current density, a key parameter to prevent electrode fouling is to provide a feedstock flow velocity sufficient to scour the electrode surfaces via turbulent fluid flow through the electrode gap. However, for some applications, increasing the feedstock flow velocity may not be feasible due to the limitations of using a single DC power supply, which may limit the ability to increase the current supplied to the electrodes so as to achieve suitable performance of constituent removal at an increased feedstock flow rate. Because EC treatment involves applying electric current to dissolve an anode in proportion to the mass of the constituent to be removed, increasing the flow rate increases the mass of the constituent to be removed, so increased electric current is required to increase the dissolution of the anode for satisfactory treatment performance. In the alternative, the total current required to achieve satisfactory treatment at an increased flow rate may be reached by using multiple EC cells, each with their own DC power supply. In this way, multiple stages of EC may be used by connecting a plurality of EC units in series, so as to achieve overall improvements in treatment performance at the increased the flow rate.
As illustrated in FIG. 5, in one embodiment of the present disclosure a plurality of EC units 1, such as the EC units 198 or 298 described above, are connected in series whereby the fluid outlet 12 of a first EC unit 10 is in fluid communication with fluid inlet 24 of a second EC unit 20, fluid outlet 22 of EC unit 20 is in fluid communication with fluid inlet 34 of a third EC unit 30, and fluid outlet 32 of EC unit 30 is in fluid communication with fluid inlet 44 of the last EC unit 40 of the plurality of EC units. The conduit 16, between fluid outlet 12 of EC unit 10 and fluid inlet 24 of EC unit 20, may be in fluid communication with a polymer pump 18, which adds an anionic polymer to the feedstock as it flows from EC unit 10 to EC unit 20; similarly, conduits 26 and 36 are in fluid communication with polymer pumps 28 and 38 which introduce the anionic polymer to the feedstock as it flows between EC units 20 and 30 and EC units 30 and 40. As described above, this alternating treatment of the feedstock with EC units and flocculation through addition of anionic polymer further increases the efficiency of removing both positively and negatively charged constituents from the feedstock. In some embodiments, feedstock exiting EC unit 40 may be delivered to other apparatuses for further treatment. It will be appreciated by a person skilled in the art that the example illustrated in FIG. 5, showing four EC units connected in series, is not intended to be limiting and that less than or greater than four EC units may be connected in series for treatment of feedstock.

Claims

What is claimed is:

1. An electrocoagulation unit for removing one or more dissolved constituents from an untreated feedstock, the unit comprising:

a non-electrically conductive housing having a fluid inlet, a fluid outlet and an interior surface,

a cathode and an anode arranged within the housing, the cathode and anode each having an ionizing surface, the ionizing surfaces of the anode and cathode in opposed facing relation so as to define a gap having a separation distance therebetween,

the cathode and the anode configured to be electrically coupled to a DC power supply in a DC electrical circuit so as to ionize and dissolve the ionizing surface of the anode, and

a controller configured to maintain the separation distance at a set value as the ionizing surface of the anode dissolves.

2. The unit of claim 1 wherein the cathode includes an inlet surface opposite the cathode's ionizing surface and at least one aperture extending through the cathode from the inlet surface to the ionizing surface, the cathode mounted to and sealed against the interior surface of the housing so as to orient the inlet surface towards the fluid inlet,

wherein the at least one aperture defines a flow path for the untreated feedstock to flow from the fluid inlet to the gap.

3. The unit of claim 1 wherein the controller comprises at least one non electrically-conductive spacer, the at least one spacer sandwiched between the cathode and the anode so as to simultaneously contact the ionizing surface of the cathode and the ionizing surface of the anode.

4. The unit of claim 3 wherein the anode is weighted so as to maintain contact between the ionizing surface of the anode and the at least one spacer.

5. The unit of claim 1 wherein the anode is replaceable.

6. The unit of claim 1 wherein the cathode is mounted to and sealed against the interior surface of the housing and the controller comprises an actuator operatively coupled to cause relative movement between the anode and cathode.

7. The unit of claim 6 wherein the actuator is actuated when a measurable parameter attains a threshold value.

8. The unit of claim 7 wherein the parameter is selected from a group comprising: unit operation time, voltage, current.

9. The unit of claim 8 wherein, when actuated, the actuator is configured so as to translate the anode towards the cathode so as to contact the ionizing surfaces of the anode and the cathode and then translate the anode away from the cathode so as to separate the ionizing surfaces of the anode and cathode by the separation distance.

10. The unit of claim 1 wherein the one or more constituents of the untreated feedstock includes at least dissolved metal ions and wherein the anode comprises magnesium so as to facilitate removal of the at least dissolved metal ions from the untreated feedstock.

11. A method of treating an untreated feedstock using the electrocoagulation units of claim 1, the method comprising:

providing a plurality of units of claim 1,

connecting each unit of the plurality of units in series by connecting the fluid outlet of one unit of the plurality of units to the fluid inlet of an adjacent unit of the plurality of units, wherein a first unit of the plurality of units has a free fluid inlet and a last unit of the plurality of units has a free fluid outlet,

operatively connecting at least one DC power supply to the anode and cathode of each unit of the plurality of units,

flowing a volume of the untreated feedstock into the free fluid inlet,

wherein a coagulated amount of at least one dissolved constituent of the volume of untreated feedstock increases within each unit of the plurality of units as the volume of untreated feedstock flows from the first unit to the last unit.

12. The method of claim 11, wherein providing the controller of each unit of the plurality of units includes providing an actuator operatively coupled to the anode so as to selectively translate the anode relative to the cathode,

detecting when a measurable parameter of any unit of the plurality of units attains a threshold value,

identifying the unit of the plurality of units in which the parameter has attained the threshold value,

actuating the actuator so as to adjust the separation distance of the identified unit so as to optimize the separation distance.

13. The method of claim 12 wherein the step of actuating the actuator further includes:

translating the anode towards the cathode so as to contact the ionizing surface of the anode against the ionizing surface of the cathode,

translating the anode away from the cathode until the separation distance is optimized.

14. The method of claim 12 wherein the measurable parameter is selected from a group comprising: unit operation time, voltage, current.

15. The method of claim 11 wherein the plurality of units connected in series includes a conduit for conducting an intermediate feedstock from the fluid outlet of one unit to the fluid inlet of an adjacent unit, wherein the method further comprises the step of adding an anionic polymer to the intermediate feedstock as the intermediate feedstock flows through the conduit so as to flocculate the intermediate feedstock.

16. The method of claim 15 wherein the one or more constituents of the untreated feedstock includes at least dissolved metal ions and wherein the anode comprises magnesium so as to facilitate removal of the at least dissolved metal ions from the untreated feedstock.