Waste to Product On Site Generator
Method and apparatus for adjusting the salinity and/or hardness of a process waste stream so that the stream may be electrolyzed to form an oxidant or disinfectant. Also an electrolytic cell having certain features such as widely spaced electrodes, flushing capabilities, and insulating dividers that can accommodate waste streams that have varying salinity, hardness, and dissolved solids content.
This application claims priority to and the benefit of filing of U.S. Provisional Patent Application Ser. No. 61/605,929, entitled “Waste to Product On Site Generator,” filed on Mar. 2, 2012, the specification and claims of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION1. Field of the Invention (Technical Field)
The present invention relates to methods and apparatuses for electrolytic processing of waste brine solutions produced by water purification or other industrial processes, thereby producing one or more oxidants and/or disinfectants.
2. Background Art
Note that the following discussion refers to a number of publications and references. Discussion of such publications herein is given for more complete background of the scientific principles and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
Electrolytic technologies utilizing dimensionally stable anodes have been developed to produce oxidant solutions from brine solutions, and these technologies have grown in market presence and interest across a variety of applications. Dimensionally stable anodes are described in U.S. Pat. No. 3,234,110 to Beer, entitled “Electrode and Method of Making Same,” wherein a noble metal coating is applied over a titanium substrate. Electrolytic cells have had wide use for the production of chlorine and mixed oxidants for the disinfection of water. Some of the simplest undivided electrolytic cells are described in U.S. Pat. No. 4,761,208, entitled “Electrolytic Method and Cell for Sterilizing Water”, and U.S. Pat. No. 5,316,740, entitled “Electrolytic Cell for Generating Sterilizing Solutions Having Increased Ozone Content.” One limitation of these technologies is the operating cost associated with the feedstock of this process, consisting of sodium chloride and other dissolved salts which are converted into solutions comprising at least one oxidant. It is well accepted that one of the major failure mechanisms of undivided electrolytic cells is the buildup of unwanted films on the surfaces of the electrodes. The source of these contaminants can be either from the feed water to the on-site generation process, or contaminants in the salt that is used to produce the brine solution feeding the system. Typically these unwanted films consist of manganese, calcium carbonate, silica, or other unwanted substances. If buildup of these films is not controlled or they are not removed on a fairly regular basis, the electrolytic cells will lose operating efficiency and will eventually catastrophically fail (due to localized high current density, electrical arcing or some other event). Typically, manufacturers protect against this type of buildup by incorporating a water softener on the feed water to the system to prevent these contaminants from ever entering the electrolytic cell. However, these contaminants will enter the process over time from contaminants in the salt used to make the brine. High quality salt is typically specified to minimize the incidence of cell cleaning operations. U.S. Pat. No. 7,922,890 describes methods and apparatuses of creating low maintenance, highly reliable electrolytic cells for creating oxidants. However, this type of approach typically only works for lower hardness waters (<20 grains/gallon for example) and higher quality salts (>99.5% dry).
Many water purification processes produce a brine solution containing enough dissolved salts to be suitable for processing into a disinfectant/oxidant. Specifically, reverse osmosis, evaporation, distillation, chemical softening, and ion exchange technologies have waste streams with high concentrations of salts. Typically, however, these waste streams also have high concentrations of contaminants (typically measured as hardness) that would foul most electrolytic cells quickly, resulting in premature electrolytic cell failure.
More recently, though, solutions providers such as GE or Veolia Water have developed offerings such as the HERO or OPUS® technologies, where waste water is pretreated to reduce the hardness prior to exposing them to the RO membranes. This makes this waste stream from the RO membranes much more desirable as a possible feedstock for electrolytic generation of an oxidant from that waste stream, as most of the undesirable contaminants for electrolysis are removed via the pretreatment process.
SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)An embodiment of the present invention is a method for producing an oxidant, the method comprising adjusting the salinity and/or hardness of a waste stream thereby forming a brine solution; and electrolyzing the brine solution to produce at least one oxidant. The adjusting step preferably comprises measuring the salinity and/or hardness of the waste stream. The adjusting step optionally comprises adding water or processed water to the waste stream to reduce the salinity of the waste stream and preferably further comprises varying the relative flow rates of the waste stream and the water or processed water being input into an electrolytic cell. The adjusting step optionally comprises adding a saturated or near saturated salt solution to the waste stream to increase the salinity of the waste stream and preferably further comprises varying the relative flow rates of the waste stream and the saturated or near saturated salt solution being input into an electrolytic cell. The adjusting step preferably comprises treating the waste stream by a method selected from the group consisting of softening, ion exchange, filtering, and reverse osmosis. The brine solution preferably has a salinity between approximately 10 g/L and 40 g/L. The adjusting step preferably reduces a cleaning frequency of the electrolytic cell.
Another embodiment of the present invention is a method for cleaning an electrolytic cell, the method comprising measuring a salinity and hardness of a waste stream to be electrolyzed, calculating a frequency for cleaning the electrolytic cell based on the measured salinity and hardness of the waste stream and a spacing between electrodes of the electrolytic cell, and cleaning the electrolytic cell in accordance with the calculated frequency. The cleaning step preferably comprises reversing a polarity of the electrolytic cell and/or flushing solid contaminants from the electrolytic cell. The flushing is preferably performed once or twice a day or after the electrolytic cell was cleaned by reversing the polarity of the electrolytic cell. The method preferably further comprises adjusting the salinity and/or hardness of the waste stream, thereby reducing the cleaning frequency.
Another embodiment of the present invention is an electrolytic cell for electrolyzing a waste stream, the electrolytic cell comprising one or more devices for adjusting a flow rate of the waste stream entering an electrolytic cell; one or more dispersion tubes for transporting the waste stream into the electrolytic cell; a plurality of holes in the dispersion tubes, the holes angled to direct a flow of the waste stream toward bottom edges of the electrolytic cell; and one or more insulators substantially parallel to electrodes in the electrolytic cell and extending from a bottom of the electrolytic cell to at least a level of bottoms of the electrodes. The additive stream may comprise water, processed water, a saturated salt solution, or a near saturated salt solution. At least one of the devices can preferably flush the cell with the waste stream or water at a flushing flow velocity higher than (preferably at least twice) the operational flow velocity of the waste stream. Spacing between adjacent holes is preferably between approximately 0.5″ and approximately 2″. The electrolytic cell preferably comprises electrodes which are spaced more widely than electrodes in an electrolytic cell designed to produce a similar quantity and strength of oxidants from a controlled brine stream. The electrolytic cell preferably comprises intermediate electrodes, wherein spacing between adjacent intermediate electrodes is preferably between approximately 0.15″ and approximately 0.5″, and more preferably 0.25″+/−0.1″.
Objects, advantages, novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
The accompanying drawings, which are incorporated into and form a part of the specification, illustrate an embodiment of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating various embodiments of the invention and are not to be construed as limiting the invention. In the drawings:
Embodiments of the present invention electrolize the waste stream from an industrial process, such as reverse osmosis, ion exchange softening, chemical softening, evaporation, distillation, produced or flowback water from oil and gas wells, to produce an oxidant and/or disinfectant. This waste stream may be highly variable in salt content, presenting a unique challenge for consistent oxidant production. For example, a water source with low dissolved salt may be injected into the electrolyte for a high salinity waste stream at a rate determined by the operating current of the electrolytic cell. When the operating current is high, more water with low dissolved salt is preferably injected to reach the target operating current of the cell. Conversely, when the operating current is low, the water with low dissolved salts may be replaced with a concentrated brine solution injection to raise the current to the desired operating condition.
As used throughout the specification and claims, the term “waste stream” means an aqueous byproduct of an industrial process or application, including but not limited to frac water, produced water from oil and gas operations, cooling towers, desalination, or evaporation, the byproduct having a sodium chloride content of greater than approximately 1 g/L.
Embodiments of the present invention utilize an electrochemical process to convert a waste brine stream into a usable oxidant; one such process is shown in
Raw water 1 can be from virtually any source. However, certain sources have, or certain industrial processes produce a waste stream that has, a somewhat higher incidence of dissolved salts in the raw water, such as seawater, produced and/or flowback water from oil and gas operations, ground water, surface water, waste from industrial processes, waste water from municipalities, potable water, etc.
Brine waste 6 is often at a fairly high salinity, often greater than approximately 40 g/L but less than that for saturated brine (317 g/L). In the event that the salinity is greater than approximately 40 g/L, dilution water 9 may be used to dilute the brine waste to a lower level that is more appropriate for electrolysis, typically between approximately 10 g/L and 40 g/L. A small percentage of processed water 5 may optionally be used as the dilution water 9.
Depending on the nature of the raw water 1 and the purification processing equipment 4, if not required softening process equipment 2 may not be included in order to reduce cost and complexity of the system.
Some industrial processes produce a brine waste that does not require complicated purification processing equipment 4 because the brine waste has the appropriate hardness to salinity ratio in the brine solution that it can be electrolyzed. Examples of this are waste water remediation and/or flowback or produced waters from oil and gas operations. Thus, in one embodiment of the invention, there is no processed water 5, and the purification processing equipment comprises or consists essentially of a simple filter to remove large particles (typically >20 microns, but preferably >100 microns) from brine waste 6.
Another embodiment of the invention is shown in
Compared to existing commercially available on-site electrolytic generators, embodiments of that required to convert waste to oxidant in accordance with the present invention are substantially different.
During operation, devices 13 can be controlled to intermittently flush the electrolytic cell with very high flow rates (preferably greater than approximately two times the operational flow rate) of water or waste stream 6. If the latter is used, flushing can occur during the electrolysis process. This flushing prevents or reduces deposits from accumulating at the bottom of the electrolytic cell. Integrated controls 15 also preferably control reversing the polarity of the cell, which removes deposits from the electrode surfaces. This process is more fully described in U.S. Patent Application Publication No. 20090229992.
Despite being exposed to high levels of hardness, suspended solids, dissolved solids, and contaminants such as silica, electrolytic cell 14 is preferably designed such that it is robust and has an adequate lifetime.
Electrolytic cell preferably comprises one or more electrical isolator blocks 17, which preferably extend from the bottom of the cell at least up to the bottom of the electrodes. One isolator block is preferably present every few intermediate electrodes 16, which prevents loss of electrical efficiency and also protects the electrodes from being exposed to voltages beyond their breakdown voltages, for example due to high salinity of the brine waste. Thus the use of these blocks enables particles to build up in the cell without arcing between electrodes taking place. Typically electrical isolator blocks 17 are spaced every 5-10 electrodes, but depending on the chemistry desired in the oxidant and the salinity of brine waste 6, one electrical isolator block 17 could be present every 3 electrodes or even up to every 40 electrodes. As shown in the perspective view of electrolytic cell 14 shown in
The characteristics of the brine waste vary considerably with different waste applications, which has implications on the frequency with which the electrolytic cell is cleaned. Specifically, the ratio of divalent cations to monovalent cations is particularly important. For a given ratio, the growth rate of contaminants on the electrodes is calculated, and for a given electrode spacing, the required cleaning frequency of the cell to prevent arcing between electrodes can be determined, after applying a given safety factor. From this cleaning frequency the expected life of an electrolytic cell can then be predicted given a certain number of cycles to failure. Thus, treating the waste stream so that the salinity and/or hardness are in optimal ranges can greatly increase the lifetime of the cell by reducing required cleaning frequency. By controlling these parameters, as well as flow rate, voltage, and current in the electrolysis cell, the system can be optimized for energy conversion efficiency as salt is a waste product for various industrial processes and is therefore is extremely inexpensive.
Example 1A waste brine stream was created by a system very similar to the system shown in
A waste brine stream consisting of produced water from an oil and gas operation was created by a system similar to the one shown in
A waste brine stream from a desalination plant was created with a system similar to the one depicted in
Waste blowdown from a cooling tower had approximately 4 g/L salt and a hardness of 180 grains/gallon. This waste blowdown was directly electrolyzied, yielding an oxidant with 650 mg/L FAC with a cleaning frequency of 0.4 days and an expected cell life of 1.2 years. When combined with a solid brine source as shown in
Although the invention has been described in detail with particular reference to the disclosed embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover all such modifications and equivalents. The entire disclosures of all patents and publications cited above are hereby incorporated by reference.
Claims
1. A method for producing an oxidant, the method comprising:
- adjusting the salinity and/or hardness of a waste stream thereby forming a brine solution; and
- electrolyzing the brine solution to produce at least one oxidant.
2. The method of claim 1 wherein the adjusting step comprises measuring the salinity and/or hardness of the waste stream.
3. The method of claim 1 wherein the adjusting step comprises adding water or processed water to the waste stream to reduce the salinity of the waste stream.
4. The method of claim 1 further comprising varying the relative flow rates of the waste stream and the water or processed water being input into an electrolytic cell.
5. The method of claim 1 wherein the adjusting step comprises adding a saturated or near saturated salt solution to the waste stream to increase the salinity of the waste stream.
6. The method of claim 1 further comprising varying the relative flow rates of the waste stream and the saturated or near saturated salt solution being input into an electrolytic cell.
7. The method of claim 1 wherein the adjusting step comprises treating the waste stream by a method selected from the group consisting of softening, ion exchange, filtering, and reverse osmosis.
8. The method of claim 1 wherein the brine solution has a salinity between approximately 10 g/L and 40 g/L.
9. The method of claim 1 wherein the adjusting step reduces a cleaning frequency of the electrolytic cell.
10. A method for cleaning an electrolytic cell, the method comprising:
- measuring a salinity and hardness of a waste stream to be electrolyzed;
- calculating a frequency for cleaning the electrolytic cell based on the measured salinity and hardness of the waste stream and a spacing between electrodes of the electrolytic cell; and
- cleaning the electrolytic cell in accordance with the calculated frequency.
11. The method of claim 10 wherein the cleaning step comprises reversing a polarity of the electrolytic cell.
12. The method of claim 10 wherein the cleaning step comprises flushing solid contaminants from the electrolytic cell.
13. The method of claim 12 wherein the solid contaminants are flushed from the electrolytic cell once or twice a day or after the electrolytic cell was cleaned by reversing the polarity of the electrolytic cell.
14. The method of claim 10 further comprising adjusting the salinity and/or hardness of the waste stream, thereby reducing the cleaning frequency.
15. An electrolytic cell for electrolyzing a waste stream, the electrolytic cell comprising:
- one or more devices for adjusting a flow rate of the waste stream entering an electrolytic cell;
- one or more dispersion tubes for transporting the waste stream into said electrolytic cell;
- a plurality of holes in said dispersion tubes, said holes angled to direct a flow of the waste stream toward bottom edges of said electrolytic cell; and
- one or more insulators substantially parallel to electrodes in said electrolytic cell and extending from a bottom of said electrolytic cell to at least a level of bottoms of said electrodes.
16. The electrolytic cell of claim 15 wherein the additive stream comprises water, processed water, a saturated salt solution, or a near saturated salt solution.
17. The electrolytic cell of claim 15 wherein at least one of the devices can flush the cell with the waste stream or water at a flushing flow velocity higher than an operational flow velocity of the waste stream.
18. The electrolytic cell of claim 17 wherein the flushing flow velocity is at least twice the operational flow velocity.
19. The electrolytic cell of claim 15 wherein spacing between adjacent holes is between approximately 0.5″ and approximately 2″.
20. The electrolytic cell of claim 15 comprising electrodes which are spaced more widely than electrodes in an electrolytic cell designed to produce a similar quantity and strength of oxidants from a controlled brine stream.
21. The electrolytic cell of claim 20 comprising intermediate electrodes, wherein spacing between adjacent intermediate electrodes of between approximately 0.15″ and approximately 0.5″.
22. The electrolytic cell of claim 21 wherein said spacing is 0.25″+/−0.1″.
Type: Application
Filed: Mar 4, 2013
Publication Date: Sep 26, 2013
Inventors: Justin Sanchez (Albuquerque, NM), Craig Andrew Beckman (Albuquerque, NM), Thomas Edward Muilenberg (Ames, IA)
Application Number: 13/784,618
International Classification: C25B 15/08 (20060101);