Process for regenerating resin in an ion exchange vessel

Abstract

A process and apparatus for enhanced boron removal from water. The process includes the steps of reacting potassium carbonate or ammonium carbonate with calcium borate in a stream of feed water to form a stream having calcium carbonate and potassium borate salt or ammonium borate salt. The stream having calcium carbonate and potassium borate or ammonium borate is introduced to an ion exchange vessel containing resin having methylglucamine in salt form with potassium carbonate or sodium carbonate to form borate and potassium sulfate or sodium sulfate. The resin in the ion exchange vessel is periodically regenerated.

Claims

1. A process for regenerating resin in an ion exchange vessel, which process comprises: maintaining a level of liquid in an ion exchange vessel having resin; pumping acid into said liquid while recirculating to a base of said vessel to percolate through said resin; removing carbon dioxide bubbles formed from a top of said vessel; removing liquid having borate to a boron tank; introducing fresh water to said vessel; and removing liquid from said vessel to a recycle tank.

2. The process for regenerating resin as set forth in claim 1 wherein said acid is passing in an upward flow until carbon dioxide is released and resin pH is less than 7.

3. The process for regenerating resin as set forth in claim 1 including the additional steps of spraying rinse water and acid on top of said resin in said vessel and removing said liquid to a recycle tank.

4. The process for regenerating resin as set forth in claim 1 wherein said borate in said boron tank is concentrated.

5. The process for regenerating resin as set forth in claim 1 wherein rinse water from said vessel is added to a recycle tank from the top.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a sectional view of a prior art ion exchange vessel;

(2) FIG. 2 illustrates a sectional view of an ion exchange vessel for use in an apparatus and process for enhancing boron removal of the present invention;

(3) FIG. 3 illustrates a simplified schematic diagram of the apparatus of the present invention;

(4) FIG. 4 illustrates a cut away diagram of a portion of the ion exchange vessel of the present invention; and

(5) FIG. 5 illustrates a sectional view of an evaporator of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(6) The embodiments discussed herein are merely illustrative of specific manners in which to make and use the invention and are not to be interpreted as limiting the scope.

(7) While the invention has been described with a certain degree of particularity, it is to be noted that many modifications may be made in the details of the invention's construction and the arrangement of its components without departing from the scope of this disclosure. It is understood that the invention is not limited to the embodiments set forth herein for purposes of exemplification.

(8) Agricultural irrigation requires very large water flows. In order to remove chemicals such as boron, this translates into many small ion exchange pressure vessels, since large diameter pressure vessels are expensive. The management and control of many small vessels requires an extensive network of valves. At high flow rates, the pressure drop across prior art ion exchange vessels can exceed 10 PSI, which makes an open ion exchange vessel appear impracticable

(9) The large pressure drop is mostly due to the large increase in water velocity past the resin as it approaches the collector at the bottom of the ion exchange vessel. For example, see Prior Art in FIG. 1. The flow rate across the resin bed is 6 gpm/sqft, while the flow across the resin near the collector is 60 gpm/sqft. Ninety-percent of the pressure drop occurs across the collector. Due to the high cost of pressure vessels, greater resin depths are favored, which also contributes to the high pressure drop across the resin vessel. See Prior Art in FIG. 1.

(10) FIG. 2 illustrates a sectional view of an ion exchange vessel 12 for use in the process and apparatus of the present invention. FIG. 3 illustrates a simplified schematic diagram of the apparatus 10 of the present invention. The ion exchange vessel 12 may include a substantially closed container with an open top which is maintained and operated at both ambient temperature and ambient pressure.

(11) Feed water, such as from a subterranean well, moved by a pump is brought to the ion exchange vessel 12, as shown by arrow 14. The feed water may contain boron, such as in the form of calcium borate. The feed water is delivered to a screen, such as a diffuser 18 having slots therein. The diffuser 18 promotes uniform flow across the resin bed (to be described) and minimizes resin agitation in the service mode. The level of water in the service mode is shown by water line 20.

(12) A blend valve 22 permits blending of treated water (to be described) with incoming feed stream water to allow any concentration level of boron between the subterranean well water boron level and the output boron level.

(13) The ion exchange vessel 12 may include a layer of gravel 24 at the base of the vessel with a layer of sand 26 thereon.

(14) Well screen pipes 30 are placed near the bottom of the vessel 12 with substantially uniform spacing such that the area of the well screen pipe is similar to the surface area of the bottom of the resin bed. Well screen spacing approximately equal to the perimeter of the well screen pipe may be preferred. The well screens 30 are connected to manifolds 32. The well screen manifolds 32 are connected to a manifold pipe 34 above the level of the resin bed.

(15) The manifold pipe 34 is connected to an irrigation pump 76 having negative pressure, such as a centrifugal pump, to draw or suck the water through the resin in the resin bed and thereafter transport the outgoing water, such as to an irrigation system. The level of water in the resin bed is maintained with a level sensor or sensors 36, which may be connected to a controller (not shown), to adjust opening of valves and speed of pumps.

(16) The boron selective resin in the resin beds contains methylglucamine in salt form, such as sulfate or chloride salt form. The resin is often macroporous polystyrene resin.

(17) Boron may be present in a feed water stream in the form of calcium borate (CaB.sub.4O.sub.7). In order to remove boron from the feed water, potassium, ammonium or sodium in hydroxide, carbonate or bicarbonate form is reacted with the feed water. In a preferred embodiment, potassium carbonate (K.sub.3CO.sub.3) or ammonium carbonate ((NH.sub.4).sub.2CO.sub.3) is delivered to and reacted with a feed stream, such as with a potassium pump 40. A stream having calcium carbonate (CaCO.sub.3) and potassium borate salt (K.sub.2B.sub.4O.sub.7) or ammonium borate salt ((NH.sub.4).sub.2B.sub.4O.sub.7) is thereby formed.

(18) In an optional initial step, potassium, ammonium, or sodium carbonate is supplied by passing a portion of feed water through a water softener resin.

(19) The stream having calcium carbonate and potassium borate salt or ammonium borate salt is introduced to the open top ambient pressure ion exchange vessel 12 and to the resin containing methylglucamine in salt form. Additionally, potassium carbonate or sodium carbonate is added. The borate is formed on the resin and potassium sulfate or sodium sulfate is also formed in the water stream.

(20) The present invention permits higher flow rates per square foot of resin and requires less resin bed depth than heretofore known.

(21) Periodically, the system is switched from a service mode to a regeneration mode so that the boron selective resin in the bed of the ion exchange vessel 12 is periodically regenerated.

(22) In order to regenerate the resin, a level of liquid in the ion exchange vessel 12 is maintained at a water line level 52. The resin bed is drained until the liquid level is just above a fluff level, which operates in conjunction with a screen 44. This serves to minimize the amount of liquid involved in regeneration. A fluff pump valve 46 is activated and the outgoing irrigation pump valve 48 is closed. The fluff pump 42 and an acid pump 50 are turned on.

(23) Liquid is passed through the manifold upward in the ion exchange vessel 12 which releases carbon dioxide (CO.sub.2) bubbles from the resin that are generated by addition of the acid. The bed is also fluidized. This is continued until nearly all of the carbon dioxide is released and pH of less than 7 is maintained. In a preferred configuration, the pH is approximately 2.1 to 2.5. Removing the carbon dioxide (CO.sub.2) bubbles prevents the regeneration from being compromised. Concentrated sulfuric acid (such as 93%) may be used to minimize volume gain. The overall acid concentration will be less than 1%.

(24) Thereafter, the outgoing pump 38 is turned on to lower the liquid level to the top of the resin in the ion exchange vessel 12. The output is directed to a boron tank 54 past boron tank valve 56. Thereafter, a recycle pump 60 and acid pump 62 deliver water from a recycle tank 64 through a spray nozzle or spray bar above the level of the resin. The acid concentration will be approximately 1% acid. In one example, spray is turned on for a combined flow of about 1 bed volume per 4 hours with an acid concentration of about 1% acid for 30 minutes. This uniformly delivers and applies the liquid to the top of the resin bed. The regen pump 38 is controlled to maintain liquid level just above the resin bed with the level sensors. Thereafter, the acid pump 62 is turned off while recycle pump 60 and regen pump remain on. The boron tank valve 56 is open so that fluid is added to the boron tank.

(25) Thereafter, the recycle pump 60 is turned off, the boron tank valve 56 is closed and a recycle tank fill valve 70 is opened. A fresh water pump 72 is turned on. The regen out pump 38 also remains on. In one example, this continues for about 2 beds of liquid volume. The recycle tank 74 is filled from the top without general mixing to maintain boron concentration gradient. It is preferred that the fresh water has minimal carbonates in order to minimize CO2 bubble formation. Much of the carbonate can be released by reducing the pH level of the water to 7 or less.

(26) If the only water available is the well water itself, optionally filtering the water with a nanomembrane can remove most of the hardness to prevent scaling in the evaporator (to be described) and minimize the amount of carbonates present.

(27) FIG. 5 illustrates a sectional view of an evaporator 80 used as a part of the invention.

(28) While efficient regeneration of the resin yields a small volume of liquid overall, it still represents a large volume of liquid for an irrigation water treatment system. An inexpensive and simple method of evaporating water is desirable.

(29) The boron tank 54 is in fluid communication with an evaporation pump 82. Fluid in the boron tank 54 is drawn from an upper portion of the tank 54. The liquid is pumped and deposited through a nozzle or nozzles above packing fill 86 which is spaced above the boron tank. The liquid progresses downward by gravity. At the same time, ambient air is drawn upward through the packing fill 86 by a fan 88 as shown by arrow 90.

(30) As liquid progresses downward, evaporation occurs and it becomes more concentrated. The liquid drops fall to the top of the boron tank as droplets. The more concentrated, super saturated colder solution is denser and naturally sinks toward the bottom of the boron tank 54. As crystals form, they are even denser, so they naturally sink and accumulate at the bottom of the boron tank 54, while the less saturated solution floats toward the top of the tank 54. The process only requires a fan 88 and an evaporator pump 82 so it is more energy efficient than known evaporators.

(31) In a preferred embodiment, the invention uses ambient air as the sole heat source. The evaporating liquid temperature is less than ambient air temperature. The invention does not require pressurized or vacuum chambers, chambers, heat exchangers, membranes, compressors, or vacuum pumps. No heat source other than the ambient air is applied to the liquid. The low temperatures and absence of heat exchangers minimizes the chance of fouling. The only energy required is a fan to move the air past liquid in an upward direction while a pump moves the liquid to the top of the packing which progress down as a falling film. In spite of its simplicity, the energy efficiency is similar or higher than complex evaporators.

(32) In an alternate process, a waste heat source, such as diesel exhaust or an air cooled radiator, provides a thermal energy source.

(33) Whereas, the invention has been described in relation to the drawings attached hereto, it should be understood that other and further modifications, apart from those shown or suggested herein, may be made within the scope of this invention.