US 3165460 A
Description (OCR text may contain errors)
' Jan. 12, 1965 J. A. ZANG ETAL 3,165,460
l ELECTROLYTIG ACID GENERATOR Filed April 11, 1962 K 2 sheets-sheet 1 FIGJ ATTORNEY Jan. 12, 1965 J. A. zANG ETAL 3,165,450
ELECTROLYTIC ACID GENERATOR Filed April 1l.` 1962 2 Sheets-Sheet 2 FIG.2 HS 4 /36 /M New l2 l//l Il lll/l/ VII VII.
HVVENTORS JOSEPH A.ZANG ERWIN M. COHEN United States Patent O 3,165,466 ELECTRGLYTIC ACID GENERATOR Joseph Albert Zang, Rockville Centre, NSY., and Erwin Morton Cohen, Stamford, Conn., assgnors to American llachine & Foundry Company, a corporation of New ersey Filed Apr. 11, 1962, Ser. No. 186,793 9 Claims. (Qi. 2134-301) This invention relates in general to acid producing devices and, more particularly, to electrolytic systems which produce acid for use in fluid treatment devices.
In the distillation of sea water to provide potable water on submarines and surface vessels and in other locations, the controlled acidification of feed water to the distillation apparatus or evaporator will prevent the formation on the heat exchanger surfaces of calcium and magnesium containing scale. This scale can quickly reduce the efficiency of an evaporator and eventually clog it to such an extent that the apparatus becomes useless. However, the desirability of acidifying the feed water of evaporators to prevent scale formation has been limited up to this time because difhculty is associated with the handling, storing and shipping of acids.
It is, therefore, a main object of this invention to provide an acid generating apparatus which produces acid from the feed water normally supplied to an evaporator to avoid the problems associated with the storing and the metered introduction of acid from an external source.
Another object of this invention is to provide an apparatus which electrolytically generates acid from the feed water of an evaporator, the acid generating apparatus not requiring the continual addition of chemicals such as sodium chloride or other salts.
Still another object of this invention is to provide an apparatus which electrolytically generates acid from feed water of an evaporator with the acid generator being able to purge itself of precipitates of CaCO3 and Mg(OH)2 and the like which reduce ilow through the acid generator and increase its electrical resistance.
A further object of this invention is to provide an electrolytic acid generator which produces an uncontaminated acidiiied product stream.
A still further object of this invention is to provide an acid generating electrolytic apparatus which may have a large capacity and have but a single pair of external electrical connections while using ion selective membranes having a relatively small area.
Yet another object of this invention is to provide an electrolytic acid generating apparatus using ion selective membranes disposed between electrodes, the acid generating apparatus being able to be completely electrically and hydraulically reversed.
Many other objects, advantages, and features of invention reside in the construction, arrangement and combination of parts involved in the embodiments of the invention and its practice as will be understood from the following description and accompanying drawing wherein:
FIGURE l is a vertical section through the tanks and the acid generating cell of this invention showing interconnecting pipes, valves, pumps and associated apparatus;
FIGURE 2 is a vertical section through an acid generating cell modied to be series connected and shown with a central portion broken away;
FIGURE 3 is a vertical section through an acid generating cell shown connected to fragments of pipes and a current source for hydraulic and electric-al reversal;
FIGURE 4 is a vertical section through a modified oc former and associated sea water feeding apparatus; and
FIGURE 5 is a vertical section through a oc former having an overow and directly recirculating uid through a connected pipe.
Referring to the drawing in detail, the numeral 10 designates a fragment of the end of a raw sea water feed pipe. A sea water by-pass pipe 11 leads about the acidification apparatus of the instant invention to the pipe 12 which may lead to a suitable CO2 stripper and an evaporator (not shown).
An acid producing cell, generally designated by the numeral 13, has the two end plates 14 and 15 and the central frames 16 and 17. End plate 14 contains a cavity forming an electrode compartment containing the anode 18 and the end plate 15 contains a cavity containing the cathode 19. Anode 18 and cathode 19 are connected to a suitable source of direct current which is not shown in FIGURE l. Disposed between end plate 14 and frame 16 is a cation permeable membrane Ztl; between the frames 16 and 17 is disposed the anion permeable membrane 21; and between the frame 17 and end plate 15 there is disposed the cation permeable membrane 22.
A pipe 23 containing a shut-olir valve 24 leads from pipe 16 parallel to by-pass 11 to the T fitting 25. A pipe 26 containing a pressure regulating valve 27 leads into frame 16 between the membranes 20 and 21. A pipe 28 leads from within frame 16 to the venturi blender 29 which mixes Huid flowing from within frame 6 with fluid flowing through the by-pass pipe 11.
End plate 14 land the tank 3u contain a dilute solution 31 of sulphuric or other acid or a dilute solution of sea water which will become acid after the first few minutes of operation. A pipe 33 leads from tank 30 through shut-off valve 34 and the pump 35. Pipe 36 leads out of end plate 14 to return fluid pumped from tank 3i) into end plate 14 back again to tank 30. Fluid losses from within end plate 14 and tank 30 are made up by introducing distilled water from a source (not shown) which flows through pipe 37 into tank 3l). Flow through pipe 37 is regulated by the valve 33 which is opened by iloat 39 when the Huid level within tank 30 falls below a given level.
Tank 4b has a pipe 41 leading to frame 17 through valve 42 and pump 43. A return pipe 44 conducts uid from within frame 17 back to tank 40. An overflow pipe 45 conducts excess fluid 46 Within tank 40 into tank 4S.
Pipe 49 leads from tank 48 into end plate 15 through valve 50 and pump 51. Pipe 52 returns fluid from end plate 15 back into tanks 4S. Excess fluid 53 within tank 48 ows out through overflow pipe 54. A cover 55 enables the blower 56 to exhaust hydrogen gas-escaping from the fluid 53 within tank 48 through suitable ducting (not shown).
Pipe 57 leads from T fitting 25 through valve 58 into the iioc former 59. Fluid passing through the overflow pipe 54 also iows into the floc former 59. A pipe 60 drains oc former 59 into the lower portion of the large settling tank 61. A drain pipe 62 extends upward beside the settling tank 61 to form the stand pipe 63 and the overflow 64. Thus the level of the fluid 65 within the floc former S5? and the settling tank 61 is determined by the level of the overow pipe 64 where it joins the stand pipe 63. A pump 66 draws fluid 65 from the upper portion of tank 61 and returns the liuid 65 through pipe 68 to the tank 40.
This invention operates in the following manner. A small quantity of raw sea water passes through pipes 23 and 26 to enter frame 16 between the cat-ion permeable membrane 20 and the anion permeable membrane 21. The cathode 19 draws hydrogen ions from within end plate 14 through the cation permeable membrane 20 into frame 16. Oxygen is formed at the anode 13 and passes upward in bubble form with the uid 31 into tank 36 through pipe 36 where the oxygen may be exhausted through suitable ducting into the atmosphere.
2.1 towards the anode 18. Within the frame 16, the hydrogen and Ichloride ions combine to form hydrochloric acid lwhich passes through pipe 28 to acidify sea water passing through pipe 12 to an evaporator.
As chlorideions pass from within frame 17V through` membraneZl, the cathode 19 attracts sodium ions through membrane 22 to pass into end plate 1,5. At the same time, hydrogen gas is evolved at cathode 19. Since uid is circulated through end plate 15 by Vpump 51 through tank 4S, the fluid 53 within tank 48 is an alkaline sea water. V1Hydrogen gas in bubble form is carried through pipe 52 to escape within tank 48 from whichit is drawn off safely by blower 56 through lid 55. As alkaline sea water overflows into oc former 59, raw sea water also passes into fioc former 59 through pipe 57. The basic solution 65 within floc former 59 will consist of sodiumy hydroxide and sodium carbonate generated at the Ioathode 19. The sodium carbonate is' formed from carbon dioxide in solution in the sea water. Sodium carbonate may also be formed from carbon dioxide which may be blown into tank 48 by a suitable blower or aspirator (not shown). Additional carbon dioxide may be obtained by stripping the carbon dioxide from the aciditied sea water product and then blowing this carbon dioxide into tank 48. Upon the introduction of raw sea water, a tloc results which is a mixture of a basic'magnesium and a calcium precipitatel suspended in sea Water. This floc passes through'pipe 6@ into the bottom of the settling tank 61. yThe settled precipitate within tank 61 passes through pipe 62 and stand pipe 63 to drain through the waste line 64. It should be noted that the amount of base which is formed at electrode 19 to pass to the iioc former 59 is dependent only on the current fed to the electrodes 18 f and 19 of the acid generating cell 13 and is, therefore,
independent of the flow rate established by the metering pump 66 through the return pipe 68.
A preferred improvement of the iloc forming and settling operation hereinbefore described makes use of a heating coil 140 or any other external source of heat which is applied to heat the raw sea water introduced through the pipe 57. This heats the floc contained in Vthe floc former 59 so that the floc entering the settling tank 61 is, for example, over 120 F. If it is desired, the oc within oc former 59 may be heated rather than the raw sea Water in pipe 57. It has been found that this heating greatly hastens the precipitation of the calv cium carbonate which may otherwise remain in solution in a super-saturated stateand which may then precipitate within the compartments of cell 13 and block its effective operation. In addition, the high temperature of the oc greatly decreases the settling time required in settling tank 61 if means are provided to maintain a relatively uniform temperature Within tank 61. A uniform temperature within tank 61 may be maintained by tank insulation or heat jacketing, for example.
Although many methods for alkali precipitation and the removal of the precipitate are well known, such as batch settling, centrifuging and ltration, such methods normally require at least periodic supervision and/ or expensive control equipment. In the practice of this invention, the effective removal of the magnesium and the calcium present in the sea Water only requires the titration of the sea water with the base to a pH of approximately 11.0 to 11.5. A proper setting of the valve 58 to deliver a relatively constant flow of sea water may accomplish this titration without any periodic supervision or expensive control equipment. In actual tests it has been found that the sea water metered to the floc former p maybe varied as much as plus or minus ten percent from Vconstant head of Water, a relatively constant ow passes through pipe 72 into the floc former 74. Floc former 74 has an overow tube 75 leading to a feed '76 connected to the settling tank 61 by pipe 61B.
The cell defined between membranes 21 and 22 within frame 17 `serves as a buffer so that the exceedingly basic solution adjacent to the cathode 19 will not contaminate the acid stream Within frame 16.with hydroxyl ions. To provide suitable softened sea Water free from magnesium and calcium precipitate to be drawn from the upper portion of settling tank 61 by pump 66, the settling tank 61 should -be of such a capacity that the Viluid within it has a two to three hour residence period.
Anothervariation` of this inventionris shown in FIG- URE 5, VIn this variation the same elements shown in FIGURE 1 are used with the exception gof the settling tank 61 which is not needed .in some applications. Floc former 59 is provided with a drain overflow 141. Pipe 142 leads from the lloc former S9 directly to pump 66 which, Vin this variation, pumps a portion of the unsettledroc to tank 40. The remainder of the floc is allowed to overow through drain 141 to waste. The fine precipitated particles of floc will pass through the channels and compartments of the acid generating cell 13 without clogging or settling within the cell. However, before any prolonged shutdown, the cell 13 and connecting pipe lines should be flushed out with distilled water or the like to preventprecipitation. While the ilusning of the cell 13 on `shutdown is some disadvantage, the eliminating of the settling system and its attendant equipment lowers the cost of the complete apparatus in a -given installation and reduces its size and weight.
Referring now to FIGURE 3, the acid generating cell 13 may haverits electrodes 1S andr19 connected to a suitable direct current Asource 77 through a reversing switch 78. Pipes 33, 36, 52, 49, 23, 26, 44 and 41 are connected to the by-pass pipes 87-94, respectively, and these pipes are connected through the valves 79-86, respectively. The by-pass pipes @7 94 contain the valves 95-162, respectively. When valves 95, 96, 97 and 98 are closed and valves 79, 30, 31 and 82 are opened, fluid will ow from pipe 33 past electrode 18 out pipe 36 while Huid flows from pipe 49 past electrodeV 19 out pipe 52. When the valves 79-82 are closed and the valves 95-98 are opened, fluid will -ilow from pipe 33, through pipe 87, past electrode 19, through pipe 88 and from pipe 36, While iluid is flowing from pipe 49, through pipe 90, past electrode 18, through pipe 89 and out pipe 52. Thus uid ow through the electrode containing end plates 14 and 15 may be reversed.V In a like manner, when valves 83- 86 are opened and valves 99-1ti2 are closed, duid flows from pipe 26 through frame 16 out pipe 28 and fluid Hows `from pipe 41 through frame 17 out pipe 44. By closing valves 83-86 and opening Valves 99102, fluid will flow from pipe 26 through frame 17 `out pipe 28 while iluid .flow from pipe 41 passes through frame 16 and out pipe 44. Thus the acid generating cell 13 may becompletely ,electrically and hydraulically reversed while streams become acidied upon reversal, any precipitates lare removed. The frequency of this reversal will depend upon particular applications; however, it will generally not be necessary more than once a week. The valves shown in FIGURE 3 may be solenoid operated and pair of valves, such as valve 79 aand valve 95 or valve 80 and valve 96, may be replaced by a standard three-way valve.
Referring now to FIGURE 2, although a single acid generating cell is all that is necessary to provide enough acid to acidify any size evaporator if its iiuid treatment path is long enough, a single cell may not lbe practical for larger applications because a great cell area would be required to provide enough acid. This may be done by arranging several cells hydraulically in parallel or series. In order 4to provide a workable membrane area, two end plates 165 and 196 may have clamped between them a number of sets of membranes 20, 21 and 22. The membranes and 22 are cation permeable and the membranes 21 are anion permeable. Between each set -of membranes 20, 21 and 22 there is clamped between adjacent frames 107 a thin unconnected platinum electrode 168. When a sufficiently high voltage current is impressed upon the anode 18 and the cathode 19, the left hand slide of each electrode 108 functions as a cathode while the right hand side of each electrode 19S functions as an anode. Suitable pipes 199 and 110 connect the anode cells in series, pipes 111 and 112 connect the acid forming cells in series, pipes 113 and 114 connect the buffer cells in series, and pipes 115 and 116 connect the cathode cells in series. This arrangement insures that there is a sufficiently long iluid treatment path through the acid generating cells to produce an acid of the desired concentration while using membranes 2t?, 21 and 22 which are of a manageable size. Furthermore, only a single pair of end blocks 105 and 106 is required and no electrical connections need be made to the central electrodes 198. Platinum foil electrodes 18, 19 and 108 have been found to work satisfactorily iu this embodiment of the invention.
If it is desired, the hydraulic and electrical reversal illustrated in FIGURE 3 may be combined with the series cell shown in FIGURE 2. Referring to FIGURE l, should it be desired, pipe 57 could conduct concentrated brine discharged from an evaporator as a substitute for the raw sea Water as shown in FIGURE l. The higher temperature and concentration of the brine would result in the advantage that the brine would lower the electrrcal resistance of the acid generating cell 13.
Referring again to FIGURE l, if it is not desired to reverse the apparatus electrically and hydraulically, pipe 68 could lead directly into tank 48 and membrane 22 and frame 17 could be removed from the cell 13. Tank 40 and its associated piping, pump and valve would then no longer be required.
Referring further to FGURE l, a pipe 143 containing a valve 144 may extend from pipe 44. This allows valve 144 to be opened to obtain a supply of softened, demineralized water through pipe 143.
As this invention has been described, it provides a fully self-contained acid generating system which requires no supervision once the valves have been properly set. All that is required to produce acid is a suitable current source for the electrodes 1S and 19 and a small amount of distilled water which is introduced through pipe 37 and raw feed water. Naturally, this invention isnot limited to the acidification of sea water used to feed evaporators, but it may find many other applications where an acid source is desired. Acid may be generated from solutions other than sea water, i.e., brines, brackish waters, etc., with suitable modifications.
What is claimed is:
l. An acid generator for a salt or brackish water feed comprising, in combination,
(a) means forming first, second, third and fourth juxtaposed fluid treatment cells,
(b) a pair of electrodes in said first and said fourth uid treatment cells,
(c) a direct current source connected to said pair of electrodes with said electrode in said first cell functioning as an anode and said electrode in said fourth cell functioning as a cathode,
(d) cation permeable membranes disposed between said first and said second and between said third and said fourth cells,
(e) an anion permeable membrane disposed between said second and said third cells,
(f) first, second, third and fourth sets of pipes leading into and out of said rst, second, third and fourth cells,
(g) means connected to said first set of pipes for circulating a dilute solution of an acid through said first cell,
(h) means for directing some feed water through said second cell through said second set of pipes,
(i) a first tank having an overiow and means for circulating iluid from said first tank through said third set of pipes through said third cell,
(j) a second tank receiving overflow from said first tank, having means for circulating fluid from said second tank through said fourth set of pipes and said fourth cell, and having an overflow,
(k) a settling tank having a pipe leading from its bottom portion, a stand pipe connected to said pipe leading from said settling tank, and a waste drain overflow leading from the upper portion of said stand rupe,
(l) a iloc former container connected to the lower portion of said settling tank, said overow of said second tank leading into said floc former,
(m) means for flowing feed water at a constant rate into said floc former container, and
(n) pump means for drawing the solution from the top portion of said settling tank and delivering the fluid from said settling tank into said second tank at a rate less than the total combined rate of said means for iiowing feed water into said fioc former container and the rate of said overow of said second tank leading into said floc former container.
2. The combination according to claim l wherein said means connected to said first set of pipes for circulating a dilute solution of an acid through said first cell cornprises a third tank connected to said first set of pipes, a dilute acid solution Within said third tank, pump means for circulating the dilute acid solution through said third tank, said rst set of pipes and said first cell, a pipe for conducting distilled water to said third tank, a valve in said pipe for conducting distilled water to said third tank, and means responsive to the fiuid level in said third tank for actuating said valve.
3. The combination according to claim l wherein said means for flowing feed Water at a constant rate into said iioc former container comprises a fourth tank having an overfiow, a pipe for conducting feed water into said fourth tank, said fourth tank containing an aperture disposed a given distance below the overflow in said fourth tank, and a pipe leading from the aperture in said fourth tank to said floc former container.
4. The combination according to claim l with the addition of a reversing switch connected between said current source and said electrodes; and with the addition of means for selectively directing flow from said first set of pipes to said fourth cell, said fourth set of pipes to said first cell, said second set of pipes to said third cell, and said third set of pipes to said second cell.
5. The combination according to claim 4 wherein said means forming first, second, third and fourth fluid treatment cells forms sets of first, second, third and fourth fluid treatment cells, and with Ithe addition of unconnected lenea-reo electrodes disposed between said sets of fluid treatment cells, said pair of electrodes being disposed in the first cell in said first set of cells and the fourth cell inthe last set of cells; and means connecting each of said first, second, third and fourth cells of each set of cells in fluid series, said first, second, third and fourth sets of pipes leading, respectively, to the first and last first, second, third and fourth cells.
6. An acid generator for salt or brackish feed comprising, in combination,"
(a) means forming at least a first, a second and a third juxtaposedV fluid treatment cell,
(b) an anode in said first fluid treatment cell,
(c) a cathode in said third fluid treatment cell,
(d) a cation permeable membrane disposed between said first and second fluid treatment cells,
(e) an anion permeable membrane disposed between said second and third fluid treatment cells7 p (f) first, second and third sets of pipes leading into and out of said first, second and third fluid treatment cells, Y
(g) means connected to said first set of pipes for circulating a dilute solution of an acid through said rst cell,
v(h) means for directing some feed water through said second cell through said second set of pipes,
(i) a first tank having an overflow and means for circulating fluid from said first tank through said third set of pipes through said third cell,
(j) a iloc former container, Isaid overflow from said first tank leading into said floc former container,
(k) drain means for draining waste from said lloc former container, f
(l) means for flowing feed water at a constant rate into said loc former'container, and
(m) pump means for drawing solution from said lloc former container and pumping this solution into said first tank at a rate less than the rate of said means flowing feed Water into said lloc former container.
7. An acid generator for salt or brackish feed comprising, in combination,
(a) means forming at least a first, a second and a third juxtaposed fluid treatment cell,
(b) an anode in said first uid treatment cell,
(c) va cathode in said third fluid treatment cell,
(d) a cation permeable membrane disposed between said rst and second fluid treatment cells,
(e) ananion permeable membrane disposed between saidV second and third fluid treatment cells,
(-f) first, second and third sets of pipes leading into and out of said first, 4second and third fluid treatment cells,
(g) means connected to said first set of pipes for circulating :a dilute solution of an acid through said first cell,
' (h) means for directing some feed water through said second cell through said second set' of pipes,
(i) ay first tank'having an overflow and means for circulating fluid from said first tank through said third set of pipes through said third cell,
(j) a lloc former container, said overflow from said first tank leading into said lloc former container,
(.'c)y a settling tank having a pipe leading from its bottom portion, a stand pipe connected to said pipe leading from said settling tank, and .a waste drain overflowV leading from the upper portion of said stand Pipe,
(l) a drain pipe leading from said lloc former container to said settling tank,
(m) means for ilowing feed water at constant rate into said lloc former container, and
(n) pump means for drawing the solution from the top portion of -said settling tank and delivering the fluid from said settling tank into said first tank at a rate less than the rate of said means flowing feed water Vinto said lloc former container.
8. The combination according to claim 7 with the addition of means for heating the solution in said lloc former container and said settling tank.
9. The combination according tot claim 8 wherein said means for heating the solution in said lloc former container and said settling tank comprises means heating feed water flowing into said floc former container.
References @ited in the file of this patent UNITED STATES PATENTS Great Britain Feb. 20,