US 3165452 A
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from the last evaporator in the series.
In the preferred operation of the invention the feed United States Patent 6 ice j This invention relates to a new and improved evaporator and a new and improved method or process for the evaporation of liquids. The invention is especially concerned with a process and apparatus for producing 190- table water from brackish well waters or brines. 7
One, of the objects of the invention is to provide a new and improved apparatus and process for evaporating liquids which :is especially adapted to the evaporation and condensation of water containing dissolved solids, such as, for example, brackish well waters and sea water.
Another object is to provide an apparatus and process of the type described in which the parts of the apparatus are less subject to scale and .encrustation than is the case with conventional evaporating and condensing equipment.
Still la further object of the invention is to provide a process and apparatus of the type described which is simple and highly eflicient in operation.
Other objects and advantages of the invention will be apparent by reference to the following description in conjunction with the accompanying drawing in which the single figureillustrates diagrammatically the best mode contemplated for the practice of the invention.
Briefly stated, the apparatus of the invention comprises (1) a heating unit in which water or other liquid to be evaporated is disposed and which is provided with a submerged combustion burner wherein the flame of the burner burns in direct contact withthe liquid beneath the liquid level and the products of combustion from the burner are discharged directly into said liquid; (2) means for removing undissolved combustion gases from the heating zone; (3) means to transfer the hot liquid containing some dissolved products of" combustion directly from said heating unit to a series of flash evaporators where the liquidemerges in such a way that a part of it flashes into vapor; (4) means to transfer the flashed vapors from the vapor space above the liquid in the flash evaporators to condensers; (5 means to recover the con densate; and (6) means'to remove the residual liquid water to the burner unit is passed through the condensers before it is introduced into the burner unit,- thereby serving to cool the vapors from the flash evaporator while the feed water itself is being preheated. 7 v
A preferred embodimenttof the invention is the provision of a stripping tower in contact with the vapor space 0f the burner unit through which the feed water is preferably introduced and which contains suitable means to permit escape of gases but to prevent escape of most of the water contained with the gases that are generated in the heating unit by combustion. Since these gases contain some water, even after passing through the stripping an ejector which connected to the condensers and serves to remove air from the condensers.
In prior pnactice these ejectors have usually been operated by means of I steam. 1
Patented Jan. 12, 1965 The direct heating of the liquid by means of a subrnergedcombustion burner makes it possible to operate with the liquid initially at a higher temperature and to effect a very substantial reduction inthe heat requirements with decreased condenser and heat exchange surfaces. The use of a heating unit in which a submerged flame is brought directly into contact with the liquid also reduces scale deposits in the evaporators and consequently reduces maintenance and the time which the apparatus is out of operation for cleaning (usually referred to as down time).
The drawing illustrates a system intended for use in making potable water from brackish waters, bnines, and the like. In this system the heating unit generally shown at l contains a submerged burner 2 which provides a flame burning in direct contact with the liquid beneath the liquid level 3. The flame is produced by passing a suitable combustible fuel and a combustion supporting fluid, preferably natural gas and air, into the burner 2 by a suitable means generally illustrated at 4. Suitable submerged burners for use in the system of the present invention are disclosed in the prior art, particularly in U.S. Patents 2,118,479 and US. 2,432,942, and reference is made to these patents for a more detailed description and functioning of the burner units which do not form a part of the present invention.
In the heat generating unit 1 Water is heated to a temperature just below the boiling point under substantially superatmospheric pressure, the conditions being suflicient to prevent the water from flashing into steam in the heat- It is preferable to operate this unit under a pressure of about 11 pounds per square inch gauge (25.7
pounds per square inch absolute) and toheat the water therein to a temperature of about 195 F.
The heated water is passed through a pipe or other suitable means 5 to the first stage flash evaporator generally indicated at 6. Flash evaporatorsare known per se and the particular construction of the flash evaporator does not form a part of this invention. The flash evaporator is preferably of a type in which the heated water is introduced near the bottom through slots in slotted horizontal pipes. The temperature of the water in the flash evaporator and the saturation pressure corresponding to the temperature of the water are lower than in the heating unit 1. In the six-stage flash evaporator system shown in the drawing, the temperature in the first unit or stage 6 is about 180 F. and the corresponding pressure about 7.5 pounds per square inch absolute. As soon as the liquid passing through the pipe 5 enters the flash evaporator 6 a portion of it flashes into steam which passes'through pipe7 to a condenser 8.
The residual liquid which does not flash into steam in the evaporator d is drawn ofl through pipe 9 to a second flash evaporator 10 and the condensate from condenser. 8 passes through pipe 11 to a second condenser 12 which is associated with evaporator 1i). p
In the second stage of evaporation in the system illustrated-in the drawing, the temperature of the flash evaporator It is around F. and the corresponding presthrough line 16 and is mixed with the condensate from flash evaporator 15 in line 17 from which'it passes into condenser 18.
The residual water from the third stage passes through line Y 19 to a fourth stage evaporator 20 which in the system illustrated is at a temperature of about 135 F.
and a pressure of 2.5 pounds per square inch absolute? The Water which is flashed into steam in flash evaporator 20 passes through line 21 into condenser 22. Thecon- 3 densate from condenser ls passes through line 23' and is mixed with the vapors from flash evaporator 20 for with the condensate from condenser 22.
The residual liquid from flash evaporator 20 passes 7 through line 24 to a fifth stage, flash evaporator 25 Where another portion of the water is flashed. into steam. The
' 355 amounts to about 349,170 pounds per. hour.
steam vapors pass through line 26 which connects with J line 27 and are condensed in condenser 28; The temperature of the fifth stage evaporator is preferably around 7 7 The a steam which is flashed off in this last stage passes through late are recovered.
to 95F, 1099 1 124.9%, 139.8? E, 1543",? and 169.S,'F, as it passes" successively throughycondensers 28, 32, 13,12 and 3 to feed water line 42from'which it is introduced into the stripping tower. 43. and thence to the heating unit: '1. The distillaterecovered-through pipe 34 as previously described amounts to about 32,830 pounds'per hour. The blowdown discarded through pipe The heated liquid passing through pipe 5 from the heating unit at a temperature of about 195 F amounts to about 382,000 pounds, per hour; 7 v
In the heating unit approximately 8600 pounds per hour of dry gas and 2140 pounds perhour ofwater pass through the stripping tower43 and line 44 to a condenser @5Where approximately 18.70 pounds 'pei honr ofdistil- V The cooling of the condenser 45 is effected With'about 99,900 pounds per hour of water-at -a temperature of 80 F. About 8600 pounds p'erhour to operate the ejector 45% line Slwhere it is mixed with'condensate coming from'the fifth stage condenser through line and is condensed in the sixth stage condenser 33. The final condensate is recovered through line 34 and the residual liquid is" lown down or discarded through line 35.
As shown in the drawing, cooling of the condensers'is preferably effected by passing the feed-Water whichcan be, for example, at an initial temperature of 80 .F.,
countercurrently through the respective condensers via pipes 36, 37,38, 39, 40, 4-1 and 42 to the heating unit ll.
In this manner thejfeed water is progressively heated to a temperature of. approximately 170 F. before it is in-- upwardly fromthe stripping tower throughline id are The introduction of the of gas and 270 poundsiper' hour of water'at a temperature of about 110 F. pass through the line 47. and aroused The operation of the submerged burner 2 requires about 540 pounds per hour 'offuelgas and 9150 pounds per hour of air. The :heat requirements of the: burner are approximately 12050000113111. per h'o ur' once con-. tinuous operation has begun. g V
The foregoing figures are based on calculations wherein the overall heat transfer coefficient ofthebondensersi. is assumed to be 500 B.t.u per sqtiarefootper,hour per F. a The inventionis applicable toany multiple stage flash evaporator system of a the type described cingwhich there are two or more flash evaporators, Thus, theinvention maybe practiced With2, ,3, 4, 5,;6, 7, 8, 9 or 10 flash evaporators, depending to afconsiderable' extent upon the space available and the output desired. -Where only a smallspace is available thefsystem can be operated with two'flash evaporators. Such a systemis particularly useful, for example, for producingpfresh' Water from sea passedinto a condenser to remove a major proportion" of the water 'contained therein. This con-denser is cooled by cooling water'at an inlet temperature of about 8 0. F.
and an outletternperature of around 100 F. The outlet 7 'cooling Water can be discarded or used for some'other purpose. The condensateor distillate is recovered through I pipe 46 and added to the condensate or distillate recovered through pipe 34.- The gas yvhich passes through the con passedthrougha line 47 to" an denser? unit is 1 preferably ejector 43. v
The ejector 48 is connected by a suitable pipe 49. to pipes 50, 51,52, '53, 54-, and ES of the condensersfi, 12, 18," 2-2, 28 and 33, respectively, to remove air from the con densers. which is discharged to the atmosphere through pipe,, 5i6;; j Removal of this air is highly desirable'from the standpoint of efiicient operation and theuse of the 'Waste gases for this purpose is an feature of this invention.
particular size, the following example illustrates the regallons of potable Waterper day;
importantbutopt'ional I While the invention'is not limited to a system ofany i quirements for a unit having annoutput of about 100,000 0 The'waterused can be brackish Well water containing 2,000 to 22,000fparts per million of dissolved solids oriit water in off-shore drilling operations. The invention'is especially useful in arid' ar'easwhere the water obtained from wells, for example, in Kuwait, is brackish and con tains substantialquantities of diss'olvedsolids. Water containing dissolved solids normally tends to form scale on the. evaporatorsbut by. heating jthe ,water, directly with combustion gases' thistendency to form scale is re} duced, apparentlydue to'the action oflthe'carbon dioxide present inisuch gases; Since the present inventionfalsomakes it possible to l-heat the feed waterto highertemperatures initia'lly,it is. possible to use a six-stage evap- 1 orator Where five-stage evaporatorwould be employed in conventional heating where'the' Water to beevap'orated J is heated: bypassing it throughya heatexchanger heated w by steam from a boiler; -As lcornparedwith this conventional process the process of the present invention uses much less heat and requires less condenser and heat exchange surface These factors, coupl'ed-withfa reduction ofsca'ledeposits in the evaporators 'with consequent reduced'maintenance and idowntimefi more'than offset the added expense. of an air compressor Which is requ red to;
supply air tothe suhmergedfburner T-he invention is hereby claimed as, follows:
1. A system' forevaporation or -liquids aud condensa I tionof the vapors therefrom comprising in combination a heating unit inwhichjthe, liquid-to be evaporated is disposedfsaid heating unit'comprising a submerged combustion burner wherein the flame oflthegburnerkburns in direct .con tactwith theliquid to be evaporated beneath the liquid level and the product s'of combustionfrom the burner a're discharged directly into sai removing undissolvedgases from, t
liquid, means for e hcombustion zone,
j a series of flash evaporatorsprovidedwitl 'ia.vaporspace abovefthe liquid, means to'transferfthefhot liquid containing said dissolved, products of combustio'n fdire'ctly ,l-from 'saidheating unitto said'series of'flash eyapo'rators F5 where apart of theliquidlis'siiccessively flashed' 'into enemas flash vapors, a condenser connected to each said flash evaporator, means'to maintain successively lower pressures and temperatures in said flash evaporators, means to transfer said flash vapors from said vapor space above the liquid in said flash evaporators to said condensers in each stage of evaporation where condensate is formed from said flash vapors, means to recover said condensate, means to transfer unvaporized liquid from one said evaporator to another in succession, means to transfer the products of combustion from the heating unit to operate an ejector connected to the vapor spaces of the condensers of each of the flash evaporators and serving to remove uncondensed gases from said condensers, and means to remove unvaporized liquid from the last evaporator in the series.
2. A method of making potable water from non-potable water containing dissolved inorganic salts which comprises heating said water in a closed vessel by means of a direct flame which burns in contact with the Water beneath the liquid level and discharges the products of combustion directly into the liquid, withdrawing the heated water from said vessel and passing it successively through a series of flash evaporators at lower temperatures and pressures than the temperature and pressure at which the water is initially heated, successively condensing the vapors which are flashed from the water in each of said evaporators, recovering the condensate, utilizing undissolved products of combustion from the flame used in heating said water to operate an ejector connected to the condensers of the flash evaporators which ejector serves to remove uncondensed gases from said condensers, and removing the residual liquid from the last evaporator in the series.
3. A process of converting non-potable water to potable water which comprises heating the non-potable water in direct contact with a flame which discharges products of combustion directly into said water beneath the liquid level in a closed vessel while maintaining superatmospheric pressure and a temperature of about F successively passing the heated Water into a plurality of closed evaporating vessels at successively lower temperatures and pressures whereby vapors are flashed from the heated Water condensing said vapors in each of said stages of evaporation, recovering the condensate, removing the residual water from the last stage of evaporation, utilizing the feed water successively for cooling in each stage of condensation in a direction countercurrent to the flow of the condensate, removing uncondensed products of combustion from the heating zone, stripping a portion of the water from said uncondensed products of combustion, condensing a portion of the remaining water from the products of combustion, recovering the condensate, and utilizing the products of combustion to operate an ejector connected to the condensation stages to remove uncon densed gases therefrom.
References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Ellis: Fresh Water From the Ocean, Published by The Ronald Press 00., New York, 1954.