CA2094571C - Improved salt basket for crystallizer and method of use in zero liquid discharge industrial facilities - Google Patents

Abstract

An improved salt basket for dewatering solids. The salt basket is ideally configured for use with a crystallizer or evaporator producing salts from industrial wastewaters. The salt basket system includes a pressurizable vessel having a screen floor situated above a bottom liquid collection head, an inlet for the brine/solids slurry from which solids are to be separated and dried, an inlet for air, an inlet for steam (the latter two inlets may be combined, where convenient), a feed brine inlet and a drain outlet (these two may by combined where convenient into a combination feed/drain connection), an automated system for introducing feed brine, and an automated system for removing the solids product, the latter system including an automated door with a fail safe clamp system design.
The vessel shape preferably includes sidewalls of substantially circular cross section with downwardly and outwardly sloping walls (either conical or flaring somewhat at the bottom) which are free from protuberances which would tend to prevent salt crystals from falling downwardly. A pivotally attached lower door has a hydraulic failsafe closure mechanism and looking safety latches to prevent the door from inadvertently opening. The process control design minimizes exposure of the salt basket interior to supersaturated solutions with precipitating solids therein, thus reducing coaling of the salt basket, by introducing feed brine rather than magma (crystal/concentrated liquor slurry) to the salt basket between crystal harvest cycles.

Description

II~ROYSD SALT BASRET FOR CRYSTALLIZER AND MSTSOD OF USE IN ZERO
LIQUID DISCBARGE INDUSTRIAL FACILITIES
TECSIJICAL FIELD OF TSE INV~1TION
The present invention relates to crystallization of salts from industrial wastewaters and more particularly, to novel, improved systems for removal of substantially dry salts from a crystallizer or crystallizing evaporator and to the application of such systems to zero liquid discharge type industrial wastewater treatment plants.
BACKGROUND
A number of systems for collecting and removing salts from crystallizers have heretofore bean proposed. One interesting summary of previously used systems is disclosed in Canadian Department of Mines publication No. 325 entitled "REPORT ON THE
SALT DEPOSITS OF CANADA AND THE SALT INDUSTRY", by L.H. Cole, issued in 1915. Such systems primarily consisted of a calandria type crystallizer with a salt basket chamber attached therebelow.
The salt basket was generally mounted on the ground or at a working platform. 'Typically, those crystallizers and the attached salt baskets were used for recovering crystals of highly soluble salts (those which (a) form highly concentrated solutions with water and which (b) are increasingly soluble at increasing temperature). Typically, the salt was shovelled out of the salt basket through manually opening side doors.
Systems of the type identified above have been in use for about one hundred (100) years and have mainly been used in the recovery and refining of various commercially utilized salts. The most significant rise of such salt baskets has been with the manufacture of sodium chloride (NaCl), or table salt. Such heretofore known systems have the decided disadvantage that they offered few automatic operational features. Also, the removal of salt typically required substantial manual labour.
Insofar as we are aware, the above described previously known salt baskets have not been utilized in combination with modern evaporator or brine concentration systems which distill the wastewaters at many industrial plants such as coal fired steam-electric generating plants, co-generation electrical generating facilities, metals smelting and refining facilities, pulp mills, chemical plants and the like. Indeed, when such modern wastewater treatment systems have been unable to utilize large solar ponds for the discharge to and drying of the concentrated brines and precipitated salts, recovery of the precipitated salts for disposal has been accomplished by resorting to the use of relatively expensive and otherwise undesirable alternatives such as filter presses, centrifuges, or spray dryers. Descriptions of such systems are found in a variety of trade publications, including: THE ECONOMICS OF WASTEWATER RECYCLING AT A LOS
ANGELES COUNTY COGENERATION PLANT, by K.P. Hammer, P.C. Egleston, Jr, and R.S. Ludham, presented at WATERTECH 1992 in Houston, Texas, November 1992; CASE STUDIES: ZERO LIQUID DISCHARGE SYSTEMS
AT THREE GAS-FIRED' POWER PLANTS, by D. Bowlin and R. Ludlum, presented at the 1992 American Society of Mechanical Engineers COGEN TURBO POWER CONGRESS Meeting in Houston, Texas in September, 1992; WATER MANAGEMENT FOR REUSE/RECYCLE, by S.D. Strauss, published in POWER Magazine, May, 1991 and EVAPORATOR AND SPRAY
DRYER COMBINATION :ELIMINATES RESIDUAL WASTEWATER LAGOONS, by R.
Mclntosh and A.E. Hodel, published in CHEMICAL PROCESSING, in February, 1990.
The use of spray dryers, centrifuges, or filter presses for water solids recovery at zero discharge type wastewater treatment plants are not without disadvantages. Spray dryers consume large amounts of energy to evaporate residual brine from the solids being dried. In addition, in many jurisdictions, an air emissions permit is required for the discharge of heated air (normally including direct combustion products) which is vented from the spray dryer. Filter presses often consume expensive chemical additives in an attempt to increase the dryness of the residual salt cake. Centrifuges are rather expensive and the high speed rotating parts not infrequently require costly repairs. For both filter presses and centrifuges, it often seems that an inordinate amount of labour is expended to coax the systems through their required service and unplanned additional maintenance requirements are a relatively common occurrence.
SUI~1ARY
We have now invented and disclose herein, certain new and improved salt basket systems which are free of the disadvantages of and otherwise superior to, the prior art solids handling systems for industrial wastewater plants of the character discussed above.
The invention in one broad aspect pertains to an improved salt basket for separation of solid crystals from a slurry containing a concentrated liquid and solid crystals. The improved salt basket comprises an upper vessel, the upper vessel comprising a downwardly and outwardly sloping sidewall, the sidewall having a lower end portion, the lower end portion defining a downward directed bottom opening and an upper flange, the upper flange extending peripherally outward from the lower end portion of the sidewall. The basket also has a door, the door being sized and displaceably located fox opening and closing of the downward directed bottom opening of the upper vessel, the door being attached by a pivot: connection to the lower reaches of the upper vessel and the pivot connection including an automatic cyclic programmable control sequence for repetitive downward-outward opening movement followed by inward-upward closing movement, which, respectively, effects the opening and the closing of the downward directed bottom opening in the upper vessel for batchwise harvest of the so7.id crystals. The door further comprises an outer edge portion, the outer edge portion sized substantially complementary to the lower end portion of the sidewall of the upper vessel, the outer edge portion further comprising a door flange extending peripherally outward therefrom. The door flange and the upper flange on the upper vessel are juxtaposed in a mating and sealing relationship, so as to pressurizably seal the downward directed :bottom. opening of the upper vessel. The door has an upper portion, the upper portion having an interior flange and a drain, the drain adapted to allow discharge of the concentrated liquid therethrough. The basket has a screen, the screen being affixed to the interior flange of the upper portion of the door, the screen shaped to define apertures therein. The screen apertures are adapted for allowing escape of the concentrated liquid therethrough while substantially preventing the solid crystals from escaping therethrough.

Another aspect of the invention provides a method of dewatering the solids which are present in a liquid and solids slurry which is produced by precipitating solids from a wastewater feed stream in a crystallizer, the method comprising introducing the slurry from the crystallizer into a pressurizable salt basket vessel, the vessel including a combination pivotable screen and bottom door portion, isolating the salt basket from the crystallizer, slightly pressurizing the salt basket vessel, so as to force the free 7.iquids through a screen and outward through a drain and to substantially retain the solids before the screen, depressurizing the salt basket apparatus, opening the bottom door portion of the salt basket apparatus to downwardly pivot the bottom door portion and the screen to substantially empty the solids from the salt basket by allowing the solids above the screen in the salt basket vessel to fall by gravity from the salt basket vessel and closing the bottom door portion of the salt basket vessel to reaurn the salt basket vessel to a pressurizable condition.
Still further the invention comprehends a process of treating a wastewater stream from an industrial plant in a selected locality, the wastewater having dissolved solids therein, at least a portion of which have solubilities which vary inversely with temperature, the dissolved solids comprising calcium, sodium, chloride and sulfate ions. The method comprises feeding the wastewater stream into an evaporation unit, evaporating the wastewater to produce vapours which are condensed to recover a distillate therefrom and to produce a concentrated brine while preferentially precipitating at least one inversely soluble solid therefrom, while nc>t appreciably exceeding the solubility limit of any of one of sodium sulfate, or sodium chloride, therein, so as to produce a brine slurry containing dissolved solids and a precipitated first. solid, feeding the waste brine slurry to a crystallization apparatus, concentrating at least a portion of the remaining dissolved solids above the solubility limit in the brine of any of sodium sulfate, or sodium chloride, to produce crystals therefrom and to thereby produce a slurry comprising free liquid and a precipitate second solids comprising any one salt selected from sodium sulfate and sodium chloride, feeding the first and the second solids to a salt basket apparatus having a lower screen portion, a drain and a door, slightly pressurizing the salt basket apparatus with a gas selected from either steam, or air, so as to force the free liquids through the screen portion and outward through the drain and to thereby substantially dry the first and the second solids, depressurizing the salt basket, automatically opening the salt basket door, so as to allow the dried first and second solids to fall by gravity into a receiver.
More particularly, the novel, improved salt basket systems, include a pressurizable vessel having a screen floor situated above a bottom liquid collection head, an inlet for the brine/solids slurry 2o9~5~i from Which the Solids are to ~s separated and dried, an inlet for ai.r., an inlet rot steam (the latter two inlat5 zaay be combined, wharQ convenient), a fpsd brine inlet and a drain outlet (these two may be combined where convenient into a combinativn,leed/drain connection), an automated system for introducing reed brine, ahd an automated system for removing the solids product, the latter system iricludiny an automated door with a fail safe clamp system design. The vessel 5hzspe i5, preferably somQwhat. bell shaped, ideally having sidewalls of substantially circular oroee section with downwardly and outwardly or bom~what conically shaped walls which are, t~ the extent practical, tree =tom protuberance3 which would tend to prevAnt salt crystals from Iallinc~ downwardly. The salt baskets components may hp fahri.cated of high Strength alloys suitable for highly corrosive environmQnts. At the same ti.ma, i-hp sySLem components are simple and relatively inc~cpcn~ive to manufacture, and the resulting sy5l.~~u5 are 30 accordingly sufficiently inexpPnsivp (particularly when compared to the previou3ly available alternatives) to bs employed in even very small ecru discharge wastewater syctPms.
rcrhapE moEt prominent among the novel features of Z5 the call. Lasket systems disclosed herein is the type of door employeCt, particularly the opening and closing 20~4~71 system and the air actuated saLety latching system. In r_ontrast to previously known manually opening salt basket doors, the door of the present invention utilises a remotely actuated arm. Far convenience, we kiave chosen to utilize a hydraulic arm with locking fitting which is normally closed to maintain hydraulic pressure in the closure arm, so that the door is kept from SHiFl;iny cr opeuiny, Even in the event of a power failure or failure of the locking safety latches to prevent the door fram.opening.
Specialized, air,actuated locking power clazaps with high strength locking arms are utilized for door latohes. Thr~ latches are biased toward the normally closed position. The latches require actuator 1~ pressurization to overcome i:he iueta-Stable ldtc:h bias mechanism, in order to release the latch toward the open position. This is quite important in the present application where the salt basket vessel may contain a hot, boiling liquid/sollds slurry and/or pressurized Z(~ si-.pam.
An additional novel feature is the process control debic~u wtiic:li minimises exposure of the salt basket Interior to supersaturated solutions with precipitating solids therein, thus reducing scaling of the salt 25 basket. More importantly, the entire salids haiic3lirsy process is essentially fully automatic, from introduction of a slurry containing solids into the unit through removal of the solids and preparing the system for another cycle of solids handling, thus reducing plant labour requirements.
From the foregoing, it will be apparent to the reader that one important and primary aspect of the present invention resides in the provision of navel, improved systems for removal of precipitated solider from wastewater treatment plants.
Related and a7.so important but more specific aspects of the invention reside:
in the provision of a method to provide substantially dry salts without the need to employ an expensive drying apparatus such as a filter press, centrifuge or spray dryer;
in the automation of a solids recovery and handling system to eliminate the need for manual labour to remove salts from a salt basket;
in the design of a fail safe closure and clamp system to prevent accidental opening of the salt basket vessel;
in the combination of an improved salt basket apparatus with conventional wastewater evaporation systems to reduce the overall life cycle costs (combined capital and operating costs) of such systems.
Other important aspects, features and advantages of the invention will be apparent to the reader from the appended claims and as the ensuing detailed description and discussion proceeds in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings;
FIG. 1 is a generalized schematic of industrial wastewater treatment systems where the improved crystallizes and salt basket solids handling sye;tem of the present invention may be employed.
FIG. 2 is a simplified process flow diagram, illustrating the operation of a crystallizes and salt basket apparatus.
FIG. 3 is a simplified side elevation view of the salt basket portion of the present invention, illustrating operation thereof.
FIG. 4 is a e~ide elevation view with partial cutaway of a crystallizes and salt basket showing key elements of construction.
_g_ FIG. 5 is a process flow diagram, illustrating the koy prv~pss ronfrol e~.ements for automatic operation of the cryetallizer and salt basket system.
FIG. s is a process floe bloelc diagram, illustrating an exemplary sequence of control for the automated operation of an imrrwpr3 crystal 1.i zer anr3 sal.i-_ basket for harvccting crystallized solids.
FIG. 7 i5 a bide elevation view of an automated sa 1 t basket with a partial cutaway or the air operateti closure latches, showing thA hydraulic door opQning mechanism and the general location of only some of the air operated closure latches.
FiG. 8 is a back elevation view ~f an at.tt~mated salt ba3ket portion of the prc~ont invention taken from 25 the perspective vt line 8-8 uL FIG. 7.
FTC. 9 is a fragmentary view of the bottom portion of the salt basket, showing the movement of the door upon opening.
FIG. 9A is an enlarged detail taken along the line 9A-9A of FIG. 9, shouting details of the upper flange, i clad flange construction with a receptacle groove and o rinq fitting therein.
FTr. 1A is a fragmentary view the bottom portion of the salt basket, showing the door details when in the closed position.
f~'1G. 11 is a top view or the salt basKet, Showing 249 i'~1 the arrangement or ttie z~ir headers used to supply air to the closure latch mechanisms.
FTG. 17 is a side vier~ of details of the locking power clamp and arm with adjustment means, showing its relationship tv the Salt basket door =lunges when in thp closed and locked position, as well ~~ whpn the lock is in the open position.
FIC. 13 is a back view of the locking power clamp.
FZG. 14 is a partial front view or the lorki.nc~
power clamp ax-m with adjustment means, shown in the open position.
_10-2094~7I
DBSC&IrTIOId Although the improved salt basket and mpthnd of operation dQSCribed herein may be adapted for ucc 'in many types of separation applications involving the removal of solid particles from liquids, it is particularly useful i.n pror_.essPS Pmploying crystallizors to produoe salts by evaporating Water from solutions.
The moSL l.rcublesome of such solutions are normally 1ti those containing both (1) the slightly soluble dppcsit forming solutes such as calcium sulfate, silica, calcium phosphates, calcium fluoride, or calcium carbonate, and (2) the highly soluble solutes such as sodium chloride, sodium sulfate, ~r the likes. Such solute combinations are commonly encountered in the process of recovering distilled water lrvm wastewaters at aero liquid discharge type industrial plants in a variety locations_ As can be appreciated by referencE to FIG. 1, water removal from brines containing mixed solutes is suitable fcr ~.ranti.~a at a wide variety of industrial plants 20.
Such plants may be coal fired power plants, electrical cu-gGneratiun plaut;5, chemical plants, oil refineries, Gulp .mills, or the like. Such plants have nl.imernus requirements for water. Water may be required for steam boilers, injection in gas turbines, cooling towers, -li-s.crubbera, flue gas desulphurization systems, and immneruble other uses. Typically, makeup water 22 to such plants contains some mineral r.~ntRnt, arid increasingly, the mineral content (amount of Eolutc) ie somewhat higher than desirable. When an insurricient quantity of high quality water 24 (low in mineral.
content) is available, some type of demineralization plant 26 is normally required at the industrial plant 20 to prepaie makeup wzcter 22 for the desired industrial lU uses, by removing a portion of the minEral content from the makeup watQr 22 and producing water product 28 with relatively low total dissolved solids (TDS) and a rejec:l:
stream 3o that is relatively high in total dissolved sc1 ids_ various tyrr~s of process are ~rell known far removing mineral content from water, such as ion-exrhanye, zwv~r5e o5i~v5i5, 5ofteninq, electodialysis, or distillation.
In zero liquid discharge type industrial facilities, once the reject stream 30 leaves the 2o demineralizer 26, or discharge stream 32 leaves the plant 20, or coolincj tower blowdown 34 loaves the pooling tower 36, the streams 30, 32, and ~4 must be c:~llec:i.ed dnd neutralised, such ds iri storage/mix tank 38, and then further concentrated. t.~ .rPdo.nP their volume by racavering relatively pure water therefrom. It i3 frequently desirable to concerltrute l.he ~ulil~l'Q1 content of these combined wastewater streams to substantially dry solids and thus in the proc:ess recover essentially all of the water from such waste streams. In one common practice, the water is recovered as distilled water 40 containing less than 10 parts per million of total dissolved solids, while the calcium sulfate and silica in the wastewater is preferentially precipitated in a brine concentrating evaporator 42 by use of calcium sulfate anhydrite nucleation crystals. That method is general described in U.S. Patent No. 4,618,429, entitled METHOD OF MAINTAINING
ADEQUATE SEED CRYSTAL IN PREFERENCIAL PRECIPITATION SYSTEMS, issued October 21, 1986 to H. R. Herrigel, the disclosure of which may be refer-red to for further assistance. Also, the evaporator 42 used in such systems to concentrate the inversely soluble salts are described in a report entitled SCALE FREE
VAPOUR COMPRESSION EVAPORATION, by the Office of Water Research and Technology, U.f~. Department of the Interior, distributed by the Superintendent ~of Documents, U.S. Government Printing Office, Stock No. 024-000--00839-9, GPO 1977 0-247-979. This latter reference, althouc,~h not essential for those trained in the art, will be of assistance to those learning the art and may be referred to for further assistance. By use of such seeded slurry technique, precipitation of salts inversely soluble with temperature such as calcium sulfate, as well as other scnle forming minerals such as silica, can be prevented from occ:us~riny um heat transfer tubes and other process equipment while the cfrculating brine is concentrated up to just below, or not appreciably above, the~crystallization point of the more soluble salts, such as sodium chloride, sodium sulfate, glauher'~ gait, nr. the .like. FPP~i t~.o evaporator d2 is normally regulatod by the level 43 of liquid in tho comp 44 and the density of such liquid is measured to control lc3 the dissolved solids concentration. as will be apprQCiatad by those trained in the art, the upper dissolved solids concentration limit setting, and the suspended solids concentration required, will vary wi dely depending upon ttie specif is mixture of so7.utes in the water, but general guidelines may be determined from literature references describing the solubility of mixed salt solutions. of course, wastewater can also be evaporated without resort to such seeded slurry technique, although alternate processes are generally 2o more troublesome due to scaling tendencies experienced daring c:nnrpntration of thp hri.ne.
In any event, onoo the desired brine aon~entration is rsa~aheri in evaporatc~i~ 42, the concer~trated circulating brine is discharged (line 45) from the Qvaporator 42 and introduced into a crystallizQr 46. A
variety of crystallizes designs arc well known, but in general such dewices~are specially daaigned to provide adequate operational characteristic;5 (true period between cleaning) When crystallizing the soluble salts.
various known types include forced circulation c;i~y5tallizers, circulating magma crystallizers, and Oslo type crystallizers, and our improved salt basKet and method may be adapted for use with any of the well known crystallizer types. We prefer the use of a propEller Calaridria type crystallicer, also 5~metime5 kIlUWl1 cS Q
draft: t~~bp haffie type crystallizer.
Hcrctofore in wastewater treatment plant instnllutiou5, in so far as we are aware, the salt 48 in crystallizer 46 upon discharge, it dewatered, has been typically dewatered in a filter press or centriFu~e, or 1~ rarely, in a spray dryer. We have noW discovered that an improved, automated salt basket 50 eliminates the labor and PxppnsP of hands i ng the produced wet salt 48 in much rclativcly high maintcnanac equipment aE the filter press Ui' c:etxtriLuge, cnil iiramatically reduces 2Cr overall system life cycle costs. r~urther, by mounting the salt basket 50 above a receiver 52 (preferably a machine transportable waste container or dumpster bin is employed, although direct discharge to a pit structure may be used) a relatively dry salt crysf.als 54 may fali 25 directly into rcccivcr 52 by gravity. Receiver 52 may be easily removed, eauptied, atld~Ur replaced dS I1CCCSSdry 20~:~~'~1 I to accommodate the quantity of dry salt crystals 5d haing produced.
llttention is now directed to flG. 2, Where the k~asics of the operation of a crystallizes Q6 and salt basket 50 are shown. 8rizle feed GO is introduced into a feed line 6~. Feed brine bU lady be a relatively solids free but high mineral content sol»tinn, or may be a luiyHly concentrated solution having therein suspended solids of sparingly soluble halts such as calcium l0 sulfate, in accord with nucleation technique mentioned above. teed line 62 terminates in the upper reaches 6d of the crystallicer ve~csel 46. The feed GO mixes with and becomes part of the circulating magma 66 (EUpersaturatad solution) from which the wpt: salt crystals 48 grow. Normally, a submerged upf low heater 68 is provide8 with an axial type pump 70 with propeller 72 to forcQ the magma 6f up through the heater 68, and the magma 66 with salt cryetals X18 suspended therein gradually fl~w5 duwnward in the direction of reference 2o arrows 74 between the outer portion 76 of the heater and the inner wall 78 of the crystallizor 46. Sham 8c.1 Zs introduced into the heater 60 to heat the eiroulating magma 66, and resulting prime condenSaLe 82 is captured and rPt.t.irnpd pl.~pwhere for reuse. The vapors 84 generated by evaporation of Water from the mar.~ma 65 bubble 86 uYwdRCi tU the liquid/vapor interface t3i3 and thence escape outward through a process vent 90 to a suitable condenser 92 (shown in FIG. 1). Generally, this type of crystallizes is often known in the trade as a propeller calandria.
For normal operation of our improved salt basket, we isolate the crystallizes 46 from the salt basket 50 via way of isolation valve I, until a sufficient quantity of crystals 48 are available in the circulation magma 66 for harvesting, as may be determined by draw-off of a aample through sample port 94. During this isolation and crystal forming period, the salt basket 50 is preferably full of feed brine 60 or another selected liquid or slurry stream; ideally the material placed in the salt basket 50 during this period will be of such composition that it will tend not to scale the interior walls 96 of the salt basket 50. When it is time to harvest the crystals 48, isolation valve I is opened.
Wet salt crystals 48 flow by gravity downward through isolation valve I and accumulate in the salt basket 50 above a bottom screen 98. After closing isolation valve I, supply of feed brine 60 is terminated by closing valve F and the drain valve D in the salt basket 50 is opened. Stream 100 and/or air 102 is introduced into the salt basket to force the free liquids surrounding wet crystals 48 downward through the screen 98 and out through the drain/liquid return line '~ 209571 lU4 and drain valve D, and thence up the foed line 62 to return the same to the inl:erior of the crystallixer ve3acl 46. After purging the free liquids from the interior of the salt baskQt 50, sufficient Steam lUU
and/or air 102 i5 introduced .through thg salt basket 50 to prod~.icP substantially dry salt 54, whereupon the supply of Eteam 100 and/or air. 102 is halted. Then, the salt baskat vessel 50 iE ventad in r.r.ppar.atiori O=
opening oz the door 108. In many applications, salt 54 is cufficisntly dry if it passes the so-called paint filter teat utiliaod by thQ United :~t~ates Environmental Protection Agency, and~similar agenciAS of the various states; reference is made to the U.S. Code of Fcdcral Rcgulationo, 40 CFR Section 2f~4.314, and EPA Ptlblical.ion SW-846, Method 9095.
Turning nOW to FIG. 3, it is clear that aE door 106 ie opAnQd, dry salt crystals 54 are allowed to fall directly downward to form a sol i ~3s pile lU~T. One convenient door 106 design utilize a hydraulic actuatnr.
30 110 t.o pul.l via shaft 112 on elbow pivot 114 of door crank 116, to pivot the door crank 116 and the door 106 aff ixc~i then eto about a main pivot pin 11 R i.n the direction indicated by reference arrow 120, to open door 106. Since befoYp opening of the door 106 the dried solids 54 are held above tha screen AR, upon opening oI
door 106 such 5ulids ~4 . slide off of the screen 98 and 209~~7I
tail downward, as does the bulk load of. solids 54 which, before opening, is held up inside the salt baekot 50.
To fully take advantage of the just descriLed salt basket 50 construction and door 106 operiirig result, overall crysta7.7.i.~er/salt -haskPt-. plant layout is important. One cuitablo aonfiguration i3 illustrated in FIG. 4. The salt Lasket vessel 50 5liape i5 preferably somewhat bell shaped, ideally having inner sidewalls 121 of substantially circular cross section which are downwardly and outwardly slanted, (or somewhat comically shaped or even outwardly Ilared walls) which are, to the extent pracaioa7, free from protizheranae.s which would tend to prevent c3lt CryGt3l~ from falling downwardly.
2lie c:i~y5t,allicer 46 dnd salt basket 50 are supported at sufficient elevation C anti R rpspPC:i-i,vely above a reference datum, preferably by support braolsctc 122 and 124 resting on structural members 126 anc3 128 respectively, so that.(1) wet salt 4~ may rlow by dravit.y from the crystallizer d6 into the closed salt ba~kct 50, and (2) the dried salt 54 may fall directly from the opened salt basket 50 into a receiver or salt bin 52 as descri hpc3 above, withrn.~t the mead for manual labor to handle the dried salt product 54. The necessary distance will vary c7ependiy up~r~ t.r~e 5ice or the various vessels, but may in particular the elevation F may bP sot to accommodate the receiver 52 and the 2~94~~~
07ParannP nPC:pssary For door 1OC when in the downward nr vcrtioal pooition ae iliuatrated in FIG. 3 above, Therefore, the height of supporting structure shoyrii iu FIG. 4, such as columns 130 and 132, may be set accordingly during the plant design stage.
Aside from the important configuration just described, clso noted in ttii5 FIG. 4 at the bottom oI
salt basket 50 are the clamps 133 which secure d~~r 1.06 from rotating about.pivot pin 118; the deEign and operation of the clamps 133 and accompanying control system are more completely described herein below.
Attention is now directed to FIG. 5 a process flow diagram, and related FIG. 6 showing the control cycle for salt crystal harvest, which figures together ate convenient to assist the reader in appreciating the unique automatic operational sequence of our crystallizes and salt basket combination. First, the crystallizes is controlled conventionally, with the major control loops providing for automatic control of (1) the liquid level 88 in the crystallizes 4G and (2) the steam pressure in the heater 68. with respect to liquid level AR, t:hp l,pvPl. RR l~ can~P:r~. by a lPVS1 transmitter ZT, with feedback to the fccd valve F, whioh iii turn admits additional feed brine 60 upon drop in liquid level 88, or reduces the flow of brine 60 upon rising liquid level 88. The liquid level 88 is 2Q9~~'~I
maintained high enough to assure that.t-.hP hPatpr fR will not become dry and thus oxpoccd to fouling and eoaling.
The density transmitter (DT) signal automatically compensates the level transmitter signal for the changing density of the circulating magma 66 as it becomes concentrated.
With respect to the c;ry5tallicer 5tedm control loop, plant steam 80 at any convenient pressure is controlled by steam valve S (with help from a' conventional pressure reducing station, if necessai-y) to supply steam la4 pressure of nominally 1v psig (pounds per square inch) entering the steam side of heater 68.
The steaia supply 134 pressure is measured and controlled by a pressure indicator controller marked PIC in FIG. 5.
As the crystallizes fouls or. sea 1 es, thp ~T'PS~IIYP Qf Supply steam 134 ie~raiEed to oompenEato for the rcduacd differential temperature in ttre ca~ysl:alli~er, to maintain crystallization rate as necessary. Normally, the crystallizes is run without significantly varying the steam flow rate.
crystal harvest is normally done batchwise, ana crystal s 4A asp harvPStpd. upon oompl ~ti ~n cf a r..rysi.-.al growth cycle. The dcn~ity and TsS (total ~u~pendcd SUllds) dre inunil.ured, and allowed tv build up to a preselected level which may vary somewhat depending upon the salts being precipitated and the cycle times _2;_ resulting in relation to plant staffing ~ahedules.
Generally, somewhere between 10% and 30$ T3S is selected for the enri of the crystallization operations and the beginning of a salt harvest cycle. We haves found that starting the harvest when the suspended solids level is between 1z and 183 TSS is normally desirable. As a convPniPnt final c:hprk, the operator may confirm the TSS
by taking a sample through port 94 and visually observing the settling solids proportions and settling 1o rate in a test cone or cylinder.
Once the decision has been made to harvest the salt, upon harvest cycle initiation, the salt basket harvest cycle is completed through the operation of a SPY1PS 4f automa-tic valves by a computerized 15 programmable logic system. While the specifics of any I
PLC (programmable logic contrulj system program will r vary depending upon trie selected hardware and software suppliers, those trained in thQ art will apprQCiatQ that the sequence of steps set forth in FIG. 6 are sufficient 2o to provide the basic crysta111zer and salt basket onera.tional ~tPrc d~.~ring a crystal harvP~t cynla, thus enabling the programming of came in any convenient operating platform. Also, it should be uciderSLuvd that i the general approach of our method of operation is to be 25 appreciatQd, and that with rQSpact to the steps set forth in FIG. G, it shall be considered as exemplary and not as exclusive it being evident to those trained in the art that certain valve openings and closings, notably at the start and end of particular segments of automated operations, such as feed of crystals, pressurization/drain, depressurization, open/dump salt, close and re-fill, may be accomplished by simultaneous as well as sequential change of valve settings, without varying from the fundamental essentials of the automated sequence of operations provided herein.
Reference is again made to FIG. 5. During the normal crystallizes 46 operations (crystal growing cycle), the salt basket 50 is isolated from the crystallizes 46 by way of isolation valve I. Also, i=or reasons which will be explained further hereinbelow, the salt basket 50 is preferably filled with feed brine 60. These conditions are considered to be the normal start conditions for a circle to harvest wet salt 48.
To start a salt harvest cycle, the vent valve V is closed and the isolation (preferably plug type) valve I between the crystallizes and t:he salt basket 50 is opened. Upon opening of valve I, salt 48 preferably drains by gravity downward through expansion joint 99 and into the salt basket 50. After a sufficient period of time to fill the salt basket 50 with salt crystals 48, norma:Lly not exceeding about 30 minutes, the valve I
is closed to again isolate the salt basket 50 from the crystallizes 46. The isolation valve I is preferably closed before any further sequence of operations take place and must be closed before any attempt to open the salt basket door takes place. Upon closure of the isolation valve I, the feed valve F is closed and the drain valve D is opened.
Located near the top of the salt basket 50 is a pressurization plug valve P, which is then opened. This valve P
and related supply piping is configured to allow either steam 100 (normally reduced from pressurized supply steam 80) or air 102 (normally reduced from system supplied air) to enter the salt basket 50 to slightly pressurize the salt basket 50 (generally not far exceeding 39 prig and normally in the range of 5 to 20 psig with a nominal open°ation at about 15 paig) to force free liquids downward out of thES salt basket 50 through the screen 98 and out past drain valve D. Once the free liquids are drained (purged) from the salt baskest 50, additional air 102 and/or steam 100 may be utilized to dry the solids to the degree desired or achievable in a given salt mixture.
Upon completion of the drying/purging cycle (up to about 15 minutes time) the pressurization valve P is closed to turn off the supply of steam 100 and air 102 and drain valve D is closed to isolate the salt basket from the liquid in feed line 62. At this time, feed valve F may be reopened. Subsequently, vent valve V is opened to vent the salt basket 50 and bring the basket to about atmospheric pressure.
When the pressure in salt basket 50 is relieved, the door clamps 133 are opened. Then, the hydraulic door actuator 110 is moved to the open position; during this movement the salt basket door 106 pivots about main pivot pin 118 from the closed, preferably horizontal position to the open, preferably vertical position noted in ;EIG. 3 above. After opening of the door 106, the vent valve V muay be closed. Upon opening of door 106, dry salt 54 is dumped <iownward into receiver 52.
Since the drain connection 104 is in the door 106 and since the door 106 moves upon the opening thereof, a flex hose 140 is utilized to allow scuch movement. Also, the flex hose is provided with quick disconnects 142 and 144 at the ends thereof, so that after securing drain valve D and shutoff valve 146, the hose can be removed to faci7.itate maintenance in case of pluggage or other problems.
After the dump of relatively dry solid salts 54 is completed, the salt basket door 106 is returned by actuator 110 to the closed position. Then, clamps 133 are reset to the closed and locked position. When this is confirmed, the block valve B is closed to block feed from entering the crystallizer 46. Instead, when feed w valve F and drain valve D are opened, the salt basket 50 is filled with feed brine 60. With respect to refilling the salt basket 50 with brine 60, it i.s important to note the use and operation of the vent valve V. This vent valve V is opened whenever the salt basket is being depressurized prior to opening the door 106. Also vent valve V is opened during the backfill or refilling the salt basket with liquid 60; completion of the fill cycle for salt basket 50 is preferably visually confirmed via sight glass 148 confirmation of overflow feed through vent valve V. The vent valve V and line 150 returning the vented vapours to the steam cavity of the crystallizes 46 is important because it allows elimination of air from the salt basket before opening of the isolation valve I. Thus, no detrimental surge of air is allowed to enter the crystallizes 46 to cause foaming or scaling tendencies.
Upon completion of filling of the salt basket 50 with brine 60, drain valve D is closed, vent valve V is closed and block valve B is opened to allow feed brine 60 to be fed to the crystallizes 46. After filling of the salt basket 50 with brine 60 is completed, the PLC will reset the system for normal crystallizes 46 operations. Those trained in the art will appreciate that a c:ontro:l system can be further automated within the PLC software to provide for further interlocks and 209~~71 safety checke to insure an caoy and safe sequence of operation. However, the specifics required ntay vary somewhat by the application and are best left to thQ
design engineer cons.idPrinc~ thQ specific application.
An important bonefit of the above described mode or operation is that because Ltie isolation valve I and drain valve D are not allowed to be open a77 of the time, hir~hly concentrated liquors are not normally pre3ent in the salt basket. This is importauL because ' io tIm Salt basket is relatively cool compared to the crystallizer, unless extra h.patinc~ steam were addod thereto. Therefore, if the cult basket 50 were, between harvest cycles, supplied with concentrated brine (having crystals therein), further crystal formation w~o7d tend 7.5 to occur therein, with resultant tendency to plug the bottom screen. We have. discovered an ideal ball basket o~rerat;ion method which avoids such difficulties. Our method includes (a) isolai-ion of the salt basket during the crystal operation, (b) the use of an intermittent 2o salt crystal harveSL;, and (c) filling the salt basKet With feed between harvest cycles. This mpthnd is a marked improvement ovQr heretofore utili2ed methods for oalt recovery and drying in wastewater treat~uent 5ysl.a~u5. Also, since scaling and fouling of the salt 25 basket 50 is time r3eppndpnt, the limited harvest cycle time utilized in our proec~.~, 3130 help3 reduce the tendency of scaling and fouling to occur in the salt basket 50.
Moreover, our method of filling the salt basket 50 with fresh feed 60 after a salt drying cycle makes the salt basket 50 essentially self cleaning.
The novel automatic crystal harvest cycle described herein provides a unique apparatus and method for drying solids in zero liquid discharge wastewater systems. Our apparatus and method considerably reduces the life cycle cost for such systems when compared to currently available alternatives. Consequently, we have found that our automated salt basket design, which requires essentially no operator handling of the solids, is a substantial improvement in the art of zero discharge wastewater treatment systems.
Details of our. improved salt basket apparatus 50 are further illustrated in FIGS. 7 through 14. In FIG. 7, a side view is provided of the salt basket 50. As shown, the vessel has a flanged feed lines 160 for receiving the brine slurry from crystallizer 46. A. vent connection 162 is provided for connection to vent valve V and vent line 150. Preferably, a lower sight glass 164 and an 'upper sight glass 166 are provided to let an operator observe t:he presence (or absence) of salt crystals 48 within the salt basket vessel 50. A drain connection 104 is provided at the bottom of door 106. Support 124 is provided to hold salt basket 50 on a selected support structure as noted above. Stiffening supports 167 are provided to strengthen the vessel and where convenient to provide support means for the peripherally located door clamps 133.
The door 106 is opened, closed and kept in place at either position by hydraulic actuator 110, the operation of which is best understood by evaluating Figs. 7 and 8 together. Brace 170 provides an anchor for upper pivot pin 172 affixed to the upper and 174 of actuator. 110. Pivot 172 allows actuator 110 to turn radially during cycling of door 106. At the lower end of actuator 110, a hydraulical7_y extended shaft 112 is provided. The shaft 112 is actuated upwardly, pulling on the elbow pivot pin 114, which in turn is ;pivotally attached to door crank 116 (which preferably has two portions, 116a and 116b, as can be better noted in FIG. 8). then shaft 112 is retracted upwardly, crank 116a and 116b pivots about main pivot pin 118, thus pulling the door outwardly and downwardly (see FIG. 9). Door 106 is attached to crank 116a and 116b by way of mounting tabs 176a and 176b and may also be secured by positioning tab 178 and securing means such as pin 179 (which ;is attached to crank 116a and 116b). The hydraulic actuator' 110 is ordinarily powered by a remote hydraulic power pack. This arrangement, in addition to having the usual hydraulic controls, is also provided ~~19~571 with normally cloned eolenoid 180, which when eeated (closed) with abaft 112 :e.ctended prevents the door 106 from opening, and normally closed solenoid 18L Which when seated (closed) and shaft 11~ rpt.ra.~tPd prevents the door 106 from closing. These are important features since the use of solenoids 180 and 182 and appropriate interlocks prevent the door lud from opening (or closing) unexpectedly during operations.
FIC. l0 further illu~trate3 the screen ~r3 position' iii Qoui~ 106. Sc:reeu 98 i5 mourrted in the upper portion 184 of door 7 06, and i s best Pmpl.~yp~l tn c-over subEtantially the full ineide dia~actcr of door 106. The screen 98 serves to separate free liquidb 185 (wtiic;h substantially pass through) from solid salts (which are substantially held above the scrQQn 98)_ The free liquids it35 and any entrained solids flow toward the drain 104 located in the lower reaches oI door 106. We have fonnc~ fhat-. a sl nttpd hrlnp s~repn 98 cuch as is available from J'ohncon ;Filtration Sy~tcm~, Inc., EB
Model E (3P) Support Gria, manufacturai~ as 93 vEE wire with U.U:1~~ slot (spacing diameter at 25U0 F) is satisfactory. we prefer usQ of MonQl (Alloy 400) for corrosion resistance, and of a design thickness to support 30 psiq ditferentlal pressure at 3000 F, although it will hp apprPC:.i.atPd by t.hcse skilled in the art that a variety of eoreon docignc and matcrial~ would -~0-be sati.sfartary. Mounting means such as flange 186 and fastonar IB8 have been found eatiefaatory to secure screen 98 in the door 106.
FIG. 10 also shoWS, upper flange 190 and door flange S 192. The door flange 192 is~urgsd upward by adjustment meanE 194 on arm 196 of clamp 133. To reduce costs, we have used clacicii.nc~ 198 and 200 for the upper flange and the door flange, respectively, of c:nrrnsi-on resistant alloy. As morA clearly shown in FIGS. 9 and 9A, to facil3tatc sealing the salt basket 50 when pt-e55uriced, we have included a groove 2UZ in the cladding 198 of.
fl.angP 19n to accommodate an o-ring typo seal 204, which is preferably adhocivcly or mechanically secured within grove 202.
Clamp 133 may be affi.xP~3 to salt basket 50 by any convenient joining means; we utilize bolt type fasteners 20G which are affixed through cUnverileiWly luc:ated apertures defined by wall 208 in housing 209 of- clamp 133.
0 FIGS. 9 and 10 disclose the po3ition and mounting c.C upper or stir-to-close manifold header 210 and the lower or air-t~-npPn manifold header 212. These headers supply preocuriacd air to the upper actuator end 214 (to closed and the lower ac;~ual.ur eud 216 ( to open) of the pneumatic cylinder 218 ot~ clamp 133.
Pressurization of air-to-closes hQadar 210 forces ~o~~~7i Shaft or rod 220 of clamp 133 t3ownward, which in turn farces arm 19a upward in thQ direction of refere:nac arrow 215 in FIG. 9 toward the door flange 192, i.e.
toward the closed and locked position. When the air--to-open header 717 is pressurized, shaft or rod 220 of clamp 133 ie pushed upward foroing arm lg4 downward in the direction of reference arrow 216 iii FIG. 10.
Operation of the. clamp 133 air supply system is better understood with the diagrammatic flow diagram at the top of FIG. il. Pressurized air 22G is supplied to a four (4) way solenoid 2z8 roc control of the clampzng syst~m_ ThP air s»pply l.i.np 234 to the air-ta-close hQadAr aio, and the air supply Line 232 to the air-to open header 212, have bi-directioizal clew. Tlial. is, each of lines l3U and l32 can be pressurized, with resultant inward flow, or vented, with rQSUltant outward flow to release air pressure therein. Soleno.i~3 22~
a55ure5 that air is being pressurized t0 only One Or the other of lines 230 and 232. The l i ne ~rhi ah i.s net. ha. ~~el prQSSUri2ed is vented via .air vent 234. Wo have- fs~~a~d it advantageous to mount both air headers 210 and 212 ~rf~
a spider type support means comprised of channel 240 arid brae.3cets 240, so that the headers piping is spa,~.e~.
outwardly from and circumferentially surrounds the salt )JaSkeC 50. That way, the air headers 210 and 2 9 ~ Can conveniently serv.i.ce the prewar. damps 133 whif~',~ ~~~~

located around the periphery of the door 106 and where as here the door is circular is shape, circumferentially about the door 106.
In the top down view of FIG. 11, the advantageous downwardly and outwardly sloping outer sidewall 248 (corresponds to the outwardly sloping inner sidewall 121) can be appreciated; sidewall 248 has a lower en<i portion 249 adjacent the flange portion 190.
The open position of the clamp 133 is better seen in FIG. 12, where locking arm 196' and related adjustment means is shown in broken lines and with a (' ) prime suffix as they appear at the open position. Clamps 133 are locking power clamps such as are available from the De-Sta-Co. Div. of Dover Corporation, Birmingham, Michigan and which are described in U.S. Patent 4,458,889, issued July 10, 1984 to A.W. McPherson, entitled LOCKING POWER CLAMP, the disclosure of which may be referred to for further assisi:ance. The clamps 133 work on an eccentric locking principle, much like commonly used vice grips. That is, once the clamps are fully positioned in a locked, closed position, they must be energized (via the air-to-open header 212) to spring the arm 196 from the closed to the open position. Simply venting the air from the c7Losing header 210 will be insufficient to cause the arm 196 to release from the locked position.
When the arm 196 is closed, you get about 1500 to ~Q94571 2000 pounds of ~l.nsing.force (between adjustment means 194 and lower flange 192) dQpending upon the air pressure used. However, once the arm 19G is snapped into the closed, loeKea position, we have sound that the arm 196 of a lorkPd. clafip 133 wi.l.1 withstand in excess of 17,000 pvundc of downward force, before a portion of clamp 133 deror~u5, eventually causing failure of clamp 133 anti and resultant opening of the salt basKet Su door 106. This type of locking mechanism is quite important in application of the salt basket 5o door 106, since this provides a unique margin of safety not available by use o,f a simply air cy7.i.nder actuator mechanism. For this application, we have provided a hardened steal clarup arm 196. Also, We have provided an adjustment means 194, preferably with threads Z:36 which may be turned on companion threads in arm 196 by bolt head 238 and tightened by nut 239. With this adjustment means, the actual closing torque on the door 106 may be 2IC~~llCtPl~ a~ nPCec~cai'y tc aahtpvp F! llnlfn?"T11 sPa1 at the o-ring 204.
AS uan be 5eet~ in l;tie pl~sn view u.C FIG. 11, the clamps 133 are arranged around the periphery of the door 106, so as to providQ rQlatively evenly spaced locking safety clamps 133. The headers 210 and 212 are supported by support channels 24o and 24Z, or any other c:~nvpnipnt means. Air from header 710 and 212 is supplied to clamp 133 via rubber hoses 35o and 352, respectively.

It is clear from the heretofore described figures that the present invention as described above provides a simple, labor saving apparatus and method for removal of salts from Zero liquid discharge type industrial wastewater treatment systems. In so far as it will be readily apparent to those skilled in the art that the terms solids and salt are not synonymous, and although the present apparatus and method is primarily directed at separation of salts, it is nevertheless well suited for separation of other solids from liquids, and the claims shall be read without limiting the term salt to its strict technical meaning, but shall include other solids where appropriate to give full effect to the scope of the claims. Also, those knowledgeable in the art will appreciate that the techniques described herein are easily adapted~to the use of evaporation and crystallization equipment which may be either of the vapor compression or multiple effect design, or to various types of crystallization apparatus, and i~o limitation of the claims is intended with respect to use of the salt basket described herein with respect thereto.
Further, it will be readily apparent to the reader that the present invention may be easily adapted to other embodiments incorporating the concepts taught herein and that the present figures are shown by way of 2~~4571 example only and not in any way a limitation. The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description; and all changes which come within the meaning and range of equivalences of the claims are therefore intended to be embraced therein.

Claims (46)

1. An improved salt basket for separation of solid crystals from a slurry containing a concentrated liquid and solid crystals, said improved salt basket comprising:
(a) an upper vessel, said upper vessel comprising:
(i) a downwardly and outwardly sloping sidewall, said. sidewall having a lower end portion, said lower end portion defining a downward directed bottom opening; and (ii) an upper flange, said upper flange extending peripherally outward from said lower end portion of said sidewall;
(b) a door, said door sized and displaceably located for opening and closing of said downward directed bottom opening of said upper vessel, said door attached by a pivot connection to the lower reaches of said upper vessel, said pivot connection includes an automatic cyclic programmable control sequence for repetitive downward-outward opening movement followed by inward-upward closing movement, which, respectively, effects the opening and the closing of said downward directed bottom opening in said upper vessel for batchwise harvest of said solid crystals, said door further comprising:
(i) an outer edge portion, said outer edge portion sized substantially complementary to said lower end portion of said sidewall of said upper vessel, said outer edge portion further comprising a door flange extending peripherally outward therefrom, said door flange and said upper flange on said upper vessel being juxtaposed in a mating and sealing relationship, so as to pressurizably seal said downward directed bottom opening of said upper vessel; and (ii) an upper portion, said upper portion having an interior flange; and (iii) a drain, said drain adapted to allow discharge of said concentrated liquid therethrough;
(c) a screen, said screen affixed to said interior flange of said upper portion of said door, said screen shaped to define apertures therein, said apertures adapted for allowing escape of said concentrated liquid therethrough while substantially preventing said solid crystals from escaping therethrough.

2. The salt basket as set forth in claim 1, wherein said pivot connection includes:
(a) a brace affixed to said upper vessel;
(b) a door crank affixed to said door;
(c) a pivot, said pivot pivotally affixed between and to (i) said door crank, and (ii) said upper vessel; and (d) a door positioner, said door positioner pivotally connected to said brace and to said door crank, wherein said door positioner is adapted to cycle said door between (i) an extended, open position, wherein said solid crystals fall by gravity from said downward directed bottom opening of said upper vessel; and (ii) a closed position, operating position, wherein said upper flange portion of said upper vessel and said door flange of said door sealingly mate.

3. The salt. basket as set forth in claim 2, wherein said door positioner comprises a hydraulic actuator.

4. The apparatus as set forth in claim 3, wherein said hydraulic actuator further comprises:
(a) a first end; and (b) a second end;
(c) said first end adapted to open said door when receiving hydraulic pressure and said second end adapted to close said door when receiving hydraulic pressure; and (d) a hydraulic power pack, said hydraulic power pack further comprising:

(i) a pressure to open line; and (ii) a pressure to close line;
(iii) said pressure to open line and said pressure to close line each extending from said hydraulic power pack to said first and to said second ends of said hydraulic actuator; and (iv) a first solenoid, said first solenoid located on said pressure to close line, said first solenoid having a normally closed position; and (v) a second solenoid, said second solenoid on said pressure to open line;
(vi) wherein upon closing said door by extending said hydraulic actuator to a downward, extended position, said first solenoid is returned to the closed position, thereby hydraulically locking said door in said closed position.

5. The apparatus as set forth in claim 1, further comprising at least one power clamp, said at least one power clamp affixed to a stiffening support that is affixed to and extending downward and outward from said upper vessel, said at least one power clamp having a clamping arm adapted to compressingly engage said door flange, said at least one power clamp having an open position wherein said clamping arm is not engaged with said door flange and a closed position wherein said door flange is compressed by said clamping arm.

6. The apparatus as set forth in claim 1, wherein said screen comprises a slotted wire type screen.

7. The apparatus as set forth in claim 6, wherein said wire type screen comprises substantially V-shaped wire.

8. The apparatus as set forth in claim 7, wherein said screen is comprised of rows of substantially V-shaped wire and wherein said rows are spaced apart by a slot distance and wherein said slot distance is approximately one hundredth of an inch

9. The apparatus as set forth in claim 1, wherein said screen has a design thickness sufficient to support differential pressure across said screen of approximately 50 pounds per square inch at about 300°F.

10. The apparatus as set forth in claim 1, wherein said upper flange further comprises a downwardly projecting U shaped groove and wherein said groove is adapted for receiving therein a resilient sealing material.

11. The apparatus as set forth in claim 10, wherein said resilient sealing material comprises an O-ring.

12. The apparatus as set forth in claim 11, wherein said O-ring is adhesively secured within said groove.

13. The apparatus as set forth in claim 1, wherein said upper flange further comprises a corrosion resistant cladding alloy face.

14. The apparatus as set forth in claim 1, wherein said door flange further comprises a corrosion resistant cladding alloy face.

15. The apparatus as set forth in claim 4, wherein said second solenoid is normally closed, so that upon opening said door by retracting said hydraulic actuator to an upward, retracted position, said second solenoid is returned to said normally closed position, thereby hydraulically locking said door in said open position.

16. The apparatus as set forth in claim 1, further comprising a plurality of power clamps, said plurality of power clamps affixed from said upper vessel, said plurality of power clamps having a closed position wherein said power clamps are adapted to compressingly engage (a) said upper flange and (b) said door flange, in a pressurizable, sealing relationship.

17. The apparatus as set forth in claim 16, further comprising power clamp adjustment means, said power clamp adjustment means adapted for adjustably setting a closing torque of said door flange against said upper flange, so as to enable power clamp closing pressure adjustment as necessary to achieve a uniform sealing pressure between said upper flange and said door flange.

18. The apparatus as set forth in claim 16, further comprising:
(a) a first, substantially circular air pressure supply manifolds for supply of air-to-close pressurized air;
and (b) a second, substantially circular air pressure supply manifold for supply of air-to-close pressurized air;
(c) a plurality of air pressure manifold support brackets, said air pressure manifold support brackets extending radially outward from said upper vessel to supportingly engage said first and said second air pressure supply manifolds;
(d) wherein said plurality of power clamps are located around the periphery of said door and whereby said plurality of power clamps are pneumatically actuated and are thus conveniently serviced with high pressure air.

19. The apparatus as set forth in claim 16, wherein each of said plurality of power clamps has a mechanical actuator and a hardened steel clamping arm and wherein said hardened steel clamping arm and said mechanical actuator have an interengaging fail-safe locking position which is protected by an eccentric portion in a housing in each of said plurality of power clamps, so that when said power clamps are positioned in said closed position, said power clamps cannot be released from said closed position except by positive actuation of said power clamp.

20. The apparatus as set forth in claim 19, wherein each of said plurality of power clamps is pneumatic and wherein said power clamps cannot be released from said closed position except by pneumatic pressurization, so that in the event of air pressure loss, said door cannot be opened.

21. A method of dewatering the solids which are present in a liquid and solids slurry which is produced by precipitating solids from a wastewater feed stream in a crystallizer, said method comprising:
(a) introducing said slurry from said crystallizer into a pressurizable salt basket vessel, said vessel including a combination pivotable screen and bottom door portion;
(b) isolating said salt basket from said crystallizer;
(c) slightly pressurizing said salt basket vessel, so as to force said free liquids through a screen and outward through a drain and to substantially retain said solids before said screen;
(d) depressurizing said salt basket apparatus;
(e) opening the bottom door portion of said salt basket apparatus to downwardly pivot said bottom door portion and said screen to substantially empty the solids from said salt basket by allowing the solids above said screen in the salt basket vessel to fall by gravity from the salt basket vessel;
(f) closing said bottom door portion of said salt basket vessel to return the salt basket vessel to a pressurizable condition.

22. The method as set forth in claim 21, further comprising, after the step of closing the bottom door portion of said salt basket vessel, the step of introducing said feed wastewater into said salt basket, so as to substantially fill said salt basket with said feedwater.

23. The method as set forth in claim 22, further comprising the step of isolating said salt basket from said crystallizer after filling said salt basket with said feedwater until such time as it is desired to introduce a new batch of solids into the salt basket vessel.

24. The method as set forth in claim 22, further including the step of dissolving at least a portion of the solids which remain in said salt basket after the step of substantially emptying solids from said salt basket.

25. The method as set forth in claim 21, wherein the step of pressurizing said vessel is accomplished by introducing steam into said vessel.

26. The method as set forth in claim 21, wherein the step of pressurizing said vessel is accomplished by introducing pressurized air into said vessel.

27. A method of dewatering the solids which are present in a slurry comprised of a free liquid and solids which have been precipitated in a crystallizer and where said solids comprise any one or more of the salts selected from the group consisting of (i) sodium sulfate, (ii) sodium chloride and (iii) glauber's salt, said method comprising:
(a) introducing said slurry from said crystallizer into a pressurizable salt basket vessel having a lower pivoting screen portion, a drain and a downwardly pivoting bottom opening door;
(b) isolating said salt basket from said crystallizer;
(c) slightly pressurizing said salt basket vessel, to force said free liquids through said screen portion and outward through said drain, to extract liquids from said vessel and to substantially retain said solids above said screen;
(d) depressurizing said salt basket apparatus;
(e) opening the door of said salt basket apparatus to downwardly pivot said door and said screen portion to discharge the solids by allowing the solids located above the screen portion to fall by gravity from the salt basket vessel;
(f) closing said door of said salt basket vessel to return the salt basket vessel to a pressurizable condition.

28. The method as set forth in claim 27, further comprising, after the step of closing the bottom portion of said salt basket vessel, the step of introducing said feed wastewater into said salt basket, so as to substantially fill said salt basket with said feedwater.

29. The method as set forth in claim 27, further comprising the step of isolating said salt basket from said crystallizer after filling said colt basket with said feedwater until such time as it is desired to introduce a new batch of solids into the salt basket vessel.

30. The method as set forth in claim 27, wherein the step of pressurizing said vessel is accomplished by introducing steam into said vessel.

31. The method as set forth in claim 27, wherein the step of pressurizing said vessel is accomplished by introducing pressurized air intro said vessel.

32. The method of claim 27, further comprising the step of locking said door after closing said door.

33. The method of claim 32, wherein said door further includes a hydraulic actuator for opening and closing and wherein the step of locking said door includes hydraulically locking the actuator in a closed door position.

34. The method of claim 32, wherein (a) (i) the bottom opening door includes peripheral flanges and (ii) the bottom of the salt basket includes companion flanges to said just mentioned peripheral flanges and (b) the step of locking said door further includes securing said peripheral and said companion flanges between locking power clamps and wherein said locking power clamps compressingly engage said peripheral flanges to said companion flanges on said salt basket vessel.

35. A method of dewatering solids which are present in a mixture comprised of a free liquid and solids which have been precipitated in a crystallizer, said method comprising:
(a) introducing said solids from said crystallizer into a pressurizable salt basket vessel having a lower pivotable screen portion, a drain, a vent and a downwardly pivoting bottom opening door;
(b) isolating said salt basket from said crystallizer;
(c) opening said drain to allow free liquids to drain by gravity from said salt basket;
(d) slightly pressurizing said salt basket vessel, to force said free liquids through said screen portion and outward through said drain, to extract liquids from said vessel while substantially retaining said solids above said screen;
(e) depressurizing said salt basket apparatus;
(f) closing said drain valve;
(g) opening the vent to allow the salt basket pressure to equalize with the ambient atmospheric pressure;
(h) opening the door of said salt basket apparatus to downwardly pivot said door and said screen portion to discharges the solids by allowing the solids located above the screen portion to fall by gravity from the salt basket vessel;
(i) closing the vent;
(j) closing said door of said salt basket vessel to return the salt basket vessel to a pressurizable condition.

36. The method of claim 35, further comprising the step of locking said door after the step of closing said door.

37. The method of claim 36, wherein said door further includes a hydraulic actuator for opening and closing and wherein the step of locking said door includes hydraulically locking the actuator in a closed door position.

38. The method of claim 37, (a) wherein (i) the bottom opening door includes peripheral flanges and (ii) the bottom of the salt basket includes companion flanges to said just mentioned peripheral flanges and (b) wherein the step of locking said door further includes securing said peripheral and said companion flanges between locking power clamps and wherein said locking power clamps compressingly engage said peripheral flanges to said companion flanges on said salt basket vessel and where said power clamps must be positively powered to disengage said clamps from the locked position.

39. The method as set forth in claim 35, further comprising, after the step of closing the bottom door of said salt basket vessel, the step of introducing said feed wastewater into said salt basket, so as to substantially fill said salt basket with said feedwater.

40. The method as set forth in claim 39, further comprising the step of isolating said salt basket from said crystallizer after filling said salt basket with said feedwater until such time as it is desired to introduce a new batch of solids into the salt basket vessel.

41. The method as set forth in claim 35, wherein the step of pressurizing said vessel is accomplished by introducing steam into said vessel.

42. The method as set forth in claim 35, wherein the step of pressurizing said vessel is accomplished by introducing pressurized air into said vessel.

43. The method as set forth in claim 35, wherein said solids comprise any one or more of the salts selected from the group consisting of (i) sodium sulfate, (ii) sodium chloride and (iii) glauber's salt.

44. A process of treating a wastewater stream from an industrial plant in a selected locality, said wastewater having dissolved solids therein, at least a portion of which have solubilities which vary inversely with temperature, said dissolved solids comprising calcium, sodium, chloride and sulfate ions, wherein the steps of the method comprise:
(a) feeding the wastewater stream into an evaporation unit;
(b) evaporating said wastewater (1) to produce vapours which are condensed to recover a distillate therefrom; and (2) to produce a concentrated brine while preferentially precipitating at least one inversely soluble solid therefrom, while not appreciably exceeding the solubility limit of any of one of sodium sulfate, or sodium chloride, therein, so as to produce a brine slurry containing dissolved solids and a precipitated first solid;
(c) feeding said waste brine slurry to a crystallization apparatus;
(d) concentrating at least a portion of said remaining dissolved solids above the solubility limit in said brine of any of sodium sulfate, or sodium chloride, to produce crystals therefrom and to thereby produce a slurry comprising free liquid and a precipitate second solids comprising any one salt selected from (i) sodium sulfate, (ii) sodium chloride;
(e) feeding said first and said second solids to a salt basket apparatus having a lower screen portion, a drain and a door;
(f) slightly pressurizing said salt basket apparatus with a gas selected from either (i) steam, or (ii) air, so as to force said free liquids through said screen portion and outward through said drain and to thereby substantially dry said first and said second solids;
(g) depressurizing said salt basket;
(h) automatically opening said salt basket door, so as to allow said dried first and second solids to fall by gravity into a receiver.

45. The process as set forth in claim 44, wherein said inversely soluble salt is calcium sulfate.

46. The process as set forth in claim 45, wherein said locality is an electrical generation plant and wherein at least a portion of the water supplied to the wastewater treatment plant for removal of dewatered salts therefrom is cooling tower blowdown.