Note: Descriptions are shown in the official language in which they were submitted.
CA 02094571 2000-08-08
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,
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CA 02094571 2000-08-08
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
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CA 02094571 2000-08-08
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.
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CA 02094571 2000-08-08
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
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CA 02094571 2000-08-08
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
-4A-
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
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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
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CA 02094571 2000-08-08
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
CA 02094571 2000-08-08
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_
209571
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
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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
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CA 02094571 2000-08-08
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
-13-
2094571
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
-14-
209471
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
-15-
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
-16-
CA 02094571 2000-08-08
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
-17-
'~ 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
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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
-19-
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
-20-
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
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CA 02094571 2000-08-08
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
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CA 02094571 2000-08-08
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
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CA 02094571 2000-08-08
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
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CA 02094571 2000-08-08
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
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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
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CA 02094571 2000-08-08
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
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CA 02094571 2000-08-08
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
-29-
~~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-
209471
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
-31-
~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~',~ ~~~~
-32-
CA 02094571 2000-08-08
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
-33-
~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.
-34-
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
-35-
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.
-36-
