GB Patent 411624 - Improvements in or relating to the separation of dissolved solids by evaporation

Description

PROVISIONAL SPECIFICATION.

Improvements in or relating to the SeparationoX Dissolved Solids by EvaporatiorL.

We, GL"O1TGE Scorr & SON LONDONI rITr2D) a13ritish Company, of Artilleryblouse, Artillery Row, London, S.W.1, andGEORGE BTILLIA}a: RILES, a British

Subject, of the Company's address, do hereby declare the nature of this invention to be as follows

This invention is for improvements in or relating to the separation of a dissolved solid from asolution thereof by evaporation or evaporation and cooling of the solution, the latter also having present in it an additional body tending to contaminate the precipitate of the separated solid.

As typical of such separations may be cited:(1) the separation of relatively pure sodium chloride from an aqueous solution of sodium chloride containing traces of soluble impurities, (2) the separation of relatively pure sodium chloride from the solution of sodium chloride and sodium hydroxide in water which results from the electrolysis of aqueous solutions of sodium chloride,(3) the separation of relatively puresodium chloridefrom an aqueousisolation ofsodium chloride and glycerol and (4) the separation of relatively pure sulphur from a solution of sulphur in carbondisulpbide or other solvent, the solution containing also traces of tar; for example, such a solution ofsulphur obtained by theestraction ofsulphur from spent oxide fromgasworks. It is to beunderstood, however, that these specific separations are cited purely by way of example, the invention being broadly applicable, that is to say,wherever the contaminationdifficulty referred to may be met.

Hitherto, it has been the practice in these separation processes, to allow thepreeinitate of solid matter to remain either in the bottom ofthe evaporator or in a vessel in communieation therewith.

The result is that the precipitate, by reason of its continued contact with the moth er liquor, which increasingly enriches in additional body as evaporation proceeds, becomes contaminated with said additional body, either by mechanical admixture with it or by adhesion

oftlle body to the faces of the crystals.

In consequence,before the separated solid

can he used or marketed, it frequently

has to besubmitted to purification, which in many cases is both troublesome and

time-consuming and also tends materially

to render the process uneconomical.

In the case; for instance, of the

separation of sulphur from a carbon

dlsnlphide solution thereof derived from

the extraction of spent oxide from gas

works, the solution of sulphur being as

usual contaminated with tar from the

spent oxide, it has been customary to

introduce the solution into a steam or

waterheated evaporator wherein the

separated sulphur is allowed to collect in

the bottom of the evaporation chamber,

or in a separate vessel in communication

therewith, with periodic removal as

necessary, until the mother liquor has

become so enriched in tar that the

sulphur produced is too contaminated

therewith to give a reasonably pure

product upon subsequent washing, the

sulphurwhich is removed from time totime as described being washed, com

pletely, separatedfrom solvent by

evaporation of the latter finally dis

charged tol store or for operation upon in

another stage of the process.

The object of the present invention is

to provide an improved method and

corresponding apparatus for effecting

separations of the type indicated above,

whereby a substantially pure precipitate

will be obtainable directly, even in cases

where the mother liquor tends early to

become so concentrated in additional body as ordinarily strongly to contaminate

the separated solid.

According tol the present invention, a

method of effecting a separation of the

type referred to is characterised by trans

ferring the precipitate of separated solid

as it forms from the immediate zone of

evaporation tot a zone isolated therefrom

but incireulatory communication for

flow of solution therewith, or causing

precipitation to take place in such an

isolated zone wholly or in part instead of

in said zone of evaporation, and flowing

the solution incoming to the evaporation sone through the body of precipitate in said zone of isolation.

By this means, as will be appreciated, the body of precipitate collecting in the zone of isolation becomes continually washed of contaminating body, even at stages in the process when the concern tration of themother liquor in the evaporator in respect of said body is relatively high, for thevolume offresh liquor continually coursingthrough the body of precipitate will considerablyexceed that of themother liquor circulating into itfiom the evaporator, owing to the rapide: of solvent from the evaporator in the form of vapour. Inconsequenee, asubstantially lacon- taminated precipitate is obtainable directly. In the case, forexample, of the precipitation of sulphur from carbondisulphide solutions obtained from spent oxide fromgasworks, a99.5% pure precipitateniay readily be obtained,

The invention further includesapp a- ratus for carrying the aforesaid method into effect, the said apparatus comprising an evaporator, a precipitate receiverseparate fronl the e evaporator and posi- tioned at a level below the normal liquid level therein, an inlet forsolution incoming to the evaporator, in the lower part of the precipitate receiver, a conduit for said solution leading from the crown of the receiverto- the interior of the evaporator, forexample, immediatelv below the said liquid level therein, and a conduit for precipitate and mother liquor leading from the bottom of the evaporator to the interior of the precipitate receiver, with or without means for agitating the - precipitate in the receiver.

Preferably, the last mentioned conduit, leading from the bottom of the evaporator to the interior of the precipitate receiver, is provided with a control valve for adjustment, as necessary, of the rate of flow of mother liquor and precipitate into the precipitate receiver and for completely closing the conduitwhen required.

Similarly and for alike- purpose, the otherconduit, leading from thecrown of the precipitate receiver to the interior of the evaporator, may also be provided with a control valve.

Conveniently, the apparatus may comprise theeombination with an evaporator of two or more precipitate receivers common to the same evaporator and coelected thereto in the manner referred to forllse in alternation, so that, forexam.ple, the in coming solution may be diverted from one receiver to the other whiletbe precipitate in said other isundergoing draining from solution, subsequent washing if necessary with fresh solvent, steaming to remove the so-applied fresh solvent and drying, the precipitate so treated being thereupon dischargeable from tile receiver in substantially pure condition.

The evaporator may be of any convenient form and type. Thus, it may be of any standard design fitted with a heating tube or tubes in surface contactwitb the solution to be evaporated.

Similarly, the precipitate receivers may be of any convenient construction.

In a preferred form, they consist of a vertical water or steamjacketted cylinder with aflat-domed crown, and a party spherical bottom, a precipitate discharge opening in the bottom of the cylinder, a grating over said discharge opening, for the support of the precipitate, a door below said grating, controlling the discharge opening, an inlet for mother liquor and precipitate in the lower part of the wall of the cylinder, an outlet for solution in the crown of the cylinder, with or without a rotary agitator for the precipitate, co-asial with the cylinder.

One actual embodiment of the invention will now be described by way of example asapplied to the recovery of substantially pure sulphur from spent oxide from gaworks. It is to be understood, however, that thisentbodiment will be described purely for the purposes of illustration andthat the invention is not in any sense limited to the detailsgivenbut includes departure therefrom widely to suit requirements in any given case.

The spent oxide from which sulphur is to be recovered is charged into a series of extractors, throughwhich a suitable solvent for the sulphur, for example, carbondisnlphide, is continuously fed from a storage tank, replenished in a circulatory manner hereinafter described.

Thecarbon disulphide or other solvent is fed through the extractors on thecounterfiow principle, first meeting oxide poorest in sulphur, then, in the next extractor of the series, oxide less poor in sulphur, and so on,through the various extractors of the series to the last, where it operates upon spent oxide in the fresh or initial condition.

The resulting solution of sulphur from the extractors then passes through a filter for separating from it fine suspended matter carried forward from the oxide in the. extractors.

Thence the solution gravitates to- a pump tank where it collects beneath a supernatant layer of water under asuffi- cient head pressure to force the solution forward to the crystallisation plant, which will now be described.

The said crystallisation plant comprises a vertical evaporator consisting.of .adoivowardlSi directed cone at the bottom, superposed first by asteam or water heated calandria and thenbv a vapour separation space having an outlet at the top for separated solvent vapour.

Incirculatory connection with the lower part of this evaporator are a pair .of precipitate receivers, each of the construction specifically referred to above,the two receivers being arranged for use in alternation in the manner described.

The sulphur solution coming forward from the pump tank enters a branch inlet of one of the precipitate receivers at a point below the supporting grating therein for the precipitate. It thence flows upwardlythrough the mass ofsulphur crystals upon the grating and out through the outlet in the crown of the receiver into the evaporatorat a point therein a little below the level of the bottom of the calandria. At toe .same time, that is to say, while the incoming

solution is flowing upwardly through the precipitate receiver in the manner stated,mother liquor and preeipitatecl sulphur, continuously but in smaller volume, flows intothe receiver through the inlet in the lower part of the wall thereoffroni the coned bottom of the evaporator, theinflow

of the liquor and precipitate being snit

ably controlled by the control valve

aforesaid.

As will be appreciated, the effect of the concurrentinflow into the receiver of fresh liquor to be evaporated and mother

liquor and precipitate from the evaporator. is to cause the precipitate upon the bottom of the receiver to becontin ucurly washed fromeontaminating tar, the large volume of fresh solution incoming from the extractors operating to displace the relatively small volume of mother liquor containing the tar upwardly and back into the evaporator, that is to say, before it has had time to adhere to or become absorbed upon the sulphur crystals.

In the main, precipitation will take place partly in the evaporator and partly inthe precipitates receiver. By suitable adjustment, However, of temperatures and concentrations, precipitationmay, if desired or necessary in any given case, be made to take place entirely inthe evaporator or even entirely in the receiver. Thus, for the latter alternative, concentration in the evaporator may be carried only to a sub-saturation point in respect ofsulphur and precipitation be. caused solely by lowering of temperature of the solution in the precipitate receiver. In thisconnexion, it may beremarked tliat the temperature of the incoming solution from the extractors will generally be in the neighbourhood of 150C., that is to say, considerably lower than the temperature of the liquor incoming to the receiver from the evaporator, and consequently the temperature of said liquor will be substantially lowered uponmeeting andmising -with theincoming solution from the extractor. If necessary, however, accession of cooling below this, for the purpose of ensuring adequate precipitation in the receiver, may be obtained by

eirenlating cooling medium instead of a

heating medium through the walljacket

of the receiver.

When the desired quantity of precipitate has formed -or collected in the receiver, the mother liquor conduit valve leadingfrom the bottom of the evaporator

to the receiver is closed and the other

receiver is broughtinto use. Thesupply

of solution from theestractors, however,

is continuedthrough the mass of crystals

intb e first receiver until the mother

liquor therein has been entirely displaced.

The inflow ofsolution to the first receiver

is then stopped, the valve in the conduit

leading from the crown of this receiver

is closed and the solution remaining in

the receiver is drained away from the

precipitate and pumped toa feed supply

or other tank forming part of the system.

The drained sulphur is then washed by

a current of cleaned sulphur free solvent,

thewashing being drained to the said

feed supplytank.

Adhering solvent is then driven offtile

sulphur, still in. position in thereceiver.

by circulatinghot water or steamthrough

the wall jacket of the receiver, or by

passing steamthrough the mass of

crystals, either upwardly, ordownwardly

The sulphur is then ready to be dis

charged from-the receiver. It is in sub

stantially pure condition, containing the

meres traces only (if any) of tar from the

evaporator.

In order to prevent the enrichment ofthe

solution in the evaporator with tar beyond

thelints. desirable, an empty precipitate

receivermatey be periodically filled from the evaporator and by means of coId water circulated through the wall jacket of the receiver, the solution so drawn from the evaporator may be cooled. This results in crystallisation of sulphur to the point ofsaturation of the solution at the reduced temperature attained. The mother liquor is then drained to a supplementary evaporator-precipitate receiver combination, wherein it is further concentrated. When the bulk of the solvent has thus been evaporated, the residue is

cooled. This results in further crystallisation of sulphur. The liquor in which this further sulphur crystallate is suspended consists largely of tar oils and is now drained from the sulphur crystals. The drained sulphur is dissolved in warm solvent,which may conveniently comprise sulphur solution proceeding from the extractors of the main evaporator. In this manner, the impure sulphur produced in the supplementary evaporator-precipitate receiver combination is returned to the main evaporator of the plant.

Alternatively, the drawn-off liquor in the precipitate-receiver so filled from the evaporator may be distilled in situ in the receiver, by admitting steam to the jacket thereof, nntil the whole of the solvent has been removed by evaporation, then separating the tar from the sulphur crystals and finally washing the latter or passing them back to the main circuit again in solution in the manner stated.

Conveniently, the plant may comprise two pump tanks operating in themainer hereinbefore described and working alternately, one receiving solvent orsulphur solution, and theother delivering solvent or sulphur solution from various parts of the plant, to the evaporator via the precipitate receiver, to the evaporator direct, to the separate tar still or toother parts of the plant.

The hot water employed in the walljackets of the precipitate receivers and in the heating tubes of the evaporator may conveniently be supplied from a heatermaintained at the requisite temperature by thermostatic control and heated forexample by steam.

The plantfurther comprises a codenser for condensing solvent and other vapours produced in the evaporator or in the precipitate receivers. This condenser is preferably placed above the solvent supply tank hereinbefore referred to so that the solvent will gravitate down to thetank and from thence to the extractors.

C03aPLETE SPECIFICATION Improvements in orrelating totile SeparationOl Dissolved Solids by Zv?oratioIl.

We, GEORGIE Scorr & SON LONDONLIMITEr, a British Company, of ArtilleryRouse, Artillery Row, London, S.W.1, and GEORGE WILLIAM RILEY, a British

Subject, of theCompany's address, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement

This invention is for improvements in or relating to the separation of a dissolved solid from a solution thereof by evaporation or evaporation and cooling of the solution, the latter also having present in it an additional body tending to contaminate the precipitate of the separated solid.

As typical of such separations may be cited: (1) the separation of relatively pure sodium chloride from an aqueous solution of sodium chloride containing traces of soluble impurities, (2) the separation of relatively puresodium chloride from the solution of sodium chloride and sodium hydroxide in water which results from the electrolysis of aqueous solutions of sodium chloride,(3) the separation of relatively pure sodium chloride from an aqueous solution of sodium chloride and glycerol and (4) the separation of relatively pure sulphur from a solution of sulphur in carbon disulphide or other solvent, the solution containing also traces of tar; forexample, such a solution of sulphur obtained bythe extraction of sulphur from the spent oxide ofgasworks. It is to be understood, however, thatthese specific separations are cited purely by way ofesample, and that the invention is broadly applicable, that is to say, wherever the contaminationdifficulty referred to is met.

Hitherto, it has been the practice inth.ese separation processes, toallow the precipitate of solid matter to remain either in the bottom of the evaporator or in a vessel in communication therewith.

The result is that the precipitate, by reason of its continued contact with the mother liquor, which increasingly enriches in additional body as evaporation proceeds, becomes contaminated with said additional body, either by mechanical admixture with it or by adhesion of the body to the faces of thecrystals.

In consequence, before the separated solid can be used ormarketed, it frequently has to besubmitted to purification, which in many cases is both troublesome andtinie-consuining and also tends materially to render the process uneconomical.

In the case, for instance, of the separation of sulphur from a carbon disulphide solution thereof derived from the extraction of spent oxide from gasworks, theisolation of sulphur being as usual contaminated with tar from the spent oxide, it has been customary to introduce the solution into a steam or water heated evaporator wherein the separatedsulphur is allowed to collect in the bottom of the evaporation chamber, or in a separated vessel in communication therewith, with periodic removal as necessary,until the mother liquor has become so enriched in tar that the sulphur produced is too contaminated therewith to give a reasonably pure product upon subsequent washing, the sulphur which isrem.oved from time to time as described being washed, completely, separated from solvent by evaporation of the latter and finally discharged to store or for operation upon in another stage of the process.

The object of the present invention is to provide an improved method and corresponding apparatus for effecting separations of the type indicated above, whereby a substantially pure precipitate will be obtainable directly, even in cases where the mother liquor tends early to become so concentrated in additional body as ordinarily strongly to contaminate the separated solid.

According to the present invention, a method of effecting a separation oftlle type referred to is characterised by transferring the precipitate of separated solid as it forms from the immediate zone ofevaporatiofr to a zone isolated therefrom but in circulatory communication for flow of solution thereto, or causing prcapitation to take placewholly or in part in such an isolated zone instead of in said zone of evaporation, and flowing the solution incoming to the evaporation zonethrough the body of precipitate in said zone of isolation.

By this means, as will be appreciated, the body of precipitate collecting in the zone of isolation becomes continually washed of contaminating body, even at stages in the process when the concentration ofthe rnother liquor in the evaporator in respect of said body isrelatively high, for the volume of fresh liquor continuallycaursing through the body of precipitate willeonsid tably exceed that of the mother liquorcircu- lating into it from the evaporator, owing to the rapid esit of solvent from the evaporator in the form ofvtpour. Inconserluene e. a substantially uncontaminated precipitate is obtainable directly. In the case, for example, of the precipitation of sulphur from carbon.

disnlphide sollitions obtained from spent oxide from gasworks, a precipitate containing 99.5% or more of sulphur may be readily obtained.

The invention further includes apparatus forcarrying the aforesaid method into effect, the said apparatus comprising an evaporator, a precipitate receiver separate from the evaporator and positioned at a level below the normal liquid leveltherein, an inlet in the lower part of the precipitate receiver for solutionincoming to the evaporator; a conduit for said solution leading from the crown of the receiver to the interior of theevap-orator, forexample immediately below the saidliquid level therein, and a conduit for precipitate and mother liquor leading from the bottom of the evaporator to the interior of the precipitate receiver, with orwithout means for agitating the precipitate in the receiver.

Preferably, the last mentioned conduit, leading from the bottom of the evaporator to the interior of the precipitaterecei.ver, is provided with a control valve for adjustment, as necessary, of the rate of flow of mother liquor and precipitateinl the precipitate receiver and for completely closing the conduit when required.

-Siniil rly and for a like purpose, the other conduit, leading from the crown of the precipitate receiver to the interior of the evaporator, may also be provided with a control valve.

Gon veniently, the apparatus maycom- prise thecombinatioa with an evaporator of two or more precipitate receiversconunon to the same evaporator and connectedthereto in the manner referred to for use in alternation, so that, forez:anple, the incoming solution may be diverted from one receiver to the other while the precipitate in said other is undergoing draining <RTI from solution,sub- sequent washing if necessary with fresh solvent, steaming toremove the so-applied fresh solvent a.nd drying, the precipitate so treated beingiliereupon dischargeable from the receiver in substantially pure condition.

The evaporator maytbe of any convenient form and type. Thus, it may be of any standard design fitted with a heating tube or tubes in surface contact with the solution to he evaporated.

Similarly, the precipitate receivers may be of any convenient construction.

In a preferred form, they consist of a vertical water or steamjaclietted cylinder witha fat-demed crown, anda. partspherical bottom, a precipitate discharge opening inthe bottom of the cylinder, agrating over said discharge opening, for the support of the precipitate, a door below said grating for controlling the discharge opening, an inlet f of temperature of the solution in the precipitate receiver26 (or 27). In this connection, it may berernarlced that the temperature ofthe incoming solution from the extractors will generally be in

theneighbonrhooci of150 C., that is to

sav, considerably lower than the tem

peratnre of the liquor incoming to the

receiver from the evaporator, and conse

quently the temperature of said liquor

will be substantiallylowered upon meet

ing and mixing with the incoming

solution from the extractor. If necessary,

however, accession of cooling below this,

for the purpose of ensuring adequate

precipitation in the receiver, may be

obtained by circulating cooling medium

instead of a heating medium through the

wall jacket37 of the receiver.

When the desired quantity of precipi

tate has formed our collected in the

receiver 26 (say), the mother liquor con

duit valve 36 leading from the bottom

of the evaporator to the receiver is closed

and the other receiver 27 is brought into

use. The supply of solution from the

extractors 1, 2, 3 however, is continued

through the mass of crystals in the first

receiver 26 until the mother liquortherein

has been entirely displaced. The inflow

of solution toi receiver 26 is then stopped,

the valve38 in the conduit leadingfrom

the crown of this receiver is closed and

the solution remaining in the receiver is

drained away from the precipitate and

pumped to a feed supply or other tank

forming part of the system.

The drained sulphur is then washed by

a current of cleaned sulphur free solvent

supplied from the storage tank 4 via pipe

lines 7 and39 (or 40),the washings being

drained to the said feed supply tank.

Adhering solvent is then driven off the

sulphur, still in position in the receiver

26, by circulating hot water from a supply

tank4.1 therefor via pipe lines 42 and43

(or 44) or steam through the wall jacket

87 of the receiver, or by passing steam

throngli the mass of crystals, either

upwardly, or downwardly.

The cleaned sulphur is then ready to be discharged fromtbe receiver 26. It is in substantially pure condition, containing the merest traces only (if any) of tar from the evaporator.

Inorder toprevent the enrichment of thesolution in the evaporator 21 with tar beyond the limits desirable, an empty precipitate receiver 45 may be periodically filled from the evaporator and by means of cold water circulated through the wall jacket37 of the receiver, the solution so drawn from the evaporator may be cooled.

This results in crystallisation of sulphur'to the point of saturation of the solution at the reduced temperature attained,

Themother liquor is then drained to a supplementary evaporator - precipitate receiver combination(nol; shown), wherein it is further concentrated. When the bulk of the solventlias thus been evaporated, the residue is cooled. This results in further crystallisation ofsulphur The liquor in which this further sulphurcrystallite is suspended consists largely of tar oils and is now drained from the sulphur crystals. The drained sulphur is dissolved in warm solvent, which may conveniently comprisesulphur solution proceeding from the extractors 1, 2, 3 to the main evaporator 21. In this manner, the impure sulphur produced in the supplementary evaporator-precipitate receiver combination is returned to the main evaporator of the plant.

.Alternatively, the drawn-off liquor in

the precipitate-receiver 44 so filledfrom the evaporator21 may be distilled in situ in the receiver, by admitting steam to the jacket37 thereof, until the whole of the

solvent has been removed by evaporation, then separating the tar fromthe sulphur

crystals and finally washing the latter or passing themback to the main circuit

again in solution in the manner stated.

Thet,vo pump tanks 19, 20 operate in the manner hereinbefore described andwork alternately, one receiving solvent or sulphur solution, and the other delivering solvent or sulphur solution from various parts of the plant, to the evaporator 21 via the precipitate receiver 26 (or 27) to the evaporatordirect, to the separate tar still or to other parts of the plant.

The hot water employed in the wall jackets of the precipitate receivers and in the heating tubes of the evaporator may conveniently be maintained at the requisite temperature by a heater operatingunder thermostatic control.

The water forthe operation of the pumptanks 19, 20 is supplied to thetanks via pipe lines 46, from a tank 47 placed at such an elevated position above the pumptanks as to provide the requisite head pressure therein. 48 is a sump collecting cold=water via pipe line 49 from thepump tanks 19, 20 and 50 is a water pump for re-cycling thewater from the sumpback to the tank 47 via pipe line 51.

The plant further comprises a condenser59 forcondensing solvent and other vapours produced in the evaporator or in the precipitate receivers and returned to the condenser 52 via pipe lines53.

This condenser is preferably placed above the solvent supply tank 4 as shown so that the solvent will gravitate down to the tank and d from thence down to the extractors.

The said condenser 52 also receives solvent vapours produced in theextractors 1, 2, 3 the vapours being returned from these elements of the plant via pipe lines54.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare thatwhat we