US1582067A - Process of and apparatus for multiple-effect evaporative separation - Google Patents

Description

I April 27 1926. 1,582Q067 H. K. MOORE I PROCESS OF AND APPARATUS FOR MULTIPLE EFFECT EVAPORKTIVE SEPARATION Filed Nov. 0. 1923 3 Sheets-She et 1 April 27 ,1926.

1,582,067 H. K. MOORE PROCESS OF AND APPARATUS FOR MULTIPLE EFFECT EVAPORAFIIVE SEPARATION Filed Nox r. so. 1923 s Sheets-Sheet z April 27 1926.

H. K. MOORE PROCESS 01-. AND AP ARATus FOR MULTIPLE EFFECT EVAPORATIVE SEPARATION Filed No 30. 1925 s Sheets-Sheetfi Patented Apr. 27, 1926. I

UNITED STATES I eeann PATENT caries- HUGH KIMOOBE, OF BERLIN, NEW HAMPSHIRE, ASSIGNOR TO BROKE/N COMIANY, F

BERLIN, NEW HAMPSHIRE,

A CORPORATION 0Z3 MAINE.

PROCESS OF AND APPARATUS FOR MULTIPLE-EFFECT EVAPORATIVE SEPARATION,

-' Application filed. November 30', 1923. Serial Nb. 677,857.

To all '10 from 2'25 may concern Be it known that I, HUGH K. MOORE, a citizen of the United States. residing at Berlin, in the county of Coos and State of New IIilll'lPSllllG, have invented new and useful Improvements in Processes of and Apparatus for l\[ultiple-Eiiect Evaporative til rial No. 595,017 filed October 26, 1022, I

Separation, of which the following is a specification.

In an application for Letters Patent Sohave illustrated and described an apparatus for and a process of evaporatively separating certain liqutns so as tosecure a maximum saving of heat, and I have therein explained in detail the principles upon. which the proccss and the apparatus are founded. The process and apparatus are therein described as utilized specifically in the evaporation and the concentration 'of waste sulphite liquors, such as result in the manufacture or production of chemical wood pulp by the sulphite process so called. The present invention has for its object to provide a process of and apparatus for evaporating and concentrating certain-liquors having characteristics which require a difierent mode of treatment. It sometimes happens that the conditions under which the evaporative separation is to occur, require the treatment of a liquor which greatly increases in viscosity with its concentration; and further that the liquor to be treated may be at a relatively high temperature at the time. when it is to be subjected to evaporation and concentration. It is desirable of course, that the heat of the incoming liquor should be conserved unless other considerations make this undesirable. Again the greatly increased viscosity of the liquor due to its concentration with a consequent low. heat tion, when concentrated to a fifty per cent solution, may be so viscous and its heat conductivity so low at, a temperature of say 6 100 F;, that while the process specifically sodium sulphide, or resulting from the di-- gestion of wood pulp by an acid liquor comprising a soluble sulphate and a soluble sulphite, have such a high viscosity when reduced to a fifty per cent solution, that a mode of treatment is desirable differing specifically or in detail from that set forth in my said application. In explanation, it may be said that, there is a directrelation between viscosity and heat conductivity, so

that it is important-that the viscosity or mobility of a solution should receive consideration'in evaporatively separating such a solution. It is of course, desirable in subjecting such'liquors to multiple-effect evaporation that the temperature difference between the liquor entering into an effect, and the steam entering the eifect for the heating of such liquor, should be relatively small so that in-consideringthe entire temperature spread, (that is, the dillerence in temperature between the initial steam entering the first-elfect of the series and the steam passing to the condenser to the last effect of the series,) should he as small as possible. Disregarding other factors, it may be stated as a general rule that the greater the mobility of a liquid (or the lesser the viscosity) at the same temperature level and the same temperature difference, the greater the heat conductivity of the liquor,-it being remembered that the temperature level of the liquor is the boiling point of that liquor at the pressureto which it may be subjected at the time.' Consequently, one liquor containing fifty per cent solids at a given temperature levehsay 100 F., when subjected to a,

"10 difference of exchange in temperature,

may have a very low heat conductivity, whereas the same liquor at a temperature level of 200 F. with the same difference of exchange, may have a greztly increased heat conductivity. Conse piently with such liquors, it may not be economically possible or desirable to pass the liquor through the several etl'ects in such way that it is subjected first to increasing pressures and temperatures, and then to progressively delot source for the evaporation process.

.It is'a principle of multiple-effect evaporation that the steam generated from the liquor in the first of a sequence of effects, passes ,to the next colder effect for the generation of steam fromthe liquor therein contained, and thus progressively throughout the remainder of the series of effects, the evaporator chamber of the "last effect of the series being connected with a vacuum apparatus and a condenser, this irrespective of theorderiof'the effects through which the liquor flows. Ordinarily in a multiple-effect evaporation, the liquor has been caused to flow through the sequence of effects in the same direction with the flow of the steam, in which case the liquor is introduced into the first effect, or else has been caused toflow through the sequence of effects in the opposite direction to the flow of the steam, in which case the liquor is introduced into the last and coldest effect. In accordance with thepresent invention, the entering liquor is introduced into an intermediate effect and is caused therefrom to flow through some of the effects inthe same direction asthe flow of steam therethrough, whereby it is subjected to decreasing pressuresahd decreasing temperatures, and is then caused to pass through the remainder of the effects in a direction opposite to the flow of the steam, whereby it is subjected to progressively increasing temperatures and' increasing-pressures. As a result of this mode of procedure the increasingly concentrated liquor,.

which becomes increasingly viscous at any given temperature with its -concentration and thus decreases in heat conductivity, is

subjected to such increasing temperatures that itsmobility and heat'conductiyity are not lessened to such an extent as to prevent tween the liquor leaving the last and coldest effect, and the temperature level of the 1iqv uor in the effect to which that liquor leav-' the liquor' from being properly treated and brought to the desiredconcentration. The liquor to be treated is at a temperature much higherthan thatof the temperature level of the liquor in the intermediate effect into which it is to be introduced, and there 'is also'a marked temperature difference being the last effect should be introduced. Consequently, in accordance with my invensteeper tion, the heat of the initial entering liquor is utilized in heating the liquor leaving the last effect in the sequence of effects, as a result of which the initial entering liquor is reduccd to. a temperature approximating the temperature levelof the intermediate effeet into which it is introduced, and the liquor leaving the last effect of the series is raised to a point more nearly a'proximating the temperature level of the efiect into which it is introduced for further passage through the remaining effects of the series.

On the accompanying drawings, I have illustrated more or less diagrammatically and conventionally in Figure 1, a multipleeffect evaporator embodying the invention, and which may be utilized in the practice of a process in accordance with theinvention.

thei

the various effects and the heat exchanges.

The multiple-effect evaporator as a'whole, 15 illustrated as comprising a series of ten effects, each effect consisting of a combined evaporator and condenser. These effects are numbered I to X, inclu sive, in the order in which theyare arranged in respect to the passage of steam through the steam line.

That is to say, steam which is externally generated, is delivered to effect. No. I, herein termed the first effect, for the evaporation of liquor contained therein. The steam generated from the liquor in effect No. I is passed to-effect No. IIfor the generation of steam fromthe liquor contained in effect No. II,and thus throughout the entire series, the last cffect No. X. having. its evaporator chamber connected with a condenser and vacuum apparatus. Thus considering the sequence of effects from Ito X,

they are progressively colder and the pressures therein are progressively reduced- ,this quite irrespective of the order of the effects in relation to the passage of the liquor th'erethrough. It is quite apparent that the liquor to be evaporated and concentrated,-

mightbe introduced into the first effect, No. i

I; and caused to pass through the effects progressively and in sequence until it was delivered from the last effect, o. X; or on the other hand, the liquonmight be introduced initially intothe' last effect of the series. to wit, No. X, andcaused. to pass therefrom through the sequence of effects to proximately 232 F.,

'ellecl No. I, but this would not in either then caused to pass throughprogressively colder ell'ccts, to wit, etl ects IX and X,

after which it. is introduced into another intermediate etl'ect, for example No. VII, and thence to pass through progressively hotter elr'ects (Nos. VI, Y. IV, III and II) until it reaches el'l'ect No. I, from which it is withdrawn at the desired degree of concen tration, this course of the liquor through the various etlects being shown in Figure Thus the liquor is first subjected to decreasing" ten'iperatures and pressures, and-then subjected to increasing temperatures and inessures during its passage through all of the citects. The number of the intermediate eil'ect of the series, into which the initial or entering liquor is first introduced, depends upon the character of the liquor and its temperature, so that it will be understood that in describing the liquor as initially entering any certain intermediate eitect ofthe series or sequence of efi'eets, it is done merely by way of illustration, and that the liquor may be introduced initiallyinto any other intermediate effect depending upon circumstances.v In the present instance, I am assuming that a liquor is being evaporatively concentrated, such as that resulting from the digestion of wood pulp with an acid liquor containing both a soluble sulphate and a soluble sulphite, and that the liquor is at the ten'iperature or approximately 172 when it is ready to be subjected to evaporation and concentration. In the present case for purposes of illustration, it may be assumed that the temperature level or boiling point of the liquor in No. I cltectat the pressure in No. I effect, is ap-' ature level or boiling point of the last effect, No. X, is 100 F. under a pressure of two 'inches absolute (or a vacuum of twenty eight inches n'iercury). Under these conditions. the temperature level of the liquor contained in eitect No. VIII is approximatelv 138 F. Inasmuch, however, as the entering liquor is at a temperature of 172 F., it would not be practicable to enterthis liquor at that temperature into effect No. VIII without an economic loss. Again the liquor linivin'r effect No. X is at a temperature of approximately 100- F., whereas the temperature level or boiling point in effect No. VII is ap n'oximately 154 F. Therefore the liquor before it enters etlect No. VIII and the liquor leaving effect No. X and betoreit diagramniatically and that the temperenters efiect No. VII, are caused to pass through a heat exchanger, whereby e liquor which enters effect No. VIII is reduced to a temperature approximating the temperature level o't'thc liquor therein, and the liquor leaving effect No. X is heated to a temperature reasonably approximatiin, the temperature level of the liquor in effect No. VII.

On the drawing, A indicates a tank for the liquor to be concentrated, which in the present case may be considered as having: a temperature of approximately 172 F. A pipe B conducts the liquor from this tank to a heat exchanger indicated as a whole at C, and from the heat exchanger a pipe I) conducts the liquor to'a pump Ill by which the liquor is introduced into intermediate effect No. VIII. After passing through. effects VIII, IX and X, which are progressively colder, the liquor delivered from the last cf fect. No. X. is pumped through pipe (t back to the exchanger C. through which it is caused to pass in counter-current flow to the liquor delivered thereto through pipe I%.

"The liquor delivered by the pipe D to the exchanger is thence delivered by a pump 112 through pipe E into the intermediate efi'ect No. VII. The liquor from effect No. -.VII is caused to traverse the pronressivelv hoti ter eiiects VI, V, IV. III. II. and I. and

diate effect, No, VIII, is utilized in raising the temperature of the liquor delivered from the coldest or last etiect. No. X, of the series, so as to bring" it to a point where it appr'oxL matcs the l'ioiling point or temperature level of" an intern'iediate effect No. VII. As a result of this mode of treatment of the liquor. theentirc temperature spread between the first and last efi'ects. Nos. I and X, may be relatively small. and a large number of intermediate ell'ects may be utilized with a relatively low tem 'ierature difference be tween ea'ch effect and the next'succecdinp; or next preceding effect. As a further result, the increasingly concentrated liquor subjected to increasingly higher temperatures and pressures as it traverses increasingly hotter etl ects VII to I. inclusive. so that I am able to compensate to a great extent for the increasing" loss in heat conductivity of the liquor due to its increased concentration and viscosity.

For reasons set forth at large in my ap-- the several effects, should not be under any hydrostatic head, and consequently, i. carrying out the process of the present invention,

tion has ceased, any residual liquor willflow' therefrom. In the present case, the pumps for delivering the liquor, to effectsI to VII, inclusive, are indicated at 91, the pump for delivcringthe liquor to effect No. VIII is I indicated at 114. and the pumps for delivering the liquor to effects IX and -X, are indicated at 115 and 117. Each effect is provided with a well 38 depending from the forward end thereof, which receives the partially concentrated liquor after passing through the conductor tubes of that'effect. and it is from this well that the liquor is forced by the pump to the spray nozzle of that effect to which it is desired to pass such liquor. The spray nozzle for each effect is indicated at 34 and by reference to Figure 8, it will be seen that I have conventionally illustrated the liquor as being sprayed into the ends of the conductor tubes, which pass through the steam chamber 30 of that effect. The steam and liquor issuing from the .forward ends of the tubes are separated in passing around the baffle plate-37, the steam w passing upwardly through the port 39 and the liquor. being collected in the well 38. The steam entering the steam chamber of ,each effect from the preceding hotter effect enters the ports 32 and the condensate is emitted through the port 31. Uncondensed steamand entrained air pass from the steam chamber through the port 83 to a condenser 74, from which the condensate is delivered to a pipe common to all of the condensers, this pipe not being shown, but the branches leading thereto being indicated at 80, as indicated in Figure 3'. Eachofthe ports 31 for the condensate from thesteam chamber. of theeft'ect with which it is associated, constitutes a well in which-the condensate ac-- cumulates, and from which the condensate is passed to the steam chamber of the next colder effect, as set forth in my said application Serial No. 595.017. Inasmuch as the means associated with each effect by which the level of the liquor in the well 38 controls the rate of flow of the liquor introduced into the effect, per se forms no feature of the present. invention. I shall omit its description inasmuch as such means is described and illust-rated in detail my. afore- I said application.

.creasingly hotter' effects.

Considering the sequence ofcffects as illustrated in Figures 1 and 2, steamat the proper pressure and temperature is delivered to the'first effect, No. I, through a pipe for the generation of steam from the liquor which is sprayed into the conductor tubes therein. The steam thus generated is con ducted by a section of the steam line indicated as a whole at (if, to the steam chamber of effect No. II, through the conduit 71. The steam line is provided with suitable valves or couplings, by which any effect may be bypassed in the event of an accident or for any other desired purpose. Finally, from effect No. X, the steam is conducted by the coldest end of the steam line to a condenser indicated conventionally at 67, with which is connected a vacuum apparatus, not shown.

Inasmuch as the liquor undergoing multiple-effect evaporation greatly decreases in volume, it may be desirable, toinsure the' proper wetting ofthe tubes in the effects numbered I and II, to provide means for circulating the liquor through those effects.

To that end, I have illustrated conventionally upon the drawing each of the last ment oned effects as having associated therewith a circulating system comprising a pump 120 for pumping the liquor from the well 38 thereof to the spray nozzle. The pipe leading from the well to the pump is indicated at119 and the pipe leading fromthe pump to the spray nozzle is indicated at 121.

Associated with effects Nos. II, III, IV, V, V and VII, I have shown heatexchangers indicated at 102, through which the concentrated liquor delivered-from the well 38 of effect No. I is passed in series, and

from which it is delivered by .p-lpe 103. These heat exchangers are utilized for heating the liquor passing from effect No. VII

to effect No. VI, and .thence through the intheseheat'exchangers need not be employcd, especially where it is desired'to conduct the oncentrated liquor directly toa combined boilerfand smelting furnace for therecovery of the inorganic content of such liquor.

Except for certain differences which have Leenhereinbefore pointed out, the apparatus as illustrated upon thedrawings is substantially similar to the apparatus illustrated by the drawings -of my-said-application Serial No; 595,017, to which reference may be made for further explanation of the various instrumentalities and the mode of operation.

Assuming that a certain waste liquor resulting from the manufacture of chemical wood pulp, contains 8 per cent solids and that it be desired to concentrate it to a point where it contains 50 per cent solids, that the liquor is initially at a temperature of about 17 2 F, that the steam entering the first effect, No. I, is at a temperature of about 252 In some cases',.

F, and that the temperature of the steam Temperatureofsteam enterin Temperature of steam leaving Temperature of liquor once more to the fact that the initial liquor somewhatroughly, as follows:

111 IV v -VI v11 VIII IX x l we m 13s i4; ias

In the-foregoing table it is assumed that in passing through the heatexehanger, the initially hot liquor is reduced to a temperature of 142 F. before entering intermediate effect No. VIII, and the liquor leaving effect NowX is raised to a temperature of 152 F. before entering effect No. VII. The.

tabulation is given merely for explanatory purposes, since condltions are varied for liquors having different characteristics and for the temperatures ofv the liquors which.

are to be concentrated. I At'the risk of repetition, I may advert ,to be evaporated "is introduced into an intermediate effect in the sequence of effects, and .that this liquor is initially at a temperature much higher than the. temperature level or boiling point of the liquor'in the effect into which it is to be introduced. If the liquor at the high temperature, say 172 F. were delivered to an effect in which the temperature level or boiling point of the liquor were relatively low, say 138 F., it can be seen that'there would be an enormous lossof heat due to self-evaporation, and that this heat would eventually be wasted in the final condenser located beyond the last effect of the series. This can be made clear .if it should be assumed that liquor ata. tempera ture of 172 'F. were delivered tothe last effect, No. X, in which the boiling point or temperature level ofithe' liquor is 100 F. Under such circumstances, the heat in the liquor above 100 F. is immediately wasted in the condenser with which the vacuum apparatus is connected. In accordance with the present invention, however, I prevent the immediate loss of heat of the liquor'entering into an intermediate effect above the 4 temperature level of the liquor in that effect by utilizing the excess heat in raising the temperature of the liquor leaving the last or No. X eflect, before it is introduced into the intermediate effect No. VII for passage through the next successively hotter efiects.

Ihis enables me to heat a relatively cold liquor to a temperature approximating that of the temperature level of the liquor in that intermediate eifect into which it is desirable to pass that cold liquor, It also enables mete employ a relatively smallfinal condenser, which is operated with a relativelysmall quantity of water, and also to obtain great economies and conservation of heat.

What I claim is:

1. A process of multiple-effect evaporation, which comprises generating steam from the liquor contained in the first effect of a sequence of effects, generating steam from the liquor in each of the remaining effects of said sequence by the steam generated from the liquor in the immediately preceding hotter efiect, introducing the liquor to be evaporated first'to an intermediate effect of the sequence, conducting such liquor successively through progressively colder effect of said sequence, then passing such liquor to an intermediate effect Which is hotter than the first mentioned intermediate effect, and thence progressively through increasingly .hotter efi'ects, whereby said liquor is first subjected to progressively decreasing temperatures, and then to progressively increasing temperatures. p

2. A process of multiple-effect evaporation, which comprises causing the liquor to flow from an intermediate effect of a series of effects, through progressively colder effects of such series, and thence through progressively hotter effects of such series.

3. A process of multiple-eflectevaporation for concentrating an initially hot liquor, which comprises introducing the liquor into an intermediate effect of a series of effects, then passing said liquor successivelythrough the next progressively colder effect's, passing such liquor therefrom successively through those effects of the series which are progressively hotter than said intermediate effect, and heating the liquor leaving said progressively colder effects by the initially hot liquor before it is introduced into said intermediate effect.

4. A process of multiple-efiect evaporation for concentrating an initially hot liquor, which comprises cooling such liquor to a temperature approximating the temperature level of the liquor of an intermediate effect of a series of effects, and then introducing the cooled liquor into said intermediate e feet, passing such liquor therefrom through one or more colder effects, then passing such liquor into an intermediate effect in the serieswhich is hotter than the first mentioned intermediate effect, and thence through progressively hotter efiects of the series, and heating the liquor before it enters the second said intermediate efiect by the liquor being delivered to the first said intermediate e-fiect.

5. process ofmultiple-effect evaporation, which comprises entering the liquor into an intermediate eflect of a series of effects, thence passing such liquor through one or more colder effects of said series, then heating such liquor and introducing itinto an intermediate effect hotter than the first mentioned intermediate effect, and passing.

. progressively higher temperatures and.pres

sures for the generation of steam, and utilizing the steam generated from the liquor at its highest temperature and pressure for the generation of steam in that portion of the liquor subjected to the next lower'temperature and pressure, and so on until the li'quorsubjected to the lowest temperature and pressure is heated by steam generated from that portion of the liquor which is subjected to the next lowest temperature'and pressure.

7 A process of multiple-effect evaporation,

which comprises generating steam from the liquor at a given temperature and pressure,

theri subjecting such liquor to lower temperature and pressure for the generation of steam, finally subjecting such liquor to progres-sively higher temperatures and presand pressure, and so on until the liquor subsures forthe generation of steam, utilizing the steam generated from the liquor .at its highest temperature and pressure for the generation of steam in that. portion of the liquor subject to the next lower temperature jectedto the lowest temperature and pressure is heated by steam generated from that portion of the liquor which is subjected to the next lower temperature and pressure, and

heating the liquor by an external source of heat after it has been subjected to the lowest temperatures and ,presures and before itis subjected to said progressively higher temperatures andpressure's.

8. In multiple-efiect evaporation of initially hot liquors which become relatively visoous when concentrated at the temperatures of the colder effects. theprocess of conserving heat which comprises cooling the sup plied liquor to approximately the temperature of one of the intermediate effects of a series of effects, introducing said liquor into weeps"? said intermediate effect, passing said liquor through the successive colder' effects, warming the liquor from the coldest effect with heat from the supplied liquor, and passing the liquor thus warmed through the successively hotter remaining effects of said series.

9. In multiple-effect evaporation of initially hot liquors which become" relatively viscous when concentrated at the temperatures of the colder effects, the process of conserving heat which comprises introducing the supplied liquor into an intermediate effect of a series of effects, such that upon passing to the successive colder effects of such series in the coldest effect, preliminarily cooling I said supplied liquor to the approximate temperature of said intermediate effect prior to its admission thereinto, passin the liquor from the coldest effect to that intermediate effect of the series which is next hotter than the first said intermediate'effect, utilizing heat from the supplied liquor to warm the liquor from the coldest effect to approximately the temperature of the intermediate effect to which. it is then passed, and further concentrating said liquor by passing it through successively hotter effects of said series of effects.

10. Iumultiple-effect evaporation of initially hot liquors which become relatively viscouswhen concentrated at the temperatures of the colder effects, the process of conserving heat which comprises introducing the supplied liquor into an intermediate effect of a series of effects, such that upon passing to the successive colder effects of such series, the liquor will have a relatively low viscosity in the coldest effect, prelim inarily cooling said supplied liquor to the approximate temperature of said intermediate effect prior to its admission thereinto, passingthe liquor from the coldest effect to that intermediate effect of the series which is next hotter than the first said intermediate effect, utilizing heat f'romth'e supplied liquor to raise the temperature of the'liquor from the coldest effect to approximately the temperature of the intermediate effect to which it is then passed, further concentrating said liquor by passing it through successively hotter effects of said series of effects, and warming the liquor passing to each successive hotter effect; with heat from the concentrated liquor from the hottest effect.

In testimony whereof 'I have affixed my signature. a

HUGH K. MOORE.

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