US2193483A - Multiple effect evaporator and the like - Google Patents

Description

March 12, 1940. w. 'r. HINCKLEY MULTIPLE EFFECT EVAPORATOR AND THE LIKE 3-Sheets-Sheet 1 Filed June 28, 1937 12, 1940- w. 'r. HINCKLEY EVAPORATOR AND THE LIKE Filed June 2a, 1937 IUL'IIPLE EFFECT 3 Sheets-Sheet 2 March 12, 1940.

w; 1'. HINCKLEY MULTIPLE EFFECT EVAPORA'I'OR AND THE LIKE Fil ed June 28, 1937 3 Sheets-Sheet 3 Patented Mar. 12, 1940 UNITED STATES PATENT OFFICE William T. Hinckley, Chicago, Ill., assignor tov Whiting Corporation,-Harvey, 111., a corporation of Illinois Application June 28,1937, Serial No. 150,748

1 Claim.

This invention relates to improvements in multiple-effect evaporators. It .will be described as applied to evaporators of the long-tube vertical type but it is to be understood that this invention 5 may be practiced on multiple-effect.evaporators of any construction. .It will be described in terms of evaporators heated by steam but it is to be understood that the heating may be carried out by any suitable vapor. .The features of the present invention involve improvements in the operation of multiple-effect evaporators in which the liquor moves from one effect to another in the same direction as the heating vapor. This method of liquor feeding is ordinarily called forward flow or forward feeding.

As the liquor flows through the system its concentration increases due to the expulsion of the moisture so that the percentage of total solids or non-vaporizable material increases until finally the desired degree of concentration is attained.

One featured the present invention relates to the provision of a scheme, or system of connections of the various effects, such that the last effect through which the liquor flows, and which in this instance is also the last'heating effect or body, is subdivided into two or more sub-effects through which the liquor flows in series; both of which sub-efiects are however, supplied with heatingmedium in parallel, although in certain 30 cases, these two sub-effects may be independently heated as will be set forth hereinafter. Furthermore the vapor heads of both of said sub-effects may be separately controlled and the pendent condensers so that the pressures and temperatures existing in said vapor heads may be independently controlled.

In order that the advantages of certain fea-- tures of the present invention may be better understood and appreciated, the following exp1anation will be helpful to an understanding of the conditions existing in the treatment of certain special classes of liquors.

In the concentration of'heat sensitive liquors u would bethe/case if such temperature were, to be vapor from them may be sent to separate or inde-' such as glue, gelatin, blood, malt syrup, fruit applied to them in a more stagnant condition, and therefore for a longer time interval.

As the liquor flows through the effects, one after the other, its concentration increases, but at the same time the volume of liquor to be'5 treated also decreases due to the removal of water or solvent therefrom, so that in the last liquor effect there is handled only a very much smaller volume of material than inthe first effect. Furthermore, in case of a forward flow system, the temperature of the liquor decreases as it passes from one effect to the next; and inasmuch as the viscosity increases with lowering of temperature'it follows that in the last effect of a forward flow system there exists a serious diificulty, since the maximum viscosity is encountered at the lowest temperature and also in that effect in which the volume of material to be handled. is smallest, so that the flow will be most sluggish under ordinary circumstances.

When applying the features of the present invention to the treatment of such liquors as the foregoing, it is possible to sub-divide the last effect so that the same comprises a group of subefiects, the liquor passing in series through the different sub-effects, and by using the features of the present invention, the last may be made of relatively smaller size than the other subelfects; also by reason of the independence of control of the vapor heads of the sub-effects, it 80 is possible to use a less vacuum in the last subeffect than in the earlier sub-effect, thus making it possible to raise the temperature of the liquor during the final treatment,'thereby also reducing the viscosity of the liquor being treated.

In connection with the foregoing it is also noted that the coefficient of heat transfer through the tubes of each effect depends to a large extent on the velocity with which the film of liquor travels up the tubes. By being able 'to somewh'at 40 increase the, temperature in the last sub-effect in the manner already explained, I am able to materially decrease the viscosity of the liquor in said last evaporation, thus making it possible to increase the velocity of the liquor film therein and maintain the heat transfer coefficient of the tubes at the maximum value. In this manner I am able to carry the final evaporation of the liquor to a high degree of concentration without serious impairment of the heat transfer coefficient of the tubes in all of the effects through which the liquor flows. Also by being able to increase the velocity of liquorin the last sub-effect by independent vacuum control,'.I am able to avoid danger of damaging the product and make it possible to successfully concentrate very viscous liquors without danger of excessive fouling of the tubes.

Otherobjects and uses of the invention will appear from a detailed description of the same which consists in the features of construction and combinations of parts hereinafter described and claimed.

In the drawings:

Fig. 1 shows a front elevation of a typical installation embodying the features of the present invention, this installation including a first effect, and a divided second effect, and being for liquor handled according to the forward flow system or operation;

Fig. 2 shows a plan view corresponding to Fig. 1 but on an enlarged scale;

Fig. 3 shows a typical flow sheet corresponding to the plan of Figs. 1 and 2; and

Fig. 4 shows a temperature and concentration diagram corresponding to Figs. 1, 2 and 3.

The arrangement illustrated includes the first effect 20 and the second effect including the subeffects 2| and 22, being designated 2a and 2b respectively. Each of these evapor'ators 29, 2i and 22 is of what is known as the long tube vertical type; and includes a heating unit in the form of upper and lower tube sheets between which there extends a series or bundle of tubes through which tubes the liquorfiows upwardly so that the concentrated liquor and vapor is discharged from the upper ends of the tubes.

Each heating unit is heated by steam or other heating medium or vapor which is circulated around the outside surfaces of the tubes, and the condensation from which is suitably removed from the lower portion of the unit; and the three units 20, 2| and 22 include the vapor heads 23, 24 and 25 respectively, into which the concentrated liquir and vapor is delivered from the heating units. Liquor is suitably withdrawn from the lower portion of each vapor head and deliv- 'ered either to the next unit or to any other suitable point.

In the arrangement illustrated in these drawings the liquor of low concentration is supplied through the connection 26 to the connection-21 leading into a conical chamber from which the liquor is supplied into the lower ends of the tubes of the heating unit of the first effect 20. The liquor rises through said tubes and the vapor and more concentrated liquor is delivered from the upper ends of the tubes into the vapor head 23; and this more concentrated liquor descends from said vapor head through the downcomer 28, into the receiver chamber 29. From the lower end of this receiver chamber a connection 30, extends across to the liquor connection 3|, of the next sub-efiect 2|; and rises through the tubes thereof into the vapor head 24; and the more concentrated liquor flows from the vapor head 24, through the downcomer 32, extending from the vapor head 24 to the receiver 33. From the receiver 33 the connection 34 delivers the liquor to the intake of a piston or plunger pump 35 from which the connection 36 leads across to the liquor inlet connection 31 for the sub-effect 22.

The liquor collecting in the vapor head 25 of the sub-effect 22 passes down through the downcorner 38 into the receiver 39; and the connection 40 extends from the receiver 39 to the intake of a reciprocating plunger pump 4| by means of which the concentrated liquor is delivered to a suitable point.

' said float chamber 43 corresponds to that of the receiver 29. The fioat Within the chamber. 43 operates a lever 46 which is connected by a rod or cord 41 with the arm 48 by means of which the valve 42 is controlled.

Inasmuch as the pressure within the sub-effect 2| or 2a, is lower than that within the first effect 20, it follows that the liquor will naturally flow across connection 30 without the need of any pump in this connection; and by the use of the float control-valve arrangement just specified there is assurance at all times that the liquor will be withdrawn from the first effect only at a proper rate to maintain a seal within said receiver.

Connected to the receiver 33 is a float chamber 49, the same being connected by the pipes 50 and 5| with the upper and lower portions of the receiver; and the float within the chamber 49 is suitably connected by a lever 49b and link 49c to the steam valve 49a by means of which the pump 35 is operated. As the liquor level within the receiver 33 rises and falls the float within the chamber 49 operates accordingly so as to decrease or increase speed of operation of the pump in order to Withdraw liquor just at the proper rate, at all times maintaining the desired lever within the receiver 33, to establish a seal therein.

Likewise, the float chamber 52 is connected to the upper and lower portions of the receiver 39 by the connections 53 and 54 respectively; and the float within the chamber 52 is connected to the steam valve 49a for the pump 4| so as to control the rate of operation, for manner and purpose similar to that already explained with regard to pump 35.

The vapor head 23 of the first effect is connected by the connection 55 with the catchall 56 wherein any entrained liquor carried over in the vapor through the connection 55 is removed. Such entrained liquor is returned by the connection 51 to the downcomer 28 and moves thence to the receiver 29.

The vapor from the catchall 56 proceeds by the connection 58 to a manifold connection 59 which branches and supplies vapor to the steam chests of both of the sub-effects 2| and 22, being 2- -a and 2-b respectively, by means of the connections 60 and GI. A valve 6|a may be provided in the connection 6|. The live steam for operation of the first effect is delivered to the steam chest of the unit 2|! through the connection 62.

The vapor coming from the vapor head 24 of the first sub-effect proceeds by the connection 63 to the catchall 64 wherein any entrained liquor is removed, such entrained liquor passing back by the connection 65 to the downcomer 32 leading to the receiver 33. The vapor from the catchall 64 proceeds by connection 66 to a suitable condenser 61, preferably of the jettype, being supplied with water through the connection 68; and the condensation is discharged outthrough the connection 69. An ejector 'HJ-or other suitable device isprovided for withdrawing air from the upper portion of the condenser 61.

The vapor and the entrained liquor from the vapor head 25 of the second sub-efiect 2-b There is a float chamber 43 con-' designated 22 passes by the connection II to a catchall 12 wherein any entrained liquor is re- The water of condensation from the steam by means of which the unit of the firsteffect is heated is withdrawn from the lower end of the heating unit of said effect through a connection 19 leading to the pump 88 by means of which the.

same is removed. Likewise the condensation connections 8| and 82 are provided from the lower portion of each of the sub-effects 2-a and 2b and the condensation from them is removed by the pumps 83 and 84.

If desired a cross connection 85 having the valve 86 may be provided between the liquor inlet connection 21 and the delivery connection 38 for the first effect; and similar cross con nections 81 and .88 together with the valves 89 and 90 may be provided between the liquor inlet connection 3| and the liquor delivery connection 34 of the sub-efiect 2-a, and between the liquor inlet connection 31 and the liquor delivery connection 40 of the sub-effect 2b. Normally the valves in these cross connections are maintainedclosed so as to insure proper circulation of the liquor through the system.

A venting connection 9| extends from the lower'portion of the heating jacket of the heatin unit of the first effect 28 up into the vapor head 23 of said first effect; so as to withdraw any non-condensable gasxor vapor from the lower portion of the heating unit of said effect. It will be noted that the normal movementof heatina steam is downwardly around the tubes of said heating unit so that the tendency'is to carry sa d non-condensable gas downwardly to the lower portion of the heating unit. Due to the lower pressure existing in the vapor head there will be a natural tendency to withdraw said non-condensable gas up. through the connection 9| in order to maintain the heating unit cleared of said non-condensable gas at all times. Likewise, similar connections 92 and 93 are provided from the lower portions of the heating units of the sub-efiects 2a and 2b respectively, upto the vapor heads of said sub-effects respectively, and

for a purpose similar to that already explained.

If desired, live steam or other heating medium of high temperature may, at times, be introduced into the heating unit of the final sub-effect 2b. designated 22, through the connection 94,. for the purpose hereinafter explained.

In Fig. 1 I have shown a connection 95 from the fiue ll of the vapor head 25, to the flue 63 leading to the catchall 64; and valves 96 in the flue H in. advance of the condenser 12, and 9 in said connection 85. By opening thevalve 91 and closing the valve 96, both of the subefiects may be run on the same condenser whereas by reversing said valves the two subeffects may be independently controlled.

In order that /the operation and usefulness of the invention ay be better understood and appreciatcd the fbllowing illustration or example may be mentioned as being typical of an operation with such an arrangement as that herein disclosed;

Assume an instance of liquor being treated and containing one hundred pounds of solids. Assume that said liquor is fed to the first effect at such a concentration as to'contain only 8% plus or minus total solids. In this instance the amount of material fed to the first efiect will amount to 1250 pounds including the one hundred pounds of solids and 1150 pounds of solvent. Assume the discharge from the first effect to be at plus or minus total solids; under these conditions the first effect will have evaporated 584 pounds of solvent leaving 666 pounds of material to be delivered to the 2-a sub-effect, designated 2|.

This 666 pounds of material at 15% plus or minus total solids will enter the second or 2-a sub-effect and we wi l assume thatin this subefi'ect the concentration is to be raised to 45% plus or minus total solids.. Such being the case 444 pounds of solvent will have been evaporated in the 2a sub-effect leaving a total of 222 pounds of material delivered from the 2--a subeiiect at a concentration of 45% plus or minus total solids.

' This 222 pounds of material at a concentration of 45% plus or minus total solids will be deliveredto the inlet of the 2b sub-effect. Assume that in said sub-eifect there is an evaporation takin place to raise" the concentration to 60% plus or minus total solids. Such being the case there will be 56 pounds of solvent removed in the 2b sub-efiect leaving the total quantity of material delivered from the 2- b sub-effect as-166 pounds and at a concentration of 60% plus or minus total solids.

The above'example will not satisfy a rigorous heat balance but the concentrations given would be changed only very slightly if a rigorous solution were to be 'made.-

From the above i lustration it willbe evident that the first effect will remove 584 pounds of moisture or solvent. the 2a. sub-effect will remove 444 pounds of moisture or, solvent, and the .2- b sub-effect will-remove only 56 pounds of moisture or solvent; but notwithstanding the relatively small amount of moisture or solvent removed therein is relatively small; but the de gree of concentration is so great that serious difficulties may be encountered in the treatment of the liquor, especially in the case of liquor which type.

The advantages of a divided last effect in those cases where the sub-efiec ts. are operated at the same pressure in the vapor -space may be seen from the following line of reasoning: If a double effect evaporator of the usual type with a single,

. as above suggested may be of the. heat sensitive last effect were used for the'example set forth above, the second effect would at all times be producing liquor of total solids. My invention is of particular importance in connection with those solutions that reach a high viscosity at the final concentration. Consequently the entire second effect, which would be producing liquor of the final concentration, would be handling liquor of correspondingly high viscosity and therefore with a correspondingly low heat transfer coefficient. The above illustration shows that to carry liquid from 15% to 45% solids involves the'evaporation of nearly eight times as much water as to carry the concentration from 45% to 60%. Consequently, in an evaporatbr with a divided last effect working, under the/conditions assumed in the above problem, eight-ninths of the total evaporation to be accomplished in the second effect is carried out in body 2a and only one-ninth in body 2?). Body 2a is producing onl 45% liquor, and-therefore handles liquor of a low viscosity and consequently has a higher coefiicient of heat transfer than body 2b. The result is that the average coefiicient of heat transfer for the entire second effect when using two subeifects in accordance with my invention, is much greater than it would be if the second effect consisted of one body only. This means that less heating surface, and therefore a smaller evaporator, may be provided when using a divided last effect than when using the last effect consisting one body only.

On the other hand compare the evaporator shown in Fig. l with a similar set of three bodies, but connected in the usual way to form a triple effect evaporator. In this case body 2| would not be provided with a condenser 61, but would supplysteam to body 22. Body 22 would not receive vapor from line 58, but only from line 66. The distribution of concentrations in the three bodies would not now be the same as in the illustration cited above, but it would be true that body 2a (2 I) of my evaporator (which now becomes the second effect of the triple effect evaporator) would be working at a concentration decidedly less than the finish concentration; whereas body 2b (22) of my evaporator (which now becomes the third effect of the triple effect evaporator) would be the only one Working on the liquor of the finish concentration. In this case, however, the temperature drops across the second and third effects would be very much smaller than the temperature drops acrossbodies 2a and Zbof my proposed evaporator. Further, if it were feasible in any given case to go to triple effect operation, then the embodiment of my invention would be a subdivision of the third effect into two bodies heated with vapor in parallel and fed with liquid in series. In other words, the evaporator of Fig. 1 cannot be logically compared with ordinary triple effect evaporators of three bodies only, but for logical comparison, it would be referred to a triple effect evaporator with a divided last effect, i. e., consisting of bodies I, 2, 3a, and 3b, (a four body arrangement).

In the treatment of some liquors in which the final concentration is relatively high it may be found, especially'when operating the sub-effect 2--b at lower vacuum, and therefore higher temperature, than the sub-effect 2--.a, that the temperature differential on the heating unit of said sub-effect 2-b is too small for satisfactory operation. In such case, the valve 6| -a may be closed, and live steam be supplied through the connection 94.

In some cases it may be found desirable torun the plant with the valve Bl-a closed and supplying live steam to the connection 94, and also supplying the sub-effect or body 22 with a differbodies 20 and 2|.

ent run of liquor from that being treated in the In such case I have provided the valve 36-- b in the liquor connection 36; and a liquor discharge connection 36-a, suitably valved, may be provided in the connection 36 in advance of the valve 36b, so that treated liquor may be discharged from the body 2|; and also a supplemental liquor inlet connection 36-c may be provided to the connection 36 beyond the valve 36-b, through which liquor may be supplied for treatment in the body 22. r

The features of construction and methods of operation mentioned in this and the preceding paragraph are disclosed merely as supplemental to my present invention to illustrate possible additional operations which may be carried out in a typical plant layout and do not comprise any portion of my present invention except in combination with other features.

Thus it will be seen that I have provided a plant of great flexibility of construction and operation, and one which may be operated in diverse manners, and either as a complete integral plant, or as a series of sub-divided plants.

By the features of the present invention which make it possible if desired to raise the temperature within thesub-effect 2b as compared to the liquor temperature discharged from the subeffect 2-a, this being accomplished by independent control of the vacuums to which the vapor heads are subjected, it follows that I am enabled if desired to raise the temperature of the liquor being delivered from the heating unit of the subtubes thereof may be kept properly filled. with liquor notwithstanding the fact that the amount of liquor to be treated is relatively small in this sub-effect.

In a typical installation for the concentration of bone glue the first sub-effect is operated at a vacuum of 26" in the vapor head 24, bringing the concentration of the liquor to 30-35% total'solids, and the second sub-effect is operated at a vacuum of 23" in the vapor head 25, bringing the concen-' tration of the liquor to about 60% total solids, without the need of using live steam at the connection 94. This example is given by way of illustration only, and not as a limitation.

. I claim In a multiple effect evaporator of the forward flow type, the combination of a series of effects, the final effect comprising a plurality of subeffects, connections for passing vapor from an effect preceding the final effect to all the subeffects of the final effect in parallel, liquor con:v

nections through the effects and the sub-effects of the final effect in series, and independent connections and means for subjecting the vapor head of the final liquor sub-effect to a lower degree of

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