IE39938B1 - Process and apparatus for recovering clean water and solids from dilute aqueous solids - Google Patents

Abstract

1457334 Recovering clean water HANOVER RESEARCH CORP 4 Oct 1974 [15 Oct 1973] 43209/74 Heading B1B Clean water is obtained from dilute dispersions, suspensions or solutions by (1) evaporating to obtain steam and a concentrate (2) condensing the steam (3) mixing the concentrate with a relatively non-volatile oil to obtain a mixture which will remain fluid and pumpable alfter the water content has been removed (4) evaporating the mixture to obtain steam and an anhydrous oil/solids slurry and (5) using the steam from step (4) as a source of heat in step (1). Step (1) may be carried out at 70-250‹F and step (4) at 160-400‹F. The process may be modified by adding a light, rolatively volatile oil bafore step (1) and separatinig any distilled oil components from the water condensed at step (2). The oil may be recovered from the anhydrous slurry and recycled. Steps (1) and (4) may be multi-stage evaporation steps. [GB1457334A]

Description

39938 This invention relates to processes and apparatus for recovering clean water and solids from dilute aqueous solids. i The economic disposal of waste solids and recovery of clean water from dilute aqueous solutions and dispersions thereof is a recognised problem. Also, the need to recover clean water and valuable solid materials from dilute aqueous ' solutions and dispersions thereof is a common occurence. Ideally, any process or apparatus for the recovery of water from dilute aqueous solids should provide ease of disposition of all constituents, avoidance of pollution, economic operation, and hygienic handling, and should, in addition and particularly, yield clean water. Furthermore, in the course of recovering clean water it is desirable to obtain by-products, both solid and liquid, which are either valuable in themselves or can be utilized to further the economics of the process. Throughout this specification the expression "dilute aqueous solids" means dilute suspensions, dispersions, solutions, mixtures and other forms of fluid association of solids with water.

In our United States Patent No. 3,716,458 are described process and apparatus for recovering clean water from a dilute solution of aqueous waste solids. In the process disclosed therein a dilute stream of aqueous solids is concentrated by heat evaporation and the evaporated water is condensed and recovered. The concentrated solution of aqueous solids is then mixed with oil and subjected to dehydration by heat evaporation. Again the evaporated water is condensed and recovered. However, the heat energy of the steam formed by evaporation in the dehydration step is given up to condensers and not recovered as useful heat. 39938 According to the present Invention there Is provided a process for recovering clean water from dilute aqueous solids (as hereinbefore defined) comprising the steps of (I) concentrating said dilute aqueous solids by heat evaporation to yield relatively concentrated aqueous solids and steam; (2) condensing said steam; (3) admixing said concentrated aqueous solids with a relatively non-volatile fluidizing oil to obtain a mixture which will remain fluid and pumpable after the removal of the water content therefrom; (4) subjecting the resultant oil-containing mixture to dehydration by heat evaporation to yield steam and a substantially anhydrous solids in oil slurry; and (5) using said steam from dehydration step (4) as a source of heat in concentration step (1).

According to the present invention there is also provided a process for recovering clean water from dilute aqueous solids (as hereinbefore defined) by evaporation while avoiding corrosion and scaling and fouling in the evaporating apparatus, said process comprising the steps of (1) adding a light, relatively volatile oil to said dilute aqueous solids; (2) concentrating said oil and aqueous solids mixture by heat in an evaporator therein said mixture comes in contact with the evaporating surface thereof to yield (i) water vapour and any distillable components of said oil and (II) relatively concentrated aqueous solids containing the remainder of said oil; (3) condensing said water vapour and distilled oil components; (4) separating liquid water resulting from said condensing step from the distilled and recondensed oil components in the liquid mixture thereof; (5) admixing said concentrated aqueous solids containing said - 3 - residual relatively volatile oil with relatively non-volatile fluidizing oil to obtain a mixture which will remain fluid and pumpable after the removal of the water content therefrom; (6) subjecting the resultant oil-containing mixture to dehydration by heat evaporation to yield steam and a substantially anhydrous solids in oil 8lurryi and (7) using said steam from dehydration step (6) as a source of heat in concentration step (2).

According to the present Invention there is also provided apparatus for recovering clean water and essentially dry solids from dilute aqueous solids (as hereinbefore defined), said apparatus comprising (1) a tank for receiving a stream of said dilute aqueous solids and provided with a stirring or agitating mechanism for mixing the dilute aqueous solids, (2) a first evaporator, (3) a conduit extending from said tank to said first evaporator wherethrough may flow a stream of dilute aqueous solids from said tank into the evaporating region of said first evaporator, (4) a condenser, (5) a conduit extending from said first evaporator to said condenser through which may flow steam formed as a result of heating of said dilute aqueous solids, (6) a fluidizing tank provided with a stirring or mixing mechanism, (7) a conduit extending from said first evaporator to said fluidizing tank wherethrough may flow a stream of relatively concentrated aqueous solids from said first evaporator to said fluidizing tank, (8) an oil reservoir, (9) a conduit extending from said oil reservoir to said fluidizing tank wherethrough may flow a stream of relatively non-volatile fluidizing oil from said oil reservoir to said fluidizing tank to become mixed with the concentrated aqueous solids therein, (10) a second evaporator, (11) a conduit extending from said fluidizing tank to said second evaporator wherethrough may flow a mixed stream of concentrated aqueous solids and relatively non-volatile 39938 t fluidizing oil from said fluidizing tank into the evaporation region of said second evaporator, (12) means for supplying evaporative heat to said second evaporator, and (13) a conduit extending from said second evaporator to said first evaporator | i through which may flow steam formed as a result of heating the mixture of concentrated aqueous solids and fluidizing oil in the second evaporator from said second evaporator to said first evaporator for supplying evaporative heat thereto.

Embodiments of the present invention thus provide processes and apparatus for recovering clean water and essentially dry solids from dilute aqueous solids. Dilute aqueous solids are concentrated by heat evaporation and the evaporated water is condensed and recovered. The concentrated aqueous solids are mixed with a fluidizing oil and subjected to dehydration by heat evaporation. The steam formed in the dehydration step is used, to supply heat for the concentration step, so that at least a portion of the heat energy of the steam formed by evaporation in the dehydration step is recovered as useful heat within the system.

The invention will now be described by way of example with reference to the accompanying drawings, in which Figure 1 illustrates the apparatus of the present invention wherein dilute aqueous solids are concentrated in a first evaporation section; the resultant concentrated aqueous solids are mixed with a relatively non-volatile fluidizing oil, and the mixture of concentrated aqueous solids and oil is subjected to dehydration in a second evaporator section.

Figure 2 illustrates a portion of the apparatus of Figure 1 depicting an embodiment wherein a light, relatively volatile oil is mixed with the dilute aqueous solids prior to the concentration ste& The water and solids recovery process to be described as applied to dilute aqueous solids comprises the steps of evaporatively concentrating the dilute aqueous waste solids with recovery of the 39938 evaporated water; mixing the concentrated aqueous solids with a -relatively non-volatile oil to obtain a mixture which will remain fluid and puinpable even After the removal of essentially its entire water content, and subjecting the 5 resulting mixture of solids, water and oil to a dehydration step by heat evaporation with subsequent recovery of a substantially anhydrous slurry of solids in oil* The steam formed in the dehydration step is used to supply heat for the concentration step. In one embodiment of this invention, a light, relatively volatile oil is mixed with the dilute aqueous solids 10 prior to evaporation. The presence of the light oil prevents scaling and fouling in the concentration evaporator, thereby affording improved beat transfer and reducing corrosion caused by corrosive solids.

Tho essentially anhydrous slurry of solids in oil may, if desirod, be separated to yield the oil and the solids in a largely dry and oil-15 free condition. This may be accomplished by mechanical pressure of either a static or a dynamic variety, or both, on the anhydrous slurry whereby the greater part of the oil is expressed from the solids. In some oases, as in the processing of sewage or slau^ter house wastes, the waste itself oontalns an appreciable amount of oil Independently of oil which may be 20 added to it prior to the dehydration step. This oil will be carried through the dehydration step along with the solids and the added oil and be subjected to being pressed out of the dehydrated slurry along with the added oil. If the dry or essentially water-free slurry be pressed sufficiently vigorously, it may thus be ende to yield oil in a quantity 25 or at-a rate equal to or in excess of that in or at which oil was previously added to the concentrated aqueous solids. Generally it is desirable that the pressing step ylold enough oil for the dehydration step that tho process will be self-sufficient with respect to oil requirements. Even core desirably, in some raseB the pressing stop will -6- 39938 produce somewhat more oil than Is needed for the dehydration step so that the process will provide a net oil yield. i The dry solids left after the pressing operation may often be utilized for purposes outside the process Itself sad thus constitute i I a process pxoduot. The pxooess and apparatus may be used to recover olean voter froa dilute aqueous solids derived from ! nuiaeroua sources; for example, In the I reoovery of water froa a variety of materials which are found In aqueous solution or water dispersion,such as, powdered coal,cement,spent lime, inorganio salts, sewage, sewage sludge, slaughterhouse effluent and rendering products, slimes, blaok liquor from the paper Industry, cannery or canning faotozy effluent, food products, animal feeds and wastes, pharmaceutical products and wastes, chemicals, etc. Accordingly, depending on the source, the dry solids recovered from thp pressing operation may be used, for exasgtle, aa fertilizer, as 'jiimal foed, or as food products for human consumption. Ftvrliier, since they are often burnable, they nay be used as fuel for the generation of steam needed to run the evaporator components of the apparatus for the concentration step and the dehydration step, and also the steam needed to run auxiliary equipment such as pumps, either directly If they be steam-driven pumps or Indirectly if they be motor driven pumps and the steam is used to run a turbo-generator directly. The process may thus be at least partly self-sufficient in respect of fuel requirements. The process and apparatus thus provide meann for the recovery of essentially clean water from dilute aqueous solids and, in addition, allow for the recovery of valuable products and by-products therefrom. 1 & & 3 8 The material to be treated should contain solids particles having a maximum size of about X inch. Larger particles may be ground to size or comminuted by existing techniques.

The oils which are utilized for admixture with the concentrated aqueous solids prior to the dehydration operation are inert, relatively non-volatile oils or fats , or other oil-like materials. Typical of these are tallow, other animal fats and vegetable oils, all of which often can be derived directly from the process operation; petroleum oils and their fractions and derivatives Including fuel oils, silicone oils, glycerines, glycols and mixtures thereof, and miscellaneous liquid wastes from industrial plants, being generally of an organic nature. It is desirable to employ an oil that Imparts process credits, that is one that can add value to the solids product, such as waste oils normally found in sewerage or industrial waste, or fuel oils, or, as suggested above, employ oils derived in the practice of the process itself so as to minimize cost factors. The quantity of oil is such that its ratio in the system is in the range of 2 to 20 parts or more by weight,based on each part of non-fat or non-oil based solids. This refers to total oil, that is that added plus that derived from the process for reuse. This amount of oil gives a fluid, pumpable mixture even in the absence of water. The term "fluid" as used here is intended to be synonomous with "liquid", that is taking the shape of the container to the extent that the mixture fills the container.

This will also include heavy, viscous fluids which are pumpable but still suitable for heat transfer purposes.

As mentioned above, in one embodiment of the present invention, a light, relatively volatile oil is mixed with the dilute aqueous solids prior to the - 8 - 39838 concentration step. The presence of the light oil during evaporative concentration results in the formation of a coating of the oil on the surfaces of the evaporator, thereby preventing fouling and the bnlld-up of scale deposits at the boiling surfaces of the evaporator such as the I Interior surfaces of the evaporator tubes. In addition, since the materials which cause fouling and scaling are often corrosive in nature, the prosenco of the oil film prevents corrosion of the evaporator heat transfer surfaces. Evaporative concentration of mixtures of light, relatively volatile oil and dilute aqueous solids yields water vapour containing at least a portion of the light oil and concentrated aqueous solids containing substantially the remainder of that oil which is carried through the subsequent dehydration step. The light oil In the evaporated water or water vapour may be separated by conventional means.

The light oils which are utilized for admixture with the dilute aqueous solids prior to the concentration oporatlon are low In vincooity and contain appreciable levels of relatively volatilo compononto. Typical of these are light lubricating oils, varools, kerosene fractions of Inedible and edible grades and feed grade derived from petroleum sources that have little or no water solubility, short ohain fatty alooholu, distillates from Ho. 2 up to No. 6 or higher viscosity heavy fuel oils, the Isopar (Registered Trade Kark) series of lsoparafflnlc oils manufacturod By Bumble Oil and Refining Company, steam dlotillable organio liquids, and combinations or blends of light and hoavy oils. In the evaporative concentration step, the mixture of light oil and dilute aqueous solids is brought into contact with the evaporating surfaces of the evaporator where oil forms a film. The volatile components of the light oil are codlstilled with the water and are thus available to wash down and form 39038 a film on the outside of the evaporator tubes* The tube surfaoaa are therofore kept clean and fouling sculing, ao veil ao oorronion, aro prevented.

The quantity of light, relatively vblatilo oil which lo to be added to tho dilute aqueous solids prior to concentration lo empirio elnoe in canoe whore sovoro corrosion or (tooling lo to be avoided, such as t in the cane of concentrating or drying eulphurlo add wastes, the dilute aqueous solids may be just a small fraction by weight of the light oil which is added to it. In general, however, the light oil represents from £96 to 5056 by weight of the dilute aqueous solids, and preferably it represents from 3% to 15% by weight of the dilute aqueous solids with which it is mixed. After concentration, any residual oil present in the concentrated aqueous Bollda will blend with tho heavy, relatively non-volatile fluidizing oil added to the system prior to evaporative dehydration.

While the concentration step and the dehydration step may each be carried out in the single stage or single effect evaporators known in the art, it Is preferred that each of these steps be accomplished in a plurality of sequential hoat evaporation steps wherein each of the successive evaporation steps is at a successively higher termerature and the resulting waste solids streams are of successively higher concentration because cf increasing dehydration, the evolved vapoure of each evaporation step supplying a substantial portion of the heat requirements of the preceding heat evaporation step.Thus the plurality of ocquential heat evaporation eteps connotes at least two. The equipments that can be osnployed are known multiple-effect evaporators including recompression type -10- 39938 evaporators such aa thermal or mechanical recompression types, etc. Functionally, evaporator equipment may be of the forced circulation, flash, falling film recirculation# single pass, rotary wiped film;or indeed any suitable type. The tea- ' 5 peratures, pressures and concentrations in each of the successive series of evaporation steps are largely empiric in nature, depending upon the systems and oils being employed.

Normal processing temperatures for the initial concentration of the dilute aqueous solids mixtures may be 10 in the range of 70°F to 200°P in the first stage and 130°P to 250°P in the second, third or final stages of a multi-effect evaporating system, that is 70°P to 250°F overall. The preferred processing temperatures are in the range of 90°F to 175°F in the first stage and 150°F to 220°F in the second, third 15 or last stages. The normal processing temperatures for the dehydration of the relatively non-volatile oil-concentrated aqueous solids mixture may be in the range of 160°F to 300°F in the first stage and 200°F to 400°F in the second, third or final stages of a nulti-effect drying system, that is 20 160°F to 400°F overall. The preferred processing temperatures are in the range of 180°F to 250°F in the first stage and 230°F to 350°F in the second, third or last stages. The foregoing ranges and progressions of temperatures are reasonable in the case where the flows through the evaporator of the 25 mixture being concentrated or dehydrated and the heating or drying steam are substantially counter-current, the evaporator in this mode of operation being called a "blackward blow" evaporator. The temperatures also depend on the desired quality of the end product and economics of fuel utilization, cooling 30 water availability, capital investment, etc.

- I1 - 39938 In the foregoing paragraph the expression "first stage" refers to that part of the evaporator equipment in which the dilute aqueous solids mixture or the relatively non-volatile oil-ooncentration aqueous solids mixture is subjected to the first step of a sequential plurality of evaporation steps, two or three or more corresponding to "second stage"t "third stage" eto. The expression "effect"* on the other hand, as in "multiple-effect" or "multi-effect", Is related to the flow and aotion of the heating medium, customarily steam, in the evaporator equipment* Where the flow of dilute aqueous so 11 da or an oil-concentrat ed aqueous solids mixture "being heated and evaporated is countercurrent to that of the heating steam (backward flow); the first- stage of the evaporator is the same as its last effect* The pressures are not critical and ore controlled with temperatures to achieve desired evaporation rates in a given design. Thus the first stage pressure will conveniently be from about £ inch Eg absolute to approximately atmospheric. The pressures then Increase in succoaalve stages responsive to the temperatures in the aforedesorlbed counter-current or backward flow case. It is advantageous to operate the first stage at aubatmoopherlo pressures, and the final stages at closo to atmoaphorlo.

The advantage of the sequential evaporation ateps may be seen from the following. For example, In a double-effect evaporator at 225#F-250#F with ratios of approximately one pound of steam utilized for approximately 1-1/2 to 1-3/4 pounds of water evaporated whereas in normal cinglo-effect operations about 1-1/2 pounds of steam could be required to achieve the same result with only one pound of water evaporated. If triple or more effect evaporation be utilized, cvon further economies in fuel consumption are made possible. It 3hould be 39938 noted that tho ovolvod vapours from each of the heat evaporation stops after the first step supply a substantial portion of the heat requirement of the preceding heat evaporation step or stage in the ease of a backward flow evaporator. Tho only net or external heat input required is that noeded to raise the temperature of the components to evaporation temperatures and aeke good for heat losses. i . Generally, more water is removed in the concentration atep or steps than in the /drying or final dehydrating atep of operation of an evaporative system handling dilute aqueous solids, Indeed the amount removed daring concentration may be several tines the amount removed dnrlng dehydration or final drying but thiB is not a necessary operating parameter.

The water from the concentration step may be combined with that from the dehydration step or, alternatively, water from the two oxeps or operations may be kept separate. The final product from the dehydration step is generally a substantially anhydrous oil-solids slurry containing no more than about 5 to ID weight percent water on a non-oil basis. The water content is such as to permit fuel efficiency when the oollds which have been soparated from the oil are burned or representation of those solids ao being in an essentially d*y state when they are disponed of as a marketable product. Thus, by operating with and according to tho disolosed apparatus and process substantially all the water is recover^1 froa a diluto aquecus solids feed or raw material in an essentially clecji state and essentially dry solids are also recovered, typically, anhydrous waste solids from raw eeuago.

This invention will be moot clearly perceived and beet undoy-stood through reference to the preferred embodiments as dlscuooed in further 39938 detail in connection with the flow diagrams ohoun in the drawings.

While thio invention is unoful for the recovery of olean water and oolids from dilute r.quooua solids generally, it is illustrated here in connection with the recovery of olean water and oolids- froa dilute aqueous waste 5 solids* In tho embodiment illustrated in Figure 1, a stream of dilute aqueous waste solids enters miring tank 4 through line 6. The fluid mixture is blended or agitated in the mixing tank 4 by means of stirring devioe 8 and then withdrawn from the mixing tank 4 by means of pump 10.

Pump 10 delivorn the dilute aqueous solids through line 12 which meets 10 recycle lino 14 at a "T" Joint or conneotion* The fluid mixture 1b conducted through line 14 to the first stage or third effect evaporator 16 of an overall concentrating evaporator assembly or array. In evaporator 16 water is boiled off at a subatmospherlo pressure which may typically be about 2 inches Qg absolute. The temperature of the partially 15 concentrated product of the entering dilute aqueous waste solids is in the range of 70°F to 200°F and preferably 90°F to 175°F,depending on the pressure In the evaporator 16. Tho ovaporator 16 is heated by steam or vapour from lino 18 which is at a temperature 30° to 40°F higher than the temperaturo of the partially concentrated dilute aqueous 20 solids. Condensate of the heating steam is withdrawn from evaporator 16 through line 20 which meats product water line or conduit 24 at a "T" joint.

Water vapour formed as a result of the concentration of the entering dilute aqueous waste solids mixture is removed from the vapour chamber of first stage evaporator 16 through lino 26 into surfaeo 25 condenser 28 witliJLn wliich a partial vacuum is maintained by means of vaouum pump JO which is connected to condenser 28 by a vacuum line 32.

Cooling water enters condonner 28 via line 34 and exltB therefrom via 3ino 36. Water vr.pour or steam entering condenser 28 through line 26 ia -14- 39938 oondennod therein, and the resulting water is (Uncharged through line 38 which meets pxoduot water line 24 at a "Tn joint cozmeotlon. Product olean water is drawn off continuously through product water line 24. If desired, part of the product vator may he renned within the system. Alternatively, all the recovered water may be restored In a rencrvoir for later use In applications In vhioh essentially olean water is required.

The partially concentrated aqueous waste solids from evaporator 16 are continuously removed through recycle line 14 with the assistance of puinp 40 which Is located therein. Line 14 meets line 42 at a "I" joint whereby part of the aqueous solids discharged from the evaporator 16 through line 14 Is recycled through line 14 back to evaporator 16 and part enters line 42 which meets reoyole line 44 at a nTn joint. The relative proportions of the aqueous waste solids which are recyoled and which enter line 42 are determined by .the setting of valve 46 which Is located In line 42. Pump 40 forces at least a portion of tho partially oonoentrated aqueous solids through line 42 and ultimately line 44 to second stage evaporator 48 of the concentration evaporator. In the second otage evaporator 48 a procedure lo followod which Is similar to that in the first otage except tbat the absolute pressure is generally higher. The absolute preaouro in each succeeding evaporator stage is usually oomewhat higher than in the preceding stage approaching approximately atmospheric pressure in the lost stage. The teinperature of the further conccr.trc.tcd product of the cocond stage evaporator ic in the range of 130°F- to 250°F "and preferably 150° to 220°F, depending on the absolute pressure in the evaporator. The heating medium is steam vhich is at a temperature 30° to 40°F higher than the temperature of the further concentrated r.qucoua vante solids leaving the second stage ovaporator 40. The heatir.j; 3tean> come3 throuch line 5® from the vapour 39938 chamber of the third or cucoecdinn conocntratlnc evaporator stage.

Condensate of the heating atean lo withdrawn fron evaporator 48 through nil* 56 which meets product water line 24 at a *Ttt Joint.

Tho further concentrated aqueous waotc Bolids from ovaporator 48 are continuously removed through recycleline 44 with the asoiotanoe of pump 58 which is located therein. Line 44 meets lino 60 at a "T" joint whereby part of the aqueouo solids discharge from evaporator 48 through line 44 is recyolod through line 44 back to evaporator 48 and part enters line 60 Which meets recycle line 62 at a "T* joint. The relative proportions of the aqueous waste solids which are recycled and whioh enter line 60 are determined by the setting of valve 64 which is located In 60. Pump 58 forces at least c portion of the further concentrated aqueous waste solids through line 60 and ultimately line 6? to third stage evaporator 66 of the concentration evaporator. In the third stage evaporator 66 a procedure lo followed which lo similar to that In the second stage except that the absolute pressure is generally higher, advantageously being approximately atmoBpherlo.

The temperature of the still further concentrated produot of third" otage evaporator 66, that is aqueous waste solids significantly reduced in wa" or content from their condition entering the concentrating evaporator through line 14, is generally greater than that of the product of second stage evaporator 48 and is within the range of 130° to 250° F, depending on the pressure in tho evaporator 66. The heating medium ie steam at a temperature 30° to 50°F higher than that of the still further concentrated aqueous waste solids product. The heating steam comes through lino 68 from the vapour chamber of the first stage evaporatox* 70 of a two-ot^ge drying evaporator. Cotulennate of the heating steam in withdrawn from evaporator 66 through lino 72 which meats produot water -16- 39938 line 24 At a "T" Joint. Tho otlll further conocntrntod aqueous wnnto noli da, now oxluting no u concentmto In wntcr solution or illupernlon, rare oontiraov.oly withdrawn fron third otago evaporator 66 through recycle iln» 62 with tV» nnoletance of pump'74 which 1b located therein* Lino 62 meets line 76 at a "T" Joint whereby part of the aqueous soil da discharged fron evaporator 66 through line 62 lo recycled through n«» 62 hack to evaporator 66 and part enters line 76* Tho relative proportions of the aqueouo waste solids which are recycled and which enter 76 are determined by the setting of valvo 78 which le located in line 76.

I\rnp 74 forces at least a portion of tho Rtill further concentratod waste solids produot, now existing as a concontxate in water solution or dispersion, through lino 76 to fluidizing tank 80.

She Batter of the degree of concentration of the aqueous waste solids la the stream of material withdrawn from the concentrating evaporator by pump 74 and conducted to fluidizing tank 80 may be considered in at least qualitative terms. This stream of material must be at least sufficiently fluid to be pumpable with essentially all of its fluidity coning from its water content although, depending upon the nature of the original waste material supplied to the illustrated system through line or conduit 6, some oils or fluid fats cay be present also and make some contribution to fluidity. As an example of an extreme condition in one direction assuming that fluidity is duo cesentially entirely to water ccntont and assuming farther that tho concorr.od vac to solids arc insoluble paper fibre wastes, a oolids concentration of no more than 3% to 4% by weight could bo achieved In tho roatorial withdrawn by pump 74. Ah uii example of an opposite extreme, again assuming that fluidity is duo essentially entirely to vater content, Vut now with the further assumption of tho concerned waoie no lid a boins .soluble nolid:i of black liquor from f* 39938 paper mill, a oolids concentration up to about 50?j by weight night well be obtainable. Generally, oolid3 which aro soluble in water may be concentrated to a much greater extont than those which are inoolublo.

It may be asnumed in any case that the non-fat waste oolids . content in the stroam of feed material supplied to the concentrating evaporator througi line 14 io very low indeed, probably not more than l/29$ by wolght and in many particular instances appreciably less than that* For evaporator design calculation purposes, therefore, the stream of material fed through line 14 may be regarded as essentially entirely water. The number of stages going to make up the overall concentrating evaporator, three or more or less, will depend to a greet extent in any specific case on the percentage amount of wator to be removed in and by the concentrating evaporator. Ao suggested hereinbefore > that in turn is a function of the amount of water which must be left in association with the aqueous waste solids to assure pumpability of tho slurry in tho last stage of that ovaporator.

Beturning to detailed consideration of Figure 1, relatively 11011-volatile fluidizing oil from centrifuge oil tank 82 is delivered through line 84 by pump 06 into fluidizing tank 80 into which is also delivered the concentrated aqueous waste oolids product. In fluidizing tank 80 the concentrated aqueouo waste solids and the relatively nonvolatile oil are nixed by stirring device 88 in a ratio that yields a pumpable fluid mixture of slurry capable of remaining pumpable even after evaporation of its relatively small remaining water content. The nlurry of wet waste solids in relatively non-volatile fluidizing oil may contain for each hundred parts of said wet waste solids two hundred to two thousand parts of said oil. The slurry of wet waste solids in -18- 10 15 20 25 39938 fluidizing oil is withdrawn from fluidizing tank 80 and diochargi d by pump 90 throuGh line 96 which meets rooyole line 98 at a "T" Joint or conneotion. Poop 90 delivers the slurry of vet oolids In fluidiiiing oil i through lino 96 end ultimately recyclo line'98 into first stage imxporator t 70 of a two-otage drying evaporator.

In tho first stage of the drying evaporator water is boi! ed off at a subataospherlo pressure which may typically he about 10 to 30 inches Hg abooltrto. The temperature of the partially dehydrated product of the entering slurry Is in the range of 160° to 300°P and preferably 180° to 250°F, depending upon the pressure in the evaporator.

The syBtem la heated by steam from line 100 which is at a temperature about 30 i to 40°F highor than the temperature of the partially dehydrated product Blurry of vaete solids in fluidizing oil. Condensate of the heating steam 10 withdrawn from evaporator 70 throu^i product water line 24. Water vapour formod on a result of the partial dehydration of the entering slurry of wet waste solids in fluidizing oil is removed from tho vapour ohambor of first stage evaporator 70 of the drying evaporator through line 68 and is conduoted to third stago evaporator 66 of the concentrating evaporator. Thus, steam formod in the dehydration step is used to supply at leaut port of the heat for the concentration step.

The partially dehydrated slurry of waste oolida in i'luidizing 011 generated in first Btaga 70 of the dxying evaporator is removed continuously through recycle line 98 with the assistance of pump 102 which is located therein. Lino 90 meets line 104 at a "T" Joint whereby part of the Blurry discharged from evaporator "JO through lino y8 io recycled tlron.^h line 98 back to evaporator JO and part enters lino 104 which moots recycle line 106 at a "T" Joint. Tho relative proportions -19- 39938 of tho partially dehydrated slurry which arc recycled to evaporator 70 and which enter lino 104 are determined by the sotting of valve 100 whioh is located In lino 104* Punp 102 forcos at least a portion of the Blurry through line 104 And ultimately lino' 106 to second stage evaporator \ ' 110 of the drying evaporator. A procedure similar to that in the first t stage of the evaporator is followed, in tho second stago thereof except that the pressure is usually higher, being olose to atoospherlo. The temperature of the essentially dehydrated waste solids and fluidizing oil mixture produced in second stage evaporator 110 of the drying evaporator is in the range of 200° to 400°P and preferably 230° to 350°F, depending upon the absolute pressure in the evaporator 110. The heating medium is steam which is at a temperature 30° to 50°F higher than tho temperature of the essentially anhydrous oil and waste solids slurry produot. This steam is generated in a boiler-furnace and conveyed to seoond stage evaporator 110 of the drying evaporator through line 112. Condensate of the heating oteam is withdrawn through lino 114 and returned to tho boiler furnace, not okown, being of any suitable and convenient design.

The substantially anhydrous slurry of waste solids in fluidizing oil withdrawn from second stage evaporator 110 is discharged by pump 116 through reoyole line 106. Line 106 meets line 118 at a "T" joint whereby part of the slurry discharged from evaporator 110 through lino 106 is recycled throu^i line 106 back to evaporator 110 and part of the slurry enters line 118. The relative proportions of the slurry which are recycled to evaporator 110 and which enter line 118 are determined by the setting of valve 120 which is located in line 118. Pump 116 forces at least a portion of the essentially anhydrous Blurry through lino 118 to continuous oentrlfuge 126 regarded generlcally aa pressing apparatus. The relatively 10 15 20 25 39^38 i non-volatile fluidizing oil is ooparated froia the woato oolids din centrlfuga 126 and is conducted therefrom via line 128 to centrifuge oil tank 82. He cove rod fluidizing oil is discharged "by pump 86 through line 84 to fluldislng tank 80 for recycling' through the system. If the process provides a net yield of fluidizing oil, It may he reoove red from centrifuge oil tank 82 and stored for use outside the system.

She waste solids are discharged from continuous oentrlfoge 126 and enter livo bottom hln 129* The live bottom of bin 129 cause s the vaste solids to advance to the exit thereof where eald vaoto solids, in aa essentially anhydrous state, are dlsoharged through line 130. Consistent vith techniques illustrated and described in our aforementioned united States Patent Ho. 3*716,458, "h«a 130 may extend to a grinder lnj which the dry I and svtostantially de-oiled or de-fatted solids" Initially in cakei or l chunk foxn are reduced to granular if .not powder form. For purposes of delivering the solids to the grinder, lino 130 may take the particular form of a conveyor belt or screw conveyor. Prom the grindor the! I ooirBilimted solids may flow to the suction side of a blower which; finally V ' discharges them into the furnace region of the boilers-furnace to be burned there as fuel for the generation of steam to operate the evaporators. Of course the boiler-furnace may be supplied vith fuel other than or in addition to the dry solids, and some or all of tho solids produced by tlw j illustrated system or apparatus removed from the system entirely! for ur.er; j or disposal altogether outside of it. 1 Figure 2 depicts a portion of the apparatus used in a modification i j of the apparatus of Figure 1 wherein a light, relatively volatile oil ! is mixed with the dilute aqueous waste solids prior to the concentration step. Tho presence of tho light oil during evaporative concentration results in a coating of the oil on the surfaces of the evaporator, thereby -21- 39938 preventing fouling of the evaporator ouch aa the interior eurfacoa of the evaporator tubes.

Referring now to tho flow diagram of Hguro 2, a stream of dilute aqueous waste solids flova into mixing tank-150 through line 152. Oil, 5 assumed to be a ligjit, relatively volatile oil, from separating tank 154 10 forced by pump 156 through line 150 to mixing tank 150. The dilute aqueous waste solids and the light oil axe mixed In tank 150 by means of an agitating device 160 and the resultant mixture is continuously withdrawn from the tank by pump 162 and discharged through line 164 which meots 10 recycle line 166 at a "T" joint or conneotion. The fluid mixture is conducted through line 166 to the first stage evaporator 168 of a multistage concentrating evaporator assembly ox array. In evaporator 163 water and part of the relatively volatilo oil axe boiled off at a Bubatmoophorlo proanure which may typically be about 2 inches ITg absolute. The 15 temperature of the partially concentrator mixture of relatively volatilo 011 aqueous waste solids is in the range of 70° to 200°F and preferably 90° to 175°Ff depending on the pressure in the evaporator 168. The evaporator 168 is heated by mixed vapours of water and volatile oil from the vapour chamber of the next higher stage of the concentrating 20 ovaporator which are conducted thereto via line 170 and which are at a temp erature 30° to 40°F higher than the temperature of the partially concentrated mixture of volatile oil and aqueous waste solids. Condensates of the heating vapours are withdrawn from evaporator 168 throu^i line 376 which meets product water/volatile oil outlet line 178 at 3 "T" joint. 25 Wator vapour and relatively volatile oil vapour formed as a result of the concentration of the mixture of dilute aqueous waste solids ami volatile oil are removed from the vapour chamber of firot stage evaporator 168 through line 180 into surface concenaer 182 vithin which a particl -22- 39838 vacuum Is maintained by moans of vacuum puiap 184 which is connected to Bald condenser by vacuum line 186. Cooling water froia a suitable source enters condenser 182 via line 100 and exits therofrom t)irough line 190. The condensate of water and volatile oil in withdrawn fi-om condenser 182 5 throu^i lino 192 which meets product water/volatile oil outlet line 178 at a T" Joint.

The partially concentrated mixturo of aqueouo waste solids and volatile oil Is continuously removed through recycle line 166 with the assistance of pump 194 which is located therein. Lino 166 meets line 196 10 at a "T" joint whereby part of the mixture discharged from evaporator 168 through line 166 is recyoled through line 166 hack to evaporator 168 and part enters line 196 throu^i vhich it ia ultimately conducted to the second stage of the ooncentxating evaporator. The relative proportions of the mixture which sure recycled and which enter line 196 are determined 15 by the setting of valve 198 which is loeated in line 196.

In the second and subsequent stages of the concentrating evaporator the procedures fo J loved are similar to that in the firnt Rtagi? except that the pressures and temperatures are generally higher. Such sequential evaporative concentration operations have been remarked upon 20 above in connection with the description of Figure 1. In each of the stages of the concentration evaporator writer and part of the relatively volatile oil are boiled off *mtil a concentrated aqueous waste eolidc product, wlilch nay contain Borne higher boiling fractions of the volatile oil, is obtained. The concentratcu aqueous vnste soliu3, and any 25 residual oil that ray be prenent therein, is nixed with a relatively non-volatile fluidizing oil ant* tho mixturo subjected to dehydration essentially as described above with regard to the discussion of Figure 1. -23- 038 The irixtwo ol' product M.-itcx* ruid volr-tllo oil from tho coiic.»n*.v.*0 Jon stop lo conducted throu^i line 170 to soparating tank 154- Tho water phase, containing somo volatile oil, is delivered by pimp 200 through line 202 to coaleacer 204* In the coaleocor 204 essentially complete separation of the remainder of the volatile oil from the product water occore. Volatile oil from coalescer 204 Is returned through line 206 to separating tank 154 froa which ie may be vith drawn through line 158 and added to tho dulute aqueous waste solids in mixing tank 150. Clean product water, essentially completely free fxoa volatile oil* is withdrawn fron coalescer 204 through line 208. If the process provides a net yield of relatively volatile oil, it may be recovered from separating tank 154 and stored for use outside the syBtem. On the other hand, if make-up volatile oil be needed it may be supplied to separating tank 154 from an outside source via line 210. While in the foregoing description of the employment of the apparatus embodiment of tho present invention shown in Figure 2 utilization of a relatively volatile oil has boen described, it will be understood that a heavy oil vith little if any volatile matorial ■ could be used In Its stead, although that would not be preferred.

While the flow diagrams as shown in the drawings have boen disousned above in connection with the concentration and subsequent dehydration of dilute aqueous waste solids, it will be understood by those skilled in the art that the invention is not limited to use with waste solids. Hence the present invention finds utility in the concentration and subsequent dehydration of dilute aqueous solids generally and may be used to advantage in the case of aqueous solids having intrinsic value. Examples of such solids are pharmaceutical products, animal feeds, and food products for human consumption. 39938 Moreover, various modifications may be made to the described apparatus, without departing from the invention as defined by the appended claims. For example, one or more additional concentrated streams may be discharged from other sources of compatible raw material into fluidizing tank 80 and dried. - 25 - 39938

Claims (14)

CLAIMS I-

1. A process for recovering clean water from dilute aqueous solids (as hereinbefore defined) conprioine the steps of (l) concentrating said dilute aqueous solids by heat evaporation to yield concentrated aqueous oolids and steam; (2) condensing said steaa} (3) admixing said cor ■'nitrated aqueous solids vith a relatively non-volatile fluidizing oil to obtain a mixture which will remain fluid and pumpable after the removal of the water content thorofroiaj (4) subjecting the resultant oil-containing mixture to dehydration by beat evaporation to yiold steaa and a substantially anhydrous solids in oil slurry; and (5) using said steaa from dehydration Btep (4) as a source of heat in concentration step (l)

2. A process according to claim 1 wherein concentration step (l) is carried out at temperatures in the range of from 70®P to 250*P and dehydration step (4) is carried out at temperatures in the range of from 160*F to 400*P.

3* A process according to claim 1 or claim 2 which further compriogs the step of separating said anhydrous solids in oil slurry to give a dry and substantially oil-free solids product and an oil.

4. A prooess according to claim 3 wJiich further comprises the step or utilizing at least part of the oil resulting from the separation of said anhydrous eolids in oil slurry as at least part of the oil admixed in step (3) with said concentrated aqueous solids fron step (l). -26-

5« A process for recovering clean water from dilute aqueous solids (as hereinbefore defined) by evaporation while avoiding corrosion and scaling and fouling in the evaporating apparatus, oaid process comprising the steps of (l) adding a light, relatively volatile oil to said dilute aqueous solidst (2) concentrating said oil and aqueous solids mixture by heat in an evaporator wherein said mixture oomes in contact with the evaporating surface thereof ( to yield (i) water vapour and any diotillable components of said oil and (ii) oonoentrated aqueous solids oontainlng the remainder of said oil) (3) condensing said water vapour and distilled oil components; (4) separating liquid water resulting froa said condensing step from the distilled and reoondensed oil components in the liquid mixture thereof} (5) admiring Bald concentrated aqueous solids containing said residual relatively volatile oil with relatively non-volatile fluidizing oil to obtain a mixture which will remain fluid and pumpable after the removal of the water content therefrom; (6) subjecting the resultant oil-containing mixture to dehydration by heat evaporation to yield steam and a subotantially anhydrous solids in oil slurry; and (7) using oaid steam from dehydration step (6) as a source of heat in concentration otep(2).

6* A process according to claim 5 wherein concentration step (2) is o 0 carried out at temperatures In the range of from 70 F to 250 F and dehydration step (6) is carried out at temperatures in the range of from 160°F to 400°F.

7. A process according to claim 6 which further comprises the step of separating said anhydrous solids in oil slurry to give a dry and substantially oil-free solids product and an oil. 39938

8. A process according to claim 7 vhicli further comprises the stop of utilizing at least part of the oil resulting from the separation of said anhydrous oolids in oil slurry as at least part of the fluidizing oil admixed in step (5) with cold conccntratod aqueous oolids containing residual oil from step (2).

9. Apparatus for recovering clean water and essentially dry solids from dilute aqueous solids (as hereinbefore defined) said apparatus comprising (l) a tank for receiving a stream of said diluto aqueous solids and provided vith a stirring or agitating mechanism for mixing the dilute aqueous solids, (2) a first evaporator, (3) a conduit extending from said tank to said first evaporator wherethrough may flow a streem of dilute aqueous solida from said tank into tho evaporating region of said first evaporator, (4) a condenser,(5) a conduit extending from npid first evaporator to caid condenser throxigh which may flow stesm formed aa a result of heating of oaid dilute aqueous solids, (6) a fluidizing tank provided with a atirrivt mechanism, (7) a conduit extending from oaid firot evaporator to said fluidizing tank wherethrough my flow a stream of concentrated aqueous solids from sa'.d first evaporator to said fluidizing tank, (8) an oil reservoir, (9) a conduit extending from said oil reoervoir to said fluidizing tank wherethrough may flow a stream of relatively non-volatilo fluidizing oil from said oil reservoir to said fluidizing tank to bccor.e mixed with the concentrated aqueous solids therein, (10) a second evaporator, (11) a conduit extending from said fluidizing tank to said socond evaporator wherethrough rv\y flow a mixed stream of conocntratcd aqueous solids and relatively non-volatilo fluidizing oil from oaid jTluiuivdn; tank into tho evaporating region of osiid tecon*! evaporator, (12) me-'uiG /'or supplying cvaporativo hvut to said peoond evaporator, and (13) a conduit -?n- 39938 i extending from said second evaporator to oaid first evaporator thro\i£& , l which nay flow steam formed aa a reault of heating the mixture of concentrated i aqueous solids and fluidizing oil in. the second evaporator from said oeoond evaporator to said first evaporator for supplying evaporative hoat » thereto*

10. Apparatus according to olaia 9 wherein said first evaporator and said second evaporator are both multi-stage evaporators and each is arranged to have fluid material to be heated and evaporated in it and vapourous material to effect that heating and evaporating flow through it countereurrently.

11. Apparatus according to olaim 9 or claim 10 which further oomprlsea a preening apparatus for effecting a separation of said mlxtum of conoentrated aqueous solids and oil Into ito components of substantially oll-froo solids and an oil following dehydration of raid mixture in naid eooond avajorator, and a conduit extending froa said oeoond evaporator to said pressing apparatus through which a dehydrated mixture of solids and oil may flow from said second evaporator to said pressing apparatus.

12. Apparatus according to claim 11 which further comprices a conduit extending from said pressing apparatus to said oil reservoir through which oil separated from said dehydrated mixture of solids and oil uaj flow from said pressing apparatus to said oil reservoir.

13. A process for recovering clean water from dilute aquoous solids, the process being substantially ao hereinbefore described with reforeneo to the accompanying drawings. -29- 39938

14. Apparafcun for recovering clean water and CBoentially dry solids fron dilute aqueoua solids, the apparatus being substantially ao hereinbefore described with reference to the accompanying dravlngo. Dated this the 7th day of October, 1974• P. R. KELLY & CO. BY: (Swi fo-ytt/y EXECUTIVE 27* Clyde Road, Bkllsbridge, Dublin 4* AGENTS FOR THE APPLICANTS. -?0-