GB2169918A

GB2169918A - Process and apparatus for removing light oil from solids

Info

Publication number: GB2169918A
Application number: GB08501443A
Authority: GB
Inventors: Charles Greenfield; Robert E Casparian; Anthony J Bonanno
Original assignee: Hanover Research Corp
Current assignee: Hanover Research Corp
Priority date: 1985-01-21
Filing date: 1985-01-21
Publication date: 1986-07-23
Also published as: GB8501443D0; GB2169918B

Abstract

In a process and apparatus for removing light oil from solids, residual light oil is removed from solids obtained in a process where aqueous solids (12) are mixed with a low viscosity, relatively volatile, water-immiscible light fluidizing oil (14) to obtain a mixture which will remain fluid and pumpable after removal of essentially its entire water content. The mixture of solids, water and fluidizing oil is subjected to a dehydration step by heat evaporation (22, 60, 76) whereby substantially all of the water and at least part of the light oil are evaporated and subsequently recovered. The light fluidizing oil is then largely separated (86) from the solids. The solids carrying residual light fluidizing oil are then brought into direct contact (100) with a hot, inert gas (108), referred to herein as "blowing gas". The hot, inert blowing gas (108) effects the removal of the residual light oil from the solids. Light oil vapour removed from these solids is separated from effluent blowing gas by condensation (126) and recovered. Effluent blowing gas, free of light oil vapour, may be recycled. <IMAGE>

Description

SPECIFICATION Process and apparatus for removing light oil from solids This invention is broadly concerned with the removal of light oil from solids and more particularly, it is concerned with the removal of residual light oil from solids obtained in a process where aqueous solids are mixed with a lightfluidizing oil and subjected to dehydration by heat evaporation.

The economic disposal of waste solids and recovery of clean water from aqueous solutions and dispersions thereof is a recognized problem. Also, the need to recover clean water and valuable solid materials from aqueous solutions and dispersions thereof is a commom occurrence. Ideally, apparatus and processesforthe recovery ofwaterfrom aqueous solids should provide ease of disposition of all constituents, avoidance of pollution, economic operation and hygienic handling, and should, in addition, 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 furtherthe economics of the process.

Forthe purposes ofthis application it is to be understood that the term "aqueous solids" is employed generally to include suspensions, dispersions, solutions, mixtures and other forms offluid association of solids in water.

Our U.S. Patent No. 3,855,079 titled "Process and Apparatus for Recovering Residual Oil from Solids Dehydrated in an Oil Medium and Grossly Deoiled" describes a process and apparatus whereby aqueous solids are admixed with a relatively non-volatile fluidizing oil to form a mixture which is dehydrated by heat evaporation. The substantially anhydrous solids in fluidizing oil slurry thus formed is the rafter separated into the oil phase and the solids phase. However, the solids have sorbed thereon appreciable amounts offluidizing oil which contaminates the solids and which will be lost to the process and contribute to unfavourable economics if not recovered. Accordingly, the fluidizing oil-laden solids are subjected to a subsequent extraction step using a relatively volatile, water-immiscible light oil.The light oil-laden solids are then brought into direct contact with blowing steam to effect removal ofthe residual waterimmiscible light oil from the solids.

Our U.S. Patent No. 4,270,974 titled "Process and Apparatus for Recovering Clean Water and solids from Aqueous Solids" describes a process and apparatus in which aqueous solids are mixed with a low viscosity, relatively volatile, water-immiscible lightfluidizing oiltoform a mixture which is subjected to dehydration by heat evaporation whereby substantally all of the water and at least part of the light oil are evaporated and subsequently recovered. The light fluidizing oil is then largely separated from the solids.

The solids, carrying residual lightfluidizing oil, are brought into direct contact with blowing steam to cause removal ofthe residual lightfluidizing oil therefrom.

According to one aspect ofthe invention there is provided a process for the separation of light oil from solids associated therewith comprising the steps of (1 ) bringing the light oil-laden solids into direct contact with a hot, inert blowing gas thereby to remove said light oil from said solids by heat evaporation and (2) conducting effluent inert blowing gas containing light oil vapour away from said solids.

According to another aspect of the invention there is provided apparatus for separating light oil from solids associated therewith, said apparatus comprising (1) a deoiler means to receive light oil-laden solids, (2) means for generating hot, inert blowing gas, (3) a conduit extending from said means for generating hot, inert blowing gas to said deoiler means wherethrough may flow hot, inert blowing gas to come into direct contact with said light oil-laden solids within said deoiler means, and (4) a venting means extending from said deoiler means wherethrough may flow effluent inert blowing gas containing light oil vapour.

The invention can thus provide a process and apparatus for separating light oil from solids associated therewith. More particularly, the invention can providea process and apparatusforthe removal of residual light oil from solids obtained from the dehydration of a mixture of aqueous solids and a fluidizing oil. In its most preferred embodiment, the fluidizing oil is a relatively volatile, water-immiscible light oil. The invention is characterized by the recovery not only of clean water from aqueous solids which are dehydrated in a light oil medium but also of residual light oil from said solids.Aqueous solids are mixed with a low viscosity, relatively volatile, water-immiscible lightfluidizing oil and the mixture subjected to a dehydration step by heat evaporation to remove substantially all of the water and part of the light oil.

The remainderofthe lightfluidizing oil is then largely separated from the solids. The lightfluidizing oil-laden solids are thereafter brought into direct contact with a hot, inert gas, referred to herein as "blowing gas", in a deoiling step. Direct contact of the light oil with the hot, inert blowing gas causes its evaporation and separation from the solids. In contrast to the processes disclosed in U.S. Patent No. 3,855,079 and U.S.

Patent No. 4,270,974 where deoiling is accomplished by contacting lightfluidizing oil-laden solids with blowing steam, the invention does not require a major oil-water separation as is required after condensation of effluent blowing steam and light oil vapour.

The invention is diagrammatically illustrated way of example in the accompanying drawings, in which:~ Figure 1 illustrates apparatus of an embodiment of the invention wherein a mixture of aqueous solids in a relatively volatile, water-immiscible lightfluidizing oil is subjected to dehydration by heat evaporation followed by separation of most of the light fluidizing oil from the essentially anhydrous solids, the essentially anhydrous solids, containing residual light oil, are brought into direct contact in a deoiler apparatus with gaseous products of combustion from a furnace and the gaseous products of combustion act as hot, The drawings originally filed were informal and the print here reproduced is taken from a later filed format copy.

inert blowing gas to facilitate the separation of residual light oil from said solids; Figure 2 illustrates apparatus of an embodiment of the invention wherein a mixture of aqueous solids in a relatively non-volatile fluidizing oil is subjected to dehydration by heat evaporation followed by separation of the major portion of the non-volatile oil from the essentially anhydrous solids, the essentially anhydrous solids have sorbed thereon appreciable amounts of relatively non-volatile oil which is removed byexraction with a relatively volatile light oil, said solids, containing residual light oil, are brought into direct contact in a deoiler apparatus with gaseous products of combustion from a furnace and the gaseous products of combustion act as hot, inert blowing gas to bring about the separation of residual light oil from said solids;; Figure 3 depicts a portion of a modified apparatus of Figure 1 or Figure 2wherein the hot, inert blowing gas is an inert gas heated in the furnace ofthe apparatus or in a heating device not otherwise associated with the apparatus of Figure or Figure 2; and Figure 4 depicts a portion of a modified apparatus of Figure 1 or Figure 2 wherein the hot, inert blowing gas is gaseous products of combustion from a furnace not otherwise associated with the apparatus of Figure 1 or Figure 2.

The process ofthe invention is characterized by the separation of light oil from solids associated therewith and more particularly,the invention is concerned with the removal of residual light oil from solids previously substantially dehydrated in afluidizing oil medium. In one embodiment, the process comprises mixing aqueous solids with a low viscosity, relatively volatile, water-immiscible lightfluidizing oil to obtain a mix ture which will remain fluid and pumpable after removal of essentially its entire water content, and thereafter subjecting the resultant mixture of solids, water and oil to a dehydration step by heat evaporation whereby substantially all of the water and at least partofthe lightfluidizing oil are evaporated and subsequently recovered.Extremely dilute aqueous solids may be concentrated by evaporation priorto mixing with the light oil. Thevapoursfrom the subsequent oil dehydration step can be used to supply the energy to this fluidizing oil-free concentration stage ofthe evaporator system. Following dehydration,the light oil is largely separated from the solids.

Those solids carrying residual lightfluidizing oil are brought into directcontactwith a hot, inert blowing gas whereby the residual light oil is removed by heat evaporation.

In another embodiment of the invention, the process comprises the steps of mixing aqueous solids with a relatively non-volatile oil to obtain a mixture which will remain fluid and pumpable after removal of essentially its entire water content and thereafter subjecting the resultant mixture of solids, water and oil to a dehydration step by heat evaporation with subsequent recovery ofthe evaporated water and substantially anhydrous slurry of solids in oil. Extremely dilute aqueous solids may be concentrated by evaporation priorto mixing withthe oil. The slurry of solids in oil is separated to yield the relatively non-volatile oil and solids laden with residual nonvolatile oil. The residual non-volatile oil is substantially removed from the solids by extraction with a relatively low viscosity light oil.The light oil-laden solids are then brought into direct contact with a hot, inert blowing gas whereby the relatively volatile light oil is removed by heat evaporation.

A critical step is the direct contacting ofthe light oil-laden solids with hot inert blowing gas thereby to effect evaporation of said light oil. If the hot, inert blowing gas be at a sufficiently high temperature it will supply the latent heatforthe evaporation ofthe light oil. On the other hand, the light oil-laden solids may be directly contacted with inert blowing gas at a lower temperature providing sufficent heat for vaporization of the light oil is supplied by an external source such as via a heatjacketed device.

By light oil is meant an organic liquid that is relatively fluid as well as relatively volatile. In the case where the light oil is afluidizing oil used in the dehydration of aqueous solids, it should also be water-immiscible. If the light oil is used only to extract a relatively non-volatile oil from solids associated therewith,thelightoil need not be water-immiscible but it should be misciblewith the relatively nonvolatile oil.

The direct contacting of light oil-laden solids with a hot, inert blowing gasfacilitatesthe ready and economical separation of light oil from the solids.

An essentially anhydrous slurry of solids in fluidizing oil is separated to recover the oil and the solids in a largely dry condition but containing sorbedfluidizing oil. This may be accomplished by gravity or by mechanical pressure of either a static or a dynamic variety, or both, on the anhydrous slurrywherebythe greater part ofthe oil is separated from thesolids. In some cases, as in the processing of food products, sewagesludge, rendering raw materials, or slaughter house wastes, the material itself contains an appreciable amount of oil independently of the fluidizing oil which may be added to it priortothe dehydration step.

If that oil be a light oil, it will be either evaporated during dehydration and subsequently recovered or carried through the dehydration step along with the solids and the major part of the added fluidizing oil and be subjectedto being separated from the dehydrated slurry along with twhe added oil. If the essentially water-free slurry be subjected to a sufficiently efficient separation, it maythus be made to yield oil in a quantity or ata rate equal to or in excess ofthat in or at which oilwas previously added to the aqueous solids.

If the oil associated with the aqueous solids by a heavy, relatively non-volatile oil and if fluidizing oil be a light relatively volatile oil, it may in effect be extracted from the essentially dry solids by the light fluidizing oil during the separation step, e.g., a pressing operating, separated from the light oil, and recovered. Alternatively, ifthefluidizing oil be a heavy, relatively non-volatile oil, the associated oil becomes part ofthe fluidizing oil. After separation of the major portion of heavyfluidizing oil, essentially dry solids containing residual heavy oil are extracted with a light oil to remove the heavy oil therefrom.

Generally it is desirable thatthe overall oil separation and deoiling stepsyield enough oil for re-use in the dehydration step so thatthe process will be self-sufficient with respect to fluidizing oil requirements. Even more desirably, in some cases the combined oil separation and deoiling steps will generate somewhat more oil than is needed for the dehydration step so that the process will provide a net oil yield.

No matter how vigorous the separation e.g. pressing, of the essentially anhydrous slurry of solids in fluidizing oil,the recovered solids will have sorbed thereon appreciable quantities of oil which, if not recovered, will be lost to the process. The liquid-solid separating means to separate the fluidizing oil from the solids may be, for example, a settling tank where separation occurs by gravity. Alternatively, separation may be by means of a mechanical press of the static variety, e.g., a reciprocating filter press, or, more advantageously, by means of a dynamic sepa rating device such as centrifuge. However, both static and dynamic presses may be used. Accordingly, most of the oil is pressed from the solids in, for example, a centrifuge, and the oil may be collected in a suitable reservoirwhere it is availablefor re-use in the process if so desired.

In the case where aqueous solids are dehydrated in a light, relatively volatile fluidizing oil, the aqueous solids may originally contain a light oil. In this instance, the light oil is recovered and my be re-used in the dehydration step. On the other hand, if the aqueous solids originally contain a heavy oil, it may be separated from the essentially anhydrous solids due to extraction bythe lightfluidizing oil during the liquid-solid separating step. If the separated oil is divided into its light oil and heavy oil components and only the light oil component recycled as fluidizing oil, the net result is a reduction in the heavy oil content of the dry solids.On the other hand, if the gross separated oil comprising lightfluidizing oil and extracted heavy oil is recycled as the fluidizing oil, an equilibrium is attained wherein heavy oil is put back into the dry solids atthe same rate as it is removed by the recycled gross fluidizing oil. The net result is essentially dry solids having substantially the same heavy oil content on a moisture-free basis as the original feed.

Since the lightfluidizing oil may have a low viscosity and a low specific gravity, e.g., light oils of petroleum origin, the dehydrated slurry from the evaporator can be transferred to a settling tank whereby a more concentrated solids in oil phase may be separated as a thickened slurry; the bulk ofthe oil remainsatthetop ofthetankfrom which it may be recycled to the process. The foregoing gravity separation operation does not require a mechanical press of either a static ora dynamic variety.

In the case where aqueous solids are dehydrated in a heavy, relatively non-volatile fluidizing oil, the aqueous solids may originally contain a light oil. In this instance, the light oil is essentially removed with the water during the dehydration step and may be recovered therefrom. If the aqueous solids originally contain a heavy oil, this oil will be carried through the dehydration step along with the solids and the added fluidizing oil and be subjected to being pressed out of the dehydrated slurry along with the added oil.

No matter howvigorous the pressing of the anhydrous slurry of solids in non-volatile oil, the recovered solids will have sorbed thereon appreciable quantities of non-volatile oil which, if not recovered, will be lost to the process. The non-volatile oil-laden solids are therefore preferably extracted with a relatively light oil to remove the non-volatile oil therefrom. The extraction may conveniently be carried out in the liquid-solid separating means in which the non-volatile oil is expressed from the solids. While the liquid-solid separating means may be of the static variety, e.g., a cage-type piston press, it is advantageous to employ a dynamic separating means such as a centrifuge.Accordingly, most of the non-volatile oil is pressed from the solids in, for example, a centrifuge, and the oil may be collected in a suitable reservoir where it is available for re-use in the process if so desired. The non-volatile oil-laden solids remaining in the centrifuge are then contacted therein with the relatively light oil, and the relatively light oil containing extracted non-volatile oil is thereafter pressed from the solids. The mixture of relatively light oil and extracted non-volatile oil may, if desired, be separated by distillation, e.g., returning to the evaporation system for recovery of light oil from the non-volatile oil, and the individual components reused in the process.

The concentrated light oil-solids slurry or solids having light oil sorbed thereon are then brought into direct contact with a hot, inert blowing gas. The blowing gas, if sufficiently hot, supplies latent heat for the evaporation of the light oil. Alternatively, inert blowing gas at a lowertemperature may be used in conjunction with external heat as from a steam jacket to supply heatfor evaporation of the light oil.

There are a number of advantages to using a hot, inert blowing gas rather than blowing steam in the deoiling step. Use of a hot, inert blowing gas rather than blowing steam places less of a load on the steam generating capacity of a system for dehydrating aqueous solids in a fluidizing oil medium. In fact, the inert blowing gas may be gaseous products of combustion from thefurnace used to generate steam forthe system, in effect, a by-product. Another advantage of inert blowing gas over blowing steam is thatthere is less needforan oil/water separation following condensation of oil vapour removed in the deoiling step. Yet another advantage of inert blowing gas over blowing steam is the possibility of more heat per unit volume of inert blowing gas compared to steam.It is known that at standard conditions of temperature and press, a volume of 22.4 litres will contain one gram molecularweight of gas. Itfollows that, the higherthe molecular weight of a gas, the greatertheweight ofthe gas in a specified volume at specified temperature and pressure. Thus, bychoos- ing an inert gas having a higher molecularweightthan water (steam), comparable volumes atcomparable pressures and temperatures would contain a greater weight of inert gas than of steam. Hence, at any one pressure and temperature, more heat (e.g., BTU's) would be available for vaporizing sorbed light oil from dry solids bya unitvolume ofthe inertgasthan by an identical volume of steam where the value of molecularweight multiplied by specific heat is greaterforthe gas. Any heavy oil present on the dry solids, however, is essentially not evaporated. An example of an inert gas having a higher molecularweightthan water (M.W. 18) is carbon dioxide (M.W. 44).

The source of hot, inert blowing gas may vary widely. One source of hot, inert blowing gas is the gaseous products of combustion from a combustion apparatus such as a furnace. Alternatively, an inert gas such as nitrogen or carbon dioxide may be heated, as in a combustion apparatus, and used as blowing gas.

In a system for dehydrating aqueous solids in a fluidizing oil, the combustion apparatus may conveniently be the furnace associated with the boiler used to generate steam for supplying evaporative heat to the evaporator in the system. Thus,thefurnace in the system may be the source of hot, gaseous products of combustion usedasthe blowing gas. Those gaseous products may include at least some excess air (non-stoichiometric combustion) and still be deemed inert for the purposes ofthe invention. Alternatively, the furnace in the system may bethe means for heating an inert gas such as nitrogen or carbon dioxide which would then be used as the hot blowing gas.It will be understood, of course, that the source of hot, inert blowing gas need not be part ofthe system for dehydrating aqueous solids in a fluidizing oil medium. For example, a furnace not otherwise associated with the system may be the source of gaseous combustion products used as blowing gas or the meansfor heating an inert blowing gas such as nitrogen or carbon dioxide.

In most cases, the choice of inert blowing gas to come into directcontactwith light oil-laden solids or concentrated light oil-solids slurry is not critical.

However, in certain applications such as deoiling materials like food products for human consumption and animal feeds, it is preferable to use an inert gas such as nitrogen or carbon dioxide ratherthan gaseous products of combustion forthe blowing gas.

The removal of light oil from the solids by direct contactwith hot, inert blowing gas may conveniently take place in a de-oiler apparatus which may be operatedatatmosphericorlessthan atmospheric pressure. Lowertemperature blowing gas may be used at atmospheric pressure where blowing steam would require a vacuum. If desired, the deoiler apparatus may be externally heated as by means of a steam jacket. Hot, inert blowing gas is passed into the deoiler apparatus containing the concentrated light oil-solids slurry or light oil-laden solids. Effluent blowing gas and vaporized light oil are conducted from the deoiler apparatus. Any heavy oil present on the solids is essentially not evaporated.

In the casewhere aqueous solids in fluidizing oil are subjected to dehydration, the solids left after removal ofthe light oil therefrom by direct contact with a hot, inert blowing gas may often be utilized for purposes outside the process itselfandthus constitute a process product The process and apparatus of this invention may be used to recover clean water and essentially dry solids from aqueous solids derived from numerous sourceswhetherthey be waste solids orsolids having intrinsisvalue.Thus, for example, this invention finds utility in the recovery of water and solids from a variety of materials which are found in aqueous solutions, in water dispersion or otherwise associated with water, e.g., divided coal, food products, animal feeds and wastes, cement, spent lime, inorganic salts, sewage, sewage sludge, slaughter house effluent and rendering materials, slimes, black Iiquoursfrom the paper industry, certain tree barks, refuse, organic streams from garbage disposal plants, pharmaceutical products and wastes, cannery or canning factory effluent, chemicals, etc.Accordingly, depending on the source,the solids recoveredfromthe hot blowing gas contacting operation may be used as fertilizer, as animal feed, or possibly as food for human consumption, e.g., a dehydrated, fat-free food product. Further, since they are often burnable, they may be used as fuel forthegeneration of steam needed to run the evaporatorcomponent ofthe apparatus, for generating hot, inert blowing gasforcontactingtheconcen- trated oil-solids slurry or the oil-laden solids, 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 used to run a turbogenerator directly.Any heavy oil remaining on the essentially dry solids also may have fuel value. The process maythus be at least partly self-sufficient in respect of the fuel requirements. The process and apparatus ofthe invention thus providemeansfortherecoveryofessentially clean water and valuable solid productsfrom aqueous solids. Furthermore, the invention is characterized by thefactthat residual light oil that is sorbed on or otherwise associated with the solids can be efficently recovered for re-use.

The material to be treated bythe process ofthe invention should contain solid particles generally smallerthan about 6 mm (1/4 inch). However, larger particles are acceptable, as in the case of bone for gelatin manufacture, provided that the clearances between heattransfersurfaces be increased accordingly. Larger particles may be ground to size or comminuted by existing techniques. This applies particularly in the case of coal.

The oils that are utilized for admixture with the aqueous solids priorto the dehydration operation are inert and water-immiscible. Typical relatively non volatilefluidizing oils orfats are tallow, other animal fats and vegetable oils, all of which often can be derived directlyfrom the process operation; petroleum oils andtheirfractions and derivatives including fuel oils; silicone oils, glycerides, higher molecular weightfatty acids, and miscellaneous liquid wastes from industrial plants, being generallyofan organic nature. It is desirable to employ an oil that imparts process credits, i.e., one that can add value to the solids product, such as waste oils normallyfound in sewage or industrial wastes, orfuel oils, or, as suggested above, employ oils derived in the practice ofthe 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 about 2 to about 20 parts or more by weight, based on each partofnon-fator non-oil based solids. This refers to total oil, i.e., that added plus that derived from the process for re-use. 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 synonymous with "liquid", i.e., taking the shape of the containerto the extentthatthe mixturefillsthe container.This will also include heavy, viscous fluids which are pumpable but still suitable for heattransfer purposes.

Lightfluidizing oils should not only be inert and water-immiscible but should in addition be sufficiently volatile to be evaporated by direct contact with hot, inert blowing gas at a temperature within the range of from about 21 "C (70"F) to about 204"C (400"F).

Generally, light oils boiling within the range of from about 650C (1 500F) to about 2880C (5500F), and preferably from about 1 490C (300"F) to about 232"C (450 F), are contemplated as being useful for this purpose. Light oils such as hydrocarbon oils boiling within the range of about 1 62"C (325"F) to about 204"C (400 F) are particularly preferred in the processing of animal feeds and food products for human consumption since this boiling range permits almost complete removal ofthe oil from the dried solids product. The usually preferred class of light oil is light hydrocarbon oil. The light hydrocarbon oil may be normal paraffinic, isoparaffinic, aromatic, or naphthenic.Examples of suitable light hydrocarbon oils are n-pentane, isopentane, lemonine, hexane, cyclohexane, benzene, isooctane, eicosane, petroleum fractions boiling in the range offrom about 149"C (300"F) to about 232"C (450 F), isohexane, xylene, octadecane, toluene, n heptane,cyclopentene,and mixturesthereof.Another class of suitable light oils is water-immiscible fatty alcohols. Examples of suitable alcohols are n-hexyl alcohol, n-heptyl alcohol, isoheptyl alcohol, n-octyl alcohol, isooctyl alcohol, n-nonyl alcohol, and n-decyl alcohol. Fatty acids such as caproic acid, caprylic acid and capric acid as well as the methyl and ethyl esters ofthose acids may also be used as the light oil.In processing food products and animal feed, a light oil such as the series of isoparaffinic oils manufactured by Humble Oil and Refining Company under the trademark "Isopar" may be used. Particularly preferred in processing animal feeds and food products for human consumption are Isopar H and Isopar L becausetheirflash points permit safe operation and their boiling temperatures, which are in the range of about 162"C (325"to 204"C (400"F), allow for almost complete removal of the oil from the dried food product. Generally, materials that are liquid at the temperature of operation, that are preferably oil-like and that are relatively volatile and essentially immisciblewith water may be employed.It is often desirable to employ a light oil that imparts process credits such as waste oils normally found in sewage 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. As in the case of heavy, relatively non-volatile fluidizing oil, the quantity of lightfluidizing oil is in the range of about 2 to about 20 parts or more byweightfor each part of non-fat or non-oil based solids.

The relatively light oils used to extractthe residual relatively non-volatile fluidizing oil from solids dehydrated therein should be inert and miscible with the non-volatile oil to be extracted. They may or may not be water-immiscible. Like the lightfluidizing oils, they should besufficientlyvolatileto be evaporated by directcontactwith a hot, inert blowing gas ata temperature within the range of from about 210C (70 F) to about 204"C (400 F). The light oils used for extraction will generally have the same boiling ranges as given above for light fluidizing oils. The light fluidizing oils exemplified above are also suitable for the extraction of residual non-volatile oil.The quantity of light oil used forthe extraction of residual nonvolatile oil from the solids is not critical and is well within the purviewofoneskilled inthe artto determine. The quantity of light oil will depend on such factors as, for example, degree of intimacy of contact of oil-laden solids with light oil; the quantity of oil-laden solids; and amount of residual oil sorbed on the solids which is a function of particle size, shape, and porosity; and the number of extractions ofthe oil-laden solids with the light oil.

While the dehydration step may be carried out in the single stage orsingle effectevaporators known inthe art, it is preferred thatthis step be accomplished in a plurality of sequential heat evaporation steps wherein each of the successive evaporation steps is at a successively highertemperature and the resulting solids streams are of successively higher concentration because of increasing dehydration, the evolved vapours of each evaporation step supplying a substantial portion of the heat requirement of the preceding heat evaporation step. Thus the plurality of sequential heat evaporation steps connotes at least two. The temperatures, 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.The normal proces sing temperatures forthe dehydration ofthefluidizing oil-aqueous solids mixture may be in the range of about (70"F) to about 121 "C (250"F) in the first stage and in the range of about38 C (100"F) to about 204"C (400"F) in the second, third orfinal stages of a multi-effect drying system. The preferred processing temperatures are in the range of about32"C (90"F) to about (175"F) in the first stage and in the range of about 52"C (1 25"F) to about 177"C (350"F) in the second, third or last stages.The foregoing ranges and progressions oftemperatures are reasonable in the case where the flows through the evaporator of the mixture being dehydrated and the heating or drying steam are substantially countercurrent, the evaporator in that mode of operation being called a "backward flow" evaporator. The temperatures also depend on the desired quality ofthe end product and the economics offuel utilization, cooling water availability, capital investment etc.

In the foregoing paragraph the expression "first stage" refers to that part of the evaporator equipment in which the fluidizing oil-aqueous solids mixture is subjected to the first step of a sequential plurality of evaporation steps, two or three or more correspond ing to "second stage", "third stage", etc. The expression "effect" on the other hand, as in "multiple-effect" or "multi-effect," is related to the flow and action of the heating medium, customarily steam, in the evaporator equipment. Where the flow of a fluidizing oil-aqueous solids mixture being heated and evaporated is countercurrent to that ofthe heating steam (backward flow), the first stage ofthe evaporator is the same as its last effect.

The pressures are not critical and are controlled with temperatures to achieve desired evaporation rates in a given design. Thus the first stage pressure will conveniently be from about 6.4 mm (.25 of an inch) Hg absolute to approximately atmospheric. The pressures then increase in successive stages responsive to the temperatures in the aforedescribed countercurrent or backward flow case. It is advantageous to operate the first stage at subatmospheric pressures and the final stages at close to atmospheric.

The advantage ofthe sequential evaporation steps may be seen from the following. For example, in a double-effect evaporator with feed entering at 270C (80"F),the material can leavetheevaporatorat 107"C to 121 "C (225into 250 F) with ratios of approximately one kilo of steam utilized for about 1.5to 1.75 kilos of water evaporated; whereas in normal single-effect operations about 1.5 kilos of steam could be required to achieve the same result with only one kilo of water evaporated. lftriple or more effect evaporation be utilized, even further economics in fuel consumption are made possible.It should be noted that the evolved vapoursfromeach of the heat evaporation steps after thefirststep supply a substantial portion ofthe heat requirements of the preceding heat evaporation step orstage in the case of a backward flow evaporator.

The only net or external heat input required is that needed to raise the temperature of the components to evaporation temperatures and to provide heat of vaporization as well asto make good for heat losses.

The final productfrom the dehydration step is generally a substantially anhydrous oil-solids slurry containing no morethan about 5-10% weight percent water on a non-fat basis.

Although backward flow evaporators are preferred, anytype may be used. Thus, backward flow evapor- ators, forward flow evaporators forward flow-backward flow evaporator combinations or, indeed, any combination thereof may be used. The equipments that are generally preferred aremultiple-effect evaporators known in the art, e.g., Mojonnier, Bufflovac, Rodney-Hunt, recompression type evaporators such as thermal or mechanical recompression types, etc.

Functionally, evaporator equipment may be ofthe forced circulation, flash, falling film recirculation, single pass, rotary wiped film, plate, or, indeed, any suitable type.

The separation of solids from fluidizing oil may, in the case of a lightfluidizing oil, be conveniently carried out by gravity separation. In the case of either light or heavyfluidizing oil, separation of solids may be carried out in a liquid-solids separating means, preferably in a dynamic press such as a centrifuge.

When dehydration is carried out in a lightfluidizing oil, the concentrated oil-solids slurry orsolids having residual light oil sorbed thereon which are recovered from the liquid-solids separating means, e.g., centrifuge, are then brought into directcontactwith hot, inert blowing gas for removal ofthe residual lightoil therefrom. Any residual heavy oil that may be present on the solids is essentially not removed by contact with the blowing gas. On the other hand, when dehydration is carried out in a heavy, relatively non-volatile oil, the solids having residual heavy oil sorbed thereon which are recovered from the liquidsolids separating means, e.g., centrifuges, are extracted with a light oil. The extraction to remove residual heavy oil may advantageously be carried out in the centrifuge.This may be accomplished,for example, in a single extraction using a continuous screen bowl centrifuge where the non-volatilefluidizing oil is separated from the solids in thefirststage of the centrifuge and the oil-laden solids are extracted with the relatively light oil in the second stage, screen bowl portion ofthe centrifuge. The solids having residual light oil sorbed thereon which are recovered from the centrifuge after the extraction step are then brought into direct contact with hot, inert blowing gas forthe removal ofthe residual light oil therefrom.

In the embodiment of the invention exemplified in Figure 1, light oil-laden solids exiting from the centrifuge in a system employing a lightfluidizing oil inthedehydration step entera deoilerapparatus operating at essentially atmospheric pressure where they are brought into direct contact with a hot, inert blowing gas. The blowing gas is gaseous products of combustion from the furnace used to heatthe boiler of Figure 1 which supplies steam forthe dehydration step and other uses. The deoiler apparatus may, if desired, be externally heated as by passing steam through a heating jacket surrounding it. The vaporized light oil and effluent blowing gas are conducted from the deoiler apparatus and the light oil vapour may advantageously be condensed and separated from the effluent gas.

In the embodiment depicted in Figure 2, solids containing residual non-volatilefluidizing oil are extracted in a centrifuge with a light oil to remove the heavy, relatively non-volatile oil therefrom. Light oil-laden solids exiting from the centrifuge enter a deoiler apparatus where they are brought into direct contactwith a hot, inert blowing gas. The blowing gas is gaseous products of combustion from thefurnace usedto heatthe boiler of Figure 2 which supplies steam for the dehydration as well as forthe heating jacket of the deoiler apparatus. Vapourized light oil and effluent blowing gas are conducted from the deoiler apparatus. The lightoilvapourmayadvan- tageously be condensed and separated from the effluent blowing gas.

In the embodiment illustrated in Figure 3, an inert gas other than gaseous products of combustion is heated in a furnace and thereafter brought into direct contactwith light oil-laden solids in a deoiler apparatus. Again,vaporized light oil and effluent blowing gas are conducted from the deoiler apparatus.

In the embodiment depicted in Figure4, the hot, inert blowing gas is gaseous products of combustion from a furnace not otherwise associated with the system, e.g., it is notthefurnace used to heatthe boiler which supplies steam for dehydrating a mixture of aqueous solids in fluidizing oil by evaporation. The hot, gaseous combustion products are directly contactedwith lightoil-laden solids in a deoilerapparatus.

Effluent blowing gas and light oil vapour are conducted from the deoiler apparatus.

In the embodiment illustrated in Figure 1, a stream of aqueous solids in solution or dispersion enters a fluidizing tank 10 th rough line ? 2. 12. Lightfluidizing oil entersthefluidizing tank 10through a line 14. Thefluid mixture in the fluidizing tank 10 is agitated by means of a stirring device 16 and then withdrawn from the fluidizing tank by means of a pump 18. The pump 18 delivers the mixture through a line20to an evaporating region of a first stage or third effect evaporator 22 of an overall drying evaporator assembly or array. In the evaporator 22 water and a portion of the light oil are boiled off at a subatmospheric pressure which may typically be about 5 to 25 cm (2to 10 inches) Hg absolute.The temperature ofthe partially dehydrated and partially deoiled product of the entering mixture of aqueous solids in light oil is in the range of about 21 "C to 1210C (70" to 250"F) and preferably about 32"C to 79"C (90" to 175"F), depending on the pressure in the evaporator. The system is heated by mixed steam and light oil vapour from a line 24which is at a temperature about 17"C to 220C (30" to 40"F) higher than the temperature of the partially dehydrated aqueous solids in oil mixture and which comes from the vapour chamber of the succeeding or second stage of the evaporator. Condensate ofthe heating vapour is withdrawn through a line 26 which meets a line 28 at a T-joint or connection.The condensate is conducted through the line 28 to an oil-water separator 30. Mixed steam-light oil vapourformed as a result of the partial dehydration ofthe entering mixture of aqueous solids in light oil is removed from the vapour chamber ofthe evaporator22througha line34intoasurface condenser 36 within which a partial vacuum is maintained by means of a vacuum pump 38 which is connected to the surface condenser 36 via a vacuum line 40.

The mixture of water and light oil vapours entering the surface condenser 36 through the line 34 is condensed by cooling water entering the condenser through a line 42 and leaving the condenserthrough a line 44. The mixed condensate of warm water and light oil is discharged from the condenserthrough a line 46 into the oil-water separator 30.

Inside the oil-water separator 30, the mixture of water and light oil, including the mixture returned from a condenser 126 mentioned hereinafter, is separated into light oil and partially clarified water containing some light oil. The separated light oil is removed from the oil-waterseparator30 through a line 48 and is conducted thereby to a light oil storage tank 50.

The partially clarified water is conducted from the oil-water separator 30 via a line 54 to a coalescer 56.

Inside the coalescer 56, the partially clarified water containing some light oil is separated into light oil and clean product water. The separated light oil is withdrawn from the coalescer 56 through a line 58, which meets the line 48 at a Tjoint, and is ultimately conducted to the light oil storage tank 50. The clean productwater is withdrawn from the coalescer56 through a line 60. If desired, partofthe product water may be reused throughoutthe system. Alternatively, all the recovered water may be stored in a reservoirfor later use in applications in which essentially clean water is required.

The partially dehydrated mixture of aqueous solids in light oil from the evaporator 22 is continuously removed through a line 62 with the assistance of a pump 64. The partially dehydrated mixture is forced through the line 62 to the evaporating region of a second stage 66 of the evaporator. In the second stage evaporator a procedure is followed which is similar to that in the first stage except that the pressure is higher.

The pressure in each succeeding evaporator stage is somewhat higherthan in the preceding stage, approaching approximatelyaymospheric pressure in the last stage. The temperature of the further dehydrrated product of the second stage evaporator is in the range of about 38" to 204"C (1 00"to 4000F) and preferably about52 to 177 C (125 to 350 F), depend- ing upon the pressure in the evaporator. The heating medium is mixed steam and light oil vapour which is at a temperature about 17"to 220C (30" to 40"F) higher than thetemperature ofthe further dehydrated aqueous solids slurry leaving the second stage evaporator.The mixed heating vapour comes through a line 68 from the vapourchamber ofthethird or succeeding evaporator stage. Condensate ofthe mixed heating vapour is withdrawn from the second stage evaporator 66through the line 28 and is discharged into the oil-water separator 30. As mentioned above, mixed steam-light oil vapourformed as a result ofthe further dehydration of the partially dehydrated mixture of aqueous solids in light oil is removed from the vapour chamber of second stage evaporator66throughthe line 24 a nd is used as the heating medium in the first stage evaporator 22.

Thefurtherdehydratedslurryofaqueoussolids in light oil withdrawn from the second stage evaporator 66 is discharged bya pump 70 through a line74.The further dehydrated mixture is conducted through the line 74 to the evaporating region of a third stage 76 of the evaporator. The pressure inthethird stage is higher than in the second stage, advantageously being approximately atmospheric.The temperature ofthe product ofthe third stage evaporator76, i.e., a slurry of solids in light oil containing about 1 % by weight of water based on the entire slurry, is greater than that ofthe second stage evaporator 66 and is within the range of about 380to 2040C ( 100"-400"F) and preferably about 650 to 1 17"C (1500 to 350 F). The heating medium forthethird stage evaporator76 is steam at a temperature about 170 to 28"C (30"-50"F) higher than that of the product, i.e. an essentially anhydrous slurry of solids in light oil.This steam is generated in a boiler-furnace 77 and conveyed to the third stage 76 ofthe evaporatorthrough a line 78.

Condensateofthe heating steam is withdrawn through a line 80 and returned to the boiler-furnace.

As already mentioned, mixed steam-light oil vapour formed as a result of the still further dehydration of the slurry of solids in light oil is removed from the vapour chamber of the third stage evaporator 76 through the line 68 and is used as the heating medium in the second stage evaporator 66.

The essentially anhydrous slurry of solids in light oil is withdrawn from the third stage evaporator 76 and is forced by a pump 82 through a line 84 to a continuous centrifuge 86. The light oil is separated from the solids in the centrifuge 86 and is conducted therefrom via a line 88 to the light oil storage tank 50. Recovered light fluidizing oil is discharged by a pump 90 through the line l4tothefluidizingtank 10for recycling through the system. If the process provides a net yield of oil, it maybe recovered from the tank 50 and stored for use outside the system.

The solids, having residual light oil sorbed thereon, exit from the continuous centrifuge 86 and enter a live bottom bin 94 via a conduit 96. The live bottom ofthe bin 94 causes the solids to advance to the exitthereof where they are conducted by gravity through a conduit 98 into a cake deoiler apparatus 100. The deoiler apparatus 100 may, if desired, be externally heated by steam generated in the boiler-furnace 77 which enters a steam jacket 102through a line 104.

Condensate ofthejacket steam is withdrawn through a line 106 and returned to the boiler-furnace. Hot, gaseous products of combustion generated in the furnace ofthe boiler-,'urnace77 are discharged through a furnace stack 107. At least a portion of the hot, gaseous products of combustion are conducted from the furnace stack 1 O7through a line 108, which is joined thereto, into the deoiler apparatus 100 where, as inert blowing gas,they come into direct contact with the light oil-laden solids and cause vaporization of said lightoil.Afan 109 in the line 108 provides pressureto conductthe gaseous products of combustion through the line 108. Effluent blowing gas and vaporized light oil exit from the deoilerapparatus through a line 110.It will be understood thatthe point atwhich the ine 108 joins the furnace stack 107 will be determined by the desired temperature ofthe gaseous products of combustion, i.e., inert blowing gas. The higherthe desired temperature, the lower will be the point on the furnace stack 107 where the line 108 joins. If maximum blowing gas temperatures are desired,the line 108 maybe connectedtothe furnace itself ofthe boiler-furnace77.

The solids, free from sorbed light oil, are discharged by gravityfrom the deoilerapparatus 100 through a conduit 114 into a live bottom bin 1 16. A screw conveyor in the bottom ofthe bin 116 conducts the solids to the exitthereofwhere said solids, free from thefluidizing light oil as well as being in an essentially anhydrous state, are discharged through a line 118 into a grinder or comminutor 119. By means ofthe grinder 119 the solids are reduced to granular if not powderform, and from the grindertheyflowthrough a line 120to a rotary selectorvalve 121 by which they may be directed to either a line 122 ora line 123. The line 122 leads to collecting or bagging equipment, and through it the solids may be withdrawn for use outside the illustrated system.The line 123, shown as active according to the setting ofthevalve 121, leads to the suction of a blower 124, and this blower discharges the comminuted solids to the combustion region of the boiler-furnace 77 through a line 125.

The effluent blowing gas and vaporized light oil exiting from the deoiler apparatus 100 are conducted bythe line 110 into the surface condenser 126. light oil vapours entering the surface condenser 126 through the line 110 are condensed by cooling waterentering the condenserthrough the line 128 and leaving the condenserthroughthe line 130. The condensed light oil and any associated water resulting from condensation of water vapour carried overfrom the product solids and/or that associated with the inert gas which is stack gas in this case are discharged from the condenserthrough a line 132 into the oil-water separator 30. Cooled effluent blowing gas is discharged from the condenser into the atmosphere through a line 134.Since effluent blowing gas is freely discharged from the condenser into the atmosphere, the pressure in the deoiler apparatus 100 is essentially atmospheric.Thedeoilingstep isthereforeconducted at essentially atmospheric pressure. While the effluent blowing gas and the vaporized light oil from the deoilerapparatus 100 are depicted in Figure 1 as being conducted to the condenser 126 where the oil vapour is condensed and separated from the effluent blowing gas, it will be understoodthattheenergyofthe blowing gas, light oil vapour mixture may be recovered by supplying heatto thefirststage evaporator 22 orthe second stage evaporator 66 or, indeed, to any evaporating stage in the system exceptto the shell side ofthethird stage evaporator76 since the oil contained therein would contaminate the condensate returned to the boiler-furnace 77 through the line 80 and also sincethetemperature ofthe mixture may not be sufficently high to provide for the heat transfer requirements. Alternatively,the effluent blowing gas and vaporised light oil may be used for preheating the aqueous solids-lightfluidizing oil mixture by injection intothefluidizing tank 10 or, indeed, at any other location in the system where recovery of its energy can offer process credits.

The foregoing description of Figure 1 applies to the case where the aqueous solids do not initially contain a heavy, relatively non-volatile oil. If there had been a heavy, relatively non-volatile oil originally associated with the aqueous solids, the heavy oil would have been extracted bythe lightfluidizing oil during the pressing operation. In the embodiment depicted in Figure 1, the entire oil fraction from the pressing operation is recycled as fluidizing oil. Accordingly, if a heavy oil were present an equilibrium would soon be attained wherein heavy oil was extracted from the aqueous solids by the fluidizing oil at the same rate it was replaced bythe recycled oil. The net resultwould be an essentially dry solids product having substantiallythe same heavy oil content as that of the original feed on a moisture-free basis.

In the embodiment ofthe apparatus depicted in Figure 2, a stream of aqueous solids in solution or dispersion enters a fluidizing tank 138 through a line 140. Non-volatilefluidizing oil enters the fluidizing tankl38througha linel42.Thefluidmixtureinthe fluidizing tank 138 is agitated by means of a stirring device 144 and is then withdrawn from thefluidizing tank by means of a pump 146. The pump 146 delivers themixturethrough alinel48toafinegrinderl50 where solid particles are ground to a maximum size of about 6 mm (one quarter of an inch). Part of the output from the grinder 150, such as hard to grind materials, is recycled to the fluidizing tank 138through a line 152 whilethe remainder of the output is conducted through a line 154to afeedtank156.Thefluid mixture in the feed tank 156 is agitated by means of a stirring device 158 and then withdrawn from the feed tank by means of a pump 160. The pump 160 deliversthefluid mixtu re th roug h a line 1 62 wh ich meets a line 1 64 at a T-joint or connection. The fluid mixture is conducted through the line 164to a first stage orfourth effect evaporator 166 of an overall drying evaporator assembly or array. In the evaporator 166,water is boiled off at a subatmospheric pressure which may typically be about5to 25 cm (2to 10 inches) Hg absolute.The temperature of the partially dehydrated product of the entering mixture of aqueous solids in non-volatilefluidizing oil is in the range ofabout2l"to 1 21"C (70" to 250"F) and preferably about 32" to 790C (90" to 1 75"F), depending on the pressure in the evaporator. The system is heated byvapourfrom a line 168 which is at a temperature about 1 7"to 220C (30"-40"F) higherthan the temperature of the partially dehydrated aqueous solids in oil mixture.

Condensate of the heating vapour is withdrawn through a line 170 to a hot well 172. Watervapour formed as a result of the partial dehydration of the entering mixture of aqueous solids in non-volatile oil is removed from the vapour chamber of the evapor ator 166 th rough a line 174 into a barometric condenser 176 within which a partial vacuum is maintained by means of a vacuum pump 178 which is connected to the condenser 176 via a vacuum line 180.

Watervapourentering the condenser 176through the line 174 is mixed with and condensed by cooling water entering the condenserthrough a line 182, and the resulting stream of warm water is discharged through a line 184 into a hotwell 186. From the hot well 186, product water is drawn offthrough a barometric discharge line 188. If desired, part of the product water may be stored in a reservoirfor later use in applications in which essentially clean water is required.

The partially dehydrated mixture of aqueous solids in oil from the evaporator 166 is continuously removed through the line 164 with the assistance of a pump 190. The line 164meetsa line 192ataT-joint whereby part ofthe mixture discharged from the evaporator 166through the line 164 is recycled through the line 164 backto evaporator 166 and partof the mixture enters the line 192 which meets a line 194 at a Tjoint. A pump 196 forces the partially dehy drated mixturethroughtheline 192 and ultimatelythe line 194to the second stage 198 ofthe evaporator. In the second stage evaporator a procedure is followed which is similarto that in the first stage except that the pressure is generally higher.The pressure in each succeeding evaporator stage is usually somewhat higher than in the preceding stage, approaching approximately atmospheric pressure in the last stage.

The temperature of the further dehydrated product of the second stage evaporator is in the range of about 38" to 204"C (1 00"-400"F) and preferably about 93"C to 1770C (2000-350"F), depending upon the pressure in the evaporator. The heating medium is steam which is at a temperature about 1 to 22"C (300-400F) higherthan the temperature ofthe further dehydrated aqueous solids slurry leaving the second stage evaporator. The heating steam comes through a line 200 from the vapour chamber of the third or succeeding evaporator stage. Condensate of the heating steam is withdrawn through a line 204 and is discharged into the hot well 172.

The further dehydrated slurry of aqueous solids in oil withdrawn from the second stage evaporator 198 is discharged through the line 194 by a pump 206. The line 194 meets a line 208 at a Tjoint whereby part of the slurry discharged from the evaporator 198 through the line 194 is recycled through the line 194 backto the evaporator 198 and part of the mixture enters the line 208 which meets a line 210 at a T-joint. A pump 212 forces the further dehydrated mixture through the line 208 and ultimatelythroughthe line 210two a third stage 214 of the evaporator. The pressure in the third stage is generally higherthan that in second stage evaporator 198 but is advantageously somewhat less than atmospheric.The temperature of the still further dehydrated mixture of aqueous solids in oil leaving the third stage of the evaporator is within the range of about 38" to 204"C (100 to 400"F), preferably about 93" to 1 77"C (200 ~350 F), and is usually somewhat higherthan thatfrom the second stage evaporator 198. The heating medium is steam at a temperature about 1 to 280C (300to 500F) higherthan that of the product, and it comes from the vapour chamber ofthe succeeding orfourth stage of the evaporator through a line 216. Condensate of the heating steam is withdrawn through a line 218 and is discharged into the hot well 172.

Thestillfurtherdehydrated slurryofsolids in oil withdrawn from the third stage evaporator 214 is discharged by a pump 220 through the line 210. The line 210 meets a line 222 at a Tjoint whereby part of the mixture discharged from the evaporator 214 through the line 210 is recycled through the line 210 back to the evaporator 214 and part of the mixture enters a line 222 which meets a line 224 at a Tjoint. A pump 226forces the slurry through a line 222 and ultimately a line 224 to a fourth stage 228 of the evaporator. The pressure in the fourth stage is usually higherthan in the third stage, advantageously being approximately atmospheric.The temperature ofthe product ofthe fourth stae evaporator 228, i.e., a slurry of solids in oil containing abour 1 percent by weight of water based on the entire slurry, is generally greater than that ofthe product ofthird stage evaporator 214 and is within the range of about 38" to 2040C (100" to 4000F) and preferablyabout930to 177"C (200"- 350"F). The heating medium is steam at a temperature about 1 7"to 280C (30" -- 50"F) higherthan that of the product, i.e., an essentially an hydrous slurry of solids in oil. This steam is generated in a boiler-furnace 230 and conveyedto the fourth stage 228 ofthe evaporator through a line 232.Condensate ofthe heating steam is withdrawn through a line 234 and returned to the boiler-furnace 230.

The essentially anhydrous slurry of solids in oil withdrawn from the fourth stage evaporator 228 is discharged by a pump 236 through a line 224. The line 224 meets the line 238 at a T-jointwhereby part ofthe mixture discharged from the evaporator 228 through the line 224 is recycled through the line 224 backto the evaporator228 and part ofthe mixture enters the line 238. A pump 240 forces the slurrythrough the line 238 to a continuous centrifuge 244 which is fitted with a solid bowl first section and a screen bowl second section. The gross or greater part ofthe relatively non-volatile fluidizing oil is separated from the solids in the solid bowl first section of the centrifuge 244 and is conducted therefrom via a line 246 to a recycle fluidizing oil tank 248. Recovered fluidizing oil is discharged bya pump 250through the line 142 to the fluidizing tank 138 for recycling through the system. If the process provides a netyieldoffluidizing oil, it may be recovered from the recycle oil tank 248 and stored for use outside the system.

The solids, containing residual fluidizing oil sorbed thereon, move from the solid bowl first section of centrifuge 244to the screen bowl second section of the centrifuge. A relatively volatile, low viscosity light oil is conducted through a line 252 into the screen bowl section ofthe centrifuge 244 where it comes into intimate contactwith the solids having residual fluidizing oil sorbed thereon. The relatively light oil extracts the fluidizing oil from the solids in the screen bowl section ofthe centrifuge 244, and the mixture of light oil and extracted fluidizing oil is conducted from the centrifuge through a line 254to a tank 256.

The solids, having residual relatively light oil sorbed thereon, exit from the screen bowl section of the centrifuge 244 and enter a live bottom bin 258. The live bottom of the bin 258 causes the solids to advance to the exitthereofwhere they fall bygravitythrough a conduit260 into a cake deoilerapparatus 262. The deoiler apparatus 262 may, if desired, be externally heated by steam generated in the boiler-furnace 230 which enters steam jacket 264through a line 266.

Condensate ofthe jacket steam is withdrawn through a line 268 and returned to the boiler-furnace 230. Hot, gaseous products of combustion generated in the furnace ofthe boiler-furnace 230 are discharged through a furnace stack 270. At least a portion ofthe hot, gaseous products of combustion are conducted from the furnace stack 270 a through line 272, which is joined thereto and which may include a dust collector of any suitable design, into the deoiler apparatus 262 where, as inert blowing gas, they come into direct contactwiththe light oil-laden solids and cause vaporization of said lightoil.Afan 274 in the line 272 provides pressure to conductthe gaseous products of combustion through the line 272.Effluent blowing gas and vaporized light oil exitfrom the deoiler apparatus through a line 276. Itwill be understoodthatthe point atwhich the line 272 joins the fu mace stack 270 will be determined by the desired temperature ofthe gaseous products of combustion, i.e., inert blowing gas. The higherthe desired temperature, the lower will bethe point on the furnace stack 270 wherethe line 272 joins. If maximum blowing gas temperatures are desired,the line 272 may be connectedtothe furnace itself ofthe boiler-furnace 230.

Thesolids,freefrom sorbed Iightoil,aredischarged by gravityfrom the deoiler apparatus 262 into a live bottom bin 278. A screw conveyor bottom of the bin 278 conducts the solids to the exit thereof where said solids, free fromfluidizing oil and light oil as well as being in an essentially dry state, are discharged through a line 280.

Effluent blowing gas and vaporized light oil exiting from the deoiler apparatus 262 are conducted bythe line 276 into a surface condenser 282. Light oil vapours entering the surface condenser 282 through the line 276 are condensed by cooling water entering the condenserthrough a line 284 and leaving the condenserthrough a line 286. The condensed light oil and any incidentally associated water are discharged from the condenserthrough a line 288 into a tank 290 which is divided into a lightoil-watertankandalightoil surge tank. Cooled effluent blowing gas is discharged from the condenser into the atmosphere through a line 292. Since effluent blowing gas is freely dis charged from the condenser into the atmosphere, the pressure in the deoiler apparatus 262 is essentially atmospheric.The deoiling step is therefore conducted at essentially atmospheric pressure. While the effluent blowing gas and the vaporized light oil from the deoilerapparatus 262 are depicted in Figure 2 as being conducted to the condenser 282 where the oil vapour is condensed and separated from effluent blowing gas,itwill beunderstoodthattheenergyofthe blowing gas-light oil vapour mixture may be recovered by supplying heatto any evaporating stage in the system exceptto theshellside ofthefourth stage evaporator 228 since the oil contained therein would contaminate the condensate returned to the boilerfurnace 230 through the line 234 and also since the temperature ofthe mixture may not be sufficiently high to provide forthe heattransfer requirements.

Alternatively, the effluent blowing gas in the vapourized light oil may be used for preheating the aqueous solids4luidizing oil mixture by injection into the fluidizing tank 138 or, indeed, at any other location in the system where recovery of its energy can offer process credits.

The mixture of relatively light oil and extracted fluidizing oil in the tank 256 is discharged by a pump 296through a line 298to an evaporatortube bundle 300 on the second stage evaporator 198. The rate rats of flowthrough the line 298 is controlled by a valve 302.

The extracted fluidizing oil fraction becomes combined with the partially dehydrated slurry of solids in oil that iswithdrawn from the second stage evapor ator 198 through the line 1 94whilethe relatively light oil is vaporized and, along with the steam, is con ducted from the vapourchamber of the second stage evaporator 198 through the line 168 to serve as the heating medium in the first stage evaporator 166. It will again be understood by those skilled in the art that an independentevaporatortube bundle 300 need not be used butthatthe mixture of light oil and extracted fluidizing oil may be discharged from the tank 256 to any evaporating stage in the system.

A line 304 is connected by a Tjoint at one end to the line 194 and by a Tjoint at its other end to the line 298.

The rate of flow of light oil and extracted fluidizing oil through the line 298, as well as the pressure in the line 298, are controlled by the valve 302 so that part ofthe slurry of aqueous solids in oil passing through the line 194 is shunted through the line 304tothe line 298 and ultimatelytotheevaporatortube bundle 300 where said slurry is subjected to further evaporation.

From the top ofthe evaporating region of third stage evaporator2l4extends a line 306 through which are conducted non-condensable materials plus entrained condensable material. Access to the line 306 is controlled by a valve 308. A line 310, controlled by a valve 312, leads from the top ofthe evaporating region of the second stage evaporator 198to the line 306 which it joins at a Tioint. Similarly, a line 314, controlled by a valve 316, connectsthetop of the independent evaporating region 300 to the line 306 and a line 318, controlled by a valve 320, connects the top of the evaporating region of the first stage evaporator 1 66 to the line 306.A partial vacuum is maintained in the line 306 by means of an ejector 324 which is supplied with steam through a line 326. By adjusting the valves 308,312,316 and 320, the desired degrees of reduced pressure may be maintained, respectively, in the third, second, and first stages of the evaporator.

Steam from the ejector 324 as well as noncondensable and condensable materials are conductedthrough a line 328to a condensables seal tank 330. Non-condensable materials and entrained condensable saterials are conducted by a line 332 from the condensables seal tank 330 to a surface condenser 334. The surface condenser 334 is cooled by cooling water entering the condenser through a line 336 and leaving through a line 338. Non-condensable mate rials exit from the surface condenser 334 th rough a line 340. Entrained condensable materials are returned to the condensables seal tank 330 from the surface condenser 334 through a line 344.Condensable materials, essentially comprising water and the relatively light oil, are conducted bya line 346 from the condensables seal tank 330 to the tank 290 which, as mentioned above, is divided into a light oil-water tank and a light oil surge tank. Condensate, essentially comprising water and the light oil, is forced by a pump 348 from the hotwell 172 to the tank 290 through a line 350.

Inside the tank 290, the mixture of water and relatively light oil is separated into essentially pure light oil which enters the light oil surge tank and partially clarified water containing some light oil which remains in the light-oil watertank. Excess light oil is forced bya pump352through a line354from the light oil surge tank part ofthe tank 290 to storage tanks. Light oil needed in the process to extract fluidizing oil from the solids is forced by a pump 356 from the light oil surge tank part of the tank 290 through the line 252 to the continuous centrifuge 244.

Partially clarified water containing some of the relatively light oi is forced by a pump 358 from the light oil-water tank part of the tank 290 to a coalescer 360 through a line 362. Clarified condensate comprising clean water is removed from the coalescer 360 through a line 364 and conducted to storage tanks.

Light oil which is separated from the water in the coalescer 360 is removed from the coalescerthrough a line 366 and through lines 368 and 370 which connect with the line 366 atT-joints. The line 366 conducts the light oil backto the tank 290 where it enters the light oil surge tank partthereofand ultimately goes to storage tanks or is conducted to the continuous centrifuge 244 forthe purpose of extracting fluidizing oil from the solids.

Figure 3 depicts a portion ofthe apparatus used in a modification of the apparatus of Figure 1 or of Figure 2 wherein the hot, inert blowing gas is an inert gas heated in the furnace ofthe apparatus or, alternatively, in a heating device not otherwise associated with the apparatus of Figure 1 or of Figure 2. The apparatus of Figure 3 differs basically from that of Figure 1 and of Figure 2 in that the hot, inert blowing gas is not gaseous products of combustion but rather is an inert gas such as nitrogen or carbon dioxide. Figure 3 is depicted as a modification ofthe apparatus of Figure 1, but it will be understood that the same modification could just as readily be applied to the apparatus of Figure 2.Also, while Figure 3 illustrates the use ofthe boiler-furnace77 of Figure 1 as the means for heating the inert gas, it will be understood that the inert gas may alternatively be heated in a heating device not otherwise associated with the apparatus of Figure 1.

Referring to Figure 3, light oil-laden solids enter the cake deoiler apparatus 100 via the conduit 98. The deoiler apparatus 100 may be externally heated by steam generated in the boiler-furnace 77 which enters the steam jacket 102 through the line 104. Condensate of the jacket steam is withdrawn through the line 106 and returned to the boiler-furnace. An inert gas within a heating coil 374 is heated inside the furnace stack 107 ofthe boiler-furnace 77. The heating coil 374 is joined at one end to the line 108 which conducts the hot, inert blowing gas into the deoiler apparatus 100 where it comes into direct contact with the light oil-laden solids and causes vaporization of the light oil. Solids, free from sorbed light oil, are discharged fromthedeoilerapparatus 100through the conduit 114.The fan 109 in the line 108 provides pressureto conductthe hot, inert blowing gas through the line 108. Effluent inert blowing gas and vaporized light oil exit from the deoiler apparatus through the line 110. It will be understood by those skilled in the artthat the position ofthe heating coil 374 in the furnace stack 107 will be determined by the desired temperature of the inert blowing gas. The higherthe desired temperature, the lowerwill be the position of the heating coil 374 in the furnace stack 107. If maximum inert blowing gas temperatures are desired, the heating coil 374 may be placed inside the furnace of the boiler-furnace 77.

Effluent blowing gas and vaporized light oil exiting from the deoiler apparatus 100 are conducted by the line 110 into the surface condenser 126. Light oil vapours entering the surface condenser 126 through the line 110 are condensed by cooling water entering the condenserthrough the line 128 and leaving the condenserthrough the line 130. The condensed light oil is discharged from the condenser through the line 132. Cooled effluent inert blowing gas is discharged from the condenser 126 through a line 376 which is connected to the other end of the heating coil 374. The inert blowing gas is accordingly recycled.

Figure 4 depicts a portion of a modified apparatus of Figure 1 or of Figure 2 wherein the hot, inert blowing gas is gaseous products of combustion from a furnace not otherwise associated with the apparatus of Figure 1 or of Figure 2. While Figure 4 is representative of a modification of the apparatus of Figure 1, it will be understood that the same modification could be applied to the apparatus of Figure 2.

In Figure 4, light oil-laden solids enterthe cake deoiler apparatus 100 via the conduit 98. The deoiler apparatus 100 may, if desired, be externally heated by steam generated in the boiler-furnace 77 which enters the steam jacket 102 through the line 104. Condensate ofthe jacket steam is withdrawn through the line 106 and returned to the boiler-furnace 77. Steam for heating the evaporator array ofthe system is also generated in the boiler-furnace 77 and conducted to the third stage 76 of the evaporator through the line 78. Condensate ofthe heating steam is withdrawn through the line 80 and returned to the boiler-furnace.

Hot, gaseous products of combustion are generated in a furnace 380, which may indeed be an industrial inert gas generator of known design, and discharged through a furnace stack 382. At least part ofthe hot, gaseous products of combustion are conducted from the furnace stack 382 via a line 384, which is joined to the furnace stack 382, into the deoiler apparatus 100 where, as inert blowing gas, they come into direct contactwith the light oil-laden solids and cause vaporization of the light oil. Solids, free from sorbed light oil, are discharged from the deoiler apparatus 100 through the conduit 114. Afan 386 in a line 384 provides pressureto conductthe gaseous products of combustion through the line 384. Effluent blowing gas and vaporized light oil exitfrom the deoiler apparatus through the line 110.As mentioned above, the point at which the line 384 is joined to the furnace stack 382 will be determined by the desired temperature ofthe gaseous products of combustion. Thus, the higherthe desired temperature of the gaseous products of combustion, the lower will be the point on the furnace stack382 where the line 384 joins. For maximum blowing gas temperature, the line 384 will be connected directly to the furnace.

Effluent blowing gas and vaporized light oil exiting from the deoilerapparatus 100 are conducted bythe line 110 into the surface condenser 126. Light oil vapours entering the surface condenser 126 through the line 110 are condensed by cooling water entering the condenserthrough the line 128 and leaving the condenserthrough the line 130. The condensed light oil is discharged from the condenserthrough the line 132. Cooled effluent blowing gas is discharged from thecondenserintotheatmospherethroughthe line 134. Since effluent blowing gas is freely discharged from the condenser into the atmosphere, the pressure in the deoiler apparatus 100 is essentially atmospheric. The deoiling step is therefore conducted at essentially atmospheric pressure.

While the effluent blowing gas and the vaporized light oil from the deoilerapparatus 100 are depicted in Figure 4 as being conducted to the condenser 126 where the oil vapour is condensed and separated from effluent blowing gas, it will be understoodthatthe energy of the blowing gas-light oil vapour mixture may be recovered by supplying heat to the first stage evaporator 22, to the second stage evaporator 66 orto any evaporating stage in the system exceptto the shellside of the third stage evaporator76 since the oil contained therein would contaminatethecondensate returned to the boiler-furnace 77 through the line 80 and also since the temperature ofthe mixture may not be sufficiently high to provide forthe heat transfer requirements.Alternatively, the effluent blowing gas and vaporized light oil may be used for preheating the aqueous solids-lightfluidizing oil mixture by injection intothefluidizing tank 10 or, indeed, at any other location in the system where recovery of its energy can offer process credits.

Thus, in its broadest sense, the invention provides a process and apparatus for removing light oil from solids. The invention is particularly applicable to the removal of residual light oil from solids obtained in a process where aqueous solids are dehydrated in a lightfluidizing oil medium and the major part of the lightfluidizing oil separated from the essentially anhydrous solids. Similarly, the invention finds utility in the removal of residual light oil from solids obtained in a process where aqueous solids are dehydrated in a heavy, relatively non-volatile fluidizing oil and the major part of the heavy oil separated from the essentially dry solids. Residual heavy oil is thereafter removed from the solids by extraction with a light oil. The foregoing processes are characterised bythe recovery of clean waterfrom aqueous solids dehydrated in a fluidizing oil medium as well as bythe recovery of residual light oil from the solids afterthe dehydration thereof. The light oil-laden solids are brought into direct contactwith a hot, inert blowing gas which removes the residual light oil by heat evaporation. Furthermore, the invention makes possiblethe winning or recovery of solids that are not only dehydrated but which are deoiled beyond the point usually attainable solely by mechanical means.

Claims

1. A process forthe separation of light oil from solids associated therewith comprising the steps of (1) bringing the light oil-laden solids into direct contact with a hot, inert blowing gastherebyto remove said light oil from said solids by heat evaporation and (2) conducting effluent inert blowing gas containing light oilvapourawayfrom said solids.

2. A process according to claim 1, including condensing the light oil vapourtherebyto separate said light oil from the effluent inert blowing gas.

3. A process forthe recovery of clean water and substantially dry, fluidizing oil-free solids from aqueous solids dehydrated in a lightfluidizing oil medium comprising the steps of (1) admixing aqueous solids with a low viscosity, relatively volatile water-immiscible lightfluidizing oil boiling within the range offrom about 65"C (1 50"F) to about 288"C (550"to obtain a mixture which will remain fluid and pumpable afterthe removal of the water content therefrom; (2) subjecting the resultant oil-containing mixture to dehydration by heat evaporation whereby substantially all the water and part of the fluidizing oil are vapourized, yielding a mixed water and light oil vapour and a substantially anhydrous solids in oil slurry; (3) condensing said mixed water and light oil vapour; (4) separating the resultant condensate into a clean waterfraction and a light oil fraction; (5) separating at least some of the relativelyvolatile, water-immiscible lightfluidizing oil from said substantially anhydrous solids in oil slurry; (6) bringing the resultant solids carrying residual lightfluidizing oil into direct contact with a hot, inert blowing gas thereby to remove said light oil from said substantially anhydrous solids by heat evaporation, and (7) combining the separated light oil fractions of steps (4) and (5) and admixing them with fresh aqueous solids and thereby recycling them through the process as fluidizing oil.

4. A process according to claim 3, wherein said hot, inert blowing gas comprises gaseous products of combustion, nitrogen or carbon dioxide.

5. A process according to claim 3 or claim 4, wherein light oil vapour in effluent blowing gas is removed therefrom by condensation and admixed with fresh aqueous solids and thereby recycled through the process as fluidizing oil.

6. A process according to claim 5, wherein said blowing gas is selected from the group consisting of nitrogen and carbon dioxide.

7. A process according to claim 6, wherein effluent blowing gas, after removal of light oil vapour therefrom, is reheated and recycledthroughthe process as hot, inert blowing as.

8. A process according to claim 5, wherein said blowing gas is gaseous products of combustion from acombustion apparatus outsidethesystem.

9. A process according to claim 3, wherein the heat evaporation step (2) is carried out at temperatures within the range of about 21"C (70"F) to about 204"C (400"F).

10. A process according to claim 3, wherein said solids carrying residual lightfluidizing oil are brought into direct contact with inert blowing gas at tempera tureswithinthe range offrom about21 C (70"F) to about 204"C (400"F).

11. A process according to claim 3, which further comprises the step of utilizing at least part ofthe oil-free solids from step (6) as at least part of the fuel for supplying heatfor heat evaporation step (2).

12. A process according to claim 3, wherein said lightfluidizing oil is a hydrocarbon oil boiling in the range of about 1 62"C (325"F) to about 204"C (400"F).

13. A process according to claim 12,wherein said light hydrocarbon fluidizing oil is Isopar H or Isopar L.

14. A process forthe recovery of residual oil from solids dehydrated in an oil medium and grossly deoiled comprising the steps of (1) admixing aqueous solids with a relatively non-volatile oil to obtain a mixture which will remain fluid and pumpable after the removal of the water content therefrom; (2) subjecting the resultant oil-containing mixtureto dehydration by heat evaporation to yield water vapour and a substantially anhydrous solids in oil slurry; (3) condensing said water vapour; (4) separating most of the relatively non-volatile oil from said solids in oil slurry; (5) substantially removing the residual nonvolatile oil from the resultant oil-laden solids by extraction with a relatively low viscosity light oil, and (6) bringing the resultant light oil-laden solids into direct contact with a hot, inert blowing gastherebyto remove said light oil from said solids by heat evaporation.

15. A process according to claim 14,wherein said hot, inert blowing gas is selected from the group consisting of gaseous products of combustion, nitrogen and carbon dioxide.

16. A process according to claim 15, wherein light oil vapour in effluent blowing gas is removed therefrom by condensation and added to the light oil used in extraction step (5), thereby being recycled through the process.

17. A process according to claim 16, wherein said blowing gas is selected from the group consisting of nitrogen and carbon dioxide.

18. Aprocessaccordingtoclaim 17,wherein effluent blowing as, after removal of light oil vapour therefrom, is reheated and recycled through the process as hot, inert blowing gas.

19. A process according to claim 16, wherein said blowing gas is gaseous products of combustion from a combustion apparatus outsidethesystem.

20. A process according to claim 14, wherein the heat evaporation step (2) is carried outattempera- tures within the range of about 21"C (70"F) to about 204"C (400"F).

21. A process according to claim 14, wherein said light oil-laden solids are brought into direct contact with inert blowing gas attemperatureswithin the range of from about 21 "C (70"F) to about 204"C (400"F).

22. A process according to claim 14,which further comprises the step of utilizing at least part ofthe oil-free solids from step (6) as at least part of the fuel for supplying heatforthe heat evaporation step (2).

23. A process according to claim 14,wherein said relatively low viscosity light oil used in extraction step (5) is a hydrocarbon oil boiling in the range of about 1 62"C (325"F) to about 204"C (400"F).

24. A process according to claim 23,wherein said light oil is Isopar H or Isopar L.

25. Apparatus for separating light oil from solids associated therewith, said apparatus comprising (1) a deoiler means to receive light oil-laden solids, (2) means for generating hot, inert blowing gas, (3) a conduit extending from said meansforgenerating hot, inert blowing gas to said deoiler means wherethrough mayflow hot, inert blowing gas to come into directcontactwith said light oil-laden solids within said deoiler means, and (4) a venting means extending from said deoiler means wherethrough may flow effluent inert blowing gas containing light oil vapour.

26. Apparatus according to claim 25, including condenser means and a conduit extending from said deoiler means to said condenser means wherethrough mayflow effluent inert blowing gascontaining light oil vapour.

27. Apparatus for recovering clean water and substantially dry, fluidizing oil-free solids from aqueous solids dehydrated in a lightfluidizing oil medium, said apparatus comprising (1) atankto receive a stream of said aqueous solids and provided with a stirring or mixing mechanism, (2) a light fluidizing oil reservoir, (3) meansfortransmitting light fluidizing oil from said light oil reservoir to said tank wherein said fluidizing oil and aqueous solids may be mixed, (4) an evaporator, (5) a conduit extending from said tank to said evaporatorwherethrough mayflow a stream of aqueous solids admixed with lightfluidizing oil from said tank into the evaporating region of said evaporator, (6) a condenser, (7) a conduit extending from said evaporatorto said condenser through which may flow a mixture ofwatervapour and light oil vapour formed as a result of heating of said aqueous solids and lightfluidizing oil mixture, (8) an oil-water separating means, (9) a conduit extending from said condensertosaid oil-water separating means wherethrough mayflow a mixed condensate of water and light oil, (10) means for separately withdrawing light oil and clean water from said oil-water separating means, (11) a conduit extending from said withdrawing means to said lightfluidizing oil reservoir wherethrough mayflow a stream of light oil, (12) a liquid-solid separating means, (13) a conduit extending from said evaporatorto said liquid-solid separat ing meanswherethrough mayflowa stream of a slurry ofsubstantiallyanhydrous solids in light fluidizing oil, (14) a deoiler means, (15) a conduit extending from said liquid-solid separating means to said deoiler means wherethrough mayflow a stream ofsolidscarrving residual lightfluidizing oil, (16) a conduit extending from said liquid-solid separating means to said lightfluidizing oil reservoir wherethrough mayflowa stream of light oil, (17) means for generating hot, inert blowing gas, and (18) a conduit extending from said means for generating hot, inert blowinggastosaiddeoilermeanswherethrough may flow a stream of hot, inert blowing gas to come into direct contactwith said solids carrying residual light fluidizing oil in said deoiler means.

28. Apparatus according to claim 27, wherein said meansforgenerating hot, inert blowing gas is a combustion apparatus associated with said evapor atorand said deoilermeansforsupplyingevaporative heattosaidevaporatorand hot, inert blowing gasto come into direct contact with said solids carrying residual lightfluidizing oil in said deoiler means.

29. Apparatus according to claim 28, wherein said combustion apparatus associated with said evaporator and said deoiler means comprises a boiler furnaceforthegeneration of steam and hot, inert blowing gas and wherein furtherthere are conduit means extending from said boiler4urnaceto said evaporatorwherethrough heating steam may flow from said boiler-furnace to said evaporator and conduitmeans extending from said boiler-furnaceto said deoiler means wherethrough hot, inert blowing gas mayflowfrom said boiler-furnaceto said deoiler means.

30. Apparatus according to claim 29,wherein said hot, inert blowing gas is gaseous products of combus tionfrom said boiler-furnace.

31. Apparatus according to claim 30, wherein the conduit extending from said boiler-furnace to said deoiler means is fitted a fan to facilitate movement of the hot, inert blowing gas through said conduit.

32. Apparatus according to claim 29, including a heat exchanger having a first and a second end disposed within the heating zone of said boilerfurnace, said heat exchanger being connected at the first end thereof to be conduit extending from said boiler-furnace to said deoiler means; a condenser; a conduit extending from said deoiler means to said condenserwherethrough mayflow a stream of effluent blowing gas containing light oil vapour; means connecting said condenserwith said light fluidizing oil reservoirwherethrough light oil vapour condensate may be returned to said reservoirfor re-use asfluidizing oil; and a conduit extending from said condenser to the second end of said heat exchangerwherethrough mayflow a stream of effluent blowing gas from which the light oil vapour has been removed.

33. Apparatus according to claim 32, wherein the conduitextending from said boiler4urnacetosaid deoiler means is fitted with a fan to facilitate movementofthe hot, inert blowing gas through said conduit.

34. Apparatus according to claim 27, wherein said meansforgenerating hot, inert blowing gas is a combustion apparatus not otherwise associated with the system.

35. Apparatus for recovering clean water and dry, essentially oil-free solids from aqueous solids dehydrated in a non-volatile oil medium, said apparatus comprising (1) a tank to receive a stream of said aqueous solids and provided with a stirring or mixing mechanism, (2) a non-volatile oil reservoir, (3) means for transmitting non-volatile oil from said oil reservoir to said tank wherein non-volatile oil and aqueous solids may be mixed, (4) an evaporator, (5) a conduit extending from said tankto said evaporatorwherethrough mayflow a stream of aqueous solids admixed with non-volatile oil from said tank into the evaporating region of said evaporator, (6) a condenser, (7) a conduit extending from said evaporatorto said condenserthrough which mayflowwatervapour formed as a result of heating of said aqueous solids and non-volatile oil mixture, (8) meansforwithdraw ingwatervapourcondensatefrom said condenser as a clean water product, (9) a liquid-solid separating means, (10) a conduit extending from said evaporator to said liquid-solid separating means wherethrough mayflow a stream of a slurry of substantially anhydrous solids in non-volatile oil, (11) a light oil reservoir, (12) a conduit extending from said light oil reservoirto said light-solid separating means wherethrough mayflow a stream of light oil from said reservoirto said liquid-solid separating means wherein said light oil may extract residual non-volatile oil remaining on said solids afterseparation of nonvolatile oil therefrom, (13) a deoiler means, a conduit extending from said liquid-solid separating means to said deoiler means wherethrough may flow a stream of light oil-laden solids, (15) meansforgenerating hot, inert blowing gas, and (16) a conduit extending from said means for generating hot, inert blowing as to said deoilermeanswherethroughmayflowastream of hot, inert blowing gastocomeintodirectcontactwith said light oil-laden solids in said deoiler means.

36. Apparatus according to claim 35, wherein said meansforgenerating hot, inertblowing gas is a combustion apparatus associated with said evapor atorandsaiddeoilermeansforsupplying evaporative heatto said evaporator and hot, inert blowing gas to come into direct contact with said light oil-laden solids in said deoiler means.

37. Apparatus according to claim 36, wherein said combustion apparatus associated with said evaporator and said deoiler means comprises a boiler furnaceforthegeneration of steam and hot, inert blowing gas and wherein furtherthere are conduit means extendingfrom said boiler-furnaceto said evaporatorwherethrough heating steam mayflow from said boiler-furnace to said evaporator and conduit means extending from said boiler-furnaceto said deoiler means wherethrough hot, inert blowing gas may flow from said boiler-furnace to said deoiler means.

38. Apparatus according to claim 37, wherein said hot, inert blowing gas is gaseous products of combustion from said boiler-furnace.

39. Apparatus according to claim 38, wherein the conduit extendingfrom said boiler-furnaceto said deoiler means is fitted with a fan to facilitate move mentofthe hot, inert blowing gas through said conduit.

40. Apparatus according to claim 37, including a heat exchanger having a first and a second end disposed within the heating zone of said boilerfurnace, said heat exchanger being connected at the first end thereof to the conduit extending from said boiler furnace to said deoiler means; a condenser; a conduit extending from said deoiler means to said condenserwherethrough mayflowa stream of effluent blowing gas containing light oil vapour; means connecting said condenser with said light oil reservoirwherethrough light oil vapour condensate may be returned to said reservoirfor re-use to extract residual non-volatile oil from said solids; and a conduit extending from said condenserto the second end of said heat exchanger wherethrough may flow a stream of effluent blowing gas from which the light oil vapour has been removed.

41. Apparatus according to claim 40, wherein the conduit extending from said boiler-furnace to said deoiler means is fitted with a fan to facilitate move ment ofthe hot, inert blowing gas through said conduit.

42. Apparatus according to claim 35, wherein said meansforgenerating hot, inert blowing gas is a combustion apparatus not otherwise associated with the system.

43. Aprocessforthe separation of light oil from solids associated therewith as claimed in claim 1 and substantially as hereinbefore described.

44. Apparatus for separating light oil from solids associated therewith substantially as hereinbefore described and illustrated with reference to the accompanying drawings.