CA1223834A - Recovery of bitumen and separation of solids from middlings and tailings associated with the hot water process - Google Patents

Abstract

Abstract The invention provides a method to remove bitumen from tailings ponds of a Hot Water Separation plant by dispersing an activated carbon gel in the tailings sludge and thereby forming a bitumen froth that can be processed in the conventional manner. After the removal of the bitumen, the remaining waste water containing relatively large amounts of suspended clay and relatively small amounts of silt can be separated into solids and clear water by conventional sedimentation-flocculation- and filtration techniques.

The invention may be adapted to remove quantitatively the rest-amounts of bitumen left after the secondary recovery stage and thus form an additional step in the Hot Water Process and thereby avoid the formation of tailings sludge to be contained in ever increasing sludge ponds.

Description

~223a34 The present invention relates to an improvement to a process wherein hydrocarbons are extracted from tar sands.
More in particular, the invention is concerned with the treatment of process and/or effluent streams of the Hot Water Extraction Process that contain relatively small amounts of hydrocarbons together with relatively large amounts of finely divided inorganic matter in aqueous su~pensions.
Bitumenous sands are also known as tar sands or oil sands. The largest known deposit of oil sands are the Athabaska ûil Sands of Northern Alberta, where oil sands underlay an area of approximately 13,000 square miles and are estimated to contain recoverable reserves in excess of 300 billion barrels of oil.
Many methods for effecting the separation of oil from these sands were investigated by private operators, corporations, and governmental research agencies. To this date, only two large scale installations with a combined capacity of about 180,000 bbls/day are in operation and both installations use the Hot Water Washing Method as developed by the Alberta Research Council under K.A. Clark (see Canadian Oil and Gas Industries 3 46 [1950]). A more detailed description of this process incorporating many improvements essential for commercial operation can be found in Canadian Patent 841581, issued May 12, 1970 to Floyd et al.
The Composition of the Athabaska Tar Sands varies considerably and can contain:
5-21% ûil and 1-10% Water, the balance being inorganic solid matter comprising sand, silt and clay.
This specification defines silt as siliceous material smaller than 325 mesh and larger than 2 microns. Clay consists of material smaller ~223834 than 2 microns and may also contain some silicious material. Clay and silt rnay comprise up to 50% of the inorganic solid matter, the balance being sand larger than ~25 mesh.
In the Hot Water Method, the tar sands are mulled with sufficient hot water having a temperature of from 75 to 85 degrees centigrade, to form a pulp which is introduced into a stream of hot water and carried to a separation cell maintained at the same elevated tempera-ture In the separation cell sand settles to the bottom and the oil rises to the top in the form of a froth. Silt, clay and a minor amount of oil stay in suspension in a so-called middlings layer. A portion of the middlings is removed to a flotation-scavenger step where by further agitation and the introduction of an air stream an additional amount of oil is recovered in the form of a froth and combined with the froth recovered from the separation cell. The oil-lean middlings stream is partly recycled to the pulp forming step at the beginning of the process and the remainder becomes part of the plant effluent.
The amount of the middlings stream that can be recycled is limited, since a build-up of fines (silt and clay) in the system affects the formation of primary oil froth in the separation cell and the recover-ability of secondary oil froth from the scavenger cell. Another variable governing the amount of the middlings stream that can be recycled is the composition of the mined tar sand that is being pro-cessed. In cases in which tar sands with a high content of fines are processed, hardly any recycling of middlings water is possible without disturbing the performance of the primary separation cell.
The fines that are discharged with the effluent from a Hot Water process are associated with a small amount of oil. During the pro-cessing of the oil sands, the process streams that eventually make ~223834 up the effluent and consist of water, silt, clay and oil become emul-sified and some of the solids suspended in such a way as to keep settling even after several years to minimal amounts of solids.
A typical effluent stream is said to contain about 55% solids and from ~.5 to 2% oil or biturnen, the balance comprising process water.
The 55% solids are made up of 45% sand and the major part of the silt and 1û% of clay with a small amount of silt. The mixture of clay, the small amount of silt, water and oil is retained in settling ponds since environmental considerations prohibit their discharge.
Actually, relatively little settling of solids is achieved in the settling or sludge ponds. For a detailed description of sludge ponds reference is made to C.P. 1,021,281 issued Nov. 22, 1977 to John E. Ashton and H. James Davitt.
The object of the invention is an improvement to the Hot Water Process whereby the effluent stream can be separated into oil froth, water and clay. A further object is the working-up of old sludge that is presntly being stored in sludge ponds and the recovery of its bitumen values.
The prior art has attempted to solve the sludge problem by the use of various settling techniques, filtering methods, flocculation, centrifuging, precipitation and any combination of these operations.
Canadian Patent 824,968 issued October 14, 1969 to R.A. Baillie teaches the reduction of sand, silt and clay from the effluent by percolating the effluent downwardly through an inclined sand pile zone into a settling pond.
In Canadian Patent 873,317 issued June 15, 1971, R.A. Baillie and E.w. Malmberg teach the reduction of clay in the effluent of ~223834 a Hot Water Plant by the use of a combination Flocculation -Centrifuging process.
A Flocculation and Vacuum pre-coat Filtration is disclosed and claimed in Canadian Patent 892,548, issued February 8, 1972 to P.S.
Hepp and F.W. Camp.
Canadian Patent 926,797 issued May 22, 1973, to W.J. Lang and D.A. Hentz claims a flocculation process using a specific flocculant.
Canadian Patent 975,697 issued October 7, 1975 to H. James Davitt teaches a method for the recovery of bitumen from sludge, wherein the sludge from a retention pond is aerated, retained in a settling zone and a bitumen froth layer is recovered.
Canadian Patent 1,003,776 issued January 18, 1977 to R. Schutte describes a process wherein middlings and/or tailings are clarified by introducing sulphuric acid into the middlings and/or tailings water to cause them to flocculate and then allowing the water in contact with the flocs to recover to a neutral pH.
Canadian Patent 1,021,281 fully identified supra discloses a method for storing sludge, including flocculation in a confined area within a retention pond having a surface layer of substantially un-polluted water containing dissolved flocculant. The presence offlocculant in the unpolluted surface layer suppressed the intrusion of sludge from lower layers.
I have now found that it is possible to remove the remaining relatively small amounts of oil or bitumen from effluent streams or sludges discharged from a tar sand separation process wherein the oil or bitumen is colloidally dispersed together with mineral matter in water having a solids content of from 5-60% by dispersing . ~
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1:~23834 in the effluent or sludge Activated Carbon Gel. The activated carbon gel provides ultra fine wetted activated carbon particles that cause flocculation of the oil when mixed with the effluent to form a froth together with the carbon that can be skimmed off the surface. For practical purposes the removal of the oil appears to be quantitatively and the remaining oil-free sludge can now be processed and is easily removed by sedimentation, followed by standard separation procedures, such as flocculation and filtering.
A substantial amount of water in clear, blank and colourless condition is recovered by sedimentation alone after a period of 2 - 3 hours. The amount is governed by the solid content of the sludge that is being treated and can reach up to 50% or more.
The activated carbon gel used for practicing the invention can be procured from TATE & LYLE, Process Technology, 55 Liddon Road, Bromley, BRl 25R, England.
The activated carbon gel as supplied by Tate & Lyle, has the consistency of a smooth paste and contains approximately 20% carbon and 80% water. The paste differs from a paste made from activated carbon powder and water in that the water content cannot be reduced by mechanical means, e.g. centrifuging or filter pressing. Wnen handling the paste, care must be taken to avoid loss of water due to accidental heating or drying out, since upon drying and the loss of a minor amount of water, the carbon becomes inactive and loses its adsorptive capabilities and the capability to flocculate the oil from the effluent. Simple rehydration of the carbon will not restore the properties lost during de-hydration. The change of the absorption characteristics of the carbon cannot readily be explained.

~223834 It is known that certain activated carbons change or lose some of their absorptive power upon drying. (HASSLER, Active Carbon, 1951 edition, Chemical Publishing Company Inc., N.Y., page 355). However, the term "Drying" as used by Hassler is understood to remove moisture by heating to between 105 and 120 degrees centigrade of activated carbons that usually contain up to 10% moisture. The carbon gel used in practicing the invention starts to lose its activity as soon as the water content is reduced from 80% to below 75%. Tne carbon gel also differs from the known "Noir Animal en Pâte" a bone char that is produced and marketed in France with a moisture content of up to 80% and used in the wine industry to beautify certain white wines by the removal of red colour. These carbons also lose their activity upon drying and cannot be reactivated by rehydration, however the loss of activity appears only when water is removed by heating to between 105 and 120 degrees centigrade, whereas moisture can be removed by filterpressing without any changes in the adsorptive properties.

Description of the Invention The present invention represents an improvement to the Hot Water Process and in addition provides a method to work up old tailings presently stored in ever increasing sludge ponds.
The essence of the invention consists in dispersing an activated carbon gel in a mixture comprising water, clay silt and oil or bitumen.
The mixture into which the gel of activated carbon is to be dispersed can either be a process stream of a Hot Water process leading to a secondary recovery unit, or an effluent stream from a Hot Water process or it may be material that is contained in a sludge pond.

' ~223834 The effluent stream as well as the material from the pond contain a small amount of bitumen that escaped the extraction process. This small amount of bitumen, generally 1 - 2% becomes emulsified during the e~traction process and prevents the clay and some of the silt ~rom settling and prohibits discharge to the environment. Furthermore, the presence of the bitumen ma~es the removal uf clay and some silt with the presently known treatment methods virtually impossible.
However, once the bitumen is removed, the filterability oF the remaining sludge upon treatment with conventional methods is increased to an extent that in laboratory tests it is possible to filter it out over a "Whatman" No. 3 Filter paper. Depending on the solids content of the sludge that has been treated with the Activated Carbon a considerable amount of water can be recovered by leaving the floc-culated sludge to settle for about 2 - 3 hours. The filter cake consisting of clay and silt and some flocculant hardens upon air drying to a hard, brittleimass, that ~Lll not soften ~pon wetting.
Samples of dried filter cake remained firm after storage of three months under water.
The raw sludge used in my experiments was obtained from a storage pond and contained 40% suspended matter as determined by air drying at 105 degrees centigrade to constant weight. This sludge as taken from a storage pond is quite viscous and the dispersion of the activated carbon gel would require an undue amount of energy. It is, therefore, advisable to dilute the sludge with water that is recovered from a later process step.
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The invention, therefore, is applicable in the treatment of ~ ~ middlings water and in the treatment of sludge from tailings ponds.
- ; The amount of activated carbon gel required to effect quantitative ~ , 1 2~3834 removal of the bitumen from the middlings water and/or sludge depends upon the type of sand that is being processed and on the degree of dispersion that can be achieved upon introduction of the carbon.
It also depends on the stability of the oil-water-clay-emulsion-suspension. The main factor governing the rate of application of the activated carbon gel and at which the oil removal is most efficient depends on the oil content of the middlings water and/or sludge.
The sludge used in my experiments had an oil content of 3%. At an oil content of this magnitude it was established that the application of at least ~% b.wt. of carbon based on the weight of oil or bitumen is required to effect flocculation and about 1% results in practically complete removal of the oil or bitumen.
If it is desired to treat a middlings water stream the activated carbon gel may be added close to and before this stream enters a centrifugal pump to assure adequate dispersion of the carbon. Sludge can be processed in the same way; however, since its solid content is up to 1û times that of middlings water, it is advantageous to reduce the solids content by diluting the sludge with a part of the water that is recovered from a leter step of the process of the in-vention. The degree of dilution is not critical, for practical purposes one could add an approximate amount of water to bring the solids content of the sludge close to the solids content of the middlings water that is being processed at the time. This manner of processing would permit the same water treatment plant, e.g., filtration equipment ; and equipment required to effect flocculation etc., to handle both the solids from middlings water and the solids recovered from sludge.
Dilution ratios from .5:1 to 4:1 are also operable. While there is no upper limit to which sludge might be diluted, it is in the interest of efficiency that one would operate with the least amount of dilution in order to dispose of the maximum amount of water.
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It is important that the activated carbon gel is completely dispersed. Dispersion of the activated carbon gel in the water to be used for the dilution of the sludge is facilitated by slurrying the activated carbon gel in the water that is used to dilute the sludge. Froth formation starts immediately after the addition of the activated carbon. The time required for the froth to rise to the surface of a treatment zone can be shortened by an air flotation operation. The froth can be processed together with the primary froth.
After the removal of the oil and/or bitumen the remaining suspen-sion of clay and silt will respond to conventional water treatment techniques. At this stage of the process it can be observed that a small amount of almost white silt will settle out after about 3û
minutes retention in a quiescent zone. The clay will remain in sus-pension and can be filtered or is advantageously subjected to floccula-tion. The flocculating ayent used is not critical. Examples of flocculating agents are: aluminum sulfate (alum); polymers of acrylic or methacrylic acid derivatives such as acrylic acid, methacrylic acid, the alkali and ammonium salts, aminoalkyl acrylamides.
After flocculation, water may be recovered by filtration, or that part of the water required for diluting the sludge can be drawn off the surface layer and the balance of sludge, flocculating agent and water is subjected to filtration.
Essentially, the process of the present invention as applied to the treatment of sludge from a hot water process comprises:
(a) Feeding retention pond sludge into a treating zone wherein water is added to decrease the solids content of the sludge to about ~ ; ~ or less of its original value and disperse an activated carbon "~

i223834 gel therein in an amount that supplies 0.5% of activated carbon based on the weight of hydrocarbons or bitumen contained in that sludge.
(b) Separating carbon containing oil or bitumen froth from the top of said treating zone.
(c) Separating silt from the bottom of said treating zone.
(d) Adding a flocculating agent.
(e) Recovering clear water and recycling amount required to step (a) and (f) Filtering the sludge and recovering the balance of the water for re-use in the hot water process.
Should the sludge as obtained from a pond contain lighter hydro-carbons that were lost in the treatment of the primary froth of the hot water plant, these hydrocarbons will also flocculate with the activated carbon and will be removed with the bitumen froth.

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Claims (9)

Claims:

1. A process for recovering bitumen and clear water from aqueous waste associated with a hot water process for extracting bitumen from tar sand comprising:
(a) adding to and dispersing in said aqueous waste an amount of activated carbon gel corresponding to at least ?% of carbon based on amount of' bitumen contained in said waste, (b) recovering a layer of froth from the surface of and (c) filtering and recovering clear water from the balance of the said waste.

2. The process of claim 1 wherein said aqueous waste is the effluent from a flotation scavenger zone of a hot water process.

3. The process of claim 1 wherein said aqueous waste is from a tailings pond.

4. A process for recovering bitumen and clear water from aqueous waste associated with a hot water process for extracting bitumen from tar sand comprising:
(a) diluting said aqueous waste with water recovered from step (d) in a ratio ranging from .5 to 1 to 4 to 1, (b) dispersing in said diluted aqueous waste an amount of activated carbon gel corresponding to at least ?% of carbon based on the amount of bitumen contained in said waste, (c) recovering a layer of bitumen froth from the surface of said waste and (d) filtering and recovering clear water as a filtrate and recycling that part of the water required in step (a).

5. The process of claim 4 wherein a flocculating agent is added between steps (c) and (d).

6. The process of claim 5 wherein a layer of silt is recovered from said waste before the flocculating agent is added.

7. A process for recovering bitumen and clear water from a mixture comprising water, clay, silt and bitumen comprising:
(a) adding to and dispersing in said mixture an amount of activated carbon gel corresponding to at least ?% of carbon based on the amount of bitumen contained in said mixture, (b) recovering a layer of froth from the surface of said mixture and (c) filtering and recovering clear water from the balance of said mixture.

8. The process of claim 7 wherein said mixture is the effluent from a flotation scavenger zone of a hot water process for extracting bitumen from tar sand.

9. The process of claim 7 wherein said mixture is from a tailing pond associated with a hot water process for extracting bitumen from tar sand.