US3751358A - Freeze-thaw separation of solids from tar sands extraction effluents - Google Patents

Abstract

THIS SPECIFICATION DISCLOSES TREATMENT OF WATER DISCHARGED FROM A HOT WATER PROCESS FOR SEPARATING BITUMEN FROM TAR SANDS. THE TREATMENT COMPRISES AGGLOMERATING CLAY DISPERSED IN THE WATER, ALTERNATELY FREEzING AND THAWING THE WATER INTO A SLUDGE LAYER AND A CLARIFIED WATER LAYER. THE CLARIFIED WATER LAYER IS SUBSTANTIALLY REDUCED IN CLAY CONTENT COMPARED TO THE WATER DISCHARGED FROM THE HOT WATER PROCESS AND IS SUITABLE FOR RECYCLE OR DISCARD.

Description

Aug. 7, 1973 o. M. ELLIOTT 3,751,358

FREEZE-THAW SEPARATION OF SOLIDS FROM TAR SANDS EXTRACTION EFFLUENTS Filed Jan. 19, 1972 United States Patent 3 751,358 FREEZE-THAW SEPAitATION OF SOLIDS FROM TAR SANDS EXTRACTION EFFLUENTS Orrin M. Elliott, Media, Pa., assignor to Great Canadian Oil Sands, Limited, Toronto, Ontario, Canada Filed Jan. 19, 1972, Ser. No. 219,039

Int. Cl. Cg 1/04 U.S. Cl. 208-41 14 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process for clarifying water discharged from a hot water process for separating bitumen from tar sands. It has been found that agglomeration followed by freezing and thawing can be applied to clay and silt containing water discharges to produce a clarified water suitable for recycle as at least a portion of the feed water to the hot water process.

Numerous deposits of bituminous tar sands exist throughout the world. The most extensive deposits are found in northern Alberta, Canada. The sands are composed of a siliceous materials, generally having a size greater than that passing a 325 mesh screen, saturated with a relatively heavy, viscous bitumen in quantities of from 5 to 21 weight percent of the total composition. More typically, the bitumen content of the sands is between about 8 to 15 percent. This bitumen is quite viscous and contains typically 4.5 percent sulfur and 38 percent aromatics. Its specific gravity at 60 F. ranges typically from about 1.00 to about 1.06. The tar sands also con tain clay and silt. Silt is defined as mineral which will pass a 325 mesh screen but which is larger than 2 microns. Clay is mineral smaller than 2 microns including some siliceous material of that size.

There are several well-known processes for effecting separation of bitumen from the tar sands. In the hot water method, the bituminous sands are jetted with steam and mulled with a minor amount of hot water at temperatures in the range of 140 to 210 F. The resulting pulp is conducted to a sump where it is diluted with additional hot water and carried to a separation cell maintained at a temperature of about 150 to 200 F. In the separation cell, sand settles to the bottom as tailings and bitumen rises to the top in the form of an oil froth. An aqueous middlings layer containing some mineral and bitumen is formed between these layers. A scavenger step may be conducted on the middlings layer from the primary separation step to recover additional amounts of bitumen therefrom. This step usually comprises aerating the middlings as taught by K. A. Clark, The Hot Water Washing Method, Canadian Oil and Gas Industries 3, 46 (1950). These froths can be combined, diluted with naphtha and centrifuged to remove more water and residual mineral. The naphtha is then distilled off and the bitumen is coked to a high quality crude suitable for further processing.

The water discharged from the hot water process must be stored, disposed of or recycled back into the process. Because this water contains bitumen emulsions, finely dispersed clay with poor settling characteristics and other contaminants, water pollution considerations prohibit discarding the water into rivers, lakes or other natural bodies of water. It has been proposed that the water be stored in evaporation ponds but this proposal would involve large space requirements and the construction of expensive enclosure dikes. It has also been suggested that the water in the effluent discharge be recycled back into the process as an economic measure to conserve both heat and water. Canadian Pat. 841,581, issued May 12, 1970 to Floyd et al., teaches that some of this water can be so recycled but that the amount of recycle is limited by the dispersed silt and clay content of the water which can reduce froth yield by increasing the viscosity of the middlings layer and retarding the upward settling of bitumen flecks. A proportion of water in the diluted tar sands pulp fed into the separation cell must therefore be fresh waterwater which is substantially free of the clay and silt found in middlings water. In fact, with some high clay content tar sands feeds, all of the water in the diluted pulp must be added as fresh water.

It has been found that water discharged from the process containing silt and clay can be made suitable for recycle as at least a portion of the hot water process water feed by treating the discharge according to a method of agglomeration, freezing, thawing and filtration as described herein. It is known that agglomeration by means such as flocculation, even with extended settling, cannot be used to clarify water from a hot water process. Flocculation-settling produces sludges of less than 10 weight percent solids from pondwater. It has been found by the present invention that agglomeration such as by flocculation, freezing and thawing produces solids compaction of greater than 10 weight percent solids up to about 30 weight percent. It has also been found that proper agglomeration of the pondwater must be combined with the freezing and thawing steps. Freezing and thawing alone will not produce a stable compacted sludge of more than 10 weight percent solids.

Although the present invention is not to be bound by theoretical explanation, it is believed that the freezing and thawing sequence causes solids compaction by concentration and compression of the clay agglomerates during the freezing step followed by settling of the larger and more dense agglomerates in the thawing step.

When pondwater is treated with an acid, or salts, the clay agglomerates. As freezing of the agglomerated clay slurry proceeds, ice crystals are formed thus compacting the clay among these crystals. This compaction continues until the sample is frozen solid. Upon thawing, the compacted agglomerates settle to the bottom of the container. Visual observation of the frozen treated pondwater has shown the existence of the two phases. The phases are randomly formed throughout the sample, one being clear; the other opaque. This fact suggests that a clear liquid phase and a sludge phase are being formed in the freezing step of the operation. Another fact which is consistent with this concept is the relative size distribution of solids in pondwater before and after treatment by the freezthaw cycle. The mechanism postulated above would predict that the particle sizes in the treated pondwater would be larger because of the concentration and compression of the solid during the process.

For the purpose of the present specification the term pondwater is defined as eflluent discharge from a hot water process which efiluent has been settled to give a composition comprising water containing up to about 20 percent solids, between to percent of which is fine clay of a size smaller than 2 microns. The effluent discharge from a hot water process comprises middlings material of depleted bitumen content which has undergone final treatment, the sand tailin-gs layer from the process and other discharged water-containing fractions which are not the primary products of the hot water process. The discharge is removed from the process area as a slurry of about 25 to 60, typically 45, percent solids by weight. The effiuent contains virtually all of the clay material which was present in the feed. Typically, the amount is 2 to 10 weight percent of the feed. This material is smaller than 2 microns and has extremely poor settling characteristics.

The present invention is describable as an improvement to the hot Water process for treating bituminous tar sands in which the hot water process comprises forming a mixture of tar sands and water, passing the mixture into a separation zone to form an upper bitumen froth layer, a middlings layer comprising water, finely divided mineral and bitumen and a sand tailings layer. The improvement comprises agglomerating finely divided minerals of at least a portion of the middlings, freezing the portion containing agglomerated finely divided minerals, thawing the portion and recovering from said thawed portion a lower sludge layer characterized by a substantially increased mineral content compared to the middlings portion and an upper clarified water layer substantially reduced in mineral content and suitable for recycle back into the hot water process as at least a portion of the water utilized to form the mixture of tar sands and water.

The present invention can be described in more detail with reference to the drawing which shows the present improvement in combination with a preferred embodiment of the hot water process.

In the figure, bituminous tar sands are fed into the system through line 1 where they first pass to a conditioning drum or muller 3. Water and steam are introduced from 2 and mixed with the sands. The total water so introduced is a minor amount based on the weight of the tar sands processed and generally is in the range of 10 to 45 percent by weight of the total mixture. Enough steam is introduced to raise the temperature in the conditioning drum to within the range of 130 to 210 F. and preferably to above 170 F. Monovalent alkaline reagents can also be added to the conditioning drum, usually in amount of from 0.1 to 3.0 pounds per ton of tar sand. The amount of such alkaline reagent preferably is regulated to maintain the pH of the middlings layer in separator zone 12 within the range of 7.5 to 9.0. Best results are obtained at a pH value of 8.0 to 8.5. The amount of the alkaline reagent that needs to be added to maintain a pH value in the range of 7.5 to 9.0 may vary from time to time as the composition of the tar sands as obtained from the mine site varies. The best alkaline reagents to use for this purpose are caustic soda, sodium, carbonate or sodium silicate, although any of the other monovalent alkaline reagents can be used if desired.

Mulling of the tar sands produces a pulp which then passes from the conditioning drum as indicated by line 4 to a screen indicated at 5. The purpose of screen 5 is to remove from the tar sand pulp any debris, rocks or oversized lumps as indicated generally at 6. The pulp then passes from screen 5 as indicated by 7 to a sump 8 where it is diluted with additional water from 9 and a middlings recycle stream 10. In the event the clay content of the tar sands is high, a relatively high rate of fresh or treated feed water introduction through 9 can be employed to compensate for the high clay introduction while a correspondingly high rate of transfer of middlings layer through line 15 as hereinafter described can be maintained. Under these circumstances recycling of of the other stream of middlings through line 10 to the sump is not required.

Modifications that may be made in the process as above described include sending a minor portion of the middlings recycle stream from line 10 through a suitable line (not shown) to the conditioning drum 3 to supply all or a part of the water needed therein other than that supplied through condensation of the stream which is consumed. Also, if desired, a stream of the middlings recycle can be introduced onto the screen 5 to flush the pulp therethrough and into the sump. As a general rule, the total amount of water added to the natural bituminous sands as liquid water and as steam prior to the separation step should be in the range of 0.2 to 3.0 tons per ton of the bituminous sands. The amount of water needed within this range increases as the silt and clay content of the bituminous sand increases. For example, when 15 percent by weight of the mineral mattter of the tar sands has a particle size below 4-4 microns, the fresh water added generally can be about 0.3 to 0.5 ton per ton of tar sands. On the other hand, when 30 percent of the mineral matter is below 44 microns diameter, generally 0.7 to 1.0 ton of water should be used per ton of tar sands. Correspondingly the amount of bitumen-rich middlings removed through line 15 will vary depending upon the rate of fresh water addition. As a general rule, the rate of withdrawal of bitumen-rich middlings to scavenger zone 16 will be 10 to 75 gallons per ton of tar sands processed when 15 percent by weight of the mineral matter is below 44 microns and to 250 gallons per ton when from 25 to 30 percent of the mineral is of this fine particle size.

Further following the process, the pulped and diluted tar sands are pumped from the sump through line 11 into the separation zone 12. This zone comprises a cell which contains a relatively quiescent body of hot water. In the cell, the diluted pulp forms into a bitumen froth layer which rises to the cell top and is withdrawn via line 13 and a sand tailings layer which settles to the bottom to be withdrawn through line 14. An aqueous middlings layer between the froth and tailings contains silt and clay and some bitumen which failed to form froth. In order to prevent the buildup of clay in the system, it is necessary to continually remove some of the middlings layer and supply enough water in the conditioning operations to compensate for that so removed. The rate at which the middlings need to be removed from the system depends upon the content of clay and silt present in the tar sands feed and this will vary from time to time as the content of these fines varies. If the clay and slit content is allowed to build up in the system, the viscosity of the middlings layer will increase. Concurrently with such increase, an increase in the proportions of both the bitumen and the sand retained by the middlings will occur. If the clay and silt content is allowed to build up too high in the system, effective separation no longer will occur and the process will become inoperative. This can be avoided by regulating the recycling and withdrawal of middlings and input of fresh water per the invention disclosed and claimed in the Floyd et al. patent. However, even when the seperation step is operating properly, the middlings layer withdrawn through line 15 will contain a substantial amount of bitumen which did not separate. Hence the middlings layer withdrawn through line 15 is, for purpose of description, herein referred to as oil-rich or bitumenrich middlings.

The oil-rich middlings stream withdrawn from separator 12 through line 15 is sent to a scavenger zone 16 wherein an air flotation operation is conducted to cause the formation of additional bitumen froth. The processing conducted in the scavenger zone 16 involves air flotation procedures conventionally utilized in processing of ores. This involves providing a controlled zone of aeration in the flotation cell at a locus where agitation of the middlings is being effected so that air becomes dispersed in the middlings in the form of small bubbles. The drawing illustrates a flotation cell of the subaeration type wherein a motorized rotary agitator is provided and air is fed thereto in controlled amount. Alternatively the air can be fed in through the shaft of the rotor. The rotor effects entraining of the air in the middlings. This air causes the formation of additional bitumen froth which passes from the scavenger zone 16 through line 17 to a froth settler zone 18. A bitumen-lean middlings stream is removed from the bottom of the scavenger zone 16 via line 19.

In the settler zone 18, the scavenger froth forms into a lower layer of settler trailings which is withdrawn and recycled via line 20 to be mixed with bitumen-rich middlings for feed to the scavenger zone 16 via line 15. In

the settler zone, an upper layer of upgraded bitumen froth forms above the tailings and is withdrawn through line 21 and is mixed with primary froth in line 13. The combined froths are at a temperature of about 160 F. They are heated with steam and diluted with suflicient naphtha or 6 treated before recycle into sump 8 for dilution of the tar sands pulp.

The drawing shows the present invention applied to pondwater in a single zone. If desired the pondwater can be removed from the pond and agglomerated, frozen and other diluent from 22 to reduce the viscosity of the bi- 5 thawed and settled in separate zones. tumen for centrifuging in zone 23 to produce a bitumen The agglomeration step on the pondwater can be product 24 suitable for further processing. carried out by adding a convent onal agglomeratlng rea- The oil-lean middlings in line 19 and the sand tailings gent to th ater with gentle agltahom Among h vlanfrom the separation zone 12 are combined to form an ous reagents useful for agglomeratlng clay are sodium effiuent discharge which is delivered via line 25 to a sand and calcium chlorides, alumlnum sulfate (alum), poly- P Zone 26 Via distiibntion P p The eillnent alkylene oxides such as polyethylene oxide, compounds tains between 25 and 60 weight percent sand and silt maof calcium such as calcium hydroxide, calcium oxide, terial which is larger than about 2 microns. The distribucalcium chloride, calcium nitrate, calcium acid phosphate, tion p p Provides iiol continuous and uniform de l y calcium sulfate, calcium tartrate, calclum citrate, calcium f t eihnent to the send P Zones Where the sand and sulfonate, calcium lactate, the calcium salt of ethylene d1- silt material is deposited- The Water in the eillnent i amine tetraacetate and similar organic sequestering agents. charge percolates d through and over the sand P Also suitable are guar flour or a high molecular weight zone t0 the pond Z0116 28 where it collects 3S pOIldac ylamide olymer such as polyacrylam de or a co. Water containing n to about 12 Weight Percent suspended polymer of acrylamide and a copolymerizable carboxylic Solids, between 80 to 100 Percent of which is a tine clay acid such as acrylic acid. Additional flocculants include Of a size smaller than 2 microns. The pondwater also 6011- the polymers of acrylic or methacrylic acid derivatives tains between ab and Weight Peioent bitumenfor example, acrylic acid, methacrylic acid, the alkali Because of the Particnlar composition of this Pondwater, metal and ammonium salts of acrylic acid or methacrylic and especially because of the extreme fineness of the susid, i id methaeryiamide, h aminoalkyl aerypended y material which has extremely P settling lates, the aminoalkyl acrylamides, the aminoalkyl methoharaetetisties, the Water cannot be discarded to y acrylamides and the N-alkyl substituted aminoalkyl esters great extent recycled back into the hot water system. f ith acrylic o1- methacrylic acids. 1

The Present invention is pp to this p i Preferably agglomeration is accomplisehd by changing clarifying the Water y back to be mixed W the 30 the pH of the water. Variation of pH causes a change in Process sends ieed- Preferably the Process is e011 the charge on the edges of the clay particles, thus allowdnoted byintlodnoing agglomefating agents into the P ing agglomeration. The efiluent discharge from the hot Water followed y altefnetely freezing and thawing the water process has a pH ranging from about 7.5 to 9.0 Water in the P Zone- In the Present invention, typically about 8.3. In this range, the contained mineral creased solids compaction is obtained by one frezing-thawmaterial is not agg1emerate i i the pH above about ing cycle of agglomerated pondwater; however. it is p 9.0 or lowering it below about 7.5 causes agglomeration. ferred that the freezing and thawing be conducted in a More preferably, agglomeration in one acoomplurality of cycles since it has been found that the amount phshed by adding lf i acid (to the middlings or Of SOlidS compaction is a function of the number Of freezefluent discharge portion as the case may be) to about PH 5. thaw oyoles Petfonned- The freezing and thawing steps can be conducted by Through alternate ffeezings and thawing steps the P any means known in the art. Preferably however, freezing water settles into a sludge at the bottom of the pond and d thawing of h pondwater i conducted i the d sets a clarified water POI'tiOIl near the pond surface. The zone by dividing the zone into two areas, The first area sludge contains about 30 Weight Percent solids and the is allowed to freeze by exposure to ambient temperatures pondwater is reduced in solids content to the extent that it below 32 Water being discharged f om the distrihu. is suitable y Vie line 29 back to line 9 as a P tion pipes through the sand zone collects in a second pond tion of the Water used to form the nliXtnIe of Weter and area. During periods when the ambient temperatures are tar sands Passed into the separation Cell greater than 32 F., the clear clarified water from the The treated Water can be introduced Via line 29 into first area is discarded or recycled. The water in the second the system as all a Portion of the Water in line 9 to the area is diverted to the first along with current runofl? from snnlP as shown can be altetnetively introduced into the the distributed pipes. This pondwater is collected until system via lines 2 10 as a screen Wash at y again average ambient temperature falls below 32 F. tiesil'ed Point of introduction into the P Another approach is to alternatively add warm water Although the invention has been described p With at various ends of a frozen pond at certain intervals over reference to the treatment of Pendwater from the hot a period when the ambient temperature is below 32 F. water process effluent discharge, it should be pointed out Thi approach results i repeated free i and h i that the invention can be practiced on y Water stream settling cycles. Another method of conducting the freezfrom the Separation ceil- For example, referring again t ing-thawing-settling technique of the present invention is to the drawing, the bitumen-lean iddlings line 19 from circulate water from beneath frozen pondwater to the sure flotation cavenger Zone 16 can be directly treated by face of the ice accompanied by addition of additionl runthe invention to make these middlings suitable for recycle of]? w te either to beneath 0 onto th surface f h i back into the process. Also the middlings in line 10 can be The following examples illustrate the invention:

TABLE I Reagent dosage, Feed, wt. Sludge, pounds/1,000 gallons percent Wt. per- Reagent clay cent clay Clear Cloudy Note Anson 13:3 it; 1313 23?, FeCl 6. 5 13. 0 7.14 a. s @8012 123g 8' 2:? H H2804 "i 0: 23:2 if? g ifi None 6. 6.5

1 Intermediate dosages not tested. Clear" indicates sample settled Within 1 hour to produce clear supernatant. Oloudy" supernatants did not settle further within 1 week. Cloudy" supernatants contained 200 p.p.m. suspended solids (by visual inspection).

2 Supernatant settled clear within 48 hours.

Several freeze-thaw runs on pondwater from a hot water process for separating bitumen from tar sands are reported in Tables I and II. In Table I pondwater feeds of various weight percent clays were treated with various agglomerating agents, then frozen, thawed and settled and compared to an untreated sample. The results in Table I indicate that various agglomerating agents can be used in the present invention and that the process of the present invention is applicable to the clarification of pondwaters of various clay compositions.

The runs in Table II were made on pondwater containing 6.5 weight percent clay to determine the extent of sludge compaction for repeated freeze-thaw cycles. These runs show that it is possible to achieve compactions of 30 weight percent solids by using the process of the present invention.

TABLE II Weight percent solids in sludge Test 1, 5.05 Test 2, 5.05 Test 3, 13.8

pounds pounds pounds Freeze-thaw cycles HgSOq/LOOO HzSOq/LOUO A12(SO4)3/ completed gallons gallons 1,000 gallons The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. -In a hot water process for treating bituminous tar sands which comprises: forming a mixture of tar sands and water; passing said mixture into a separation zone to form an upper bitumen froth layer, a middlings layer comprising water, finely divided mineral and bitumen and a sand tail-ings layer; and separately removing said bitumen froth layer, middlings layer and tailings layer; the improvement which comprises:

(a) agglomerating finely divided mineral of at least a portion of the middlings;

(b) freezing the portion of middlings containing agglomerated finely divided mineral; I

(c) thawing the frozen middlings portion and (d) recovering from a thawed portion a lower sludge layer characterized by a substantially increased mineral content compared to said middlings portion and an upper clarified water layer substantially reduced in mineral content.

2. The process of claim 1 in which the agglomerating step comprises adding an agglomerating agent to agglomerate said mineral component.

'3. The process of claim 1 in which the agglomeration step comprises adjusting the pH of said middlings portion below about 7.5.

4. The process of claim 1 in which the agglomeration step comprises adjusting the pH of said middlings portion to above about 9.0.

5. The process of claim 1 in which said Water layer substantially reduced in mineral content is recycled back into the hot water process as at least a portion of the water utilized to form said mixture of tar sands and water.

6. The process of claim 1 in which said freezing and thawing steps are repeated.

7. The process of claim 1 in which said lower sludge layer of step (d) comprises greater than 10 weight percent solids.

8. In the hot water process for treating bituminous tar sands which comprises: forming a mixture of bituminous sands and water; passing the mixture to a separation zone to form an upper bitumen froth layer, a middlings layer comprising water, clay and some bitumen and a sand tailings layer; recovering said froth layer; and passing at least a portion of the middlings layer and tailings layer to a settling pond zone; the improvement which comprises:

(a) agglomerating the clay in at least a portion of the water contained in said settling pond zone;

(b) freezing said portion containing agglomerated fine- 1y divided mineral;

(c) thawing said frozen portion and (d) recovering from said thawed portion a lower sludge layer characterized by a substantially increased mineral content compared to said middlings portion and an upper clarified water layer substantially reduced in mineral content and suitable for recycle back into the hot water process as at least a portion of the water utilized to form said mixture of tar sands and water.

9. The process of claim 8 in which the agglomeration step comprises adding an agglomerating agent to agglomerate said mineral component.

10. The process of claim 8 in which the agglomeration step comprises adjusting the pH of said middlings portion below about 7.5.

11. The process of claim 8 in which the agglomeration step comprises adjusting the pH of said middlings portion to above about 9.0.

12. The process of claim 8 in which said water layer substantially reduced in mineral content is recycled back into the hot water process as at least a portion of the water utilized to form said mixture of tar sands and; water.

13. The process of claim 8- in which said freezing and thawing steps are repeated.

14. The process of claim 8 in which said lower sludge layer of step (d) comprises greater than 10 weight percent solids.

References Cited UNITED STATES PATENTS 3,526 ,5- 9/1970 Camp 208-11 3,314,881 4/1967 Tuwiner 2l060 CURTIS R. DAVIS, Primary Examiner US. Cl. X.R.

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