System and Integrated Method For Treatment of Tailings From Bitumen Extraction Process

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from Canadian Patent Application number 2,813,828 which was filed on Apr. 22, 2013, which is incorporated herein by reference.

FIELD

The present disclosure relates generally to the field of processing of mined oil sands. More particularly, the present disclosure relates to the treatment of tailings from a froth treatment process that generates tailings. More particularly, the present disclosure relates to the treatment of tailings from a paraffinic or a naphthenic froth treatment process.

BACKGROUND

Oil sands are deposits comprised of bitumen, clay, sand and connate water, and make up a significant portion of North America's naturally-occurring petroleum reserves. To produce a marketable hydrocarbon product from the oil sands, the bitumen must be recovered or extracted from the oil sands matrix. Depending on the reserve type, bitumen may be recovered by surface mining or in-situ thermal methods, such as steam assisted gravity drainage (SAGD), cyclic steam stimulation (CSS), vapor extraction process (VAPEX), liquid addition to steam for enhancing recovery (LASER) or derivatives thereof.

Because the bitumen itself is a tar-like, highly viscous material, separating it from the sands poses certain practical difficulties. An example of a common extraction technique is known as a water-based extraction process, where hot water, air, and typically process aides are added to crushed ore at a basic pH to form a slurry. An oil-rich froth “floats” or rises through the slurry as a hydrocarbon phase which can be skimmed off from the top of a separation vessel. The result is an extract that typically comprises two parts: a hydrocarbon phase known as a bitumen froth stream, made up of bitumen, water and fine solids, and an aqueous phase known as extraction tailings, made up of coarse solids, some fine solids, and water. The bitumen froth typically comprises bitumen (approximately 60% by weight), water (approximately 30% by weight), and solids (approximately 10% by weight), and must undergo a froth treatment process to separate the organic content from the water and solid contaminants. Due to its high viscosity, the first step is typically the introduction of a solvent, usually a hydrocarbon solvent such as naphtha or a paraffinic solvent. This step is known as froth separation, and helps to accelerate the separation of solid particles dispersed within the froth by increasing the density differential between the bitumen, water, and solids as well as reducing the viscosity of bitumen. Separation is carried out by any number of methods, such as centrifugation or gravity separation.

Paraffinic froth treatment is understood to have several advantages over naphtha-based treatment, as discussed in Canadian Patent Nos. 2,149,737 and 2,217,300. One example of a benefit is the partial rejection of asphaltenes: adding a paraffinic solvent to bitumen froth causes some of the asphaltene component of the bitumen extract to precipitate from the froth and consolidate with the solid components, such as minerals and clays. A further benefit of paraffinic froth treatment is that, as a result of the adsorption of water droplets and clays to the hydrophilic sites of the asphaltene molecules, the final bitumen product contains only a small amount of emulsified droplets and clay particles which can be sources of corrosion and catalyst poisoning. The details of one method of paraffinic froth treatment are set out in Canadian Patent No. 2,587,166 to Sury.

The result of the paraffinic froth treatment process is diluted bitumen and a second tailings stream, known as froth treatment tailings, made up of water, solids, and residual hydrocarbon (solvent, rejected asphaltenes, and un-recovered bitumen) which undergo further treatment to prepare the tailings for safe disposal. Dilution water is added to avoid foaming within the TSRU (described below) and also the blockage of associated tubings and internals. The first step in this further treatment is to recover solvent through any number of processes known collectively as tailings solvent recovery. Recovered solvent may then be reused in the froth separation process. Tailings from a tailings solvent recovery unit (TSRU), known as TSRU tailings, are then disposed of. Table 1 sets out an example of the composition of TSRU tailings:

TABLE 1

TSRU Tailings Composition

Component
Weight Percent

Maltenes
1

Asphaltenes
5

Solvent
0

Fines
6.5

Sands
3.3

Water
84.3

TOTAL:
100

The specific properties of the tailings will vary depending on the extraction method used, but tailings streams are essentially spent water, asphaltenes, unrecovered hydrocarbon, reagents, and waste ore left over once the usable bitumen has been removed.

While effective, the treatment process requires the use of large quantities of heat, solvent, and water in the form of steam and process water (dilution water), which significantly increases the cost associated with recovery of petroleum from the bitumen-laden oil sands.

One known method of recovering the water is to simply direct the TSRU tailings into reservoirs known as tailings ponds, and allow the solid components to settle and separate from the water over time. Residual heat escapes into the atmosphere, while the tailings water is retained for future use, with some loss due to evaporation. This method is not preferred for at least three reasons. First, a significant amount of time is required for most of the solid materials to precipitate out of the tailings by operation of gravity alone. Secondly, it does not allow for the recovery of any of the large amount of energy contained within the tailings stream in the form of heat. The heat lost is high, as tailings dumped into the ponds are at temperatures between 70° C. and 90° C. Thirdly, tailings ponds do not readily permit recovery of any of the residual hydrocarbon component within the tailings.

Rather than simply disposing of TSRU tailings, it is desirable to recover a portion of the usable components of the TSRU tailings stream to reduce the overall cost of extracting petroleum resources from oil sands and improve the environmental performance. The energy and water recovered can ideally be reused in further steps of the extraction process or recycled to the TSRU to be used as dilution water. This has the advantage of improving the overall energy efficiency of the extraction process. It is further desirable to minimize the volume of tailings that must be disposed. By removing a certain amount of water from the tailings, the streams can be substantially reduced to minerals and unrecovered hydrocarbon.

Several attempts to recover heat, water, and other reagents from tailings streams are known. Methods are disclosed in U.S. Pat. Nos. 4,343,691, 4,561,965 and 4,240,897, all to Minkkinen. These patents are directed to heat and water vapor recovery using a humidification/dehumidification cycle. U.S. Pat. No. 6,358,403 to Brown et al. describes a vacuum flash process used to recover hydrocarbon solvents from heated tailings streams. There has been, however, a lack of success in effective water and energy recovery.

Canadian Patent No. 2,674,660 to Esmaeili et al. is directed to systems and methods for treating tailings from bitumen extraction.

SUMMARY

It is an object of the present disclosure to obviate or mitigate at least one disadvantage of known systems or methods.

In one aspect, the present disclosure provides a method for treating tailings from a froth treatment process, the tailings comprising sand, clay comprising kaolin, water, and hydrocarbons, the method including dewatering the tailings comprising a primary water separation and a secondary water separation to produce dewatered tailings and recovered water, the dewatered tailings having a hydrocarbon content and a solids content to support combustion of the dewatered tailings, combusting the hydrocarbons in the dewatered tailings in a combustion chamber to cause a dehydration reaction converting kaolin into metakaolin and to produce fly ash and bottom ash, and recovering calcined fines comprising metakaolin from the fly ash or from the bottom ash, or from both the fly ash and the bottom ash.

In an embodiment disclosed, the dewatered tailings have a solids content of at least 40 wt percent following the primary water separation. In an embodiment disclosed, the dewatered tailings have a solids content of at least 50 wt percent following the secondary water separation. In an embodiment disclosed, the dewatered tailings have a solids content of at least 60 wt percent following the secondary water separation.

In an embodiment disclosed, the combustion is carried out at 500° C. to 1000° C. In an embodiment disclosed, the combustion is carried out at 800° C. to 900° C.

In an embodiment disclosed, fine tailings are added to the combustion chamber to increase the kaolin content or to control a maximum combustion temperature. In an embodiment disclosed, the fine tailings comprise a middling stream, froth flotation tailings, paraffinic froth treatment tailings prior to dewatering, naphthenic froth treatment tailings, mature fine tailings, or a combination thereof. In an embodiment disclosed, the fine tailings stream has been at least partially dewatered or concentrated.

In an embodiment disclosed, water, a substantially hydrocarbon free wet tails, or a combination thereof are added to the combustion chamber to control a maximum combustion temperature.

In an embodiment disclosed, the combustion is staged to control a maximum combustion temperature.

In an embodiment disclosed, the combustion chamber comprises a combustion bed comprising sand and fines. In an embodiment disclosed, the combustion bed comprises limestone for in-situ sulfur removal.

In an embodiment disclosed, the combustion chamber is a fluidized bed combustion chamber. In an embodiment disclosed, the dewatered tailings are fluidized for combustion, with air having an air velocity of between 0.1 m/s and 2.0 m/s. In an embodiment disclosed, the air velocity substantially 0.4 m/s.

In an embodiment disclosed, the tailings are tailings solvent recovery unit (TSRU) tailings.

In an embodiment disclosed, the bottom ash and bitumen extraction tailings are combined for solidifying or stabilizing the bitumen extraction tailings.

In an embodiment disclosed, calcined fines comprising metakaolin are recovered from the bottom ash. In an embodiment disclosed, metakaolin is separated from the calcined fines. In an embodiment disclosed, the recovered calcined fines are added to bitumen extraction tailings for solidifying or stabilizing the bitumen extraction tailings. In an embodiment disclosed, the recovered calcined fines are added to cement, cementitious materials or concrete.

In an embodiment disclosed, the metakaolin separated from the calcined fines is added to bitumen extraction tailings for solidifying or stabilizing the bitumen extraction tailings. In an embodiment disclosed, the metakaolin separated from the calcined fines are added to cement, cementitious materials or concrete.

In an embodiment disclosed, the fly ash is added to bitumen extraction tailings for solidifying or stabilizing the bitumen extraction tailings. In an embodiment disclosed, the fly ash is added to cement, cementitious materials or concrete.

In an embodiment disclosed, the calcined fines comprising the metakaolin are recovered from the fly ash. In an embodiment disclosed, metakaolin is separated from the calcined fines.

In an embodiment disclosed, the recovered calcined fines are added to bitumen extraction tailings for solidifying or stabilizing the bitumen extraction tailings. In an embodiment disclosed, the recovered calcined fines are added to cement, cementitious materials or concrete.

In an embodiment disclosed, the metakaolin separated from the calcined fines is added to bitumen extraction tailings for solidifying or stabilizing the bitumen extraction tailings. In an embodiment disclosed, the metakaolin separated from the calcined fines is added to cement, cementitious materials or concrete.

In an embodiment disclosed, the bitumen extraction tailings comprise mature fine tailings, thickened tailings, a middling stream, froth flotation tailings, or coarse tailings.

In an embodiment disclosed, the fly ash or the bottom ash or both and a tailings stream and a chemical modifier are mixed to provide a trafficable deposit.

In an embodiment disclosed, the chemical modifier comprising a sodium silicate solution. In an embodiment disclosed, the chemical modifier comprising caustic.

In an embodiment disclosed, the tailings stream is mature fine tailings having substantially 30 wt % solids content.

In an embodiment disclosed, the tailings are treated according to the recipe:

50 gr of combustion ash, 250 gr of MFT with 30% solid content, 20 gr sodium silicate solution, and 2.5 gr dry caustic.

In a further aspect, the present disclosure provides a system for treating tailings from a froth treatment process, the tailings comprising sand, clay comprising kaolin, water, and hydrocarbons, the system including a dewatering unit comprising a primary water separation unit and a secondary water separation unit for removing water from a tailings stream, producing a dewatered tailings stream and a tailings water stream, a combustion chamber for combusting the dewatered tailings stream, carrying out a chemical reaction whereby kaolin converts to metakaolin, and producing a fly ash and a bottom ash, and a fly ash recovery unit for recovering calcined fines comprising metakaolin from the fly ash.

In an embodiment disclosed, the system includes a metakaolin recovery unit for recovering metakaolin from the calcined fines. In an embodiment disclosed, the system further includes a bottom ash recovery unit for recovering metakaolin from the bottom ash.

In an embodiment disclosed, the primary water separation unit provides thickener underflow having a solids content of at least 40 wt %. In an embodiment disclosed, the secondary water separation unit provides a high solids content stream having a solids content of at least 50 wt %. In an embodiment disclosed, the high solids content stream comprising cake. In an embodiment disclosed, the secondary water separation unit provides cake having a solids content of at least 60 wt %.

In an embodiment disclosed, the dewatering unit comprises a thickener unit for primary water separation and a centrifuge unit for secondary water separation. In an embodiment disclosed, the dewatering unit comprises a thickener unit for primary water separation and a filter unit for secondary water separation.

In an embodiment disclosed, the dewatering unit comprises a thickener unit for primary water separation and an air drying unit for secondary water separation. In an embodiment disclosed, the air drying unit is adapted to deposit the dewatered tailings on the ground for moisture release by evaporation to provide dried material. In an embodiment disclosed, the combustion chamber adapted to combust the dried material.

In an embodiment disclosed, the thickener unit uses a flocculent, a coagulant, dilution water or combinations thereof to flocculate fine particles for removal. In an embodiment disclosed, the flocculent and the coagulant are added to the thickener unit at a single injection point. In an embodiment disclosed, the flocculent and the coagulant are added to the thickener unit at multiple injection points. In an embodiment disclosed, the flocculent or the coagulant are added upstream of the thickener unit at one or more locations. In an embodiment disclosed, the dilution water is a portion of primary water from the thickener unit. In an embodiment disclosed, the dilution water comprises recovered water from the dewatering unit.

In an embodiment disclosed, the tailings are tailings solvent recovery unit tailings.

In an embodiment disclosed, the combustion chamber is operated at between 500° C. to 1000° C. In an embodiment disclosed, the combustion chamber is operated at between 800° C. to 900° C.

In an embodiment disclosed, the combustion chamber is a fluidized bed combustion chamber. In an embodiment disclosed, the fluidized bed combustion chamber comprises a bed, the bed further comprising material from the dewatered tailings stream, and inert products derived from bitumen mining.

In a further aspect, the present disclosure provides a method for treating tailings from a froth treatment process to provide a trafficable deposit, comprising mixing the tailings with combustion ash and a chemical modifier.

In an embodiment disclosed, the chemical modifier comprising a sodium silicate solution. In an embodiment disclosed, the chemical modifier comprising caustic.

In an embodiment disclosed, the tailings comprising mature fine tailings (MFT) with substantially a 30 wt % solid content. In an embodiment disclosed, the tailings comprising thickened MFT or thickened flotation tails.

In an embodiment disclosed, the tailings are treated according to the recipe: 50 gr of combustion ash, 250 gr MFT with 30 wt % solid content, 20 gr sodium silicate solution, and 2.5 gr dry caustic.

In a further aspect, the present disclosure provides a method for treating TSRU tailings to provide a trafficable deposit, including receiving a TSRU tailings stream, dewatering the TSRU tailings stream to provide cake having at least 50% solid content, combusting the cake at between about 800° C. and about 900° C., to provide fly ash and bottom ash, and mixing the bottom ash or fly ash or both with the tailings to provide the trafficable deposit.

In an embodiment disclosed, the tailings comprise MFT.

In an embodiment disclosed, a chemical modifier is mixed with the ash and tailings. In an embodiment disclosed, the chemical modifier comprises sodium silicate solution. In an embodiment disclosed, the chemical modifier comprises caustic.

In an embodiment disclosed, the TSRU tailings are treated according to the recipe: 50 gr combustion ash, 250 gr MFT with 30 wt % solid content, 20 gr sodium silicate solution, and 2.5 gr dry caustic.

Other aspects and features of the present disclosure will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will now be described, by way of example only, with reference to the attached Figures.

FIG. 1 is a flow diagram illustrating an overview of a method of tailings treatment in accordance with one disclosed embodiment;

FIG. 2 is a schematic of an example of a tailings treatment system in accordance with one disclosed embodiment;

FIG. 3 is a schematic of an example of a tailings treatment system in accordance with one disclosed embodiment;

FIG. 4 is a schematic of an example of a dewatering process using a thickener unit in accordance with one disclosed embodiment;

FIG. 5 is a schematic of an example of a dewatering process using a thickener and a centrifuge in accordance with one disclosed embodiment;

FIG. 6 is a schematic of an example of a dewatering process using a thickener and a filter in accordance with one disclosed embodiment;

FIG. 7 is a schematic of an example of a tailings treatment system using a thickener and air drying in accordance with one disclosed embodiment;

FIG. 8 is a is a schematic of an example of a process for separating combusted materials in accordance with one disclosed embodiment;

FIG. 9 is a further example of a process for separating combusted materials in accordance with one disclosed embodiment; and

FIG. 10 is a schematic of an example of a method of forming a trafficable deposit in accordance with one disclosed embodiment.

DETAILED DESCRIPTION

Generally, in one embodiment, the present disclosure provides a method and system for treating TSRU tailings using combustion to recover usable solid components and steam. The following description sets out several embodiments of the present disclosure using the example of tailings produced from paraffinic froth treatment processes. However, the embodiments discussed herein are also applicable to other treatment processes for bitumen froth or another industrial application that results in combustible, kaolinite-bearing tailings.

Flow Diagram

FIG. 1 shows a high-level outline of the steps involved in the tailings treatment process in accordance with one embodiment of the disclosure. Once froth separation tailings undergo tailings solvent recovery processing such as discussed above, they form a stream of TSRU tailings 100 comprising water, solid materials, unrecovered hydrocarbons, and unrecovered solvent. Dilution water may be added to avoid foaming within the TSRU and also to avoid the blockage of associated tubing and internals. In addition, the TSRU tailings 100 contain a significant amount of heat energy, as they may be released from a TSRU at a temperature of approximately 70° C.-93° C., or about 90° C. Owing to the high specific heat capacity of water, much of the heat energy of the tailings is stored within the water portion of the tailings. As such, both the water and a significant portion of the enthalpy lost to TSRU tailings can be extracted from the tailings stream and used in, for example, other steps in the oil sands extraction process. Accordingly, one embodiment of the disclosure provides for a dewatering unit 110 where recovered hot water 106 is extracted from the TSRU tailings 100.

In an embodiment disclosed, dewatering 109 includes primary water separation 112 where primary recovered water 114 is extracted from the TRSU tailings 100 to provide thickener underflow (UF) 122, and secondary water separation 116 where secondary recovered water 118 is extracted from the thickener underflow 122 to provide cake 124. The primary recovered water 114 and the secondary recovered water 118 may be combined as recovered hot water 106. The resulting cake 124, or dewatered tailings 115, are reduced in both volume and water content, so the following combustion process requires less heat energy.

As noted above, the TSRU tailings 100 contain a substantial amount of hydrocarbons (e.g. asphaltenes, unrecovered bitumen and solvent). In accordance with one embodiment disclosed, these hydrocarbons can be used as a source of energy for combustion once the TSRU tailings 100 are sufficiently dewatered to provide combustible dewatered tailings. Examples of dewatering methods are described below with reference to FIGS. 4 to 7. Using these hydrocarbons may mitigate the environmental challenge of tailings disposal, since the amount of solvents and asphaltenes released into the environment can be significantly reduced. Accordingly, in one embodiment of the disclosure, dewatered tailings 115 undergo combustion 128 using the hydrocarbons as a fuel following the dewatering 109. The combustion 128 may be more efficient as a result of the dewatering 109, as dewatered tailings 115 will combust more readily owing to the removal of recovered hot water 106. In an embodiment disclosed the dewatered tailings 115 have a solids content of greater than about 50 percent by weight. In an embodiment disclosed, the dewatered tailings 115 have a solids content of about 60 wt percent. Ammonia, urea, and limestone may be added to the combustion 128 for emission control.

As noted above, a constituent element of the solid portion of TSRU tailings is kaolinite, or solids rich in kaolin. Kaolin, which has a chemical formula of Al₂Si₂O₅(OH)₄, undergoes dehydration at temperatures of approximately 500° C.-1000° C. to form metakaolin according to the following chemical reaction:

2Al₂Si₂O₅(OH)₄→2A1₂Si₂O₇+4H₂O

Accordingly, during combustion 128, the kaolin content of dewatered tailings 115 will undergo the above dehydration reaction to form metakaolin once the temperature during combustion is high enough to reach the activation energy threshold for the reaction. Combustion 128 results in two product streams: flue gas 135 and bottom ash 140.

In one embodiment, the metakaolin product of the reaction will form as a fine solid, and exit the combustion 128 as a component of flue gas 135. Heavier particles will settle and be removed with the bottom ash 140. Flue gas separation 148 is then used to extract calcined fines 190, including metakaolin, which has several industrial applications owing to their cementitious, or pozzolanic, properties. The remaining components of flue gas 135 are then released as low solids flue gas 151 emissions, for example CO, CO₂, SOx, NOx, and particulates are further treated.

Metakaolin is a well-known supplement for Portland cement; in addition, it is known to increase the comprehensive and flexural strengths of cement, and improves the resistance of concrete against corrosive chemicals and freeze-thaw conditions. Similarly, metakaolin may be used as a main ingredient of a geopolymer for stabilizing and solidifying waste streams. Accordingly, the calcined fines 190 extracted from flue gas 135 or the bottom ash 140 or both may be used to treat other tailings streams, such as mature fine tailings (MFT), coarse tailings, or another suitable tailings streams resulting from the various stages of oil sands extraction processes.

The bottom ash 140 comprises the coarse tailings remnants from the combustion 128, which may include sand, clays (including larger sized meta-kaolinite particles), minerals, heavy metal oxides, gypsum, and unreacted limestone. Heavy minerals are defined herein as minerals having a specific gravity greater than about 2.85, and including, without being limited to, such minerals as rutile, ilmenite, leucoxene, siderite, anatase, pyrite, zircon, tourmaline, garnet, magnetite, manzite, kyanite, staurolite, mica, and chlorite. Among these, rutile and zircon are considered valuable materials; for example, zircon is particularly valued for its applications as an abrasive and an insulator as well as its refractory properties, while rutile is used in the preparation of pigments and refractory ceramics. One embodiment of the disclosure provides for heavy minerals recovery 170 to extract a portion of the valuable constituents of the bottom ash 140. Examples of methods to remove heavy minerals 175 include gravity, magnetic, and electrostatic separation. De-mineralized bottom ash 176 comprises the remaining minerals and clay portions left over following heavy minerals recovery 170, and may then be disposed of, used for tailings stabilization, or used for further separation of gypsum and unreacted limestone.

In an embodiment disclosed, a trafficable deposit 192 may be prepared by mixing 193 calcined fines 190 or de-mineralized bottom ash 176 from the combustion 128 process or both and tailings, for example mature fine tailings (MFT) 197. In an embodiment disclosed, the de-mineralized bottom ash 176 or the calcined fines 190 or both are mixed 194, along with a chemical modifier 196 to prepare the trafficable deposit 192.

In an embodiment disclosed, the heavy minerals recovery 170 is optional, and if not present, the bottom ash 140 could be provided for mixing 193 for preparation of the trafficable deposit 192.

Tailings Treatment System

FIG. 2 shows a system in accordance with one disclosed embodiment. TSRU tailings 200 from bitumen froth treatment processes (for example paraffinic or naphthenic froth treatment) enter dewatering unit 210 where a portion of, or much of, the water in the TSRU tailings 200 is separated. In an embodiment disclosed, the dewatering unit 210 may include primary water separation (PWS) 212 and secondary water separation (SWS) 216. Non-limiting examples of suitable dewatering operations methods using a hydrocyclone, centrifuge, filters, settling vessels, or thickeners, all with or without the addition of chemical aids; however, another process capable of removing water from a TSRU tailings stream may function within this embodiment of the disclosure. As a result of the dewatering, TSRU tailings 200 have been split into tailings water 205 and dewatered tailings 215. In an embodiment disclosed, the primary water separation 212 is preferably a thickener. In an embodiment disclosed, the secondary water separation 216 is a centrifuge or a filter. In an embodiment disclosed, a polymeric flocculant such as Anionic polyacrylamide (Anionic PAM) may be used with the option of adding a coagulant. In an embodiment disclosed, the coagulant is a polymeric coagulant such as Diallyldimethylammonium Chloride (DADMAC). In an embodiment disclosed, the coagulant may be an inorganic coagulant such as alum, lime, or gypsum. In an embodiment disclosed, the flocculant is provided in a dosage range of about 50 to about 200 ppm. In an embodiment disclosed, the dosage is about 100 ppm. In an embodiment disclosed, the coagulant is provided in a dosage less than about 200 ppm. In an embodiment disclosed, the coagulant is DADMAC provided in a dosage about 40 ppm.

The tailings water 205, from primary recovered water 214 and secondary recovered water 218, then optionally enters a fines removal unit 220 to recover fine particulate matter that may not have been removed by the dewatering unit 210. Non-limiting examples of fines removal units include filters, centrifuges, thickeners, clarifiers and cyclones. Non-limiting examples of dewatering methods are described further below with reference to FIGS. 4 to 7. Recovered hot water 206 may then be used in any number of suitable applications. As noted above, the TSRU tailings 200 may be released from the TSRU at temperatures of approximately 90° C., so recovered hot water 206 may leave the fines removal unit 220 with enthalpy that may be used in, for example, another step of the oil sands extraction or treatment processes or both that require heat energy. Further, the recovered hot water 206 itself may be reused in other extraction or treatment steps including, but not limited to, froth treatments. The recovered hot water 206 may be recycled to the TSRU to be used as dilution water. Any fines 207 recovered by fines removal unit 220 may then be added to dewatered tailings 215 and undergo additional treatment along with the solid components from the dewatering unit 210 (including primary water separation 212 and secondary water separation 216).

Dewatered tailings 215 then enter combustion chamber 230. Optionally and preferably, the combustion chamber 230 is a fluidized bed combustion chamber. Broadly speaking, fluidized beds contain solid materials, usually particulate, that are subjected to certain conditions to cause them to exhibit the properties and behaviors of a fluid. In the fluidized bed combustion in accordance with this embodiment of the disclosure, solid fuels (shown as chamber bed 231) are suspended on an upwardly-blowing current of air 234, causing a tumbling action that mixes gas and solid. In an embodiment disclosed, air is provided to provide an upwardly-blowing current of air 234, within the combustion chamber 230, of between about 0.1 m/s to about 2 m/s. In an embodiment disclosed, the velocity of the air 234 is about 0.4 m/s.

In an embodiment disclosed, chamber bed 231 is at least partially made up of particulate matter from the dewatered tailings themselves. The fluidized bed combustion should be operated at a temperature so as to form metakaolin. Limestone, ammonia and urea may be added for emission control. In an embodiment disclosed, due to a high sulfur content of the fuel, the combustion bed comprises limestone and the fuel is added, for example by spraying on to the fluidized bed.

Dewatered tailings 215 contains hydrocarbon molecules such as asphaltenes rejected during paraffinic froth treatment, unrecovered bitumen and residual solvent that may not have been recovered by the TSRU. When ignited, these hydrocarbon components will combust within the chamber, releasing heat energy. As one of ordinary skill in the art will appreciate, fluidized bed combustion allows for effective reactions and transfer of heat. The presence of non-combustible solid material in combustion chamber 230 may not adversely affect the combustion process, and the presence of some water within the boiler feed, which in this case is dewatered tailings 215, may reduce the combustion temperature in the combustion chamber 230 depending on the technology employed. In combustion processes, the presence of a certain amount of water moderates the flame or the bed temperature. Advantageously, this may reduce the amount of NOx formed during the combustion since a lower combustion temperature reduces the NOx generated from the combustion air. In an embodiment, combustion chamber 230 is a modified circulating fluid bed combustion boiler where the bed 231 comprises tailings, sand, fines, and other solids added for control of bed properties.

According to another embodiment of the disclosure, heat generated during the combustion operation may be recovered. Water 232, for example boiler feed water (BFW), is introduced to, for example, a series of pipes or a compartment within combustion chamber 230 so that it is in thermal contact with the interior of the combustion chamber. As the combustion proceeds, generated heat energy flows into water 232. As a result of sufficient heat transfer water 232 will convert to steam 233 and exit combustion chamber 230. Steam 233 may be at any pressure and temperature desired for use as to drive a steam turbine, as a heat and/or water source for any other step of the oil sands extraction or treatment processes or any other industrial process that may require it.

In some cases, there may be a high sulfur content in the TSRU tailings 200, particularly in the asphaltene components. As such, a SOx removal step may be considered for the design of any combustion process used in accordance with one embodiment of the disclosure. In an embodiment disclosed, a limestone bed may be used as part of a SOx removal. In an embodiment where both bitumen and asphaltenes are high in sulfur, this SOx removal using limestone in the fluidized bed is required. In a non-limiting example where combustion chamber 230 is a fluidized bed boiler, the introduction of limestone in the fluidized bed is effective for the SOx removal. In one embodiment disclosed, the presence of a caustic within the TSRU tailings stream can mitigate a SOx problem, as it is known that caustic reacts with SOx. Caustic is known to react with acidic gases like SO₂that will naturally form in the combustion process as the hydrocarbon in the tailings contains sulphur. Moreover, the solid content of TSRU tailings contains materials with similar molecular building blocks to that of natural zeolites; they may help to reduce SOx emissions during the process.

The combustion proceeds, burning the tailings and converting them to two streams: flue gas 235 and bottom ash 240. As discussed above, the kaolin clay component in the tailings undergo dehydration synthesis to form metakaolin when the temperature inside the combustion chamber reaches the 500° C.-1000° C. threshold. In one embodiment, fine tailings sourced from any stage of the oil sands extraction process (i.e. MFT, middlings, or flotation tailings) that produces kaolin-containing fine tailings 229 may be introduced into combustion chamber 230. In this manner, additional tailings can be added, thus increasing the kaolin content of the tailings in combustion chamber 230 and, consequently, the production of metakaolin by dehydration synthesis. Moreover, any residual hydrocarbon in the fine tailings will be combusted, recovering useful heat from an otherwise waste product. The produced metakaolin as well as other fines, such as illite and smectite will emit from the combustion chamber as a portion of flue gas 235 or bottom ash 240. As used herein, fines are less than or equal to 44 microns.

It should be noted that the temperature in combustion chamber 230 may exceed 1000° C. during combustion. This may have a negative impact on the pozzolanic properties of the calcined fines; accordingly, one embodiment of the disclosure provides for a optimal design for the combustion for example, by using a staged combustion, primary, secondary, tertiary air addition, proper temperature distribution within the chamber can be achieved and the length of exposure of the calcined fines to high temperatures can be reduced, thus mitigating any damage to the fines. The addition of water, inert or near inert products (such as mature fine tailings (MFT) with a low hydrocarbon content) may also be admitted in various locations to assist in temperature control or limit in addition to providing additional meta-kaolinite production.

In one embodiment, calcined fines 290 contained within flue gas 235 are separated by flue gas separation unit 250. Non-limiting examples of appropriate separation devices include a cyclone and a bag house filter.

Following separation, flue gas 235 is reduced to low solids flue gas 251, which may be made up of the gaseous components released during combustion. In general, the low solids flue gas 251 contains a very low solids content, approaching zero, but may, for example, include some residual particulate. In a further embodiment, heat energy contained in low solids flue gas 251 may be reused in other stages of the oil sands extraction or refinement processes or both. For example, low solids flue gas 251 may be used to dry other tailings streams such as MFT using a spray dryer. A spray dryer is a type of dryer in which the materials to be dried are sprayed to the dryer and the water is removed by contacting with hot air or hot gas. In this case, the hot gas may comprise low solids flue gas 251. As noted above, bottom ash 240 comprises sand, gypsum, unreacted lime, metakaolin, and may contain valuable heavy minerals. In one embodiment, bottom ash 240 is introduced into heavy minerals recovery unit 260 where they are subjected to recovery operations to retrieve usable and valuable components from the tailings. Non-limiting examples of heavy minerals recovery unit 260 include devices typically used for electrostatic or magnetic separation techniques, although another suitable method for extracting heavy minerals from a coarse or fine particulate solid or coke may be used in additional embodiments of the disclosure. The resulting products from heavy minerals recovery unit 260 include heavy minerals 262 and de-mineralized bottom ash 261, which is mainly made up of sand, calcined fines, gypsum, unreacted limestone and impurities. De-mineralized bottom ash 276 may then be disposed of or used in any appropriate manner.

In an embodiment disclosed, a trafficable deposit 292 may be prepared by mixing the bottom ash 240 or the flue gas solids (e.g. calcined fines 290) or both from the combustion chamber 230, with tailings, for example mature fine tailings (MFT) 297. In an embodiment disclosed, de-mineralized bottom ash 276 or calcined fines 290 or both are combined with MFT 297, for example in mixing unit 294, along with a chemical modifier 296 to prepare the trafficable deposit 292.

In an embodiment disclosed, the heavy minerals recovery unit 260 is optional, and if not present, the bottom ash 240 could be provided to the mixing unit 294 for preparation of the trafficable deposit 292.

Tailings Treatment System

FIG. 3 shows a system in accordance with one disclosed embodiment.

TSRU tailings 300 are dewatered in dewatering unit 310, comprising primary water separation 312 and secondary water separation 316. The primary water separation 312 at least partially dewaters the tailings to provide thickener underflow 322 and primary recovered water 314. The thickener underflow 322 enters the secondary water separation 316 and is further dewatered to provide secondary recovered water 318 and cake 324. In an embodiment disclosed, thickener underflow 322 has a solids content greater than between about 30 and 50 weight percent. In an embodiment disclosed, thickener underflow 322 has a solids content greater than about 40 weight percent. In an embodiment disclosed, thickener underflow 322 has a solids content of about 45 weight percent.

In an embodiment disclosed, cake 324 has a solids content of greater than about 50 weight percent. In an embodiment disclosed, cake 324 has a solids content of greater than about 60 weight percent.

The primary recovered water 314 and the secondary recovered water 318 may be used for heat recovery processes or the water itself may be used in other processes.

The dewatered tailings 315 (i.e. cake 324) enter combustion chamber 330 and the hydrocarbon and other combustible components burned to release energy. In an embodiment disclosed, a surge bin or stock pile of cake may be created or used for storing solids prior to combustion. This may separate the production and treating of dry tails from the combustion process. In an embodiment disclosed, the combustion chamber 330 operates between about 800° C. and about 900° C. In an embodiment disclosed, air 334 is supplied for fluidization in the combustion chamber 330, for example to a feed distributor, sparger, grid or other means for distributing the air 334 across the combustion chamber 330. In an embodiment the air 334 provides an upward air-current velocity, within the combustion chamber 330, of about 0.4 m/s. In an embodiment disclosed, limestone 336 is added to the combustion chamber 330. In an embodiment disclosed, the dosage of limestone 336 is between about 0 to 5 (molar) Ca/S. In an embodiment disclosed, the dosage of limestone 336 is about 2.5 (molar) Ca/S. In an embodiment disclosed, limestone or other materials or chemicals can be added to reduce SOx emissions to below regulatory limits. The range is dictated by process conditions, limestone particle size, etc. In an embodiment disclosed, the dosage of limestone 336 of about 2.5 (molar) can capture between about 90 to 95 percent of SOx emissions.

In an embodiment disclosed, a trafficable deposit 392 may be prepared using ash from the combustion process, mixed with tailings, for example MFT 397. Ash, including fly ash 355 or bottom ash 340 or both is conveyed to a mixing unit 394 and mixed with tailings, such as MFT 397. In an embodiment disclosed, chemical modifiers 396 are added to chemically modify the mixture to improve the strength or other material property of the trafficable deposit 392. In an embodiment disclosed, the chemical modifier 396 includes sodium silicate or caustic or both. The caustic may be provided by dry caustic, caustic solution or other sources of caustic known to one skilled in the art.

FIGS. 4 to 7 show examples of dewatering and fines removal to prepare the feed for the combustion process described herein.

Thickener

FIG. 4 outlines a dewatering method for primary water separation 412 utilizing a thickener unit 408.

A flocculent 402 or a coagulant 404 or both are added to TSRU tailings 400 and this mixture is added to the thickener unit 408. Primary recovered water 414 is recovered from the thickener unit 408, and partially dewatered tailings as thickener underflow 422 are sent to secondary water separation 416. A portion of thickener underflow 422 may be recycled in order to control the bed height within the thickener unit 408. The portion of thickener underflow 422 may be recycled to the thickener unit 408 feed after or before the chemical addition. A portion of primary recovered water 414 may be recycled to thickener unit 408 as spray 411, or recycled upstream of the thickener unit 408 for mixing with the flocculent 402, coagulant 404, and TSRU tailings 400, or recycled both as spray 411 and as recycle water upstream of the thickening unit 408.

Thickener and Centrifuge

FIG. 5 outlines a two stage dewatering method utilizing a thickener unit 508 for primary water separation 512 and a centrifuge unit 542 for secondary water separation 516.

A flocculent 502 or a coagulant 504 or both may be added to TSRU tailings 500 and this mixture is added to a thickener unit 508. Primary recovered water 514 is recovered from the thickener unit 508, and partially dewatered tailings as thickener underflow 522 are sent to secondary water separation 516. A portion of primary recovered water 514 or secondary recovered water 518 may be recycled to thickener unit 508 as spray 511, or upstream of the thickener unit 508 for mixing with the flocculent 502, coagulant 504, and TSRU tailings 500, or recycled both as spray 511 and as recycle water upstream of the thickening unit 508.

The dewatered tailings, as thickener underflow 522, are received by a centrifuge unit 542 for secondary water separation 516. In an embodiment disclosed, the thickener underflow 522 is a paste with between about 30 to 50 wt percent solids content. In an embodiment disclosed, the paste has about 40 to 45 wt percent solids content. In an embodiment disclosed, a portion of the thickener underflow 522 may be recycled in order to control the bed height of the thickener unit 508. The portion of thickener underflow 522 may be recycled to the thickener unit 508 feed after or before the chemical addition.

A flocculent 544 or a coagulant 546 or both may be added to thickener underflow 522 upstream of the centrifuge unit 542.

Secondary recovered water 518 is recovered from the centrifuge 542, and dewatered tailings as cake 524 are sent to combustion chamber 530. In an embodiment disclosed cake 524 has a solids content between 40 and 65 wt %. In an embodiment disclosed cake 524 has a solids content of about 55 wt %.

A portion of the primary recovered water 514 or the secondary recovered water 518 may be recycled to centrifuge unit 542, or upstream of the centrifuge unit 542 for mixing with the flocculent 544, coagulant 546, and TSRU tailings 500, or recycled as recycle water upstream of the centrifuge unit 542.

Thickener and Filter

FIG. 6 outlines a two stage dewatering method utilizing a thickener unit 608 for primary water separation 612 and a filter unit 643 for secondary water separation 616.

A flocculent 602 or a coagulant 604 or both may be added to TSRU tailings 600 and this mixture is added to a thickener unit 608. Primary recovered water 614 is recovered from the thickener unit 608, and partially dewatered tailings as thickener underflow 622 are sent to secondary water separation 616. A portion of primary recovered water 614 may be recycled to thickener unit 608 as spray 611, or upstream of the thickener unit 608 for mixing with the flocculent 602, coagulant 604, and TSRU tailings 600, or recycled both as spray 611 and as recycle water upstream of the thickening unit 608.

The dewatered tailings, as thickener underflow 622, are received by a filter unit 643 for secondary water separation 616. In an embodiment disclosed, the thickener underflow 622 is a paste with about 40 wt percent solids content. In an embodiment disclosed, a portion of the thickener underflow 622 may be recycled in order to control the bed height of the thickener unit 608. The portion of thickener underflow 622 may be recycled to the thickener unit 608 feed after or before the chemical addition.

A flocculent 644 or a coagulant 646 or both may be added to thickener underflow 622 upstream of the filter unit 643.

Secondary recovered water 618 is recovered from the filter unit 643, and dewatered tailings as cake 624 are sent to combustion chamber 630. In an embodiment disclosed cake 624 has a solids content between 40 and 70 wt %. In an embodiment disclosed cake 624 has a solids content of about 60 wt %.

A portion of the secondary recovered water 618 may be recycled to filter unit 643 as spray 654, or upstream of the filter unit 643 for mixing with the flocculent 644, coagulant 646, and TSRU tailings 600, or recycled both as spray 654 and as recycle water upstream of the filter unit 643.

Thickener and Air Dryer

FIG. 7 outlines a two stage dewatering method utilizing a thickener unit 708 for primary water separation 712 and an air drying unit 726 for secondary water separation 716.

A flocculent 702 or a coagulant 704 or both may be added to TSRU tailings 700 and this mixture is added to the thickener unit 708. Primary recovered water 714 is recovered from the thickener unit 708, and partially dewatered tailings as thickener underflow 722 are sent to secondary water separation 716. A portion of primary recovered water 714 or secondary recovered water 718 may be recycled to thickener unit 708 as spray 711, or upstream of the thickener unit 708 for mixing with the flocculent 702, coagulant 704, and TSRU tailings 700, or recycled both as spray 711 and as recycle water upstream of the thickening unit 708.

The dewatered tailings, as thickener underflow 722, are received by the air drying unit 726 for secondary water separation 716. In an embodiment disclosed, the thickener underflow 722 is a paste with between about 30 to 50 wt percent solids content. In an embodiment disclosed, the paste has about 40 to 45 wt percent solids content. In an embodiment disclosed, a portion of the thickener underflow 722 may be recycled in order to control the bed height of the thickener unit 708. The portion of thickener underflow 722 may be recycled to the thickener unit 708 feed after or before the chemical addition.

Secondary recovered water 718 (released water) is recovered from the air drying unit 726, and dewatered tailings as cake 724 are sent to combustion chamber 730 for combustion 728. In an embodiment disclosed cake 724 has a solids content between 70 and 85%. In an embodiment disclosed, cake 724 has a solids content of about 80 wt %.

A portion of the secondary recovered water 718 (released water) may be recycled to an extraction or tailings area.

Combustion Products

FIG. 8 is an example outlining the separation of combusted materials. The dewatered tailings 815 (such as cake 824) are shown entering the combustion chamber 830. Limestone, urea, ammonia and fine tails 829 may also be added. Flue gas 835 is fed to a flue gas separation unit 850 from which low solids flue gas 851 flows along with fly ash 855. The fly ash 855 is fed to a separation process 863 along with bottom ash 840 exiting the combustion chamber 830. In the separation process 863, some of the materials that may be separated include heavy minerals and metakaolin (collectively 864) and sand, gypsum, unreacted limestone, and impurities (collectively stream 865). Alternately, the bottom ash 840 may be treated separately from the fly ash 855.

Combustion Products

FIG. 9 is another example outlining the separation of combusted materials. Elements 915, 924, 929, 930, 935, 940, 950, 951, 955, 963, 964, and 965 are like elements or streams with corresponding numbers in FIG. 8. However, in FIG. 9, a distinct separation process 966 is used to separate elements such as heavy minerals and metakaolin (collectively 967) and sand, gypsum, unreacted limestone, and impurities (collectively stream 968) from the fly ash 955. Separation process 963 is used to separate such materials from the bottom ash 940.

Trafficable Deposit

FIG. 10 is an example outlining the preparation of a trafficable deposit using ash from the combustion process and tailings, for example mature fine tailings (MFT).

Ash, including fly ash 1055 or bottom ash 1040 or mixtures thereof, is conveyed to a mixing unit 1094 and mixed with tailings, such as MFT 1097. In an embodiment disclosed, chemical modifiers 1096 are added to chemically modify the mixture to improve strength of the trafficable deposit 1092. In an embodiment disclosed, the chemical modifiers 1096 include sodium silicate or caustic (dry or wet) or both.

In an embodiment disclosed, Table 2 sets out an example recipe which produces trafficable deposit 1092 having a shear strength of about 10 kPa within about sixty minutes. The timeframe indicated includes a cooling or setting of the mixture for about sixty minutes. The ash may be warm or hot from the combustion process or may have cooled to ambient temperature.

TABLE 2

Mixture Recipe

Component
Amount

Combustion Ash
50 gr

MFT
250 gr

with between about 20 and

45 wt % solids content, for

example 30 wt % solids

content

Sodium silicate solution
20 gr

Dry Caustic
2.5 gr

Several other advantages of treating tailings streams through combustion in accordance with embodiments of the present disclosure may include, but are not limited to: recovering of hot water from TSRU tailings, eliminating or mitigating the need to purchase gas or other fuels for extraction, producing steam for extraction and mining processes, eliminating or reducing the volatile organic compound content of emissions from tailings, producing usable meta-kaolinite through dehydration synthesis of the kaolinite content of TSRU tailings, recovering heavy minerals and/or heavy metal oxides from TSRU tailings, reducing the need to store tailings streams in ponds, and reducing the volume or surface area of such ponds.

The calcined fines comprising metakaolin and/or the metakaolin produced in the bottom ash may be used to solidify or stabilize a fine tailings stream (e.g. mature fine tailings (MFT)) resulting from bitumen extraction, or as an additive to cement. The strength of materials used in tailings pond dykes may be improved with the addition of meta-kaolinite, providing benefit in reduced material consumption and more flexible mine planning. When added to cement, metakaolin may mitigate an alkaline condition and may provide a greater heat resistance. As an example of how metakaolin can be used as an additive to cement, Advanced Cement Technologies, LLC (Blaine, Wash., USA) markets PowerPozz™, a high reactivity metakaolin. According to their publicly available data sheet, the product has been successfully incorporated into applications for concrete and related products including high performance, high strength, and light weight concrete; precast and repetitive products; fiberglass products, ferrocement, and glass fiber reinforced concrete; dry bagged products such as mortors, stuccos, repair material, and pool plaster; and specialty uses such as blended cements, oil well cementing, shotcrete, decorative interior concrete fixtures, and sculture.

As used herein, caustic (for example used as a chemical modifier) may include caustic known to one skilled in the art, including but not limited to dry caustic, caustic solution, or combinations thereof.

As used herein, froth treatment process (for example, as a source of tailings) may include froth treatment processes known to one skilled in the art, including but not limited to paraffinic froth treatment processes, naphthenic froth treatment processes, or combinations thereof.

In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the embodiments. However, it will be apparent to one skilled in the art that these specific details are not required.

The above-described embodiments are intended to be examples only. Alterations, modifications and variations can be effected to the particular embodiments by those of skill in the art without departing from the scope, which is defined solely by the claims appended hereto.

System and Integrated Method For Treatment of Tailings From Bitumen Extraction Process

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