Patent Application
20200181499
This application claims the benefit of Canadian application number 3,026,676 filed Dec. 6, 2018, the subject matter of which is incorporated herein by reference in its entirety.
The technical field generally relates to primary extraction in oil sands processing, and more particularly to primary extraction operations of an oil sands slurry that include caustic dosing techniques.
High clay contents in oil sands ore can be responsible for lower bitumen recovery rates, as clay is an undesirable component of bitumen streams and interferes with bitumen separation mechanisms. High clay contents in oil sands ore can also result in additional volumes of tailings production and higher bitumen content in tailings. During separation processes, clay minerals can attach to bitumen and prevent attachment of bitumen to air bubbles for aeration and flotation. Clays have large active surfaces areas which can interact with other components of the slurry during separation and downstream processing of bitumen and tailings streams. Processing oil sands ore having a high clay content can lead to reduced bitumen recovery, lower efficiency in terms of primary separation vessel (PSV) performance, and poorer product quality.
Addition of an alkaline agent, such as caustic, sodium silicate, sodium bicarbonate and sodium phosphate, to increase the pH of the oil sands slurry can enhance bitumen recovery and bitumen froth quality obtained from primary separation processes. Dosing of the alkaline agent has been generally based on the grade of the oil sands ore, for instance with regard to the bitumen content, mineral solids content or fines content of the oil sands ore.
There is still a need for enhanced separation technologies for treatment of oil sands slurries with regard to caustic dosing, in particular to improve primary separation processes of mined oil sands ore.
Techniques described herein provide enhanced PSV operations, for example by dosing an alkaline compound based on both measured clay content and water characteristics. Multiple dosing intervals can be pre-determined for respective combinations of clay content and dissolved solids, and then the properties can be monitored in order to adapt the alkaline dosing accordingly.
In some implementations, there is provided a method for operating a primary separation vessel (PSV) receiving an oil sands slurry that includes oil sands ore and water and producing a bitumen froth overflow stream, a middlings stream, and a tailings underflow stream, the method comprising:
In some implementations, when both the clay content and the dissolved solids content are below the lower predetermined clay content threshold and the lower predetermined dissolved solids content threshold, respectively, the dosage of the alkaline compound added to the oil sands slurry is zero.
In some implementations, when the clay content is within a first clay content range below the lower predetermined clay content threshold; or the clay content is within a second clay content range and the dissolved solids content is within a first dissolved solids content range below the lower predetermined dissolved solids content threshold; or the clay content is within a third clay content range and the dissolved solids content is within the first dissolved solids content range below the lower predetermined dissolved solids content threshold; the dosage of the alkaline compound is zero.
In some implementations, when the clay content is within the second clay content range and the dissolved solids content is within a second dissolved solids content range; or the clay content is within the second clay content range and the dissolved solids content is within a third dissolved solids content range; or the clay content is within the third clay content range and the dissolved solids content is within the second dissolved solids content range; or the clay content is within a fourth clay content range and the dissolved solids content is within the first dissolved solids content range below the lower predetermined dissolved solids content threshold; the dosage of the alkaline compound is above zero and within a low dosage interval.
In some implementations, when the clay content is within the second clay content range and the dissolved solids content is within a fourth dissolved solids content range above a higher predetermined dissolved solids content threshold; or the clay content is within the third clay content range and the dissolved solids content is within the third dissolved solids content range; or the clay content is within the fourth clay content range and the dissolved solids content is within the second dissolved solids content range; the dosage of the alkaline compound is above zero and within an intermediate dosage interval.
In some implementations, when the clay content is within the third clay content range and the dissolved solids content is within the fourth dissolved solids content range above the higher predetermined dissolved solids content threshold; or the clay content is within the fourth clay content range and the dissolved solids content is within the third dissolved solids content range; or the clay content is within a fifth clay content range above a higher predetermined clay content threshold and the dissolved solids content is within the first dissolved solids content range below the lower predetermined dissolved solids content threshold; the dosage of the alkaline compound is above zero and within a high dosage interval.
In some implementations, when the clay content is within the fourth clay content range and the dissolved solids content is within the fourth dissolved solids content range above the higher predetermined dissolved solids content threshold; the dosage of the alkaline compound is above the high dosage interval.
In some implementations, the lower predetermined clay content threshold is about 0.8 meq/100 g. In some implementations, the lower predetermined dissolved solids content threshold is about 1250 mg/L. In some implementations, the second clay content range is between about 0.8 meq/100 g and about 1.0 meq/100 g. In some implementations, the third clay content range is between about 1.0 meq/100 g and about 1.2 meq/100 g. In some implementations, the fourth clay content range is between about 1.2 meq/100 g and about 1.6 meq/100 g. In some implementations, the higher predetermined clay content threshold is about 1.6 meq/100 g. In some implementations, the second dissolved solids content range is between about 1250 mg/L and about 2500 mg/L. In some implementations, the third dissolved solids content range is between about 2500 mg/L and about 3500 mg/L. In some implementations, the higher predetermined dissolved solids content threshold is about 3500 mg/L. In some implementations, the low dosage interval is between about 100 mg/tonne and 200 mg/tonne of the alkaline compound. In some implementations, the intermediate dosage interval is between about 200 mg/tonne and 400 mg/tonne of the alkaline compound. In some implementations, the high dosage interval is between about 400 mg/tonne and 500 mg/tonne of the alkaline compound.
In some implementations, measuring the clay content comprises using a methylene blue index (MBI) technique, an NIR technique or a K40 technique.
In some implementations, the predetermined dissolved solids content threshold is a predetermined total dissolved salts threshold.
In some implementations, the target recovery threshold of bitumen is determined based on an empirical assessment of the clay content and the dissolved solids content in the process water, with or without addition of the alkaline compound.
In some implementations, the target minimum bitumen recovery level is between 85 wt % and 95 wt %, or between 90 wt % and 95 wt %.
In some implementations, the alkaline compound comprises at least one of caustic soda, sodium silicate, sodium bicarbonate, and sodium phosphate.
In some implementations, the alkaline compound is added to at least one of the oil sands slurry upstream of the PSV and directly into the PSV.
In some implementations, during a start-up phase of the method the process water comprises fresh water and the dissolved solids content is below the lower predetermined dissolved solids content threshold.
In some implementations, after the start-up phase the process water comprises recycled process water and the dissolved solids content increases over time such that at a second operating phase of the method the dissolved solids content exceeds the lower predetermined dissolved salt content threshold. In some implementations, the recycled process water is recycled from a tailings pond. In some implementations, determining the dissolved solids content of the process water comprises determining the dissolved solids content of the recycled process water. In some implementations, during the second operating phase of the method the process water comprises exclusively recycled process water, and the dissolved solids content of the process water is above the predetermined dissolved solids content threshold.
In some implementations, the method includes transmitting information related to at least one of the clay content and the dissolved solids content to an analyzer operatively connected to at least one controller; and automatically dosing the alkaline compound for addition in the oil sands slurry through the at least one controller in response to the at least one of the clay content and the dissolved solids content.
In some implementations, the method includes determining a water content of the oil sands slurry.
In some implementations, the method includes supplying dilution water to the oil sands slurry upstream of the PSV.
In some implementations, the oil sands slurry is a diluted oil sands slurry, the clay content is measured on the diluted oil sands slurry, and the alkaline compound is added to at least one of the diluted oil sands slurry and the PSV.
In some implementations, measuring the clay content comprises obtaining a clay content indicator.
In some implementations, measuring the clay content of the mined ore, the crushed ore, and/or the oil sands slurry is conducted in-line.
In some implementations, there is provided a method for operating a primary separation vessel (PSV) receiving an oil sands slurry that includes oil sands and water and producing a bitumen froth overflow stream, a middlings stream, and a tailings underflow stream, the method comprising:
In some implementations, determining the dosage based on the clay content and the dissolved solids content comprises when at least one of the clay content and the dissolved solids content is below a lower predetermined clay content threshold and a lower predetermined dissolved salt content threshold, respectively, the dosage of the alkaline compound added to the oil sands slurry is zero; and when the clay content is above the lower predetermined clay content threshold and the dissolved solids content is above the lower predetermined dissolved solids content threshold, the dosage of the alkaline compound added to the oil sands slurry corresponds to a determined amount.
In some implementations, when both the clay content and the dissolved solids content are below the lower predetermined clay content threshold and the lower predetermined dissolved salt content threshold, respectively, no alkaline compound is added to the oil sands slurry.
In some implementations, the method includes transmitting information related to at least one of the clay content and the dissolved solids content to an analyzer operatively connected to at least one controller; and automatically dosing the alkaline compound for addition in the oil sands slurry through the at least one controller in response to the at least one of the clay content and the dissolved solids content.
In some implementations, the target recovery threshold of bitumen is determined based on an empirical assessment of the clay content and the dissolved solids content of the process water, with or without addition of the alkaline compound.
In some implementations, the target minimum bitumen recovery level is between 85 wt % and 95 wt % or between 90 wt % and 95 wt %.
In some implementations, the alkaline compound comprises at least one of caustic soda, sodium silicate, sodium bicarbonate, and sodium phosphate.
In some implementations, the alkaline compound is added to at least one of the oil sands slurry upstream of the PSV and directly into the PSV.
In some implementations, the process water comprises recycled process water, and determining the dissolved solids content comprises determining the dissolved solids content of the recycled process water.
In some implementations, the recycled process water is recycled from a tailings pond and is fed to the mixing unit to form the oil sands slurry.
In some implementations, the method includes supplying dilution water to the oil sands slurry upstream of the PSV.
In some implementations, the oil sands slurry is a diluted oil sands slurry, the clay content is measured on the diluted oil sands slurry, and the alkaline compound is added to at least one of the diluted oil sands slurry and the PSV.
In some implementations, measuring the clay content comprises obtaining a clay content indicator.
In some implementations, measuring the clay content of the oil sands slurry is conducted in-line.
In some implementations, the dosage of the alkaline compound is performed based on alkaline dosage intervals corresponding to respective determined combinations of clay content ranges and dissolved solids content ranges.
In some implementations, there is provided a method for operating a primary separation vessel (PSV) receiving an oil sands slurry that includes oil sands ore and water and producing a bitumen froth overflow stream, a middlings stream, and a tailings underflow stream, the method comprising:
In some implementations, there is provided a method for dosing an alkaline compound for addition to an oil sands slurry subjectable to separation in a primary separation vessel (PSV), the oil sands slurry comprising oil sands ore and water and the PSV being configured to produce a bitumen froth overflow stream, a middlings stream, and a tailings underflow stream, the method comprising:
In some implementations, at least five operating envelopes are determined. In some implementations, at least ten operating envelopes are determined.
In some implementations, the dosage of the alkaline compound is within a low dosage interval, an intermediate dosage interval, or a high dosage interval, and each one of the low dosage interval, the intermediate dosage interval, and the high dosage interval corresponds to at least one of the operating envelopes.
In some implementations, each one of the low dosage interval, the intermediate dosage interval, and the high dosage interval corresponds to a plurality of operating envelopes.
In some implementations, when at least one of the clay content and the dissolved solids content is below a lower predetermined clay content threshold and a lower predetermined dissolved solids content threshold, respectively, the dosage of the alkaline compound added to the oil sands slurry is zero; and when the clay content is above the lower predetermined clay content threshold and the dissolved solids content is above the lower predetermined dissolved solids content threshold, the dosage of the alkaline compound added to the oil sands slurry is within one of the low dosage interval, the intermediate dosage interval, and the high dosage interval.
In some implementations, when both the clay content and the dissolved solids content are below the lower predetermined clay content threshold and the lower predetermined dissolved solids content threshold, respectively, the dosage of the alkaline compound added to the oil sands slurry is zero. Other dosing schemes as described herein are also possible.
In some implementations, there is provided process for producing a bitumen product from oil sands, the process comprising:
In some implementations, there is provided a system for processing oil sands slurry, comprising:
In some implementations, the controller is configured such that the dosage of the alkaline compound is performed based on alkaline dosage intervals corresponding to respective pre-determined combinations of clay content ranges and dissolved solids content ranges
In some implementations, the pre-determined combinations are pre-programmed into the controller.
In some implementations, the clay analyzer comprises a methylene blue index (MBI) analyzer. In some implementations, the clay analyzer comprises a K40 analyzer.
In some implementations, the water analyzer is configured to determine total dissolved salts.
In some implementations, the target minimum bitumen recovery level is between 90 wt % and 95 wt %.
In some implementations, the alkaline compound comprises caustic soda, sodium silicate, sodium bicarbonate, and/or sodium phosphate.
In some implementations, the alkaline addition line is configured to add the alkaline compound to the feed line of the oil sands slurry upstream of the PSV.
In some implementations, the alkaline addition line is configured to add the alkaline compound into the PSV.
In some implementations, there is provided a method for processing oil sands ore, comprising:
It is noted that various other features as described herein can be combined with the methods and systems described above.
Techniques described herein relate to methods for dosing the addition of an alkaline compound, such as caustic, in the context of primary extraction processes of oil sands ore obtained from surface mining. Enhancements described herein include the dosing of caustic in the context of hot water extraction in a primary separation vessel (PSV) that receives an oil sands slurry for separation into bitumen froth, middlings and tailings. Dosing of the caustic for addition at one or more locations of the primary extraction process can be based on certain parameters, such as the clay content, the clay-to-water ratio (CWR), and the process water chemistry of the oil sands slurry. These caustic dosing techniques can contribute to enhanced bitumen recovery, bitumen froth quality, and efficient operation of the primary separation.
The methods can include determining the clay content of the oil sands slurry and the dissolved solids content of the process water used to form the oil sands slurry, and then dosing the alkaline compound, such as caustic, based on different predetermined operating envelopes of the clay and dissolved solids contents. The caustic dosage process can be automated such that measurements regarding clay and dissolved solids content are automatically obtained and used to control the concentration or flow rate of the alkaline compound stream added to the oil sands slurry or to the PSV.
With reference to
The aqueous slurry 18 can then be shear conditioned to prepare the slurry for extraction of the bitumen from the solid minerals and water. The conditioning of the aqueous slurry 18 is typically performed through hydrotransport via a pipeline, which facilitates increased mixing, aeration and breakdown of lumps of oil sands ore in preparation for bitumen separation.
The aqueous slurry 18, which can optionally be further diluted with process water 14, is transported to a primary separation vessel (PSV) 20, which can also be referred to as a primary separation cell, “sep cell”, or gravity separation cell. The PSV typically uses flotation and gravity mechanisms to separate bitumen from coarse sand and other solid particles. In the primary separation process, bitumen in the aqueous slurry 18 detaches from solid particles and attaches to air bubbles that are injected into the PSV 20, thereby allowing bitumen droplets to rise and float to the top of the PSV 20, forming the primary bitumen froth 22 that is recovered typically as an overflow stream. Coarse particles contained in the aqueous slurry 18 are relatively heavy and tend to sink to the bottom of the PSV 20. The portion of the aqueous slurry 18 that is not heavy enough to sink to the bottom of the PSV 20 but not light enough to float tends to remain in the middle of the PSV 20, and can be referred to as middlings 26. The aqueous slurry 18 is thus separated into three streams withdrawn from the PSV: a primary tailings underflow stream 24 (also referred to as coarse tailings), a middlings stream 26, and a bitumen froth overflow stream 22.
In some implementations, the middlings 26 can be sent to a secondary separation vessel 28 to be separated into secondary bitumen froth 30 and secondary tailings 32 (which can also be referred to as a fine tailings stream herein as they contain higher fines content compared to the coarse tailings). As shown in
Still referring to
The primary tailings 24 and secondary tailings 32 generally include between about 45 wt % and about 55 wt % solid materials, between about 45 wt % and about 55 wt % water, and residual bitumen (typically between about 1 wt % and about 3 wt % bitumen). The solid materials in the primary and secondary tailings 24, 32 are mainly sand and other fine hydrophilic mineral materials. The primary tailings 24 and secondary tailings 32 can then be disposed of in a tailings pond 50 or further treated to extract bitumen.
The bitumen froth 22 is treated in a froth treatment process 34 in which the bitumen froth 22 is diluted with a diluent or solvent 36 to obtain a diluted bitumen froth. Froth treatment can also be referred to as secondary extraction which is performed after the froth is produced by primary extraction. The diluent 36 can be either a naphthenic type diluent or a paraffinic type diluent. The naphthenic type diluent can for example include toluene, naphtha or other light aromatic compounds. The paraffinic type diluent can for example include C4 to C8 aliphatic compounds and/or certain natural gas condensates. When a paraffinic compound is used, it can be referred to as a “solvent” rather than a “diluent”, and when used under certain conditions the paraffinic solvent induces precipitation of asphaltene aggregates that contain asphaltenes, water and fine mineral solids. The diluted bitumen froth is then separated into a bitumen product 38 (which can be further upgraded, if desired) and froth treatment tailings 40 including solid materials (hydrophilic mineral materials, heavy minerals and insoluble organic materials), water, residual diluent and residual bitumen.
Still referring to
Optionally, an overlying water phase can be pumped out of the tailings pond 50 and reused as recycled process water 52 in the mixing unit 16 to obtain the aqueous slurry 18, as well as in various other applications within the oil sands processing facility.
One or more alkaline agents, such as caustic soda (NaOH), sodium silicate, sodium bicarbonate, sodium phosphate and the like, can be added directly to the aqueous slurry 18 to chemically condition and prepare the aqueous slurry 18 for bitumen extraction and separation. Alkaline agent(s) can be added to the process water 14, to the mixing unit 16, to the aqueous slurry before, during or after hydrotransport, and/or can be added directly into the PSV 20. Features and implementations of caustic addition and dosing will be described in further detail below.
Clay Content of Oil Sands Slurry and Interactions of Clays with Bitumen
As mentioned above, the aqueous slurry 18 includes bitumen and solid particles including coarse sand and finer mineral material. Particles having a diameter larger than 44 microns are considered coarse particles, and particles having a diameter smaller than 44 microns are considered fines. Very small particulate material in the range of 2 to 4 microns and having active surface areas can be referred to as clays. “Low grade” ores typically have a higher clay content and can be difficult to process since clays can impair the separation process, which can result in a significant amount of bitumen being lost to the middlings and the tailings streams.
Clays can be defined in terms of their composition, activity and/or size. Clays are phyllosilicate mineral solids that have a size below 2 or 4 microns, and that have active surfaces that can interfere with the separation process of bitumen from the bitumen slurry. Due to their activity and small size, when clays are present in high concentrations in a bitumen slurry, their impact tends to dominate over other mineral solid particles, such as larger “fines” and coarse sand. Clays found in oil sands are mostly composed of kaolinite and illite, although oil sands can also contain fractional amounts of chlorite, smectite, feldspar and montmorillonite.
The surface chemistry of clays contributes to how they interact with bitumen. Generally, clays have surfaces that are negatively charged and edges that are positively charged. Bitumen is negatively charged, enabling attachment of bitumen to air bubbles to form a bitumen-rich froth. However, the positive charges of the clays can also attract the negative charges of the bitumen, thereby neutralizing the charge of the bitumen and resulting in loss of hydrophobicity of bitumen. Air bubbles are thus prevented from selectively attaching to bitumen droplets, impairing the floatability of bitumen and separation of bitumen from the fines, which can result in bitumen losses to the middlings and tailings streams and thus a reduced bitumen recovery. Recovery of the bitumen from the middlings can still be performed in highly aerated flotation cell, however rendering the bitumen extraction longer and more expensive.
Addition of an alkaline agent, such as caustic soda (NaOH), to a bitumen slurry can contribute to enhancing bitumen recovery and improving the quality of the bitumen-rich froth 22 during the primary extraction stage in the PSV 20. Increasing the pH of the bitumen slurry 18 is thought to charge clays negatively such that the clays tend to repel each other and that attachment of bitumen droplets to clays is prevented, which can contribute to avoiding their agglomeration and facilitate dispersion and flotation of bitumen for the separation process.
Providing a proper dosage of caustic soda by taking into consideration characteristics of the aqueous slurry can contribute to improve bitumen recovery and bitumen froth quality. The dosage of caustic soda can take into account at least two variables, namely an amount that is sufficiently high to lead to repulsion of the clays, and an amount that is sufficiently low such that dissolved salts contained of the aqueous slurry, especially positively charged cations such as Na+ and Mg2+, do not lead to gelling, or sludging, of the fines and clays together. In addition, ion exchange, for instance between Na+ and Ca2+, can form calcium naphthenates with the naturally occurring naphthenic acids in the oil sands, which can be detrimental to bitumen froth quality. Too much caustic soda can also lead to additional Ca2+ in the bitumen froth and can be problematic with catalysts used in the refinery plant, and can cause emulsification of bitumen and smaller bitumen droplets, which can impair bitumen recovery.
Correlation of Caustic Dosage with Clay-Related Variables
It has been found that the dosage of caustic correlates with variables such as clay content of the oil sands ore and water chemistry of process water. As mentioned above, clay content is different from fines content, since clays are a subset of fines and have certain mineralogical and chemical properties.
The clay content of the oil sands ore and the water chemistry of process water can be measured at one or more locations in the separation process, and the dosage of caustic can be controlled accordingly. For instance, in some implementations, clay content can be evaluated upstream of the mixing unit 16 to obtain a clay content of the mined oil sands ore, either prior to the mined ore being broken down into lumps, or after. In other implementations, clay content can be evaluated once process water has been added to the to the mined ore to form the oil sands slurry, which is subsequently fed to the PSV, or on a sample taken directly from the PSV. In some implementations, a parameter that is indicative of clay content of the oil sands slurry or the clay's relative concentration with respect to other components of the oil sands slurry, such as CWR, can also be used for determining caustic dosage.
Clay content can be evaluated according to various measurement techniques. For instance, clay content can be measured by using a methylene blue index (MBI) test, a K40 system, or near-infrared (NIR) techniques. These different types of measurement techniques will be discussed briefly below.
MBI testing can allow obtaining an estimate of clay content based on a titration method that uses methylene blue, and is generally expressed as milliequivalents (meq) per 100 g of sample. In particular, MBI testing is an estimate of cation exchange capacity (CEC) of clays. When using this technique, the active clay particles/sheets that are negatively charged are coated with cationic MB dye molecules, resulting in a distinct dark blueish color until CEC has been reached. Excess MB that is not bound to clay remains in solution and results in a blue-green color that forms a “halo” around the dark blueish spot. Formation of a persistent blue-green halo indicates that the clays have reached their absorption capacity of the MB dye.
The K40 system is configured to measure emissions from a radioactive potassium isotope. The K40 system can measure isotope emissions not only from clays but also from coarser particles that include the isotope. It follows that for a slurry having a low clay content, the measured isotope emissions will not represent an accurate measure to evaluate clay content. In contrast, the K40 system provides a general trending of clay content of the oil sands slurry for oil sands slurries having high-clay levels.
NIR techniques are based on spectral measurements of an oil sands slurry or other oil sands materials and can be used to determine clay content based on predetermined correlations between clay concentration and NIR spectra. NIR-based calibration curves can be developed based on oil sands having known clay levels (e.g., clay levels measured in a laboratory using other techniques), and the resulting calibration curves can be used to determine clay content based on NIR measurements of the oil sands slurry stream or the oil sands directly.
Process water chemistry can refer to characteristics of process water in terms of electrical conductivity, pH, and/or dissolved solids, which includes dissolved metals and dissolved salts (e.g., sodium, potassium, calcium, magnesium, and iron) as well as other compounds such as dissolved organic matter. In some implementations, an indicator of water chemistry is a measure of total dissolved solids (TDS), which represents the sum of cations and anions present in the water and can be expressed for instance in mg/L or in ppm. Total dissolved salts is a subset of TDS and can also be referred to as salinity. There are various ions that can contribute to the salinity of water, such as sodium, potassium, calcium, magnesium, etc., balancing with chloride, sulfate, bicarbonate, and carbonate ions.
In some implementations, where an oil sands slurry having a high clay content is subjected to a primary extraction process, bitumen recovery and/or froth quality can decrease as salinity of the process water increases. On the other hand, in implementations where an oil sands slurry having a low clay content is subjected to a primary extraction process, process water salinity can have less of an impact on bitumen recovery and/or froth quality. This aspect will be described in further detail below.
Caustic addition is thought to mitigate the impact of salinity and thus can contribute to extend the salinity tolerant range without sacrificing bitumen recoveries at higher sodium ion concentration. For instance, when oil sands ore is mixed with process water to form an oil sands slurry, clay-cation exchange can occur and can result in variations of sodium, potassium, calcium and/or magnesium concentration in the oil sands slurry. With caustic addition to the oil sands slurry, it was found that calcium and magnesium concentrations are reduced in the middlings, a phenomenon thought to be attributed at least in part by CaCO3 and CaMg(CO3)2 precipitation due to a pH increase of the process water, which in turn can contribute to an increased bitumen recovery.
In addition, OH− ions of the caustic soda (NaOH) added to an oil sands slurry can attach to positively charged clays instead of to bitumen droplets, leaving hydrophobic bitumen free to attach to air bubbles, which can be beneficial for bitumen recovery.
Process water chemistry can evolve through time, from the moment a plant is put into operation and fresh water is used to start up processes, to many years later when processes have reached an equilibrium in terms of recycled process water that has gone through multiple cycles of separation processes. For instance, water from a plant's recycle pond and/or tailings pond can be reused as process water to mix with the oil sands ore and produce the oil sands slurry, and this recycled process water can have a different water chemistry compared to fresh water. After a certain number of years of a plant's operation, i.e., once the plant could be said to be “mature”, process water chemistry can reach an equilibrium stage. In this regard, studies that have assessed the role of water chemistry on caustic addition in the context of primary separation processes for bitumen recovery have done so based on process water having already a relatively high TDS. In contrast to a mature plant, water chemistry of process water used at a new start-up plant can change substantially in the first few years of operation, in particular with regard to TDS, which can play an important role in determining when to begin caustic addition and determining caustic dosage for primary extraction processes. It follows that as a plant is transitioning from a start-up mode using mainly fresh water having a low TDS, to a mature mode using process water having a higher TDS, tailoring the dosage of caustic may become useful to maintain a target recovery level of bitumen from the oil sands.
Provided herein are relationships between clay content and water chemistry to help guide caustic dosage requirements, for instance through a plant's lifecycle, which in turn can provide guidance to dose caustic more accurately in order to achieve enhanced bitumen recovery (e.g., by avoiding underdosing of caustic) and reduce the deleterious impact of downstream treatment and product quality (e.g., by avoiding overdosing of caustic).
As mentioned above, it was found that the use of an alkaline compound such as caustic soda in the process water, in the mixing unit, in the aqueous slurry before, during or after hydrotransport, and/or directly into the PSV, can be determined according to a correlation with both clay content and water chemistry. In general terms, such a correlation can be obtained by determining a clay content, or clay indicator, of the oil sands slurry and a dissolved solids content of the process water used to form the oil sands slurry, thus obtaining different predetermined operating envelopes according to various combinations of the clay content and the dissolved solids content. The dosing of the alkaline compound can then be based on one of the predetermined operating envelopes. In other words, an operating envelop can be determined according to a combination of a given clay content, or clay indicator, and a dissolved solids content; and for each operating envelop, there can be a corresponding dosage, or dosage range, of the alkaline compound. In some implementations, the corresponding dosage or dosage range of the alkaline compound can be determined to achieve a target bitumen recovery level of bitumen.
For instance, in some implementations, there can be a first, a second, a third, a fourth and a fifth clay content range, the first clay content range being below a lower predetermined clay content threshold, and the fifth clay content range being above a higher predetermined clay content threshold, the values of the clay content increasing from the first clay content range to the fifth clay content range. There can also be there can be a first, a second, a third, and a fourth dissolved solids content range, the first dissolved solids content range being below a lower predetermined dissolved solids content threshold, and the fourth dissolved solids content range being above a higher predetermined dissolved solids content threshold, the values of the dissolved solids content increasing from the first dissolved solids content range to the fourth dissolved solids content range. Each combination of the first, the second, the third, the fourth and the fifth clay content ranges and the first, the second, the third, and the fourth dissolved solids content ranges, for a total of twenty combinations, corresponds to a corresponding operating envelop of alkaline dosage. To each operating envelop is associated a dosage or dosage range of the alkaline compound, which can be for instance a low dosage interval, an intermediate dosage interval, or a high dosage interval. By way of example, in some implementations, the low dosage range of the alkaline compound can be associated with the operating envelop corresponding to the combination of the third clay content range and the second dissolved solids content range. It is to be understood that there can be any number of clay content ranges as well as any number of dissolved solids content ranges, and that each operating envelop can have an associated alkaline compound dosing interval but that more than one operating envelop can be associated with a same alkaline compound dosing interval.
In some implementations, the correlation is determined between clay content measured according to the MBI test, and TDS of the process water. In such implementations and with reference to Table 1 below, it was found that for oil sands having a clay content according to the MBI test below 0.8 meq/100 g, no addition of caustic soda was necessary across the range of water chemistry tested, i.e., first for a TDS level below 1250 mg/L, then for a TDS level between 1250 mg/L and 2500 mg/L, then for a TDS level below 2500 mg/L, and finally for a TDS level below 3500 mg/L. In other words, it appears that for a low clay content (below 0.8 meq/100 g according to the MBI test), it is possible to achieve the target recovery level for a TDS level of up to at least 3500 mg/mL, without having to proceed with caustic soda addition. In the scenario presented in Table 1, the expression “total dissolved solids” refers to the total concentration of sodium, potassium, calcium, magnesium, chloride, bicarbonate, sulfate and carbonate ions etc. in the process water. Still in the scenario presented in Table 1, concentrations of sodium, potassium, calcium and magnesium ions were determined using an Inductively Coupled Plasma Mass Spectrometry (ICP-MS) method, and concentrations of HCO3, and SO4 were determined using an Ion Chromatography (IC) method. It is to be understood that other suitable methods can be used to determine concentrations of ions, as known in the art.
The target bitumen recovery level can depend on various factors, such as ore quality, for instance with regard to bitumen content and clay content. In some implementations, target bitumen recovery levels are between about 85 wt % and about 95 wt. %. In other implementations, target bitumen recovery levels are between about 90 wt % and about 95 wt. %. The target bitumen recovery level can be a single value, such as 92 wt % or 95 wt %. To determine a given target recovery level of bitumen, empirical testing can be conducted where the clay content of an oil sands slurry and/or the water chemistry of the process water are/is varied, with or without addition of given doses of caustic, and corresponding bitumen recovery levels can be compiled for the different clay-content slurries and corresponding doses of caustic, if applicable. In some implementations, the target bitumen recovery level is determined as the bitumen recovery level obtained when processing an oil sands slurry with a reference process water, for instance a process water from a given source and having a given water chemistry. For instance, in some scenarios, the target bitumen recovery level is determined when using water from the Athabasca river as process water for the recovery process of bitumen form an oil sands ore.
On the other hand, it was also found for a clay content up to about 1.2 meq/100 g according to the MBI test, no caustic soda addition was necessary to achieve a target bitumen recovery level when the TDS level was concomitantly below 1250 mg/L.
Then, still referring to Table 1, it can be observed that as clay content and TDS level of the process water increase, dosage of caustic soda should be increased as well. For instance, a relatively low dose (100 to 200 mg/L) of caustic soda would be required for addition to the process water when the clay content of the bitumen is above 1.2 meq/100 g according to the MBI test, when the TDS is below 1250 mg/L, whereas more than 500 mg/L of caustic soda would be required for a similar clay content, but for a TDS level above 3500 mg/L. The dosage of caustic soda, according to this correlation, thus ranges from less than about 100 mg/L to at least about 500 mg/L, depending on the combination of clay content and TDS level. For a clay content above 1.6 meq/100 g according to the MBI test and a TDS level above 1250 mg/L, it was found that it is not recommended to proceed with the primary extraction process, at least in part because an acceptable or target bitumen recovery level would likely not be achieved, and/or the high amount of caustic soda that would be required to achieve an acceptable bitumen recovery level could lead to an excess in Ca2+ ions, which can be detrimental to subsequent processes occurring as part of the refinery plant and to settling mechanisms when tailings are stored in a tailings pond later on. This is not to say that such high TDS and high clay materials should not be processed, but it would be recommended that such processing be adapted for such input materials.
The dosage of caustic can be expressed in various units. Table 1 shows a dosage in mg of caustic soda per tonne of oil sands slurry, which could also be expressed in ppm. Another option is to express the caustic dosage according to a given flow rate.
Table 1 offers an overview of the combined impact of clay content of an oil sands ore, tested according to MBI testing, and water chemistry of process water used to either constitute and/or dilute the oil sands slurry, expressed as a TDS level, on the caustic dosage expected to be required to achieve a target bitumen recovery level. The general concept that emerges from this overview can be viewed as caustic soda having to be added to the oil sands slurry when at least one of clay content and TDS reached a respective given threshold. This concept can be applied to various methods and techniques other than MBI and TDS used to determine clay content and water chemistry. For instance, values expressing a clay content obtained from NIR or K40 testing could be used to obtain a corresponding gradation in clay content.
With reference to
Still referring to
In the context of the present disclosure, when referring to water chemistry assessment, it is to be understood that different variables can be obtained in accordance with the information that can be useful for subsequent contribution to the determination of an enhanced dosage of caustic soda to reach a predetermined target recovery level of bitumen.
In some implementations, clay content and/or water chemistry can be monitored continuously, in contrast to an offline monitoring performed once a day for instance, to facilitate enhanced dosing of caustic soda for enhanced bitumen recovery performance. In some scenarios, the continuous monitoring can be an advantageous strategy for determining the amount of caustic soda required for achieving a target recovery level of bitumen as a processing plant evolves from a startup plant to a mature plan. In particular, as the processing plant evolves from a start up to a mature plant, water chemistry can change as fresh water is progressively replaced by recycled water to be used as process water, and/or characteristics of oil sands ore can change, particularly in terms of clay content, which can influence caustic soda dosing requirements.
There are various methods described herein for performing automated real-time, or online, control of caustic addition in response to continuous monitoring of clay content and water chemistry of process water in order to facilitate bitumen recovery and separation performance.
There may be an interest in monitoring the transition from a very low caustic dosage, even no caustic addition at all, to a higher caustic dosage to mitigate the effects of water chemistry changes as a plant evolves from a startup phase to a mature phase, particularly as the salinity of the process water increases with recycle water having gone through many process cycles. On the other hand, real-time caustic dosage adjustments based on measured characteristics may not be as beneficial in the first few years of operation of a process plant, especially as long as mainly fresh water is used as process water. Indeed, in accordance with the correlation described above, for a total dissolved salt level below 1250 mg/L and clay content of up to 1.2 meq/100 g according to the MBI testing, no caustic addition is expected to be required to achieve a target bitumen recovery level. However, when using recycled water as process water, which is expected to have a higher salinity than fresh water, it can be advantageous to monitor the water chemistry to adjust caustic dosage addition within a desirable operating dosing range, taking into account the clay content of the oil sands slurry as well. When low-grade oil sands ore is mined and supplied to a mixing unit to produce an oil sands slurry, the oil sands slurry can have a high clay content that is consistently above a determined threshold level, for instance above 1.0 meq/100 g when MBI testing is used, and thus continuous caustic dosage determination can be advantageously implemented. It is also noted that the water properties and clay content of the ore can fluctuate, e.g., when changing from one water source or another or when mining a new section of the formation, and thus a rapid adjustment of caustic dosage can facilitate adapting to variable characteristics in the slurry feed to the PSV.
With reference to
Still referring to
Regarding automated or inline implementations, controller(s) 29 can be used and can be operatively connected to the analyzer 27 to control the dosage of caustic soda 21 for addition to the mixing unit 16, the conditioned slurry 18, and/or to the PSV 20, according to the data related to clay content 17 and water chemistry 19 that has been obtained. As schematically represented on
The output values of the analyzer 27 may be sent to the controller 29, which can compare a target bitumen recovery level to a real-time bitumen recovery level. The controller 29, operatively connected to respective caustic dosing valve(s), can then control the amount of caustic to be added in response to the output values to achieve the target bitumen recovery level. The bitumen recovery level can be expressed either as the primary recovery, the secondary recovery, or the total recovery, according to the following formulas:
The above formulas are typically used when assessing recovery levels in a laboratory setting. It is important to note that when a total recovery level is calculated in a so-called real plant setting, the total recovery level can be calculated differently, and can include for instance bitumen recovered from scavenger froth, e.g., tertiary froth. As noted above, clay content may be a single input variable provided to the controller 29, but additional variables can also be measured and provided to enhance the control strategy, such as the amount of water added to the oil sands slurry. Thus, the analyzer 27 can be configured to receive multiple input variables and to provide an output variable related to the dosage of caustic soda that can be added at various locations in the process. The multiple variables may be different clay-based measurements taken from different streams or locations in the facility, and/or various variables related to the water chemistry of the process water. For example, clay content measurements can be made on oil sands ore, oil sands slurry, tailings streams, bitumen enriched streams, middlings streams, and so on. Multiple clay measurements can facilitate redundancy and higher accuracy for the caustic addition control techniques described herein. In some situations, clay can be tracked through the overall facility and various units can be controlled to enhance separation of clay from bitumen and promote high bitumen recovery levels.
In some implementations and with reference to
In some implementations, the clay content of the oil sands ore can be based on an online analysis. K40 and near infrared (NIR) methods can perform in-line measurements and provide clay content in real-time, although other clay measurement methods can be used. In other implementations, an automated MBI analysis can be performed.
Various experiments were conducted to illustrate some aspects of the processes and systems described herein.
With reference to
With reference to
Turning to
With reference now to
With regard to total froth quality for these nine oil sands,
Experiments were conducted to assess the impact of caustic soda (NaOH) addition and salinity levels on total bitumen recovery and total froth quality (B/S) for oil sands having different characteristics, especially in terms of clay content. The impact of caustic soda addition on total bitumen recovery and froth quality (B/S) can be observed as the salinity of the process water is increased.
| Number | Date | Country | Kind |
|---|---|---|---|
| 3.026.676 | Dec 2018 | CA | national |
