Determination of the Settling Rate of Aggregates Using the Ultrasound

Aug 29, 2016 - Characteristic settling curves of diluted bitumen froth were obtained by two independent methods: visual observation and an ultrasound ...
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Determination of the Settling Rate of Aggregates Using the Ultrasound Method during Paraffinic Froth Treatment Dominik Kosior,*,†,‡ Edwina Ngo,† and Tadeusz Dabros† †

Natural Resources Canada, CanmetENERGY, 1 Oil Patch Drive, Devon, Alberta T9G 1A8, Canada Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, 30-239 Krakow, Poland

‡

ABSTRACT: This paper presents results of a study on the settling rate of aggregates formed during paraffinic treatment of bitumen froth. Experiments were performed at temperatures ranging from 30 to 90 °C and various solvent/bitumen ratios, using n-pentane, isopentane, and n-hexane as paraffinic solvents. Characteristic settling curves of diluted bitumen froth were obtained by two independent methods: visual observation and an ultrasound technique. The ultrasound study showed that the hindered settling zone interface can be accurately tracked in place using an ultrasound velocity profiler. Problems associated with determining the settling rate by fitting a linear function to the initial part of the settling curve of the upper interface at higher temperatures were avoided by applying the so-called lower interface method. Settling rates determined using the upper and lower interface methods showed good agreement, confirming interchangeability of the methods.

1. INTRODUCTION Recovery of bitumen from mined oil sand involves mixing raw oil sand with hot, aerated water to remove the coarse sand and produce an oil-rich froth.1 Because typical bitumen froth contains 60 wt % bitumen, 30 wt % water, and 10 wt % solids, subsequent processing is required to meet bitumen specifications for pipeline transport and upgrading. This critical process step is called froth treatment.1−3 Paraffinic froth treatment (PFT) uses aliphatic solvent at a solvent/bitumen ratio (S/B) higher than the threshold for the onset of asphaltene precipitation and offers several advantages over conventional froth treatment.4−7 The bitumen product is cleaner, free of emulsified water, solids, and corrosive contaminants, and the process allows for the control of levels of asphaltenic components as well as metals and other heteroatoms.8 The partially deasphalted bitumen product has a reduced viscosity, making it suitable for pipeline transport to distant upgrading and refining facilities.1,2 The PFT product is also more readily processed into value-added products than bitumen produced by conventional means. When bitumen froth is diluted with a paraffinic (aliphatic) solvent at S/B above a certain value, water droplets, dispersed mineral solids, and precipitated asphaltenes tend to aggregate.5,6,8 The settling rate of the aggregates that form in solventdiluted bitumen is one of the most important process parameters and dictates the size of the settler and other separation equipment needed for bitumen froth treatment. It has been established that the settling rate of porous aggregates depends upon their structure, e.g., compactness and size.5,6 Manipulating the aggregate structure thus provides the possibility of enhancing the settling rate. It is well-known that parameters including S/B,4,8 type of paraffinic solvent,6,8 temperature,6 and even mixing intensity9 can significantly affect the settling rate. One of the main difficulties in experimental studies of bitumen froth treatment is rooted in the fact that the suspension of aggregates in diluted bitumen is a completely Published XXXX by the American Chemical Society

opaque mixture. Although the settling rate of the aggregates can be determined by visual observation using glass settlers,5,6,9 it is difficult to investigate the settling rate at elevated temperatures and pressures, where most experiments are carried out in metal autoclaves. Therefore, new instrumental and analytical techniques are needed to study the settling behavior of diluted bitumen froth over a wide range of temperatures and agitation conditions. Besides the video analysis,5,10,11 there are a number of alternative techniques of tracking settling processes, such as turbidity meters,12,13 near-infrared (NIR) spectroscopy,14 electrical capacitance or conductance,15−17 electrical impedance tomography (EIT),18 γ-ray,19,20 X-ray,21,22 and nuclear magnetic resonance (NMR).23 However, most of these techniques are not suitable for froth treatment processes as a result of limitations of working with specific particle concentrations, complex and expensive setups, or even timeconsuming signal analysis.24 In comparison to the above-mentioned methods, the use of ultrasound techniques seems to be very promising for industrial applications. The ultrasonic method exhibits some crucial advantages, including rapid, precise, and non-destructive and non-invasive measurement, instrument design flexibility, and almost no restrictions in operating in dense and optically opaque suspensions.25 The ultrasonic method enables measurement of such parameters as sound velocity, acoustic impedance, and signal attenuation and scattering. The responses of acoustic velocity and attenuation are observed and measured to understand settling processes,26−29 whereas measurements of scattering and absorption of ultrasound signals propagating through a dispersion are used to gain information about the size and concentration of particles.30,31 In addition, a technique combining pulsed ultrasound with Doppler-shift measurement Received: July 12, 2016 Revised: August 27, 2016

A

DOI: 10.1021/acs.energyfuels.6b01714 Energy Fuels XXXX, XXX, XXX−XXX

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provides so-called ultrasound velocity profiling, a method useful for the studies of liquid flow. In this method, an ultrasound pulse propagating through a dispersion strikes small particles in the liquid. As the moving particles scatter the ultrasound energy, the reflected Doppler-shifted echoes travel back to a transducer/receiver that converts the signals into particle velocities.32,33 The ultrasound velocity profiler (UVP) technique has been successfully applied for studies of velocity profiles and rheological flow properties34−37 as well as for tracking settling processes.38 Recently, Hunter et al.39,40 examined the applicability of an acoustic backscatter system that directly measures the voltage strength of an ultrasonic pulse echo as it penetrates through dispersions, providing information about concentration changes along the measurement axis and demonstrating the applicability of this method for determination of the settling rate. Moreover, ultrasound techniques have found application in studies of the behavior of asphaltenes in heavy oils, where the speed of sound and attenuation profiles provide information about phase separation and diffusion mechanisms in heavy oil−solvent mixtures.41,42 The remarkable versatility of ultrasound techniques shows promise of their potential for tracking aggregate settling during bitumen froth treatment. This paper presents a study on the settling rate of aggregates formed during PFT under various conditions. The main objective of this work was to demonstrate the adaptation of an ultrasound technique for measuring the settling rate of aggregates during froth treatment. Settling rates obtained using ultrasound were compared to data obtained by the traditional visual method. This work also includes results from the determination of the influence of the temperature and type of solvent on settling rates and bitumen quality.

Figure 1. (A) Autoclave cell and (B) impellers used for the settling tests.

73 mm below the surface of the test sample, with the actual depth depending upon the solvent, S/B, and temperature. The autoclave vessel was loaded with bitumen froth and solvent at known feed S/B such that the total mass of the mixture was 340 g. All settling tests were performed using froth A. The bitumen froth and the solvent were mixed at 600 rpm and heated over a period of 15 min to the desired temperature (30−90 °C). Once the desired temperature was reached, the mixing speed was increased to 1200 rpm and stirring was continued for another 30 min at a constant temperature. The pressure inside the autoclave was maintained at about 120 psi using pressurized nitrogen supplied from an external tank. When mixing was stopped, visual observation of settling inside the vessel started. The experiment was recorded at a rate of 30 frames per second using a Nikon D800E digital camera equipped with a macro lens (AF-S Micro Nikkor 105 mm). After another 30−60 min (dependent upon the solvent used and the settling rate), 150 mL of diluted bitumen (supernatant) sample was collected in a sampling container. The transfer of the sample from the autoclave to the sampling container was driven by the pressure difference between the autoclave and the ambient atmosphere. The experiment was run at least 2 times for each condition investigated. The video images recorded during the settling test were processed and analyzed using VirtualDub and ImageJ software (GNU General Public License). 2.2.2. Settling Rate. Treatment of bitumen froth with a paraffinic solvent results in the formation of aggregates that consist of emulsified water droplets, dispersed mineral solids, and precipitated asphaltenes. During PFT, the system proceeds in a zone mode, whereby various distinct zones develop during the settling of the aggregates. At least three distinct zones and two interfaces have been confirmed to develop during PFT.5,6 The three zones are identified as an upper clean oil zone (COZ), a middle hindered settling zone (HSZ), and a bottom consolidation zone (CZ). Moreover, a sharp upper interface (UI) can be observed between the COZ and the HSZ, and a lower interface (LI) can be observed between the HSZ and the CZ. Figure 2 presents an typical settling curve obtained by tracking the movement of the interfaces. The settling rate, defined as the descent velocity of the UI, is determined by fitting a linear function to the initial part of the settling curve of the UI; the slope of the fitted line is taken as the settling rate. This method for determining the settling rate has been successfully applied to systems where the movement of the UI could be easily monitored visually.5,6,14 The application of this UI method for determining the settling rate encounters serious difficulties when the visual tracking of the UI is impossible as a result of the lack of a distinct UI and/or rapid settling of the aggregates.9 This issue arises in the case of PFT carried out at elevated temperatures (>60 °C). Problems in determining the settling rate can be avoided by tracking the movement of the LI. At some point during the settling process, the UI and the LI merge, the middle HSZ disappears, and consolidation starts.5,6 This part of the settling curve represents a local maximum

2. EXPERIMENTAL SECTION 2.1. Materials. Two types of bitumen froth produced from the Athabasca oil sands were used as received for this project. Froth composition was determined by Dean−Stark extraction,43 and asphaltene content in the bitumen was measured using the n-pentane precipitation method according to the CANMET procedure for asphaltene analysis. Data for both froths are presented in Table 1. Reagent-grade isopentane (iC5, Fisher Chemicals, 95%), n-pentane (nC5, OmniSolv, 98%), and n-hexane (nC6, Fisher Chemicals, 95%) were used as solvents.

Table 1. Bitumen, Water, and Solids Contents of Bitumen Froths and Asphaltene Content in Bitumen content (wt %) bitumen water solids total asphaltenes in bitumen

froth A

froth B

57.3 32.0 10.7 100 17.1

69.6 16.7 13.7 100 16.7

2.2. Methods. 2.2.1. Settling Tests. Settling tests were carried out in a 630 mL stainless-steel autoclave cell (Parr Instruments Co.) with an inner diameter of 63 mm and a height of 200 mm (Figure 1A). The autoclave cell was equipped with a glass window (25 mm wide × 155 mm high) to allow for visual observation of settling, four baffles, 6 mm wide × 135 mm high each, and two coupled pitched-blade impellers, 35 mm in diameter, to mix the froth with the solvent (Figure 1B). Bottom clearance of the lowest impeller and spacing between the two impellers were 7 and 63 mm, respectively. The top impeller was 60− B

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Diluted bitumen used for the SoS measurement was produced during PFT at T = 30 °C according to the process described under the Settling Tests. Once the settling of aggregates was finished, the autoclave was cooled and opened and the overflow (supernatant) was collected using a glass pipet. The process was repeated to obtain a sufficient volume of diluted bitumen for the next step. The autoclave was then filled with collected supernatant, and the SoS was measured. The SoS in the measurement dialogue of the UVP software was iteratively adjusted such that the signal changes on the measured profile indicating that the wall agreed with the actual measured distance. Figure 4 presents the measured distance between the

Figure 2. Typical settling curve of diluted bitumen froth. called the consolidation point (CP). Thus, the settling rate (ULI) determined by the LI method can be calculated as

ULI =

(Hc − H0) tc

(1)

where H0 is the total height of the bitumen froth solvent mixture in the autoclave (treated as the UI height at t = 0) and Hc and tc are the height and time at CP, respectively. 2.2.3. Ultrasound. A Met-Flow UVP-DUO ultrasound velocity profiler was used for the ultrasound studies. The UVP-DUO can calculate particle velocity using the Doppler-shift method and can also track solid walls or interfaces using an internally calibrated attenuation reading.38,44 In our studies, a single custom-made transducer−receiver probe, designed such that it can be mounted inside the autoclave and works under high pressure (up to 150 psi) and high temperature (up to 110 °C), was used. Its working frequency and active diameter were 4 MHz and 5 mm, respectively. The probe was designed and manufactured by the Imasonic SAS Company. The transducer− receiver probe was connected using a BNC connector to the proper input in the UVP-DUO instrument. Additionally, the echo signal output was used to monitor the received echo by displaying this signal on a Tektronix 2230 oscilloscope. The echo signal was monitored online during experiments to make sure that the proper reflection from the wall or interface was measured. The experimental setup used in our studies on PFT is presented schematically in Figure 3.

Figure 4. Change in the distance to the column base as measured by the UVP-DUO, as a function of different input SoS. The dashed line represents the correct distance value. ultrasound probe and the base of the cylinder for various SoS inputs for n-pentane-diluted bitumen at feed S/B = 1.6 and different temperatures. The dashed line represents the correct distance; thus, points being crossed by the line represent proper values of SoS for the specific conditions. Once the proper value of SoS at a fixed temperature was found, diluted bitumen was warmed by 10 °C and the procedure was repeated, delivering calibration curves for SoS as a function of the temperature (see Figure 5). A similar procedure was applied for supernatants produced using other solvents, i.e., isopentane and n-hexane. After the calibration curves were obtained, the ultrasound probe, simultaneously with visual observation, was used during PFT for tracking the settling processes. 2.2.4. Sample Analysis. Product S/B was obtained by separating the solvent from the diluted bitumen sample using a rotary vacuum evaporator (Rotavapor). The asphaltene content in bitumen was analyzed using the CANMET asphaltene analyzer (NIR spectroscopy),45 and the density of the diluted bitumen was measured at 25 °C using an Anton Paar density meter (DMA 4500).

3. RESULTS AND DISCUSSION 3.1. Settling Rate via Image Analysis. Figure 6 presents settling curves obtained by visual observation, i.e., camera for bitumen froth diluted with n-pentane at S/B = 1.6 and various temperatures. For process temperatures ranging from 30 to 70 °C, the UI was sharp enough to visually monitor its movement. Thus, settling rates were determined by fitting a linear function to the initial part of the settling curve of the UI. In the case of T = 90 °C, where the UI was difficult to observe, the settling rate was determined by tracking the LI. Here, the settling curve passed through a local maximum at tc ≈ 6 s and Hc ≈ 45 mm. Knowing H0 = 148 mm and the position of the CP, it was

Figure 3. Schematic view of the experimental setup for PFT.

The UVP-DUO uses a single probe acting as both a transducer and receiver; thus, distance calculations require information on the speed of sound (SoS) through the studied medium. As the distance from the ultrasound probe to the autoclave base was fixed at 131.5 mm, the SoS of the studied medium was obtained by tracking the measured distance to the autoclave base for different input values of SoS. C

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Figure 7. Settling curves of bitumen froth diluted with n-pentane at S/ B = 1.6 and T = 70 °C. Figure 5. SoS in solvent-diluted bitumen as a function of the temperature.

PFT in the oil sand industry. Accordingly, isopentane was set to the same value as for n-pentane; i.e., S/B = 1.6. In the case of PFT performed with n-hexane, S/B was fixed at 2.4 to maintain similar asphaltene rejection as for settling tests performed with n-pentane at S/B = 1.6.8 The settling rates determined for all studied solvents as a function of the temperature are presented in Figure 8. The red circle on the graph marks the values of the

Figure 6. Settling curves of bitumen froth diluted with n-pentane at S/ B = 1.6 and various temperatures determined using a camera.

found on the basis of three independent runs that the settling velocity of the aggregates was 1130 ± 40 mm/min. Figure 7 shows settling curves obtained for three experimental runs carried out at the same condition, i.e., bitumen froth diluted with n-pentane at S/B = 1.6 and T = 70 °C. Runs 1 and 2 verify the good repeatability of the settling tests. Additionally, at this condition, tracking of the UI (runs 1 and 2) as well as the LI (run 3) was found to be easily performed and the results obtained using the LI and UI methods were compared. Settling rates were determined to be 301 ± 10 and 279 ± 13 mm/min for the UI and LI methods, respectively. Similarly, good consistency and interchangeability between the two methods were found for experiments carried out at other conditions. The straight dotted black line on Figure 7 connecting the local maximum with H0 was added to the graph to mimic the UI curve for run 3. Settling tests of diluted bitumen froth were also performed using paraffinic solvents other than n-pentane, i.e., isopentane and n-hexane. The S/B for bitumen froth diluted with npentane was set to 1.6 because this value is commonly used for

Figure 8. Settling rates of bitumen froth diluted with various solvents as a function of the temperature determined using a camera.

settling rates determined using the LI method. As seen, all settling rates below 500 mm/min were found by tracking the UI. Figure 8 also shows a clear correlation: the higher the process temperature of PFT, the higher the settling velocity of the aggregates. It is also seen that settling velocities for PFT using isopentane are always much higher than those using npentane. Settling for n-hexane is slower than for the other two solvents, even though the S/B of n-hexane was the highest. According to these results and literature data,5,14,45 the settling rate dependence upon the solvent used has the following order: isopentane > n-pentane > n-hexane. Although a detailed study of asphaltene precipitation is beyond the scope of this work, a closer look into the results D

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Figure 9. (A) Asphaltene content in bitumen product and (B) product S/B of diluted bitumen as a function of the temperature.

Figure 10. Color graph from UVP-DUO for bitumen froth diluted with n-hexane at T = 30 °C and S/B = 2.4.

obtained from the analysis of the diluted bitumen was performed to provide some additional information about product (supernatant) quality. Figure 9A shows the asphaltene content in the bitumen product (after solvent removal) as a function of the process temperature. The black dashed line marks the asphaltene content in bitumen before PFT (see Table 1). As seen, asphaltene solubility increases with increasing the process temperature, reaching a maximum around 70 °C, and starts to decrease slightly above that temperature. The results obtained are in good agreement with trends for paraffinic solvents presented in the literature.8,46,47 S/B of the diluted bitumen product decreases with increasing the temperature (see Figure 9B), which is probably related to higher bitumen recovery during the process. Additionally, the product S/B is always higher than the corresponding feed S/B for all process conditions, probably for two main reasons: (1) all maltenes not being extracted during the process and (2) the loss of asphaltenes from the bitumen during PFT. Moreover, product S/B of bitumen diluted with isopentane is a little higher than that for n-pentane, even though the feed S/B is similar. This result can be directly related to higher asphaltene precipitation in the case of PFT performed using isopentane. 3.2. Settling Rate via Ultrasound Measurement. Figure 10 presents a color graph from the UVP software obtained for bitumen froth diluted with n-hexane at T = 30 °C and S/B = 2.4. The graph shows the changing instantaneous velocity profiles down the length of the settling column length (y axis) with time (x axis). Because the color graph is formed in terms of absolute distance from the transducer/receiver, then the distance L = 0 mm responds to the probe face. The color chart

bar is used to indicate various velocity regimes and to determine the UI level. Mixing was stopped 30 s after UVPDUO had started, and thus, the mixing stage is indicated at the very beginning of the color graph by a red/orange color. Because the probe was always immersed 10−15 mm below the gas/liquid interface (dependent upon the solvent and temperature), the interface of the HSZ appeared after some time, i.e., when the UI level dropped below the probe face. Two simultaneous processes can be distinguished in the vicinity of UI: (1) settling of the aggregates and (2) upflow of the liquid from the HSZ/CZ into the COZ.48,49 As a result of those processes, the summary velocity at the UI level decreases to near zero values, which is marked on the color graph by a distinct change in color (measured velocity values) to black.38,44 Thus, the settling profile of the UI of the settling zone is represented clearly by the dark curve. It is not yet clear what is responsible for the measured velocities in the COZ. The origin of this signal may be the liquid flowing up from HSZ/CZ, resulting in negative measured velocity values (movement through the probe face), the green color on the chart bar. Additionally, the observed signal could be related to the Brownian motion of asphaltenes and fine solid particles remaining in the supernatant. The dark region in the vicinity of the probe face is associated with the fact that the probe was still in the signal transmission mode, preventing signal acquisition from small distances during that time. Besides the use of the color graph, the UI level was evidenced by tracking the amplitude of raw ultrasound echo directly by the UVP software and additionally by the oscilloscope, where the UI appeared as a series of peaks. E

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probably because of high signal attenuation, which made it impossible to distinguish the required signal from the noise. The study showed that the HSZ interface can be accurately tracked in place using an ultrasound method. The main limitation of this method is the necessity to know the SoS in the studied medium. Thus, some additional studies on SoS in diluted bitumen were performed. At first, we checked if the composition of the bitumen froth influences the SoS of the diluted bitumen. As with froth A, a sufficient volume of diluted bitumen was prepared during PFT using froth B and n-pentane at S/B = 1.6 and T = 30 °C. SoS in diluted bitumen was then measured as described in the Methods. The SoS measurement procedure was repeated for samples of diluted bitumen obtained using froth A and n-pentane and for various S/B. The results of these measurements as a function of the temperature are presented on Figure 13.

Ultrasound measurements were performed simultaneously with visual observation of the settling process, allowing for validation of the results obtained by the UVP-DUO instrument. Settling curves determined using both ultrasound and visual observation (camera) for bitumen froth diluted with n-hexane at S/B = 2.4 at various temperatures are presented in Figure 11.

Figure 11. Settling curves of bitumen froth diluted with n-hexane at S/ B = 2.4 at various temperatures determined using ultrasound and camera.

Furthermore, settling rates for all experiments were obtained by fitting a linear function to the initial part of the settling curves of the UIs and are shown for both methods in Figure 12. Settling curves as well as calculated settling rates show very good agreement between results obtained using the two methods. Unfortunately, it was impossible to obtain complete settling curves for processes carried out at T = 70 °C for iC5 and at T = 90 °C for nC5 and iC5. Tracking of the UI with ultrasound was possible only at a distance up to 30 mm from the probe face. We were unable to obtain proper echo from “deeper” distances,

Figure 13. SoS in n-pentane-diluted bitumen at various S/B as a function of the temperature.

As Figure 13 shows, SoS for samples of diluted bitumen prepared using froth A and froth B in the studied temperature range was identical. This is not surprising because the results of analysis of both supernatants, i.e., density, asphaltene content in bitumen, and product S/B, are very similar (see Table 2). S/B Table 2. Analytical Results for Diluted Bitumen Produced during PFT at T = 30 °C and Used for SoS Measurement solvent

froth

S/B (feed)

S/B (product)

asphaltene (wt %)

density (g/cm3)

SoS (m/s) (T = 30 °C)

nC5 nC5 nC5 nC5 nC5 iC5 nC6

A A B A A A A

1.4 1.6 1.6 1.8 2.2 1.6 2.4

1.55 1.82 1.83 2.01 2.65 1.92 2.71

12.9 10.2 9.50 7.82 5.95 6.25 10.0

0.7377 0.7260 0.7245 0.7144 0.6988 0.7168 0.7256

1091 1073 1076 1070 1055 1042 1121

has a noticeable influence on the SoS of diluted bitumen, unlike the composition of bitumen froth. Results presented in Figure 13 show that increasing S/B causes a decrease in SoS; according to data in Table 2, this effect can be directly related to changes in the density of diluted bitumen.

Figure 12. Settling rates determined by ultrasound and visual observation (camera). F

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(4) Tipman, R. N.; Long, Y. Solvent Process for Bitumen Separation from Oil Sands Froth. U.S. Patent 5,876,592 A, March 2, 1999. (5) Long, Y.; Dabros, T.; Hamza, H. Stability and Settling Characteristics of Solvent-Diluted Bitumen Emulsions. Fuel 2002, 81, 1945−1952. (6) Long, Y.; Dabros, T.; Hamza, H. Structure of Water/solids/ asphaltenes Aggregates and Effect of Mixing Temperature on Settling Rate in Solvent-Diluted Bitumen. Fuel 2004, 83, 823−832. (7) Shelfantook, W. E. A Perspective on the Selection of Froth Treatment Processes. Can. J. Chem. Eng. 2004, 82, 704−709. (8) Long, Y.; Dabros, T.; Hamza, H. Selective Solvent Deasphalting for Heavy Oil Emulsion Treatment. In Asphaltenes, Heavy Oils, and Petroleomics; Mullins, O., Sheu, E., Hammami, A., Marshall, A., Eds.; Springer: New York, 2007; pp 511−547, DOI: 10.1007/0-387-689036_20. (9) Zawala, J.; Dabros, T.; Hamza, H. Settling Properties of Aggregates in Paraffinic Froth Treatment. Energy Fuels 2012, 26, 5775−5781. (10) Rahmani, N. H. G.; Dabros, T.; Masliyah, J. H. Settling Properties of Asphaltene Aggregates. Energy Fuels 2005, 19, 1099− 1108. (11) Lu, X.; Liao, Z.; Li, X.; Wang, M.; Wu, L.; Li, H.; York, P.; Xu, X.; Yin, X.; Zhang, J. Automatic Monitoring and Quantitative Characterization of Sedimentation Dynamics for Non-Homogenous Systems Based on Image Profile Analysis. Powder Technol. 2015, 281, 49−56. (12) Lawler, D. M.; Brown, R. M. A Simple and Inexpensive Turbidity Meter for the Estimation of Suspended Sediment Concentrations. Hydrol. Processes 1992, 6, 159−168. (13) Jethra, R. Turbidity Measurement. ISA Trans. 1993, 32, 397− 405. (14) Long, Y.; Dabros, T. Monitoring the Settling of Water−Solids− Asphaltenes Aggregates Using In-Line Probe Coupled with a NearInfrared Spectrophotometer. Energy Fuels 2005, 19, 1542−1547. (15) Xie, C. G.; Williams, R. A.; Simons, S. J. R.; Beck, M. S.; Bragg, R. A Novel Sedimentation Analyser. Meas. Sci. Technol. 1990, 1, 1216. (16) Uribe-Salas, A.; Vermet, F.; Finch, J. A. Apparatus and Technique to Measure Settling Velocity and Holdup of Solids in Water Slurries. Chem. Eng. Sci. 1993, 48, 815−819. (17) Vergouw, J. M.; Anson, J.; Dalhke, R.; Xu, Z.; Gomez, C.; Finch, J. A. An Automated Data Acquisition Technique for Settling Tests. Miner. Eng. 1997, 10, 1095−1105. (18) Tossavainen, O.-P.; Vauhkonen, M.; Kolehmainen, V.; Youn Kim, K. Tracking of Moving Interfaces in Sedimentation Processes Using Electrical Impedance Tomography. Chem. Eng. Sci. 2006, 61, 7717−7729. (19) Kearsey, H.; Gill, L. A Study of the Sedimentation of Flocculated Thoria Slurries Using a Gamma-Ray Technique. Trans. Inst. Chem. Eng. 1963, 41, 296−306. (20) Kaushal, D. R.; Tomita, Y. Experimental Investigation for nearWall Lift of Coarser Particles in Slurry Pipeline Using γ-Ray Densitometer. Powder Technol. 2007, 172, 177−187. (21) Chu, C. P.; Ju, S. P.; Lee, D. J.; Tiller, F. M.; Mohanty, K. K.; Chang, Y. C. Batch Settling of Flocculated Clay Slurry. Ind. Eng. Chem. Res. 2002, 41, 1227−1233. (22) Yang, Z.; Peng, X. F.; Chu, C. P.; Lee, D. J.; Su, A. Sedimentation of Permeable Floc. Drying Technol. 2006, 24, 1277− 1282. (23) Pilhofer, G. M.; McCarthy, M. J.; Kauten, R. J.; German, J. B. Phase Separation in Optically Opaque Emulsions. J. Food Eng. 1993, 20, 369−380. (24) Williams, R. A.; Xie, C. G.; Bragg, R.; Amarasinghe, W. P. K. Experimental Techniques for Monitoring Sedimentation in Optically Opaque Suspensions. Colloids Surf. 1990, 43, 1−32. (25) McClements, D. J. Ultrasonic Characterisation of Emulsions and Suspensions. Adv. Colloid Interface Sci. 1991, 37, 33−72. (26) Howe, A. M.; Mackie, A. R.; Robins, M. M. Technique to Measure Emulsion Creaming by Velocity of Ultrasound. J. Dispersion Sci. Technol. 1986, 7, 231−243.

4. CONCLUSION Results obtained during settling tests confirmed that the temperature and type of solvent play critical roles in settling processes. Increasing the temperature causes significant increases of the settling velocity of aggregates. On the basis of visual observation of settling processes, the satisfactory agreement between results obtained by the two methods, UI and LI, confirms the accuracy and usefulness of the LI method for settling rate determination in cases where a sharp UI is not observed. Adaptation of the ultrasound method for tracking aggregate settling processes during PFT delivered promising results. Settling rates obtained using ultrasound were in very good agreement with data obtained by the traditional visual method. Despite limitations associated with a need for calibration of the instrument (SoS measurement), the UVP method would likely be useful for determining the settling rate of aggregates during PFT. On the basis of studies on the SoS in diluted bitumen, two factors can be emphasized. First, the type of paraffinic solvent used during PFT has the main influence on SoS in diluted bitumen. Second, for a given solvent, increasing S/B reduces SoS in diluted bitumen.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank Dr. Kim Kasperski for her insightful comments and suggestions. The authors express their gratitude to the Canadian government Program of Energy Research and Development (PERD) for financial support of this project.

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NOMENCLATURE COZ = clean oil zone CP = consolidation point CZ = consolidation zone HSZ = hindered settling zone iC5 = isopentane LI = lower interface nC5 = n-pentane nC6 = n-hexane PFT = paraffinic froth treatment S/B = solvent/bitumen ratio SoS = speed of sound UI = upper interface UVP = ultrasound velocity profiler

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REFERENCES

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DOI: 10.1021/acs.energyfuels.6b01714 Energy Fuels XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.energyfuels.6b01714 Energy Fuels XXXX, XXX, XXX−XXX