Reduce Overdosing Effects in Chemical Demulsifier Applications by

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Reduce overdosing effects in chemical demulsifier applications by increasing mixing energy and decreasing injection concentration Jeng Yi Chong, Marcio B Machado, Sujit Bhattacharya, Samson Ng, and Suzanne Marie Kresta Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b00621 • Publication Date (Web): 04 May 2016 Downloaded from http://pubs.acs.org on May 15, 2016

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Reduce overdosing effects in chemical demulsifier applications by increasing mixing energy and decreasing injection concentration

Jeng Yi Chong1, Marcio B. Machado1, Sujit Bhattacharya2, Samson Ng2, Suzanne M. Kresta1,* 1 2

Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB, Canada Syncrude Research and Development Centre, Edmonton, AB, Canada

* [email protected] ABSTRACT

It has been known for years that the performance of demulsifier in diluted bitumen dewatering improves up to a certain demulsifier bulk concentration. After this limit, the water removal deteriorates. This phenomenon is called overdosing. In this paper, the effects of mixing energy and demulsifier injection concentration on water removal are studied in systems with high bulk demulsifier concentration. The experiments were conducted in a confined impeller stirred tank (CIST), which provides well controlled mixing conditions with more uniform turbulence and flow than a conventional stirred tank. The results show that an increase in mixing energy and pre-dilution of demulsifier may be able to overcome overdosing effects at high bulk (mean) concentration. If the mixing conditions are well designed, high local demulsifier concentrations at the feed point are avoided and the demulsifier can perform well even at high bulk concentrations. The best demulsifier performance in an overdosed system was obtained with a combination of high mixing energy and low injection concentration, where over 80% of the water content was separated at a demulsifier bulk concentration which showed severe overdosing behavior at poor mixing conditions.

Keywords Mixing energy, overdosing, demulsifier, CIST, bitumen, oil sands.

1. Introduction There is a rich literature on the impact of formulation on the performance of demulsifiers. This literature considers variables such as temperature, pH, salinity, ethylene oxide number, HLB (hydrophilic-lipophilic balance), fluid dynamics and thermodynamics of the surfactant adsorption monolayer, and demulsifier concentration.1-15 Many of these studies are motivated by applications in reservoirs,16 where there is no possibility of impacting local mixing. The bottle test, where samples are shaken in flasks at “high speed” on a shaker table3, 17-21 is frequently used 1 ACS Paragon Plus Environment

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for mixing at the bench scale. The shaker flask, or bottle test, has recently been studied22, 23 and shown to be very low energy devices. At the other end of the spectrum, high speed mixers may be used3, 24 with incomplete specification of the mixing conditions. After mixing, or during gentle mixing, samples may be left to equilibrate for 24 hours if equilibrium is one of the desired conditions in the study.2, 24 There is usually no variation of mixing conditions in these studies, although the effects of mixing on emulsification are clearly reported by Salager, et al. 25 and are well documented in other rate sensitive applications.26 In contrast, during the processing of diluted bitumen, demulsifier is added to very large volumes of fluid and local mixing conditions can vary dramatically. The role mixing plays in bitumen de-watering is still not completely understood, but there is a dramatic difference in the time required to reach a homogeneous concentration if the fluid is added drop wise at a high concentration, or is pre-diluted to be added with a larger volume of fluid at a lower concentration.27 For many years, full scale evidence has indicated that mixing plays an important role in bitumen clarification, but small scale mixing studies have often delivered conflicting results. In recent years, a number of mixing test vessels have been developed to provide well quantified conditions for scale-down tests of the impact of mixing on process performance28. One of these is the confined impeller stirred tank (CIST),29 specifically designed to provide a more quantitative alternative to the bottle test under mixing conditions which more closely replicate conditions found in most processing equipment (e.g. pipes).30 Bitumen froth has water and solids contents of approximately 30% and 10% by mass, respectively. The sum of final water and solids content needs to be decreased to less than 3 % before upgrading. 31, 32 A chemical demulsifier is often used to destabilize the emulsion and minimize the water and fines/clays content in naphtha diluted bitumen.8, 33 Demulsifier performance improves with the bulk demulsifier concentration up to an optimal level. Once the concentration exceeds this limit, the chemical is overdosed and its performance deteriorates. 7, 11, 34 It is also known that high local concentrations can drive this multi-mechanism process in unexpected directions. 35 The local concentration of additive and mixing conditions at the feed point are crucial to achieve optimal performance. When the feed rate is greater than the local mixing rate, a plume of high concentration can form before the additive is dispersed into the continuous phase. This phenomenon is known as meso-mixing in the mixing literature. 28, 36, 37 Meso-mixing is eliminated by avoiding high local concentrations. This can be achieved by increasing the turbulence at the feed point, decreasing the feed rate, or decreasing the injection concentration.3740

Laplante, et al. 27 showed that increased mixing has a positive effect on demulsifier performance for diluted bitumen dewatering. Increasing mixing time and/or mixing intensity gave the same demulsifier performance with half the bulk demulsifier concentration. The authors 2 ACS Paragon Plus Environment

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also showed an improvement in performance with pre-dilution of the additive. Both of these observations indicate that in this system there are meso-mixing effects due to high local concentrations in the feed plume. Laplante, et al. 27 also showed that the mixing variables mixing time (tmix) and energy dissipation (εimp) can be lumped into a single variable, the mixing energy (J = εimp*tmix). The results presented by Laplante, et al. 27 indicated that a good set of mixing conditions could significantly improve demulsifier performance under normal dosing conditions. On occasion, the feed quality may change due to a change in the ore body being mined, or due to other changes in the operating conditions. At this point, the water content can drop considerably and the demulsifier dosing may move away from the optimum dose and into an overdosed region. This work sets out to study how mixing and injection concentration affect demulsifier performance when a very high chemical dosage is used, relative to the feed water content.

2. Experimental

The objective of this work is to determine whether mixing energy (J) and demulsifier injection concentration (IC) can overcome overdosing effects. A demulsifier bulk concentration (BC) of 300 ppm was used in most of the experiments. This value is 6 times higher than the concentration sufficient to separate the water droplets 41 and is much higher than the normal operating concentration. The levels of the mixing variables (J and IC) are given in Table 1. The favorable mixing conditions are indicated in bold in the text which follows (+J –IC). Experiments at bulk concentrations of 27 ppm and 50 ppm were carried out to verify that the effects of local concentration and mixing are distinct from the effects of bulk (mean) concentration. The confined impeller stirred tank (CIST), shown on the right hand side of Figure 1, was used as the mixing test cell. Machado and Kresta 29 showed that the CIST provides active circulation and fully turbulent flow all the way to the surface at Re = 3 000. Fully turbulent flow at the surface, where the demulsifier is added, is ideal for decreasing the dissolution time and reducing high local concentration, avoiding meso-mixing effects and providing reproducible bench scale experimental data which can be used to specify local mixing conditions in the plant. The CIST provides a number of other advantages over conventional mixing devices: • It is designed to have a uniform turbulence distribution in order to provide reliable mixing specifications for scale-up: o The vessel is filled with at least five impellers per three standard tank volumes (one standard tank volume is defined as a tank where H=T) whereas a standard 3 ACS Paragon Plus Environment

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• • • •

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stirred tank would have only one impeller per standard tank volume. Five impellers provide more uniform agitation and turbulence distribution. o The upper impeller is placed at one impeller diameter below the surface, a large enough submergence to avoid air entrainment42 but close enough to the surface to increase turbulence at the feed point, thus reducing high local additive concentrations quickly. o The inactive volume in transitional flow is considerably smaller than in a conventional stirred tank (3% instead of 33%).43, 44 It can provide different ranges of energy dissipation by using different impeller geometries.45, 46 The vessel has a high H/T ratio, ideal for tests where settling height is important. The CIST allows for immediate settling after mixing without sample transfer. The footprint per CIST is smaller, which allows for several simultaneous experiments in one fume hood. Details of the dimensions and geometry are provided by Machado and Kresta 29. The CIST can be used for smaller sample volumes (1 L) compared to standard bench scale stirred tanks (10 L). This significantly reduces the material handling (feed and waste).

As the CIST has a non-standard geometry, scale-up has to be done based on the reproduction of the total mixing energy (J/kg)47, 48 at both bench and industrial scales. Machado and Kresta 30 provide a procedure showing how to mimic conditions from an industrial scale pipeline in the CIST.

2.1.Experimental procedure

A single batch of diluted bitumen provided by Syncrude Research was used as the feed in the experiments. The diluted bitumen had a naphtha to bitumen ratio (N/B) of 0.7 by weight. The kinematic viscosity of the diluted bitumen measured at 80 ºC was 6.1x10-6 m2/s and the density was 860 kg/m3. The samples were stored in 4 L paint cans upside down at 5°C in a refrigerator until use. The demulsifier belongs to a class of chemical that contains propylene and ethylene oxide copolymer and is used to break the water-in-bitumen emulsion. The carrier fluid contains mostly xylenes. The formulation is known to be successful for this application. Since the objective of this study is to quantitatively assess the impact of mixing on demulsifier performance, the demulsifier formulation, diluted bitumen concentration, and temperature were all held constant.

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The protocol for testing the demulsifier performance as reported by Laplante, et al. 27 was followed. A schematic is shown in Figure 1.The experimental procedure is divided into three steps: sample preparation, demulsifier injection and dispersion, and batch gravity settling. In the pre-heating and re-suspension step shown on the left hand side of Figure 1, the diluted bitumen sample in metal container was first agitated by hand before heating. The container was then installed in the mixer and heated for 30 minutes to 60°C without mixing. The sample was then mixed for 15 minutes using a 45° PBTD impeller (N = 1000 rpm, D = T/2) while heating to 76.5°C. A set of baffles (w = T/10) was used to promote solids and water suspension. At the end of the pre-mixing step, a sample was withdrawn from the can for Karl Fischer titration to determine the initial amount of water in the diluted bitumen. The premixed diluted bitumen was then transferred to two CISTs (right hand side of Figure 1) using a Masterflex Pump and disposable tubing. The CIST tank geometry and mixing specifications are given in Table 2. The CIST is a 1 L baffled stirred tank (H/T = 3), agitated with either 6 Intermig or 5 Rushton impellers. The lower impeller had an impeller off-bottom clearance C=D/3 and the upper impeller had a submergence S=D. The impellers were evenly spaced over the shaft. The power numbers as a function of Reynolds number for each impeller were measured using triethylene glycol at 25ºC (kinematic viscosity = 6 x10-6 m2/s) by Machado and Kresta 29 using the methodology described by Chapple, et al. 49 The temperature was held constant at 76.5°C throughout the mixing and settling periods. The demulsifier was diluted with xylenes to the desired injection concentration. It was injected 1 minute after the impeller was turned on using an appropriately sized syringe or a syringe pump connected to 0.3 cm polyethylene tubing. The injection took place directly above the upper impeller blade tip over 2 seconds to promote high initial dispersion of demulsifier. For cases with a diluted demulsifier volume larger than 1 ml, the injections were carried out using a syringe pump at a controlled flow rate. Mixing continued until the specified mixing time was reached, as given in Table 1. Samples were collected 60 seconds after demulsifier injection and 30 seconds before the end of mixing and analyzed for water content. The samples were taken 3 cm below the liquid surface using 0.6 cm ID polyethylene tubing attached to an auto-pipette. Following the mixing period, the diluted bitumen was left in the CIST and allowed to settle by gravity for 60 minutes. The diluted bitumen was sampled 3 cm below the liquid surface at 1, 3, 5, 7, 10, 30, and 60 minutes. One sample was collected at each time step and the water content was measured in triplicate within 24 hours using a Kam Controls Karl Fischer titration apparatus. Since water removal from the product (top) layer is the main focus of this work, sampling was limited to the top layer. Additional samples were taken for microscope analysis. A Zeiss Axio Scope A1 Light Transmission Microscope was used along a Zeiss Axio Cam ICc 1 (1.4 megapixel camera) attachment. The full experimental procedure was reported by Leo 50. 5 ACS Paragon Plus Environment

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3. Results

The change in water content over the batch settling time at BC = 300 ppm is shown in Figure 2. The initial water content varied between the samples, from 1.21 to 1.45 wt%, so the normalized water contents are presented here (Cw/Co). The experiment where the total mixing energy is high and injection concentration is low (+J -IC) gave the best performance and 80% of the water was removed. This combination of conditions provides the best mixing performance because the additive is already pre-diluted, limiting the maximum local concentration, and the high mixing energy provides rapid dispersion of the demulsifier. In the opposite condition, when total mixing energy is low and demulsifier injection concentration is high (-J +IC), the worst demulsifier performance is obtained and less than 20% of the initial water is removed after 60 minutes of settling. In this case, zones of high concentration can form before dispersion and dissolution, which forces the demulsifier towards alternate paths which are favored at high demulsifier concentrations, e.g. micelle formation. The exact mechanism is unknown and remains open to further investigation. The use of carefully controlled local mixing conditions also affects the settling rate. For both cases where high mixing energy was used, 60% of the water was separated in the first 10 minutes. This may allow the use of smaller vessels and shorter settling times, or higher throughput in existing vessels. When at least one of the variables is changed to a more favorable level: (-J -IC) and (+J +IC), the performance of the demulsifier was considerably improved. The effect of increasing the total mixing energy is greater than the effect of pre-diluting the demulsifier. 60% of the water was removed in Case (+J +IC) and 40 % of the water was removed in Case (-J -IC). In terms of absolute water content, the trends are the same and the final values were 0.21 wt% for (+J -IC), 0.52 wt% for (+J +IC), 0.77 wt% for (-J -IC) and 0.99 wt% for (-J +IC). In order to determine which variable has the largest impact on the results, the batch settling data was subjected to a multiple linear regression analysis at each instant in time using the regression equation: Cത(t) = β଴ + β୎ X ୎ + β୍େ X ୍େ + β୎∗୍େ X ୎ X ୍େ

(1)

where Cത(t) is the predicted normalized water content, β is the regression coefficient and x is the level of the mixing variable from Table 1 (+1 or -1). Figure 3 shows the effect of each variable in the experimental design at each settling time and the results lead to the same conclusion. Mixing energy has the most significant impact on the water removal when the demulsifier is overdosed. 6 ACS Paragon Plus Environment

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Injection concentration has an increasing impact over increasing settling time. The interaction effect βJ*IC was not significant, so the variables can be considered independent. Diluted bitumen samples were also observed using a microscope to study the behavior of water droplets when the demulsifier dosage was very high. Figure 4a shows the micrograph from the experiment at low mixing energy and low injection concentration (-J –IC) and Figure 4b shows the micrograph from the experiment at high mixing energy and low injection concentration (+J –IC) after 30 minutes of settling. Figure 4a, at low mixing energy (-J –IC), shows abundant tiny water droplets spread evenly throughout the image. The average drop size was ~2µm. Similar images were obtained for experiments (-J +IC) and (+J +IC) where either one or both of the variables mixing energy and injection concentration were unfavorable. The high final water content in these experiments was due to the formation of water droplets that are difficult to coalesce and settle. The formation of tiny water droplets at high dosage is commonly called an overdosing effect. Figure 4b shows an image obtained from the experiment where mixing energy was high and injection concentration low (+J –IC). Large water droplets, with an average drop size of ~4µm, are observed and these droplets coalesce and settle easily. This experiment presented the lowest water content of the four runs. Meso-mixing is avoided and the demulsifier acts under the desired mechanism. This shows that, at least in some cases, overdosing can be overcome with good mixing and pre-dilution. In these cases, overdosing could also be described as a mesomixing effect. Further experiments were conducted to assess the effects of mixing and injection concentration at different bulk concentrations of demulsifier (BC). The performance of bulk concentrations of 27, 50 and 300 ppm was compared at high and low mixing energy. Figure 5a shows the normalized water content over settling time for low mixing energy (J = 120 J/kg) and an injection concentration of 12 wt% at different bulk concentrations. Past 50 ppm, an increase in bulk concentration does not improve the performance of the demulsifier. Low injection concentration itself is not sufficient to ensure good demulsifier dispersion at a high demulsifier bulk concentration. Only 40% of the water was removed when BC = 50 and 300 ppm, and at BC = 27 ppm only 20 % of the water was removed. Figure 5b repeats the experiments in Figure 5a using high mixing energy (J = 24 000 J/kg) and low injection concentration (12 wt %). The water content follows a clear trend where a higher BC removes more water. For instance, at bulk concentrations of 300, 50 and 27 ppm the amounts of water removed from diluted bitumen are 80%, 50% and 40% respectively at 60 min settling time. In all cases, increasing J increased the total water removal. In this case, the demulsifier can still function well at very high bulk concentration, with no undesired overdosing effects, if the mixing and injection concentration levels are both optimized.


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In a recent study of formulation effects17, a significant improvement in formulation increased the water removal by 14%. In our study, a 60% difference in percent water removal, fully 4x larger than the formulation effect, was achieved by controlling mixing conditions between the worst mixing conditions and the best mixing conditions, using the same formulation and bulk concentration of demulsifier.

4. Conclusions

This study shows that high mixing energy combined with pre-dilution may be able to overcome the effects of demulsifier overdosing. If the mixing conditions are well designed, high local concentrations of demulsifier are avoided at the feed point and the demulsifier can perform well even at concentrations significantly higher than the recommended condition. The combination of high mixing energy with low injection concentration (+J –IC) provided the best demulsifier performance. In this case over 80% of the water content was separated at a bulk concentration that would have otherwise caused overdosing with only 2040% water removal. Increasing mixing intensity at the point of injection and lowering injection concentration levels led to the formation of large water droplets, which coalesce and separate easily. If one or both of these variables was compromised, tiny water droplets formed which do not separate. This has important implications for operations, where there is often pressure to inject additive in the concentrated, as-shipped state. Plant conditions are very different from more typically reported laboratory conditions, where very small volumes are mixed in bottle tests at an unknown J or, in some cases, allowed to equilibrate for 24 hours before emulsification and separation. While this study considers a limited range of conditions, it is part of a much larger body of work27, 41, 50-52 which consistently shows the importance of local mixing conditions and mesomixing effects in the process of bitumen dewatering using demulsifiers.

Acknowledgments

The authors would like to thank NSERC and Syncrude Canada for financial support, Shaun Leo for the images showed in Figures 4a and b, and Syncrude Canada for the permission to publish the results.


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Nomenclature

BC

demulsifier bulk concentration, ppm

C

impeller off-bottom clearance, m

C0

initial water content, wt%

Cw

water content, wt%

D

impeller diameter, m

H

liquid height, m

IC

demulsifier injection concentration, ppm

J

mixing energy, J kg-1

N

impeller rotational speed, rpm

NP

power number

P

power, W

PBTD

pitched blade turbine – down-pumping

S

impeller submergence, m

T

tank diameter, m

tmix

time, min

VIMP

impeller swept volume, m3

VTANK

tank volume, m3

XIC

injection concentration, ppm

XJ

mixing energy, J kg-1

β

regression coefficient

εave

rate of dissipation of turbulent kinetic energy per unit mass, W kg-1

εimp

rate of dissipation of turbulent kinetic energy per unit mass in the impeller swept volume, W kg-1

ρ

density, kg m-3

References 9 ACS Paragon Plus Environment

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20. Pensini, E.; Harbottle, D.; Yang, F.; Tchoukov, P.; Li, Z.; Kailey, I.; Behles, J.; Masliyah, J.; Xu, Z., Demulsification Mechanism of Asphaltene-Stabilized Water-in-Oil Emulsions by a Polymeric Ethylene Oxide–Propylene Oxide Demulsifier. Energy & Fuels 2014, 28, (11), 6760-6771. 21. Mohammed, R. A.; Bailey, A. I.; Luckham, P. F.; Taylor, S. E., Dewatering of crude oil emulsions 3. Emulsion resolution by chemical means. Colloids and Surfaces A: Physicochemical and Engineering Aspects 1994, 83, (3), 261-271. 22. Weheliye, W.; Yianneskis, M.; Ducci, A., On the fluid dynamics of shaken bioreactors- flow characterization and transition. AIChE Journal 2013, 59, (1), 334-344. 23. Rodriguez, G.; Weheliye, W.; Anderlei, T.; Micheletti, M.; Yianneskis, M.; Ducci, A., Mixing time and kinetic energy measurements in a shaken cylindrical bioreactor. Chemical Engineering Research and Design 2013, 91, (11), 2084-2097. 24. Rondón, M.; Bouriat, P.; Lachaise, J.; Salager, J.-L., Breaking of Water-in-Crude Oil Emulsions. 1. Physicochemical Phenomenology of Demulsifier Action. Energy & Fuels 2006, 20, (4), 1600-1604. 25. Salager, J.-L.; Bullón, J.; Pizzino, A.; Rondón-González, M.; Tolosa, L., Emulsion Formulation Engineering for the Practitioner. In Encyclopedia of Surface and Colloid Science, 2nd ed.; Taylor and Francis: New York, 2010. 26. Kresta, S. M.; Etchells, A. W.; Dickey, D.; Atiemo-Obeng, V. A., Advances in Industrial Mixing: A Companion to the Handbook of Industrial Mixing. Wiley: 2015. 27. Laplante, P.; Machado, M. B.; Bhattacharya, S.; Ng, S.; Kresta, S. M., Demulsifier Performance in Froth Treatment: Untangling the Effects of Mixing, Bulk Concentration and Injection Concentration using a Standardized Mixing Test Cell (CIST). Fuel Processing Technology 2015, 138, 361-367. 28. Machado, M. B.; Kresta, S. M., Update to Turbulence in Mixing Applications. In Advances in Industrial Mixing: A Companion to the Handbook of Industrial Mixing, Kresta, S. M.; Etchells, A. W.; Dickey, D. S.; Atiemo-Obeng, V. A., Eds. John Wiley & Sons, Inc.: 2015. 29. Machado, M. B.; Kresta, S. M., The confined impeller stirred tank (CIST): A bench scale testing device for specification of local mixing conditions required in large scale vessels. Chemical Engineering Research & Design 2013, 91, (11), 2209-2224. 30. Machado, M. B.; Kresta, S. M., When Mixing Matters: Choose Impellers Based on Process Requirements. Chemical Engineering Progress 2015, 111, (7), 27-33. 31. Rao, F.; Liu, Q., Froth Treatment in Athabasca Oil Sands Bitumen Recovery Process: A Review. Energy & Fuels 2013, 27, (12), 7199-7207. 32. Gray, M.; Xu, Z. H.; Masliyah, J., Physics in the oil sands of Alberta. Physics Today 2009, 62, (3), 31-35. 33. He, L.; Lin, F.; Li, X.; Sui, H.; Xu, Z., Interfacial sciences in unconventional petroleum production: from fundamentals to applications. Chem Soc Rev 2015, 44, (15), 5446-94. 34. Eisenhawer, A.; Jantunen-Cross, K., Specialty Chemicals in Oil Sands Extraction. In Handbook of Theory and Practice of Bitumen Recovery from Athabasca Oil Sands. Volume II: Industrial Practice, Czarnecki, J.; Masliyah, J.; Xu, Z.; Dabros, M., Eds. Kingsley Canada, 2013. 35. Czarnecki, J.; Moran, K.; Yang, X. L., On the "rag layer" and diluted bitumen froth dewatering. Canadian Journal of Chemical Engineering 2007, 85, (5), 748-755. 36. Patterson, G. K.; Paul, E. L.; Kresta, S. M.; Etchels, A. W., Mixing and Chemical Reactions. In Handbook of Industrial Mixing: Science and Practice Paul, E. L.; Atiemo-Obeng, V. A.; Kresta, S. M., Eds. John Wiley & Sons, Inc.: 2004. 37. Bourne, J. R., Mixing and the Selectivity of Chemical Reactions. Organic Process Research & Development 2003, 7, (4), 471-508. 38. Bhattacharya, S.; Kresta, S. M., Surface feed with minimum by-product formation for competitive reactions. Chemical Engineering Research & Design 2004, 82, (A9), 1153-1160.


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39. Baldyga, J.; Bourne, J. R.; Hearn, S. J., Interaction between chemical reactions and mixing on various scales. Chemical Engineering Science 1997, 52, (4), 457-466. 40. Baldyga, J.; Bourne, J. R.; Yang, Y., Influence of feed pipe diameter on mesomixing in stirred tank reactors. Chemical Engineering Science 1993, 48, (19), 3383-3390. 41. Chong, J. Y. Mixing Effects on Chemical Demulsifier Performance in Diluted Bitumen and Froth. University of Alberta, Edmonton, AB, Canada, 2013. 42. Bhattacharya, S.; Hebert, D.; Kresta, S. M., Air entrainment in baffled stirred tanks. Chemical Engineering Research & Design 2007, 85, (A5), 654-664. 43. Machado, M. B.; Bittorf, K. J.; Roussinova, V. T.; Kresta, S. M., Transition from turbulent to transitional flow in the top half of a stirred tank. Chemical Engineering Science 2013, 98, 218-230. 44. Bittorf, K. J.; Kresta, S. M., Active volume of mean circulation for stirred tanks agitated with axial impellers. Chemical Engineering Science 2000, 55, (7), 1325-1335. 45. Machado, M. B.; Nunhez, J. R.; Nobes, D.; Kresta, S. M., Impeller characterization and selection: Balancing efficient hydrodynamics with process mixing requirements. AIChE Journal 2012, 58, (8), 25732588. 46. Kresta, S. M.; Wood, P. E., The flow field produced by a pitched blade turbine: characterization of the turbulence and estimation of the dissipation rate. Chemical Engineering Science 1993, 48, (10), 1761-1774. 47. Liné, A., Energy consumption to achieve macromixing revisited. Chemical Engineering Research and Design 2015, doi: 10.1016/j.cherd.2015.11.016. 48. Orban, J. A.; Parcevaux, P. A.; Guillot, D. J. In Specific Mixing Energy: A Key Factor for Cement Slurry Quality, SPE Annual Technical Conference and Exhibition, New Orleans, Lousiana, 5-8 October, 1986; Society of Petroleum Engineers: New Orleans, Lousiana, 1986. 49. Chapple, D.; Kresta, S. M.; Wall, A.; Afacan, A., The effect of impeller and tank geometry on power number for a pitched blade turbine. Chemical Engineering Research & Design 2002, 80, (A4), 364372. 50. Leo, S. Measurement and Analysis of Changes in Drop Size Distribution during Bitumen Clarification using Image Analysis. University of Alberta, Edmonton, AB, 2013. 51. Arora, N.; Awosemo, A.; Machado, M. B.; Kresta, S. M., Comparison of Sampling Orientation for Water/Solids Settling Experiments in a Diluted Bitumen System. In 15th European Conference on Mixing, Abiev, R., Ed. Department of Optimization of Chemical and Biotechnological Apparatuses, Saint Petersburg State Institute of Technology: St. Petersburg, Russia, 2015; pp 34-39. 52. Laplante, P. On Mixing and Demulsifier Performance in Oil Sands Froth Treatment. University of Alberta, Edmonton, AB, Canada, 2011.


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Energy & Fuels

Table 1: Variable levels of the 2 factor 2 level design Variable Mixing Energy, J (J/kg) εimp (W/kg) tmix (min) Impeller geometry Injection Concentration, IC (wt%)

(-) 120 1 2 Intermig 12

(+) 24000 40 10 Rushton 39


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Table 2: CIST geometry and mixing specifications Tank Geometry Tank diameter, T (m)

0.075

Tank volume, VTANK (m3)

9.94E-04

Liquid height, H (m)

0.225 Impeller Geometry

Impeller Type

Intermig

Rushton

6

5

Impeller diameter, D (m)

0.05

0.038

Impeller speed, N (rpm)

250

600

Off-bottom clearance, C (m)

0.017

0.013

Submergence, S (m)

0.05

0.038

1.68E-04

4.31E-05

Transitional NP per impeller*

1.3

4.6

εave = P/ρ Vtank (W/kg)

0.18

1.71

εimp ~ P/ρ Vimp (W/kg)

1.08

39.48

Number of impellers

Total impeller swept volume, Vimp (m3)

Reynolds number, Re 1715 2315 *Power number for the CIST was measured using a Torque Transducer and ethylene glycol at 25ºC with a kinematic viscosity of 6x10-6 m2/s.29


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List of figure captions

Figure 1: Schematic of experimental setup and procedure. The sample was pre-mixed and heated to 76.5 ºC and then transferred to the confined impeller stirred tank (CIST). Demulsifier was injected, mixed with the diluted bitumen, and the sample was allowed to settle. There were two CIST’s operating in parallel. Source: Laplante, et al. 27

Figure 2: Diluted bitumen normalized water content during batch gravity settling at BC = 300 ppm. Variable order: (XJ, XIC).

Figure 3: Effects of the variables over settling time at BC = 300 ppm.

Figure 4: Micrographs taken at 30 minutes of settling for BC = 300 ppm: a) Case at low mixing and low injection concentration, tiny water droplets were formed as a result of overdosing effect, b) Case at high mixing energy and low injection concentration, large water droplets that easily separate were formed since the overdosing was overcome.

Figure 5: Normalized water content during batch gravity settling for different bulk concentration of demulsifier. a) XJ = 120 J/Kg, XIC = 12 wt%; b) XJ = 24000 J/KG, XIC = 12 wt%.


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Figure 1: Schematic of experimental setup and procedure. The sample was pre-mixed and heated to 76.5 ºC and then transferred to the confined impeller stirred tank (CIST). Demulsifier was injected, mixed with the diluted bitumen, and the sample was allowed to settle. There were two CIST’s operating in parallel. Source: Laplante, et al. 27 548x441mm (120 x 120 DPI)

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Figure 2: Diluted bitumen normalized water content during batch gravity settling at BC = 300 ppm. Variable order: (XJ, XIC). 241x182mm (96 x 96 DPI)


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Figure 3: Effects of the variables over settling time at BC = 300 ppm. 377x270mm (96 x 96 DPI)


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Figure 4: Micrographs taken at 30 minutes of settling for BC = 300 ppm: a) Case at low mixing and low injection concentration, tiny water droplets were formed as a result of overdosing effect, b) Case at high mixing energy and low injection concentration, large water droplets that easily separate were formed since the overdosing was overcome. 101x179mm (96 x 96 DPI)


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Figure 5: Normalized water content during batch gravity settling for different bulk concentration of demulsifier. a) XJ = 120 J/Kg, XIC = 12 wt%; b) XJ = 24000 J/KG, XIC = 12 wt%. 252x381mm (144 x 144 DPI)


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Reduce Overdosing Effects in Chemical Demulsifier Applications by

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