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On the Deposition of Paraffin Wax in a Batch Oscillatory Baffled Column

10th Meeting of Process Intensification Network, June 2004. Chemical Engineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh. Centre for Oscillatory Baffled Reactor Applications (C.O.B.R.A). www.COBRA.hw.ac.uk.

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On the Deposition of Paraffin Wax in a Batch Oscillatory Baffled Column

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  1. 10th Meeting of Process Intensification Network, June 2004. Chemical Engineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh Centre for Oscillatory Baffled Reactor Applications (C.O.B.R.A) www.COBRA.hw.ac.uk On the Deposition of Paraffin Wax in a Batch Oscillatory Baffled Column Mr Lukman Ismail, Dr Robin E. Westacott and Professor Xiong-Wei Ni School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS

  2. Outlines of presentation: • Introduction • Experimental set-up and procedure • Result and discussion • Conclusion and future work

  3. Introduction Research objective To investigate the effect of several vital parameters (e.g. T, DT, cooling rates, frequency & amplitude of oscillation) on paraffin wax deposition in a batch oscillatory baffled column (OBC) in order to understand the mechanisms of wax deposition and subsequent prevention and removal in oil pipelines. Can oscillatory motion break up and suspend deposition in pipelines?

  4. Introduction Wax deposition problem • Paraffin wax continues to be a leading problem area in the production and transportation of crude oil. • Severe plugging from the deposition. • Production loss and replacement of pipelines.

  5. Introduction Oscillatory Baffled Column Oscillatory baffled column/reactor is a relatively new mixing technology and offers more uniform mixing and particle suspension than traditional reactors. a) Oscillating the fluid at the base b) Oscillating the baffles at the top

  6. 3-D CFD simulation Real system Reo = 1250 (xo = 4 mm, f = 1 Hz)

  7. Parameters of importance • Three geometrical --- tube diameter (D), baffle diameter (Do) and baffle spacing (L) • Three operational --- oscillation frequency (f), oscillation amplitude (xo) and fluid velocity (u) • Two physical --- fluid viscosity () and fluid density ()

  8. Two Dimensionless Groups Oscillatory Reynolds number  Strouhal number 

  9. Research Strategy Wax deposition without oscillation Wax deposition with baffle oscillation • Effect of time • Effect of temp., DT etc. • Effect of oscillatory parameters in OBC eg. oscillating frequency, amplitude, baffle design, etc.

  10. Experimental set-up Computer Motor Oscillation Thermocouple Hot water reservoir (at initial temp.) Cold water reservoir (at final temp.) Baffles Peristaltic pump • Specifications of the rig: • Diameter 25 mm • Length 130 mm • Baffle spacing 35 mm • Baffle free area 30 % • No. of baffles 2 Figure 1: Experimental set-up

  11. Material selection Wax - most common problem in crude oil compared to other substances eg. asphaltenes and resins. Paraffin wax - Aldrich Chemical, m.p 52-58 oC. Oil Diesel • Less hazardous, less volatile, less error in wax deposit measurement. • - Cheap and easily obtained. - National Oil Company.

  12. Procedure Wax deposit measurement • Stock of wax-oil solution prepared with certain wax-diesel ratio. • Wax-oil was heated to desired initial temperature using hot water in the reservoir. • The column was cooled down for certain designated time. • Uncrystallised wax and oil were then collected by putting the column upside down. • Wax deposit then measured as weight percentage of wax deposited to the total wax-oil weight.

  13. Result and Discussion (w/o osc.) Effect of deposition time • Wax deposition increased steadily with time reaching asymptotic value of 100% . • No liquid flowed out of the column after 7 min. • The wax deposit was in the form of an oil gel. Figure 2: Effect of time on wax deposition for 50 mL of wax solution, 10% initial wax content, initial temperature of 40oC and final temperature of 10oC.

  14. Result and Discussion (w/o osc.) Effect of varying the volume of wax-oil solution in the column • Using different volume of wax-oil solution may affect the result thus fixed volumes were used in every experimental study. • The smaller the volume the more likely the error. Fig. 3: Effect of volume on wax deposition for initial wax of 15.5% with Tinitial =40 oC, Tfinal=15 oC, deposition time of 4 min, cooling water pump speed of 100 rpm

  15. Result and Discussion (w/o osc.) Effect of initial temperature • The higher the initial temperature, the less wax deposited. • The higher the initial temperature, the more heat load in the solution thus less crystallisation. Fig. 4: Effect of initial temperature with constant final temperature of 10 oC on wax deposition. Wax-oil volume is 50mL, deposition time was 2 min., and cooling water pump speed was 100rpm.

  16. Result and Discussion (w/o osc.) Effect of final temperature • The higher the final temp., the less wax deposited. • At temp. of 24 oC, no deposition occurred for 10% initial wax content. Fig. 5: Effect of final temperature on wax deposition with initial temperature of 40 oC, deposition time of 2 min. Cooling-water pump speed was 100 rpm, wax-oil volume was 50 mL and initial wax content was 10%.

  17. Result and Discussion (w/o osc.) Effect of temperature difference (DT) Const. Tinitial – wax deposition increased rapidly Const. Tfinal – Wax deposition decreased gradually Thus, final temperature has more influence on wax deposition Tfinal const. (10oC) Tinitial const. (40oC) Fig. 6: Effect of temperature difference on wax deposition. Comparison between constant DT with constant Tinitial of 40oC and constant DT with constant Tfinal of 10 oC. The initial paraffin wax content used was 10%, deposition time was 2 minutes and cooling water pump speed was 100 rpm

  18. Result and Discussion (w/o osc.) Effect of constant temperature difference with varied initial and final temperature • The higher Tfinal and Tinitial, the less wax deposited. • Effect of Tfinal were more evident. Fig. 7: Effect of constant DT (of 20oC) with varied initial and final temperatures. The initial paraffin wax content used was 10%, deposition time was 2 minutes and cooling water pump speed was at 100 rpm.

  19. Result and Discussion (w/o osc.) Effect of cooling rates • The higher the cooling rates, the less wax deposited. • The longer the crystallisation period, the bigger the crystal, thus more deposit. Fig. 8: Effect of cooling rates (oC/min) on wax deposition . Initial wax content was 40%. Tinitial = 40 oC, Tfinal = 30 oC. Different cooling rates were achieved by varying the cooling water pump speed (25, 50, 100, 150 & 200 rpm).

  20. Result and Discussion (w/o osc.) Effect of initial wax percentage - Wax deposition increased with higher initial wax content with non-linear relation Fig. 9: Effect of initial paraffin wax content (wt..%) on wax deposition. The initial wax content was 10, 20, 40 and 60%. Deposition time was 2 minutes, with cooling water pump speed at 100 rpm, wax-oil volume of 60 mL, Tinitial = 50 oC and Tfinal = 15 oC.

  21. Result and Discussion (with osc.) Effect of oscillation frequency – preliminary results Wax on baffle – less wax collected with oscillation, agitation effect. Wax on column wall – more wax deposited with oscillation, better heat transfer thus better cooling Total wax deposition – generally reduced with oscillation but small increase for higher frequency due to better heat transfer and enhanced cooling. Fig. 10: Effect of oscillation frequency on wax deposition. Initial paraffin wax content was 20%. Deposition time was 2 min., amplitude of oscillations = 30 mm, Tinitial = 40 oC, Tfinal = 15 oC and wax-oil volume = 60 mL.

  22. Result and Discussion (with osc.) Effect of oscillation amplitude – preliminary results • higher amplitude cause earlier crystallisation. • Total wax deposition was reduced over the time Fig. 11: Effect of oscillation amplitudes on wax deposition. Initial paraffin wax content was 20%, frequency of oscillations = 0.86 Hz, Tinitial = 40 oC, Tfinal = 15 oC and wax-oil volume = 60 mL.

  23. Conclusion • The effect of time, initial & final temperature, temperature difference, wax-oil volume, wax-oil ratio and cooling rates without baffle and oscillation had been investigated, and an optimal condition established. • From the preliminary results, increasing in oscillation frequency decreases wax deposition, though increasing the magnitude of the frequencies causes small increase in the total wax deposition. • From the preliminary results, increasing the oscillation amplitude generally decreases the amount of wax deposition.

  24. Future work • More experiments with fluid oscillation to cover a wide range of mixing intensity. • Different baffle designs. • Effect of using other oil such as Octane (C8) and Decane (C10). • Continuous flow system.

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