Professor Barry Crittenden Department of Chemical Engineering - PowerPoint PPT Presentation

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Professor Barry Crittenden Department of Chemical Engineering

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Professor Barry Crittenden Department of Chemical Engineering
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Professor Barry Crittenden Department of Chemical Engineering

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  1. INTENSIFIED HEAT TRANSFER TECHNOLOGIES FOR ENHANCED HEAT RECOVERY - INTHEAT Professor Barry Crittenden Department of Chemical Engineering University of Bath, Bath, UK, BA2 7AY INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  2. OUTLINE • Bath and its University • INTHEAT work packages • Experimental capability • CFD capability • Fouling & threshold model capability • Compensation plot INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  3. CITY OF BATH Population 85,000 (with two Universities) UNESCO World Heritage City Excellent transport links 40 km from Bristol International Airport 160km west of London INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  4. Modern campus-based university on a 81 hectare site Consistently within the top 10 UK universities in national league tables Research-driven, with high quality teaching and a small, friendly campus THE UNIVERSITY OF BATH Received Charter in 1966 Located on a hill overlooking the City of Bath 13,000 students, including 3,400 international students from over 100 countries Department of Chemical Engineering (9 West) Three Faculties: Engineering & Design Science Humanities & Social Science & School of Management INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  5. INTHEAT WORKPLAN TABLES * Lead: Bath INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  6. INTHEAT WORK PACKAGE 1 Overall objective: Enhancing our understanding of heat exchange under fouling ▪ To develop an advanced CFD tool to improve the heat exchanger performance by adjusting both operating conditions and equipment geometry ▪ To gain in-depth understanding of fouling mechanisms and kinetics of fouling through experiments Task 1.1: Experimental fouling investigation Task 1.2: CFD research on heat transfer Task 1.3: Testing of possible anti-fouling additives Deliverable D1.1: Report on technical review of fouling and its impact on heat transfer (Month 3) Deliverable D1.2: Report on experimental fouling investigation and CFD research on heat transfer enhancement (Month 12) INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  7. FOULING CAN BE VERY COMPLEX AND EXPENSIVE INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  8. EXPERIMENTAL FACILITY Up to 30 bar Up to 300oC bulk Up to 400oC surface Up to 120 kW/m2 flux INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  9. TYPICAL FOULING CURVE (CRUDE B, ≈ 6 WT% ASPHALTENE) Stirred cell conditions: 500 W & 200 rpm (Tso≈ 375oC; Reynolds Number = 12700) For comparison: BP Rotterdam; Downey et al., 1992 Initial fouling rate = 3.5 E-07 m2K kJ-1;Tso = 260oC; Re = 30,000 INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  10. ARRHENIUS PLOT FOR PETRONAS B (@ 200 RPM) 1000/T (K) ln (dRf / dt) = A – E/RT INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  11. EFFECT OF SURFACE SHEAR STRESS ON FOULING RATE (CRUDE A) Shear stresses are obtained by CFD simulation for different stirring speeds Increasing the wall shear stress decreases the rate of fouling for any given surface temperature. Negative fouling with existing deposits can occur for low surface temperatures and high surface shear stresses; this means fouling deposit being removed by surface shear stress. INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  12. PETRONAS B: 2D CFD SIMULATION FLOW & TEMPERATURE FIELDS200 rpm, 500W, 106 kW/m2 Streamlines are shown in both gas and oil phases INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  13. SIMULATION FOR ACTUAL 3-D GEOMETRY Petronas B, 500W, average heat flux: 106 kW m-2, 200 rpm Velocity field Temperature field INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  14. CFD SIMULATION FOR FLUID FLOW IN TUBE WITH INSERTS Velocity field 0 0.013 Z (flow direction) Tube (19mm ID) with medium density inserts (hiTRAN) Linear flow rate: 1m/s, bulk temperature: 423K Vertical slice INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  15. WALL SHEAR STRESS DISTRIBUTION Shear stress data are obtained from the velocity gradient and the turbulent viscosity by CFD simulation Z position begins at just behind the loop edge, ends at the same position of the next loop INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  16. PARTICLE SEDIMENT TEST AT CAL GAVIN Sediments seem to form behind the loop where the shear stress is a minimum INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  17. EQUIVALENT VELOCITY CONCEPT FOR ENHANCED SURFACES Obtain equivalent bare tube velocity by matching surface shear stress of enhanced surface with that of a bare tube Example: hiTRAN medium density insert ■: Velocity; ¤: Shear stress INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  18. APPLICATION OF THE MODEL DEVELOPED FOR FOULING IN BARE TUBE TO TUBE WITH INSERTS ▪ Modified Yeap’s model – replace the velocity in the fouling suppression term with wall shear stress. This model is capable of modelling the effect of velocity more accurately including the velocity maximum behaviour seen for Maya crude ▪ Using equivalent linear velocity in the fouling growth term: ▪ Adopting the concept of equivalent linear velocity would allow the fouling data obtained from experiments with bare tubes to be used for prediction of the fouling in tubes with inserts. INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  19. MODEL APPLICATION Experimental data using Maya crude oil in both a bare tube and a tube fitted with medium density hiTRAN insert (Crittenden et al. 2009). Activation energy E = 50.2 kJ/mol by curve fitting INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  20. THRESHOLD CONDITIONSFor a bare tube and tube fitted with an insert Experimental data using Maya crude in bare tube and tube fitted with medium density insert (Don Phillips 1999). INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  21. COMPENSATION PLOT FOR ALL CRUDE OIL FOULING □: New points added – Crude A Whether the effect is “true” or “false” is not known at present but is probably “false”. Crittenden B D, Kolaczkowski S T, Takemoto T and Phillips D Z, Crude oil fouling in a pilot-scale parallel tube apparatus, J Heat Transfer Eng, 30: 777-785, (2009) INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  22. ISSUES RELATING TO APPARENT ACTIVATION ENERGY Apparent activation energies increase with increasing wall shear stress (ie with velocity & Re). Phenomenon has been observed before for reaction and crude oil fouling systems: Crittenden B D, Hout S A, Alderman N J, Model experiments of chemical reaction fouling, TransIChemE 65A: 165-170, (1987). Crittenden B D, Kolaczkowski S T, Takemoto T and Phillips D Z, Crude oil fouling in a parallel tube apparatus, J Heat Transfer Eng 30: 777-785, (2009). Bennett C A, Kistler R S, Nangia K, Al-Ghawas W, Al-Hajji N and Al-Jemaz A, Observation of an isokinetic temperature and compensation effect for high temperature crude oil fouling, J Heat Transfer Eng 30: 794-804, (2009). Young A, Venditti S, Berrueco C, Yang M, Waters A, Davies H, Hill S, Millan M and Crittenden B D, Characterisation of crude oils and their fouling deposits, J Heat Transfer Eng (in press, 2011). Apparent activation energies increase also with fouling threshold temperatures. Threshold fouling models must use apparent activation energies; if actual activation energies are used then they must be modified using shear stress (or velocity or Re) such as Ebert & Panchal. This begs the question: how can the actual activation energy be determined for use in the Ebert & Panchal, Epstein, and Yeap models? INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  23. CONCLUSION Batch stirred cell can be used to provide crude oil experimental data under various conditions of bulk temperature, surface temperature and surface shear stresses. Threshold conditions can be obtained. Chemicals can be added but long-term non-fouling experiments are not desirable. Within limits, the cell can be used with enhanced surfaces. 3-D CFD modelling allows predictive study of geometric changes including the use of enhanced surfaces. Using the concept of equivalent velocity, a model that has been validated for a bare tube can then be applied to a tube with enhanced surfaces. Moreover, the fouling threshold conditions can be predicted. Temperature and heat flux distributions can also be simulated by CFD. Enhanced external surfaces need to be studied in much the same way. Some experimental validation would, in principle, be possible by adding a simple enhancement to the heat transfer surface of the batch stirred cell. INTHEAT KICK-OFF MEETING 17 DECEMBER 2010

  24. QUESTIONS? INTHEAT KICK-OFF MEETING 17 DECEMBER 2010