Your Success is Our Goal OPTIMIZATION OF HEAT TRANSFER ZONES IN DISTILLATION COLUMNS X International PHOENICS Users Conference Melbourne, May 2004

Your Success is Our Goal Distillation_2004.ppt Slide 2 © IT PS 2004 Vacuum Towers Chemtech Solutions

Your Success is Our Goal Distillation_2004.ppt Slide 3 © IT PS 2004 Vacuum Towers Chemtech - A Siemens Company, Rio de Janeiro / RJ – Brazil Petrobras / CENPES, Rio de Janeiro / RJ – Brazil Bruno de Almeida Barbabela Flávio Martins de Queiroz Guimarães Silvia Waintraub Glaucia Torres AUTHORS

Your Success is Our Goal Distillation_2004.ppt Slide 4 © IT PS 2004 Vacuum Towers INTRODUCTION The use of empty spray sections (no packing) in heat transfer regions of vacuum towers allows a high deep cut operation, due to the reduction of the pressure drop along the column. Simulation studies show that a reduction of 1 mmHg in pressure results in an increase of approximately 0.3% in the gas oils yield. This represents a profit of about US$ 13,000,000 per year for a typical unit with a feed rate of 30,000 m 3 /day. Other benefits are the decrease in investment and maintenance cost. Petrobras has four vacuum towers in Rio de Janeiros refinery designed by Badger Limited in 1975 without any device in the top pump-around section. In the present work we will present the CFD model developed to analyze this kind of tower.

Your Success is Our Goal Distillation_2004.ppt Slide 5 © IT PS 2004 Vacuum Towers INTRODUCTION Spray Nozzles Chimneys

Your Success is Our Goal Distillation_2004.ppt Slide 6 © IT PS 2004 Vacuum Towers PHOENICS VERSION: PHOENICS VERSION: 3.4 MULTI-PHASE MODEL: MULTI-PHASE MODEL: IPSA FULL INTERPHASE PROPERTIES: INTERPHASE PROPERTIES: By GROUND Coding. Customization based on PETROX (Petrobras Process Simulation Tool) routines for calculation of petroleum fractions properties; SPRAY FORMATION MODEL: SPRAY FORMATION MODEL: By GROUND Coding. Spray formation sources based on nozzle characteristics; GENERAL SETTINGS

Your Success is Our Goal Distillation_2004.ppt Slide 7 © IT PS 2004 Vacuum Towers VALIDATION PHASE OPTIMIZATION PHASE TUNNING PHASE Two-dimensional model (simplified) Three-dimensional model Two-dimensional model (simplified) Three-dimensional model SIMULATION STRATEGY

Your Success is Our Goal Distillation_2004.ppt Slide 8 © IT PS 2004 Vacuum Towers GEOMETRY – THE EMPTY SPRAY SECTION

Your Success is Our Goal Distillation_2004.ppt Slide 9 © IT PS 2004 Vacuum Towers GEOMETRY – THE SPRAY NOZZLES

Your Success is Our Goal Distillation_2004.ppt Slide 10 © IT PS 2004 Vacuum Towers GEOMETRY – THE CHIMNEYS

Your Success is Our Goal Distillation_2004.ppt Slide 11 © IT PS 2004 Vacuum Towers ANALYSIS – THE CHIMNEYS VELOCITY ISO-SURFASE

Your Success is Our Goal Distillation_2004.ppt Slide 12 © IT PS 2004 Vacuum Towers Spray generated droplets have a constant and uniform diameter (though it can change along the tower); No interaction between droplets; Since the droplets are very small, they behave as a film, without temperature gradient from the bulk of the droplet to the interface; The vapor phase has an ideal gas mixture behavior; Only the main petroleum fractions were considered for the properties calculation; Diffusive transport of the petroleum fractions into the same phase was not considered. CONSTRAINTS

Your Success is Our Goal Distillation_2004.ppt Slide 13 © IT PS 2004 Vacuum Towers ENERGY TRANSFER The heat transfer between phases is presented below (without convective and diffusive terms) and was based on the heat transfer of small spherical droplets in a continuous vapor phase: Heat Transfer Coefficient (h) Nusselt Number

Your Success is Our Goal Distillation_2004.ppt Slide 14 © IT PS 2004 Vacuum Towers MASS TRANSFER The mass transfer follows the model below and was based on the petroleum fractions properties calculated by the PETROX routines: Mass Transf. Coef. Molar Flux (N i )

Your Success is Our Goal Distillation_2004.ppt Slide 15 © IT PS 2004 Vacuum Towers ATOMIZATION DROPLET SIZE Sauter Diameter (D 32 ) Correlations for the Sauter diameter are presented at Mugele [10] and Lefebvre [12]. The Sauter diameter is employed in atomization efficiency studies where mass transfer and chemical reactions are presented.

Your Success is Our Goal Distillation_2004.ppt Slide 16 © IT PS 2004 Vacuum Towers

Your Success is Our Goal Distillation_2004.ppt Slide 17 © IT PS 2004 Vacuum Towers VALIDATION

Your Success is Our Goal Distillation_2004.ppt Slide 18 © IT PS 2004 Vacuum Towers VALIDATION

Your Success is Our Goal Distillation_2004.ppt Slide 19 © IT PS 2004 Vacuum Towers VALIDATION

Your Success is Our Goal Distillation_2004.ppt Slide 20 © IT PS 2004 Vacuum Towers VALIDATION – CONCLUSIONS The computational model fits well the experimental data for the 2D model, although it must be enhanced for the 3D model. No significant drag of the oil droplets was notified at the current operational conditions. From the analysis of the results, the current 60 o spray cone seems to be not suitable. A wide range nozzle is recommended.

Your Success is Our Goal Distillation_2004.ppt Slide 21 © IT PS 2004 Vacuum Towers

Your Success is Our Goal Distillation_2004.ppt Slide 22 © IT PS 2004 Vacuum Towers CAPACITY FACTOR ANALYSIS RESULTS – CS = 0.05 ft/s TemperatureVelocity

Your Success is Our Goal Distillation_2004.ppt Slide 23 © IT PS 2004 Vacuum Towers CAPACITY FACTOR ANALYSIS RESULTS – CS = 0.10 ft/s TemperatureVelocity

Your Success is Our Goal Distillation_2004.ppt Slide 24 © IT PS 2004 Vacuum Towers CAPACITY FACTOR ANALYSIS RESULTS – CS = 0.20 ft/s TemperateVelocity

Your Success is Our Goal Distillation_2004.ppt Slide 25 © IT PS 2004 Vacuum Towers CAPACITY FACTOR ANALYSIS RESULTS – CS = 0.30 ft/s TemperatureVelocity

Your Success is Our Goal Distillation_2004.ppt Slide 26 © IT PS 2004 Vacuum Towers CAPACITY FACTOR ANALYSIS RESULTS – CS = ft/s TemperatureVelocity

Your Success is Our Goal Distillation_2004.ppt Slide 27 © IT PS 2004 Vacuum Towers CAPACITY FACTOR ANALYSIS RESULTS – CS = 0.35 ft/s TemperatureVelocity

Your Success is Our Goal Distillation_2004.ppt Slide 28 © IT PS 2004 Vacuum Towers RESULTS – SPRAY STABILITY Heat Transfer Height vs. Cs Capacity factor (Cs) Height (m)

Your Success is Our Goal Distillation_2004.ppt Slide 29 © IT PS 2004 Vacuum Towers RESULTS – DROPLET SIZE Dragged Liquid vs. Droplet Size Droplet diameter (micron) Dragged Liquid (%)

Your Success is Our Goal Distillation_2004.ppt Slide 30 © IT PS 2004 Vacuum Towers WIDE RANGE NOZZLE (90 o CONE) RESULTS – CS = 0.14 ft/s TemperatureVelocity

Your Success is Our Goal Distillation_2004.ppt Slide 31 © IT PS 2004 Vacuum Towers WIDE RANGE NOZZLE (90 o CONE) RESULTS – CS = ft/s VelocityTemperature

Your Success is Our Goal Distillation_2004.ppt Slide 32 © IT PS 2004 Vacuum Towers TWO SETS OF NOZZLES (90 o CONE) RESULTS – CS = 0.14 ft/s TemperatureVelocity

Your Success is Our Goal Distillation_2004.ppt Slide 33 © IT PS 2004 Vacuum Towers TWO SETS OF NOZZLES (90 o CONE) RESULTS – CS = ft/s TemperatureVelocity

Your Success is Our Goal Distillation_2004.ppt Slide 34 © IT PS 2004 Vacuum Towers TWO SETS OF NOZZLES (90 o CONE) RESULTS – CS = 0.40 ft/s VelocityTemperature

Your Success is Our Goal Distillation_2004.ppt Slide 35 © IT PS 2004 Vacuum Towers CONCLUSIONS The maximum capacity factor allowed for spray cone stabilization simulated (between and ft/s) was similar to the values reported by experimental observations and experts opinions; Since the simulations showed that the effective height of the heat transfer zone has low dependence on the mean droplet size, it is recommended that the spray nozzles were adjusted to be biased toward the generation of greater droplets in order to minimize the liquid drag; The use of wider angles of sprays reduces the effective height of heat transfer zone despite the loss of spray stability; The use of two levels of distributors is recommended for improve the spray cones stability and reduce the effective height of the heat transfer zone.

Your Success is Our Goal Distillation_2004.ppt Slide 36 © IT PS 2004 Vacuum Towers CONCLUSIONS Although some improvements have to be made, CFD seems to be an useful tool to analyze the performance of heat transfer and spray formation in vacuum towers. The use of this technology on the optimization of current towers and on the project of new ones is recommended to improve their performance.

Your Success is Our Goal Distillation_2004.ppt Slide 37 © IT PS 2004 Vacuum Towers NEXT STEPS Petrobras will use the model to perform other studies: Variation of the liquid reflux temperature Variation of the height of the spray nozzles Calculation of the global heat transfer coefficient To enhance the model of the petroleum mixture, considering more fractions in it.

Your Success is Our Goal Distillation_2004.ppt Slide 38 © IT PS 2004 Vacuum Towers Kontaktadresse: Peter Muster I&S GC Schuhstraße Erlangen Tel: Mail: Your Success is Our Goal Contact: Flávio Guimarães Senior Manager Tel: +55 (21) THANK YOU