Scaling down/up three phase reactors

Transcription

1 UGent Francqui Chair 2013 / 5th Lecture Scaling down/up three phase reactors Nikos Papayannakos, Professor National Technical University of Athens School of Chemical Engineering Unit of Hydrocarbons and Biofuels Processing

2 Contents : Origin of Chemical Engineeing Scale down Hydrotreatment Operation of Small Scale Reactors Conclusions

3 A View on the Origins of Chemical Engineering The idea of an Engineer associated with Chemical Processes existed before 1839 First Appearance of the term Chemical Engineering : Dictionary of Arts, Manufacturers and Mines, published in 1839

4 A View on the Origins of Chemical Engineering First official attempts to initiate the Chem Engng profession 1881 G.E. Davis Proposed the formation of a Society of Chemical Engineers in London 1887 G.E. Davis Presented a series of 12 Lectures on the Operation of Chemical Processes ( Unit Operations ) at the Manchester Technical School 1888 M.I.T. / Professor Lewis Moll Norton The first course was offered : Course X Chemical Engineering 1901 G.E. Davis Published a Handbook of Chemical Engineering / Second edition 1904

5 G.E. Davis Industrial Alkali inspector from Manchester, UK Most responsible person for applying the term Chemical Engineering to the emerging profession In his Handbook he stressed the value of A Unit Operations approach Safety practices Large Scale Experimentation (Pilot Plant precursor)

6 Scope of Scaling Down Study at Smaller Scale a Process/Reactor operation with a view to obtain reliable information for Process/Reactor Simulation Design Scale up Benefits of Scaling down Production of data at much smaller effort and time Improved Safety ( Smaller is safer ) Improve the knowledge of Process Characteristics

7 Scaling Down Characteristics Easy to achieve controllable process parameters T, P, flow rates Use of less materials : catalysts, feeds Less energy consumption and disposal problems Higher vessel surface to volume ratios Lower superficial velocities to keep the same space velocities for CF Reactors

8 Hydrotreatment Process I Widely used in refineries Improvement of petroleum product quality Arrange the required product distribution First Commercial Applications ,2 based on data from Pilot Plants Scale Up Bench Scale Units Catalyst Testing 1 J.J.van Deemter, 3 rd Eur. Symp. Chem. Reac. Eng., Pergamon, London, L.D. Ross, Chemical Engineering Progress, 61 (10), 1965

9 Hydrotreatment Process II Trends of current research - Needs Test / Develop Catalysts Activity Deactivation Selectivity (Hydrogenation/Hydrocracking/HDS/HDN/HDO) Spectrum of feeds / Bio-Oils Follow up Improve performance of existing Units Design new Reactors (Industry, Data)

10 HDT Simulation and Design Tools Prediction of Reactor Performance Engineering Software Reliable data from small scale Units Small Scale Units / HDT Reactors Catalyst Volume Bed Height Pilot Scale 1-4 lt 2 4 m N.D. Bench Scale cc cm N.D./ D. Mini Scale 5 10 cc 5 10 cm D.

11 Scaling Down to Mini Scale Reactors Simulation of the Operation of Industrial Three Phase Hydrotreaters Using Data from Mini Scale Reactors

12 Simulation of the Operation of Three Phase Hydrotreaters Industrial Reactors Laboratory Reactors Reaction Kinetics Mass Transfer Hydrodynamics

13 Sulfur Limits in Diesel Oil (EU) Year ppm Catalyst Activity % 500 %

14 Deep Hydrodesulfurization/Hydrocracking Existing HDS Catalysts of Moderate Activity Operating Conditions Reaction temperature Gas and Liquid Flow Rates X Reaction Kinetics Simple and reliable kinetic equations Lumped Power law forms Refractory Sulfur Compounds : Substituted Dibenzothiophenes (DBT) Kinetics of DBTs HDS depends on matrix effects

15 Sterical effects Reagent Structure Relative activity (Houalla et al., 1980) dibenzothiophene S 1.0 2,8- dimethyldibenzothiophene S ,7- dimethyldibenzothiophene S ,6- dimethyldibenzothiophene S methyldibenzothiophene S 0.090

16 Kinetic Equations (1) Compounds - S + s HDS H 2 Hydrocarbons + H 2 S (2) Non Saturated Hydrocarbons + s HYD H 2 Saturated Hydrocarbons (3) Oxygenated Hydrocarbons + shyd H2 Saturated Hydrocarbons R HDS,i E = k R T HDS,ie HDS C 1+ k n H L,i HDS 2 C S,HDS L,H C 2 L,H 2 S R HYD,i E = k R T HYDe HYD C 1+ k n H L,i HYD 2 C S,HYD L,H C 2 L,H 2 S

17 Liquid Phase Mass Balances Boundary condition at the inlet Boundary condition at the outlet Gas Phase Mass Balances Boundary condition at the inlet [ ] [ ] = = = = i L L i L L i L AX x C u x C u d dx C D 0 = =L i dz dx ( ) S H L S,HDS H H n i n L RT E HDS,i L BED i L i i L V LG,i i L AX i L L x C k x x C e k β ε ρ x C H Py β ε a K d dx C D d d d x C u d HDS HDS HDS = + ( ) ( ) = i L i i L V LG,i i G G x C H Py β ε a K d y C u d 1 = = = 0 0 i y i y UGent/FCh13/5L

18 Bench 50 g Mini 5.5 g Experiments with Mini and Bench scale reactors Cylindrical particles Ni-Mo/γ-Al 2 O 3 Gas oil ppm S P : 54 bar T : C G/L : Nl/kg WHSV : h -1 For the diluted beds SiC 250 μm was used Characteristics : The cross section area of the bench reactor is 10 times higher The superficial velocities and the bed height was the same in both reactors

19 Definition of Apparent Activity C S,0 C S,0 BED 1 Same T, P, G/L WHSV, C S,in BED 2 C S,1 C S,2 R = k HDS exp(-e/rt) f(c i,p i ) k HDS,1 k HDS,2 Bed 1 = Reference bed Apparent Activity : η = k HDS,2 / k HDS,1

20 Comparison of Mini Scale and Bench scale reactor performance 1,2 1,0 Diluted Non Diluted Diluted 0,8 η 0,6 0,4 Non Diluted 0,2 0,0 Mini Reactor Bench scale reactor

21 Performance of the Mini Reactor η Mini Reactor WHSV (h -1 ) T1 downflow T2 downflow T3 downflow T1 upflow T2 upflow T3 upflow The same performance in upflow and downflow mode No significant flow effects

22 Distribution of Sulfur groups in up/downflow ppm total S Downflow Upflow CS (ppm) Alkyl-th BT C1-BT C2-BT C3-BT C4-BT DBT C1-DBT C2-DBT C3-DBT+

23 Sensitivity Tests Effect of Péclet on the activity Effect of k L a V on the activity 0.8 η WHSV=2 1/h, T=320 C WHSV = 2 h -1, T1 Diluted Bed WHSV = 1 h -1, T1, Diluted Bed Pe η WHSV=1 1/h, T=320 C, 65 ppm S WHSV = 2 h -1, T1, WHSV=2 Diluted 1/h, T=320 Bed C, 526 ppm S Non-diluted (Upflow) Pe : 9 20 Diluted (Upflow/Downflow) Pe : k L a V (s -1 )

24 Estimation of mass transfer for Mini and Bench reactors M T.. = Pyi ( k a ) C x = ( D ) lgi v opt H i L i i,eff a l V opt Py Hi i C L x i Bench Reactor upflow Mini Reactor upflow Bed Non Diluted Diluted Non Diluted P T u LS u GS a V / l a V / l a V / l (bar) (ºC) (mm/s) (mm/s) (m -2 ) (m -2 ) (m -2 ) 51 T T

25 Mass transfer effects Interfacial M.T. coefficient in Diluted Bench and Mini Reactors the same Same particles, conditions and feeds Same superficial velocities and bed lengths Bench reactor CL bubble Η 2 bubble Η 2 S Wetted catalyst Mini reactor CL bubble Η 2 Η 2 S bubble Wetted catalyst Radial mass transport resistance of the reactants H2 and S-compounds

26 Gas oil kinetics experiments at deep HDS conditions Mini Reactor HAGO and trilobe Ni-Mo catalyst Dilution with 60 μm SiC WHSV: h -1 Τ (ºC) P (bar) G/L (Nl/kg) u GS (mm/s) u LS (mm/s) Evaporation (% wt.) P H2S (bar) C L,H2S (mol/l) T T T T

27 Simulation with 5 pseudo-compounds, the same reactivity Optimization using the points C S >10 ppm and WHSV 2 h η WHSV (h -1 ) T1 T2 T2, G/L+ T3

28 Apparent activity vs. product C S, One or Five preudo-compounds Optimization using the points with C S >10 ppm and WHSV 2 h ± 5% 0.8 η Ultra-Deep HDS T1 T2 T2, G/L+ T C S (ppm)

29 Extrapolation to industrial applications Adiabatic regime Continuous catalyst deactivation Various feed qualities Temperature (K) QUENCH A QUENCH B 605 L 1 = 2.64 L 2 = 5.66 L 3 = Reactor Length (m)

30 A hybrid model for the simulation of industrial hydrotreaters INDUSTRIAL PERFORMANSE (C S,out, Tprofile, HC) MODEL FEED QUALITY (w i, d15, C S,in, T TAIL ) OPERATION VARIABLES (ML, Q, T, P) OPTIMIZER NEURAL NETWORKS DEACTIVATION, KINETIC PARAMETERS MODEL PREDICTION

31 1.5 Prediction of deactivation Training Data Test data 1.0 η % deactivation/year t (days on stream)

32 Dependence of conversion on reactor diameter. Reaction : Acetic acid HDO Reaction Conditions : 0.07 MPa, 150 o C, Gas Phase : Hydrogen (80 %) Nitrogen Liquid Phase : Acetic Acid Catalyst : sulphided NiMo/A l2 O 3 Reaction Conditions : 15 MPa, 450 o C, Gas Phase : Hydrogen (80 %) Nitrogen - Acetic Acid Catalyst : sulphided NiMo/Al 2 O 3 Joshi N., Lawal A., Chemical Engineering Science, 2012, 84,

33 Question : Is it possible to build a reactor in which all the catalyst particles to be equally accessible by the liquid and gaseous reactants? Avoid problems associated with low fluid velocities : Catalyst by-passing Poor gas and liquid distribution through the catalyst bed

34 Spiral Reactor Reactor dimensions Internal Diameter : 0.20 cm Catalyst Length : cm Typical Loaded Catalyst Mass: g Flow mode: ascending and descending No thermowell inside Advantages Structured and repeatable loading > 10 times higher velocities Uniform radial temperature Easy construction Reactor walls partile particle Reactor walls

35 Concluding Remarks Effective reactor Scaling Down must be carefully designed The Mini reactors produce more reliable data for deep HDS simulation than the corresponding Bench Scale one The lower apparent activity of the Bench Scale reactor for low gas and liquid flow rates is attributed to mass transport limitations Conventional kinetic formulations can not be used for ultra deep desulphurization ( exit sulphur concentration < 15 ppm ) Spiral reactor appears very promising for upscale/downscale applications involving three phase catalytic reactions.

36 Thanks are due to : G. Bellos K. Gotsis L. Kallinikos K. Metaxas G. Stefanidis C. Templis Acknowledgements and to : I.F.P., Air Liquide, EL.PE. and M.O.