Korean Journal of Chemical Engineering

, Volume 21, Issue 2, pp 308–317 | Cite as

Operating strategies for Fischer-Tropsch reactors: A model-directed study

  • Hyun-Seob Song
  • Doraiswami Ramkrishna
  • Sinh Trinh
  • Harold Wright
Article

Abstract

A comprehensive parametric study for a Fischer-Tropsch (FT) synthesis process has been conducted to investigate the relation between process parameters and reactor characteristics such as conversion, selectivity, multiplicity, and stability. A flexible model was employed for this purpose, featuring the dependence of Anderson-Shultz-Flory (ASF) factor on composition and temperature. All variable process parameters in industrial FT reactors were subject to variation, including reaction temperature, reactor pressure, feed ratio, inlet mass flux, feed temperature, heat transfer coefficient, catalyst concentration, catalyst activity, etc. While typical trade-off was encountered in most cases, i.e., the change of a parameter in one direction enhances one aspect but deteriorating another, the change of feed conditions gave some promising results. It has been found that decreasing the feed rate (or increasing the residence time) and/or lowering the feed concentration can successfully enhance the conversion up to more than 90% for our specific case, without hurting the product selectivity as well as effectively condense the region of multiple steady states. The benefits and limitations accompanied with the variation of the parameters were discussed in detail and a rational start-up strategy was proposed based on the preceding results. It is shown that the decrease of inlet mass flux (say, 85% decrease of the feed rate or 60% decrease of the feed concentration from the nominal condition chosen here) or the decrease of H2/CO ratio (specifically, below about 0.25), or their combination can eliminate multiple steady states. The resulting unique relation between temperature and manipulated variable (i.e., coolant flow rate) appears to assure a safe arrival at the target condition at the start-up stage.

Key words

Fischer-Tropsch (FT) Synthesis Multiplicity Stability Conversion Selectivity Start-up Strategy 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Adesina, A.A., “Hydrocarbon Synthesis via Fischer-Tropsch Reaction: Travails and Triumphs,”Appl. Catal. A: General,138, 345 (1996).CrossRefGoogle Scholar
  2. Adesina, A. A., Hudgins, R. R. and Silveston, P. L., “Fischer-Tropsch Synthesis Under Periodic Operation,”Catal. Today,25, 127 (1995).CrossRefGoogle Scholar
  3. Barshad, Y. and Gulari, E., “Modification of Product Distribution Through Periodic Operation: Fischer-Tropsch Synthesis Over Ru/ Al2O3,”Chem. Eng. Commun.,43, 39 (1986).CrossRefGoogle Scholar
  4. Bhattacharjee, S., Tierney, J.W. and Shah, Y. T., “Thermal Behavior of a Slurry Reactor: Application to Synthesis Gas Conversion,”Ind. Eng. Chem. Process Des. Dev.,25, 117 (1986).CrossRefGoogle Scholar
  5. Kirillov, V.A., Khanaev, V. M., Meshcheryakov, D., Fadeev, S. I. and Lukyanova, R.G., “Numerical Analysis of Fischer-Tropsch Processes in Reactors with a Slurried Catalyst Bed,”Theor. Found. Chem. Eng.,33, 270 (1999).Google Scholar
  6. Lox, E. S. and Froment, G. F., “Kinetics of the Fischer-Tropsch Reaction on a Precipitated Promoted Iron Catalysts. 2. Kinetic Modeling,”Ind. Eng. Chem. Res.,32, 71 (1993).CrossRefGoogle Scholar
  7. Maretto, C. and Krishna, R., “Modelling of a Bubble Column Slurry Reactor for Fischer-Tropsch Synthesis,”Catal. Today,52, 279 (1999).CrossRefGoogle Scholar
  8. Russo, L. P. and Bequette, B.W., “Impact of Process Design on the Multiplicity Behavior of a Jacketed Exothermic CSTR,”AIChE J.,41, 135 (1995).CrossRefGoogle Scholar
  9. Shah, Y. T., Dassori, C.G. and Tierney, J.W., “Multiple Steady States in Non-isothermal FT Slurry Reactor,”Chem. Eng. Commun.,88, 49 (1990).CrossRefGoogle Scholar
  10. Sie, S. T., “Process Development and Scale Up: IV. Case History of the Development of a Fischer-Tropsch Synthesis Process,”Rev. Chem. Eng.,14, 109 (1998).Google Scholar
  11. Song, H.-S., Ramkrishna, D., Trinh, S. and Wright, H., “Diagnostic Nonlinear Analysis of Fischer-Tropsch Synthesis in Stirred Tank Slurry Reactors,”AIChE J.,49, 1803 (2003a).CrossRefGoogle Scholar
  12. Song, H.-S., Ramkrishna, D., Trinh, S., Espinoza, R. L. and Wright, H., “Multiplicity and Sensitivity Analysis of Fischer-Tropsch Bubble Column Slurry Reactors: Plug-Flow Gas and Well-Mixed Slurry Model,”Chem. Eng. Sci.,58, 2759 (2003b).CrossRefGoogle Scholar
  13. Stern, D., Bell, A. T. and Heinemann, H., “A Theoretical Model for the Performance of Bubble-Column Reactors Used for Fischer-Tropsch Synthesis,”Chem. Eng. Sci.,40, 1665 (1985).CrossRefGoogle Scholar
  14. Van Der Vaan, G. P. and Beenackers, A. A. C. M., “Kinetics and Selectivity of the Fischer-Tropsch Synthesis: A Literature Review,”Catal. Rev. Sci. Eng.,41, 255 (1999).CrossRefGoogle Scholar
  15. Withers, H. P., Eliezer, K. F. and Mitchell, J.W., “Slurry-Phase Fischer-Tropsch Synthesis and Kinetic Studies over Supported Cobalt Carbonyl Derived Catalysis,”Ind. Eng. Chem. Res.,29, 1807 (1990).CrossRefGoogle Scholar
  16. Yermakova, A. and Anikeev, V. I., “Thermodynamic Calculations in the Modeling of Multiphase Processes and Reactors,”Ind. Eng. Chem. Res.,39, 1453 (2000).CrossRefGoogle Scholar

Copyright information

© Korean Institute of Chemical Engineering 2004

Authors and Affiliations

  • Hyun-Seob Song
    • 1
  • Doraiswami Ramkrishna
    • 1
  • Sinh Trinh
    • 1
    • 2
  • Harold Wright
    • 1
    • 2
  1. 1.School of Chemical EngineeringPurdue UniversityWest LafayetteUSA
  2. 2.Conoco Inc.Ponca CityUSA

Personalised recommendations