APPLICATIONS TO REACTOR DESIGN
If we include coke ovens as a typical batch reactor in our definition of gasification, then practically all of these idealized reactor forms have been applied at some time or other in the search for an optimum gasifier design. Of course, what is optimum in any particular case is heavily dependant on the application in hand (chemical or power), the nature of the feedstock, the size of the plant, and a number of other factors as well as the classical trade-off between investment and operating costs. It is therefore not surprising that representatives of most reactor forms still find commercial application today. The various basic gasification processes are discussed against this background and that of the basic theoretical models of PFR and CSTR in Chapter 5, where the implications for some of the commercial processes are also shown.
The systems described in this chapter are extremely complex, which has to date placed limitations on the application of kinetic models to commercial gasification reactor design. Nonetheless “the availability of increasingly powerful computers with a deeper understanding of the physical and chemical processes of coal combustion
now enables the development and use of greater sophistication in the models employed” (Williams etal. 2002). In particular, applications are emerging where their incorporation into computational fluid dynamics (CFD) is proving to be of practical material benefit.
The most important practical applications to date from the knowledge of actual coal kinetics are in the field of combustion, particularly in the field of NOx prediction. However, although CFD already has an important place as a design aid in describing the combustion of coal in utility furnaces, increasing demands are being made to provide quantitative rather than qualitative results (Williams etal. 2002).
Progress is now being made in applying CFD to gasification. In their discussion of the application of CFD to burner developments for Lurgi’s MPG oil gasification burner, Hofmockel, Liebner, and Ulber (2000) describe including kinetic models for bulk and pore diffusion. (This is further detailed in Ulber, 2002). An example from their results of CFD is given in Figure 3-8.
Bockelie etal (2002) have presented initial results for various entrained-flow coal gasifiers, illustrating, for example, performance variations when using different feedstocks. This work is part of an ongoing program to investigate generic improvements for the operation and design of such gasifiers.
The complexity of kinetic calculations ensures that any practical quantitative results are only likely to be accessible via CFD and will therefore remain the realm
of the specialist. Current developments in this field are encouraging, even if the path ahead is still a long one. Optimization of burners and reactor design, as well as their influence on one another, is the area most likely to be a fruitful field of application in the near future.
REFERENCES
Bockelie, M. J., Denison, M. K., Chen, Z., Linjewile, T., Senior, C. L., Sarofim, A. F., Holt, N. A. “CFD Modeling for Entrained Flow Reactors.” Paper presented at Gasification Technologies Conference, San Francisco, October 27-30, 2002.
Biirkle, S. “Reaktionskinetische Charakterisierung abfalltypischer Stoffe und deren Verbrennung in einem Drehrohrofen unter Sauerstoffanreicherung.” Ph. D. diss., Engler - Bunte-Institut der Universitat Karlsruhe (TH), 1998.
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Hofmockel, J., Liebner, W., and Ulber, D. “Lurgi’s Multipurpose Gasification Application and Further Development.” Paper presented at IChemE Conference, “Gasification for the Future,” Noordwijk, The Netherlands, April, 2000.
Jiintgen, H., and van Heek, К. H. Kohlevergasung. Munich: Thiemig, 1981.
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Smoot, L. D., ed. Fundamentals of Coal Combustion. Amsterdam: Elsevier, 1993.
Smoot, L. D., and Smith, P. J. Coal Combustion and Gasification. New York: Plenum, 1985.
Thoenes, D. Chemical Reactor Development. Dordrecht: Kluwer Academic Publishers, 1994.
Ulber, D. “Modellierung der Flugstromdruckvergasung von Ol-Riickstanden.” Ph. D. diss., Rheinisch-Westfalische Technische Hochschule, Aachen: 2003.
Westerterp, K. R., van Swaaij, W. P. M., and Beenackers, A. A. С. M. Chemical Reactor Design and Operation. New York: John Wiley & Sons, 1987.
Williams, A., Backreedy, R., Habib, R., Jones, J. M., Pourkashanian, M. “Modeling Coal Combustion: The Current Position,” Fuel 81 (March 2002):605-618.
Williams, A., Pourkashanian, M., Jones, J. M., Skorupska, N. Combustion and Gasification of Coal. New York: Taylor and Francis, 2000.
Chapter 4
