Slurry reactor scaleup

J.R. Inga, Scaleup and Scaledown of Slurry Reactors A New Methodology. Ph.D. Thesis, University of Pittsburgh, 1997. 

Chapters 7 and 8 present models and data for mass transfer and reaction in gas-liquid and gas-liquid-solid systems. Many diagrams are used to illustrate the concentration profiles for gas absorption plus reaction and to explain the controlling steps for different cases. Published correlations for mass transfer in bubble columns and stirred tanks are reviewed, with recommendations for design or interpretation of laboratory results. The data for slurry reactors and trickle-bed reactors are also reviewed and shown to fit relatively simple models. However, scaleup can be a problem because of changes in gas velocity and uncertainty in the mass transfer coefficients. The advantages of a scaledown approach are discussed. 

In recent years, the use of coal as a raw material for the productions of hydrocarbons, liquid transportation fuels, chemical feedstocks and solid fuel is gaining importance. Tliree important processes for the achievement of this goal are (1) direct (2) removal of sulfur from coal by oxydesul-indirect coal liquefaction or the Fischer-All of these processes employ three-phase slurry reactors. In this overview, a present state of the art for the models, scaleup, design and other operational problems associated with these processes are briefly evaluated. 

All three processes considered here are exothermic. Since slurry reactors on an industrial scale are operated under close to adiabatic conditions, a major scaleup problem is that of the thermal control of such reactors. Recently, Shah and Carr (10) have described a custom made agitated adiabatic slurry reactor, which can be used to evaluate the thermal behavior of the large scale reactors. 

The design, scaleup and performance prediction of slurry reactors require models which must consider not only the hydrodynamic and mixing behavior of the three phases, but also the mass transfer between the phases along with the intrinsic kinetics. In the DCL and FTS processes, an axial dispersion model is applicable, with the solid phase assumed to follow sedimentation or dispersed flow model. However, in the CCC, where the solid particles take part in the reaction, dispersion model is no longer applicable. 

Various factors should be considered during the scaleup of slurry reactors such as flow regime, backmixing in the different phases, temperature control, controlling regime of the overall reaction, etc. Details of the effects of various factors on scaleup are available in the literature (1,11,21,30,34). In this section, some of the factors which influence the scaleup of slurry reactors as applied to coal technology are briefly mentioned. 

POSSIBLE SCALEUP PROBLEJIS IN SLURRY REACTORS IN COAL TECHNOLOGY... 

Results of simulations. Comprehensive computations have been carried out to detect the behavior of the FT slurry bubble column reactors ( 15, 85). Owing to space limitations only few results will be presented here which are related to reactor scaleup. 

Inga JR. Scaleup and scaledown of slurry reactors a new methodology [Ph.D. thesis]. Pittsburgh (PA) University of Pittsburgh 1997. 

Conventional reactor technologies such as fixed beds and slurry reactors suffer from serious drawbacks. Mass transfer resistance is the crucial factor in the scaleup of processes. Laboratory experiments are often carried out with catalyst particles with diameters clearly less than 1 mm, whereas industrial reactors typically operate with larger catalyst particles ranging from 1 mm to 1 cm. The scale dimensions are illustrated in Figure 9.1. Intrinsic kinetics is thus inevitably coupled to the modeling of mass transfer, as has been illustrated in previous chapters. Internal mass transfer limitations can be suppressed by decreasing the particle size, but the particle sizes in industrial processes cannot be diminished limitlessly, because this would lead to a tremendous increase in the pressiue drop. To overcome this problem, new innovations and structured reactors have been developed, such as catalytic packing element reactors, monoliths, and fiber structures. The aim of these innovations has... 

There are several practical scaleup lessons with heterogeneous catalysts in batch slurry reactions. One often uses four times the catalyst concentration in the lab to achieve the same results in the plant reactor. Plant charge is 1 wt. part for 1000 wt. part, where as in the lab one uses 5 grams or more per 1000 grams. A common error is the confusion between wet (gross) weight and dry weight (net)... 

Solids play different roles in the different processes. In direct coal liquefaction, a part of the solid is dissolved in liquid (mainly in the preheater) and a part (i.e. mineral matter) may act as a catalyst for the hydrogenation reactions. In Fischer-Tropsch slurry processes, solids are catalysts. Finally, in chemical cleaning of coal, only a part of solid (i.e. sulfur) takes part in the reaction following the shrinking core diffusion/ reaction mechanism. The role of solids in the design and scaleup of the reactors for the three processes is therefore different. 

Sehabiague L. Modeling, scaleup and optimization of slurry bubble column reactors for Fischer-Tropsch synthesis [Ph.D. Thesis]. University of Pittsburgh 2012. 

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