Stirred-tank reactor solid suspension

Various reactor combinations are used. For example, the product from a relatively low solids batch-mass reactor may be transferred to a suspension reactor (for HIPS), press (for PS), or unagitated batch tower (for PS) for finishing. In a similar fashion, the effluent from a continuous stirred tank reactor (CSTR) may be transferred to a tubular reactor or an unagitated or agitated tower for further polymerization before devolatilization. 

Stirred tanks are typically used for the thermochemical pretreatment. To simulate flow of corn stover slurries in stirred tanks, the rheologic properties of these suspensions must be known. The corn stover slurries in stirred tank reactors typically range from 10 to 40% solids (3). 

FIGURE 7A.9 Hydrodynamic regimes in three-phase (gas-Iiquid-soHd) stirred tank reactors downflow pitched turbine. A, no dispersion of gas solid settled on bottom B, gas dispersed beginning of solid suspension C, gas dispersed off-bottom suspension of solids D, recirculation of mixture and possible surface aeration. (Reproduced from Rewatkaret al. 1991 with permission from American Chemical Society. 1991, American Chemical Society.)... 

Similar to there is absolutely no information in the literature on the critical speed for suspension of solids, in stirred tank reactors fitted with cooling coils. Nikhade et al. (2005) have provided Equations 7A.32,7A.33, and 7A.34 for AA, for the three impellers referred to earlier. is defined as the difference between... 

Guichardon etal. (1994) studied the energy dissipation in liquid-solid suspensions and did not observe any effect of the particles on micromixing for solids concentrations up to 5 per cent. Precipitation experiments in research are often carried out at solids concentrations in the range from 0.1 to 5 per cent. Therefore, the stirred tank can then be modelled as a single-phase isothermal system, i.e. only the hydrodynamics of the reactor are simulated. At higher slurry densities, however, the interaction of the solids with the flow must be taken into account. 

The stirred-tank continuous reactor may be used where a high degree of agitation is necessary, possibly where a solid is held in suspension, where the reaction requires a relatively low holding time, and where backmixing is not detrimental to the yield. 

Solid particle size in stirred tank reactos, loop reactors and bubble columns is usually in the range of 100 - 200 and solid concentration is rather low whereas in multiphase fluidized beds the solid concentration as well as solid particle size is larger. The density difference of liquid and solid usually is large, except in bioreactors, where one is faced also with agglomeration problems and nonnewtonian behavior of the suspension. 

Processes for precipitation of solid products from dissolved reactants are almost always carried out in stirred tanks. The reactors are operated either semi-batchwise or continuously. In both operation modes, one reactant is added to a stirred solution containing an excess of the other reactant. The functions of the stirrer are mixing of the reactants, suspension of the formed solid particles, and promotion of heat transfer to the wall. 

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