Reactor-Design Issues

For the partial heat-transfer coefficients the following equations can be applied [6]  

Cooling of a gas from a tube filled with spheres  

Re = wsdpPg/T g is the Reynolds number in which dp refers to particle diameter, us superficial velocity, pg gas density and r g dynamic viscosity. The exponential term accounts for the enhancement effect due to the catalytic bed. in the Nusselt number the characteristic length is the tube diameter, such that Nu = awdt/7tg. For hydrogen-rich mixtures the thermal conductivity is remarkably high. 

As a typical design, we consider a superficial gas velocity of 0.25 m/s, 6-mm particles, a tube diameter of 50 mm, as well as a density of 1.39 kg/m3, a viscosity of 1.44 x l(T5Ns/m3, a thermal conductivity of 7.40 x 10 5kW/m/K, and a heat capacity of 2.32 kj/kg/K. One gets Rep = 145, which gives heat-transfer coefficients between 70-100W/m2K (Table 5.12). The conclusion is that the gas side indeed controls the overall heat transfer. 

Figu re 5.10 Hot-spot occurrence in the phenol hydrogenation reactor. 

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Reactor design issues for synthesis-gas fermentations. Biotechnol. Prog. 1999, 15 (5), 834-844. 40. 

Additional reactor design issues studied during RRT included the effect of petcoke particle size on conversion,and the effect of reactor temperature on gas composition and HiiCO ratio. 

The recurring themes are the selection and summary of the data associated with the choice of coolant, feel and structural materials, reduction of the steel weight, simplification of the plant design/layout, other important fast reactor design issues, and how to solve feese problems. 

In this section a brief introduction to some of the reactor design issues of relevance to the rest of the chapter is given. For greater depth the authors recommend texts such as Chemical Reactor Engineering by Levenspiel (2007). 

Key reactor design issues are catalyst addition point, polymer withdrawal point, distributor plate design, aspect ratio, operating velocity, and temperature control. Temperature uniformity is critical as the reactor operates close to the polymer melting point. Maldistribution can result in polymer sheet formation or bed collapse under severe eonditions, there ean be complete solidilieation of the reactor. 

Redesigning inlet nozzle ( outlet nozzle) their orientation Pursue other significant reactor design issues... 

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