Design Considerations for Tubular Reactors

Tubular reactors are rarely scaled in series because of pressure limitations. The great exception to this statement is the high-pressure process for LDPE, where reactor lengths are measured in kilometers. The diameter of the tube is strictly limited to about 5 cm to avoid thermal runaway. A few tubes in parallel, possibly with separate ethylene compressors, can be used to achieve greater capacity, but conventional shell-and-tube designs present a serious problem of tube-to-tube instability. 

Scaleup to large-diameter tubes is generally possible only when the adiabatic temperature rise is acceptable. A practical example of such scaleup is the adiabatic post-reactor that is sometimes added to polystyrene reaction trains as an inexpensive way of boosting capacity. Tubular pilot reactors should be run adiabatically or if some removal of heat is needed, they should be run at the same value of the thermal diffusion group, where oct is the thermal diffusivity. This means run- 

Scaleup of polycondensation reactions involving multifunctional monomers (for example, phenol/formaldehyde) in tubular reactors has proven especially difficult. Even though the overall stoichiometry (for example, formaldehyde at 75 mol% of the entering phenol concentration) is set to avoid crosslinking, locally crosslinked regions near the tube walls can result when the diffusion group, is too 

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R. Shinnar, F. J. Doyle, H. M. Budman, and M. Morari. Design considerations for tubular reactors with highly exothermic reactions, AICHE J., 38, 1729 (1992). 

Shinnar, R., Doyle, F. J., Budman. H. M., and Morari, M. Design Considerations for Tubular Reactors with Highly Exothermic Reactions, AIChE J., 38,1729-1743 (1992). van Heerden, C. Autothermic Processes—Properties and Reactor Design, Ind. Eng. Chem., 45, 1242-1247 (1953). 

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