Computational studies of transients in packed tubular chemical reactors



Concentration and temperature transients in a packed-bed tubular chemical reactor were calculated from mathematical models in order to detemine the effects upon the reactor dynamics of several phenomena. The phenomena studied are the thermal capacity of the packing, the resistance to heat flow between the packing and the fluid, the coupling of temperature and concentration through the rate of chemical reaction, axial fluid mixing, radial fluid mixing, and the loss of heat at the wall. Three mathematical models were used: a two-dimensional finite-stage model, a one-dimensional finite-stage model, and a one-dimensional first-order differential model. The chemical reaction considered in these models was an exothermic, homogeneous, liquid phase, second-order reaction.

Machine calculations of transients following step changes in feed temperature or concentration showed that only the first three phenomena were important. It was also found that concentration transients in some cases initially moved in the direction leading away from the final steady state or overshot the final steady state. Further, a concentration node point was found to exist in the reactor under some circumstances. The one-dimensional models considered were shown to be simple but quantitatively and conceptually useful.