THERMAL REGIMES IN COCURRENTLY COOLED FIXED-BED REACTORS FOR PARALLELREACTIONS - APPLICATION TO PRACTICAL DESIGN-PROBLEMS

The conditions of existence of the seven feasible thermal regimes for exothermic first-order parallel reactions occurring in cocurrently-coo led fixed-bed reactors are derived here. The diversity of thermal regi mes offered by the cocurrent scheme was applied to solve practical opt imization problems. Theoretical optimal temperature profiles inside th e reactor tubes which maximize the outlet yield of the desired product were determined. These ideal thermal trajectories were very well trac ked by attainable thermal profiles generated by simulation of a cocurr ently-cooled fixed-bed reactor represented by a plug-flow pseudo-homog eneous model. In fact, the objective function values found at feasible operation conditions were very close to the optimal ones. These resul ts indicate that the conventional designs such as constant coolant tem perature or the countercurrent scheme (where only hot-spot or decreasi ng profiles can be generated) could not handle the optimization proble ms as efficiently as the cocurrent configuration. Moreover, the cocurr ent design allows, among other advantages, to reach the specified leve l of conversion (or yield) with higher selectivity and lower maximum t emperature values than the common constant coolant temperature configu ration. These findings imply the possibility of a significant improvem ent in the economics of the plant. (C) 1997 Elsevier Science Ltd.