Design and control of tubular reactor systems with both gas and liquid recycles

Previous studies of tubular reactor systems have explored flowsheets with e ither a gas recycle or a liquid recycle. In this paper, we extend this work to consider a flowsheet with two recycle streams: a large gas recycle from a separator drum and a small liquid recycle from a distillation column. Bo th the steady-state economics and the dynamic controllability of this dual- recycle system are compared with those of single-recycle processes. Three k inetic cases are considered: an irreversible reaction with moderate activat ion energy, an irreversible reaction with high activation energy, and a rev ersible reaction. Results demonstrate that the dual-recycle flowsheet is le ss expensive than the liquid-recycle system for the irreversible reaction c ase, particularly for the high activation energy where the total annual cos t is 50% less. In the reversible reaction case, the liquid-recycle system i s less expensive, because of the need for a high-purity recycle. Control st ructures are developed for all three flowsheets. that provide effective reg ulatory control for large disturbances.