Effect of desired product split ratio on the design and control of processes with reversible consecutive reactions

This work considers the plantwide control of continuous processes that produce multiple products. The reactions studied are A+B⇔M+C A+M⇔D+C A+D⇔T+C The first part considers a two-product process in which the first two reversible reactions giving desired products M and D occur. The second part considers a three-product process in which the desired products are M, D and T. Steady-state design and dynamic control are explored for both parts. In the two-product case, two fresh feed flowrates of A and B give unique product flowrates. But this is not true for the other case. Some of M is recycled back to the reactor in both cases. In the two-product case, it is sometimes necessary to recycle some D. In the three-product case, a recycle of D or T is required, but not both for most cases.; The control structures for both cases must be able to achieve different production rates. Several conventional control structures are studied in which the flowrates of the fresh feed streams are fixed or manipulated by level or composition/temperature controllers, and the production rates are not directly set. Several “on-demand” control structures are also developed in which the product streams are flow controlled. The control system must adjust the conditions in the plant and the fresh feed streams to achieve the desired product flowrates. The most effective on-demand control structure requires no reactor composition analyzer and has only the necessary recycle of product streams. In the three-product process the product flowrates of M and T set the ratio of the fresh feeds, and the production rate of D sets D or T recycle flowrates.