The constraints of output variables

input variables and intermediate variables exist generally in chemical process control.The inconsistency in different constraints cannot make all of constraints satisfied

and optimal controller does not have feasible solutions

which adversely affects production.Based on convex polyhedron geometry

the feasibility analysis of constrained optimal control in chemical processes was transformed into whether two convex polyhedra intersect or not

and the reasonable constraints adjustment was transformed into a series of linear programming or nonlinear programming when the constrained optimization problem was infeasible.An algorithm for feasibility analysis and automatic constraints adjustment of constrained optimal control independent of user intervention was proposed. Simulation results of typical control problem of a heavy oil fractionator proposed by Royal Dutch/Shell Group showed that when the constrained optimization problem was infeasible the proposed algorithm could make constraints adjustment automatically and effectively

with small overshoot

smooth change of control action

and a certain control overdesign.