Integrated continuous stirred-tank reactors and distillation columns with recycle (CSTR-DC-recycle) are essential components in chemical processes. This paper proposes a method to establish a normal operating zone (NOZ) model to represent allowable variations of the CSTR-DC-recycle chemical processes. The NOZ is a geometric space containing all safe operating points of the CSTR-DC-recycle chemical processes

so that it is an effective model for process monitoring. The novelty of the proposed method is to establish the NOZ model based on boundary points. The boundary points make it possible to capture the actual geometric space irrespective of the space shape. In contrast

existing methods represent the NOZ of processes by fixed mathematical models such as ellipsoidal and convex-hull models; they are not suitable for the CSTR-DC-recycle chemical processes whose NOZs cannot be exactly defined by fixed mathematical structures. Simulated case studies based on Aspen Hysys software are given to illustrate the proposed method.