A practical method for identifying the propagation path of plant-wide disturbances

Disturbances in a continuous process often travel along the product stream and affect the performance of the process. To isolate the root cause and find the path along which the disturbance propagates requires an understanding of the cause-and-effect relationships between multiple variables. One way of identifying these relationships is through the time delays between process variables. A practical and robust approach is proposed that uses the cross-correlation function to estimate the time delay between process measurements and derives a qualitative model of the propagation path in the form of a causal map. The approach was applied to an industrial case study of a process affected by a plant-wide disturbance and was able to decide between two alternative root cause explanations. It was also applied successfully to a process with a recycle. The advantages of the proposed method are its ease of implementation and automation as well as simple interpretation of the resulting causal map.