Validation of CUSUM control chart for biofouling detection in heat exchangers

Abstract

Biofouling is an undesirable phenomenon in heat exchangers, which adheres slowly and progressively to the inner surface of the tubes, results in a reduction of the heat transfer, and increases the operating and maintenance costs. Controlling this phenomenon is essential to ensure that the equipment operates under optimal conditions.Different biofouling detection methods are currently available, depending on the properties of the fluid or by means of intrusive elements in the process. In this paper, the validation of the CUSUM control graph as an alternative technique to conventional detection methods is proposed. This type of graph is very efficient in the early detection of slow and progressive changes within a process.In a pilot plant, formed by two tubular heat exchangers, biofouling was allowed to grow until experimental variables indicated that growth had occurred. The biofouling growth was monitored through the evolution of the heat transfer resistance Rf, which is a technique that has been widely validated for this purpose, and through the CUSUM control graphs.The variable Rf, clearly indicates the different phases of growth. However, the evolution of this variable depends on the physical-chemical characteristics and biological activity of water. The CUSUM graphs demonstrated a greater predictive capacity with regard to changes in the biological adherence process. Additionally, their results do not depend on the characteristics of water. This new tool could be simply and economically implemented regardless of the heat exchanger’s location.