Poly-optimization of cleaning conditions for pipe systems and plate heat exchangers contaminated with hot milk using the Cleaning In Place method

Abstract

Devices used in food industry that are connected by pipelines are usually cleaned using Clean In Place method. Such a system of cleaning generates high consumption of energy, water and requires the use of chemical cleaning solutions. In this study, we aimed to activate the physical factors in the process of cleaning and minimize the energy consumption. The variable factors considered within this study were flow velocity, pressure, temperature of the cleaning medium (pure water), and cleaning time. The effects of cleaning efficiency and the energy consumed in the cleaning process were taken as the criteria for the evaluation of the cleaning process in Clean In Place station. For the purpose of optimization, these evaluation criteria were opposed to each other; namely, they sought a high cleaning efficiency with a minimal input of energy. Both functions were based on a set of experimental results using the technique of experimental design. A 5-level experimental design, orthogonal and rotatable, was employed. These equations were used in multi-objective optimization process. A polyoptimal model of cleaning conditions was developed. Results were calculated by using Matlab scripts and showed a set of acceptable solutions on the plane of controllable variables (cleaning factors) because of accepted criteria (energy and cleanliness). The dominated and non-dominated points were appointed. These points described cleaning conditions for which it was possible to obtain a better cleanliness without increasing the amount of energy (the dominated points) and conditions for which we were not able to improve any of the tested criteria (the non-dominated points). Finally, the polyoptimal results defining the favorable effects of a cleaning fluid without the use of chemical agents were determined. The results obtained during this study are important from an ecological aspect of the effectiveness of the Cleaning in Place system and may be applied in real conditions for the development of cleaning programs of the analyzed objects (e.g. in a dairy industry for which these experimental studies have been carried out). The obtained set of optimal solutions constitute a basis for further studies in the aspect of energy consumed and an effectiveness of the cleaning process in Clean In Place system.