Otimização da limpeza CIP (clean in place) por meio de vazão pulsada

Abstract

The food industries strive to maintain the quality of their products, reduce costs and avoid problems of food contamination and public health. The sanitizing step is the key to keeping equipment and piping surfaces in proper condition. The objective of this work was (1) to analyze the clean in place (CIP) conventionally employed in the dairy industry; (2) to evaluate the effect of pulsed flow on the CIP process sanitization step, (3) to model and control the flow system in a milk circulation line simulator prototype and (4) to investigate the velocity and shear stress profiles experienced by the using the computational fluid dynamics (CFD). A prototype CIP system with three stainless steel surfaces, typically present in the industry, was used in the shape of two straight cylindrical tubes and an elbow attachment. The coupons were subjected to natural contamination with raw milk for a period of two hours at 37 ° C to promote adhesion and biofilm formation. They were then submitted to conventional CIP sanitization. Alternatively, these coupons were contaminated and sanitized using pulsed flow in different configurations in the sanitization step, according to central composite planning. In both scenarios, the microbial populations were evaluated by rinsing and plating. The flow system was modeled by first order transfer function with dead time (FOPDT) and the pulsed flow control was performed by a PID controller, which was scaled by four different methods: Direct Synthesis, Internal Model, Integral Error (ITAE) and the Hagglund Astrom method and adjusted with fine tuning. In addition, the use of filters for the smoothing of sporadic high-magnitude noises and high-frequency noise was evaluated. Fluid dynamics simulation using FLUENT Academic software was performed to investigate the velocity and shear stress behavior in conventional and alternative sanitization. The modeling of the system with transfer function was satisfactory to represent the flow dynamics, as well as the use of filters smoothed the noise in the measurements collected. In the hygiene, the reduction of the number of colonies was more expressive in the straight stretches as compared to accessory elbow in the conventional hygiene. The ripple and pulsation period variables were significant for the removal of adhered cells to the surface in both evaluated coupons. The CFD technique allowed to know the dynamics of the flow in relation to the speed and shear stress. The larger undulations W> 1 promoted higher decimal reductions of the adhesion due to the annular effect experienced by the surfaces. Thus, it was possible to reduce the operating time of the sanitation stage with the pulsed flow strategy as well as the reduction in energy consumption.