Design and Performance of Conventional and Fuzzy Controls for a High Temperature Short Time Pasteurization System

Abstract

Fuzzy control was applied in a high-temperature short time (HTST) pasteurization system and experimentally evaluated and compared with proportional-integralderivative (PID)/feedback and PID/feedback/feedforward controllers. The product, a juice model solution, was pasteurized for 91C/40 s in a three-stage plate heat exchange (regeneration, heating and cooling sections). Hot water and propylene glycol were responsible to heat and cool the product, respectively. A control system was designed to assure the pasteurization temperature manipulating the hot fluid flow rate. Controllers were evaluated by means of dynamic behavior of the pasteurization temperature and performance criteria after the imposed step changes of the product inlet temperature. Configured controllers kept the process temperature within HTST requirements, having a variation of Ϯ0,5C, and the similar values of performance criteria indicate an efficiency for all three tested controllers. PRACTICAL APPLICATIONSThe continuous need for better food products, standardized within the consumer demands, has expanded the applications and the search for solutions using automation and control techniques. The use of control strategies and automation in chemical, petroleum and other industrial processes are more intensive as compared with the same applications in food industries. The complex execution of experimental tests in lab-scale or pilot plants is the main reason for the great number of simulations in the process control area. Based on the importance of accomplishing experimental errors and uncertainties, this paper results from an extensive research developed in a pilot plant of HTST process. Theoretical methods for tuning controllers were applied and evaluated. Conventional controllers (PID/feedback and PID/ feedback/feedforward) were tuned and compared with fuzzy control, one of the most recognized nonconventional controllers. Results showed that the requirements to maintain pasteurization temperature after changes in inlet process conditions were performed in all three strategies, indicating the accomplishment of the research purpose.cessing. It is used to sterilize a wide range of liquid foods, including milk, fruit juices and concentrates, cream, yogurt, salad dressing, egg and ice cream mixes (Fellows 2000). Orange juice pasteurization studies have been demonstrated that lower temperatures are sufficient to inactivate microorganism activities, although, to prevent the loss of cloudiness, bs_bs_banner Journal of Food Process Engineering ISSN 1745-4530 58 Journal of Food Process Engineering 36 (2013) 58-65

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