Modelo matemático, análisis y control de comportamiento dinámico de los sistemas frigoríficos de fábricas de congelados vegetales

Abstract

[SPA] El uso del frío es imprescindible en muchos procesos de fabricación dentro de las distintas industrias agroalimentarias. El correcto diseño y funcionamiento del sistema frigorífico como sistema auxiliar de los sistemas de proceso es muy importante para garantizar el éxito del proceso de producción. Además, las instalaciones frigoríficas absorben una parte importante del consumo energético total de las industrias agroalimentarias, como es el caso de una fábrica de alimentos congelados. Los modelos desarrollados, e implementados en esta tesis en el lenguaje de programación C++, simulan el comportamiento dinámico de las instalaciones frigoríficas y de los equipos a los que dan servicio, congeladores y cámaras de conservación de congelados con un reducido número de ecuaciones y parámetros. Con ellos se simula dinámicamente, por una parte, el consumo eléctrico de las instalaciones frigoríficas y sus parámetros de funcionamiento más importantes, y, por otra, la temperatura del aire en el interior de los congeladores y las cámaras de conservación de congelados, como parámetro más importante de funcionamiento de estos equipos.

[ENG] The use of refrigeration is essential in most of food industry. The correct design and good operating of refrigeration systems is very important for success of production. Moreover, the refrigeration systems intake a great part of the total energy consumption in the food industry, like the frozen food plant. In addition, in the food process engineering, the advances in modelling and simulation techniques, permitting a better knowledge of process, make possible an increasing use of modelling applications at industry level. Moreover, the modelization and optimized control of refrigeration systems may have a great incidence in the reduction of energy and manufacturing costs, and on the frozen food quality. The models developed in this thesis simulate the dynamic behaviour of refrigeration systems and process equipments, such as freezing equipments and frozen stores, at its service. Besides, these models are built with a reduced number of equations and parameters. In this manner they are simulated dynamically, the energy consumption of refrigerated systems and their most important working parameters, and, on the other hand, the air temperature inside the freezing equipments and frozen stores. Once the models are determined, they have been linearized to obtain the transfer functions necessary to proceed to the development of control systems. As first step in the construction of the control systems had been proceeded to analyse by means of RGA technique, to obtain the best strategies of control. Two control techniques have been used. The control of compressor by fuzzy logic permits a “smooth” control action, and energy savings. Moreover, the QFT control technique allows the cold store temperature control at different working conditions, the inaccuracy and uncertainties of model, and, above all, the disturbances, in form of energy inputs, like those due to doorway open cycles. Finally a software has been built, named CIMFROZEN. This software performs the simulation of a complete frozen food plant, which makes it possible to analyse the optimum working conditions according to criteria of energy consumption and production scheduling. All these results has been able to validate the utility of modelization and control tools to obtain an energy save and the optimum working conditions inside minimum margins of temperature, of the refrigeration system and cold store for frozen foods.