Desenvolvimento de um sistema automático para um secador de produtos agrícolas

• Autor(a) principal: Rodrigues, Cristiano Lúcio Cardoso
• Data de Publicação: 2010
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/692
• topic: Automação; Controle; Secagem de grãos; Automation; Control; Grain drying; CNPQ::CIENCIAS AGRARIAS::ENGENHARIA AGRICOLA::ENERGIZACAO RURAL

A prototype of a dryer for agricultural product was developed, and an automatic control system for monitoring and controlling the operation of the prototype was implemented. The fixed bed dryer prototype was developed with recirculation system of the drying airflow, and has three trays with possibility for thin and thick layer drying tests. The heating system of the drying air was composed by four electric resistances with a total power of 3200W. The input of air in the dryer was done by a centrifugal fan coupled to a three-phase induction motor, controlled by a frequency inverter. A control panel was implemented where the devices, which constituted the main and the control circuits of the heating and ventilation systems were installed. For monitoring and control purposes, temperature, relative humidity, and pressure sensors were installed at specific positions inside the dryer, in addition to actuator devices to control temperature and airflow, implemented with 1-WireTM technology. To measure airflow it was used a Pitot tube coupled to a differential pressure sensor. Through the dynamic pressure from the sensor, it was possible to determine the average velocity of the air in the duct and, consequently, the drying airflow, by knowing the cross section area of the duct where air circulates. The moisture content of the product during the drying process was determined by the law of mass conservation. The mass of product at each time was obtained by an automatic weighing system based on load cells. The DS2890 digital potentiometer from the 1-WireTM technology was used to control the operation of the ventilation system, and the heating system of the dryer. The control of the drying airflow was performed using a frequency inverter. The variation of the drying air temperature was performed using a micro-controlled power converter. The devices network was managed by a computer program, responsible to activate the system, and control the ventilation and heating systems. Moreover, the computer program recorded all the measurements and the performed commands, generated graphs and reports and shut down the system when the desired final conditions were met. To validate the system, drying tests were performed with corn, to obtain the drying curves. The results, obtained using the automated system, were: real time data acquisition; control of the temperature and the drying airflow; generating of graphs and reports in the form of text file; and the drying curves. The automatic control system, developed for real time data acquisition, was reliable, versatile and of easy installation and maintenance.