Estudo da automação de trocadores de calor do tipo casco e tubos

Abstract

This work was motivated from the author's experience as an automation engineer for the transportation industry of petroleum and derivatives, working on improving the temperature control of heavy oil from a heat exchanger shell and tube type. Associated with the inherent problems of industrial thermal systems such as inertia, resistance and thermal capacitance, hysteresis and dead time, there are also limitations due to oversizing or undersizing these plants. Therefore, singlevariable classic controls are ineffective in regulating and reducing the variability of teperature oil, and may take values up to ± 60 º C around the setpoint. This work investigates strategies for controlling the temperature applied to the heat exchanger in accomplishing the task of regulating the temperature of the oil output under load (flow of oil and steam power). Basically, it bring up information about the thermodynamic mechanisms governing the operation of the exchanger. Then, we propose a model based on physical parameters such as dimensions, input and output flows of oil and steam and steel mass of the hull and tubes. Are presented and compared the results of proposed model with real data from an exchanger. The main contribution of this study was to propose a combination of control strategies to regulate the energy consumed by the exchanger, based on the feedback flow of steam and oil inlet. Information flow, pressure and temperature were unified in the variable power and control techniques associated with PID feedback, feedforward and Smith predictor. The arrangement was able to compensate for variations in load as much oil as the flow of steam lines, reducing the variability up to ± 10 ° C. The method of controlling power and strategies of associations was confronted with the classical PID feedback monovariable that besides reducing the wear of the actuator was able to reduce energy waste by up to 69%. At the end of the paper presents simulation results of the proposed controller on the modeling and instrumentation arrangement for implementing the method discussed.