Projeto de controle de um reator cerâmico para produção de cloreto de alumínio anidro utilizando microcontroladores de hardware livre

Abstract

Aluminium chloride (AlCl3) is a salt commonly applied in industry since it is a Lewis acid. Such feature makes aluminiun chloride a good catalyst in the production of several organic compounds. Between its main applications, there is the production of ethyl benzene and dyes in general. Many raw materials can be used in AlCl3 synthesis by the chlorination of a aluminum source. In one of these paths, vapour hydrogen chloride reacts with metallic aluminum in high temperatures, producing aluminum chloride and hydrogen gas. Alumina based ceramic reactors are used in this case, since the raw materials have a corrosive behavior and to avoid possible contamination of the product with other metals, such as iron from metallic alloy reactors. Ceramic reactors are sensible to fast temperature variations, which could cause fractures by cycle or thermal shock. For this reason the temperature control must be smooth, without fast variations of the supplied power. Therefore, the objective of this work is tuning a temperature feedback control system for a tubular ceramic reactor to produce anhydrous aluminum chloride. The model used is a PID (proportional-integral-derivative) control, which is traditionally used in process control. PID control action on the manipulated variable is proportional to the deviation in the controlled variable (difference between its current value and the desired value), to the integral and to the derivative of this deviation. Two programmable microcontrollers were chosen for the reactor control. The first one was the nodeMCU ESP-8266 with a ESP12F module. This microcontroller can communicate by Wi-Fi signal with other devices, which allows its use for IoT, the “Internet of Things”. Furthermore, it uses a 32-bit processor with a maximum clock of 80 MHz, a good advantage in relation to Arduino Uno, which have a clock of 16 MHz. The second controller used was the Arduino Uno itself. Despite its lower processing capacity, it is more consolidated in market, so it has an advantage in terms of support. The temperature control was realized by the manipulation of the reactor heat supply through the control of the power provided to resistance heating alloy. The relay method was applied for the initial tuning of PID parameters in the reactors without reaction. With this control, we reduced the time of heating until the operating temperature of the reactor about 2 times and the temperature variation caused by external perturbations.