Engenharia Química

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Use of hydrodynamic cavitation as an alternative for biodiesel production
(2009-08-30) SANTOS, S. L. DOS; FERREIRA, M. S.; Maristhela Passoni de Araújo Marin; Luis Novazzi
© 2009 by ABCM.Biodiesel is known as an alternative to conventional petrodiesel because of its renewability and better combustion performance, in addition to reducing emissions, harmful to the environment. Biodiesel production consists on the transesterification of triglycerides with an alcohol and the reaction is affected by the alcohol type, temperature, molar ratio of alcohol to oil and catalyst type and amount. Since this reaction is a heterogeneous one, reagent mixing is also of crucial importance and traditionally the blending is carried out by using mechanical mixers. In this work a different approach is proposed, where the mixing is induced by hydrodynamic cavitation provoked by an orifice plate connected to the suction of a centrifugal pump. Biodiesel production was carried out at 45°C with a 1:8 molar ratio of soybean oil to ethanol. It was observed that the method assisted by hydrodynamic cavitation promotes the enhancement of biodiesel yield in comparison to the conventional method that uses mechanical stirring. In comparative tests carried out from 0 to 40 minutes, the hydrodynamic cavitation always showed conversion rates larger than the mechanical agitation. Although specific energy consumption in biodiesel production is slightly higher for hydrodynamic cavitation when compared to conventional mechanical mixing, it was observed that in the alternative approach the equipment employed is simple and has a low acquisition cost, showing that it has a great potential to be scaled up and used in industrial processes.
Multivariable control of a heat exchanger with bypasses
(2009-07-15) Delatore, F.; DA CRUZ, J. J.; Fabrizio Leonardi; Luis Novazzi
A myriad of different multivariable control techniques, ranging from the simplest isolated PID controllers to the most sophisticated model predictive controls, are presented in the literature and applied to chemical plants. This work intends to present an intermediate control solution between the simplest and the most complex control design, with a relative simplicity, in combination with a superior performance when compared to traditional PID controllers. The proposed strategy, based on a Linear Quadratic Regulator (LQR), was applied to a heat exchanger with bypasses, which is a typical equipment in industries' processes. Even though the LQR is relatively straightforward to design, with a simple tuning procedure, some simulations' results demonstrated that the proposed approach leaded to a reasonable control performance, i.e., process variables became almost totally decoupled, no offset was observed and the output responses presented an small time constant.
Optimal control of heat exchanger networks
(2009-01-05) Luis Novazzi; ZEMP, R. J.
Energy integration among chemical process streams can lead to quite complex heat exchanger networks (HEN) with difficulties in terms of control. In the HEN, the control system primary objective is to keep outlet stream temperatures in a specified range. This objective can be achieved by manipulating bypasses in the exchangers or heat loads in coolers or heaters, which results in a positive degree of freedom, since the number of possible manipulated variables is greater than the number of controlled variables. Thus, a secondary control objective can be set: minimization of utility consumption. In this work HEN dynamics and steady state aspects were addressed with the aim of proposing a control strategy that minimizes utility consumption and satisfies imposed restrictions. With the tools developed in this work it was proposed a feedforward optimal control strategy, which consisted in the minimization of a steady state objective function, connected to utility consumption and subjected to constraints in outlet stream temperatures. The suggested approach is an interesting one since rigid or flexible control objectives can be set. The solution of the minimization problem resulted in optimal bypasses positions in the HEN, which were dynamically implemented using a ramp function and a step function. It was verified that ramp implementation was better, with tolerable dynamic violations. © 2009 Elsevier B.V. All rights reserved.

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