Process Control Project – Control of an Industrial Furnace

Abstract

The aim of the project was to devise a suitable control strategy for an industrial furnace; to maintain a steady outlet temperature for the crude stream T_out (at 560K) and oxygen concentration in the fuel gas C_o2 (at 5%) under various conditions. The furnace is modelled in Paragon 5.4, in which all the simulations are done. The degrees of freedom analysis is first done to give insight into the process. Transfer function models relating to changes in T_out and C_o2 to changes in flowrates of oil (F_oil), gas (F_gas) and air (F_air) as well as flowrate and temperature of the crude supply (F_in and T_in) are then identified using a first order plus time delay (FOPTD) model. Using relative gain analysis (RGA), the best pairing is found to be F_gas controlling T_out and F_air controlling C_o2. Keeping the C_o2 loop open, the best Pband and integral time were found to be 3.0 and 1.4 respectively for the temperature loop, which exhibits the best compromise among small overshoot, short settling time and small sum of squared error. A similar approach is applied to the C_o2 loop, for which 3.7 and 0.4 are adapted as optimum Pband and integral time. To reject disturbances and further reduce loop minimizations, detuning, decoupling and feedforward control schemes are implemented. The best strategy found is to detune T_out loop, decouple C_o2 loop and feedforward F_in. Finally, the performance of the devised strategy is tested on set-point and disturbance changes set by supervisors. Results suggest that a second decoupler on T_out loop and a feedforward controller on T_in might be useful.