Towards the Real-Time Control of Nonlinear Multiple Stage Evaporators: Design of IMC with Process Delay

With the increase in utilization of biofuels to ensure sustainability, black liquor (waste residue from paper mills) finds use as high value energy transporter. To guarantee an effective use of black liquor as a biofuel, the black liquor is concentrated in a multiple stage evaporator (MSE), a nonlinear complex energy intensive unit. The energy optimization and tight control of product quality, therefore, becomes essential. This stresses on the dynamic model simulation of MSE to design an appropriate controller for set-point tracking. Moreover, in real time, the MSE unit encounters process delay which needs to be addressed. In this context, we present an efficient IMC controller with the inclusion of process delay toward the concentration control of black liquor in MSE. The main aim is to simulate the nonlinear steady-state and transient models for designing the IMC controller. To realize this objective, we estimate the steady-state unknown process parameters by solving the steady-state nonlinear model. The nonlinear dynamic model is then solved to obtain the system transfer functions, wherein a process delay is introduced. These transfer functions are then utilized to design the IMC controller. Furthermore, the time response specifications of the proposed IMC are compared with conventional PID controller. The results reveal that the proposed IMC can effectively handle variations in set-point for the real-time MSE system with time delay.