Process control, automatic time delays

The challenges in SMB control are not only the complex nonlinear process dynamics, but also the long delays of the effect of disturbances. The required control strategy has to be able to handle multivariable dynamics with time-delays and hard constraints. Model Predictive Control (MPC) has been proven to be the most effective control strategy for this type of problems [1,2]. Only recently, a few scientific publications have addressed the automatic... 

The use of modern, sophisticated control features is the latest development in ore sintering. Fig. 6.8-36 shows the instrumentation installed at a sinter plant in China [B.56, pp. 450-454]. The multi-variable process control is adaptive in nature, that is it keeps track of variations and automatically adjusts the operation to the most optimal conditions. To overcome the time delays that are inherently experienced in a process of long duration, a prediction algorithm has been included. However, since random, unpredictable disturbances are often experienced, a proportioning expert system is necessary to yield rational and uniform results. 

Automatic control of purities is difficult due to the long time delays and the complex dynamics that are described by nonlinear distributed parameter models and switching of the inputs, leading to mixed discrete and continuous dynamics, small operating windows, and a pronouncedly nonlinear response of the purities to input variations. Because of the complex nonlinear dynamics of SMB processes, their automatic control has attracted the interest of many academic research groups and many different control schemes have been proposed however, few of them have been tested in experimental work for real plants with limited sensor information. 

The on-line instrumentation development needs can be divided along the traditional lines of quality control and process control instrumentation The interrelationship between the two and the proposed mode of interaction are shown in Figure 9 The quality control instruments, in an operational and a practical sense, are located outside the preparation plant As a result of data obtained on product quality, the quality control instrument interacts with the plant feed and the process control instrumentation to optimize the use of raw material consistent with the desired product specifications This feedback loop can be automatic however, current practice places the preparation plant superintendent or engineer in the loop and the quality control measurement in a remote laboratory, resulting in manual control scheme with a long time delay The process control instrumentation controls a single unit operation and the instrumentation is unique to each unit operation Their set points are established by the output from the quality control Instruments ... 

Synthetic turbidity standards are generally used in the quantitative measurement of turbidity. Alternatively, calibration curves can be obtained by precipitating known amounts of the substance to be measured. However, grain size depends not only on precipitation conditions, but also on the time delay between precipitation and measurement. so conditions must be standardized carefully to ensure reproducible results. Nephelometric and turbidimetric methods have also become important in recent years in continuous automatic on-line process control (e.g.. of wastewater). 

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