Control scheme design

Table 33.1. Checkhst, i.e. basic control scheme design procedure.

For complex processes that required close control, the weakest link in the control scheme design was usually the dynamic description or model of the process. The response of the sensor, valve, and controller could easily be modelled to within 5 per cent. The modelling error in predicting the dynamic behavioiu of the process... 

As always, it is important to verify the control scheme dynamically with the use of a suitable dynamic simulator. Other application examples that are documented in the literature [11,19,20] include a substantial emphasis on the importance of dynamic simulation for control scheme design validation and performance evaluation. 

Distillation control scheme design using steady-state models... 

DISTILLATION CONTROL SCHEME DESIGN USING STEADY-STATE MODELS 203... 

Automated control schemes employ one or more sets of controls, which will fit into three categories (1) control loops which are used to regulate the addition of tlocciilant, (2) control loops to regulate the withdrawal of Iindertlow, and (3) rake dri e controls. Usually, the feed to a thickener is not controlled and most control systems ha e been designed with some tlexibility to deal with changes in feed characteristics, such as an increase in oliirne or alteration in the nature of the solids thernseh es. In se ere cases, some equalization of the feed is required in order to allow the control system to perform effecth ely. 

A proposed control scheme by Drew and Burns (1992) uses an LQG design, whereby the three process parameters are controlled in an optimal manner, their values (particularly the moisture control) being estimated. 

The discussion is organized in the following order First the advantages of HRC scheme, relative to the industrial (i.e., heterogenous) process are briefly commented on second, the relevance of celMose activation and the physical state of its solution to optimization of esterification are discussed. Finally, the use of recently introduced solvent systems and synthetic schemes, designed in order to obtain new, potentially useful cellulose esters with controlled, reproducible properties is reviewed. A comment on the conformity of these methods with the concepts of green chemistry is also included. 

The primary objectives of the designer when specifying instrumentation and control schemes are ... 

The detailed design and specification of the automatic control schemes for a large project is usually done by specialists. The basic theory underlying the design and specification of automatic control systems is covered in several texts Coughanowr (1991), Shinskey (1984) (1996) and Perry et al. (1997). The books by Murrill (1988) and Shinskey (1996) cover many of the more practical aspects of process control system design, and are recommended. 

As the flowsheet becomes more firmly defined, the detailed process and mechanical design of the equipment can progress. The control scheme must be added and detailed hazard and operability studies carried out. All this is beyond the scope of the present text. However, all these considerations might require the flowsheet to be readdressed if problems are uncovered. 

Determine the transfer functions of the feed-forward control scheme assuming linear operation and negligible distance-velocity lag throughout the process. Comment on the stability of the feed-forward controllers you design. 

The response of the kiln to a 20% increase in coke on the catalyst from the reactor is shown in Fig. 27 for no control and for schemes (a) and (b). The simpler scheme (b) is clearly superior to scheme (a) although steady-state considerations predicted that scheme (a) would be the better strategy. The fluctuations in the total air rate of scheme (a) that maintains a constant amount of oxygen to the kiln causes this difference and outweighs the effects of the fluctuations in oxygen amounts present in scheme (b). This comparison showed that control strategies designed... 

Here, a control law for chemical reactors had been proposed. The controller was designed from compensation/estimation of the heat reaction in exothermic reactor. In particular, the paper is focused on the isoparafhn/olefin alkylation in STRATCO reactors. It should be noted that control design from heat compensation leads to controllers with same structure than nonlinear feedback. This fact can allow to exploit formal mathematical tools from nonlinear control theory. Moreover, the estimation scheme yields in a linear controller. Thus, the interpretation for heat compensation/estimation is simple in the context of process control. 

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