Design of control scheme

In this chapter, the design of a control scheme for an entire plant will be discussed. On the basis of the relationship between process outputs and inputs, the control scheme will be developed. The first part of the procedure is similar to the procedure for the development of an environmental model, which is identifying the inputs and outputs of the process. Measurement problems and costs of the correcting devices, however, should now also be taken into consideration. The result of this procedure is a table with interactions, in which the relationships between the manipulated and controlled variables is shown. The static relationship determines the power of control the dynamic relationship determines the speed of control. The design procedure is illustrated by an example. Subsequently, methods for optimization and extension of the control scheme are discussed. [Pg.465]

It is not a trivial task to develop a systematic procedure for the design of control schemes for process units and entire plants. It is even not without risk, since the designer may think that by following the procedure the task will be completely finished But it is of extreme importance to verily an intermediate result in different ways and if necessary to start the design procedure all over again. [Pg.465]

It is not very meaningful to search for the ultimate control scheme for a particular process. The magnitude and nature of disturbances, the frequency of changes and the way the process is operated (for example at maximum load or maximum efficiency), the flexibility of the plant and the knowledge of operating and maintenance personnel all play a cracial role in the control scheme selection process. It is very well possible, that a particular process is heavily instrumented and automated in one plant and is hardly automated in another plant. It is therefore reconunended to review the control scheme after the plant has come online and make changes in the control scheme if reqnired (this can easily be done with modem instrumentation systems). [Pg.465]

Sometimes, the expansion of a plant can have consequences for control of the older part of the plant. For example, after an expansion of the nnmber of boilers, it is advantageous to operate a new boiler at full load, since it has a higher efficiency than the older boilers. This also has conseqnences for the control scheme for the older boilers, which should cope with the changes in steam demand. [Pg.465]

Process Dynamics and Control Modeling for Control and Prediction. Brian Roffel and Ben Betlem. 2006 John WUey Sons Ltd. [Pg.465]

In the previous chapter the procedure for the design of control schemes was discussed. The procedure was illustrated on a reactor with recycle. The selection of appropriate combinations of controlled and manipulated variables was relatively simple, since the interactions were limited. In this chapter the procedure will be applied to a distillation column. This is a unit operation with many interactions between the corrections that are made. Using a basic knowledge of the process dynamics, a basic control scheme is designed. Subsequently, two control schemes will be compared a basic control scheme based on material balance control and a control scheme based on "energy balance control. The distillation column can also be used to demonstrate the optimization of the control scheme. The principle is that the control scheme should be designed in such a way, that an objective function can be maximized. [Pg.487]

Scheme 1 Elemental reactions of DC chemistries used for design of controlled graft architecture...

It is possible to design multipath control schemes in which the laser phase cancels out of the interference term. One possibility is a diamond path configuration, co + 0)2 vs 0)2 + o), with a resonance near o) contributing a phase to the first path and a resonance near 0)2 contributing a phase to the second path. As before, the total probability is the square of the sum of the amplitudes for each path, but here the phases of the two laser beams appear in both paths and cancel in the cross term. In this case the control parameters are the laser frequencies, which determine the detuning from the resonances. This technique was used by Daniel Elliott and coworkers to control the differential cross sections for the ionization of Ba and NO. [Pg.150]

The trade-offs among process design, optimization and control must be considered. The hierarchical or distributed nature of the plant or process may need to be exploited in an advanced control scheme. The operation of energy-integrated plants requires design of control systems which are decentralized (such as with microprocessors) but which respond to overall plant objectives via a communication link to a larger computer. [Pg.96]

At the other extreme, it may be argued that the traditional low-dimensional models of reactors (such as the CSTR, PFR, etc.) should be abandoned in favor of the detailed models of these systems and numerical solution of the full convection-diffusion reaction (CDR) equations using computational fluid dynamics (CFD). While this approach is certainly feasible (at least for singlephase systems) due to the recent availability of computational power and tools, it may be computationally prohibitive, especially for multi-phase systems with complex chemistry. It is also not practical when design, control and optimization of the reactor or the process is of main interest. The two main drawbacks/criticisms of this approach are (i) It leads to discrete models of very high dimension that are difficult to incorporate into design and control schemes. [Pg.207]

Figure 1 Scheme for the design of controlled drug delivery system. [Pg.281]

Real design problems involve discrete design decisions, such as layout of reactors and choice of control scheme, as well as selection of continuous design parameters, such as reactor sizes and controller tuning. The design tools pre-... [Pg.342]

A variety of control schemes can be incorporated in the design of a reverse osmosis plant. However, this subject is beyond the scope of this manual. [Pg.290]

Note that the example SIL levels provided in this chapter are only examples. They are not to be assumed recommended levels of protection. The selection of an appropriate Safety Integrity Level (SIL) is site-specific and the analysis requires selecting criteria for tolerable risk, and evaluating process conditions, specific chemicals, equipment design-limits, control schemes, process conditions, and unique hazards. Experts in process engineering, instrumentation, operations, and process safety should imdertake SIL selection. [Pg.215]

ABSTRACT This paper deals with the design of control systems. The aim of the proposed method is to optimize the instrumentation scheme while satisfying criteria of financial cost and dependability. This method uses a structural model that describes qualitatively the different relations that link the physical variables. By analyzing this model, it is possible to obtain the different ways to estimate the unknown variables in function of the measurements provided by the sensors. The number of these ways may be interpreted as a fault tolerant level of the estimation possibilities. In this context, the optimization consists in finding the instrumentation scheme that satisfies the required fault tolerant level constraints with the lowest financial cost. The two main contributions of this paper are first an extension of the structural model in order to take into accoimt different operating modes and their specific features and second a clear formalization of the optimization problem that takes into account the costs of devices and specified fault tolerant level. [Pg.1322]

Sample Distribution and Frequency. The number of samples to be distributed in each round depends on whether the scheme covers a range of concentrations, as well as on the statistical design of the scheme. The frequency often relates to the field of application and the availability of reliable and stable quality control materials. The number of samples per analyte in each series should be below six so as not to burden the laboratory work, and to obtain information on the trends in a laboratory s performance the frequency of sample distribution in any series should not be more than every fortnight and not less than every 4 months. [Pg.57]

The Engineering models were developed early on as they were used during the detailed engineering phase for validation of the plant design and control schemes. They were used for the development of APC and may in future be used for fiirther optimisation. [Pg.163]

With regard to future work, several issues should be studied, among them are, the development of ways to combine the inverse and direct optimality methods, the design of control structures with compatible passivity and detectability structures, the development of measures of stability, passivity, and detectability, the consideration of other control schemes like model predictive control, and the design of dedicated observers for control or monitoring purposes. [Pg.633]

Figure 15.1 Independent factors important in the design of controlled drug delivery systems. The pathophysiology of a disease also plays a critical role in the definition of the final goal of this scheme-development of an optimal dosage form [23].

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