Instrumentation and process control

Process control and the associated instrumentation were mentioned in relation to the process selection (Section 3.1). To reiterate those comments, these aspects of plant design must be considered during the process selection stage and at other subsequent stages in the design of the plant. Do not assume that any item of equipment or an entire plant that can be designed can also be operated and controlled efficiently. It should be established early in the design that the control and instrumentation aspects are not only feasible but that the cost is within acceptable limits. 

Ignoring the control and instrumentation requirements may mean that (at best) the capital cost is higher than necessary, and that operation and control remain difficult. 

Instruments which can monitor the important process variables during plant operation must be specified. These instruments must be capable of measuring the variables and should have an acceptable accuracy and repeatability of measurement, usually the latter attribute is more important than the former on chemical plant measurements. The instruments may be used for manual measurements or included in automatic control loops. Automatic alarms may also be required to indicate deviations outside acceptable limits. If possible, direct measurement of the process variable should be made, however it is often easier to measure a dependent variable, e.g. temperature measured as an indication of composition for distillation column top product. 

The specification of a control scheme and the associated instrumentation for a chemical plant should satisfy several main objectives. First, the plant should operate at all times in a safe manner. Dangerous situations should be detected as early as possible and appropriate action initiated, also the process variables should be maintained within safe operating limits. Second, the plant should operate at the lowest cost of production. Finally, the production rate and the product quality must be maintained within specified operating limits. These objectives may be conflicting, and the final control scheme to be adopted is based upon a realistic and acceptable compromise between the various factors. The main conflict is between the need to design and operate as safe a plant as possible and the desire to produce the chemical at the lowest cost. Safe plant operation can be expensive, both in terms of the capital cost of instrumentation and the annual operating costs, e.g. maintenance. 

Experienced process control engineers are usually responsible for the design and specification of automatic control schemes on large chemical plants. The book by Shinskey (1979) provides details of the practical 

Adequate process control and its associated instrumentation are essential for product quality control. The goal in some cases is precise adherence to a control point. In other cases, maintaining the temperature within a comparatively small range is all that is necessary. For effortless controller tuning and lowest initial cost, the processor should select the simplest controller (of temperature, time, pressure, melt flow rate, etc.) that will produce the desired results. This section primarily will review temperature control, which is applicable to all the processes, as it is usually the most critical parameter. The basic approach described here can be applied to the other required controls (2). 

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More microprocessor-based process equipment, such as smart instruments and single-loop controllers, with digital communications capability are now becoming available and are used extensively in process plants. A fieldbus, which is a low-cost protocol, is necessary to perform efficient communication between the DCS and these devices. So-called mini-MAP architec ture was developed to satisfy process control and instrumentation requirements while incorporating existing ISA standards. It is intended to improve access time while... 

Process controls and instrumentation only provide feedback for conditions within the process system. They do not report or control conditions outside the assumed process integrity limits. Fire and gas detection systems supplement process information systems with instrumentation that is located external to the process to warn of conditions that could be considered harmful if found outside the normal process environment. Fire and gas detection systems may be used to confirm the readings of major process releases or to report conditions that process instrumentation may not adequately report or be unable to report (i.e., minor process releases). 

Feb Competition and Business Strategy Product Design (1) Indoor air survey (2) Prototype Chemical Design and Processing (1) Adsorbents (2) Catalysts. Process Safety Analysis Process Control and Instrumentation Environmental Impact Assessemsnt Report Writing... 

Communication Satellites. The next example illustrates an expert system similar to those under development in process control and instrumentation companies. These systems are designed to diagnose faults and suggest corrective actions. 

Although not mentioned so far in this section, the process control and instrumentation requirements (see Section 8.2.2) must be considered when selecting the process route. The ability to provide suitable operational control over the process and the availability and cost of necessary instrumentation are major considerations. If these aspects are ignored at this stage, it could well be that the detailed plant design is at... 

Action Prepare detailed designs for the chemical engineering units in the plant. Consider energy conservation measures and the process control and instrumentation required as the designs are performed. Prepare a design specification sheet for each unit. Detail the specific energy conservation schemes considered and adopted,... 

Instrummiaiion flow sheets are useful in determining the requirements for process control and instrumentation. The Instrument Society of America has pioneering standardization of instrumentation flow plan symbols. These systems of nomenclature are illustrated in Tables 3-1... 

These matters are dealt with much more fully than in earlier editions of the Handbook, with the object of giving the mechanical and electrical engineers (including those concerned with process control and instrumentation) in cement manufacture a better understanding of the problems involved. 

Q3. In normal operation safety related parameters such as negative draught, oxygen and dust concentration, and temperature should be controlled automatically without action from the operators. Process control and instrumentation parameters are listed in para. 804. 

Process controls and instrumentation only provide feedback for conditions within the process system. They do not... 

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