Plant control systems

Defining the requirements for a pilot-plant control system is often difficult because process plant experience for comparison and evaluation is commonly lacking and the design is frequentiy performed by personnel inexperienced in either instmmentation systems or pilot-plant operations. The isolated and often intermittent nature of pilot-plant operations also inhibits evolution and promotes individual unique installations. This compHcates the selection process. 

Simplification of a hydroelectric power plant control system. 

Davlin, Tom, "PLCs Upgrade Power Plant Control System," Intech, Volume 40 No 10, October 1993, pp. 38-39. 

The plant control system functions to limit temperature rates of change during plant load change and upset events. This is achieved at two different levels. In the time asymptote the control system through control variable set points (with values assigned as a function of steady-state power) takes the plant to a new steady-state condition. The set point values are chosen so that hot side temperatures remain little changed. In the shorter term the control system manages the dynamic response of the plant so that the transition between steady states is stable and with minimal overshoot of process variables. 

The plant control system was designed with several objectives in mind. First, reactor outlet temperature was to be maintained at 885°C using the reactor outlet temperature controller described above. Second, to minimise thermal stresses in the IHX, the flows on the hot and cold side of the IHX are maintained near equal over the course of the transient. To accomplish this primary system inventory is adjusted by a PI controller to force the differential between primary and PCU flow rate to track a set point of near 0 kg/s. Third, to maintain high PCU efficiency in the presence of a changing electric generator load (forcing function) inventory control is used. Inventory is adjusted by a PI controller to force shaft speed to track a constant set point of 60 Hz. Fourth, cooler powers are adjusted (via cold side flow rates) for heat removal consistent with PCU operation under inventory control. This essentially means that heat rejection should scale with shaft power. 

Most plant control systems are very simple and are normally standard feedback controllers, either P-, PI- or PID controllers. These will be described in more detail in this section, together with two techniques that can be used to tune these controllers. First, however, we need to define the control objective, i.e. what do we want the controller to do, and define what we mean by feedback control. 

The different types of computer control systems are shown in Fig. 8, while their advantages and disadvantages listed in Table 7. Most new systems are stand-alone systems based on personal computers except for larger research organizations, which may be able to justify the more expensive distributed control systems (see Fig. 9 for a roadmap to selecting a pilot plant control system). 

Stop Reinventing Pilot Plant Control Systems... 

HSS (see High selector switch) Hydraulics, of distillation trays, 72 Hydrodealkylation of toluene plant control system design, 519-29 description, 516-19... 

Two very useful review articles on the various aspects of complete plant control system design with lists of relevant references are the following ... 

As mentioned above, elimination of all feedback control systems from the reactor and secondary heat transport systems makes the 4S plant control system very simple and economic. 

Plant Control Data and Instrumentation System Plant Control System... 

A read-only communications link should exist between the ESD and plant control systems to allow the display of alarm and status irrftnmation to the operator... 

Accident analysis of any of the events should justify the proper selection of conservative initial and boundary conditions, single failure, actions of the operator and plant control systems and other relevant assumptions. 

A modern commercial mass spectrometer will incorporate a computer or will offer a facility to communicate with a computer via a data link, for example, to a plant control system using serial, ethernet or analog, and/or digital signals. This allows data to be stored and manipulated, often in real-time , so that results can be displayed to the user in a convenient form or to be utilized for process control either automatically via a closed loop or for operator fine-tuning . A mass spectrum may be displayed as a continuous scan over a specified mass range similar to a strip-chart, but this is difficult to interpret, and is not directly quantitative. 

Most ion-exchange systems are provided with PLC control. This should be partly integrated into the main plant control system. Section 11.2.2.3C already discussed this issue in connection with filter systems. The considerations here are essentially the same. 

The plant control system provides for non safety plant control functions. The Diverse Actuation System provides for an alternative means for initiating the reactor trip and the emergency safety features by integrating a complete diverse actuation system within the plant control system. 

The plant control scheme is based on the "reactor follows turbo generator" principle. The plant control system is used to maintain certain parameters at setpoint value by the automatic operation of actuators so as to ensure the safe and stable operation of the plant. It comprises the following major subsystems ... 

The plant control systems are non-safety-related. However, for high reliability, three channels are used in all control loops that are directly involved in the generation of power. The median of the three is used for control, and the other two are used to identify channel failures with no interruptions in the power generation process Two channels are used to control auxiliary systems that are needed frequently Single channels are used for auxiliary systems that see infrequent use... 

The instrumentation and control system consists of the reactor protection system, engineered safety features opmtion system, plant control system and reactor monitoring system. The reactor protection syston has two diverse shutdown ems. The engineered safety features are the decay heat removal system (PRACS) and the containment system. 

The plant control system is hierarchical. The top level control task is to receive grid dispatcher demands and to coordinate load demands on each module. Each module has its module controller, which coordinates the turbine generator controller and local controllers (set points, diagnostics and operator actions). Each module has two emergency AC power units (diesel generator). The plant control system has its own emergency power units (both AC and DC) for power plant control. These power units can provide its power to each module. 

Plant control system reduce initiator frequency... 

Definition of physical equipment including equipment-under-control, control systems and procedures The normal transport system has both traffic control systems and plant control systems, including ventilation in undersea tunnels... 

The basic requirement of the sulphonation plant control system is to allow production of the desired quality acids and pastes in a safe manner within the design capacity limitations of the plant. 

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