Control philosophy

The philosophy of reactor control azid safety In the Hanford reactors had its origin In the days of the Manhattan Project. The original philosophy has satisfactorily stood the test of time and has carried on through the years with few changes. It was only natural then that the Initial thoughts with respect to reactor control and safety for the HPR followed closely the traditional Hanford philosophy. 

---

Thickener control philosophies are usually based on the idea that the Iindertlow density obtained is the most important performance criterion. The o ertlow clarity is also a consideration, but this is generally not as critical. Additional factors which must be considered are optimization of tlocciilant usage and protection of the raking mechanism. 

Control philosophies for clarifiers are based on the idea that the overflow is the most important performance criterion. Underflow density or suspended sohds content is a consideration, as is optimal use of flocculation and pH control reagents. Automated controls are of three basic types (I) control loops that optimize coagulant, flocculant, and pH control reagent additions (2) those that regulate underflow removal and (3) rake drive controls. Equahzation of the feed is provided in some installations, but the clarifier feed is usually not a controlled variable with respect to the clarifier operation. 

Control philosophies applied to continuous countercurrent decantation (CCD) thick eners are similar to those used for thickeners in other applications, but have emphasis on maintaining the CCD circuit in balance. It is important to prevent any one of the thickeners from pumping out too fast, otherwise an upstream unit could be stai ved of wash liquor while at the same too much underflow could be placed in a downstream unit too quickly, disrupting the operation of both units as well as reducing the circuit washing efficiency. Several control configurations have Been attempted, and the more successful schemes... 

Process control philosophy (e.g., computerization that removes supervisory control from the operator and may lead to inability of the operator to respond effectively to an abnormal situation)... 

Written procedure does not match physical equipment or control philosophy... 

I suggest an initial determination of at least sufficient human evidence, limited human evidence supported by animal or short-term tests, or sufficient animal evidence for a conclusion of probable human carcinogenicity as warranting the most conservative regulatory control philosophy. Limited animal evidence without substantial support from short-term tests or mechanistic data indicative of potential human risk would warrant less heroic controls. Yet, these controls would be more protective than those developed from an ADI determination and sufficient to preclude any significant risk in the event that further studies raised the classification. 

Section 1 - Project and Process. This starts with the project definition (objective, description, location, product and raw material specifications, quantity, quality, output requirements, throughput for equipment sizing purposes). Closely linked with this is a statement of the mode of operation (e.g. day time only or 24 hour operation, continuous or batch processing) and expected control philosophy (centralised computer or local, methods of data collection and storage, programmable controllers or hard-wired ). 

An appropriate design team will demonstrate expertise in contamination control philosophies, space planning, code compliance, and mechanical and electrical design and will be familiar with materials of construction currently being used in pharmaceutical projects. It is frequently helpful to include a member of the construction team in the front-end planning effort to advise on constructibility of the facility being planned. Unrealistic construction schedules will be avoided and field rework will be minimized if appropriate attention is paid to the construction phase early in the planning process. 

Facility operation/instrumentation control philosophy stated and documented,... 

Underflow is usually withdrawn continuously on the bases of bed level, rake torque, or underflow solids concentration in a feed-back mode. Most installations incorporate at least two of these parameters in their underflow withdrawal control philosophy. For example, the continuous withdrawal may be based on underflow solids density with an override to increase the withdrawal rate if either the rake torque or the bed level reaches a preset value. In some cases, underflow withdrawal has been regulated in a feed-forward mode on the basis of thickener feed sohds mass flow rate. Any automated underflow pumping scheme should incorporate a lower limit on volumetric flow rate as a safeguard against line pluggage. 

Instrumentation control philosophy, sophistication control room requirements, etc. 

Many of the controls are sequential and on-off thus, the control philosophy is particularly amenable to PLC (Programmable Logic Controller), PC (Personal Computer), or Distributive Microprocessor Controls. Proportioning controls can be easily incorporated into such a system. A Graphic Panel Display with digital indicating and recording modes will add clarity for the operators of the plant. 

Underflow is usually withdrawn continuously on the bases of bed level, rake torque, or underflow solids concentration in a feedback mode. Some installations incorporate two or more of these parameters in their underflow withdrawal control philosophy. For example, the... 

Control philosophies applied to continuous countercurrent decantation (CCD) thickeners are similar to those used for thickeners in... 

PFD The Process Flow Diagram (PFD) shows the basic layout of the unit. A heat and mass balance is included in the flowsheet. Some flowsheets will show the basic control philosophy [851]. 

The purpose of modelling these systems and in particular (1) and (2) was to establish the control philosophy, rather than an in-depth evaluation of control system tuning. One of the largest simulations developed was the steam system. 

This chapter is devoted mainly to the control philosophy of the whole plant, what nowadays is called plantwide control . Clearly, it is desirable to make use, as much as possible, of standard control loops at the unit level, because the global control strategy should be independent of the implementation and tuning of local controllers. 

The plantwide control philosophy has been discussed already in Chapter 13, and illustrated by Fig. 17.8. The following plantwide control structures is proposed ... 

Before developing a control philosophy, it is important to answer two questions. 

---