Process control techniques

Another important aspect related to both process technology and equipment design is the need for yield management and process control techniques embedded in the tools, which will have to provide accurate and reliable means for avoiding yield losses in manufacturing and contributing to overall improvement. From this point of view, it is expected that standards in equipment and in characterization techniques will be developed or implemented if already available. 

Concurrent validation is conducted under a protocol during the course of normal production. The first three production-scale batches must be monitored as comprehensively as possible. The evaluation of the results is used in establishing the acceptance criteria and specifications of subsequent in-process control and final product testing. Some form of concurrent validation, using statistical process control techniques (quality control charting), may be used throughout the product manufacturing life cycle. 

Mechanical pulping has higher yields but lower-strength pulps when compared to full chemical pulps. Improvements are constantly being made, and considerable gains have been made in adapting different types of wood and different forms of wood (sawdust versus chips) to mechanical pulping via advanced process control techniques. 

The production of material of a consistent quality is one of the major goals of development work. Quality problems in a product are identified by the constant monitoring and analysis of the output from the plant, using statistical process control techniques [D-4]. Some of these methods have already been mentioned in Section B, 3.4.2. The avoidance of product quality problems results in direct cost benefits and also brings about a reduction in the environmental impact of its manufacture. This is because material does not need to be reworked, recycled or sent for disposal. A reduction in the number of inferior quality batches of material leads to an increase in output from the plant. More material is produced for the same effort, with the added benefit that it can be consistently supplied to the sales warehouse or be used in consuming processes. 

Fig. 5.12. Process control techniques for the in situ characterization of film and process properties and closed-loop control strategies for optical film deposition by reactive sputtering...

The bioseparation technique which is probably the most readily adapted to modern process control techniques is extraction. Liquid-liquid extraction is a mature unit process with application in industrial-scale protein separation.30 Control techniques used on similar systems in other industrial applications should be readily adaptable to bioprocessing, the primary difficulty being the lack of data on the partitioning and related behavior of the product. 

Periodic reviews should include an assessment of system performance, changes, authorized user access privileges, network integrity and operating procedures. Analysis equipment calibration results can be reviewed using statistical process control techniques to indicate the health of equipment. 

In addition to the improvements involved in resin technology and better process control techniques, there are different methods applicable to producing wood products with lower (minute amounts of) formaldehyde emissions as well. To recap firstly, resin formulation can be changed or ageing can be applied to it - emissions decay considerably with time so that within a year or so, their level can be as low as the backgroimd ambient levels. 

Some significantly good payback times (1-7 years) have been achieved [14,17,133], mainly with simple and cheap dryers. The chances for the extensive use of high-performance systems may be improved by integrated construction and multipurpose operation. Using modem process control techniques, the efficiency of solar dryers can be increased. Due attention must be paid to system maintenance and training of the operating personnel. 

The in-die force monitoring and process control technique helps eliminate one variable (the press) and applies measurements to the other two (the die and material). 

Quality assurance (QA) program for analyzer and sample system This is closely related to the control chart concept. The capability of the analyzer (e.g., accmacy, reproducibiHty, etc.) and the sample system (e.g., temperatme, pressure, flow, etc.) should be estabHshed as soon as possible after installation. The control charts (mentioned above) of statistical process control technique should indicate the capabilities of the analyzer system. The analyzer should be checked against a calibration... 

Feedback control is a fundamental concept that is employed in FID controllers as well as in advanced process control techniques. Figure 18.52 shows a simplified instrumentation diagram for feedback control of the stirred tank discussed earlier, where the inlet flow is equal to the outlet flow (hence, no level control is needed) and outlet temperature is controlled by the steam pressure. Figure 18.53 shows a generic block diagram for a feedback control system. In feedback control the controlled variable is measured... 

Once, a noted expert on advanced process control techniques lectured our engineering staff. Having understood nothing of the lecture, I discussed the subject with my colleagues. They too had failed to absorb this advanced technology. Moreover, it became apparent that almost none of us had a grasp of the fundamentals of process control. 

Models can often be used to guide the designed experiments that need to be run on the commercial process as part of the qualification effort. Out of this activity come the aims and limits of the process variables, which either directly or indirectly are under closed-loop feedback control and some of which are then monitored by statistical process control techniques (Ref 2). 

However due credit must be given to MVC as a major step forward in the development of APC (advanced process control) techniques. This book focuses on how to get the best out of its application, rather than replicate the technical details that appear in many text books, papers and product documentation. 

R. D. Benson, Statistical process control techniques using near-infrared reflectance spectroscopy, in Proc. World Conf. on Emerging Technologies in the F and Oils Industry, A. R. Baldwin (Ed.), American Oil Chemists Society, 1986. 

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