Process control Advanced

Advanced process control schemes can be either smart combination of simple controllers, or nonlinear controllers using short-cut or even dynamic models. In both cases the design of such feedback loops is nontrivial when several actuated 

The large volume of buffers needed often for biotechnological and pharmaceutical applications led to the development of inline dilution systems. Such systems intend to produce the just in time solvent/buffers by mixing water with a concentrated solution, instead of storing the final very diluted solutions in tanks that require obviously a high storage capacity. 

Storage costs can be so minimized as well as inventory and capital costs. By adjusting the amount of purified water to the concentrated buffer a large range of diluted buffer concentrations can be achieved. A better scalability and flexibility to process requirements is the result. Given the trend toward multiproduct facilities such systems become state-of-the art within modern biotechnology processing. 

The inline dilution system shall allow the preparation of buffers with an inline dilution factor ranging from 1 to 10. This factor determines the ratio of water to concentrated buffer. Larger ratios are of course feasible, but there is a trade-off between the process accuracy and flexibility to be taken into account. The systems shall cope as well with process disturbances and shall be robust again changing process conditions (such as pressure drop in a chromatography column or a sudden change in pressure or flow rate in the primary water supply). The robustness of such systems is crucial since pharmaceutical processes are validated to run in certain predefined limits. Any deviations to such limits will lead to additional investigation costs that could have severe consequences, in the extreme situation the withdrawal of the produced product. 

Special attention has to be though paid to the robustness and overall performance of such systems. A common inline dilution system has been developed for the filtration and chromatography system. Additionally specific measures have been added to the chromatography systems that are more sensitive toward disturbances in the water loop. 

Advanced process control (APC) is a vague term often with different interpretations. In this chapter, it is meant to be a controller that is linear or nonlinear in nature, 

Flgure4.12 (a) M FI trend for a certain grade without APC. (b) MFR trend for a certain grade with ARC. 

An APC system can control melt flow index and polymer density within specification limits, with maximum production rates under certain constraints. In order to control the polymer qualities, the above-mentioned soft sensors can be applied. The APC system can increase production rates, speed up grade transitions, and allow the plant to run more consistently within a grade with less variance. APC installations can be realized with the software of a commercial APC vendor. 

Schwibach, M., Buback, M., and Buscb, M. (1999) Chemie-Ingenieur-Technik, 71, 1391. 

2 Kiparissides, C., Verros, G., and McGregor, J.F. (1993) Journal of Macromolecular Science Reviews in 

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Economic Incentives for Automation Projects Industrial applications of advanced process control strategies such as MFC are... 

In the pressure balance section, the significance of the pressure balance in debottlenecking the unit is discussed. Finally, fundamentals of both basic and advanced process controls are presented. 

To maximize the unit s profit, one must operate the unit simultaneously against as many constraints as possible. Examples of these constraints are limits on the air blower, the wet gas compresst>r. reactor/regenerator temperatures, slide valve differentials, etc. The conventional regulatory controllers work only one loop at a time and they do not talk to one another. A skilled operator can push the unit against more than one constraint at a time, but the constraints change often. To operate closer to multiple constraints, a number of refiners have installed an advanced process control (APC) package either within their DCS or in a host computer. 

A properly configured advanced process control (APC) system could allow for on-line, continuous optimal unit operation and push the FCC operations to multiple constraints simultaneously. 

Advance Process Control (APC) is a mechanism which manipulates regulatory controls toward more optimum unit operation. 

W.H. Ray. Advanced process control. McGraw-Hill, New York, 1981. 

J. C. Edwards and P. J. Giammatteo, Detailed hydrocarbon analysis of naphtha by on-line NMR integration of real-time NMR Feed analysis with advanced process control and optimization, Presented at Eastern Analytical Symposium, Somerset, NJ, November 18-21, 2002. 

G. Dishon, D. Eylon, M. Finarov, A. Shulman, Dielectric CMP Advanced Process Control Based on Integrated Thickness Monitoring, Third International CMP for ULSI Multilevel Interconnection Conference, Santa Clara, CA, pp. 267-274, Feb. 19-20, 1998. 

L. Kane, ed., Advanced Process Control Handbook, Hydrocarbon Process., Sept. 1991. 

Economic Incentives for Automation Projects Industrial applications of advanced process control strategies such as MPC are motivated by the need for improvements regarding safety, product quality, environmental standards, and economic operation of the process. One view of the economics incentives for advanced automation techniques is illustrated in Fig. 8-41. Distributed control systems (DCS) are widely used for data acquisition and conventional singleloop (PID) control. The addition of advanced regulatory control systems such as selective controls, gain scheduling, and time-delay compensation can provide benefits for a modest incremental cost. But... 

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 advanced process control strategies that are most applicable to the optimization of the distillation process are usually based on white-box modeling, where the theoretical dynamic models are derived on the basis of the mass, energy, and momentum balances of this well-understood process. Although the optimization techniques described here can improve productivity and profitability by 25%, this goal will only be achieved if the distillation process is treated as a single and integrated unit operation and the variables, such as flows, levels, pressures, etc., become only constraints, and the controlled and optimized variables are productivity and profitability. 

DOW in Midland, USA, performed metallocene-catalyzed polymerization of ethylene using a homebuilt tube reactor setup with advanced microflow tailored plant peripherals for heating, temperature monitoring, pressure control and dosing via smart valves and injectors. Screening of process conditions was a driver [19]. Also, flexibility with regard to temperature and pressure at low sample consumption was an issue. Quality of the information is another motivation due to the advanced process control and sensing. 

Peters and Timmerhaus Plant Design and Economics for Chemical Engineers Probstein and Hicks Synthetic Fuels Ray Advanced Process Control... 

FIGURE 3.5 Schematic illustration of the evolution of CMP tools from stand-alone, dry-in/dry-out to those with advanced process control (APC). 

Manens et al. [27] reported that charge-based end-point detection coupled with advanced process control (APC) can be used to adjust the amount of copper removed and compensate for the large variations in incoming Cu thickness. Figure 11.13 shows wafers with various incoming Cu thicknesses ranging from 3500 A to more than 6000 A, which simulates, in an extreme fashion, the variations that can be observed from wafer-to-wafer and lot-to-lot... 

Manens A, Miller P, Kollata E, Duboust A. Advanced process control extends ECMP process consistency. Solid State Technol Feb 2006. 

WTW and RTR control of thickness are improved by the use of end-point detection systems and advanced process control. End-point detection, whether mechanical or optical, monitor the state of the wafer surface (film thickness, reflectivity, etc.) or of the entire polishing system (friction, slurry by products, etc.) in an attempt to predict when the desired amount of material has been removed (i.e., the end of process). End-point detection is most successful in processes where a change in the films on the wafer surface leads to an abrupt change in the optical or mechanical properties of the wafer surface. For example, copper CMP end point is easy to detect by optical means due to the large difference in reflectivity of the copper film compared to the barrier films. In contrast, end-point detection for small amounts of ILD removal is difficult due to the lack of change in the wafer surface or the wafer-pad interface. 

Birchfleld, G. S., Trends in optimization and advanced process control in the refinery industry. Chemical Process Control V, Tahoe City, CA (1996). 

Advanced Process Control Handbook 2, Hydrocarbon Processing, March (1987). 

New tools have been recently developed allowing a thorough analysis of each application in terms of statistical distribution of active variables and of process variability. The last Solomon APC Study has evidenced the fact that the company has a good position among the leading oil companies with respect of advanced process control and automation performance in general. 

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