Control systems, paper machines

Sodium chlorite has also been used for treatment and removal of toxic and odorous gases such as hydrogen sulfide and mercaptans. Chlorine dioxide from chlorite is also useful for microbial and slime control in paper mills and alkaline paper machine systems (164,165). The use of sodium chlorite in textile bleaching and stripping is well known. Cotton is not degraded by sodium chlorite because the oxidation reactions are specific for the hemiceUulose and lignin components of the fibers. 

The rate of pulp lay-down F on a paper machine is controlled by controlling both the pressure P and the height of slurry h in a feeder drum with cross-sectional area A. F is proportional to the square root of the pressure at the exit sHt. The air vent rate G is proportional to the square root of the air pressure in the box P. Feedback controllers set the inflow rates of air Gq and slurry Fq to hold P and h. The system is isothermal. 

In theory, the Smith predictor gives significant improvement in control. In practice, only modest improvement can be achieved in many processes. This is due to the sensitivity of the stability of the system to small changes in system parameters. If the controller is tightly tuned and there is a small shift in the actual deadtime of the process, the system can go unstable. Therefore, most of the successful applications have been in processes which have gains, time constants, and deadtimes that are well known and constant. Examples include paper machines, steel rolling mills, and textile manufacturing. 

Industrial applications of these controllers have been successfully carried out in Sweden on paper machines (9.) and on an ore crusher system (3.). A good discussion of the practical aspects of the approach and an application to the control of a packed bed tubular reactor is contained in a paper by Harris et al. (12). 

Acidity. For many years the pH of the paper has been considered an important characteristic affecting peramnence. Permanency specifications exist which call for paper with a pH of 6.5 or higher. Other specifications say that the pH should not be lower than 5.5. There is no disagreement, however, about the poor permanency of paper when it is under pH 5.5 (4). In this context, paper pH is determined by the extraction procedure already described. The acidity that is present in the paper will promote acid hydrolysis of the glucosidic bonds of cellulose. To prevent this type of degradation and to produce paper with a high extract pH, the paper machine process water system must be controlled at a neutral to alkaline pH with a minimum of total acidity, preferably with an excess of alkalinity. The term total acidity is used to describe the concentration of all dissolved ions and particles in the process water that contribute to acidity in the system and a low extract pH in the paper. For example, papermaker s alum dissociates to alumi-... 

The neutral or alkaline pH of the paper machine system necessary for a high extract pH in the paper is not compatible with the rosin size-alum sizing system. To set rosin size properly on fiber, alum is required. Since total acidity is an approximate measure of the amount of alum in solution, it is often used as a control in connection with rosin sizing. The most effective size-alum precipitate forms at a papermaking pH between 4.2 and 4.8 and a total acidity between 90 and 150 ppm. The low pH of the process water, high total acidity, excess alum, and the size-alum precipitate all place a severe limit on the permanency properties of paper. 

F. P. Demello and C. Concordia, Concepts of synchronous machine stability as affected by excitation control. IEEE Transactions on Power Apparatus and Systems, Paper No. 68 TP 129-PWR, Vol. PAS-88, No. 4, Pages 316 to 329, April 1969. 

The more closely specified wet process product would be suited to closely defined, ordered systems such as pulp-based line paper machines. Wet-end charge balancing could be carefully controlled. 

Uses Effluent system defoamer for foam control in textile, paper, and municipal effluent systems in aeration ponds, flumes, and at river outfall paper machine defoamer esp. for recycled fiber furnish foam control agent for coatings based on starch, casein, and waxes Features General purpose exc. dispersing props. 

In 2005, he was leading a multidisciplinary engineering team responsible for the design and implementation of the Distributed Control System (DCS) of a fuUy operational pulp and paper mill with a complete paper machine in a new 11,000 m building on campus, representing a total investment of 80 million Canadian dollars, 10 % of which came directly from industry. This DCS manages over 3,000 I/Os and 500 control loops and its flexibility is still unique worldwide. 

This paper has presented the development of a dynamic, predictive and optimal control method for the wet end of a papermaking system. The control of this part of the papermaking process is difficult because of its complex, multivariable and non-linear nature with long time delays. The main objective of this work has been to develop a closed loop control strategy suitable for control of the wet end processes of a paper machine. This includes industrial implementation directed towards achieving optimal control of the wet end of a paper making system. 

To be able to produce a suspension having a controlled solids content, often of more than 70w/w%, special dispersants are required. Without such dispersants, a mixture containing a mineral, such as calcium carbonate, with only 30w/w% water is no longer flowable. Pigment and filler producers have developed highly active polymer systems, especially for the use of mineral slurries in the paper industry, which allow such concentrations to be achieved without destroying the complex chemistry of a paper machine. 

The ACTICO concept is a sophisticated combination of an automation and COj injection system which can be tailored to individual paper machines. The pH control system provides total pH control in the wet end and minimises pH variations (see Fig. 6.23). 

The use of pay points is appropriate where banks are not available and when their use lowers beneficiaries transaction costs. At the same time, their use requires excellent scheduling and control mechanisms. If the transactions are recorded using paper and pencil, the control system could be operated by local observers such as community elders or local government officials who could help safeguard against corruption by ensuring that the correct people receive the cash. The use of electronic systems such as POS machines and cell phones can improve the transparency and accuracy of transactions. 

This paper describes a project covering the development of a program system for the failure mode and effects analysis of plant and machine control systems in several steps. The project leader was Mr. Demski of the TOV Rheinland. The result also takes account of the experiences gathered by Dr. Germer, BIA, and Mr. Six, Technische Universitat Braunschweig, when using PASS I in practice. 

Within the fuel route there are 4 main centres of plant control and interlocking, namely the fuelling machine (the control system is carried "on board"), the irradiated fuel dismantling cell, the ponds and the maintenance cells. Because of its varied duties the fuelling machine control system is the largest and most complex of those listed and is considered in detail in this paper. The same philosophy and methods, however, have been applied to all 4 systems. 

Automation by fast, stable and accurate control loops for consistency, flow, pressure and level is elementary for providing the necessary constancy in the approach flow system. Variations in pressure for example will mainly directly influence the MD profile whilst stock consistency deviations will affect both CD and MD basis weight profiles. In addition the retention on the paper machine and the chemical conditions of the water systems must be kept constant. Here a retention control loop is standard in many appHcations keeping the white water consistency constant by adapting the quantity of retention agent added. Controls for filler, color, air content, cationic demand or zeta potential are also available today. Combining the different controls to a total control concept will lead from purely functional controls to control systems which also address quality and production issues. 

Control systems for paper machines can be categorized in different ways. The following terms are those most commonly used ... 

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