Advanced ex-press sheet management.Traditionally, very little is either measured or controlled between the forming section and ex-press of the paper machine. This is especially true when one considers that the majority of the sheet's characteristics are born in this part of the process. For example, nearly half the water in the sheet is mechanically removed between these two points, with virtually no process visibility available to optimize this part of manufacture. In addition, there are few universal and widely accepted measurements to help describe the condition of the forming fabrics, press felts, and transport belts involved in the dewatering Dewatering (dē′wöd·ər·iŋ) is the removal of water from solid material or soil by wet classification, centrifugation, filtration, or similar solid-liquid separation processes. process. Yet most modern paper machines will change press felts every 15 to 30 days as their age and diminishing efficiency reduces productivity and quality. There is a clear requirement and justification to do two things: examine the sheet at the ex-press position and use this information to improve sheet quality and runnability of the machine through its pressing operations. EX-PRESS MOISTURE MEASUREMENT Quality control systems (QCS QCS Quadro Comunitario di Sostegno (Italian: Community Support Network) QCS Quality Control System QCS Queensland Core Skills (exam for Australian schools in Queensland) ) are traditionally positioned either prior to the size press or at the reel and their measurements are used to control various machine direction (MD) disturbances and cross direction (CD) profiles. This measurement and control strategy does not guarantee that an optimal sheet is presented to the dryers following the press section. Also, it cannot be used to either optimize press section operations or be used for press felt management purposes. The limitation of this approach is that it can only measure and control a composite moisture profile that is the product of the express, ex-main dryers and in some cases ex-size press conditions. Moisture measurement following the press section, however, represents a sound strategic starting place for both measurement and control purposes for the following reasons (see Figure 1). 1. Location: It is the first available location on the paper machine that provides measurement focusing on the dewatering processes rather than downstream conventional drying. 2. Diagnostics: The measurement focuses on events upstream of the press section and excludes any downstream dynamics. This expanded level of process visibility allows operators to adjust the following items with confidence and eliminate guesswork: * Press roll loads * Control crowns * Uhle box vacuums * Press felt showers * DuoCleaner activity * Felt guide roll skewing The measurement can also be combined with high-frequency vibration monitoring techniques in order to identify problematic felts and rolls in the press section. 3. Control: The location permits faster control response, as the measurement does not have the built in process time delay of the dryers. As a consequence, profile optimizers using steam boxes and sectionalized zone control rolls can provide superior control performance. 4. Process optimization Process optimization is the practice of making changes or adjustments to a process, to get results. Optimization is the use of specific techniques to determine the most cost effective and efficient solution to a problem or design for a process. : Ex-press moisture averages can be minimized while the moisture profile shape entering the dryers can be optimized for reduced steam consumption, shrinkage Shrinkage The amount by which inventory on hand is shorter than the amount of inventory recorded. Notes: The missing inventory could be due to theft, damage, or book keeping errors. and dryer breaks. 5. Press clothing: By integrating advanced human/machine interface (HMI (Human Machine Interface) The user interface in a manufacturing or process control system. It provides a graphics-based visualization of an industrial control and monitoring system. ) displays and commercial databases, press clothing can be monitored and analyzed an·a·lyze tr.v. an·a·lyzed, an·a·lyz·ing, an·a·lyz·es 1. To examine methodically by separating into parts and studying their interrelations. 2. Chemistry To make a chemical analysis of. 3. to achieve optimal dewatering. The measurement can also be used to reduce felt run-in times, such that quality and productivity are not compromised during this period. This facility also provides the user with a historical record of felt performance that can be used to support selection of appropriate felts for each position. [FIGURE 1 OMITTED] 6. Quality and productivity: Flatter express moisture profiles entering the dryer section reduces the total volume and zone-to-zone water application of downstream rewet actuators, and steam consumption is also reduced in the main dryer section. This type of measurement, control and diagnostics should not be viewed as a conventional quality control system (QCS). Rather, it is an expanded definition providing application-specific embedded Inserted into. See embedded system. functionalities designed to optimize individual elements of paper manufacture, such as the press section. The measurement has a wider application than simply measuring moisture in the sheet. The measurement and control system offers expanded capabilities for analysis of press section clothing, roll condition, identification of high-frequency disturbances, and a historical database archiving for quality, clothing and roll condition. The system also includes an HMI (Human Machine Interface) with diagnostic displays that provides the operator with advanced decision support to quickly identify process problems. THE EX PRESS MEASUREMENT SYSTEM In response to the need for advanced measurement, control, and diagnostic systems (or Embedded Solutions), Voith Automation has developed a unique moisture measurement system called EnviroScan. As this measurement is required to perform in hostile, inaccessible inaccessible Surgery adjective Unreachable; referring to a lesion that unmanageable by standard surgical techniques–eg, lesions deep in the brain or adjacent to vital structures–ie, not accessible. See Accessible. environments, its maintenance requirements are minimal. As measurement failure, for any reason, cannot be fixed until the paper machine is shut, the system is accurate, repeatable, and has a high MTBF (Mean Time Between Failure) The average time a component works without failure. It is the number of failures divided by the hours under observation. MTBF - Mean Time Between Failures (mean time between failure). DEMANDING ENVIRONMENT This measurement is designed to operate in demanding environments, particularly following the press section. The outer walls are insulated in·su·late tr.v. in·su·lat·ed, in·su·lat·ing, in·su·lates 1. To cause to be in a detached or isolated position. See Synonyms at isolate. 2. to avoid condensation while also serving to keep the scanner interior cool. The external skin is constructed from 316 stainless steel stainless steel: see steel. stainless steel Any of a family of alloy steels usually containing 10–30% chromium. The presence of chromium, together with low carbon content, gives remarkable resistance to corrosion and heat. around an internal beam structure of 304 stainless steel. Due to its compact external dimensions of 483 X 280mm, it can be mounted in demanding locations. The beam is mounted at 50-100mm from the surface of the sheet and can be orientated o·ri·en·tate v. o·ri·en·tat·ed, o·ri·en·tat·ing, o·ri·en·tates v.tr. To orient: "He . . . at any angle to allow use in limited space areas. The measurement system is designed for operation in 120 degrees Celsius, 98% RH non-condensing environments. The scan speed is rated at 400mm/second, which provides fast scanning data acquisition for tight profile control at the wet end. The measurement sensor is embedded within the scanner frame envelope for compactness and reliability and is transported across the sheet on linear bearings that help ensure head carriage rigidity rigidity /ri·gid·i·ty/ (ri-jid´i-te) inflexibility or stiffness. clasp-knife rigidity and measurement accuracy. The sensor is cooled via a vortex cooling system cooling system: see air conditioning; internal-combustion engine; refrigeration. cooling system Apparatus used to keep the temperature of a structure or device from exceeding limits imposed by needs of safety and efficiency. and does not require water for operation. The sensor is based on infrared technology that simultaneously processes four infrared wavelengths. This provides the ability to measure and diagnose process disturbances for moisture and temperature up to 200Hz using fast Fourier analysis Fourier analysis n. The branch of mathematics concerned with the approximation of periodic functions by the Fourier series and with generalizations of such approximations to a wider class of functions. . By using proprietary optics and modeling the infrared light Noun 1. infrared light - electromagnetic radiation with wavelengths longer than visible light but shorter than radio waves infrared emission, infrared radiation, infrared path in the sheet, it renders the overall measurement insensitive in·sen·si·tive adj. 1. Not physically sensitive; numb. 2. a. Lacking in sensitivity to the feelings or circumstances of others; unfeeling. b. to furnish fur·nish tr.v. fur·nished, fur·nish·ing, fur·nish·es 1. To equip with what is needed, especially to provide furniture for. 2. composition, formation, and scattering scattering In physics, the change in direction of motion of a particle because of a collision with another particle. The collision can occur between two charged particles; it need not involve direct physical contact. coefficients. This also provides improved measurement accuracy and easier, more rationalized calibration calibration /cal·i·bra·tion/ (kal?i-bra´shun) determination of the accuracy of an instrument, usually by measurement of its variation from a standard, to ascertain necessary correction factors. . The sensor has an integral air curtain
The moisture measurement range is from bone dry to 75% percent moisture, providing application opportunities for the wet end, size press, coaters and tissue machines. MEASUREMENT APPLICATION AND RESULTS To date, 8 systems have been sold and installed on machines manufacturing the following grades: newsprint newsprint low grade paper used for newspapers. Old newspapers are fed to cattle as an alternative roughage and may occasionally be ingested by dogs. Significant amounts of lead are accumulated in tissues; no cases of poisoning have been recorded in cattle, though it has been , super calendered cal·en·der n. A machine in which paper or cloth is made smooth and glossy by being pressed through rollers. tr.v. cal·en·dered, cal·en·der·ing, cal·en·ders magazine, lightweight coated base, fine papers, and sack kraft. Seven of the systems are currently operating on either new paper machines or major machine rebuilds. The measurement is installed either in the press itself or directly following the press section. One system is installed prior to a Clupak unit on a sack kraft machine. [FIGURE 2 OMITTED] Papermakers typically use the system as a diagnostic tool. By measuring the quality of the sheet as it leaves the wet press, they are able to make valid decisions and take actions prior to the press section and quantitatively assess the results. GOOD ACCEPTANCE Production personnel have accepted the measurement as a diagnostic tool to help improve the runnability of their machines. It has also contributed toward improved quality and reduced energy costs. Measurement at the ex-press position by definition provides exclusive upstream information, while conventional scanning systems will include the effect of the dryer section into their profiles. The key benefit of the system is the ability to distinguish the source of a potential quality or productivity problem, allowing operators to effectively manage more press section variables. This has produced reduced ex-press moisture averages with flatter moisture profiles entering the dryer section. Ex-press moisture can be reduced in the region of 1.5%-2.0% using the process visibility afforded by the system. This equals a 5-10% saving in either steam consumption or speed increase, depending on process operational constraints. Also, as the sheet will be entering the dryer section at a higher dryness, it will be stronger and suffer less shrinkage, translating into 10%-20% fewer dryer breaks. The system has contributed toward improved felt run-in times and total felt performance over the useful life of the felt. The measurement includes valuable information regarding the overall condition of the press and its clothing. Operators can use the moisture information to adjust and optimize their Uhle box vacuums, felt showers, press crowns and zone control rolls in order to achieve flatter profiles with new felts. WHAT YOU WILL LEARN: * There is a lack of measurement and control between the forming section and ex-press. * Why moisture measurement following the press section represents a sound strategic starting place for correcting this problem. * How a new moisture measurement system can help meet measurement and control goals. ADDITIONAL RESOURCES: * A complete version of this article, including several figures and examples, is available online at www.tappi.org. Click on the Solutions! link at the bottom of the home page and go to "Online Exclusives" for the August issue. Editor's Note Editor's Note (foaled in 1993 in Kentucky) is an American thoroughbred Stallion racehorse. He was sired by 1992 U.S. Champion 2 YO Colt Forty Niner, who in turn was a son of Champion sire Mr. Prospector and out of the mare, Beware Of The Cat. Trained by D. : A complete version of this article, including several figures and examples, is available online at www.tappi.org. Click on the Solutions! link at the bottom of the home page and go to "Online Exclusives" for the August issue. RAYMOND P. SHEAD, VOITH PAPER AUTOMATION ABOUT THE AUTHOR: Raymond P. Shead is business director, Voith Paper Automation, Heidenheim, Germany. Contact him by email at ray.shead@voith.com [ILLUSTRATION OMITTED] |
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