US3748224A - Control system for the pre dryer section of a paper machine - Google Patents

Control system for the pre dryer section of a paper machine Download PDF

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Publication number
US3748224A
US3748224A US00092347A US3748224DA US3748224A US 3748224 A US3748224 A US 3748224A US 00092347 A US00092347 A US 00092347A US 3748224D A US3748224D A US 3748224DA US 3748224 A US3748224 A US 3748224A
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United States
Prior art keywords
temperature
drum
steam
pulp
signal
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Expired - Lifetime
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US00092347A
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English (en)
Inventor
W Tillie
J Carleton
R Putman
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Westinghouse Electric Corp
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Westinghouse Electric Corp
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Publication date
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Publication of US3748224A publication Critical patent/US3748224A/en
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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
    • D21G9/00—Other accessories for paper-making machines
    • D21G9/0009—Paper-making control systems
    • D21G9/0036—Paper-making control systems controlling the press or drying section
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S162/00—Paper making and fiber liberation
    • Y10S162/09—Uses for paper making sludge
    • Y10S162/10—Computer control of paper making variables
    • Y10S162/11—Wet end paper making variables

Definitions

  • the pulp in a head box passes through a slice gap or slit onto a wire comprising a fine wire screen in the form of an endless belt, usually several feet wide. Vibration of the screen spreads the material in a thin uniform layer or web. As it is carried along on the wire, much of the water in the soft mass drains out. To prevent the material from running over the edges of the wire, rubber belts are usually placed on either side. Mechanical suction removes much of the water from the wet pulp mass, after which the web passes between rollers to a thick woolen felt which is carried between a series of heaw rollers.
  • the paper Passing between these, the paper is pressed into a firm thin sheet, and thereafter passes over a series of heated drying rolls.
  • the Web passes over the initial rolls while it is still on the felt mat; however, after suflicient drying has taken place, the web may be separated from the felt mat and passed over the remaining drying rolls to a sizing press without any external support.
  • the initial drying roll or rolls over which the web passes are ordinarily referred to as the pre-dryer.
  • the main function of the pre-dryer is to heat the pulp web or sheet to a predetermined temperature. It has been found from actual operating experience that if the web, upon leaving the pre-dryer, is at a certain desired temperature (which in one case is 160 F.), then the remaining dryers can be operated much more efiiciently. There is no theoretical justification for this; it is something that must be found out from experience.
  • the temperature of pulp issuing from the pre-drying drum of a papermaking machine is controlled by conducting a heat balance around the drum to generate a feed-forward signal indicative of the pressure and temperature of the steam necessary to raise the temperature of the web from a known input temperature to a desired output temperature.
  • This feed-forward signal is then modified by a feedback signal derived by comparison of desired output temperature with the actual output temperature of the web to derive an error signal for controlling the pressure of the steam in the drying drum.
  • the feed-forward signal is generated from a consideration of the fact that the heat, Q required to heat up the paper web from an incoming temperature, T to an outgoing temperature, T equals the heat, Q transferred from the inside of the dryer drum or drums to the web.
  • the heat, Q transferred from the inside of the drum to the Web can be calculated from a consideration of the heat transfer characteristics of the drum, the temperature of the steam within the drum, and the sheet temperatures, T and T at the input and output of the drying drum or drums, respectively.
  • the heat required to heat up the paper web from temperature T to temperature T can be calculated from the mass flow rates of pulp and water flowing onto the drying drum, the specific heats of the fiber and water, and the temperatures T and T Since Q must always be equal to Q an equation can be derived for determining the temperature, T,,, of the steam.
  • This temperature then comprises a feed-forward signal which is modified by a comparison of the desired output temperature with actual output temperature to vary the steam flow into the pre-dryer drum.
  • the embodiment of the invention shown includes a felt belt 10 which carries, on its upper surface, a moist Web of pulp 12 which is to be dried and pressed into paper sheet.
  • the felt passes over a pre-dryer 14 comprising a rotatable drum having a hollow interior into which steam from line 16 is introduced.
  • the exhausted steam passes out of the hollow interior of the drum 14 through conduit 18 to a condenser or separator 20.
  • the pre-dryer drum 14 is the first drying drum in the process of drying and rolling pulp into paper and may comprise a series of drums rather than the single drum shown herein.
  • the drum normally comprises a cast iron cylinder with a wall thickness of about 1% inches, the heat of the steam within the hollow interior of the drum being transferred through the wall of the drum to the felt 10 and pulp 12.
  • F predetermined temperature
  • the temperature of the pulp issuing from the predryer is measured by a temperature measuring device 22 which produces an electrical signal on lead 24 proportional to that temperature.
  • the temperature of the incoming pulp is measured by a temperature measuring device 26 which produces anelectrical signal on lead 28 proportional to the measured temperature.
  • the density of the pulp on felt is measured and converted into a proportional electrical signal by a beta gauge 30. This electrical signal is multiplied by a constant, K at 32 to produce a signal M which is proportional to the pounds of dry fiber pulp per minute passing along the felt belt 10. This, of course, assumes a constant speed of the belt 10. If the speed of the belt should vary, then a tachometer generator and compensating circuitry will have to be employed for variations in speed.
  • N nurnber of rolls in the pre-dryer (one in the example given);
  • the desired steam temperature T,,* can be calculated from Equation 14; and this is performed in computer circuitry identified by the reference numeral 34 in the drawing to produce an electrical quantity comprising the feed-forward signal.
  • the computer circuitry 34, as well as the other circuit blocks shown herein, may comprise part of a general purpose computer which is programmed to perform the calculation of Equation 14 and the other control functions described herein to produce an electrical quantity comprising the feed-forward signal. However, it is shown as hard-wired logic in the drawing to facilitate explanation.
  • the quantity M is derived in block 36 by multiplying M times a constant K. That is, it is assumed that a certain rate of dry pulp flowing to the drum 14 will contain a fixed percentage of water.
  • the quantity T is entered into the computer circuitry 34 from block 38 and is selected by an operator.
  • the parameter to be controlled is the actual exit temperature T this temperature is compared with the desired temperature T at 40 and the quotient or ratio subtracted from 1 in block 42 to derive a corrective feedback signal which is integrated in integrating controller 44 and multiplied with the quantity T,,* at the output of circuit 34 at 46.
  • This corrected value T is then applied to circuit 48 where it is multiplied by a factor 1 from a steam table 50 stored in the computer memory to derive P*.
  • P* is the desired pressure of the steam within the drum 14 to achieve an exit temperature equal to T
  • the actual steam fed into the drum 14 is controlled by means of valve 52 connected to a pressure controller 54 which receives a set point signal from integrating controller 56.
  • the set point of controller 56 is derived by comparing in comparator 60 P* from block 60 with the actual steam pressure P as derived from a pressure sensing device 58.
  • a servo loop is established in which any change in the value of P* will cause an adjustment in the setting of valve 52 which, in turn, will vary the output of pressure sensing device 58 until the two signals, P* and P, are equal, at which time the pressure in the drum 14 is equal to the calculated desired pressure P*.
  • the quantity U the overall heat transfer coeflicient, includes losses to the air blowing across the pulp and perhaps the tightness of the felt and other factors. For this reason, the quantity U is not a fixed value but changes and, consequently, it is desirable to update the quantity U. This is achieved by measuring the amount of condensate coming out of the dryer at 60 and converting this at 62 into the amount of heat actually given up by the steam by multiplying pounds of condensate by a constant K This, then, can be compared with calculated heat transferred, Q in circuitry 64 and the difference derived at 66 integrated at 68 and used to multiply U*, the predicted heat transfer coefficient, at 70. This gives a corrected value of U which is fed back to circuit 34.
  • said means for computing the desired temperature of the steam within said drum including a device for measuring the actual temperature of pulp passing tothe drying drum and means for determining the weight per unit of time of dry pulp and moisture passing to the drying drum, means responsive to the desired steam temperature thus computed for generating a feed-forward error signal for controlling the admission of steam into said drum,
  • valve control means responsive to said feed-forward signal as and if modified for controlling said control valve and, hence, the admission of steam into said drying drum.
  • T,,* is the desired temperature of the steam within said drum
  • T is the temperature of the pulp passing to the drying drum
  • T is the desired output temperature of the pulp as determined by an operator
  • N is the number of rolls over which the pulp passes
  • U is the overall heat transfer coefiicient of the drying drum
  • A is the contact area of the pulp with the periphery of the drying drum
  • M is the bone dry pulp rate
  • C is the specific heat of the dry pulp
  • M is the moisture in the incoming sheet
  • C is the specific heat of water
  • F is N -U-A w w+ fib+ ib 4.
  • said means for computing the desired temperature T,,* produces an electrical signal proportional to T,,* and includes means for comparing an electrical signal proportional to T with an electrical signal T proportional to actual output temperature to derive an error signal for modifying the electrical signal proportional to T,,*.

Landscapes

  • Paper (AREA)
  • Drying Of Solid Materials (AREA)
  • Control Of Temperature (AREA)
US00092347A 1970-11-24 1970-11-24 Control system for the pre dryer section of a paper machine Expired - Lifetime US3748224A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US9234770A 1970-11-24 1970-11-24

Publications (1)

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US3748224A true US3748224A (en) 1973-07-24

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US00092347A Expired - Lifetime US3748224A (en) 1970-11-24 1970-11-24 Control system for the pre dryer section of a paper machine

Country Status (3)

Country Link
US (1) US3748224A (enrdf_load_stackoverflow)
JP (1) JPS523007B1 (enrdf_load_stackoverflow)
FR (1) FR2115949A5 (enrdf_load_stackoverflow)

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4170073A (en) * 1977-12-01 1979-10-09 Kay-Ray, Inc. Wide dynamic range multi-zone drying method and apparatus for controlling product moisture
US4499668A (en) * 1983-11-25 1985-02-19 Midland-Ross Corporation Automatic minimum differential pressure control for dryer cylinders
US4753017A (en) * 1987-03-23 1988-06-28 Gilbert Sr Lyman F Heat control of steam-heated rollers
US4875297A (en) * 1987-06-16 1989-10-24 Schwabische Huttenwerke Gmbh Device for treating a material web
WO2000034574A1 (en) * 1998-12-04 2000-06-15 Metso Paper, Inc. Method and equipment for regulation of the initial part of the dryer section in a paper machine
US20100269996A1 (en) * 2007-07-24 2010-10-28 Grattan David A Method of detecting and reducing contamination in papermaking boiler systems
CN102561089A (zh) * 2011-12-23 2012-07-11 广东工业大学 一种瓦楞纸生产过程热缸加热自动控制装置及控制方法
CN104264524A (zh) * 2014-09-18 2015-01-07 陕西科技大学 造纸机烘缸表面温度无线检测系统
DE102024104630A1 (de) * 2024-02-20 2025-08-21 Voith Patent Gmbh Verfahren und Maschine zur Herstellung einer Materialbahn mit einem optimierten Aufheizvorgang

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS63140405U (enrdf_load_stackoverflow) * 1987-03-09 1988-09-16
JP3094798B2 (ja) * 1994-08-16 2000-10-03 王子製紙株式会社 抄紙機の抄替時の製品水分の制御方法およびその装置

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4170073A (en) * 1977-12-01 1979-10-09 Kay-Ray, Inc. Wide dynamic range multi-zone drying method and apparatus for controlling product moisture
US4499668A (en) * 1983-11-25 1985-02-19 Midland-Ross Corporation Automatic minimum differential pressure control for dryer cylinders
US4753017A (en) * 1987-03-23 1988-06-28 Gilbert Sr Lyman F Heat control of steam-heated rollers
US4875297A (en) * 1987-06-16 1989-10-24 Schwabische Huttenwerke Gmbh Device for treating a material web
WO2000034574A1 (en) * 1998-12-04 2000-06-15 Metso Paper, Inc. Method and equipment for regulation of the initial part of the dryer section in a paper machine
US20020007927A1 (en) * 1998-12-04 2002-01-24 Harri Vahatalo Method and equipment for regulation of the initial part of the dryer section in a paper machine
US6423184B2 (en) * 1998-12-04 2002-07-23 Metso Paper, Inc. Method and equipment for regulation of the initial part of the dryer section in a paper machine
US20100269996A1 (en) * 2007-07-24 2010-10-28 Grattan David A Method of detecting and reducing contamination in papermaking boiler systems
US8906202B2 (en) * 2007-07-24 2014-12-09 Nalco Company Method of detecting and reducing contamination in papermaking boiler systems
CN102561089A (zh) * 2011-12-23 2012-07-11 广东工业大学 一种瓦楞纸生产过程热缸加热自动控制装置及控制方法
CN104264524A (zh) * 2014-09-18 2015-01-07 陕西科技大学 造纸机烘缸表面温度无线检测系统
DE102024104630A1 (de) * 2024-02-20 2025-08-21 Voith Patent Gmbh Verfahren und Maschine zur Herstellung einer Materialbahn mit einem optimierten Aufheizvorgang

Also Published As

Publication number Publication date
JPS523007B1 (enrdf_load_stackoverflow) 1977-01-25
FR2115949A5 (enrdf_load_stackoverflow) 1972-07-07

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