Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F5/00—Dryer section of machines for making continuous webs of paper

Definitions

• the invention relates to a hood for a paper and / or board machine.
• Paper or board machines have dryer sections, in which the wet paper or board web is dried by supplying convection heat or radiant heat usually by means of a cylinder drying. Efficient air systems are used to increase the process reliability and to optimally support the drying process to dissipate the high moisture or moisture content of the air, which can sometimes exceed 200 g per kg of dry air.
• a fume hood is placed over the dryer section of the paper or board machine, thereby enclosing this area. Via the extractor hood and an associated ventilation system, the moist air is removed and continuously replaced by newly supplied drier air.
• the hood parts are made of aluminum or stainless steel and are bolted to a stable, galvanized steel construction with a sealing system and insulated with dimensionally stable mineral wool.
• a leader's side lift gates with window band are provided.
• a dew point control and also heat recovery from the hood exhaust air can be provided.
• the energy consumption or primary heat consumption of the dryer section of the paper machine is important, which is lower with higher moisture content of the exhaust air.
• the problem of precipitation or condensation of water vapor on the inside of the housing of the hood increasingly important, especially then occurs when the temperature at the inner surface of the housing is lower than the dew point or the condensation temperature of the air with the respective moisture content.
• This condensation problem is very disadvantageous and, in particular, due to drops of water falling on the paper or board web, leads to damage or tearing of the paper or board web and thus to considerable failures. Furthermore, the condensation also leads to corrosion on the hood.
• the temperature in the drying section is typically around 100 ° C to 120 ° C. Due to the comparatively high temperatures in the interior of the hood, metals such as aluminum or stainless steel are currently used at least on the inner surface of the hood housing and no plastics or other heat-insulating materials.
• the moisture content of the exhaust air depends on the dew point of the air. For example, at a dew point of 60 ° C, a moisture content of 160 g / kg dry air can be dissipated at a dew point of 72 ° C, a moisture content of 400 g / kg dry air. In a modern paper machine typically 1 million m 3 / h of exhaust air can be discharged through the hood and about 100,000 kg of water / h.
• Out DE 33 36 998 C2 is a method of ventilation in drying sections with closed housing of paper machines is known in which hot air and moist air is blown from nearby side rooms of the housing of the hood, thereby making it possible to increase the moisture content and the temperature level in the area of the passages of the housing and thereby the To reduce excessive drying of the paper web edges and the heat loss at the ends of the drying cylinder and thus to improve the heat evaporation of the dryer section.
• the air flows down through nozzles or down obliquely from air channels in the housing. As a result, the air moves in the vicinity of the side walls and the surface temperature of the inner walls of the housing increases, whereby the risk of condensation is reduced.
• the blown air may be either air from within the housing, or partially air from the housing and partially dry replacement air.
• DE 33 36 998 C2 also prevents condensation when the humidity of the exhaust air of the housing in sizes up to 200g / kg dry air lie.
• DE 33 36 998 C2 It is reported that high moisture loading condensation of 200 g / kg dry air can no longer be avoided by increasing the thickness of the casing wall insulation and is often due to high local humidities or low surface temperatures that occur at thermal bridges or leaks, particularly on doors and windows of the housing. Elimination of thermal bridges and loss spots would require such an expensive solution that this could not be done in practice.
• a heat insulating wall of the housing of the hood is provided with an approximately 1 mm thick aluminum sheet on both sides and inside a thermal insulation of 100 mm mineral wool. This interconnected structure has a thermal resistance of 0.833 m 2 ° C / Watt, including thermal bridges. Insulated glass windows are used for the windows with 23 mm thick insulation plates and a 15 mm wide air gap.
• DE 3925595 A1 discloses a method and an apparatus for measuring the dew point of gases, in particular the exhaust gas of a drying hood of a paper machine.
• the process gas is cooled down to the dew point with the aid of a cold glass, and then the dew point is determined on the basis of light scattered by the resulting mist.
• so-called "cooling mirror” detectors that measure optically a precipitating moisture on a mirror polished plane or dew point sensors based on the change in capacitance or resistance, as well as indirect measurements of the dew point by absorption in UV or IR spectra or microwaves, or even a method using acoustic emissions.
• Out DD 249 954 A1 discloses a method for reducing the energy consumption in a closed drying system of a paper machine by dew point control. Regardless of different outdoor air conditions and a type program traveled on the paper machine, a tentatively determined optimal exhaust air condition is achieved with the highest possible dew point by controlling the carrier air amount, the temperature of the introduced air is kept constant and the carrier air quantity for water vapor transport by reducing the supply and exhaust air is reduced.
• an exhaust air humidity sensor which is located in the exhaust duct between an outlet of the hood and a variable speed exhaust fan, the absolute humidity of the hood air is measured and by comparison with an exhaust air humidity setpoint, the exhaust air moisture is controlled to the desired value by changing the exhaust air.
• From the GB2 102 598 A is a method for increasing the thermal efficiency in a dryer system, in particular a paper dryer system in which moist exhaust air is removed at a temperature of about 120 ° C via an exhaust duct.
• the moisture content of the exhaust air is measured by means of a measuring device in the region of the exhaust air line and then controlled to a value that results in an optimized efficiency for the dry cycle. As measured outside the hood in the exhaust air flow, only a limited dew point control is possible with this arrangement.
• the invention is an object of the invention to provide a fume hood for a paper and / or board machine, in which the problem of condensation Kon is at least partially reduced and / or at which the operating dew point can be increased.
• the invention is based on the consideration to provide on the inner surface of the housing of the hood a condensation sensor arrangement or a condensation sensor system with which or the inner surface of the hood is monitored for a possible or imminent condensation formation.
• a droplet formation and thus a possible negative influence on the drying process is thus sensory anticipated or detected and an incipient condensation can be detected early and process technology prevented.
• the operation of the hood is safer and more controlled and the hood exhaust air volumes and the process air supply can be optimized.
• the (theoretical) operating dew point of the hood of the paper or board machine can be increased and existing system reserves can be reduced to a safe minimum. Furthermore, this results in an energy saving both based on the steam savings in the process air and in the power savings of the supply air fans and exhaust fans.
• the moisture removal efficiency can be increased and with the same amount of air more moisture can be dissipated or with the same moisture removal, the amount of air can be reduced and thereby a lower flow velocity and thus a lower load of the wet paper web can be achieved by the air flow.
• the condensation sensors are preferably arranged at critical points or partial areas of the hood inner surface where condensation is most likely or most likely to occur.
• the hood roof or the region of the hood housing lying above the dryer section of the paper machine and / or the inlet region the paper and / or board machine in the hood and / or the outlet region of the paper and / or board machine in the hood provided with condensation sensors.
• the condensation sensors can be subdivided or spaced apart into individual sections or arrangements, in particular in the form of grids or other patterns.
• condensation sensor preferably electrical condensation sensors are used, which detect a change in electrical capacitance or electrical resistance between electrical conductors due to a change in the humidity of the intervening air or an at least partial replacement of the intervening air as a medium by a condensed condensate and as a measure for an emerging or already occurred condensate formation.
• film sensors made of a carrier material (substrate) with mounted conductor tracks, which are arranged in pairs, are used as condensation sensors.
• An evaluation device is used to measure the change in an electrical voltage or an electric current between or in the conductor tracks or the conductivity or capacitance as a sensor signal.
• the evaluation of the sensor signals of the condensation sensors is scalable or can be carried out with different measuring ranges or measuring sensitivities, wherein or by which an assignment to different predetermined droplet sizes of the condensate, which is reflected in particular between the printed conductors, can take place.
• condensation sensors may be provided, for example, the in DE 39 25 595 A1 described dew point sensors.
• the measurement signals or measurement data of the condensation sensors become individual for each condensation sensor during operation of the extractor hood or for groups of condensation sensors, in particular in the individual sections, continuously monitored or evaluated and can in particular be visualized, for example, displayed on a display in the form of numerical values or graphically, and / or archived or stored.
• the sensor signals or sensor values can also be processed further by means of an evaluation unit, in particular a computer, and the evaluations are made available, for example, via an interface, in particular a bus interface, to a higher-order process control system.
• a known dew point control is cascaded with a dew point sensor in the total exhaust air or in the exhaust duct of the hood via a setpoint shift.
• the control system is set or leveled, with preferably low safety margins are adjustable. The dew point is therefore driven close to the point detection or the limits of the condensation sensors.
• the reference variable of the dew point control is reduced again until an uncritical operating state is reached again so that the condensation detected by the condensation sensors again falls below the maximum permissible level.
• temperature sensors may also be provided at the subregions in which condensation sensors are arranged in order to measure the local temperature and if necessary to obtain from the signals or data of the temperature sensors and the condensation sensor information about thermodynamic variables such as the dew point. In this way, a temperature compensation of the sensor signals of the condensation sensors or their scaling can be carried out via the temperature measured values or measuring signals.
• the extractor hood is subdivided into individual zones, for example three zones in the direction of paper or board web conveying, and the described condensation monitoring by means of the condensation sensors and preferably also the control of the dew point depending on this condensation monitoring are carried out separately for each of the zones , As a result, the efficiency can be specifically optimized for each of these zones depending on the respective moisture load in the respective zone.
• the air flow distribution in the interior or the zones of the hood can be adjusted by targeted control of the amounts of air individual air supply ducts and / or Heilabsaugkanäle depending on the condensation monitoring.

Landscapes

• Paper (AREA)
• Drying Of Solid Materials (AREA)
• Auxiliary Devices For And Details Of Packaging Control (AREA)
• Cartons (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=37307099

Family Applications (1)

Country Status (8)

Families Citing this family (7)

Family Cites Families (8)

• 2005
  • 2005-06-23 DE DE102005029602A patent/DE102005029602A1/de not_active Withdrawn
• 2006
  • 2006-06-09 DE DE502006005794T patent/DE502006005794D1/de active Active
  • 2006-06-09 CN CN2006800225901A patent/CN101258286B/zh not_active Expired - Fee Related
  • 2006-06-09 BR BRPI0613331A patent/BRPI0613331B1/pt active IP Right Grant
  • 2006-06-09 ES ES06776046T patent/ES2338156T3/es active Active
  • 2006-06-09 AT AT06776046T patent/ATE453752T1/de active
  • 2006-06-09 WO PCT/EP2006/005539 patent/WO2006136298A1/de not_active Application Discontinuation
  • 2006-06-09 EP EP06776046A patent/EP1910614B1/de not_active Not-in-force
• 2007
  • 2007-12-21 US US11/962,575 patent/US20080155851A1/en not_active Abandoned

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