Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
  • D21D5/00—Purification of the pulp suspension by mechanical means; Apparatus therefor
  • D21D5/26—De-aeration of paper stock

Definitions

• the invention relates to a method for monitoring and controlling a papermaking process.
• Air and other gases both as dissolved and in gaseous form, occur in the stock and water circulations of a paper or board machine. Air (nitrogen and oxygen) gets into stock in connection with thick stock, circulation waters, pulping and mixing as well as because of leakages in process devices. Gases are also produced in the process as a result of bacterial activity (methane), decomposition (carbon dioxide) of carbonates or other compounds. Gases can cause various kinds of harm. They can, among other things, increase the consumption of energy, hamper the operation of pumps, cause contamination of the process, make the dewatering in the wire section more difficult, and reduce the quality of the paper being manufactured. Attempts are usually made to reduce the drawbacks caused by gases by means of mechanical deaeration and/or by adding deaerating chemicals.
• An object of the invention is a new way of monitoring and controlling a papermaking process based on measurements made from the process.
• An object is also a method that provides a more accurate picture than heretofore of the operation of the process, thus facilitating control of the process.
• the invention is characterized by what is stated in the characterizing part of claim 1.
• a papermaking process is monitored by measuring the amount and quality of gas from a gas flow discharging from a process device and by controlling the process based on the information obtained.
• Said process device can be, for example, a deaeration tank, a passive deaeration duct (for example, an OptiAir Flume produced by the applicant), a cyclone, a centrifugal cleaner, a screen, a pulp chest or a water tank, a sampling device or another equivalent process device through which air and gases are removed from the process.
• the amount of gas is meant the total amount of air and the gases originating from the process.
• quality of gas is meant, among other things, the proportion of a given gas component in the total amount of gases.
• the amount and quality of gas is also measured from one or more other material flows.
• the content of one or more gases present in the process can be measured from a stock and/or water circulation of the process and from gas flows leaving the process.
• the gas to be measured can be nitrogen, methane, oxygen or carbon dioxide or any other gas present in the process.
• the gas can be in soluble or gaseous form.
• deaerator can be controlled based on the amount and quality of gas.
• deaeration devices are often operated, to be on the safe side, at high capacity because the exact amount of the gases in the process is not generally known.
• a substantial saving is achieved, for example, because, as a result of the monitoring of gases, the vacuum used in the deaerator can be reduced.
• An increase in the methane content indicates that anaerobic bacterial activity occurs in the process.
• An increased carbon dioxide content in turn indicates a change in pH, which has led to the decomposition of carbonate and some other compounds.
• An increased oxygen or nitrogen content can be an indication of leakages or disturbances in a pump or in another process device in the control of the liquid-level of tanks/chests.
• the measurement of the amount and quality of gas at several points of the process makes it possible to determine a gas balance in different sections of the process, such as for the short circulation, the long circulation, stock lines, broke lines, etc. This makes it easier to locate the cause of disturbance and to direct corrective action at a right location.
• the amount and quality of gases is measured at point M10 from a water flow passed from the wire water tank 22 along the line 23 to the deaerator 9.
• the gas flow discharging from the deaerator 9 is monitored at point M8.
• the amount and quality of gases is measured at point M9 from the water flow discharging from the deaerator 9.
• deaerator it is also possible to use deaerators that are based on delay times, such as an OptiAir FlumeTM deaeration duct, a conventional wire pit and/or cyclone.
• the amount and quality of gases is measured at point Mi l from the wire water flow passed from the wire water tank 22 to the disc filter 27.
• the gas content and the quality of the gases of the wet broke conducted along the line 28 to the disc filter 27 are monitored at point Ml 2.
• the gas content and the quality of the gases of the filtrates obtained from the disc filter 27 are monitored at points Ml 3 and M14.
• the amount and quality of the gas emerging from the deaeration tank 9 can be measured at point M8.
• the quality of the gas for example, the content of methane or nitrogen changes as a result of increased microbial activity in some preceding process step
• attempts are made to remedy the problem by controlling the metering of biocide to the process.
• the data on the amount and quality of gases obtained from the different measurement points M1-M14 can be combined in a desired manner to form a gas balance of the process or a single section thereof.
• the operation of the deaerator can be controlled based on one or more measurements, so that the vacuum level of the deaerator can be limited to correspond to the actual degasification need.
• Based on the monitoring of gases it is possible to control the feed amount and location of defoaming chemicals or the quality, amount and feed location of antimicrobial chemicals. In this way, chemicals can be applied where they are most needed and where they are most useful.
• the measurement of the amount and quality of gas can also be used for monitoring disturbance situations in the process. Monitoring reveals, for example, leakages in pump seals or disturbances in the control of the level in tanks. In that connection, information about a disturbance situation can lead to the initiation of process control or repair action.
• any methods known in themselves can be used in the measurement of the amount and quality of gas which has dissolved or is in the form of bubbles. These include, for example, ultrasound- or microwave-based methods, an acoustics-based free gas measurement method, a measurement method based on imaging and image processing, volume quantity measurement of gases and gas content measurement based on the compression and expansion of gases.
• the quality of gas can be measured, among other things, by specific gas sensors and by means of gas chromatography. Quality can also be monitored by measuring the distribution of the gas bubble size or the ratio of dissolved gas and gas in the bubble form by means of a measuring device intended for this purpose.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Paper (AREA)

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Citations (4)

• 2004
  • 2004-03-15 FI FI20040395A patent/FI119111B/fi not_active IP Right Cessation
• 2005
  • 2005-03-14 AT AT0903305A patent/AT502428B1/de not_active IP Right Cessation
  • 2005-03-14 DE DE112005000263T patent/DE112005000263T5/de not_active Withdrawn
  • 2005-03-14 WO PCT/FI2005/050078 patent/WO2005088007A1/en active Application Filing

Patent Citations (4)

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