Method and arrangement for measuring and controlling chip and/or liquid level

Abstract

A method for measuring and controlling a chip level and/or a chip-liquor combination level and/or liquor level height of a liquid-steam phase digester or a hydraulic digester which digester comprises a chip screw for feeding chips into a digesting volume. The method comprises mounting electrode pairs in certain heights and vertically at distances from each other in the digesting volume of the digester, the electrode pairs being formed of electrodes; connecting the electrode pairs to electric circuits; measuring in each electric circuit a current or voltage value during operation of the digester; determining, based on the measurement, type of material layer (for example, steam, chips, combination of chips and liquor, or liquor) located in a certain height, based on the electrical conductivity of the materials in the digesting volume. An arrangement for measuring and controlling a chip level and/or a chip-liquor combination level and/or a liquor level height of a liquid-steam phase digester or a hydraulic digester.

1 . A method for measuring and controlling a chip level and/or a chip-liquor combination level and/or a liquor level height of a liquid-steam phase digester or a hydraulic digester which digester comprises a chip screw for feeding chips into a digesting volume; and the method comprising mounting electrode pairs in certain heights and vertically at distances from each other in the digesting volume of the digester, the electrode pairs being formed of electrodes; connecting the electrode pairs to electric circuits; measuring in each electric circuit a current or voltage value during operation of the digester; determining, based on the measurement, type of material layer located in a certain height, based on the electrical conductivity of the materials in the digesting volume. 
     
     
         2 . The method according to  claim 1  comprising arranging a potential difference between the electrodes of the electrode pairs and measuring the current in the electric circuit. 
     
     
         3 . The method according to  claim 1  comprising supplying a constant current to the electric circuit of the electrode pairs and measuring the voltage in the electric circuit. 
     
     
         4 . The method according to  claim 1  comprising using the determined height information of the chip level and/or the chip-liquor combination level and/or the liquor level as control for the digesting process and repeating the measuring and control steps of the method. 
     
     
         5 . The method according to  claim 1  comprising arranging a changing potential difference between the electrodes of the electrode pairs which is preventing generation of precipitation on electrode surfaces. 
     
     
         6 . An arrangement for measuring and controlling a chip level and/or a chip-liquor combination level and/or a liquor level height of a liquid-steam phase digester or a hydraulic digester which digester comprises a chip screw for feeding chips into a digesting volume; and the arrangement comprises electrode pairs which are formed of electrodes and mounted in certain heights and vertically at distances from each other in the digesting volume of the digester; and the electrode pairs are connected to electric circuits such that, during operation of the digester, a current or voltage value measured in each electric circuit is determining the type of material layer located in a certain height, based on the electrical conductivity of the materials in the digesting volume. 
     
     
         7 . The arrangement according to  claim 6 , wherein the arrangement comprises a circuit measuring means which is during operation of the digester arranged to measure current of the circuits when potential differences are arranged between the electrode pairs. 
     
     
         8 . The arrangement according to  claim 6 , wherein the arrangement comprises a circuit measuring means which is during operation of the digester arranged to measure voltage of the circuits when current is supplied in the circuits. 
     
     
         9 . The arrangement according to  claim 6 , wherein the arrangement comprises an output for communicating the height information of the chip level and/or the chip-liquor combination level and/or the liquor level from the circuit measuring means for the control of the digesting process. 
     
     
         10 . The arrangement according to  claim 6 , wherein the electrode pairs are arranged under the chip screw. 
     
     
         11 . The arrangement according to  claim 6 , wherein the arrangement comprises one or more measuring rods to which is/are mounted electrodes for the electrode pairs.