Method in the bleaching of pulp and a device for the bleaching of pulp

Abstract

Bleaching device for pulp includes a container to which a supply of pulp and bleaching chemicals containing peroxide as well as discharge of bleached pulp are connected. The device comprises an oxygen measuring device a temperature measuring device and/or a carbon monoxide measuring device, which are arranged to measure oxygen concentration, temperature and/or carbon monoxide concentration, respectively, from the contents of the container such as from the gas volume of the same, or from a substance flow coming from the container, such as gas flow. The measuring device is connected to a data processing unit which is coupled to a controller for automatic control of the process. The process is especially a high consistency pulp bleaching of mechanical pulp, in which the consistency of pulp in the reaction area is at least 25%, advantageously at least 30%.

What is claimed is:  
     
         1 . A bleaching process for pulp comprising: 
 contacting cellulose-containing fibrous pulp with peroxide in a process area;    measuring oxygen concentration, temperature and/or carbon monoxide concentration in the process area; and    adjusting the bleaching process based on results from measuring oxygen concentration, temperature and/or carbon monoxide concentration.    
     
     
         2 . The process according to  claim 1 , wherein that the oxygen concentration, temperature and/or carbon monoxide concentration is measured from a gas volume in a container containing the process area.  
     
     
         3 . The process according to  claim 2 , wherein the oxygen concentration, temperature and/or carbon monoxide concentration is measured from an upper part of a bleaching tower in a process area  
     
     
         4 . The process according to  claim 2 , wherein the oxygen concentration, temperature and/or carbon monoxide concentration is measured from a vent gas flow coming out of the bleaching tower.  
     
     
         5 . The process according to  claim 1  or  2 , wherein the oxygen concentration is measured and the process is adjusted on the basis of the results obtained from this measurement.  
     
     
         6 . The process according to  claim 1  or  2 , wherein the temperature and/or the carbon monoxide concentration is measured and the process is adjusted on the basis of the results obtained from this measurement.  
     
     
         7 . The process according to  claim 4 , wherein the temperature is measured directly from the gas volume in the container containing the process area, from an upper part of the bleaching tower by means of a sensor placed therein, and the carbon monoxide concentration is measured from a vent gas flow coming out of the container.  
     
     
         8 . The process according to  claim 7 , wherein the carbon monoxide concentration is measured from a vent gas flow from a bleaching sensor.  
     
     
         9 . The process according to the results from measuring oxygen concentration, temperatuer and/or carbon monoxide concentration are utilized to control an alkali/peroxide ratio of the process area.  
     
     
         10 . The process according to  claim 9 , wherein one of the amounts of alkali and peroxide is kept constant and the other is changed.  
     
     
         11 . The process according to  claim 1 , wherein the oxygen concentration, temperature and/or the carbon monoxide concentration is monitored by means of a measurement conducted at intervals or continuously and the process is controlled automatically on the basis of the results.  
     
     
         12 . The process according to  claim 1 , wherein a set value is defined for the oxygen concentration, and by means of this value a feedback control of the process is performed.  
     
     
         13 . The process according to  claim 11 , wherein a set value of the oxygen concentration is a fixed maximum value, and the control is performed when this maximum value is exceeded.  
     
     
         14 . The process according to  claim 1 , wherein a set value is defined for the temperature and/or carbon monoxide concentration, and by means of this value a feedback control of the process is performed.  
     
     
         15 . The process according to  claim 13 , wherein that the set value of the temperature and/or the carbon monoxide concentration is a fixed maximum value, and the control is performed when this maximum value is exceeded.  
     
     
         16 . The process according to  claim 1 , wherein the process is a high consistency pulp bleaching, in which the consistency of pulp in the reaction area is at least 25%.  
     
     
         17 . The process according to  claim 16 , wherein the process is a high consistency pulp bleaching in which the consistency of pulp on the reaction area is at least 30%.  
     
     
         18 . A bleaching device for pulp, comprising a container that includes a supply for pulp and bleaching chemicals containing peroxide, and a discharge for bleached pulp, wherein the bleaching device contains an oxygen measuring device, a temperature measuring device and/or a carbon monoxide measuring device, which is/are effective for measuring oxygen concentration, temperature and/or carbon monoxide concentration, respectively, from the contents of the container.  
     
     
         19 . The bleaching device according to  claim 18 , wherein it comprises at least an oxygen measuring device.  
     
     
         20 . The device according to  claim 19 , wherein the oxygen measuring device is arranged to measure the oxygen concentration from the gas volume of the container or from a gas flow coming from the container.  
     
     
         21 . The bleaching device according to  claim 18 , wherein it comprises at least a temperature measuring device and/or a carbon monoxide measuring device.  
     
     
         22 . The bleaching device according to  claim 21 , wherein the carbon monoxide measuring device is a measuring device connected to a gas flow coming out of the container.  
     
     
         23 . The bleaching device according to  claim 22 , wherein the measuring device is a gas analyzer.  
     
     
         24 . The bleaching device according to  claim 22 , further comprises a measuring device which is arranged to measure the concentration of a gas component other than carbon monoxide, from the contents of the container.  
     
     
         25 . The bleaching device according to  claim 24 , wherein the measuring device is effective for measuring oxygen.  
     
     
         26 . The device according to  claim 25 , wherein the measuring device is a gas analyzer, connected to the gas flow coming out of the container.  
     
     
         27 . The bleaching device according to  claim 26 , wherein the gas analyzer is effective for measuring oxygen.  
     
     
         28 . The device according to  claim 18 , wherein the oxygen measuring device, the temperature measuring device and/or the carbon monoxide measuring device is/are connected to a data processing unit (U) which is connected to a controller for automatic control of the process.  
     
     
         29 . The device according to  claim 28 , wherein the device comprises both a temperature measuring device and a carbon monoxide measuring device.  
     
     
         30 . The device according to  claim 29 , wherein the temperature measuring device is a temperature sensor placed in a gas volume of the container.