Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Chemical analysis
Patent
1997-04-11
1998-11-24
Kemper, Melanie
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Chemical analysis
702 25, 702 30, G01N 3334, D21C 910
Patent
active
058421505
DESCRIPTION:
BRIEF SUMMARY
This is the national stage of International Application No. PCT/EP95/04030, filed on Oct. 10, 1995.
FIELD OF THE INVENTION
The present invention is directed to a method for qualitative and quantitative determination of various parameters reflecting the pulp or paper quality and environmental impact of pulp and paper production, and more particularly to a spectroscopic method for the instantaneous and continuous analysis of the various parameters reflecting the quality of the pulp and paper as well as the environmental impact of the effluents paper, performed on the aqueous phases from the process stages in a pulp mill or paper mill.
BACKGROUND OF THE INVENTION
The main constituents of wood are cellulose, hemicellulose, lignin and extractives. The quality of pulp or paper is strongly related to its content of cellulose i.e a higher cellulose content increases the quality. Especially lignin, which is an aromatic crosslinked polymer, is an unwanted constituent in the pulp and affects the quality of the pulp negatively. In chemical pulp production the major part of the lignin is removed in the cooking process.
The remaining lignin is removed in a process, referred to as bleaching, by chemical oxidation. The bleaching process consists usually of 3-5 stages. Examples of oxidation chemicals used for bleaching are molecular chlorine, chlorine dioxide, hydrogen peroxide and ozone. Usually an alkaline extraction stage is employed between the different oxidation stages. From each bleaching stage an aqueous discharge is obtained, containing the degradation products of mainly lignin. This water soluble organic material reflects the mechanisms and removal efficiencies of the oxidation processes.
The bleached pulp is characterized by e.g. the kappa number, paper whiteness, measured as ISO-90 or similar parameters, paper strength, commonly measured as viscosity, tear index, tensile index or burst index.
The measurement of the kappa number in the aqueous phase is a relatively crude measurement of the reduction in the lignin content after each stage. According to the Technical Association of Pulp and Paper Industries (TAPPI) the kappa number reflects the relative hardness, bleachability or degree of delignification. The kappa number is defined as the degree of consumption of potassium permanganate (TAPPI Standard Method T 236 cm-85). Another, very similar and standardised method methods is SCAN-C 1:77.
The viscosity is a surrogate parameter reflecting the pulp strength and is often used instead of the more tedious determination of paper strength by tear index, tensile index and burst index.
Another important quality parameter is the whiteness or the brightness of the pulp and paper, which usually is measured as ISO-90.
The environmental impact of pulp and paper mill effluents is often assessed using parameters reflecting the organic content. Such parameters are the chemical oxygen demand (COD), the biological oxygen demand (BOD 5, BOD 7 and BOD 28), the total organic content (TOC), the colour of the effluent, adsorbable organohalogenes (AOX), suspended organic material and washing losses, the latter expressed as COD or sodium sulphate.
One major drawback with methods according to prior art of monitoring the efficiency of the bleaching process is the delay between the sampling of the bleach plant effluent and the determination of the kappa number and other conventional parameter, currently in use.
This delay may lead to important quality losses as appropriate measures are unnecessarily delayed. Another disadvantage with prior art methods are that the characteristics and distribution of this chemically very complex organic material is not very well described by these simple methods. It is obvious that there is a definite need for more convenient and relevant methods for characterising the quality of the pulp and the organic material in pulp mill effluents. The present invention has for object to offer a solution to the mentioned and similar problems, by providing a method that allows the continuous monitoring of pulp mi
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Renberg Lars
Sparen Anders
Eka Chemicals AB
Kemper Melanie
Mancini Ralph J.
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