Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Patent
1994-03-11
1996-07-16
Willis, Davis L.
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
25033407, 250343, G01N 2135
Patent
active
055369421
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of determining properties of a fibre or pulp-suspension, such as pulp kappa numbers, for instance, with the aid of near-infra-red-spectroscopy. The invention also relates to an arrangement for determining these properties and also to an arrangement for treating the suspension.
The kappa number of pulp is measured repeatedly during a wood-pulping process in order to monitor delignification of the pulp. These measurements are carried out manually and are highly time-consuming--each measuring process takes about 40 minutes. This manual measuring process includes determining the dry solids content of the suspension, diluting or thinning the suspension with water to a given, very precise concentration, adding a solution of permanganate and sulphuric acid to the system, adding a potassium iodine solution precisely 10 minutes later so as to interrupt the reaction, and titrating released iodine with a thiosulfate solution.
STFI (Svenska Traforskningsinstitutet) have recently developed a method in which the kappa number is measured with the aid of UV-spectroscopy. This method employs the use of a transparent cuvette through which a washed and diluted fibre suspension is passed, wherein the reflected and transmitted UV-light is measured over a time period of one minute. The kappa number is then calculated on the basis of these measurements and also on the basis of the concentration of the suspension.
According to a similar method developed by BTG, a pulp sample is taken from the pulp line and the sample is screened, the fibres repeatedly washed and the sample is thinned or diluted to a consistency within the range of 0.20-0.40%, whereafter the sample is circulated in a circuit in which the suspension is measured; whereafter the process is repeated subsequent to further thinning the sample. The measuring process is effected with the aid of two sensors, one for UV-light and one for visible light, wherein the lignin content is determined with the UV-sensor and the pulp consistency and the properties are measured, or determined, with the visible light sensor.
The drawbacks of these systems is that the systems are not time and temperature stable. Aging of the lens system and detectors results in drifts in the system which can result in measuring errors. Deposits in the optical part of the system can also result in drifting or deviation of the system. Variations in ambient temperatures and of sample temperatures can also influence the system in several ways. For instance, wavelength shifts and changes in the optical properties of the system and in the response characteristic of the detector can occur when the temperature changes. In addition to these stability aspects, it is also necessary to take into account that the pulp may contain different types of wood which give different absorbency spectra. The measurement values become widely spread unless sample specific calibrations are made at close intervals in conjunction with sample assaying processes.
U.S. Pat. No. 4,743,339 describes a method of determining the kappa number and other characteristic properties of a pulp-suspension with the aid of FTIR-spectroscopy (FTIR =Fourier Transform InfraRed). According to this method, the infrared absorption is measured within the IR-range of the non-diluted sample in a transparent cuvette within the wave number range of 1600-1700 cm (the wavelength range of 6300-7800 nm). The kappa number can be determined subsequent to correcting the spectrum of the base line, whose level is determined by the water content and the fibre concentration of the sample. 200 sweeps within the wavelength range are required for each sample. The drawback with this method is that measurement accuracy is determined to a high degree on just how precisely the base line correction can be carried out. It is necessary to recalibrate the spectrometer for each type of pulp, process and sampling station in the station. Furthermore, it is necessary to carry out the measuring processes at room temperature.
The object of the p
REFERENCES:
patent: 4743339 (1988-05-01), Faix et al.
patent: 4971441 (1990-11-01), Damlin et al.
patent: 5104485 (1992-04-01), Weger
"Svensk Papperstiddning" No. 16--1985, pp. 14-16 and 19-23.
Barringer Niklas
Norder Stig
Honig Richard
Procheck AB
Willis Davis L.
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