Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Patent
1994-07-19
1996-02-13
Hannaher, Constantine
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
162 49, D21C 700, G01N 2135
Patent
active
054913403
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns on-line measurement of refiner mechanical pulp quality indices such as freeness, specific surface, fiber distribution, tear strength or average fiber length.
More specifically, the invention concerns a method according to the characterizing part of claim 1 for determination of refiner mechanical pulp properties.
Furthermore, the invention concerns an apparatus for determination of refiner mechanical pulp quality indices.
DESCRIPTION OF BACKGROUND ART
Conventionally, refiner mechanical pulp quality is characterized by different kinds of pulp strength indices, freeness and optical properties.
Forgacs investigated the strength properties and particle size distributions of refiner mechanical pulp in 1962. The outcome of his investigations was that the properties of a refiner mechanical pulp web such as burst strength, tear strength, bulk and wet web tensile strength could be predicted for a wide range of SGW pulps on the basis of only two pulp characterization indices:
1. Length factor (in short, L factor), which is characteristic of the fiber length distribution.
2. Form factor, which is characteristic of the degree of fiber surface fibrillation. Forgacs characterized this factor as specific surface (also called the S factor) of the +100 mesh fraction obtained using the Bauer-McNett classifier).
Later analyses on the results obtained by Forgacs and others have shown that the following equation is valid over a very wide range of pulp production methods and different wood grades:
A.sub.L =specific surface (m.sup.2 /g) of a fiber fraction with a weighted average fiber length L
K=K factor, an index characteristic of the degree of fiber surface fibrillation (essentially equal to the Forgacs' S factor).
The Canadian Standard Freeness (CSF) test is basically a measurement of the fiber specific surface. According to the literature, the following logarithmic relationship exists between the fiber specific surface and CSF:
A.sub.TOT =total specific surface of refiner mechanical pulp (m.sup.2 /g).
Conventional Freeness Testers and Their Operating Principles
Freeness can be measured from pulp taken from the latency chest 2 which is in line immediately next to the stage II refiner 1 in the system illustrated in FIG. 1. Some testers incorporate a built-in latency elimination, thus requiring no separate latency chest. Such testers as well need some kind of intermediate container in which pulp consistency is essentially lower than in the pulp immediately discharged from the refiner. With the help of a steam-phase carrier, the pulp is transferred from the refiner along a blow pipe 3 further in the process.
Conventional, almost on-stream measuring freeness testers can be divided into two categories on the basis of their operating principle: filtration and permeability testers.
Filtration Testers
Filtration is defined by the following equation: ##EQU1## where V=flow volume
A.sub.S =screen cross-flow area
dP=differential pressure over pulp bed
.mu.=viscosity coefficient
c=consistency
R=average filtration resistance imposed by fibers.
Assuming P to be constant and taking into account the physical dimensions and boundary conditions of the tester, the filtration time of the tester can be solved: ##EQU2## where R=average specific filtration resistance of the pulp
V.sub.1 =measurement chamber volume from screen to lower electrode
V.sub.2 =measurement chamber volume from screen to upper electrode
t.sub.1 =filtration time to volume V.sub.1
t.sub.2 =filtration time to volume V.sub.2
dt=filtration time measured by the tester
With the tester operating at constant temperature and consistency, the filtration time has a linear relationship with the specific filtration resistance R:
The value of R is affected by the specific surface and volume of the fibers. At high freeness values, the correlation between R and CSF is good, but at lower freehess values (50 . . . 100 ml) a significant loss of sensitivity is encountered.
Permeability Testers
These
REFERENCES:
patent: 4040743 (1977-08-01), Villaume et al.
patent: 4514257 (1985-04-01), Karlsson et al.
patent: 4743339 (1988-05-01), Faix et al.
patent: 4800279 (1989-01-01), Hieftje et al.
patent: 4886576 (1989-12-01), Sloan
patent: 5104485 (1992-04-01), Weyer
Oskar Faix, Hans-Ludwig Schubert and Rudolf Patt, "Continuous Process Control of Pulping by FTIR Spectroscopy." TAPPI Proceedings--1989 Wood and Pulping Chemistry pp. 1-8.
ABB Stromberg Drives OY
Hannaher Constantine
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