Streaming potential measuring cell

Details Streaming potential measuring cell Streaming potential measuring cell

1993-11-12

1996-03-05

Williams, Hezron E.

Measuring and testing

Liquid analysis or analysis of the suspension of solids in a...

Paper or wood suspension

73 5304, 324 711, G01N 2700

Patent

active

054957516

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a measurement cell for use in measuring an electrokinetic potential of a fibrous dispersion and to a measurement system using such a cell.
The furnish or stock supplied to a paper-making machine has certain electrical characteristics associated with it which affect the formation of the paper web on the Foudrinier wire. In particular there is a potential known as Zeta potential which is more usually monitored by measurement of a related potential known as streaming potential. Quality control in paper making has increased the demand for reliable, on-line measurement of streaming potential.
Streaming potential is measured by means of a cell containing a chamber divided into two compartments by a filter mesh. A sample of the furnish is introduced into one compartment, the other being open, and a pad of fibrous material is formed on one side of the mesh. A controlled pressure differential is applied to the fluid in the compartments and appears across the measurement pad. This results in the development of streaming potential which is measured by two electrodes in the cell located on opposite sides of the pad.


BACKGROUND OF THE INVENTION

Embodiments of cells for measuring streaming potential are described in European patent EP-B-0 079 726. The patent also describes a preferred measurement system in which the cell is to be connected and a measurement cycle for reliably obtaining streaming potentials. The cell has been found to provide a good, reliable on-line performance. However, certain problems can arise with prolonged on-line operation.
The cell construction disclosed in the above patent comprises two frusto-conical compartments with their wider ends adjacent but separated by the mesh on which the pad is formed from the fibres in the furnish. The narrower ends of the cones provide inlet and outlet ports respectively. The cell assembly is mounted vertically with the mesh horizontal. The pad is formed on the underside of the mesh by introducing furnish to the lower compartment. After measurement the pad is back-flushed from the mesh by fresh water admitted through the upper compartment port. To aid flushing an apertured cone is located in the upper compartment with the intention of distributing flushing water over the whole pad area. The pad is very firmly compacted on the mesh and it has been found that it is not always easy to remove it entirely.
A second problem is that in forming the pad, fines, that is finer fibres and particles in the furnish, flow through the mesh into the upper compartment. Their presence in the upper compartment may affect the potential measured. Over a number of measurement cycles, these fines may accumulate on the upper side of the mesh with increasing effect and may also obstruct the back flushing procedure.
The present invention enables us to provide a means for better ensuring that the pad material is flushed from the mesh before the next measurement cycle commences and evacuating fines from the upper compartment in each measurement cycle.


SUMMARY OF THE INVENTION

According one aspect of the present invention there is provided a measurement cell for measuring an electrokinetic potential of a fibrous dispersion comprising a housing having an internal chamber divided into two compartments by a filter mesh, a port in one compartment for introducing a fibrous dispersion into the chamber to form a fibrous pad on one side of the filter mesh, and means for introducing a fluid into the other compartment to flush the pad from the filter mesh, characterised in that:
said fluid-introducing means comprises a nozzle adapted to provide a cone of pressurized-fluid spray over the side of the filter mesh facing said other compartments.
Preferably the above-mentioned nozzle is adapted to provide the cone of pressurized spray with the axis of the cone aligned with the central axis of the filter mesh.
The other compartment of the cell may further comprise a port allowing fluid from the nozzle to be circulated through the other compartment to flu

REFERENCES:
patent: 2602325 (1952-07-01), Campbell et al.
patent: 4535285 (1985-08-01), Evans et al.
patent: 4687986 (1987-08-01), Eriksson
patent: 5069753 (1991-12-01), Nishi

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