Fluid handling – Processes – With control of flow by a condition or characteristic of a...
Patent
1997-04-07
1998-11-03
Ferensic, Denise L.
Fluid handling
Processes
With control of flow by a condition or characteristic of a...
137 89, 137 92, 137 93, 137 5, E03B 100
Patent
active
058294660
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a fluid treatment system which includes a device, such as a streaming current detector (SCD), for measuring the charge in a fluid sample. The invention may be used in the paper-making field, where a suspension of finely divided particles are made to coagulate by the addition of a flocculating agent, the dosing of the flocculating agent being controlled in accordance with measurements taken from the charge-measuring device.
A streaming current detector (SCD) is an instrument which is used to detect the charge condition in a fluid, such as water. The data obtained by this charge detection can be used for the control and monitoring of various water based processes.
A number of instruments using the so-called streaming current principle have been developed over the years, one example being disclosed in our UK Patent No. 235 782 and illustrated in FIG. 1 of the accompanying drawings. The cell 10 illustrated receives at its inlet 32 a sample fluid tapped via a sample supply line 20 from a main fluid supply 15. The sample fluid enters a sample chamber 33 in the form of a through passageway and passes over a sample cell 38 and out to drain via fluid outlet 34. The reciprocating movement of a piston 42 by a motor (not shown) within the bore of an insulating body 39 repeatedly draws a small sample of fluid from the flow of fluid through the chamber 33 down into the measuring cell 38 and the resultant charge measurement is made across annular electrodes 51 and 50 set into the cylindrical wall of the bore in the insulating body 39.
The above general principal of streaming current detection using a reciprocating piston and spaced electrodes in the piston receiving bore of an insulating body is used by a number of manufacturers of streaming current detectors.
In a fluid treatment system illustrated in FIG. 2 in which a chemical A which is being used to treat the main fluid supply for coagulation or flocculation of the liquid is added to the main fluid supply 15 line 20, the sample which is applied to the above streaming current cell will contain this chemical A. This chemical provided the predominant background charge and the signal output from the SCD cell 10, which signal can be employed as a feedback in the dosing control equipment, is therefore attributable mainly to this background charge. A typical block diagram of a simple fluid treatment system is provided in FIG. 2. Where the chemical has been added to the main fluid, the quality of the sample supply is then determined by the streaming current detector which will measure the resultant charge of both chemical addition and sample quality. Assuming a given rate of dosing of the chemical A,any variation of the signal output from a predetermined setpoint associated with that dosing rate can only be due to variation in the sample quality. The dosing rate can then be adjusted accordingly.
Automation of this system is effected in a manner illustrated in FIG. 3. In this FIG. 3 system, the signal 11 from the SCD 10 is connected to a process controller 54 which will monitor the changing sample quality and adjust the rate of chemical addition to the main fluid, to restore the SCD signal to the predetermined setpoint.
This feedback control technique employed in the system shown in the configuration in FIG. 3 is used in the majority of coagulation control systems which are in use at the present time.
While this feedback technique for fluid monitoring and treatment may be satisfactory when used in a relatively simple system, for example in a water supply/purification plant, where there are no other significant influences upon the charge level in the sample supply, the system's effectiveness is much reduced in more complex applications, such as in the paper-making and sewage treatment industries. Here, numerous other influences and chemicals have an effect on the fluid supply under test, eg. on the fluid paper stock, and these will so affect the charge condition of the sample supply as to the overwhelm the influence of the particular chemical A (for f
REFERENCES:
patent: 4031912 (1977-06-01), Lu
patent: 4855061 (1989-08-01), Martin
Farid Ramyar
Ferensic Denise L.
Lasertrim Ltd.
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