Liquid purification or separation – Processes – Including controlling process in response to a sensed condition
Patent
1994-02-14
1995-10-24
Drodge, Joseph W.
Liquid purification or separation
Processes
Including controlling process in response to a sensed condition
73 6163, 95 20, 21033301, 210791, B01D 3512
Patent
active
054607337
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a control system for a filtration assembly, and particularly a control system for the filtration assembly described in Swedish patent application no. 8903267 corresponding to PCT/SE90/00639.
BACKGROUND OF THE INVENTION
With filtration according to the aforementioned applications, one uses a stationary filter disposed in a pressure vessel, wherein after completion of the filtration, a reset operation is carried out, comprising back-flushing of the filter before the start of the next filtration. The filtration takes place through at least one substantially vertically disposed filter element covered with a filter mesh surrounding at least one filter duct, through which flows the filtrate obtained during the filtration, e.g., white liquor or green liquor, while the filtered material, for example lime sludge (calcium carbonate) is deposited on the filter mesh. The pressure vessel is provided with at least one inlet for the suspension that is to be filtered, an outlet for the filtrate obtained, an outlet for the obtained material and an inlet for the medium for resetting the filter.
According to the prior art, in the utilization of a stationary filter during the lye treatment, the separation of white liquor and lime sludge is carried out in a so-called tube filter, i.e., downwardly suspended perforated tubes covered with filter mesh, where the filter outlet is directed upward. This tube filter is divided into discrete units having separate white liquor outlets from each section. While sections of the tube filter are being back-flushed, which is done with liquid that has already been filtered, i.e., white liquor, the filtration takes place in the other sections. This results in, inter alia, a low rate of utilization of the filter. In addition, during the entire process there is a continuous production of deposited material, i.e., lime sludge, from the back-flushing. This entails the disadvantage, among others, of the lime sludge having a high content of unfiltered liquid with a high content of chemicals.
Swedish patent application no. 7909774 describes a pressure filter and a method of filtration wherein the filtration time is altered as a result of the filterability of the suspension that is introduced. This means that one will have no indications of the condition of the filter.
SUMMARY OF THE INVENTION
By utilizing the present invention, it is possible for the amount of suspension being introduced to the filtration assembly to be kept constant and continuous, regardless of the suspension's filterability. In addition, the system will provide feedback on the condition of the filter and on the eventual need to replace one or more filter meshes.
This is achieved according to the invention with a control system that is characterized in that the working cycle of the filtration assembly is altered when the pressure difference across the filter mesh increases over a certain period of time, where the control system is capable of differentiating between the filterability of the medium introduced and the condition of the filter mesh. The filtration assembly comprises two or more filters, and the working cycle for all the filters is readjusted simultaneously. In the event of a change in the filterability of the medium introduced and/or the condition of the filter mesh, it is the reset time that is altered. If the reset time is reduced to a predetermined value, a fluid is passed through the filter mesh to determine the drop in pressure across the filter mesh.
BRIEF DESCRIPTION OF THE DRAWINGS
Additional details and features of the invention will be apparent from the further description of a preferred embodiment form, with reference to the accompanying drawings.
FIG. 1 shows a filtration system having two pressure vessels to which the control system is specially adapted.
FIG. 2 shows the operational sequence of the control system in three different cases where the filterability of the suspension and/or the condition of the filter is changed.
DETAILED DESCRIP
REFERENCES:
patent: 2572436 (1951-10-01), Boucher et al.
patent: 3455146 (1969-07-01), Smith et al.
patent: 4264445 (1981-04-01), Lumikko et al.
patent: 4482461 (1984-11-01), Hindman et al.
patent: 5053141 (1991-10-01), Laiho
patent: 5149449 (1992-09-01), Strid et al.
Horlyk Lars
Oswaldsson Rolf
Rasmussen Sigmund
Strid Kent
Caustec AB
Drodge Joseph W.
LandOfFree
Control system distinguishing filterability of medium filtered does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Control system distinguishing filterability of medium filtered, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Control system distinguishing filterability of medium filtered will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1884419