Liquid purification or separation – Processes – Separating
Patent
1990-08-07
1992-07-28
Dawson, Robert A.
Liquid purification or separation
Processes
Separating
210225, 100198, B01D 2534
Patent
active
051338840
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and means for pressure filtering used to carry out said method according to the preamble of
The invention relates particularly to solutions of problems of loosening and discharging the filter cake from such pressure filters. For this purpose it has already been suggested that the filter cloths be subjected to vibrations. DE-C 3 341 636 and DE-A 3 527 735 describe already known pressure filters, in which the filter cloths are suspended from slewing brackets and springs which are raised on the pressure plates. The pressure chambers are opened up one at a time and the filter cake is loosened by means of a movable vibration device, which directly influences the suspension rod of the respective filter cloths. However, these constructions have a drawback. The discharge is very time-consuming, since the filter chambers are emptied one at a time.
In order to empty all the filter chambers simultaneously it is suggested in U.S. Pat. No. 4,900,454, that the suspension rods of the filter cloths be movably suspended in a horizontal direction in the longitudinal direction of the pressure filter on two flexibly or elastically suspended guide rails, which are provided with vibration devices in order to vibrate all of the suspension rods and the corresponding filter cloths at the same time. The positions of the suspension rods when the pressure plates are brought apart are obtained by means of flexible and/or pivotable spacer means fastened to the ends of the suspension rods, which spacer means connect the suspension rods to each other and to the movable gable plates of the pressure filter. Such a pressure filter allows a very fast loosening of the filter cakes from the filter cloths and consequently short filtering cycle times.
This already known pressure filter functions very satisfactorily for most types of materials, with an excellent cake loosening effect. However, as far as certain quite adhering or in other ways difficult to loosen types of materials are concerned vibrations of filter cloths produced in this already known pressure filter are not adequate, since they do not always result in a reliable and complete discharge of the filter cakes. Consequently, portions of or even entire filter cakes may remain in one or several of the filter chambers after a terminated filter cake discharge. Such remaining filter cake portions are particularly found in the upper parts of the filter chambers. This results in an inferior filtering capacity, because during the next filtering cycle portions of the available filter chamber space already are occupied by the remaining filter cake residues. Such remaining filter cake residues usually will remain also during the subsequent filtering cycles and increasingly stick to the walls of the filter chamber, i.e. the filter cloths. Thus, the deterioration of the filtering capacity of the pressure filter will be permanent.
Said remaining filter cake residues can at least be partly removed by spraying a rinsing fluid onto the filter cloths, at least during certain filtering cycles. The filter cake residues will then be brought back to a container or the like for a liquid suspension of filter materials. The filter cake residues which have been loosened by washing will then form a circulating load on the pressure filter, which worsens the filtering capacity of the system. Also, large loosened and washed away filter cake residues may lead to shutdowns and/or other disturbances in the rinsing liquid circulation system.
Due to the above-mentioned drawbacks of already known pressure filters the purpose of the present invention is to suggest a method of efficiently and completely loosening the filter cakes from the filter cloths in the filter chambers during the cake discharge period. An additional purpose of the invention is to suggest a device to carry out said method.
The method according to the present invention advantageously can be combined with a vibration of all of the filter cloths at the same time according to what is set forth in U.S. Pat. No. 4
REFERENCES:
patent: 4900454 (1990-02-01), Hedlund et al.
Carlsson Mats
Jonson Torbjorn
Dawson Robert A.
Sala International AB
Savage Matthew O.
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