Liquid purification or separation – Processes – Separating
Reexamination Certificate
1999-08-11
2001-08-28
Drodge, Joseph W. (Department: 1723)
Liquid purification or separation
Processes
Separating
C210S085000, C210S196000, C210S231000, C210S259000, C210S400000, C210S774000, C210S783000, C210S805000
Reexamination Certificate
active
06280638
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an apparatus for continuous purification of liquids, dewatering and drying of the separated non-filtering solids.
DESCRIPTION OF PRIOR ART
No apparatus is known for continuous purification of liquids and dewatering and drying of the separated non-filtering solids in which the non-filtering solids are accumulated in the inflowing liquid to be purified thus forming a mixture (suspension) which is dewatered and dried after reaching a definite density.
(The proposed invention consists basically of functionally interconnected belt filter and elastic thermo-filter press, and we will therefore consider the already known similar apparata.)
A belt filter is known (U.S. Pat. No. 4,212,745, Yellesma) which comprises a filter belt, moving synchronously upon two conveyor belts, located in sequence one after another.
The conveyor belts are sliding on the upper part of two unloading blocks connected to vacuum pumps and outlet pipes effecting the filtration process.
A disadvantage of this belt filter is the complicated synchronization required to be maintained during the movement of the filter and conveyor belts.
Another disadvantage is that in the described structure no hydrostatic pressure can be exerted on the filter belt, which hydrostatic pressure would speed up the filtration process.
A further disadvantage of this belt filter is that only the upper surface of the two unloading blocks is used and thus the capacity of the filtered liquid is reduced significantly.
Still another drawback of this belt filter is that the unloading of the dewatered cake is effected by scraping of the filter belt which lead to a rapid wear of the filter cloth, reduces its operating life and impairs the filtration process.
A belt filter acting by subpressure—vacuum (EP 0391091 A1, Teckentrup, Heinrich) is known, comprising a container of a definite volume, where the suspension to be filtered flows in. A closed chamber connected to the vacuum pump is located on the bottom of the container. There are apertures at the upper portion of the chamber. A drain belt lies over these apertures, and over the drain belt there is a continuous filter belt. The filtered liquid is carried out by vacuum from the closed chamber, and the residual cake on the filter belt is separated by means of a rotating brush ands is disposed of through an appropriate hole.
A disadvantage of the belt filter with subpressure is that only the upper surface of the closed chamber is employed for filtration and therefore the filtering capacity is diminished considerably.
A further drawback of the belt filter with subpressure is that not more than one chamber can be used with it. This leads to a manifold reduction of the amount of filtered liquid and the capacity of the belt filter.
Another disadvantage of the belt filter with subpressure is that it cannot act as a thickener. The filter belt carries the wet cake out and ensures a continuous process. This is unquestionably useful, but the process is accompanied by the following unfavourable technological results:
The wet cake sticking to the filter cloth can be separated with difficulty;
The separation of the cake from the filter cloth is not complete and a layer of fine solids remains which impairs its filtering capacity;
The mechanical separation of the wet cake reduces the filter cloth's operation life;
The produced wet cake cannot be fed further for additional filtration in a filter press where the mode of dewatering is better and a lower final humidity can be achieved.
The obtained wet cake can practically only be dried in an appropriate drier which would cause high costs for heating energy and contamination of the environment by dust and hazardous vapours.
A filter press (U.S. Pat. No. 3,608,610, Greatorex) is known, in which dewatering is carried out in two stages:
The first stage is completed by traditional compression of a given suspension in the chambers of a filter press, and the liquid phase is filtered through the filter belt whereafter cake with a high content of residual liquid phase remains in the chambers.
In the second stage additional dewatering of the cake is achieved, and special elastic hydraulic membranes mounted in the cells of the filter press swell, whereby the volume of the chambers is reduced and thus the residual liquid phase in the cake is driven through the filter belt.
A disadvantage of the filter press is that the elastic membranes are situated opposite to the filter belt and are therefore limiting each filter chamber by an area equal to its filtering area. The residual amount of liquid in the cake driven out by the hydraulic swelling of the membrane is equal to the inflowing amount of hydraulic liquid.
Another disadvantage of the filter press is the expensive and difficult realization of a structural connection between the elastic hydraulic membranes and the supporting surface they are lying upon, because the hydraulic liquid is fed under pressure between the elastic hydraulic membranes and the supporting surface of each filter chamber.
A further disadvantage of the filter press is that no full drying of the cake to the extent of a final dry product can be achieved in it without the need for its additional transportation and drying with the help of appropriate drying equipment.
A method and filter press for dewatering of suspensions and drying of the filtered cake is known (U.S. Pat. No. 4,999,118, and U.S. Pat. No. 5,143,609, B. Beltchev).
The basic element in this apparatus is a filter press with heating and filtering plates. Dewatering and drying in the filter press is effected in two stages:
The first stage is completed after the traditional compressing of a given suspension in the chambers of the filter press, whereas the liquid phase is filtered through the filter plates and cake with a high content of liquid phase remains in the chambers.
The second stage begins by providing power supply to the heating membranes embodied in the heating plates.
The higher temperature of the heating membranes evaporates part of the residual liquid phase in the cake and a “steam jacket” is formed around the heating membranes. Under the impact of the steam pressure, the “steam jacket” drives the residual liquid phase from the capillaries of the cake and in mixture of vapours and liquid thus obtained is drawn under vacuum by means of the filtration plates. The effect generated by the “steam jacket” ensures a considerable lowering of the consumption of heat energy as compared with the known drying apparatuses.
A disadvantage of the method and apparatus for dewatering of suspensions and drying of the filtered cake is that during the second stage the residual liquid in the cake's capillaries is driven out only under the action of the “steam jacket” without providing for additional compression and thickening of the cake in the chambers of the filter press.
Another drawback of the method and apparatus for dewatering of suspensions and drying of the non-filtering cake is that the filter press cannot be effectively used in the process of thickening.
SUMMARY OF THE INVENTION
The aim of the invention is to create an apparatus for continuous purification of liquids and dewatering and drying of the separated non-filtering solids (cake), whereas the liquid to be purified is continuously flowing into the apparatus and the purified liquid is continuously flowing out from it, and the separated non-filtering solids are accumulated in the apparatus and are mixed with the inflowing liquid to be purified and develop a suspension of constantly increasing thickness to reach a predetermined value.
Another objective of the invention is to ensure a rapid dewatering and drying of the suspension which has reached the predetermined value with a minimum power consumption and a minimum industrial floor area.
The task has been solved with an apparatus comprising functionally interconnected belt filter and elastic thermo-filter press. The belt filter consists of feed container, filter sector and thickening cone. The filter sector is located under the feed
Belchev Belcho Alexandrov
Drodge Joseph W.
Pennie & Edmonds LLP
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