Liquid purification or separation – Plural distinct separators – Filters
Patent
1995-07-20
1997-04-15
Walker, W. L.
Liquid purification or separation
Plural distinct separators
Filters
210334, 210402, 210404, B01D 3380
Patent
active
056205988
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a suction head arranged between a filtrate channel and a barometric leg of a rotating filter having at least one filter means communicating with the filtrate channel, the filtrate channel being connected to the barometric leg through the suction head.
According to the state of art (FIGS. 1 and 2 referring to a disc filter) the suction head tapers in the shape of a downwardly inclined cone towards the barometric leg and is connected thereto by a likewise conically tapering connecting piece, the outlet end of which has the cross-sectional area of the barometric leg. A problem observed for a long time in rotating filters is that the air accompanying the filtrate through the filtrate channel tends to settle in the upper part of the suction head and expands there due to the prevailing sub-pressure, resulting in that relatively large air bubbles intermittently are brought along by the air flow accelerating towards the barometric leg. As a result of the pressure successively decreasing with increasing flow rate, the volume of the air bubbles increases further, which results in that an unsatisfactory portion of the height of the barometric leg transports merely air. It can be mentioned as typical, that in a barometric leg of seven meters of height the air bubbles brought along may reduce the capacity of the barometric leg to correspond to merely three meters of water column. Thus, a very large saving in space and costs could be made if an effective barometric leg of in this case only three meters of height could be utilized. Further, the conveyance of air bubbles results in that the sub-pressure in the filtrate channel varies or lies at a constantly low level, which in turn results in a varying or low filtering capacity and a varying or low dry content in the filter cake deposited on the filter medium. It is, thus, also a desire that the sub-pressure shall be kept constant.
Consequently, the object of the present invention is to provide a suction head that does not allow the accumulation of air bubbles but continuously brings them along as soon as they arrive into the suction head from the filtrate channel.
This object is achieved in that the upper internal boundary of the suction head as regards flow towards the barometric leg is nowhere located at a level above the upper internal boundary of the barometric leg. Thereby pockets are avoided in which air bubbles may accumulate, and occurring small air bubbles are immediately pulled along by the filtrate flow without managing to combine into larger air bubbles.
Thus, the upper internal boundary of the suction head as regards flow towards the barometric leg may raise in the flow direction towards the barometric leg. However, this boundary is preferably straight and horizontal and merges with the upper internal boundary of the barometric leg. In such case, also this should be straight and horizontal. This involves the favourable effect that the barometric leg gains further in height without the total height of the structure increasing. It is also suitable that the connection of the suction head towards the barometric leg has the dimension of the barometric leg, so that the barometric leg can be directly connected to the suction head. Hereby the filtrate flow assumes the flow rate in the barometric leg already at the outlet end of the suction head. Thus, the filtrate has accelerated to full flow rate in the suction head, which further contributes to the conveyance of existing air bubbles.
In the following description of two embodiments of the present invention, the invention is applied to disc filters having at least one filter disc including a plurality of filter sectors communicating with a respective filtrate channel in the centre shaft of the filter. However, the invention is equally applicable to disc filters having one single filtrate channel in the centre shaft common to all filter sectors, as well as to other types of rotating filters, such as drum filters, provided a barometric leg is employed to create the sub-pressure necessary
REFERENCES:
patent: 3024839 (1962-03-01), Beachler
patent: 4626351 (1986-12-01), Fuhring
patent: 4929355 (1990-05-01), Ragnegard et al.
patent: 5047123 (1991-09-01), Aranitakis
Kvaerner Hymac AS
Walker W. L.
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