METHOD AND DEVICE AT PRECOAT PREPARATION AND APPLICATION

Abstract: Method at the preparation and application of precoat, comprising a precoat and water, at rotating vacuum filters comprising a rotating drum. According to the invention, water (B) is introduced into the drum interior, whereafter the precoat is transported into the drum interior below the surface of the water (B), whereafter the precoat is suspended in the water (B) by rotation of the drum, whereafter the suspended precoat is applied on the outer shell surface of the drum. The invention further comprises a device for carrying out the method.

Description: He±hoc an .4eyice-.at,-precoat-.pα?.eparafcion and.application **> This invention relates to a method for use at the prepar¬ ation and application of a filter auxiliary (precoat) on a rotating drum filter, and to a device for carrying out this 5 method. It is known when filtering on a rotating vacuum filter to apply in advance a layer of a filter auxiliary, precoat, for example kieselguhr, starch, cellulose or the like, on the filter drum. It also is known to mix the precoat prior to 10 its application on the drum with water to a suspension cont¬ aining 2 to 10% precoat. The mixing takes place in a separate mixing container provided with stirring means. The mixture is thereafter pumped or by gravity transferred either to the trough beneath the filter drum from where it is sucked onto 15 the drum, or to a distributing pipe located above the rotating drum. The precoat in most cases is transported in sacks, which are emptied directly into the mixing container, which in ad¬ vance partially has been filled with water. At this transport 20 of precoat to the open mixing container serious dusting problems arise.The inhaling of dust, for example from diatomite, has proved harmful. In some cases the precoat is transported pneumatically to a separate mixing container which, when it is completely closed and subjected to vacuum for the precoat 25 transport, is an expensive auxiliary equipment to the filter. The costs of such a closed precoat dissolver increase with the filter size, because the container volume must be adapted to the size of the filter 'surface. In order to achieve.maximum filtering capacity already 30 from the start of the product filtering, it is known to skin the unevennesses in the precoat layer at the end of the pre- coating period. At existing bottom-trough filters this skinning can be carried out by means of the take-off knife for the filter cake. 'BUREAU OMPI Due " to the fact that the trough and th.e take-off knife are located in fixed positions relative to each other ' , the pre¬ coat skinned must be taken care of manually or be handled by separate conveying means or a separate conveyor screw for re-cycling. These additional auxiliary apparatuses often are expensive. At so-called top-feed filters CLUNDIN filters) the skinning requires a separate precoat knife, which is prov¬ ided with a separate adjusting means for selecting the layer thickness. In this case the device is located so that the precoat skinned drops down ' directly into the trough or to the precoat dissolver and is thereafter used again. This extra precoat knife with adjusting means is also an expensive solution at the present filters. The present invention solves the aforesaid problems. The invention, thus, relates to a method at the prepar¬ ation and application of precoat at rotating vacuum " drum filters comprising a rotating drum with associated pump means and is characterized, in that water is introduced into the drum interior, and that the precoat is transported into the drum interior below the water surface, whereafter the precoat is suspended in water by rotation of the drum, and the sus¬ pended precoat is applie " on the outer shell surface of the drum. The invention further relates to a device of the kind and having the characterizing features as defined in claim 5. The invention is described in greater detail in the follow ing, with reference to the accompanying drawing, in which the upper half of the Figure is a section through a vacuum filter transversely to the rotation axis of the filter, and the lower half of the Figure is a section in parallel with the rotation axis of the filter. According to the invention, a filter is equipped with vacuum systemsseparated from each other and connected to a common vacuum source 1, which, for example, may be one or several vacuum pumps and/or f ns. According to the invention the suspension of precoat takes place in the interior of the drum where a vacuum system A is utilized and a definite amount of water B is introduced. The water amount is selected so thai the amount of suspension of waterZprecoat corresponds to the demand of a precoat application, The concentration of precoat in the " suspension can amount to 8 to 1S% precoat Cweight per volume water " ) , The " precoat is introduced into the " drum pneumat- ically from a sack 2 or container, in that the drum is evacuate by the vacuum system A. The precoat hereby is introduced into the rotating drum below the liquid surface through the pipe 3. The " vacuum in the drum can amount to 0,1 to 0,5 bar for the transport. By means of the transporting air for the precoat and owing to the drum rotation,the suspension is thoroughly mixed. This arrangement and this method are of greatest import¬ ance, because they render separate expensive dissolvers with precoat pump and stirrers for mixing the precoat superfluous, and the dusting problem in connection with the handling of the precoat is entirely eliminated. 2 Example: Filter surface 8 m . Such a filter has a gross volume in the drum of 3400 liters at 1,7 4 and 1,5 m width. For a precoat layer of 70 mm thickness about 220 kg precoat are required. At a concentration of precoat in the suspension of 15%, 1500 liters of water are required, corresponding to filling the inner volume of the drum to 45%. The suspension completely mixed in the drum is transferred by action of compressed air via the duct 4 to the trough 5 or another device for applying precoat on the drum in known manner. The mixture can be transported through the same pipe 3, through which the precoat was transported into the drum. While the filter layer is sucked onto the drum, rhe suspension in the drum interior or in the trough is diluted in known manner with the entire return water filtered off, or with parts thereof, via the duct 6, so that the concentration of the suspension at the contact with the drum is 5 to 10%. The trough beneath the drum according to the invention is movable and can be placed in two different positions, viz. the position marked by E during the filtering period, and, respect- ively, the position marked by F during the precoat application. By this arrangement the precoat skinned can at position F be returned directly to the trough for immediate re-use at both top-feed and bottom-trough filtering. The ordinary take-off knife for the cake and, respectively, the " top-feed box Cde lector) can be used or skinning at the levelling of the layer prior to the start of the " product filtering. Thus, no extra auxil¬ iary equipment is required for skinning and re-using the precoa 5 at the levelling of the precoat layer before the start. At the position E the filter cake passes the trough at the take¬ off both at top-feed and at bottom-trough filtering, where¬ after the filter cake is recovered and handled in known manner. The product filtering is carried out on the precoat layer ° externally on the drum in known manner by utilizing a vacuum system C from the common vacuum source. Due to the fact that the vacuum system A for transport of precoat to the drum inter¬ ior is entirely separated from the vacuum system C for product filtering, a new mixture of precoat for subsequent precoat 5 application can be prepared in the drum before the product filt- -ring going on has been finished. The amount of precoat remaining on the drum after the filt¬ ering is finished, about 5 to 10% of the original amount, is collected according to the invention together with the scaveng- 0 ing water at the cleaning of the filter and is transferred to a suction box by means of a further vacuum system D. The numeral 7 in the Figure designates a filter net over a suction box, the numeral 8 designates a filter pump.

Claims: s Claims 1, A method at the preparation and application of precoat, comprising precoat and water, at rotating vacuum drum filters com¬ prising a rotating drum with associated pump means, c h a r a c t e r z e d' n that water CB) is introduced into the drum interior,and that the precoat is transported into the drum interior below the surface of the water (B), whereafter the ' precoat is suspended in the water by rotation of the drum, whereafter the suspended precoat is applied to the outer shell surface of the drum. 2. A method as defined in claim 1, c h a r a c t e r i z e d i n that a vacuum is created by said pump means over the surface of the water (B) for effecting the introduction of the precoat, which thereby is sucked in via a pipe (3) opening into the lower portion of the drum, i.e. below the water surface. 3. A method as defined in claim 2, c h a r a c t e r i z e d i n that the suspended precoat by an overpressure created in the drum!interior by compressed air is transferred via the pipe (3) opening into the lower portion of the drum to a trough or other known means for sucking in known manner the precoat onto the outer shell surface of the drum. . A method as defined in claim 3, c h a r a c t e r i z e d i n that said trough (5) is moved so that by means of a take¬ off knife arranged in known manner for skinning and levelling precoat applied to the drum precoat skinned is fed down direct¬ ly into the trough (5) for re-use of the precoat prior to product filtering. 5. A device for preparing and applying precoat, comprising a precoat and water, at rotating vacuum filters- comprising a rotating drum with associated pump means , c h a r a c t e r -, i z e d i n that it comprises a duct C4) opening into the OMPI upper portion of the drum interior, which is connected to the pump means for creating a.vacuu -or overpressure in the drum interior, and that a further duct C3) is- connected to a sack C2) or container intended to contain precoat, through which duct C3) precoat is intended to be transported into the drum interior for suspension in a water amount, which further duct C3) besides is optimally connected via valves to a trough (5) located in known manner beneath the drum for transferring suspended precoat from the drum interior to the trough (5) . 6. A device as defined in claim 5, c h a r a c t e r i z e d i n that said trough is movable substantially in a horizontal direction so that the distance between the shell surface of the drum and the edges of the trough thereby is variable, whereby at levelling of precoat on the drum the precoat is fed down directly into the trough for re-use prior to product filtering, when the trough so is moved that said distance is greater on that side of the trougiwhere a known take-off knife is located. " BU O

Inventors: ERIKSSON SVEN, LUNDIN INGVAR, LUNDIN PER OLOF
Applicants: ERIKSSON SVEN, LUNDIN INGVAR, LUNDIN PER OLOF
Application year: 1981
Main classification: B01D37
IPC codes: B01D37