FI59205C - TRYCKFILTER - Google Patents

Description

I5SFT] [B] «ij ADVERTISEMENT PUBLICATION

Wjft l J '' UTLAGCNINGSSKMFT b y Z U 0

JgVg C (45) Fa + cr.ttl Uy ': 7 V Ί ^' r “" ^ (51) K ».ik.3 / im.ci.3 B 01 D 29/38 ENGLISH I—> FI N LAN D (21) P »» i »ttJh» k * mu * - PttMtanalHcnlng 79357 ^ (22) HakemlipiM - Aiw6knlnpd «g 15.11-79 (23) AlkupUvl — GIM | hM * d« f 28.11.78 (41) Tullut iulMsuksI - Bllvtt offmtllg 29.05.80

FmtenttU and the National Board of Registers .........-.,. ,.

. . (44) Date of issue and date of issue. - or Al

Patent · och regisUrstyrelaen '' AnsMuwutUgdoehutUkrifunpuUtcand Ji.uj.oi (32) (33) (31) Privilege requested »Begird prloritet (71) Enso-Gutzeit Osakeyhtiö, Kanavaranta 1, 00160 Helsinki 16, Finland-Finland (FI) (72) Juha Lumikko, Savonlinna, Matti Lankinen, Savonlinna, Jaakko Savolainen, Savonlinna, Martti Tolvanen, Savonlinna, Yrjö Luukkainen, Savonlinna, Holger Engdahl, Savonlinna, Finland -Finland (FI) (71+) Oy Heinänen Ab (5l +) Pressure filter The present invention relates to a batch pressure filter for thickening a solid suspension, comprising a filter tank with a supply line with a feed pump for feeding the filterable suspension through the pressurized feed and filtrate flows and which are internally connected to the above, closed structures thus collecting sludge on its outer surface, which is arranged to be periodically removed by depressurizing the filter tank by opening an outlet flow to the suspension there through an outlet line connected to the washing tank. through the filtrate outlet line under the effect of the pressure generated by the feed pump in the suspension inlet line.

Such a pressure filter is very well suited for the filtration of white liquor from lime milk in the regeneration of cooking liquor in a sulphate pulp mill, but it can also be well used for other filtration tasks.

59205

A problem with known pressure filters of this type is the removal of sludge from the surface of the filter elements. According to the invention, this problem is solved in a simple manner. The invention is characterized in that the sludge is arranged to be removed from the surface of the filter elements by means of the hydrostatic pressure of the filtrate in the collection tank by subjecting the discharge line of the collection tank to the pressure of the outside air. The filtrate then flows countercurrently through the filter elements and separates the sludge from the filter elements.

The outlet line of the filter tank is usually connected to the wash tank. A preferred embodiment of the invention is then characterized in that the filtrate outlet line is connected to the wash tank by a downcomer with a valve and that the outlet line can be brought under outdoor pressure by opening this valve in the downcomer.

According to the invention, the collecting tank can be divided by partitions into blocks, each of which leaves a branch line provided with a shut-off valve, these branch lines being connected as a common outlet line. With this arrangement, an arbitrary block can be excluded from operation. This is necessary when it has been found that the filtrate entering this block is impure. This is an indication that some of the filter elements, i.e. the filter sock, sending the filtrate to this block are damaged.

The invention will now be described with reference to the accompanying drawing, in which

Fig. 1 shows a pressure filter according to an embodiment of the invention, cut to shark and placed in the operation diagram.

Fig. 2 shows a cross-section of a pressure filter according to another embodiment.

Fig. 3 shows a section taken along the line III-III in Fig. 2.

The suspension to be filtered, i.e. in this case lime milk, enters the filter tank 2 along the inlet line 1 fed by the feed pump 5. In the roof 3 of the tank 2 hangs cylindrical filter elements 4. There may be, for example, 200 of these, but only one filter element is shown in the drawing, greatly enlarged.

3 59205

The white liquor of the lime milk is filtered by the pressure in the filter tank 2 through the sock in the filter element and the solid of the lime milk, i.e. the mesa, is deposited on the surface of the filter sock. Inside the sock there is a sturdy metal mesh that prevents the sock from sinking into the pile. The filtrate, i.e. the white liquor, enters the collecting tank 6 located above, from where it is pressed by the feed pump 5 into the filtrate outlet line 7 and further into the digester or storage tank. The removal of the filter element 4, i.e. the lime deposited on the sock, takes place as follows. The supply pump 5 is stopped and valves 8 and 9 are closed. Valves 1C and 11 are opened. The pure lye in the collection tank 6 now flows through the filtration elements 4 into the filter tank 2, detaching the lime layer from the surfaces of the socks. Through the outlet line 13, the lime and lye flow into the washing tank 12, from where the mixture is pumped either to a suction filter or clarified. During this washing step, the filter sucks air through the valve 11.

When the filter has been emptied, the valve 10 is closed and the valve 8 is opened and the feed pump 5 is started. When the filter is thus refilled, the valve 11 is closed and the valve 9 is opened, whereby a new filtration cycle begins. All of these activities can, of course, be arranged to happen automatically. 7

The filter thus operates periodically, divided into a filtering cycle and a washing cycle. The length of the filtration period is determined by the honey content of the lime milk fed as follows:

Honey content Filtration period 1000 mg / 1 6 h 500 "12" '• 300 "20" 150 "38"

The length of the washing cycle is 1-5 min, in which case the filtration time is more than 99% of the total operating time. The purity of the white liquor after filtration is less than 10 mg / l, and the purity of the feed liquor does not substantially affect the final result.

The pressure filter according to Figures 2 and 3 differs from the above in that the collecting tank 6 is divided by vertical partitions 14 into blocks 15. Each block has its own branch line 16 provided with a shut-off valve 17. After the valves 17, the branch lines can be connected as a common discharge line 7. In this embodiment block shut down if this loh 59205 size becomes impure lye, which in turn is a sign that some sock is broken.

It will be apparent to those skilled in the art that various embodiments of the invention may vary within the scope of the claims set forth below. Thus, the pressure filter according to the invention can also be used for filtering non-lime from lime milk.

/

Claims (2)

5 59205 A intermittent pressure filter for thickening a solid suspension, comprising a filter tank (2) having an inlet line (1) with a feed pump (5) for supplying the suspension to be filtered under pressure and an outlet line (13) with a valve (10) for removing thickened sludge and a plurality of roof-suspended filter elements (4) through which the filtrate flows and which are internally connected to the closed filtrate collection tank (6) located above and thus collect sludge on its outer surface, which is arranged to be periodically removable by relieving the pressure from the filter tank (2) by opening via an outlet line (13) connected to the washing tank (12), the filtrate in the collecting tank (6) passing countercurrently through the filter elements (4), in which pressure the filtrate is arranged to be removed during the filtration step through the filtrate outlet line (7) characterized by the supply pump (5) in the inlet line (1) of the suspension, characterized in that the sludge is arranged to be removed from the surface of the filter elements (4) by hydrostatic pressure of the filtrate in the collection tank (6). Pressure filter according to Claim 1, characterized in that the filtrate outlet line (7) is connected to a washing tank (12) by a downcomer with a valve (11) and that the outlet line (7) can be pressurized to open by opening this valve (11) in the downcomer.