GB2117659A

GB2117659A - Continuous-operation filtration process

Info

Publication number: GB2117659A
Application number: GB08309158A
Authority: GB
Inventors: Esko Riikonen
Original assignee: Larox Oyj
Current assignee: Outotec Filters Oy
Priority date: 1982-04-02
Filing date: 1983-04-05
Publication date: 1983-10-19
Also published as: FI65378C; FI821147L; CA1217675A; GB2117659B; FI65378B; JPS591096A; FI821147A0; JPS6035240B2; DE3311869A1

Abstract

Sludge (3) to be filtered is fed onto a moving endless filter cloth (1) by two feeders (4), and is removed by two scrapers (5) located after the feeders. The feeders are positioned so that the sludge (3) is fed onto opposite sides of the cloth, so that the liquid passing through the cloth removes the solid matter that the preceding scraper failed to remove. The sludge (3) can be compressed by means of moving compressing belts (8) or rollers which force the cloth into a tubular form between feeders and scrapers (see Figs. 3-7). <IMAGE>

Description

SPECFICATION Continuous-operating filtration process and equipment This invention is designed as a continuous-operation filtration technique that employs a moving endless filter cloth or similar onto which the sludge is fed at a certain feeding point and from which the solid cake is removed at a later point, in regard to the direction of rotation of the cloth.

In order to obtain high efficiency, it is of vital importancethatthe properties ofthefilter cloth, screen or other medium remain as constant as possiblethroughoutthe process. One general disadvantage of known filtration techniques in continuous operation is the rapid blocking ofthefilter cloth which is caused by particles embedding in the cloth. For this reason, the filter cloth must be continuously washed during the process, which can be done most effectively by means of the so called reversed flow method.

The purpose of this invention is to provide a continuous-operation filtration technique in which the filter cloth or otherfilter medium is cleaned by employing the reversed flow method in a simpler and more effective way than before. It is characteristic of the invention that sludge is fed onto the cloth attwo points on different sides ofthe cloth; consequently, the particles that the removal unitfailsto remove are washed away by the liquid passing through the cloth.

In otherwords, this invention makes it possible to clean the cloth automatically in the course of the process wherefore no special cleaning operations are required.

As such, the idea of using both sides of the filter cloth is a known method. The filtration process referred to does not, however, involve continuous operation, nor is the associated equipment so designed asto provide sufficient cleaning by means of the process itself. Therefore, the equipment is fitted with separate cleaning devices which spray cleaning agent on both sides ofthe cloth between filtration phases. This new invention does not require such cleaning devices, although they can be used in addition to the reversed flow.

Characteristic of one of the application of this invention is that the sludge to be filtered is compressed by an upper belt which moves in the same direction as the cloth, along the length of the cloth from where the sludge is introduced to where the cake is removed.

Pressure accelerates the separation of liquid from solid particles in the sludge, effecting a powerful flow of liquid through the cloth, which, in turn, removes the remaining solid material from the other side ofthe cloth.

Characteristic of another application of this invention is that pressure is applied to the sludge between the feeding and removal points by means of rollers which force the filter cloth into a bag-shaped form. In this way, sludge is prevented from escaping sideways, which is particularly important if the internal friction of solid particles is low.

The invention involves also equipmentdesignedto utilize the continuous-operation filtration technique described above. This equipment comprises a moving endless filter cloth, devices forfeeding the sludge onto the cloth at a certain point as well as devices for removal of the solid cake from the cloth at a certain point which is located further on in the direction of rotation ofthecloth; it is characteristic of the equipment that it has two separate feeding points and two separate removal points, so positioned that sludge is fed on different sides of the cloth the two points, thus allowing the liquid passing through the cloth to removethesolid matterthatthe removal unit failed to remove.

The equipment designed on the basis of this invention can comprise a compressing belt which moves in the same direction as the cloth between the feeding unit and the removal unit, or the equipment can be fitted with rollers, placed betweenthefeeding and removal units, which apply pressure on the sludge by forcing the cloth into a bag-shaped form.

The invention is presented in detail by means of the following examples in which reference is made to the enclosed drawings where Figure 1 shows one type of filtration equipment based on the invention; sludge is compressed by means of a belt Figure 2 shows Il-Il cross section offigurel Figure 3 depicts another filtration equipment based on the invention; the filter cloth is forced into a bag-shaped form when pressure is applied on the sludge Figure 4 shows IV-IV cross section of figure 3 Figure5showsV-V cross section of figure 3 Figure 6 shows VI-VI cross section offigure 3 and Figure 7 shows the equipment depicted in figure 3 from above Figures 1 and 2 showthefiltration equipment in which filtration is effected by means of the continuous-operation filtration cloth (1).The equipment comprises two feeding units (2) which feed the sludge (3) through pipes (4) onto the cloth (1). Both feeding units (2) are succeeded by removal units (5) which remove the solid cake (6) from the cloth (1) by means of a scraper. Between the feeding and removal units, the sludege is compressed by the pressing belt (8), or by rollers (9), which move in the same direction as the cloth (1); additional support is provided bythe support belt (10) moving underthe cloth. When the sludge is compressed,the liquid passes through the filter cloth (1 ) and support belt (10), as indicated by the arrows (11) in figure 1.

The essential point in the filtration process described in figures 1 and 2 is that the sludge (3) is fed by the feeding units (2) onto different sides of the cloth (1). In this process, the liquid, separated from the sludge (3) and passing through the cloth (1), removes the solid matter embedded in the cloth in the preceding phase of filtration. Thus the process provides reversed flow cleaning of the cloth, and no separate cleaning units is required.

The filtration process described in figures 3-7 differs from the one presented in figures 1 and 2 in that the filter cloth (1), and the net-like belt supporting it, are forced into a bag-shaped form between the feeding and removal units. This is achieved by means of rollers(12) which simultaneously effect the separa tion of liquid from solid matter is indicated by arrows (11)infigures3-6.Reversedflowcleaningofthe cloth takes place as described above; this process is especially suitable for sludges with low internal friction which can in this way be retained on the cloth during the compressing phase.

It is obvious to a professional thatthe applications of the invention are not confined to the examples presented above; they mayvarywithin the framework of the enclosed patent claims.

Claims

1. Continuous-operation filtration technique employing a moving, endless filter cloth (1 ) or similar onto which the sludge (3) to be filtered is fed by a feeding unit (2) at one point and from which the resulting solid cake (6) is removed by a removal unit (5) located further on in the direction of rotation of the cloth, characterized by the factthatsludge (3) is fed onto the cloth (1 ) by two separate feeding units (2) in such awaythatthesludge is deposited on different sides oftheclothwhereforethe liquid filtering through the cloth removes the solid matterfrom the other side of the cloth that the preceding removal unit failed to remove.

2. Filtration technique in accordnace with patent claim 1, characterized by the factthat sludge (3) is compressed betweenthefeeding unit (2) and removal unit (5) by a pressing belt (8) moving in the same direction as the cloth.

3. Filtration technique in accordance with patent claim 1, characterized bythefactthe sludge (3) is pressed between the feeding unit (2) and removal unit (5) by rollers (12) whichforcethe cloth (1 ) into a bag-shaped form.

4. Equipment employing the filtration technique as described in the patent claims above, comprising a moving, endless filter cloth (1), devices (4) forfeeding the sludge (3) to be filtered onto the cloth at a certain point (2) as well as devices (7) for removing the resulting solid cake (2) from the cloth at a certain point succeeding the feeding unit; characterized by the fact that the equipment comprises two separate feeding units (2) with two succeeding removal units (5), so positioned that the sludge (3) is fed onto the cloth on different sideswhereupon the liquid filtering through cloth removes the solid matter that the preceding removal unit failed to remove from the cloth.

5. Filtration equipment in accordance with patent claim 4, characterized bythefactthattheequipment is provided with a compressing belt (8) which applies pressure to the sludge (3) and moves in the same direction as the filter cloth (1) between the feeding unit (2) and the removal unit (5).

6. Filtration equipment in accordance with patent claim 4, characterized bythefactthatthe equipment is fitted with rollers (12), located between the feeding unit (2) and the removal unit (5), which apply pressure on the sludge and force the cloth (1) into a bagshaped form.