GB2174014A - Moving belt filter - Google Patents

Abstract

A cloth filter belt 7 is supported by an endless carrier belt 1 where it passes over vacuum box 25. The belt 1 is made in two layers bonded together, the outer layer having relatively low tensile strength (e.g. rubber, polyurethane), and the inner layer having high tensile strength (e.g. steel, nylon, reinforced polymers). Additional reinforcing cards or cloth may be bonded between the layers. The outer layer has drainage grooves or the like leading to holes through the inner layer. Magnetic particles incorporated in the inner layer may cooperate with bar magnets in the vacuum box grid to reduce friction by magnetic repulsion. <IMAGE>

Description

S#EClFlCATlON ConWDnu @iN:iDSter a ap#e#tus This invention relates to Slurry Filter Belts particularly but not exclusively for use with vacuum filters.

Atypical vacuum filter is used for example in the extraction of solids from typically granular slurries requiring efficient washing. The filter may consist of a wide continuous flexible primary belt mounted on two drums spaced apart horizontally to maintain the belt in tension, one of the drums being driven to produce belt travel. A separate cloth belt, longer than the primary belt, is also mounted on a sequence of rollers and is arranged so that a horizontal section of it extends above and in close contact with the upper horizontal portion of the primary belt. The cloth belt is driven in synchronism with the primary belt. The upper portion of the primary belt is supported by a vacuum chamber or chambers arranged to collect the filtrate and pass it to a storage tank or tanks.To enable the filtrate to pass through the primary belt the latter is formed with transverse grooves and holes extending through the belt. The under surface of the primary belt upper section makes a rough seal with the edges of the vacuum chamber which may be formed in a number of separate sections for sequential washing stages. The filter cloth departs from the primary belt at the downstream drum and continues to a take-off roller where it reverses direction and the cake is detached. The filter cloth then returns by way of various cleaning stages to the upstream end of the primary belt where further slurry is deposited on it.

The primary belt is required to be fairly substantial in order to perform its support function while at the same time being sufficiently flexible to traverse the drums on which it is mounted. The continuous flexing and straining of the belt produce wear in the belt structure which necessitates replacement at intervals and consequent expense. A further difficulty is caused by the stiffness of the belt which requires substantial driving power from the driven drum.

It is an object of the present invention to alleviate these difficulties to a large extent.

According to the present invention therefore a continuous primary belt for filter apparatus has an inner section providing tensile strength and an outer section of relatively flexible material and of relatively low tensile strength.

The outer surface of the belt preferably contains grooves from which holes extend through the belt to the inner surface, the arrangement being such that filtrate can collect in the grooves and pass to the inner surface of the belt.

The belt may comprise inner and outer sections of rubber or plastics material bonded together. The grooves may be formed solely in the outer section.

There may be included reinforcing members between the inner and outer sections.

According to a feature of the invention the inner section of the belt may have magnetic elements incorporated to cooperate with corresponding magnetic elements in a filter bed over which the belt is adapted to pass in operation.

The magnetic elements in the belt or in the belt and the filter bed may be magnetic particles.

Alternatively the magnetic element may be bar magnets arranged so that like poles are superposed successively as the primary belt passes over the filter bed.

The filter bed maybe a grid surface of a vacuum chamber.

Avacuum slurryfilter incorporating a belt in accordance with the invention will now be described by way of example with reference to the accompanying drawings, of which Figure 1 is a diagrammatic elevation of a horizontal vacuum filter and Figure 2 is a part cross-section of a belt in accordance with the invention.

Referring to the drawings a primary belt 1 is mounted on drums 3 & 5 the drums being spaced apart horizontally in such manner as to maintain the belt in tension. One of the drums (3) is freely rotating and the other (5) is driven. In an alternative arrangement both drums may be driven in synchronism.

A cloth filter belt 7 also of continuous form but significantly longer than the primary belt is mounted on a sequence of rollers, 9, 11, 13, 15, 17 & BR< 19. This belt is also maintained in tension and is arranged so that it has a straight horizontal upper section 21 overlying the upper section of the primary belt.

A slurry feed duct 23 opens on to the upstream end of the cloth filter just beyond the roller 19. The cloth filter then extends beyond the end of the downstream drum 5 and passes over the roller 9 which overhangs a collecting tank. The cloth filter is driven in the same direction as the primary belt but friction between the two, especially when aided by vacuum pressure, maintains the two belts in intimate contact.

Avacuum chamber may be divided into several compartments to permit sequential washing stages.

Each such compartment drains into a respective tank. The successive filtrates may then be used to wash the preceding stage in the vacuum chamber.

In order to facilitate the passage of filtrate through the filter cloth. and primary belt the latter is formed with transverse grooves in its upper surface which thus form channels between the primary belt and the cloth filter belt. Each groove has one or more holes passing through the primary belt and opening into the vacuum chamber when in the appropriate position on the belt. The primary belt also includes side flanges 10 which support the slurry and prevent it running off the side of the cloth filter belt.

Figure 2 shows a vertical longitudinal section through the primary belt at a position coinciding with a hole 27. The belt consists of an inner section 29 of material providing substantial tensile strength such as terylene (RTM), carbon fibre, devlar, rayon, steel, nylon, or fiberglass etc. The outer section 31 is formed of a more flexible material having relatively low tensile strength, e.g., natural rubber, synthetic rubber, polyurethane, polyamide, synthetic elastomers. The two materials are bonded together, for example by vulcanisation in the case of rubber.

The relative thickness of the two sections is determined bytheirfunctions. Thus the inner section must, depending upon its inherent strength, be sufficiently thick to withstand the tensile forces to which it is subjected by the driven drum. The outer section need only have sufficient thickness for the depth of the grooves.

The structure of the primary belt in two sections simplifies the provision in manufacture of the grooves 3, since the grooves may be moulded or completely punched out of the outer section when made as a separate element. Holes 27 are then punched right through the inner section in positions which will register with the grooves to be superimposed. Alternatively, the holes can be punched afterthe bonding of the two sections to obviate problems of aligning the two sections.

Further reinforcing may be included in the primary belt in the form of metal strips or nylon cords 35 bonded in position between the two sections of the belt. This reinforcement may alternatively consist of a woven sheet of high tensile material such as nylon.

It will be clear that ribs or pimples may be used on the upper surface of the primary belt as an alternative to grooving. The inner surface of the belt must be smooth to provide a vacuum seal between the belt and the edges of the vacuum chamber.

Bonding of the flexible reinforcing members (where of metal) between the two sections of the belt provides protection for the members for contact with process chemicals where the filtering is concerned with corrosive materials.

Where the reinforcement is provided by individual members these may be joined before the outer section is bonded in position.

The invention provides a reduction in power requirements, longer service life, ease of installation and fitting, and further, allows a wide selection of materials of construction.

In a modification of the above embodiment the inner section of the primary belt has permanent magnets incorporated in it. The supporting grid of the vacuum chamber, that is, the filter bed on which the primary belt is carried between the drums 3 & 5, also has magnets incorporated but in such a direction as to repel the belt The belt is therefore partly supported by the opposing magnetic fields against the combined forces of the vacuum and gravity.

Frictional resistance between the primary belt and the vacuum chamber is therefore greatly reduced and the power required to move the belt reduced accordingly.

The magnets in the belt inner section may be constituted by magnetic particles impregnated in the material and magnetised in a direction transverse to the belt surface, arranged regularly in lines along the belt and extending laterally across it.

Corresponding lines of bar magnets are then arranged in the vacuum chamber grid surface, the magnets extending transversely, so that each belt magnet overlies the fixed magnets of a line successively. Engaging magnets are of course arranged in the same direction to produce mutually repelling fields.

In a further alternative the fixed magnets may be electromagnets which can be controlled in strength to suit the operating conditions-weight of slurry etc.

Claims (11)

1. A continuous primary belt for filter apparatus the primary belt having an inner section providing tensile strength and outer section of relatively flexible material and of relatively low tensile strength.

2. A filter belt according to Claim 1, wherein the outer surface of the belt contains grooves from which holes extend through the belt to the inner surface, the arrangement being such that filtrate can collect in the grooves and pass to the inner surface of the belt.

3. A filter belt according to Claim 1 or Claim 2, wherein the belt comprises inner and outer sections of rubber or plastics material bonded together.

4. A filter belt according to Claim 2 wherein the grooves are formed solely in the outer section.

5. Afilter belt according to any preceding claim wherein there are included reinforcing members between the inner and outer sections.

6. Afilter belt according to any preceding claim, wherein the inner section of the belt has magnetic elements incorporated to cooperate with corresponding magnetic elements in a filter bed over which the belt is adapted to pass in operation.

7. A filter belt according to Claim 6 wherein the magnetic elements in the belt or in the belt and the filter bed are magnetic particles.

8. Filter apparatus including a filter belt according to Claim 6, wherein the magnetic elements in both belt and filter bed are bar magnets arranged so that like poles are superposed successively as the belt passes over the filter bed.

9. Filter apparatus according to Claim 8, wherein the filter bed is the grid surface of a vacuum chamber.

10. A primary filter belt substantially as hereinbefore described, with reference to the accompanying drawings.

11. Filter apparatus substantially as hereinbefore described, with reference to the accompanying drawings.