GB2350070A - Screening belt - Google Patents

Abstract

A screening belt for screening a fluid flow 40 (e.g. sewage) for debris comprises permeable link elements 32 and receptacle elements (50, Fig 5) hingedly connected within the belt, said receptacle elements being capable of receiving and retaining fluid from the fluid flow. The belt moves around a pair of remotely disposed axes 34 and 36. The belt preferably has at least one chain in a continuous loop to which the elements are affixed, the chain(s) being disposed around sprockets 35 and 37 on axles coincident with the remotely disposed axes. The receptacle element is preferably substantially V-shaped with one limb longer than the other for attachment to the chain(s) of the belt. The receptacle element may have a bucket portion which is pivotally connected within the receptacle element about an axis parallel with one of the remotely disposed axes. The receptacle element may also be provided with a cam surface to engage a stationary cam which may be mounted near the belt to cause the bucket portion to rotate and empty its contents. The perforated elements provide a screening effect for the fluid and debris in the flow, with debris mounting on these elements until the belt is moved. The receptacle elements retain fluid as well as debris, so that when the belt is moved and the receptacle elements pass over the uppermost axle, the captured fluid is emptied into a screenings processing unit and aids the washing of the screenings into the processing unit.

Description

2350070 Screening Apparatus This invention relates to screening apparatus

used in the separation of sewage solid matter from the fluid which flows through said screen.

Aside from faecal matter, a sewage fluid flow can contain all manner of solid debris including cigarette butts, sanitary items and the like, and therefore an effective means is required at a sewage treatment works for separating the solid debris from the liquid before the said liquid can be treated further.

The solid fraction of the sewage fluid flow will hereinafter be referred to as debris, and it is to be further mentioned that although the invention is described with particular reference to screening apparatus adapted to be disposed in fluid flow channels of fairly narrow width, perhaps of the order of 1-2m, it is foreseeable that the invention could be applied to apparatus for any width of sewage channel.

The current separation process is as follows:

Screening apparatus is disposed in a channel into which sewage flows. The sewage mixture cannot traverse the apparatus without first passing through said apparatus which consists of an escalating screening belt provided with a plurality of steel sections provided with 6mrn or other perforations through which the fluid can flow. The raw sewage is a mixture of debris and liquid which is separated from the debris by the screening belt which is disposed around a pair of axles at either end of the belt and provided with sprockets at either end which engage chain links by which the perforated steel sections are supported. One or other of the axles is intermittently rotationally driven dependent on the build up of fluid and matter on 2 the front surface of the portion of belt with which the sewage flow first comes into contact. As the debris clogs the perforation, the fluid begins to build up on the surface of this portion and creates a pressure differential across the belt. Once a predetermined pressure differential level has been reached, the axles are rotated and that particular portion of the belt is raised out of the sewage fluid flow.

The screening belt is generally inclined to the horizontal surface of the channel in which it is disposed, and the debris is lifted from this channel on the surface of the screening belt by one of two mechanisms. In one circumstance, most of the debris is compressible and may become compacted against the surface of the belt and in particular become lodged in the perforations as a result of the compressive force provided by the build up of fluid and other debris in front of the screening belt while it is stationary. The second mechanism for debris removal results from the shape of the perforated steel sections which are provided with a ledge towards their uppermost edge, said ledge being inclined to both the front face portion of the steel section which is typically squarely presented to the oncoming sewage flow, and inclined to the chain to which said steel sections are attached. The angles of inclination of the apparatus and the ledge portion are such that in use, the ledge portion of the steel section is commonly horizontal, and debris can therefore be supported thereon and lifted from the sewage flow.

As the screening belt is intermittently actuated, respective portions thereof move upwardly out of the sewage flow and ultimately over the uppermost axle by which the belt is supported and into contact with a cylindrical brush substantially the same width as the belt which can rotate about an axis parallel with the axis of the uppermost axle. The brush may also be intermittently actuated simultaneously with the belt such that as the various steel sections rotate about the uppermost axle, they come into contact with the 3 brush which ideally rotates in opposite direction and cleans the compacted debris, which at this stage is more commonly termed "screenings" from the belt.

As the brush rotates, the screenings drop into a trough within the apparatus along which the said screenings can be urged towards maceration and compaction apparatus, or alternatively may be transferred to other processing apparatus.

Once the screenings have been separated from the sewage flow, and fall from the brush provided in the screening apparatus, the "screenings processing" phase of the overall process commences, and it is the enhancement of the screenings processing to which this invention is directed.

A fundamental disadvantage of modern screenings processing apparatus is that a separate "wash water" pump is required to provide water for the screenings processing unit. The pumping arrangement is typically entirely separate from the screenings processing apparatus and therefore the construction and integration of the wash water pumping arrangement can be costly. Furthermore, the reliability of wash water pumps is notoriously poor, and the cost of repairs can often be excessive.

It is an object of this invention to provide screenings processing apparatus whose requirement for separate wash water pumping means is eradicated, while nevertheless maintaining the efficiency of the overall screening processing system.

According to the invention there is provided screenings apparatus comprising a screening belt comprising of a plurality of perforated elements hingedly interconnected to form said belt, said belt being at least intermittently caused to move around a pair of remotely 4 disposed axes, one of said axes being disposed within a sewage flow channel such that the sewage flow comes into contact with at least part of one of said perforated elements, and the other axis being disposed thereabove and also substantially above a screenings processing unit, characterised in that at least one unperforated element is hingedly connected within the belt which can receive a quantity of liquid when said element is beneath the level of the sewage flow, and transport said quantity over the upper axis, said unperforated element emptying its contents substantially into the screenings processing unit as it rotates around said axis.

Preferably the unperforated element is a bucket-type element.

Preferably the screenings processing unit comprises a trough.

Preferably an unperforated element is hingedly connected within the belt after a group of a predetermined number of perforated elements have been hingedly connected together, and the belt is thus made up of groups of perforated elements interspersed by unperforated bucket-type elements.

Preferable the unperforated elements are substantially V-shaped in crosssection and of a similar or identical width to the perforated elements to which it is connected.

Preferably, the unperforated elements define a receptacle or bucket which can receive and transport sewage when the belt is stationary and moving respectively.

Preferably the elements are connected on either side to chains which are disposed around sprockets provided at each end of a pair of axles coincident with the axes around which the screening belt travels.

According to a second aspect of the invention there is provided an element for connection within a screening belt for use in screening apparatus, said element being hingedly connectable to other elements in the belt, characterised in that the element forms a receptacle for carrying and transporting an amount of liquid and debris whereas other elements in the belt simply screen fluid for debris.

Preferably the element is substantially V-shaped with one limb of the V being longer than the other to allow for secure attachment to chains at that side of the element.

The provision of an unperforated receptacle or bucket-type element within the screening belt automatically precludes the need for a wash water pumping system to pump wash water into the screening unit because such water can now simply be lifted from the sewage channel and flushed over the brush and into the screenings processing unit. The existence of debris in the bucket element is irrelevant because the screenings processing unit is already receiving screenings from the surfaces of the perforated elements of a similar size and nature. The addition to this of debris from the bucket element simply increases the quantity of screenings which are to be processed, and even this addition does not prejudicially affect the screenings processing.

A yet further advantage of the screening apparatus proposed is that although the quantity of wash water provided by the bucket element cannot be altered, the number of bucket elements within a belt can be altered, and therefore the volumetric flow rate of wash water can be adjusted by simply adding more bucket elements within the belt.

6 A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings wherein:

Figure 1 shows a schematic plan view of a sewage processing plant, Figure 2 shows a schematic end elevation of screening apparatus according to the invention, Figure 3 shows a schematic side elevation of the processing plant of Figure 1, Figure 4 shows a further schematic end elevation of the screening apparatus of Figure 1 Figures 5-6 show respectively an end elevation and a plan view of the screening belt element according to the invention, and Figure 7 shows a schematic side elevation of screening apparatus according to the invention.

Referring firstly to Figure 1 there is shown a sewage processing plant 1 consisting of a pair of sewage inlet channel 4, 6 in which are disposed separate screening apparatus 8, 10 each of which feeds a screening trough 12 which leads to macerating apparatus 14 which in turn feeds compaction apparatus 16. The compaction apparatus 16 simply compacts the macerated screenings from the macerator by means of an Archimedes screw 18, and the compacted screenings are urged upwardly through an exit spout 20, the open end of which allows the screenings to fall into a suitable collection vessel (not shown).

7 Each of the channels 4, 6 is separated by a channel wall 22 and the screening apparatus 8, 10 are disposed within the channels such that all the sewage flow within said channels comes into contact with a screening belt, portions of which are shown in Figures 2 and 7. Each of the said screening apparatus is also provided with separate water pumping apparatus 24, 26 which pump wash water into the screenings trough both for the purposes of washing the screenings along said trough, and also for washing the portions of the apparatus which constrain the screenings to drop into said trough. A screening chute 28 is provided on each of the apparatus for this purpose.

Referring to Figure 2, the screening apparatus consists of a screening belt 30 which consists of a number of elements 32 hingedly interconnected to form a belt which is wrapped around a pair of remotely disposed axles 34. 36 each of which is provided at their ends with a sprocket 35, 37. The sprockets engage a chain to the links of which each of the elements 32 is connected to complete the construction of the belt. One or other of the axles 34, 36 is intermittently rotationally driven such that the belt rotates around the lower axle (and in a similar direction around the upper axle) in the direction shown at 38.

The flow direction of the sewage is shown at 40 and the height of the channel wall 22, by which the apparatus is support at 41A, 41B, is shown at 42. It will be understood that as sewage flows towards the apparatus, there will be a build up in front of the inclined screening belt because each element within said belt is provided with perforations only of the order of 6mm diameter, and therefore the majority of sewage cannot pass therethrough. Once the build up of sewage causes a predetermined pressure differential level across the belt to be attained, belt is driven to present a further set of perforated elements to the oncoming sewage flow.

8 Screen drive motors 44, 46 can be seen on Figures 3, 4. Additionally in Figure 4 there is shown a screen back wash connection at 48 which emerges within the cavity defined by the straight belt portions between the sprockets. This connection is provided to flush stubborn debris from the portion of the screen belt on its downward cycle towards the lower sprocket by spraying water from behind said screen portion.

The requirement for a screen back wash connection and the wash water pumping arrangement is mitigated by the invention which is characterised by the addition of receptacle elements 50 of the type shown in Figures 5 and 6 to the screening belt.

The element shown in these figures is of solid wall construction having a rear wall 52, a front wall 54 connected at its lowermost edge to the rear wall, and an upper ledge portion 56. An opening 58 is defined along the entire width of the element which is mounted to the chain which supports the belt by end plates shown in Figure 6. The element shape is basically identical to the perforated elements from which the screening belt is primarily constructed with the exception that the perforated elements allow the passage of liquid therethrough, and the perforated elements are of a box construction of similar cross-sectional shape to define a horizontal ledge on which debris can be separated from the sewage flow as the inclined belt is translated out of said flow.

Alternatively, the receptacle elements receive an amount of sewage liquid and debris which is transported upwardly away from the lower axle 34 as the belt is driven therearound. With particular reference to Figure 7 there is shown a receptacle element 70 within the construction of the belt 30 and carrying an amount of sewage liquid and debris. lt will be understood that as the straight, forward facing 9 portion 72 of the belt 30 is urged upwardly by virtue of the driven rotation of the sprockets 35, 37, the contents of the said element 70 will fall under gravity therefrom as the said element is upturned as it rotates around the uppermost axle 36. The contents of said element will thus be evacuated above the region of the chute 28 in which there is often a build up of screenings from the surface of the perforated elements, either as a result of the action of a driven brush 74 on the surface of said perforated elements, or simply because the debris is prone to build up on the side walls 28X, 28Y of the chute before landing in the trough 12.

The wash water provided by the receptacle container overcomes the necessity for effective wash water pumping in the region of the chute.

As discussed above, the sewage flow is entirely screened because none of said flow can flow through the apparatus unscreened. Indeed, within the channels 4, 6 the sewage is subjected to two screening processes because liquid is force to pass through both the forward facing portion of the screening belt 72 and also the rearward facing portion, which is allowed to sag slightly to prevent "bunching" of the elements as shown at 76. A rubber flap 78 with resilient plastic strip holding mechanism 78 contacts the elements in the lowermost region of the screening belt to ensure that the sewage flow cannot escape underneath the belt. In any event, the build up of debris and liquid which occurs upstream of the apparatus when the belt is stationary serves to urge the flap against the adjacent element and therefore effective screening is ensured.

1

Claims (12)

1 ' A screenings processing apparatus having a screening belt with a plurality of perforated elements hingedly interconnected to form said belt, said belt being at least intermittently caused to move around a pair of remotely disposed axes, one of said axes being disposed within a sewage flow channel such that the sewage flow consisting of liquid and debris comes into contact with at least part of one of said perforated elements, and the other axis being disposed thereabove, said apparatus further having a screenings processing unit disposed above level of the sewage flow, characterised in that at least one receptacle element is hingedly connected within the belt which can receive and retain a quantity of liquid therein when said element is beneath the level of the sewage flow, and transport said quantity upwardly out of the sewage flow as the belt moves to later depositing said quantity in said screenings processing unit.

2. A screenings processing apparatus according to claim 1 characterised in that receptacle element comprises a bucket portion which can receive sewage when the belt is stationary and transport sewage when the belt is moving.

3. A screenings processing apparatus according to either claim 1 or 2 characterised in that the receptacle element substantially empties its contents into the screenings processing unit as it rotates around said uppermost axis.

4. A screenings processing apparatus according to claim 2 characterised in that the bucket portion is pivotally connected within the receptacle and capable of rotation about an axis parallel with one of said remotely disposed axes such that the contents of 11 said bucket element can be emptied into the screenings processing unit at any desired level above the sewage flow.

5. A screenings processing apparatus according to claim 4 characterised in that the receptacle element is provided with a cam surface which engages a stationary cam mounted proximate the belt causing said bucket element to rotate and thus empty its contents into the screenings processing unit.

6. A screenings processing apparatus according to any preceding claim characterised in that the screenings processing unit comprises a trough.

7. A screenings processing apparatus according to any preceding claim characterised in that a receptacle element is hingedly connected within the belt after a group of a predetermined number of perforated elements have been hingedly connected together, the belt being thus made up of groups of perforated elements interspersed by receptacle elements.

8. A screenings processing apparatus according to any preceding claim characterised in that the receptacle elements are substantially V-shaped in cross-section and of a substantially width to the perforated elements to which they are connected.

9. A screenings processing apparatus according to any preceding claim characterised in that the various elements are connected on either side to chains which are disposed around sprockets provided at each end of a pair of axles coincident with the axes around which the screening belt travels.

10. An link element for connection within a screening belt for use in screening apparatus, said link element being hingedly connectable 12 to secondary link elements in the belt which are substantially permeable to and/or allow screening of fluid flow for debris when disposed in such a fluid flow, said link element and said secondary link elements being connected to a chain to form the belt, characterised in that the link element forms a receptacle for receiving and retaining an amount of fluid from the fluid flow which can be carried out of said fluid flow when said belt is moved so as to raise said link element out of said fluid flow.

11. An element according to claim 10 characterised in that the element is substantially V-shaped with one limb of the V being longer than the other to allow for secure attachment to chains at that side of the element.

12. A screening belt comprising permeable link elements hingedly connected to one another for use in screening apparatus, said belt being constituted of at least one chain in a continuous loop to which the elements are affixed arid said permeable link elements being permeable to fluid flow within a channel or providing a means of screening said fluid flow for debris, characterised in that receptacle elements are intermittently connected within the belt which are capable of receiving and retaining an amount of fluid from the fluid flow which can be carried out of said fluid flow when said belt is moved so as to raise said receptacle element out of said fluid flow.