WO1989002775A1

WO1989002775A1 - Device for settling tanks and method of discharge

Info

Publication number: WO1989002775A1
Application number: PCT/SE1988/000474
Authority: WO
Inventors: Berne Andersson; Klaus Dieter Zickert
Original assignee: K.Z. Handels Aktiebolag
Priority date: 1987-09-22
Filing date: 1988-09-20
Publication date: 1989-04-06
Also published as: SE8703653D0; SE8703653L; SE458987B

Abstract

The present invention relates to a device at sedimentation basins and similar arrangements in order to move and remove precipitate and/or sludge gathered in the lower part of the basin (1), whereby a number of laminae (7) are rotatably arranged around one of their ends, whereby the laminae in a first position are arranged to take a substantially vertical position and in a second position they are arranged to take a horizontal position, whereby the laminae (7) in their second position creates a substantially second bottom above and at some distance from the bottom (2) of the sedimentation basin (1). The invention further relates to a process for emptying of sludge and a process for recirculation of sludge.

Description

DEVICE FOR SETTLING TANKS AND METHOD OF DISCHARGE

DESCRIPTION Technical field

The present invention relates to a devi ce at sedimentation ba- sins and simi lar arrangements in order to move and remove pre¬ cipitate and/or sludge gathered in the lower part of the basin, as well as a process for the emptying of sludge, as well as a process for the rec i rcu Iati on of sludge.

The object of the present invention is to obtain a device, par¬ ticularly for light flocks, preferably for sludge in water pu¬ rification plants, i .e. in the production of tap water.

Background of the invention in many sedimentation basins one has hitherto used chain scra¬ pers to remove the sludge which precipitates little by litt le on the bottom of the basin. These chain scrapers consi sts of on or more scraping blades extending straight across the bottom of the basin and which are dragged forwardly by means of contin- ously running chains in a pater noster movement . These const¬ ructions have some advantages by providing a good cleansing re¬ sult and have besides a high functional security as long as the construction is in tact. However, in spite of its genuine basi c construction serious breakdowns often occur. These depend on the heavy corrosion which all components, including the chains, are subject to. In the sedimentation basins of the purification plants the environment is thus very corrosive due to the acidic aluminium- and i ron salts used in the chemical precipitation steps included, which salts are used inter alia for the preci- pitation of phosphorous.

It has also been proposed an overhead crane which is driven above the water surface of the basin. An elevated scraper is mounted on arms on the crane. One drawback of thi s construction is that it i s compli cated in being used at present basins, ^' which are being provided with different equipments above the basin, such as footways, and other equipment being a hindrance. Further the sedimentat on is disturb by the vertical means holding the scraper.

It has further been proposed wiredrawn scrapers or scraping de- vices where one or more wires drag a scraping holding wagon or sleigh on or close by the bottom of the basin in a reciprocat¬ ing movement. (SE-B-423,968; US-A-2,866,557 ; US-A-2,768,749; US-A-4,090,966; GB-A-1 , 504,518) . The technique means an impro¬ vement vis-a-vis the previous known chain driven scrapers by a considerab ly more simple, lighter and cheaper construction. However, the system means that different devices are needed to turn the scraper blades and to guide this turning, from a ver¬ tical to a horizontal position and vice verse during the reci¬ procating movement being carried by the wire's. The scraper blades consisting of metal blades often provided with a rubber strip being vertically positioned in the scraping di rection extend over the width of the basin, perpendicular to the direc¬ tion of transport. At the to-and-fro going movement of the scraper blades, however, sludge is whirled up, so called escap- ing sludge due to the formation of turbulence behind the blades and thus a maximum efficiency can not be reached. The load on the device also means that they have to be manufactured of me¬ tal and they have to be made of an acid-resistant material if the corros on shall not destroy them too fast, which increases costs .

All the devices referred to above functions more or less well at heavier types of sludge, such as sludge present at sewage purification plants where very heavy particles are bound into the flocks created by the flocculation agents used, such as aluminium hydroxide flocks and fern^* hydroxide flocks. At the production of tap water aluminium hydroxide is also used as flocculation agent, but due to the small amount of heavy mate¬ rial normally present in raw water used in the production of tap water the flocks become extreme light and thereby they be¬ come readily movable and can not stand practically any turbu¬ lence at all in the sedimentat on basin but obtaining escaoing s l ud g e .

Thus there exists a desi re for other types of devi ces for ga¬ thering and transporting sediment and sludge within sedimenta- 5tion basins, parti cularly in the production of tap water where another load is obtained. Further, one wishes to increase effi¬ ciency by minimizing escaping sludge.

One object of the present invention is to obtain a device whi ch "lOfulfi ls these demands. Further objects wi ll be evident from the fo 11 owi ng .

Description of the present invention

It has now surprisingly been shown possible to be able to meet

15 these requi rements by means of the present invention whi ch is chara terized in that a sedi entation basin i s provided with a number of laminae being rotatably arranged around one of its endpoints, whereby the laminae in a fi rst position are arranged to take a substantially vertical position and in a second posi-

20 tion they are arranged to take a horizontal position, whereby they in their second position creates a substantially second bottom of the said sedimentation basin whi ch bottom i s arranged at some distance from and above the bottom of the sedi entat on bas i n . 5

According to one object of the present invention there i s ob¬ tained a process for the elimination of sludge from a sedimen¬ tation basin which process is characterized in that said second bottom at its one end is being opened and water i s being allow- 0 ed to stream in below said second bottom at the end opposite to the inlet opening of water.

According to another object of the present invention a smaller part of the sludge compartment below said second bottom be 5 shielded off and the sludge therein contained be removed for rec i rcu lat i on to a flocculation vessel. Further characteristics are evident from the accompanying claims.

By means of the present invention a minimum of turbulence is obtained around the sludge separation and at the sludge remo¬ val. The device according to the invention can be given a length which is carefully adapted to the form and length of the intended basin. Further the length and height of the laminae can be adapted to the size of the basin and the quality of the sludge present. The construction of the laminae herein proposed means that a very simple hydraulic and/or pneumatic operation of the movement of the laminae can be used which is also reli¬ able in running .

The invention wi ll be descr bed more in detail in the following with reference to the accompanying drawing, wherein FIG. 1 shows a side view of a sedimentation basin provided with a device according to the present invention; FIG. 2 shows a device of the present invention seen from the side when the laminae are in a closed position.

1 denotes a long sedimentation basin. The basin 1 is limited by a bottom 2, two longitudinal sides 3, a rear short end side 4, and a front short end side 5. In the front part of the basin there is preferably, but not obligatory, provided a sludge hop¬ per 6.

7 denotes a number of laminae having the width/height 30 to 70 cm being arranged cross above the sedimentation basin 1 at some distance above its bottom 2. The laminae 7 are at each their ends arranged to the side of the basin 1, suitably to a carrier Cnot shown) mounted thereto. At the upper edge of the laminae 7 there is a drag link, a chain or a wire 9 arranged, which link, chain or wire 9 can be operated with a reciprocating movement by means of a wire or chain 10 being operated by a motor 11 and a lever 12. Depending on the width of the basin one or more drag links 9 or drag wires 10 can be used. When the drag wire 10 is in a fi rst position, FIG. 1 , the laminae are in an up¬ right position, and the drag wi re 10 i s in a second position, FIG. 2, the laminae are in a horizontal position. The basin 1 is in its lower part, at the sludge hopper 6 according to the 5 Figures, provided with an outlet 13. At the longitudinal side/s of the basin 1 one or more inlets and out lets 14 are provided.

The drag wi re 10 or drag chain 10 are at thei r ends attached to the driving device 11, 12 via four pulley wheels 15 a, b, c, d; 0 two at each end of the basin 1, which device drags the wi re 10 in either one or the other direction. The driving device 11 , 12 can hereby consist of a gear reduction motor provided with a wi re drum, or a hydraulic pi ston system having a reciprocating movement, at the end of which the wi re 10 i s being attached. By 5 partly placing the pulley wheels 13 a and b at a level shortly above the bottom 2 of the basin, part ly by the tension of the wi re 10 the laminae 7 can be risen to a vertical position, and lowered to a horizontal position, respectively. When the lami¬ nae 7 are lowered to a horizontal position they wi ll form a se- 0 _Cond bottom of the basin 1 , whereby a sludge zone 18 i s created underneath this second bottom. By arranging the laminae 7 in such a way that they do not extend al l the way up to the short end side 4, or the lamina 7 closest to the short end side 4 is made individually vertical ly positionable an opening 16 i s pro- 5 vided between the main volume 17 and the sludge zone 18 of the basin 1.

The device of the present invention functions according to the fo 11 owi ng : θAt the sedimentation of floes in the water coming into the ba¬ sin via an inlet 19 and passing out after the sedimentation as a pure water, via an out let 20 the laminae are placed in a first vertical position. The floes wi ll hereby fall down bet¬ ween the laminae 7 and down into the sludge zone 18. When the 5 _sludge zone 18 has become fi lled with floes the laminae 7 are rotated to a second horizontal position by means of the motor 12 and the driving device 11 via the drag wi re 10. The outlet 13 is opened and, as a second bottom is now present in the ba¬ sin 1 by means of the horizontal position of the laminae 7, and water is now streaming through the opening 16 at the short end side 4, from the one short end of the basin 1 through the slud- ge zone 18 and out through the outlet 13 and hereby drags the sludge formed by the precipitated floes. When the sludge has been eliminated the outlet 13 is closed and the laminae 7 are again raised to a vertical position, whereby a new sedimenta¬ tion cycle can start again.

Those floes that falls down into the end of the basin facing away from the inlet 19 are the lightest ones. In one aspect of the present invention f L ocs /sludge having precipitated is re¬ moved via a side outlet 14 and is returned/ reci rcu lated to the water purif cation process in order to thereby reduce the costs of chemicals of the water plant. Hereby any part of the sludge zone 18 can be removed by adding water through one inlet 14 and is removed by one outlet 14, i.e., one or more sections of the sludge zone 18 can be emptied from sludge. Hereby the laminae 7 are closed in the same way as at a total emptying of the sludge zone, as described above and the side outlets 14 are opened; water is now streaming from the short end side 4 or an inlet 14 only to the opened side outlet 14 and thus empties only this part of the sludge zone 18. Depending on where these side out- lets 14 are being placed the amount and quality of the return sludge can thus be determined.

The Laminae 7 can suitably be provided with a sealing device arranged along its edge, such as of rubber, in order to let a minimum of water pass through the laminae 7 when in a lowered position. The Laminae 7 are suitably manufactured of a polymer, a steel sheet, or a composite material.

At very Large widths of the basin a centrally placed supporting device may be arranged to eliminate the bending downwards of the Laminae 7, particularly when in a lowered position. The laminae 7 leads to that the turbulence in the basin is be^¬ ing minimized and thereby the escaping sludge.

Claims

1. Device at sedimentation basins and similar arrangements in order to move and remove precipitate and/or sludge gathered in the Lower part of the basin, characterized in that it comprises

5a number of Laminae (7) being rotatably arranged around one of their ends, whereby the Laminae in a first position are arrang¬ ed to take a substant a L Ly vertical position and in a second position they are arranged to take a horizontal position, whe¬ reby the Laminae (7) in their second position creates a subs- lOtantially second bottom of the said sedi entation basin (1) for the creation of a sLudge zone (18) between said second bottom and the bottom (2) of the sedimentation basin.

2. A device according to claim 1, characterized in that the La- 15minae (7) extend in a horizontal position towards the short end side (4) of the basin (1) so that an opening (16) is arranged between said short end side (4) and said second bottom into said sludge zone (18).

203. A device according to claim 1, characterized in that the la¬ mina (7) arranged closest to the short end side (4) of the ba¬ sin (1) is arranged to be separately placed in a vertical posi¬ tion to the formation of an opening into said sludge zone (18).

254. A process for the sedimentation and removal of sludge from a sedimentation basin, preferably at a water plant, characterized in that one arranges a second bottom above and at some distan¬ ce from the bottom (2) of the sedimentation basin (1) to the formation of a sludge zone (18) underneath said second bottom,

30 and that one arranges an inlet opening (16) at the one end of said second bottom into said sLudge zone (18) and arranges an outlet C13) at the opposite end (5) of the said bottom and al¬ lows water to stream through said sludge zone (18) for removing the sLudge present in said sLudge zone 818) .

35

5. A process according to claim 4, characterized in that in¬ lets/outlets (14) are arranged along the side/s of the sedi- mentation basin (1) and that sludge is removed by letting water stream through said sludge zone (18) from said opening (16) and/or an inlet (14) to said out let (14) whereby the sludge thus eliminated is reci rculated to a water purification pro- cess .