NO773680L - PROCEDURE FOR SEPARATION OF SUSPENDED SOLID FROM LIQUIDS - Google Patents

Description

The present invention relates to the separation of suspended solids

solids from liquids.

Different apparatus are known such as a centrifuge or thickener, in which solid material suspended in a liquid is allowed to separate under the influence of gravity in a settling tank to enable the removal of concentrated sludge from the bottom of the tank and the removal of clarified liquid from the upper regions of the tank.

As far as the applicant is aware, most if not all known solid-liquid separation devices suffer from one or more disadvantages. Consequently, it is an object of the present invention to provide an improved separation of solids from liquids.

According to the invention, a method is provided for separating solid material from a liquid where a sludge body is formed,

a supply of liquid containing solids is introduced downwards into the sludge body, at least part of the incoming supply material is deflected radially and upwards due to a sealing effect of denser sludge in the sludge body, sludge from the sludge body is circulated in the path of the deflected supply material, deflected feed material and circulated sludge are mixed, at least a portion of the sludge/diverted feed mixture is directed radially outward to a zone above the sludge body, clarified liquor is removed at a level above the sludge body, and concentrated sludge is removed from a lower region of the sludge body.

It will be clear that depending on the size and weight distribution

of solid particles and/or flocs and/or agglomerates in the incoming feed, such solid particles and/or flocs and/or agglomerates may or may not have different

individual hindered settling rates relative to the liquid phase.

In a case where there are different individual hindered settling velocities in relation to the liquid phase and depending on the conditions existing in the zone where the incoming feed material is deflected, it is possible that parts of the incoming feed material comprising solid particles and/or flocs and/ or agglomerates have sufficiently high individual hindered settling velocities relative to the liquid phase and cannot be deflected with the rest of the incoming feed material,

but may continue along a downward path of movement and separate from the rest of the incoming feed material. Relatively fast-settling particles and/or flocs and/or agglomerates can thus segregate from radially deflected material and penetrate into a concentrated mud flow.

The feed material which continues along a downward path of movement may move mainly directly into contact with concentrated sludge in the sludge body to increase its density.

Hydrostatic pressure differences can prevent or limit penetration into the mud body of at least a larger proportion of the liquid content of the incoming supply.

Hydrostatic pressure differences can cause circulation of

sludge from the sludge body into the path of and in a direction substantially opposite to the radial deflection of the feed material, whereby concentrated sludge and radially deflected feed material are mixed and/or deflected upwards together.

The incoming feed can be introduced into the sludge body in a

zone that lies mainly directly above a zone in which concentrated sludge is removed from the lower part of the sludge body.

Concentrated sludge can be removed in a central zone located

itself under a central intake zone.

Alternatively, the concentrated sludge can be taken out in an annular

zone extending circularly around the vertical axis of a supply intake zone.

The flow rate of the incoming feed may decrease as the incoming feed reaches the entry zone. Thus, the incoming supply can be directed towards the entry zone along a downward path whose cross-sectional area increases in the downward direction.

The flow of incoming feed to the intake zone can be stabilized to minimize turbulence.

A flocculating or other settling agent may be added to the incoming feed before it reaches the entry zone.

The velocity of the upwardly deflected sludge/deflected feed mixture may increase as the mixture rises. Thus, the cross-sectional area of the zone in which the sludge/deflected feed mixture is deflected upwards can increase in the upward direction.

The incoming feed can be introduced into the sludge body in a central intake zone and the sludge/deflected feed mixture can be deflected upwards in an annular zone around the central intake zone. The mud body may be retained in an annular region surrounding the annular deflection zone. The sludge body can reach up to a level above the intake zone.

Co-concentrated sludge from the sludge/deflected feed mixture can

is directed radially outward from the annular deflection zone to a zone above the sludge body in the annular region surrounding the annular deflection zone at a level where the sludge concentrations in the annular deflection zone and in the zone above the sludge body are substantially equal.

Operating parameters such as removal of concentrated sludge and/or supply of incoming feed and/or flocculation dosing and/or the geometric parameters of the supply system can be regulated as desired. There can be a continuous addition of incoming feed and clarified liquid can be removed continuously to provide a continuous process where concentrated sludge is removed continuously or in batches if desired.

The scope of the invention also includes a method for separating solid material from liquid, where a sludge body

is formed, a feed of a solids-containing liquid containing solid particles and/or flocs and/or agglomerates having different individual hindered settling velocities relative to the liquid phase is introduced downward into the sludge body, parts of the incoming feed material are deflected, parts of the incoming feed material consisting of solids particles and/or flocks and/or agglomerates which have sufficiently high individual hindered settling rates in relation to

the liquid phase continues along a downward path into the sludge body and separates from deflected feed material, clarified liquor is removed at a level above the sludge body, and concentrated sludge is removed from a lower region of the sludge body.

It will be clear that by appropriate control of the operating conditions, the relative proportions of feed material that is deflected and feed material that continues along a downward path of movement will be varied.

According to another aspect of the invention, apparatus for separating solid material from liquid includes a set boiler, a concentrated sludge outlet towards the bottom of the set boiler, an outlet for clarified liquid towards the top of the set boiler, an intake pipe which descends into the boiler and includes a downwardly directed discharge mouth which is located in the lower area of the set boiler, and an annular plate with an open end which surrounds the intake pipe.

Preferably, the intake pipe extends downwards in the boiler, and the annular plate is placed in the longitudinal direction in relation to the intake pipe around at least a lower part thereof.

The discharge mouth of the intake pipe and the lower end of the plate can be positioned in an appropriate manner in relation to each other and/or to the bottom of the crucible.

The lower end of the plate may be below or above the discharge mouth or may be at the same level as the discharge mouth depending on the particular separation of the material required, provided that in use either the lower end of the intake pipe or the lower end of the plate or both. is at such a level that the constant density of the sludge in the sludge body is higher than the density of the deflected incoming feed material discussed above. The density of the deflected incoming feed material may be . equal to the density of the incoming supply or be less in density than the incoming supply where part of the incoming supplied material continues in a downward movement path in a concentrated mud flow as indicated above.

The plate and tube may be arranged relative to each other such that, thanks to a sealing effect of denser mud in the mud body, deflected incoming feed material will not be able to penetrate radially through the gap between the lower end of the plate and the bottom of the settling vessel, but is directed completely into the annular zone between the intake pipe and the plate.

The annular plate may extend to above the level of clarified liquid outlet from the set boiler, and may be provided with openings through this in an area between the ends. It is

also possible for the plate to comprise two separate sections placed vertically apart, the lower part surrounding a lower part of the intake pipe and the upper part surrounding an upper part of the intake pipe and extending above the level of the clarified liquid outlet.

The method and the apparatus according to the invention are suitable for use with pulp with highly varying flow characteristics.

For a clear understanding of the invention, preferred embodiments will now be described as examples with reference to the attached drawings: Fig. 1 shows a vertical section for separation apparatus according to the invention which is suitable for thickening metallurgical or other pulp where the concentrated sludge is not free-flowing. Fig. 2 is a schematic vertical section of the type of apparatus illustrated in fig. 1 which shows the flow pattern in the apparatus during operation. Fig. 3 is a schematic vertical section of separation apparatus according to the invention which is suitable for water treatment where the concentrated sludge is essentially free-flowing.

With reference to fig. 1 and 2 first, includes the device

a circular settling tank 1 comprising a cylindrical upper part 1a and an inverted conical bottom 1b. An outlet 2 for concentrated sludge. is located in the center of the bottom lb at the tip of this and is connected to the pipe 3 for the removal of concentrated sludge from the tank 1. An overflow pipe 4 defines an overflow comb 4a for clarified liquid and goes circularly around the cylindrical part 1a of the tank 1 near its upper end and is connected to pipe 5 for removing clarified liquid from the overflow pipe 4. The overflow comb 4a actually constitutes an outlet for clarified liquid from the tank 1.

The round inlet pipe 6 with an open end is located in the middle of the tank 1 above the outlet 2 for concentrated sludge and comprises a cylindrical upper part 6a and a truncated conical lower part 6b which defines a downwardly directed discharge mouth 7 at its lower end. The intake pipe 6 extends downwards into the settling tank 1

and the discharge mouth 7 is placed in the lower third of the cylindrical part 1 a of the tank 1 directly above the outlet 2 for concentrated sludge. The inner radius R^ of the discharge mouth 7 can lie between 0.2R - 0.4R where R is the inner radius of the cylindrical part 1 a of the tank 1. Supply line 8 is placed across the intake pipe 6 above the overflow pipe 4 and is connected to the upper cylindrical part 6a of the intake pipe 6 below the upper end of the cylindrical part 6a.

Radially placed anti-swirl plates 9 are placed in the upper cylindrical part 6a of the inlet pipe 6 below the supply line 8. The supply line 10 is placed to introduce flocculation or other settling aid in the upper cylindrical part 6a of the intake pipe 6. Rotary mixing device 11, which rotating blades, a turbine etc. for careful mixing of solids/liquid suspension at low shear with a minimum of floc breakdown is found in the lower truncated conical part 6b below the outlet of the supply pipe 10.

Rotating rake device 12 is placed below the discharge mouth 7 of the inlet pipe 6 in the bottom of the tank 1 at a distance from the bottom lb and is adapted to rotary operation by an axis 13 which goes upwards through the intake pipe 6 to drive a motor (which does not .. is shown) placed above the upper end of the intake pipe 6. Rotating mixing device 11 is also mounted on the axis 13 so that it is driven by the rotating rake device from the drive motor.

The annular plate 14 is placed around and spaced outwards radially from the intake pipe 6. The lower end 14a of the plate 14 can reach a level of at least 0.2 m, preferably from 0.2 - 0.5 m below the level of the discharge mouth 7 of the intake pipe 6 and the upper end 14b of the plate 14 can extend to a level of at least 0.2 m, preferably from 0.2 - 0.5 m above the upper edge of the overflow comb 4a.

The plate 14 is provided with openings 15 across in a

zone which may extend from a lower limit by a distance'

in the range from 0.15 - 0.6 m below a predetermined mud level X to an upper limit located at a distance of 0.3 -

1.2 m above the predetermined mud level X. The vertical extent of the perforated zone 15 can lie in the range 0.5 - 1.5 m.

The inner diameter R2 of the plate 14 can lie in the range from 0.28R - 0.6R so that the minimum cross-sectional area of the annular zone 16 between the intake pipe 6 and the plate 14 can lie from 0.75 - 1.25 times the maximum cross-sectional area of the cut off the conical part. 6b of the intake pipe 6 at the discharge mouth 7 .

Lamella clearing and/or thickening agents 17 of the type covered by our South African patent application No. 77/2422

is placed around the plate 14 in the area of the perforated zone 15 of the plate 14.

The mud level detector 18 is connected to the concentrated mud pump

19 in pipe 3 for concentrated sludge removal and is arranged to control the pump 19's operation and thereby control the removal of concentrated sludge through the sludge outlet 2 at the bottom of the tank 1 so that the sludge level X is controlled so that it lies within predetermined limits.

During use, a feed comprising liquid containing solids is supplied along the supply pipe 8 to the intake pipe 6 and introduced downwards along the intake pipe 6 into the settling tank 1 to establish the operating conditions to be described below.

Anti-eddy plates 9 prevent or at least reduce eddy currents in the incoming feed in the intake pipe 6 which can lead to an unwanted entrainment of air in the feed stream.

A flocculant. such as a polymeric flocculant. is introduced into the incoming feed via the feed pipe 10 in a position well above the discharge mouth 7 oa is mixed well but carefully with the incoming feed by rotating mixing devices 11 to cause flocculation of solid particles in the incoming feed.

The incoming supply flows along the truncated conical part 6b of the intake pipe 6 with its cross-section increasing downwards so that turbulence and flow velocity are minimized to avoid flock degradation.

A concentrated sludge body is formed in the settling tank 1, the sludge body comprising a bottom part which is located in the bottom region 20a of the tank 1 below the discharge mouth 7 of the intake pipe 6 and an annular part which is located on the bottom part in the annular zone 20b around the plate 14 which holds the annular part of the mud body so that it rises to a higher level X.

The upper end of the cylindrical portion 6a of the intake pipe 6 extends above the level of the overflow comb 4a so that the incoming feed can build up a column of feed material comprising solids suspended in the liquid up to level

Y in the intake pipe 6 while the column has sufficient hydrostatic pressure to introduce incoming feed downwards into the sludge body through the discharge mouth 7 of the intake pipe 6 against the hydrostatic pressure of the more concentrated sludge in the bottom part of the sludge body in the bottom area 20a of the tank 1 as shown by arrows A.

For if it is desired to control sliming in the apparatus, separation of clarified liquid from incoming liquid containing solids and collection in the intake pipe 6 above the supply level, the pipe 8 can be emptied from the intake pipe 6 in a zone above the supply pipe 8 in the annular zone 16 between the intake pipe 6 and

the annular plate 14, the discharge rate of clarified liquid being controlled so that entrainment of solids in clarified liquid flowing upwards towards the discharge zone is avoided or minimized. In other words, the upward velocity of clarified liquid should be less than the settling velocities of essentially all solids.

For controlled emptying of clarified liquid from the intake pipe 6

a series of openings (not shown) may be arranged circularly around the wall of the intake pipe 6 at a location above the supply line 8, the openings being provided with movable gates or other closing means suitable for controlling a discharge of clarified liquid through the openings which as a result of the clarification of discharge liquid. Alternatively, clarified liquid can flow over the upper end of the intake pipe 6 and the latter can be provided with a telescopically movable upper part 6c as shown in fig. 2 which can be raised and lowered depending on the clearance of waste liquid and thereby control the flow of.

clarified liquid over the upper end of the upper part. The operation of the closing means for the discharge openings or operation

The opening of the telescopically movable upper part 6c of the intake pipe 6 can be effected by a servo mechanism (not shown) which is controlled by a detector (not shown) which is sensitive to the clarification of waste liquid. It is also possible that clarified liquid is emptied from the intake pipe 6 by means of a pump or that the entire intake pipe 6 is movable up and down to control a flow of clarified liquid over its upper end.

The supply originating from discharge mouth 7 meets more concentrated sludge of the sludge body which flows down towards the outlet 2 for concentrated sludge. The higher density of the concentrated sludge prevents the short circulation directly to the outlet 2 for concentrated sludge of parts of the incoming feed material with an insufficiently prevented settling velocity in relation to the liquid phase, and hydrostatic pressure differences cause a part of the feed to flow slowly and gradually to deflect in a direction radially outward as indicated by arrows B.

However, where the incoming feed contains solid particles and/or flocs and/or agglomerates with different individual hindered settling velocities relative to the liquid phase, the rapid setters segregate solid particles and/or flocs and/or agglomerates with sufficiently high hindered settling velocities relative to the liquid phase that have been determined at the conditions in the deflection zone from the radially flowing supply stream to join the main mud stream towards the outlet 2 for concentrated mud and thus causes a further increase in the density of this stream.

The proportion of the added material that segregates out and continues along a downward movement path can be controlled

by the correct choice of parameters such as the cross-sectional area of the lower end of the annular zone 16 around the intake pipe 6 and/or the distance of the discharge mouth 7 to the intake pipe 6 and/or the lower end 14a of the plate 14 from the bottom lb of the settling tank 1.

Then. the concentrated sludge in the annular zone 20b around

lower part 14d of the plate 14 which is not pierced is denser than the deflected part of the supply flow, the hydrostatic pressure in the annular region 20b at the level of the lower end 14a of the plate 14 is higher than the hydrostatic pressure at the same level in the plate 14, where concentrated sludge is forced upwards from the zone 20b into the annular zone 16 between the plate 14 and the intake pipe 6 as indicated by arrows C, thereby providing one sludge recirculation flow. The radially deflected supply current indicated by arrows B cannot pass through the space between the lower end 14a of the plate 14 and the bottom 1b of the tank 1 because the sealing effect of the denser sludge flowing in a generally opposite direction as indicated by arrows C. Recycled sludge (arrows C) encounters radially deflected incoming feed (arrows B) across each other in the lower portions of annular zone 16 (where recycled sludge and incoming feed are mixed and deflected upwards in annular zone 16

where mixing and final flocculation take place.

This mixing action accelerates flocculation and de

smaller flocks are caught in the newly formed, relatively concentrated pulp to thereby increase setting and compress ion speeds.,

increase concentrated sludge density and improve overflow clarity.

The relatively concentrated pulp formed from the recirculated sludge/incoming feed mixture flows up along annular zone 16 with upwardly increasing cross-sectional dimensions so that the velocity of the pulp decreases as the pulp rises thereby minimizing turbulence and accompanying flock degradation.

ring.

As the pulp rises as shown by arrows D, it is further concentrated because setting takes place within the annular zone 16 and also as a result of the sludge penetrating through the lower part of the perforated zone 15 of the plate 14 from region 20b into the annular zone 16 as a result of a hydrostatic pressure gradient. Furthermore, a part of the faster settling flocs that do not segregate in the previous step and newly formed faster settling flocs that form as a result of flocculation within the annular zone 16 can now segregate and move down the outer surface of the truncated cone-shaped part 6b/ and slide down along the sloping surface until they join the main mud flow which flows down towards the mud outlet 2 and thereby contribute further to the density of the mud.

The rising concentrated sludge resulting from the recycled sludge/incoming feed mixture in annular zone 16 readily spreads outward and passes from annular zone 16 through the central portion of perforated zone 15 in plate 14 into zone 20c above the annular portion of the main sludge body in zone 20b as indicated by arrows E2. This occurs at a height where "steady state" concentration of the pulp in the range 20c corresponds to recycled sludge/incoming feed mixture. In zone 20c, concentrated sludge is deposited and compressed gradually under completely calm conditions without influence from incoming supply from discharge mouth 7 of intake pipe 6 or from convection currents, thereby contributing to the concentrated main sludge body which flows radially inwards through the space between lower end 14a of plate 14 oq the bottom lb of the tank 1 towards the sludge outlet 2 under the influence of hydrostatic pressure and also of the rake device 12 which facilitates further water separation. A part of this sludge stream will continue to flow towards the sludge outlet 2 as shown by arrows F and a part will recycle back to mix with the incoming feed as indicated by arrows C and described above. The ratio of forward sludge flow (arrows F) and sludge recycling (arrows C) and the residence time in the annular zone 16 depends on the design parameters of the intake pipe 6 and the plate 14 and can in principle be controlled within desired limits by these parameters such as the diameter of the plate 14 in relative to this for the intake pipe 6 and/or the level of the lower end of the plate 14 and/or of the intake pipe 6 in relation to the tank bottom lb.

The relatively concentrated pulp that is introduced into the main sludge body

in region 20b from region 20c leads to a sludge level or demarcation that is more sharply defined than is normally achieved with conventional apparatus and thereby facilitates control of sludge level X by means of the detector 18 which is operatively connected to the sludge pump 19. Operation of the sludge pump 19 is controlled by

the detector 18 depending on the sludge level X so that withdrawal of concentrated sludge from the tank 1 is controlled to control the sludge level

X within predetermined limits.

With the device according to the present invention, a relatively deep mud layer can be maintained in region 20b and thereby hydrostatically induce a recirculation of concentrated mud from region 20b into annular zone 16 in the direction of arrows C. By also

to control the operation of Dump 19 so that sludge level X is kept within predetermined limits, the apparatus can always operate at optimum capacity in contrast to conventional under-loaded thickeners or clarifiers. If the supply is too small, the extraction rate for concentrated sludge can be reduced accordingly so that the device will still be able to operate at optimum capacity with increased concentrated sludge density. Within certain limits, maximum separation can be achieved under all given conditions.

Discharge opening 7 is located in the lower third of the tank

1 below the sludge level X and at or below a level where the "steady state" concentration gradient in tank 1 is equal to the incoming feed concentration, whereby a hydrostatic pressure pumping action is achieved for the circulation, mixing and deflection of concentrated sludge and incoming feed material.

Clarified liquid collects in the upper region 20d of the tank 1 above the concentrated pulp in region 20c and a relatively sharply defined pulp/liquid interface M can be obtained. The clarified liquid flows from the tank 1 over the comb 4a into the overflow tube 4 and can be taken out through line 5.

While the annular zone 16 between intake tube 6 and plate 14 mainly functions as a flocculation zone, it is possible that phase separation can also be achieved by perforated zone 15. A part of the carrier liquid which has already been separated in annular zone 16 flows radially outward through the upper part of perforated zone 15 as indicated by arrows El and flows briefly to the overflow comb 4a. A mixture of incoming feed and concentrated sludge passes radially outward above sludge level X through the central part of the perforated zone 15 as indicated by arrows E2. The rest of the carrier fluid will be released as a result of settings-

and contraction processes in the main mud body and flows upwards as shown by arrows G. to reach the cleared fluid layer in the om-^

advised 20d. It is possible that some concentrated sludge may flow back from the sludge body in zone 20b into the circular zone 16 through the lower part of the perforated zone 15 as indicated by arrows H.

The rate of addition of the flocculation medium through the supply pipe 10 can be controlled automatically by a detector (not shown) which is sensitive to the clarity of the overflow liquid. Flock degradation is minimized by the introduction of incoming supply along the supply pipe 8 below the supply level Y in intake pipe 6, the inhibition of eddy current within the intake

pipe 6 by means of anti-vortex plates 9, gradual reduction of the flow rate as a result of increasing the cross-sectional area of the intake pipe 6 and annular zone 16 in the flow direction,. prevention of unwanted acceleration effects by correct ratios between R^ and R^ and by gradual, careful and even deflection and leading incoming supply from discharge mouth 7 by hydrostatic pressure from the more concentrated mud body.

Intake of air into the intake pipe 6 is minimized by the submerged entrance of incoming supply from the supply pipe 8

and the effect of anti-swirl plates 9. However, any entrained air present in the supply stream may pass up-

ad and escape through the openings. upper ends of the intake pipe .6

and off the plate 14 and thereby provide aeration of the pulp supply to the main sludge body through the openings 15 in the plate 14. All solids or flocks that float due to released air bubbles are prevented from entering the overflow and reducing the overflow clarity at the upper part 14c of the plate 14 which are not per-

lined and which reaches an upper level well above the liquid overflow level Z and also a lower level well below the overflow level Z. Such

solids or flocs will thus sediment back or can be removed periodically. A separate overflow system can be provided for the plate 14 in the event that lighter flocks

than the carrier liquid is present in a significant quantity. Clarification and thickening occurring in areas 20b and 20c is accelerated and increased by the placement of the auxiliaries 17. It has been found that under certain circumstances when the apparatus is operated with a dense slurry, the capacity can be limited by a rise in the pulp/liquid interface M until it reaches the comb 4a so that sliming of the apparatus occurs with solid material that passes out through the outlet 5.

It has been found that a rise in the pulp/liquid interface M can be controlled by collecting clarified liquid separating from the incoming feed in the upper part of the intake pipe 6 above the feed line 8 and draining the clarified liquid at a controlled rate from the upper part of the intake pipe 6 into the annular zone 16 between the intake pipe 6 and the plate 14

as described above. The device can thus be operated stably under conditions that would otherwise lead to sliming and thereby enable an increase in the device's capacity.

The level of the pulp/liquid interface Mf can also be stabilized by limiting the maximum height of the interface M above the lower end of the perforated zone 15 of the plate 14 to allow concentrated sludge originating from the recycled sludge/incoming feed mixture in the circular zone 16 to spread radially outwards through the perforated zone 15 into the zone 20c as shown by arrows E2, and to collect fine particles by induration in the upper parts of the zone 20c.

It is - clear that many detail variants are possible without going beyond the scope of the attached requirements. E.g. more than one supply line 8 for supply streams for different compositions can be placed in the intake pipe 6. Mixing devices 11 can be used to mix the different streams and/or

to mix the undercurrent and overcurrent feed streams in the case of countercurrent decantation. The wall part 6b of the intake pipe 6

may have any suitable slope relative to the vertical

axis and can in certain cases be vertical.

In certain applications of the invention, the anti-swirl plates 9 and/or the mixing devices 11 and/or the supply pipe 10 and/or the aids 17 for clarification and/or thickening can be omitted. In cases where the incoming supply material contains no air at all, there is no need to include the upper plate part 14c. The openings 15 can also be omitted and only the lower closed part 14d retained.

In cases where the sludge level or interface X does not take the form of a relatively sharply defined step, the level of the sludge body in the settling tank can be checked by detecting the solid/liquid interface M and controlling the operation of the sludge pump 19 depending on the interface M's level. Certain numerical ratios between parts of the apparatus are given above as examples, but such numerical values may be varied depending on the particular circumstances. The invention and apparatus are not limited to the particular numerical values given above.

An extended overflow system including peripheral comb 4a

runs circularly around the settling tank 1 and likewise one or more radial chambers (not shown) may be present. The comb or combs may be smooth or serrated.

Any suitable mixing means such as rotating blades, a turbine,

a grinding mixer etc. which can gently mix solid material/liquid suspensions at low shear, ■ may be present.

All suitable means can be used to control the sludge level

in the settling tank 1 or the level of a pulp/liquid interface above the same t.

Any suitable detector such as an optical or supersonic device or differential pressure sensors can be used for automatic control of the operation of the concentrated sludge pump 19 depending on the sludge level X and/or the pulp/liquid interface level M.

It is also possible to control the operation of pump 19 manually.

All suitable agents to aid clarification and/or thickening i

in addition to laminar aids 17 can be used.

Means for controlling the clarity of liquid flow from settling tank 1 can be used. Thus, all suitable means for demonstrating the clarity of the overflow liquid and checking the addition of a flocculation or other setting aid to the incoming supply can be available.

The apparatus described; above with reference to fig.

1 and 2 in the drawings are suitable for thickening metallurgical or other pulps, in which the concentrated sludge is not free-flowing. Where concentrated pulp is essentially free-flowing, as is often the case with water treatment, it may be advantageous to modify the separation apparatus in certain respects. Thus, instead of placing a centrally located concentrated sludge outlet, a peripherally located concentrated sludge outlet can be placed on or near the bottom of the settling device so that concentrated sludge can be removed from a lower part of the sludge body in a perfect zone therein.

A sludge level detector for. control of the sludge level can be avoided by

providing a concentrated sludge outlet path connected to the concentrated sludge outlet and including a portion extending down from a zone of maximum height which can be at a variable level depending on the desired sludge level.

Instead of providing the settling tank with an inverted conical bottom

with a downward-pointing tip, the bottom of the settling tank may be mainly horizontal or be conical with an upward-pointing tip.

The rake device can also be omitted.

With reference to fig. 3 which illustrates separation apparatus according to the invention which is suitable for mainly free-flowing sludge, the apparatus comprises a circular settling tank 1 comprising a cylindrical, vertically placed side wall la and a flat horizontal bottom lb. The open end hole 20 is placed in the tank 1 at a distance from the side wall la. A compartment 21 is provided between the side wall 1a and the annular opening 20 between the upper and lower ends of the latter to divide the annular space between the side wall 1a and the ring 20 into two separate liquid parts 22 and 23.

The lower end of the ring 20 is separated from the tank bottom 1b to provide a perfect underflow comb which defines a concentrated sludge outlet 24 into the portion 23 which extends peripherally around the side wall 1a of the tank 1. A sludge discharge path 25 which is designed to

lead concentrated sludge from the part 23 to a zone 25a of maximum height before the concentrated sludge is led downwards, can be provided. The level N at the zone 25a determines the sludge level X and the latter can be varied by varying the level N. Any suitable adjustable sludge discharge paths 25 can be produced to provide variation of the level N. Thus relatively movable pipes and/or containers can

which are located one within the other and describe a path including a portion extending downward from a zone of maximum height that can be located at a variable level, is used. A valve 25b to the atmosphere may be provided to prevent siphoning.

The upper end of the ring 20 is located below the lower end

of the side wall la and describes an overflow comb 4a into the part 22 which is connected to the pipe 5 for withdrawal of clarified liquid from the part 22. The upper end of the pipe 20 thus constitutes an outlet for a clarified liquid from the tank 1.

The rest of the apparatus is similar to what has been described

above with reference to fig. 1 and 2 in the attached drawings with the exception that there is no rake device.

Any suitable flocculation step as described above with reference to fig. 1 and 2 in the drawings can be present in the upper part of the intake pipe 6. Alternatively or in addition, any suitable pre-flocculation step can be present before the intake pipe 6.

If a very clear liquid overflow is required, lamellar clearing elements 17 of the type described in South African patent application no. 77/2422 can be provided.

Where the incoming feed contains a certain proportion of solids that are lighter than the liquid together with a major proportion of solids that are heavier than the liquid, such lighter solids will tend to accumulate at the liquid surface Z between the intake pipe 6 and the plate 14 above the perforated zone 15 and can be removed either periodically or continuously by means of a secondary overflow comb located at level Z near the upper end 14b of the plate 14.

The hydrostatic pressure difference driving the recirculation of concentrated sludge from the sludge body 20b in the direction of arrows C is lower in the case of water treatment than in the case of thickening of metallurgical pulps, since in the case of water treatment a typical density difference between concentrated sludge and incoming feed is of the order 0.04 - 0.08 g/cm 3 compared to a density difference of the order of 0.2 - 0.4 g/cm 3 in thickening metallurgical pulps However, typical concentrated sludge in ' <£orcombination with water treatment characterized wood is much lower viscosity than with thickened metallurgical pulps and it must therefore be expected that the lower viscosity will compensate for the lower driving force.

With water clarification, there is no or little tendency for rapidly settling solids in the incoming supply to short-circuit directly from the discharge mouth 7 of the intake pipe 6

to the sludge body 20a as is the case with metallurgical pulps. Where the pulp is mainly free-flowing, it is therefore possible to omit a central underflow outlet and to use a peripheral underflow comb as described above.

A well-known problem with water clarifiers that is not normally found with thickeners is short-circuit current. It has been suggested that the problem can be overcome or minimized by transferring the energy of the incoming feed flow to pressure by extracting the energy as work or dissipating the energy as hydraulic loss.

The device according to the present invention avoids or

at least the short-circuit current problem is minimized as the energy of the incoming feed stream is used hydrostatically to pump a stream of recycled concentrated sludge into annular flocculation zone 16 and is finally dispersed hydraulically due to the losses in the recycling stream. Before it is dispersed, the energy of the incoming feed stream provides a pumping action in the clarification system by recirculating concentrated sludge, thereby providing a thorough incoming feed/concentrated sludge mixture and accelerating the flocculation rate.

Many detail variations are possible without going outside the scope of

the attached requirements.. If e.g. the incoming feed contains some coarse particles, the bottom 1b of the tank 1 may be inverted conical in shape with a central secondary discharge outlet (not shown) in addition to the peripheral underflow outlet 24 to enable continuous or batch discharge of settled solids through the secondary outlet.

It is also possible to fit an extended overflow system. Such an extended overflow system can comprise a circular comb such as comb 4a, as well as radially extended combs in connection with the circumscribing comb. As shown in the attached drawings, an outlet outlet 26 can be found at the bottom of the settling tank 1.

For applications where the concentrated sludge is not completely free-flowing, the peripheral underflow outlet 24 can be omitted and the tank 1 equipped with an inverted conical bottom and a central underflow outlet at the tip of the bottom. mud-

level X can be controlled by means of a valve in the underflow discharge line which is controlled by any possible suitable interface detector or sensor. The detector or sensor can be of the optical, ultrasonic or differential pressure type. Depending on the nature of the concentrated sludge, it is possible

to work without rake equipment.

With the device according to the present invention it is possible

to achieve circulation and mixing of concentrated sludge and in-

incoming feed material using hydrostatic pressure differences without requiring a mechanical or jet pump. Mixing of concentrated sludge and incoming feed under such conditions has the advantages that: (a) it tends to improve flocculation and floc coalescence and thereby enhance separation of solids from liquids: (b) it tends to give a relatively concentrated mass that acts as a filter for capturing smaller particles

and prevent them from passing into the overflow liquid and thereby

improve the clarity of the overflow, setting and compression speed and the density of the underflow,

(c) a more sharply defined sludge level or limitation may

is achieved.

It is also possible with the device according to the present invention to achieve a relatively high segregation rate of relatively quickly settling solids coming from the supply inlet into the settling tank, mainly directed into the concentrated sludge and at a place above the sludge outlet from the settling tank. This has the advantage that:

(a) concentrated sludge density is increased,

(b) fast-settling solids tend to settle in the immediate vicinity of the sludge outlet so that only a small limited twist is needed to rake such solids toward the outlet, thereby reducing the total rake twist required to discharge solids and thus equipment costs are minimised, (c) rapidly settling solids in the incoming supply mainly move directly towards the sludge discharge zone and pass the main operating path.

It is a further advantage of the invention that with a relatively simple apparatus construction it becomes possible not only to achieve

more efficient separation of solids from liquid, but also easy to perform in a single unit related functions that are normally performed with separate equipment setups. E.g. flocculation, aeration, mixing of more than one supply stream and venting can be carried out in the same apparatus unit.

The main slurry body is also compacted under completely calm conditions without any disturbance from incoming feed material.

The method and the apparatus according to the present invention are suitable for a large range of clarifying and thickening applications with possible small modifications to meet the special requirements of special applications. It can thus be used on metallurgical pulps and counter-flow decantation systems and can be used in the chemical as well as the food and paper industry.

It can also be used to concentrate crystals between the crystallizer and dewatering filter or centrifuge and for the treatment of impure water and domestic and industrial emissions.

It is described above that the annular plate 14 can have

a diameter so that the minimum cross-sectional area of the annular zone 16 between the intake pipe 6 and the plate 14 lies in the range from 0.75 - 1.25 times the maximum cross-sectional area of the cut-off conical part 6b of the intake pipe 6 at the discharge mouth 7. It is It is advisable that the minimum cross-sectional area of the annular zone 16 be at least 0.75 times and preferably at least as large as the maximum cross-sectional area of the intake tube 6. Under certain circumstances, the minimum cross-sectional area of the annular zone 16 may be up to two times or more of the maximum cross- cross-sectional surface of the intake pipe 6.

Claims (39)

1. Process for separating solid material from a liquid where a sludge body is formed, a supply of liquid containing solids is introduced into the sludge body, liquid is separated from solids, clarified liquid is removed at a level above the sludge body, and concentrated sludge is removed from a lower part of the sludge body, 'characterized in that incoming feed comprising liquid containing solids is introduced downwards into the sludge body, at least part of the incoming feed material is deflected radially and upwards due to the sealing effect of denser sludge in the sludge body, sludge from the sludge body is circulated into the path of the deflected input material, deflected . supply material and circulated sludge are mixed, and at least part of the sludge/deflected supply mixture is fed radially out to a zone above the sludge body. 2. Method according to claim 1, characterized in that the incoming feed material contains solid particles and/or flocks and/or agglomerates in the incoming feed material with different individually hindered deposition rates in relation to the liquid phase and parts of the incoming feed material comprising solid particles and/or flocks and/or agglomerates with sufficiently high individually hindered deposition rates relative to the liquid phase continue along a downward trajectory and are separated from deflected feed material. 3. Method according to claim 2, characterized in that supply material which continues along a downward movement path is moved mainly in direct contact with concentrated sludge in the sludge body in order to increase its density. 4. Method according to claims 1-3, characterized in that hydrostatic pressure differences prevent or reduce penetration into the sludge body for at least the main part of the liquid content in the incoming supply. 5. Method according to claims 1-4, characterized in that hydrostatic pressure differences cause mud circulation from the mud body into the path to and in a direction generally opposite to the radial deflection of the feed material, whereby concentrated mud and radially deflected feed material are mixed and/or deflected upwards together. 6. Method according to claims 1-5, characterized in that the incoming supply material is introduced into the sludge body in a zone which is essentially located directly above a zone in which concentrated sludge is removed from the lower region of the sludge body. 7. Method according to claim 6, characterized in that concentrated sludge is removed in a central zone located below a central introduction zone. 8. Method according to claims 1-7, characterized in that the flow rate of the incoming supply decreases when the incoming supply reaches the zone in which the incoming supply enters the sludge body. 9. Method according to claim 8, characterized in that the incoming supply is directed towards the introduction zone along a downward path whose cross-sectional area increases in the downward direction. 10. Method according to claims 1-9, characterized in that the flow of incoming supply to the zone in which the supply enters the sludge body is stabilized in order to minimize the turbulence. 11. Method according to claims 1-10, characterized in that a deposition aid is added to the incoming supply before this reaches the zone in which the incoming supply enters the sludge body. 12. Method according to claims 1-11, characterized in that the speed of the upwardly deflected sludge/deflected supply mixture decreases as the mixture rises upwards. 13. Method according to claim 12, characterized in that the cross-sectional area of the zone in which the sludge/deflected feed mixture is deflected upwards increases in an upward direction. 14. Method according to claims 1-13, characterized in that the incoming supply is introduced into the sludge body in a centrally located intake zone and the sludge/deflected supply mixture is deflected upwards in an annular zone located around the intake zone. 15. Method according to claim 14, characterized in that the sludge body is retained in an annular region surrounding the annular deflection zone. 16. Method according to claim 15, characterized in that concentrated sludge from sludge/deflected feed mixture is led radially outward from the annular deflection zone to a zone above the sludge body in the annular region surrounding the annular deflection zone at a height where the sludge concentrations in the annular deflection zone and in the zone above the sludge body are essentially the same. 17. Method according to claims 1 - 16, characterized in that the sludge body extends to a level above the zone in which incoming supply enters the sludge body. 18. Method for separating solid material from a liquid in which a sludge body is established, a supply of liquid containing solids is introduced into the sludge body, liquid is separated from solids, clarified liquid is removed at a level above the sludge body, and concentrated sludge is removed from a lower region of the sludge body, characterized in that incoming feed comprising liquid containing solids comprising solid particles and/or flocs and/or agglomerates with different individual hindered deposition rates in relation to the liquid phase is introduced downwards into the sludge body, parts of the incoming feed material are deflected and parts of the incoming feed material comprising solid particles and/or flocs and/or agglomerates with sufficiently high individual hindered deposition rates in hold until the liquid phase continues along a downwardly directed path of movement into the sludge body and is separated from deflected feed material. 19. Apparatus for separating solid material from liquid comprising a settling tank, a concentrated sludge outlet towards the bottom of the settling tank and an outlet for clarified liquid towards the top of the settling tank, characterized in that an inlet pipe extends down into the settling tank and includes a downwardly directed discharge mouth which is located in a lower part of the settling tank, and an annular plate with open ends located in the longitudinal direction of the intake pipe and which surrounds at least a part thereof at or near the lower end thereof. 20. Apparatus according to claim 19, characterized in that the settling tank comprises a cylindrical wall which extends upwards from a bottom where the discharge mouth of the intake pipe is located in the lower third of the cylindrical part of the settling tank. 21. '; Apparatus according to claim 19 or 20, characterized in that the intake pipe has an open upper end which is located above the level for the outflow of clarified liquid from the settling tank. 22. Apparatus according to each of claims 19-21, characterized in that the intake pipe slopes outwards towards the discharge mouth. 23. Apparatus according to claim 22, characterized in that the intake pipe comprises an upper cylindrical part with an open upper end and a lower truncated conical part whose walls slope radially outwards from the cylindrical part towards the discharge mouth. , 24. Apparatus according to claim 23, characterized in that the inner diameter of the lower cut-off conical part of the intake pipe at the discharge mouth lies in the range from 0.2R - 0.4R where R is the inner radius of the upper cylindrical part of the settling tank. 25. Apparatus according to claim 22 or 23, characterized in that a supply pipe which is placed transversely to the intake pipe and is connected to the upper cylindrical part thereof at a level which is above the level for the outlet of clarified liquid from the settling tank. 26. Apparatus according to each of claims 19-25, characterized in that the intake pipe contains means which serve to minimize eddy currents through the intake pipe. 27. Apparatus according to each of claims 19-26, characterized in that the intake pipe contains mixing agents. 28. Apparatus according to each of claims 19-27, characterized in that it contains means for introducing treatment medium into the intake pipe. 29. Apparatus according to each of claims 19-28, characterized in that the annular plate extends to above the level for the outflow of clarified liquid from. the deposition tank. 30. Apparatus according to each of claims 19-29, characterized in that the annular plate has openings in a zone between its ends. 31. Apparatus according to claim 30, characterized in that the perforated zone of the annular plate extends from below to above a predetermined sludge level in the settling tank. 32. Apparatus according to each of claims 19-31, characterized in that the annular plate has. a diameter such that the minimum cross-sectional area of the annular zone between the intake tube and the plate is at least 0.75 times the maximum cross-sectional area of the intake tube. 33. Apparatus according to claim 32 insofar as this depends on claim 24, characterized in that the inner diameter of the annular plate lies in the range from 0.28R - 0.6R. 34. Apparatus according to each of claims 19-33, characterized in that the lower end of the annular plate extends to a level which is at least 0.2 m below the level of the discharge mouth of the intake pipe. 35. Apparatus according to each of claims 19-34, characterized in that the upper end of the annular plate extends to a level located at least .0.2 m above the level of the outlet for clarified liquid from the settling tank. 36. Apparatus according to each of claims 19-35, characterized in that it contains means to aid clarification and/or thickening and which is placed in the annular part of the settling tank outside the annular plate. 37.. Apparatus according to claim 36, characterized in that the aids are placed in the area of the perforated zone of the annular plate. 38. Apparatus according to each of claims 19-37, characterized by a raking device in the bottom area of the settling tank below the discharge mouth from the intake pipe. 39. Apparatus according to claim 38, characterized in that a drive axis of the rake device which extends upwards from the rake device leads through the intake pipe to a drive motor located above it.