A feedwell assembly for a thickener/clarifier including a feedwell body, at least one feed channel connected at a downstream end to the body, and a plate member disposed in the feed channel for separating froth from an incoming slurry stream to where the separated froth may be dissipated by a liquid spray directed onto the plate member. The plate member may include a planar upstream portion inclined upwardly from an upstream end of the plate member and may further include a planar downstream portion inclined downwardly from a downstream end of the upstream portion. At least one spray nozzle may be disposed above an elevated portion of the plate member so as to direct a liquid spray onto the plate member in a region about the joint, for further dissipating froth guided onto the plate member.

BACKGROUND OF THE INVENTION

This invention relates to thickener/clarifier tanks used to separate liquid and solids components of an influent feed slurry and specifically relates to feedwell apparatus employed in such thickener/clarifiers to enhance the clarification process.

Thickener/clarifier tanks are used in a wide variety of industries to separate influent feed slurry comprising a solids- or particulate-containing fluid to produce a “clarified” liquid phase having a lower concentration of solids than the influent feed slurry and an underflow stream having a higher concentration of solids than the influent feed slurry. Thickener/clarifier tanks conventionally comprise a tank having a floor and a continuous wall, which define a volume within which the clarification process takes place. Thickener/clarifier tanks also include an influent feed pipe for delivering influent feed to the tank, an underflow outlet for removing settled solids from the tank and a fluid discharge outlet for directing clarified liquid away from the tank. Thickener/clarifier tanks may also include a rake assembly having rake arms for sweeping along the floor of the tank, and may include an overflow launder or bustle pipe for collecting clarified liquid near the top of the tank.

Thickener/clarifier tanks of the type described operate by introducing an influent feed stream into the volume of the tank where the influent is retained for a period long enough to permit the solids to settle out by gravity from the fluid. The solids that settle to the bottom of the tank produce a sludge bed near the bottom of the tank, which is removed through the underflow outlet. Clarified liquid is formed at or near the top of the thickener/clarifier tank and is directed away from the tank for further processing or disposal. Settling of solids may be enhanced in some applications by the addition of a flocculent or polymer that forms agglomerates that settle more readily. In many applications, an objective of fluid clarification is to enhance the settling process to achieve a high throughput of solids, and thereby enhance solids recovery.

Many thickener/clarifier tanks are constructed with a feedwell, usually centrally located within the tank, into which the influent feed stream is delivered. The feedwell generally serves the purpose of reducing the fluid velocity of the incoming influent feed stream so that the energy in the stream may be dissipated to some degree before entering the tank. Dissipation of energy in the influent feed stream lessens the disruptive effect that the incoming influent feed has on the settling rate of the solids in the tank. In other words, introduction into a thickener/clarifier of an influent feed stream under high fluid velocity tends to cause turbulence in the tank and compromises the settling rate of solids. A feedwell may be structured in a variety of ways, therefore, to create or enhance dissipation of energy in the influent feed. For example, the feedwell and influent feed pipe may be structured to introduce influent feed to the feedwell at two opposing directions and into an annular space, such as is disclosed in U.S. Pat. No. 4,278,541 to Eis, et al.

Froth and/or air in a thickener/clarifier feed stream in existing methods of feedwell entry unavoidably contacts the flocculent and results in air being locked into the flocculated solids structure. This material then is slow to settle and is more persistent on the tank surface with resultant loss of solids to overflow and poor settling efficiency.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide an improved feedwell assembly for thickener/clarifiers.

A more specific object of the present invention is to provide a feedwell assembly wherein the incidence of froth or air in a thickener/clarifier feed stream is reduced.

An even more specific object of the present invention is to provide a feedwell assembly wherein the incidence of froth or air in a thickener/clarifier feed stream is reduced prior to contact of the feed stream with a flocculent.

Yet another object of the present invention is to provide such a feedwell assembly wherein froth and air reduction is accomplished inexpensively and simply.

These and other objects of the present invention will be apparent from the drawings and description herein. Although every object of the invention is believed to be attained by at least one embodiment of the invention, there is not necessarily any one embodiment of the invention that achieves all of the objects of the invention.

SUMMARY OF THE INVENTION

A feedwell assembly for a thickener/clarifier comprises, in accordance with the present invention, a feedwell body, at least one feed channel connected at a downstream end to the body, and a plate member disposed in the feed channel for separating froth from an incoming slurry stream. Optionally a liquid spray directed onto the plate member may dissipate the separated froth.

The plate member may be one flat, substantially horizontal or inclined plate section or take the particular form of a plurality of planar plate sections. The plate member may include an upstream portion that may incline upwardly from an upstream end of the plate member and may further include a downstream portion inclined downwardly from a downstream end of the upstream portion. The plate member has a leading edge that is disposed at a froth-liquid interface.

In one embodiment of the present invention, the upstream portion and the downstream portion of the plate member meet along an elongate joint. At least one spray nozzle may be disposed so as to direct a liquid spray onto at least a portion of the plate member in a region about the joint.

A feedwell assembly for a thickener/clarifier more particularly comprises, in accordance with the present invention, (i) a feedwell body, (ii) a pair of infeed pipes connected at downstream ends to the body at locations spaced longitudinally and circumferentially along the body, (iii) a launder header, the infeed pipes being connected at upstream ends to the header, and (iv) a plate member disposed in the header so that an upstream end of the plate member is disposed approximately at a froth-liquid interface.

Optionally, at least a portion of the plate member is disposed above the liquid level. In that case, the plate member may have an upstream portion that is upwardly inclined from the froth-liquid interface, proceeding in a downstream direction. The inclined upstream portion may be a planar plate section. A second plate section, exemplarily planar, may extend from a downstream end or edge of the inclined upstream portion. The second plate section may extend downwardly.

The separated froth on the plate member naturally dissipates or collapses on its own. However, at least one spray nozzle may be disposed for directing a liquid spray onto at least a portion of the plate member to knock down or further dissipate froth thereon.

Where the plate member includes an upstream plate section inclined upwardly from the upstream end of the plate member and a downstream plate section inclined downwardly from a downstream end of the upstream portion, the plate sections meet along an elongate joint, with the at least one spray nozzle being disposed so as to direct a liquid spray onto at least a portion of the plate member in a region about the joint. The feedwell body may include a lower portion and an upper portion, where the upper portion has a larger transverse dimension (e.g., diameter) that the lower portion. In that case the infeed pipes are connected to the lower portion, while the plate member extends to the upper portion.

A method for reducing froth and air fed to a feedwell in a thickener/clarifier comprises, in accordance with the present invention, (a) disposing, in a feed channel or launder header, a plate member in a position and orientation for separating froth from an incoming slurry stream, (b) attaching the plate member in the position to the feed channel or launder header, and (c) diverting froth from along an upper surface of the slurry onto the plate member, while feeding the slurry separated from the froth through the feedwell feed pipe.

The method may further comprise disposing at least one spray nozzle above the plate member, and ejecting a spray from the nozzle onto the froth on at least a portion of the plate member, thereby collapsing the froth into solids and liquid components and releasing air entrapped in the froth. The separated and collapsed froth may be guided to a feedwell body. Where the feedwell body includes a lower portion and an upper portion, the feed pipe may extend to the lower portion, while the plate member extends to the upper portion. The disposing of the plate member may include positioning the plate member so that an upstream end of the plate member is disposed at or below an operational liquid level in the feed channel or launder header and so that at least a portion of the plate member is disposed above the liquid level.

The disposing of the plate member may further include positioning the plate member so that an upstream portion is inclined upwardly from the upstream end of the plate member and a downstream portion of the plate member is inclined downwardly from a downstream end of the upstream portion.

Where the upstream portion and the downstream portion of the plate member meet along an elongate joint, the disposing of the spray nozzle may includes positioning the spray nozzle so as to enable a directing a liquid spray onto the plate member in a region about the joint.

DETAILED DESCRIPTION

As shown inFIGS. 1 and 2, a feedwell assembly12for a thickener/clarifier comprises a cylindrical feedwell body14, a pair of feed pipes16and18each connected at a downstream end to the body, the feed pipes extending from a feed launder or channel20, and a plate member22disposed at least partially upstream of the feed pipes16and18for separating froth from an incoming slurry stream guided along feed launder or channel20. A liquid spray24directed onto the plate member by one or more spray nozzles26disposed generally above the plate member can dissipate the froth separated by plate member22.

Feed pipes16and18each include an angled upstream inlet portion28and30connected to launder or channel20in a region about plate member22. Feed pipes16and18each further include a substantially horizontal inlet portion32and34connected to the respective upstream portion28and30and extending to feedwell body14. Horizontal inlet portions32and34are connected to feedwell body14on opposite sides thereof and at staggered elevations, so that slurry enters the feedwell body14from feed pipes16and18traveling in opposed circumferential directions in vertically spaced planes P1and P2.

Feedwell assembly12further includes a triumvirate of flocculent feed pipes36,38,40extending from a vertical manifold pipe42inwardly to feedwell body14along a common plane P3sandwiched between slurry infeed planes P1and P2.

Plate member22includes an upstream portion44inclined upwardly from an upstream end of the plate member and further includes a downstream portion46inclined downwardly from an elongate linear joint48at a downstream end of upstream portion44. Upstream portion44and downstream portion46take the particular form of planar plate sections. Spray nozzles26are disposed so as to direct liquid spray onto plate member22in a region about joint48.

Accordingly, infeed pipes16and18are connected at downstream ends to feedwell body14at locations spaced longitudinally and circumferentially along the body. Plate member22is more particularly located in a launder header50, the infeed pipes16and18being connected at upstream ends to the header. Plate member22is disposed in header50so that an upstream end of the plate member is disposed at or below an operational liquid level52in the header and so that at least a portion of the plate member is disposed above the liquid level. Spray nozzles26are disposed for directing a liquid spray onto that portion of plate member22above the liquid level52to knock down or dissipate froth thereon.

Feedwell body14includes a lower portion66and an upper portion68. Upper portion68has a transverse dimension or diameter that is larger than the corresponding transverse dimension or diameter of lower portion66, with an annular inclined shelf70being provided between an outer wall (not separately designated) of upper portion68and an outer wall (not separately designated) of lower portion66. This allows volume for the froth to accumulate in the feedwell14so as to allow time for the froth to dissipate naturally or with sprays so as to keep the froth from escaping to the overflow. The expanded area of upper portion68provides a containment area (size can be designed based on perception of the problem) where froth can be accumulated and knocked down as required. The froth solids that leave this zone pass through the floc addition zone where they have an opportunity to be flocculated to further enhance their settling. This expanded zone with or without sprays is optional.

Infeed pipe sections32and34are connected to lower feedwell body portion66, while downstream portion46of plate member22extends to upper feedwell body portion68.

A related method for reducing froth and air fed to a feedwell in a thickener/clarifier comprises providing plate member22and disposing the plate member in feed launder or channel20or launder header50at least partially upstream of one or more feedwell feed pipes16and18in a position and orientation for separating froth from an incoming slurry stream. Plate member22is attached in that position to feed launder or channel20or launder header50, spray nozzle(s)26being positioned above the plate member, particularly in an exposed region of the plate member. During operation of the feedwell assembly12(and the associated thickener/clarifier), slurry is directed into feed launder or channel20and, optionally, launder header50so that froth along an upper surface of the slurry is guided onto plate member22. A spray is ejected from nozzle(s)26onto the froth on plate member22, thereby collapsing the froth into solids and liquid components and releasing air entrapped in the froth. The slurry is fed in together with the solids and liquid components of the collapsed froth through the one or more feedwell feed pipes16and18.

Plate member22is positioned so that an upstream end of the plate member is disposed at or below an operational liquid level52in the feed launder or channel20or launder header50and so that at least a portion of the plate member is disposed above the liquid level. Plate member22is preferably positioned so that upstream portion44is inclined upwardly from the upstream end of the plate member and a downstream portion46of the plate member is inclined downwardly from a downstream end of the upstream portion.

Where upstream portion44and downstream portion46of plate member22meet along elongate joint48, spray nozzle(s)26may be positioned so as to enable a directing a liquid spray onto the plate member in a region about the joint.

Launder or channel20is connected to header50along a joint54by a plurality of bolts and nuts56. Launder or channel20is suspended from bridge girders58and60by cross support angles62and threaded rods64.

As depicted inFIGS. 3-5, another feedwell assembly72for a thickener/clarifier comprises a cylindrical feedwell body74and a pair of eductor feed channels76and78each connected at a downstream end to the feedwell body. Feed channels76and78include open-top inlet port sections80and82having converging walls (not separately designated), open-top middle sections84and86of reduced and uniform transverse cross-sectional area, and outlet or discharge sections88and90of diverging walls (not separately designated) and concomitantly increasing cross-sectional area.

Directional nozzles92and94of thickener feed pipes96and98are disposed at least partially within inlet port sections80and82of eductor feed channels76and78. Feed channels76and78are located below the liquid level of the clarifier tank (not shown) so that liquid at the top of the clarifier tank is entrained to flow with the thickener feed stream through eductor feed channels76and78into feedwell body74. As described in U.S. Pat. No. 5,389,250, eductor feed channels76and78function as jet pumps to educt previously clarified liquor from the clarifier tank of settling basin to dilute the influent feed stream.

As depicted inFIGS. 4 and 5, middle sections84and86of eductor feed channels76and78are oriented substantially horizontally, whereas outlet or discharge sections88and90are downwardly inclined and are provided at their downstream ends with horizontally oriented end portions100and102that are coupled to feedwell body74and serve as inlets thereto. Inlet portions100and102are connected to feedwell body74at staggered elevations, inlet portion102being located below inlet portion100, so that slurry enters the feedwell body74from feed channels76and78traveling in opposed circumferential directions in vertically spaced planes P4and P5. In accommodating the different vertical heights of eductor end portions100and102, middle section84of eductor feed channel76is longer than middle section86of eductor feed channel78, and discharge section90is longer than discharge section88.

Eductor feed channels76and78are provided with respective froth-separation plates104and106disposed at least partially upstream of inclined discharge sections88and90for separating froth from incoming slurry (diluted thickener) streams guided along middle sections84and86of the eductor feed channels. Nozzles (not shown) may direct liquid spray onto plates104and106for dissipating the froth separated from the slurry streams by the plate members.

Froth separation plates104and106each include a respective upwardly inclined upstream section108and110and a respective downwardly inclined downstream section112and114. Spray nozzles (not shown) may be provided in zones generally above linear joints116and118between upwardly inclined upstream plate sections108and110, on the one side, and downwardly inclined downstream plate sections112and114, on the other side. Downwardly inclined downstream plate sections112and114extend to respective froth inlets120and122to feedwell body74.

At points below upwardly inclined upstream plate sections108and110discharge sections88and90of eductor feed channels76and78have closed upper ends so as to deflect the slurry or diluted thickener streams downwardly towards inlet portions100and102.

Feedwell assembly72further includes (A) a first flocculent feed pipe124extending to inlet port sections80and82of eductor feed channels76and78, (B) a second flocculent feed pipe126extending to middle sections84and86of eductor feed channels76and78, (C) a third flocculent feed pipe128extending to feedwell body74, and (D) a fourth flocculent feed pipe130extending to a clarifier feed pipe132. As shown inFIG. 4, clarifier feed pipe132extends to a clarifier inlet port134on feedwell body74.

Eductor feed channels76and78are connected at downstream ends to feedwell body74at locations spaced longitudinally and circumferentially along the body. Froth separation plates104and106are disposed in feed channels76and78so that upstream edges of the plates are disposed at or below operational liquid levels (slurry-froth interfaces) in the feed channels and so that at least a portion of each plate member104and106is disposed above the respective liquid level.

A method related to the apparatus ofFIGS. 3-5for reducing froth and air fed to feedwell72in a thickener/clarifier (not shown) comprises providing plates104and106and disposing the plates in feed channels76and78in positions and orientations for separating froth from incoming slurry streams. Plate104and106are attached in that position to channels76and78, spray nozzles being positioned above the plates, particularly in exposed regions of plates. During operation of the feedwell assembly72(and the associated thickener/clarifier), thickener is introduced into inlet ports80and82from feed pipes96and98and accelerated along middle channel sections84and86so that froth along upper surface of the slurry streams is guided onto plates104and106. A spray is ejected from nozzles (not shown) onto the froth on plates104and106, thereby collapsing the froth into solids and liquid components and releasing air entrapped in the froth. The slurry is fed in together with the solids and liquid components of the collapsed froth through the discharge sections88and90of feed channels76and78.

It is to be noted that a froth separation and dissipation plate member as disclosed herein may be horizontal, multi-angled, and/or variously inclined upwardly or downwardly at any number of different angles relative to the horizontal. In addition, the plate member may be adjustably mounted both to enable variation in the angle of inclination, as well as variation in the height or vertical location of the leading edge of the plate member, for instance, to enable positioning of the leading edge precisely at the froth-liquid interface.