Liquid purification or separation – Diverse distinct separators – Including a filter
Reexamination Certificate
2001-10-15
2004-05-04
Reifsnyder, David A. (Department: 1723)
Liquid purification or separation
Diverse distinct separators
Including a filter
C210S295000, C210S512100, C210S513000, C210S532100, C210S538000
Reexamination Certificate
active
06730222
ABSTRACT:
This invention relates to a hydrodynamic vortex separator, and is particularly concerned with such a separator for use in separating floatable matter, such as grease, from a liquid flow which comprises the floatable matter. The invention also relates to a separator for separating from each other, and from the liquid stream in which they are present, a settleable material and a floatable material such as grit and grease present in a waste water stream. Also disclosed herein is a new inlet arrangement for a hydro-dynamic separator.
Hydrodynamic vortex separators are well known and are based on initial research work carried out in the 1950's and 1960's (
Design, Construction and performance of vortex overflows
, Bernard Smisson, Symposium on Storm Sewage Overflows, Institution of Civil Engineers, 1967, pages 99-110). They have found application as combined sewer overflows (CSOs) and as grit separators.
Separators known as “Hydro-Dynamic” separators are low energy devices which operate on the principle of allowing a liquid containing suspended solid material to rotate in a cylindrical vessel so that the solid material falls under gravity to the base and there is swept to a central lower outlet by an inward sweeping effect caused by complex flow patterns in the device. It is known that the device is suitable for providing enhanced settlement of solids material from a liquid/solid mixture. Thus, such devices have been used in sewage treatment for separating hard grit from the incoming raw sewage, with the resultant degritted sewage then being passed to a conventional sewage treatment plant. They are also used as “storm water overflows” upstream of conventional sewage treatment works to ensure that gross contamination is separated from liquid waste during storm conditions when the sewage treatment works is unable to cope with the high flow. “Hydro-Dynamic” separators of this type are described and claimed in, for instance, British Patent Specifications Nos. 2082941 (corresponding to U.S. Pat. No. 4,451,366) and 2,158,741 (corresponding to U.S. Pat. No. 4,747,962).
The known hydro-dynamic separator is a simple device with no moving parts. The simple geometry of the device however, hides an internal complexity of flow structure. The mean flow pattern observed is a downward helical flow in the outer region and an upward helical flow near the central region of the separator. These two spiral flow regimes are separated by a shear zone region. The combination of underflow and overflow leads to a non-uniform axial flow profile. The effects of fluid viscosity, boundary layers and momentum transfer between adjacent zones of flow moving at different velocities, cause velocity gradients and vorticity (rotation) to be present. These result in a secondary flow, superimposed on the primary flow, which in turn results in solids being swept towards the underflow channel (or solids collection trough/hopper). The hydraulic regime in the separator ensures very little short-circuiting with a near plug-flow type flow regime.
As discussed above, the principle of hydrodynamic separation has heretofore been used to facilitate the separation of settleable material (i.e. material which tends to settle under the action of gravity) from a liquid flow. It has now surprisingly been found that this same principle may be used for the separation of a floatable material from a liquid flow. Put simply, this is achieved by arranging the elements of the known hydrodynamic separator in the opposite orientation. Surprisingly, the flows generated in use act to concentrate floatable solid matter, which naturally rises in the vessel as a result of its buoyancy, at a central upper region where it can be directed away from the normal flow of liquid through the vessel, and collected for disposal.
Thus, according to a first aspect of the present invention, there is provided a hydrodynamic separator for the treatment of a liquid flow containing floatable material to separate the floatable material from the liquid containing it, said separator comprising a separating vessel having:
a cylindrical outer wall;
an inlet means for introducing said liquid into the vessel in a manner to promote a rotational flow of liquid in the vessel;
a base at one end;
an upper wall at the end opposite the base, the upper wall including an axial outlet opening for receiving a flow containing floatable material separated from the liquid flow to the vessel; and
an outlet means, separate from the outlet opening in the upper wall, comprising a conduit for removing a primary liquid flow from the vessel, which conduit communicates with the interior of the vessel at a substantially axial location between the base and the upper wall.
The separator of the first aspect of this invention may further include an annular dip-plate spaced from the outer wall of the vessel. The dip plate helps in stabilising the flows in the vessel and in particular delimits an outer faster moving flow and an inner slower moving flow. The precise radial position of the dip plate may be chosen to give the optimum performance for a given design of separator, depending on the likely character of the liquid flow to the vessel. Normally, the annular dip plate will be located between about 0.2 and 0.8 of the distance between the axis of the vessel and the outer wall. The height of the dip plate is not critical. In some embodiments it will be relatively shallow in height relative to the height of the vessel; in other embodiments, however, it may be quite deep. Normally, the dip plate will be of a height which is at least the height of the inlet opening into the vessel and normally it will at least partially overlap the inlet opening in the vertical direction.
The separator of this aspect of the invention may also comprise a flow-modifying member provided within the vessel to define with the top wall an annular opening which is spaced from the outer wall. The axial outlet in the top wall referred to above opens inward of the said annular opening. The said flow modifying member body may be generally conical in form with its base uppermost, and aligned about the central axis of the vessel; the cone may be hollow or solid and may be provided with a central opening extending through the cone and aligned with its axis. In preferred embodiments, the cone is frusto-conical, that is to say with a truncation plane parallel to the base.
The upper wall preferably slopes upwardly towards the annular opening at its central region. The annular opening should preferably be positioned between about 0.2 and 0.8 times the radius of the vessel, more preferably between about 0.4 and 0.6 times the radius of the vessel from the central vertical axis.
The axial outlet opening in the upper wall may communicate with a chamber above the vessel, for collecting floatable matter. This chamber may include an outlet means whereby said floatable matter may be removed. Alternatively, the axial outlet opening may communicate directly with a suitable conduit whereby the floatable matter may be continuously directed away from the separator.
The base of the vessel preferably slopes downwards towards the central axis of the vessel. The base may include an axial outlet opening inward of the annular opening for receiving a flow containing settleable matter separated from the liquid flow to the vessel. This outlet opening may communicate with a chamber or sump which is itself provided with a outlet via which settled matter may be conveyed away from the vessel.
With a separating device having the features specified, when a liquid containing floatable matter is introduced in the vessel and caused to circulate about the vertical axis of the vessel, a complex flow pattern is established which gives rise to an efficient separation of floatable matter. The complex flow patterns established can be simplified and expressed as a circulating flow about the central vertical axis of the vessel, the circulating flow being divided between an outer, relatively fast flow and an inner relatively slow flow, the shear zone between these tw
Andoh Robert Yaw Gyamfi
Faram Mike
Le-Cornu Paul
Hydro International PLC
Petry Marvin
Reifsnyder David A.
Stites & Harbison PLLC
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