Liquid purification or separation – Processes – Separating
Reexamination Certificate
2000-07-28
2001-10-23
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Separating
C210S795000, C210S274000, C210S275000, C210S293000
Reexamination Certificate
active
06306310
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to apparatus for distributing gas and liquid simultaneously from a common main conduit to filter underdrains for backwash of filter media.
2. Description of the Prior Art
In a typical gravity filter for filtering water and wastewater, one or more filter tanks are arranged in adjacent or opposing batteries. Filter underdrain laterals are laid on the floor of the filter tank one next to the other in parallel rows to define gas and liquid flow conduits below a bed of filtering media. The conduits make possible the collection of filtered liquid during filtration and the distribution of gas and liquid for backwash. A common main conduit (known as a “flume”) is located immediately next to the filter tank to collect the filtered liquid from the underdrain laterals during filtration and to distribute gas or liquid to the underdrain laterals during gas (typically air) or liquid (typically water) backwash. The common main conduit also distributes gas and liquid simultaneously to each of the underdrain laterals during concurrent gas and liquid backwash. In some installations, the common main conduit has its floor located somewhat lower than the elevation of the filter floor (see
FIG. 2
) or even on the same elevation as the filter floor (see FIG.
1
). Consulting engineers and contractors prefer these arrangements, known as “recessed flume” and “flat bottom flume”, because they are easier and cheaper to install. In retrofitting old filters with new underdrains, it is preferable to maintain the existing flume structure to reduce costs.
The interface of gas and liquid in the underdrain laterals during concurrent gas and liquid backwash is only a few inches above the filter floor. The interface of gas and liquid in the common main conduit at this time would be even lower than that inside the laterals due to friction loss through the wall sleeves. The wall sleeves connect the common main conduit to the underdrain laterals. There is, therefore, practically no room in flat bottom flumes and insufficient room in some recessed flumes for distribution of liquid to the underdrain laterals during concurrent gas and liquid backwash. In these cases, the air space is disproportionately large in the common main conduit.
In order to provide near uniform distribution of liquid to the underdrain laterals, the maximum flow velocity of liquid inside the common main conduit should be limited to two feet per second or lower. Generally, the smaller the cross-sectional area for the flow path of liquid, the greater the velocity. Since the floor of the conduit is on the same elevation as the filter floor in flat bottom flumes, and the floor of some flumes may be insufficiently recessed, the only way to provide a greater cross-sectional area for the flow of liquid to keep maximum velocity at less than two feet per second is to raise the interface of gas and liquid from the floor or deepen the flume recess. If the flume is insufficiently recessed, as shown in
FIGS. 8 and 9
, passage for the gas to the underdrain laterals may be blocked by the liquid during concurrent gas/liquid backwash.
The alternatives are to provide adequate room below the interface of gas and liquid inside the common main conduit by lowering the floor elevation for liquid distribution (see FIG.
3
), or by providing separate means for the controlled conveyance and distribution of gas and liquid (see
FIGS. 4
,
5
,
6
and
7
).
In the case of
FIG. 3
, extra excavation, form work and concrete structural work are required. This is very expensive for both retrofit jobs and new construction. In addition, baffles or individual wall sleeves with lateral inlet elbows are required to direct liquid to the laterals. In the case of
FIGS. 4
,
5
,
6
and
7
, a stainless steel gas header with tubular branches to each individual underdrain lateral is very expensive to fabricate and install. The individual gas tubes from the gas header to each underdrain lateral, shown in
FIGS. 6 and 7
, may cause cross connection problems between unfiltered and filtered water if leaks occur, since the individual tubing must go through the filter media bed.
It is, therefore, an object of this invention to create more room inside the common main conduit by raising the interface of gas and liquid in a unique manner during concurrent gas and liquid backwash, while at the same time providing clear passages inside the common main conduit for gas flow to the underdrain laterals. This is to be accomplished without raising the overall dynamic pressure within the backwash system.
SUMMARY OF THE INVENTION
Accordingly, there is provided a concurrent backwash distribution apparatus for a filter having a filter tank. The filter tank may have a plurality of underdrain laterals positioned in the filter tank and a filter media bed positioned above the underdrain laterals. A common main conduit (or “flume”) is positioned adjacent the filter tank and in fluid communication with the filter tank. A floor of the filter tank is somewhat above the floor of the common main conduit, or has the same elevation as the floor of the common main conduit.
The concurrent backwash distribution apparatus comprises a separator device positioned in the common main conduit so that it defines an auxiliary flume between the separator device and the filter tank. The auxiliary flume is in fluid communication with the common main conduit and the filter tank. The separator device has at least one flume liquid metering orifice.
A flow distribution plate may be positioned between the auxiliary flume and underdrain laterals in the filter tank, the flow distribution plate having at least one lateral liquid metering orifice and at least one gas metering orifice. The lateral liquid metering orifice may be contiguous with its corresponding gas metering orifice forming an inverted T-shape, or other shapes or configurations.
The separator device may be a baffle which preferably extends to a height which is less than a height of the common main conduit to define a clearance above the baffle. The flume liquid metering orifice is preferably positioned in a lower part of the separator device, but can be positioned at any appropriate location in the separator device according to the particular design of the common main conduit and the filter tank with which it is connected.
The apparatus may include a filter tank wall separating the auxiliary flume and the filter tank, the filter tank wall having at least one opening therein for fluidly connecting the auxiliary flume with the filter tank. The flow distribution plate may be positioned between the filter tank wall and laterals in the filter tank. The opening in the filter tank wall is preferably sufficiently large to provide passage of both gas and liquid therethrough during concurrent gas/liquid backwash operations.
The baffle may be an upstanding partition positioned in the main conduit and spaced from a sidewall thereof. Alternatively, the baffle may be an inverted L-shaped partition, having a vertical portion and an upper horizontal portion. The upper horizontal portion has a plurality of openings therein to facilitate gas flow and excess fluid flow. Further possible alternatives include an L-shaped baffle and a crescent-shaped baffle.
As an alternate to the baffles, a stand-pipe can also be provided for each lateral. The liquid metering orifices can be provided at appropriate locations on the stand-pipes to meter liquid flow from the flume to the stand-pipe during gas/liquid concurrent backwash.
The invention also includes a method of introducing a backwash gas and a backwash liquid to a filter having a filter tank. Particularly, the method includes concurrently introducing the backwash gas and backwash liquid into an enclosed flume positioned adjacent the filter tank. A first gas/liquid interface is established in the enclosed flume, and backwash liquid is then passed through a stand-pipe positioned in the enclosed flume, with the backwash liquid passing through at least one flume liquid meteri
Bergmann Eugen O.
Geibel John
Hsieh Richard W.
Barry Chester T.
The F. B. Leopold Company, Inc.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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