Gas and liquid contact apparatus – Fluid distribution – Pumping
Reexamination Certificate
1999-05-10
2001-04-03
Bushey, C. Scott (Department: 1724)
Gas and liquid contact apparatus
Fluid distribution
Pumping
C261S037000, C261S122100, C210S150000
Reexamination Certificate
active
06209855
ABSTRACT:
This invention relates to a gas/liquid mixing apparatus and method.
BACKGROUND OF THE INVENTION
The use of hollow, microporous fibers for the aeration of waste water containing organic pollutants was proposed many years ago, see for example U.S. Pat. No. 4,181,604, dated Jan. 1, 1980, H. Onishi et al.
More recently, it has been proposed to transfer gas to a liquid in a bubbleless manner using hollow, microporous fibers, see for example U.S. Pat. No. 5,034,164, dated Jul. 23, 1991, M. J. Semmens. The bubbleless transfer of gas into the liquid is highly efficient and reduces the loss or waste of gas significantly. Semmens (column 5, lines 27 to 48) teaches the use of a thin, smooth, chemically resistant, non-porous, gas permeable polymer coating on the exterior surface of a major portion of each fiber to inhibit the accumulation of debris and microorganism which tend to clog the surface through which the gas diffuses under high pressures of 20 to 60 psi on the interior of the fibers, while achieving higher gas transfer rates and preventing the loss of gas in bubbles. Semmens further states that if the fibers are uncoated, the pressure differential, that is, the pressure of the gas in excess of that of the liquid, has to be below 2 psi. To avoid bubbles. However, Semmens (column 4, lines 39 to 42) states that generally speaking a gas pressure of at least 45 psi above the water will be used. Clearly, at low gas pressures where no bubbles were formed, the transfer was not considered adequate, and sufficient gas pressure was thought necessary to transfer trapped liquid out of the file membrane (see column 4, lines 34 to 36). While the device of Semmens is useful, the gas permeable polymer coating necessitates the use of elevated gas pressures, while the relatively low liquid pressures will ultimately limit the achievable dissolved gas concentration.
It has also been proposed in U.S. Pat. No. 4,950,431, dated Aug. 21, 1990, A. J. Rudick et al, to provide an apparatus, for making and dispensing carbonated water, in which CO
2
, pressurized to 31 psi, from hollow semi-permeable membrane fibers is mixed with chilled municipal water in a carbonator housing. It is stated that as long as the water pressure is equal to or greater than the CO
2
pressure inside the hollow fibers, CO
2
will be absorbed directly into the water without the formation of bubbles (column 4, lines 13 to 31). The CO
2
is provided by an input line having a spring biased spool valve which maintains the interior of the carbonator housing pressurized to the level of the CO
2
, i.e., 31 psi, and provides the driving force for dispensing the carbonated water (column 4, lines 2 to 8). Further, when the incoming water pressure is greater than 31 psi to the carbonator housing, the carbonator functions as a simple in-line continuous carbonator during a dispenser operation.
Rudick et al is concerned with producing and dispensing carbonated water which will effervesce at atmospheric pressure. Thus, while CO
2
may be aborbed directly into the water without formation of bubbles, it is necessary for the absorbed portions of CO
2
to be of sufficient size to readily coalesce and effervesce, in the manner of a carbonated beverage, when vented to atmospheric pressure by being dispensed by the Rudick et al apparatus. For this to occur, the carbonated water has to be delivered to the drinking cup in a turbulent state.
While the processes of Semmens and Rudick et al are useful, there is a need to not only further enhance the way that gas is transferred to the liquid, but also to increase the amount of gas available in the liquid by increasing the dwell or residence time during which microscopic portions of the gas remain discrete in the liquid before coalescing and exiting from the liquid in the form of bubbles.
SUMMARY OF THE INVENTION
According to the present invention there is provided a gas/liquid mixing apparatus comprising:
a) a casing having a gas inlet, a liquid inlet, and a gas/liquid mixture outlet,
b) a microporous membrane in the casing, the membrane having,
i) effective, gas/liquid contacting, pore pathway diameters generally in the range of 0.01 to 5 &mgr;m, and
ii) a side that is repellent to the liquid to be mixed,
the membrane dividing the casing interior into a liquid path, on the liquid repellent side, between the liquid inlet and gas/liquid mixture outlet, and a gas chamber from the gas inlet,
c) fluid pressure regulating means connected to the casing to regulate the gas/liquid pressure relationship therein so that,
i) the gas pressure does not exceed the liquid pressure, and
ii) pressurized liquid does not pass through the membrane micropores, and
d) a low liquid turbulence incurring, gas/liquid mixture conveying and delivering device connected to the gas/liquid mixture outlet.
In some embodiments of the present invention, a gas outlet is provided from the casing, the microporous membrane is one of a plurality of similar, microporous, hollow fibers bundled together in the casing, a first block of epoxy resin is at one end of the bundle, and seals that end of the bundle, with open ends of the fibers at that end of the bundle communicating with the gas inlet, a second block of epoxy resin is at the other end of the bundle, and seals that end of the bundle with open ends of the fibers at that end of the bundle communicating with the gas outlet, and the gas inlet and gas/liquid mixture outlet are on opposite sides of the casing for liquid to flow across substantially the whole outer surface of the fibers.
The bundle of fibers may comprise the warp of a woven, open mesh structure, and solid, water repellent fibers are provided forming the weft, and the open mesh structure is coiled to form the bundle.
The apparatus may further comprise a tank, and a pump connected to deliver liquid to the liquid inlet, and the low liquid turbulence incurring, gas/liquid mixture conveying and delivering device, is connected to the tank to gently deliver gas/liquid mixture thereto.
Preferably the membrane has a porosity of at least about 10%.
Further, according to the present invention, there is provided a method of mixing gas with a liquid, comprising:
a) bringing a liquid into contact in a casing with a mixing liquid repellent side of a microporous membrane having effective, gas/liquid contacting pore pathway diameters generally in the range 0.01 &mgr;m to 5 &mgr;m,
b) bringing a gas into contact in the casing with the opposite side of the microporous membrane to that contacted by the liquid,
c) regulating the gas/liquid pressure relationship in the casing so that,
i) the gas pressure does not exceed the liquid pressure, and
ii) liquid does not pass through the membrane micropores,
whereby discrete, microscopic portions of the gas are brought into contact with the liquid, and
d) conveying the gas/liquid mixture thus produced in a low turbulence incurring manner from the membrane to a receiving vessel therefor.
The microporous membrane may be one of a plurality of similar microporous, hollow fibers, and the gas is passed down the hollow fibers, while the liquid is passed over the liquid repellant outer side of the hollow fibers.
Gas/liquid mixture in the receiving vessel may be frozen to increase the retention time of the discrete, microscopic portions of the gas in the liquid.
Preferably the gas pressure is at least 0.07 kg/cm
2
less than that of the liquid.
Until the present invention was made, it was not possible to produce discrete, microscopic portions of the gas mixed with the liquid, which would remain stored in the liquid in the discrete form for such long periods of time as to provide a useful novel product which for example, could be used in aerobic or chemical processes to provide oxygen for hitherto unattainable lengths of time without the need of more “forced” means of aeration.
The present invention provides a novel gas/liquid mixture which, when compared to known gas/liquid mixtures, has:
a) a surprisingly greater mass of gas in a given volume of liquid, to the point of supersaturation, and
b) exhibits a vastly increas
Bushey C. Scott
Canzone Limited
Seaby George A.
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