Chemistry: molecular biology and microbiology – Process of utilizing an enzyme or micro-organism to destroy... – Treating gas – emulsion – or foam
Reexamination Certificate
1999-08-05
2001-06-12
Beisner, William H. (Department: 1744)
Chemistry: molecular biology and microbiology
Process of utilizing an enzyme or micro-organism to destroy...
Treating gas, emulsion, or foam
C435S300100, C435S301100, C422S004000, C055S385400, C096S218000, C095S161000, C095S174000, C095S266000
Reexamination Certificate
active
06245553
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to treatment of liquids and gases, and in particular to control of odor and emissions in a contained system.
BACKGROUND OF THE INVENTION
Waste-treatment systems may operate over a wide area, drawing sewage from numerous collection points to one or more central facilities for treatment. Offensive and even toxic gaseous emissions may be generated throughout the system wherever complete containment is impossible. For example, typical municipal waste-treatment systems utilize gravity flow to transport sewage to the central facility. In systems that serve even moderately sized areas, it is impractical to conduct waste along a single stretch of conduit from the most remote collection point to the treatment center; the declivity between end points of the conduit that would be necessary to maintain adequate flow would be too great (requiring, for example, locating the discharge point at the treatment center many feet underground). Instead, the sewage path is divided into segments short enough to require only a few feet of incline. Between segments, “lift stations” increase the height of the flowing material so that the declivity between stations can be roughly the same.
A lift station may be visualized as a large containment vessel within which the volume of liquid is periodically changed. Gas dissolved or generated in the liquid as well as vapor from the liquid rise from its surface within the vessel, and as the liquid level rises, the effect is like that of a piston: the gas is compressed and vessel pressure increases. To avoid damage to such vessels, which ordinarily cannot tolerate large pressures, some of the gas must be discharged. Odor control is therefore important. Typical systems employ filters, scrubbers, oxidation systems, and/or biosystems that reduce the concentration of offensive or environmentally deleterious material in the gas. See, e.g., U.S. Pat. No. 5,354,545. Such systems may be complex and require high throughput capacity to efficiently process large volumes of gas discharged as the liquid level rises in the vessel.
The problem of odor containment is not restricted to systems in which liquid levels vary. In waste-digestion systems, for example, internal pressure may increase as a result of the biological processes utilized to treat the waste, which create gaseous byproducts. The volumes of gas generated may vary substantially over the treatment cycle, necessitating frequent venting and, as a result, the use of filtration systems capable of processing the peak levels in order to maintain constant internal pressure.
DESCRIPTION OF THE INVENTION
Brief Summary of The Invention
In accordance with the present invention, the need for gas filtration is reduced or eliminated by maintaining, within a containment vessel, conditions that concentrate most of the gaseous contaminants away from the vessel exits. In one embodiment, this is achieved by continuously heating and humidifying gas drawn from the region near its source (typically the surface of the liquid in the vessel) and discharging the hot, moist gas to another region of the vessel—usually nearer the vents. The discharged gas already has a reduced density and therefore a lower contaminant concentration relative to the source gas. In the general area of the discharge, the concentration decreases further as convection draws the discharged gas back to its source. So long as the gas flows within the containment vessel are non-turbulent, this concentration gradient remains substantially static, and the vents remain exposed only to low concentrations of contaminants.
In a second embodiment, the amount of gas in the containment vessel is reduced in molar amount prior to being re-introduced. This may be accomplished by reacting the gas with a catalyst or otherwise causing constituents thereof to assume solid or liquid form, or by causing gaseous constituents to react with one another so as to reduce the molar amount of gas, or by a combination of these techniques. Once again, a concentration gradient is established between the regions of gas withdrawal and re-introduction, and non-turbulent gas flows ensure that this concentration gradient remains substantially static.
In accordance with either embodiment, the amount of gas that must be actively withdrawn from the system is limited. Even in a variable-volume system, such as a lift station, it is generally unnecessary to process gaseous volumes equivalent to all of the discharged gas. Instead, moderate increases in liquid levels that do not create gas turbulence will not substantially degrade the quality of the air at the vents, since the additional discharged air still arrives from the low-concentration side of the gradient. Continuous, low-volume processing in effect creates a largely static internal environment that obviates or at least reduces the need for outflow processing.
Accordingly, in a first aspect, the invention comprises a method of limiting gaseous emissions from a containment vessel. Gas is withdrawn from a first location within the containment vessel, and the withdrawn gas is heated and moistened, caused to react so as to decrease in molar volume, or both. At least a fraction of the treated gas is returned into the containment vessel at a second location therein. The withdrawal and return of gas are preferably conducted so as to create a substantially unchanging gas-concentration gradient between the first and second locations. In some embodiments, an external arrangement recirculates heated liquid past a gas venturi which is fluidly coupled to the containment vessel and provides the suction to withdraw gas therefrom. The gas enters the recirculating liquid stream and is returned with vapor derived from the stream. Alternatively, the gas may be heated and moistened by a humidifier arrangement contained entirely within the vessel.
In accordance with the second embodiment, the withdrawn gas may be treated to deplete, reduce, or chemically modify constituents thereof. For example, the recirculating liquid in the just-described venturi arrangement may be charged with digestive microorganisms or an abiotic catalyst, so that the vapor derived from the liquid has a reduced concentration of undesirable constituents. It should be noted that the catalyzed reaction need not be limited to the undesirable gaseous components. If any of the components of the withdrawn gas are reduced in molar amount (e.g., sequestered from gas phase entirely by conversion to liquids and/or solids) or reactively combined such that the molar volume of returned gas is less than that withdrawn, a concentration gradient will result; the site of gas re-introduction is chosen such that this gradient places cleaner air near points of possible emission from the vessel. Moreover, if the level of the liquid in the vessel is not rising, the gradient will cause clean air to be drawn into the containment vessel from the external environment, precluding emissions from the vessel. As with the first embodiment, gas processing can take place externally or within the vessel.
In a second aspect, the invention comprises hardware arrangements for accomplishing the foregoing methods.
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Beisner William H.
Testa Hurwitz & Thibeault LLP
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