Gas separation: apparatus – With gas and liquid contact apparatus – Diverse means for adding liquid for gas and liquid contact
Reexamination Certificate
2003-01-27
2004-12-14
Chiesa, Richard L. (Department: 1724)
Gas separation: apparatus
With gas and liquid contact apparatus
Diverse means for adding liquid for gas and liquid contact
C095S217000, C095S219000, C096S274000, C096S326000, C261S079200, C261S112100
Reexamination Certificate
active
06830608
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to apparatus and methods for creating and maintaining controlled mass transfer, heat transfer, or chemical reactions, and more particularly to an apparatus and method for contacting industrial volumes of gas and liquid phases in close microscopic scale proximity with each other for the purpose of creating and maintaining controlled mass transfer, heat transfer, or chemical reaction to achieve a particular process.
2. Brief Description of the Prior Art
A wide variety of industrial operations depend on contacting a gas and a liquid together to achieve a process. These operations can generally be categorized by transport phenomenon where two (2) or more components in a system having a gradient will naturally equilibrate. Gradients occur in the system due to differing concentrations, temperatures, or simply by differences in energy or motion between the components being brought into contact each with the other. Where the gradient is concentration, the transport is either by molecular mass transfer or convective mass transfer or both. In the cases where there are chemical interactions between the components, the transport equilibria may or may not be over shadowed by the driving force of chemical equilibrium. In general, these complex interactions which occur by contacting gas and liquid together can be categorized by the common terms mixing, stripping, evaporation, absorption, reaction, etc.
The literature dealing with mass transfer generally suggests that molecular mass transfer by diffusion plays a significant role even in a fast moving system regardless of whether the system is chemically reactive or non-reactive. Diffusion occurs across spatially separated components due to a natural tendency to equilibrate. Depending on the system of interest, the process may be limited by the diffusivity or by time. Diffusion may be vastly improved by minimizing the spatial distance between components. Contacting large volumes of gas and liquid together in conventional equipment generally involves creating the largest amount of liquid surface area by whatever means attainable in a limited volume. The result of this approach is most often a tall tower containing either trays or packing material where the liquid is sprayed into a gas phase or the gas is bubbled into the bulk liquid phase. In either case, the spatial separation between components is improved, but the overall volume required to accomplish the contact conditions on a commercial scale can be quite large.
An obvious parameter necessary for either approach to tower design is the acceleration of the components due to earth's gravity. Tower bubble trays containing liquid rely on gravity to keep the liquid in the trays. Spray towers rely on gravity to accelerate liquid droplets downward. It is clear that neither method would work well in the absence of gravitational acceleration. For this reason and others, tower design is typically a large volume, low energy method for creating gas-liquid contactors.
Miller, U.S. Pat. Nos. 4,279,743; 4,397,741; 4,399,027; and Miller et al, U.S. Pat. Nos. 4,744,890 and 4,838,434 disclose air sparged hydrocyclone apparatus (ASH unit) primarily for use as a type of air flotation device for removing particulate matter from a liquid.
Atwood, U.S. Pat. No. 4,997,549 discloses an apparatus and method utilizing an air sparged hydrocyclone apparatus (ASH unit) for separating hydrophilic particles from a fluid suspension containing both hydrophilic and hydrophobic particles.
Grisham et al, U.S. Pat. Nos. 5,529,701; 5,531,904; 5,662,811; 5,730,875, and 6,004,386 disclose a compact, high energy apparatus and method for contacting gas and liquid (the group of patents being hereinafter referred to as the “Grisham, et al Patents”). The “Grisham, et al Patents” are based on accelerating a thin film of liquid in a helical flow pattern around and along the inside walls of a microscopically porous tube and sparging gas into the outside of the tube causing the gas to also pass through the thin liquid film. The goal central to these references is to decrease the diffusion distance between components by creating closely spaced gas bubbles in a fast moving liquid so that gas-liquid interfaces are abundantly available for mass transfer equilibrium to occur in a time as near instantaneously as is possible.
U.S. Pat. Nos. 5,529,701; 5,531,904; 5,662,811; 5,730,875, and 6,004,386, (the “Grisham, et al Patents”), in which the inventor of the present invention was also a co-inventor, are hereby incorporated by reference to the same extent as if fully set forth herein.
Cairo, Jr. et al, U.S. Pat. No. 5,591,347 discloses a simplified single cell apparatus and method for removal of suspended impurities in liquids using gas flotation and filtration. The method and apparatus are preferably directed toward induced gas flotation separation of suspended impurities in combination with a filter media for filtration removal of remaining suspended impurities. A filter media is contained within the single cell apparatus such that liquid exiting the vessel must pass through the filter media after having been subjected to flotation treatment.
A foreign treatise written on a compact, high intensity gas/liquid contactor, “Stripping Performance of a New High Intensity Gas/Liquid Contactor”, B. Waldie and W. K. Harris, Dept Mechanical and Chemical Engineering, Heriot-Watt University, Edinburgh, UK exists in the literature. A complete reference for this work is not known, but it appears to have been the culmination of a funded research supported by the UK EPSRC and several oil operating companies as part of an MTD programme on “Treatment of Water Offshore-III”. This paper deals with the comparative mass transfer performance of a laboratory device similar to both the Grisham, et al Patents” and ASH units and a small packed column. The results given were for HTU or ‘Height of Transfer Unit’ correlation whilst stripping toluene or oxygen from seawater and from fresh water. The conclusion states a 250-fold improvement in process performance of the compact device over a packed column.
In general, the prior art has taught a definite shift in thinking by the researchers and developers working in this field. The shift is recognition that liquid surface area can be increased by orders of magnitude over gravity dependent methods by containing liquid in an acceleration field and introducing gas into the acceleration field. The introduction of gas through porous media and further into the liquid provides a convenient way to control the gas bubble size by choosing beneficial porous media shape, porosity and permeability properties. It is desirable to obtain the smallest practical gas bubble size distribution flowing through a thin liquid film to achieve the largest liquid surface area per unit volume. A flat porous plate with a fast moving liquid film and introduction of gas from the underside of the plate would be a nice model to analyze mathematically, however, a cylindrical porous containment is more practical to build and offers better control over liquid film thickness and fluid dynamics in general. The result of a radial acceleration field is that it is, for all practical purposes, independent of its orientation with respect to earth's gravitational field.
The Grisham et al. patents teach a device that is generally horizontally disposed relative to earth's gravitational field. The Grisham et al. patents also teach a device that comprises at least one cylindrical porous tube that is coaxially aligned with a non-porous outer jacket, more particularly, a long porous element divided into segregated pressure chambers along the length of the porous tube. The porous element may be divided into two or more segments and mated together end to end to form a longer tube. The acceleration stated to operate the device is up to 1500 times the earth's gravitational acceleration or 32.2 ft/s
2
(g) or about 48,000 ft/s
2
or as little as 400 g or roughly 13,000 ft/s
Chiesa Richard L.
Jaeco Technology, Inc.
Roddy Kenneth A.
LandOfFree
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