Agitating – Stirrer within stationary mixing chamber – Pump type
Reexamination Certificate
1998-10-01
2001-06-26
Cooley, Charles E. (Department: 1723)
Agitating
Stirrer within stationary mixing chamber
Pump type
C366S328100, C366S330200, C366S330300, C261S093000, C416S23100A, C416S235000
Reexamination Certificate
active
06250797
ABSTRACT:
The present invention relates to mixing impeller systems, and particularly to axial flow impeller systems.
The invention is especially suitable for providing stirred reactors for gas-to-liquid or liquid-to-liquid dispersion and mass transfer by providing impeller blades which establish clashing or interfering flows of the fluid being pumped with the other fluid (gas or liquid) which is being dispersed or mass transferred into the fluid being pumped. The invention also provides a multiple axial flow impeller system having a series of sparges which introduce the fluid (gas or liquid) being sparged which is delivered to each impeller. The invention is also especially suitable for use in large axial flow impeller systems wherein the impellers are of a size commensurate with the diameter of the tank or the zone between the baffles in the tank in which the impellers rotate or where the tank has limited access, for example, through a manway of size less than the diameter of an impeller or even the width or length of an impeller blade. The blades can be assembled from segments smaller than the diameter of the zones, tanks or size of the manways in the tank. The segments may be assembled leaving gaps which provide flow paths for improving gas dispersion and mass transfer.
Accordingly, it is a feature of the invention to provide improved mixing impeller or agitator system for dispersion and mass transfer in gas-liquid or liquid-liquid systems, also known as stirred reactor systems, wherein bubble growth is controlled thereby improving the performance of the systems and the efficiency of mass transfer, as well as the reduction of undesirable forces and movement of the rotating mechanism which may cause mechanical failures. The growth of bubbles of viscous liquid, especially of viscosity higher than water is inhibited in an impeller system provided in accordance with this feature of the invention.
Another feature of the invention is to provide an improved impeller system which enables use of impellers with large blades, especially impellers for producing axial flow. By large blade is meant a blade which is difficult to install because the size thereof, when assembled into an impeller having a plurality of blades, especially when the assembled impeller is of a diameter commensurate with the diameter of the tank or the zone of the tank in which the impeller is installed. The invention facilitates the installation of large impellers or the replacement of blades or the retrofit of the impellers, for example impellers are the order of 5 to 20 feet in diameter. Many stirred reactors have entrances (called manways) into the tank which do not pass large impeller blades or in which installation and repair or retrofit is difficult due to the space constraints imposed by the size of the tank. The blades may be assembled from segments which can be spaced apart to provide the flow passages for enhanced fluid dispersion for gas-to-liquid and liquid-to-liquid mass transfer. The blade segments are desirably connected at the hub but can be connected at the blade tips, if strengthening is desired.
BACKGROUND OF THE INVENTION
Air moving propellers and turbines have been provided with slots through the blades thereof or assembled with overlapping blades in close proximity. These slots may be formed as scoops to enhance rather than disrupt the flow on the concave or suction side of the propeller or turbine blades to prevent flow separation (sometimes called cavitation). Such propellers or turbines are not used in gas-to-liquid or liquid-to-liquid mass transfer applications. The flow patterns introduced by the slots or gaps in impeller blades provided by the invention are effective to break up bubbles which tend to grow due to the coalescing of the gas or liquid being dispersed on the suction side of the blades thereby enhancing the efficiency of mass transfer and the mass transfer coefficient kLa of the mass transfer process. Propellers, turbines and blades with slots designed to prevent flow separation on the suction side of the blades and multi-blade designs are shown, for example in the following patents: Faber, U.S. Pat. No. 2,003,073, May 28, 1935; Chajmik, U.S. Pat. No. 3,044,559, Jul. 17, 1962; Sheets, U.S. Pat. No. 3,195,807, Jul. 20, 1965; Schaw, U.S. Pat. No. 4,102,600, Jul. 25, 1978; Levin, et al., U.S. Pat. No. 4,130,381, Dec. 19, 1978; Thompson, U.S. Pat. No. 4,285,637, Aug. 25, 1981; Zeides, U.S. Pat. No. 4,636,143, Jan. 13, 1987; Spranger, U.S. Pat. No. 4,913,670, Apr. 3, 1990; Schindling, DE 182,680, Mar. 26, 1907; and a slotted scimitar shaped blade known as the Velmix which has curved slots spaced inwardly from the tips of the blades.
SUMMARY OF THE INVENTION
Accordingly, it is the principal object of the present invention to provide improved mixing impeller systems.
It is a still further object of the present invention to provide improve stirred reactor processes using mixing impellers to disperse and provide mass transfer of a first fluid into a second fluid (gas-to-liquid or liquid-to-liquid) which utilizes axial flow impellers.
It is a still further object of the present invention to provide an improved impeller system having blades assembled from segments which may access the tanks of mixing systems and mixing reactors without interference due to the constraints imposed by tank or manway size, thereby facilitating the installation, replacement or retrofit of impellers having large blades.
It is a still further object of the present invention to provide an improved mixing impeller system wherein gas may be introduced in sparging stages below and between the impellers of the system, thereby enhancing the efficiency of operation of the system.
Briefly, the invention provides a system (method and apparatus) for mass transfer of a first fluid into a second fluid having less density or more viscosity than the first fluid, where the second fluid is released into a tank containing the first fluid from a source thereof or because of a chemical reaction in the tank. The fluids are agitated with an axial flow impeller having a plurality of blades. The blades have suction and pressure sides and tips at the radially outward ends thereof. The size of bubbles on the suction side of the blades are reduced by providing flow pathways for the second fluid through the blades. The pathways extend inwardly from the tips of the blades, and can be generally perpendicular to the suction sides. The pathways can be provided by slots extending from or adjacent to the tips generally radially inward of the blades. The blades may be provided by segments which are assembled to a hub on the shaft which rotates the impeller so as to provide gaps extending generally radially inward from the tips of the blades. The segments may have widths of one-third of one-half the diameter of the impeller, or in any event, sufficient to readily access the tank via a manway or other entryway. The segments may be assembled in the tank and can be butted against each other if flow passways are not needed for the process being carried out in the tank. A multi-impeller system in accordance with the invention has axial flow impellers which are spaced from each other and from the bottom of the tank. Piping is introduced between the lower most impeller and the bottom of the tank and between adjacent impellers to sparge the fluid being dispersed and mixed in a series of stages. The pressure for the lower most sparge piping may be higher than the pressure to the upper sparges, but sufficient to overcome the head in the tank where the sparges are disposed.
The foregoing and other objects, features and advantages of the invention, as well as presently preferred embodiments and the best mode now known for carrying out the invention will become more apparent from a reading of the following description in connection with the drawings, brief descriptions of which are as follows:
REFERENCES:
patent: 285212 (1883-09-01), Bell et al.
patent: 1135829 (1915-04-01), Macdonald
patent: 2003073 (1935-05-01), Faber
patent: 2045918 (1936-06-01), Moody
patent:
Cooley Charles E.
General Signal Corporation
Pepper Hamilton LLP
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