Chemineer™ CD-6 Concave Disc Impeller The Chemineer Concave Disc (CD-6) impeller is revolutionizing the field of agitated gas dispersion. In applications of high energy agitation and high gas rates, this impeller will significantly improve the mass transfer factor, k La. Given the same conditions of power per volume and superficial gas velocity, mass transfer factors can nearly double when the CD-6 impeller is used instead of the conventional flat blade disc impeller. In addition to significantly improving mass transfer factors, the CD-6 impeller will handle at least 46% more gas before flooding than the flat blade disc impeller. This capability gives added benefit in operations where upset conditions could otherwise flood the flat blade disc style impeller. Most applications designed with the CD-6 impeller also use our HE-3 or XE-3 high efficiency impeller for pumping within the vessel. This configuration utilizes a combination of impellers; the bottom impeller is the CD-6 and the upper impellers, at times as many as four, are HE-3s or XE-3s. The CD-6 accomplishes the primary dispersion while the HE-3 or XE-3 high efficiency impeller provides good overall top to bottom flow and rapid blend times. In applications such as Fermentation, this combination results in uniform dissolved oxygen distribution within the fermenter and shorter blend times for additives. The CD-6 impeller improves the mass transfer rate as much as 50% in gas dispersion operations. Impeller Development The original concave blade concept was developed in the 1970s at Delft University by a group led by John M. Smith. Independent testing has been done over the past decade by private research groups and the findings have confirmed that at the high end of gas flow rates and agitator energy density, the concave blade disc impeller can show dramatic improvements in mass transfer factors over the standard flat blade disc design. The CD-6 impeller was developed by Chemineer as a result of our extensive study of this concept. Parameters which affect power draw, pumping capacity, etc., were investigated thoroughly in addition to the mass transfer characteristics. Testing was done using two different configurations: the CD-6 alone and combined with the HE-3 high efficiency impeller in the upper positions. The testing was done in a clean water mass transfer testing facility in our laboratory. Data collection and analysis was facilitated by a computer based data acquisition system. Laboratory testing under fixed conditions, however, may not always be a true representation of actual operating conditions. We have verified our laboratory testing by many field proven installations. Our industrial experience includes dozens of installations utilizing the CD-6 impeller in gas dispersion operations, including applications to 1000 horsepower. These installations have confirmed power draws predicted during gassing and have demonstrated improved mass transfer rates by as much as 50% over the flat blade disc impeller.

Mass Transfer Advantage of a CD-6 Impeller Process Performance Fundamentally, the mass transfer rate, normally expressed in engineering terms, is the product of the mass transfer coefficient, the interfacial area per unit volume of liquid and the mean gas concentration deficit. In agitated gas dispersion, the mass transfer factor, kLa, has been correlated against mixer inputted power per unit volume and superficial gas velocity: kLa = (P/V)b(Vsg)c where P/V = power per unity volume Vsg = superficial gas velocity The degree of mass transfer is directly proportional to the mass transfer factor,...