| 摘要 |
A mixing system for dispersing gas or other fluids in liquid which may have a solid suspension so as to improve mass transfer to the liquid or its solids suspension while maintaining a flow pattern which is substantially axial (up and down) in the tank containing the liquid thereby also facilitating mixing (blending) utilizes an (unshrouded) axial flow impeller which provides the desired single stage axial flow downwardly to the bottom of the tank and upwardly along the sidewalls of the tank with radial flow confined principally to the bottom region of the tank. A sparge system which releases the gas or other fluid in the region at the bottom of the tank where the flow is predominantly radial allows attainment of gas rates with complete dispersion of gas throughout the tank, which rates are much higher (about four times as great) as when conventional sparge systems are used with axial flow impellers. The gas rate is maximum when the impeller has a plurality of blades which are located at an elevation of fifteen to twenty-five percent of the impeller diameter from the bottom of the tank and the outlet ports of the sparge which delivers the gas are located at a radius greater than the radius of the impeller and at about the same elevation from the bottom of the tank as the elevation of the lower edges of the impeller's blades. The condition known as flooding where the escaping gas, rather than the impeller, controls the flow pattern in the tank (the escaping gas then not flowing with the liquid as it is pumped by the impeller but rather rising due to its own energy and geysering out of the liquid) does not occur, even though an axial flow pattern is maintained by an impeller of the axial flow type which pumps by virtue of the pressure differential across the impeller blades, rather than by direct impact with the liquid as in a radial flow impeller. |
