Appendix ADOE-HDBK-1015/1-93BASIC SEPARATION THEORYRev. 0CH-01Page A-13In the Badger stage, about 50% of the process gas entering a converter diffuses through thetubing and flows to the stage above. This fraction is called the "cut." A cut of 50% has beenfound to yield the best separation. As mentioned previously, the "cut" in a Badger Cluster stagemay be more or less than 50% depending upon its position in the cluster.DiffusionIt is necessary to have a higher pressure inside the barrier tubes than outside in order to havea flow through the walls of the tubes. This inside pressure is called the fore pressure or highside pressure (H.S.P.), and is measured at an arbitrary point inside the tubes near the middle ofthe second pass. The pressure outside the tubes is the back pressure or low side pressure(L.S.P.), and is measured at an arbitrary point outside the tubes near the middle of the secondpass.The fore pressure is regulated by a control valve in the "B" stream, or down flow, from theconverter. Actually, the control valve regulates the pressure immediately above it. This iscalled the control pressure and is the pressure which is indicated at the cell panel. It is slightlylower than the fore pressure due to the pressure drops in the converter and piping.The rate of diffusion through the tubing walls for any given pressure drop across the barrier isdetermined by the permeability of the barrier. Mathematically, this is a dimensionless quantitywhich is the ratio of the rate of gas flow through the barrier to the rate of gas flow through thesame area which would take place if the barrier were not there. The term, usually calledpermeability, is used to relate the actual permeability to the design permeability. For example,if the flow through the barrier has decreased 10% due to plugging of the barrier holes, thepermeability would be 90%.
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