High Efficiency Multiple Screw Pumps

Figure 2. A ROSE ® process 600-deg F twin screw pump.as 600-deg F (315-deg C) have been achieved in twin screwpumps for the ROSE ® deasphalting process (see Figure 2).Timing gears and bearings are force cooled while the pumpbody is jacketed for a hot oil circulating system to bring thepump to process temperature in a gradual, controlled manner.Three screw pumps have been applied to the same elevatedtemperature, more commonly on asphalt or vacuum tower bottomsservices in refineries.To quote Dushyant Mehra, research analyst with Frost &Sullivan, “The primary challenge for oil & gas pump manufacturersis to improve the energy costs and efficiency of theirpumps.” 1 The pump user can also contribute to their bottomline by using the most efficient technology to move liquidproducts. Many times this is a positive displacement pump, notFigure 2A. A typical multiple screw pump performance curve.a centrifugal pump. Figure 2A shows excellent efficiency over abroad range of discharge pressures.In multiple screw pumps, each wrap of screw thread effectivelyforms a stage of pressure capability. High pressure pumpshave 5 to 12 stages, or wraps, whereas low pressure pumps mayhave only 2 or 3 wraps. This staged pressure capability is illustratedin Figure 3. More wraps are incorporated into pumpsdesigned for higher pressure service.Figure 3 (above left). Staging effects of screw pumps.Figure 3A (left). A diesel driven three screw pump on a heavy crude pipeline in Central America.Figure 3B (above). A heavy crude three screw pump on pipeline service in Western Canada.Pumps & Systems www.pump-zone.com April 2007 55