A Case History - Improvements To An Existing Cooling Tower Sump And Horizontal Split Case Pumps

Abstract

In adding a second urea plant in 1974 at a Midwestern nitrogen plant, higher cooling water requirements necessitated the construction of an additional cooling tower. A 130 million Btu/hour cooling tower was installed with two 18X20-22H horizontal split case pumps rated for 13,000 gpm at 115 ft total dynamic head. From nearly the beginning of the continuous operation of these two pumps, severe vortices were visible in the cooling tower sump, as well as high amounts of noise and vibration. Maintenance costs on these units were higher than expected due to cavitation erosion on the impellers and replacement every 2.5 years. Of course, with the accelerated wear of the pumps, the required capacity and the efficiency were affected. A change in the material of construction of the impeller was made in an effort to increase the mean time between repairs. With the inherent design of this pumping system, it is not economically feasible to correct all the elements that prevent these units from operating at preferred industry standards. This paper discusses the investigation in the analysis of the problems, concentrating on the review of the cooling tower sump, the improvements made utilizing published recommendations, and the results of the alterations. Other methods of increasing the pump life and efficiency of the units are discussed. The effects of these additional changes are also discussed.