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Cooliog Water Pump Failures

Kites rise highest against the wind, not with it.

Winston Churchill, Politician, Author, Statesman.

Author: V. Narayan

Location: 2.1.4 A Large Petroleum Refinery

Background

When carrying out refining processes, large quantities of heat have to be removed. High-grade heat can be reused for product-to-product heat transfers, but low grade heat is invariably discarded. In this refinery, we used air cooled heat exchangers (fin-fan coolers) to discard low grade heat. Final cooling to ambient temperature was sometimes required after the air cooling. We used sea-water coolers for this purpose. A Public Utility Company supplied the cold sea water. Once used in the coolers, the warm cooling water was returned to the sea. The Utility Company provided elevated concrete supply and return channels, and we had to pump the warm water up about 30 feet. We had three large vertical cooling water pumps to pump out the warm water. Two of these were needed to cope with the volume involved, while the third served as a spare unit.

A concrete channel was used to transport the water from the process plants to the pump-house. This was about 12 feet wide and 10 feet deep, with the top (covered with removable slabs), about 6" above ground level. From the channel, water flowed into an open concrete reservoir through an inverted weir. There was a 'waterfall' effect, as the drop was about 12 feet. This caused a lot of turbulence, and there was plenty of 'white water' in the reservoir.

The pumps' suction pit was oriented perpendicular to the inlet channel, so the water changed direction by 90° in the reservoir. At the entrance to this pit, there were trash racks to catch large debris such as wood pieces. Figure 41.1 shows the layout of the cooling water pump house.

These pumps suffered from a series of failures, resulting in their inability to meet their specified flow requirements. Eventually all three pumps had to operate to meet the capacity requirements. If a pump came out for repairs during this period, we had to reduce the refinery throughput. This situation was clearly unacceptable.

310 Chapter 41

 
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