Use of Shitalakhya River Water as makeup water in power plant cooling system

Abstract

The use of Shitalakhya River Water (SRW) as makeup water in power plant cooling systems is a matter of great concern due to its degraded water quality resulting from polluted discharges from different industries. The present study assesses corrosion and scaling scenarios in closed-loop recirculating cooling systems while using SRW at 2.5 cycles of concentration, the recommended concentration for SRW in a proposed cooling systems. Computation of Langelier Saturation Index and Ryznar Stability Index showed very high corrosion and low scaling potential of the cooling water. A synthetic recipe, prepared considering typical concentrations of inorganic constituents of the cooling water, was used in bench-scale experiments with mild steel and copper alloys. The corrosiveness of the cooling water towards mild steel and copper alloys was found to be unacceptable according to corrosion criteria. Use of sodium nitrite, an anodic corrosion inhibitor, reduced the corrosion rate of both metal alloys by more than 90% and within acceptable range. Presence of organic matter in the SRW reduced the corrosion rate of the metal alloys. Surface analysis of exposed metal alloy samples indicated formation of fewer corrosion products while using sodium nitrite corrosion inhibitor. No mineral scaling was observed on the metal alloy specimens from surface analysis.