Keywords: chloride removal, recycled cooling water, pH, lime softening, aluminium sources, calcium chloroaluminate, water recycling, solid solutions, UHLA, scale–forming compounds, aluminium hydroxide, waste alum sludge, sodium aluminate
Evaluating alternative aluminium sources for chloride removal from recycled cooling water
Chloride is important in promoting corrosion in cooling water systems, which leads to reducing the efficiency of heat transfer surfaces and shortening equipment life. Ultra–high lime with aluminium process (UHLA) is a potential new technology that has the ability to remove chloride and sulfate from recycled cooling water in addition to removing the majority of scale–forming compounds. The purpose of this paper is to evaluate alternative aluminium sources for chloride removal from recycled cooling water using UHLA process. Three aluminium sources (freshly precipitated aluminium hydroxide (Al(OH)3), waste alum sludge, and sodium aluminate (NaAlO2)) were used. Results of lab experiments indicated that at low aluminium doses, chloride removal is similar for all three aluminium sources. However, at high aluminium doses, chloride removal efficiency was higher with Al(OH)3 than with NaAlO2 or alum sludge at the same lime dose. Much of the differences among them could be attributed to differences in pH.