Analysis of the lime softening treatment process of industrial cooling water using MINTEQ geochemical model

This report investigated the economic feasibility of using lime softening treatment for the Saturn Corporation cooling tower in Spring Hill, Tennessee. The MINTEQ geochemical equilibrium model was used to simulate hydrated lime and soda ash addition to the make-up water in a clarifier. Model predictions of precipitates and clarifier effluent species concentrations were used to determine cycles of concentrations possible in the cooling tower without scale formation. The component costs for construction, operation, maintenance, labor and electricity were estimated for all systems required in the softening treatment process. Sludge and blowdown water disposal on-site and off-site were considered in the cost estimates. The results of the research determined that for on- site disposal of the blowdown water and sludge, the minimum total cost for make-up softening treatment only was $22,983/month at 18.8 cycles of concentration, as compared to $23,099/month at four cycles of concentration without softening. For off-site disposal, the minimum cost with make-up softening only would be $44,736/month at 15.1 cycles of concentration, as compared to $35,058/month at four cycles of concentration without softening. Using cost ratios found in the literature, the cost for a combination of make- up and sidestream softening is 30% of the cost for make-up softening only. It was concluded that it was not economically feasible to use softening treatment for make-up water only. It was economically feasible to use a combination of make-up and sidestream softening. For a well designed cooling tower operating at zero blowdown, the drift losses would limit the cycles of concentration to 11.0.