The term Cycles of Concentration (Cycles) refers to the ratio of dissolved solids in the system water to the dissolved solids in the make-up water. Solids increase due to evaporation. Solids can only be decreased by blowdown. Evaporation contains no solids.
Cycles are normally calculated based on chlorides but can also be done based on conductivity.
Cycles of Concentration = Chlorides in System Water / Chlorides in Make-up Water
Cycles of Concentration is a valuable tool for maximizing water savings and reducing chemical costs.
Cooling towers are designed to cool water through evaporation. When water evaporates, pure water evaporates and dissolved and suspended solids remain in the cooling tower. The higher the tower can be cycled, the more money can be saved on water and chemicals.
For example lets look at a cooling tower that runs at 900 tons of average cooling and has makeup water with 300 ppm of total hardness. Due to scaling considerations, most chemical programs don’t carry hardness levels in the tower above 600 ppm. At that rate, only 2 cycles of concentration can be achieved.
Based on these conditions and assuming the Delta T is 10 degrees F and the system runs 24/7/365, we can make the following calculations:
Tonnage (900) x 0.18 x Delta T (10) = 1,620 gph of evaporation
Evaporation (1,620 gph) / [Cycles (2) – 1)] = 1,620 gph of blowdown
Evaporation (1,620 gph) + Blowdown (1,620 gph) = 3,240 gph of makeup
3,240 gph x 24 hours x 365 days = 28,382,400 gallons per year of makeup
Based on make-up water costs of $3.00 per 1000 gallons and sewer costs of $4.00 per gallon (rates vary by municipality), water costs would amount to $85,147.20 per year for make-up water and $56,764.80 per year for sewer fees.
This assumes that you are being given proper credit from your municipality for evaporating over 14,000,000 gallons and not being charged sewer based on incoming water.
For a review of your water bills and to find out about eliminating blowdown altogether, go to Zero Blowdown Technology or give us a call at (800) 839-1000.