C 1

Drift reduces the blowdown requirement because it continually takes with it the elevated levels of total dissolved solids (TDS). If not known, drift may be approximated, in English units, as:

D = flow ratex 0.0002

Including drift, the blowdown rate can be expressed as: E - [(C-1) x D]

If, for example, the flow rate is 10,000 gpm, the water temperature differential is 15°F, and the desired concentration ratio is 5, the required blowdown rate would be:

B _ (10,000 x 15 x 0.0008) - [(5 - 1) x (10,000 x 0.0002)]

Blowdown requirements resulting from air washing are generally not calculated, but are determined empirically based on field monitoring results.

Annual water use can be estimated based on the WMR in gpm (lpm) and an estimate of equivalent full-load hours (EFLH). This is calculated as:

WMR x 60 min/h x EFLH_ gallons/yr (liters/yr) (36-8)

In the example considered above, WMR is estimated at 152 gpm (575 lpm), including 120 gpm evaporation, 28 gpm blowdown, and 4 gpm drift. Assuming the system runs 1,500 EFLH per year, total water usage based on Equation 36-8, is:

152 gpm x 60 min/h x 1,500 EFLH 1,000 gal/kgal

_ 13,680 kgal/yr (52,460 kl/yr) If the cost of water is $2.50 per kgal, the annual water cost is:

Water usage is often measured in hundred cubic feet (Ccf) or cubic meters (m3) for water utility billing. Since there are approximately 748 gallons per Ccf, kgal can be converted to Ccf by dividing by 0.748. Thus:


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