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What are the Costs of Operating a No Recycle System vs. a Closed-Loop Water Recycling System?

Purpose:

To analyze some costs of operating an in-line aqueous cleaner that drains to a sewer (no recycle) compared to an aqueous cleaner with all of its water reused in a closed-loop water recycling system. Energy calculations are based on the use of an electric heater.

Operating Assumptions:

Rinse flow (gpm) 4 Water/sewage fees($/gal) $0.005
Operating hours(weekly) 30 Cost of power($KWH) $0.050
Weeks/year 48 Recycle system dumps(gal/yr) 10,000
Operating temerature(degrees F) 140 Evaporation loss in cleaner(% total throughout) 4%
Tap water Temperature(degrees F) 50 Energy loss(estimated) 10%
Heat Capacity 1 BTU/1B-degree F Cleaner drain temperature(degrees F) 135

Note: Other values more specific to your application can be used for the above operating assumptions.


A. No-recycle water/heat costs

1. Water cost

Minutes/yr = 30hr/wk x 60 min/hr x 48 wk/yr = 86,400 minutes/yr
Gallons/yr = 86,400 min/yr x 4 gal/min = 245,600 gallons/yr
Water cost = 345,600 gallons/yr x $0.005 (water/sewage fees/gal) = $1,728.00/yr

2. Heat cost

Heat required = 1 lbs tap water/yr x heat capacity x (oper. temp - tap temp)
Heat required = 345,600 gals/yr x 8.33 lbs/gal x 1 x (140 -50) = 259,096,320 BTU
Heat cost = 259,096,320 BTU/yr x 0.0002923 kwh/BTU x $0.05/KWH = $5,514.69/yr

Total water and heat costs = Water cost + heat cost = $1,728.00 + $3,786.69 = $5.514.69/yr


B. Recycle water/heat costs

1. Water cost

Gallons/yr - Dumps + Evaporation losses = gal water dumped/yr + (% loss x gal/yr for
no-recycle system) = 1000 gal/yr + 4% (345,600/yr) = 14,824 gal/yr.
Water cost = 14,824 gal/yr x $0.005 (water/sewage/fees/gal) = $74/yr.

2. Heat cost

Heat for tap water = tap water (lbs/yr) x heat capacity x (oper temp - tap temp) = 123,484 x 1 x (140 -50) = 11,113,560 BTU/yr

Heat required for recycled water:
Lbs recycled/yr = total rinse flow (lbs/yr) - evaporation losses = 345,600 gals/yr x 8.33
lbs/gal - 10%(2,878,848) = 2,590,963 lbs/yr

Heat for recycled - lbs/yr recycled x heat capacity x (oper temp - drain temp) = 2,590,963 x 1 x (140 -135) = 12,954,815 BTU/yr

Total heat required = heat for tap water + heat for recycled water = 11,113,560 +
12,954,815 = 24,068,375 BTU/yr

Heat cost = 24,068,375 BTU/yr x 0.0002923 KWH/BTU x $0.05/KWH = $352/yr
Total water and heat costs = Water cost + Heat cost = $74 + $352 = $426/yr


C. Summary

Recycled No-recycle Savings

Water/sewage $74 - $1,728 = $1,654
Heat $352 - $3,787 = $3,435

Total $426 - $5,515 = $5,089

 

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