July† 1996††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††† Volume 2†† Issue 13
COST-EFFECTIVE WATER USAGE
††† Whether your company is buying water from a municipal water system or is paying the electricity bill to pump it from an expensive well, water is not cheap.† Especially for food processors, water-related costs are usually a significant operating expense.† Included among these costs are water acquisition costs that may involve drilling a well, pumping from an existing body of water, or hooking up to a municipal water system.† Also included are water disposal costs, including the cost of waste processing and/or sewerage fees.†
††† Complicating the matter further, both acquisition and disposal must be handled in ways that donít cause environmental harm.† Both are subject to environmental regulations, and meeting the requirements sometimes involves additional expense.† Because of all this, it makes sense for plant personnel to think about water use within the plant and, where possible, to take steps that reduce water-related costs.†
††† In this issue of $mart Energy User we consider five approaches to the problem.†
1.† DETERMINE YOUR PLANTíS WATER-RELATED COSTS
††† Is water a significant cost in your facility?† Is the outlay enough to be concerned about?† Letís say your plant uses water at a rate of 100 imperial gallons per minute (igpm), 8 hours a day, 21 days a month.† If you get your water from the Charlottetown Water and Sewer Utility through a 2-inch meter, your water bill will come to about $1765 per month.† (Included in the price is the right to feed that much water back into the sewer system ó with certain restrictions on what the wastewater can contain beside just water.)
††† If you pump your 100 igpm from one or more wells, the monthly outlay is less.† But there is also a capital investment to amortize, and eventual maintenance expenses.† Letís assume that to get
Vertical turbine radial flow pumps similar to this are used for water pumping from deep wells.†† Pumping expense will be minimized if pumps (including this type) are driven by 3-phase motors rather than single-phase motors.
those 100 igpm of water your plant has invested in a single deep well with an 8-inch casing and a 10 horsepower (hp) submersible pump and motor.†† If the electrical power input to the motor is 7.5 kW, and electricity costs $0.10 per kWh, $126 worth of electricity will be used each month to pump the water.† The capital cost of well, pump, pipe and wiring for the sort of well described is likely to be in the neighborhood of $15,000.†
††† In many plants there are additional water-related costs.† Water must be pumped between and within processes, for instance.† Water must be stored in tanks so itís available at the right time.† And in some plants, waste water must be treated before it can be discharged to the environment.
2.† USE LESS WATER
††† Review plant processes to see what might be done to reduce water use.†
∑ Is it time to replace a water flume with a mechanical conveyor?†
∑ Is the flow of water to cool the refrigeration condenser being controlled according to the actual need for condenser cooling?
∑ Is the amount of water entering production processes being controlled according to the real need of the process?† Or does water sometimes flow even when not needed, or in greater quantity than needed?†
∑ In some situations could water use be reduced without causing any problems?† Downsize water sprays, perhaps?† Make changes that would allow waste removal, dilution, or treatment to be accomplished with less water?
∑ Could steam-based cooking replace water-based cooking ?
3.† USE THE SAME WATER FOR MORE THAN ONE PURPOSE
††† Another approach to saving water is to recyle it ó to use the same water more than once before sending it to drain.† Two examples:
∑ If water is now being used only for cooling and then sent directly to drain, could that water also be used for product washing, cleanup, or some other purpose?
∑ Could the water used to flume potato peel waste to a strainer be reused to wash soil off potatoes?
4.† IMPROVE PUMPING AND DISTRIBUTION EFFICIENCY
††† Not all pumps and motors are created equal.† In planning new installations, the matter of pump/motor efficiency and life should be explored with pump vendors.† Choosing a reliable, efficient unit in the beginning, even though somewhat higher in price, can more than return the difference through reduced operating and maintenance costs.†
††† The wells of some older plants may still use pumps powered by single-phase motors even though the plant now has 3-phase power.† It costs appreciably more to run a single-phase motor than a 3-phase motor of the same power rating.† If the plant now has three-phase power, consider replacing the single-phase motor with a 3-phase motor the next time the pump and motor must be pulled from the well.
5.† MONITOR WATER USAGE
††† Our final suggestion for reducing water costs is to monitor water usage daily.† The basic idea is simple: To manage water use, you need to know how much water you are using.†† Particularly if your plant uses a lot of water, install a cumulative-use water meter to measure total plant use.† Checking that meter each day can give you early warning of excessive use and associated problems.†
††† Flow-rate water meters can also be helpful.† Instead of just turning a valve until the water flow ďlooks about right,Ē a flow-rate meter lets the operator adjust the flow to a consistent value day after day.† The process benefits because water flow is always adequate, and the water bill benefits because the flow is never excessive.