WATER CONSERVATION STRATEGIES

Reduce Bleed-off in Cooling Towers, Evaporative Condensers and Fluid Coolers

Evaporating a small percentage of the re-circulating flow cools water used in cooling towers, evaporative condensers and fluid coolers. As water is evaporated the dissolved solids in the remaining re-circulating water concentrate. Some bleed-off of this water is necessary to prevent these dissolved from precipitating as sludge and scale.

The rate of evaporation is dependent on load and is not adjustable. However, opportunities for water conservation exist in controlling and minimizing the amount of bleed-off necessary to prevent deposition.

The amount of bleed-off needed is determined by the ability of the treatment program to prevent the precipitation of calcium carbonate. All-organic programs may hold 400 -1,000 ppm as CaCO3 in solution. Programs using acid for pH control may hold up to 3,000 ppm as CaCO3 in solution (but then have to deal with the potential for corrosion if overfed. Water softeners remove calcium before it enters the cooling tower that effectively eliminates the potential for calcium carbonate formation (but makes the water more corrosive, particularly at higher cycles of concentration).

The H-O-H Green Machine- removes hardness and alkalinity using electrolytic principles. It is the preferred technology for minimizing bleed-off, especially on high-hardness waters.

Bleed-off is measured by a term called cycles of concentration. By definition, the ratio of makeup water to bleed-off is called cycles of concentration. Raising cycles reduces bleed-off and therefore minimizes water losses. Water conservation is maximized by using control systems that accurately control the amount of necessary bleed-off. Good control equipment will prevent wide fluctuations in bleed-off, thereby preventing precipitation and wasting water.

Steam Boiler Water Pretreatment

When steam is produced in a boiler, the dissolved solids stay in the boiler water as the steam leaves. These solids will concentrate with steam production. At some point, the boiler requires blowdown (the discharge of boiler water with concentrated dissolved solids). Energy, water and chemical savings are achieved by reducing boiler blowdown.

Hardness is most efficiently removed via water softeners installed to treat makeup to the boiler (the alternative is to add chemical which adds dissolved solids, increasing the need for blowdown).

Dissolved oxygen is most efficiently removed by preheating and venting (most commonly done with a deaerator, but sometimes done with a simple sparging nozzle and vent).

Dramatic reduction in dissolved solids (and a corresponding increase in water, chemical and energy) occurs when reverse osmosis is used as part of the pretreatment equipment.

Blowdown is measured by a term called cycles of concentration. By definition, the ratio of makeup water (or feedwater) to blowdown is called cycles of concentration. Raising cycles reduces blowdown and therefore minimizes water losses. Water conservation is maximized by using control systems that accurately control the amount of necessary blowdown. Good control equipment will prevent wide fluctuations in blowdown, thereby preventing precipitation and wasting water and the energy used to heat that water.

Recycling Wastewater Streams

In many facilities water is discharged without considering whether it may be recycled. Examples of water discharge that may be potentially recycled are: softener backwash; reverse osmosis reject water; grey water sources like rainwater; and certain wastewater streams. It is often possible to treat these systems either mechanically or chemically so that may be reused as a makeup water source for cooling towers. A good example is reverse osmosis reject water which can easily be used as cooling tower makeup after passing through an H-O-H Green Machine.