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What Is Cooling Tower Bleed-Off / Blowdown?

What Is Cooling Tower Bleed-Off / Blowdown?

Cooling tower bleed-off/blowdown is the flushing of a portion of high mineral concentration cooling tower system water down the drain, while simultaneously replacing it with fresh water. This process dilutes the system water mineral concentrations that steadily increase due to water evaporation. Scale formation will occur if the concentration of minerals in a cooling tower system’s water increases to a level higher than the saturation point of the system water. The mineral content above the saturation point will fall out of the solution of the water and form hard mineral scale throughout the system.

A typical cooling tower (500 ton, running 24 hrs day. 365 days per year) will flush over 3.9 Million gallons of water down the drain each year. This breaks down to approximately 10,800 gallons of waste per day, 450 gallons per hour, or 7.5 gallons per minute being flushed down the drain from the cooling tower system 24 hours a day, 7 days a week. That’s a lot of water!

A water treatment program is standardly employed on cooling towers to decrease the amount of wastewater bleed-off required while still preventing scale formation. This is achieved by increasing the saturation point of the system water using a scale inhibitor treatment. By increasing the saturation point, more minerals can exist in the system water and remain in the solution of the water without falling out of solution and forming scale.

Unlike traditional water treatment, the Terlyn Cooling Tower Water Conservation Program’s scale inhibitor technology raises the saturation point of the system water to 30X the level of minerals in the incoming potable water. This means that the system water’s mineral concentration can be allowed to increase to 30X the level of minerals in the make-up water without forming scale. This is possible because our scale inhibitor treatment, CWT3, has a molecular bonding strength that is 30x higher than the strongest traditional scale inhibitor. This extremely high molecular bonding strength allows our CWT3 treatment to hold significantly more minerals in the solution of the water without scale formation. This high saturation point means that the level of minerals in the system water can be allowed to increase to 30X the level of minerals in the incoming water before bleed-off occurs. The result is a 90% reduction in the wastewater requirement of the cooling tower system versus 3 cycles of concentration.
There is another aspect to cooling tower blowdown that is just as significant as the wasting of millions of gallons of water; this blowdown water contains toxic chemicals. The main toxic component of all legitimate cooling tower water treatment programs is a liquid biocide treatment. The purpose of a biocide is to kill any bacteria or organisms that try to live inside the cooling tower”s water (ie. algae, legionella, etc.). This biocide is used on a constant basis to prevent biological growth in a cooling tower.

So in our example above, that 500 ton cooling tower is flushing 3.9 Million gallons of cooling tower water containing this toxic biocide down the drain every year. In some cases, cooling towers are allowed to flush their blowdown water not into the sanitary sewer system, but into the stormdrain that flows directly into the environment with no treatment whatsoever.

As you can see, cooling tower water conservation is not only important for general water conservation, but also from a pollution prevention standpoint. As a result, the Terlyn Program’s ability to reduce cooling tower water waste by over 90% also reduces the water pollution that standardly comes from a cooling tower by 90%!