An improperly maintained cooling tower will produce warmer cooling water, resulting in a condenser temperature 5-10 F higher than a properly maintained tower – reducing efficiency and reliability of the chiller while wasting energy, increasing costs, and shortening tower operating life.
Many power plant operators tend to overlook the importance of the cooling tower in the plant’s overall energy efficiency. Because chillers use about five times the energy of the cooling tower, more attention often is paid to the chiller than the cooling tower.
In reality, however, the chiller’s efficiency improves with cold condensing water from the cooling tower. According to engineers’ estimates, chiller efficiency will increase 2-3 percent for every degree cooler the tower water is that’s supplied to the chiller.
In addition to chiller efficiency, a number of other factors can contribute to improving cooling tower efficiency, including:
* Proper sizing of the tower – most cooling towers are undersized to save money
* Age of the tower – older towers often degrade over time
* Using more effective fill materials
* Using variable frequency drive fan motors
* Replacing old spray nozzles
Poor cooling tower performance
Cooling tower performance tends to degrade when efficiency of the heat transfer process declines. Some of the common causes of this degradation include:
* Excessive scale build-up – Water evaporating from the cooling tower leaves scale deposits on the surface of the fill from minerals that were dissolved in the water. Scale build-up acts as a barrier to heat transfer from the water to the air.
* Contaminants settlement – Heavier contaminants settle to the bottom of the cooling tower basin, creating “dead” areas that shield the basin surface and the corrosion-preventing chemicals added to the water. The result is under-deposit corrosion of the metal surfaces – eventually forming blisters that release oxide particles and add more suspended solids to the condenser water stream.
* Clogged spray nozzles – Algae and sediment collecting in the water basin – as well as excessive solids getting into the cooling water – can clog the spray nozzles, causing uneven water distribution over the fill that results in uneven air flow through the fill and reduced heat transfer surface.
* Poor air flow – This can be caused by debris at the inlets or outlets of the tower or in the fill – as well as by loose fan and motor mountings, poor motor and fan alignment, poor gear box maintenance, improper fan pitch, damage to fan blades, or excessive vibration. Reduced airflow due to poor fan performance can ultimately lead to motor or fan failure.
* Poor pump performance – Cooling tower pump, used in an indirect cooling tower to maintain proper water flow and thereby achieve optimum heat transfer, performs poorly from loose connections, failing bearings, cavitations, clogged strainers, excessive vibration, and non-design operating conditions, resulting in reduced water flow, reduced efficiency, and premature equipment failure.
Cooling tower maintenance program
Proper cooling tower maintenance must be an ongoing endeavor. Lapses in regular maintenance can result in system degradation, loss of efficiency, and potentially serious health issues. Cooling tower maintenance is key to optimizing heat transfer – which in turn helps power plant equipment operate more efficiently and enables operators to identify strategies for upgrading tower performance. Read more…
“Proper Cooling Tower Maintenance Increases Power Plant Efficiency,” Energy-Tech Magazine. http://www.energy-tech.com/article.cfm?id=18388/ (accessed March 15, 2010).