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Descaling of Condensers

One of the services we offer is a descaling service.  Scale deposits are formed by precipitation and crystal growth at a surface in contact with water. Precipitation occurs when solubilities are exceeded either in the bulk water or at the surface. The most common scale-forming salts that deposit on heat transfer surfaces are those that exhibit retrograde solubility with temperature.

Although they may be completely soluble in the lower-temperature bulk water, these compounds (e.g., calcium carbonate, calcium phosphate, and magnesium silicate) supersaturate in the higher-temperature water adjacent to the heat transfer surface and precipitate on the surface.

Scaling is not always related to temperature. Calcium carbonate and calcium sulfate scaling occur on unheated surfaces when their solubilities are exceeded in the bulk water.  Metallic surfaces are ideal sites for crystal nucleation because of their rough surfaces and the low velocities adjacent to the surface. Corrosion cells on the metal surface produce areas of high pH, which promote the precipitation of many cooling water salts. Once formed, scale deposits initiate additional nucleation, and crystal growth proceeds at an accelerated rate.

In forced draft condensers the high volume of air enhances scale deposits.  There are even conditions that exist when water pumps are cycled on and off while the air is still moving causing the precipitation of salts.

There are also things that occur unexpectedly.  Generally these are related to mechanical issues.  Although we test the flow of bleed valves on our regular scheduled service, they can fail in between service dates. A failed bleed valve causes a rise in calcium carbonate and its solubility is exceeded in the condenser leading to the accumulation of calcium carbonate on the surfaces.

We start this service by using a pressure washer to mechanically remove the calcium carbonate.  After this the condenser is drained and vacuumed.  Then the condenser is filled with water and a combination of cleaning agents and neutralizers are used in order to remove the remaining calcium carbonate.  This process can be repeated several times.

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