Condensers hardly operate under clean conditions for a long time. The ills to which they are generally prone include fouling of tube surfaces, tube sheet or tube fouling, deficient air removal capacity etc. Here we are going to discuss about condenser tube fouling and their characteristics.
Every condenser experiences tube sheet or tube fouling at some point of time. Most of the condensers that circulate water sources have dissolved solids, which precipitate and become deposited on tube’s inner surfaces affecting unit heat rate adversely. The deposits may even contribute to different kinds of corrosion and if they are not removed from time to time, corrosion eventually penetrates tube wall enabling the circulating water to leak into contaminate condensate.
Fouling not only affects the unit heat rate but even the capacity of turbine to generate its load capacity. To combat tube fouling effectively, one should first understand the characteristics of it and how it applies to the site-specific situations. Condenser tube fouling usually falls into one of following categories:
Scale Fouling: This takes place on heat transfer surfaces under combination of dissolved mineral concentration as well as temperature effects. Mineral crystallization of a few constituents in natural water is upheld by elevated temperatures. There are also some kinds of scale-forming minerals that form at a cooler temperature. Scaling may diminish heat transfer drastically.
Microbiological Fouling: It occurs routinely in natural waters. Temperature at interior wall of condenser tubes is perfect for bacterial growth. Resulting mass is often low in the organic solids and most of the constituents are the inorganic particulates from cooling water, which become incorporated to microbiological slime. Even a very thin layer of fouling may be detrimental to the heat transfer.
Particle Deposition Fouling: This usually takes place when flow rate is poor to keep the particulates in suspension. This may be a problem if water box isn’t full and upper tubes get intermittent flow. Low flow areas result from partial blockage on tube sheet. Particle deposition may or may not cause heat transfer loss for condenser but it can serve as the place of initiation for corrosion. The common kinds of fouling particulates include silt/sediment, coal dust, diatoms and minerals precipitated from cooling water.
Corrosion Products Fouling: These products may become thick on surfaces of particular tubes inhibiting heat transfer. Deposition or scale actually causes the growth of copper oxide layer. Condenser tube cleaning brushes are to be used for cleaning these layers.