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Condenser maintenance guide 2

EPRI Licensed Material FOULING Fouling of the condenser includes any organisms organic or inorganic that interfere with the circulating water in the tubes and ultimately with the heat transfer process When there is an increase in condenser pressure and a decrease in cooling water ow fouling is the most likely cause Other indications of fouling include an increased pressure drop and a reduction in temperature change for the inlet and outlet cooling water Fouling impacts the output of the plant as it a ?ects the condenser backpressure The plant availability can be a ?ected during seasonal changes that produce annual ?sh runs grass movement seaweed deposition accumulation of leaves and so on The deposits on the tube reduce heat transfer rates decrease cooling water ow and increase pumping costs The formation of these deposits is a function of the cooling water environment ow velocity and the season In addition the solubility of certain compounds such as calcium carbonate decreases with increasing water temperature Key Technical Point There are two main types of biofouling macrofouling and microfouling Macrofouling is de ?ned as the blockage of condenser tubes by organic or inorganic debris such as sticks leaves ?sh mussels and so on Microfouling is the accumulation of deposits inorganic scales or organic growths on the inside of the tubes The following sections discuss macrofouling microfouling chemical treatment water regulations chemical application methods and a fouling monitor Macrofouling Organic or inorganic debris can occur from traveling screen carryovers or from growth of organisms on the condenser and water conduit walls The organisms eventually dislodge and plug the tubes Macrofouling upstream of the circulating water pumps can reduce the available net positive suction head This results in pump cavitation and reduced ow Debris lodged at the entrance to or inside the condenser tubes can increase ow velocities around the debris This increased velocity will erode any protective ?lm and subsequently corrosion at this part will occur at a higher rate Copper-alloy tubes are more prone to this phenomenon while stainless steel and titanium tubes are less susceptible to this attack Organic debris left in the condenser tubes during outages decomposes biologically This process of decomposition can be highly corrosive and produces compounds that can promote pitting or - CFouling EPRI Licensed Material stress corrosion cracking in copper and brass alloy tubes Pitting can also occur in copper nickel and in series stainless steel under these conditions Prevention of macrofouling depends on site-speci ?c conditions causing macrofouling If the source is debris such as seaweed or freshwater vegetation then traveling screens at the circulating water intake might prevent the debris from owing into the condenser If the source is an organism such as clams then a biocide is needed Many plants have the capability to backwash the condenser to remove macrofouling Strategies for backwashing depend on circulating water conditions and trends in condenser performance To determine methods that control macrofouling problems it is important to understand certain characteristics of various fouling agents The freshwater and