Air pockets occur in areas where there can be localized air ingress (cracked weld) and/or areas where steam flow through those particular tubes may be lower than adjacent tubes. On units operating in the South western USA these units can experience what is deemed as air logging in certain sections of the ACC. This is commonly the direct result of a unit reaching it’s maximum condensing load along with other environmental impacts, e.g. sun providing external localized heating, high winds starving fans, etc… The folks that operate these units and who routinely experience this phenomena have stated to me that they have learned to “Burp” the ACC in order to clear the air logged section(s). This is done by manipulating the fans in modules adjacent to the air logged zone. By stopping adjacent fans these areas become hotter and condensation decreases which allows for more steam to flow towards the air logged area due to differences with internal pressures between the hot and cold tube bundles. Normally the removal of the air logging occurs rather quickly but the fan configuration should remain for 10-15 minutes to ensure adequate air removal in that zone. If air returns rather rapidly once returned to normal fan configuration then one may want to investigate further as to localized air ingress. One more thing, A low dissolved O2 doesn’t necessarily equate to the absence of air ingress. A robust and properly functioning air removal system will ensure that dissolved O2 is removed from the condensate to design levels. Marty
