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I would agree with the use of a 2-3″ wide strap looped over the end of the blade and tied off to the motor bridge handrail or some other visible place. As an added equipment safety measure a LOTO tag should be applied to the strap and be recorded as part of the LOTO to ensure that the strap is removed before the fan is returned to service.I’ve also witnessed some facilities utilize a large, 2 piece, pipe clamp, with extended length that is bolted to the motor drive shaft after the guards are removed. The extended length of the pipe clamp would then contact the yoke area on the motor (as applicable).
Not all fan motor/gearbox will have this sort of access so the easiest and quickest means of securing fan blades
I would agree with the use of a 2-3″ wide strap looped over the end of the blade and tied off to the motor bridge handrail or some other visible place. As an added equipment safety measure a LOTO tag should be applied to the strap as part of the LOTO to ensure that the strap is removed before the fan is returned to service.
I’ve also witnessed some facilities utilize a large, 2 piece, pipe clamp, with extended length that is bolted to the motor drive shaft after the guards are removed. The extended length of the pipe clamp would then contact the yoke area on the motor (as applicable).
Not all fan motor/gearbox will have this sort of access so the easiest and quickest means of securing fan blades
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
Because the ACC operate under saturated steam conditions, e.g. the condensate is always in contact with the steam from whence it came and therefore sub-cooling is of little concern for provided that the ACC is free from air ingress. For an ACC operating in automatic with a fixed backpressure setpoint sub-cooling will occur if air ingress is greater than the air extraction equipments’ capabilities. As the air collects and blinds the surface area, ACC backpressure will increase resulting in the control system in either speeding up the operating fans (VFD equipped) or starting additional fans. It is the increased air flow that will cause the condensate and the air take off NCG’s to become sub-cooled. Sub-cooling can also occur without major air ingress should the ACC be operated in manual mode supplying more air flow than is required. In this case the backpressure and saturation temperature will decrease.
Toshameer,
If I understand you correctly, you are asking if it is OK to dump flash steam to an ACC that is at atmospheric pressure. Short answer is NO. The ACC is a heat exchanger. When any heat exchanger is full of air it cannot exchange heat ie. condense steam.
My questions to you are; Why do you want to dump flash steam to the ACC prior to ACC start-up? How long would you want to dump steam to the ACC prior to ACC start-up?
Marty Cyr
SPX Dry Cooling USA, Inc.
martin.cyr@spxdrycooling.com
