These short studies review the use of Rheotherm CWFF meters at 3 power plants: why they were needed and what the plants gained from having them installed. The last section lists scenarios when use of these instruments might be beneficial to a plant.
Case Study 1
Reason for interest in CWFF: A plant chemist was aware of chronic poor condenser performance including chronic high condensate dissolved oxygen. The chemist needed information about condenser design issues, microfouling of condenser tubes and the effectiveness of a new chemical biocide treatment.
Installation summary: CWFF meters and supplemental thermocouples were installed in one bundle of a quad-bundle, dual waterbox, single pass Southwestern Engineering condenser (~750MW) unit during a spring outage; tubes were brush cleaned just prior to meter installation during the same outage.
Intek data analysis results: Meter data indicated that 40% of the entire unit surface area became macrofouled in the first month after returning to operation following the spring outage. From this initial data, Intek provided analysis, recommendations and action items to be taken to execute an inspection. Visual inspection during an unscheduled outage confirmed this indication. Subsequently, the plant implemented a condenser retrofit to provide capability for reverse flushing of the condenser as our analysis recommended. Additionally, CWFF meter data flow velocity variations was correlated with river water level, over a six month period, to show that it was having a significantly greater effect on total circulating water flow rate than the plant anticipated. Finally, our analysis provided values for tube heat transfer coefficient improvement for evaluating an experimental chemical biocide treatment to the plant.
Case Study 2
Reason for interest in CWFF: A condenser engineer was aware of MIC attack on SS tubes of 2 generating units. The engineer was interested in obtaining information about condenser circulating water issues and the effectiveness of implemented MIC prevention methods and tube coating impacts on tube heat transfer.
Installation summary: CWFF meters and thermocouples were installed in one bundle of an 8-bundle, quad waterbox, single pass Westinghouse condenser (~800MW) unit during a spring outage; tubes were brush cleaned just prior to meter installation during the same outage.
Project results: Standard plant operations called for 3 of 4 circulating water pumps to be on at all times. Single tube circulating water velocities were measured to be lower than 4 ft/sec for a majority of the monitored time period of 8 months and as low as 1.7 ft/sec under certain operating conditions. Intek provided analysis, recommendations and action items for inspection. The plant found, as diagnosed by Intek using CWFF, that all 8 waterbox eductors were 100% plugged with debris, causing an upper waterbox air bubble and nonuniform flow. New procedures were implemented to clear debris from the eductor ports on a regular basis. The plant changed to all 4 pumps running to maintain higher velocities thus mitigating MIC attack and achieving a lower net unit heat rate. The plant located the identified valves causing cooling water flow to bypass the condenser. Debris bar rack pressure differentials were previously used to trigger reverse flushing; after reviewing the CWFF meter data, the plant implemented a more frequent reverse flushing cycle for improved results.
Engineering Services – Our engineering group designs cost effective retrofit and new design solutions to achieve optimal condenser performance.
Case Study 3
Reason for interest in CWFF: Plant engineers were faced with a challenge to change from Admiralty to SS tubes even though the unit was load limited in the summer months. Other challenges included chronic elevated condensate dissolved gases and low tolerance to air in-leakage levels >10-20 SCFM. CWFF meters assisted a diagnostic effort by validating model predicted size and magnitude of air bound regions of the Westinghouse designed condenser bundle. A retrofit project to improve the Westinghouse condenser performance was approved. A retrofit was installed during the retubing outage and post retrofit performance was monitored with instrumentation that included another CWFF meter system.
Installation summary: CWFF meters and thermocouples were installed before the retrofit in one bundle of a quad-bundle, dual waterbox, single pass Westinghouse condenser (~500MW) Admiralty tube unit during a fall outage. CWFF meters and thermocouples were installed after the retrofit in the same bundle, now SS tubes, with the steam side Intek designed retrofit to improve steam flow paths, eliminate air bound regions and improve overall condenser heat transfer.
Project results: CWFF confirmed predictions about location and magnitude of air bound regions. Pre-retrofit thermal stratification exceeded 12°F in monitored locations. Post retrofit thermal stratification was reduced to <5F. All other operating conditions, including air in-leakage, were comparable with the exception of condenser pressure. All guaranteed retrofit project benefits were exceeded, additional benefits to circulating water chemistry were defined, and overall unit heat rate was significantly reduced. After the retrofit, macrofouling events correlated with waterway dredging and a total of ~30% macrofouling over a continuous 6 month run was indicated by CWFF data and was confirmed by visual inspection during the outage. The plant is using this information to determine root cause for the fouling and determine a cost effective approach to mitigate future fouling.