Precision Flow Measurement

FLOW MEASUREMENT  PROBLEMS?
Many plants suffer from issues relating to flow accuracy.  Deposits on nozzles and degradation on other flow measuring devices prohibit plant personnel from accurate calculation of heat rate and other critical indicat
ors of a plant’s behavior.  Often this can cause dispatching or environmental limit problems. True North Consulting offers a comprehensive solution, combining our unique plant knowledge and services with state of the art flow measurement devices (1% accuracy or better) such as AMAG’s CROSSFLOW device, to determine flows not currently measured or to calibrate existing flow meters. 

CURRENT INDUSTRY  PRACTICES 
Historically, ultrasonic transit time meters are used to measure flows in power plants.  However, transit time meters have limitations.  Transit time technology injects an ultrasonic signal diagonally through the fluid and then measures the difference in the time that it takes for the ultrasonic pulse to travel upstream versus downstream.   It is very sensitive to temperature change and to transducer installation discrepancies due to alignment and pipe conditions.  Measured time difference, which is on the order of a few microseconds, has to be measured with an accuracy of a few nanoseconds.  In most cases these sensors have a temperature limit that is below the final feedwater temperatures found in most power plants.

WHAT IS CROSSFLOW?
The CROSSFLOW Cross Correlation approach measures the velocity of the fluid by determining the time that it takes for the fluid to pass a set distance between two ultrasonic beams.  An ultrasonic beam is injected perpendicular to the axis of the pipe, rather than diagonally as is required for the transit time meter, providing a very robust and stable ultrasonic path, which is not affected by the temperature change and is not sensitive to transducer alignment.

IS ACCURACY IMPORTANT?
Calculated plant heat rate is directly related to feedwater flow accuracy.  Many plants currently suffer from issues relating to flow accuracy either due to erroneous feedwater flow measurements or other important flow measurements in the secondary cycle.  The limitations of time of flight meters have been overcome by the Cross Correlation method.  

WHAT FLOWS CAN BE  MEASURED?

  • Feedwater 
  • Condensate 
  • Boiler Attemperation 
  • Condenser Cooling Water 
  • Pump Discharge 
  • Heater Drains 
  • Service Water 
  • Any Other Flows

BENEFITS OF CROSSFLOW

  • Increased accuracy of feed water flow and heat rate. 
  • Less sensitive to flow velocity profile and temperature effects. 
  • Easy to install. 
  • Uncertainty analysis can be provided with measurements. 
  • True North Consulting’s extensive thermal performance experience.

 

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