PULVERIZER TESTING

EXPERIENCE

FERCo has successfully tuned many different pulverizer systems in order to provide the owner with the optimum air and fuel balances (pipe-to-pipe). We use both the RotorProbe™ and the new portable MIC One real-time coal flow measurement system. The dirty air pitot is then also used for primary air flow measurements. The focus of FERCo's recent pulverizer tuning and balancing has been on emissions reduction. This is most often accomplished by balancing burner flows as closely as possible. The balance is typically optimized by orifice changes in the burner lines. A typical test program includes:

• PA flow distribution (pipe-to-pipe)
• Coal flow distribution (pip-to-pipe)
• Pulverized coal fineness distribution
• Pulverizer operating data

TYPICAL BENEFITS

Benefits of improved coal and air flow distributions often include:

• Reduced emissions
• Improved flame stability
• Reduced ash deposition
• Reduced carbon in ash
• More uniform combustion

FERCo has purchased a portable, on-line, real time coal flow measurement system from MIC - USA.  The system is based upon microwave technology and allows for rapid assessment and balancing of the coal flow distribution between burner lines of a pulverizer.  This approach will allow burner line coal flows to be balanced quickly with proven accuracy when compared with the ISO RotorProbe™ procedure. 

The system uses non-intrusive microwave sensors that are attached directly onto the burner lines using common test ports (ball valves).  The sensor (containing both a transmitter and receiver) is positioned flush with the inside of the burner line.  The microwave energy is reflected only by the moving coal particles in the stream.  The signals from all sensors are sent to a control box by means of twisted pair wire, and the control box is connected to an industrial grade laptop computer.  The laptop computer displays the percent coal flow distributions for all burner lines in real time and logs the data for future analysis.  Thus, it is possible to balance the coal flows in real time using adjustable orifices and to log the distribution changes as other variables change, such as coal feed rate and primary air flow.

Two significant items were noted from this testing.  First, the individual MIC sensor data indicated that the majority of the coal flow (approximately 75%) was located in the bottom one-third of the burner lines.  These results help to explain why the RotorProbe™ often returns inaccurate results when sampling from horizontal burner lines.

Second, since the RotorProbe™ provides only a “snapshot” of the distribution data (approximately two recovered samples @ 4 minutes each), it may not be totally representative if variability occurs in the coal and primary airflow.  The MIC One measured slight changes in the percent coal flow deviations over the entire test time of approximately eight hours.  For the comparison, the sensor data were averaged for the entire test period.  FERCo has presented these results, and results from other tests, in several papers that are available upon request.

It should be noted that the MIC system is not an extractive sampling system.  That is to say, if coal mass flows are required for air/fuel ratio calculations or recovery rates, then a traditional sampling system, such as the RotorProbe™, is required.  An extractive method is also required for pulverized coal fineness analysis.  FERCo highly recommends the RotorProbe™ over other extractive methods due to its international acceptance and its proven accuracy.  FERCo has used the RotorProbe™ to measure and/or balance the coal flow distribution on more than 80 pulverizers over the last ten years. Our coal flow balancing experience with the RotorProbe™ is summarized in separate literature on this subject. This new MIC portable microwave technology compliments our current program of providing our customers with accurate and professional consulting services for coal flow distribution testing.  We would welcome the opportunity to discuss this new technology and assist in its application at your site.

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