Energy Tab: December 2018

Wednesday, December 12, 2018

Volumetrric Vs Gravimetric Mode : Feeder

Coal properties constantly vary due to sizing differences and the adverse impact of moisture. These affect heating value, flow characteristics and density.The resultant density changes are measured by the Gravimetric Feeder.
The gravimetric feeder compensates for the variation in bulk density and feeds a fixed weight of coal in response to a boiler fuel demand
This ability to accurately weigh the coal provides significant improvement over volumetric types in terms of matching the fuel delivered by the feeder to the actual process energy required on coal fired units.

Benefits of Gravimetric Feeder

Gravimetric feeder weighs material on a belt between two fixed points (span) precisely located in the feeder body.
A roller, located midway in the span and supported at each end by precision load cells, supports half the weight on the span
The load cells generate an electrical signal directly proportional to the weight supported.
The microprocessor takes samples of the output of each load cell many times a second.
If the load cell outputs are within the expected range, they are added to obtain total weight per unit of belt length.
Belt speed is determined by sampling the output of a tachometer attached to the motor shaft, multiplied by a calibration factor to convert it into a belt speed signal
The microprocessor multiplies the speed and weight signal for the feeder rate of fuel output.
Finally, the microprocessor matches the feeder output to the output required by the boiler control, by adjusting the feeder motor speed.
Feeders provide an accuracy of +/- ½ of one percent of totalized weight when calibrated and maintained

Volumetric feeder is Open-loop device
Volumetric mode is set-speed constant , choke-fed or flooded infeed of a particulate solid and it feeds by volume only.
Feed must have consistent bulk density
As there is no information on feedback of feeder ouput and drive control system

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