- The bunkers are mounted on four active load cells which can tender better
than 0.5% accuracy. With help of bunker load cells, on line calibration of belt
weigher can be done at definite intervals. - The feed coal can be measured with following ways:
a. Installed belt weigher has accuracy of ±0.25% with four live load cells which
will give ongoing instant ton per hour material feed and total conveyed coal
as on time. On daily basis counter can be reset and re-started at particular
time. There is bunker weighing system with which operator can know the
performance of the belt weigher and cumulative coal quantity for particular
duration. Hence, coal consumption for a definite time span can be obtained
from belt weigher. Coal bunker is mounted on three active load cell and
capable to measure coal storage quantity better than 0.5% accuracy.
b. The variable frequency drives are installed on bunker extraction points to
feed desired quantity of coal in boiler furnace. The speed of variable
frequency drive can be translated into tph for a given sample of coal. In DCS
total coal consumption can be calculated for particular time span using VFD
speed curve with 1.0% accuracy which can be timely re-checked with
bunker weighing system.
The coal consumption can also be measured by batch operation of bunkers. There
are two bunkers for coal feeding to boiler furnace. One can be under plant
operation and other can be under coal filling. The capacity of each coal bunker is
450MT which is quite sufficient for (8) eight-hour operation. Hence, batch
operation is most suitable for coal feeding in bunkers in order to insure accurate
coal consumption, material handling system reliability.
9.3 Raw Material Weighing System in Cement / Power Plants
Measurement Principle of Weigh Feeders
- Any dynamic weighing system requires basically two Transducers namely load
cell & Tachometer for load and Speed measurements respectively. - The weigh feeder is weighing cum control machine used to deliver controlled
flow rate of solid materials. - There is small belt mounted on steel structure with weighing scale and variable
frequency drive geared unit, pulse counter tachometer. - The weighing assembly measures the weight of the bulk material passing over
it for one-meter span and speed of the belt is calculated with pulse counter
tachometer. - Flow rate of the material is calculated by measured weight multiplied by speed
of the belt - The total feed rate is calculated as under:
Flow Rate = Material load on unit length of Belt x Belt Speed
Flow Rate in (Tph) = Weight of material (in kg) x Belt speed (in m/sec) x 3600
1000