9.2 Coal Weighing System in Power Plants
Coal consumption is only the raw material for thermal power plant. The quality
and consumption of coal directly impacts to per unit cost of power generation.
The performance of thermal power plant only depends upon per unit cost of coal
consumption. The coal booking becomes a big problem if the power plant is
integrated with cement plant and its input coal yard is common for the both.
In some of the plants, coal consumption booking is done based upon heat rate
cycle of the steam circuit assuming a certain efficiency of the boiler as per given
guarantee parameters given by the boiler manufacturer. But this is not the right
way of booking the coal consumption as it does not help in analysis of plant
operational.
The second method of coal consumption booking is the direct weighment from
the coal feeding system and calorific value along with moisture percentage is
measured from laboratory test.
With help of above, unit cost of power generated is calculated. This also helps in
measurement of boiler efficiency using heat rate cycle of the steam circuit.
The accurate coal consumption gives clear cut information about operational
efficiency of the boiler or quality of purchased coal. Small improvement in the
quality of coal purchased or operational efficiency may results saving of lacs of
rupees per annum for the organization.
We are herewith illustrating an effective and efficient method of coal measurement
system in thermal power plant which may help for correct coal consumption as
well as may confirm the quality of coal purchased.
Process of coal feeding and coal consumption measurement in new generation
captive power plant can be followed as under.
Coal is stored in common coal storage pile (for cement and power plant) after
crushing by primary crusher which is installed in cement plant. The size of storage
coal is less than 75 mm
- The coal (-) 75 mm is reclaimed from common storage pile by re-claimer which
is 150 tph and fed to primary screen installed in power plant fuel handling system. - The fine coal of (-) 6 mm size is filtered by primary screen and directly fed to
coal bunker of the power plant. - The coarse fuel of primary screen is fed to coal crusher where feed coal is
crushed from 75 mm to 6 mm size and fed to secondary screen with help of
belt conveyor. - At secondary screen fine coal (-) 6 mm is filtered and conveyed to power plant
bunker through belt conveyor whereas (+) 6 mm and above coal is re-circulated
to crusher for further crushing. - There is belt weigher on bunker feed belt for measurement of conveyed coal.
The accuracy of belt weigher is 0.25% with periodic calibration.