| CESC’s Pulverized Fuel fired Generating
Stations have boilers, using different combustion technologies. Titagarh Generating
Station‘s Steam Generators use Babcock’s combustion technology, “Front
fired boiler” boiler. Southern Generating Station uses Combustion Engineering (CE)
technology, “Corner fired Boiler” boiler and Budge Budge Generating Station uses
a special type of combustion technology of Babcock in their “Down Shot Fired”
type of boiler to burn low volatile coal. The older stations (Non PF) are designed for
using high grade of coal suitable for Babcock supplied Chain grate stoker fired boilers.
This is a result of the prevailing technology when the generating stations were conceived.
The quality of coal received at the Generating Stations is frequently different from that
for which the boiler is designed. The change of quality of coal has an effect on boiler
efficiency as boiler losses are different not only at different load but also at different
quality of coal it burns. We get coal from many Collieries and difference in quality is
wide. We have reasons to believe here that coal quality better than design may not
necessarily be better for a boiler when optimization of all controllable parameters are
considered comprehensively. But as the poor quality of coal & the part loading affects
the stability of the boiler, the oil consumption also becomes high. The Change of coal
quality also has effect on the coal mill performance as far as it’s output, loading,
wear, quantity of mill rejects & pf fineness are concerned. Perspective environmental
implications are also there.
The efficiency of Turbo Alternator improves with load. This can be proved that
heat required for a change of load is summation of (a “fixed heat”and
incremental heat * load). For a contemporary designed machine this fixed heat is around
5-7% of full load heat consumption. Ideally the incremental heat is constant for any load
change. So at low load unit runs at higher heat consumption. CESC’s all the power
stations are subjected to this feature because of the very typical daily load curve of
CESC area. These phenomena aggravate the situation further in winter season. So running
the units at higher load to achieve higher thermal efficiency is not always possible at
CESC’s Generating Stations. This is a constraint to which CESC does not have any
control. At part load, although the works power reduces, the percentage works power rises.
Due to support for ignition as well as cut in /cut out of coal mills to accommodate load
cycling and two shifting, the oil consumption also goes high increasing the heat rate of
the station and for the Stoker fired Boilers ‘banking Loss’ increases.
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