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KISPL provides superior grade low ash coal, 24% or less ash content
Efficiency Table of Coal Fired Power Station*
Power Units
Efficiencies %
Sub-Critical Steam Conditions
Built over the last forty years
36-40%
Super-Critical Units
Modern
40-44%
Ultra-Super-Critical Units
Under construction
46% 50% (with further material advances)
* The efficiencies apply to power stations of units larger than 350 MW. Older and smaller units will have lower efficiencies
Coal Quality Requirements and Specifications*
1.Stoker Stoker is a type of coal firing in boiler. A stoker is also a device consisting of a feed and a grate and is used for feeding coal (or other solid fuel) into a furnace, distributing it over a grate, admitting air to the coal for combustion and providing a means for discharge of ash.
PARAMETER
LIMITS
COMMENTS
Total Moisture
8 - 15% (AR)
If too low, fines can be blown away from the bed without burning.
Ash
7 – 30% (ad)
3 – 35% (ad)
For overfeed stoker.
For spreader stoker.
Minimum ash content required so grate will be protected from reflected heat.
Volatile Matter
25 – 40% (daf)
Maximum size
30 mm
Size consist
Max. 30% - 3mm
Min. 25% +6mm
If too high can be blown from bed.
Ash fusion temperature
IDT min. 1200°C.
Ash melts and clinkers if too low.
Crucible swelling number
Max. 3
High swelling coals give uneven combustion.
2.Pulverised coal (known as pf, pulverised fuel) firing is combustion of powdered coal suspended as a cloud of small particles in the combustion air. It avoids the need for a supporting grate and therefore eliminates restrictions on equipment size, and the reason for its wide scale adaptation is its suitability in very large boilers. Substantially more heat is released per unit volume than in stoker firing. Because the coal is carried by the combustion air, residence times are much shorter than for stokers; just a few seconds. Despite the short residence time, good burnout can be achieved as long as the coal is sufficiently finely divided.
* Whilstcoals outside the following ranges can be burned and following specifications should normally be adhered to:
PARAMETER
LIMITS
COMMENTS
Total Moisture
15% (ar)
Reduces net calorific value. Creates handling problems if too high. Limits higher for lignites and low rank coals.
Ash
Max. 20% (ad)
Reduces calorific value. Generally should be low.
Volatile Matter
Min. 20 – 25% (daf)
For conventional pf burners.
Max.20-25% (daf)
For down fired pf burners.
Calorific value
As high as possible
With suitable equipment almost any calorific value fuel can be utilised.
Sulphur
Generally Max. 1% (ad)
Can be higher if blending or FGD is employed. Overall is dependent on local emission regulations.
Nitrogen
Max. 1.5-2.0% (daf)
Various limits apply in a few countries only because of nox emissions.
Chlorine
Max. 0.2-0.3% (ad)
Figure normally for inland coals. In general export coals well below 0.05%.
Hardgrove grindability index
Min. 45 – 50
Lower HGI values require larger grinding capacity and more energy.
Maximum size
Max. 40 – 50 mm
Dependent on capacity of grinding equipment.
Fines content (- 3mm)
High fines content can increase moisture content and create handling problems.
Ash fusion temperatures
Various
Dry bottom boiler - IDT greater than 1200°C. Wet bottom boiler - flow temperature less than 1300°C.
Knowledge = Power…
Coal Basics
A picture is worth a thousand words.
Select a term from the list
=coal that includes TOTAL MOISTURE, ASH, VOLATILE MATTER, and FIXED CARBON
