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KISPL meets coal quality specification for Cement Production
JANUARY 10, 2008, NEW DELHI The two basic processes in cement production are the wet and dry processes which are named after the manner in which the raw mix is introduced into the kiln. In the wet process the mix is introduced into the kiln as a slurry with 20-40% moisture. The mix is introduced dry into the kiln in the dry process. Dry process kilns are generally shorter because there is no need to evaporate the slurry moisture from the mix. Reduction of moisture content improves plant fuel efficiencies.
Cement production is very energy intensive involving both heat (clinker production) and electricity (grinding of feed and clinker). The most modern plants in operation today which use the dry process and have pre-calcination and pre-heaters consume around 80 kwh of electricity per tonne of clinker and 600 kcals of heat for each kg of clinker produced. Less modern dry process plants use up to 1100 kcals of heat/kg of clinker and older wet process plants can use up to 1700 kcals/kg of clinker produced.
Approximate coal consumption in cement plants
Type of plant
HEAT REQUIRED KCAL/KG CLINKER
TONNES CLINKER PER TONE COAL*
TONNES COAL* PER 106 TONNES CLINKER
Most modern—dry process, pre-heating
600
10.0
100,000
Less Modern—dry process—semi dry process
1100
5.5
180,000
Least modern-wet process
1700
3.5
280,000
*Calorific value = 6000 kcal/kg net as received basis.
Coal quality requirements
There are few limitations on coal quality for cement production, some are as follows:
PARAMETER
LIMITS
COMMENTS
Total Moisture
Max. 15% (ar)
Creates handling problems if too high
Ash
Max. 25% (ad)
Generally little influence composition must suit kiln feed composition.
Volatile Matter
Virtually no limit (ad)
Best quality coking coals 20-35%. High volatile matter results in lower coke yield.
Calorific value
Various
Depends on grinding capacity and throughput
Sulphur
Max. 2% (ad)
Dry process. Limit less severe for wet process
Chlorine
Max. 0.1% (ad)
Dry process. Limit less severe for wet process.
Hardgrove grindability index
Various
Limit set by capacity of grinding equipment and CV of coal used.
Maximum size
Max. 30-50mm
Depending on grinding equipment.
Fines content (- 3mm)
Max. 25-30%
Creates handling problems if too high.
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Coal Basics
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Select a term from the list
=coal that includes TOTAL MOISTURE, ASH, VOLATILE MATTER, and FIXED CARBON
Combined cycle (power generation)
A two-stage electrical generation process. In the first stage, electricity is generated by a gas turbine. The waste heat from this process then passes through a heat recovery boiler which produces steam for additional power generation in a conventional steam turbine. This results in an increase in overall power generation efficiency.
