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M.Tech (GET), 1st Semester
Centre For Green Energy Technology
• The process of converting coal into coke is called as
carbonization of coal.
• When a coking coal is heated in the absence of air, the
porous, hard and strong residue left is called coke.
• Coke is white, lustrous, dense porous coherent mass.
Depending on the behavior of coal, when heated in the
absence of air, the coal is classified into;
(i) Non-coking coal which undergoes practically no fusing
effect and also called as free burning coal.
(ii) Coking coal which gives porous, hard and strong residue
after heating in the absence of air. The residue is used for
metallurgical purposes and is known as coke. They are
quite strong and not crushed under the weight of
ore, flux and coal in big furnaces.
Properties of Coke
• Hard, Porous, Carbonaceous materials
• Three important properties of coke;
- Ascertained by moisture,ash, sulphur,phosphorus content
-By Shatter and Micum test
-By specified minimum porosity calculation
-It is also measured with respect to air,CO2,Steam,Sulphur
Generally used for production of soft coke or char or
High temperature gradient was employed for
carbonisation in reasonable time as coal a poor conductor.
Normally it is a economical upgradation method of low
rank coal like lignite.
The major products are semicoke, low temp.
liquor,crude low temp.spirit and gas.
Typical yield temp.is 600˚C
Typical Yields(on dry basis)
Semi-coke(clean fuel) 75-80%
Properties of Gas by LTC
• Specific gravity(in reference to air) - 0.6
• Calorific value - 6500Kcal/Nm3
Composition in percentage(%)
Application of Products by LTC
• Semicoke as highly reactive produce smokeless flame ideal
for domestic solid fuel.
• Also semicoke &char utilized for gasification into fuel or
synthesis gas for chemicals and fertilizers industries.
• The gas obtained is rich in HC’s(hydrocarbons)&poorer in H2
compared to that obtained by HTC(high temp.carbonisation).
• Calorific value is high although yield is low.
• Alternate source to biomass used for domestic hearths
providing clean fuel concept.
• Commercially practised in coke oven for coke and in gas retorts for
• Coke oven is of two types;
a. Beehive type (coke completely burnt)
b. By-product slot type (coke by product obtained)
• Similarly gas retorts are of three types producing coal gas;
a.Horizontal type retort
b.Intermittant vertical retort
c.Continuous vertical retort
Typical Yields from HTC
Products Amount(in %)
Crude benzol 0.8
Ammonium Sulphate 1.0
Coke oven gas 330Nm3 /tonne
Coke Oven gas Composition
Gross calorific value =5020Kcal/Nm3 (dry condition)
=4450Kcal/Nm3 (wet condition)
Difference between LTC &HTC
Characteristics Low Temperature
1. Heating temperature 500-7000C 900-1200°C
2. Yield of coke 75−80% 65−75%
3. Volatile matter content 5−15% 1−3%
4. Mechanical strength Poor Good
5. Calorific value 6500−9500 kcal/m3 5400−6000 kcal/m3
6. Quantity of by-product
130−150 m3/tone 300−390 m3/tone
7. Coke produced Soft Hard
8. Smoke produced Smokeless Smoky
9. In gas, percentage of
(a) Aromatic hydrocarbons
(b) Aliphatic hydrocarbons
10. Uses Domestic Metallurgy
• A briquette is a block of flammable material used as fuel to
start and maintain a fire.
• Common types of briquettes are charcoal briquettes
and biomass briquettes.
Briquette density, t/m³ 1.0-1.2
Heat content, MJ/Kg 19.3-20.5
Ash content, % 0.5-1.5
• Briquetting consists in applying pressure to a mass of particles
with or without addition of binders& converting to
• Main objective is to convert low grade solid fuel to one of
(Generalised Briquetting Process)
Briquetting of Lignites
• Briquetting used because of structural quality & as is
obtained as fines during mining.
• Briquetting requires no binder & comparatively low pressure
suffices compaction of particles.
• Some important parameters for briquetting;
Particle size 8mm(after crushing from
Moisture 9-11%(reduced from50-56%)
Optimum temperature 70˚C
Briquetting of Bituminous Coal
• Briquetting of fine grade coals like bituminous takes place
with binders like coal,tar,pitch,petroleum bitumen .
( Typical Briquetting Process)
Parameters for briquetting:-
Size 80%lessthan0.5 mm(coal)
93%less than 0.88mm(pitch binder)
Moisture content 2-4%
Briquetting pressure 150kg/m³
Optimum temperature 150-160˚C
Pitch content(binder) 7-8%