Coke Production12.09.09

Ms. Sumbal Salim

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When many bituminous coals are heated, they soften and form a plastic mass that swells and resolidifies into a porous solid.

Coals that exhibit such behaviour are called caking coals. Strongly caking coals, which yield a solid product (coke) with

properties suitable for use in a blast furnace, are called coking coals.

Coking coal is best if it has a very narrow range of volatility and plasticity.

Thermoplastic properties are dependent on petrographic composition. For example, liptinite macerals exhibit very high fluidities, while inertinite macerals do not. Vitrinites are intermediate between these two groups.

Thermoplastic properties are undesirable for combustion and gasification because a combustor or gasifier can be choked by the resulting fused mass.

Thermoplasticity in coals

Metallurgical cokes are high quality blast furnace or foundry cokes characterized by relatively high strength and stability.

A typical blend is composed of high volatile, highly caking bituminous coals i.e. the "caking coals", and medium and/or low volatile bituminous coal i.e. "coking coals”

A coal blend should not exert a high coke oven wall pressure and should contract sufficiently to allow the coke to be pushed from the oven.

Metallurgical Coke

The coke making process involves carbonization of coal to high temperatures (1100°C)

oxygen deficient atmosphere. The commercial coke making process can

be broken down into two categories: a) By-product Coke making and b) Non-Recovery/Heat Recovery Coke

making.

Coke Production

From about 370°C to 470°C, the coal decomposes to form plastic layers.

At about 470°C to 620°C, there is a marked evolution of tar, and aromatic hydrocarbon compounds.

At 620°C to 1100°C contraction of coke mass, structural development of coke and finally hydrogen evolution.

Once, the plastic layers have met at the center of the oven, the entire mass has been carbonized

By- Product Coke Production

Carbonization reactions can be illustrated in the following simplified manner:

CH0.8S0.2O0.1N0.01 (coal molecule)+heat

CH4 H2 CO (coke oven gas)+

H2O (water vapor)+

NH3 (ammonia)+

tars & light oils+ C (carbon)

Carbonization Reactions

A coke oven battery consists of 10-100 individual coke ovens.

The long thin coking chambers (Height 6-22 ft., Length: 3-52 ft, Width: 1-2 ft)

There are heating chambers on both sides of each coking chamber to provide even heating.

Regenerative chambers recover the flue gas heat. On top of the coke oven battery are coal charging cars. On the pusher side of the battery is the large

pusher/leveler that levels the input charge and then pushes the hot coke out of the oven.

On the coke side of the oven, quench cars take the incandescent coke to the quenching system.

By-Product Coke Oven Battery

By-Product Coke Oven Battery

Coke oven batteries

Coke Oven Batteries-charging

Coke Oven Batteries-Leveling

Coke Oven Batteries-quenching

Coke ProductionIncandescent coke in the oven waiting to be "pushed".

When discharged the coke pieces are in sizes of 200mm (i.e. 8in)

Each ton of coke produced requires 1.37 tons of coal.

PSM produces approx 750,000 ton/yr of coke. Coal is imported from Australia & Canada.

About 65% of the input coal energy goes into the coke itself.

Coke oven gas equals 15% of the input coal energy.

Recovered tars, oils, and other chemicals contain about 12% of the input energy, and about 8% is consumed as fuel for the process.

Energy consumption

By-products from coke-ovens

The evolved coke oven gas is at high temperatures approaching 19000F.

Coke-oven gas contains: H2 , N2 , CH4 , H2O,

CO & CO2.

Raw coke oven gas also contains various contaminants:

Tar vapors Light oil vapors (aromatics), consisting mainly of

benzene, toluene and xylene (BTX) Naphthalene vapor Ammonia gas, Hydrogen sulfide gas, Hydrogen

cyanide gas

By-Products from coke-ovens

Stream Destination Typicalquantities, basedon 1 million tonsper year coke

Coke oven gas Used in coke oven batteries & in iron making

50 million std.cu.ft/day

Flushing Liquor Recirculated

Tar Sold 46,500 tons/yr

Ammonia/ammonium sulphate

Sold 17,200 tons/yr

Sulphur/sulphuric acid Sold 12,500 gallons/day

Light Oil Sold

By-Products from coke-ovens

The carbonization process takes place from the top by radiant heat transfer and from the bottom by conduction of heat through the sole floor.

Non-Recovery/Heat Recovery Coke Production

Carbonisation time & temp affect its strength & abrasion resistance of coke (shatter & abrasion index)

Thermal stability. High carbonisation temp & heat soak encourage thermal stability of coke.

Effect of carbonisation temperature

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