WARNING: Coke oven gas contains some pretty nasty stuff!

Coke Oven Gas Generation and Usage
Coke is an essential input for the ironmaking process. For making coke, coal is heated in the absence of air to drive volatile matter (VM) from it. Conversion of coal to coke is called coal carbonization and the process is carried out in coke ovens. A coke oven battery consists of 60 coke ovens. 
The coal is heated in a completely reducing atmosphere and the volatile products are recovered in an associated by-product plant. The coke ovens used for this method of coal carbonization are called by-product ovens and the coke oven battery is called the by-product coke oven battery. During the carbonization of coking coal in a by-product coke oven battery, the VM consisting of around 25 % to 30 % of the coal charged is driven off as effluent gas which leaves the coke oven chambers as the hot raw coke oven gas. Raw coke oven gas is a flammable gas and has a yellowish brown colour and an organic odour.

The by-product plant is an integral part of the by-product coke making process. The operation of each oven is cyclic, but the battery contains a sufficiently large number of ovens to produce an essentially continuous flow of the raw coke oven gas. The individual ovens are charged and emptied at approximately equal time intervals during the coking cycle. Coking proceeds for 15 hours to 18 hours to produce BF coke. During this period, VM of coal distills out as raw coke oven gas. The time of coking is determined by the coal blend, moisture content, rate of under firing, and the desired properties of the coke. When demand for coke is low, coking times can be increased to 24 hours. Coking temperatures generally range from 900  C to 1100 C.
The gases and hydrocarbons which evolve during the thermal distillation are removed through the off-take system and sent to the by-product plant for recovery.
The large amount gas generated is treated in an adjacent by-product plant. During the cycle of coking, the gas is produced during majority of the coking period. The composition and rate of evolution of the CO gas changes during the period and the evolution of CO gas is normally complete by the time the coal charge in the battery reaches 700 deg C. This gas is known as raw coke oven gas and is processed in the by-product plant. The functions of the by-product plant are to process the raw gas to recover valuable coal chemicals and to treat the raw coke oven gas sufficiently so that it can be used as a clean, environmentally friendly fuel. Raw coke oven gas after treatment in the by-product plant is called clean coke oven gas or simply CO gas.

The typical composition of the main components in the raw coke oven gas is in Tab 1.

Tab 1 Composition of raw coke oven gas (% Volume)
Hydrogen  52-59
Methane  26-33
Nitrogen  1.9-5.7
Carbon monoxide  4.5-7.0
Ethylene  2.0-2.8
Carbon dioxide  1.4-2.1
Hydrogen sulphide  0.4-1.2
Hydrogen cyanide  0-1.2
Ethane  0.7-1.1
Ammonia  0-1.1
Benzene  0-1.0
Carbon disulphide  0-0.3
Toluene  0.1-0.2

FOR MORE INFORMATION ...visit... Coke Oven Gas Generation and Usage – IspatGuru