Blast furnace gas is a by-product of blast furnaces that is generated when the iron ore is reduced

Redox

Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....

 with coke

Coke (fuel)

Coke is the solid carbonaceous material derived from destructive distillation of low-ash, low-sulfur bituminous coal. Cokes from coal are grey, hard, and porous. While coke can be formed naturally, the commonly used form is man-made.- History :...

 to metallic iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

. It has a very low heating value, about 93 BTU/cubic foot, because it consists of about 60 percent nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

, 18-20% carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 and some oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

, which are not flammable. The rest is mostly carbon monoxide

Carbon monoxide

Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

, which has a fairly low heating value already. It is commonly used as a fuel within the steel

Steel

Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

 works, but it can be used in boiler

Boiler

A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Materials:...

s and power plants equipped to burn it. It may be combined with natural gas

Natural gas

Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

 or coke oven gas before combustion or a flame support with richer gas or oil is provided to sustain combustion. Particulate matter is removed so that it can be burned more cleanly. Blast furnace gas is sometimes flared

Gas flare

A gas flare, alternatively known as a flare stack, is an elevated vertical conveyance found accompanying the presence of oil wells, gas wells, rigs, refineries, chemical plants, natural gas plants, and landfills....

 without generating heat

Heat

In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

 or electricity

Electricity

Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

.

Blast Furnace Gas is generated at higher pressure and at about 100 °C (212 °F)-150 °C (302 °F) deg.C in a modern Blast Furnace. This pressure is utilized to operate a generator (Top-gas-pressure Recovery Turbine - i.e.TRT in short), which can generate electrical energy up to 35 kwh/t of pig iron

Pig iron

Pig iron is the intermediate product of smelting iron ore with a high-carbon fuel such as coke, usually with limestone as a flux. Charcoal and anthracite have also been used as fuel...

without burning any fuel. Dry type TRTs can generate more power than wet type TRT.

Auto ignition point of blast furnace gas is approxmiate 630 °C (1,166 °F)-650 °C (1,202 °F) and it has LEL (Lower Explosive Limit) of 27% & UEL (Upper Explosive Limit) of 75% in an air-gas mixture at normal temperature and pressure.

Higher concentration of carbon monoxide makes the gas hazardous.

Sources

• International Energy Agency