Coking Coal Introduction

Coking coal, also known as met coal or metallurgical coal, is used to create coke, one of the key inputs for steel production. The property that really sets coking coals apart from other coals (thermal coals) is caking ability, which is the specific property required to make coke suitable for steel.

 

What is Coal ?

 

Coal is a fossil fuel and its the altered remains of prehistoric vegetation that originally accumulated in swamps and peat bogs. Coal formation began during the carboniferous period - known as the first coal age - which spanned 360 million to 290 million ago. The build-up of slit and other sediments, together with movement in the earth's cust - known as tectonic movements - burried swamps and peat bogs, often to great depths. With burial, the plant material was subjected to high temperatures and pressures. This caused physical and chemical changes in the vegetarian, transforming in into peat and the into coal.

 

Coalification and Types

 

The quality of each coal deposit is determined by :

• varying types of vegetarion from which the coal originated
• depths of burial
• temperatures and pressures
• length of time the coal has been forming in the deposit

The degree of change undergone by a coal as it matures from peat to anthracite is known as coalification. Coalification has an important bearing on coal's physical and chemical properties and its referred to as the "rank" of the coal. Ranking is determined by the degree of transformation of the plant material or carbon. The ranks of coal, from those with the least carbon to those with the most carbon, are lignite, sub-bituminous, bituminous and anthracite.

 

Initially the peat is converted into lignite or "brown coal" - these are coal - types with low organic maturity. In comparison to other coals, lignite is quite soft and its colour can range from black to various shades of brown.

 

Over many more millions of year, the continuing effects of temperature and pressure produces further change in the lignite, progressively increasing its organice maturity and transforming it into the range known as "sub-bituminous" coals.

 

Further chemical and physical changes occur until these coals became harder and blacker, forming the "bituminous" or "hard coals". Under the right conditions, the progressive increase in the organic maturity can continue, finally forming anthracite.

 

In addition to carbon, coals contain hydrogen, oxygen, nitrogen and varying amounts of sulphur. High rank coals are high in carbon and therefore heat value, but low in hydrogen and oxygen. Low-rank coals are low in carbon buh high in hydrogen and oxygen content. 

Historycal Coking Coal

The second largest use of coal is the manufacture of coke for the metallurgical industry. Iron and its alloys (particularly the various kinds of steel) are perhaps the most versatile metalic construction materials known to humankind.

Beginning in about the 16th century, the population of Europe began to expand rapidly, and as the population increased, so did the market for new items, such as housegold goods and farm implements. At the same time, industrial progress was also being made. Both of these fators resulted in an increasing demand for iron.

In the 1600s, the preferred reducing agent for oberating metallic iron from its ores was charcoal. Charcoal is made by heating wood in the absence of air, driving out the moisture and variety of other products and leaving behind the carbon-rich porous solid. The greatly increased cinsumption of wood to make the charcoal led to such restricting the establishment of new iron foundries.

As early as 1609, attempts were made subtitute coal for charcoal in iron-making. As coal is heated, some volatile compounds are released from it. When using coals containing appreciable amounts of volatile matter, the escaped volatiles could react with, or dissolve in, the iron metal as it is being formed. The impurities in the iron were very undesirable, because they weakened the metal and make it difficult to shahe useful obejects from the iron.

A similar problem had been encountered in the brewing industry, where charcoal had been used to dry the malt used in the brewing process. Subtituting coal for charcoal led to horrible tastes in the beer or ale, because the volatiles escaping from the coal were absorbed by the malt and ruined its flavour. The brewers discovered that if coal is heated in an inert asmosphere to drive off the volatiles, the remaining residue (which is largely the fixed carbon, called shar or coke) is still very usefull as a fuel.

When many kinds of bituminous coals are heated in an inert atmosphere, they soften and swell to form a plastic mass. the escaping volatiles pass through this plastic material, which then resolidifies to a carbon-rich solid upon further heating. Coals that pass through a plastic stage on heating are called caking coals. Some caking coals resolidify on heating to form a hard, very strong, carbon-rich porous mass suitable for use as a reducing agent in the metallurgical industry.

This material is called coke, and the special class of caking coals that yield a satisfactory coke are known as coking coals. (It is unfortunate that the words caking and coking is similar, but they are not synonymous. All coking coals are necessarily coking coals, but not all caking coals area coking coals).