Coal Carbonization for Coke Production Dec08

Coal Carbonization for Coke Production...

Coal Carbonization for Coke Production Coal carbonization is the process by which coal is heated and volatile products (liquid and gaseous) are driven off, leaving a solid residue called coke. Carbonization of coal involves heating coal to high temperatures either in the absence of oxygen (O2) or in control quantity of O2. A gaseous by-product referred to as coke oven gas (COG) along with ammonia (NH3), water, and sulphur compounds are also thermally removed from the coal. The coke which remains after this distillation largely consists of carbon (C), in various crystallographic forms, but also contains the thermally modified remains of various minerals which have been in the original coal. These mineral remains, usually referred to as coke ash, do not burn and are left as a residue after the coke is burned. Until recently, the carbonization of coal was considered as ‘destructive distillation’, but with the increased importance of the products of carbonization, this phrase is falling out of use. Now, the coal carbonization is considered to be a physico-chemical process which depends on the coking rate, operating parameters, coal blend properties and the transport of thermal energy. The heating rate of coal influences the strength and the fissuring properties of coke. In order to arrive at a homogeneous quality, the heating of the coal cake in a coke oven is therefore to be uniform over the total length and height of the oven. In addition to this, the plastic layer migration rate influences the level of thermal stress in the re-solidified mass and therefore, the level of fissuring. The coal carbonization process started at the beginning of the 18th century by carbonizing good quality of coking coal in heaps on the ground, which subsequently led to the development of beehive ovens of...

Carbonization of Coal for Metallurgical Coke Production Nov15

Carbonization of Coal for Metallurgical Coke Production...

Carbonization of Coal for Metallurgical Coke Production Carbonization of coal is also known as coking of coal. The process consists of thermal decomposition of coals either in the absence of air or in controlled atmosphere to produce a carbonaceous residue known as coke. Carbonization of coal can be carried out at the following three temperature ranges. Low temperature carbonization is normally carried out in the temperature range of 500 deg C to 700 deg C. In this type of carbonization, the yields of liquid products are higher and there is lower gaseous product yield. The coke produced is having higher volatile matter and is free burning. Medium temperature carbonization is done at temperature range of around 800 deg C. This carbonization produces smokeless soft coke. By products produced are similar in characteristics to high temperature carbonization. Medium temperature carbonization is rarely practiced these days. High temperature carbonization is carried out at a temperature which is above 900 deg C. This carbonization gives higher yield of gaseous products and lower yield of liquid products. This carbonization produces hard coke and is normally employed for the production of metallurgical coke from coking coals. Process of carbonization of coal The coal to coke transformation takes place as the coal is heated. When the state of fusing is reached, the layer of heated coal softens and fuses. From about 375 deg C to 475 deg C, the coal decomposes to form plastic layer.  Destructive distillation reactions proceed rapidly in the plastic layer with evolution of volatile products. At about 475 deg C to 600 deg C, there is a marked evolution of tar, and aromatic hydrocarbon compounds. The gas and condensable vapour are entrapped in the plastic mass and, as they expand tend to swell it. As the...