Thermal coal conversion - tar and benzole recovery

The pyrolytic conversion of coal into coke, gas and aromatic liquid products is the oldest and, in quantitative terms, most important coal-refining process. In the absence of air, carbonization processes are considered to occur in stages up to 150 °C, carbon dioxide, water and volatile C2 to C4 hydrocarbons are evolved. At pyrolysis temperatures above 180 °C the volatile components also contain aromatics. At temperatures in excess of 350 °C, rapid degasification occurs, which continues to around 550 °C, leading to semi-coke. The rate of degasification approximately follows a reaction of the 1st order, which can be explained by the rupture of the bonds of the macromolecules in the coal. In the secondary degasification of the semi-coke (600 to 800 °C) hydrogen and methane are the main products. 

The 750 to 850 °C hot gaseous products which are released during carbonization are taken to the gas-collection main by ascension pipes. The cmde gas is quenched to around 80 to 100 °C by ammonia liquor, removing 60 to 70% of the crude tar. The aqueous phenolic condensate which arises at the same time undergoes extractive dephenolation. The phenols can be processed together with the phenolic products of the distillation of tar (see Chapter 3.2.3). Cooling the cmde 

1 Coke oven 2 Gas separator 3 Pre-cooler 4 NHa-spray saturator 5 Final cooler  

6 Cooler 7 H2S scrubber 8 Gas purification 9 Benzole cold scrubber 10 Benzole column 11 Underground condensate tank 12 Tar separator 13 Phenol extraction 14 Benzole regeneration 15 NH3 separator 16 Ammonium sulfate slurry container 17 Filter 18 H2S separator 19 H2S combustion 20 SO2 oxidation 21 Absorption column 22 Dilution vessel 

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