PROCESSING OF BY-PRODUCTS FROM CARBONIZATION OF NON-CAKING COALS - RECOVERY OF TAR ACIDS

Recovery of tar acids from ammoniacal liquor and middle oil fraction ( 170-270 degrees C) of tar produced in the Woodall-Duckham type carboni ser of Dankuni Coal Complex (DCC), using non-caking coals, has been in vestigated. About 99.5% of the phenols contained in ammoniacal liquor can be extracted with isobutyl acetate in five stages of extraction us ing a feed:solvent ratio of 8:1 (v/v) and the phenols content of the l iquor can be reduced from about 6000 to 30 ppm. A comparison of produc ts obtained from tar distillation under laboratory conditions to those under actual plant operation has been made. The optimum yields of the middle oil, under standard laboratory distillation and tar distillati on plant, were 27.12% and 22.5%, respectively, on dry tar and the cont ent of the refined tar acids in these oil fractions were found to be 9 .35% and 7.6% ton dry tar), respectively. However, in actual plant pra ctice, this level of yield has not been achieved yet, due to loss of s ubstantial quantity of tar acids in processing units. With a view to o ptimising the yield, various aspects of plant operation and process st reams were investigated. The yields of tar acids and the other process ing streams of DCC have been compared with those of metallurgical coke plants and variations in composition of tar acids discussed. The dihy dric phenols (ca. 16% of tar acids) obtainable from DCC, have been sho wn to offer an attractive potential. The environmental aspects related to discharge of waste streams have been dealt with. (C) 1998 Elsevier Science B.V. All rights reserved.