Process Development for Production of Hard Pitch from Coal Tar for Electrode Industries

Abstract

Coal tar pitch is a residue of coal tar distillation and can be processed suitably to produce hard pitch of desired quality in terms of softening point (SP), benzene insoluble (BI), quinoline insoluble (QI), β-resin and coking value (CV). As per customer requirement, these properties could be achieved by controlling coal tar quality, different parameters during distillation of tar and processing of soft and medium pitch. Coal tar pitch with CV in the range of 55-58%, BI content of 30-32%, QI content of 13-16% and SP of 95-105°C, finds its use as a binder for manufacture of electrodes. During 1993, Bokaro Steel Plant (BSL), SAIL produced poor quality coal tar with high BI and QI content in it due to poor health of coke oven batteries. The by product plant, found it difficult to produce hard pitch to the specification of aluminium and electrode industries. The R & D Centre at SAIL in association with BSL undertook a project of process development for converting high BI and QI content tar to hard pitch by blending it with low BI and QI tar from other plants in an appropriate ratio, modifying operating procedure (tar flow rate to pipestill, second stage evaporator temperature, air flow rate & temp. of soft pitch in a batch reactor) to the customer's requirements. Bokaro Steel Plant produces and sells about 3 000t/year of hard pitch to electrode industries.