Distillation tower corrosion: synergistic effects of chlorine and phenolic compounds in coal liquids

Severe corrosion problems were encountered in the fractionator area of major solvent refined coal (SRC) pilot plants. Chemical characterization and corrosion experiments using liquids from the T-105 fractionating tower of the Wilsonville, Alabama SRC plant are described. Tower feed liquids were obtained when the plant was processing low and high chlorine content coals without additives. Liquids from individual trays were obtained when the plant feed included additions of sodium carbonate. In summary, the experimental results in this report clearly show that for the plant feed and operational conditions discussed here: (1) much of the chloride in the liquid feed to the T-105 tower is in a water soluble chloride form when a high-chlorine coal is processed; (2) 40 to 50 weight percent of the liquid in the trays in the T-105 tower at the Wilsonville demonstration plant are phenols; these are primarily phenol, cresols, and dimethylphenols; (3) ammonium chloride, when added to the T-105 tray 9 liquid, causes a dramatic (10 fold or more) increase in the corrosion rates of selected coupons; 665 ppM chloride gives laboratory corrosion rates that are close to the high rates observed in the demonstration plant; (4) ammonium chloride addition to the oil fraction (traymore » 9 liquid with the phenols extracted) does not cause an increase in the corrosion rate; however, the high corrosion rate is observed when the phenol fraction is added back to the oil fraction; (5) the synergistic effect of the ammonium chloride and phenol combination was demonstrated; high solubility of the ammonium chloride in tray 9 liquid, but not in the tray 9 liquid after phenol extraction, indicates that ammonium chloride solubility is at least in part responsible for this synergistic effect. It is likely that a similar cooperative effect is responsible for the Wilsonville tower corrosion.« less