Co-firing coal and the residue from acid hydrolysis of Discorea zingiberensis is an efficient approach for the residue disposal. This paper reports the results of our experimental work on chlorine release in co-firing coal and the residue. The experimental work was done in two steps: to determine the amount of Cl release from different fuel types at different temperatures first, and then to determine the optimum amount of calcium based sorbents to reduce HCl emissions in flue gases. Different types of fuel were tested, including pure residue, pure coal, and coal-residue mixture. Coal briquette that was a 1:1 (mass ratio) mixture of coal and residue and contained 2% (mass) CaO was prepared under compaction at 5 MPa. Chlorine emission can be reduced by adjusting the ratio of residue to coal in the mixture, and effectively controlled when the ratio is between 1:1 (50%) and 1:5 (16.7%). The fuel composition and calcium based sorbents also have great impacts on chlorine retention. The most efficient sorbent is calcium acetate. Although the retention ratio of chlorine increases with the increase in the amount of calcium sorbent added, the mass ratio of around 5% CaO should be the best choice. (C) 2006 Elsevier Ltd. All rights reserved.