Modification of precipitated kraft lignin through the addition of calcium - reduction of SO2 emission

Ways in which precipitated black liquor lignin can be modified by adding calcium in order to reduce SO2 emission in the flue gases after combustion were investigated. In this study, precipitated kraft lignin was modified by adding calcium in different amounts: 0-20 w/w-%. The experimental results indicated that the lignin was saturated with calcium ions at about 0.8 mmol Ca/g lignin. The flue gases from combustion (at 700 degrees C) of the modified lignin and the unmodified lignin were analysed with respect to content of SO2. The ashes from combustion tests were also analysed using X-ray diffraction. The results from combustion tests showed that the SO2 emission could be reduced by approx. 50% by adding calcium. Furthermore, the X-ray diffraction analyses of the ashes showed that calcium sulphate was formed during the combustion of the modified lignin.