KINETIC-MODEL FOR THE CAUSTICIZING REACTION

Industrial causticizing systems are operated as open stirred tank reac tors at temperatures near 100 degrees C. Lower causticizing efficiency , ineffective liquor strength control, and higher energy consumption a re some of the inherent problems associated with this system. Pressuri zed causticizing at elevated temperatures with appropriate sensors wou ld lend itself to better control and minimize the above problems. This will result in uniform white liquor supply to the digester and, in tu rn, will yield improved pulp uniformity, productivity, and overall cos t efficiency. A laboratory pressurized reactor was developed and analy tical grade lime and synthetic green liquor were used to develop a kin etic model without mass transfer effects. A pseudo homogenous liquid p hase kinetic model that can predict causticizing efficiency based on l iquor properties has been developed. The model parameters were estimat ed with experimental data using standard optimization routines. The mo del predictions were found to be within 1% of the measured efficiency. Mass transfer effects encountered in an industrial system can be easi ly incorporated in this model, on the basis of data obtained for indus trial lime and mixing conditions. The mill-specific model, supplemente d with on-line liquor property measurements, will allow closure of the control loop to produce uniform white liquor with improved causticizi ng efficiency.