investigating heat-treated bagasse-based kraft black liquor for physicochemical and rheological properties

Heat treatment is a promising approach to reducing the viscosity and improving the combustion behavior of black liquor. the bagasse-based kraft black liquor was heated in a series digester at a constant temperature of 180˚c in three batches for 15, 20, and 25 min to investigate its physicochemical and rheological properties before and after heat treatment. black liquor heated for 25 min showed the highest residual active alkali consumption of 28.37%. the optimum heat treatment time was 20 min, and the heat-treated black liquor at this condition exhibited residual active alkali 5.02% as na2o and an increase in swelling volume ratio from 12 ml/g to 18 ml/g. rheological studies of original and heat-treated black liquors were carried out in a rotational rheometer at 90˚c and 105˚c in the shear rate range of 1-100 s-1. 20 min heat-treated black liquor showed 74.09% and 71.56% reduction in viscosity at 90˚c and 105˚c, respectively, for 65% solids concentration. the effect of temperature and solids content on the rheological properties of black liquor was discussed. the results showed that black liquors obtained after heat treatment were non-newtonian (pseudoplastic) in nature with a power law index less than unity (n<1). the power law (ostwald de waele) model best fits the obtained viscosity data of heat-treated bagasse black liquor. the work presented here gives an insight into the importance of the heat treatment process for the viscosity reduction of bagasse black liquor. it may help better understand various physicochemical properties and the flow behavior of heat-treated bagasse black liquor for chemical recovery.