Liquor Heat Treatment Of Wheat Straw Black Liquor To Facilitate Recovery Process In A Paper Mill

Research Article
Tarun, Dhermander Kumar and Harit Kasana
Recovery boiler, residual active alkali, viscosity reduction, swelling volume ratio

Recovery boiler combustion of black liquor to recover energy and cooking chemicals is becoming a necessary technique for non- wood pulping also. However, black liquor viscosity increases exponentially with solids content and therefore causes processing problems for paper industry by being a limited factor due to the high viscosity of non-wood based liquors. The present study highlights the work carried out on liquor heat treatment (LHT) to reduce viscosity and to improve the combustion behaviour of the wheat straw black liquor. Liquor heat treatment is one possible way to overcome the disadvantage of present recovery system. The process is based on the depolymerisation of larger molar mass organic components into lower mass components. This ultimately results in the lowering of viscosity of black liquor and reduction in polysaccharide content which shows up decreased energy consumption in pumping and also lesser scaling in strong liquor pipes. Also the sidewise increase in dry solid concentration raises the boiler capacity and efficiency. Studies were carried out to optimize the LHT process in respect of residual active alkali, treatment temperature and retention time. From the results it could be concluded that a temperature of 1800 C for 15 minutes at a RAA level of 5.5% (w/w as NaOH) was enough for LHT which results in 78% viscosity reduction as well as 55% increment in swelling of wheat straw black liquor.