Desilication of agro based black liquor and green liquor using jet loop reactor

Abstract

Non-wood fibers represent the largest resource of fibrous materials for many developing countries in the world. Attention is now being focused on cellulose bearing agricultural residues, which can be used as raw materials for production of paper. Though chemical pulping of these raw materials poses no problem, major difficulty arises in the recovery of heat and chemicals from the spent cooking chemical (black liquor). The presence of silica in black liquor obtained from agro based pulp and paper mill causes serious problems at filtration, washing, evaporation, burning, recausticizing and clarification levels of chemical recovery. It is, therefore, necessary to remove silica before the black liquor is concentrated to high solid content. The success of the desilication process by carbonation lies in accurate pH control otherwise lignin co-precipitation occurs during desilication. In the present work, a high mass transfer efficient, compact Jet Loop Reactors (JLR) or some times called as Highly Compact Reactor (HCR) is used for desilication to obtain exact pH control. The experiments were carried out in a 15 L reactor at room temperature as well as at higher temperatures. The results obtained in JLR are compared with those obtained by Bubble Column Reactor (BCR). Desilication of green liquor in both the reactors at different temperatures is also studied. The results show that desilication in JLR is more efficient at higher temperatures.