Chemistry of Wheat-and Rice-Straw Based CTMP Black Liquor

Abstract

"Chemithermomechanical pulping (CTMP) is an ideal process for producing highyield pulp from wheat and rice straw. It involves low concentrations of cooking chemicals and ultimately elutes black liquor with very low dissolved solids, high in organics and relatively low in inorganic components. This work characterizes the behavior of this liquor in the chemical recovery process. Chemical analysis of the black liquor reveals a high silica content, which indicates a risk of silica scaling in the concentrators. High proportions of total sodium (10.96% o.d. basis) and total sulfur (2.42% o.d. basis) in the inorganic components allow efficient recovery of both these key elements. High organics content helps to maintain low density and high viscosity. This high viscosity increases the solubility of sodium carbonate and sodium sulfate and decreases the risk of burkeite scaling in the concentrators, but increases the risk of heavy scaling after the recovery boiler. For these reasons, chemical recovery of this black liquor will be possible only through decreasing the high viscosities and designing the recovery boiler to generate high steam rates as a result of the high heating values of the relatively higher quantities of organic components."