Abstract
In pulp and paper mills, the aqueous solution extracted from the pulping process in the wood digester is called black liquor, which consists of organic and inorganic compounds. When leaving the digester sector, black liquor has about 15 wt% of solids and to be used as a fuel in the recovery boiler it is necessary to raise this solids content to 75 wt%, removing water in a battery of multiple effect evaporators.
Some black liquor physical properties, such as, salt contents and boiling point rise (BPR), are strongly dependent on the kind of wood processed (hardwood or softwood) and on operational conditions during the digestion process. Knowledge and comprehension of the relationship between these physical properties of black liquor are essential for studies aiming at a greater energetic performance of the black liquor evaporation unit.
The continuous increasing of the production rate of pulp and paper mills around the world also causes an increasing of black liquor production, and then the concentration process of this liquor may represent a bottlenecking problem when operational problems arise from scaling formation in evaporators.
The concentration of solids in black liquor above 75 wt% causes scaling formation on the heat transfer surfaces of evaporators and concentrators, due to precipitation of sodium salts, reducing the overall efficiency of this equipment.
The aim of this work is to evaluate the potential of some traditional thermal analyses techniques, TG and DSC, as alternative methods to estimate solids content in eucalyptus black liquor, since this information is essential to understand scaling formation process. These alternative methods may represent a faster and safer option when compared with conventional gravimetric methods.
The results have shown that it is possible to use these alternative techniques to obtain fine and accurate results, but it is important to observe that the cost-benefit relationship of the traditional technique is much greater. This work represents an important contribution since there are not many works in the literature dealing with the use of these techniques for eucalyptus black liquor samples.
