(614f) Determination of Pyrolysis Characteristics of Agricultural Residues Black Liquor Using Thermogravimetric Analysis

Black liquor is a by-product of pulp mills that produce paper-grade pulp from woody and non-woody plant materials. Conventionally, the black liquor is subjected to thermo-chemical conversion process to recover the energy and the chemicals. Adequate knowledge of thermal behavior of the black liquor is essential for efficient design and operation of the recovery process. In the present work, thermal degradation of black liquor solids obtained from soda pulping of an agricultural residue (wheat straw) was studied using thermogravimetric analysis (TGA). The agri-residue black liquor solids were pyrolysed in nitrogen atmosphere from ambient temperature to 1000 ^oC. The experiments were conducted at four different heating rates of 5, 10, 15 and 20 ^oC temperature-rise per minute.

Thermogravimetric analysis showed that there were three stages of mass loss in pyrolysis of agri-residue black liquor; evaporation of the moisture, separation of the volatile material, and reduction of the alkali salts. Carbonates and silicates of sodium remained as residue after the pyroysis. The rate of heating showed a small effect on the thermogravimetric (TG) and differential thermogravimetric (DTG) curves; mass loss peaks were shifted towards slightly higher temperatures.  The TGA curves suggested that the black liquor pyrolysis could be considered as combination of three reactions, and the TGA curves could be fitted with a high correlation coefficient to a summation of three Weibull distribution functions. Ozawa and Kissinger methods were used to find out the kinetic parameters such as activation energy and pre-exponential factor for the pyrolysis of black liquor.