Thermal processing of straw black liquor in fluidized and spouted bed

Nowadays, black liquor recovery is important for the economics of the pulp and paper production industry. As a result of the high capital cost of the recovery unit, the corrosive nature of the smelt, and the risk of smeltwater explosions, alternatives to the conventional recovery cycle are under research in order to achieve more efficient and environmentally cleaner processes. These alternatives fall into two categories: high-temperature and low-temperature, according to whether or not the melting point of the black liquor inorganics is reached. The advantage of low-temperature processes is to avoid the formation of smelt. In this work, the feasibility of the thermal processing at low temperature of straw black liquor in two different bench scale reactors has been tested. In the fluidized bed, the loss of fluidization due to bed agglomeration was found to be the main problem in the reactor used. The second reactor used, a spouted bed, presents different characteristics from the fluidized bed, and has been tested in order to overcome the agglomeration observed. Experiments in different operating conditions were carried out in order to get a basic knowledge about the behavior of this residue during pyrolysis, gasification, and combustion processes. To work below the melting point of the black liquor inorganics, reaction temperature was kept under 600 degreesC. Liquid black liquor and dry black liquor were used as feedstocks. Nitrogen, air, and nitrogen-oxygen mixtures were considered as reaction atmospheres.