Simultaneous prediction of steam production and reduction efficiency in recovery boilers of pulping process

The role of the recovery boiler in the process of pulping is vital as it renders the industrial plant environmentally and economically viable. This boiler reduces the environmental impact of directly disposing liquor. Moreover, the equipment produces "green" steam without the use of fossil fuels as it burns the byproduct (black liquor). The reduction efficiency is the most important variable used to verify the completeness of black liquor combustion. However, because of the need to ensure green steam production, vapor generation in recovery boilers has become an important variable for evaluation. In the literature, only one of the cited variables (reduction efficiency and vapor generation) is found at a time. In this study, a recovery boiler is simulated using Aspen Plus (R) commercial software to determine the effect of airflows on both the reduction efficiency and green steam production simultaneously. The free energy minimization method is used to predict the composition and production of smelt and the composition of exhaust gas. The results are compared with industrial and literature data, and the model predictions are found to agree with the measurements. Furthermore, a sensitivity analysis is performed on the airflow rates to verify the possibility of increasing steam production without impairing the reduction efficiency. The observations indicated a feasibility of increasing steam by 1 t/h, resulting in a reduction of 675,840 Nm(3)/year of natural gas usage in conventional boilers. Reduction of CO, SOX, and NOX emissions by 57, 76, and 22%, respectively, can also be achieved owing to these improved airflow rates. (C) 2020 Elsevier Ltd. All rights reserved.