Recovery and Purification of Gas Emissions from Pulp Production

For pulp production, large-scale enterprises have been built which, while in operation, are subject to new requirements, different from the design ones, for economic efficiency, labour safety, as well as impact on the local population and the environment. Significant success in this work has been achieved by changing the liquor recovery technology, switching to burning black liquor of increased concentration, which makes it possible to almost completely eliminate the largest source of hydrogen sulfide and methyl mercaptan emissions with flue gases, reduce sulfur losses and improve energy efficiency of soda recovery boilers. Another significant source of soda recovery boiler emissions is a smelt dissolving tank vent. An important technological operation of dissolving molten sodium salts with weak white liquor supplied from the causticization shop takes place in the tank. The modern development of smelt leaching technology is related to the improvement of equipment compatible with the technology of regeneration of chemical reagents for pulp production. Heat exchangers and gas purifiers of “gas-liquid” systems, easier to adapt to technological requirements compared to other systems, are installed on the dissolving tank vent. The installation of such equipment provides the change in the smelt leaching technology, and affects the technology of causticization and lime recovery. This article covers the research of the relationship between the technical solutions ensuring the safety of personnel in the boiler shop, heat and chemicals recovery, as well as purification of gas emissions and the changes in the technology of smelt leaching in the soda recovery boiler of the pulp mill. On the basis of experimental data and a mathematical model of the movement of the vapour-gas mixture in the smelt dissolving tank vent, the technological feasibility of installing heat exchangers at different heights of the vent and the possibility of effective purification of gas emissions using a direct-flow sprayer have been considered. The applicability of the irrigation of the steam-gas flow with weak white liquor, which is formed during the cycle of chemical regeneration in pulp production, as well as the conditions for ensuring reliable operation of gas purification equipment, have been investigated. The quantitative characteristics of the necessary change in consumption and composition of weak white liquor and the methods of its supply to the dissolving tank have been obtained.