Chemical Recovery Division, Central Pulp and Paper Research Institute, Saharanpur-247001 UP, India

Chemical recovery system is an integral part of pulp and paper units and the efficiency of chemical recovery play an important role in economics. With today’s increasingly high energy and chemical costs and stringent environmental regulations, the need for improved recovery of chemicals from the pulp and paper making process has become a critical economic factor in the industry. It is essential that mills maximize steam and power production capacity, reduce re-circulating chemical dead loads and minimize chemical losses. Although earlier agro-based mills were not having recovery furnace due to high silica content of black liquor and smaller capacity, however now chemical recovery in agro-based mills have been made mandatory. Pulp and Paper mills have a desire to increase their pulp production or to adopt the oxygen delignification (ODL) from environmental point of view and also to improve their economy. In such cases, the recovery boiler is often one of the major bottleneck. To debottleneck the recovery boiler, lignin has been extracted from the black liquor, which decreases the load of the boiler in proportion to the lignin extraction. Separation of lignin will affect the properties of the black liquor and the recovery boiler operation. Thus in the present study, optimization of the lignin removal process (LRP) has been done along with the optimization of the mixing of LRP filtrate with the original black liquor to obtain the conditions which can serve the best for enhancing marginal capacity of recovery boiler. A key observation of the results shows that the mixing of the filtrate in the original black liquor in the ratio of 85:15 (black liquor: filtrate) is the most suitable one for its processing in chemical recovery system.

Keywords:Black Liquor (BL); Chemical Recovery; Lignin Removal Process (LRP); Marginal capacity expansion: Oxygen Delignification (ODL).