CASE STUDY
Robust Valves to Handle Black Liquor Efficiently and Effectively
Pulp mills that use a kraft process to convert wood into wood pulp must invariably deal with black liquor . As this by-product of the digester has several challenging properties , processing it can have a significant impact on valves .
By Nilou Baniassadi , Pulp & Paper Market Lead – Armour Valve
What is Black Liquor
Black Liquor is a combination of lignin , hemicellulose , spent chemicals , and water and is comprised of 15 % solids , 40-45 % soaps , 35-35 % lignin , and 10- 15 % other organics . Approximately 7 tonnes of black liquor are produced in the manufacture of one tonne of pulp . Once produced , black liquor must be pumped to an evaporation plant where is it is concentrated . It is then burnt to produce energy and recover the cooking
Black liquor . Image credit : https :// web . fpinnovations . ca /
chemicals . The strenuous nature of this process puts a significant amount of demand on the valves involved . As black liquor is thick , sticky , and has a high solid content , robust valves are necessary to avoid failure .
Evaporation Plant Efficiency
For black liquor to be combustible , it must reach at least 60 % dryness . As the liquor leaves the washing station , it is made up of about 15 % dry substances , so it must be pumped into an evaporation plant to be concentrated .
Ideally , operators want to evaporate black liquor in the most cost-effective way . Connecting several evaporators in a series and running the liquor through them in sequence has several advantages , as each evaporator handles a portion of the temperature change . About 0.2 tonne live steam is sufficient to evaporate 1 tonne of water from the black liquor ; the steam from one evaporator
Image credit : https :// www . controlsouthern . com / industries / pulp-and-paper / power-and-recovery / heavy-black-liquor-flow /.
36 Valve World Americas | September 2022 • www . valve-world-americas . net