Several properties of black liquor - including residual alkali, temperature, and solids content - are regularly monitored in order to monitor pulping, washing, and evaporation processes at kraft pulp mills. Residual alkali is monitored during cooking to ensure that sufficient residual alkali is present and prevent lignin redeposition. Weak black liquor, strong black liquor, and heavy black liquor solids are observed to monitor washer, evaporator, and concentrator performance, and ensure consistent solids contents to the evaporators and recovery boiler. Other analyses, including heating value, elemental, inorganic, and organic analyses, are used for research, design, and troubleshooting purposes.
Learning Objectives
At the end of this module, you will be able to:
- Describe the basic stages and flow path of black liquor in the kraft pulping liquor cycle
- List the typical components of black liquor
- Describe what happens to the inorganic compounds, organic compounds, and water in heavy black liquor in a recovery boiler
- Define "viscosity," "density," "specific heat," "thermal conductivity" and "boiling point rise"
- Describe the importance of black liquor solids testing and monitoring
- Recognize how more advanced analyses - including heating value, elemental, inorganic, and organic analyses - are used for research, design, and troubleshooting purposes