At what concentration is black liquor considered safe to fire?

Black liquor is a byproduct of the kraft process of pulping wood to produce paper and is primarily composed of water, organic matter, and inorganic chemicals. The concentration of black liquor is a critical factor in determining its safety for combustion in recovery boilers.

At a concentration of around 58%, black liquor contains enough solids to be effectively fired in recovery boilers while still being manageable in terms of viscosity and combustion characteristics. When black liquor is too dilute, it can lead to inefficient combustion and increased emissions, while concentrations that are too high may cause issues with handling and flow in the boiler system. Therefore, a concentration of 58% strikes a balance, ensuring that the liquor can be combusted efficiently without risking operational problems or safety hazards associated with higher concentrations.

Understanding the characteristics of black liquor at varying concentrations informs operational decisions in papermaking and recovery processes, making it essential for power engineers to have a good grasp of these thresholds.