ANDRITZ LignaRec™ lignin recovery - Recovering high-quality lignin from black liquor

Lignin is a main wood component that is separated during the cooking process and combusted in the chemical recovery boiler as an organic compound in concentrated black liquor.

For kraft mills, lignin recovery presents an opportunity to generate new revenue streams by replacing fossil materials with lignin. This process is particularly advantageous when there is a need to remove and recover lignin from the recovery boiler to alleviate bottlenecks. Lignin has immense potential for various end-use applications, including its use in composites and as a substitute for phenol and aromatic compounds.

There is also the potential to create an additional revenue stream as high-quality lignin is a bioproduct in demand as a raw material for composites or as a substitute for phenolic and aromatic compounds.

Depending on the intended use of the lignin, ANDRITZ tailors the lignin recovery system to achieve a mill’s exact goals. The LignaRec lignin recovery process is designed to remove lignin from black liquor at 35–45% dry solids, having a typical pH of 12–13. After filtration and washing, the dry solids lignin content is typically 60–62% before the drying stage and 95% afterwards.

In its most complete form, LignaRec lignin recovery consists of these sub-processes:

• Precipitation: where the lignin in black liquor from the evaporation plant is precipitated out of the solution and the slurry is filtered to separate the precipitated lignin from the lignin-lean black liquor.
• Acid wash: where impurities (mostly sodium) are leached from the lignin with sulfuric acid in a dilution wash and the lignin is displacement-washed with hot water to remove the sodium sulfate formed during the dilution wash. Since sulfuric acid is used for the acid washing, this process is highly synergistic with the ANDRITZ SulfoLoop™ sulfuric acid plant utilizing the Wet-gas Sulfuric Acid (WSA) technology.
• Drying: where the moist lignin is reduced to proper-sized particles and then dried.

As with many ANDRITZ solutions, the company can deliver a complete plant – with the process design; main equipment including lignin recovery process with ANDRITZ filter presses, dryer, and lime kiln burner, as well as automation, and erection – from one source.

LignaRec™ lignin recovery is part of the ANDRITZ’s CircleToZero initiative, which includes new technologies aimed at optimizing pulp mill side streams. This global initiative for our pulp and paper customers brings together the continuous development and improvement of existing ANDRITZ technology solutions with an ambitious innovation goal for the future: To eliminate unused side streams, create new added-value products, and lay the foundation for zero emissions and zero waste production.