ANDRITZ Lignin Recovery systems
ANDRITZ began pilot plant testing Lignin Recovery alternatives in 2010 and then proceeded to design a portable pilot plant unit that was transported to various mills. This helped solidify the design for a flexible system (one stage without washing, two stages with acid washing, or two stages with acid washing and drying).
Depending on the intended use of the lignin, ANDRITZ tailors the Lignin Recovery system to achieve a mill’s exact goals. As with many ANDRITZ solutions, the company can deliver a complete plant – with the process design; main equipment including presses, crushers, dryer, bag filter, and lime kiln burner; as well as automation, and erection – from one source.
In its most complete form, the Lignin Recovery system consists of these sub-processes:
- Precipitation: where the lignin in black liquor from the evaporation plant is precipitated out of 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 washed in a displacement washer with hot water to remove the sodium sulfate formed during the dilution wash.
- Drying: where the moist lignin is reduced to proper size particles and then dried.
The ANDRITZ 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 content of lignin is typically 60-62% before the drying stage, and 95% after.