Recovered lignin cake
  • Pulp & Paper
  • Pulp
  • Kraft pulp
  • Chemical recovery solutions
  • Lignin recovery in kraft mills

A-Recovery+ chemical recovery concept for lignin recovery in kraft mills

Recovering high-quality lignin from black liquor

ANDRITZ's innovation called A-Recovery+ shines a new light on the chemical cycle in a kraft mill. It offers tailored solutions to optimize the chemical balances in the mill and the ability to generate additional revenue and/or avoid the purchase of costly make-up chemicals.

A-Recovery+ lignin recovery with A-lignin


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 with limited recovery facilities, there may be a need to remove and recover some of the lignin outside of the recovery boiler to debottleneck the boiler. 

This is where the A-Recovery+ lignin recovery concept is best used – to debottleneck a recovery boiler and substitute a sustainable biofuel in place of purchased fossil fuels. 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 A-Recovery+ 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.

Recovered lignin cake

Recovered lignin cake


In its most complete form, A-Recovery+ 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 A-Recovery+ sulfuric acid plant utilizing the Wet-gas Sulfuric Acid (WSA) process.

  • 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.

Flowsheet of ANDRITZ lignin recovery process

The ANDRITZ Lignin Recovery process


Benefits of A-Recovery+ lignin recovery

  • Environmental and economic savings
  • Debottlenecking of recovery boiler
  • Substitute biofuel for lime kiln
  • Additional revenue stream as bioproduct raw material