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  • PULP & PAPER products
  • Pulp production
  • Kraft pulp
  • A-Recovery+
  • Sulfuric acid production

A-Recovery+ chemical recovery concept for on-site production of sulfuric acid in kraft mills

Producing commercial-quality sulfuric acid on site from concentrated non-condensable gases

ANDRITZ’s innovation called A-Recovery+ chemical recovery concept 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+ sulfuric acid production


Softwood mills often have a sulfur surplus due to additional sulfur inputs such as a tall oil plant. The traditional way to manage sulfur surplus has been to dump recovery boiler fly ash. The ash consists mainly of sodium sulfate (Na2SO4) and sodium carbonate (Na2CO3) – meaning that, in addition to dumping sulfur, valuable sodium is also dumped. The lost sodium is compensated by purchasing sodium hydroxide (NaOH). This can be expensive.

An alternative is the on-site production of sulfuric acid (H2SO4) to significantly reduce, or to even eliminate, the need for recovery boiler fly ash dumping. The A-Recovery+ chemical recovery concept produces concentrated commercial-quality H2SO4 from concentrated non-condensable gases (CNCG) using the Wet-gas Sulfuric Acid (WSA) process developed by Haldor Topsoe, which uses catalytic conversion and condensation. Up to 99.9% of the sulfur in CNCGs can be converted into concentrated sulfuric acid with the WSA process. 

The sulfuric acid from WSA is commercial-grade since the liquefaction of H2SO4 is performed at 100% condensation. This is critical, especially for demanding applications such as ClO2 generation. Additional sulfur capacity can also be created by extracting more than just the surplus sulfur as CNCG, which can save money in the optimization of make-up chemicals – as the internal Na2SO4 stream can be used as sodium make-up instead of purchased NaOH. 

There are over 150 references for the WSA technology operating worldwide on a variety of sulfurous gas streams as well as spent sulfuric acid. It is a very well-proven and robust technology.

WSA plant (3D rendering)


WSA plant (3D rendering)


Benefits of A-Recovery+ sulfuric acid production

  • Environmental and economic savings
  • Helps manage and control the mill’s sodium sulfur (Na/S) balance
  • Avoids costs for dumping recovery boiler fly ash
  • Avoids costs for purchase of make-up chemicals

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