picture of stirox white liquor oxidation reactor

ANDRITZ technologies for modifying cooking liquors

In addition to its technologies for the traditional conversion of green to white liquor in a pulp mill, ANDRITZ PULP & PAPER has developed advanced technologies to improve pulp yield and reduce the load in the chemical recovery process.

picture of stirox white liquor oxidation reactor

StiroX white liquor oxidation reactor

White liquor sulfide-to-polysulfide conversion equipment

White liquor sulfide-to-polysulfide conversion at MetsäFibre Joutseno, Finland.

Modified liquors as an alternative to extended cooking

One method of lowering the kappa number in certain pulp grades is to extend the cooking process.  This often results in a considerable reduction in the consumption of bleaching chemicals, reduces the effluent load, and improves heat economies. However, extended cooking also has certain drawbacks.

These drawbacks can be minimized or eliminated with the correct combination of using conventional white liquor, oxygen delignification, and modified cooking liquors (e.g. polysulfide). The challenge in using this combination is to arrive at the most efficient and economical method of producing the modified liquor in order to achieve the highest possible yield gain from the combination.

Two ANDRITZ technologies for producing modified liquors

ANDRITZ has two technologies available for generating modified delignification liquors. The most common is Moxy – a technology that uses catalytic air oxidation to convert the sulfides in the white liquor to polysulphides.  For non-catalytic oxidation, ANDRITZ offers an oxygen-based technology alternative called StiroX.  

StiroX – pressurized white and green liquor oxidation with oxygen gas

  • White liquor with low residual sulfide content for oxygen delignification
  • Oxidized white liquor helps control mill sodium and sulfur balances
  • Excess heat energy from exothermic oxidation reaction is recovered as hot water
  • Less emissions

MOXY – white liquor sulfide-to-polysulfide conversion

  • Effective, proven method for increasing cooking yield
  • Optimal conditions for a polysulfide reaction are achieved by blowing air and white liquor through a catalyst bed of activated carbon

Find out more ...

  • pp-pulpchemical-whiteliquorplant-moxyupgrade-polysulfide-en.pdf
    Polysulfide cooking

    Polysulfide cooking - Improved pulp yield and pulp properties

    PDF : 122 KB
  • Metsä Fibre Joutseno - SPECTRUM 28 PDF : 592 KB