Modified cooking liquor technology
To enhance pulp yield and reduce load in the chemical recovery process
One trend in certain pulp grades has been the extension of kraft pulping to lower the kappa number of the pulp. This results in a considerable reduction in the consumption of bleaching chemicals, it reduces the effluent load, and it improves heat economies. However, extended cooking also has certain drawbacks.
The combination of conventional white liquor, oxygen delignification, and modified cooking liquors (e.g. polysulfide) often eliminates the drawbacks of extended cooking. The challenges, however, are to find the most efficient and economical method of generating the modified liquor and to obtain the highest possible yield gain from the combination.
The most common generating technology in use today is catalytic air oxidation of the sulfide in the white liquor or green liquor. ANDRITZ offers two technologies for generating modified delignification liquors.
Processes and technologies available from ANDRITZ
StiroX – pressurized white and green liquor oxidation with oxygen gas
- White liquor with low residual sulfide content for oxygen delignification
- Oxidized white liquor helps to control mill sodium and sulfur balances
- Excessive heat energy from exothermic oxidation reactions is recovered as hot water
- Less emissions
MOXY – white liquor sulfide-to-polysulfide conversion
- Polysulfide cooking offers a means of increasing cooking yield
- Optimal conditions for a polysulfide reaction are achieved by blowing air and white liquor through a catalyst bed with activated carbon