Washing delignified pulp
Lower the pH of the pulp to improve drainage.
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Application of CO₂ for paper mill production optimisation
We can find different phases in the paper production line where the use of CO₂ for pH safe acidification leads to a relevant improvement by upgrading the drainage or recovering chemicals.
Kraft pulp pH control
Replaces the strong acids to provide more consistent control.
Tissue paper pH control
CO₂ can be used at the pH control of the pulp at two different points.
Flotation system improvement
Replace part of the compressed air with CO₂ as a carrier gas during flotation.
PCC production
CO₂ is used to produce precipitated calcium carbonate for the production of printing paper.
Kraft pulp pH control tower
Benefits
|
1
Reduce the pH of the
pulp to have better draining. |
2
Reduction of dilution
factor. |
3
Increase content of
black solids. |
4
Increase
productivity. |
In case the washed pulp goes to the bleaching process, CO₂ also allows a reduction of the chlorinated agents used at the first stage, (CDO).
Replace strong acids
CO₂ can also be used after the refining pulp process, to fine tune the pH level.
CO₂ is generally used to replace strong acids (H₂SO₄), SO₂ and aluminium sulphate, providing a smoother control, and avoiding great variations at the pH values. It allows a reduction of the consumption of aluminium sulphate dosed for pH control, which is, a partial substitution of the aluminium sulphate.
In plants that work with recycled paper as raw material
After bleaching with peroxide and NaOH, the CO2 is injected to adjust the pH level to values around 7.0 to avoid brightness reversion.
In mills that use cellulose as raw material
CO2 is used for the pH control of the pulp near the head box of the paper machine. This pH control provides a better draining performance at the wire in the paper machine.
Flotation System
CO₂ is used in effluent treatment in flotation system to replace part of the compressed air used as a carrier gas during flotation (primary treatment of fibre recovery).
As CO₂ has more affinity with the liquid phase than the air, so along the process it creates small bubbles, and improves flotation during the process, improving the flotation. Efficiency can be increased by around 15%. Usually, CO₂ replaces from 40 to 60% of the total compressed air used.
PCC production
CO2 is used for PCC (Precipitated Calcium Carbonate); production, PCC is used as a filler in the alkaline sizing papers production (print paper).
Kraft pulp pH control tower.
CO₂ is used to replace strong acids (HCO₂ SO4 ), and aluminium sulphate providing a smoother control, it avoids great variation at the CO₂.
It's used before or after the refining process, aiming a thin adjustment of the pH level, and consequently, a reduction of the consumption of aluminium sulphate or sulfuric acid dosed for pH control, which is, total or partial to neutral / alkaline sizing of paper.
CO₂ control to press high consistency
Special packaging paper Bags. (bags of cement, multi-wall bags).
CO₂ is used to eliminate aluminium sulphate providing a smoother control, and avoiding great variation of pH values. CO₂ is used in high consistency press, aiming adjustment of the pH and, consequently improve the pulp drain-ability. The consistency expected is around 30%. A reduction on the consumption of aluminium sulphate dosed for pH control is significant. The mechanical properties of this type of paper are improved. This is very important for tear resistance of paper bags.
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