black liquor Treatment kraft making

1. Black Liquor Treatment
• Black liquor from pulping process in the
papermaking industry is one of the most
industry wastewater to treat owing to it’s high
color and very high chemical oxygen demand.
• Approximately 7 tons of black liquor are
produced in the manufacture of one ton of
pulp
• The black liquor structure, which comprises
lignin and polysaccharide clusters, salt ions and
water.

2. Black Liquor Treatment
• The lignin, the bonding agent of wood or
fibrous plant fibers, is a polymer formed by
phenyl-propane structures.
• During the pulping operation, the lignin is
fragmented and the carbohydrates are
dissolved and converted into acids of low molar
mass, this polysaccharide survives from the
pulping operation to compose the black liquor.

3. Black Liquor Structure

4. Major characteristics
• Major characteristics of Black liquor before
treatment:
materila pH Solid
content %
COD mg/l SiO2 g/l Lingin g/l
Black liquor 13.4 8.2 92700 0.2 24

5. Black liquor Treatment
The black liquor Pre-Treatment Acidification Flocculation
Filtration
Pulping Concentration Modification Dryness
lignin
Water
reducing
agent
In our project we will reuse black liquor in Kraft
process which will be explained
Black liquor treatment goes on traditional
steps which is

6. Black Liquor in kraft process

7. Evaporation
First step is Evaporation of water from black
liquor which come from two sources:
1 - Weak BL from washers
15-20% solids and 80-85% water
2 - BL to recovery boiler
65-85% solids and 15-25% water

8. Evaporation Principle

9. Evaporation Plant
• Example of evaporator officiency

10. Recovery Boiler
Combustion of black liquor in the recovery
boiler happens in four stages.
1 – Drying : In the drying stage, most of all water
in droplet is evaporated, it takes 1-2 seconds for
an average size droplet, Temprature rise rapidly
to nearly 150c and then increase slowly to 300c.

11. Recovery Boiler
2 – Devolaitization: For droplets burned in air, a
birght yellow flame appears at the droplets
surface, this is marks of begining second stage of
burning which is burning organic matter.

12. Recovery Boiler
Char Burning: During his stage the temprature of
droplet rises rapidly nearly 800c and at the end
of this stage the flame disappears totally
indicating the droplet has lost all of its volatile
orgranic matter and the droplet shrinks more
and more.

13. Recovery Boiler

14. Green Liquor preparation
3 – Green liquor preparation:
Solution of the smelt of the recovery boiler in
water from condensation tanks and fresh white
liquor. It contains Na2S and Na2CO3

15. White liquor preparation:
4 - The process is simple chemical reactive
followed by some steps. This step prodecs
cooking liquor for degester from recycled
inorganic chemical generated in the recovery
boiler .

16. White Liquor preparation

17. White liquor preparation:
Lime slaking:
- CaO is added to the green liquor
- CaO reacts in a exothermic reaction with
water:
- The Calciumhydroxide reacts with the
Natriumcarbonate

18. White liquor preparation:

19. White liquor preparation:
Lime separation:
Lime has to be separated from the white liquor
with a pressurized disc filtration.

20. White Liquor preparation
Clarification and Filtration:
Removal of solid particles with a clarifier and a
cross flow filter

21. White Liquor preparation

22. White Liquor preparation

23. White Liquor preparation
– Lime washing: Seperated lime mud is
going to be washed. As washing liquid also
condensed water can be used.
- Washed lime is taken to the lime kiln
- Seperated white liquor is going to the
digester for cooking wood chips again.

24. References
• Black Liquor Combustion in Kraft Recovery Boilers-Numerical
Modelling ISBN 91-7283-301-7 by Reza Fakhrai
• Compution of black liquor droplets M. Hup departmanet of
chemical engineering Turku Finland
• Black liquour evaporators design and operation Kean-Claude Patel
AH Lungerg association Inc. IL 60565
• General charaster
• istics of kraft black liquor recovery boilers Dr. Terry N Adams
Tacoma WA USA
• Evaporation principles and black liqior properties David T Clay,Ph.D
Jacobs Engineering Lake Oswego 97035
• Reuse Of Water In The Pulp And Paper Industry Using The Water
Source Diagram As Tool Marques, S.V.; Delgado, B.E.P.C.; Pessoa,
F.L.P.; Queiroz, E.M. DEQ/EQ/UFRJ