Transcript Kraft Process

Chemical Department
Prepared by:
Jalak Patel (141260105029)
Pranay Patel (141260105036)
Kuldip Maniya (141260105021)
Kiran Patel (141260105031)
Yash Patel (141260105042)
Guided by:
Jyoti Verma

White liquor.
◦ Fresh pulping liquor for the kraft process containing
NaOH, Na2S, and a variety of impurities.

Black liquor.
◦ The waste liquor from the kraft pulping process.
Contains most of the original inorganic components
(most in different forms) and a high concentration of
dissolved organics.

Green liquor.
◦ Partially recovered kraft liquor (intermediate liquor in
recovery sequence).
2
White Liquor
Digester
Black Liquor
Lime
Kilm
Green Liquor
Recovery
Furnace
This is a very
simplified
diagram.
There are
several steps
between each
box. We will
discuss this
whole
sequence in
depth in a later
lecture.

The kraft process (also known as kraft
pulping or sulfate process) is a process for
conversion of wood into wood
pulp consisting of almost pure cellulose
fibers. It entails treatment of wood chips
with a mixture of sodium hydroxide and
sodium sulfide, known as white liquor, that
breaks the bonds that link lignin to the
cellulose.
Kraft Process
Manufacturing Process

Wood pulp for sack paper is made from softwood by the kraft
process. The long fibers provide the paper its strength and wet
strength chemicals are added to even further improve the strength.
Both white and brown grades are made. Sack paper is then
produced on a paper machine from the wood pulp. The paper
is microcrepped to give porosity and elasticity. Microcrepping is
done by drying with loose draws allowing it to shrink. This causes
the paper to elongate 4% in the machine direction and 10% in the
cross direction without breaking Machine direction elongation can
be further improved by pressing between very elastic cylinders
causing more microcrepping. The paper may be coated
with polyethylene (PE) to ensure an effective barrier
against moisture, greaseand bacteria. A paper sack can be made of
several layers of sack paper depending on the toughness needed.
Kraft paper is produced on paper machines with
moderate machine speeds. The raw material is
normally softwood pulp from the kraft process.
Maintaining a high effective sulfur ratio or sulfidity
is important for the highest possible strength using
the kraft process.
The kraft process can use a wider range of fiber
sources than most other pulping processes. All
types of wood, including very resinous types like
southern pine, and non-wood species like bamboo
and kenaf can be used in the kraft process.



The majority of the chemicals used in the
pulping process are recoverable for use in
further pulping operations
Large amounts of energy are produced in the
recovery boilers during the recovery process
The Kraft process can pulp pine trees
•Various
byproducts containing hydrogen sulfide, methyl
mercaptan, dimethyl sulfide, dimethyl disulfide, and other
volatile sulfurcompounds are the cause of the malodorous air
emissions characteristic for pulp mills utilizing the kraft
process.
•The sulfur dioxide emissions of the kraft pulp mills are much
lower than sulfur dioxide emissions from sulfite mills
•The wastewater effluent can also be a major source of
pollution, containing lignins from the trees, high biological
oxygen demand(BOD) and dissolved organic carbon (DOC),
along with alcohols, chlorates, heavy metals,
and chelating agents.
Thanks