The document discusses different methods of depithing bagasse, a waste material from sugar cane processing that has potential as a fiber source for papermaking. However, bagasse contains pith that is undesirable for papermaking as it lowers pulp yield, increases chemical usage, and causes quality problems. The document examines dry depithing, moist depithing, and a combination method, finding that residual pith content is still over 15% with conventional approaches. It then proposes using a disc mill depithing method that can achieve residual pith levels under 5%, making bagasse a higher quality fiber source. The disc mill approach is analyzed in terms of its operating mechanism and economic feasibility for a 100 ton per day pulp plant

1. SUBMITTED BY : SURJEET PANDEY
B.TECH 2ND YEAR
NIET GREATER NOIDA

2. 
 Paper industry is always on the look out for
alternative materials that can be used as a source of
fibre.
 Many countries have been using bagasse, which is a
waste material left after the crushing operations in
the sugar mills producing sugar from sugar cane
 Though bagasse is a potential raw material for the
paper industry, has one of the serious drawback of
pith associated with the fibrous portion.
INTRODUCTION :

3. 
 Along with the fibrous portions of the bagasse, there is
pith, which is undesirable from the point of view of paper
making.
 The presence of pith in the bagasse has adverse effect in
respect of lower pulp yield, high chemical consumption
and quality related problems besides exhibiting
runnability problems on the paper machine.
 Thus, there has always been interest in the efficient
removal of this pith from the fibrous portion of bagasse so
that the same can be used for pulp and paper making in
an efficient and better manner.
Continue…..

4. 
DRY DEPITHING
MOIST DEPITHING
COMBINATION OF BOTH
TYPES OF DEPITHING

5. 
 Depithing process have been mainly on methods which
have used the DRY/MOIST depithing or a combination of
moist and wet depithing.
 In both the processes the bagasse is mechanically abraded
to break the clusters of pith away from the fibrous portion
of bagasse
 Dry depithing has been accomplished by using a hammer
mill followed by dry screening.
 In the wet depithing, a suspension of previously moist
depithed bagasse is made in water, wherein after the pith
is separated by utilizing the difference in the densities of
the fiber and pith.
COMPARISON

6.  Moist depithing involves direct depithing of bagasse
after crushing of sugar cane at a moisture of around
50%.
 However, even by the best available methods, there
is still some residual pith left in the bagasse (of the
order of more than 15%).
 Moreover, in the wet depithing operations there is
the associated problem of a negative environmental
impact as the pith is obtained in a slurry form which
poses disposal problems besides huge capital and
operational expenses in the process.
Continue………….

7.  Thus there is a demand from the industry to develop
an efficient, depithing process which does not have
the problem from an environmental standpoint.
Continue………….

8. 
 Depithing operations in the Indian pulp and paper
industry are being carried out by the conventionally
available methods of the dry, wet or a combination
of the two methods. In the Indian mills, the average
depithing efficiency is only of the order of 50%,
thereby generation at best a bagasse having a
residual pith of about 15-27%. Even in case of the
most efficient depithing operations being practiced
in India, the residual pith content in the depithed
bagasse has never been less than 15%.
What is PITH ??

9. 
The pith is composed mainly of
parenchyma cells. Pith can’t be
converted into a satisfactory pulp
despite its resemblance to fiber in
chemical composition because of its
small dimensions non fibered
physical nature and close
association with dust.
What is PITH ??

10. 
 Lower yield and high cooking chemical consumption as pith
consumes the chemical reducing their availability for pulping
and bleaching operations thereby necessitating use of high
chemical doses.
 Slower drainage rate at all dewatering stages. Typically higher
soda loss during brown stock washing operation.
 Requirement of more bleaching chemicals and other effects on
paper machine.
 NOTE: (The residual pith content in the depithed bagasse has
never been less than 15%).
Drawbacks of pulping
bagasse with PITH

11. 
Bagasse which is a potential raw material for the paper
industry,has serious problem of PITH associated with
the cellulosic fibrous material which is undesirable
from the point of view of papermaking.
DEPITHING OF
BAGASSE
Whole
bagasse
Dissolved
Matter(10%)
Useful
Fibre(57%)
PITH(33%)

12. 
The presence of pith in the bagasse results in lower
pulp yield,high KAPPA NO. and high chemical
consumption during pulping.There has always been
interest in the removal of this pith from the fibrous
portion of bagasse so that the same can be effectively
for high quality pulp production.
Continue………

13. 
 Pith separation from the fibre is essential to upgrade
the quality of raw material.
 Pith constitutes nearly 30-35% of bagasse the rest
being useful fibre (60-65)and soluble (5%).
 The chemical properties of fibre and pith are more or
less similar but they differ vastly in physical and
morphological properties.
 Pith contains a lot of soft , thin walled irregular
shaped parenchymatous cell with higher quantity of
inorganic ASH and high absorbency.
BAGASSE PREPARATION

14. 
A. DRY DEPITHING PROCESS : It is carried out on
stored bagasse having a moisture content of less
than 35%.
 Hammers and shredder are used in the separation of
pith from bagasse .
 This method has several disadvantage like heavy
wear and tear of the process equipment, loss of
valuable fiber along with the pith and production of
lots of dust etc.
 The depithing efficiency of the process is quite low
and not more than 40%.
DEPITHING OPERATIONS

15. DRY DEPITHER

16. 
 The depithed bagasse obtained by this process still
contain 20%residual pith as against the original pith
content of 30-35% in the original bagasse.
B. MOIST DEPITHING: This type of depithing is
generally done at the sugar mill when the wet bagasse
has about 50% moisture.
 Several type of depithers such as Horkel, Rieth,
Gunne, Peadco and others are commerciallly used
for moist depithing.
 These depithers are designed to break open the fiber
DEPITHING OPERATIONS

17. 
Bundles and to dislodge the pith by mechanical
rubbing and mild disintegrating action.
 The unit consist of a rotor with sewing or rigid
hammer attached to it.
 The hammers are enclosed fully or partially by
perforated screen plates through which pith fraction
is discharged.
 Upto 50% of the original pith content in bagasse is
removed by this method.
Continue……

18. MOIST DEPITHED BAGASSE
USEFUL
FIBER
(68.5%)
PITH (25%)
DISSOLVED
MATTER
(6.5%)

19. 
 The process is suitable for entire baled bagasse delivered
from bulk storage.
 This method is more applicable at the pulp mill for the
final cleaning and depithing just before bagasse enters the
digester.
 The bagasse is fed to the hydropulper where it is
thoroughly wetted and broken up at a consistency of
around 2 ti2.5% which maintained by continuous
recirculation of process water.
 Residual pith content not less than 14-15%and depithing
efficiency is around 70%.
C. WET DEPITHING PROCESS

20. WET DEPITHED
BAGASSE
USEFUL
FIBER(85.5%)
PITH (12.5%)
DISSOLVED
MATTER(2%)

21. 
DISC MILL DEPITHING

22. 
 The use of disk mill method for depithing results in a
clean raw material having a residual pith content of
nearly 5%.
 The procedure can also work with most bagasse
having moisture content of 5o%
Continue……

23. DISC MILL DEPITHED
BAGASSE
USEFUL
FIBER(91.5%)
PITH(<5%)
DISSOLVED
MATTER(2.5%)

24. RAW
MATERI
AL
MAGNET
IC
SEPARA
TOR
CONVEY
ER BELT
SCREW FEEDER
TREATMENT CHAMBER WITH DISC AND MILLING
ELEMENTS
PITH/FIBER SEPARATING SYSTEM WITH ENDLESS
ROTATING BRUSH AND SCREENS
O/P SEPARATED PITH AND FIBER PORTION OF BAGASSE
IN TWO OUTLETS
FLOW CHART

25.  The use of disk mill method for depithing results in a clean raw material having a residual
pith content of nearly 5%. The procedure can also work with most bagasse having a higher
moisture content of 50%.
 The balanced rotating disk is mounted on a shaft with a friction brush assembly. The shaft
is mounted in a castiron housing supported by double ball bearing.
 There are specially designed milling component fixed along the periphery of both the
disks. Each of the milling component is fixed on to the disk using a groove-screw method.
 The diameter of the disks and the size of the milling component fixed on the disk depends
on the size and throughput desiredfrom the equipment/set up.
 In any case one milling component is placed at every 15 degrees on the disk. The length
and width of the milling component is therefore fixed accordingly, depending on the
diameter of the disks. The gap between the rotating and the stationary disk is adjusted by
means of a device mounted on the basic housing of the shaft.
 The whole assembly of the disks and the gap adjustment mechanism are mounted on a
welded steel profile frame. The incoming raw material is distributed evenly with the help
of special structures protruding over the surface of the rotary disk.
 The separated pith and fibrous material falls though the sieves by gravity and is collected
separately with the help of hoppers at the bottom of the sieves. The positioning of the
sieves and the opening per linear inch is optimized to separate out the pith from the
fibrous portion of bagasse.
Continue…..

26. 
0
5
10
15
20
25
30
35
WHOLE
BAGASSE
DRY DEPITHED WET DEPITHED DISC MILL
Residual Pith Content in Bagasse
After Depithing
P
I
T
H
C
O
N
T
E
N
T
%

27. 
Assumptions
Pith in Original Bagasse :30%
Pith in Conventional Depith Bagasse :18%
Pith in Disc Mill Depith Bagasse :5%
Accept after disc milling :70%
Pulp Mill Capacity :100TPD
Pulp Yield from Conventionally Depith Bagasse :48%
Pulp Yield from Disc Mill Depithed Bagasse :50%
Raw Material required for 100 Ton Pulp Production
Disc Mill depith Bagasse (yield 50%) :100TPD
Original Bagasse (accept 70%) :(l00x200)/70 = 286 TPD
 Raw Material to be processed will be 15 tonlhr for 20 working hrs. Three-disc
mill of 5 tonlhr capacity each are required.
 Drive Motor Capacity (3 nos.) : 250 kw
COST ECONOMICS OF DISC MILL DEPITHING
PROCESS FOR SETTING UP
100 TON PER DAY PULP PLANT

28. 
Cost of three disc mills (3 x 8lacs) :24lacs
Cost of three motors (3 x 4lacs) :12lacs
Cost of Conveyers and other accessories :14lacs
Total Equipment Cost :50lacs
Cost of Disc Mill Depithing per Ton of Pulp
Equipment cost :50lacs
Depreciation per year (10%) :5lacs
Interest per year (10%) :5lacs
Interest & depreciation per day :Rs3000
Electricity consumption per day (100 x20 x3) :6000kwh
Cost of electricity per rate @ Rs. 4.5 per unit :Rs27000
Maintenance (2% of equipment cost) per day :Rs300
Manpower cost per day :Rs900
(Three shifts two persons per shift)
Rate 150 per day per person (6 x 150)
Total operating cost for producing 100TPD bleached
bagasse pulp =3000+27000+300+900 =31200Rs
COST OF PLANT

29. 
Cleaner Production Principle :
The chemical properties are of obvious importance in manufacturing of cellulose
derivatives. The chemical properties of cellulose cannot be regarded as fixed since
cellulose undergoes appreciable chemical change upon aging as evidenced by the
deterioration, which occurs even during storage of pulp and aging of paper.
Cellulose is influenced a lot by heat, air, light, alkalinity, acidity etc.
COMPARISON
Base & present Process: In practice the fibers suffer considerable damages during
sugar extraction and hammering during moist/dry Depithing. The mechanical
depithing process contributes a lot of environmental disposal problem . In this
mechanical process the 8-10 % pith cell removed and 20-25 % useful fiber lost due
to hammering and subsequently in wet depithing or washing further generate
heavy amount of wet pith with 70 -80% moisture contents, which create heavy
disposal problem. Whereas this wet depithing process removed 3-5 % of pith and
loss of useful fiber is up to 12-15%
DEPITHING OF BAGASSE BY CHEMICAL
TREATMENT PROCESS

30. 
 Process Changes as adopted: These alternatives for depithing of bagasse,
In place of putting bagasse in mechanical depithers or hammerers, the
chemical treatment by soaking process was adopted, to avoid any type of
physical losses of fiber. Chemical treatment by pre-treatment solution at
ambient temperature is just a pre requisite for opening up the crystalline
structure of bagasse, which is made up of lignin, hemicelluloses - xylan,
mannose, arabidoglactan and cellulose (more than 50%). Chemical
treatment causes hydrolysis, which breaks open the structure, releasing
these components and larger amount of the pith cell removed easily
during the subsequent washing process. This is as simple as soaking the
cloths in detergents and rinsing with water under agitation. Moreover
the spent liquor can be recycled at any number of time with little make of
chemical by way of on line pH control.
 Screw types de-watering device is further helpful to control the moisture
contents in pith and reduce the water usage. Pith with lower moisture
contents can be readily fire in boiler.
Continued…………………

31. 
ANALYSIS OF BAGASSE
ANALYSIS OF WHOLE BAGASS
MOISTURE
FIBER
PITH AND
FINES
SOLUBLE
%
%
%
%
52
57
35
8

32. 
Blank
With
water
Chemicall
y treated
Chemicall
y treated
Chemicall
y treated
Chemicall
y treated
15 DAYS 15DAYS 30DAYS 45DAYS 60DAYS
FIBER 59.64 75.02 77.28 78.98 80
PITH
FINES
32.16 15.08 14.36 16.26 18.02
SOLUBL
E
08.20 09.9 08.36 04.76 01.98
SUGAR Positive NILL NILL NILL NILL
RESULT

33. 
 Net removal of pith is at par with mechanical
process.
 Saving of useful fiber up to 25-30%
 There is increase in yield of fibres as time goes on.
 No damages of fibers
 Swelling of fiber makes wet depithing easier.
 Wet pith disposal is not a problem, by adopting
dewatering system
NOTE

34. 
An alternative method of chemical pre-treatment for the use of sugar-cane bagasse
depithing permits to recover more useful fiber in the regular process, instead of
mechanical hammering depithing process. This kind of process is of great
importance saving of useful fiber and reduction of solid waste generation. Hence
following advantages can be drive :
 Net removal of pith is at par with mechanical process.
 Saving of useful fiber up to 25-30%
 No damages of fibers under the changed process of wet condition
 Swelling of fiber makes wet depithing easier.
 Chemical treatment losses polysaccharides-lignin bond which can be digested
with low alkali, hence saving of alkali up to 20-25%.
 Wet pith disposal is not a problem, by adopting dewatering system.
 Cost of chemical treatment can be off set by saving of heavy power consumption
in mechanical depithers.
 Saving of heavy consumption of power used in hammering
Environmental and Economic
Benefits