(A study of Chemical treatment system - A viable alternate to eliminate dry/moist-depithing process in bagasse pulping. As a drive of wastage reduction)

This study has been conducted by Navin Maheshwari, Dr. R.K. Sharma, Aditi Maheshwari a working group of environmentalist & Biotechnologist New Delhi for the development of cleaner technology in pulp and paper Industries. A Program supported by Century Pulp & paper (A Birla Group Company) Lalkua, India.

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.

 

                    

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%

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.

  Analysis of whole Bagasse
  Moisture
%
52.12

  Fiber
%
57.51

  Pith & fines
%
35.21

  Soluble
%
07.28
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Saving of entire quantity of whole fibers, app. 20-25%
Mixing chest
  Chemical Impragnation
 Chemical dosing @105 Liter per M3
Recycling of liquor to comletely exhust the chemical
Wet Storage
Bio Liquor system
Washing or wet
  depithing
 Removal of pith/fines app. 12-15%
Generation of wet pith solid waste of app. 70-80% water contents

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Blank With water

Chemically treated
Chemically treated
Chemically treated
Chemically treated
15 days
15 days
30 days
45 days
60 days
Fibre
59.64
75.02
77.28
78.98
80.00
Pith/Fines
32.16
15.08
14.36
16.26
18.02
Soluble
08.20
09.9
08.36
04.76
01.98
Sugar
Positive
Nil
Nil
Nil
Nil

Note: -

  • 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.

(Results of Alkali Cooking)

S.No.

Pulping condition

Blank with 14% Alkali

Chemically treated
10% Alkali

Chemically treated
14%Alkali

1
Alkali % as Na 2 O
14
10
14
2
Steaming time (mint)
90
90
90
3
Cooking time
60
60
60
4
Cooking temp. ºC
165
165
165
5
Unbld.yield %
53.59
59.12
57.42
6
Rejects %
0.08
0.32
0.05
7
U. Bld. Screened yield %
53.51
58.8
57.35
8
Kappa No.
9.04
14.4
9.4
9
R.A.A.GPL. as Na 2 O
8.9
6.2
8

Unbleached strength property act 35° SR.

1

Burst Factor

27
22
20
2
Tear Factor
42
43
38
3
Breaking Length mtrs
4400
3950
3890
4
Unbld Brightness %
44.9
36.3
43.4

Results

  • There is substantial increase of 6-7% in yield in comparison with conventional cooking.
  • Kappa No. also achieved with in limit.
  • Tear factor also indicate good strength properties
  • Present experiment shows high saving of caustic by 25-30%, however residual recovery of alkali is little less.
  • By reducing the alkali percentage in cooking, the load on recovery can be partly or fully lifted.
  • Silica is not consuming alkali in the case of chemical pre-treatment.
  • Light brushing has to done during washing on pulp to increase the yield further.
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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.

Constraints:   None reported.

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Navin Maheshwari

J-11,2nd Floor,
Kirti Nagar
New Delhi-110015

Fax / phone.: 091-11-25451809, 65450853, 09868039747

E-mail: navinmaheshwari50@rediffmail.com 0r meta_kem@yahoo.com

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Subsequently the case study has undergone another technical review by Dr. Anuradha Salpekar, Director, Indian Institute of Ecology & Environment, New Delhi.