The present invention relates to the introduction of a new concept of Total Oxidative Bleaching (TOB) process in pulp & paper industry by replacing the alkaline extraction stage reinforced with hydrogen peroxide by oxidative stage with the use of oxidative chemical (Sodium percarbonate) in ECF sequence, which has resulted in
a) Improved fiber recovery
b) Reduction in effluent load
c) With improved pulp quality.
BACKGROUND OF THE INVENTION
The conventional method for pulp bleaching employs multi-stage bleaching sequence which traditionally based on the use of Chlorination stage/ alkali extraction stage/ hypochlorite stages (CEHH).
In general, pulp and paper mill effluents contain a complex mixture of various classes of organic compounds, such as degradation products of carbohydrates, lignin, and extractives.
In conventional bleaching process (CEHH) the generation of AOX level was very high therefore a new technology was adopted i.e. Elemental Chlorine Free (ECF) bleaching. In the ECF bleaching normal sequence being adopted are chlorine dioxide/ alkaline extraction reinforced with hydrogen peroxide / Chlorine dioxide. (Do/Eop/Di)
In ECF Bleaching, most of the pollutant load in effluent is generated from initial caustic extraction stage which produces about75% of the dissolved organic material, 60% of the COD load, 40 to 50% of the BOD, and 80% of the color-imparting substances of bleach plant effluents are reportedly contributed by extraction-stage effluents. Therefore, a treatment method that can degrade, de-chlorinate, and decolorize extraction-stage effluent

can tackle most of the environmental pollution problems associated with bleach plant effluent.
For the protection of the environment, and also to satisfy legal requirements, it is necessary for the industry to remove harmful materials from effluent before it is discharged to the environment. Accordingly, it is an object of the present invention to provide a method for reduction of effluent pollution load on ETP with improvement in strength properties of the final pulp produce.
OBJECTIVE OF THE INVENTION
Main objective of the invention is to make pulp bleaching process as Total oxidative Bleaching (TOB) through which improved yield of final bleached pulp and reduction in effluent load in terms of colour, COD and BOD with improved pulp quality by substituting alkaline extraction stage reinforced with hydrogen peroxide with oxidative stage by using oxidative chemical (Sodium percarbonate) in pulp bleaching sequence.
SUMMARY OF THE INVENTION
The present invention is focused to replace hydrogen peroxide (H2O2) reinforced alkali extraction stage of ECF pulp bleaching sequence by oxidative chemical (sodium percarbonate) which generates maximum pollutant load in effluent.
The experiments were conducted with oxidative chemicals in Lab scale as well as in plant scale in Bindals Papers Mills Ltd, Muzaffarnagar U. P. India. Oxidative cheimical (Sodium percarbonate) and caustic dose were optimized. A number of multi-dimensional results were obtained in form of effluent load reduction and better yield of bleached pulp with improved quality of final pulp produce. The economics of the oxidative chemical' (sodium percarbonate) works out well, in-place-of extraction stage by elimination cost of hydrogen peroxide and reduction of 50% caustic consumption. So there, is no additional cost required to run the bleach plant with oxidative chemical. The kappa no. of the pulp is reduced by 0.2 to 0.4 points. Improvement was noticed in dram-ability of pulp. Operating temperature in extraction stage was reduced by 10 to 15%. The major benefits that come across are reduction in BOD (18-20%), COD (20-25%) and colour (40-45%) in effluent.

DETAILED DESCRIPTION OF THE INVENTION
In accordance with the process of the present invention, all set of laboratory and plant experiments were conducted at BINDALS PAPERS MILLS LTD. Pulp was bleached by Do-Eop-Di bleaching sequence ( where D represents chlorine dioxide and Eop represents Hydrogen Peroxide reinforced alkaline extraction) using "Bagasse & Wheat straw" as a raw material. A systematic approach was followed in adopting Total oxidative bleaching (TOB) process.
A Laboratory trial of oxidative chemical (Sodium percarbonate) against Hydrogen Peroxide after Do stage pulp was conducted in research and development, laboratory keeping all the parameters same as that of plant condition.
Experiment-1 (Lab trial of Oxidative chemical v/s existing extraction process)
Pulp obtained from Do stage was used in lab trial for comparative study of oxidative chemical (Sodium percarbonate) and hydrogen peroxide inriched alkaline extraction stage of pulp bleaching process. Pulp characteristics are given in Table no.1:
Table no.-l: Characteristics of Dn stage pulp used for lab trial

Initial pH Kappa no. Brightness (%) Yellowness (%) Whiteness (%)
4.5 4.9 49.0% 27.0%. 2.52%
Four sets of laboratory experiment were performed by giving 8 kg/ton dose of hydrogen peroxide at temperature 70°C in set no.l and 8 kg/t dose of oxidative chemical (Sodium percarbonate) at temperature 60°C in remaining sets. Caustic dose 40 kg/t was given in set no. 1 and set no. 2. Caustic dose 30 kg/t and 20kg/t was given in set no.3 and set no.4 respectively. Conditions and results of the experiment are given in talkie no.2.

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Table: 2: Conditions of Alkaline extraction stage

Parameter Unit Set no. 1 Set no. 2 Set no. 3 Set no.4
Conditions
H202 Kg/ton 8 - - -
Oxidative Chemical Kg/ton ( 8 8 8
Caustic dose Kg/ton 40 40 30 20
PH - 11.0 9.6 8.2 8.1
Retention Time min. 90 90 90 90
Temperature uc 70 60 60 60
Results
Kappa no. - 2.6. 2.35 2.40 2.42
Brightness % 65.0 62.6 62.7 62.8
Whiteness % 45.0 42.0 41.8 41.6
The results show that slight reduction in kappa no. with lower level of brightness which is an indication of better strength with approx. 15 % temperature reduction.
Experiment-2 (Optimization of Oxidative chemical dose)
After the laboratory trial of oxidative chemical (Sodium percarbonate) against hydrogen peroxide, a further Lab trial was conducted to optimize the dose of oxidative chemical.
Do stage pulp was used in lab trial for optimizing the dose of oxidative bleach chemical (Sodium percarbonate) in H2O2 reinforced alkaline extraction stage of pulp bleaching process. Pulp characteristics are given below:
Table no.-3: Characteristics of Pulp used for lab trial

Initial pH Kappa no. Brightness
(%) Yellowness (%) Whiteness
(%)
4.6 5.0 48.1% 26.5% 2.61%
Four sets of laboratory experiment was performed for optimizing the dose of oxidative bleach chemical (Sodium percarbonate), different doses 6, 8, 10 and 12 kg/ton of oxidative chemical were given at 60 C temperature for 90 min. retention time. Conditions and results of the experiment are given in table no.4v

Table no.-4: Optimization of Oxidative bleach chemical dose

Parameter Unit Set no. 1 Set no. 2 Set no. 3 Set no.4
Conditions
Oxidative Chemical Kg/ton 6 8 10 12
Caustic dose .Kg/ton 20. 20 20 20 ■
PH - 8.3 8.3 8.4 8.6
Retention Time mm. 90 90 90
Temperature uc 60 60 60 60
Results
Kappa no. - 3.1 2.8 2.6 2.4
Brightness % 60.5 62.8 64.5 66.3
Yellowness % 16.10 15.5 14.7 14.1
Whiteness % 42.0 42.6 43.0 43.2
The results show that on increasing the dose of oxidative chemical (Sodium percarbonate) kappa no. decreases from 3.1 to 2.4 and brightness increases from 60.5 to 66.3.
The Oxidative chemical, pulp was further treated with chlorine dioxide to attain a brightness level of 83.0-84.0% in. the final stage. The findings are shown below in table no.5.
Table no.-5: Y>i_ stage followed by Extraction stage

Parameters Set no. 1 Set no. 2 Set no. 3 Set no.4
Conditions
C102 kg/ton 10 10 10 10
pH 2.5 2.5 2.4 2.5
Retention time (min.) 180 180 180 180
Temperature (UC) 70 70 70 70
Result
Brightness (%) 82.0 82.6 82.9 83.5
Yellowness (%) 6.05 5.94 4.18 3.86
Whiteness (%) 71.9 72.86 73.54 74.05
During the Laboratory trial for optimization of newly introduced Oxidative chemical (Sodium percarbonate), different doses were monitored to achieve the Brightness level to

i v

60-62% & kappa no. (3.0-3.1) in the required stage. The level of required parameters was well achieved with the doses of @ 8kg/ton of Oxidative chemical.
Experiment:-3 (Plant trial of Oxidative chemical in comparison of mill existing process)
Chemical dosing system was modified for introduction of Oxidative Chemical (Sodium percarbonate) in the plant i.e. Installation of Metering Screw along with the charging Hopper. (Fig.l)
Based on above Laboratory findings, plant trial with different doses of Oxidative chemical (Sodium percarbonate) was conducted. Following three conditions were studied in the plant. The detailed study on plant trial of oxidative chemical (Sodium percarbonate) has shown appreciable reduction in Caustic and Steam consumptions.
A comparative study was done in plant i.e. bleaching with addition of hydrogen peroxide @8kg/t, and bleaching with addition of Oxidative chemical @8kg/t and &10kg/t.
Table no.-6: Plant trial with H2O2V/S Oxidative Chemical

Parameters With H202 With Oxidative chemical

@ 8kg/t @8kg/t @10kg/t
Conditions for Alkaline Extraction Stage
Caustic charge (kg/ton) 40 . 20 20
pH 11.0 8.3 8.4
Retention time (min.) 90 90 90
Temperature (UC) 70 : 60 60
Result of Alkaline Extraction Stage
Kappa No. 2.2-2.8 2.0-2.6 1.8-2,4
Brightness 62.0-65.0 60.4-62.0 62.0-63.8
Yellowness 10.29-12.54 17.3-18.0 15.2-16.5
Whiteness 48.2-54.9 34.0-38.5 39.4-42.5
Chlorine di Oxide (Di) Stage
C102 Consumed (kg/t) 8.0 8.0 7.5
Di final brightness 83.0-84.0 83.0-84.0 83.0-84.0+

After the Plant trial was completed and its Findings were evaluated, we came across several tangible and intangible benefits from its outcome. Brightness of the. pulp remained unchanged. Kappa no. is lowered by 0.2 to 0.4 points, which helped to maintain the Brightness at D] stage. Strength properties of Di stage pulp were improved. (Table no.-7)
Table no.-7: Strength properties of Di^ stage pulp

Parameter With Extraction Stage With Oxidative Chemical
Breaking Length (meters) 2900 2000
Tear (Nm.m2/g) 47 51
Burst (Pa.m2/g) 14 16
Bulk (Cc/g) 1.54 1.58
• . Di-stage pulp freeness (°SR) decreased in oxidative bleaching than H2O2 reinforced alkaline extraction ECF bleaching.
Table no.-8: Freeness of D^ stage pulp

Parameter With Extraction Stage With Oxidative Chemical
Freeness (USR) 20-22 . 18-20
Reduced operating temperature of the Oxidation stage has helped in reducing the
temperature of bleach plant effluent mix by 10 C (Earlier it was 60-65°C which reduced to
50-55°C). This has minimized the load on ETP cooling tower for reducing the effluent
temperature
REDUCTION OF EFFLUENT LOAD IN ETP
The major benefits that came across is reduction in effluent pollution load. By using oxidative chemical in oxidation stage of pulp bleaching process pollution load reduces in form of BOD, COD and COLOUR of mill effluent (Table-9).

CLAIMS

The.present invention is concerned with an establishment of a "Total Oxidative
Bleaching (TOB) Process" in pulp & paper industry.
Bleaching sequence Do-Eop-Di has been changed to Do-Ox-D|.
The oxidative chemical (Sodium percarbonate) works at neutral/alkaline pH (between7.5
to 8.5) and selectively removes residual lignin from fiber and facilitates bleaching.
Caustic consumption reduces approx. 50% as this oxidative chemical (Sodium
percarbonate) works in the range of pH 7.5 to 8.5.
Oxidative chemical (Sodium percarbonate) replaces 100% hydrogen peroxide in
oxidative stage of pulp bleaching process.
Kappa no. reduces 5-10% in oxidative stage of pulp bleaching process.
Strength properties of final bleach pulp are improved.
Effluent load reduces 20-25% in case of COD" & 18-20% in BOD and 40-45% in colour.
Temperature reduction (15-16%) in oxidative stage of pulp bleaching. . There is no additional cost to run the plant with Oxidative chemical (Sodium
percarbonate) . Pulp yield improved by 1 -2% of final bleach pulp.