A.Manufacturing process of “Bagasse and Rice Straw” Pulp:

i) Raw Material Preparation:


Bagasse is received both in bales and in loose form, which is fed to debaler through the underground belt conveyor, where the bales are disintegrated. After disintegration it is sent to depither by belt conveyor. Raw bagasse contains about 28% to 30% pith. The depither removes most of the pith and the accepts will go to wet cleaning system for washing. The wet cleaned bagasse is fed to an Aqua Separator to remove the wash water and the left over pith and dirt from it. The cleaned bagasse is fed through Screw Press for further removal of water and then fed to Continuous Digester system for cooking. The outlet pulp of the Continuous Digester system is taken to a Blow Tank for Storage. In Continuous Digester system, Caustic and Steam are injected at 7 kg/cm2 (g) as cooking media chemicals.

Rice Straw:

The Rice Straw is mixed with Caustic Soda thoroughly in Caustic Lye Mixer and digested in Rotary Digesters. It is cooked with steam of 7 kg/cm2(g) at 165ºC for about 2 hours and stored in blow tank.

ii) Washing & Screening:

The Bagasse Pulp received from Blow Tank along with Rice Straw Pulp is washed in 4 stages Brown Stock Washing System in a counter current vacuum filter system and the filtrate known as Black Liquor from first stage brown stock washing system is sent to Chamical Recovery Plant for the recovery of Chemicals. The 4 stage washed pulp is subjected to cleaning in Centrifugal Screen, Centricleaners are then thickened in a thickener. Now the pulp is ready for bleaching.

iii) Bleach Plant:

Washed and cleaned pulp is subjected to bleaching in C-E-H-H (Chlorination, Alkali Extraction Hypo-I & Hypo-II) sequence. The unbleached pulp is mixed with Chlorine water in Chlorine Mixer and then passed through upflow retention tower. It is then washed in Chlorine washer and at the outlet of Chlorine washer alkali is mixed and then passed to down flow alkali retention tower through heater mixer. After alkali extraction, the pulp is washed in alkali washer. At the outlet of alkali washer, Calcium hypo chlorite is added and then passed through down flow Hypo-I retention tower. After the hypo-I retention tower, the pulp is washed in Hypo-I washer. At the outlet of Hypo-I washer, second stage calcium hypo chlorite is added and then passed through Hypo-II washer. Now the pulp is ready to make white variety paper.

B. Process of Wood Pulp:

Bleached hard wood pulp/soft wood pulp is purchased from various industries in the form of sheets or cakes. The sheets are pulped in a pulper in water medium and then stored in a chest. Then it is refined through a refiner batch wise in a chest, and then stored in wood pulp storage chest.


C. Paper Machine Section:

The pulp i.e., Bagasse and Wood are taken in required proportions to stock preparation section and blended. The required sizing chemicals, colours etc., are added depending upon the quality of the paper. The blended pulp is forwarded to head box through S.R box after dilution with white water. From Head box, the stock is distributed evenly and uniformly across the wire section. The major part of the water is removed in wire part and then the paper web is passed to press section where further removal of water is effected and the web is passed to drier section. In the drier section the paper is heated indirectly by steam and the water content in the paper is evaporated and final sheet of paper is reeled on POPE Reel after passing through calendars. Paper is converted into required size reels on rewinder and then converted into sheets on sheet cutters, packed and despatched after finishing operation.


D. Chemical Recovery Section:

Chemical recovery system consists of three major units viz., Evaporation plant, Chemical Recovery Boiler and Re-causticizing Plant. The details of which are given below.

i.Evaporation Plant:

The evaporation plant is of tubular falling film type. The evaporator system consists of six evaporators. Evaporation plant will evaporate the weak Black Liquor from 8% solids to 48%-52% solids.

ii. Chemical Recovery Boiler

The chemical Recovery Boiler is a top suspended, single drum furnace and boiler. The boiler is equipped with a cascade evaporator to concentrate black liquor from evaporator plant to 60%-63% dry solids. The boiler has an efficient combustion air system followed by an ESP for flue gas cleaning. Concentrated black liquor from evaporation section will be fired in the chemical recovery boiler. Before the actual firing in the recovery boiler, the black liquor concentration from Evaporators is further increased by the heat available from flue gas in direct contact in cascade evaporator to a solid content of 62%-63% and it will enter recovery boiler furnace and there it is fired initially by auxiliary fuel (natural gas) and subsequently by on its own firing because of the high temperature in the furnace. During this process of burning in the recovery boiler, all the organic contents will be burnt to CO2 producing steam, while the inorganic consisting of mainly sodium carbonate will collect at the bottom of recovery boiler furnace (this is called smelt) and this smelt will be taken into dissolving tank where it will be dissolved in weak white liquor (low concentration recovered sodium hydroxide solution). This liquor in the smelt-dissolving tank, known as green liquor, is sent to causticizing section for converting to sodium hydroxide solution by reacting with lime solution.

iii. Re-Causticizing Plant:

The causticizing plant is a conventional uniclarifier type with Rotary slaker, recausticisers and dregs washing system, two-stage mud washing and lime mud filter. The green liquor from recovery boiler after clarification is treated with slaked lime by which process the sodium carbonate will be converted into sodium hydroxide and Calcium carbonate. The causticizing operation consists of no. of large diameter tankages with slowly moving rake agitator for producing clear sodium hydroxide solution known as white liquor clarifiers is washed off in clarifiers known as mud washers for recovery of residual sodium hydroxide, if any. Relatively pure lime sludge is taken into vacuum filters for increasing the concentration to around 50% and then disposed off.



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