After reading this article you will learn about:- 1. Profile of Indian Pulp and Paper Industry 2. Process Technology used in Pulp and Paper Industry 3. Raw Material Consumption 4. Solid Waste Generation 5. Solid Waste Management.
Profile of Indian Pulp and Paper Industry:
World paper industry assumes nearly 3.5% of the world industrial production and 2% of world’s trade. Demand of paper and boards worldwide will reach 470 million tonnes in 2010 with an average annual increase of paper demand of about 3.7%. Paper and boards demand is estimated to reach 640 million tonnes in 2020.
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The wood consumption in the world is expected to increase from 861 million tonnes in 1995 to 1777 million tonnes in 2020. With merely 17 units in 1950 with production of 0.11 million tonnes paper, presently we have about 380 mills with a total installed capacity of around 4.2 million tonnes.
There are 28 large mills and the remaining are small paper mills. Per capita consumption of paper in India is a meagre 3.2 kg against Asia and world average of 18 kg and 47.7 kg respectively. Per capita consumption of paper in different parts of world is given in Fig. 1. Projected demand of paper board in India is given in Table 1.
Per capita consumption of newsprint is 0.6 kg as compared to Asian average of 1.9 kg and world average of 6 kg. Per capita consumption is expected to grow to 0.8 kg by 2010 AD. The demand of paper and board is estimated to be around 54.80 kg lakh tonnes by 2005-06. Profile of Indian paper industry is given in Fig. 1 and 2.
Major raw materials used by paper industry is bamboo, wood, bagasse, waste paper and agricultural residue like wheat straw, rice straw, jute sticks etc. Apart from this, paper industry consumes large amount of chemicals like caustic soda, sodium sulphide, sodium carbonate, chlorine, hypochlorite, mineral acid; coal, talcum powder etc. Process technology used is craft pulping, mechanical pulping, semi chemical pulping. Bleaching sequences used are CEH and CEHH in majority of mills while chlorine dioxide bleaching and oxygen delignification is used by very few mills.
Acute shortage and high cost of wood based raw materials has been the most important factor restricting the growth of Indian paper industry and its development into a globally competitive industry. Expert Group Committee constituted by paper industry indicates that short fall in supply of indigenous fibre based on projected demand and possible production may be much larger (Table 1).
Agricultural residues like rice straw, wheat straw and bagasse are the promising raw materials for paper industry. Availability of bagasse and straw are estimated to be 2.5 million tonnes and 30 million tonnes respectively, India ranks second in world in utilisation of non-wood fibres.
Process Technology used in Pulp and Paper Industry:
Raw Material Preparation, Pulping, Bleaching:
1. Raw Material Preparation:
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Debarking and Chipping (Wood and bamboo) Cutting and De-pithing (Agricultural residues)
2. Pulping, Washing, Screening, Bleaching:
Separation of fibre for chemical or mechanical pulping, removal of knots, washing of pulp for recovery of chemical, rejects uncooked material, sand and other foreign material. Bleaching of pulp with bleaching chemicals-chlorine, caustic, hypochlorite, chlorine dioxide, ozone, hydrogen peroxide, sodium hydrosulfite. Commonly used bleaching sequences are (CEHH, CEH, CEHDED, CEDED). Some of the mills in India have also gone for oxygen delignification.
Stock Preparation:
Beating and refining for imparting suitable properties by making paper, addition of sizing chemicals, colour and additives.
Paper Making:
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Conversion of pulp from stock preparation into a sheet of paper.
Chemical Recovery:
Concentration of spent liquor, burning, causticising and classification of liquors. Apart from the above other units which are integral part of paper mills are waste paper processing, steam and power generation, effluent treatment plant.
Process flow diagram for manufacture of pulp and paper in a large integrated and small paper mill is given in Fig. 1 and Fig. 2. Various process technologies involved in pulping process are Kraft pulping, soda pulping (sulfite pulping, neutral sulfite semi chemical pulping, mechanical pulping) stone ground, thermo-mechanical, cold soda refiner mechanical pulping and refiner mechanical pulping.
Raw Material Consumption in Pulp and Paper Industry:
All large integrated paper mills in India are based on Kraft pulping process using bamboo, wood, and waste paper. The small paper mills which account for about 50% of total production in India are based on soda pulping and waste paper pulping and use agricultural residues-wheat straw, rice straw, bagasse etc. and waste paper as raw material. The newsprint mills are based on Kraft pulping and various mechanical processes utilizing bamboo, wood, bagasse etc.
Apart from large quantities of chemicals in the form of cooking liquor: sodium hydroxide, sodium sulphide, sulfurous acid and/or alkali salts (Na+, Mg++, Ca++); bleaching chemicals: Chlorine, Chlorine dioxide, ozone, hypochlorite, hydro-sulphite; filters, Clay, Calcium Carbonate; lime; additives like retention aids, strength agents, biocides, corrosion inhibitors; sizing agents; fuel-coal, fuel oil, bagasse, rice husk etc. Raw material consumption in small and large integrated mill is given in Table 2.
Solid Waste Generation in Pulp and Paper Industry:
Solid waste arises at different stages of pulp and manufacture and paper application stages. The types of solid waste and their quantities varies from plant to plant depending on the raw material consumed, in-plant plant control measures, external control measures, house-keeping, waste utilisation, collection and recycling practices.
Solid waste generation can be dealt separately as solid wastes generated due to off plant operation, in-plant plant operation and application generated.
Various solid waste generated due to off plant activities are generation of leaves, bark, unused branches of trees, during forest operation, generation of solid waste during mining of coal, lime stone which are being used in large quantities in paper industry.
Solid waste generated at various stages of pulp and paper making during in plant operations are:
1. Dirt, sand and other impurities from bamboo washing.
2. Bamboo and wood dust in chipper house.
3. Pith from bagasse pulping plant.
4. Knotter, screen and centric leaner rejects in pulp mill.
5. Lime dust from lime handling and slaker.
6. Grit, dregs, lime sludge in recovery section.
7. Particulate matter from recovery furnace, dissolving tank, lime kiln.
8. Centric leaner rejects from paper machines.
9. Contaminated material from waste paper plant.
10. Sludge from effluent treatment plant.
11. Sludge from raw water clarifier.
12. Boiler bottom ash and fly ash from power generation plant.
Quantity of solid waste generated due to various activities during pulp and paper manufacture is given in Table 3. Solid waste generation in agro-based paper mills is given in Table 4.
Application generated solid waste are generation of waste paper from household activities, government offices, printing houses waste, newsprint and magazine, printing presses, packaging waste. The waste paper waste may be in the form of old news-paper, high grade paper offices, computer, magazine, mixed paper and packaging waste like corrugated containers, box board, etc.
On weight basis paper constitutes major portion in municipal solid waste which may be to the tune of 25-40% of total waste, Due to improper collection and recycling practices, waste paper in municipal solid waste is high. Paper content of solid waste in Delhi municipal waste is given in Table 5 which show that further improvement is required for more recycling.
Solid Waste Management in Pulp and Paper Industry:
Waste generation is the first and most crucial element of waste management. Quick identification, and measurement of solid waste generated at the various stages of pulp and paper manufacture is the beginning of sound waste management. A balance solid waste management functions reduction recycling and disposal should be optimally designed for reducing the wastivity.
Solid waste generated can be:
(a) Reduced by using preventive measures in some of the cases.
(b) Reusable and then recycled inside the plant or other systems where they can be utilised as raw material.
(c) If find no use, it should be disposed of with care not to damage environment or cause public health hazard.
Table 3 gives brief description of the solid waste generated in pulp and paper manufacture and applications and effective way of utilisation of these wastes.
Although the solid wastes generated at various stages of pulp and paper manufacture are unavoidable, however, with better in-plant control measures and good house-keeping and general consciousness at all levels, the quantum of solid waste generated can be reduced to a great extent.
These steps are:
a. Bamboo and wood washing to minimise the dust losses and subsequent carry-over of silica and other impurities to system.
b. Better utilisation of fines from chipper house either by cooking separately and blending with virgin pulp or cooking with chips, however, proper control of blending is essential.
c. Timely change and replacement of chipper knives.
d. Running of screens and centric leaners at optimum efficiency to have minimum fibre drainage.
e. Maximum possible utilisation of recovered fibre from clarifier in various quantities without any prejudice.
f. Prevention of spillage overflows; collection of spillage and recycling to the system; reduction and collection of fibre drained from chests and machines during order change which is a major source of fibre loss in paper section.
g. Use of good quality lime which will reduce the quantity of lime sludge and hypo sludge, at the same time it will reduce the alkali and chlorine losses.
h. Electrostatic precipitator and other dust control equipment’s to run at maximum efficiency to avoid loss of chemicals in form of particulate matter.
i. Minimise the fibre and paper wastes of various sections by having strict watch and control. More recycling of waste paper by better collection, sorting and utilisation, especially in case of household waste. Municipal solid waste contains appreciable quantity of paper which still unrecovered.
Use of fibre and filler retention aids.
Some of the solid waste, bamboo dust, rice husk, bark, bagasse pith, saw dust, wood sawing’s, municipal refuse can be utilised as fuel and for manufacture of activated carbon. Heating value of some of the waste materials are given in Table 6.
The table shows that these waste materials can be used as fuel. Bagasse pith which is one of the major solid waste from bagasse based mills can be used as fuel. Bagasse pith which is one of the major solid waste from bagasse based mills can be used either as fuel or it can be composted along-with effluent plant sludge.
Lime sludge which is one of the major solid wastes from large integrated Kraft mill is still disposed as landfill in most of the mills except for mills which are using wood as major portion of their cellulosic material Because of high silica in bamboo which is major source of cellulosic raw material and high alkali c intent of lime sludge due to poor washing are major constrain in utilisation of lime kludge in re-burning.
Characteristics of lime sludge are given in Table 7:
Some of the option for reducing silica content are:
(i) Raw material cleaning,
(ii) Desalination of either black liquor green liquor,
(iii) Two stage causticising of green liquor,
(iv) Massive lime treatment, and
(v) Carbonization of green liquor for precipitation of silica. Lime sludge can also be used as raw mix for cement plant and manufacture of masonry cement.
Table 7 shows that chemical characteristics of lime sludge, limestone used in cement plant, it may be seen that sludge has high CaCo3 content and can be good substitute of limestone. Higher fineness and water retention capacity of lime sludge are the two important characteristics which make the utilisation of lime sludge in masonry cement more attractive.
Some of the major constrain in utilisation of lime sludge in cement plant are—high moisture content, high alkali content, variation in the quality of sludge. Use of lime sludge has been also reported as soil conditioner along-with solid waste like fly ash and paper mill sludge.
The effluent treatment plant sludge which is about 40-50 kg per tonne of paper and contain about 40-70% organic matter mainly fibre in form of fines. It can be used in making briquettes, cement sludge products, moulded products etc. as fertiliser after composting, Paper mill sludge has been successfully used as low permeability capping material, in lieu of clay or geosynthetic material as the properties of sludge materials themselves resemble the physical properties of clay soils used to construct caps.
Chinnaraj and Mohan Rao, 1999 have reported composting of organic solid waste sludge generated from activated sludge process and bagasse pith as a promising solution to disposal and management of organic solid wastes. They have reported composting of waste sludge from activated sludge process, bagasse pith and bagasse clarifier under flow sludge and found effective as manure. Veena has also reported use of sludge in agricultural soil amendment after composting.
Waste paper generation is an important aspect of paper utilisation. Large quantities of waste paper generated are not still properly collected and recycled in India. In India, the recycle rate is only 20% of total paper waste generation against the worldwide average of 35% and 55% in Japan.
There is large scope for recycling of waste paper through designing of proper collection system which is aimed to segregate different types of waste to usable or unusable waste. Segregation of municipal solid waste and designing proper collection system can play important role in proper utilisation of waste paper in order to meet the raw material requirement of paper industry.
Conclusion:
Although solid waste generation during various stages of pulp and paper manufacture are unavoidable however, some of solid wastes like chipper house dust, screen and centric leaner rejects, loss of pulp due to overflow, leakages, wastage of paper can be reduced substantially by in-plant control measures. By proper designing of municipal waste collection system paper and board can be collected effectively and recycling of paper can be enhanced which will result in conservation of the forest raw material.
In order to overcome the solid waste disposal problems some of the areas which need immediate attention and consideration are re-burning of lime sludge after desilication, utilisation of flyash in cement manufacture, exploring the possibility of use of lime sludge in cement plant and for masomy cement, fly ash and effluent sludge as soil conditioner by educating the farmers, better utilisation of bark and pith, utilisation of bamboo and wood dust as such or by making fire bricks for energy generation, composting of sludge and other waste biomass.
As the municipal solid waste contain large quantities of waste paper; increased recycling through proper collection can direct this valuable material from landfill and can offer an opportunity for reuse which will reduce the impact on forests and reduce the energy consumption.
