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PROCESS OF MANUFACTURING WRITING & PRINTING PAPER
Proposed project is based on manufacturing of bleached verities of paper using agricultural residues mainly wheat straw, Bagasse, rice straw, sarkanda and Waste paper( indigenious and imported ). Pulping process of these raw materials is well proven and accepted in Indian paper industry.
In general following steps are involved in paper making process
- Raw material preparation
- Wet Washing
- Pulping of raw material
- Washing, screening and cleaning
- Chemical recovery
- Bleaching
- Stock preparation
- Paper making
- Finishing and packaging
RAW MATERIAL PREPARATION
In the case of agricultural residue, raw material received from the source requires less conditioning for preparation for pulping. Straws and Bagasse received from the fields contains dust, fine particles, pith etc. These and other non-fibrous material require to be separated from the raw material before pulping. Screening and de-dusting of raw material is done in raw material preparation section. In case of Bagasse, depithing (dry and moist) is necessary to remove pith (non-fibrous sticky material) before pulping.In case of sarkanda, a cutter is required for cutting the whole sarkanda stick in small parts suitable for pulping.
WET WASHING
Agro based materials like Wheat Straw, Bagasse and Sarkanda shall come to Wet Cleaning System after thorough cuttings and dry de-dusting through Deduster, Depither and Cutter. Even after dry dedusting, lot of dust, sand, solids etc. remain attached to the raw materials.
In Wet Cleaning System, raw material is passed through water vat and mechanically beating/thrashing is done to de-attach sand, soil and kept for some time to get Chemicals in the raw-materials dissolved and then wet raw material is passed through Equa separator to remove free flowing water and further passed through screw press to get desired solid percentage of raw-material suitable for cooking process.
PULPING
After the wetwashing these rawmaterials put in the diegesters alongwith required ratio of caustic soda for cooking. Ratio of chemicals to the raw materials, temperature of cooking, time of cooking, bath ratio etc. are the important parameters for pulping process. We are installing continuous digesters. In this arrangement there is a long tube with a screw inside it and raw material, steam, chemicals are feed at one end and cooked pulp discharges at other end.
Continuous cooking process has its own advantages in terms of uniform quality of pulp, efficient use of chemicals and steam etc. This system gives better productivity and more uniform quality of pulp.
Cooked pulp is blown to a vertical spherical tank known as blow tank. In blow tank there is a atmospheric pressure, at the time of blowing some flash vapors are generated in blow tank which are taken to heat recovery system to recover its heat and re-used in the system.
WASHING, SCREENING AND CLEANING
From the blow tank, pulp slurry is pumped to knotter screen, which are located before the brown stock washer. Knots and fiber bundles in pulp slurry results in poor cake formation and non-uniform washing operation. Removal of these knots and other uncooked material results in a formation of a uniform, dense, easily washable cake in washing operation. It ultimately improve the washing efficiency. Accepted pulp from this screen goes to washer and rejects goes to digester house for re-cooking or thrown out from the system.
BLEACHING
After the washing, screening and cleaning of Pulp the bleacing process is done. Bleaching is a method of pulp purification, before this process the pulp slurry having the brown color and thorugh this prosess the color of pulp changed to white .In this process chlorine dioxide is used for getting the required whitness and brightness of end product.
BLENDING AND STOCK PREPARATION
Before the sheet formation, the water suspension of pulp is subjected to some mechanical and chemical treatment in stock preparation section. Main mechanical treatments are beating and refining. In agro residue pulp, not much beating and refining are required. Mild refining is sufficient to break the fiber bundles to increase its surface for strong bonding.
In chemical treatment rosin, alum and different types of dyes are added in the pulp suspension to impart different properties in end product. Filler (soap stone or china clay) is also added in pulp stock preparation section. Different type of dyes are added to the pulp suspension to maintain the same colour or shade of end product.
Ratio between different type of pulps in the furnish is also controlled in stock preparation. Required quantity of basic raw material pulps, purchsed pulp and broke pulp are mixed in desired ratio in stock preparation section.
PAPER MAKING
In the operation of all types of continuous paper making machines it is necessary to supply fibers, fillers and other material in fluid suspension. These are supplied continuously and uniformly to a moving porous and woven wire screen. A head box of inlet is a principal component of the paper machine stock supply system. The main function of head box is proper and uniform discharge of stock across the wire and uniform distribution of fiber in stock.
The pre dominant method used to make the sheet, involves filtration from a dilute fiber suspension in water to an end less wire mesh i.e. fine enough to retain most of the fiber. This section of paper machine is called forming section or wire section. It receives the fiber suspension in continuous jet from the head box and after drainage by gravity, vacuum, it delivers self-supporting sheet. The position and direction of the fiber in the sheet structure is almost entirely determined by the forming process.
The press section of paper machine increases the consistency of the sheet by removal of portion of free water contained in the sheet. There are various type of press section are available and its selection depend upon machine design, furnish and speed of the machine.
Dryness after press section should be in the range of 42 – 48 %. After press section paper enter in dryer section where remaining water is removed from the sheet by the means of heating.
Size press is used between the dryer section, this system consist of rubber coated roll and paper sheet passes between these rolls. Starch, china clay solution can be applied on paper surface in size press. This improves surface properties like smoothness, gloss etc.
After the size press paper again enter in dryer section (post dryers) and leaves at 92 – 95% dryness. Calendar stack is necessary to produce the desired finish and caliper. Finish is varied to the desire degree by increasing or decreasing the number of rolls in the calendar, by loading or unloading the weight of the roll system to create higher or lower nip pressure. Heating and cooling can also applied at calendar roll to produce better finish and gloss etc.
Pope reel is the last part in paper making process. After the calendar paper is passed through a cylinder and rolled on spool. It controls binding condition of paper reel which is required in finishing section.
FINISHING SECTION
As used in the paper industry, the word “finishing” refers to those operations perform after the machine in order to make the paper ready for sale. These operations include slitting and rewinding to produce rolls of the size desired by the customer, and cutting of the paper into sheet if required.
Inspection of the paper is an integral part of the finishing operation and is carried out to some degree on the slitter rewinder or on sheeter. Higher quality grades of sheeted paper are subject to further manual inspection.After finishing, packaging of reels or sheets is done for proper transportation.
CHEMICAL RECOVERY
The black liquor consisiting of water, chemicals and lignin upto 48%, resulting from washing is fed to evoporation plant where the water is evaporated. The black liquor, after water evaporation, is fed to the chemical recovery boiler where lignin is burnt and chemical (caustic) is recovered back.During the process of burning of black liquor, steam generation at 45kgcm2 which passes through Turbine to generate power and steam at lower pressure i.e. 4 Kgcm2 shall come out as bleed for the process i.e evaporator. The recovered caustic, in molten form, is sent to re-causticising plant where lime, salt cake and casutic etc. are added whereby white liquor is formed, which is reused in the digester for cooking.
The loss of alkali in the un-recovered spent liquor is an economic burden because of the cost of chemicals as also for otherwise lost energy content of the spent liquor. It is possible to raise the profitability of a mill by lowering the chemicals and energy inputs to lowest levels by installing a chemical recovery plant.
Chemical recovery plant mainly consists following 3 sections.
1. Storage and evaporation of dilute black liquor.
2. Burning of black liquor solids in recovery furnace.
3. Recovery of caustic by recausticising.
Dilute black liquor would be collected in storage tanks in evaporation sections. Multiple effect falling film evaporator would be used for the evaporation of water from black liquor. A multiple effect evaporator of several units, connected in series by vapour piping, in which the water vapour boiled off the liquor in one effect acts as heating steam in the steam tube of the next effect. The steam is furnished only to the steam chest of the first effect.
Inlet concentration of dilute black liquor is about 8 – 10% while outlet concentration would be about 45 – 50 % black liquor solids.
In falling film type evaporators, black liquor is distributed from the top of the body and it comes down in the form of thin film , steam flows from downwards to upwards of the body and heat transfer takes place in between . In falling film evaporators liquor and steam flows in opposite direction (counter current heat transfer) while in rising film type liquor and steam flows in same direction (co current heat transfer). From the last effect, vapours are condensed in a surface condensor. Vacuum for operation is created by means of an steam jet ejector assembly.
The semi concentrated black liquor from the evaporator plant is first taken to a direct contract evaporator to further concentrate to about 60 – 70 % of black liquor solids. It is then sprayed into the recovery furnace, where the black liquor gets dehydrated and drops to furnace hearth as dry solids. The combustion of organic compound of black liquor is controlled by the temperature of black liquor and air flow at primary and secondary levels. Inorganic compound come out from the bottom of furnace in the form of molten smelt. This smelt is dissolved with weak white liquor to form green liquor.
The heat generated in combustion zone, goes in boiler zone with flue gases. In the boiler zone, steam is generated. After the boiler zone, flue gases pass through direct contact evaporator where balance heat is used to concentrate the black liquor further.
Green liquor is converted in to white liquor after the reaction with lime in causticising section.
From causticising section white liquor (NaOH) goes to pulp mill and mud (CaCO3) disposed off after its proper washing. Water comes out from mud washing is known weak white liquor.
The recovery of chemicals can be as high as 98% on the total inputs of chemicals.
PROCESS OF MANUFACTURING KRAFT PAPER
The Existing Plant is installed for manufacturing of Semi Kraft Paper using Agricultural Residues mainly Bagasse, Wheat Straw, Rice Straw, Sarkanda, Jute Waste and Indigenous and Imported Waste Paper. In general, the following steps are involved in Paper Making process: -
- Raw Material Preparation
- Wet Washing
- Pulping (Cooking of Raw Material)
- Washing, Screening and Cleaning
- Refining
- Blending and Stock Preparation
- Paper Making
- Finishing and Packing
RAW MATERIAL PREPARATION
In the case of agricultural residue, raw material received from the source requires conditioning for preparation of pulping. Straws and Bagasse received from the fields contained dust, fine particles (other than raw material), pith and so many other undesirable materials. These non-fibrous materials require to be separated from the raw material before pulping. In case of Bagasse, dry depithing is carried out to remove pith which is non-fibrous material before cooking. For this process, Depither is installed.
For Wheat Straw, Deduster is being used to remove dust, sand etc.
In case of Sarkanda, a Cutter is installed to cut it in small pieces of around 10-12 MM in length to have proper penetration of the Chemicals. Then it is also dedusted and sent for Cooking.
With regards of Jute, it is sorted to remove undesired materials like Bitumen/Plastic Bags, Laminated, rotten etc. which are harmful for the Paper Making and then it is cut in small size of ½” and dedusted prior to the Cooking.
For Waste Paper, sorting is done to remove Plastic Strips, Oily Bitumen, laminated, Paper Pins, Clips, and other foreign/undesirable material and then sent for pulping through Hydro Pulper. The Waste Paper normally does not require any Cooking except wet strength Paper.
WET WASHING
Agro based materials like Wheat Straw, Bagasse and Sarkanda shall come to Wet Cleaning System after thorough cuttings and dry de-dusting through Deduster, Depither and Cutter. Even after dry dedusting, lot of dust, sand, solids etc. remain adhere to the raw materials. Even some of the inherent Silica and Chemical like chloride which are soluble, get dissolved and taken out through washing and pressing.
In Wet Cleaning System, raw material is passed through water vat and mechanically beating/thrashing is done to de-attach sand, soil and kept for some time to get Chemicals in the raw-materials dissolved and some of the inherent silica and then wet raw material is passed through Equa separator to remove free flowing water and further passed through screw press to get desired solid percentage of raw-material suitable for cooking process.
PULPING
It is proven that for Paper making only fibrous material particularly cellulose is required and there is a need to remove non-fibrous constituent like lignin, pentasons, Resin, Pectin etc. and so on. For this, all non-fibrous components require delignification by cooking. Generally cooking is done by soda process in which mainly Caustic Soda is used in the percentage of 10-12% for Kraft Paper and 14-16% for White Grade of Paper. Raw-Material combindly Wheat Straw, Bagasse, Sarkanda etc. are cooked in Globe Digester under steam pressure of 6-7 Kgs./Cm2 and temperature of 160-165 Degree C. The Globe Digester is rotated for 4 Hours for re-action of this process and then it is blown in Blow Tank to segregate the excess steam and Pulp. In further steps Pulp is screened to remove undesirable material including uncooked fiber, if any. After screening, the Pulp is passed through Single Disc Refiner to give mild refining to make homogenous slurry to have better and proper washing in washing section.
WASHING, SCREENING AND CLEANING
In Washing Section all undesirable components which are in liquid form including spent caustic liquor is removed through filtration process. Then pulp is passed through Double Disc Refiner to make homogenous slurry for smooth further processing and sent for Screening. From Johnson Screen, Stock is sent to Delkor Horizontal Belt Washer (Imported from South Africa) for washing of Pulp.
REFINING
After thorough Washing, Pulp is collected in a Storage tank and finally Pulp is refined through Double Disc Refiners and Tri Disc Refiners to make pulp suitable for paper making and to impart better fiber bonding condition which improves the physical strength of the Paper.
Similarly cut and dedusted jute is cooked in Globe Digester in the same manner to remove lignin, wax, oil etc. and to make the jute softer for pulp making. Cooked Jute is chopped through Chopper Breaker and some refining is also given in the same process as well. Washing also takes place applying drum washer in between. This pulp is again screened through 6 MM hole Johnson Screen and passed through number of Centricleaners to remove sand and other impurities which remains with the Pulp. This Pulp is thickened and refined through Tri Disc Refiner to impart desired physical strength to the Pulp.
The Waste Paper does not require any cooking before pulping. It is directly slushed in Hydro Pulper in presence of Water and Mechanical Thrashing. This material is also passed through Screening System to two stage i.e. turbo separator and refiner. All three type of Pulp which are kept separately sent for blending in Stock Preparation.
BLENDING AND STOCK PREPARATION
Different type of Pulp i.e. Agro, Jute, and Waste Paper are taken in the measuring tank in desired proportion according to the quality of Paper to be made. In same Chest some Chemicals and additives are added like around 0.4% Rosin, 5% Alum and 0.2% additives to impart physical and Chemical properties to the Paper. The Pulp is kept for 30-35 Minutes for re-action before sending for further processing. Next step is taken to make pulp more homogenous using Refiners i.e. refining is done through Tri Disc Refiner, Cleaning through Nos. of Centricleaners Bottles in three stages to remove uncooked, undesirable, sand, fines etc. from the pulp if any. Screened Pulp is passed through Pressure type Screening Equipment which has got 2.6 MM perforation which works on centrifugal force to remove longer fiber which is undesirable for Paper making. The accepted Pulp is taken on Paper Machine and rejected Pulp is taken separately for further processing to remove the rejects from the System.
PAPER MAKING
For Paper making Paper Machine is having number of different sections, which has got different functions like: -
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HEAD BOX
Head Box is Equipment which receives cleaned pulp from the Stock Preparation and discharge on fourdrinier machine which has got wire mesh for sheet formation and the filtration of the fiber. The main function of the Head Box is to deliver the Pulp on the fourdrinier in such a manner so that the fiber can be spreaded across the width and on Machine direction uniformly.
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FOURDRINIER
Fourdrinier section consist a forming board, Hydro Foils, Suction Boxes, Table Rolls etc. Pulp poured on the Wire in the consistency of 1% fiber and 99% Water. Over and above, this fourdrinier is supported with wire mesh and number of drainage elements. During formation of Sheets, Water drainage takes place in control manner to have uniform and strong paper sheet.
Basically fourdrinier work is to form a proper uniform fiber sheet by draining the Water. The Pulp slurry at inlet is 1% consistency and at the outlet of the fourdriner the consistency is raised to 20-22% by using gravitational discharge of Water by employing hydro foil and table rolls. More Water is removed through Vacuum Suction Boxes.
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TOP WIRE
Ruchira Paper has installed Top Wire which imparts extra strength by fine sheet formation and lamination in wet condition. Top Wire consists of all Component similar to the Fourdrinier. By using top wire, low strength of raw-materials is being used which contribute in keeping lower cost of production and giving better quality of product to the Customers.
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PRESSES
Formed sheet with the consistency of 22% passed through in between two heavy rolls under 70 Kgs. linear pressure to make paper sheet compact and to remove Water to make it more drier. Similar type of Presses are installed in 3 stage where load applying go on increasing upto 200 Kgs. linear pressure at 3 rd Press and finally Paper dryness is achieved about 42-43%.
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DRYER SECTION
Pressed paper sheet with the moisture of 57-58% is passed through number of cylindrical dryer cylinders which are heated through steam to evaporate water to make the Paper dry. At the moisture of around 45% the paper sheet is passed through M.G. Cylinder to impart one side glaze to the Paper which is basic requirement of Semi Kraft Paper. At last, number of Dryers are used to dry the Paper to 6-8% moisture contents.
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FINISHING AND PACKAGING
Finally the Paper is wound on Pope Reel and sent for Slitting Rewinder to cut it in small sizes in Reel Form as per the requirement of the Customers. Cut Reels are packed and dispatched to the market.
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