Century Paper and Board Mills Limited (CPBM)
PULP & PAPER INDUSTRY Prepared for Training Department Century Paper and Board Mills Limited
July 2010
Prepared by: MUSHAHID ALI Intern at Production Site
Email: mushahidali143@gma
[email protected] il.com Contact: 03457441340
School of Chemical and Materials Engineering (SCME)
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For any given industry, each topic could alone be the subject of a lengthy volume. However in order to produce a manageable document, this article focuses on providing summary information for each topic. This format provides the reader with a synopsis of each issue, and references where more in depth information is available. In this article, a brief description related to Paper Industrial processes specially used by the Century Paper and Board Mills is provided. Text within each profile was researched from a variety of sources, discussions, and was usually condensed from more detailed sources pertaining to specific topics. This approach allows for a wide coverage of activities that can be further explored based upon the citations and references listed at the end of this report.
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Author is thankful to Almighty to Almighty Allah, Allah, For His unlimited blessings and bounties, And for keeping him sane, sound and successful; successful; His parents and friends, For all their support and trust tr ust in him and his aims; His teachers and guides, For teaching him things he knew not; NUST Career Development Centre, For bringing the opportunity of this excellent learning and exposure; And last and the most most important Management and Employees of Century Paper and Board Mills Especially his mentor Mr. mentor Mr. Nadeem the Production Manager And all the shift coordinators, coordinators, supervisors, trainee engineers, engineers, board men and area operators at Plant For their utmost help, guidance and time Which made author make most of his internship at plant site;
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.................................................. ................................. .................................. .................................. ................................. ...................... ......2 Objective: .................................. Sodium Sulfite: ................................ ................................................. .................................. ................................. ................................. .................................. .................2
................................................. ................................. ................................. .................................. .................................. ................... ...2 Procedure:................................. Strength of Sodium Sulfite: ................................ ................................................ .................................. .................................. .............................. ..............3
................................................ ................................. ................................. .................................. .......................... ........5 Sodium Hypochlorite: ................................ Procedure:................................. ................................................. ................................. ................................. .................................. .................................. ................... ...5
................................................ .................................. ................................. ...................... ......5 Strength of Sodium Hypochlorite:............................... Major Instruments used in Chemical House: ................................. ................................................. .................................. .......................... ........7
................................................ .................................. ................................. .................................. .................................. ................... ...7 Steam Pits: ............................... Furnace: ................................. ................................................. ................................. .................................. .................................. ................................. ...................... ......7
................................................. .................................. ................................. .................................. ............................... ..............7 Cooling Tower: ............................... Blower: .................................. .................................................. ................................. .................................. .................................. ................................. ...................... ......7 Valve:.................................. ................................................... ................................. ................................. .................................. .................................. ......................... ........7
................................................. ................................. .................................. .................................. ................................. ...................... ......7 Reactor: ................................. Heat Exchanger: ................................. ................................................. ................................. .................................. .................................. ............................ ...........7 ....................................................................
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.................................................. ................................. .................................. .................................. ................................. ...................... ......9 Objective: .................................. ................................................ .................................. .................................. .................................. ................................. ...................... ......9 Straw Plant:............................... .................................................. ................................. ................................. .................................. .......................... ........9 Primary Cleaning: .................................. Secondary Cleaning: ................................ ................................................. .................................. ................................. ................................. ....................... ......9
.................................................. .................................. ................................. ................................. ................................. ................10 Cooking plant: ................................. Calculation for the amount of Sodium Sulfite added: ................................ 10 ................................................. ........................... ..........10
................................................. .................................. ........................... ..........12 Major Instruments used in Cooking House: ................................ 12 ............................................................................
.................................................. ................................. .................................. .................................. ................................. ..................... .....13 Objective: .................................. ................................................. .................................. ................................. ................................. ................................. ................13 Washing Plant: ................................ Bleaching plant: .................................. ................................................... ................................. ................................. .................................. .............................. .............15
................................................... ........................ .......15 Calculations for the amount of Sodium Hypochlorite: .................................. 15 iv
Major Instruments used in Bleaching House: ................................. 17 ................................................. .................................. ......................... .......17
................................................ ...................... .....17 Dewatering Filter or Rotary Drum Vacuum Filter (RDVF): ............................... 17 Blow Tank: ................................. ................................................. ................................. ................................. .................................. .................................. .................. ..17
................................................. ................................. .................................. .................................. ........................... ..........18 Johnson Screen: ................................. Centre-cleaners: ................................. ................................................. ................................. .................................. .................................. ........................... ..........18
................................................. ................................. ................................. .................................. ......................... .......18 Thick Stock Pump: ................................. ..............................................................
.................................................. ................................. .................................. .................................. ................................. ..................... .....19 Objective: .................................. .................................................. ................................. ................................. .................................. ......................... .......19 Waste Paper Plants: .................................. ................................................ .................................. ................................. ................................. ...................... .....19 Waste paper plant 1: ............................... 19 ................................................. .................................. ................... ..22 Major Instruments used in Waste Paper Plant 1 : ................................ 22 Dewatering Filter or Rotary Drum Vacuum Filter: ............................... 22 ................................................ ................................. ................22
.................................................. ................................. ................................. .................................. ................... ..22 High Pressure Screen: ................................. 22 Turbo Separator: ............................... ................................................ .................................. .................................. .................................. ........................... ..........22
................................................ .................................. .................................. .................................. ................................. ..................... .....22 Deflaker: ............................... Separ Plast: ............................... ................................................ .................................. ................................. .................................. .................................. .................. ..23
.................................................. ................................. .................................. .................................. ........................... ..........23 Centre-Cleaner: .................................. Refining Plants: ................................ ................................................. .................................. ................................. ................................. ................................. ................24
................................................. ................................. .................................. .................................. ........................... ..........25 Refining Plant 1: ................................. Refining Plant 2: ................................. ................................................. ................................. .................................. .................................. ........................... ..........27
................................................. ................................. .................................. .................................. ........................... ..........29 Refining Plant 3: ................................. Refining Plant 4: ................................. ................................................. ................................. .................................. .................................. ........................... ..........31
................................................. ................................. .................................. .................................. ........................... ..........33 Refining Plant 5: ................................. ................................................. ................................. .................................. .................................. ........................... ..........35 Refining Plant 6: ................................. Major Instruments used in all the Refining Plants: ................................. 37 .................................................. ................................. ................37
................................................. .................................. ................................. ................................. ...................... .....37 Double Disk Refiner: ................................ 37 ..................................................................................
................................................ .................................. ................................. ................................. ...................... .....38 Approach Flow System: ............................... 38 Paper Machine: .................................. ................................................... ................................. ................................. .................................. .............................. .............40
.................................................. ................................. .................................. .................................. ................................. ..................... .....40 Process:.................................. Calculation for the flow and head on the Machine: ............................... 41 ................................................ .............................. .............41
................................................ ................................. ................................. ................................. ................41 Major parts of the Machine: ............................... Wire Part: .................................. .................................................. ................................. ................................. .................................. .................................. .................. ..41
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Press Part: ................................. ................................................. ................................. ................................. .................................. .................................. .................. ..44
................................................. ................................. ................................. .................................. .................................. .................. ..47 Dryer Part: ................................. Difference between Paper and Board Machine: ............................... 50 ................................................ .................................. ...................... .....50 .................................................................................
Objective: .................................. .................................................. ................................. .................................. .................................. ................................. ..................... .....56
.................................................. ................................. ................................. .................................. ................... ..56 Preparation of chemical: ................................. 56 Process: .................................. ................................................... ................................. ................................. .................................. .................................. ........................ .......57 .........................................................................................
Objective: .................................. .................................................. ................................. .................................. .................................. ................................. ..................... .....59
.................................................. ................................. ................................. .................................. ......................... .......59 Preparation of Glue: .................................. Quality tests for the Glue: ................................. 59 ................................................. .................................. .................................. ............................. .............59
.................................................. ................................. .................................. .................................. ........................... ..........59 Corrugators Plant: ..................................
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Pulp and Paper Industry INTRODUCTION: Paper is very useful for our daily life. We get lots of new information and ideas in our daily life but these ideas and information may lose if we don't save it. And the paper is very basic and cheaper way of saving the information and knowledge. Paper and Pulp Industry is the major Industry of any country which performs a major role for the growth and development of a literary society in any country. The first known operating paper mill was in operation in 794 in Baghdad. From here, the technology spread to Europe. Today, paper mills use great amounts of water, energy, and wood and follow a complex process in order to produce paper. These modern machines are as much as 500 feet in length and move at speeds of over 100 mph, which makes them capable of producing sheets of paper as much as 400 inches wide. A paper mill is a type of factory that makes paper from wood pulp and other special ingredients. This is accomplished through a variety of special machines, including a tree chipper, a digester, and a paper machine. Due to the Kraft process used to separate the lignin from the plant products used in the paper making process resulting in a sulfur byproduct, paper mills are associated with unpleasant smells. The undesirable smell associated with paper mills only occurs if the mill is also a pulp mill. In some cases, mills focus on only pulp processing or paper processing. All of the major mills, however, engage in both processes. The offensive smell is caused by the cooking process used to soften the pulp in order to form it into paper. Despite the bad smells they emit, the airborne particles are not harmful to a person’s health. Century Paper Mill is one of the largest Mills in Pakistan. It has been showing its tremendous performance for many years and still it is the best. I have added a brief introduction related to processes involved for the production of Pulp and preparation of different quality of papers from the pulp in the Century Paper Mill . Century Paper Mill has divided its work into different departments to maintain its efficiency level. And I will discuss each department here and explain all the programs working in all the respective departments.
CHEMICAL HOUSE: Chemical House is the first approach towards the preparation of Paper. Two plants are installed in the Chemical House. One is for the preparation of Sodium Sulfite and the other is for Sodium Hypo-Chloride. Sodium Sulfite is used in the Cooking House for the cooking of Wheat Straw and Bagasse while Sodium Hypo Chloride is used in the Bleaching House for the Bleaching of Unbleached Pulp.
Objective: The objective is to provide the continuous flow of Sodium Sulfite and Sodium Hypochlorite to the respective departments.
Sodium Sulfite: In Century Paper Mill the procedure followed for the preparation of Sodium Sulfite is given below; Procedure:
First of all, the sulfur in powdered form is poured onto the steam pits manually. With the help of steam pits, sulfur melts and converts into the melted form. This melted sulfur is transferred to the Furnace with the help of Dozing Pumps. These are actually Centrifugal Pumps. These pumps transfer the melted sulfur to the furnace. The temperature of the o o furnace is maintained from 900 C to 1100 C. A continuous supply of oxygen is maintained to the furnace with the help of blower. The reaction takes place and sulfur dioxide is produced according to the following equation. S + O2 ------------> SO2 Sulfur dioxide produced in the furnace moves towards the cooling tower. It reduces the temperature of sulfur dioxide. In the cooling tower there is a counter-current flow occurs between sulfur dioxide and water and direct interaction occurs between them. And the o o temperature of the sulfur dioxide decreases up to 60 C to 65 C. During this reaction a few of the sulfur dioxide converted into liquid form and drain out from the cooling tower. While most of the sulfur dioxide move towards the reaction chamber. On the other hand the second reactant is Sodium Carbonate (Soda Ash) which comes in the powdered form. This powdered soda ash is poured into a dissolver tank where it is mixed with the water. Solution of soda ash and water is prepared. Now Soda Ash moves towards the reaction tower. Sulfur dioxide enters from the lower side of the reaction tower and meets with the countercurrent flow of the liquefied Soda Ash. It is to be noted that Soda Ash is always be used in the presence of water. Century Paper Mill gets Soda Ash from ICI Pakistan. During the reaction Sodium Sulfite and Carbon Dioxide is produced according to the following equation. Na2CO3 + SO2 ------------> Na 2SO3 + CO2 The carbon dioxide gas is drain out from the chimney of the reaction chamber. While on the other hand the required product is shifted to the storage tank. As sodium sulfite is a very acidic chemical so to make the solution basic or to increase the pH of the solution, 50% solution of Caustic Soda NaOH is added to sodium sulfite so it may not be dangerous for the material of the storage tank.
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Strength of Sodium Sulfite:
The required strength of Sodium Sulfite is 140 grams/liters. To maintain the required strength of it, we use specific amounts of the reactants. To calculate the exact quantity of reactants, we follow the method of Stoichiometry. Basis = 1 liter The chemical equation for the process is Na2CO3 + SO2 ------------> Na 2SO3 + CO2 (106 g) (64 g) (126 g) (44 g) According to the equation: To produce 126 grams of Na 2SO3, 106 grams of Na 2CO3 is required To produce 1 gram of Na 2SO3, 106/126 grams of Na2CO3 is required To produce 140 grams of Na 2SO3, 106/126 * 140 = 117.78 1 17.78 grams of Na 2CO3 will be required And To produce 126 grams of Na 2SO3, 64 grams of SO 2 is required To produce 1 gram of Na 2SO3, 64/126 grams of SO 2 is required To produce 140 grams of Na 2SO3, 64/126 * 140 = 71.11 grams of SO2 will be required Amount of CO 2 produced can be calculated as 106 grams of Na2CO3 will produce 44 grams of CO 2 1 gram of Na2CO3 will produce 44/106 grams of CO 2 117.78 gram of Na2CO3 will produce 44/106 * 117.78 = 48.89 grams of CO 2
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Sodium Hypochlorite: Sodium hypochlorite is a chemical compound with the formula NaOCl. Sodium hypochlorite solution, commonly known as Bleach, is frequently used as a disinfectant or a bleaching agent. In Century Paper Mill, the procedure followed for the preparation of Sodium Hypochlorite is given below;
Procedure:
First of all, liquid Chlorine is brought in the Chemical House. Chemical House buys this chlorine from Sitara Chemical Industry. This chlorine is kept in the cylinders and then with the help of small pipe lines the liquid chlorine is transferred to the Evaporator. The evaporator works on the principle of a Heat Exchanger. In the evaporator there is a counter current flow of the liquid chlorine and steam. After exchanging the heat, chlorine converted into gas form. And after changing the physical state of the chlorine it is passed from the reactor. On the other hand the NaOH in the form of liquid is first passed through a heat exchanger to reduce its temperature. After reducing the temperature it moves towards the reactor. An exothermic reaction occurs in the reactor. Sodium hypochlorite is produced in the reactor. The reaction can be explained with the help of following chemical equation: 2NaOH + Cl 2 ---------> 2NaOCl + H 2 Due to its high temperature it moves towards a heat exchanger. Heat Exchanger used chilled water to reduce the temperature of the sodium hypochlorite. As the reaction is continuous so the flow of chilled water passes through the heat exchanger which comes from a chiller is also continuous. After passing through the heat exchangers sodium hypochlorite moves towards the storage tank. Strength of Sodium Hypochlorite:
The required strength of Sodium Hypochlorite is 40.4 grams/liters. To maintain the required strength of it, we use specific amounts of the reactants. To calculate the exact quantity of reactants, we follow the method of Stoichiometry. Basis = 1 liter The chemical equation for the process is 2NaOH + Cl 2 ---------> 2NaOCl + H 2 (80 g) (71 g) (149 g) (2 g) According to the equation: To produce 149 grams of NaOCl, 80 grams of NaOH is required To produce 1 gram of NaOCl, 80/149 grams of NaOH is required To produce 40.4 gram of NaOCl, 80/149 * 40 .4 = 21.7 grams of NaOH will be required And To produce 149 grams of NaOCl, 71 grams of NaOH is require d To produce 1 gram of NaOCl, 71/149 grams of NaOH is required To Produce 40.4 grams of NaOCl, 71/149 * 40.4 = 19.25 grams of NaOH will be required Amount of H2 produced can be calculated as: 149 grams of NaOCl produces 2 grams of H 2 1 gram of NaOCl produces 2/149 gram of H2 40.4 grams of NaOCl produces 2/149 * 40.4 = 0.54 grams of H 2
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Major Instruments used in Chemical House: The details of instruments used in the chemical house are given below: Steam Pits:
Pits are used to heat the sulfur and convert into the melted or paste like form. These pits are small pipes and steam passes through them when sulfur is poured onto these pits, the heat which evolves from these pits it converts the sulfur into liquid form. Furnace:
Furnace is used to heat the sulfur and oxygen to make the reaction possible in the required conditions. It maintains the required temperature and pressure. Different types of furnaces can be used according to the demand. In Chemical House the furnace used is heated with the help of fire which is promoted by diesel. The furnace has nickel coating on the outer side and in the inner side the asbestos sheet is used and the top inner side the fire bricks are used to insulate the furnace and to reduce the loss of heat. Cooling Tower:
Cooling Tower is used to reduce the temperature. Two types of flow may occur in the cooling tower. Counter current flow Co-current flow The flow of SO 2 and water is counter current flow. Blower:
Blower is used to supply the air. A 100 hp of motor is used in the blower. It maintains the continuous supply of air and oxygen in the furnace during the preparation of SO 2 . Valve:
Valve is the instrument used to control the flow rate of any liquid or gas. Although many different types of valves are used to control the flow of fluids, the basic valve types can be divided into two general groups: stop valves and check valves. The valves used in the chemical house are Stop Valves. The names of the valves are given below. Butterfly valves Gate valves (Fixed Stem) Two way valves Reactor:
Two different types of reactors are used in the chemical house. The major difference between them is of size. The material used for both the reactors is Aluminum so that the solutions of low pH may not spoil it. Heat Exchanger:
Heat Exchanger is a device used for efficient heat transfer from one liquid to another without mixing them into one another. In Chemical House, the type of heat exchangers Plate heat exchanger. One is composed of multiple, thin, slightly-separated plates that have very large surface areas and fluid flow passages for heat transfer. This stacked-plate arrangement can be more effective, in a given space, than the shell and tube heat exchanger. 7
IMPORTANT DEFINITIONS: Before moving towards the Cooking House and Bleaching House, some important definitions should be explained to make the up-coming information easy and understandable. Pulp:
Fibrous material in wheat straw and Bagasse is called Pulp. Crude pulp:
Pulp attained by cooking of Straw/Bagasse is called Crude Pulp. Unbleached Pulp:
Pulp achieved after washing and cleaning of crude pulp is called Unbleached Pulp. Bleached Pulp:
Pulp achieved be chemical treatment of Un-bleached pulp is called Bleached Pulp. Consistency:
Oven dried weight of pulp in 100 ml of suspension is called Consistency. Accept:
Useful fiber is called Accept. Reject:
Un-wanted fiber is called Reject. Residual:
Remained bleaching chemicals in pulp are called Residual. SRo:
Degree of freeness Freeness:
Amount of water drained from pulp suspension is called freeness. GE o:
Degree of brightness Back Water:
Removed after from washing and bleaching filters is called back water.
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COOKING HOUSE: Cooking House is the second step towards the preparation of paper. Two plants are being operated in the cooking house. First is the straw plant and the second is for the cooking of wheat straw. Cooking House is doing a tremendous job for the preparation of fine Pulp.
Objective: The objective of cooking plant is to provide a continuous flow of quality pulp to the bleaching house after adding liquor up to required consistency.
Straw Plant: Straw plant is used for the primary and secondary cleaning of the wheat straw. Processes involved in this plant are discussed below: Primary Cleaning:
For this purpose the raw wheat straw that comes in the form of bales is manually shifted to a conveyer belt. The belt moves and takes the straw towards a suction pipe. The suction pipe is connected with the blower. In the start of the suction pipe, heavy stones are separated in the stone collector. The suction pipe transfers the wheat straw to the double shaker. In the double shaker the unwanted material is separated from wheat straw. There is a screen in the double shaker which vibrates and helps to separate the unwanted material. The size of the holes in the screen is round about 8mm. another suction pipe continuously extracts the wheat straw next to the cleaner. The double shaker is air tight so that the vacuum inside the chamber is maintained. And the flow of straw remains continuous. And passing through the vibrating screen the wheat straw is shifted to the cleaner in the same chamber. There is also a screen in the cleaner which separates the unwanted material. The size of the holes in the screen of the cleaner is between 2.5mm to 3mm. Two brushes named Scrapers continuously clean the holes to avoid the blockage. In the cleaner, dust particles and sand is removed from the wheat straw. A cyclone is attached with the cleaner that extracts the low weight particles from the wheat straw with the help of blower. A continuous supply of water is provided in the cyclone due to environmental hazards. These low weight particles are drained out in the water. The last point of the pipe of cyclone is continuously dipped into the water to keep the atmosphere clean. Now the useful wheat straw is shifted to the single shaker. A special type of exhauster is used to maintain the vacuum during the transfer of straw. The vacuum is necessary for the suction. Single shaker is the last step of Primary Cleaning of wheat straw. Single shaker also removes the unwanted material from the wheat straw. It has a screen which vibrates and separates the unwanted material. Difference b/w Double Shaker and Single Shaker:
The working principle of both shakers is the same. The only difference exists in the holes of the sheets. The holes in the sheet of the double shaker are about 8mm and the holes in the sheet of single shaker are about 3mm. Secondary Cleaning:
Wheat straw is extracted from single shaker to the Dust Cleaner with the help of suction pipe. Dust Cleaner is a first stage of Secondary Cleaning of straw. This is the same dust cleaner that was used in the Primary Cleaning after the double shaker. The screen of the
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dust has the holes of 3mm. After that the wheat straw is transferred to the Scale Belt giving way towards the mixer. An exhauster is used to maintain the vacuum in the cleaner.
Cooking plant: After the secondary cleaning, the raw wheat straw is shifted to the Scale Belt. Scale belt takes the straw towards the mixer. Sensors on the scale belt calculate the weight of wheat straw according to the unit "ton/hour". Two shafts rotate in the mixing chamber. One rotates in clockwise direction and the other rotates in anti-clockwise direction. A motor having power of 40hp is used to rotate these shafts. These shafts have speed of 1470 rpm. A known quantity of water and sodium sulfite is added to the mixer. The consistency of liquor which is added in the mixer is 13%. These rotating shafts have side wings attached on equal distances to help the process of mixing. From the mixing chamber raw material is shifted to a conveyer belt. The conveyer belt poured wheat straw into the digester. There are total ten 3 digesters installed in the cooking plant. There are six digesters having the capacity of 60m 3 and four digesters having the capacity of 50m . The raw material is poured into the digester according to its capacity. The digester is closed and heating is started. Steam is used for the heating process. The temperature of the digester rises slowly. The heating time is 1 hour and 5 minutes. And the cooking time is 4 hours and 5 minutes. The pressure of the steam is o maintained at 7 to 7.2 bars. And the temperature is 165 to 168 C. A motor of 10 hp is used to rotate the digester continuously during the process of cooking to homogenize the material present in it. A gear system is attached to control the speed of the motor. As the reaction is endothermic so heat is absorbed by the system. After completing the required cooking time the pulp is prepared which moves towards the blow tank. The movement of the pulp from digester to blow tank is due to the pressure of steam. And vacuum is maintained throughout the movement of pulp to stop the leakage of steam. The steam pipes are totally insulated with led and wool coating to avoid heat loss. Calculation for the amount of Sodium Sulfite added:
Before calculations, we must know about the following abbreviations, A.D. = Air dried; O.D. = Oven dried; Liquor = Sodium Sulfite; As we know that, A.D. = O.D. + water Mass flow rate on A.D. basis = 8ton/hour; Moisture contents measured = 19%; So 8 * 0.19 = 1.52; Now Mass flow rate on A.D. basis = 8 – 1.52 = 6.48 ton/hour; Required consistency of liquor = 13%; So Amount of liquor added = (O.D. * liquor consistency) / (liquor strength) = (6.48 * 0.13) / (140.4) = 0.006 ton/hour.
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Major Instruments used in Cooking House: The details of instruments used in the chemical house are given below: Dust screens Shakers Digester Mixer Exhauster
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BLEACHING HOUSE: Bleaching house is third step for the preparation of paper. Two processes are operated here. First is the washing of pulp and the second is towards the bleaching of pulp. Bleaching house collects the pulp from cooking house and after cleaning processes and bleaching processes it transfers it to the next plant. Bleaching house is working through a continuous process for the cleaning and bleaching process. Bleaching house has two lines for both washing and bleaching. Capacity for washing of line 1 is 100 ton/day and for line 2 is 150 ton/day. The bleaching capacity of line 1 is 80 ton/day and of line 2 is 70 ton/day.
Objective: The objective is to clean and bleach the pulp to produce a better quality pulp and forward it continuously towards the Stock Preparation Plant which is the next step for the preparation of paper.
Washing Plant: The pulp obtained from the cooking plant is received in the blow tank. An agitator works in the blow tank to make the pulp homogeneous throughout the tank. Next the pulp is transferred to a chest. There is a cage in the chest which separates the stones or heavy particles from the pulp. Now the pulp is transferred to a stone collector with the help of pump. This stone collector works with the help of centrifugal force and separates the stones and other particles from the pulp. In this way the quality of the pulp is improved. Now the pulp is sent to a vibratory screen. This screen is called Johnson screen. This also helps to improve the quality of the pulp with the help of its vibratory screens. It separates the unwanted material and drains it and shifts the required pulp for the further processes. Next the pulp comes in the washing plants. Four rotary drum filters are used for the washing of pulp. During washing of pulp, known amounts of lignin, salts, iron and sand particles are removed and we try to get the more refined form of un-bleach pulp. After passing through rd 3 rotary drum filter, the pulp passed through the centre-cleaners. Three stage centrecleaners are installed in the mill to give the quality pulp for the process of bleaching. Pulp passes through these cleaners with the help of pump. These centre-cleaners work with the help of centrifugal force and help to remove the reject more effectively. From these cleaners it moves towards the de-watering filter. It reduces the water from the pulp and increases the pulp consistency 8 to 10%. And in the last of the washing plant the pulp is shifted to the back water chest. And it transfers it to the storage tower.
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Bleaching plant: It is the second process working the bleaching house. In this plant, we bleach the pulp with the help of bleaching agent sodium hypochlorite. Sodium hypochlorite is provided by the chemical house. In this process the un-bleach un -bleach pulp from the storage tank of washing plant is transferred to buffer chest with the help of pump. Water is also added to the chest to decrease the pulp consistency up to 3%. And from the buffer chest it moves towards the pre-hypo filter. This pre-hypo filter is also a rotary drum filter. In this filter 3.5% of sodium sulfite is added to the pulp. In this way, the consistency of pulp decreases up to 1%. This pre-hypo filter transfers the pulp to single shaft mixer which further forwards it to the Thick Stock Pump. Thick Stock Pump has the power 60 hp and works accordingly. Thick Stock Pump transfers the pulp to the hypo-tower 1. In the hypo-tower, the temperature of the o pulp increases slowly round about 40 to 42 C. 5% of sodium hypochlorite is also added on O.D. bases. The reaction time in the reaction tower is given up to 2.5 hours. An agitator also works in the tank to make the solution homogeneous. After reaction time is completed, the pulp moves towards hypo filter 1 which again filter the pulp and try to develop more refined form of pulp. It transfers the pulp to another thick stock pump which transfers the pulp to hypo tower 2. In this tower the same process is repeated again under the same physical conditions. After the reaction the tower transfers the pulp to high density tower in which the consistency of pulp is 8 to 10%. And from this tower the pulp is shifted to the Stock Preparation Plant. It is to be noted that total water requirements for washing and bleaching is 16.77 liters/sec. Calculations for the amount of Sodium Hypochlorite:
As we know that A.D. = O.D. + water; Volumetric flow rate on A.D. basis = 2200 liters/min; Volumetric flow rate = Mass flow rate / Consistency (density); Mass flow rate = Volumetric flow rate * Consistency; Mass flow rate = 2200 liter/min * 0.03; Mass flow rate = 66 kg/min; Mass = 66 kg; 5% of 66 kg = 66 * 0.05 = 3.3; So 3.3 kg/min of Sodium Hypochlorite is added in 66 kg/min of slurry.
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Major Instruments used in Bleaching House: Major instruments used in the Bleaching House are discussed below. Dewatering Filter or Rotary Drum Vacuum Filter (RDVF):
The process of the RDVF is continuous. Each revolution of the drum consists of cake formation, cake washing (if needed), dewatering or drying, and cake discharge. 1- As the drum rotates, it is partially submerged in the feed slurry. 2- Vacuum draws liquid through the filter medium (cloth) on the drum surface which retains the solids. 3- The vacuum pulls air (or gas) through the cake and continues to remove moisture as the drum rotates. 4- If required, the cake can be washed to remove impurities or to extract more product. Additional drying of the cake follows washing. 5- Finally, the cake is discharged from the drum to a conveyor or chute to the next process step. 6- The filtrate and air pulled through the medium flow through internal filtrate pipes and pass though the rotary valve and into the filtrate receiver. 7- The liquid stream is separated from the vapor stream in the receiver. 8- Liquid filtrate is then pumped to the next step in the process. 9- Vacuum is applied using a liquid ring vacuum pump or other means.
Blow Tank:
In batch digestion, the pulp and black liquor are mechanically conveyed or "blown" into an atmospheric blow tank upon completion of the cooking cycle. The tank is a large cylindrical vessel which functions as intermediate storage of the cooked pulp, and from which the pulp (now called "Brown Stock" due to its color) 7
is discharged in an even flow to a washing process. Johnson Screen:
There is machine used for screening purposes named Johnson Screen. It helps to separate the unwanted fibers during its vibration. It has a screen having holes in it. The required pulp passes through the screen but the reject does not pass through it and drains out. Centre-cleaners:
Paper stock contains impurities that, if not removed, would affect the quality of paper produced and cause damage to the wire. Cleaners are used to remove small, heavy, dense contaminants, such as shives, sand, pipe scale, and metal flakes. The smaller impurities are easily removed by the cleaners. This process improves the appearance of the paper and increases the life of the wire and the calendar rolls. Multiple stage cleaners are used to prepare the stock for the paper machine for two reasons: Cleaners are only able to process a little stock at a time. Cleaners reject a small portion of good fibers as well as contaminants in the cleaning process. “It works on the principle that centrifugal force acts on different bodies proportional to their mass/unit ma ss/unit volume.” Higher the force more swirl will be generated. A small pressure difference is provided to facilitate the separation of the less swirling substance. Due to centrifugal force the heavy materials moves downward and light material moves upward streams and then the heavy and light material is collected from their respective points. Thick Stock Pump: It is a pump which has two basic functions. The first function is to screen the unwanted material from solution of high consistency and second function of the pump to transfer the material towards the next process.
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STOCK PREPARATION PLANT: Stock Preparation Plant is the fourth step for the preparation of paper. It is the only department which controls the nine different processes separately. In these nine processes 3 processes are of waste paper treatment and 6 processes are of refining of different types of wood pulp.
Objective: The objective is to provide a continuous flow of pulp for the machine chest after preparing the recipe of customer's demand.
Waste Paper Plants: There are total three waste paper plants working in the Century Paper Mill. I am going to discuss waste paper plant 1 here. The flow diagrams of all three plants are attached in the report. Waste paper plant 1:
First of all, the waste paper collected from different parts of country is brought into the Mill. This paper is manually transferred onto the conveyer belt. It moves and pours all the material into the pulper. There are different supplies of back water in the pulper. The pulp consistency is maintained 3.5 to 4.5% in the pulper. An agitator continuously rotates in it which helps to mix the pulp with back water. After the mixing time, the material moves towards the ditch. Ditch is a tank which collects the pulp. It separates the stones and unwanted heavy material on the basis of gravity which drain out. The required pulp is shifted to the chest. Next the pulp moves towards the High Density Cleaners (HDC) with the help of pump. There are three high density centre-cleaners that clean the pulp and stones like materials depending on their density are separated with the help of centrifugal force. The pulp goes to the first H.D.C. The reject of it moves towards the second H.D.C. And the required material goes towards the Turbo-Separator. Accept of the second H.D.C. goes towards the dump chest and again goes to the first H.D.C. The reject of the second centrecleaner goes towards the third H.D.C. Accept of the third H.D.C. goes towards the first H.D.C. and cycle goes on. Accept of the first H.D.C. that goes to the turbo-separator. Turboseparator separates the solid particles from the raw material. It has a round large size plate having holes of 3mm in it. The material that passes through the holes is called accept and the material that does not pass through the holes is reject. Light reject and heavy reject are separated. Heavy reject is drain out and light reject is shifted to the Separ Plast. Separ plast helps to remove additives of plastic like PVC present in it. Accept of separ plast goes to the dump chest again again while reject is drain drain out. Accept of Turbo separator separator moves towards the Deflaker. It is a motor which also tries to remove solid particles from raw material and separates fibers. All processes are carried out to enhance the quality of raw pulp. Next the pulp passes through three stages centre-cleaners. Each stage of centre-cleaner consists of multiple centre-cleaners. Accept of first stage centre-cleaner moves towards the chest and the by-pass stream moves towards the de-watering filter. While on the other hand, reject of the first stage centre-cleaner moves towards the second stage centre-cleaner. Accept of the second centre-cleaner goes to the inlet of the first stage centre-cleaner. Reject of the second centre-cleaner moves towards the third stage centre-cleaner. Accept of the third stage centre-cleaner goes to the inlet of the second stage centre-cleaner and reject is drain out. These three stages of centre-cleaners try to improve the quality of pulp. Chest transfers 9
the pulp to high pressure screen. This screen has a round plate having holes of 3mm in it that separates unwanted particles. Accept of HPS transfers to the de-watering filter. A small quantity of accept is shifted to the pulper to enhance the properties of pulp in the pulper. On the other hand, reject of HPS moves towards F00 Screen. This screen also has sieve plates in it which helps to remove unwanted material. Accept goes to the inlet of HPS again and reject drains out. Dewatering filer has a rotary drum which has holes in it. The water removes through suction produce in the small pipe lines present in the inner side of the drum. Waste water goes to the thickener water chest. Thickener water chest supplies water to the various equipments in the plant. The water is called back water. Accept of dewatering filter goes to the storage chest with the help of pump and this storage chest supplies pulp to the machine chest to make a recipe for a perfect paper.
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Major Instruments used in Waste Paper Plant 1: The major instruments used in the waste paper plant 1 are discussed below. Dewatering Filter or Rotary Drum Vacuum Filter:
I have discussed it with all details in the previous section of Bleaching House. High Pressure Screen:
The principle of pressure screen is that the leading edge of the rotating foil accelerates the stock and then, in back, vacuum is produced, the impurities remains in vacuum section while the accept moves through openings. This is a mechanical separation technique reliant on exploiting the physical size difference between a fiber and the contaminant to be removed.
Turbo Separator:
It is used for effective separation of heavy and light impurities. The minimum fiber loss is 3.4%. The accept stock passes through the screen fitted behind the rotor. In Turbo Separator, a force vortex is formed in the separator by a Stainless Steel rotor. The heavy particles are carried outward by Centrifugal force into the junk trap. The rotor & screen are designed to slush paper chips and remove all the non fibrous material which goes out as light reject and further treated in secondary separator of Johnson Screen. Deflaker:
The aim is to mechanically treat the fiber flakes and bundles of fibers in the stock in order that they are broken down into individual fibers in a suspension if possible. This is done for a number of reasons and in a number of positions within the system. It can be installed to reduce remaining flakes after a pulper, in the broke system to 22
reduce flakes going back to the machine from the broke pulpers and can also be used in the final stages of a screening system in a recycled fiber line to treat the concentrated rejects and the flakes contained within it.
Separ Plast:
Separ Plast is used for the separation of unwanted materials of polymer and plastics from the pulp. It is formed by a cylinder carrying hardened tip blades, rotating at high peripheral speed inside a perforated basket, accommodated into housing supplied with inspection and out-let doors. Its operating consistency is 3.5 to 5%. The screen hole Size 3.5 to 6 mm depending on the grade of furnish and on the cleanliness requirements.
Centre-Cleaner: Centre Cleaners have been discussed in the Bleaching House with full details.
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Refining Plants: These plants are used to refine the wood pulp. Wood pulp is imported from different countries by the Century Paper Mill. It has different types. The names of some of the types which are used by the Century Paper Mill are given below: Soft Bleach Kraft Pulp (SBKP):
The pulp use to produce white paper is called Bleach Kraft Pulp. The chemicals used to bleach pulp have been a source of environmental concern, and recently the pulp industry has been using alternatives to chlorine, such as chlorine dioxide, oxygen, ozone and hydrogen peroxide. Bleach Chemical Thermo Mechanical Pulp (BCTMP):
Thermo mechanical pulp is pulp produced by processing wood chips using heat (thus thermo) and a mechanical refining movement (thus mechanical). It is a two stage process where the logs are first stripped of their bark and converted into small chips. These chips have a moisture content of around 25-30% and a mechanical force is applied to the wood chips in a crushing or grinding action which generates heat and water vapor and softens the lignin thus separating the individual fibers. The pulp is then screened and cleaned; any clumps of fibers are reprocessed. This process gives a high yield of fiber from the timber (around 95%) and as the lignin has not been removed, the fibers are hard and rigid. Un-bleach Kraft Pulp (UKP):
Kraft pulp is what you get after you place a chip of wood in a pressurized vessel in the presence of hot caustic soda and sodium sulfide. The cooking process attacks and eventually dissolves the phenolic material called lignin that glues the fibers to each other in the wood. The word "Kraft" means "strong" in the language of its origin. German manufactures of pulp discovered that addition of the sulfur to a "soda cook" improved the selectivity of the process - dissolving the lignin with less damage to the cellulose. The fibers initially liberated by kraft pulping usually are brown, similar to a typical grocery bag (paper type) or corrugated box. Kraft pulps tend to be more flexible than fibers produced by purely mechanical refining of pulp. Hard Bleach Kraft Pulp (HBKP): This is a type of pulp which we get by bleaching of hard wood. This type of pulp is used for the preparation of multi-layers board.
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Refining Plant 1:
This plant is used to refine the wood pulp. The type of pulp which is refined in the Refining plant 1 is called SBKP. This is an abbreviation of Soft Bleach Kraft Pulp. First of all, pulper is 3 filled with 12m of water. And 2 bales of wood pulp are poured into the pulper. An agitator continuously rotates in the pulper to dissolve the wood pulp in the water and helps to make a homogeneous solution. The pulper shifts the pulp to the chest with the help of pump. In the chest heavy stones lay down due to gravity. Next the pulp is shifted to double disk refiner. There are three double disk refiners installed in series in the refining plant 1 that refine the pulp with the help of motor. All the three refiners help to separate the fibers and transfer the pulp to storage chest. A block diagram of Refining Plant 1 is shown.
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Refining Plant 2:
The type of wood pulp which is refined in Refining Plant 2 is called SBKP. This is the same wood pulp which is refined by Refining Plant 1. But the procedure of refining in the second plant is a bit different. First of all we add the bales of pulp with the fresh water in the pulper according to required consistency. Pulper transfers the mixture into the Dump Chest. Dump Chest separates heavy particles present in the mixture with the help of gravity. Next the pulp moves towards the Double Disk Refiner. It refines the pulp and transfers it to the storage chest. In the previous plant, we had three Double Disk Refiners available for refining but here we have only one refiner. In this way the required pulp is in less refined form.
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Refining Plant 3:
The type of wood pulp which is refined in this plant is called BCTMP. This is an abbreviation of Bleach Chemical Thermo-mechanical Pulp. There are two pulpers installed in this plant. These pulpers are installed in the series. The wood pulp is added with the fresh water into the pulpers according to required consistency. Both the pulpers transfer the pulp into the Dump Chest. Heavy Particles are separated due to gravity in the dump chest. Next the pulp moves towards High Density Cleaner. The cleaner removes the stones of high density and helps to clean the pulp. From the cleaner the accept moves toward the deflaker. Deflaker separates the fibers and the pulp transfers to the Double Disk Refiner. There are two refiners installed in this plants that enhances the refining capability of the plant. After passing through these two refiners the pulp moves towards the storage chest. There are 3 3 two storage chests. First has the capacity of 70 m and second has the capacity of 20 m .
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Refining Plant 4:
The type of wood pulp which is refined in this plant is called UKP. This is an abbreviation of Un-bleach Kraft Pulp. First of all the wood pulp is added with the fresh water into the pulper according to required consistency. The pulper transfers the pulp into the dump chest with the help of pump. Heavy particles are separated in the chest due to gravity. Dump chest transfers the pulp to High Density Cleaner with the help of pump. It removes the heavy particles from the pulp and enhances the quality of pulp. HDC transfers accept to Single Disc Refiner. There are two single disc refiners installed in this plant that use for refining purposes. These two refiners are connected in series. After passing through the refiners the pulp moves towards the F00 screen. The screen helps to remove unwanted particles from 3 the pulp. And next the pulp finally transfers to the storage chest having capacity of 37 m .
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Refining Plant 5:
The type of wood pulp which is refined in this plant is called UKP. This is an abbreviation of Un-bleach Kraft Pulp. UKP is added with fresh water in the pulper. After having specific time in the pulper, pulp shifts to the Dump Chest. Heavy particles are separated due to gravity in the chest. Next the pulp moves towards the High Density Cleaner. Cleaner tries to remove the contaminants present in the pulp and transfers accept towards the deflaker. Deflaker separates the fibers from each other and transfers the pulp towards the Pilao. Two pilaos are installed in this plant in the series. An agitator works in the pilao. In the last step of 3 refining the pulp shifts to the storage tank having capacity of 80m .
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Refining Plant 6:
The type of wood pulp which is refined in this plant is called HBKP. This is an abbreviation of Hard Bleach Kraft Pulp. First of all wood pulp is added with fresh water into the pulper. After having specific time in the pulper it moves towards the Dump Chest. Heavy particles are separated due to gravity. Next the pulp transfers to the deflaker. Deflaker separates the fibers from each other and transfers the pulp to Pilao. Pilao shakers the pulp and make a homogeneous solution. In the last step, the pulp transfers to the storage tank.
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Major Instruments used in all the Refining Plants: Double Disk Refiner:
A double disk refiner and inducer for the same that mixes fiber in low consistency (6% or less by weight) stock and urges it towards both pairs of refiner disks of the double disk refiner. In a preferred embodiment, the inducer comprises an impeller that has at least one flight extending radially outward from an inner hub. Each flight is angled and also can be curved so as to substantially continuously mix and urge stock toward the disks. In one preferred embodiment, the inducer is an impeller that has two helical flights that are axially spaced from one another but that overlap in an axial direction. In a preferred method, the low consistency stock is urged by the inducer toward the disks preventing clumping of fibers in the stock and breaking up any clumps already present in the stock. As a result, the gap between the disks can be increased from between one thousand and three thousandths of an inch to increase the output of the refiner.
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MACHINE HALL: Machine Hall is the strongest department of Century Paper Mill. There are total six Paper Machines in Machine Hall. Among these machines there are three paper machines and three board machines. All the machines are producing different quality of paper and board. All the administration and workers of Machine Hall are performing a tremendous job to maintain the quality of production. Before shifting pulp to the head box of machine, the process which is controlled by machine hall administration is called Approach Flow System. This is the last process used to control the quality of pulp.
Approach Flow System: The term approach flow includes i ncludes the piping system present in between recycling chest and head box. The components discussed in the approach flow system are:
Recycling Chest Machine chest White water tank Fan Pump Cleaners Pressure screens Head Box
Recycling Chest (Or Recycling Tank):
The various pulp and broke stock are proportionally mixed in the blend pipe and then delivered to the Blend Chest. The Recycling Chest receives its stock from the Blend Chest and sent to Machine Chest. The over flow of the Machine Chest is recycled to Recycling Chest. The basic purpose of Recycling Chest is to provide stock to Machine Chest in such a way that the level of Machine Chest remains constant. Machine Chest (Or Recycling Tank):
The Machine Chest is last storage volume of stock before it is diluted and pumped to the head box. The basic Purpose of Machine Chest is to provide constant flow of stock at the inlet of fan pump. Level of Machine Chest is maintained constant to provide constant head at the inlet of Machine Chest pump. White Water Tank:
The white water tank is a large holding tank that is located behind the breast roll end of the wire in the stock approach system. The tank receives the white water as it drains through the wire, away from the forming paper web. The cleaner pump pulls white water from the tank for diluting the stock to less than 1% consistency. The level of the tank should remain constant, excess white water from the tank overflows to the excess tank. Fan Pump:
This is an axial flow pump that uniformly mixes stock with white water. It's impeller is like a close impeller. Fan pump takes water from tank. During the operation tank head should be constant and white water in the tank should be free of air. Centre Cleaner:
I have previously discussed Centre Cleaners in the Bleaching House with full details.
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Pressure Screen: I have previously discussed Pressure Screen in W aste Paper Plant with full details. Head Box:
The Head box distributes stock at an even rate across the width of the paper machine. The flow of stock through circular pipes must be converted to a horizontal or linear flow. This enables the stock to be spread evenly across the entire width of the paper machine. The basic components of a Head box are the stock inlet and the slice. The stock inlet feeds stock into the Head box. The stock then flows out of the slice and onto the forming fabric (wire). The slice has an adjustable slice (top) lip and apron lip (bottom).
Early Head boxes were simply open rectangular tanks that held the stock. Weight of the column of stock or head pressure provided force to push the stock through the slice. Adjusting Head box height varied the head pressure, therefore it influenced machine speed. Maximum practical height of the box limited the operating speed of machine and therefore flow speed limited onto the wire. To achieve higher operating speeds pneumatic and hydraulic Head boxes were developed. They are sealed units pressurized by air or by the liquid stock. The following are important criteria for good Head box design. No surging of feed entering the Head box No dead (no flow) areas inside the Head box No sharp internal corners or edges to catch the stock Maintain a uniform fiber dispersion Eliminate entrained air Distribute stock uniformly across the full width of the machine Head box Design: There are following different types of head boxes on the basis of design. 39
Pressurized Head box:
Pressurized Head boxes have a cushion of air in the Head box. The air p ressure regulates the rate, or jet velocity, of the stock out of the Head box. Increasing the air pressure increases the jet velocity. Stock flows from a set of laterals into a chamber. The stock fills the chamber to a level over two perforated rolls. These rolls, which are called rectifier rolls, break up small clumps of fibers and keep the fibers in the stock dispersed. The rolls also smooth out small variations in the stock flow by keeping the flow going in one direction toward an opening called a slice. The slice is adjusted to regulate the stock flow from the Head box to the forming section. Hydraulic Head box:
Hydraulic Head boxes are designed differently from pressurized Head boxes. The Head box and the entire line from the stuff pump to a hydraulic Head box are completely filled with stock, so this type of system behaves much like a hydraulic system. The dynamic liquid pressure established by the fan pump forces the stock through the box and to the slice. The stock flow and the jet velocity are generally higher with hydraulic Head boxes than with pressurized Head boxes. Hydraulic Head boxes are often used with high speed paper machines. Head box Tapered Header:
The purpose of the tapered header is to keep stock flow uniform across the width of the paper machine and to maintain an even pressure along the entire length of the header. Tapered header gets its name from the tapered pipe that supplies stock to the Head box. It extends across the width of the machine. The taper keeps the pressure at one end of the header close to the pressure at the other end. The taper evens the pressure that is felt across the width of the Head box. The major parts of the tapered header are: Recirculation line Balance line
Paper Machine: After passing through approach flow system, pulp moves towards the machine. The process operated on the machine is given below. Process:
First of all the pulp is equally distributed on the wire part of the machine by the head box of machine. Wire part of the machine helps to remove water present in the pulp. it increases the pulp consistency 20 to 24%. A breast roll present just below the head box. First the pulp passes through the forming board. This is the first step towards the formation of the paper. It also helps to remove water initially. After passing through the forming board, pulp passes through hydro foils, vacuum foils and vacuum boxes. These foils and boxes are used to reduce the water content present in the pulp and helps to increase the consistency of the pulp. A roll named Dandy Roll is also used in between the vacuum foils and vacuum boxes. This is the first step towards the formation of sheet of the paper. At the end of the wire part, sheet of the paper moves towards the press part of the machine. In the press part, sheet of paper is pressed by applying pressure. The major equipment used in the press part is called Nipko Press. Next the sheet moves towards the Dryer Part. In the dryer part of the machine, sheet passes through rotary drums. These rotary drums are heated with the help of steam. The water present into the steam and sheet dries. There are two types of dryers in 41
the machine. One is the Pre-dryer and second is the post dryer. In the pre-dryer, only a single felt is used to transfer the sheet while on the other hand in the post dryers two different felts are used to transfer the sheet. After passing through the dryer part of machine, sheet moves towards the online sizing process. Again the sheet is dried after sizing. The process of sizing gives quality to the paper. After passing through the dryer, it moves towards the calendar. Calendar controls the caliber and thickness of the sheet by passing in between the pressure rolls. Next the sheet moves towards the pope where a roll is winding and sheet is collected on that roll. Calculation for the flow and head on the Machine: Flow Calculation: 2
Flow (lit/min) = {Speed(m/min) x Deckle(m) x Grammage(g/m )} / {Consistency (g/100ml) x 10} Head Calculation: 2
2gh = V 2 h = V /2g where: h = head box head of machine (m) V =Machine Speed (m/min) 2 g = Acceleration due to Gravity (m/sec ) Through put = Machine Speed x Deckle x Grammage
Major parts of the Machine: There are three major parts present on the machine.
Wire Part: After the head box pulp is delivered to wire section through forming board. This section through forming board pays basic role in the sheet formation since the quality of paper product and its suitability for the market place is often determined by formation. The wire allows the water to
drain away from the stuff, leaving a fibrous mat that is carried toward the press section. The purpose of the wire section of the paper p aper machine is to: Receive diluted stock from the Head box Remove water from the fibers Generate the proper activity (turbulence) to ensure a good, even formation of the fibers throughout the sheet The wire removes water from the sheet, increasing consistency from less than 1% to 20% off the couch roll. It is important that dewatering of the sheet is maximized on the wire, because it is more economical than on the press and dryer sections. WIRE COMPONENTS:
The wire accepts and supports the stock coming from the slice on the head box. Wire components drain water from the sheet so that it is strong enough to withstand the forces that are exerted on it without breaking in the press section. i. Breast roll ii. Forming board iii. Foil boxes iv. Vacuum foils 4
v. vi. vii. viii. ix. x. xi.
Flat boxes Water Cutters Dandy roll Couch roll Forward drive roll Guide roll Stretch roll
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Press Part:
The primary objective of pressing is to remove as much water as possible mechanically before the sheet enters the dryer section. In addition, the press section consolidates consolidates the web by forcing the fibers closer together without harming or degrading the quality of sheet. There are two main causes of press part: i. Water removal ii. Consolidation the web
The press operation is an extension of the water-removal process that starts at the paper machine forming section. It is far more economical to remove water by mechanical means than by heat. Water removal should be uniform across the machine so the pressed sheet has a level moisture profile when it enters the dryer section. Sheet consolidation is a crucial phase of papermaking. It is here that the fibers are forced into close contact so that good fiber-to-fiber bonding develops during drying. If the consolidation phase were to take place after the dryers, the product would invariably be weak and bulky. Press section equipment is important in terms of mill economics. It is far more economical to remove water mechanically in the press section than to produce steam and remove water through evaporation in the dryer section. Water Removal:
Pulp leaves the head box at less than 1% consistency. consistency. Initially, water removal from the sheet is performed easily and readily. However, as sheet consistency consistency increases, the the removal of water becomes gradually more difficult and more expensive in terms of both the capital and operating costs. As the sheet travels down the forming table, the forces of gravity, vacuum, and centrifugal force bring the sheet from the low consistency to about 18% to 20% consistency. The gravity dewatering is the most economic economic means of removing water. At a certain point, the water can no longer be removed by gravity or vacuum, so a mechanical compression must be applied. The vacuum and the air flow it generates generates will eventually no longer be able to remove water since it is not free water, which means it is bound in some way to the fibers. An attempt is made to maximize the sheet dryness out of the press section with the value varying by grade. Some press configurations on specific grades have been able to achieve dryness in excess of 50%. In fine papers, the sheet sheet consistency after the the last press varies from about 35% to 45%. The water that remains in the sheet after the last press must be evaporated by means of steam-heated dryers. The drying of paper is a comparatively long and expensive process. The figure below represents the relative cost of water removal in each section of the paper machine. The sheet leaving the former is about about 80% water. Some of this water is carried in the the void areas between the fibers, and the remainder remainder is carried in the fibers. The press loads are normally increased in each successive press, but as the sheet dries, the water becomes harder to remove. Paper Consolidation:
By raising the solids content of the sheet, the tensile strength of the sheet is significantly increased. The tensile strength is needed to minimize sheet breaks breaks on fast machines.
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The wet pressing improves machine operation, and efficient pressing makes the machine more economical to operate, but it also changes the sheet characteristics, such as: Smoothness Tensile Strength Density Thickness Tear strength The moisture profile must must also be uniform with with a uniform basis weight profile. If the moisture profile is non-uniform, the weight profile is usually adjusted to compensate, and this can result in over drying, increased cost, poor operation, and off-quality paper. Prior to the press section, the fibers in the sheet have not made good fiber-to-fiber bonds. The consolidation that occurs in the press section is critical to the final strength of the sheet after drying. The pressing process mechanically mechanically forces the fibers into close contact. This results in good fiber bonding. The well-bonded sheet is able to travel through the rest of of the machine without breakage. In a press nip, the wet web is pressed between two rolls, which may be separated by either one or two press fabrics. The water that is pressed out of of the sheet either goes through the the fabrics and into the voids in the press rolls or is absorbed by the press fabric. The water that is absorbed by fabric is carried by the press fabric to the Uhle boxes, where it is removed by vacuum. The water that finds its way through the fabric to the press roll is either doctored doctored off the roll surface, thrown out by centrifugal force into a saveall, or vacuumed into the roll (press suction roll).
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Dryer Part:
Dryer part is the heaviest part of any machine. There are more than thirty rotating drums that are used for the drying purpose. These drums are heated with the help of steam which is supplied by the boiler. There is a complete lining system within the rotating tank that accepts the steam and drain out the liquid water. It is to be noted that each dryer must have the speed according to the movement of the sheet given by the previous parts.
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Difference between Paper and Board Machine: To know the difference between paper and board machines, we first need to know the difference between paper and board. Paper is a single layer product and board is a multilayer product. Board machine is different from paper machine due to multi-layers of board. Board machine of century paper mill is producing three layers board. The major difference that is present in the start of the machine is number of head boxes. There are three head boxes for each separate layer. One is for top layer, second is for back layer and third head box is for filler. Usually the mid layer or filler is made of waste paper while on the other hand top and back layers are made of fresh wood pulp. In the dryer part of the board machine, yankee is the major part of dryers. Yankee has the same objective for drying but the main importance of yankee is due to its large cross sectional area provided for the drying of board. Infrared heating system is also installed on the machine for drying purposes just after the online coating process. I have added a picture to show the differences between paper and board machine.
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COATING PLANT: Board that is manufactured in the machine hall is brought to the coating plant. Coating is done to enhance the quality and to give an extra shine to the paper or board. Another 2 2 purpose of coating is to increase the gramage of board round about 20 g/m to 30 g/m
Objective: The objective is to maintain the quality of the board according to the requirement.
Preparation of chemical: There are two steps for coating of board and for each step, chemicals are prepared separately. For pre coating the names and quantity of the chemicals are given below.
No.
Names
Quantity (Kg)
Used as
1
No.2 CaCO3
1200
Pigment
2
Poly salt S
5
Dispersant
3 4 5
Caustic Hydro carb - 90 No.2 China Clay
1 375 375
pH Controller Pigment Pigment
6
Titanium dioxide
50
Pigment
7 8 9 10
Binder Sterocoll FD Busan 1078 Etingal – Etingal – S
600 26 1 1
Binder Thickener Preservative De-foamer
All the above chemicals are added into the given sequence in the mixing tank. An agitator works continuously in the mixer and mixes all the chemicals to make the solution homogeneous. The preparation time for the final product is one hour and thirty minutes. In the last step the chemical moves to the storage tank. Final product must have the following qualities. 1. 62% to 63% solid contents 2 2 2. 11g/m to 12 g/m coat weight 3. 500 cps to 1000 cps viscosity For top coating the names and quantity of the chemicals are given below: No.
1 2 3 4 5 6 7 8 9
Names
Water Poly salt S Caustic Anti-mussol Leucopher U60 Hydro carb - 90 No.1 China clay Sterofan PVA GL-05
Quantity (Kg)
500 liters 10 1 1 14 625 1250 125 1
Used as
Solvent Dispersant pH Controller Anti foam OBA Pigment Pigment Plastic Pigment Rheology modifier 56
10 11 12 13 14 15
Binder Carta-bond Sorbitol Sterocoll FD Busan 1078 Etingal - S
620 20 10 7 1 1
Binder Synthetic Insolubilizer Stabilizer Thickener Preservative De-foamer
All the above chemicals are added according to the given sequence into the mixing tank. An agitator continuously works in the tank to make the solution homogeneous. The preparation time is given up to 1.5 hours and finally the chemical transfers to the storage tank. Standard product must have the following properties. 1. Solid Contents 62% to 63% 2 2 2. Coat weight 14 g/m to 15 g/m 3. Viscosity 1800 cps to 2300 cps
Process: First of all, the chemical is brought into a chest with the help of pump. There is another pump that shifts the chemical to the high pressure filter. It helps to obtain the better quality of the chemical after removing the reject. The roll of paper is attached to the un-winder. After passing through different rolls, the paper is pressed between two rolls. Next the paper moves towards the pre coating stand. It has two rolls and chemical for coating is applied here to the paper. A metallic plate is attached to the roll that controls the quantity of chemical stick to the paper. As the process is continuous so the paper moves towards the next step of coating. The paper reaches on the Top coating stand. Same process is revised and paper moves towards the dryers. There are total five tunnel dryers working on the coating machine. Steam is used to heat the metallic plates of the dryers. The phenomenon of heat exchanging happens and sheet of the paper is dried. After passing through the tunnel dryers, sheet moves towards the rotary drum dryers. These are the same dryers that were used in the paper machine. Steam is used to heat the dryers. Sheet of the paper passes through these dryers and moves towards the pope. The coated sheet is packed on the roll and forwarded towards the finishing plant.
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BOX PLANT: Box is basically a combination of more than one layer of paper and board. In box plant of Century Paper and Board Mill, two types of boxes are produced. One is three layers box and the other is five layers box.
Objective: The objective is to produce the three and five layers boxes continuously while maintaining the quality according to the demand of customer.
Preparation of Glue: The major component that is used in the box plant is glue. It helps to stick the layers of board with channels of corrugators. The procedure for the preparation of glue is discussed here. First of all, 18 0 liters of water is taken in a tank. The tank is known as Primary Tank. The temperature o of 60 to 65 C is maintained in the primary tank. 60 kg of Starch Sure bond (Corn Starch) is added into the water. The mixture is agitated continuously in the tank. After 5 to 10 minutes of mixing, 17 kg of caustic soda is added in the breaks. Caustic Soda is added in 20 to 25 minutes. Now 480 liters of o water is taken in another tank. This tank is known as Secondary Tank. Temp of 38 to 39 C is maintained in the tank. Then 5.5 kg of Borax is added. Next 250 kgs of Coragon Maize (Corn) Starch is added to the solution. The mixing time of 15 minutes is given to the solution. Now two solutions are prepared. Add the solution of primary tank into the secondary tank slowly in 25 minutes. The agitator also works slowly but continuously during the mixing process. Now the reaction time is given to the solution upto 15 minutes. Viscosity is checked and that should be 60 to 70.
Quality tests for the Glue:
Following tests are done to check the quality of glue in the lab. i. Viscosity Test ii. Jell Point Test iii. Concentration of solid contents
Corrugators Plant: It is a plant where box is prepared. First of all, according to the demand it is decided that either we have to prepare three layers box or five layers box. I am going to discuss the preparation of five layers boxes for the reader's understanding. No. of corrugators are also selected according to the demand and the budget requirement. If the budget is high the no. of corrugators in one meter of the paper will be large and vice versa. Firstly three layers box are prepared and secondly another two layers are pasted with the help of Glue. So for the preparation of three layers box, a role of straight paper is attached on the machine. There are two types of straight papers. One is the Duplex Liner and second is the Test Liner Paper. And this is selected according to the demand. Just above the role of the straight paper there is another role of paper attached with the Corrugator Roll. The sheet of that paper passes through the Corrugator roles and channels of the corrugators are produced. This sheet of the paper passes through the different roles and come towards the Single Facer No.1. The straight paper is passed through the preheater where a steam dryer o is used. The temperature and pressure within the heat dryer is maintained at 140 to 180 C and 9 to 13 bars respectively. Next sheet moves towards the Single Facer No. 1. Another role of the Corrugator Medium paper is attached on the opposite side of the Single Facer No. 1. That sheet of the paper also passes through another preheater present on the 59
opposite side of the Single Facer No.1 and after passing through the preheater, this sheet also moves towards the Single Facer No.1. This Single Facer No.1 combines these three layers of the paper with each other in such a way that the corrugator paper in the middle and straight paper on the top and bottom sides of the corrugator paper. These layers are attached permanently with each other due to the presence of the Glue. After this formation, if one meter of paper has 120 to 130 channels of corrugators we may call this sheet as C-Flout. It is measured according to International Recognized Standards. After this the sheet moves towards another operation. There are another two roles of different papers. The sheets of the papers are attached with the help of glue and next this layers sheet of the paper moves towards the previously pre viously manufactured three layers sheet. Both the layers pass through the Duplex Heater separately on different roles. After passing through the Duplex Heater the temperature of the sheets increases and on the next roles the glue is pasted on the sheets and these two sheets make their way towards turning roles. Turning roles presses these sheets and the five layers sheet moves towards the Double Baker for heating. After the Double Baker, sheet passes through the Slitter. Slitter is a round cutter that cuts the sheet length according to the measurements given by the computer. These cuttings are made according to the demand of the customer. And after that it moves towards the storage compartment.
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