Paper mill process, piping and piping guide

INTRODUCTION

2008-02-01T07:04:00.010+05:30

INTRODUCTION PULP MILL PAPER MAKING CHEMICAL RECOVERY WASTEWATER TREATMENT PIPING SITE MAP CONTACT ME

INTRODUCTION: SEE YOUR LEFT SIDE RIGHT SIDE FRONT SIDE OR BACK SIDE

You can see the paper. It may be into your valuable place or dustbin. Do you know the HISTORY of the PAPER? Before going up: I want to tell something. This is a site which contains the paper mill process and some piping tips. I think this site must very helpful to the MECH , PROCESS AND OTHER RELEATED ENGINEERS. Thousands of Mechanical Engineers are out coming per year. Some mechanical engineers are going into IT line. Many mechanical engineers are going to production and design field. All are good field if they are all effectively. By considering the design field, the engineers must be have the knowledge in AUTO CAD. Its one of the drafting tool. By using this tool the drawings are made. Here we are discuss about PAPER INDUSTRY AND PIPING DESIGN. PAPER MILL OVERVIEW: Paper is a major product of the forestry industry, and is used widely in our society. Paper products are used not only in their obvious applications in the publishing industry and for writing on, but also in a variety of specialty papers, cardboards, brown papers etc. In addition, various chemicals are produced as a byproduct of the pulp and paper industry. Paper is made by pulping wood, bleaching this pulp and then spreading it out into sheets to make it into paper. At various stages of the process, chemicals are used to give the paper particular properties, such as the bleaching chemicals that make paper white (and which also enable it to subsequently be coloured). The pulping process is known as "kraft pulping" which relies on a combination of heat, chemicals and mechanical pulping to convert the wood into a smooth, soft pulp suitable for use in paper making. Kraft pulping is the main pulping process (together with mechanical pulping) used today. The kraft process has several advantages: • It can be used with virtually all wood species • It can easily handle the extractives in most coniferous wood • The pulp has very good strength (the word 'kraft' means 'strong' in Swedish) • The recovery process for the chemicals is well established However, there are also disadvantages: • The pulp yield is quite low at about 45 - 50% • The equipment used for the chemical recovery is extensive and costly to install • Sulphurous compounds, which are odorous in the parts per billion range, are formed in the process • Fairly complicated processes are required for bleaching the pulp Lignin The main component of wood that needs to be removed to turn it into paper is a compound known as lignin. This name refers to a group of chemicals that are essentially three dimensional polymers of trans-coniferol, trans-sinapol and trans-p-coumarol (see below), along with hemicelluloses and aromatic carboxylic acids. Lignin is the reinforcing compound that is deposited on tree cell walls to make the wood strong enough to carry the weight of the tree crown. However, it is also the compound that makes wood pulp brown, so it is removed from all wood pulp except that used to make brown paper and some cardboards. AREA OF PAPER MILL: There are four major area of paper mill: · PULP MILL · PAPER MAKING · CHEMICAL RECOVERY · WASTWATER TREATMENT PLANT __________________________________________________________

CONTACT ME

2008-01-31T00:01:00.002+05:30

INTRODUCTION PULP MILL PAPER MAKING CHEMICAL RECOVERY WASTEWATER TREATMENT PIPING SITE MAP CONTACT ME

Any comments? Contact me to below id with subject of “PAPERMILLPIPING” amnoorulaman@gmail.com

SITE MAP

2008-01-30T23:55:00.001+05:30

INTRODUCTION PULP MILL PAPER MAKING CHEMICAL RECOVERY WASTEWATER TREATMENT PIPING SITE MAP CONTACT ME

INTRODUCTION PAPER MILL OVERVIEW Lignin PULP MILL Wood preparation Cooking FIBRE LINE: Pulp washing Pulp screening Bleaching Oxygen delignification Final bleaching PAPER MAKING Stock Preparation Wet End Operations Dry End Operations CHEMICAL RECOVERY Chemical Recovery Process Steps EVAPORATION PLANT CHEMICAL RECOVERY BOILER RECAUSTICISING PLANT LIME MUD REBURNING KILN WASTEWATER TREATMENT PIPING SITE MAP CONTACT ME

PIPING

2008-01-30T23:24:00.008+05:30

INTRODUCTION PULP MILL PAPER MAKING CHEMICAL RECOVERY WASTEWATER TREATMENT PIPING SITE MAP CONTACT ME

Piping design is a part of paper mill. Here some basic tips are given for piping design. It will very useful to not only freshers but also piping expertise. If anybody willing to go to piping design area, it will very helpful to them. Click here for more information about piping PIPING GUIDE

WASTWATER TREATMENT

2008-01-30T23:02:00.000+05:30

INTRODUCTION PULP MILL PAPER MAKING CHEMICAL RECOVERY WASTEWATER TREATMENT PIPING SITE MAP CONTACT ME

Description of the Process Kraft pulp mills treat wastewater using primary (physical) and secondary (biological) treatment to reduce pollutant discharges to receiving waters. Kraft mills typically collect and treat the following wastewaters: ! Water used in wood handling and barking ! Digester, turpentine recovery, and evaporator condensates ! Wastewater from brown stock screening ! Bleach plant effluent ! Paper machine white water ! Spent pulping liquor spills from pulp processing areas Figure shows a typical sequence of the major equipment systems in the wastewater treatment plant. The function of each of these systems is described below. Primary treatment Mills use primary treatment to remove suspended solids from wastewater, then treat the wastewater further in secondary treatment. Primary treatment processes used by kraft mills typically involve screening followed by either sedimentation or flotation. Sedimentation Kraft mills use mechanical clarifiers or, occasionally, settling ponds that provide sufficient holding time to enable suspended solids to settle. After settling occurs in the mechanical clarifier, the resulting sludge (which contains up to six percent solids) is pumped from the clarifier to sludge handling facilities where it is dewatered prior to disposal. Mechanical clarifiers can remove as much as eighty to ninety percent of suspended solids. Settling ponds It is a less sophisticated alternative to mechanical clarifiers, also remove suspended solids by sedimentation. Settling ponds may be clay-lined, synthetic-lined, or unlined and earthen, and have longer retention times than clarifiers. Settling ponds produce a less constant solids loadings than mechanical clarifiers, but still provide sufficient solids removal prior to secondary treatment. Flotation Flotation is a solids removal process that introduces a gas, usually air, into the wastewater stream. The gas adheres to the suspended solids, reducing their density and causing them to rise to the surface of the water, where they are skimmed off. The advantage of flotation clarification over sedimentation is that lighter particles that require very long retention times to settle are removed more quickly. A common modification of this process is dissolved air flotation (DAF), in which air under pressure is injected into the wastewater. DAF units are more efficient than conventional flotation clarifiers because more air is introduced into the wastewater, thereby removing more solids. Secondary treatment Kraft mills employ secondary treatment to reduce biochemical oxygen demand (BOD5 ) and toxicity in wastewaters. This process makes use 5 of microorganisms (mostly bacteria and fungi) under aerobic conditions to digest the organic matter in the wastewater. The organic matter is removed as sludge and the treated wastewater is discharged into receiving waters. Because pulp mill wastewater is deficient in nitrogen and phosphorus relative to its high carbon load, these nutrients are usually added to the process to enhance microbial activity. Kraft mills generally use one (or more) of two basic types of secondary treatment processes described below. Aerated and non-aerated stabilization basins About seventy-five percent of U.S. kraft mills use aerated stabilization basins. These basins are equipped with continuous mechanical aerators or diffusers to introduce air into the wastewater. By aerating the wastewater, an increased amount of oxygen is introduced into the wastewater stream. This action significantly speeds up the biological activity compared to a non-aerated basin, so that a retention time of five days may achieve ninety percent BOD5 removal. The continuous aeration also provides thorough mixing which allows mills to operate effective aeration lagoons at depths up to twenty-five feet. These basins are typically lined with clay or a combination of synthetics and clay. Some kraft mills use basins without mechanical aerators. Known as stabilization basins, this is the simplest form of aerobic treatment. This process uses shallow basins that cover very large areas and relies on natural diffusion of air into the wastewater to create aerobic conditions. At depths greater than four feet, anaerobic micro-organisms will become active in the lowest levels; thus, stabilization basins are shallow. Typically, the basin is earthen; however, some are lined with compacted clay. Wastewater retention time may last up to thirty days to achieve up to ninety percent BOD5 removal. Some kraft mills use both aerated and non-aerated basins. The stabilization basin, which may precede or follow the aerated stabilization basin, serves as a "polishing" or "holding" pond to remove additional organic wastes, including biological solids, or to control final effluent discharge to receiving waters. Activated sludge system This system features a microbial floc held in suspension in an aeration chamber. Soluble organic matter in the wastewater is metabolized by the microbial floc which changes it into solids, thereby increasing the suspended solids load. After aeration, treated wastewater is routed to a clarifier where the settled solids are removed as sludge. A significant fraction of this sludge is recycled back to the aeration chamber to maintain the high level of microbial floc (this is the "activated sludge"). The sludge that is removed is dewatered and disposed. Retention time for this system can range from less than six to over 12 hours.

CHEMICAL RECOVERY

2008-01-29T22:43:00.000+05:30

INTRODUCTION PULP MILL PAPER MAKING CHEMICAL RECOVERY WASTEWATER TREATMENT PIPING SITE MAP CONTACT ME

Chemical Recovery Process Steps • Black liquor evaporation: concentrates the black liquor to increase solids content • Black liquor combustion (recovery boiler): burns the organic portion of black liquor to generate steam and produce molten smelt from the spent inorganic cooking chemicals • Recausticizing: regenerates white liquor from the smelt for reuse in pulp cooking • Calcining: recovers calcium oxide (lime) for reuse in the recausticizing process • Byproduct recovery: recovers byproducts such as tall oil EVAPORATION PLANT Process Description For evaporating black liquor a 7-effect 11-body Falling Film type evaporator plant is proposed as a basic process. Finisher effect is provided with three bodies with Lamella type heating surface and rest 2nd to 7th effects consist of Tubular heating surface. The Finisher and second effect consists of three bodies out of which one body will be kept as standby. The vapour is condensed inside the elements and the liquor is distributed on the top of the elements. The liquor flows freely on the outside of the elements to the bottom of the body. A circulation pump (with 100% stand-by) on each of the units circulates the liquor from the bottom to the top and the amount of liquor that is being circulated is very large compared to the evaporation rate. The secondary vapour is released from the liquor immediately upon generation and escapes horizontally outward from the elements to the vapour body and further through the entrainment separator. There is approximately 30-35 mm of free space in the lamella assembly between the elements on the liquor side in finisher effect. The heating surface for 2nd to 7th Effects evaporator bodies comprises 12000 mm long stainless steel tubes. A circulation pump (with 100% stand-by) on each of the units circulates the liquor from the bottom to the top and the amount of liquor that is being circulated is very large compared to the evaporation rate. This ensures that the heating surfaces will all the time be adequately wetted and no dry boiling will occur in any of the units. In the bottom sump of the units there will be a quantity of liquor that ensures that variations in ALILd of liquor or other disturbances will not cause troubles due to lack of liquor in the units, but each unit will always have adequately wetted surfaces. Liquor Flow The weak black liquor from the liquor tank is pumped through the 3 nos. flash tanks to the seventh effect. The flash vapours thus generated are sent to fifth, sixth and seventh effect respectively. From the seventh effect the liquor goes to sixth, fifth, fourth and third in series. From the Third effect the liquor is pumped to one of the units II-A, II-B & II-C. From the second effect the liquor is pumped to any one of the unit I-A, I-B or I-C. In both Finisher and second effects provision is made available so that the liquor sequence can be switched in order to obtain a wash cycle. This provision has been specifically incorporated considering Straw liquor characteristics and the liquor sequence can be switched in order to obtain a wash cycle for both Finisher and second effects. Steam / Vapour Flow The live steam is fed in parallel to two units of first effect. The vapour that is released from effect I is then taken to 2 effect. From this the vapour goes to effect III and so on further to effect IV, V, VI & VII. The vapour from VII effect is condensed in the tubular type surface condenser. Non condensable gases are evacuated by means of vacuum pump in regular operation. Condenser Tubular type Primary and secondary stage surface condensers will be utilized to condense the vapour generated in effect VII including non condensable gases. The vapours generated from VII effect are condensed in primary condenser. The NCG gases collected from II effect to VII effect are handled in secondary condenser. The water enters both the condenser parallely at 35°C and leaves at 45°C. Vacuum Non-condensable gases are evacuated by means of vacuum pump for start-up as well as continuous running. A standby vacuum pump is also provided. Condensate Flow The live steam condensate from the effect I is flashed in three stages to second, third and fourth effects. All live steam condensate is then collected and pumped out separately. Vapour condensate from effect II is expanded to the pressure in effect III and the combined condensate of II and III effects flashed further to effect IV. The vapour condensate from effect V is expanded to effect VI. We have considered separate flash tanks for all stages of primary condensate and secondary condensate flash tanks instead of directly flashing into the respective steam / vapour headers. Washing of the Plant The concentrator i.e. I effect consists of three separate units. During the normal operation the liquid flow sequence will be as follows: Finisher washing sequence: Incoming liquor - IA - IB – Flash tank – IC (Stand-by) Incoming liquor - IC - IA – Flash tank – IB (Stand-by) Incoming liquor - IB - IC – Flash tank – IA (Stand-by) Provision is available to change liquor cycle to allow either one of the three units to be washed by remote control. In this alternative the incoming liquor from II effect will wash the finisher effect, which is under wash. Incoming liquor - IA - IB - IC - flash tank Incoming liquor - IC - IA - IB - flash tank Incoming liquor - IB - IC - IA - flash tank Also provision is made in such a way that any unit in effect I can be independently fed with thin liquor, steam condensate, secondary condensate water or even chemical cleaning agent for washing. In the case that thin liquor is used, the discharge from the washed circuit can be taken back into thin liquor tank. The falling film unit, handling the highest concentration, is an open construction in the liquor space. There will always be possibilities for the cleaning agent such as thin liquor, water, condensate or even chemical cleaning agent to detach the scale. The large amount of liquor in the bottom of the units, which is circulated over the heating surface, ensures that the heating surface always will be wetted even if the liquor flow into the unit is very low. The Washing sequence of Second effect is also like I st effect. Turn Down Capacity The plant operates with a forced circulation principle, enabling the units to operate independently from each other and also independently in the respect of liquor transport from available temperature difference. This means that the turn down capacity will be decided by the instrumentation characteristics rather than from evaporation characteristics. A turn-down capacity of 50% is a reasonable figure to mention. Plant Operation Due to the falling film principle and the forced circulation principle on all of the evaporator units, the plant will be extremely easy to operate. Start-up time will be 3-4 hrs, from empty units depending on the liquor tank situation. There is a limited risk for foaming during the start-up period. After shorter stop, when the evaporators need not be emptied, the start-up time will be even shorter, 1-2 hrs. The design capacity of the evaporation plant is 170 tph of water evaporation and the dry solids content of product liquor leaving the plant is 70%. For evaporating black liquor, a 7-effect 11-body Falling Film combination of tubular and Lamella type plant is proposed. Finisher is provided with three separate units. The vapour is condensed inside the elements and the liquor is distributed on the top of the elements. The liquor flows freely on the outside of the elements to the bottom of the body. A circulation pump on each of the units circulates the liquor from the bottom to the top and the amount of liquor that is being circulated is very large compared to the evaporation rate. This ensures that the heating surfaces will all the time be adequately wetted and no dry boiling will occur in any of the units. In the bottom sump of the units, there will be a quantity of liquor to ensure that variations in ALILd of liquor or other disturbances will not cause troubles due to lack of liquor in the units, but each unit will always have adequately wetted surfaces, which is not the case in conventional LTV units. The secondary vapour is released from the liquor immediately upon generation and escapes horizontally outward from the elements to the vapour body and further through the entrainment separator. There is approx. 30-35 mm of free space in the lamella assembly between the elements on the liquor side in finisher effect. Liquor Flow The weak black liquor from the liquor tank is pumped to the two (2) flash tanks. The WBL is flashed in two stages to fifth and sixth effects. Weak liquor from the second stage flash tank goes to seventh effect, from the seventh effect the liquor goes to sixth, fifth, fourth, third and second effects in series. From the second effect, the liquor is pumped to one of the units I-A, I-B (or) I-C and the liquor sequence can be switched in order to obtain a wash cycle. Effect II is provided with a standby body for 100% capacity. This provision has been specifically incorporated considering bagasse liquor characteristics and the liquor sequence can be switched similar to finisher in order to obtain a wash cycle. Crystallisation Technology The product liquor is pumped to HBL tank and a part of the liquor from HBL tank is pumped to ash mixing tank and returned to the same tank. From the HBL tank liquor is pumped to first effect for crystallisation. The product liquor is pumped to the HBL storage tanks. CHEMICAL RECOVERY BOILER Process description The boiler has both radiant and convective heating surfaces arranged suitably in order to cool the combustion gases and to facilitate effective cleaning of the heating surfaces. The boiler operates with natural circulation. The water walls of the boiler furnace are all welded construction with 63.5 mm diameter tubes and 12.7 mm fins in between, forming a gas tight construction with tubes on 76.2 mm centers. The furnace has a decanting bottom. In the bottom area there are suitable numbers of air inlet openings on two levels in order to control the bed shape. A third level of air inlet openings is higher up to finalise the combustion. The flue gases leaving the furnace’ nose pass through a furnace screen and then passes through three stage superheaters. The superheaters are arranged in three stages with desuperheaters in between the stages for steam temperature control. The flue gases leaving the superheaters pass through a rear wall exit screen and then enter the panel boiler bank. The boiler is a single drum radiant type unit. The boiler bank is a convective heating surface consisting of vertical tube platens. Compared to the conventional bi-drum cross flow boiler bank, the arrangement of axial flow panel type boiler bank gives superior performance with regard to plugging behavior, ease of erection and operational safety. The flue gases leaving the boiler bank enter a three-stage vertical panel type economiser. The economiser panels are axial flow type which is the optimum arrangement resulting in the minimum pluggage of the economiser heating surfaces. The economisers have been sized for a maximum flue gas outlet temperature of 180°C. The superheaters, boiler bank and economiser heating surfaces will be cleaned by long retractable soot blowers. The soot blowers are operated through a remote/auto sequence. Blankets will be provided as insulation in order to minimize heat loss by radiation to the surroundings. The mineral wool will be covered with aluminum/pre-coated sheets for protection against mechanical damage. The boiler will be supported from a steel ceiling structure above the boiler roof thus allowing free expansion downwards when the boiler is warmed up. Fuel Oil System For starting up the boiler and for stabilising the furnace conditions during low load operation and / or firing liquor of low heating value, 4 nos. start-up oil burners are provided. The starting burners consist of oil burners located in separate openings above the furnace hearth. Black and Green Liquor Handling System The liquor is supplied to the burners at dry solids concentration of 70%. The incoming black liquor from Evaporator Plant flows in to the mixing tank where it is mixed with Economisers, Boiler bank, precipitator ash and salt cake. From the mixing tank, the liquor is pumped through black liquor heater to the black liquor burners and the return liquor from black liquor firing circuit will go to the mixing tank. The black liquor is sprayed into the furnace through 8/ Nos. black liquor guns. During 100% MCR firing, only 6 guns need to be operated. The smelt flows from the furnace bottom through three (3) water-cooled spouts into the dissolving tank, where the smelt is dissolved in weak white liquor. The resulting green liquor is delivered to the recausticising plant. A two way automatic cross over connection between green liquor and white liquor is provided as required in the Bid. The smelt spouts are provided on the furnace rear wall, underneath the nose, to avoid any plugging of the spouts due to ‘chunks’ of accumulated deposits in the superheater region falling down. Air and Flue Gas System The combustion air is admitted to the furnace at three levels through three nozzle rows i.e. a primary, and secondary and tertiary nozzle row. There are three backward curved fans for supplying the total combustion air requirement of the boiler. The primary and secondary air is heated in independent steam coil air preheaters. The PA fan supplies the primary air and the secondary fan supplies air to the secondary air nozzle rows and the tertiary fan caters to the need to tertiary air nozzles. For regulating airflow rate the primary and secondary air fans will be provided with VFD’s. The tertiary air fan provided with inlet guide vane control operated from DCS. Flue gases leaving the Economiser will be cleaned through twin chamber electrostatic precipitator. Ash collected in the precipitator as well as in the boiler bank and economiser ash hoppers will be transported to the mixing tank. After the electrostatic precipitator the gases are exhausted to the stack through the induced draft fans. The required draft in the flue gas system will be maintained by two centrifugal type ID fan (2 x 70 % MCR) equipped with variable speed drive units. Each ID fan shall be designed for test block conditions of 100% MCR. Design features The black liquor fired recovery boiler will have following main features · Natural circulation · Single drum construction, radiant boiler with an axial flow boiler bank · Radiant, water-cooled, welded water wall furnace · The steam drum is provided with a system of drum internals, to effectively separate the moisture, from steam water mixture · The platen superheaters are arranged in three stages with desuperheaters arranged in between the superheaters for steam temperature control · The boiler bank section is arranged as a single pass axial flow type design, to minimize gas side pluggage problems. · Two stage vertical panel economiser of axial flow type · The complete pressure part system will be suspended from the ceiling structure and allowed for free downward expansion · The unit is provided with a three level air system in the furnace, to ensure optimum combustion, low carry over and achieve high reduction efficiency · An on load cleaning system, with steam soot blowers has been provided for the heating surfaces in the pressure part sections · The black liquor firing system will be of the stationary firing design to ensure low carryover and high reduction efficiency. · Four (4) start-up oil burners have been provided for start up and furnace stabilization during low load operation /low calorific value fuel spraying into furnace · A water washing system through the soot blowing system including a fail safe isolation system to eliminate water entry during normal operation · The boiler is provided with twin chamber Electrostatic Precipitator · A dry ash handling system — has been proposed for conveying ash from electrostatic precipitator as well as boiler bank and economiser ash hoppers. · Facility is providing for automatic divert of black liquor to mixing tank and suspended firing in the unlikely event of black liquor concentration being less than 62 % DS. · The boiler pressure parts have been designed for a superheater outlet steam pressure of 65 kg/cm2 (g) and 460+10-00C steam temperature. RECAUSTICISING PLANT Process description The recausticising plant is designed to prepare white liquor (with a high degree of purity) necessary for cooking digester house. As post of the renovation, basically, the existing equipments shall be used to the extent possible. The system is such a way modified to have two stage slaking / causticising to reduce the silica content as far as possible. Lime slaking and Causticising Green liquor from 1st stage causticising plant green liquor is fed to the new slow motion slaker. Quantity controller adjusts green liquor flow and, at the same time, the required. Burnt lime is added into the slaker in a uniform manner. That is, lime from the lime bin is fed to slaker by the lime feeder. The lime feeder is a variable speed screw/belt coneyor. Lime is fed to the outer periphery of the upper part of the slaker tank, from where the lime fells to the bottom level. From where the agitator blades pushes it to the outer periphery. Un slaked lime and gritty matters fall from the outer periphery to the classifier, which removes it from the process as waste. Alkali present in the waste is taken back to the process by washing the grits with hot water at the grits discharge end. Grits falls into the grits container for subsequent disposal. Sealing water flow to the classifier screw must be continuous. Flow is indicated by local flow meter. There is an alarm for insufficient flow. The liquid from the slaker- classified flows as overflow from the classifier. This ensures the correct level in the slaker –classifier. The temperature in the out flowing liquor is measured on the classifier part by a thermometer, which is equipped with, upper and lower limit alarms. The temperature in the slaker tank also is indicated by local thermometer. The first reaction of lime and liquor (lime slaking) takes place in the slaker. This reaction generates a lot of heat. The causticizing reaction starts immediately after slacking. This reaction produces white liquor and lime mud. For the separation of the white liquor and lime mud, it is important that the feed ratio of the lime and green liquor is correct so that the causticity degree of the white liquor will be about 80 to82%. If the causticity degree is higher, it causes problems in filtration at normal liquor concentration. If the causticity degree is lower it results in appropriate, useless circulation of powerless liquor. Causticity is adjusted by lime feed by regulating the speed of rotation of lime feeder. The ratio between green liquor and lime feed ca be adjusted by ratio controller which changes the total lime feed in the speed of rotation of lime feeders according to the green liquor flow. The correct lime quantity is checked regularly with analysis and lime feed is corrected according to the analysis results. Samples are taken from cauticiser the reactions having at this stage precede far enough for the final results. Further more, the causticity, it is possible to switch on temperature controller, which compares the temperature of the incoming green liquor and the temperature in the classifier in order to control the set value of the ratio controller and in this way to control the speed of burnt lime feeder. The temperature controller is in operation only if the slaker has not reached the boilering temperature (102-104°C) for lime mud dilution. The scrubber is equipped with inspection opening for monitoring the cleanliness of the vapour channels. The causticized liquor is taken into WLC ie uni-clarifier. The white liquor is separated and mud is pumped out & washed counter-currently in two mud washers. The under flow of secondary mud – washer is pumped out to mud tank where required water is added. Then mud slurry is pumped to lime mud CD filter to separate the mud for clacining purpose. LIME MUD REBURNING KILN Process description The make up limestone needed for meeting the burnt lime production is taken from the silo and fed at even rate to the kiln. The lime sludge from the filter is transported by belt conveyor and transferred to a feed screw conveyor, delivering the lime sludge into the kiln. In the kiln, the lime sludge is dried, heated up and burned to the required degree. Drying and heating are affected by the combustion gases, using a system of chains and lifters for improved gas/material heat transfer. The wet sludge is basically dried in the chain zone, leaving it almost dry. Zone length and chain density are thus obviously dependent on the solids content in the sludge and will be decided individually for each case. After drying, the lime sludge enters the preheating zone of the kiln, provided with a two-layer insulating refractory and lifters. The lifter systems are used for improved heat transfer during the subsequent heating of the sludge. Metallic lifters are used for gentle lifting and better mixing of the sludge. Lime is finally calcined in the burning zone, usually at the temperature of 1100 to 1200°C. A retention dam at the kiln discharge end is used to build﷓up a pool of material in the burning zone, meaning a longer retention time and better protection of the kiln lining. The long retention time means that the kiln can be operated at a lower temperature, resulting in higher product reactivity and lower oil consumption. The sensible heat in the kiln product is recuperated by a heat exchanger (UNAX® cooler), which brings the lime temperature to a level suitable for further handling. The burned lime leaves the kiln through a number of outlet openings and enters the planetary Unax cooler tubes at high temperature. The cooling air moves counter currently, cools the lime and enters the kiln as preheated combustion air. The kiln product passes through the coolers and is discharged in the cooler casing. The limekiln is provided with a variable speed drive for flexible operation. Kiln speed, fuel rate, feed rate and kiln draught are important operational parameters used to control production level and product quality. The fuel economy of the limekiln is much dependent on good insulation of the kiln shell. Most of the shell is therefore provided with insulating back﷓up lining, reducing the shell temperature and the corresponding losses. The heat for burning the lime is provided by a burner system, which is designed for oil/bio gas and producer gas. The burner pipe accommodates the ignition burner, the main burner concentric channels for primary air, fuel, etc. The unique top suspension of the burner permits easy retraction in case of emergency, inspection and maintenance. The burner station is provided with all necessary controls for fuel flow, pressure, etc. as well as an electrical unit with controls, interlocks and flame supervision system. The flue gas, leaving the kiln, contains a considerable amount of lime dust, which has to be separated and re﷓introduced in the kiln for both environmental and economic reasons. The flue gas is cleaned in an electrostatic precipitator (ESP) to an emission level of 50 mg/Nm3. In the ESP, a system of discharge and collecting electrodes is used to separate the dust from the flue gas. The dust is collected in the bottom hopper by a conveyor, discharged through a rotary valve and returned directly to the kiln via dust conveyors or (preferably) by flow of gravity. The flue gas is led to a stack by means of the ID fan, with provision for control of gas volume and induced pressure. The burned lime leaving the cooler is divided into two streams: finished product (size less than 25 mm) and oversize lumps. The finished product goes to the lime silo through a belt conveyor. The oversize material is directed to a lump crusher for reduction to less than 25 mm and feeding into the belt conveyor.

PAPER MAKING

2008-01-29T20:37:00.003+05:30

INTRODUCTION PULP MILL PAPER MAKING CHEMICAL RECOVERY WASTEWATER TREATMENT PIPING SITE MAP CONTACT ME

Process Overview Papermaking begins with the preparation of homogeneous pulp slurry (stock), where various chemicals and mineral additives may be added to achieve the desired final product. The slurry is then fed into the papermaking machine, where it is formed into a sheet and subsequently subjected to pressing and drying operations. The dry sheets are collected on reels for off-machine finishing operations. Further surface treatments may be necessary, depending on the intended end use of the paper. Papermaking operations are divided into two sections - “wet end” and “dry end”. The wet end involves all the equipment and operations between the machine chest (where the stock is stored) and the press section (including the paper machine). The dry end begins after the press section and includes the drying section and finishing operations. A flow diagram for a typical papermaking process is shown in Figure Stock Preparation Helps Control Final Paper Properties Stock preparation is an important intermediate step between the pulp mill and the paper machine, as it determines the final properties of the paper. In an integrated mill, thick stock is discharged from highdensity pulp storage and then diluted to create the slurry. In an independent paper mill, dry pulp bales are repulped in water to form the slurry. Stock preparation involves refining, incorporating additives, blending, screening and cleaning. Refining Refining is a crucial step in papermaking. During refining the pulp fibers are mechanically beaten to achieve the appropriate papermaking properties for the particular product being made. The slurry then passes through a machine that cuts and declusters the fibers to improve fiber bonding properties. Incorporation of wet-end additives A number of mineral and chemical agents can be added to the stock, either to impart specific properties to the paper product (functional additives) or to facilitate the papermaking process (control additives). Because it is inexpensive and easily imparts surface brightness, clay has traditionally been the most common additive. However, the trend towards improved paper surface properties, such as brightness, is leading to the displacement of clay with ground calcium carbonate (GCC) and precipitated calcium carbonate (PCC). Control additives are used as needed to enhance the process. Metering and Blending The various fibrous and non-fibrous furnish components are continuously combined and blended to form the papermaking stock. Screening and Cleaning Small unwanted particles of dirt and grit are removed through the use of centrifugal cleaners.
Papermaking machine
Papermaking Machines Have Been in Use Since the Early 19th Century
After preparation, the stock is sent to the papermaking machine. Papermaking machines are very
expensive and extremely large in size. Today’s machines can exceed 550 feet in length with installation
costs as high as $550 million. While the size and speed of papermaking machines has increased over the
years, production capacity has grown as well. Older machines typically produced 150,000 tons or less per
year. Today’s machines have average capacities of 400,000 tons per year.
Modern papermaking machines are characterized by lower operating costs and higher product quality
than conventional paper machines. However, many paper companies continue to make their products
with older machinery. The modern paper machine is wider, faster, able to integrate off-line operations,
and able to incorporate new technology to improve quality and productivity and reduce operating costs.
Updated papermaking machines boast improved configurations, better drying capabilities from the roll
press sections (reducing energy costs in drying), and higher design speeds.
Along with advances in machinery, technological innovations such as improvements in sensors, controls,
and automation have increased the quality, productivity, and cost of modern papermaking. For example,
sensors help increase product quality by detecting unwanted particles, monitoring water systems, and
increasing wet-end chemistry control. Automated processes, such as full-sheet web scanning systems,
can measure with high precision the level of moisture, thickness, ash contents, and many other properties
of a web.

A variety of papermaking machines are in use today.
Papermaking Machines in
the United States by Type (2000)
Fourdrinier Machines 865
Cylinder Machines 192
Twin Wire Machines 178
Other 93

The first industrial papermaking
machine and still the most widely used today, the
Fourdrinier was created by the Fourdrinier brothers at
the beginning of the 19th century. The machine consists
of a flat, horizontal wire that runs through a series of
foils and dewatering devices.
The Fourdrinier machine illustrated in Figure is
suitable for a wide range of paper grades.
In many cases these machines have been modified to
handle certain specialty papers or grades, incorporating
operations such as surface sizing and coating, or special
calendering treatments.

The paperboard machine is characterized by four separate flat wires, where the board plies are formed
and then couched together. The twin wire machine, popularized in the 1970s and still in use today for
production of coated free-sheet and newspaper, employs two wires where the paper is formed (Figure). A wire is a flat belt consisting of a plastic wire mesh. Other machines differ from the
first four in the method used for drying and include multi-dryer machines, yankee machines, and combined paper machines.

Wet End Operations Wet end operations include the flow spreader, headbox, papermaking table and web, and press, as illustrated in Figure. Sheet formation is critical, as it dictates the quality of the paper product. Sheet Formation is a Crucial Stage of Papermaking The papermaking process begins with a flow spreader which evenly distributes the pipeline flow of the stock using a flow spreader. In this step, the stock flows through a headbox which creates a uniform layer of stock across the width of the machine and on the moving forming fabric. In many modern papermaking machines, the flow-spreader is an integral component of the headbox. The design and operation of the headbox is crucial to the papermaking process, as it directly impacts the formation and uniformity of the final paper product. The flow-spreader and headbox ensure even currents of the delivered stock, level out any velocity gradients, control turbulence, and produce an even discharge of the stock at specific angles, direction, and location. In a Fourdrinier machine, the moving fabric forms the fibers into a continuous matted web. Today’s papermachine forming fabrics are almost all comprised of plastic mesh, although the fabric is still often referred to as wire (phosphor bronze mats were used until the late 1960s). With other papermaking machines, sheet formation may be accomplished by formation of a web between two fabrics, on a fabriccovered cylinder, or by other means. A dandy roll is sometimes used to impart a design on the web of paper, such as a laid effect or weave. A watermarking dandy roll incorporates symbols, letters, and other designs into the paper. Pressing Removes Moisture and Imparts Smoothness and Strength Pressing removes water from the web, imparting a total dryness of 45% - 55%. Pressing operations also consolidate the sheet, provide surface smoothness, reduce bulk, and increase web strength. It is during the pressing stage where the fibers are compacted to enable fiber-to-fiber bonding during drying. In a suction press, drainage is accomplished by applying pressure to the mat while vacuum boxes below the mat create suction forces. The suction press consists of a hard press roll (solid roll) and a perforated shell containing a suction box (suction roll). Water drops are sucked out from the felt through the holes of the suction roll’s shell and collected in a tray. In a grooved press, drying occurs without the use of a vacuum. Instead, a solid roll presses water from the paper to the felt, and from the felt to a grooved roll. In this way, water flows into the grooves of the roll and is drawn away by centrifugal force. Shoe presses, which use a long nip formed against a stationary shoe, allow better compaction of the web and increased water removal. The extended nip shoe press commercialized in 1980 substantially improved press performance. Further improvements resulted in the development of enclosed shoe presses that can be used in the manufacture of all grades of paper. Dry End Operations Dry end operations include the dryer section, calender stack, reel building, and off-machine finishing operations, as shown in Figure. The drying section is massive, and represents the most costly operation in paper making in terms of both capital and operating costs (mostly due to high steam requirements). Drying Occurs Through Several Mechanisms After pressing, the sheet passes through a dryer section where additional water is removed via evaporation. Evaporation is accomplished by pressing the sheet against hot, steam-filled dryer drums. Dryer felts hold the paper web against the drum, which provides better heat transfer and maintains the flatness of the sheet. Meanwhile, the air over the web circulates to avoid vapor saturation from the evaporated water. Three drying processes occur at the same time: (1) flow of heat from the surface of the drying cylinder to the paper (contact drying), (2) cooling of the paper as heat is used to evaporate the water in it (flash drying), and (3) flow of heat from the surrounding air to the paper (convection drying). The following variables affect the rate of water removal: • Temperature and volume of the steam entering the dryer drums • Effectiveness of steam condensate removal from inside the dryer drum • Contact time, and contact pressure between the dryer and the sheet • Felt properties • Hot air circulation • Pocket ventilation Dryer Steam Cans Ready for Shipment In a multi-dryer machine, the pressed web is subjected to a number of rotating steam-heated cylinders. The number of cylinders used ranges from 40-90, depending on the drying rate and evaporative load. Groups of cylinders operate at different steam pressures within the machine. The first cylinders with which the paper makes contact are at the lowest pressure and temperature. As the drying process continues, cylinders have increasingly higher temperatures and pressures. This methodology prevents the paper from sticking to the surface of the cylinders. To improve heat transfer, dryer fabrics are used to press the paper web against the cylinders. Pocket ventilation removes saturated air from the pockets formed by the paper, the dryer cylinder surface, and the dryer fabric. A yankee machine has only one main drying cylinder, which can be twice the diameter of those found in multi-drier machines. The yankee cylinder operates at high pressure, with the inner surface of its shell grooved to collect the steam condensate. In the yankee machine, one or two hot-press rolls are used to press the paper against the outer surface of the cylinder. The two press rolls alone aid the dewatering process, creating an approximate 50% dryness on the sheet. Tissue paper drying is a typical application of yankee machines. In tissue paper drying operations, both a yankee cylinder and hot air at a temperature of 400°C are used. When drying paper grades other than tissue, a low drying rate is employed to prevent the formation of air pockets between the paper and the surface of the cylinder. The combined paper machine has a machine-glazed (MG) cylinder, similar to the yankee cylinder, and also a multi-dryer section. Kraft paper and paperboard can be partially dried with an MG cylinder. This cylinder imparts glossiness on the paper by conveying the smoothness of the cylinder onto the surface of the paper web and allowing for shrinkage of the web fibers during the drying process. Unlike multi-dryer and yankee machines, combined paper machines are not commonly found in today’s paper mills. The MG cylinder requires a specific level of web moisture to operate without causing bottlenecks, and other state of the art techniques have been developed to produce similar results. Calendering Imparts Smoothness and Improves Uniformity Calendering is the term used for pressing the sheet with a roll. This process imparts a smooth surface to the paper for printing, and improves the cross-direction uniformity of certain properties, such as thickness, which is important for downstream collection on the reel and finishing operations. Calendering can be performed on both dry and partially dried paper. The calender stack consists of a series of vertically stacked, solid rolls. The paper passes between the top rolls, and makes its way to the bottom in a snakelike course. The bottom roll is usually larger in diameter than the others. Some conventional stacks are being replaced by “soft calenders” which employ shoe press nips. Paper is Collected on a Reel for Storage and Finishing After the calendering process is completed, the paper must be collected in a convenient form for subsequent processing off-machine. The reel is the last part of the paper machine. In the reeling unit, the paper is wound around a rotating spool and stored for off-machine operations. Finishing Includes Rewinding, Trimming, Coating, and Other Operations Finishing operations are usually called “converting” operations. Converting takes place after the paper is manufactured, and can include rewinding, trimming, sheeting, coating, printing, saturation, and boxmaking. Winding refers to the process where the paper from the large reels is cut into smaller widths and rewound onto smaller rolls. Sheeting consists of cutting the webs into large sheets—a sheeter machine also stacks the large sheets onto a pallet. Saturation consists of distributing a saturating material throughout the entire sheet. This treatment process is commonly used to strengthen the paper and/or induce stiffness (overlays, countertops, and laminates undergo a saturating process). Coating is used on the surface of the paper to induce brightness, gloss, smoothness, and uniformity. Common coatings include pigments and polymers. Summary of Inputs/Outputs The following is a summary of the inputs and outputs of the main processes involved in papermaking. Stock Preparation Inputs High density pulp slurry or pulp bales Wet-end chemicals and mineral additives Outputs Refined pulp slurry (>95% moisture) Paper Manufacture – Wet End Operations Inputs Papermaking stock Outputs Fiber sheet (55-60% moisture) Paper Manufacture – Dry End Operations Inputs Fiber sheet (55-60% moisture) Outputs Reel of finished paper (<5%>

PULP MILL

2008-01-29T19:06:00.001+05:30

INTRODUCTION PULP MILL PAPER MAKING CHEMICAL RECOVERY WASTEWATER TREATMENT PIPING SITE MAP CONTACT ME

PULP MILL Pulp - the aqueous stuff containing disintegrated cellulose fibre from which paper is made. There are two main kinds of pulp, mechanical and chemical Mechanical

If pulping is done mainly by mechanical or physical means, the product is called groundwood or "mechanical" pulp. Lignin is deliberately left in this kind of pulp, for economic reasons. Groundwood is made by grinding whole wood logs against a rotating stone. Mechanical pulps are made from wood chips by passing the chips through refiners. The refiners produce refiner mechanical pulp; if heat is used, thermomechanical pulp; if chemicals are used, chemimechanical; and if both heat and chemicals are used, thermochemimechanical (or chemithermomechanical) pulp. Mechanical pulps are used to make newsprint and magazine paper, as well as boxes and a variety of other products. (Although grocery bags are brown, they are made not from mechanical pulp, but from unbleached kraft.) If mechanical pulp will be used for printed matter, it is bleached, usually with hydrogen peroxide, which is able to whiten the pulp without removing the lignin. Chemical There are two main chemical pulping processes: kraft or sulphate (alkaline), and sulphite (which may be acid, neutral or alkaline). Most pulp mills in the U.S. and worldwide use the kraft process, while most European mills use one of the sulphite processes. Many people assume that the chemicals used in pulping give the fibers a permanent and fixed pH; that is, if an alkaline pulping process is used, they believe paper made from that pulp will be alkaline. Not true. The pulp is washed at the pulp mill, and when it gets to the paper mill, the pH of the stock is under the complete control of the papermaker. The paper produced can have a pH anywhere from 4.0 to 10.0 (or even outside that range, for specialty papers), regardless of the pulping or bleaching process it underwent earlier.

Wood preparation

Wood is delivered to the kraft mill in one of two ways: whole logs and sawmill chips (residuals from sawmills). The logs have their bark removed, either by passing through a drum debarker or by being treated in a hydraulic debarker. The drum debarker, which consists of a slightly inclined, rotating drum is best suited to small diameter logs. The hydraulic debarker, which uses high pressure water jets, can handle large diameter logs. The removed bark is a good fuel, and is normally burnt in a boiler for generating steam. After debarking, the logs are chipped by multi knife chippers into suitable sized pieces, and are then screened to remove overlarge chips. The thickness of the chips is the most important parameter, as this determines the speed and the thoroughness of the impregnation of the cooking chemicals into the wood chip. Neither debarking nor chipping are usually necessary for sawmill chips.

Cooking

The "cooking process" is where the main part of the delignification takes place. Here the chips are mixed with "white liquor" (a solution of sodium hydroxide and sodium sulphide), heated to increase the reaction rate and then disintegrated into fibres by 'blowing' - subjecting them to a sudden decrease in pressure. Typically some 150 kg of NaOH and 50 kg of Na2S are required per tonne of dry wood. This process is, like any chemical reaction, affected by time, temperature and concentration of chemical reactants. Time and temperature can be traded off against each other to a certain extent, but to achieve reasonable cooking times it is necessary to have temperatures of about 150 - 165oC, so pressure cookers are used. However, if the temperature is too high then the chips are delignified unevenly, so a balance must be achieved.

The kinetics of the kraft pulping is quite well understood, but the reaction is heterogenous and therefore difficult to examine. To determine when to interrupt the cooking, a model relating time, temperature and cooking chemical charge is used. The degree of delignification is the most important parameter for determining pulp quality, and is normally expressed in what is called a "Kappa number". This number is directly related to the amount of lignin still remaining in the cooked pulp. There are two different cooking systems; batch and continuous. In batch cooking, chips and white liquor are charged to a pressure vessel and are then heated with steam to a set temperature for a set time. When the correct delignification has been achieved, the cook is "blown" (the pressure is suddenly released so that the cooked chips disintegrate into fibres). In the continuous process, chips and white liquor are fed continuously to the top of a tall pressure vessel. The chips move down the 'digester' by gravity (as a plug) to be finally blown from the bottom of the vessel. The cooking time cannot be varied in this case (it is set by the production rate) and only the temperature and the chemical charge can be controlled. Many developments have taken place during the last decade to improve the 'science' of kraft pulping. The challenge has been to remove as much of the lignin as possible with out degrading the cellulose and without losing too much yield. It is now well known that the concentrations of NaOH, Na2S and dissolved lignin during the various phases of the delignification are of crucial importance for the pulp strength. Generally speaking, it is desirable to have a high sulphide concentration in the beginning of the cook, a low lignin concentration in the liquid phase towards the end of the cook, and an even alkali concentration during most parts of the cook. How to achieve this in practice under conditions of high temperature and high pressures has been a challenge, and much development is still going on.

FIBRE LINE: Pulp washing

Because of the high amounts of chemicals used in the cooking wood in kraft pulping, the recovery of the chemicals is of crucial importance. The process where the chemicals are separated from the cooked pulp is called pulp washing. A good removal of chemicals (inorganic and organic) is necessary for several reasons: • The dissolved chemicals interfere with the downstream processesing of the pulp • The chemicals are expensive to replace • The chemicals (especially the dissolved lignin) are detrimental to the environment There are many types of machinery used for pulp washing. Most of them rely on displacing the dissolved solids (inorganic and organic) in a pulp mat by hot water, but some use pressing to squeeze out the chemicals with the liquid. An old, but still common method is to use a drum, covered by a wire mesh, which rotates in a diluted suspension of the fibres. The fibres form a mat on the drum, and showers of hot water are then sprayed onto the fibre mat.

Pulp screening

Apart from fibres, the cooked pulp also contains partially uncooked fibre bundles and knots. Modern cooking processes (together with good chip screening to achieve consistent chip thickness) have good control over the delignification and produce less "rejects". Knots and shives are removed by passing the pulp over pulp screens equipped with fine holes or slots.

Bleaching

Pulp produced by the kraft process is brown. This presents no problem for certain uses, e.g. for sack paper, most corrugated boxes, some bag paper etc. However, a major proportion of the kraft pulp that is made is used for white or coloured papers such as writing and printing papers, and then the pulp needs to be bleached. Bleaching involves removing virtually all of the lignin that still remains after cooking, as the lignin contains the chromophoric groups which make the pulp dark. Strictly speaking, bleaching and cooking are both delignification processes, and modern developments have tended to blur the difference between the two processes. However, traditionally the name 'bleaching' is reserved for delignification that is taking place downstream of the cooking process. In practice, there are two separate "bleaching" process steps: oxygen delignification and final bleaching. To measure the lignin content in pulp, a number called the "Kappa number" is used. The Kappa number is directly proportional to the lignin content of the pulp. Pulp from the digester has a Kappa number of 20-35 for softwood and 15-20 for hardwood (hardwood contains less lignin and can therefore be cooked to a lower Kappa number). Oxygen delignification removes about half of the lignin remaining after the cooking process, so that the Kappa number of the oxygen delignified pulp is typically 12-18 for softwood. The final bleaching removes all remaining lignin and decreases the Kappa number to zero.

Oxygen delignification

In oxygen delignification, washed pulp is treated with a highly alkaline solution of sodium hydroxide. The high pH ionizes phenolic groups in the lignin, which are then attacked by molecular oxygen. The aromatic part of the lignin is partly destroyed and it is then depolymerised to lower molecular weight compounds. These are more soluble in water and can be removed from the fibres. It is important that the pulp has been at least partly washed beforehand because the black liquor solids in unwashed pulp consume oxygen. After the oxygen delignification stage, the pulp has to be washed very well, as otherwise the organics carry over to the final bleaching process, consuming chemicals there and also decreasing the environmental benefits. The highly alkaline conditions of oxygen delignification also make carbohydrate fractions in the fibres react with oxygen to a certain extent. As these reactions break down the polymer chains of cellulose, and thus decrease the pulp strength, these reactions must be kept to a minimum. It has been found that it is the radical species of oxygen which are particularly harmful to the carbohydrates. The formation of radicals is promoted by the presence of certain metal ions. However, it has been found that magnesium salts inhibit metal ion activity, and magnesium sulphate is therefore normally added as a protector in oxygen delignification. Oxygen is only sparingly soluble in water, and the controlling factor on the reaction rate is therefore normally the concentration of dissolved oxygen around the fibre. Originally a high pulp consistency (30-40%) was used to overcome this restriction. However, modern high intensity mixers can distribute the oxygen in very small bubbles on the fibres, and these mixers have made it possible to operate at "medium consistency" (10-12%). Medium consistency has several advantages: the equipment is simpler and the risk of fire (because of the use of oxygen) is virtually eliminated. Oxygen delignification can significantly decrease the water pollution from the final (normally chlorine or chlorine dioxide based) bleaching. In addition, it is an effluent free process. All dissolved lignin and other organics (as well as the inorganic chemicals) are recovered in the black liquor and returned to the chemical recovery system, rather than being discharged as effluent as they are in chlorine-based bleaching. Finally, oxygen is a fairly cheap bleaching chemical, although the capital costs are high for an efficient system. On the properly.

Final bleaching

The final bleaching is always carried out in several stages to improve the efficiency of the chemicals used, and to decrease the strength loss of the pulp. There are quite a number of bleaching chemicals used commercially, and many more have been tried in the laboratory. The chemicals used are: • Chlorine • Chlorine dioxide • Sodium hypochlorite • Oxygen • Peroxide • Ozone Of these chemicals, the first three contain chlorine atoms, whilst the last three use nonchlorine oxidizing compounds. Elemental chlorine (Cl2) was for many years the work horse of the bleaching process. It is efficient in bleaching the pulp and (if properly used) does not degrade the pulp strength. However, it produces a large amount of chlorinated organic compounds in the effluent, and strenuous efforts have therefore been made to decrease its usage. For the same reason, the use of sodium hypochlorite (which also tended to affect the pulp strength) is now virtually eliminated. Modern bleach plants therefore use no elemental chlorine. They are what is called ECF plants: elemental chlorine free bleach plants. Chlorine dioxide, which is used instead (in addition to non-chlorine compounds), is environmentally much more benign than Cl2. However, while chlorine dioxide is good at preserving pulp strength, it is not as effective as elemental chlorine in delignification/bleaching. ECF plants therefore have to have a rather low incoming Kappa number, and this is normally achieved by using oxygen delignification ahead of the final bleaching. Most ECF plants use a three step bleaching process of chlorine dioxide followed by a mixture of NaOH, O2 and peroxide (the 'extraction' stage) and then finally chlorine dioxide again. At Kinleith, because of the efficiency of the oxygen delignification, the peroxide is no longer necessary and a sequence of chlorine dioxide then NaOH and O2 followed by more chlorine dioxide is used. The chlorine dioxide stages normally run at a pH of 3-4.5, and the'extraction' stages at a pH of 10-11. The temperature is kept at 70-80 oC to achieve sufficiently fast rate of reaction. The amount of chlorinated toxic compounds in the effluent from a correctly operated ECF plant is small (especially after secondary treatment) and the effects on the environment appear rather insignificant. However, especially in Europe, there is a perception that using "chlorine" in any form when bleaching is undesirable, and bleaching without using any form of chlorine compounds, so-called total chlorine free bleaching (TCF bleaching) has been developed. In TCF bleaching only oxygen, peroxide and ozone (in addition to caustic and certain chelating agents) are used. TCF bleached pulp can nowadays reach virtually the same brightness as ECF bleached pulp, but the strength is somewhat lower. Such plants require inevitably oxygen delignification and also, usually, cooking to a lower Kappa number. Chemical costs are also normally higher.

INTRODUCTION

2008-01-28T22:44:00.001+05:30

INTRODUCTION PULP MILL PAPER MAKING CHEMICAL RECOVERY WASTEWATER TREATMENT PIPING SITE MAP CONTACT ME

UPDATED ON 12th FEB 2008 INTRODUCTION: SEE YOUR LEFT SIDE RIGHT SIDE FRONT SIDE OR BACK SIDE You can see the paper. It may be into your valuable place or dustbin. Do you know the HISTORY of the PAPER? Before going up: I want to tell something. This is a site which contains the paper mill process and some piping tips. I think this site must very helpful to the MECH , PROCESS AND OTHER RELEATED ENGINEERS. Thousands of Mechanical Engineers are out coming per year. Some mechanical engineers are going into IT line. Many mechanical engineers are going to production and design field. All are good field if they are all effectively. By considering the design field, the engineers must be have the knowledge in AUTO CAD. Its one of the drafting tool. By using this tool the drawings are made. Here we are discuss about PAPER INDUSTRY AND PIPING DESIGN. PAPER MILL OVERVIEW: Paper is a major product of the forestry industry, and is used widely in our society. Paper products are used not only in their obvious applications in the publishing industry and for writing on, but also in a variety of specialty papers, cardboards, brown papers etc. In addition, various chemicals are produced as a byproduct of the pulp and paper industry. Paper is made by pulping wood, bleaching this pulp and then spreading it out into sheets to make it into paper. At various stages of the process, chemicals are used to give the paper particular properties, such as the bleaching chemicals that make paper white (and which also enable it to subsequently be coloured). The pulping process is known as "kraft pulping" which relies on a combination of heat, chemicals and mechanical pulping to convert the wood into a smooth, soft pulp suitable for use in paper making. Kraft pulping is the main pulping process (together with mechanical pulping) used today. The kraft process has several advantages: • It can be used with virtually all wood species • It can easily handle the extractives in most coniferous wood • The pulp has very good strength (the word 'kraft' means 'strong' in Swedish) • The recovery process for the chemicals is well established However, there are also disadvantages: • The pulp yield is quite low at about 45 - 50% • The equipment used for the chemical recovery is extensive and costly to install • Sulphurous compounds, which are odorous in the parts per billion range, are formed in the process • Fairly complicated processes are required for bleaching the pulp Lignin The main component of wood that needs to be removed to turn it into paper is a compound known as lignin. This name refers to a group of chemicals that are essentially three dimensional polymers of trans-coniferol, trans-sinapol and trans-p-coumarol (see below), along with hemicelluloses and aromatic carboxylic acids. Lignin is the reinforcing compound that is deposited on tree cell walls to make the wood strong enough to carry the weight of the tree crown. However, it is also the compound that makes wood pulp brown, so it is removed from all wood pulp except that used to make brown paper and some cardboards. AREA OF PAPER MILL: There are four major area of paper mill: · PULP MILL · PAPER MAKING · CHEMICAL RECOVERY · WASTWATER TREATMENT PLANT ___________________________________________________