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Energy Consumption Reference
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REPORT
ÅF-Engineering ABFrösundaleden 2, SE-169 99 Stockholm, Sweden.Phone +46 10 505 00 00. Fax +46 10 505 00 10. www.afconsult.comVAT No SE556224801201. Registered office Stockholm.
http://km.afconsult.com/projects/10090/documents/reports/fine paper/fine paper final.docx
Date
20 January 2011Version No
1
Energy consumption in the pulp and paperindustry - Model mills 2010
Integrated fine paper mill
ÅF-ENGINEERING ABMarket Area Forest Industry
ÅForsk Reference: 09-163
Contents
Page
1 INTRODUCTION 5
2 MODEL MILL - OVERVIEW 62.1 General Design Criteria 62.2 Mill production and capacity 62.3 Energy systems and balances 9
3 MODEL MILL – PROCESS DESCRIPTION 133.1 Wood Supply 133.2 Woodyard 133.3 Digester 133.4 Brownstock deknotting and screening 153.5 Oxygen delignification 153.6 Pulp washing 153.7 Bleaching 163.7.1 System closure and degree of bleach plant filtrate recovery 173.8 Chlorine dioxide generation 183.9 Evaporation 193.9.1 Handling of condensates 203.9.2 Handling of non-condensable gases 203.9.3 Tall oil recovery 213.10 Recovery boiler 213.11 Causticizing 233.12 Lime kiln 243.13 Paper Mill 253.13.1 Capacity 253.13.2 Stock preparation 273.13.3 Bleached kraft supply 273.13.4 Broke system 273.13.5 Mixing/machine chest 273.13.6 Filler supply 273.13.7 Short circulation 283.13.8 Paper machine 283.13.9 Fresh water system 303.13.10 White water system and buffer volumes 303.13.11 Energy aspects of the paper machine 303.14 Power boiler 323.15 Steam turbines and steam distribution 333.16 Cooling and recovery of low-temperature heat 333.17 Effluent treatment 343.18 Spill handling system 353.19 Water supply and treatment 36
4 MODEL MILL - ENERGY BALANCE 38
5 COMPARISON OF MODEL MILL AND TYPICAL MILL415.1 Type mill –process description 435.1.1 Digester 435.1.2 Oxygen stage 445.1.3 Pulp washing 445.1.4 Bleaching 445.1.5 Paper machine 455.1.6 Evaporation 465.1.7 Recovery boiler 465.1.8 Lime kiln 475.1.9 Power boiler 475.1.10 Steam turbines and steam distribution 475.2 Energy balance comparison – Model mill vs type mill 48
6 REFERENCES 53
Appendices
Appendix 1 Model mill - Mass balance block diagramsAppendix 2 Model mill - Energy balancesAppendix 3 Model mill – Secondary heat balance
Integrated fine paper mill Page 520 January 2011
1 Introduction
The purpose of this ÅForsk financed study is to update the hypotheticalreference mills developed in the 2005 FRAM project to reflect the technicalchanges that have occurred in recent years. The main emphasis in this study ison the technical changes which have affected energy consumption andproduction.
Four different types of pulp and paper mills are considered:
Bleached market kraft pulp mills – one softwood mill (pine), and twohardwood mills (birch and eucalyptus)
Integrated fine paper mill, with the pulp mill producing softwood andhardwood pulp in campaigns
Kraftliner mill
Magazine paper mill, bleached super calendered (SC) TMP
There was no eucalyptus kraft pulp mill in the FRAM project, but such a millhas been included in this study.
Each of the reference mills from the FRAM project has been reviewed by ÅF.The kraft pulp mills have also been reviewed by Innventia. Modifications madein this study are based on ÅF/Innventia experience with existing mills, and insome cases data from the major mill equipment suppliers. Material and energybalances have been calculated for the 2010 model mill using spreadsheetmodels developed by ÅF.
The FRAM project also included type mills which represented typical, existingNordic mills. To help highlight potential energy improvements in existingmills, the type mill is included here for comparison to the model mill. The typemills in this study are identical to the type mills from the FRAM project,
In the FRAM project the energy consumption of the type mills considered datafrom a survey of energy consumption and production in the Swedish pulp andpaper industry which was conducted in 2000. This survey was updated in 2007,and indicated that the main development in the existing Nordic pulp and papermills between 2000 and 2007 has been an increase in cogenerated power, andan increase in biofuel usage.
Integrated fine paper mill Page 620 January 2011
2 Model mill - overview
2.1 General Design Criteria
The integrated fine paper mill produces softwood and hardwood pulp incampaigns in the pulp mill. The pulp mill is similar to the bleached kraft marketpulp mills in this study except for the dryer and paper machine parts. The milldesign is based on best available and commercially proven technology in theNordic countries.
The design of the mill considers:
high, consistent paper quality which is competitived on the internationalmarket
the product is elemental chlorine free (ECF)
low specific consumptions of wood, chemicals and water
high energy efficiency
maximized production of bio-energy, and minimal usage of fossil fuels
low environmental emissions; on the level of newer modern mills
cost-effective solutions
Different suppliers offer different process equipment. The model mill is notbased on equipment from any one supplier. In general the key process data usedin the balances in this study are conservative and should not exclude any of themajor pulp mill equipment suppliers.
2.2 Mill production and capacity
The pulp mill produces bleached softwood and hardwood pulp in compaigns.
The needed capacities of the various departments in the pulp mill are differentwhen producing softwood and hardwood pulp. The main difference betweenhardwood and softwood is that hardwood has a higher yield. This means thatthe black liquor dry solids per ton of pulp is higher for softwood than forhardwood, and consequently the required capacity of the chemical recovery line
Integrated fine paper mill Page 720 January 2011
is greater for a softwood mill compared to a hardwood mill with the same pulpproduciton capacity.
The pulp mill has a maximum continuous rate (MCR) of 2000 ADt/d forsoftwood and 2500 ADt/d for hardwood. At these production rates the load onthe recovery boiler is approximately constant.
Mass balances have been prepared for the pulp mill at mill MCR conditions todetermine the capacity requirements for the main mill areas. The balances covermainly wood/fibre-, dry solids-, evaporation-, causticizing and lime.
Block diagrams which summarize the mass balances for both softwood andhardwood operation are included in Appendix 1. Table 2-1 summarizes the keyoperating and dimensioning data and for the pulp mill.
The fine paper mill has two paper machines with the same design andproduction. The total production is 3130 t/d at pulp mill MCR. The papermachine furnish consists of 19% bleached softwood pulp, 56% bleachedhardwood pulp and 25% filler. The paper is surface sized with starch toimprove strength properties of the paper.
Table 2-2 summarizes the key operating data for the paper machines.
Integrated fine paper mill Page 820 January 2011
Table 2-1. Summary of pulp mill key operating data.
Softwood Birch
Pulp production ADt/24 h 2 000 2 500
Wood yard
Wood to digester t/24 h 4 072 4 610
Bark and wood waste t/24 h 420 642
Digester Plant Cont Cont
Kappa number 30 17
Unscreened deknotted digester yield % 47.0 51.0
Alkali charge on wood as effective alkali NaOH,% 20,0 18.5
Sulphidity (white liquor) mole-% 35 35
Oxygen Stage
Kappa number after oxygen stage 12 12
Alkali charge as NaOH kg/ADt 25 18
Oxygen charge kg/ADt 20 14
Washing Department
Dilution factor in the last stage m3/ADt unbl. 2.5 2.5
Evaporation PlantWeak black liquor to evaporation,excl.spill t/h 913 981
ditto dry solids content % 16.0 15,7Strong black liquor, dry solids contentincl. ash % 80 80
Total evaporation, including spill t/h 771 840
Recovery BoilerEstimated higher heating value of virginDS MJ/kg 14.0 13,8
Strong liquor virgin solids to mixing tank t/24 h 3 477 3 668
Net useful heat from liquor, virgin solids MJ/kg DS 10.3 10.0
Net useful heat from liquor MW 413 426
Causticizing and Lime Kiln
Causticizing efficiency mole-% 82 82
Total white liquor production m3/24 h 7 541 7 831
Lime kiln load t/24 h 534 554
Active CaO in lime % 90 90
Lime kiln fuel Bark / wood waste
Integrated fine paper mill Page 920 January 2011
Table 2-2. Summary of paper mill key operating data.
Speed at pope m/min 1 690
Width on pope M 9
Grammage g/m2
80 (75-160)
Production on pope (100% eff.) t/h 73.1
Paper dryness % 93
PM furnish composition
-Hard wood % 56
-Soft wood % 19
-Filler % 25
-Surface size of paper (starch) % 3
Paper mill efficiency % 82
Operating days per year Days 355Paper production net (PM1 + PM2),Kraft mill MCR t/day 3 100
Paper production net (PM1 + PM2) t/a 1 022 000
Bleached hardwood consumption ADt/a 573 000
Bleached softwood consumption ADt/a 191 000
Filler consumption t100/a 235 000
Starch consumption t100/a 27 600
2.3 Energy systems and balances
The fine paper model mill is very energy efficient and the black liquor aloneproduces enough steam to satisfy the process steam consumption of the millduring softwood campaigns.
During hardwood campaigns the steam from the recovery boiler is notsufficient for the mill’s requirement, and additional steam from the power boileris required.
The lime kiln is fired with bark powder, or gasified bark, and the remainingbark from the woodyard and chip screening is burned in the power boiler.
When all available falling bark is burned in the power boiler there is an excessof steam which is utilized in a condensing turbine to produce in power. In bothsoftwood and hardwood campaigns the power produced is still not sufficient tomeet the mill’s demand, and additional power is purchased.
Integrated fine paper mill Page 1020 January 2011
Some key items which have been changed in the model mill compared to thereference mill in the FRAM study include:
HP steam data 100 bar(g), 505oC (increased from 80 bar(g) and 490oCin the FRAM project)
Feed water preheating to 175oC to increase HP steam generation(increased from 146oC in the FRAM project)
Recovery boiler flue gas cooler to reduce LP steam consumed in airpreheating
Top preheating of all recovery boiler combustion air to 205oC (85% ofcombustion air heated to 165oC in the FRAM project)
Latest technology for pulp digesting which has a lower cookingtemperature than other systems
7 effect evaporation plant (6 effect evaporation plant in the FRAMproject)
Digester steam consumption has increased increased slightly with thenew liquor extraction
Steam consumption in the bleach plant is reduced; more chlorinedioxide and less hydrogen peroxide allow a lower bleaching temperature
Dryness the papermachine press section to the dryer has been increasedfrom 50% in the FRAM project to about 52%, based on mill experience
Paper machine power consumption has been reduced from 600 kWh/t to550 kWh/t, based on mill experience
A net reduction in mill steam demand compared to the FRAM studymakes a condensing turbine a feasible option.
Additional factors (which were also relevant in the FRAM project) which makethe model mill energy efficient include:
Recovery boiler sootblowing steam is extracted at 25 bar(g) from theturbine instead of using HP steam
Low pressure steam used in the paper ,machine Pressurized condensate system High temperature of hot water, 85 - 90oC, and maximum use of hot
water instead of steam in the bleach plant, and paper machine Bark press for bark to the power boiler
Table 2-4 compares the overall steam and power balances for the 2010 modelmill and the FRAM reference mill.
Integrated fine paper mill Page 1120 January 2011
Table 2-3. Summary of steam and power balances – FRAM reference.
Softwood Hardwood
STEAM BALANCE GJ/ADt pulp GJ/t paper GJ/ADt pulp GJ/t paper
Generation
Recovery boiler 17.97 11.46 14.78 11.74
Power boiler 1.38 0.88 1.64 1.30
Secondary heat 0.39 0.26 0.35 0.27
Total steam generation 19.74 12.60 16.77 13.31
Consumption
Process steam 15.51 9.90 13.20 10.48
Back pressure turbine 4.23 3.57 2.70 2.83
Condensing turbine - - - -
Total steam consumption 19.74 12.60 16.77 13.31
POWER BALANCE kWh/ADt pulp kWh/t paper kWh/ADt pulp kWh/t paper
Generation
Back pressure power 1139 728 1203 769
Condensing power - - - -
Purchased power 236 151 222 142
Total power generation 1375 879 1425 911
Consumption
Total power consumption 1375 879 1425 911
Integrated fine paper mill Page 1220 January 2011
Table 2-4. Summary of steam and power balances- Model mills 2010.
Softwood Hardwood
STEAM BALANCE GJ/ADt pulp GJ/t paper GJ/ADt pulp GJ/t paper
Generation
Recovery boiler 17.82 11.39 14.71 11.75
Power boiler 1.53 0.98 2.43 1.94
Secondary heat 0.35 0.22 0.36 0.29
Total steam generation 19.69 12.59 17.50 13.98
Consumption
Process steam 13.61 8.70 11.80 9.42
Back pressure turbine 4.30 2.75 3.72 2.97
Condensing turbine 1.78 1.14 1.98 1.58
Total steam consumption 19.69 12.59 17.50 13.98
POWER BALANCE kWh/ADt pulp kWh/t paper kWh/ADt pulp kWh/t paper
Generation
Back pressure power 1152 736 998 797
Condensing power 174 111 194 155
Purchased power 128 82 0 0
Total power generation 1455 930 1191 951
Consumption
Total power consumption 1455 930 1191 951
Integrated fine paper mill Page 1320 January 2011
3 Model mill – process description
3.1 Wood Supply
The softwood raw material consists of 50% pine (Pinus sylvestris) and 50%spruce (Picea abies). The relation between roundwood with bark and sawmillchips is 70% roundwood and 30% sawmill chips.
The birch is mainly Betula spp. with about 10% other hardwoods, mainlyaspen. The supply is 100% as roundwood, with bark.
3.2 Woodyard
The debarking is performed in dry debarking drums which are designed for abarking efficiency of 95%. There is a closed re-circulation of sprinkling and de-icing water. The de-icing water is heated by the means of heat exchanging withsurplus hot water. The effluent is collected together with the press water fromthe bark presses in a sedimentation basin for re-circulation. The sludge from thesedimentation basin is burned in the power boiler.
A portion of the bark is utilized as fuel for the lime kiln; the rest is burned in thepower boiler.
After debarking the logs are transported to a metal detector and a water stonetrap. In the chipper, logs are cut to chips. Consistent chip thickness is importantfor uniform cooking and a low pins fraction is important for the runnability ofthe digester. The chips are therefore screened to get an optimal chip size.Accepted chips are transported to a chip silo. Over-thick, over-sized chips aretaken to a re-chipper and then back to chip screening. Fines are stored andburned in the power boiler.
3.3 Digester
Either continuous or batch digesting can be used, and both alternatives havepros and cons. Continuous digesters are the dominant technology for bothexisting and new mills. Also, in general the batch processes, as marketed todayhave higher steam consumption than the continuous processes. Thus thecontinuous cooking process has been selected for this study.
The Metso Compact Cooking concept, see Figure 3-1, is one example of amodern cooking system. Chips are presteamed and impregnated with white
Integrated fine paper mill Page 1420 January 2011
liquor and black liquor at atmospheric conditions in a vessel, and the cooking isperformed at a relatively high alkalinity with co-current liquor flow at relativelylow temperature. The cooking temperature is about 143oC for softwood, and138oC for hardwood. Black liquor is extracted for evaporation via a single stageflash tank from the impregnation vessel, the transfer circulation between theimpregnation vessel and the digester.
Andritz DownFlow LoSolids cooking system without or with pressurizedimpregnation vessel is another example of a modern cooking system.
Figure 3-1. Example continuous cooking system (Metso Compact Cooking).
Table 3-1. Digester key figures.
SW HW
Kappa number, digester blowline 30 17
Deknotted digester yield % 47 51
White liquor AA concentration NaOH, g/l 140 140
Alkali charge on wood as effective alkali NaOH,% 20.0 18.5
Sulphidity, white liquor % 35 35
Extracted turpentine kg/ADtdig 2 0
In order to improve yield and fibre strength the kappa number after cookingcould be increased by some units. This should however be balanced with thedelignification in the oxygen stage.
Integrated fine paper mill Page 1520 January 2011
3.4 Brownstock deknotting and screening
There are several important quality parameters for pulp. One of them is veryhigh cleanliness, i.e. a low content of shives and coloured spots originatingfrom the pulpwood (resin and bark) as well as foreign materials such as sand,plastic, rubber and rust.
Pressurized deknotting separates knots from the pulp. After deknotting the pulpis screened at 3-4% consistency by barrier (slotted) screens in three or fourstages. The knots are recooked. Screen rejects from the last screening stage endup as effluent treatment sludge which is burned in the power boiler.
3.5 Oxygen delignification
Oxygen delignification is done in two stages without intermediate washing to akappa number of 12 for softwood and 10 for hardwood. Oxidized white liquoris the primary alkali source. To optimise the delignification in the initial andfinal phases the reaction time is approximately 10 minutes in the 1st stage andapproximately 60 minutes in the 2nd stage.
Table 3-2. Oxygen delignification key figures.
SW HW
Kappa number after oxygen stage 12 12
Dissolved DS (yield losses) % 3.8 1.6
MgSO4 charge 2,3 1.0
Alkali charge oxidised WL, as NaOH kg/ADt O2 25 18
Oxygen charge kg/ADt O2 20 14
Temperature ºC 95/98 95/101
3.6 Pulp washing
The brown stock wash consists of:
Two stages of pre-oxygen washing for hardwood and three stages forsoftwood. Either wash presses or drum displacement (DD) filters can beused.
Post oxygen washing with one 2-stage DD washer before the oxygenbleached storage tower. Alternatively two wash presses could be used.These wash presses may both be placed after the oxygen bleached
Integrated fine paper mill Page 1620 January 2011
storage tower or, one of the presses could be before the tower and oneafter (pre bleach press).
Figure 3-2 shows one alternative for brownstock washing.
The brownstock washing dilution factor is 2.5 m3/ADt.
The carryover of COD from the oxygen delignification to the bleach plant iscalculated to be approx 5 kg COD/ADt, excluding the bleach plant filtrate re-circulated to brown stock washing.
Figure 3-2. One example of a typical brownstock washing system (Metso).
3.7 Bleaching
Both the softwood and birch pulps are bleached to a final brightness of 90%ISO.
The bleach plant is designed with four bleaching stages. For softwood pulp thefirst stage is operated as a “conventional” D-stage, and the sequence isD(EPO)DP. For hardwood pulp the first stage is operated as a Dhot-stage, andthe sequence is Dhot(EPO)DP.
Wash presses are used for all washing in the bleach plant.
The main reasons for selecting a hot first D stage for hardwood pulp are that alower charge of ClO2 is required to attain the required pulp brightness and lessbrightness reversion of the fully bleached pulp. These benefits are, however, notattained on softwood pulps as they contain considerably less hexenuronic acidsthan hardwood pulps. Hexenuronic acids are effectively removed in Dhot-stages.
Integrated fine paper mill Page 1720 January 2011
The last bleaching stage could be a D-stage instead of a P-stage. This is partlyan economic decision which depends on the prices of chlorine dioxide,hydrogen peroxide and sodium hydroxide. A final P-stage in place of a final D-stage may also decrease brightness reversion of the pulp.
The expected bleach plant chemical charges and conditions are summarized inTable 3-3, and Table 3-4.
Table 3-3. Expected chemical charges for the SW kraft pulp with the sequenceD(EPO)DP to 90%ISO brightness ( kg/ADt). ClO2 as ClO2 and not as active Cl. Kappanumber of pulp to bleaching: 12.
StageTemp(C)
Time(min) pH ClO2 O2 H2O2 NaOH H2SO4
SO2 orNaHSO3 as SO2
D 70 60 ~2,5 9 4
(EPO) 80-85 75 10.5-11 6 1 13
D 75-80 150 3.5-4 5 1 0.5
P 75-80 150 ~10 6 6 1.5 (a)
(a) After P-stage
Table 3-4. Expected chemical charges for the birch kraft pulp with the sequenceDhot(EPO)DP to 90%ISO brightness ( kg/ADt). ClO2 as ClO2 and not as active Cl.Kappa number of pulp to bleaching: 10.
StageTemp(C)
Time(min) pH ClO2 O2 H2O2 NaOH H2SO4
SO2 orNaHSO3 as SO2
Dhot 85-90 120 ~3 7 6
(EPO) 85-90 60 10.5-11 3 1 12
D 75-80 150 3.5-4 5 1 0.5
P 75-80 150 ~10 6 6 1.5 (a)
(a) After P-stage
For softwood the bleaching sequence results in a yield of 98%, whichcorresponds to a total yield of about 44%. For hardwood the bleachingsequence results in a yield of about 97.5% and a total yield of about 49%.
3.7.1 System closure and degree of bleach plant filtrate recovery
A high degree of system closure can create problems with scale formationwithin the bleach and evaporation plants, high bleaching chemicalconsumption, corrosion and plugging problems in the recovery boiler andproblems controlling the Na/S balance of the mill. Bleach plant liquors must behandled in an optimal manner; for example mixing should be performed withincritical temperature and pH limits, where the risk for scaling is the lowest.
Integrated fine paper mill Page 1820 January 2011
Based on experience a relatively conservative approach regarding systemclosure has been adopted to ensure sustained trouble free operation with goodeconomics.
The bleach plant is designed to release 10-15 t/ADt of effluent. This rangeincludes an allowance for up to 5 t/ADt of fresh water. This extra intake offresh water can be used for dilution at any position in the bleach plant wherethere is a risk for precipitation. The extra intake of fresh water also makes itpossible to bleed out metals and Cl--ions.
Additionally, 6 t/ADt of effluent is discharged from the paper machines.
Figure 3-2 shows the approximate liquor flows in the bleach plant. Hot water isused as wash liquor on the wash press after the P-stage. The filtrate from thiswash press is then used as wash liquor on the 2nd D stage wash press. Freshwater is used as wash liquor on the (EPO) stage wash press and condensate isused as wash liquor on the 1st D-stage press. The filtrate from the (EPO) washpress is then transferred as wash liquor to the 2nd wash press after the oxygenstage.
3.8 Chlorine dioxide generation
The selection of the chlorine dioxide process (R8 or R10) is mainly based onthe millwide sodium/sulphur balance. (R8 and R10 are the trade names fromErco. Eka (Akzo Nobel) has similar processes called SVP.)
4.1 t/ADt 4.1 t/ADt
4.5 t/ADt ~10t/ADt ~5 t/ADtTo treatmentTo treatment
Clean condensate
PDEPOD
To 1st O2
washer
Hot waterHot/cold water
~5 t/ADt
Chemicals
~2 t/ADt
HD
O2
Hot waterxx t/ADt
Figure 3-3. The approximate liquor flows (t/ADt) of the ECF bleach plant. The dilution factor isabout 2 t/ADt.
Integrated fine paper mill Page 1920 January 2011
In both the R8 and R10 processes purchased sodium chlorate reacts withsulphuric acid, with methanol as the reducing agent, to produce chlorinedioxide and the by-product Na3H(SO4)2. The R10 process however has anadditional step where Na3H(SO4)2 is split into Na2SO4 and H2SO4, and theH2SO4 is returned to the ClO2 generation process.
In the softwood mill the R8 process is selected. The (Na3H(SO4)2) by product,is used to partially replace sulphuric acid used for soap splitting.
Since there is no soap splitting and an excess of sulphur in the hardwood millthe R10 process is selected to minimize the amount of excess sulphur (which ispurged as recovery boiler precipitator ash).
3.9 Evaporation
The evaporation plant is a conventional 7-effect system utilising LP and MPsteam (Figure 3-4). It is designed to produce 80% dry solids liquor (includingrecovery boiler ash).
All evaporator bodies are of the falling-film type, and the seven effects aredesigned to operate in counter-current fashion, i.e. with live steam being fed tothe first effect and weak liquor to the seventh effect. Tanks are installed forweak, intermediate and strong black liquors well as for soap, spills andcondensates. The firing liquor storage tank is pressurized due to the high drysolids content.
Ash mixing is done before the first effect. Firing liquor at 80% DS is producedin the first effect. The first effect is divided into three bodies connected in serieson the liquor side. Washing of the first effect is done one body at a time usingweak black liquor. To avoid upsets in firing liquor concentration when washing,and to facilitate ash mixing, a strong black liquor storage tank is placed after thesecond effect.
The body operating with the strongest liquor in the first effect is heated byintermediate pressure steam from a steam ejector driven by MP steam andcompressing LP steam. The other two bodies in the first effect are heated by LPsteam only.
Sludge from the biological treatment is mixed into the black liquor in anintermediate storage tank.
Integrated fine paper mill Page 2020 January 2011
3.9.1 Handling of condensates
A stripping system for foul condensates from the digester and evaporationsystems is included. The stripping column is integrated within the evaporationplant to reduce the live steam consumption (Figure 3-4). A methanolrectification column with turpentine decanter and foul methanol liquid storageis also included. The methanol is incinerated in the recovery boiler.
Evaporation condensates are divided depending on contamination degree anddistributed to different consumers within the mill. Approximately 4.5 m3/ADtof the cleanest condensate (approximately 200 mg/l COD; 80oC) is used aswash liquor in the bleach plant. Approximately 3.5 m3/ADt intermediatecondensate (approximately 1000 mg/l COD, 65oC) is used in the causticizingplant. The remaining condensate is also clean condensate, and is discharged aseffluent.
The surface condenser is designed for a warm water temperature of 50°C and togive condensate separation in principle as for the evaporators.
Figure 3-4. Evaporation plant including condensate stripper.
3.9.2 Handling of non-condensable gases
Non-condensable gases (NCGs) are collected throughout the mill. Both stronggases and weak gases are burned in the recovery boiler.
In mills which have a large excess of sulphur, an alternative is to incinerate thegases in a dedicated boiler.
Integrated fine paper mill Page 2120 January 2011
3.9.3 Tall oil recovery
Soap that separates in the weak and intermediate black liquor tanks is decantedto a soap decanter and then led to a separate storage tank. The soap is thenpumped to the tall oil plant, where it is upgraded to crude tall oil. The amountof soap depends on the wood used for pulping. With 50% pine and 50% spruce,the tall oil production is assumed to be 35 kg/ADt for softwood. There is nosoap from hardwood.
The most common type of tall oil plant uses sulphuric acid for soap splitting,and sulphur is thus added to the recovery cycle. Mills that use an R8 process forchlorine dioxide generation can use the sodium sesquisulphate (Na3H(SO4)2)by-product to partly replace H2SO4 that would otherwise have been used forsoap splitting.
Some mills use carbon dioxide to pre-treat the soap. The product after this pre-treatment is a mixture of soap and tall oil (soap oil), and a water phasecontaining sodium bicarbonate. The water phase is separated from the soap oil,and then the soap oil is treated with sulphuric acid as in a traditional tall oilplant. Pre-treatment with carbon dioxide however reduces the sulphuric acidrequirement by about 40%.
3.10 Recovery boiler
The optimum recovery boiler steam pressure and temperature is not the same indifferent regions. In Sweden the majority of existing recovery boilers weredesigned when electricity prices were low. These boilers were in generaldesigned for 60 bar steam pressure and corresponding temperatures. At highersteam temperatures more expensive metallurgy is required for the superheater,which means a sharp increase in investment and maintenance costs. Highersteam pressure and temperature cannot be economically justified with lowelectricity prices.
In contrast, Finland, for example, has had higher electricity prices, and themajority of recovery boilers operate at 80-90 bar. Newer boilers are oftendesigned for greater than 100 bar pressure to maximize power generation.
With increasing electricity prices three new recovery boilers in Sweden havebeen designed for higher steam pressure and temperature.
In this study the recovery boiler is designed to produce high pressure steam at100 bar(g) and 505C.
Integrated fine paper mill Page 2220 January 2011
Some of the key factors in the recovery boiler design which are related tomaximizing power generation include:
Feedwater preheating which increases steam generation andconsequently the power generation. One drawback of feedwaterpreheating is increased flue gas temperature after the economiser whichincreases the flue gas loss and increases the cost of the precipitator.
Flue gas cooling after the precipitator – the heat uptake in the cooler willtypically replace LP steam for combustion air preheating. The LP steamcan instead be sent to a condensing turbine to produce power. Alsoreduces the negative impact of increased flue gas temperature due tofeedwater preheating.
Top preheating heating of all combustion air to about 205oC to increasepower generation.
Sootblowing steam is extracted from the turbine instead of using highpressure steam from the recovery boiler.
HP steam 100 bar(g), 505 °C
Dust recycle(mixed with b.l.in evap. plant)
Dust purge
Black liquor80 %DS(incl. dust andbiosludge)
Weak wash
Green liquor
Fluegas
SmeltDissolver
ElectrostaticPrecipitator
Sootblowing steam 25 bar (g)
Top preheatedCombustion air
NCGs
Boilerfeedwater
Flue gascooler
FWheater
FWheater
Integrated fine paper mill Page 2320 January 2011
Figure 3-5. Recovery boiler and smelt dissolver.
The high liquor concentration contributes to a high bed temperature, whichleads to low sulphur emissions from the bed. Combustion air is distributed onmultiple levels to facilitate complete combustion and minimize NOx formation.Dust that is not captured in the economizer section is removed in theelectrostatic precipitator (ESP). Most of the dust is recycled and mixed with theblack liquor in the evaporation plant, as described in section 3.9. A fraction ofthe dust is purged, mainly to control sulphur and sodium, with the additionalbenefit of reducing potassium and chloride concentrations in the liquor cycle.
With increased recovery boiler temperature and pressure the tolerance forpotassium and chloride in the black liquor is reduced. At the design pressureand temperatures for this boiler the maximum chloride concentration in theliquor is about 0.3 wt% and about 2.0% for potassium. Exceeding theseconcentrations increases the risk for recovery boiler corrosion and pluggingproblems.
Softwood and birch have relatively low levels of chloride and potassium, so thelimits for chloride and potassium can be met by purging a small amount ofprecipitator dust (which is anyways necessary to maintain the sulphur andsodium balance).
3.11 Causticizing
The mill is equipped with conventional causticizing with both green liquor andwhite liquor filtration. The green liquor is filtered in two parallel green liquorfilter units. The dregs are washed and dewatered in a filter press before beingdischarged. Condensate from the evaporation plant is used for dregs washing.Dregs and grits are combined and sent to landfill.
Green liquor from the storage tank is cooled in a flash-type green liquor coolerbefore the lime slaker-classifier. Slaking and causticizing is performed in asingle line with causticizing vessels in series.
The causticized liquor is filtered in a pressure disc filter. The main advantage ofa disc filters over other types of white liquor filters is the low liquor content ofthe discharged lime mud which eliminates the need for a separate lime mudwashing stage. Alternatively the causticized liquor could be filtered using tubefilters followed by another set of tube filters for the weak wash.
Integrated fine paper mill Page 2420 January 2011
Figure 3-6. White liquor preparation (white liquor disc filter option).
Lime mud from the lime mud vessel is pumped to the agitated lime mud storagetank. The lime mud is washed and dewatered on a lime mud disc or drum filter.Condensate from the evaporation plant is used for lime mud dilution and hotwater for the lime mud filter wash showers.
Spills are reclaimed from two spill sumps and pumped to the weak washstorage tank.
3.12 Lime kiln
The lime kiln is equipped with an external lime mud dryer and modern productcoolers.
The external lime mud dryer consists of a vertical flue gas duct where the limemud is dried and preheated by the hot flue gases. The dry mud is separated fromthe flue gases in a cyclone and then introduced to the kiln. This arrangementallows a shorter kiln compared to a conventional kiln where the lime mud isdried inside the kiln. External lime mud dryers are incorporated in the majorityof new kilns today, and since the late 1980’s a large number of existing kilnshave been equipped with an external dryer to increase kiln capacity.
Modern types of product coolers demand less space and have lower radiationheat losses than conventional planetary coolers.
Slaker
Causticizer
White liquor filter
Disk filter
Green liquor
Clarified white liquor
Lime kiln
Condensate
Lime mudremoval
Lime mudfilter
Weak wash tosmelt dissolver tank
Green liquor dregs
Integrated fine paper mill Page 2520 January 2011
Dust is removed from the flue gases by means of an electrostatic precipitator.The ID fan is installed downstream the precipitator.
A fraction of the lime mud is purged, primarily to control phosphate levels.Limestone is used for make-up.
To save on oil consumption, a number of European mills use bark or woodresidues as fuel for the lime kiln. The biomass is either pulverized and fireddirectly, or gasified and then fired in the kiln. There are many differencesbetween these two processes, however, in terms of the overall mill energybalance they are similar, and either can be used. A detailed review of thebiomass fuel is not in the scope of this project; however the main fuel for thelime kiln is bark or wood residue.
3.13 Paper Mill
3.13.1 Capacity
To match the capacity of the kraft pulp mill, the the paper mill has two identicalpaper machines. Both PM1 and PM2 produce uncoated fine paper fromsoftwood and hardwood. Each paper machine has an annual production of511 000 t/a. The furnish composition is shown below.
PM furnish compositionFiller 25%Fibre 75%- Bleached softwood 19%- Bleached hardwood 56%
The corresponding furnish requirements for each paper machine are:
Bleached hardwood 573 000 ADt/aBleached softwood 191 000 ADt/a
Filler 235 000 t100/a
Starch 27 600 t100/a
A block diagram for PM1 and PM2 is shown in Figure 3-7.
Integrated fine paper mill Page 2620 January 2011
Figure 3-7. Process concept of the fine paper machines
Refiner
Disc filter
Mixingchest
Soft wooddosing chest
deaeration
Bleachedsoft wood
Wire silo
Bleachedhard wood
Refiner
Hard wooddosing chest
Headbox
Wiresection
Press
Dryer
Calender
Sizer
Pulper
Pulper
Pulper
Pulper
Broketower
FilterScreen
Screen anddeaeration
White watertank
White watertower
Brokedosing chest
Reel/Finishing
Bl. hard woodpulp chest
Bl. soft woodpulp chest
FillerStorage tower
Filler
Machinechest
White waterto bleaching
plant
After dryer
Intermediatepulp
Intermediatepulp chest
Pulper
Pulper
Refiner
Disc filter
Mixingchest
Soft wooddosing chest
deaeration
Bleachedsoft wood
Wire silo
Bleachedhard wood
Refiner
Hard wooddosing chest
Headbox
Wiresection
Press
Dryer
Calender
Sizer
Pulper
Pulper
Pulper
Pulper
Broketower
FilterScreen
Screen anddeaeration
White watertank
White watertower
Brokedosing chest
Reel/Finishing
Bl. hard woodpulp chest
Bl. soft woodpulp chest
FillerStorage tower
Filler
Machinechest
White waterto bleaching
plant
After dryer
Intermediatepulp
Intermediatepulp chest
Pulper
Pulper
Integrated fine paper mill Page 2720 January 2011
3.13.2 Stock preparation
3.13.3 Bleached kraft supply
The pulp mill produces softwood and hardwood in campaigns of 30 h and 70 hrespectively. There are three MC-storage towers of 10 000 m3 each forhardwood and three MC-storage towers of 7 500 m3 each for softwood. Sincethere is not a perfect plug-flow through the pulp mill, there will be someintermediate pulp produced when changing from hardwood to softwood. Thisintermediate pulp is stored in a 3 500 m3 MC-tower.
From the MC-storage towers, pulp is diluted and pumped to their respectivepulp chest. From the pulp chests, the pulp is diluted and pumped via refiners tothe hardwood and softwood dosing chests. In this mill hardwood and softwoodare refined separately to optimise their properties. Intermediate pulp is pumpedvia the hardwood refiner to the hardwood dosing chest. From the dosing chests,pulp is diluted and proportioned to the mixing chest.
3.13.4 Broke system
Broke from all the pulpers on the machine is pumped via the couch pit to thebroke storage tower (3500 m3). From the broke tower, the pulp is dewatered ona thickener and taken to the broke dosing chest at about 4% consistency.Broke, which is proportioned to the paper machine, is pumped via a deflaker tothe mixing chest and some of the pulp is re-circulated to the tower to increasethe consistency in the tower.
3.13.5 Mixing/machine chest
After the mixing chest there is a final consistency control and the thick stock isscreened with slotted barrier screens. The barrier screening system is installedbetween the mixing chest and the machine chest and in this position will screenboth the virgin pulp supplied to the paper machine as well as the broke.
3.13.6 Filler supply
Filler is dissolved and stored in a 1 000 m3 storage tower at 40% concentration.Filler is added to the short circulation of the paper machine.
Integrated fine paper mill Page 2820 January 2011
3.13.7 Short circulation
As a consequence of the barrier screening, it is possible to reduce the powerconsumption by eliminating the hydrocyclone system in the short circulation.The short circulation then consists of the wire silo, de-aeration equipment, fanpump and machine screening in two stages. The headbox is of dilution controltype and the system includes two speed-controlled pumps, de-aeration and apressure screen.
Filler is charged ahead of the head box pump. The charge is controlled by theQCS-system to give a constant filler level in the paper independent of theamount of broke added.
Retention aids are added before the machine screen and after the machinescreen, or alternatively only after the machine screen
3.13.8 Paper machine
The paper machine is based on a concept to allow for a high quality fine paperproduction at a high machine efficiency and high speed. The paper machine isdimensioned for 1850 m/min.
The paper machine headbox is of a cross profile dilution type, which means thatdilution water is added via special control valves across the machine width inthe headbox. Each valve setting is based on information from the measuringframe in the dry end, the QCS-system. Since this correction is not made by theslice lip, but through local changes in stock consistency, fibre orientation is notinfluenced.
The wire section is a modern twin wire section to give the best paper uniformitywith regard to formation, basis weight profile, ash profiles and sheet structure.
The press section is designed for optimum runnability of the machine by meansof a closed web run from the wire section to the dryer section. A high drynesscontent of the web leaving the press section as well as an equal-sidedness areother important factors the press section has to perform. The press concept istwo straight shoe presses following each other giving a final dryness after thepress section of approx. 52%.
The dryer section consists of a pre-dryer section and an after dryer section.The pre-dryer section is a combination of drying cylinders in an upper row andvacuum assisted rolls in a lower row integrated with an air handling systemincluding web stabilising equipment for increased runnability and minimumenergy consumption.
Integrated fine paper mill Page 2920 January 2011
The sizer after the pre-dryer section adds surface size to both sides of the webby means of an application roll system to increase strength properties of thepaper.
The sizer is followed by the after dryer section which is a combination of dryercylinders and vacuum rolls in the first part followed by a conventional dryersection with drying cylinders both in top and bottom position. Thisarrangement is for curl control of cutsize papers which need specialconsideration regarding flatness and runnability in copying machines etc.
The calender is of soft calender type in a tandem arrangement to give theoptimum surface properties.
To build a high quality parent roll with a diameter of 3.4-3.6 m the nip load aswell as the parent roll torque has to be controlled and this is the case with allmodern reel system today. This way of building a parent roll will give the bestconditions when handling the roll in the winder.
Winding fine paper is not so critical as winding coated paper and for this reasona centre winder is not needed. For finished rolls with a diameter of 1.2-1.4 m acommon two drum winder is sufficient, but with a roll diameter of 1.5-1.6 m awinder type giving a lower linear nip load between finished roll and supportingwinder rolls is needed.
Main data for the papermachines are presented in Table 3-5.
Table 3-5. Main data for papermachines
Speed design m/min 1 850
Speed at pope m/min 1 690
Width on pope m 9
Grammage g/m2 80 (75-160)
Production on pope (100% eff.) t93/h 73.1
Paper dryness % 93
PM furnish composition
-Hardwood % 56
-Softwood % 19
-Filler % 25
Surface size of paper (starch) % 3
Paper mill efficiency % 82
Operating days per year days 355
Paper production net, annual average t93/day 1 439
Integrated fine paper mill Page 3020 January 2011
Paper production net, Kraft mill MCR t93/day 1 565
Paper production net t93/year 511 000
3.13.9 Fresh water system
The warm water system is the main fresh water consumer in the paper mill.Warm water is mainly used for high pressure cleaning showers in the wire- andpress sections and for dilution of different chemicals. The process related freshwater consumption is about 6 m3/t of paper. Warm water is received from thekraft mill.
Used cooling waters and other uncontaminated process waters are collectedseparately and re-circulated via a cooling tower to the fresh water systems.
3.13.10 White water system and buffer volumes
The paper machine white water system consists mainly of a white water tankfor paper machine excess water connected to a disc filter save-all. Clear filtratefrom the disc filter is used for showers in the wet end and is also stored in awhite water storage tower (5 500 m3) to be used for consistency control and forbroke dissolving. The surplus clear filtrate is pumped to the bleach plant.
Accidental discharges are avoided with a dimensioning of broke, pulp andwhite water storage buffer volumes in balance, which means that the whitewater storage towers in the system should have a volume corresponding to thetotal sum of all pulp storage towers. To be correct it is not the physical volumesthat should be equal, it is the used buffer volume that is important. A whitewater tower which is always filled provides no buffer volume.
A correct dimensioning and use of the storage buffer volumes also meansminimal variations in the flow of waste water to the external treatment plantwhich should result in higher treatment efficiency and lower investment andoperation costs for the external treatment plant.
3.13.11 Energy aspects of the paper machine
The main input of energy to the paper machines is steam for drying of thepaper. About 3.0 GJ/t evaporated water is needed for drying. The efficiency ofthe paper machines (need for re-drying of broke) and the dryness of the paper
Integrated fine paper mill Page 3120 January 2011
after the press section are of great importance for the steam consumption. Witha press dryness of 52%, a final dryness of 93%, 3% surface size and 10%redrying, the heat consumption for drying is 3.77 GJ/t paper. Steam is alsoused for heating purposes on the paper machine. In the press section a 3.5 barsteam box heats the web to increase dryness and improve dryness profile. Theair to the blow boxes must also be heated with steam. The total consumption ofsteam on the paper machine is about 4.23 GJ/t paper.
The total consumption of electric energy for the paper machine is about550 kWh/t. The main part of this power consumption is in motors for pumps,screens, drives and refiners in the paper mill. Most of this energy is going intothe process flow as thermal energy and contributes to keeping the systemtemperature on a high level. The desired level is somewhere in the range 52-55oC. A high temperature improves the dewatering on the wet end andminimises bacteriological and slime problems.
On the wire section, the process water loses about 10 MW of heat to thesurrounding air by evaporation. The high dryness of the pulp from the pulpmill means that only a small amount of thermal energy is transferred with thepulp from the pulp mill. To maintain the desired white water temperature, heatis transferred from the heat recovery system of the drying section to the papermachine white water.
Table 3-6. Paper machine energy consumption data
Dryness to dryer % 52
Paper dryness % 93
Evaporated t/t paper 0.82
Evaporated sizing t/t paper 0.32
Sum evaporated t/t paper 1.14
Redrying etc % 10
Total evaporation t/t paper 1.26
Heat consumption GJ/t evap. 3.0
Heat consumption drying GJ/t paper 3.77
Heat consumption miscellaneous GJ/t paper 0.46
Total heat consumption paper mill GJ/t paper 4.23
Power consumption incl. refining kWh/t paper 550
Water consumption m3/t paper 6.0
Integrated fine paper mill Page 3220 January 2011
3.14 Power boiler
The recovery boiler alone does not produce enough steam to meet the demandof the integrated fine paper mill. A power boiler is therefore used to producethe additional steam.
The power boiler is fuelled with wood residues from the woodyard and chipscreening areas, plus sludge from the effluent treatment plant.
The power boiler is designed to provide steam for mill start-up and shut downs,and there is no need for an additional fossil fuel fired boiler dedicated for start-ups and shut downs.
The power boiler is designed with a bubbling fluidised bed (BFB).
HP steam100 bar(g), 505 °C
Falling Bark
Fluegas
ElectrostaticPrecipitator
Sootblowing steam25 bar(g)
Combustion air
Sec. Biosludge
Boilerfeedwater
Primary Sludge
Figure 3-8. Bubbling fluidised bed power boiler
Integrated fine paper mill Page 3320 January 2011
3.15 Steam turbines and steam distribution
Steam is reduced through a backpressure steam turbine to 3.5 bar(g). Thispressure has been selected to facilitate maximum electric power productionwithout requiring unnecessary large evaporator bodies or heat surfaces in thepaper machines. Intermediate pressure steam of 25 bar(g) is extracted for sootblowing and 9 bar(g) steam is extracted to the MP-steam system.
MP steam and LP steam are de-superheated with boiler feedwater beforedistribution.
HP steam not required in the process is utilised in a condensing steam turbinefor further electric power generation.
Table 3-7. Steam data.
°C bar(g)
HP steam 505 100.0
IP steam, extracted for sootblowing 275 25.0
MP steam, desuperheated 200 9.0
LP steam, desuperheated 150 3.5
3.16 Cooling and recovery of low-temperature heat
In addition to normal heat losses of different kinds, approximately one third ofall the energy that is introduced with the fuel to the system will have to becooled away by a cooling system. The secondary energy system comprises therecovery of heat that is generated from steam and electricity and that is finallywithdrawn from the system by cooling. In principle, the system can be dividedinto two parts: one where heat is recovered for the production of warm and hotwater, another part where excess heat is cooled by the means of a coolingtower. The design of the model mill is conventional, except for the very lowfresh water consumption.
Low-temperature heat is recovered from a number of sources in the kraft mill,e.g., the surface condenser of the evaporation plant, the smelt dissolver vapourcondenser, and the turpentine condenser. The heat is used for hot waterproduction and for boiler feedwater heating. Condensate from the evaporationplant is used in the pulp washing and in the lime mud wash.
The cooling water system is integrated with the process water system. Coolingis carried out in cooling towers.
See Appendix 3 for the secondary heat balance.
Integrated fine paper mill Page 3420 January 2011
3.17 Effluent treatment
Pulp is produced in campaigns with softwood 25% of the time and hardwood75% of the time. Effluent treatment is designed for hardwood campaigns, anddischarges are calculated as long term mean averages.
Effluent treatment consists of pre-treatment, (cooling equipment andneutralisation), primary treatment and biological treatment.
In the pre-treatment there is a primary clarifier to remove fibre sludge. Theestimated suspended solids content of the effluent from the mill pulp and papermill is about 100 mg/l. After the clarifier the suspended solids content is about50 mg/l. The primary sludge is dewatered in a centrifuge and incinerated in thepower boiler (alternatively the primary sludge could be sold to a fluting mill orsimilar, depending on the price). After the primary clarifier the effluent isscreened, cooled to about 37oC with heat exchangers or cooling towers, and thepH is adjusted to about 7.
Table 3-8. Inlet data to biological treatment.
Softwoodcampaigns
Hardwoodcampaigns
Total effluent m3/d 60 000 70 000
COD mg/lkg/d
1 22073 000
1 20084 000
SS mg/lkg/d
503 000
503 500
Temperature °C ~37 ~37pH ~7 ~7Primary sludge kg DS/d 3 000 3 500
For biological treatment there is a bio-film reactor with suspended carriersfollowed by an activated sludge system. The activated sludge system iscomprised of an aeration basin and secondary clarifier. The system isdesigned for low bio-sludge production and low nutrient discharges. CODreduction is estimated to be about 65-70% for softwood and about 70-75%for the hardwood mill.
Suspended solids out from the secondary clarifier are about 50 mg/l.The biological sludge is dewatered to about 10% in a centrifuge and mixedwith intermediate black liquor in the evaporation plant, before firing in therecovery boiler.
Integrated fine paper mill Page 3520 January 2011
Figure 3-10. Effluent treatment plant
Table 3-9. Outlet data from biological treatment.
Softwood HardwoodFlow m
3/d 60 000 70 000
COD reduction % 65-70 70-75COD out kg/d < 25 550 < 25 200SS out
mg/l 50 50kg/d 3 000 3 500
Biological sludge kg/d ~ 7 100 ~9 700
3.18 Spill handling system
Accidental spills caused by abnormal operation or equipment failures can be asignificant contribution to the effluent emissions from the mill, and therefore itis important to minimise spills.
The mill is designed with a comprehensive sewer system to collect accidentalspills as close to the source as possible and directly recycle them to the properprocess stage. The evaporation plant is designed with additional capacity to takecare of black liquor spills in that area, as well as possible liquor contaminatedcondensates.
The spill system includes: Adequate instrumentation to minimise the risk for overflow of tanks and
equipment, and to detect accidental spills. Provisions to take care of process liquors when it is necessary to empty
tanks or equipment for maintenance Retention dams around tanks and equipment. Floor channels connected to pump sumps from which liquids can be
pumped back to the process.
NutrientsAcid/Base (if necessary)
(if necessary)
Screen
From Kraft Pulp mill
From Fine paper millAir
Return sludge Biological sludge
Polymer
Primary sludge for fiber reuse
Intermediate To recoveryblack liquor boiler
Cooling
Biofilmreactor withsuspended
carriers
Aeration basinSecondary
clarifier
Centrifuge
80-90°C
Primaryclarifier
Centrifuge
Integrated fine paper mill Page 3620 January 2011
Emergency effluent treatment pond for major spills or upset conditionsin the effluent treatment plant.
Well-educated and trained personnel who understand the importance ofspill handling.
3.19 Water supply and treatment
Water is basically used for two purposes in the mill: process water and cooling.
The raw water quality is normally good in Nordic rivers. The mill water systemhas only one quality, chemically treated water, with the following treatmentsequence:
Water intake with coarse screening. Chemical treatment in a dissolved air flotation (DAF). Sand filtration. Clear water well, including storage capacity for fire fighting.
Table 3-10. Data, raw water treatment.
Flow m3/d 70 000 – 80 000
Raw water sludge kg/d ~2 700
The raw water intake should be arranged and designed to minimize the amountsand and other debris which enters the mill.
As precipitation chemical some kind of Al-salt and polymer is used. Raw watersludge is discharged to the receiving water together with treated effluent.
The cooling water system is semi-open, which means that part of the processwater comes from the cooling water system. The cooling is performed in acooling tower. There are filters in the cooling water system to avoid impuritiesin the mill process water.
The amount of process water coming from the cooling system is controlled sothat the cold water temperature is maintained at about 18oC.
There is a separate cooling water loop for the turbine. The water from theturbine oil cooler is dumped. Other coolers in the mill are connected to thegeneral mill process water system. Water from such coolers that couldcontaminate the water should also be dumped.
Integrated fine paper mill Page 3720 January 2011
Figure 3-11. Water treatment.
Al AirPolymer
Screen
Raw water intake
Raw water sludge
Clear waterwell
Dissolved airflotation
Sand filtration
Integrated fine paper mill Page 3820 January 2011
4 Model mill - energy balance
The model integrated fine paper mill is very energy efficient. During softwoodcampaigns the recovery boiler alone produces sufficient steam for processsteam consumption and cogeneration of power in the back-pressure turbine. Inthis case there is a slight excess of steam, and all falling bark could be sold.
During hardwood campains however, the recovery boiler alone does notproduce sufficient steam, and therefore the mill has a small bark boiler. In thiscase there is still an excess of bark which could be sold.
During both hardwood and softwood campaigns the back pressure powergeneration is not sufficient to meet the mill requirement. Since the mill has abark boiler and excess falling bark, a condensing turbine is included tomaximize power generation, and make use of the excess recovery boiler steamwhich otherwise would be wasted during softwood campaings.
Note that even with the condensing turbine the mill still needs to purchaseelectricity during both hardwood and softwood campaigns. In this study it isassumed that only falling bark is available, and the resulting bark boiler andcondensing turbine are relatively small. An alternative that must be evalulatedin reality is purchasing bark to further increase power generation to meet thefull demand of the mill and possibly produce power for sale. Such an economicevaluation is very mill specific, and depends on investment cost, fuel price,marginal steam cost, and electricity prices.
Key factors which make the model mill energy efficient include:
High HP steam data, 100 bar(g), 505oC Feed water preheating to 175oC to increase HP steam generation Recovery boiler flue gas cooler to reduce LP steam consumed in air
preheating Top preheating of all recovery boiler combustion air to 205oC Recovery boiler sootblowing steam is extracted at 25 bar(g) from the
turbine instead of using HP steam Latest technology for pulp digesting which has a lower cooking
temperature than other systems 7 effect evaporation plant Steam consumption in the bleach plant is reduced; more chlorine
dioxide and less hydrogen peroxide allow a lower bleaching temperature Low pressure steam used in the paper machine
Integrated fine paper mill Page 3920 January 2011
Pressurized condensate system High temperature of hot water, 85 - 90oC, and maximum use of hot
water instead of steam in the bleach plant, and paper machine Bark press for bark to the power boiler
An overview of the energy system and balances for the model mill duringsoftwood and hardwood campaigns are shown in Figure 4-1 and Figure 4-2, andfurther details of the balances are included in Appendix 2.
Figure 4-1. Overall energy balance – softwood campaigns
Model Fine paper SW campaign 100 bar(g)
Pulp ADt/d 49,3
SW ADt/d Soot blowing
HW ADt/d Bark Recovery Air preheat Steam flows t/h
Boiler Boiler Feedwater
Market ADt/d Preheating
35 MW 412 MW 0,0 1,7 Air preheater bark boiler
0,0 MW 46,7 Digester
6,7 Bleaching
MP-steam 2,5 Oxygen stage
15,4 Evaporation
0,8 Chemical preparation
46,7 35,9 Feedwater preheat
3,4 Miscellaneous, losses
594,4
0,0 Air preheater recovery boiler
146 °C 96,0 MW 2,5 Air preheater power boiler
0,0 Smelt shattering
0,0 Digester
111,4 0,0 Bleaching
46,7 25,0 bar(g) 9,0 bar(g) 0,0 Pulp machinePower balance 0,0 Pulp machine, white water system
Consumption MW 26,2 MW 117,2 Evaporation
Process 121,3 2,5 Chemical preparationSold 0,0 0,0 Causticising
Sum 121,3 237,4 Paper machine
0,0 Building heatingProduction 0,0 Blow off
Back-pressure 96,0 Make-up 11,1 Miscellaneous, lossesCondensing 14,5 Sec heat 119,1 3,5 bar(g) 45,4 Steam to feedwater tank
Bought 10,7 MW 15 °CSum 121,3 434,0 Condensate return
Bark to lime kiln, tDS/d 203
Bark to bark boiller, tDS/d 217
Sold bark, tDS/d 0
46,7
35 °C
8,0
34 °C75 °C
113 °C
62,6
14,5 MW
128 °C
0,0
505 °C
420,4
0
2 000
0
2 000 591,8
GG
Mixedbed
Integrated fine paper mill Page 4020 January 2011
Figure 4-2. Overall energy balance – hardwood campaigns
Model Fine paper HW campaign 100 bar(g)
Pulp ADt/d 97,8
SW ADt/d Soot blowing
HW ADt/d Bark Recovery Air preheat Steam flows t/h
Boiler Boiler Feedwater
Market ADt/d Preheating
70 MW 426 MW 0,0 3,4 Air preheater bark boiler
0,0 MW 52,1 Digester
21,9 Bleaching
MP-steam 3,1 Oxygen stage
16,8 Evaporation
1,0 Chemical preparation
64,9 37,1 Feedwater preheat
4,2 Miscellaneous, losses
644,3
0,0 Air preheater recovery boiler
146 °C 103,9 MW 4,9 Air preheater power boiler
0,0 Smelt shattering
0,0 Digester
137,5 0,0 Bleaching
64,9 25,0 bar(g) 9,0 bar(g) 0,0 Pulp machinePower balance 0,0 Pulp machine, white water system
Consumption MW 36,4 MW 127,7 Evaporation
Process 124,0 3,1 Chemical preparationSold 0,1 0,0 Causticising
Sum 124,1 237,4 Paper machine
0,0 Building heatingProduction 0,0 Blow off
Back-pressure 103,9 Make-up 11,5 Miscellaneous, lossesCondensing 20,2 Sec heat 144,0 3,5 bar(g) 51,8 Steam to feedwater tank
Bought 0,0 MW 15 °CSum 124,1 453,5 Condensate return
Bark to lime kiln, tDS/d 211
Bark to bark boiller, tDS/d 432
Sold bark, tDS/d 0
64,9
35 °C
10,5
32 °C75 °C
112 °C
66,0
20,2 MW
129 °C
0,0
505 °C
440,9
0
0
2 500
2 500 611,4
GG
Mixedbed
Integrated fine paper mill Page 4120 January 2011
5 Comparison of model mill and typical mill
To indicate potential energy savings, energy balances for a typical fine papermill, from the FRAM project, is included here. The type mill has energyproduction and consumption similar to existing Swedish mills.
Table 5-1 and Table 5-2 summarize the key operating and dimensioning datafor the type mill, compared to the model mill.
Integrated fine paper mill Page 4220 January 2011
Table 5-1. Summary of key pulp mill data – Model mill vs. Type mill.
SoftwoodModel
SoftwoodType
HardwoodModel
HardwoodType
Pulp production ADt/24 h 2 000 1 000 2 500 1 250
Wood yard
Wood to digester t/24 h 4 072 2 065 4 610 2 328
Bark and wood waste t/24 h 420 193 642 298
Digester Plant
Kappa number 30 27 17 17
Unscreened deknotted digester yield % 47.0 46.1 51.0 50.5
Alkali charge on wood as EA NaOH,% 20.0 20.0 18.5 19.0
Sulphidity (white liquor) mole-% 35 35 35 35
Oxygen Stage
Kappa number after oxygen stage 12 14 12 10
Alkali charge as NaOH kg/ADt 25 25 18 20
Oxygen charge kg/ADt 20 20 14 14
Washing Department
Dilution factor in the last stage m3/ADt unbl. 2.5 2.5 2.5 2.5
Evaporation PlantWeak black liquor to evaporation,excl.spill t/h 913 441 981 475
ditto dry solids content % 16.0 16.9 15.7 16.5Strong black liquor, dry solids contentincl. ash % 80 73 80 73
Total evaporation, including spill t/h 771 359 840 393
Recovery BoilerEstimated higher heating value ofvirgin DS MJ/kg 14.0 14.0 13.8 13.9Strong liquor virgin solids to mixingtank t/24 h 3 477 1 778 3 668 1 866Net useful heat from liquor, virginsolids MJ/kg DS 10.3 9.5 10.0 9.3
Net useful heat from liquor MW 413 195 426 200
Causticizing and Lime Kiln
Causticizing efficiency mole-% 82 82 82 82
Total white liquor production m3/24 h 7 541 3 984 7 831 4 215
Lime kiln load t/24 h 534 272 554 288
Active CaO in lime % 90 90 90 90
Integrated fine paper mill Page 4320 January 2011
Table 5-2. Summary of paper mill key operating data.
Model Type
Speed at pope m/min 1 690 980
Width on pope M 9 7.8
Grammage g/m2
80 (75-160) 80 (75-160)
Production on pope (100% eff.) t/h 73 37
Paper dryness % 93 93
PM furnish composition
-Hard wood % 56 56
-Soft wood % 19 19
-Filler % 25 25
-Surface size of paper (starch) % 3 3
Paper production net (PM1 + PM2),Kraft mill MCR t/d 3 100 1570
Paper production net (PM1 + PM2) t/a 1 022 000 512 000
Bleached hardwood consumption ADt/a 573 000 287 000
Bleached softwood consumption ADt/a 191 000 96 000
Filler consumption t100/a 235 000 118 000
Starch consumption t100/a 27 600 13 800
5.1 Type mill –process description
Following is a brief description of the type mill, with emphasis on the factorswhich are different from the model mill, and which affect the mills’ energybalances.
5.1.1 Digester
Many existing mills still use the old “conventional” two flash digester, withoutchip bin presteaming. The loading of the digester is also normally raised overthe years and therefore the cooking temperature is higher than in new digesters.The type mill has a two flash digester and a cooking temperature of 165ºC forsoftwood and 162ºC for hardwood. To achieve maximum production in thedigester, the alkali charge is increased.
Integrated fine paper mill Page 4420 January 2011
5.1.2 Oxygen stage
The type mill has a single oxygen stage with limited kappa reduction from 27 to16 on softwood. Hardwood is the same as in the reference mill, 17 to 10.Washing before the stage is on a vacuum filter.
5.1.3 Pulp washing
Vacuum filters were once the standard equipment for pulp washing and manyare still in use. These require more washing liquid than wash presses andtherefore increase the water consumption and the heat needed for heating thewater. The type mill is assumed to have a retrofit oxygen stage with vacuumfilter before oxygen stage and wash presses after. The bleach plant has vacuumwashers in all positions.
5.1.4 Bleaching
The ECF bleach sequence in the typical mill uses much more ClO2 and lessH2O2 than in the model mill.
The bleach plant is a little more open than in the model mill, which togetherwith the higher wash water flows needed for filters results in about twice theeffluent from the bleach plant compared to the model mill.
Table 5-3. Expected chemical charges for the SW kraft type mill with the sequence(OO)D(EOP)DD) to 90% ISO brightness ( kg/ADt). ClO2 as ClO2 and not as active Cl.
StageTemp(C)
Ox. WL(NaOH) O2
ClO2
H2SO4 NaOH H2O2 MgSO4 SO2
(OO) 95 30 21 2D0 70 8 4
(EOP) 90 7 17 2 1
D1 70 7 2 0.5
D2 70 3 1
Table 5-4. Expected chemical charges for the HW kraft type mill with the sequence(OO)D(EOP)DD to 90% ISO brightness ( kg/ADt). ClO2 as ClO2 and not as active Cl.
StageTemp(C)
Ox. WL(NaOH) O2
ClO2
H2SO4 NaOH H2O2 MgSO4 SO2
(OO) 95 23 16 2D0 70 7 5
(EOP) 90 5 14 2
D1 70 6 2 0.5
D2 70 3 1
Integrated fine paper mill Page 4520 January 2011
Figure 5-1. The liquor flows (m3/ADt) of the type mill ECF bleach plant. The dilutionfactor is 2.5 m3/ADt.
5.1.5 Paper machine
The type mill fine paper machines operate at lower speed, about 1000 m/min,and production is usually not greater than 255 000 t/a.
The forming section if of hybrid type, i.e., an initial fourdrinier formingfollowed by twin-wire forming, giving higher energy consumption.
The approach flow system is equipped with cleaners and is therefore morepower consuming than the reference mill which has “guard screening” systems.
The press is a four-nip press section with a steam box before the fourth nip.The dryness after the press section is lower than in the reference mill; about46%.
The water consumption is higher, thereby giving a higher cost for heating
The total consumption of electric energy is higher than the model mill; about700 kWh/t.
Table 5-5 summarizes consumption data for the papermachine.
8.3 ton/ADt 7.8 ton/ADt 8.3 ton/ADt 4.9 ton/ADt
0.4 ton/ADt 0.2 ton/ADt 0.9 ton/ADt 0.4 ton/ADt 0.01 ton/ADt
4.4 ton/ADt 8.1 ton/ADt 9.1 ton/ADt 1.8 ton/ADt
To effluent
treatment
To effluent
treatment
To effluent
treatmentTo effluent
treatment
To D1-filter
D2D1OPD0
H20 H20 D2-filtrate H20
Integrated fine paper mill Page 4620 January 2011
Table 5-5. Paper machine consumption data – Model mill vs Type mill
Model Type
Dryness to dryer % 52 46
Paper dryness % 93 93
Evaporated t/t paper 0.82 1.06
Redrying etc % 10 10
Total evaporation t/t paper 1.26 1.50
Heat consumption GJ/t evap. 3.0 3.0
Heat consumption drying GJ/t paper 3.77 4.51
Heat consumption miscellaneous GJ/t paper 0.46 0.46
Total heat consumption paper mill GJ/t paper 4.23 4.97
Power consumption incl. refining kWh/t paper 550 700
Water consumption m3/t paper 6.0 10
5.1.6 Evaporation
The capacity of existing evaporation plants can easily be increased in smallsteps by adding new evaporator bodies. Earlier most evaporation plants werebuilt with five-effect economy. After increasing the evaporation plant manyexisting mills therefore have a combination of five- and six-effect economy. Forthe type mill it is assumed that the evaporation plant on average operates with5.5 effect economy. The strong liquor from the evaporation plant has 72% drysolids content and only LP-steam is used for the evaporation.
A stripper for the evaporation plant is nowadays standard, but has not alwaysbeen. Many strippers today are therefore not fully integrated in the evaporationplant, some are completely separate and some recover the steam partly in theevaporation plant. Also only the most contaminated condensate is stripped. Thetype mill has a separate stripper for 2 m3/ADt.
5.1.7 Recovery boiler
The recovery boiler in the type mill does not have flue gas cooling as in themodel mill.
The type mill has a conventional combustion air system where approximately85% of the combustion air is heated to 165oC (compared to preheating of 100%of the combustion air to 205oC in the model mill).
The type mill has a feedwater temperature of 125oC, compared to the modelmill where feedwater is preheated from 146oC to 175oC.
Integrated fine paper mill Page 4720 January 2011
The soot blowing steam is extracted from the recovery boiler directly and notfrom the turbine. Due to the assumed high load on the recovery boiler the steamconsumption for the soot blowing is increased from 1 to 1.5 GJ/ADt.
5.1.8 Lime kiln
The lime mud has a dryness of 70% and the lime kiln is fired with mineral oil.
5.1.9 Power boiler
With higher steam consumption in the type mill compared to the model mill,wood fuel must be purchased for the power boiler. There is no bark press andthe bark is fired at 40% dryness.
5.1.10 Steam turbines and steam distribution
The very clearly dominating data for the HP-steam in typical mills in Swedentoday is 60 bar and 450ºC. Some mills operated at 40 bar and in Finland 80 baris also common. The type mill uses 60 bar and 450°C.
The MP-steam pressure in the mill is normally set according to the demandsfrom the digester. The model mill has a modern digester with low cookingtemperature. Older digesters like the one chosen for the type mill, which areoften overloaded, need higher cooking temperatures. The MP-steam pressure istherefore increased from 9 to 10 bar(g) in the typical mill.
The common feedwater temperature of 125ºC is used in the type mill comparedto 146oC in the model mill.
Typical mill have increased production over the years with debottleneckingmeasures and the steam turbines have consequently become too small to takecare of all the steam. Part of the HP-steam must therefore be reduced directly tolower pressures by pressure reducing valves, PRVs. The efficiency of theturbine is also lower than for modern turbines, due both to wear and lessoriginal efficiency.
When the typical mill was originally built there was no steam surplus fromliquor and falling bark, and therefore no condensing turbine.
Integrated fine paper mill Page 4820 January 2011
5.2 Energy balance comparison – Model mill vs type mill
Steam and power balances, as well as bark balance for the model mill arecompared to the type mill from the FRAM project in Table 5-6 to Table 5-11.
Table 5-6. Steam balance, GJ/ADt pulp
Softwood HardwoodConsumption Model Type Model TypeRecovery boiler soot blowing 1.02 1.71 0.85 1.31Recovery boiler blow down 0.05 0.03 0.04 0.03Power boiler 0.02 0.01 0.04 0.01Woodyard 0.00 0.14 0.00 0.13Digester 1.55 2.57 1.38 2.09Oxygen stage 0.08 0.18 0.08 0.21Bleaching 0.22 0.35 0.58 0.40Paper machine 6.62 7.79 5.30 6.20Evaporation 3.49 4.45 3.04 3.97Stripper 0.00 0.54 0.00 0.53Chemical preparation 0.10 0.10 0.10 0.07Causticising 0.00 0.05 0.00 0.05Hot water production 0.00 0.37 0.00 0.36Heating etc 0.00 0.09 0.00 0.07Miscellaneous, losses 0.45 0.66 0.39 0.59Total process consumption 13.61 19.03 11.80 16.05
Surplus steam (blow off LP) 0.00 0.00 0.00 0.00Back-pressure turbine 4.30 3.14 3.72 2.34Condensing turbine 1.78 1.98Total consumption 19.69 22.17 17.50 18.40
ProductionRecovery boiler 17.82 16.77 14.71 14.01Bark boiler 1.53 4.89 2.43 3.94Secondary heat 0.35 0.51 0.36 0.45Total production 19.69 22.17 17.50 18.40
Integrated fine paper mill Page 4920 January 2011
Table 5-7. Steam balance, (GJ/t paper).
Softwood HardwoodConsumption Model Type Model TypeRecovery boiler soot blowing 0.65 1.09 0.68 1.04Recovery boiler blow down 0.03 0.02 0.03 0.02Power boiler 0.01 0.01 0.03 0.01Woodyard 0.00 0.09 0.00 0.10Digester 0.99 1.64 1.10 1.66Oxygen stage 0.05 0.11 0.06 0.17Bleaching 0.14 0.22 0.46 0.32Paper machine 4.23 4.96 4.23 4.94Evaporation 2.23 2.83 2.43 3.16Stripper 0.00 0.34 0.00 0.42Chemical preparation 0.06 0.06 0.08 0.06Causticising 0.00 0.03 0.00 0.04Hot water production 0.00 0.24 0.00 0.29Heating etc 0.00 0.06 0.00 0.06Miscellaneous, losses 0.29 0.42 0.31 0.47Total process consumption 8.70 12.12 9.42 12.78
Surplus steam (blow off LP) 0.00 0.00 0.00 0.00Back-pressure turbine 2.75 2.00 2.97 1.86Condensing turbine 1.14 0.00 1.58 0.00Total consumption 12.59 14.12 13.98 14.65
Production
Recovery boiler 11.39 10.68 11.75 11.15Bark boiler 0.98 3.11 1.94 3.14Secondary heat 0.22 0.32 0.29 0.36Total production 12.59 14.12 13.98 14.65
Integrated fine paper mill Page 5020 January 2011
Table 5-8. Power balance, kWh/ADt pulp
Softwood Hardwood
Power consumption Model Type Model Type
Wood yard 45 45 40 40
Digester 44 44 39 39
Washing and screening 60 90 54 80
Oxygen stage 60 80 54 72
Bleaching 80 100 72 89
Final screening 45 45 689 40
Paper machine 861 939 125 756
Evaporation 27 30 24 25
Causticising, lime kiln incl. fuel gasifier 59 30 40 24
Boiler house 80 100 64 80
Cooling tower etc 20 0 12 0
Raw water treatment and distribution 17 22 15 20
Effluent treatment 17 30 15 27
Chem preparation 10 10 9 9
Miscellaneous, losses 30 35 24 28
Sum 1455 1600 1191 1329
Sold power 0 0 0 0
Total 1455 1600 1191 1329
Power production
Back-pressure power 1152 829 998 631
Condensing power 174 0 194 0
Bought power 128 771 0 698
Sum 1455 1600 1191 1329
Integrated fine paper mill Page 5120 January 2011
Table 5-9. Power balance, kWh/t paper
Softwood Hardwood
Power consumption Model Type Model Type
Wood yard 29 29 32 32
Digester 28 28 31 31
Washing and screening 38 57 43 64
Oxygen stage 38 51 43 57
Bleaching 51 64 58 71
Final screening 29 29 550 32
Pulp machine 550 598 100 602
Evaporation 17 19 19 20
Causticising, lime kiln incl. fuel gasifier 38 19 32 19
Boiler house 51 64 51 64
Cooling tower etc 13 0 10 0
Raw water treatment and distribution 11 14 12 16
Effluent treatment 11 19 12 21
Chem preparation 6 6 7 7
Miscellaneous, losses 19 22 19 22
Sum 930 1019 951 1058
Sold power 0 0 0 0
Total 930 1019 951 1058
Power production
Back-pressure power 736 528 797 502
Condensing power 111 0 155 0
Bought power 82 491 0 556
Sum 930 1019 951 1058
Table 5-10. Bark balance, DS t/ADt pulp.
Softwood Hardwood
Model Type Model Type
Bark from woodyard 0.210 0.196 0.257 0.240
Bark to lime kiln 0.101 0.000 0.084 0.000
Remaining bark 0.109 0.196 0.173 0.240
Purchased bark 0 0.182 0 0.063
Bark to bark boiler 0.109 0.376 0.173 0.303
Integrated fine paper mill Page 5220 January 2011
Table 5-11. Bark balance, DS t/t paper.
Softwood Hardwood
Model Type Model Type
Bark from woodyard 0.134 0.125 0.205 0.191
Bark to lime kiln 0.065 0.000 0.067 0.000
Remaining bark 0.070 0.125 0.138 0.191
Sold bark 0.000 0.116 0.000 0.050
Bark to bark boiler 0.070 0.239 0.138 0.241
Integrated fine paper mill Page 5320 January 2011
6 References
Delin L, Berglin N, Sivård Å, Samuelsson Å, Backlund B, Lundström A,”Bleached market kraft pulp mill”, Report FRAM 09, 2004
Delin L, Berglin N, Eriksson T, Andersson R, Sivård Å, Samuelsson Å,Backlund B, Lundström A, Åberg M, ”Integrated fine paper mill”, ReportFRAM 10, 2004
Delin L, Berglin N, Eriksson T, Andersson R, Sivård Å, Åberg M, ”Kraftlinerreference mill”, Report FRAM 11, 2003
Delin L, Stenberg E, Lundström A, Sivard Å, Åberg M, ”Magazine paper mill”,Report FRAM 12, 2004
Wiberg, R “Energiförbrukning I mass- och pappersindustrin 2007”, SkogsIndustrierna rapport, 2007
Wiberg, R “Energiförbrukning I mass- och pappersindustrin 2000”, SkogsIndustrierna rapport, 2000
Model mill - Softwood bleached kraft pulpPRODUCTION DESIGN BASIS:
OPERATING DAYS PER YEAR
MILL EFFICIENCY
AVERAGE DAILY PRODUCTION
PULP MILL CAPACITY, MCR
ANNUAL PULP PRODUCTION
WHITE NCG BLACK LIQUOR ALKALI as NaOH O 2 ClO2 H2SO4 H2O2 SO2
LIQUOR NaOH O 2 MgSO4
LOSS AS WHITE LIQUOR
WHITE LIQUOR
NCG METHANOL
Storage losses
Screen Losses 90% CaO
BYPRODUCT SALT CAKE (Na2SO4)
CaCO3 CaO
SAW MILL CHIPS
MeOH H2SO4 NaClO3
Losses
TO BIOMASS BOILER
ROUNDWOOD
WOOD SUPPLY DIGESTER AND OXYGEN DELIGNIFICATION PULP YIELD AND LOSSES WHITE LIQUOR SPECIFICATION BLEACH AND CHEMICAL PLANTS
Pine Kappa out of digester
Spruce EA to digester, as NaOH kg/ADt t/d t/ADt t/d
AA to digester, as NaOH Chip storage Na ClO 2 H2SO4
Roundwood with bark Knotted, unscreened yield Chip screen K NaOH CH 3OH
Bark on unbarked logs Digester S O2 NaClO3
Saw mill chips Kappa out if O2 stage Knots OH-H2O2
Solid wood density Total alkali to O2 delig., NaOH Reject HS-H2SO4
Moisture O2 to oxygen delig. Oxygen delig. S2O32- SO2 ÅF Engineering, Forest Industry
MgSO4 to oxygen delig. Bleaching SO42-
STOCKHOLM
Lignin in wood Final screen CO32-
SWEDEN
Cl in wood Dilution factor, brownstock wash Total yield AA OVERALL MATERIAL BALANCE, MCR
K in wood (from dig feed) TTA Bleached Softwood
S in wood EA
Extractives in wood %SULPHIDITY ON AA PROJECT
Model mills 2010
DRAWING v. 1.0
19 BDt/d
1933 BDt/d 1914 BDt/d 1913 BDt/d 1840 BDt/d
355 d/a
92%
1840 ADt/d
2000 ADt/d
KNOTS
653200 ADt/a
1,0% 0,1 % REJ.
21 905 t/d 1,0 BDt/d
7 085 m3/d 16,0 %
1840 BDt/d 1804 BDt/d 1800 BDt/d
2148 ADt/d 2127 ADt/d 2126 ADt/d 2045 ADt/d 2045 ADt/d 2004 ADt/d2000 ADt/d
0,5% REBURNT LIME WEAK WASH 3 477 t/d DS
50,0 t/d 41 t/d 5 t/d
14 m3/d
443 m3/d
4 072 BDt/d
771 t/h evap
20 BDt/d 534 t/d 79 %
4 BDt/d
MUD GREEN LIQ. VIRGIN DS
14,0 MJ/kg DS
BLEACH PLANT CHLORIDE DIOXIDE PLANT
2,0%
400 BDt/d 420 BDt/d
3 268 BDt/d
4 097 BDt/d
1 229 BDt/d
50% 20,0 % % % g/L ACTUAL g/L as NaOH
50% 30 YIELD LOSSES
11,0
70 % 47,0 % 0,5 3,8 22,0 44,0 0,20 2,8
24,2 % 0,1 93,4 6,9 13,8 0,80
4,0 8,0
420 kg/m3 25 kg/ADt 0,1 20,2 15,0 30,0
22,1
30 % 12 1,0 49,1 4,0 8,0
11 % 47,0 21,8 6,0 12,0 1,6
2 kg/ADt 98,0 3,3
27,5% 0,2 15,0
50,0 % 20 kg/ADt 96,2 1,9
20100426
80 mg/kg DS 115,5 2000 ADt/d
3,0% 35%
60 mg/kg DS 2,50 44,2 140,0
400 mg/kg DS 160,0
SODIUMCHLORATEHANDLING
CAUSTICIZINGPLANT
RECOVERYBOILER
CHLORINEDIOXIDE PLANT
MgSO4HANDLING
EVAPORATIONPLANT
WHITELIQUOR
OXIDATION
METHANOLHANDLING
SULPHURICACID
HANDLING
HYDROGENPEROXIDEHANDLING
OXYGENHANDLING
CAUSTICHANDLING
D(EPO)DP
BLEACH PLANT
PRESSUREKNOTTERS
DIGESTERPLANT
PRESSURESCREENS
OXYGENDELIGNIFI-
CATIONHD-STORAGE,
TO PULP MACHINE
POST-OXYGENWASHING
BLOWTANK
PRE-OXYGENWASHING
BR
OW
NS
TO
CK
ST
OR
AG
E
LIME KILN
CHIP STORAGE& SCREENING
DE-BARKING &CHIPPING
SO2 HANDLINGPURCHASEDLIMESTONEHANDLING
PURCHASEDLIME
HANDLING
CAUSTICHANDLING
SULF8_1 model mills 2010.xlsm
Model mill - Bleached hardwood pulpPRODUCTION DESIGN BASIS:
OPERATING DAYS PER YEAR
MILL EFFICIENCY
AVERAGE DAILY PRODUCTION
PULP MILL CAPACITY, MCR
ANNUAL PULP PRODUCTION
WHITE NCG BLACK LIQUOR ALKALI as NaOH O 2 ClO2 H2SO4 H2O2 SO2
LIQUOR NaOH O 2 MgSO4
LOSS AS WHITE LIQUOR
WHITE LIQUOR
NCG METHANOL
Storage losses
Screen Losses 90% CaO
BYPRODUCT SALT CAKE (Na2SO4)
CaCO3 CaO Ash
SAW MILL CHIPS
MeOH H2SO4 NaClO3
Losses
TO BIOMASS BOILER
ROUNDWOOD
WOOD SUPPLY DIGESTER AND OXYGEN DELIGNIFICATION PULP YIELD AND LOSSES WHITE LIQUOR SPECIFICATION BLEACH AND CHEMICAL PLANTS
Birch Kappa out of digester
Other hardwoods EA to digester, as NaOH kg/ADt t/d t/ADt t/d
AA to digester, as NaOH Chip storage Na ClO 2 H2SO4
Roundwood with bark Knotted, unscreened yield Chip screen K NaOH CH 3OH
Bark on unbarked logs Digester S O2 NaClO3
Saw mill chips Kappa out if O2 stage Knots OH-H2O2
Solid wood density Total alkali to O2 delig., NaOH Reject HS-H2SO4
Moisture O2 to oxygen delig. Oxygen delig. S2O32- SO2 ÅF Engineering, Forest Industry
MgSO4 to oxygen delig. Bleaching SO42-
STOCKHOLM
Lignin in wood Final screen CO32-
SWEDEN
Cl in wood Dilution factor, brownstock wash Total yield AA OVERALL MATERIAL BALANCE, MCR
K in wood (from dig feed) TTA Hardwood
S in wood EA
Extractives in wood %SULPHIDITY ON AA PROJECT
Model mills 2010
DRAWING v. 1.0
19 BDt/d
2370 BDt/d 2351 BDt/d 2350 BDt/d 2312 BDt/d
355 d/a
92%
2300 ADt/d
2500 ADt/d
816500 ADt/a
KNOTS
0,8% 0,1 % REJ.
23 545 t/d 1,2 BDt/d
7 414 m3/d 15,7 %
2312 BDt/d 2255 BDt/d 2250 BDt/d
2633 ADt/d 2612 ADt/d 2611 ADt/d 2569 ADt/d 2569 ADt/d 2505 ADt/d2500 ADt/d
0,5% REBURNT LIME WEAK WASH 3 668 t/d DS
45,0 t/d 36 t/d 3 t/d
17 m3/d
400 m3/d
4 610 BDt/d
840 t/h evap
23 BDt/d 554 t/d 79 %
9 BDt/d
MUD GREEN LIQ. VIRGIN DS
14,0 MJ/kg DS
0 BDt/d
2,0%
619 BDt/d 642 BDt/d
5 261 BDt/d
4 642 BDt/d
0 t/d
CHLORIDE DIOXIDE PLANT
10% 18,5 % % % g/L ACTUAL g/L as NaOH
90% 17 YIELD LOSSES BLEACH PLANT
13,8
100 % 51,0 % 0,5 6,2 22,0 55,0 0,20 3,5
22,4 % 0,2 92,7 6,9 17,3 0,80
4,0 10,0
495 kg/m3 18 kg/ADt 0,1 20,2 15,0 37,5
27,6
0 % 12 0,8 49,1 4,0 10,0
11 % 51,0 21,8 6,0 15,0 1,6
1 kg/ADt 97,5 3,3
22,0% 0,2 15,0
45,0 % 14 kg/ADt 98,4 1,9
20100426
80 mg/kg DS 115,5 2500 ADt/d
2,5% 35%
150 mg/kg DS 2,50 48,8 140,0
450 mg/kg DS 160,0
SODIUMCHLORATEHANDLING
CAUSTICIZINGPLANT
RECOVERYBOILER
CHLORINEDIOXIDE PLANT
MgSO4HANDLING
EVAPORATIONPLANT
WHITELIQUOR
OXIDATION
METHANOLHANDLING
SULPHURICACID
HANDLING
HYDROGENPEROXIDEHANDLING
OXYGENHANDLING
CAUSTICHANDLING
D(EPO)DP
BLEACH PLANT
PRESSUREKNOTTERS
DIGESTERPLANT
PRESSURESCREENS
OXYGENDELIGNIFI-
CATIONHD-STORAGE,
TO PULP MACHINE
POST-OXYGENWASHING
BLOWTANK
PRE-OXYGENWASHING
BR
OW
NS
TO
CK
ST
OR
AG
E
LIME KILN
CHIP STORAGE& SCREENING
DE-BARKING &CHIPPING
SO2 HANDLINGPURCHASEDLIMESTONEHANDLING
PURCHASEDLIME
HANDLING
CAUSTICHANDLING
CP
ENERGY BALANCE Model Fine paper SW campaign
ASSUMPTIONS Enthalpy etc Temp Pressure°C bar(g)
Make-up water before preheating kJ/kg 63 15Make-up water, preheated by sec heat °C 315 75Turbine cond., preheated by sec heat kJ/kg 315 75Feedwater to boilers kJ/kg 622 146HP-steam kJ/kg 3386 505 100,0MP2-steam, desuperheated kJ/kg 2944 275 25,0MP-steam, desuperheated kJ/kg 2827 200 9,0LP-steam, desuperheated kJ/kg 2748 150 3,5Mech./el efficiency turbine 0,97
ADt/dProduced pulp, MCR 2000of which softwood 2000of which hardwood 0
Market pulp 0Paper machine 3130
EnerbalNew JTLDn6.xlsmSteamBal1
STEAM CONSUMPTION Steam Condensate HeatFlow Temp Flow Effect
t/h °C t/h MWHP-steamBack-pressure turbine 99,5MP2-steam (62,6)MP-steam (111,4)LP-steam (420,4)
Condensing turbine 41,3condensing steam 46,7 35 46,7
Direct reduction HP-MP (0,0)Direct reduction HP-LP (0,0)Soot blowing recovery boiler 0,0 0,0 0,0Blow down recovery boiler 3,0 0,0 1,1Soot blowing bark boiler 0,0 0,0 0,0Blow down bark boiler 0,2 0,0 0,1Total HP-steam 50,0 46,7 142,0
MP2-steamSoot blowing recovery boiler 29,6 0,0 23,7Air preheater recovery boiler 18,3 160 18,3 (11,6)Feedwater interheater 17,8 200 17,8 (10,4)Soot blowing power boiler 0,5 0,0 0,4Total MP2-steam 66,2 36,1 24,1
MP-steamAir preheater recovery boiler 0,0 170 0,0 (0,0)Air preheater bark boiler 1,7 170 1,7 (1,0)Feedwater preheater 35,9 180 35,9 (20,6)Digesting 46,7 170 0,0 35,8Bleaching 6,7 180 0,0 5,1Oxygen stage 2,5 100 0,0 1,9Evaporation 15,4 140 14,6 9,7Chemical preparation 0,8 100 0,0 0,6Paper machine 0,0 100 0,0 0,0Miscellaneous, losses 3,4 100 1,0 2,5Total MT-ånga 113,1 53,3 55,7
LP-steamAir preheater recovery boiler 0,0 148 0,0 (0,0)Air preheater bark boiler 2,5 148 2,5 (1,5)Smelt shattering 0,0 0,0 0,0Woodyard 0,0 0,0 0,0Digesting 0,0 0,0 0,0Bleaching 0,0 0,0 0,0Evaporation 117,2 140 111,3 71,2Chemical preparation 2,5 100 2,0 1,7Causticising 0,0 100 0,0 0,0Paper machine 237,4 105 225,5 153,3Heating etc 0,0 100 0,0 0,0Blow off 0,0 100 0,0 0,0Miscellaneous, losses 11,1 100 3,3 8,0Steam to feedwater tank 45,4 45,4Total LP-steam 416,0 390,0 234,1
EnerbalNew JTLDn6.xlsmSteamBal2
Steam Condensate HeatSUMMARY STEAM CONSUMPTION Flow Temp Flow Effect
t/h °C t/h MWHP-steam 50,0 46,7 142,0MP2-steam 66,2 36,1 24,1MP-steam 113,1 167 53,3 55,7LP-steam 416,0 117 390,0 234,1Make-up water 119,1TOTAL STEAM CONSUMPTION 645,3 645,3 455,9
STEAM PRODUCTION Flow Effectt/h MW
Recovery boiler t/ADtHP-steam 7,10 591,8 454,5soot blowing 0,0 0,0blow down 3,0 0,6feedwater preheat MP -20,6feedwater preheat MP2, inter eco -10,4air preheating, LP-steam 0,0air preheating, MP-steam 0,0air preheating, MP2-steam -11,6
Sum 594,8 412,5Extern överhettare 0,0
Bark boiler t/ADtHP-steam 0,59 49,3 37,8soot blowing 0,0 0,0blow down 0,2 0,1air preheating, LP-steam -1,5air preheating, MP-steam -1,0
Sum 49,5 35,4
MP-steam from boilers 0,0 0,0desuperheating water MP2-steam 3,6desuperheating water MP-steam 1,7drainage water LP-steam -4,4Secondary heat for preheating make-up water 8,0TOTAL STEAM PRODUCTION 645,3 455,9
POWER CONSUMPTION kWh/ADt MWWood yard 45 3,8Digester 44 3,7Washing and screening 60 5,0Oxygen stage 60 5,0Bleaching 80 6,7Final screening 45 3,8Paper machine 861 71,7Evaporation 27 2,3Causticising, lime kiln incl. fuel gasifier 59 5,0Boiler house 80 6,7Cooling tower etc 20 1,7Raw water treatment and distribution 17 1,4Effluent treatment 17 1,4Chem preparation 10 0,8Miscellaneous, losses 30 2,5
Sum 1455 121,3Sold power 0 0,0Total 1455 121,3
POWER PRODUCTIONBack-presssure power 1152 96,0Condensing power 174 14,5Bought power 128 10,7
Sum 1455 121,3
EnerbalNew JTLDn6.xlsmSteamBal3
ENERGY BALANCE Model Fine paper HW campaign
ASSUMPTIONS Enthalpy etc Temp Pressure°C bar(g)
Make-up water before preheating kJ/kg 63 15Make-up water, preheated by sec heat °C 315 75Turbine cond., preheated by sec heat kJ/kg 315 75Feedwater to boilers kJ/kg 622 146HP-steam kJ/kg 3386 505 100,0MP2-steam, desuperheated kJ/kg 2944 275 25,0MP-steam, desuperheated kJ/kg 2827 200 9,0LP-steam, desuperheated kJ/kg 2748 150 3,5Mech./el efficiency turbine 0,97
ADt/dProduced pulp, MCR 2500of which softwood 0of which hardwood 2500
Market pulp 0Paper machine 3130
EnerbalNew JTLDn6.xlsmSteamBal1
STEAM CONSUMPTION Steam Condensate HeatFlow Temp Flow Effect
t/h °C t/h MWHP-steamBack-pressure turbine 107,7MP2-steam (66,0)MP-steam (137,5)LP-steam (440,9)
Condensing turbine 57,3condensing steam 64,9 35 64,9
Direct reduction HP-MP (0,0)Direct reduction HP-LP (0,0)Soot blowing recovery boiler 0,0 0,0 0,0Blow down recovery boiler 3,1 0,0 1,1Soot blowing bark boiler 0,0 0,0 0,0Blow down bark boiler 0,5 0,0 0,2Total HP-steam 68,4 64,9 166,3
MP2-steamSoot blowing recovery boiler 30,6 0,0 24,5Air preheater recovery boiler 19,8 160 19,8 (12,5)Feedwater interheater 18,4 200 18,4 (10,8)Soot blowing power boiler 1,0 0,0 0,8Total MP2-steam 69,7 38,2 25,2
MP-steamAir preheater recovery boiler 0,0 170 0,0 (0,0)Air preheater bark boiler 3,4 170 3,4 (2,0)Feedwater preheater 37,1 180 37,1 (21,3)Digesting 52,1 170 0,0 40,0Bleaching 21,9 180 0,0 16,8Oxygen stage 3,1 100 0,0 2,4Evaporation 16,8 140 16,0 10,6Chemical preparation 1,0 100 0,0 0,8Paper machine 0,0 100 0,0 0,0Miscellaneous, losses 4,2 100 1,3 3,1Total MT-ånga 139,6 57,7 73,6
LP-steamAir preheater recovery boiler 0,0 148 0,0 (0,0)Air preheater bark boiler 4,9 148 4,9 (2,9)Smelt shattering 0,0 0,0 0,0Woodyard 0,0 0,0 0,0Digesting 0,0 0,0 0,0Bleaching 0,0 0,0 0,0Evaporation 127,7 140 121,3 77,5Chemical preparation 3,1 100 2,5 2,1Causticising 0,0 100 0,0 0,0Paper machine 237,4 105 225,5 153,3Heating etc 0,0 100 0,0 0,0Blow off 0,0 100 0,0 0,0Miscellaneous, losses 11,5 100 3,5 8,3Steam to feedwater tank 51,8 51,8Total LP-steam 436,4 409,4 241,2
EnerbalNew JTLDn6.xlsmSteamBal2
Steam Condensate HeatSUMMARY STEAM CONSUMPTION Flow Temp Flow Effect
t/h °C t/h MWHP-steam 68,4 64,9 166,3MP2-steam 69,7 38,2 25,2MP-steam 139,6 167 57,7 73,6LP-steam 436,4 117 409,4 241,2Make-up water 144,0TOTAL STEAM CONSUMPTION 714,1 714,1 506,4
STEAM PRODUCTION Flow Effectt/h MW
Recovery boiler t/ADtHP-steam 5,87 611,4 469,5soot blowing 0,0 0,0blow down 3,1 0,6feedwater preheat MP -21,3feedwater preheat MP2, inter eco -10,8air preheating, LP-steam 0,0air preheating, MP-steam 0,0air preheating, MP2-steam -12,5
Sum 614,4 425,6Extern överhettare 0,0
Bark boiler t/ADtHP-steam 0,94 97,8 75,1soot blowing 0,0 0,0blow down 0,5 0,1air preheating, LP-steam -2,9air preheating, MP-steam -2,0
Sum 98,3 70,3
MP-steam from boilers 0,0 0,0desuperheating water MP2-steam 3,8desuperheating water MP-steam 2,1drainage water LP-steam -4,6Secondary heat for preheating make-up water 10,5TOTAL STEAM PRODUCTION 714,1 506,4
POWER CONSUMPTION kWh/ADt MWWood yard 40 4,2Digester 39 4,1Washing and screening 54 5,6Oxygen stage 54 5,6Bleaching 72 7,5Final screening 40 4,2Paper machine 689 71,7Evaporation 24 2,5Causticising, lime kiln incl. fuel gasifier 40 4,1Boiler house 64 6,6Cooling tower etc 12 1,3Raw water treatment and distribution 15 1,6Effluent treatment 15 1,6Chem preparation 9 1,0Miscellaneous, losses 24 2,5
Sum 1191 124,0Sold power 1 0,1Total 1191 124,1
POWER PRODUCTIONBack-presssure power 998 103,9Condensing power 194 20,2Bought power 0 0,0
Sum 1191 124,1
EnerbalNew JTLDn6.xlsmSteamBal3
1
4,0 4,0
1,3 1,0
9,4 0,0 1,0
1,4
24,3
18 °C 39,6 3,49 GJ/ADt 50 °C 4,1 1,8 1,0
55,4 29 °C 65 °C 0,19 GJ/ADt 90 °C 5,3 10,5
15,6 0,26 GJ/ADt 3,1
1,13 GJ/ADt
0,0
1,9 0,00 GJ/ADt 0,0
45,4 1,6
0,93 GJ/ADt 0,12 GJ/ADt 3,6 4,5 7,3
5,5
109,3 0,38 GJ/ADt
8,4 0,0
0,17 GJ/ADt 0,0 3,9
0,00 GJ/ADt
15,6 0,0 4,3
0,32 GJ/ADt 0,6 0,0
0,05 GJ/ADt
1,1 110,4
25 °C 29 °C 0,35 GJ/ADt 50 °C
2,46 GJ/ADt
1,13 GJ/ADt
35 °C
Total
t/ADt Water consumption 24,3
Water balance °C Total effluent 22,2
Warm and hotwater 22,2 35 °C
Model Fine paper SW campaign, SW
3,3
Cooling liquor tohiheat wash
Evaporation Terpentinecondenser
Turbinecondenser
Cooling liquor toevaporation
Diss. Tankcondenser
Cooling bleachfiltrate
CoolingO2-filtrate
Cooling tower
Bleaching
Paper machine
Liquor
Causticising
Cooling tower
Misc. cooling
Chemicalpreparation
Make-upBoilers
Preheatingcondensate andmake-up water
ClO2
Misc.
Pulp wash
Effluent treatment
Cooling HC-tower
Bleachcooling
Wood yard
Building heating
Printed 2010-07-08
1
4,0 4,0
1,5 1,0
8,2 0,0 1,0
1,4
23,1
18 °C 34,5 3,04 GJ/ADt 50 °C 3,2 1,8 0,8
63,4 29 °C 65 °C 0,19 GJ/ADt 89 °C 4,2 8,6
14,5 0,20 GJ/ADt 2,5
1,26 GJ/ADt
0,0
3,7 0,00 GJ/ADt 0,0
40,3 2,6
0,80 GJ/ADt 0,23 GJ/ADt 3,8 4,0 7,2
4,9
124,1 0,40 GJ/ADt
9,2 0,0
0,18 GJ/ADt 0,0 3,3
0,00 GJ/ADt
25,7 0,0 4,3
0,51 GJ/ADt 1,2 0,0
0,10 GJ/ADt
1,2 125,3
25 °C 29 °C 0,36 GJ/ADt 47 °C
2,67 GJ/ADt
0,98 GJ/ADt
35 °C
Total
t/ADt Water consumption 23,1
Water balance °C Total effluent 20,3
Warm and hotwater 20,3 35 °C
Model Fine paper HW campaign, HW
3,3
Cooling liquor tohiheat wash
Evaporation Terpentinecondenser
Turbinecondenser
Cooling liquor toevaporation
Diss. Tankcondenser
Cooling bleachfiltrate
CoolingO2-filtrate
Cooling tower
Bleaching
Paper machine
Liquor
Causticising
Cooling tower
Misc. cooling
Chemicalpreparation
Make-upBoilers
Preheatingcondensate andmake-up water
ClO2
Misc.
Pulp wash
Effluent treatment
Cooling HC-tower
Bleachcooling
Wood yard
Building heating
Printed 2010-07-08