Energy Consumption Reference

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.


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


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.


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


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.


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.


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


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


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


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.


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


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.


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.


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.


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.


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.


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.


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


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.


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


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.


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


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.


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.


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


-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


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


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


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


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.


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.


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


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.


Figure 3-11. Water treatment.

Al AirPolymer

Screen

Raw water intake

Raw water sludge

Clear waterwell

Dissolved airflotation

Sand filtration


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


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


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


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.


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


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


-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.


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


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


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.


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.


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


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


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


Bought power 128 771 0 698

Sum 1455 1600 1191 1329


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


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


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


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


A400744

TextBox

Appendix 2 - Softwood

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


A400744

TextBox

Appendix 2 - Softwood

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


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


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Appendix 2 - Hardwood

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


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Appendix 2 - Hardwood

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

Documents

Energy Consumption Reference