kraft pulping past current & futurepast, current &...

Kraft Pulping Past Current & FuturePast, Current & Future

3rd Annual Light Green Machine Institute 3 d ua g t G ee ac e st tuteConference. Atlanta , 22 – 24 January 2012

A d Hj tAnders HjortMetso Paper Sweden AB

Karlstad, Sweden,

Continuous Cooking

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The continuous digesterPast – Current - FuturePast Current Future

Content• The development of the continuous digester• The first generation of digesters, ca 1950 – 1980

- Conventional cooking in single and two vessel digestersg g g

• Second generation, modified cooking, ca 1980 – 2000- MCC, EMCC, ITC, BLI, etc.

• Current ca 2000 ????• Current, ca 2000 - ????- Compact cooking- ImpBinTM

• M difi ti f ld di t• Modification of old digesters

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• Generation two. Modified cooking, ca 1980 – 2000- MCC, EMCC, ITC, BLI, etc.

• Current ca 2000 ????• Current, ca 2000 - ????- Compact cooking- ImpbinTM


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Those who did it!!!The inventors of the continuous digester ~ 1950 Kamyr AB Karlstad SwedenThe inventors of the continuous digester ~ 1950, Kamyr AB, Karlstad Sweden

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First pilot plant 1944 – Kalix, SwedenVersion 1Version 1

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First pilot plant 1944 – Kalix, SwedenVersion 2Version 2

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First working High Pressure Feeder

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Second generation High Pressure Feeder

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Modern High Pressure Feeder

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Conventional chip feeding system

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• Generation two. Modified cooking, ca 1980 – 2000- MCC, EMCC, ITC, BLI, etc.



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Digester types

Single vessel steam/liquor

Single vessel hydraulic

Two vessel hydraulic

Two vessel

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hydraulicsteam liquor

First reference list

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Typical continuous digester 1950 – 1980Typical operating figures:

• Cross sectional load 25 28 admt/m2 (2 3 2 6• Cross sectional load 25 – 28 admt/m2 (2.3 – 2.6 bdst/ft2)

• Cooking temperature soft wood 165 °C / 329 F

• Cooking temperature hard wood 160 °C / 320 FCooking temperature hard wood 160 C / 320 F

• Top pressure 7 bar(g) / (100 psig) steam phase type

• Top pressure 10 bar(g) / (145 psig) hydraulic type

• Residual alkali 6 8 g/l as EA• Residual alkali 6 – 8 g/l as EANaOH

• Wash factor 2 m3/admt (after 1960)

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Continuous Cooking Development

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The four rules – slightly modified

1. The alkali concentration should be as even as possible

2. The temperature should be low throughout the cook to minimise p gcarbohydrate degradation

3. The concentration of HS- should be as high as possible

4. The concentration of dissolved lignin has no negative effect as long as the alkali concentration is sufficiently high

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Two vessel S/L digester with MCCSoftwood exampleSoftwood example

Con current cookingCon current cooking158 oC / 316 F

C t t ki

Impregnation125 oC / 257 F

Counter current cooking162 oC / 324 F

Counter current washing135 oC / 275 F

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After MCC came ITC

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Two vessel S/L digester with MCC and ITCSoftwood exampleSoftwood example

Con current cookingCon current cooking156 oC / 313 F

C t t ki

Impregnation125 oC / 257 F

Counter current cooking zone 1156 oC / 313 F

Counter current cooking zone 2156oC / 313 F

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The development from 1960 – 1990SummarySummary

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By 1990 the complexity had reached it’s peak!Single vessel hydraulic digester with MCC & ITCSingle vessel hydraulic digester with MCC & ITC

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It was necessary to do something!!!Reduce the number of screens in the digester!Reduce the number of screens in the digester!

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• Current ca 2000 ????• Current, ca 2000 - ????- CompactCookingTM

- ImpbinTM


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Continuous cookingP hi h li iPushing the limits

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Continuous Cooking Development

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The four rules – slightly modified

1. The alkali concentration should be as even as possible

2. The temperature should be low throughout the cook to minimise carbohydrate degradation

3 Th t ti f HS h ld b hi h ibl3. The concentration of HS- should be as high as possible

4. The concentration of dissolved lignin has no negative effect as long as the alkali concentration is sufficiently highas the alkali concentration is sufficiently high

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ImpregnationRelative rates for diffusion and reactionRelative rates for diffusion and reaction

Th b t i ti iThe best impregnation is obtained by a low temperature and a long impregnation timeimpregnation time

Cooking chemicalsCooking chemicals penetrate the chip without being consumed.

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CompactCookingTM™ G2Alkali profilingAlkali profiling

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A short retention time – increased temperature

The H-factor contribution is increasing exponentially with an increased temperature. The increase is drastic when the temperature exceeds 165 °C

oC

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HS- concentration profiles

Recirculate black liquorAvoid dilution with wash liquorAvoid dilution with wash liquor

A high HS- concentration brings: Increased delignification rate

Decreased amount of residual phase lignin

Increased cooking selectivity

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CompactCookingTM™

R & D had shown:

• Alkali & HS- profiling is crucial• A low temperature is important for carbohydrate retention

The big question was: How do we do this?

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Which way to go?A two vessel system was chosenA two vessel system was chosen

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CompactCooking™

It was obvious that a two vessel digester must be used!

B t h d t th hi i t th di t ?But how do we get the chips into the digester?

Customers had started to ask for production levels unheard of before!!Customers had started to ask for production levels unheard of before!!

2000 t/d 3000 t/d 4000 t/d ????

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CompactCooking™

R d d ki (SW)Reduced cooking temperature (SW)

356 F

338 F

320 F

302 F

384 F

CompactCooking G2CompactCooking G2Optimizes the process conditions

Low cooking temperature

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Low cooking temperature

CompactCooking™ G2 – cooking developmentR d d i d i lReduced operating and capital costs

Comparison based on a HW 2500-3000 ADMT/24h cooking system.

MCC/ITC™ COMPACT COOKING™G1

COMPACT COOKING™G2

Rejects (%) ~1-2 ~0,5-1 <0,5

Power Consumption (kWh/admt) ~35 ~30 ~20Power Consumption (kWh/admt) 35 30 20

Steam Consumption (kg/admt) ~500 ~450 ~400

No. of Rotating Machines 25-28 20-22 11-13

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Conversion of an old hydraulic digester to CompactCooking™ G2CompactCooking G2The conventional feeding line is gone and so are the flash tanks. A pressure diffuser has been added to improve the washing.

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