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Cooking and bleaching equipment

Cooking equipment

1.  Flexible forced-circulation digester – 1 kg scale

A flexible digester-system where all modern pulping processes can be carried out with injections, withdrawal and displacement of cooking liquor/s at controlled compositions, temperatures and pressures. The digester-system consists of a digester (1 kg a d wood) with forced circulation and includes four liquor tanks; two with both internal steam heating coils and electrical heating. Two of the tanks can be pressurized to 20 bar. An atmospheric tank to simulate the counter-current cooking systems can also be connected to the digester. The system includes ceramic membranes that can be used for fractionation of black liquor at full cooking temperature.

The 1 kg flexible forced-circulation digester system can perform all types of pulping processes.

2. Equipment for simultaneous shearing and compression

The flexible forced-circulation digester system can be used in 500 g a.d. scale to study:

  • The impact of simultaneous shearing and compression forces for evaluating strength delivery losses in industrial pulping.
  • The impact of wood chip size distribution on liquor pressure drop during delignification.
  • The influence of chip column pressure on compaction of the chip column.
  • The effect of different raw material combinations on hydraulics and materials-exchange processes during delignification.

Beskrivning: Outline of digester

The impact on the pulp strength potential of shearing and compression forces during pulping can be studied.

3.  Digester with forced circulation – 2 kg scale

4.  Digester with forced circulation – 40 kg scale

Pilot digester for 40 kg a.d. wood or other biomass with forced circulation and 250 - 300 L liquid. Heating through indirect heat exchange liquor-steam. The main applications are to produce large volumes of cooking liquor and pre-treatment liquids in alkaline or acidic conditions as well as pulp fibres or other materials. Temperatures of up to 170°C and a liquor-to-wood ratio of 6:1 or higher.

Beskrivning: 40 kg batch digester

Large volumes of process liquors and/or fibre material can be produced in this steam-heated, forced-liquor circulation batch digester

5.  Flow-through digester – 200 g scale

A digester for 200 g a.d. wood, giving full control of the cooking liquor composition during the cook. We can thereby study the influence of e.g. liquor composition, ionic strength and sulphidity on pulp properties in each phase of the cook.

6.  Autoclaves – 5-300 g scale

Autoclaves of different sizes, from 5 to 300 g a.d. wood. The autoclaves are heated electrically or using indirect steam in a glycol bath.

Defibration of pulps with high kappa number

Pulps with a high kappa number can be defibrated in a laboratory scale Sprout Waldron refiner. The refining is mostly carried out in water at room temperature, but it is also possible to use other solutions and temperatures if desired, up to a maximum of 80°C. The refining slit is adjustable between 0.15 and 0.5 mm.

Oxygen delignification and bleaching equipment

Innventia has equipment for all types of laboratory scale bleaching of chemical pulp, for example:

  • Multi-stage oxygen delignification with different configurations
  • Bleaching using chlorine dioxide, hydrogen peroxide, ozoneperacetic acid, etc.
  • Bleaching using chlorine and hypochlorite

Oxygen delignification and hydrogen peroxide bleaching at high temperature (> 100 °C) and high pressure is carried out in rotating Teflon-coated autoclaves. Oxygen delignification can be performed with different multi-stage configurations.

For liquid bleaching stages (chlorine dioxide (D), hydrogen peroxide (P), peracetic acid (Paa)) and treatment with chelating agents (Q) at bleaching temperatures below 100 °C, the more conventional and established technique with polyethylene bags is used.

Ozonation at medium consistency, 10%, takes place in a high-shear mixer. Ozonation at high consistency, 40 %, takes place in different kinds of rotating vessels.

Technical data for the Innventia equipment for oxygen delignification and bleaching operations:



Pulp Sample


Max. temp.

Max. press.


High intensity mixer






Teflon coated, Water jacketed

Rotating vessels

1-3, 13

40, 200




Only ozone







Teflon coated, Polyglycol bath/electrically heated

Polyethylene bags






Water bath




Elisabeth Bergnor
08 676 7276
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A comparison of fibre deformations from mill like and laboratory kraft cooking of softwood
Salmén L, Hornatowska J
Nordic Pulp Paper Research J. 29(2014):2, 211-217


Sulphur-free process for dissolving pulp
Karlström K, Sjögren B, Kulander I
5th Nordic Wood Biorefinery Conference (NWBC), Stockholm, Sweden, March 25-27, 2014, Proceedings pp 253-254


Environmental performance of modern ECF bleaching
Axegård P, Bergnor E
Int. Pulp Bleaching Conference, Portland, OR, USA, Oct. 5-7, 2011, Proceedings pp 31


Salmén L. and Lundqvist F. (2011)
Effects of mechanical forces on strength delivery in softwood kraft cooking
Appita 64(1): 89-94.


Effects of mechanical forces on strength delivery in softwood kraft cooking
Salmén L, Lundqvist F
Appita 64(2011):1, 89-94


Impact of ionic strength on alkalinity during kraft cooking and impact on process economy
Lundqvist F, Olm L, Tormund D
ABTCP 2008, Sao Paulo, Brazil, Oct. 13-16, 2008


Continuous kraft cooking: research and applications
Annergren G, Lundqvist F
STFI-Packforsk, Stockholm 2008, 82 pp (ISBN 9789186018160)