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Pulp & Paper

Nature in Every Fiber

Corrugated cardboard close-up. Paper industry

Paper production involves several key processes, beginning with the grinding of wood into pulp. This pulp is cleaned and processed into a mass that is then formed into paper sheets or rolls on special machines. Moisture, pressure and temperature are precisely controlled to achieve the desired paper properties.

What is the paper industry?

The pulp and paper industry is a major industry that produces paper and paper products from natural resources such as wood fiber. This industry plays a central role in our daily lives, providing the basis for a wide range of products, from newspapers to packaging and hygiene products.

The production of paper requires complex manufacturing processes that take into account both technological innovation and environmental concerns. In this context, the industry is also focusing on sustainability efforts and the responsible use of resources.

What is black liquor?

Black liquor is a byproduct of the pulp and paper industry that is generated during the production of pulp from wood fibers. It is a highly alkaline solution containing various chemical compounds such as lignin, inorganic salts, and other organic substances. Due to its high alkalinity and the impurities it contains, black liquor is harmful to the environment and requires careful treatment.

What happens to black liquor?

The papermaking process consists of four main parts. The first is the cooking process, which physically and chemically treats the wood. Second, cellulose and pulp production, and third, paper production in the paper machines. The remaining fourth part of this production is the black liquor treatment, a complex and costly process to reduce energy and environmental costs and make the entire paper production process economical.

Herstellung von Papier. Ein wesentlicher Teil des Prozesses beschäftigt sich mit der Aufbereitung der Schwarzlauge

Approximately seven tons of black liquor must be processed for each ton of pulp. It is concentrated to a higher dry mass in an evaporation process. The concentrated liquor is then injected into the recovery boiler where it is burned. This is the technical heart of black liquor processing, producing high-pressure steam that is fed to turbogenerators to reduce steam pressure for use in the mill and to generate electricity; it also recovers most of the valuable chemicals in several recovery stages.

During the incineration process, anhydrous sodium sulfate (Na₂SO₄) is reduced to sodium sulfide (Na₂S) by thermochemical reduction (Na₂SO₄ + 2C → Na₂S + 2CO₂).

The melt discharged at the bottom of the boiler is further recycled in recausticizing processes where sodium carbonate (Na₂CO₃), calcium carbonate (CaCO₃) and calcium oxide (CaO) are reacted to regenerate sodium hydroxide (NaOH).

White paper on a roll, slightly unrolled, you can see the individual strips
Paper mill

Non-Process Elements (NPE)

Remaining mineral residues from the combustion process, called non-process elements (NPE), which contain sodium, chloride and potassium compounds (Na₂SO₄, Na₂CO₃, NaCl, K₂SO₄, K₂CO₃ und KCl) must be separated to prevent corrosion and can be recycled to the preceding processes. The life of the recovery boiler is also extended by preventing deposits on the heat exchangers, thus avoiding unplanned downtime.

Soot blowers are used to clean and collect the mineral deposits from the heat exchangers. Electrostatic precipitators (ESPs) collect volatile salts from the air downstream of the combustion section that can clog the gas path heat exchangers of the recovery boiler. These mineral-rich streams can be treated in separate facilities.

ARC or CRP Mineral Recovery Processes

NPE recovery systems are either leaching or crystallization processes downstream of sootblowers and electrostatic precipitators to recover sodium carbonate (NaCO₃), chloride (Cl⁻) and potassium (K⁺) salts or to reduce their concentrations in the effluent stream.

Special ARC and CRP systems allow savings by recovering sodium carbonate (NaCO₃), anhydrous sodium sulfate (Na₂SO₄) or converting sulfates into saleable potassium sulfate (SOP oder K₂SO₄). SIEBTECHNIK TEMA pusher centrifuges or CONTURBEX centrifuges, usually made of high-alloy stainless steels, are used for the separation of 1000 kg/h to 30000 kg/h of NPE salts per machine, depending on the size of the recovery vessel.


Schubzentrifuge SHS in der Düngemittelproduktion
Schubzentrifuge SHS für Natriumsulfat in der Werkshalle in Mülheim an der Ruhr
CONTURBEX sieve screw centrifuge-for sodium carbonate or soda ash
CONTURBEX sieve screw centrifuge-for sodium carbonate or soda ash
Paper industry: CRP system with centrifuge for mixing salts containing sodium, chloride and potassium compounds (Na₂SO₄, Na₂CO₃, NaCl, K₂SO₄, K₂CO₃ and KCl)
CRP Plant with CONTURBEX centrifuge for the removal of mixed salts containing sodium, chloride and potassium compounds
CONTURBEX H250 sieve screw centrifuge in the paper industry - mixed salts containing sodium, chloride and potassium compounds (Na₂SO₄, Na₂CO₃, NaCl, K₂SO₄, K₂CO₃ and KCl)
CONTURBEX H250 sieve screw centrifuge - for separating mixed salts containing sodium, chloride and potassium compounds
CRP Plant - Ash & Chloride Removal - Pulp & Paper_Mixed salts containing sodium, chloride and potassium compounds (Na₂SO₄, Na₂CO₃, NaCl, K₂SO₄, K₂CO₃ and KCl
Mixed salts containing sodium, chloride and potassium compounds (Na₂SO₄, Na₂CO₃, NaCl, K₂SO₄, K₂CO₃ and KCl)
Screw screen centrifuge H450 in the paper industry - Application: Mixed salts containing sodium, chloride and potassium compounds (Na₂SO₄, Na₂CO₃, NaCl, K₂SO₄, K₂CO₃ and KCl)
Sieve screw centrifuge CONTURBEX H450 - for the separation of mixed salts containing sodium, chloride and potassium compounds

Wear Protection

SIEBTECHNIK TEMA centrifuges are specially optimized for the respective separation task. When selecting materials, austenitic and ferritic stainless steels have proven themselves in centrifuge construction for applications subject to normal stresses.

For processes in which abrasive materials are processed, the centrifuges must be provided with effective wear protection. Starting with hard coal processing, we have been continuously developing wear protection systems since 1922.

Our centrifuges can be equipped with highly developed wear protection systems made of e.g. tungsten carbide, Stellite® or ceramic tiles, to name but a few. Rubber coatings or matrix coatings have also proven themselves in various applications.

If required, our engineers develop new and efficient solutions in coating, bonding and joining technology for our customers worldwide.

Centrifuge Components Materials

Centrifuge components must not only withstand high forces, but also process-related stresses such as corrosion, wear and high temperatures. Cost and availability of materials also play an important role. Our customers select the necessary product-contacting materials according to these very specific requirements.

Duplex and high-alloy stainless steels, Hastelloy® and titanium materials for a wide variety of processes and stresses are part of our daily business in centrifuge construction. Our quality management has developed very detailed and cost effective processes for design, manufacturing processes and component testing based on European guidelines.

Typical sheet metal and forging materials for centrifuge wetted components include

  • EN 1.4404 / AISI 316L
  • EN 1.4571 / AISI 316Ti
  • EN 1.4462 / AISI 318LN / Duplex
  • EN 1.4410 / AISI F53 / Super Duplex
  • Lean Duplex
  • EN 1.4539 / AISI 904L
  • EN 1.4547 / 254SMO®
  • EN 1.4529 / AISI 926
  • EN 2.4819 / INCONEL® Alloy C-276
  • EN 2.4602 / Hastelloy® C22
  • EN 2.4610 / Hastelloy® C4
  • EN 3.7035 / Ti-II / Titan 994-Ti-grade 2
  • EN 3.7235 / Ti-IIPd / Titan 994 Pd-Ti-grade 7
  • and their casting materials
SIEBTECHNIK Siebschneckenzentrifuge CONTURBEX H700 für Lactose - Hallenansicht mit mehreren Maschinen

Screen scroll centrifuge CONTURBEX

The CONTURBEX is a continuously operating, filtering centrifuge with a very wide range of applications.

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Schubzentrifuge SHS in der Düngemittelproduktion

SHS pusher centrifuge

The SIEBTECHNIK TEMA SHS pusher centrifuge has established itself and proven itself as a modern high-performance unit in many industries.

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