The X-groups as part of the A-groups in spruce lignin.

The degree of sulfonation may be calculated as:

Degree of sulfonation _

Sulfur _S_

Methoxy groups _-OCH3_

The specific energy consumption affects the property of mechanical pulps, and

is at least 2 MWh t–1 o.d. pulp for strongly fibrillated TMP and CTMP pulps from

Spruce. The processing of pine chips increases specific energy consumption by

The data in Fig. 4.26 illustrates how strength properties are dependent

Upon on specific energy consumption. The so-called F-value in Fig. 4.26 is a

Mechanical Pulping Processes

Strength value that combines tensile strength and tear strength, according to the

following equation:

F-value = 10. breaking length (km) + 0.1. tear strength (mJ m–1)

Fig. 4.26 F-value (strength value) depending on specific

energy consumption (according to Suttinger [22]).

The refiner process is carried out mostly as a one- or two-stage process. In twostage

Processes, the main part of energy is used in the first stage. The defibration

Concentration in the refining zone of the first refining stage is of major importance

for the quality of the mechanical pulp, and should range from 20 to 45%,

with 25% as an optimal value.

As for grinding, spruce wood is also the most suitable raw material for refining,

Though pine or hardwood with a low density may also be used. Again as with

Grinding, a high wood moisture is needed for refining. The size distribution of

The wood chips should constitute only a small part of fines fraction, and they

Must be of a certain degree of purity. Sand and other minerals are abrasive for the

Refiner plates; hence, the wood chips are often washed before defibration.

4.2.3

Machines and Aggregates for Mechanical Pulping by Refining

Disc refiners of different construction are widely used in the refining procedure,

Mostly as single-disc or double-disc variants. Other commercially available

Designs include several types of large-capacity refiners, such as the Twin concept

Or conical disc concept.

Single-disc refiners have one fixed and one rotating disc (Fig. 4.27), while

Double-disc refiners have two counter-rotating discs (Fig. 4.28). Two types of largecapacity

TMP refiners are available: the Twin concept was introduced by Sprout

(today Andritz), and is characterized by two parallel single-disc refiner gaps (i.e.,

Three discs, with the center disc rotating and the outer discs fixed; see Fig. 4.29).

Refiner Processes

Somewhat later, Sunds Defibrator (today Metso) developed the RGP CD (= conical

Disc) system. Conical-disc refiners have a single-disc refining gap followed by

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