- •Isbn: 3-527-30999-3
- •Introduction
- •Isbn: 3-527-30999-3
- •1072 1 Introduction
- •Isbn: 3-527-30999-3
- •Inventor of stone groundwood. Right: the second version
- •1074 2 A Short History of Mechanical Pulping
- •In refining, the thinnings (diameter 7–10cm) can also be processed.
- •In mechanical pulping as it causes foam; the situation is especially
- •In mechanical pulping, those fibers that are responsible for strength properties
- •Isbn: 3-527-30999-3
- •In mechanical pulping, the wood should have a high moisture content, and the
- •In the paper and reduced paper quality. The higher the quality of the paper, the
- •1076 3 Raw Materials for Mechanical Pulp
- •1, Transversal resistance; 2, Longitudinal resistance; 3, Tanning limit.
- •3.2 Processing of Wood 1077
- •In the industrial situation in order to avoid problems of pollution and also
- •1078 3 Raw Materials for Mechanical Pulp
- •2, Grinder pit; 3, weir; 4, shower water pipe;
- •5, Wood magazine; 6, finger plate; 7, pulp stone
- •Isbn: 3-527-30999-3
- •4.1.2.1 Softening of the Fibers
- •1080 4 Mechanical Pulping Processes
- •235 °C, whereas according to Styan and Bramshall [4] the softening temperatures
- •Isolated lignin, the softening takes place at 80–90 °c, and additional water
- •4.1 Grinding Processes 1081
- •1082 4 Mechanical Pulping Processes
- •1, Cool wood; 2, strongly heated wood layer; 3, actual grinding
- •4.1.2.2 Defibration (Deliberation) of Single Fibers from the Fiber Compound
- •4 Mechanical Pulping Processes
- •Influence of Parameters on the Properties of Groundwood
- •In the mechanical defibration of wood by grinding, several process parameters
- •Improved by increasing both parameters – grinding pressure and pulp stone
- •In practice, the temperature of the pit pulp is used to control the grinding process,
- •In Fig. 4.8, while the grit material of the pulp stone estimates the microstructure
- •4 Mechanical Pulping Processes
- •4.1 Grinding Processes
- •Is of major importance for process control in grinding.
- •4 Mechanical Pulping Processes
- •4.1.4.2 Chain Grinders
- •Is fed continuously, as shown in Fig. 4.17.
- •Initial thickness of the
- •4 Mechanical Pulping Processes
- •Include:
- •Increases; from the vapor–pressure relationship, the boiling temperature is seen
- •4 Mechanical Pulping Processes
- •In the pgw proves, and to prevent the colder seal waters from bleeding onto the
- •4.1 Grinding Processes
- •In pressure grinding, the grinder shower water temperature and flow are
- •70 °C, a hot loop is no longer used, and the grinding process is
- •4 Mechanical Pulping Processes
- •Very briefly at a high temperature and then refined at high
- •4.2 Refiner Processes
- •4 Mechanical Pulping Processes
- •Intensity caused by plate design and rotational speed.
- •4.2 Refiner Processes
- •1. Reduction of the chips sizes to units of matches.
- •2. Reduction of those “matches” to fibers.
- •3. Fibrillation of the deliberated fibers and fiber bundles.
- •1970S as result of the improved tmp technology. Because the key subprocess in
- •4 Mechanical Pulping Processes
- •Impregnation Preheating Cooking Yield
- •30%. Because of their anatomic structure, hardwoods are able to absorb more
- •Is at least 2 mWh t–1 o.D. Pulp for strongly fibrillated tmp and ctmp pulps from
- •4 Mechanical Pulping Processes
- •4.2 Refiner Processes
- •1500 R.P.M. (50 Hz) or 1800 r.P.M. (60 Hz); designed pressure 1.4 mPa
- •1500 R.P.M. (50 Hz) or 1800 r.P.M. (60 Hz); designed pressure 1.4 mPa;
- •4.2 Refiner Processes
- •4 Mechanical Pulping Processes
- •In hardwoods makes them more favorable than softwoods for this purpose. A
- •4.2 Refiner Processes
- •Isbn: 3-527-30999-3
- •1114 5 Processing of Mechanical Pulp and Reject Handling: Screening and Cleaning
- •5.2Machines and Aggregates for Screening and Cleaning 1115
- •In refiner mechanical pulping, there is virtually no such coarse material in the
- •1116 5 Processing of Mechanical Pulp and Reject Handling: Screening and Cleaning
- •5.2Machines and Aggregates for Screening and Cleaning
- •5 Processing of Mechanical Pulp and Reject Handling: Screening and Cleaning
- •5 Processing of Mechanical Pulp and Reject Handling: Screening and Cleaning
- •5.3 Reject Treatment and Heat Recovery
- •55% Iso and 65% iso. The intensity of the bark removal, the wood species,
- •Isbn: 3-527-30999-3
- •1124 6 Bleaching of Mechanical Pulp
- •Initially, the zinc hydroxide is filtered off and reprocessed to zinc dust. Then,
- •2000 Kg of technical-grade product is common. Typically, a small amount of a chelant
- •6.1 Bleaching with Dithionite 1125
- •Vary, but are normally ca. 10 kg t–1 or 1% on fiber. As the number of available
- •1126 6 Bleaching of Mechanical Pulp
- •6.2 Bleaching with Hydrogen Peroxide
- •70 °C, 2 h, amount of NaOh adjusted.
- •6.2 Bleaching with Hydrogen Peroxide
- •Is shown in Fig. 6.5, where silicate addition leads to a higher brightness and a
- •Volume (bulk). For most paper-grade applications, fiber volume should be low in
- •Valid and stiff fibers with a high volume are an advantage; however, this requires
- •1130 6 Bleaching of Mechanical Pulp
- •6.2 Bleaching with Hydrogen Peroxide
- •Very high brightness can be achieved with two-stage peroxide bleaching, although
- •In a first step. This excess must be activated with an addition of caustic soda. The
- •Volume of liquid to be recycled depends on the dilution and dewatering conditions
- •6 Bleaching of Mechanical Pulp
- •6 Bleaching of Mechanical Pulp
- •Is an essential requirement for bleaching effectiveness. Modern twin-wire presses
- •Is discharged to the effluent treatment plant. After the main bleaching stage, the
- •6.3 Technology of Mechanical Pulp Bleaching
- •1136 6 Bleaching of Mechanical Pulp
- •Isbn: 3-527-30999-3
- •7.3 Shows the fractional composition according to the McNett principle versus
- •1138 7 Latency and Properties of Mechanical Pulp
- •7.2 Properties of Mechanical Pulp 1139
Is fed continuously, as shown in Fig. 4.17.
The chain grinder operation can be controlled either by constant feed (grinding
pressure) or by constant load, though from a technological aspect the constantpressure
operation is preferred. The pulp produced has an even quality, although
problems with automatic feeding (e.g., uneven log distribution) cause load fluctuations,
and a better approach with regard to economy of energy may be to operate
under constant load.
Today, chain grinders are designed with up to 5 MW driving power, and pulp
stone speeds of 30 m s–1 (circumferential speed). A daily production may be up to
70 t, with log lengths of 1–1.5 m and pulp stone diameters of 1.5, 1.6, 1.8, 1.9 or
2.0 m. Water is important as a lubricant and a cooling agent. A shower water flow
of 2000–3000 L min–1 have pressures of 350 to 600 kPa (3.5–6 bar). Coming from
closed loops, the shower water must be filtered to remove, for example, pulp particles.
The weir level can be regulated either manually or by mechanical adjustment
of the overflow.
1090
4.1 Grinding Processes
Fig. 4.15 The chain grinder. 1, Pulp stone; 2, feeding drive;
3, feeding chains; 4, stone sharpening equipment; 5, shower
water pipe; 6, grinding pit.
1091
4 Mechanical Pulping Processes
Fig. 4.16 The feeding hydraulics system in a chain grinder.
Fig. 4.17 The continuous feeding system for a chain grinder.
Several scientific-technological investigations and further developments, especially
in the field of grinding control, have allowed the optimization of chain
grinding to obtain modified groundwood pulps. One example is the thermo
groundwood (TGW), as introduced by Voith in 1984. The most important difference
to the conventional chain grinder is the temperature impound in the grinder
shaft (the lower part of the log magazine) and control of the grinding zone temperature.
4.1.4.3 Pulp Stones
The pulp stone is the most important part of the groundwood process. During the
early days of industrial grinding natural stones were used, but for more than 100
years these have been replaced by artificial pulp stones. In Europe, the pulp stones
were made from cement-based concrete, whilst in North America the modern-day
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4.1 Grinding Processes
ceramic-based stones were developed. The use of artificial stones has enabled tailor-
made surface structures of the pulp stones to be developed. After an exact
adjustment of the pulp stone, it is fixed on the grinder shaft with flanges (see
Fig. 4.18), and the free distance between the stone and flange is sealed with either
concrete or sulfur.
120.000 – 140.000 m.
Production efficiency during
operating time (based on
stacked wood)
Operating time 3.5 – 5.0 years
450 – 500 t
Specific grinding efficiency
(produced o.d. pulp per mm
grinding layer)
Sharpening interval 350 – 500 hours
60 – 75 mm
Initial thickness of the
abrasive layer
Operation parameters
Fig. 4.18 Structure of an artificial pulp stone.
The structure of a ceramic stone that is most commonly used today is shown in
Fig. 4.18 (left). The stone consists of a steel-reinforced core to which the honeycombed
ceramic segments are fixed with anchor screws. The spaces between the
segments have elastic joint material filling. Although the abrasive layer, at 60–
75 mm thickness, is much thinner than that of a concrete pulp stone, much longer operating times are attained. The abrasive layer material estimates the quality of the ceramic pulp stone, and differs in basic mineral, grit size, and grit
size distribution. The basic abrasive minerals used are aluminum oxide (Alundum)
or silicon carbide (Crystolon), and these are manufactured in several grades
of hardness and density. The ceramic bonding is achieved with the use of a sintered
silicon-based bonding agent.
Fig. 4.19 Scheme of a macrostructure before and after sharpening
(according to Suttinger). 1, Material removed by abrasion
during a sharpening interval; 2, material removed by the
subsequent sharpening.
Pulp Stone Sharpening
The pulp stone requires a certain surface structure to produce a certain groundwood
quality, the so-called “macrostructure” (Fig. 4.19). This is achieved by sharpening
the pulp stone with a special device, although the abrasive layer becomes
worn-out during grinding. The top area of the structure profile becomes wider,
1093