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- •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
4 Mechanical Pulping Processes
_ The quality of the mechanical pulp produced is constant over a
longer time interval than for groundwood, because there are no
sharpening fluctuations.
The development of the refiner process has been enforced by much better designs
of the refiners, highly efficient refiners, and the development of wear-resistant
plate materials.
4.2.2
Mechanical, Thermal, and Chemical Processes in the Refiner Process
Fiber deliberation from the fiber compound can occur in the refiner process as
follows:
_ Softening of the lignin in the middle lamella and in the primary
wall of the wood fiber by pressure load frequencies in the refiner;
this is mechanical softening.
_ Softening of the lignin in the middle lamella and in the primary
wall of the wood fiber by thermal influences; this is thermal softening.
_ Softening of the lignin in the middle lamella and in the primary
wall of the wood fiber by chemical pretreatment; this is chemical
softening.
Many process parameters are considered responsible for the character and properties
of the mechanical pulp produced, including: (a) the pressure and temperature
during thermal pretreatment; (b) the duration of thermal pretreatment; (c) the
addition of chemicals; (d) the specific energy consumption; (e) the energy distribution
within the refining stages; (f) the consistency in the refining zone of the
first refining stage; (g) the wood chip quality; (h) the refiner design; and (i) refining
Intensity caused by plate design and rotational speed.
The duration of thermal pre-treatment has only minimal influence on pulp
quality, since in practical terms this stage lasts for only 1–3 min, and a minimum
time is striven for.
The defibration temperature is as important as for the grinding process, and
should be 100–130 °C. By raising the temperature to 140 °C, the lignin becomes
well-softened and the fiber requires minimal mechanical energy for its liberation
from the fiber compound. This mechanical pulp has an unsuitable quality for
papermaking, however, as it is harsh and coarse. The softened lignin solidifies at
the fiber surface to a hard substance; the pulp has a high refining resistance. If
the defibration temperature is lower than the softening temperature of the lignin,
then the mechanical pulp produced is coarse and has only a low level of strength
properties. When the refining temperature is very close to the softening temperature,
a high percentage of the fibers can be defibrated without being destroyed.
The primary wall of these fibers can be damaged, and this allows fibrillation of the
secondary wall. According to Giertz [19], the shearing frequency in a refiner is be-
1100
4.2 Refiner Processes
tween 10 kHz and 1 MHz. Based on the fact that the softening temperature for
high polymers increases by 7° when the frequency increases by 1 tenth, it can be
assumed that the lignin of moist chips will be softened in the refiner at 120–
135 °C.
The shearing frequency is estimated by rotational speed, disc diameter, and
plate pattern. Moreover, the type of refining – whether single disc, double disc or
conical disc – is also important. If the refining temperature is slightly above the
softening temperature of the wood chips, then defibration occurs mainly in the
zones with a high lignin concentration (i.e., in the middle lamella). In this way, a
high proportion of fibers is deliberated without being damaged. At the same time,
the middle lamella and primary wall are removed and milled down to fines, while
the outer secondary wall (S1) is fibrillated [19]. The mechanical and thermal processes
during refining can be divided into three phases: