- •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
70 °C, a hot loop is no longer used, and the grinding process is
simplified. In mill applications, white water is cooled in a separate
heat exchanger installed in the grinder shower water line.
Fig. 4.23 Relative pit pulp properties at CSF 80 mL for
different groundwood types (data are based on Refs. [14–18]).
The reference pulp is PGW95.
1097
4 Mechanical Pulping Processes
The properties of PGW differ from the conventional stone groundwood (SGW).
Especially important is the higher long-fiber content that causes increased initial
wet web strength and tear resistance [about 40% higher strength values for PGWS120
compared to atmospheric SGW; see Fig. 4.23]. Average values for the fiber
length are 1.3–1.5 mm for PGW from spruce, compared to 0.7–0.8 mm for SGW
from the same wood species.
An overview of the different groundwood pulp properties, depending on the
grinding method, is provided in Fig. 4.23. All pulps are compared at the same
freeness level of CSF 80 mL, while the reference pulp is PGW95, set as 100% in
all properties.
Pressure grinding produces a pulp with higher long-fiber content and higher
strength level than does atmospheric grinding, and their properties are comparable
to those from refiner mechanical pulp (see Section II-4.2). One main advantage
of pressure grinding is a better exploitation of the raw material without additional
specific energy input and loss in optical properties, and a pulp quality that
enables the saving of amounts of chemical pulp in pulp blends.
4.2
Refiner Processes
4.2.1
Principle and Terminology
A typical flow sheet of a refining process is shown in Fig. 4.24.
Fiber logs are cut down into wood chips that are then defibrated to mechanical
pulp by means of disc refiners. Depending on the type of chip pre-treatment or
chip post-treatment, several processes can be carried out, each of which is specifically
defined.
_ RMP (Refiner mechanical pulp): The refining of chips at atmospheric
pressure in a refiner (in some cases, the refiner outlet
may be pressurized).
_ TMP (Thermo-mechanical pulp): Thermal pre-treatment and
refining of the chips under pressure, with the second refiner also
under pressure in most cases (the pressure allows heat recovery)
_ RTS™ (Retention time, temperature, speed): Chips are preheated
Very briefly at a high temperature and then refined at high
speed.
_ Thermopulp™ (Thermo pulp): This differs from TMP in that the
pulp is heated to a very high temperature (ca. 170 °C) briefly
before the second refining stage.
_ CMP (Chemimechanical pulp): Chips are pre-treated, usually
with sodium sulfite and caustic, and then refined without pressure.
1098
4.2 Refiner Processes
_ CTMP (Chemithermo mechanical pulp): Chips are pre-treated in
the same way as for CMP, but with a lower chemical charge, and
then refined under pressure.
Fig. 4.24 Typical flow sheet of a modern refining process.
The industrial production of RMP began in 1960, since which time the refiner
process has been extensively developed as result of the increasing demand for
pulp fibers and the commissioning of large and highly efficient paper machines.
The advantages of refiner processes can be summarized as follows:
_ Chips as a raw material allows the processing of wood that cannot
be used for grinding (size of the logs, wood species), for example,
saw mill chips or sawdust. With chemical pretreatment, some
hardwoods can also be used successfully.
_ There are good possibilities of process automation and minimal
operating effort. Wood transportation and log handling are no
longer necessary.
_ Pulps with a high content of long fibers and good strength properties
can be produced.
1099