- •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
In the paper and reduced paper quality. The higher the quality of the paper, the
1076 3 Raw Materials for Mechanical Pulp
fewer bark particles should be retained on the wood stems after debarking. In line
with the morphological construction of the bark layer, bark removal should take
place at the contact area between the phloem and cambium. One measure of characterization
of the ability to wood be debarked is the debarking resistance or the
power and force, respectively, per cm2 of bark that is needed to remove the bark
from the wood stem. Debarking resistance is influenced by:
_ Wood type
_ Felling time (season)
_ Moisture content of the wood
_ Storage duration of the wood
_ Temperature in the cambium area
_ Type of pretreatment
For example, debarking resistance is highest for birch, followed by spruce and
pine, but it also depends very heavily on the felling season of the wood (Fig. 3.1).
Seasonal differences in debarking resistance are also related to the morphological
differences, depending on growth. During spring and summer, when cell division
activity is very high, the radial walls of the cambial cells and the neighboring
phloem cells are very thin and weak, and at this time the debarking resistance is
low. However, if cell division activity is low or is stopped, and liquid transportation
though the cells is very restricted, debarking resistance is increased significantly.
0
2
4
6
8
10
12
14
Debarking resistance [N/cm * 2.5]
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
1
2
3
Fig. 3.1 Seasonal development of debarking resistance.
1, Transversal resistance; 2, Longitudinal resistance; 3, Tanning limit.
Debarking resistance also increases with decreasing moisture content of the
wood. Wood that has been stored under dry conditions for a longer time has a
higher debarking resistance. When the type of storage keeps the moisture content
high and rather constant, a longer storage time does not increase the debarking
resistance to any great degree. In order to maintain the state of low debarking
3.2 Processing of Wood 1077
resistance from wood that has been felled in the spring, water storage would be
the best approach.
Although wet debarking may be carried out with a lower debarking resistance
and better debarking results, dry debarking in continuous drum debarkers is preferred
In the industrial situation in order to avoid problems of pollution and also
to achieve lower investment costs (shorter drum constructions, no effluent treatment).
For technical applications of dry debarkers, see Chapter I-3, Wood yard
operations.
3.2.3
Wood Log Chipping
The uniformity of chip size distribution, bulk density and wood source are the
most important factors that determine chip quality for mechanical pulping. The
average chip length of 22 mm is less than that of chips used for kraft pulping.
The shorter the chip is along the grain, the more fibers have been cut; consequently,
short chips result especially in a lower tear strength. The impact of
extreme chip fractions on thermomechanical pulp (TMP) are detailed in Tab. 3.1.
Tab. 3.1 Impact of extreme chip size fractions on thermomechanical pulp processing and quality.
Chip fraction Impact
Over-large fraction – Causes uneven feed to the refiner.
– Reduces pulp quality.
Over-thick fraction – Contains most knot wood present in groundwood logs.
– Causes unstable refining and increase of energy consumption.
– Decreases fiber length and long fiber portion.
– Impairs strength properties and brightness.
Fines fraction – Lowers energy consumption.
– Decreases pulp strength, sheet density, brightness and light-Scattering
coefficient.
– Increases shives content and causes linting problems.
The technical applications of wood chipping are explained in detail in Chapter
I-3, Wood yard operations.