- •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
Isbn: 3-527-30999-3
©2006 WILEY-VCHVerlag GmbH&Co .
Handbook of Pulp
Edited by Herbert Sixta
epochal invention turned the paper production into a totally new direction, it represents
– together with the invention of the paper machine – one of the largest
technical progress since the invention of paper itself” [2].
Fig. 2.2 Left: Friedrich Gottlob Keller (1816–1895), the
Inventor of stone groundwood. Right: the second version
of Keller’s grinding machine.
1074 2 A Short History of Mechanical Pulping
1075
3
Raw Materials for Mechanical Pulp
Jurgen Blechschmidt and Sabine Heinemann
3.1
Wood Quality
The quality of wood obtained from the forest is of special importance for mechanical
pulping. This raw material that is useful for mechanical pulp and chemical
pulping is often also termed “pulpwood”. In mechanical pulping, the requirements
of fiber wood are higher for grinding than for refining. The most important
requirements of fiber wood include:
_ Wood quality: The wood should be healthy, possibly grown
straight, less knotty and free from rot.
_ Wood moisture: The moisture of the wood should be as high as
possible. It should be over 35% in order to exceed the fiber saturation
point.
_ Wood diameter: Useful wood diameters in grinding are 10–20 cm.
In refining, the thinnings (diameter 7–10cm) can also be processed.
_ Debarking state: Three different debarking states can be distinguished
for the wood:
– Bark is completely removed from wood (tanned, white peeled).
– Bark is removed from wood with some retention of phloem
(spotted, barked).
– Wood is completely or partly surrounded by bark (not debarked).
_ Resin content: A high resin content in wood is disadvantageous
In mechanical pulping as it causes foam; the situation is especially
poor with pine.
_ Wood species: Spruce uniquely serves the purpose for mechanical
pulping, especially in grinding. In refining procedures, both softwood
and hardwood species can be processed. Poplar and aspen
are also suitable for grinding.
In mechanical pulping, those fibers that are responsible for strength properties
are of major importance. In softwood, these are tracheids, and in hardwood they
are the libriform fibers. Tracheids cover about 90% of cell material in softwood
Handbook of Pulp. Edited by Herbert Sixta
Copyright © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Isbn: 3-527-30999-3
©2006 WILEY-VCHVerlag GmbH&Co .
Handbook of Pulp
Edited by Herbert Sixta
species, whilst in hardwoods the amount of libriform fibers differs, depending
upon the wood species. As a mean value, they cover only 50% of the cell material,
and this is the reason why different wood species show different suitabilities in
mechanical pulping.
3.2
Processing of Wood
3.2.1
Wood Log Storage
In mechanical pulping, the wood should have a high moisture content, and the
processing of forest-fresh wood is the best way to achieve this. The storage period
of wood should be of short duration, and the wood should be processed in as fresh
a state as possible. Nevertheless, most mills have high-capacity wood storage units
with capacities of between 10 000 and 500 000 m3.
The storage of wood can be performed using four basic approaches:
_ as irregular round log stacks (piles)
_ as round log water storage
_ as chip storage for refiner pulps
_ as regular round log stacks
Today, irregular piles are the preferred storage form, with the cone-shaped piles
reaching heights of up to 30 m and being fed by so-called stackers. In summer,
and in order to keep the moisture content high enough, water sprayers are used.
Water storage – or even better, under-water storage – is the best way to maintain a
high moisture content of the wood. For this, the wood is stored in bundles in
lakes, sea bays or watering ponds, with the log bundles being moved and turned
using special boats.
3.2.2
Wood Log Debarking
For further processing, the wood must be debarked. Bark cells are formed outside
the living part of the tree (the cambium), and consist of the phloem (inner bark)
and bark (outer bark). Phloem cells are responsible for the transportation of
assimilates and storage, while the bark protects the living parts of the wood from
drying, temperature influences or damage. Depending on the wood type, the
thickness of the bark layer is between 2 and 40 mm. This corresponds to a bark
portion of 5 to 28%, in relation to the total wood stem.
The different chemical and morphological composition of the bark compared to
that of the wood makes it necessary to remove the bark from the wood before
mechanical pulping is carried out. Bark particles are responsible for dirty points