- •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
4.2 Refiner Processes
Fig. 4.34 Selected examples of refiner plate designs.
Refiner plates are hard-wearing tools with a working lifetime of between 300
and 1000 h. Selected examples of mechanical pulp lines using the refiner process
are shown in Figs. 4.35–4.37.
Fig. 4.35 Single-stage TMP line with Metso-Double disc
refiners RGP 68DD (Union Bruk Norway, 1999).
1109
4 Mechanical Pulping Processes
Fig. 4.36 Two-stage TMP line with two-stage reject refining
and fractionation for LWC paper (Metso Paper).
Fig. 4.37 Modern CTMP refining in one or two stages (Metso Paper).
To date, the production of pulp for fluting has been the most common use of
semi-chemical hardwood pulps. The dominant process for this product is the neutral
sulfite semi-chemical process (NSSC), with sodium or ammonium sulfite as
cooking chemicals. The pulp yield is in the range of 70–80% depending on the
wood species. Birch, beech, maple, oak and eucalyptus are the most frequently
used hardwoods for fluting production, often as the sole component in furnish.
Primarily, the demand on a fluting pulp is high stiffness and good crush resistance.
A combination of short, stiff fibers and a high proportion of hemicellulose
In hardwoods makes them more favorable than softwoods for this purpose. A
semi-mechanical pulping process is illustrated schematically in Fig. 4.38.
1110
4.2 Refiner Processes
Fig. 4.38 Semi-mechanical pulping process.
1111
1113
5
Processing of Mechanical Pulp and Reject Handling:
Screening and Cleaning
Jurgen Blechschmidt and Sabine Heinemann
5.1
Basic Principles and Parameters
The aim of mechanical defibration of wood is the deliberation of fibers from the
wood, without their destruction. This happens only ideally, and in reality a mixture
of different fiber components and debris is created immediately after defibration,
and is characterized as follows:
_ Shives (unsuitable particles that must be separated from the
pulp).
_ Fibers, divided into:
– Long fibers; length 800–4500 lm; width 25–80 lm
– Short fibers; length 200–800 lm; width 2.5–25 lm
_ Fines, divided into:
– Fibrillar fines (slime stuff); length up to 200 lm, width about
1 lm
– Flake-like fines (flour stuff); length 20–30 lm; width 1–30 lm
Additionally, wood pieces of different dimensions and shapes, sand and other
nonwood particles are found (Fig. 5.1).
Separating by suitable screening brings the mechanical pulp to the following
composition, depending on its process parameters during defibration:
_ Shives content: 2–6% (extreme values up to 20%)
_ Fiber content: 50–80%
– Long fiber content: 25–55%
– Short fiber content:25–40%
_ Fines content: 20–50%
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
Fig. 5.1 Ground wood components. (a) Long fibers;
(b) short fibers; (c) flake-like fines; (d) fibrillar fines.
There are two basic process principles for screening in mechanical pulping:
_ Pulp classification –that is, separation of the pulp into fractions
of different particles size (applied for shives removal fromthe pulp).
_ Separation according to particle density –that is, separation of
pulp and minerals such as sand and other heavy material (applied
for pulp cleaning).
The separation process can be characterized by a simple scheme, as shown in
Fig. 5.2.
Feed Accept
Reject
Fig. 5.2 Parameters of the screening principle.
5.2
Machines and Aggregates for Screening and Cleaning
No screening process can result in a complete or exact separation of accepts and
rejects. There are always particles retained in the reject that are smaller than the
separation size (slot width or mesh size), and there are also larger but slender and
flexible particles in the accept.