- •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
1078 3 Raw Materials for Mechanical Pulp
1079
4
Mechanical Pulping Processes
Jurgen Blechschmidt and Sabine Heinemann
4.1
Grinding Processes
4.1.1
Principle and Terminology
Round logs are pressed against a rotating pulp stone under specified conditions
of pressure and temperature (Fig. 4.1).
Fig. 4.1 Grinding principle. 1, Pulp stone;
2, Grinder pit; 3, weir; 4, shower water pipe;
5, Wood magazine; 6, finger plate; 7, pulp stone
sharpener; 8, sharpening roll; 9, wood logs.
Depending on the position of the log in the grinder magazine, it can be distinguished
between:
_ Transversal groundwood: Wood logs (and evidently also the
fibers) are loaded in the magazine or pocket of the grinder transversally
(perpendicularly) to the rotational direction of the stone
(in practice the only used orientation).
_ Longitudinal groundwood: Wood logs are loaded parallel to the
rotational direction of the stone (only applied in research studies).
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
Grinding procedures may be categorized as atmospheric grinding, pressure grinding,
and thermo grinding. The principles of each process are illustrated schematically
in Fig. 4.2.
Fig. 4.2 Principles of the grinding procedures.
4.1.2
Mechanical and Thermal Processes in Grinding
Grinding is a thermomechanical process that is divided into two parts, each of
which overlaps one another: (a) Softening and breakdown of the fiber structure;
and (b) peeling of the softened fibers from the wood matrix in the grinding zone
4.1.2.1 Softening of the Fibers
The wood logs are pressed against a rotating pulp stone, applying suitable pressure
and temperature conditions (see Fig. 4.2). Just before entering the grinding
zone, the wood logs are still cold and thermally untreated. The stone grits pass
over the wood matrix at very high frequencies. In a so-called compression/decompression
process, the fibers are cyclically stressed or relaxed. Depending on the
rotational speed of the pulp stone, and also on the surface profile of the stone,
pressure pulsations up to 40 kHz occur on the logs.
The fiber matrix is loosened due to the fatigue work done by the grits. Finally,
when they enter the boundary area between the revolving stone surfaces, the
1080 4 Mechanical Pulping Processes
fibers are peeled from the outermost layer of the softened wood, much in the
same way that tape is torn from a paper surface. Both processes warm up the
wood and break down the fiber structure. Due to the viscoelastic nature of the
wood, the temperature at 1–2 mm above the actual grinding zone increases very
quickly, and this rise in temperature causes the lignin to soften. The resulting
so-called “softening temperature” depends on the water content of lignin and the
frequency. In 1963, Goring [3] demonstrated how the softening temperature of
lignin is dependent upon the water content (Fig. 4.3).
Fig. 4.3 Softening temperature of lignin depending on water
content (according to Goring [3]).
The softening temperature is understood to represent the transition of an amorphous
polymer such as lignin from a glass-like and brittle state into a weak and
plastic one. Goring [3] identified the softening temperatures for lignin as 135 °C to