- •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
4.1 Grinding Processes
pulp grades from board to high value printing pulps. Thus, high specific energy
consumption will lead to the production of a finer groundwood pulp with higher
strength properties (see Fig. 4.10). The parameter of specific grinding energy consumption
Is of major importance for process control in grinding.
80
100
120
140
160
180
1.2 1.7 2.2
Specific energy consumption [MWh/t]
Strength development [%]
Fig. 4.10 Strength properties of stone groundwoods, depending upon
specific grinding energy consumption (according to Suttinger [22]).
4.1.4
Grinders and Auxiliary Equipment for Mechanical Pulping by Grinding
A typical flow sheet for a groundwood process is shown in Fig. 4.11.
Today, grinding can strictly be divided into two different processes – atmospheric
and presurized grinding. In contrast, the ring grinder, which operates in a
totally different manner (Fig. 4.12), was developed in 1939 and used in the USA
and Canada. The manually fed logs are ground inside a drum, but this system has
now almost disappeared completely because of the very high manual effort
involved.
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1088 4 Mechanical Pulping Processes
Fig. 4.11 A typical flow sheet for a groundwood process.
Fig. 4.12 A ring grinder.
4.1 Grinding Processes
4.1.4.1 Pocket Grinders
Pocket grinders were the first designs of industrial grinders, and were further developed
from the spindle-type grinder (first built in 1867). Figure 4.13 (left) shows
a pocket grinder with four magazines that has to be fed manually. A further development
of the pocket grinder is the magazine-type grinder (Fig. 4.14), which was
first built in 1910 to improve the manual feeding of logs to the pockets.
Fig. 4.13 Pocket grinders. Left: A pocket grinder with four
magazines. Right: An atmospheric, two-pocket grinder.
Fig. 4.14 A magazine-type grinder.
Today, pocket grinders are widely used in Scandinavia and America as twopocket
grinders (Fig. 4.13, right). The two-pocket pocket grinder has, in accordance
with its name, two separate grinding pockets that operate batch-wise. The
1089
4 Mechanical Pulping Processes
magazine above a pocket can hold just one pocket filling of logs. Irrespectively as
the one pocket filling is pressed hydraulically towards the pulp stone and grinded,
the other pocket can be filled for the next batch. Today, the Metso grinders have
pulp stone diameters of 1.8 m, and both grinding zones are from 1.0 to 1.5 m in
length. The width of the feeding gate opening is 600 mm, and the pocket reloading
time is approximately 30 s. A hydraulic pressure of between 1.2 and 5 MPa
(12 and 50 bar) – it is about 120 kPa and 500 kPa on the wood – moves the logs
towards the pulp stone.
The advantages of modern pocket grinders compared to chain grinders include:
_ Small design height
_ Simple operating
_ Short pocket changing times
_ Quick pulp stone change
The increased importance of the pocket grinders is related to the development of
pressurized grinding (see Section II-4.1.5).
4.1.4.2 Chain Grinders
The chain grinder, which is widely distributed throughout Europe, except for
Scandinavia, was first designed 1921 by Voith, in Heidenheim. The operating
principle is shown schematically in Fig. 4.15. The logs are stored in the log magazine,
located above the pulp stone. From the magazine, the logs are caught by the
cams of the permanent moving chain elements and pressed down continuously
towards the pulp stone with a pressure which is related to the feeding speed. The
chains are driven hydraulically by gears or screw gears (Fig. 4.16), and the magazine