- •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 Mechanical Pulping Processes
and the pulp stone becomes dull so that the quality and quantity of the groundwood
produced is changed. To regain the original surface structure, the stone
must be sharpened. The surface profile (macrostructure) before and after the sharpening
process is shown in Fig. 4.19. The sharpening interval is the timebetween two
sharpening actions, during which the groundwood quality changes significantly.
Traditionally, sharpening of the pulp stone has been carried out with metallic
burrs. For this purpose, a sharpening lathe is installed on the top of a pocket grinder,
or on the side of a chain grinder. The burr itself is installed into a burr holder
that is fastened to the sharpening lathe. The burr sharpening produces a spiral
pattern having grooves and areas, in turn, in the pulpstone surface. Sharpening
deepens the grooves and reduces the land area, and also exposes fresh abrasive
grits and removes impurities from the stone pores and surface. A smaller land
area provides a higher unit grinding pressure, which results in a coarser pulp having
a higher degree of freeness. The deeper grooves with a higher void area at the
stone surface bring more water to the grinding zone, and consequently are able to
carry more pulp out of the grinding zone.
The most important parameters that can be varied in the sharpening pattern
Include:
_ Tooth frequency of the burr, pitch of the burr, pitch of the burr
_ Tooth angle (mainly 28° in spiral burrs)
_ Sharpening depth
The pitch of the burr and sharpening depth are used for burr specification. For
each pulpstone type, there is a minimum width for the base of the land to be
strong enough to support the grinding load. If finer burrs are used, it is highly
probable that the lands break and the pulp quality is impaired. Some characteristics
of spiral burrs are shown in Fig. 4.20.
Fig. 4.20 Characteristics of spiral burrs.
The sharpening of grinding stones with spiral burrs is being increasingly
replaced by the use of ultrahigh-pressure water. This waterjet conditioning with
water pressures set at 50 to 240 MPa (500 to 2400 bar) allows accurate control of
the pulpstone sharpness, and results in a stable pulp quality and higher produc-
1094
4.1 Grinding Processes
tion. This in turn leads to an improved stability of the total grinding and screening
process. Compared to conventional spiral burr sharpening, waterjet conditioning
is carried out during the grinding process, and variations in pulpstone sharpness
may be reduced by 50–60%. The resultant groundwood had a more even distribution
of well-bonding fibrillar particles. The tensile index of long fibers was
increased by 15% and the tear index by 15–20%, while the apparent density was
reduced by 30%.
4.1.5
Pressure Grinding
Groundwood production has been carried out under atmospheric pressure, as
indicated by Keller with its invention. Further investigations into temperature
relationships in grinding have led to the introduction of higher pressures in
grinding processes [11]. Although early small-scale trials have been successful, the
technical realization required much development. By 1970, only the former Tampella
factory [today part of Metso Paper (Metso Corp.)] had been able to develop
the first industrial pressure grinder [12], though by 1982 almost 2.5% of the
world’s production of groundwood was manufactured by pressure grinding.
Goring [3] highlighted the importance of water content in wood during mechanical
defibration. A high water content lowers the softening temperature of
lignin and hemicelluloses (see Fig. 4.3). Still in atmospheric grinding, the Defibration
takes place at temperatures below the softening temperature of wood.
With high pressures of 100–300 kPa (1–3 bar), the boiling temperature of water