- •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
235 °C, whereas according to Styan and Bramshall [4] the softening temperatures
for softwoods are about 135 °C and for hardwoods about 100 °C. In lignin, the plasticizing
effect of water has a limit at water contents as low as 5%. For water-saturated
Isolated lignin, the softening takes place at 80–90 °c, and additional water
does not result in any considerable further softening of lignin. Under typical mechanical
pulping conditions, the softening temperature for lignin as part of the
wood fiber matrix is higher (in the range of 100–130 °C). The lignin polymer,
being the stiffest wood component under the conditions used in mechanical pulping,
represents the most important component for the thermal softening of wood.
Preferably, wood for mechanical pulping should have a moisture:wood ratio of
over 0.5.
Knowledge of the thermal processes in grinding is important step when completing
the grinding process. In evaluating investigations made by Luhde [5], the
relationship between thermal relationships during grinding process is illustrated
schematically in Fig. 4.4, while the five temperature-dependent regions of Fig. 4.4
are described in more detail in Tab. 4.1.
4.1 Grinding Processes 1081
1082 4 Mechanical Pulping Processes
Fig. 4.4 Thermal relationships in the grinding process.
1, Cool wood; 2, strongly heated wood layer; 3, actual grinding
zone; 4, fiber suspension zone; 5, pulp stone surface.
Tab. 4.1 Temperatures at different zones during the grinding process.
Zone Temperature Process
1
Cold wood
Depending on
surrounding
temperature
(related to
season)
The wood is cold and thermally untreated when entering
zone 2.
2
Strongly heated
wood layer
100–170 °C The temperature in the wood about 0.1 mm above the
grinding zone is high, due to by heat impound, but below
the carbonizing temperature of wood (206 °C) [6]. These high
temperatures are the reason for the softening of lignin. The
resulting equilibrium temperature depends on the water
content in the wood.
3
Actual grinding
zone
80 °C (SGW)
125 °C (PGW)
The actual grinding zone is only ca. 0.1 mm thick (according
to Steenberg and Nordstrand [7]), and has a temperature
usually close to 100 °C (higher in pressurized grinding). This
temperature increases with increasing pit consistency and
pit temperature. At this point, the fibers are deliberated from
the fiber compound. Here, the resulting equilibrium temperature
also depends on the water content in the wood.
4
Fiber suspension
zone
80–100 °C
(SGW)
100–140 °C
(PGW)
It is assumed that the temperatures in the pulp suspension
zone and the actual grinding zone are similar. The pulp
suspension is a mixture of water, fibers and broken fiber
parts moving along the grinding zone towards its end. This
pulp suspension also acts as a lubricating and cooling agent.
5
Pulp stone surface
100 °C or more The surface temperature of the pulp stone is under 100 °C, and
depends on the shower water temperature and pit consistency.
4.1 Grinding Processes
It can be summarized that the temperatures in the grinding zone vary over a
wide range, depending on the moisture content of the wood and of the system
used (atmospheric or pressurized grinding). According to Steenberg and Nordstrand
[7], the actual grinding zone is only 0.1 mm thick. Above this zone, the
temperatures in the wood are higher. In practical trials, Atack and May [8] have
measured the upper limit of the wood temperature as 206 °C, which corresponds
to the carbonizing temperature.