- •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
70 °C, 2 h, amount of NaOh adjusted.
1128
6.2 Bleaching with Hydrogen Peroxide
silicate solutions favors the precipitation of silicates (silicic acid sols), and this can
lead to the removal of potential decomposing compounds. Because such precipitation
can cause problems with scaling, the amounts of silicate added are typically
adjusted to lower levels. Despite these difficulties, the advantage of silicate addition
normally keeps this product in the mill’s receipt. A clear example of the benefit
Is shown in Fig. 6.5, where silicate addition leads to a higher brightness and a
wider maximum. In the presence of silicate, the receipt for composition of the
chemicals tolerates deviations more easily. The standard addition of silicate is
around 2%, calculated as commercial solution with 38–40 Be density. Silicate solutions
with a higher alkalinity have a lower average molecular weight for the silicic
acid polymer, and this permits a lower level of addition, with identical effects.
1,0 1,5 2,0 2,5
66
68
70
72
74
76
Na silicate 0 % 1.5% 3%
Brightness [% ISO]
NaOH-charge [%]
Fig. 6.5 Impact of sodium silicate stabilization on brightness
development in thermomechanical pulp (TMP) bleaching.
The amount of caustic soda applied correlates directly with the effluent load
[35]. Taking the data from Fig. 6.2 and plotting the input of caustic soda against
the resulting COD load, the points in the graph show the linear dependency
(Fig. 6.6). This applies not only to the COD but in parallel to total organic carbon
(TOC). Because the amount of dissolved compounds must correlate with the pulp
yield, bleaching to a very high brightness decreases the yield. Fines are extracted
and freeness is increased. The extraction effect not only affects pulp yield and opacity,
but also has an impact on fiber properties. With intense extraction, hardwood
fibers collapse, making it difficult to produce highly bleached fiber with a high
Volume (bulk). For most paper-grade applications, fiber volume should be low in
order to allow a smooth surface. In the production of white board, the opposite is
Valid and stiff fibers with a high volume are an advantage; however, this requires
to carry out bleaching with other alkali sources.
1129
1130 6 Bleaching of Mechanical Pulp
0,4 0,8 1,2 1,6 2,0 2,4
20
25
30
35
1% H
2
O
2
2% H
2
O
2
3% H
2
O
2
4% H
2
O
2
COD [kg/t]
NaOH-charge [%]
Fig. 6.6 Increase of the COD load with increasing caustic
soda addition in bleaching with hydrogen peroxide.
The substitution of caustic soda with magnesium hydroxide is a useful alternative
[36], although because of the limited solubility of Mg(OH)2, effective mixing
becomes even more important. The particle size is similarly important, as a fine
product is distributed better. The amount of Mg(OH)2 can be kept low; the limited
solubility would only result in a high neutralization demand. It is sufficient to add
about 1–1.2% to activate the bleaching process with 2–4% H2O2. The demand for
sodium silicate is even lower, and an input of only 0.5–1% will result in the best
response. The moderate impact on hemicellulose extract becomes apparent with a
lower COD load (see Fig. 6.7).
2 3 4 5
10
15
20
25
30
35
COD [kg/t]
Mg(OH)2
NaOH
H2O2 [%]
Fig. 6.7 Impact of an exchange of NaOH by Mg(OH)2 in
bleaching pressurized groundwood with increasing amounts of
H2O2 and NaOH or Mg(OH)2 as alkalization source [NaOH
amount variable, Mg(OH)2 input 0.75% at 2% H2O2, all other
bleaches 1%, 2% sodium silicate, 70 °C, 3 h, 20% consistency].