- •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
1116 5 Processing of Mechanical Pulp and Reject Handling: Screening and Cleaning
5.2Machines and Aggregates for Screening and Cleaning
Feed Feed Feed
Accept
Reject
semi-open closed open
f = Hydrofoil
Fig. 5.5 General construction forms of pressure screen rotors
(according to Niinimaki et al. [27]).
A Foils
B Bumps
C Radial vanes
D Tapered surface
Fig. 5.6 Rotor types with different pulsation elements (according to Bliss [28]).
Slotted screen plates have been found to have superior shives removal efficiency
compared to holed screen plates, but the capacity of the latter is better because of
a larger open area. Contoured screen plates have further increased the capacity of
slotted screens, and slotted screens manufactured from wedge wires (Fig. 5.7) provide
about 100% greater open surface area than screen plates with machine slots.
W S
P
W Wire width
S Slot width
P Contour height (profile height)
Fig. 5.7 Example of a wedge wire screen basket [29].
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5 Processing of Mechanical Pulp and Reject Handling: Screening and Cleaning
Continuous slotted screen Perforated cylinder
AFT MacroFlow™
Fig. 5.8 Pressure screen basket designs (AFT).
AFT EP Rotor™
Engineered Pulse™
AFT Gladiator™
HC Rotor
Fig. 5.9 Pressure screen rotor designs (AFT).
Some examples of industrial designs of screen baskets and rotors are shown in
Figs. 5.8 and 5.9.
Separation according to material density is carried out using hydrocyclones
(Tab. 5.1 and Fig. 5.10). In almost all of these apparatus, the pulp suspension is
fed tangentially by pump pressure into a cylindrical or conical pipe and moves as
a spiral downwards at the outer wall of the pipe. Heavy particles are found outside
of the downward stream moving slowly through an opening at the lower end of
the pipe into a dirt collector. The main stream is turned up above this opening
and rises in the middle of the pipe to the outlet. Depending on the design, the
pressure drop in this hydrocyclones is from 60 to 300 kPa (0.6 to 3 bar).
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5.2Machines and Aggregates for Screening and Cleaning
Fig. 5.10 Operation principle of a hydrocyclone.
1,Pulp suspension inlet; 2,accepts; 3, rejects.
Tab. 5.1 Parameters of centrifugal separation principle for different cleaner types.
Parameter Centricleaner Low-consistency cleaner
Pulp consistency [%] < 1 < 1
Pressure drop, [kPa (bar)] 300 (3) 160 (1.6)
Acceleration 550 g 150 g
Inlet flow rate [m s–1] 20 12
Fiber loss [%] 2 Practically none
Specific energy consumption [kWh t–1] 0.4–0.5 0.08
It is impossible to design a screen for mechanical pulps that is able to separate
particles depending on the screen size absolutely. In practice, there is always only
a certain amount of shives separated, and this depends mainly on the overflow
rate. In addition to the efficiency grades of the single separation aggregates, a
combination of all single screens estimates the efficiency and economy of the
screening stage.
Some schematic examples of modern screening concepts are illustrated in
Figs. 5.11–5.13.
1119