Sulfite Process Advantages
Sulfite Process Advantages
Sulfite Process Advantages
Lecture 2
Category of Pulping Process
• Chemical Pulping
- Sulphate (Kraft) process
- Sulphite process
- Neutal
• Semi-chemical
• Chemi-mechanical
• Mechanical pulping
Mechanical Pulping
• Stone Groundwood (SGW) – wood logs
• Thermo-mechanical pulp (TMP)
• Chemi-thermo-mechanical pulp (CTMP)
• Bleached CTMP (BCTMP)
• Pressure Groundwood (PGW)
Stone Groundwood (SGW)
1300 KW/ton
Yields: 93 – 95%
Sharpening must done
after 50 – 150 hr
The important grinding variables are:
• Wood species and other wood variables.
• Type of pulpstone.
• The use (or not) of a water-filled grinding pit.
• Type of burr pattern on the stone.
• Stone surface speed.
• Hours on the stone since last burring.
• Pressure of wood against the stone.
• Temperature of grinding surface, 130-180°C
• Amount of water used (and, therefore, the final
pulp consistency).
1900 A.D.
Pressure Grindwood (PGW)
Similar as SGW:
• By pressurizing the wood with steam at
temperatures of 105-125°C , the wood is heated
and softened prior to the grinding process.
• This gives better separation of fibers with less
cutting action and lower fines generation.
• This process yields a pulp that has higher tear
strength and freeness and is brighter than SGW.
• Lower power requirements.
Refiner Mechanical Pulp (RMP)
• Chips are used.
• Power requirements are 1600-1800 kWh/ton.
• Disk refiners are up to 1.5 m in diameter and rotate at
1800 rpm with 60 Hz power; this gives a velocity at the
periphery of up to 140 m/s.
• The plates containing the metal bars must be replaced
every 300-700 hours or low quality pulp is produced and
energy use increases.
• Refining is usually carried out in two stages. The first is at
20-30% consistency to separate the fibers, while the
second is at 10-20% consistency to alter the surface of
the fibers for improved fiber bonding in the final paper.
RMP
Thermo-Mechanical Pulp (TMP)
• Most important mechanical pulping method.
• The TMP process is very similar to the RMP process
except that pulp is made in special refiners that are
pressurized with steam in the first stage of refining.
First stage: Elevated T (110-130°C, just below the glass
transition temperature of lignin 140°C, enhance
fibrillation) & P. second stage: Ambient T, P
• Higher pulp strength. Energy req. 1900-2900 kWh/ton
• An even consistency of 20-30% is ideal
• The pulp yield is 91-95%
Chemi-Mechanical Pulping (CMP)
• C before SGW, PGW, RMP or TMP.
• The grinding requirements were about half
that required without pretreatment and the
CSF was 300-350 ml.
• 2 stage: Chemical Pretreatment + Mechanical
pulping
• Chemical Pretreatments:
– Hot sulfite: brighter, low strength
– Cold soda: drains faster, coarse fiber,
Alkaline Peroxide Mechanical Pulping (APMP)
• Sulfidity
• Causticity
• Causticizing efficiency
• Reduction efficiency