Paper Technology International 2024 - Journal - Page 148
PAPERTECHNOLOGYINTERNATIONAL
Figure 19: Remarkable power consumption savings with the
same pumping head.
Figure 21: Chemical injection points in MC pumping and mixing
system.
Figure 20: Production rate increase from 1’700 to 2’500 admt/d
without increasing the power consumption.
Ef昀椀cient mixing of chemicals
Mixing of chemicals and steam
Mixing chemicals and stock is one of the most important
operations in pulp bleaching. Good mixing provides homogenous
bleaching conditions, reduces the consumption of chemicals and
energy, improves product quality, and reduces the environmental
load. Proper chemical mixing is a key factor in the success of new
bleaching sequences.
The stock is 昀氀uidized in the MCE pump as the 昀椀ber network
is disintegrated, and the gas is also separated. This allows ef昀椀cient
mixing of various liquid chemicals in the MDL dropleg and in the
MCE pump. Most of these chemicals can be fed at a low pressure to
the suction side of the
MC pump. The new MCE pump provides a chemical mixing
arrangement also for concentrated sulfuric acid applications.
All gaseous chemicals and steam are mixed with a separate
SX chemical mixer. The chemical injection points are in different
locations for different chemicals. Each chemical and steam has
its own features and special, detailed selection and dimensioning
guidelines that need to be followed when injecting the chemicals into
the MC system.
148
Mixing of chemicals with the SX chemical mixer
The SX chemical mixer is designed for mixing both gaseous
and liquid bleaching chemicals into paper pulp. The SX chemical
mixer is used for a consistency range of 3 to 20%, and the product
sizes cover capacity ranges up to 5’500 admt/d. The small size
of the SX chemical mixer and valves and thus the small space
requirement and light weight make the installation and maintenance
easy. The SX chemical mixers are manufactured of stainless steel,
titanium, Hastelloy or 654SMO depending on the chemical to be
mixed and on the bleaching stage arrangement.
The rotor of the mixer 昀氀uidizes the stock together with the
casing turbulence generators. This disrupts the 昀椀ber network and
results in optimum mixing, with no gas separation. Perpendicular
positioning of the rotor and the unique three-dimensional turbulence
zone prevent the separation of gas. An inhomogeneity of 5 to 10%
is normally considered acceptable in bleaching. The SX chemical
mixer reaches an inhomogeneity value as low as 3 to 6%. This
con昀椀rms the excellent mixing results – with low power consumption.
Figure 22: SX chemical mixer design
