Reference Manual

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Chapter 10B
Kamyr
R
Continuous Digesters
Kamyr
R
continuous digesters vary depending
upon the type of raw material, end product, the
cost of chemicals, steam or power, as well as
geographical location of the mill. There are five
basic configurations:
D Single vessel hydraulic digester (the original
design).
D Two vessel hydraulic digester (with separate
high pressure impregnation vessel).
D Single vessel steam/liquor phase digester
(with high pressure feeding system). Developed
primarily for sulfite cooking, it has also been used
for Kraft, pre-hydrolysis Kraft, and neutral sulfite
semi-chemical pulp.
D Two vessel steam/liquor phase digester (with
separate high pressure impregnation vessel)
D Steam/Liquor Phase Digester (with asthma
feeder) used for pulping sawdust, shavings or
non-wood fibers such as straw, bamboo, jute, etc.
The single vessel hydraulic digester was the
original Kamyr digester. It is so named because
the digester consists of a single vessel, which is
operated completely full of liquor (no vapor being
present). Digester heating is accomplished by
heating the cooking liquor indirectly in heat
exchangers using 150 to 175 psi steam and
circulating this heated cooking liquor through the
downward flowing chips in the digester vessel.
Over the years, this hydraulic digester system has
constantly improved. The modern single vessel
hydraulic digester has an improved steaming and
feeding system, which improves its tolerance of
dry and degraded chips. The combination
improved cooking circulations and steps in the
vessel diameter have made it possible to produce
a more uniform pulp, with a poor quality of chip
furnish.
The main features of a hydraulic digester are:
D Metering and steaming of the wood chips.
D Feeding chips to the digester via the high
pressure feeder and top circulation loop.
D High pressure impregnation of the chips with
cooking liquor.
D Heating to cooking temperature through
liquor circulation, using indirect heating.
D Hi-heat-in-digester washing followed by a
diffusion washer.
The hydraulic type digester with its long
impregnation and cooking times produces a very
uniform, high quality, strong pulp and is suitable
for the production of either liner grade or
bleachable grade pulps.
The two vessel hydraulic digester was originally
designed to provide optimum pulp quality in very
large digester systems (above 1200 TPD), but has
been used for smaller tonnages.
For large tonnages, the digester vessel becomes
large in diameter. This, in turn, makes it more
difficult to ensure uniform circulation in the normal
cooking liquor heating system.
In order to ensure uniform heating of the larger
chip mass, an impregnation vessel is added to
heat the chips to cooking temperature before they
enter the second vessel (digester). This allows for
all of the chips to be heated to exactly the same
cooking temperature, helping to optimize pulp
uniformity.
This digester is essentially unaffected by varying
chip furnish, as there is a homogeneous chip