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| cylinder drainage heating system process control |
Heating System |
The heating system is as customized, as the concept of a paper machine. Two different systems are mostly introduced:
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The cascade system |
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The heating of a paper machine have to take place, that for the drying the optimal heating
curve can be adjusted. The first cylinders are operating with lower
temperatures in order to heat the paper easily to prelude the drying process.
The temperature is limited, because to prevent forming a
steam bag between the cylinder and the paper web. A steam bag takes effect
like an insulation between the cylinder and the paper web and would disturb
the heat transfer to the paper.
Furthermore the temperature difference between the paper web and the cylinder don’t have to be too big, because that would be lead to a plucking of the paper web. In the course of the heating process the cylinder temperature can increase, because there is no more unattached water on the surface of the paper that can form a steam bag. A steam and condensate system with a cascade circuit takes account on this conditions. The cascade system uses the driving steam of the drying group with higher pressure on an upstream group with a lower steam pressure. This process can be done step by step whereby the condensate as a result of the pressure drop is evacuating of the drying cylinders and separating from the steam in the separators. |
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The circulation system |
| The circulation system with thermo compressors offers the advantage that every drying group
can be run independently. The quintessence of such a system is that high
pressure driving steam the stream steam is compressing and can be reused in
the same drying group for the heating . Thereby the necessary blow through
steam for the cylinder drain can be used directly in the heating group.
With circulation systems can be obtain higher average steam pressures in
the drying group. |
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Thermo compressor |
 Thermo
compressors are introduced in different processes to save energy expenses.
Thermo compressors are able to compress big steam volume streams in a
relative simple way. The drive of this pump takes place with high pressure
steam. In a blast pipe the steam is bringing by relaxation to the most
possible high speed and direct behind the blast pipe mixed with the vacuum
steam. As a result of this, a part of the kinetic energy is going on the
vacuum stream. In the diffuser that follows the mixing line the kinetic
energy is transforming into
pressure energy, so that the entire steam stream is evacuating of the
thermo compressor with a pressure that lays between the vacuum pressure and
the driving pressure. The high speed allows an easy handling of high steam volumes.
In the steam and condensate system of a paper machine therefore it is
possible to control the pressure difference for the cylinder draining
between steam entrance and condensate exit with thermo compressors by
changing the driving steam mass. A thermo compressor with a adjustable
blast pipe is able to handle variegating conditions of vacuum and mixing
pressures and volume streams without throttling the drive pressure to
guarantee the cylinder draining. |
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