Dichte fase pneumatisch transport.
Report 97.3.TT.4946, Transport Engineering and Logistics.
Pneumatic conveying means the transport of solid materials with a conveying-gas
which flows through a pipeline due to pressure-differences. The materials which
are being conveyed are in most cases powders or pellets.
When the pressure in the pipeline is higher than the atmosferical pressure
of 1 bar, the material is blown though the pipelines. Because the
pressure-difference in de pipelines can be high, up to 8 bar, the materials
can be conveyed over distances up to several kilometres. In a system where the
pressure is lower than 1 bar, the material is being sucked through the
pipelines. Systems like this are used for unloading ships. Also combinations
of the two mentioned systems are being used.
Pneumatic conveying can be divided into dilute phase conveying and dense phase
conveying. With dilute-phase, the conveying velocity of gas and material
through the pipelines is high. Disadvantages of dilute-phase transport are the
high gasflow required and the amount of wear which can occur due to the high
conveying speed. These disadvantages are smaller in dense-phase conveying
which is being used more often. The conveying speed is lower and the gasflow
is lower. Especially when the conveyed material is abrasive, the conveying
velocity has to be low.
The components of a dense-phase conveying system are: compressor,
heat-exchanger, material gate, conveying pipelines and a material-gas
separator. There are several different designs of these components.
The material properties of the conveyed material are important parameters in
the design of a dense-phase conveying system, especially material size,
abrasiveness, cohesiveness and the amount of moist in the material. These
properties can cause severe problems like excessive wear and blockages in
the operational system.
There are several ways to design a pneumatic conveying system. These are:
design with the help of test facilities, using experience and mathematical
models and formulas. In most cases a combination of these methods is being
used to design a new system. Much research is being done to improve the
mathematical models. At the moment, these models are not precise enough.
Most operational problems are wear at bends and valves, blockages of the
system and degradation of the conveyed material. Wear can be reduced by
lowering the conveying velocity. There are several systems which can be used
to avoid blockages by injecting air at the places where a blockage occurs.
Product degradation can occur due to wear and melting of the product.
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