Delft University of Technology
Faculty Mechanical, Maritime and Materials Engineering Transport Technology
J.R. Dunselman Dichte fase pneumatisch transport.
Literature survey, 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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