Hi Friends,
We are well aware about the design, engineering, fabrication, installation and operation of Double pipe heat exchangers for heating the clod stream of fluid using saturated steam or any other hot stream. In the present post, we will focus ourself it's suitability for heating ground Bauxite slurry using low pressure steam as heating media.
The installation of Double pipe heat exchanger is very easy as it has two concentric pipes where in the Buaxite slurry is pumped through the inner pipe and steam flows in the the annular area resulting in indirect heating of Bauxite slurry feeding to Desilication circuit. Initially, the system gives favourable results with reasonably high heat transfer rate but over a short duration of its operation (about six to eight months), the heat transfer co-efficients drops drastically affecting the performance of the system due to scaling in the inner surface of the tube.
As the nature of scale is very hard because of the presence of silica and alumina, hence it becomes very difficult to clean the scales by chemical method.
In many Alumina refineries of the World, Double pipe heat exchangers have been tried for similar duty but the results were not found encouraging, hence forced to replace within short duration.
With this experience, it may be concluded that Double pipe heat exchanger is not suitable for heating the Bauxite slurry mainly because of its maintenance problems due to hard scales on inner surface of pipes.
Regards.
Kunwar Rajendra
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