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A Rolling Success – part two

World Cement,

Latest technology

The 2-way system

The 2-way system has sub-rollers that de-aerate and compact the raw material bed on the grinding table. This system, developed by UBE, was first introduced in 1984, and later became the main system for slag and cement grinding. With the company’s latest design, sub-rollers are optimally pressurised and their structure is simplified in order to optimise both cost-efficiency and performance.

Optimisation of the gas flow inside the mill

Conventional design

In recent years, UBE has been researching ideal gas flow through gas flow analysis technology. 

In particular, in cross section Z=9m, there is an area where the speed of the gas flowing into the separator is fast. Furthermore, in Z=12m, in addition to the gas flowing in, there is uneven velocity within the separator. In other words, the analysis indicates an uneven gas flow inside the mill.

If velocity occurs in the vicinity of the separator, the classified particle size distribution becomes either big or small in the circumferential direction of the separator. As a result, the increase in internal circulation causes an increase in mill differential pressure, deteriorating capacity and power consumption, which results in mill vibration. The deterioration in product quality becomes a concern from the widened particle size distribution. Additionally, uneven velocity within the mill can lead to abrasion, thus increasing maintenance cost.

By studying the analysis of the conventional design, the company discovered that the uneven velocity on the side in which gas flows into the separator is strongly impacted by the positioning of the mill inlet duct. Likewise, uneven velocity on the side in which gas flows out of the separator is strongly affected by the positioning of the duct and its design.

Latest design

As a countermeasure for uneven velocity occurring on the side flowing into the separator, UBE installed uniquely designed flow-rectification plates inside the inlet duct. The flow-rectification plates, together with the installation of nozzles (blade ring) on the outside of the table, improved the gas flow and even flow was achieved in circumferential direction. Additionally, the company was able to make gas flow from mill to separator more uniform by improving the shape and speed of the blade ring.

To correct the uneven velocity occurring on the side flowing out of the separator, the company designed a unique separator. The distinctive feature of this design was the decentring of the outlet duct from the separator. By decentring the duct from the centre of separator to X, Y direction, it was possible to suppress the fast gas-flow directly beneath the duct and smooth the discharge of revolving airflow from the separator.

This is part two of a three-part article written for World Cement’s February issue and abridged for the website. Subscribers can read the full issue by signing in, and can also catch up on-the-go via our new app for Apple and Android. Non-subscribers can access a preview of the December 2015 issue here.

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