ADVANCES IN DURUM MILLING
3.4.3.2
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Application of the eight-roller mill system
The eight-roller mill constitutes an optimal solution, in particular when size reduction systems have to be added or expanded and the available space is restricted. When existing four-roller mills are replaced by eight-roller mills, the roll length can be doubled within the identical space without the need for changing existing pneumatic lifts or sifter passages. Figure 3.8 illustrates a reduction passage with double grinding. This flow sheet allows the semolina particle size distributions currently available on the market to be produced. These also include traditional semolina without flour fraction. The flour produced in these semolina grades, with their low ash content, is separately extracted and can be stored in bins for subsequent admixing to fine semolina or for direct marketing, as required.
Fig. 3.8 Reduction passage with double grinding
3.4.4 Addition of durum flour 3.4.4.1 General considerations Fine semolina with particle sizes less than 355 pm is generally produced with a flour fraction. As the flour fraction in this product does not affect the quality of the semolina, it is possible to add low-ash flours which are not accepted by the market in traditional semolina, to the fine semolina in mixing installations.