(264a) Investigation of a Pendular Roller Mill

Due to new applications, such as high performance concrete, the demand for very fine particles at high throughputs is increasing rapidly. At the same time a growing concern for our planet’s resources has raised the demand for energy efficient processes.

By being able to produce particle size distributions with a d₉₇ < 10 µm while evidencing comparatively low power consumption values and high solids throughputs Roller mills in general and specifically pendular roller mills are up for the challenge.

The design of the pendular roller mill is thus far relying heavily on the experience gathered from industrially utilized mills. Due to the lack of experience in the new and coming fields of application a new, physically sound scale-up method must be developed to guarantee a successful design process. In order to determine scale-up rules that are valid for all product particle size distributions the operating behavior of pendular roller mills must first be fully understood.

The process occurring in roller mills can be subdivided into the following steps: comminution between the rollers and the grinding ring, solids transport between milling zone and classifier and classification of the crushed solids. In order to establish a reliable scale-up method all process steps must be completely characterized.

While both the classification and conveying process were investigated by measuring the pressure loss and the respective power consumption special attention was given to the comminution process. For that reason a new measuring method was developed with which the milling gap between the rollers and the grinding ring and the rotation speed of the rollers can be determined simultaneously.

The measurements were carried out on a pilot scale pendular roller mill during coarse and fine grinding processes to investigate the influence of process settings on the comminution, conveying and classification conditions.

By measuring the milling gap the correlations between parameters such as energy input, solids through put, solids hold-up or pressure loss on the one hand and the milling gap on the other hand can be acquired for the first time. With these correlations a physical model of the comminution process can be derived. Measurements of the rotation speeds of the rollers make it possible to detect slippage between the rollers and the grinding ring, allowing for a better evaluation of the efficiency of the comminution process.

With the gathered information a new scale-up rule is developed which accounts for the mills different operating behavior at different product particle size distributions.

After giving an insight into the working principle of pendular roller mills at different operating conditions the presentation will introduce a new scale-up procedure for pendular roller mills.