In-line Particle Size Measurement for Control of Jet Milling

Abstract

Jet milling is suitable for the production of very fine powders with a well-defined particle size distribution (PSD). The major disadvantage of the process is the poor energy efficiency. In practice jet mills have to be operated below their maximum capacity in order to avoid the production of off-specification material, due to operation disturbances. Therefore, it is important to automate operation with a real-time PSD instrument for quality control. In this paper, a study for in-line particle size measurement using laser diffraction is presented to improve operation control. This measurement system uses a novel CMOS pixel array, which has a robust and flexible feature for the application. It also includes an in-line cell system, where direct measurement is implemented in the product particle stream coming from the mill and an air purge for the cell window allows continued operation. Experiments were conducted on a 10-inch spiral jet mill pilot plant with alpha-Al2O3 as test material. The milling process is investigated by varying the operational conditions. The measurement results are useful to build a grinding model for control purpose.