On-line detection technology for continuous determination of particle size uniformity

The particle size distribution in powdered substances has an important influence on the effective ingredients and properties of inorganic salts, lactose, drugs, etc.: fine powder particles have a large total surface area and can react quickly, so they have stronger (drug) adsorption performance; granular powders have good fluidity and strong anti-adhesion ability.

Although sampling of raw material particles to be crushed and combining laboratory screening analysis can provide very accurate test data, it is impossible to achieve real-time adjustment at the production site based on these test data. Therefore, Frewitt decided to develop a new online detection method for powder particle size. The company used inorganic salts to conduct experiments on two grinders using sensor detection technology.

Frewitt is testing online particle size measurement technology

The online particle size detection is based on the extended Ortsfilter technology. The shadow line formed by each particle converts the tiny particles into detectable signal data. The movement speed and movement time of the particles are detected by optical fiber components, and the movement of each particle is displayed by optical equipment.

The online detection equipment has a high detection capacity, and the number of particles that can be detected per second is as high as several thousand. The computer in the detection system calculates the size of the particle size based on the detected data, and can provide real-time particle size data with a particle size range of 50~6000μm. The total number of particles of different particle size grades is permanently stored in the ring memory, thereby ensuring that the current particle size data can be provided at any time, and also ensuring that the data has good traceability, providing the most original data for editing relevant technical documents and records. Unlike other online detection technologies, there is no mathematical model of particles here, but detection is carried out according to the visibility of each particle.

Figure 1 D90 value: data obtained from online particle size detection and screening analysis (laboratory test)

The online particle size detection system was tested on the HammerWitt-Lab and ConiWitt-200 equipment of Frewitt. The HannerWitt grinding equipment used is a hammer mill (impact load), which is suitable for crushing small batches of products with a maximum speed of 7000r/min. In this hammer mill, the rotor is eccentrically designed and can rotate on the cutting side (long fibrous raw materials) and on the hammering side (crushing hard raw materials). The ConiWitt-200 used is a continuously working screening mill (shear load) with a maximum speed of 1800r/min, which is suitable for crushing agglomerated raw materials and fine grinding of dry and wet powdery objects. In both HammerWitt-Lab and ConiWitt-200 equipment, the particle size online detection sensor is installed horizontally at the outlet of the equipment.

Figure 2 Changes in particle size at high speed

In the HammerWitt-Lab hammer mill, 9 tests were conducted in seven stages with a particle size of 0.5 to 2.0 mm. The test results are shown in Figure 1. The test results are presented graphically: The advantage of this presentation method is that one obtains not only data on the average particle size, but also data on the largest and smallest particle sizes in the test sample.

As test and comparative data, the D10, D50 and D90 values ​​were measured. D90 is a very important parameter for measuring particle size. For example, the D90 data for test number 1 in Figure 1 is 200 μm, which means that 90% of all the particles tested have a particle size less than 200 μm. In this test method, the test data are judged according to volume-diameter (D(V)), which indicates the distribution of the mass of the particles in the material. The results of the online test were confirmed in the screening analysis in the laboratory (Figure 1).

At 11:03, the rotor speed of the ConiWitt-200 screening mill was 5 m/s. Before the rotor speed was increased from 5m/s to 14m/s, the D90 value of the ground material was about 250μm and the D50 value was 90μm. After the rotor speed was increased to 14m/s, the detected D90 value was 100μm and the D50 value was 70μm. After adopting this detection method, the distribution difference of particle size is smaller, and the powdery raw materials after crushing and grinding are more uniform (Figure 2).

This intelligent online particle size detection technology can continuously measure the particle size of particles in the production equipment and reflect these data in real time. Its simple use preparation, convincing test results, and visual data display function make it very helpful in various processes of batch production and continuous production.