Abstract
Problem statement: The measurement of powder flowability is a major c oncern for most industrial processes that deal with the handling of bulk solids as raw materials, intermediates, or products. Approach: The influence of particle size on the flowability of silica gel was investigated using aerated and non-aerated methods. The aerated method involved the measurement of the Hausner Ratio (HR) and Angle Of Repose (AOR) using a Hosokawa Powder Tester (PT-S), while the non-aerated method involved a Cohesion Index (CI) measurement based on a Stable Micro Systems TA.XT Plus texture analyzer. The mean size diameters of the fine and coarse powders used in this work were 9.4 and 60 µm, with densities of 2.1262 and 2.1290 gm cm -3 , respectively. The experiments were conducted immediately after drying with a range of sizes of the chosen powder. Results: The three measured parameters confirmed the general expectation that the fine powders are cohesive and the coarse powders are free-flowing. T he HR values indicated that the mixture was a free-flowing one above the 40 µm size. A transition in flowability occurred when the size was between 28 and 40 µm, while the mixture became cohesive when the particle size was below 28 µm. All three of the flowability indicators corresponded well wit h each other, signifying that the selected indicato rs correctly predicted the flowability. Conclusion: The new non-aerated method, where CI was measured, was proven to be a reliable indicator in predicting flow characteristics.
Highlights
Powders account for more than 50% of the raw materials used in the chemical industry
The results demonstrated a large diversity in flowability and cohesive properties for the powders examined
Methodologies: Hausner ratio: The ratio between tapped and aerated bulk density is known as the Hausner ratio and it is often used as an internal friction index for cohesive powders (Geldart et al, 1984)
Summary
Powders account for more than 50% of the raw materials used in the chemical industry. Numerous operations in process industries involve powder handling, such as: Storage of powders in hoppers and bins, transportation of powders from storage to the processing area, grinding or milling of powders, mixing of different powders to produce a desired quality, compression of powders in moulds to obtain a preformed solid product, granulation of powders to obtain larger grains which can be more transported and processed, and aeration by blowing gas upwardly through a powder bed in order to improve the contact between the powder particles and the aerating gas. The capability of predicting powder flowability is helpful for preventing production stoppages in all bulk solid handling. Some of the factors that affect the flowability of bulk solids and powders include particle size, moisture content, humidity, flow agents, temperature, and pressure
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