Keywords: Screening, separation, screening efficiency, vibrating screen, sifter, grading, particle size analysis.
Screening is the process of separating dry materials based on particle size. The performance of a screening machine has a significant impact on the quality and quantity of product produced in a given process. Optimising screening performance will lead to maximisation of profitability. The performance of any screener is a function of variables such as:
· Screen motion whether vibrating, gyratory, linear or stationary.
· Screen loading, which is expressed in feed rate or unit area.
· Screen slope and corresponding effective aperture.
· Material characteristics such as particle size distribution, particle shape, bulk density, moisture, friability and static charge.
To evaluate a screener’s required performance, the objectives of the operation must be defined. The evaluation of performance requirements generally involves answering two questions:
· Does the screener deliver an acceptable product i.e. what is the required product quality?
· How much product in the feed was actually recovered as good product i.e. what is the screener’s efficiency?
The fertiliser industry is no different. The screener needs to consistently produce a specific product quality at a rate determined by the plant’s production requirements under varying operating conditions.
The paper first offers an overview of general screening fundamentals and considerations such as material characteristics, product quality and product quality measurements before moving onto how screening technology is applied to the granulated urea industry. A typical granulated urea process is defined, the location of the screeners and the duties the screeners must perform is explained which leads into the product quality requirements of the granulated urea fertiliser industry. Like many industries, the urea industry is global and markets can differ dependent on location. Due to this factor, the product quality and screener performance requirements can fluctuate from plant to plant. The screener adjustments required to cope with these variations are also examined.
This publication is based on the experience Rotex Global LLC has gained from over 100 years of screening machine manufacture, screening applications experience, involvement with fertiliser projects, end user and licensor feedback, empirical data and laboratory testing.
Neil E Smith, Rotex Europe Ltd., Aston Lane North, Whitehouse Vale, Runcorn, Cheshire WA7 3FA, UK.
38 pages, 20 figures, 8 tables, 5 references.