DESCRIPTION

Technical Description

Zigzag sifters permit classification of solid compounds. The solid compound being separated is charged into the feed hopper. The compound is fed into the zigzag duct of the sifter at mid-height by way of a vibrating trough. An air flow flows upwards through the vertical duct. Depending on the geometry and density of the particles, they are carried along by the air or drop down due to gravity. At every bend in the duct the solid compound passes through the air flow and falls onto the opposite wall of the sifter. This corresponds to one sifting stage. Owing to the flow conditions, a vortex wake is formed between two bends of the zigzag duct. It ensures that the solid matter moves roughly perpendicular to the air flow. In this way, a transverse sift takes place at every bend. Sequencing of large numbers of such stages results in very fine separation. CE 275 features a 20-stage zigzag duct. Transparent material provides optimum observation of the processes in the duct.

A fan generates the air flow. The volumetric air flow rate and the solid mass flow are adjustable. The fine material transported upwards with the air flow is separated by a cyclone. Pressure measurement points at the relevant positions in the trainer enable the pressure loss to be determined.

Activated carbon in different particle sizes is recommended for use as the feed material. For particle size analyses of the feed and of the coarse and fine material, a balance and a screening machine (CE 264) are recommended.

The well-structured instructional material sets out the fundamentals and provides a step-by-step guide through the experiments.

Learning Objectives / Experiments

- learning the fundamental principle of wind sifting (gas flow classification)

- sorting
* coarse material fraction
* fine material fraction

  dependent on solid mass flow rate and volumetric air flow rate 

- classifying (with CE 264)
  * fraction balance
  * separation function
  * separation size
  * sharpness of separation

  dependent on solid mass flow rate and volumetric air flow rate
- pressure losses of
  * sifter
  * cyclone

  dependent on solid mass flow rate and volumetric air flow rate