Coal Preparation » Gravity Separation
A feasibility study of a new cyclone design concept for fine coal was completed at the JKMRC pilot plant as ACARP project C7043. This study covered two types of cyclones - dense medium cyclones and classification cyclones. Numerous comparison tests were conducted under similar conditions between a new dense medium cyclone and a DSM cyclone, and between a new classification cyclone and two commercial classification cyclones, all 100mm in diameter. Fine density tracers and fine coal samples were used in the study.
The new cyclone design increases centrifugal force inside the cyclone, and mitigates the adverse impacts of the short-circuiting flow on particle separation. As a result the new cyclone can significantly improve particle separation, in particular for very fine particles (0.25-0.125mm).
The feasibility study has demonstrated that the new cyclone design concept can be used in both dense medium and classification cyclones. It has the potential to considerably improve both processes in coal preparation plants providing that the new cyclone design is properly scaled-up.
The new classifying cyclone was scaled up to 200mm in diameter and optimised in geometry in ACARP Project C8048. Many different dimensions of the six cyclone parts (feed entry, top part, middle part, bottom part, vortex finder and spigot) were trialed, and the cyclone performance was compared with a 150mm-diameter commercial cyclone.
A total of 111 tests for the new cyclone were completed. At similar feed pressure, the new cyclone consistently showed the following advantages:
| ||JK Cyclone - 200 mm ||Conventional Cyclone - 150 mm |
|Sharper separation - a value ||4.0 - 6.0 ||3.0 - 4.0 |
|Lower flow ratio ||18 - 24% ||over 24% |
|Lower separation size ||0.04 - 0.05 mm ||over 0.05 mm |
This clearly demonstrates the superiority of the new cyclone design concept.
To find an effective means for reducing the amount of water and very fine particles reporting to the underflow, the effects of cyclone inclination were investigated using the new 200 mm diameter cyclone and a 250 mm diameter commercial cyclone. The changes of the cyclone inclinations were in the range of 0° (normal vertical upward position) to 180° (vertical upside-down position) in the increments of 30° and 15° respectively.
Cyclone inclination had a significant influence on performance. For the tests using the new cyclone, as the inclination increased from 0° to 90° (horizontal position), the flow ratio to the underflow was decreased up to 42%, and the particle separation became even better. However, the separation size was slightly increased and the feed rate was slightly decreased. When the inclinations passed over 90° until 180°, the cyclone performance became poor.
For the conventional cyclone, changes in performance showed similar features with the change of the cyclone inclination. However, the relative decrease of the flow ratio was 28% when the inclination changed from 0° to 90°, which is smaller than that for the new cyclone.
The inclination of classifying cyclones at 75° - 80° seems to be best for achieving a high efficiency and a low flow ratio, while allowing draining the cyclones on shutdown. This may be of benefit to plants requiring an improvement in particle separation and flow ratio, while allowing a lower feedrate and a coarser separation size.