Coal Preparation » General
The project's objective is to develop a portable prototype measurement system using a digital camera and a laptop computer to measure screen aperture and open area. The measurement of the screen aperture will include the number of aperture measurements made, the mean, histogram and the standard deviation of those measurements. The open area measurement will be inclusive of pegging and the system will have the ability to calculate total screen open area from the input of screen parameters.
The device has been successfully tested at three Bowen Basin plants on over 9 plant screens using commonly used screen panels, including wedge wire, by both researchers and consultants (Table 3 section 6).
The system outputs the mean aperture, the standard deviation of the aperture readings and a histogram of the measurements for each panel and logs the aperture, standard deviation, open area of a clean deck and percent pegging of the analysed region of interest (ROI), however this can be adjusted to give data on each individual measurement within the ROI as required.
Percent pegging has been qualitatively estimated in the past by some consultants and researchers when considering the relationship between efficiency and effective open area. This system gives quantitative data that has not previously been available. Similarly the estimate of standard deviation and the concept of a measurement histogram have not previously been quantitatively available to researchers, consultants or plant personnel.
Aperture standard deviation is an important parameter when examining the data from the screen decks. In effect this figure will give an indication of the "condition" of the panel, screen deck or screen section such as the screen drain or rinse. High standard deviations are indicative of irregular screen apertures, which may result from unequal panel wear.
The histogram of the aperture measurements is a convenient visual method to describe the variation in measurements. The histogram can be produced for individual panels, for the entire screen or for screen sections and can be used to visually observe the panel wear.
This system provides a method to quantitatively measure screen aperture, effective open area, percent pegging and panel wear (standard deviation and histogram) for plant maintenance purposes and screen efficiency calculations. Regular use of the system may enable operators to predict a panel or screen's critical wear point (where wear has caused sufficient oversize material to report the underflow leading to measurable screen inefficiencies that affect product yield).
The new technique for screen deck measurement, through the analysis of digital images of individual screen panels, promises to provide a robust method for the measure of screen panel aperture and actual screen panel open area. The technique was able to achieve realistic results over a range of scenarios including various screen panel designs, panel conditions and screening applications. The image analysis software provides a mechanism for the measurement of screen panel aperture that is less dependent on the operator than current visual measurement techniques, although the selection of the segment of the deck to be analysed remains at the discretion of the operator. Commercialisation of the device would be via a local equipment or screen manufacturer with international links. The industry would use this device as a means to plot screen wear with time in order to determine the critical wear point where the efficiency of the screen has decreased to the point where the cost of the lost product Vs screen replacement is high. These measurements would also lead to an improved ability to predict residual panel service life, lower material usage and reduce the frequency of unplanned shutdowns.