Coal Preparation » Dewatering
This project examines the installation of an on-line instrument to measure cake moisture in horizontal bed filters, in real-time. This will allow operators and process engineers to accurately adjust process parameters to meet the desired product moisture. It would also eliminate the costly need to manually sample the filter belts, which in many cases are carried out only every two hours.
In the early stages of this project Callidan Instruments undertook to develop a microwave based moisture analyser which would predict the moisture content of the fine coal bed across the conveyor belt. The analyser was designed to independently determine the percentage moisture at three different locations across the conveyor belt. For each location a microwave transmitter was located below the conveyor and an opposing microwave receiver located above the conveyor and filter cake product. One of the major design concerns for this application was to develop the correct microwave operating parameters to cater for approximately 20- 40mm of filter cake which could vary in moisture from 20% to 50%.
The first half of the project concentrated on the design and construction of the analyser. The remainder of the project was conducted at the Gregory Coal Mine whereby the analyser was installed, commissioned and calibrated. The last phase of the project was the investigation of how the on-line moisture result could be used to better control the horizontal belt filter to obtain the optimum filter cake moisture.
The analyser was presented with filter cake which varied in moisture significantly, manual sampling and laboratory analysis reported moistures in the range of 23% - 48%. For the purpose of calibration of the moisture analyser, this proved very fortunate as the large range of moisture enabled a true test of the analyser’s operating range. The results of the calibration and verification of the analyser suggested an analyser accuracy of better than 0.5% (1 std dev) over the range of 20% -30% total moisture and better than 1.0% (1 std dev) over a range of 20% - 50% total moisture.
It is believed that these levels of accuracy would be sufficient to enable tighter control of fine coal moisture and are a significant improvement over a manual sample taken every two hours.
Included in this report are also the performance plots of the relationship between cake depths, flocculant levels, belt speed against the on-line filter cake moisture. Performance plots such as these displays clearly the advantage of “on-line” data in developing control strategies for the horizontal belt filter.