When we talk about the screen, we can imagine a surface having an open unit area throughout its surface, in which a particle is fed on the Screens. Fed material move on the surface of the screen, if the apparent diameter of the feed particle is smaller than the diameter of the open unit area then the particle will report below else it will move forward and report on the other end(Overflow).
As we all known about the widespread use of screens around the all mineral processing plant. We can unequivocally say that each mineral processing plant consists screen on vary degree of use. In the market, we can found various types of screens for different purposes. Before installation, we must know the efficiency of the screen to get information about the performance profile of the equipment.
Moreover, screens can be a single surface- single deck or multiple decks depends on its use in a plant. Therefore, for a numerous deck, the underflow of the above screen is feed for that screen.
Screen Efficiency:
It means how much amount of output material present in the output side. In simple terms, the ratio of the amount of desirable material in the output side to the amount of desirable material in the feed stream.
In the screen, we can found two outputs; underflow and overflow. Therefore, there will be two efficiencies for a particular stream. The multiplication of both efficiency value gives the overall efficiency of the screen.
Hence, Efficiency of overall screen.
(if you need detailed derivation then please ask in the comment section)
At this point, we must know that screen have a particular efficiency equation at the specific flow speed of the particle. In case the feed TPH is more than average, then the particle will not come to contact with the screen. Hence, bed depth is essential to maintain efficiency.
Partition curve:
Feed for screen consist of various class of particle sizes with varying degrees of grade percent. Hence, the probability of a particle getting separate is different. To calculate what is the sharpness of the screening process, tromp gave plausible theory in 1937. According to him, we can calculate the efficacy of the screening process by putting a graph of a chance of particle to get separate VS mean size of particles.
Tromp gave a term - Partition coefficient, which means the amount of misplaced material to an output stream.
(if you want to know more about the detailed method to draw the partition curve, then please let me know in the comment section)
After plotting a curve for P.C Vs. Mean particle size, we can predict the chance of particle to get misplaced for any size value. With this, we can also calculate the possible particle size, which has an equal opportunity to report both the side. One of the significant importance of the performance curve is to calculate d50 material. If the d50 material is more than blocking of material will happen, which will lead to a decrease in separation efficiency.
Another thing which we should know about is ideal separation: In the ideal case there is no the material at the d50 size and rest of the material has a perfect chance to report at only one side.
In a real situation, a particle with more than the aperture size, also reports to undersize, which means there is a short circuit that is happening. To calculate the amount of material in bypass is by calculating the area of the deviated graph from the ideal one. Another way to calculate the error in the process is by measuring Ecart probable value. If you want to more about this method, then please comment down below.
Capacity
In the case of screening, we can increase the feed as want, but as the feed value increase, the bed depth will also increase, which leads to inefficient separation. Now the appropriate capacity for the screen can be calculated using the following formula:
I hope you enjoyed my writing if you are reading up to this line. Please comment below if you have a suggestion of a recommendation to share.
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