Question

An air screen grain cleaner unit of capacity one ton·h\(^{-1}\) with two screens was evaluated with a feed containing 8.5% impurities. During the operation, the clean grain at blower outlet, overflow of first screen, and underflow of second screen were found to be 0.3%, 1.2% and 0.8%, respectively. If the clean grain contains 0.6% impurities, the cleaning efficiency of the cleaner unit in percent would be \(\underline{\hspace{1cm}}\) (round off to one decimal place).

Hint:

Cleaning efficiency is the percentage of impurities removed from the feed material.

Answer 1

Correct Answer: 93

Let the total feed to the cleaner be \(100%\). The grain with 8.5% impurities enters the cleaner. After cleaning, the grain contains 0.6% impurities. Thus, the percentage of impurity removal can be calculated. The cleaning efficiency formula is: \[ \text{Cleaning efficiency} = \frac{\text{Impurity removed}}{\text{Total impurity}} \times 100 \] \[ \text{Efficiency} = \frac{(8.5 - 0.6)}{8.5} \times 100 = \frac{7.9}{8.5} \times 100 = 93.53% \] Thus, the cleaning efficiency is \( \boxed{93.5}% \).