Question

The gross energy requirement, to reduce a very large feed of coal to such a size that 80% of the product passes through a 100 \(\mu\text{m}\) screen, is 13 kWh per ton of feed. In a process, 250 tons \(\text{h}^{-1}\) of coal is crushed. The range of feed sizes is such that 80% of the feed passes through an opening of 100 mm. The product size range is to be such that 80% of the product passes through an opening of 25 mm. According to Bond's law, which one of the following is the power consumption (in kW)?

• A. 12.8
• B. 25.7
• C. 51.4
• D. 102.7

Hint:

First find $W_i$ from the infinite-feed data point ($F_{80}\to\infty$ gives $W_i=13$), then reapply Bond's law with $F_{80}=100$ mm and $P_{80}=25$ mm.

Answer 1

The Correct Option is D

Working in mm with calibration constant K=10Wi: $13=K(1/\sqrt{0.1}) \Rightarrow K=4.111$. Applying to process (P80=25mm, F80=100mm): $E=4.111(0.2-0.1)=0.4111$ kWh/ton. $P=0.4111\times250=102.8\ \text{kW}$.\[ \boxed{P \approx 102.7\ \text{kW}} \]