Question

What is the purpose of rotary scoop shaped rejecter arms in impact mill?

(a) To send back the coal back into grinder for second run

(b) To throw the large particles back into the grinder

(c) To eliminate ash from the pulverizer

(d) To eliminate rocks and solid particles that has mixed up with the coal

The question was posed to me in final exam.

This intriguing question comes from Pulverised Mills in division Steam Power Plant of Energy Engineering

Answer 1

Right answer is (b) To throw the large particles back into the grinder

For explanation: The finely pulverized coal in the final stage of grinding is carried with the air to the burner through the rotating scoop rejecter arms which throw the large particles back into the grinding section. The final stage grinding consists of pegs carried on a rotating disk and travelling between stationary pegs.