Question

What is the purpose of fixed vanes in the ball and race mill?

(a) Forms a cyclonic flow

(b) For easy movement of the coal

(c) For directing the airflow

(d) For barring the exhaust air to enter back into mill

This question was posed to me in an interview for internship.

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

Answer 1

The correct answer is (a) Forms a cyclonic flow

To explain: The fixed vanes make the entering air to form a cyclonic flow throwing the oversized particles to the walls of classifier. The oversized particles slide down for further grinding in the mill. The coal particles of required size are taken to the burners with air from the top of the cylinder.