ANS:B - ball mill

Coal is finally pulverized to 200 mesh size for burning in boilers by a ball mill.

Explanation:

• Pulverization of Coal:
  • Coal is pulverized to achieve a fine powder size suitable for combustion in boilers. This process ensures efficient burning and maximum energy extraction from coal.
• Method Used:
  • Ball Mill: A ball mill is commonly used for pulverizing coal to achieve the desired particle size. In a ball mill, coal is introduced at one end and is pulverized as it passes through the mill, where grinding media (steel balls or rods) are used to crush the coal into a fine powder.
• Other Options:
  • Hammer Crusher: Typically used for crushing coal into smaller sizes initially but not for achieving the fine powder size required for combustion.
  • Roll Crusher: Used for secondary or tertiary crushing of coal, producing larger chunks than required for pulverization to 200 mesh size.
  • Gyratory Crusher: Used for primary crushing of large lumps of coal but not suitable for achieving the fine pulverized size needed for burning in boilers.
• Mesh Size: Pulverizing coal to 200 mesh size ensures that the coal particles are small enough to be efficiently burned in boilers, providing optimal heat release and combustion efficiency.