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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Equipment used for pulverizing the coal is known as
Ball mill
Hopper
Burner
Stoker
Ball mill
A ball mill is a mechanical device used in thermal power plants to grind coal into a fine powder, which increases the surface area for rapid and efficient combustion. Pulverization ensures the coal burns like a gas, significantly improving the thermal efficiency of the furnace.
A ball mill is a mechanical device used in thermal power plants to grind coal into a fine powder, which increases the surface area for rapid and efficient combustion. Pulverization ensures the coal burns like a gas, significantly improving the thermal efficiency of the furnace.
P=rm⋅v2 — Centrifugal force acting on balls
Ek=21mv2 — Kinetic energy of grinding media
The ball mill consists of a rotating horizontal cylinder partially filled with steel balls. As the cylinder rotates, the balls are lifted and then fall onto the coal particles, subjecting them to impact and attrition forces. This continuous grinding action reduces the coal to a fine dust size (typically 70-80% passing through a 200-mesh sieve).
Pulverized coal (PC) firing allows for precise control of combustion air and fuel ratio.
Ball mills are classified as low-speed mills.
The fineness of coal is essential for reducing unburnt carbon loss in ash.
High reliability and long service life.
Capable of handling low-grade, abrasive coals.
Minimal maintenance required compared to high-speed mills.
High power consumption per unit mass of coal ground.
Occupies large floor space in the power plant.
Higher initial capital cost and weight.
Thermal power plants for coal-fired boilers.
Cement industry for grinding raw materials.
Mining and mineral processing.
Standard fineness for pulverized coal is often specified as 70% passing through 75 micrometers (200 mesh).
Option B (Hopper) is a storage vessel; Option C (Burner) is where combustion occurs; Option D (Stoker) is used for manual/automatic feeding of coal on a grate, not for pulverization.
A is correct — A ball mill is the primary equipment used in power plants to pulverize raw coal into fine particles for efficient suspension firing.
Always remember that ball mills are low-speed mills; high-speed mills like 'Ball and Race' mills are used when the moisture content of the coal is relatively low.