JNTU B.Tech IV BASICS OF POWER PLANT ENGINEERING Previous Question Paper (September - 2022 - R18)

A supercritical boiler operates at a pressure above the critical pressure of water, which is 221.2 bar. At this point, the distinction between liquid and vapor phases disappears, and the water undergoes a continuous transition into steam without boiling in the traditional sense. This eliminates the need for a steam drum, as the fluid density changes gradually from a liquid-like state to a gas-like state.

Key advantages of supercritical boilers include:

• Higher thermal efficiency compared to subcritical boilers due to increased operating temperatures and pressures.
• Reduced fuel consumption and lower carbon dioxide emissions per unit of electricity generated.
• Faster response to load changes and improved operational flexibility.
• Lower auxiliary power consumption as there is no requirement for circulation pumps in once-through designs.

The hydraulic ash handling system uses water to transport ash from the furnace to a disposal site. This method is highly effective for large-scale power plants as it is dust-free and capable of handling significant quantities of ash.

The process involves the following components and steps:

• Ash Collection: Ash from the furnace hopper falls into a water-filled trough or a high-velocity water stream.
• Transportation: The ash-water mixture, known as slurry, is transported through pipes or open channels (sluiceways) using high-pressure water jets.
• Disposal: The slurry is directed to a sump or a settling pond. In the sump, centrifugal pumps are used to pump the slurry to a distant disposal area, such as an ash pond or a landfill.
• Water Recovery: In many modern systems, the water is separated from the ash at the disposal site, clarified, and recirculated back into the system to minimize water consumption.

The primary advantage of this system is the complete suppression of dust, which improves the working environment, though it requires significant water supply and effective wastewater treatment facilities to manage the effluent.