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AFBC BOILER

GENERAL DESCRIPTION OF AFBC BOILER

ASHWINI has the capacity to manufacture the FBC Boiler upto 150 TPH for different types of fuels having sizes below 6 mm and free from foreign materials with outlet steam parameter is upto 125 Kg/cm^2(g).

Capacity Pressure SH Temperature Application
Upto 150 TPH Upto 125kg/cm2 Upto 540 Deg C Power & Process

The “FBC” is a fluidized bed combustion boiler with the following features.

  • Compartmentalized combustion chamber
  • Under bed fuel feeding system
  • Single- Drum OR Bi–Drum water tube type

PRINCIPLE OF FLUIDIZED BED COMBUTION

    FLUIDIZED BED

  • When air or gas is passed through an inert bed of solid particles such as sand supported on a fine mesh or grid, the air initially will seek a path of least resistance and pass upward through the sand. With further increase in the velocity, the air bubbles through the bed and the particles attain a state of high turbulence. Under such conditions, the bed assumes the appearance of a fluid and exhibits the properties associated with a fluid and hence the name ‘Fluidized Bed’.

    • MECHANISM OF FLUIDIZED BED COMBUSTION

  • If the sand, in a fluidized state, is heated to the ignition temperature of the fuel and the fuel is injected continuously into the bed, the fuel will burn rapidly and the bed attains a uniform temperature due to effective mixing. This, in short, is fluidized bed combustion.
  • If velocity is too low, fluidization will not occur and if the gas velocity becomes too high, the particles will be entrained in the gas steam and lost. Hence to sustain stable operation of the bed, it must be ensured that velocity is maintained between minimum fluidization velocity and particle entrainment velocity.


    • ADVANTAGES OF FBC BOILERS

  • Considerable reduction in boiler size is possible due to high heat transfer rate over a small heat transfer area immersed in the bed.
  • Low combustion temperature of the order of 750’-900°C facilitates burning of coal with low ash fusion temperature, prevents Nox formation, reduces high temperature corrosion and erosion, and minimizes accumulation of harmful deposits due to low volatilization of alkali components.
  • High sulphur coals can be burnt efficiently without much generation of Sox by feeding limisestone continuously with the fuel.
  • The unit can be designed to burn a variety of fuels including low grade coals like floatation slimes and washery rejects without much sacrifice in operation efficiency, because only about 1% by wt. of carbon content in the bed can sustain the fluidized bed combustion.
  • High turbulence of the bed facilities quick start-up and shut down.
  • Full automation of start-up and operation using simple reliable equipment is possible.
  • Inherent high thermal storage characteristics can easily absorb fluctuations in fuel feed rate.
  • There is reduced possibility of formation of local hot spots on heat transfer surfaces. Through having comparatively low efficiency, fluidized bed coal fired boilers offer the following distinct advantages over pulverized coal fired boilers, especially when using low rank coals:
  • High thermal inertia helps to overcome the problems of flame stability. It eliminates the necessity of supplementary oil firing to prevent extinction of flame when moisture and ash content of coal are high.
  • The formation of sticky deposits on the fire side of the tubes because of lowering of ash fusion temperature by sodium components in ash is avoided due to low bed temperature.
  • Lower coal crushing cost due to higher particle size.
  • 10 Efficiency of 80% and above can be achieved.