Thermal Performance Analysis of A Furnace

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Thermal Performance Analysis of A Furnace

• P M V Subbarao
• Professor
• Mechanical Engineering Department

Test for Cooling Capacity of Furnace Surface.
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Further Geometrical Details of A Furnace
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Determination of Furnace Size

• ? 30 to 50O
• ? gt 30O
• ? 50 to 55O
• E 0.8 to 1.6 m
• d 0.25 b to 0.33 b

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Heat Transfer in A Furnace

• The flame transfers its heat energy to the water
  walls in the furnace by Radiation.
• Convective Heat Transfer lt 5.
• Only Radiation Heat Transfer is Considered for
  Performance Analysis!

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Simplified Approach

• Emitted Radiation heat flux of flame

• Emitted Radiation Available Heat
• Heat flux absorbed by walls

Thermal efficiency factor, y.

• The rate of heat absorption

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Coal fired furnace

• Two functions of coal fired furnace
• Release of chemical energy by combustion of fuel
• Transfer of heat from flame to water walls
• Combustion space surrounded by water walls

Furnace Exit
Structure of water walls
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Burner arrangement flame shapes

• An array of burner installed on walls or at
  corners of furnace
• Fuel and combustion air projected from the each
  burner create a complex shape of flame.
• Intense mixing of fuel and air stream at the
• centre

Opposed wall fired furnace
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Classification of Radiation
Surface radiation Gas radiation
Surface phenomena Volumetric phenomena
Constant radiation intensity Variable intensity
Basic radiation quantity- emissive power Basic radiation quantity- intensity
Simple analysis Complex analysis
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Types of Radiation from Flames

• Tri-atomic gases - CO2, H2O and SO2
• Soot particles
• Coke particles
• Ash particles

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Radiation inside furnace

• Types of radiation Surface and volumetric
  radiation
• Characterization of participating media usually,
  the radiant energy is scattered, absorbed and
  emitted by tiny suspended particles or gases like
  CO2 and water vapor, such media are called
  participating media.
• Gas radiation involved
• Absorption attenuation of intensity ? absorption
  coefficient ?
• Emission augmentation of intensity? emission
  coefficient
• Scattering ? scattering coefficient ?
• Radiant heat transfer occur from the source
  (Flame) to sink (water walls) in a furnace

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Gas radiation-Governing equation

• Assumptions
• All six boundaries are diffuse and gray
• Absorbing, emitting, non scattering gray medium
• Same absorption coefficient at all points
• Thermophysical properties e.g. density, specific
  heat, thermal conductivity and optical property
  like extinction coefficient are constant.
• Absorption coefficient emission coefficient

Co-ordinate system for cubic enclosure
Governing equation for participating media (RTE)
Where S is line of sight distance in the
direction of propagation of the radiant intensity
I
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Basic models for RTE in gas radiation
2-Flux 4-Flux Multiflux DOM
Zone MCM Numerical (FD, FV)
Moment Modified- Moment PN - Approx.