Thermal Performance Analysis of A Furnace

1. Thermal Performance Analysis of A Furnace P M V Subbarao Professor Mechanical Engineering Department Test for Cooling Capacity of Furnace Surface….

2. Further Geometrical Details of A Furnace

3. Determination of Furnace Size •  = 30 to 50O •  > 30O •  = 50 to 55O • E = 0.8 to 1.6 m • d = 0.25 b to 0.33 b

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

5. 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

6. 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* Hot Exhaust gases Heat Radiation & Convection Flame Burner

7. Tangential fired furnace* Down fired furnace 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

9. Classification of Radiation

10. Types of Radiation from Flames • Tri-atomic gases - CO2, H2O and SO2 • Soot particles • Coke particles • Ash particles

11. 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

12. Face 1 Face 5 n North Face 3 H y η w Face 4 μ East x West e z ξ s South W Face 6 Face 2 L 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

13. RTE Optically Thin Self-absorbing Optically Thick Directional Averaging Differential Approximation Energy Hybrid DTM Ray Tracing Radiation Element Basic models for RTE in gas radiation 2-Flux 4-Flux Multiflux DOM Zone MCM Numerical (FD, FV) Moment Modified- Moment PN - Approx.