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Closure to Furnace Analysis P M V Subbarao Professor Mechanical Engineering Department Verification of Simplified Analysis……
Furnace Energy Balance Enthalpy to be lost by hot gases: Water walls Economizer Furnace
Other Radiative Exits of A Furnace
Platen Superheater • Platen Superheater : Flat panels of tubes located in the upper part of the furnace, where the gas temperature is high. • The tubes of the platen SH receive very high radiation as well as a heavy dust burden. • Mechanism of HT : High Radiation & Low convection • Thermal Structure: – No. of platens – No. of tubes in a platen – Dia of a tube – Length of a tube
Geometry of Thermal Structure : Platen SH • • The outer diameter of platen SH is in the range of 32 – 42 mm. The platens are usually widely spaced, S 1 = 500 – 900 mm. The tubes within a platen are closely spaced, S 2/d = 1. 1. The number of parallel tubes in a platen is in the range of 15 – 35. • Design Problem: To find out – Length of tubes. – Number of PSHs. • Design Constraints: Max. allowable steam flow rates.
Thermal Balance Equation for Platen SH • Energy given out by flue gas: • Energy absorption for a Platen SH: The radiative heat coming from the furnace may not be completely absorbed by PSH. The gas in PSH tube matrix radiates some heat out to next section.
• Radiation coming from furnace • Radiation lost from PSH • b is the width of PSH. • Radiation energy emitted by gas in tube space.
Convection Heat Transfer in PSH • The convective heat lost by flue gas • Overall Coefficient of Heat Transfer,
Ash Deposition Coefficient 1. non-slagging coal, 2. Medium Slagging Coal with soot blowing, 3. Medium slagging coal without soot blowing, 4. Combustible shale.
Performance of Analysis of Furnace • • Get Fuel Ultimate Analysis. Compute Equivalent Chemical Formula. Select recommended Exhaust Gas composition. Carry out first law analysis to calculate Adiabatic Combustion Temperature. • Total number of moles of wet exhaust gas for 100 kg of fuel : nex. gas = P+Q+R+T+U+V • 100 X CV of fuel = Snex. Gashf, gas • Calculate Adiabatic Flame Temperature. • Calculate total heat transfer area of furnace, Afur
Furnace Characterization Criteria • • • M Temperature Field Coefficient Tad or Tfl Theoretical combustion temperature Tout Furnace Exit Gas Temperature Afur Total surface area of furnace mc Flow rate of fuel
1225 0 C 1200 1175 1150 1125 1100
Effect of Coal Quality on Furnace Size
Furnace Exit Hot Exhaust gases Heat Radiation & Convection Flame Burner
Structure of Furnace Wall
Structure of Furnace Wall