1. OPTIMIZATION OF EXCESS AIR IN COAL FURNACE
P M V Subbarao
Professor
Mechanical Engineering Department
Selection of Sufficient Air to use the Entropy Vehicles…..

2. Typical values of Excess Air vs Fuel
Fuels
% Excess air
Solid
Coal(P)
Coke
Wood
Bagasse
25 – 45
Liquid
Oil
3 – 15
Gas
Natural Gas
5 – 10
Refinery gas
8 – 15
Blast-furnace gas
15 – 25
Coke-oven gas
5 - 10

3. Typical Layout of A Model Furnace
Hchimney
Tatm
TCh,gas A B
pB = pfan,s
pA = pfan.f
Fuel

4. Air Supply Systems

5. Energy Potential of Post Combustion Gases
Total Thermal Power of post combustion gases:
Thermal Power of Chimney gases with heat
Exchange to working fluid :
Total Thermal Power of gases available for Utility:

6. Measures of Inefficient Combustion
Unburned carbon losses
For every 100 kg of fuel (as received)
QUCL = nc * MC * Calorific Value of Carbon : kJ
QUCL = nc * 12 * kJ.
Incomplete combustion losses
For 100 kg of fuel (as received):
QICL = nCO * MCO * CV of CO. kJ.
QICL = nCO* 28 * kJ.

7. Selection of Optimal air for Best Performance
Air-Fuel Ratio

8. Results for Best Efficiency

9. Effect of Excess Air on Emissions

10. Selection of Optimal air for Eco-Friendliness

11. Learning about Impact of Excess Air

12. Study of Impact of Excess Air

13. Unified Optimization Methods

14. Methods to Apply the Optimization

15. Monitoring of Optimal Excess Air

16. Air Ingression Due to Better Combustion Conditions

17. Effect of Air Ingression on Actual Available Excess Air

18. Excess Oxygen at Furnace Exit

19. 13 Essentials of Optimum Combustion
Fuel Preparation
1. Fuel feed quality and size shall be consistent.
2. Fuel feed shall be measured and controlled as accurately as possible. Load cell equipped gravimetric feeders are preferred.
3. Fuel line fineness >75% passing a 200-mesh screen, and 50 mesh particles <0.1%.
Distribution to Burners
4. Primary airflow shall be accurately measured and controlled to ±3% accuracy.
5. Primary air to fuel ratio shall be accurately controlled when above minimum.
6. Fuel line minimum velocities shall be ~ 15m/s.
7. Fuel lines shall be balanced by “Clean Air” test to within 2% of average.
8. Fuel lines shall be balanced by “Dirty Air” test to within 5% of average.
9. Fuel lines shall be balanced in fuel flow to within 10% of average.

20. 13 Essentials of Optimum Combustion
Distribution to Burners
4. Primary airflow shall be accurately measured and controlled to ±3% accuracy.
5. Primary air to fuel ratio shall be accurately controlled when above minimum.
6. Fuel line minimum velocities shall be ~ 15m/s.
7. Fuel lines shall be balanced by “Clean Air” test to within 2% of average.
8. Fuel lines shall be balanced by “Dirty Air” test to within 5% of average.
9. Fuel lines shall be balanced in fuel flow to within 10% of average.

21. 13 Essentials of Optimum Combustion
10. Over-fire air shall be accurately measured and controlled to ±3% accuracy.
11. Furnace exit shall be oxidizing; 3% oxygen is preferable.
12. Mechanical tolerances of burners and dampers shall be ±1/4’’.
13. Secondary air distribution to burners shall be within 5-10% of average.