PART 2
POWER
575
CHAPTER 16
COMBUSTION
Eric G. Eddings
Department of Chemical Engineering
University of Utah
Salt Lake City, Utah
1 FUNDAMENTALS OF
COMBUSTION
575
1.1 Air–Fuel Ratios
575
1.2 Fuels
578
2 THERMAL ASPECTS OF
COMBUSTION
580
3 FLAME AERODYNAMICS
584
3.1 Premixed Flames
585
3.2 Diffusion-Mixed Turbulent
Flames
591
3.3 Turbulent Diffusion Flame
Types
592
4 FIRING SYSTEMS
594
4.1 Gaseous Fuels
597
4.2 Liquid Fuels
599
4.3 Solid Fuels
601
5 POLLUTANT EMISSIONS
606
5.1 Control of Nitrogen Oxides
(NOx)
606
5.2 Control of Other Gaseous
Emissions
607
5.3 Control of Particulate Emissions
607
6 SAFETY CONSIDERATIONS
608
7 OXY-FUEL FIRING
612
REFERENCES
613
1 FUNDAMENTALS OF COMBUSTION
1.1 Air–Fuel Ratios
Combustion is rapid oxidation, usually for the purpose of changing chemical energy into
thermal energy—heat. This energy usually comes from oxidation of carbon, hydrogen, sulfur,
or compounds containing C, H, and/or S. The oxidant is usually O2—molecular oxygen
from the air.
One can perform basic chemical reaction balancing to permit determination of the air
required to burn a fuel. For example, consider the following reaction:
CH 2O → CO 2H O
4
2
2
2
where the units are moles; therefore, 1 mole of methane (CH4) produces 1 mole of CO2; or
1000 moles of CH4 requires 2000 moles of O2 and produces 2000 moles of H2O. Knowing
that the atomic weight of C is 12, H is 1, N is 14, O is 16, and S is 32, one can determine
molecular weights for each of the species involved in the reaction, and thus predict weight
flow rates: 16 lb/hr CH4 requires 64 lb/hr O2 to burn to 44 lb/hr CO2 and 36 lb/hr H2O.
If the oxygen for combustion comes from air, it is necessary to know that dry air is 20.99%
O2 by volume and 23.20% O2 by weight, most of the remainder being nitrogen (N2).
It is convenient to remember the following ratios:
Air/O 100/20.99 4.76 by volume
2
N /O 3.76 by volume
2
2
Mechanical Engineers’ Handbook: Energy and Power, Volume 4, Third Edition.
Edited by Myer Kutz
Copyright
2006 by John Wiley & Sons, Inc.