Heat Recovery Steam Generator (HRSG) Learning Center
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Thermal properties of water and steam Thermal properties of flue gas Combustion, supplementary firing Heat transfer coefficients Intube pressure drop Gas side pressure drop across tubes Ducting pressure losses Acid dew point of flue gas NOx and other considerations

Combustion, supplementary firing


The supplemental combustion in HRSG systems takes place in a burner which usually is located in the flue gas stream going to the HRSG. However, some systems because of high firing requirements and low O2 in the flue gas, may require to be fired externally to the flue gas stream and may reuire additional combustion air. The types of burners and how they function are not covered in detail in this section. The amount of heat released can be easily calculated for a gas when we know the composition of the fuel and the heating values of the various components. For liquid fuels, the heating values are obtained by a calorimeter test.
From these values and using the standard combustion equation, we can determine the composition of the flue gas leaving the burner. As an example, the combustion of methane could be stated :

CH4 + 2O2 --- > CO2 + 2H2O
Of course for fuel gases containing many more components and burning in flue gas rather than pure oxygen, the equation gets more complicated. Therefore, a task that in itself is quite simple, becomes a burden to do by hand, but can be easily accomplished by a simple computer program. The heating values normally used in HRSG design are the LHV, lower heating values.
To try some calculations, click the button below to open another window to do some fuel combustion calculations:


The following Lower Heating Values(LHV) are used in this script:

ComponentBtu/lb ComponentBtu/lb ComponentBtu/lb
CH421,520 C2H620,432 C3H819,944
N-C4H1019,680 I-C4H1019,629 N-C5H1219,517
I-C5H1219,478 C6H1419,403 CO4,347
H251,623 N20 CO20
C14,093 S3,983 C2H420,295
C3H619,691 C4H819,496 C6H617,480
H2O0 O20 H2S6,545

Disclaimer:

The formulas and correlations presented herein are all in the public domain and are to be used only as a learning tool. Note that any product, process, or technology in this document may be the subject of other intellectual property rights reserved by sponsors or contributors to this site. This publication is provided as is, without any warranty of any kind, either expressed or implied, including, but not limited to, the implied warranties of fitness for a particular purpose, or non-infringement.

The formulas, correlations, and methods presented herein should not be considered as being recommended by or used by the sponsors of this site. The purpose of this site is educational and the methods may or may not be suitable for actual design of equipment. Only a fired heater design engineer is qualified to decide if a calculation or procedure is correct for an application.