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combustion(turbines/engines)

How to calculate the real air excess and the exhaust gases flow using indirect method? by jcll
Posted: 31 Aug 02

This is avery commom problem in the combustion process whatsoever system is used(engines, turbines, boilers, etc...).

In the real field test the follwoing items are known:

1.-fuel composition(main components)
2.-exhaust gas composition(main components) by one standard analysing equipment relative low price and good quality in the market.
3.-Stechiometry  relationships

With the values mentioned above one iterative process can be prepared with the follwing steps:

(a)fuel composition
m(excess air): (suppossed to be iterated)

consider 100 units of cble

vCH4:known by fuel analysis
vC2H6:"     "
vC3H8:"     "
vH2:  "     "
vN2:  "     "
vCO:  "     "

(b)stechiometry relations
CO2->CO2
CO+1/2O2->CO2
CH4+2O2->CO2+2H2O
CH4+3/2O2->CO+2H2O
N2->N2
N2+O2->2NO
C2H6+7/2O2->2CO2+3H2O
C3H8+5O2->3CO2+4H2O
H2+1/2O2->H2O

(c)exhaust gas analysis

vO2hs: with analysis equipment
vCOhs:"         "
vNOxhs:"        "


(d)calculations

Exhaust flow --> vhs:vCO2hs+vN2hs+VO2hs+vCOhs+vNOxhs

vCO2h:by stechiometrical relations (from above)
vN2hs:"     "
vO2hs:"     "
vH2Oh:"     "

(e)iterative process( 2 to 4 iterations ok if air excess(o) aqurate

vO2hs(d) = vO2hs(c)-->yes(m ok)
                      No (m')--->(e)

(f)exhaust flow

Units cble/h cble:(intro real data from cble flow measurement device)

Nm3 exhaust/h:vhs x Units cble/h
kg/h exhaust:vhs x density(tabulated)
Nm3/h air:m x A(stechiometric air required)

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