Page 132 - Handbook of Energy Engineering Calculations

and show that either 3.784 or 3.78 is a sound assumption which seems to be
wrong, but in reality is not. In the above equation for W , the carbon,
a
hydrogen, or sulfur coefficient, C = (MO /DO )M , where MO is the
x
2
2
x
2
molecular weight of oxygen, O ; DO is the decimal fraction for the percent,
2
2
by weight, of oxygen, O , in dry air containing “atmospheric nitrogen,” (N ),
2
2
and small amounts of inert and inactive gases: M is the formula weight of
x
the combustible element in the fuel, as indicated by its relative amount as a
reactant in the combustion equation. The alternate evaluation of C is
x
obtained from stoichiometric chemical equations for burning the combustible
elements of the fuel, i.e., C + O + (?)N → CO + (?)N ; 2H + O + (?)N 2
2
2
2
2
2
2
→ 2H O + (?)N ; S + O + (?)N → SO + (?)N . Evidently, C = [MO + (?
2
2
2
2
2
2
2
x
× MN )]/M , where MN is the molecular weight of nitrogen, N , and the
2
2
2
x
other items are as before.
Equating the two expressions, C = [MO + (? × MN )]/M = (MO /DO )
x
x
2
2
2
2
M , reveals that the M terms cancel out, indicating that the formula weight(s)
x
x
of combustible components are irrelevant in solving for (?). Then, (?) = (1 −
DO )[MO /[MN × DO )]. From the above-mentioned book by Kiefer, et al.,
2
2
2
2
DO = 0.23188. From Marks’ Standard Handbook for Mechanical
2
Engineers, McGraw-Hill, Inc., 1996, MO = 31.9988 and MN = 28.0134.
2
2
Thus, (?) = (1 − 0.23188)[31.9988/(28.0134 × 0.23188)] = 3.7838. This
demonstrates that the use of (?) = 3.784, or 3.78, is justified for combustion
equations.
By using either of the two evaluation equations for C , and with accurate
x
values of M , i.e., M = 12.0111; M = 2 × 2 × 1.00797 = 4.0319; M =
H
C
x
s
32.064, from Marks’ M.E. Handbook, the more precise values for C , C ,
H
C
and C are found out to be 11.489, 34.227, and 4.304, respectively. However,
S
the actual C values, 11.5, 34.5, and 4.32, used in the formula for W are both
x
a
brief for simplicity and rounded up to be on the safe side.
ANALYSIS OF REGENERATIVE-GAS-TURBINE CYCLE

What is the cycle air rate, lb/kWh, for a regenerative gas turbine having a