Page 388 - Air Pollution Control Engineering

08_chap_wang.qxd 05/05/2004 4:26 pm Page 363
Thermal Oxidation 363

1. Density of flue gas stream, D = 0.0739 lb/scf
e
2. Density of fuel (methane or natural gas), D = 0.0408 lb/scf
f
3. Emission stream flow rate, Q = 15,000 scfm
e
4. Mean heat capacity, C = 0.269 Btu/lb-ºF for the interval 77–1800ºF
p air
5. Emission stream temperature, T = 1296ºF
he
6. Combustion temperature, T = 1800ºF
c
7. Reference temperature, T = 77ºF
r
8. Lower heating value of natural gas, h = 21,600 Btu/lb
f
9. Heat content of flue gas, h = 55.4 Btu/lb
e
Solution
Because the emission stream is very dilute and has an oxygen content greater than 20%,
Eq. (2) is applicable. The natural gas flow rate is then calculated to be
.
Q = (0 0739. )(15 000 0 269, )[ . (1980 − 1296 − 7 7 ) − 55 41. ]
f )]
.
0 0408 [21 600, − 1 1. (0 269. )(1800 − 77
Q = 163 scfm
f
The following should be noted before calculation:
Q ,h Input data
e e
D 0.0739 lb/scf, if no other information available
e
D 0.0408 lb/scf, if no other information available
f
h Assume a value of 21,600 Btu/lb if no other information available
f
C p air See Table 8 for values of C p air at various temperatures
T Obtain value from Table 3 or from permit applicant
c
T Use the following equation if the value for T is not specified:
he he
T = (HR/100)T + [1 − (HR/100)]T
he c e
where HR is the heat recovery in the heat exchanger (percent); assume a value of 70% for
HR if no other information available
T 77ºF, if no other information available
r

Example 5

Determine (1) the flue gas flow rate under standard conditions, (2) the actual flue gas flow
rate, and (3) the combustion chamber volume for a proposed thermal incinerator, under the
following design conditions:

1. Maximum HAP emission stream flow Q = 15,000 scfm
e
2. Natural gas flow rate Q = 163 scfm
f
3. Combustion temperature T = 1800ºF
c
4. Combustion residence time t = 0.75 s
r
Solution
1. The flue gas flow rate Q is
fg