Page 298 - Materials Chemistry, Second Edition

VOC-Laden Air Treatment 281

a solid waste. The heating value of an air stream containing organics can be
determined by:

Heatingvalue of an airstreamcontainingVOCs(in Btu/scf)
=VOC’s heatingvalue (inBtu/lb) × Mass concentrationofthe VOC(lb/scf)

(7.15)
We can divide the heating value of a waste air stream in Btu/scf by the
density of the air to obtain the heating value in Btu/lb.

Heatingvalue of an airstreamcontainingVOCs(in Btu/lb)
=Heating value(in Btu/scf) Densityofthe airstream(lb/scf)÷ (7.16)

The density of an air stream under the standard condition can be found as:

Molecularweight
Densityofanair stream (inlb/scf) = (7.17)
392
Since air consists mainly of 21% oxygen (MW = 32) and 79% nitrogen (MW =
28), people normally use 29 as the molecular weight of the air. Consequently,
the density of the air is 0.0739 lb/scf (= 29/392). This value can also be used
for VOC-laden air, provided the VOC concentrations are not extremely high.

Example 7.7: Estimate the Heating Value of an Air Stream
Referring to the remediation project described in Example 7.1, a thermal oxi-
dizer is also considered to treat the off-gas. Estimate the heating value of the
air stream that contains 800 ppmV of xylene.

Solution:
(a) Use the Dulong’s formula (Equation 7.14) to estimate the heating
value of pure xylene:
Molecular weight of xylene (C H (CH ) ) = 12 × 8 + 1 × 10 = 106
6
4
3 2
Weight percentage of C = (12 × 8) ÷ 106 = 90.57%
Weight percentage of H = (1 × 10) ÷ 106 = 9.43%
 O 
Heatingvalue (inBtu/lb) = 145.4 C+ 620  H − 8  + 41 S


 0 
= 145.4(90.57) + 620 9.43 −  + 41(0)



8
= 19,015