Page 379 - Air Pollution Control Engineering

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Thermal Oxidation 355

Table 4
Theoretical Combustion Temperature Required for 99.99% Destruction Efficiencies
Compound Combustion temperature (ºF) Residence time (s)
Acrylonitrile 1344 1
Allyl chloride 1276 1
Benzene 1350 1
Chlorobenzene 1407 1
1,2-Dichloroethane 1368 1
Methyl chloride 1596 1
Toluene 1341 1
Vinyl chloride 1369 1
Source: ref. 2.

efficiency to equipment parameters, because design equations are seldom used in
hand analysis.

3. SUPPLEMENTARY FUEL REQUIREMENTS
Supplementary fuel is added to the thermal incinerator to attain the desired combustion
temperature (T ). For a given combustion temperature, the amount of heat needed to main-
c
tain the combustion temperature in the thermal incinerator is provided by (1) the heat
supplied from the combustion of supplementary fuel, (2) the heat generated from the
combustion of hydrocarbons in the emission stream, (3) the sensible heat contained
in the emission stream as it leaves the emission source, and (4) the sensible heat
gained by the emission stream through heat exchange with hot flue gases.
In general, emission streams treated by thermal incineration are dilute mixtures of
VOC and air and typically do not require additional combustion air. For purposes of this
handbook, it is assumed that the streams treated will have oxygen contents greater than
20% in the waste gas stream, which is typical of the majority of cases encountered. The
following simplified equation can be used to calculate supplementary fuel requirements
(based on natural gas) for dilute VOC streams:
e[
DQ C (11. T − T − 01. T ) − h e]
p
r
e
c
he
Q = air (2)
f f[ T − )]
Dh − 11. C ( c T r
f
p
air
where Q is the natural gas flow rate (scfm), D is the density of the flue gas stream
f e
(lb/scf [usually 0.0739 lb/scf]), see Eq. (4), D is the density of fuel gas (0.0408 lb/scf for
f
methane), see Eq. (4), Q is the emission stream flow rate (scfm), T is the combustion
e c
temperature (ºF), T is the emission stream temperature after heat recovery (ºF), T is
he r
the reference temperature (77ºF), C p air is the mean heat capacity of air between T and
c
T (Btu/lb-ºF) (see Table 7), h is the heat content of the flue gas (Btu/lb), and h is the
r e f
lower heating value of natural gas (21,600 Btu/lb). T can be calculated by using the fol-
he
lowing expression if the value for T is not specified:
he
T = ( T ) + −( T )]
he HR 100 c [ 1 HR 100 e (3)