Page 49 - Air Pollution Control Engineering

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Air Quality and Pollution Control 29

cases, the combined emission parameters must be determined from the mass and heat
balances. This section provides calculation procedures for combining emission stream
and single-emission-stream parameters.

7.2. Emission Stream Flow Rate and Temperature Calculations
Gas flow rates must be converted to standard conditions (77ºF, 1 atm) before flow
rates can be added together. The calculation procedures for converting gas flow rates to
SC and then combining gas flow rates are presented below. (Note: Because the emissions
are approximately at atmospheric conditions, pressure corrections are not necessary in
the following examples.)
Q = 537 Q e a ( 460 + T ) (20)
e1 1, e1
where Q is the flow rate of gas stream 1 in cubic feet per minute at standard condi-
e1
tions (scfm), Q is the flow rate of gas stream 1 in at cubic feet per minute actual
e1,a
conditions (acfm), and T is the temperature of gas stream 1 (ºF).
e1
The flow rate for each emission stream is converted to SC by using Eq. (20). After
all emission streams are converted to SC, the total volumetric flow rate for the combine
emission stream at standard condition (Q ) is determined by summing these flow rates,
e
as follows:
Q = Q + Q + Q + ... + Q (21)
e e1 e2 e3 en
where Q is the flow rate of the combined gas stream at standard conditions (scfm).
e
To convert combined volumetric flow rate at standard conditions (Q ) to flow rate at
e
actual conditions (Q ), the temperature of the combined gas stream (T ) must be deter-
e,a e
mined. This is accomplished by first determining the enthalpy (sensible heat content) of
each individual stream. The calculation procedures are presented as follows:
e1(
H = Q T − 77° )( 0 018 Btu ft 3 ° ) F (22)
.
F
s1 e1
where H is the sensible heat content of gas stream 1 (Btu/min) and T is the temper-
s1 e1
ature of gas stream 1 (ºF). Repeat this calculation for each emission stream. The total
sensible heat content for the combined emission stream is determined by summation of
sensible heat contents, which is shown in the following:
H + H + H + H + . .. + H (23)
s s1 s2 s3 sn
where H is the sensible heat content of the combined gas stream (Btu/min). The tem-
s
perature of the combined stream can now be determined from
T = ( H Q ) (0 018 Btu ft º ) F (24)
3
.
e
s
e
where T is the temperature of the combined gas stream (ºF).
e
3
The factor 0.018 Btu/ft ºF is obtained by multiplying specific heat at constant pres-
3
sure (c = 0.240 Btu/lb ºF) by the density (γ= 0.0739 lb/ft ) of air at 77ºF. With the tem-
p
perature of the combined gas stream (T ) and the flow rate of the combined gas stream
e
at SC, the actual combined gas stream flow rate is determined as follows:
Q = Q (460 + T ) 537 (25)
,
ea e e