Page 303 - Materials Chemistry, Second Edition

286 Practical Design Calculations for Groundwater and Soil Remediation

(d) The flow rate of oxygen in the effluent = (20%)(240) = 48 scfm
The flow rate of nitrogen in the effluent
= The flow rate of nitrogen in the influent = 1,080 scfm
The flow rate of carbon dioxide in the effluent
= carbon dioxide in the landfill gas + carbon dioxide produced
from combustion
= 80 + 120 (CH :CO = 1:1) = 200 scfm
2
4
The flow rate of water vapor in the effluent
= water vapor produced from combustion (CH :H O = 1:2)
2
4
= (2)(120) = 240 scfm
The total effluent flow rate = 48 + 1,080 + 200 + 240 = 1,568 scfm

Discussion:
1. The following table summarizes the flow rate of each component
in this process:

H 2 O
CH 4 O 2 N 2 CO 2
Influent (scfm) 120 2(120)(1.2) = 288 1,080 80 0
Effluent (scfm) 0 288 − 240 = 48 1,080 80 + 120 = 200 240
2. The flow rates of the total influent and total effluent are the
same at 1,568 scfm.

7.3.5 Supplementary Fuel Requirements
The VOC concentration of the off-gas from soil/groundwater remediation
can be very low and insufficient to support combustion. If that is the case,
auxiliary fuel would be needed. The following equation can be used to deter-
mine the requirement of supplementary fuel [1]:

T ) −
DQ C[ (1.1 T c − T he − 0.1 r H ]
Q sf = w w p w (7.19)
DH[ sf − 1.1 CT( c − T )]
p
sf
r
where
Q = flow rate of the supplementary fuel, scfm
sf
D = density of the waste air stream, lb/scf (usually 0.0739 lb/scf)
w
D = density of the supplementary fuel, lb/scf (0.0408 lb/scf for methane)
sf
T = combustion temperature, °F
c
T = temperature of the waste air stream after the heat exchanger, °F
he
T = reference temperature, 77°F
r
C = mean heat capacity of air between T and T r
p
c