A mixture containing benzene, chlorinated benzene, ethyl
benzene, toluene, and xylene is incinerated and the combusted gases are passed
through an absorber that absorbs hydrochloric acid, before leaving the
stack. The flow rate from the incinerator
is measured at a flow 12,500 dry standard cubic feet per minute. The oxygen concentration in the stack is 7
percent.
Data is provided in the first four columns of the
table. Data includes incinerators’ (1)
inlet flow rate, (2) outlet flow rate of benzene, chlorobenzene, ethylbenzene,
toluene, and xylene. In addition, stack
emission data is provided for hydrochloric acid and particulate matter. Molecular weight information is listed in
the fourth column. We are required to
calculate (1) destruction and removal efficiency (DRE) for all organic
compounds, (2) hydrochloric acid removal efficiency of the absorber, and (3)
particulate concentration leaving the system in grains per dry standard cubic
foot.
Solution:
Destruction efficiency is calculated simply by subtracting
amount of the component leaving from the amount entering the system and
dividing by amount entering the incinerator unit.
For benzene, this value is 2,015 minus 0.537 divided by
2,015 equals 99.9733 percent. These
values are also listed for chlorobenzene, ethylebenzene, toluene, and xylene.
There is only one component in the feed that has chlorine
atom and that is chloroenzene. The
amount of chlorobenzene destroyed in the incinerator is 1,150 minus 0.109 or
1,149.891 pounds. This destroyed amount
would provide chlorine atom and produce hydrochloric acid in the amount of
1,149.891 times 36.45 divided by 112.5 equals 372.56 pounds. Please note that 36.5 is the molecular
weight of hydrochloric acid and 112.5 of chlorobenzene. Amount of hydrochloric acid leaving the
absorber is reported to be 10.7 pounds.
Thus, hydrochloric acid removal efficiency of the absorber is 372.56
minus 10.7 divided by 372.56 equals 97.128 percent.
Finally, concentration of particulate is calculated by
multiplying mass emission rate with volumetric flow rate in consistent
units: This translates to 23.4 times
7000 divided by 12,500 divided by 60 equals 0.2184 grains per dry standard
cubic foot. Please note that the number
7000 is a conversion factor between a pound and grains.