United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 2771 Tx w ^
Research and Development
EPA-600/S2-83-065 Oct. 1983
c/ERA Project Summary
Treatment of Gaseous Emissions
from Steelplants Containing
Small Concentrations of
Hydrocarbon Vapors
H. X. Lambert and Julian Szekely
In this research, the feasibility of
using a shallow fluidized bed of activated
charcoal to remove small concentrations
of hydrocarbon vapors in the presence
of water vapor is investigated. This
system can be applied to cleaning off-
gases from sinterplants, coke ovens,
rolling mills, oil quenching, and/or
foundries. The investigated range of
hydrocarbon vapors is 100-500 ng /cm3
air.
It is found that a shallow fluidized bed
of activated charcoal can efficiently
remove hydrocarbons in preference to
moisture at 80°C. The overall mass
transfer coefficient can be calculated
from data obtained in a laboratory
apparatus, and the influence of various
parameters on the overall reaction rate
is discussed.
A mathematical model based on
adsorption theory is presented, which
provides a means for testing the validity
of the assumptions and also for prelim-
inary scale-up calculations.
This Project Summary was developed
by EPA's Industrial Environmental
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fulfy docu-
mented in a separate report of the same
title (see Project Report ordering
information at back).
Introduction
The purpose of this investigation was to
explore the possibility of developing a
suitable secondary or tertiary treatment
technique for the removal of hydro-
carbons, present at low concentration
levels, say of the order of 0.01-0.02
gr/ft3, from effluent gases.
Problems of this type are of importance
in steelplant operations, where the
effluent gases from sinterplants may
contain hydrocarbons at such concentra-
tion levels upon exiting from the electro-
static precipitator unit. Other potential
sources of effluent gases containing low
levels of hydrocarbons are certain rolling,
oil quenching, and coking operations,
and/or foundries.
Since at present there are no satis-
factory demonstrated means for tackling
this problem, this research effort was
thougnt to be of both theoretical and
practical interest.
The proposed approach was toexamine
the feasibility of removing these hydro-
carbons by passing the effluent gases
through a shallow fluidized bed of porous
.adsorbent particles.
The project was initiated through the
funding of this program by the American
Iron and Steel Institute. The U.S. EPA
provided co-funding with AISI of this
investigation for the period May 1,1977-
April 30, 1979, the last 2 years of the
program. • . '
Preliminary experiments have shown
that hydrocarbons may be effectively
adsorbed onto the surface of activated
charcoal particles, in a shallow fluidized
bed, operating at room temperatures.
However, when the gas stream contained
moisture as well as hydrocarbons,
adsorption of moisture interfered with
the removal of hydrocarbons. For this
reason it was decided to construct an
apparatus (see Figure 1) which allowed
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operation at somewhat elevated temper-
atures; i.e., the 70-100°C range.
In essence this apparatus consisted of
a gas train, a hydrocarbon saturator,
together with appropriate arrangements
to produce a gas stream containing a
known amount of hydrocarbons. The gas
exiting the bed was analyzed using a gas
chromatograph. The dimensions of the
fluidized bed are shown in Figure 2.
Summary of Results
A selection of typical experimental runs
isshown inTable 1 and in Figures, where
it is seen that satisfactory operation of the
system is feasible at about 80°C where
the activated charcoal has a good
capacity to adsorb hydrocarbons, but at
the same time only very little moisture is
being adsorbed.
Experiments were also carried out
using porous alumina particles as the
adsorbent. However, it was found that
alumina is not a suitable adsorbent for
hydrocarbon? in the presence of moisture,
because alumina tends to adsorb moisture
preferentially.
A mathematical model was also devel-
oped to represent the adsorption process
in fluidized beds, where allowance has
been made for external mass transfer,
adsorption kinetics, and the back-mixing
of the gas stream. The resultant differ-
ential equations were solved numerically.
Figure 4 compares the theoretical predic-
tions and the experimental measurements:
the good agreement is readily apparent.
It is concluded that activated charcoal
would be a suitable medium for the
selective adsorption of hydrocarbons in
the presence of moisture, when the
system operated at a temperature of
about 80°C. A suitable contacting ar-
rangement could involve the use of
shallow fluidized beds (say 1-2 cm deep)
operated near the minimum fluidization
velocity (say at 2-3 times the minimum
fluidization velocity).
Some preliminary design calculations
have been made to outline an industrial
scale operating system. These calcula-
tions, together with additional experi-
mental details and details of the mathe-
matical model, are contained in the
project report.
Key:
/ . Cylinder of compressed air
2. Silica bed
3. Charcoal bed
4. Filter
5. Rotameters
6. Hydrocarbon saturator
7. Water saturator
8. Inlet heater
i
Air
T
1
A
Air
He
H2
12.
13.
9. Fluidized-bed heater
10. Fluidized bed
11. Temperature controller
12. Recorder
13. Gas chromatograph
0 1-3/8 in.
1/16-in.
Fluidized
Activated
Charcoal "*^
Porous
Material
\
Figure 2.
The bed.
Figure 1. The apparatus.
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Table 1. Adsorption of Hydrocarbon on Activated Charcoal
Run
No.
C9
C10
C11
C12
Temp
°C
25
80
100
125
Inlet
cone.
g/cm3
1.1x10~7
0.92x1 0~7
0.31x10~7
0.23x10~7
Duration
of run
mn
300
330
360
345
HC
removed
%
95
96
74
60
Moisture
adsorbed
mg
25
15
10
2
HC
adsorbed
gmol/g
132x10'5
164x1Q-5
32xW~5
23x10~s
180
Figure 3. Effect of temperature on uptake.
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700
80
60
40'
20-
Computed
' C17
0 2 4 >
Time, hr
Figure 4. Hydrocarbon uptake in the solid phase vs time.
10
H. X. Lambert andJ. Szekely are with the Massachusetts Institute of Technology,
Cambridge. MA 02139
John S. Ruppersberger is the EPA Project Officer (see below).
The complete report, entitled "Treatment of Gaseous Emissions from Steelplants
Containing Small Concentrations of Hydrocarbon Vapors," (Order No. PB 83-
246 082; Cost: $13.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
irUS GOVERNMENT PRINTING OFFICE 1983-659-017/7204
United States
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