United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-86/032 Dec. 1986
Project Summary
Control of Sulfur Emissions
from Oil Shale Retorting
Using Spent Shale Absorption
K. D. VanZanten and F. C. Hass
This study investigated the environ-
mental advantages/disadvantages of
absorbing SO2 onto combusted re-
torted oil shale. The objective of this
program was to obtain more informa-
tion in support of Prevention of Signifi-
cant Deterioration (PSD) permitting
decisions on sulfur control and to deter-
mine if emission of other pollutants
such as nitrogen oxides (NOX) and trace
elements might be significantly in-
creased by the combustion process.
The program consisted of two phases:
Phase I developed an engineering as-
sessment and costs for application of
this sulfur absorption process to se-
lected leading retorting processes, and
Phase II was experimental work in an
integrated oil shale pilot plant to define
operability, proof of principle, and trace
element emissions.
Based on the pilot plant data ob-
tained in this study, fluid bed operating
conditions are recommended to opti-
mize SO2 and NOX control. In general,
conditions that favor low SO2 emis-
sions also favor low CO and trace hy-
drocarbon emissions but do not favor
low NOX emissions. The general ranges
of operating conditions which pro-
duced reasonable results from both op-
erating and emissions viewpoints are
given in the report. Results of the trace
element tests indicated some relative
trends with regard to emissions but,
because of the brevity of the sampling,
no hard conclusions can be reached
which would allow extrapolation of re-
sults to long-term steady-state opera-
tions.
This Project Summary was devel-
oped by EPA's Air and Energy Engineer-
ing Research Laboratory, Research Tri-
angle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report or-
dering information at back).
Introduction
Background
Control of sulfur emissions consti-
tutes a major portion of the environ-
mental control cost for oil shale facili-
ties. For example, Denver Research
Institute estimated costs (in 1980 dol-
lars) in the range of $1 to $3 per barrel of
shale oil produced. These substantial
sulfur control costs have encouraged
developers to seek less costly but
equally or more effective methods for
limiting sulfur emissions. Recently, a
strong industry trend has been to look
toward the potential for combusting
carbonaceous retorted shale to recover
its energy value (a plus in terms of eco-
nomics and resource conservation),
while exploring the possibility of ab-
sorbing the sulfur gases produced dur-
ing retorting onto the calcined carbon-
ate material present after combustion of
retorted western oil shale.
The ASSP Concept
The ability of combusted carbonate-
containing spent shale to absorb S02
gives rise to a novel concept for con-
trolling sulfur emissions in oil shale
plants. This concept is the Absorption
on Spent Shale Process (ASSP).
The ASSP concept has several poten-
tial advantages over conventional sulfur
removal technologies:
• The sorbent is cheap and inherently
abundant in oil shale plants.
• The process requires combustion
of the spent shale which is already
-------
incorporated into several of the re-
torting technologies or which
would be a useful add-on to recover
residual carbon values.
• Since non-H2S compounds are con-
verted to S02 by combustion, ASSP
could represent a more efficient re-
moval relative to gas sweetening
processes which remove only H2S.
The ASSP concept uses a fluidized
transport system to combust either raw
or retorted shale, thereby providing the
vehicle for converting sulfur com-
pounds to S02 and absorbing the S02 in
the shale matrix. The concept envisions
either a conventional dense-phase flu-
idized bed or a dilute-phase contactor
(lift pipe). Key elements of the process
are shown in Figure 1.
Phase //— Pilot Plant Program
Phase II involved pilot scale experi-
mental testing of the ASSP concept in a
pilot plant used by Tosco Corporation to
develop their Hydrocarbon Solids Proc-
essing (HSP) process. The pilot plant
has a nominal capacity of 6 tons (5440
kg) per day of oil shale and contains an
18 in. (46 cm) diameter fluidized bed
combustor.
Key questions addressed in the
Phase II tests were:
• How effective ASSP in controlling
sulfur emissions?
• Will ASSP produce large quantities
of NOX?
• What are the most favorable oper-
ating conditions to achieve maxi-
Steam
Heated Process Gases
Retorted Shale
and/or
Raw Shale Fines
Supplemental Fuel (If Required)
To Atmosphere
i Process Gases
Steam
HiO
Moisturizer
To Disposal
Figure 1. ASSP Process flow diagram.
Phase I—Engineering
Evaluation/Conceptual
Process Designs
The engineering assessment of the
ASSP concept evaluated three types of
retorting processes: direct heated, indi-
rect heated, and indirect heated with
combustion integrated into the process.
Specific retorting technologies and
sites were selected as representative of
these three retort types:
Retort Type
Process
mum sulfur control while holding
NOX emissions to a minimum?
• Will retorted or raw oil shale com-
bustion produce significant emis-
sions of trace elements such as
mercury or cadmium?
The pilot plant was operated for 10
days between October 14 and 25,1985.
A total of 44 tests were conducted dur-
ing which plant operating data were
recorded.
Site
Direct heated
Modified In-situ with
Unishale C
Cathedral Bluffs (Tract C-b)
Indirect heated
Integral combustor
Integral combustor
Unishale B
Lurgi
Unishale C
2
Union Oil (Parachute Creek)
Rio Blanco (Tract C-a)
Union Oil (Parachute Creek)
Selected process variables were cor- ,
related with their effect on S02 and NOX (
emissions and other key dependent
variables. Recommendations on the de-
sign and operation of a fluid bed com-
bustor for SO2 or NOX control are given.
Quality assurance/quality control proce-
dures, as applied to sampling and anal-
ysis, are discussed.
Summary and Conclusions
The results of the Phase I study indi-
cate that the ASSP concept is techni-
cally and economically viable compared
to conventional sulfur removal tech-
nologies for most oil shale retorting
processes. The Phase II results indicate
that the ASSP concept is quite effective
in controlling sulfur emissions and, with
carefully controlled operating condi-
tions, NOX emissions can also be re-
duced by more than 85%. The pilot plant
program also determined that some
trace elements are volatilized by fluid
bed temperatures in the range of 670 to
840°C.
Phase I Conceptual Design and
Economics
For evaluation purposes, specific
projects were chosen as representative
of the three retort types:
• Direct
heated —Modified In-situ
with Unishale C—
Cathedral Bluffs
site
• Indirect
heated —Unishale B—Union
Oil site
• Integral
combustor —Lurgi—Rio Blanco
site
—Unishale C—Union
Oil site
The study assumed that methyldi-
ethanolamine (MDEA) absorption is
used to remove acid gases from indirect
heated retort gases and that regener-
ated acid gases are burned in the ASSP
combustor. MIS gases were assumed to
be processed in the ASSP combustor
without pretreatment.
For comparison purposes, conven-
tional sulfur removal processes were
evaluated:
• Direct
heated —Case A; Unisulf
+ flue gas desulfu-
rization on com-
busted MIS gases
—Case B; Unisulf
+ Stretford on MIS
gases
-------
• Indirect
heated —Unisulf on
Unishale B gases
• Integral
combustor —DEA + Stretford on
Lurgi gases
—Unisulf on
Unishale C gases
Major equipment costs were taken
from EPA Pollution Control Technical
Manuals (PCTMs). ASSP equipment
was sized and costs factored from in-
house data and PCTMs. Costs were fac-
tored to first quarter 1985.
Results of the cost study showed
changes in incremental capital and op-
erating costs for ASSP relative to con-
ventional processing (see Table 1).
These cost comparisons show that
the best potential for application of
ASSP are processes that already have a
spent shale combustor integrated into
the retorting process (e.g., Lurgi, Uni-
shale C, Chevron STB, and Tosco HSP).
Capital and operating cost savings for
Unishale C and Lurgi are primarily a re-
sult of deleting the Unisulf and Stretford
plants.
Economics for the indirect and direct
heated retorts are good to marginal.
Factors which will affect the economics
are:
• How effectively combustor heat
can be utilized (simple steam
raising is the least desirable).
• The value of steam.
• The use of fast or circulating fluid
beds to reduce investment in com-
bustor equipment.
Phase II Pilot Plant Testing
Pilot plant tests were performed in a
bubbling fluid bed combustor of the
type which is integrated into the retort
process. A total of 44 individual tests
were performed. Variables evaluated
were combustor temperature, solids
residence time, gas residence time, oxy-
gen concentration, inlet gas sulfur con-
centration, staged combustion, and raw
shale injection. Over the entire range of
conditions tested, emissions of primary
pollutants were:
Component
Range
S02
NOX
CO
Trace Hydrocarbon
1-38 ppmv
80-670 ppmv
0.05-1.80 vol%
51-8465 ppmv
Key findings of the tests were:
• S02 emissions were easily con-
trolled to low levels at virtually all
conditions tested, probably as a re-
sult of the high Ca/S ratios used.
• NOX emissions were primarily sen-
sitive to oxygen concentration, as
were S02 emissions to a lesser ex-
tent (Figure 2). Reasonably good
NOX control could be obtained with
flue gas oxygen concentrations
below about 3 vol %. The lowest
NOX concentrations were seen at O2
levels approaching zero but at the
expense of higher CO and trace hy-
drocarbon emissions.
• CO and trace hydrocarbon emis-
sions were primarily sensitive to
flue gas oxygen concentration (Fig-
ure 3). Good control of both could
be obtained at 02 levels above
about 2 vol %.
Emissions of NOX move in a direction
opposite to S02, CO, and trace hydro-
carbon emissions. Thus, operating con-
ditions that minimize all four represent
a compromise. One test was run which
produced nearly optimum results.
Conditions for this test were:
Bed Temperature 664°C
Solids Residence
Time 9.4 min
Gas Residence Time 0.9 sec
Gas Supply
Velocity 134.1 cm/sec
Flue Gas 02 2.6 vol %
Ca/S Mole Ratio 10.3
Raw Shale/Spent
Shale Ratio 1:36
At these conditions the following re-
sults were obtained:
S02 11 ppmv
NOX 160 ppmv
CO 0.27 vol %
Trace Hydrocarbon 388 ppmv
Combustion Efficiency 89 %
Table 1. Cost Comparison
Retort Type
Retorting Process
For ASSP
Direct Heated
Case A, Case B
MIS/Unishale C
Indirect
Heated
Unishale B
Integral Combustor
Lurgi Unishale C
During selected tests, both combus-
tor flue gas and retort gas were sampled
and analyzed for selected trace ele-
ments: mercury, cadmium, arsenic,
lead, beryllium, and fluorine. During
these tests, solids streams were also an-
alyzed for trace elements in an attempt
to determine where trace elements go.
One run was performed where a spike
solution of mercury and cadmium was
added to the combustor.
Results of the trace element tests indi-
cated some relative trends with regard
to emissions but, because of the brevity
of the sampling, no hard conclusions
can be reached which would allow ex-
trapolation of results to long-term
steady-state operations. Some of the
key observations were:
• Lead, beryllium and fluorine were
found to have low volatility; i.e., of
the amounts present in raw shale,
only very small percentages were
volatilized to the gas streams.
• Arsenic was found in significant
concentrations in the retort gas
(100-400 ppmv), although the
amount of arsenic found repre-
sented less than 15% of that in the
raw shale.
• So little mercury was present in the
raw shale that mercury emissions
could not be characterized with high
accuracy. Mercury emissions were
very low except during the spike in-
dicating that mercury, if present in
higher concentrations in the raw
shale, could possibly pose emis-
sions problems.
• Although significant amounts of
cadmium was found in the gases at
higher retort and combustor tem-
peratures, emissions represented
less than 10% of cadmium present
in raw shale.
There is some evidence that mercury
and cadmium introduced to the com-
bustor during the spike test condensed
within the retort equipment and
revolatilized over time. However, be-
cause of the limited number of samples
taken, it would not be prudent to draw
any conclusions. Longer term steady-
state operations would have to be stud-
ied to determine the fate of mercury and
cadmium with more certainty.
ASSP Incremental
Cap. Cost, $106 -71.2 -63.2
ASSP Incremental
Annual Oper. Cost, $W6/yr +10.83 +12.07
+90.2 -13.0 -32.1
-19.21 -2.29 -1.56
-------
I
3
40
35 .
30-
25 -
20-
15-
10-
5 .
0
Flue Gas 02, vol %
Figure 2. Effect of flue gas oxygen on SOi and NO* emissions.
700
600
500 s.
I
-400
-500
200
roo
0
i
Flue Gas Oi, vol %
Figure 3. Effect of flue gas oxygen on CO and trace hydrocarbon emissions.
-------
K. D. VanZanten and F. C. Haas are with J & A Associates, Golden, CO 80401.
Edward R. Bates is the EPA Project Officer (see below).
The complete report, entitled "Control of Sulfur Emissions from Oil Shale
Retorting Using Spent Shale Absorption," (Order No. PB 87-110 516/AS;
Cost: $18.95, 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:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park. NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S7-86/032
0000329 PS
U S ENVIR PROTECTION AGENCY
REGION 5 LIBRARY
111 S QEARBORN STREET
CHICAGO I»-
------- |