vvEPA
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S7-80-161 Dec. 1980
Project Summary
Environmental Assessment of
Waste-to-Energy Process:
Union Carbide's Purox®
Process
Paul G. Gorman, Mark Marcus, K. P. Ananth, and Harry M. Freeman
The Environmental Protection
Agency (EPA) is currently supporting
a research program to conduct an
environmental assessment of various
waste-to-energy conversion systems.
As part of this program, on-site testing
was carried out at Union Carbide
Corporation's Purox® facility at South
Charleston, West Virginia. The Purox®
system pyrolyzes municipal solid
waste, using oxygen, to produce a fuel
gas with a heating value of 14.6
MJ/Nm3 (370 Btu/scf).
Sampling at the facility included
four input/output streams (refuse,
slag, water, and stack emissions).
Water sampling included the pilot
scale Unox® wastewater treatment
system.
The boiler stack emissions were
sampled when firing the Purox® gas
and when firing natural gas. Analysis
was carried out for most conventional
pollutants (CO, NO«, etc.), but
included many special analyses (poly-
nuclear aromatic hydrocarbons) and
many of the analyses prescribed under
the EPA's Level 1 environmental
assessment protocol. The data
obtained were used to evaluate the
emissions in each effluent stream on
the basis of existing standards or
criteria and on the basis of the EPA's
recent Source Analysis Model (SAM/
1 A). Thus, this was the most extensive
environmental assessment of a waste-
as-fuel system that has yet been
carried out.
This publication is a summary of the
complete project report, which can be
purchased from the National
Technical Information Service.
Introduction
An on-site testing program, for pur-
poses of environmental assessment,
was carried out at Union Carbide's
Purox* facility in South Charleston,
West Virginia. This work was done by
Midwest Research Institute (MRI) under
contract to the U.S. Environmental Pro-
tection Agency (EPA). The main purpose
of the environmental assessment effort
was to identify potential environmental
impacts resulting from this process and
to identify control technology needs
where appropriate.
Basically, the Purox process produces
a fuel gas with a heating value of about
14.6 MJ/Nm3 (370 Btu/scf) by pyro-
lyzing shredded municipal waste. Efflu-
ent streams sa mpled in the test progra m
consisted of reactor slag, fuel gas
scrubber liquid effluent, and air emis-
sions from a boiler when fired with the
Purox fuel gas, and when fired with
natural-gas.
'Purox is a registered trademark of Union Carbide
Corporation
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Description of Purox
Pyrolysis Process
The Purox facility at South Charles-
ton, West Virginia, is a demonstration-
scale unit capable of processing 181
Mg/day (200 tons/day) of solid waste.
Usually, the product gas is flared. For
purposes of this test program, however,
the product gas was combusted in a
package boiler and emissions resulting
from it were characterized. As a base-
line comparison, the same boiler was
also fired with natural gas. The test
program was carried out in September
1977.
Figure 1 is a schematic illustration of
the Purox process. Raw refuse is
received by truck in the plant's storage
building. It is moved and stacked m the
storage area by a front end loader. The
same loader picks up the stored waste,
weighs it on a platform, and dumps it on
a conveyor leading to the shredder, a
150 Kw (200 hp) vertical hammermill.
The refuse is shredded to a 7.6cm(3-m.)
size. Magnetic material is removed by a
ferrous recovery system.
The refuse is fed into the top of the
reactor, the principal unit in the process,
by two hydraulic rams. There are three
general zones of reaction within the
reactor: drying, pyrolysis, and
combustion. The reactor is kept full of
refuse which slowly descends, by
gravity, from the drying zone, through
the pyrolysis zone, and into the combin-
ation zone. A counterflow of hot gases,
rising from the combustion, zone at the
bottom, dries the incoming moist
refuse. As the material progresses
downward, it is pyrolyzed to form fuel
gas, char, and organic liquids.
Oxygen is injected into the bottom
hearth section at a ratio of about 20% by
weight of incoming refuse. The oxygen
reacts with char formed from the refuse
to generate temperatures of 1370° to
1650°C in the lower zone, which con-
verts the noncombustibles into a molten
residue. This residue is discharged into
a water quench tank where it forms a
slag. The typical composition of the slag
is reported to be 60% Si02, 11% AI2O3,
11% CaO, 9% Na2O, 5% FeO, 2% MgO,
and 2% other oxides. Of course, the
composition may very depending on the
feed.
The hot gases from the hearth section
are cooled as they rise through the
zones of the reactor. After leaving thi
reactor, the gases are passed through ,
recirculating water scrubber. Entrainei
solids are separated from the scrubbe
water in a solid-liquid separator am
recycled to the reactor for disposal. Thi
water product discharged from thi
sepjrator system is sent to a plant treat
ment system. The gas leaving thi
scrubber is further cleaned in ai
electrostratic precipitator (ESP) and
then, cooled in a heat exchanger prioru
combustion in a flare combustor. Durinc
the tests the gas was burned in a pack
age boiler transported to the site fo
these tests. The fuel gas consists o
about 40% CO by volume, 23% C02, 5°/i
CH4, 26% H2, and the rest being N2
C2H2, C2H4, etc.
According to Union Carbide, for even
megagram of refuse and 0.2 Mg o
oxygen fed into the reactor, the residue
or slag is 0.22 Mg, the fuel gas is 0.7 Mg
and the wastewater from gas scrubbinc
is 0.28 Mg
The package boiler that was used ir
these tests was a water tube boiler with
a name plate rating of 31.6 X 106 kJ/hi
(30 X 106 Btu/hr). Other specifications
for this boiler are given below
Off Gas
Shredded
Refuse —»
Oxygen -*
River Water
~ — — -"\ pecycle
oii\Water
' X*>l
\y
Fuel Gas
Cooling Water
LA
To Atmosphere
Fuel
Molten
Material
Water
Char
Flare
Combustor
To Atmosphere
Note: "A"denotes flowduring "normal"operation.
or as plant was intended to operate.
"B" denotes flow during testing, without
recycle.
Figure 1. Flow diagram for Purox® process.
2
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Manufacturer. E. Keeler Company
Year Built: 1957
Model: DK-9-8
National Board No.:2985
Rated capacity: 10,872 kg/hr steam
Design pressure: 1,723 kPa (250 psig)
Total heating surface:203 m2
Water wall heating
surface: 51 m2
Furnace volume. 16.5 m3
A special multi-fuel burner, designed by
Coen Company, Inc., was installed in
the boiler to facilitate firing with either
natural gas or Purox gas. The boiler
operated well during the tests and there
appeared to be good flame stability and
complete combustion when burning
either fuel.
Sampling and Analysis
Program
Sampling at the Purox facility was
directed to the three effluent streams.
slag, scrubber effluent, and gaseous
emissions from a boiler when fired with
Purox gas, and when fired with natural
gas. Sampling and analysis of each
stream was rather complex, being
concerned with conventional pollutants
but including, among others, priority
pollutants m water samples and
sampling of both liquid and gaseous
emissions for most of the analyses
prescribed under EPA's Level 1 environ-
mental assessment protocol. Panicu-
late emission sampling in the boiler
stack was conducted according to EPA
Method 5, using a High Volume
Sampling System (HVSS), because of
the expected low particulate loading.
Boiler stack sampling also included use
of the Level 1 Source Assessment
Sampling System (SASS) train on one
test day when burning natural gas, and
on one test day when burning Purox
gas.
Presentation and Discussion of
Test Results
Although it was originally intended
that sampling would occur only when
the process was operating "normally,"
process mechanical problems dictated
that some allowances be made. The
deviations from "normal" operation
were as follows during this testing
effort- (a) the Purox facility was opera-
ting at only 90 Mg/day (100 tons/day)
instead of its rated capacity of 181
Mg/day (200 tons/day); (b) the char
recycle system (the unit operation for
reusing the char removed in the
scrubber) was not operational and,
consequently, the scrubber had to be
operated with once-through river water
instead of recycle water; and, (c) it was
learned that the oil collected by the ESP
was discarded rather than being
recycled into the converter, as would be
the case in commercial plants. These
latter variations are shown by the
dashed lines in Figure 1.
Due to limitations in the amount of
Purox gas produced during the testing
as a result of low refuse feed rates and
the gas required to maintain a continu-
ous flare,the boiler was operated at a
heat input rate of about 13.7 X 106
kJ/hr (13 X 106 Btu/hr). This is well
below the rated capacity of 31.6 X 106
kJ/hr (30 X 106 Btu/hr). The low firing
rate, as well as other variations noted
above, could have a possible effect on
emissions measured during the testing.
Although this might mean that the trace
constituent analyses, shown herein, are
not representative, it is unlikely that the
fuel properties of the gas would change.
The above considerations should be
kept in mind when reviewing the data
and interpretations thereof, which are
presented below, in order of slag, liquid,
and gaseous effluents. In each of these
three sections, the abbreviated test
results for each effluent stream are
summarized and are evaluated in terms
of effluent criteria or standards
wherever possible. Since the data on
each stream was extensive, only
summaries of results are presented in
this paper. At the end of these sections,
all of the effluent stream data are incor-
porated into an environmental assess-
ment based on EPA's recent Source
Analysis Model (SAM/1 A).
S/ag-Durmg the test program, the
Purox unit was operated at a rate of
about 80 Mg/day. Periodic sampling of
the slag stream showed that the system
produced about 15 Mg/day, equivalent
to 0.18 Mg of slag per megagram of
refuse.
Samples of the slag, which were
taken on an hourly basis during each
test day, were composited as a daily
sample for analysis. Results of these
analyses are presented m the complete
project report and include anions, PAH,
PCB, and some trace metals As
expected, the slag had high ash content
(97%) and low heating value 785 kJ/kg
Anion analysis of the slag showed
that CI", F~, and Br were not, m general,
any higher than those present m the
input refuse. Anion CN and NOs were
below the analytical detection limits.
Measured SO^ = concentrations of 80
to 220 jug/g were considerably lower
than values reported for ash from an
incinerator.
PAH and PCB were found to be
present in the slag, but at relatively low
concentrations. Metals analysis
showed, as expected, that many metals
were present at higher concentrations
in the slag than in the refuse feed, but
the concentrations were not drastically
different than those reported in inciner-
ator ash. However, some of the more
volatile metals (e.g., Sb, Hg, and Pb)
were lower in the slag than in the
refuse, indicating that they may have
exited the pyrolysis reactor with the
gases. More details on the slag analysis
results, including elemental analysis by
spark source mass spectrometry
(SSMS), are presented in the final report
on this work.
Wafer-Samples of input river water
and effluent scrubber water were taken
each test day, during the non-normal
operating conditions mentioned earlier.
In addition, during one day, grab
samples were also taken at the pilot-
scale Unox* water treatment plant
including "Unox in," dilution river
water, and "Unox out" samples.
Results of the analyses of water
samples, for general water quality para-
meters, are tabulated in the complete
project report; results indicated that
almost all parameters were much
higher in the scrubber effluent than in
the inlet river water. Samples from the
Unox system indicated that it did
improve most of the general water
quality parameters with exception of
TSS and DO. However, neither TSS nor
BOD would meet secondary treatment
criteria of 30 mg/liter. Also, even
though the Unox system did decrease
the phenol level from about 90 mg/liter
down to 0.7 mg/liter, these levels may
not be sufficient to meet stringent water
quality criteria for phenols, which may
be as low as 0.001 mg/liter.
Anion and trace metal analyses were
carried out on the water samples with
the results shown in the complete
project report. Again, the measured
anions were considerably higher in the
scrubber effluent and, except for CN",
the Unox system did not decrease in
concentration considering the dilution
with river water. Of these anions, CI"
*Unox is a registered trademark of Union Carbide
Corporation
-------
may be of most concern, because it
exceeds at least one state's criterion of
100 mg/liter. Evaluation of the trace
metal results were difficult due to lack of
specific criteria or standards. Lacking
any other criteria, comparisons with
drinking water standards indicated that
concentrations of Pb, Fe, Mn, and Zn
exceeded these standards.
Water samples were also analyzed for
priority pollutants, but the data was too
lengthy for inclusion in this paper. The
results of these analyses showed that a
few of these pollutants were present at
detectable levels in the scrubber efflu-
ent, but the Unox system effectively
reduced these concentrations.
Scrubber influent and effluent
samples were also analyzed according
to EPA's Level 1 protocol, but again, the
data was too lengthy to include in this
paper. Also, the results were difficult to
interpret, except in terms of the
SAM/1 A methodology presented at the
end of this paper. However, it was noted
in the'results that the scrubber effluent
showed a predominance of polar
organic compounds, when it was
expected that the constituents would
primarily be nonpolar organic
compounds. It has been theorized that
these may have been present, but they
may have been absorbed by the char in
the water, which was removed by
filtration after the samples were taken.
Boiler Stack Emissions—As men-
tioned earlier, emissions from the boiler
stack were sampled, both when firing
Purox gas and when firing natural gas.
Results of this part of the sampling and
analysis program are summarized here.
1. The Purox system successfully
demonstrates that production of a
combustible fuel gas from solid
waste is possible.
2. Of the criteria pollutants that result
from combustion of the Purox gas,
only NOX and particulate show a
significant increase at the outlet of
the .boiler.
3. The NOx emissions from the Purox
gas would exceed the Federal New
Source regulation of 0.086 kg/106
(0.2 lb/10 Btu), but this regulation
applies only to boilers with heat
inputs greater than 260x106kJ/hr
(250 x 106 Btu/hr). The Purox NOX
emissions would also exceed the
California regulation of 80 ppm,
but, again, this applies only to gas
fired power plants with heat inputs
greater than 53 x 106 kJ/hr (50 x
106 Btu/hr}.
Since there are no emission
standards for boilers of the size
tested in this project, 36 x 106 kJ/hr
(30 x 106 Btu/hr), no reasonable
conclusions can be drawn
regarding the level of NOX control
required in burning Purox gas.
Furthermore, NOX formation is a
complex phenomenon, which can
be affected by excess air, peak
flame temperature, burner
modifications, hydrogen levels in
the gas, and nitrogen bearing
compounds in the gas. These
various factors could not be
investigated as part of the subject
program, making it impossible to
draw firm conclusions on the level
of NOx present in the stack
emissions.
4. Particulate concentrations from
Purox gas combustion vary from 6
to 14 mg/dNm3. These concentra-
tions are less than 0.004 kg/106 kJ
(0.01 Ib/million Btu), which is well
below the federal standard of 0.08
kg/106 kJ (0.2 Ib/million Btu) for a
power plant.
5. SOz levels from burning Purox gas
do not appear to be of concern
based on present emission
standards.
Source Analysis Model (SAM/1A)—
Because of the difficulty involved in
interpreting mucnof the data collectec
in this program, especially the Level 1
analysis results, the environmenta
assessment work was extended tc
include application of the methodology
known as the Source Analysis Mode
{SAM/1 A) recently developed by EPA
Basically, this model compares the
measured concentrations of pollutants
with approximate emission concentra
tion guidelines known as MATE value;
(minimum acute toxicity effluents)
These MATE values have been tabu
lated for several compounds or classes
and there is a specific MATE concentra
tion for each compound and for each
type of effluent stream (solid, liquid, oi
gaseous). The MATE values are usedtc
compute the ratio of the measurec
concentration to the MATE concentra
tion, and this ratio is termed the "degree
of hazard." The "degree of hazard" foi
each pollutant is then summarized tc
provide the "degree of hazard" for th€
effluent stream under consideration
This value, when multiplied by the efflu
ent flowrate in specific units (e.g., liters
per second), establishes the "toxic unii
discharge rate" (TUDR) for the stream,
This SAM/1A methodology was
utilized to analyze the data obtained foi
each of the three primary effluem
streams from the Purox process (slag
scrubber effluent, and boiler stack gas)
The results of this application are con
tained in Table 1. The table does noi
show MATE values and observec
Table 1. Summary of results from SAM/1A methodology.
Health -
Based
Ecological-
Based
Degree of hazard
Slag
River water
Scrubber effluent
Flue gas (natural gas)
Flue gas (Purox gas)
Toxic unit discharge rate
Slag
9,700
420
23,000
5,600
7,300
66,000
20,000
220,000
3.1
54
1,500,000 10,000,000
River water(\/sec)
Scrubber effluent (I/sec)
Flue gas (natural gas) (m3/sec)
Flue gas (Pu.rox gas) (m3/sec)
24,000
130,000
9,200
9,500
1 10,000
1,200,000
5.2
70
-------
concentrations for each of the various
pollutants or the summation of the
"degree of hazard" for each pollutant,
because this mass of data is too volum-
inous to be included in this paper. It is,
however, contained in the complete
project report. As shown in Table 1, the
scrubber effluent had the highest
"degree of hazard," being considerably
greater than the "degree of hazard" for
the input river water. However, the slag
stream had the highest "toxic unit
discharge rate." The boiler flue gas
effluent had the lowest "degree of
hazard" and the lowest ''toxic unit dis-
charge rate." Both of these values were
comparable to be baseline values
computed for boiler flue gas when
burning natural gas.
Results for the scrubber effluent
showed the highest "degree of hazard,"
due primarily to phenols and the organic
extract fractions LC3,6, and 7 defined in
the Level 1 Environmental Assessment.
This "degree of hazard" seems to con-
firm that this effluent would have to be
treated prior to discharge. However, the
finding that the slag has the highest
"toxic unit discharge rate," due to the
presence of metals (Cr, Mn, and Fe)
which were expected in this stream, is
somewhat difficult to understand. This
finding would seem to indicate that this
stream should receive the highest
priority for control or removal of specific
metal constituents. Considering the
nature of this material and its possible
use/disposal, further work should be
carried out to determine if it would
represent any environmental hazard.
Finally, the SAM/1 A methodology
should also be applied to other types of
solid effluent (e.g., refuse, foundry slag,
boiler bottom ash) to provide a relative
comparison.
Conclusions
Conclusions derived from this envi-
ronmental assessment of the Purox are
listed below, in the sequence of general
plant operation, followed by each speci-
fic effluent stream, and concluding with
results of the SAM/1A assessment
methodology.
Plant Operating Parameters
More definitive data needs to be
obtained when the process is
operated with the .char recycle
system in service and with the
recirculation of scrubber water.
The quantity of slag produced per
unit of refuse input may be less
than that reported by UCC, and the
quantity of fuel gas produced may
also be less.
The quantity of gas used in tuyeres
and torches may be significant,
especially on a heating value basis.
Slag
Analysis of slag does not indicate
concentrations of PAH, PCB, or
metals at levels that would exceed
those in other types of solid waste
streams..
Water
Water discharged from the process
would have to be treated and
phenols, TSS, BOD, DO, and Cf
may be of special concern.
Except for phenols, Unox treatment
of water effectively reduces most
organics in the water effluent that
would be of concern.
No pesticides were detected in the
scrubber effluent.
Level 1 analysis of water samples
indicated predominance of polar
organic compounds, leading to a
suspicion that nonpolar organics
may have been adsorbed by the
char.
Fuel Gas
Particulate and NO* concentrations
in the Purox fuel gas are low.
Boiler Stack Emissions
Boiler stack emissions of HC and
CO are low.
NOx and SOz emissions increase
when burning Purox gas, as com-
pared to natural gas, but SOz
emissions are still quite low.
Hg and CI" concentrations in the
boiler stack are higher when
burning Purox gas, but not to an
extent that they would be of envi-
ronmental concern.
Emissions of particulate from the
boiler, when fired with Purox gas,
are quite low and most of it is less
than 1 /urn in size.
PAH levels in the boiler stack
emissions are generally low in
comparison with conventional
combustion sources.
High PCB blank values occur in the
XAD-2 resin used in the sampling
train, preventing report of PCB
results in boiler stack gas.
Sampling of stack' emissions with
sampling trains constructed of
stainless steel is not advisable, due
to corrosion, especially for sources
that contain high chloride concen-
trations.
SAM/1A Assessment
Methodology
Results of the SAM/1A environ-
mental assessment methodology
show that the scrubber effluent has
the highest H value in comparison
with the other effluent streams,
confirming the need for treatment
prior to discharge.
SAM/1A methodology showed
that the slag effluent had the
highest TUDR, due primarily to the
metals contained in this stream.
Stack effluent had the lowest H
value and the lowest TUDR, both of
which were comparable to those for
natural gas baseline tests.
Recommendations
Results of the testing at the Purox
facility have produced several recom-
mendations, generally, with regard to
the process and test results, and specifi-
cally, with regard to the sampling and
analysis procedures that were em-
ployed. These recommendations are
presented below under the same sub-
headings as in the previous section.
Plant Operating Parameters
Some additional testing should be
carried out, especially on water
effluent, when the process is
operating normally with the char
recycle system in operation.
More accurate measurements
need to be made to determine the
quantity of slag and fuel produced
per unit of input refuse, with con-
sideration of fuel used in tuyeres
and torches.
Refuse
Better methods need to be devel-
oped for the analysis of PCB in
refuse samples.
-------
Slag
Further evaluation of slag analyses
data needs to be carried out with
regard to results of SAM/1 A
assessment methodology.
Water
More work needs to be done to
assess treatment capabilities for
reduction of phenols in scrubber
effluent, and Level 1 organic extract
fractions LC3, 6, and 7.
Level 1 organic analyses of water
samples needs to be revised to (a)
include an option to use a GC/MS
for complex sample characteriza-
tion; and, (b) to substitute the use of
a direct inlet MS for high TCO
samples, with a GC/MS procedure
to separate sample from solvent.
SAM/1 A Assessment
Methodology
Further evaluation of the results of
the SAM/1A environmental
assessment methodology employed
herein, should be carried out to
determine if further .testing is
required, and to determine what
should be included m that testing,
especially with regard to the slag
stream which had the highest
TUDR.
Fuel Gas
Additional analysis of the fuel gas
should be carried out to investigate
the presence of nitrogen bearing
compounds.
Stack Gas
Additional work should be carried
out to investigate the causes of
increased NOx emissions when
burning Purox gas.
HVSS and SASS sampling
equipment should be evaluated to
determine if corrosion problems
can be overcome.
More sensitive IR equipment
should be utilized for Level 1
analysis of SASS samples.
Further work on boiler stack emis-
sions should be carried out to
investigate the constituents in
XAD-2 resin extract fraction LC3,
even for natural gas.
Stability of the XAD-2 resin, under
field sampling conditions, should
be evaluated. This would also
include investigation of high PCB
blank values in XAD-2 resin.
Future environmental assessments
should include, as prescribed under
Level 1 protocol, on-site analysis of
gases and bioassay tests.
Paul G. Gorman. Mark Marcus, and K. P. Ananth are with the Midwest Research
Institute. Kansas City. MO 64110.
Harry M. Freeman is the EPA Project Officer (see below).
The complete report, entitled "Environmental Assessment of Waste-to-Energy
Process: Union Carbide Purox® System," (Order No. PB 80-1O0711;
Cost: $21.50, subject to change) will be available 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
Cincinnati, OH 45268
« U.8. OOVBMMENT HUNTING OFFICE 1M1 -757-064/0249
-------
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