EPA-670/2-75-025
February 1975 Environmental Protection Technology Series
HIGH-TEMPERATURE VORTEX INCINERATOR
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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EPA-670/2-75-025
February 1975
HIGH-TEMPERATURE VORTEX INCINERATOR
By
Robert C. Thurnau and Donald A. Oberacker
Solid and Hazardous Waste Research Laboratory
Program Element No. 1DB063
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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REVIEW NOTICE
The National Environmental Research Center-
Cincinnati has reviewed, this report and approved
its publication. Mention of trade names or com-
mercial products does not constitute endorsement
or recommendation for use.
11
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FOREWORD
Man and his environment must be protected from
the adverse effects of pesticides, radiation, noise
and other forms of pollution, and the unwise manage-
ment of solid waste. Efforts to protect the
environment require a focus that recognizes the
interplay between the components of our physical
environment—air, water, and land. The National
Environmental Research Centers provide this multi-
disciplinary focus through programs engaged in
studies on the effects of environmental
contaminants on man and the biosphere,
and
a search for ways to prevent contamin-
ation and to recycle valuable resources.
The research efforts described herein repre-
sents a valiant attempt to advance the state-of-
the-art of solid waste incineration. In addition
to the goals of improved combustion efficiency,
volume reduction, and mechanical reliability, this
program sought to drastically reduce or eliminate
completely the well-known environmental insults
associated with many incineration practices.
Andrew W. Breidenbach, Ph.D.
Di rector
National Environmental
Research Center, Cincinnati
m
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CONTENTS
Page No.
Review Notice ii
Foreword iii
Contents iv
Acknowledgement v
Conclusion 1
Introduction 2
Incinerator Concept and Design 3
Experimental Apparatus and Methods 4
Experimental Results 6
Conditions in the Combustion Chamber 6
Conditions in the Stack 13
Discussion 18
References 19
Appendix A 20
Appendix B 22
Figures
No.
1. Vortex Incinerator 5
2. Average Temperature vs. Burning Rate 8
3. Volume Percent Greater Than Stated Size vs. Particle Diameter 12
Tables
1. Burning Rate for Typical Run 7
2. Furnace Emissions Based on Design 10
3. Stack Participate Analysis 11
iv
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ACKNOWLEDGMENT
Although this report was written by Bob Thurnau
and Don Oberacker, many others had a significant in-
put into the concept, testing, or actual fabrication
of the equipment. We acknowledge and thank,
Russ Creager, Mark Dornhelm, Stan Graydon, Don King,
Ken McHaffey, Boyd Riley, and John Sliter.
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CONCLUSION
It was demonstrated that the experimental incinerator's design
accomplished all of its anticipated goals except one. The main con-
clusion of this study was that efficient air pollution control devices
are needed with incinerators, regardless of how well the combustion
chamber is performing.
It was found that significant amounts of oxides of nitrogen were
formed during the incinerators high temperature operation. These
emissions could be controlled somewhat by allowing them to disinter-
grate automatically, and possibly be eliminated by installing a taller
stack or extra duct work.
The feelings of those closely connected with this project indicate
that the project was a significant step forward in advancing the art
of incineration, particularly that of combustion chamber design.
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INTRODUCTION
Problems of solid waste and its disposal are not new to
mankind. When society was agrarian, the waste was simply
stored out of the way or scattered about the landscape and
nature took care of disposal.
As industrialization took over, however, and people be-
gan to concentrate in small geographical areas, the problems
of waste management became quite pronounced. The move to the
cities, coupled with a change in buying habits (hence disposal),
magnified this problem to the point that it took political
overtones.
Many communities followed earlier practices of letting
nature take care of disposal and employed open-buring dumps as
their answer to solid waste management. Communities with more
foresight began to investigate composting, sanitary landfilling
or incineration as better alternatives. These alternatives did
not always live up to their expectations. Sanitary landfills
began to resemple the old open dump, composting operations were
expensive and an additional disposal method had to be used to
account for the inorganic fraction of the waste, and incinera-
tors produced a very poor quality residue, with associated smoke
and odor problems. All in all, solid waste management techniques
were quite poor.
The state-of-the-art for incineration progressed very little
from its beginning in 1880 to the end of World War II. A short
time after the war the age of one-way containers and other lux-
ury items began in earnest. The character of the waste changed
dramatically as did its volume. By the sixties, solid waste
management had become a national problem as evidenced by the
Solid Waste Act of 1965. Under the act, the disposal practices
of the Nation were to be upgraded, and obviously one of the
ways to accomplish this was to upgrade incineration practices.
To help fill the gap between antiquated incinerators and the
solid waste problem, work was initiated on a new type of in-
cinerator- -a high-temperature vortex incinerator. The project
was sponsored by the U.S. Environmental Protection Agency,
National Environmental Research Center-Cincinnati, Solid and
Hazardous Waste Research Laboratory. Specifically, the incin-
erator was designed and built at the Center Hill Pilot Plant
of SHWRL, and used only untreated municipal waste as its fuel.
The project was initiated in 1967 and terminated in 1970.
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INCINERATOR CONCEPT AND DESIGN
The power generating industry has explored the combustion
of fossil fuel quite extensively. Although numerous texts and
handbooks on fuels and combusion have been published, very little
is published on using solid waste as a fuel or the characteris-
tics of its combustion. Utilities use the heat derived from
combustion to generate their product, and hence, they try to
maximize the amount of heat that can be obtained from the fuel.
Incinerators, on the other hand, are more interested in process-
ing a prescribed amount of refuse per day without trying to
maximize their heat release. In fact, many incinerators are
designed to operate at relatively low temperatures, and effi-
cient heat release would damage the combustion chamber. Thus,
borrowing from the power companies, the intent of this project
was to maximize the amount of heat released by the refuse while
not damaging the combustion chamber, thus burning solid waste
in an efficient manner with minimal air pollution.
If temperature is no longer a restraining force, then con-
sideration must be given to other areas of the incinerator that
will be affected by the increase in temperature. Changes in
refractory type and design, elimination or modification of the
grates, slag formation and removal, charging and stoking mech-
anisms, and air pollution control equipment would have to be
made if the idea of improved incineration by increased heat re-
lease were to become reality.
The final concept envisioned a horizontal refractory-lined
cylinder into which refuse was fed by a hydraulic ram. The
stoking action would be accomplished by the incoming refuse
pushing the burning refuse across the floor of the incinerator
and finally out the other side into the residue pit. This kind
of stoking would also eliminate the need for grates. Any slag
that was formed would flow or be pushed into the residue pit.
The combustion air would be delivered to the combustion cham-
ber via a manifold, and distributed in such a manner as to set
up a circular or vortex action. This, in addition to providing
mixing and turbulence, would also aid the stoking mechanism by
exposing more burning surface to combustion. Since high temper-
ature was one of the design objectives, heating the incoming
combustion air was necessary. This was accomplished by a coun-
ter-current heat exchanger where the hot exhaust gases pass
through a refractory-lined cyclone and were finally delivered
to the atmosphere by a 15-foot-high stack.
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EXPERIMENTAL APPARATUS AND METHODS
Construction of the incinerator proceeded with very few changes in
the original concept. The finished unit was a horizontal cylinder 3.66 in
(12 ft) and 1.83 m (6 ft) in diameter. The inside diameter was 1.22 m
(4 ft) with 0.3048 m (1 ft) of fire brick and castable refractory , o
surrounding the combustion chamber. Refuse was stored in a 2.29 m3 (3 ft. )
hopper and was charged to the incinerator by a hydrolyic system through a
rectangle opening whose cross sectional area was 0.372 m2 (4 ft2). The
combustion air was supplied by two manifolds with 15 nozzels each. The
manifolds were located on the incinerator to produce a cyclonic or vortex-
ing action when suppling air. The nozzels were 1.27 cm (1/2"), 1.59 (5/8)
and 1.91 (3/4) and were used to regulate velocity and volume of the pre-
heated combustion air. A blower capable of suppling 42.48 standard cubic
meters (1500 ft3) of air per minute at a pressure of 1.397 m (55") of
water was used as the source of the combustion air. A counter current
heat exchanger of 12, 7.62 cm (3") tubes was over the exit of the incin-
erator and used to preheat the incoming air to about 260° C (500°F). The
desired burning rate was 453.6 Kg/hr (1000 lbs/hr) with a 90% volume re-
duction and an QQ% weight reduction. The cyclonic movement of the gases
down the combustion chamber was to provide at least 1/2 second residence time
at temperatures in excess of 1315°C (2400°F). Figure 1 shows the final
design of the incinerator.
The main parameter measured was temperature. By viewing temperature
profiles during operation one could observe how efficiently the unit was
operating. Chromel-alumel thermocouples were used in all locations ex-
cept for directly over the burning face. The extreme temperatures of the
primary combustion area necessitated a Rodium type thermocouple. Tempera-
tures cited during the text of the paper refer to this thermocouple
unless stated otherwise.
Gas sampling for carbon monoxide, carbon dioxide, oxygen, nitrogen,
oxides of nitrogen, and HC1 were carried out using the proportion sampling
techniques. A sample rate of about 1 1/min. was employed for both intre-
grated bag samples as well as on line infarred analyzers.
Particulate sampling was done in accord with the methods and techniques
published in the Federal Register Volume 36, Number 247, December 23, 1971.
This method is commonly known as the "EPA Method."
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Figure 1. VORTEX INCINERATOR
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EXPERIMENTAL RESULTS
The results observed in operating the experimental vortex incinerator
will be discussed in two groups, conditions in the combustion chamber, and
conditions in the stack.
I. Conditions in the Combustion Chamber:
A. Burning Rate:
Municipal incinerators are usually identified by the amount
of waste they can burn during a twenty-four hour day. Typical
municipal units are rated at about 226.8 m-tons/day (250 tons/
day). Thus the identification of a unit is also its burning
rate and this parameter becomes one of the standard criteria in
incinerator design and construction. If the burning rate is
overloaded, the combustion chamber cannot effectively handle
the load resulting in poor combustion, excessive particulate
entrainment, and poor residue quality. If the incinerator is
underloaded, the pollution problems might not be as severe,
but it may become uneconomical to run and could generate
vaporous odors.
The experimental vortex incinerator was designed to burn
about 454.6 Kg/hr (1000 lbs/(hr) of untreated municipal refuse.
Table 1 is a summary of the burning rates for a typical run.
After a warm-up period of about 3 to 4 hours, steady state
conditions appear to exist and the incinerator burned on the
average 616 Kg/hr (1240 Ibs/hr) with a maximum of 757 Kg/hr
(1730 Ibs/hr) and a minimum of 494 Kg/hr (1090 Ibs/hr). When
compared with the designed burning rate, the actual burning
rate is about 24 percent higher.
After preheating the unit, it was expected that the burn-
ing rate would be constant. This assumes, however, that the
other operating parameters are reasonably constant, and that
maximum heat is being released. However, as the temperature
varies, so does the burning rate. If the data from Table 1
j[s plotted (Fig. 2), the burning increases as the temperature
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Table 1. BURNING RATE FOR TYPICAL RUN
Hopper Weight Charged Burning Time Average Temp
No. Kg Min. Cc
8
9
10
11
12
13
14
15
16
17
174
211
251
247
283
219
227
202
162
237
20
23
22
30
25
22
18
19
19
20
Average burning rate
1189
1239
1211
1244
1194
1250
1333
1319
1319
1341
=
. Burning Rate
Kg/hr
527
550
685
494
679
597
757
638
512
718
616
increases and levels off at about 650 Kg/hr (1430 Ibs/hr).
This is to be expected because at this point the amount of
oxygen delivered to the combustion chamber becomes the limit-
ing factor in this relationship. Using 1.293 g/1 (0.0808 Ibs/
ft3) as the density of air and assuming oxygen to be twenty
percent of the air it is found that oxygen is being supplied
at a rate of 660 Kg/hr (1454 Ibs/hr) or being used as fast
as it was supplied.
Once the burning rate has been established, the size of
the combustion chamber, and hence the overall size of the
incinerator will also be known. This is very important
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00
o
o
UJ
CC
CC
LU
Q_
LU
I-
LU
O
CC
LU
1400--
1300--
1200--
1100--
1000-v
900
400
—I 1 1 1 h—
500 600 700 800 900
BURNING RATE (KG/HR)
Figure 2. AVERAGE TEMPERATURE VS. BURNING RATE
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especially since the costs seem to be exponentially related
to the size. Presently,?the guideline used by many grate
designers is 293 Kg/hr/nf (60 lbs/hr/ft2). The grate area
of the vortex incinerator was 1.48 m2 (16 ft2) anc| if the
average burning rate is used, the burning rate per square
meter of grate was 413.7 Kg/hr (77.5 lbs/hr/ft2).
B. Combustion Chamber Efficiency:
In addition to the burning rate, the design of the com-
bustion chamber can greatly influence the efficiency of com-
bustion. A poorly designed combustion chamber will allow
particulates and gaseous combustion products a direct route
to the atmosphere. To insure superior combustion, the experi-
mental incinerator was specifically designed to increase
turbulance in the combustion zones, increase the residence
time of both solids and gases, and increase the agglomeration
of the refuse while burning. The evaluation of combustion
efficiency can be conducted in several ways.
One measurement of combustion efficiency is the concentra-
tion of carbon dioxide in the combustion chamber and throughout
the incinerator system. Initially, the carbon dioxide, measured
as percent by volume, was distributed in the incinerator as:
Combustion Chamber 2.75
Midstack 10.3
Top stack 10.7
It appeared as though the oxidation of combustion gases to
carbon dioxide was taking place outside the primary combustion
chamber. This was not the design condition since some of the
heat release was outside the primary chamber. To alleviate the
incomplete combustion of carbon dioxide in the combustion chamber,
a baffle wall that caused additional mixing and turbulence was
added. After the baffle wall was added, carbon dioxide distri-
bution improved:
Combustion Chamber 10.2
Midstack 11.5
Top stack 11.7
These relatively high carbon dioxide levels indicate that the
combination efficiency of the vortex incinerator's combustion
chamber was quite good, and with the slight modification of a
baffle wall meet the design specifications.
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A second method for judging combustion efficiency is to
observe the amount of unburned organic material in the exhaust
gas. Poor combustion efficiency will result in high concentra-
tions of organic pollutants, and usually reflect the, inefficient
design of the combustion chamber. Data taken from the vortex
incinerator showed that the organic fraction varied between 1.1
and 2.0 weight percent of the total. Data presented at the 1970
National Incinerator ConferenceCU showed that a pilot scale
unit utilizing a scrubber and an afterburner had about a 10 per-
cent by weight organic fraction, and full scale commercial units
averaged about 14.6 percent by weight. These data clearly show
that the vortex incinerator was efficiently burning municipal
waste by its low output of organics.
A third method of judging combustion chamber efficiency is
to observe the concentration of particulate being emitted from
the furnace. It was found that the particulate loading for a
typical run was 2.243 g/sm3 (0.98 grains/sft3). Furnace.emissions
for a 226.8 Kg/hr (500 Ibs/hr) incinerator pilot plantt2) showed
a somewhat larger value of 2.816 g/sm3 (1.23 grains/5ft3). Fur-
nace emissions from three types of municipal incinerators are
presented for comparative purposes. Because the data were not
taken in the government-endorsed manner (i.e., the condensable
fraction was not collected) only the dust loadings from the
combustion chamber before entering apy»of the air pollution con-
trol devices are compared (Table 2).13)
Table 2 Furnace Emissions Based on Design
Type Gram Loading Per /5m3
Experimental vortex incinerator 0.757
250 T/D traveling grate 1.265
250 T/D reciprocating grate 1.587
120 T/D rocking grate 0.778
The results indicate that the furnace emissions from the experi-
mental incinerator are lower than either the pilot scale incin-
erator or full scale commercial units.
Another facet of furnace emissions is the size of the
emitted particle. Under normal conditions the more complete the
combustion the smaller the particulate. To better understand
the overall combustion characteristics, the particle size of the
particulate being emitted from the experimental incinerator were
determined (Table 3).
10
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Table 3. STACK PARTICULATE 'ANALYSTS
Source of
particles
(filter #)
0246
0153
0156
0158
Lab. Wt. of
sample particles
no. analyzed
164
160
162
163
32.9
89.2
92.3
6.8
Percent by weight, in specified fraction
A
(>125 y)
3.95
2.58
1.84
0.00
B
(<125 y
>105 y)
0.00
0.67
0.00
4.41
C
(<105 y
3.04
6.06
4.11
7.35
D
(<47 y i
>12 v)
1.22
4.37
1.74
0.00
E
(<12 y)
91.79
86.32
92.31
88.24
It can be easily seen that most of the parti oil ate was 12 y or less. To
understand the particle size of the 12 y fraction its distribution was
studied. ( igure 3). At least 50 percent of the sample was less than 2
microns. It should be noted that the particle size distribution was
carried out on material collected after the air pollution control device,
and not on the dust emitted directly from the combustion chamber. It is
believed that the data is representative and the vortex incinerator is
responsible for the small particle size.
The more classical approach to evaluating incinerator combustion
chambers revolved around volume and weight reductions of the fuel, and heat
release rates.
Refuse is a bulky fuel with low density, and the volume reduction or
densification is a standard criteria for measuring efficiency. When 50.5
cubic meters (66 yd3) of refuse was burned in the vortex incinerator, the
resulting residue occupied 2.29 cubic meters (3 yd3), a 95 percent volume
reduction. Conventional incinerators are usually designed for volume re-
duction of 80 to 90\4) percent. In comparison to conventional incinera-
tors the volume reducing ability of the vortex incinerator was very good.
Weight reduction of the waste is also of interest to incinerator
designers and operators. The weight of the residue is compared with the
weight of the refuse, and the difference is the overall weight reduction.
For the case sited above, the weight reduction was 70 percent; this com-
pares favorably with published data on incinerator design.(5)
Another parameter used to design incinerators is the heat release
rate per cubic meter (ft3) of chamber volume. If too much heat is released,
11
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LU
N
Q
lU
100--
CC
LU
1LI
OC
O
UJ
50--
O
0.5 1.0
PARTICLE SIZE (MICRONS)
10.0
Figure 3. VOLUME PERCENT GREATER THAN STATED SIZE
VS. PARTICLE DIAMETER
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serious damage could be caused to the metal sections of the
combustion chamber, and if too little heat is released, poor
combustion will result. A common value employed as the heat
release rate design standard is 106,855 K cal/hr/m3 (12,000
BTU/hr/ft3).(6) Using a calorific value of 3365 cal/g
(6057 BTU/lb) for the refuse and 850 cal/g (1530 BTU/lb) for
the residue, the heat release rate for the vortex incinerator
was 384,000 K cal/hr/m3 (43,132 BTU/hr/ft3). This heat release
rate is about 3 times the accepted value and demonstrated that
high heat release rates could be used with municipal solid
waste.
II. Conditions in the Stack:
The underlying aim of the vortex incinerator project was to develop
and test an incinerator that would burn untreated municipal refuse
efficiently at high temperatures with a minimum amount of air pollution.
As discussed earlier the combustion chamber performed were, but oddly
enough the efficient burning resulted in several emission problems.
Particulates:
An earlier point was that the better the combustion, the finer the
resulting ash. This type of ash is desirable when considering combustion
efficiency but undesirable from an air pollution control standpoint.
In Table 4, the data from two stack tests are presented so that the
relative amounts of the solid, water soluble, and organic fraction of
the total particulate can be observed. The emission rate endorsed by
the Government at the time of the test was 0.458 grams per standard
cubic meter corrected to 12 percent carbon dioxide (0.2 grains/scf at
12% C02). It can be seen that on both occasions the incinerator
failed to meet the emission regulations with the best effort being
1.428 grams per standard cubic meter corrected to 12 percent carbon
dioxide.
In conjunction with the second test, the removing efficiency of the
cyclone was determined. The ratio of the amount of dust removed to the
total incident dust loading is defined as efficiency. It was found
that only 0.81 grams per standard cubic meter corrected to 12 percent
carbon dioxide (0.35 grains/scf @ 12% C02) was collected out of 1.646
grams per standard cubic meter corrected to 12 percent carbon dioxide
(0.709 grains/scf @ 12% C02) or 50 percent efficiency.
Gases:
In addition to the particulate problems originating in the combustion
chamber, the elevated temperature and excellent oxidizing conditions
13
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Table 4 STACK INVENTORY
July 1970
Jan. 1971
July 1970
Jan. 1971
July 1970
Jan. 1971
CONCENTRATION
EXPRESSION
grams/son
(grains/set)
g rams /s cm
(grains/scf )
grams/son @
(grains/scf @)
12% C02
grams/son @
12% C02
(grains/set @)
12% C02
grams/scm @
50% Excess Air
(grains/scf @
50% Excess Air
grams/scm @
50% Excess Air
grains/scf @
FRACTION
PARTICULATE WATER SOLUBLE
(PROBE & FILTER) (CYCLONE & IMPINGERS)
0.727
(0.313)
0.834
(0.359)
0.873
(0.376)
0.817
(0.352)
0.715
(0.308)
0.887
(0.382)
0.506
(0.218)
0.625
(0.269)
0.601
(0.259)
0.615
(0.265)
0.492
(0.212)
0.662
(0.285)
ORGANIC CONDENSABLE TOTAL
(IMPINGERS)
0.021
(0.009)
0.019
(0.008)
0.030
(0.013)
0.016
(0.007)
0.030
(0.013)
0.019
(0.008)
1.254
(0.540)
1.477
0.636
1.483
(0.648)
1.428
(0.624)
1.233
(0.531)
1.567
(0.675)
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Table 4 (Continued)
en
FRACTION
July 1970
Jan. 1971
CONCENTRATION
EXPRESSION
grams/cm @
stack conditions
grains/cf @
stack conditions
grams/cm @
stack conditions
grains/cf @
PARTICULATE
(PROBE & FILTER)
0.176
(0.076)
0.239
(0.103)
WATER SOLUBLE
(CYCLONE & IMPINGERS)
0.121
(0.052)
0.183
(0.079)
ORGANIC CONDENSABLE
(IMPINGERS)
0.023
(0.010)
0.005
(0.002)
TOTAL
0.320
(0.138)
0.427
(0.184)
stack conditions
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produced several undesirable gaseous emissions.
Oxides of nitrogen occur in most combustion processes. The
general belief is that they result from the direct fixation of
atmospheric oxygen and nitrogen at elevated temperatures, and are
monitored because they are quite toxic. The experimental incinerator
attempted to control oxides of nitrogen by controlling the combustion.
If refuse were burned stoichiometrically, there would be no oxygen
left to be fixed with the nitrogen. The incinerator, however, was not
consistently run at stoichiometric conditions and significant amounts
of oxides of nitrogen were produced.
In Table 5, the oxide of nitrogen data are presently chronologically,
and the results show a trend toward decreased emissions. The reason
proposed for this trend is that better combustion conditions were
achieved, i.e., closer to stoichiometric and less available oxygen for
reaction with nitrogen. Initially, the incinerator ran at about 80
percent excess air, but as work continued on the unit this figure
dropped to about 50 percent.
It was clear that oxides of nitrogen were not controllable by con-
trolling the combustion, and therefore another method of control was
employed. Oxides of nitrogen are unstable compounds and the reverse
reaction (i.e., going to oxygen and nitrogen) is favored over the for-
ward reaction. As long as the reaction is not quenched (sudden drop
in temperature) the reverse reaction continues and lessens the nitrogen
oxide concentration. A typical oxide of nitrogen profile for the vortex
incinerator is shown below. The emissions from the combustion chamber
were the highest, but dropped significantly as the gas passed through
the system to the atmosphere.
Combustion chamber 113 ppm
Midstack 80 ppm
Top stack 49 ppm
At the time of the project there were no oxides of nitrogen emission
regulations, but if the project was to continue for a long period of
time an alternate method of oxides of nitrogen control would be desired.
Hydrochloric acid was also determined with oxides of nitrogen. On
the average, hydrochloric acid was found to be 150 parts per million
by volume. No correlation was found between the operating parameters
and the acid concentration, but it is suspected that relationship be-
tween fuel composition and acid concentration could be found if studied.
16
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Table 5. OXIDES OF NITROGEN CONCENTRATIONS
Date
1/29/70
2/4/70
2/20/70
3/4/70
4/2/70
4/7/70
5/16/70
NO concentration
142
132
125
152
173
216
140
177
128
131
146
128
106
132
129
184
158
240
73
171
184
266
Date NO concentration
/\
5/26/70 158
237
182
6/9/70 122
100
193
160
104
7/14/70 102
146
86
9/24/70 93
47
43
10/1/70 58
93
21
10/10/70 94
68
79
17
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DISCUSSION
The data collected on the vortex incinerator's combustion chamber
indicated that it did a very effective job in burning untreated munici-
pal refuse. Low particulate concentration, small particle size, high
heat release rates, and high carbon dioxide concentrations indicated
the combustion chamber did the job for which it was designed. The
burning rate was higher than the design specifications, but was necessary
to sustain high combustion temperatures. The result of the elevated
burning rate was a poorer quality residue even though the volume and
weight reductions were acceptable.
Conditions in the stack are what led to the termination of the
project. On the two occasions that a complete stack test was conducted,
the concentration of particulate (as defined by EPA) was in excess of
the established regulation. There are several reasons why the incinera-
tor failed the particulate emission regulations. First, was the selec-
tion of a large diameter [1.37 m (4-1/2 ft] cyclone. This was initially
selected because it could be refractory lined and withstand the hot
temperatures [815 C, (1500 F], It is common knowledge that the larger
the diameter of a cyclone, the more inefficient it becomes. As stated
earlier, the cyclone had an efficiency of about 50 percent and this is
just not good enough to meet federal regulations.
The second reason why the incinerator failed to meet the emission
regulations revolves around how particulate is defined. At the time of
the test "Any material that was a solid or liquid at 760 mm @21.1 C
(29.92 inches Hg @70°F) was considered particulate." Table 4 shows the
breakdown of the data in relation to where it was caught, and how it is
expressed. The particulate fraction refers to the actual solid material
caught in the probe, in the cyclone and on the filter. The water soluble
fraction is determined by what is left after evaporation of the water
collected in the cyclone and impingers. The organic fraction is extracted
from the collected water with chloroform and ether and evaporated. Total
particulate is then (by definition) the sum of these three fractions. A
close inspection of the data in Table 4 shows about 40 percent of the
particulate to be present in the water of the combustion gas. Since the
cyclone usually doesn't disintrain gases (for moisture), 40 percent of the
accountable particulate is escaping untouched. Thus, this condition makes
it almost impossible to meet any regulations.
A combination of poor cyclone efficiency and a large water soluble
fraction of particulate led to unsatisfactory levels of particulate in
the stack.
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REFERENCES
1. Achinger and Daniels, "An Evaluation of Seven Incinerators"
Proceedings of 1970 National Incinerator Conference, pp 32-64.
2. Ibid
3. Walker, A. B., and Schmitz, F. W., "Characteristics of Furnace
Emissions from Large Mechanically Stoked Incinerators."
Proceedings of 1964 National Incinerator Conference, pp 126-27
ASME, New York (1969).
4. DeMarco, J., Keller, D., Leekman, I., and Newton, I.
"Municipal-Scale Incinerator Design and Operation," U.S. Dept.
of Health, Education and Welfare, Public Health Service, Consumer
Protection and Environmental Health Service, Environmental Control
Administration, Bureau of Solid Waste Management, Cincinnati, Ohio
(1969).
5. Ibid
6. Ibid
19
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APPENDIX A
The concept of this vortex incinerator may seem straight forward,
but its design, development, and fabrication was far from trouble free.
It is not the intent of this report to belabor the project's mistakes
and failures, but some of the larger problems and their solutions bear
some mention.
Probably the biggest problem associated with the incinerator was
the existence of a large, positive pressure in the combustion chamber.
This positive pressure resulted from a combination of the high-velocity
inflow of combustion air necessary for the stoking and vortex action
and the frictional pressure losses of the heat exchanger and cyclone.
The positive pressure forced a change from continuous operation to batch
operation. For the incinerator to run at all, the combustion chamber
had to be sealed off at the feed end. This was accomplished by a
charging chute cover. Gaskets and clamps on this cover helped to seal
the pressure in, but we found it impossible to prevent some smoke leakage
from the charging chute. Leakage meant that whenever we wanted to add
refuse to the charging chute, the pressure had to be reduced by (1)
shutting the combustion air off and then (2) opening the charging chute
cover. This interruption caused many problems, including the overheating
of our heat exchanger and a severe, combustion-chamber temperature drop.
This batch operation undoubtedly affected the stack samples that were
taken during the various tests.
Problems were also experienced with the materials handling system.
A plug of compacted refuse would not keep the smoke from backing out
unless the plug was packed so tight that it jammed the chute. In addition,
problems of insufficient stoking and unreliable residue removal were encoun-
tered. Materials such as cardboard and large pieces of plastic would not
be sheared by the ram and would bind in the hopper. Every time a jam
occurred, the operation had to be shutdown and the jam broken manually.
Adding a system of blades, cables, and pulleys inside the hopper later
solved this problem. Whenever the ram was pushed forward, a blade was
pulled up the back of the hopper freeing up any materials that had a
tendency to bridge. On the ram's back stroke, the blade would return
downward forcing the refuse in front of the ram into the chute for charging.
This technique was very effective and eliminated about 90 percent of the
binding problems.
The residue and its removal from the combustion chamber presented
another problem. Since there were no grates, we had to rely on the in-
coming fuel to push the residue out. As the temperature increased, the
20
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metal cans and glass bottles began to soften and fuse together. When
pushed toward the residue pit, they began to bind and catch in the
opening and thus, closed off the residue removal. To overcome this
problem, an extension of the ram was added so that it would push any
bridged material into the residue hopper. This extension was water
cooled so that it could exist at the elevated temperatures. The ram
extension performed quite well.
21
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APPENDIX B. HEAT EXCHANGER DESIGN
I. Design Conditions
The principle of preheating combusion air is called either
"recuperation" or "regeneration" in the coal-fired, boiler field.
In the case of this incinerator, the principle is recuperation
since the heat is transferred directly to the air.Regeneration,
by contrast, involves an intermediate heat storage material such as
pebbles or heat storage liquids.
The heat exchanger design was based on the following condi-
tions:
- Combustion air flow rate: 71.22 kilograms per minute
(157 pounds per minute) or 58.34 cubic meters per minute
(2,060 cubic feet per minute) at standard conditions.
- Blower heating effect: ambient air is friction-heated to
65.6°C (150°F).
- Heat-exchanger air side-pressure drop: approximately 8.89
centimeters (3.5 inches) of water.
- Air temperature desired at heat exchanger outlet: 315°C
(600°F) up to 426°C (800°F).
The conditions on the flue gas side of the heat exchanger are:
- Flue gas flow rate: 198.2 cubic meters per minute (7,000
cubic feet per minute).
- Flue gas temperature: 1,204°C (2,200°F), average.
- Allowable pressure drop: 0.51 centimeters (0.2 inches) of
water.
Other considerations in the heat exchanger design were:
- Physical size: space approximately 40.6 centimeters (16
inches) x 48.3 centimeters (19 inches) x 182.9 centimeters
(72 inches). The 182.9 centimeter dimention was a horizontal
plane. A counterflow design for maximum recuperative heat
transfer.
- Materials of Construction: mild, structural grade steel for
reasons of minumum cost ana maximum availability. Future units
would require a material with optimum high-temperature service
qualities; for the experimental units, a short service life
was considered acceptable.
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II. Design Calculation, Round Tube Heat Exchanger
The first heat exchanger unit tried was a bank of 12 round
tubes. Each tube was a 1.83 meter (6 feet) length and 7.62 centi-
meters (3 inches) black-iron pipe. Combustion air flowed on the
inside of the 12 pipes while the flue gases flowed over the outside.
The design calculations for this first unit are:
- Tube size: 1.83 meters (6 feet) length os 7.62 centimeters !
(3 inches) block-iron pipe; outside diameter 8.89 centimeters
(3.5 inches): inside diameter 7.793 centimeters (3.068 inches).
- Combustion air velocity: 17.77 meters per second (58.3 feet
per second) inside the tubes.
- Reynolds number inside tube: 36,600.
- Air-to-air heat transfer coefficient: 61.52 kilocalories per
hour per square meter per degree Centigrade (10.7 BTU per
hour per square feet degrees Fahrenheit) based on Nu = 0.02
(Re)0-8.
- Flue qas velocity over outside of pipe: 51.56 kilometers per
hour (47 feet per second).
- Flue gas Reynolds number: 24,300.
- Flue gas heat transfer coefficient: 87.98 kilocalories per
hour per square meter per degree Centigrade (15.3 BTU per
hour per square feet per degrees Fahrenheit) based on Nu ~ 0,02
(Re)0-8
- Overall heat transfer coefficient 34.5 kilocalories per hour
per square meter per degree Centigrade (6.0 BTU per hour per
square feet degrees Fahrenheit).
- Heat transfer area: 145,152 kilocalories per hour (576,000
BTU's per hour) at approximately one-half of design air flow.
- Heat transfer area: 5.44 square meters (58.5 square feet)
(actually, about 11.24 square meters (121 square feet) would
be required at full design air flow).
- Combustion air outlet temperature: 315.5 degrees Centigrade
(600 degrees Fahrenheit) predicted at half of design air flow.
This first heat exchanger with twelve 7.62 centimeters (3 inches)
pieces was operated for approximately 50 hours at which time the pipe
material disintegrated. The condition of the pipes is shown in the
following pictures. Metallurgical analysis determined that the dis-
integration was caused by high-temperature oxidation.
The thermal performance of the first heat exchanger was unsatis-
factory. The combustion air temperatures leaving the heat exchanger
were only 148.9 to 204.4°C (300 to 400°F) for air flows between 42.48
and 56.64 cubic meters per minute (1500 to 2000 cubic feet per minute).
The 12-pipe configuration lacked sufficient heat transfer area, 5.44
square meters (58.5 square feet) compared with the required 11.24
square meters (121 square feet) needed when full air flow exists.
23
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The design selected for the second heat exchanger was also a
bank of tubes with the combustion air flowing inside the tubes,
Flue gases passed over the outside of the tubes in counterflow
fashion. This time, the tubes were 3.81 centimeters (1-1/2 inches)
(outside dimension) square tubes with a wall thickness of 0.476
centimeters (3/16 inches). Seventy tubes were stacked in seven
vertical columns, 10 tubes hich with a 3.81 centimeters (1-1/2
inches) spacing between each column. This design, shown in the
following pictures, effectively increased the air preheating. The
air-side heat transfer area increased by a factor of 3 and the flue
gas-side area increased by a factor of 2. In addition, this design
effectively lowered the tube material operating temperature, and
thereby increased the heat exchanger life.
Some representative design calculations for the 70-tube heat
exchanger are:
- Heat exchanger tubes: quantity 70; square; 3.81 centimeters
(1-1/2-inch) outside diameter, 0.478 centimeter (0.188 inch)
wall thickness, 182.9 centimeters (72 inches) long.
- Combustion air flow area: 8.162 square centimeters (1.265
square inches) per tube, 571 square centimeters (88.5 square
inches) total (0.0571 square inches).
- Air flow velocity: 28.13 meters per second (9.13 feet per
second).
- Air Reynolds number 23,600, average.
- Air pressure drop: 6,655 centimeters (2.62 inches) of water
(tube only).
- Air side heat transfer area: 14.63 square meters (157.5
square feet).
h CDy 2/3 _ .023 0 ?
ClGJL 'TEG]-0'2
p K y
h = 64.407 kilocalories per hour per square meter per degree
Centigrade (11.2 BTU per hour per square feet of degree
Fahrenheit).
- Flue gas-side calculations: gas-side heat exchanger aara
9.755 square meters (105 square feet).
- Flue gas heat transfer coefficient: h = 0.30 CpG 0<6
jyTTi*
- h = 71.883 kilocalories per hour per square meter per degree
Centigrade (12.5 BTU per hour per square feet degrees Fahren-
heit).
- Flue gas temperature entering heat exchanger: 1,204°C
(2,200°F).
- Flue gas temperature leaving heat exchanger: 782°C (1,440°F).
24
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- Log mean temperature: 793°C (1,460°F).
- Quantity of heat transferred: 277,200 kilocalories per hour
(1,100,000 BTU's per hour).
- Overall heat conductance coefficient 401.5 kilocalories per
hour per degree Centigrade (752 BTU's per hour per degree
Fahrenheit).
- Flue gas flow area: 0.116 square meters (1.25 square feet).
- Calculated combustion air preheat temperature: 343.3°C
(640°F).
The upper four pictures (Views A-l show the incinerator's
cyclone and stack area during a typical stack sampling test. View
E shows the incinerator feed hopper and air manifold. View F,
inside the feed hopper, shows the ram blade.
25
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing}
1. REPORT NO.
EPA-670/2-75-025
3. RECIPIENT'S \CCESSION>NO.
4. TITLE AND SUBTITLE
HIGH-TEMPERATURE VORTEX INCINERATOR
5. REPORT DATE
February 1975; Issuing Date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Robert C. Thurnau and Donald A. Oberacker
8. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORGANIZATION NAME AND ADDRESS
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
10. PROGRAM ELEMENT NO.
1DB063; ROAP 24ALL; Task 03
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Same as above
13. TYPE OF REPORT AND PERIOD COVERED
In-house
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This study was designed to help fill the gap between antiquated incinerators and
the solid waste problem. Work was initiated on a new type of incinerator—a high-
temperature vortex incinerator. The project was sponsored by the U.S. Environ-
mental Protection Agency, National Environmental Research Center-Cincinnati, Solid
and Hazardous Waste Research Laboratory. Specifically, the incinerator was designed
and built at the Center Hill Pilot Plant of SHWRL and used only untreated municipal
waste as its fuel.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
^Incinerators
Refuse
Research
Waste disposal
Slagging
Solid waste
High temperature vortex
incinerator
*High volume reduction
13B
8. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
32
20. SECURITY CLASS (This pa ft)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
26
&U.S. GOVERNMENT PRINTING OfFICE: 1975-657-590/53*0 Region No. 5-1
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