EPA-650/2-73-018
August 1973
Environmental Protection Technology Series
liilLill
i R eifi
>
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EPA-650/2-73-018
CATALYTIC COMBUSTION,
A POLLUTION-FREE MEANS
OF ENERGY CONVERSION ?
by
R. E. Thompson,
D. W. Pershing, and E. E. Berkau
Control Systems Laboratory
National Environmental Research Center
Research Triangle Park, N. C.
Program Element No. IA20I4
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, N. C. 27711
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This report has been reviewed by the Environmental Protection Agency and
approved for publication. Approval does not signify that the contents
V* -
necessarily reflect the views and policies of the Agency, nor does
mention of trade names or commercial products constitute endorsement
or recommendation for use.
11
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CONTENTS
Page
Acknowledgements vi
Abstract vli
Introduction 1
History 1
Purpose 2
Summary 3
Background 5
Experimental Approach 7
Samples Examined 7
Standard Fuels 8
Test Plan 8
Probe Design 11
Analytical Procedures 14
Analysis of Results 15
Phase I - - Commercial Units 15
Phase II - - Controlled Testing 20
Toxicology 31
Domestic Applications 32
Conclusions 35
Recommendations 37
Bibliography 39
Appendices 41
iii
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FIGURES
Page
1 Schematic of Test Facility 9
2 Original Probe 12
3 Integral Sampling Probe 13
4 Emission Profile 21
5 Cutaway of Typical Propane Unit 22
6 Typical Case of Hydrocarbon Emissions for 24
Different Pad Thicknesses
7 Typical Case of Carbon Monoxide Emissions for 25
Different Pad Thicknesses
8 Comparison of Pad Types Versus Hydrocarbon 26
Emissions
9 Comparison of Pad Types Versus Carbon Monoxide 27
Emissions
10 Hydrocarbon Emissions Versus Surface 29
Stoichiometric Ratio (Propane)
11 Carbon Monoxide Emissions Versus Surface 30
Stoichiometric Ratio
D-l Analytical System 48
iv
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TABLES
No. Page
1 Pollutant Emissions from Commercial Units at 16
Maximum Heat Output
2 Performance Characteristics of Commercial 17
Units at Maximum Heat Output
3 Comparison of Commercially Available Units 19
4 Comparison of Catalytic Heating Emissions 33
with a Domestic Oil Burner
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ACKNOWLEDGEMENTS
The authors gratefully acknowledge the many contributions,
\
throughout the program, of Dr. George J. Benvegno and Mr- John P.
Manley, Jr. of Colonial Metals, Inc., Elkton, Maryland. We also
wish to acknowledge the help of Dr. John Hood and Associates of
Matthey Bishop, Inc., Malvern, Pennsylvania, in supplying the
catalyst pads for the Phase II testing. Finally the authors grate-
fully acknowledge the help of Mr. Robert G. Yountz and Mr. Walter
Geer, EPA, Research Triangle Park, North Carolina,in preparing this
report.
VI
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ABSTRACT
The report gives results of a study to determine the potential
of catalytic combustion for pollution-free domestic heating applications.
fourteen commercially available catalytic heaters were tested. Nine
units operated on propane and the other five, on lead-free gasoline.
Based on the results with the commercial heaters, a second phase of con-
trolled testing was undertaken. Substrate thickness, catalyst type and
concentration, and fuel rate were the parameters examined.
The results show that hydrocarbon (HC) emissions could not be re-
duced to levels approaching those currently possible with conventional
domestic heating units. However, nitrogen oxides (NOV) emissions were
J\
very low from nearly all the heaters. In the controlled testing,sub-
strate thickness and catalyst treatment had small effect on emissions.
Fuel rate was the most important parameter, especially in its effect on
HC emissions. Also, some of the commercial units produced extremely high
levels of carbon monoxide (CO) which the performance of other units and
the controlled testing showed to be preventable. Because of the high HC
emissions, more research is necessary before catalytic heating can be
considered a viable domestic heating alternative.
vii
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INTRODUCTION
History
The Control Systems Laboratory (CSL) of EPA's Office of Research
and Development is charged with the responsibility for finding and
developing techniques by which coal, oil, and natural gas can be
burned without producing harmful emissions such as combustible
particulates and nitrogen oxides (NO ). A recent survey has shown
A
that domestic sources account for a significant amount of these
emissions, particularly with respect to NO . The study further revealed
A
that 95 percent of these units are burning either natural gas or light
234
oil. In-house studies ' ' have shown that, while 30 percent reductions
in NO can be achieved through careful burner design, no completely
/\
effective technique is available. Modifications such as flue gas
recirculation, staged combustion, and water injection are too expensive
for home units. To overcome these difficulties various new concepts
are being considered by the CSL. This document is the final report
on an in-house study conducted on one such concept, catalytic combustion.
Mention of company and product names herein does not constitute
endorsement by the U. S. Environmental Protection Agency.
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Purpose
The purpose of this program was to determine the potential of cata-
lytic combustion for pollution-free domestic heating applications. Phase
I was directed toward the testing of current commercially available cata-
lytic heaters on both relative and absolute bases. Phase II addressed
itself to more fundamental considerations; namely, optimization of the
surface combustion concept by studying catalyst concentration, pad thick-
ness, catalyst material, and fuel rate. Phase II was necessary because of
the wide variation in performance observed during Phase I.
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SUMMARY
Fourteen commercially available catalytic heaters were tested in
Phase I of this study: nine units operated on propane; and the other
five, on lead-free gasoline. Each heater was tested at two fuel rates:
(1) the maximum rate at which the heater would operate under the manu-
facturer's control system,and (2) a common rate of 770 scc/min (4000 Btu/hr).
In general the liquid fuel units had higher CO and unburned HC emissions than
the propane units. NO^ emissions were very low (less than 20 ppm) from
nearly all heaters. An analysis of the results revealed that there was
no direct relationship between retail cost and performance; higher priced
units do not necessarily provide low emissions (or more heat output).
Finally, the fact that some of the units emit extremely high levels of
CO (in excess of 1500 ppm) cannot be overlooked due to the actual danger
involved.
In an effort to determine the cause of the performance variations
in Phase I, Phase II was undertaken. This more fundamental testing con-
sidered the effects of substrate thickness, catalyst type and concentra-
tion, and fuel rate. Pad thickness had little effect on emissions, but
doubling the platinum concentration 'decreased HC emissions slightly (by
50 to 300 ppm). The addition of 1 percent manganese to the catalyst treat-
ment also slightly decreased HC emissions. The most important parameter
encountered during the study was fuel rate, which had an especially strong
effect on HC emissions. It appears that part of the difference in per-
formance of the commercial units could be due to incorrect fuel rate de-
sign for the pad area.
- 3 -
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The Phase II data also confirms that high CO levels are unnecessary
and the manufacturers, whose products perform so poorly, should be en-
couraged to improve them. Under no conditions, however, was it possible
to reduce HC emissions, to a level approaching that currently possible
with, conventional domestic heating units (0.05 g per kg of fuel burned}.
Therefore, more research is necessary to develop catalytic heating as
a viable domestic heating alternative.
-* 4
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BACKGROUND
Previous metal gauze catalysts have long been employed in industrial
processes such as the manufacture of nitric acid by the partial oxidation
of ammonia and the related Andrussow process in which a mixture of ammonia,
air, and natural gas is converted to hydrocyanic acid. Application of such
catalytically active metals as platinum, palladium, and rhodium on a variety
of substrates (for the oxidation of lower order aliphatic hydrocarbons such
as propane) in small scale .heating uses was suggested by Webster and Weiss
in the late 1950's. The global reaction is:
C3H8 + 5 °2 •" 3 C02 + 4 H20
in which the initiation steps for the classical, high temperature combustion
are postulated to be:
C3Hg + OH «-»• C3H? + H20
C-H0 + 0 *-*. C0HC + HCHO
JO C. D
C3H8 + H ~ C3H7 + H2
In a catalytic heater, this type mechanism is replaced by low tempera-
ture (<427°C, <800°F) reaction path utilizing the catalyst present; however,
the details of the latter are not well documented. Experiments on the oxida-
( Q
tion of hexene and toluene in excess air with platinum screen catalyst have
shown that above 370°C (700°F) the oxidation occurs via a mass-transfer-
8 0
controlled reaction. Satterfield and Cortex have shown that below 370 C
(700°F) the effectiveness of the platinum falls off sharply with decreasing
g
temperature. Similar results have been obtained in studies of the oxidation
of methane and CO with palladium-impregnated surfaces. They also concluded
that, for oxidation of small amounts (ppm) of methane in air, palladium was
- 5 -
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far superior to platinum. Recent data obtained by Benvegno shows.that
platinum is superior for catalytic heating concentrations.
Most commercially available catalytic heaters utilize a catalyst
in the form of finely divided particles of catalytically active platinum
deposited on a porous, inert, thermally resistant substrate such as asbestos
cloth or fibrous silica-alumina. One technique by which the catalyst
material can be impregnated on the support material consists of dissolving
a thermally reducible compound of the catalytic metal Ce-9-» H^PtClg) in a
solvent, mixing it thoroughly with 10-micron activated alumina, and heating
the mixture to reduce the metal and precipitate the metal particles on the
alumina. The resultant dry powder is then mixed with water to make a slurry
and sprayed onto the support material.
During the operation of the unit,the fuel is conducted to the back of
the catalyst pad, allowed to diffuse through the inert backing, and com-
busted over the face of the unit. Gaseous fuels are fed in via a gas spud
haying a small central orifice. Liquid units utilize a wick formed of non-
12
combustible fibers such as fiberglass and require that the fuel vaporize
between the wick and the back of the catalyst pad. Both types of units re-
quire preheating, which is accomplished by lighting raw fuel at the pad
surface. When the unit achieves a high enough temperature, the catalytic
action begins and the flame goes out.
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EXPERIMENTAL APPROACH
Samples Examined
During Phase I of the program, 14 commercially available heaters were
procured either through manufacturer solicitation or off-the-shelf purchase.
Appendices A and B contain a detailed description of all the units and their
respective manufacturers. Nine of the 14 units operate on propane (LPG);
the remaining 5 require lead-free ("white") gasoline. All of the units have
a heat rating between (1260 kcal/hr and 2016 kcal/hr; 5,000 and 8,000 Btu/hr)
based on the heat content of the inlet fuel. These heaters are commonly
used by sportsmen in tents, camping trailers, hunting lodges, houseboats,
etc. and by industry in railroad cars, warehouses, farm buildings, etc.
For Phase II of the program, 16 custom-built pads were procured from
a firm currently engaged in production of the catalytic pads for several
of the heater manufacturers. These pads, constructed per the authors'
specifications based on the results of earlier testing, are described in
detail in Appendix C. Basically, the 16 pads consisted of four groups,
each group treated with different catalysts. Each group contained four
alumina-silica fiber pads of different thicknesses:. 0.95 cm, 1.27 cm, 1.95 cm
and 2.54 cm (3/8, 1/2, 3/4 and 1 inch). The first group of pads had been
treated with the "standard" platinum loading; the second group had twice
13
the standard loading. Previous fuel additive studies by Martin et al.
had shown manganese compounds to be effective in the reduction of one product
of incomplete combustion; i.e., carbon particulate. Since the total CO and
HC emissions encountered in the additive tests was so low, it was thought
- 7 -
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that manganese might have some potential for their reduction when these
incomplete combustion products were present in higher amounts. Therefore,
the third and fourth groups of the present program had the standard
platinum loading plus 0.25 percent and 1.0 percent manganese, respectively.
Standard Fuels
In order to provide uniform test fuels throughout the evaluation,
large quantities of two standard fuels were obtained. For the propane
heaters, a mixture of Gulf Refinery and Texas Eastern Pipeline—95 per-
cent natural grade (HD5 or better)--was used. The fuel contained only
traces of petrolene and butane and was sulfur- and nitrogen-free. For the
liquid gas heaters, commercially available Coleman brand liquid fuel was
used: it is a refined petroleum naphtha product (high grade gasoline) con-
taining no lead and no halides.
Test Plan
Phase I of the test program was a complete characterization of the
14 commercial hsaters and, more specifically, measurement of the fuel con-
sumption rate Cheat input) and combustion products of each. All of the
heaters were first put through a break-in period of full-out firing for 2
hours, after which they were allowed to cool completely before any testing.
Throughout the testing each heater was allowed to warm up for a period of
1 hour.,before any sampling. Figure 1 is a schematic of the test system
used for the 1_P heaters. The system for the liquid-fired heaters was the
same, but each heater utilized its own self-contained fuel supply.
Before the initial test, each heater was permitted to operate full-out
under its own control system; i.e., the control valve was wide open on the
- 8 -
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EXPANSION
CHAMBER
PAD
MANUFACTURER'S
VALVE ASSEMBLY
(AS SUPPLIED)
FUEL PRESSURE
GAUGE
SMALL j ]
LP TANK U
TOGGLE
VALVES
TWO-STAGE PRESSURE
REGULATOR
IS]
ORIFICE
INTEGRAL
SAMPLING
PROBE
TO
ANALYZERS
HEATER
DIRECT-READ
CALIBRATED
ROTAMETER
PANEL (3 SCALE)
MICRO-
NEEDLE
VALVES
NOTE: ALL TUBING STAINLESS STEEL 316
MAIN
LP FUEL
SUPPLY
Figure 1. Schematic of test facility.
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LP units and the "high" setting was on the liquid fuel ones. During this
time the fuel rate and inlet orifice pressure were recorded. In-line
pressure gauges and rotameters were used for the propane, while an overall
weight loss determination was utilized with the liquid fuel.
Once the operating characteristics of each LP unit had been determined,
the fuel supply was switched over to the large tank of standard propane.
This switching was necessary to ensure that the results were not affected
by pressure variation in the small cylinders of propane normally used with
these units. This, of course, was not a problem with the liquid fuel
heaters. The first emissions test was run at the "full-out" condition; i.e.,
the fuel rate from the large tank was adjusted until it matched the rate
measured when the heater was "wide open" under the manufacturer's control
system. Again, for the liquid-fuel units this "high" setting was used.
Continuous emissions measurements were made until the unit reached equilibrium
operation.
As a second part of Phase I, all of the heaters were rerun and sampled
at a common fuel rate, and therefore a common heat input value (1>008 kcal/
hr, 4,000 Btu/hr). This was done in order to have a second, and possibly
more valid, basis for comparison. The first test simulated the way the
heaters are used in actual practice; the second allowed comparison of the
quality of the catalyst pad and fuel delivery system. The common value of
(1,008 kcal/hr, 4,000 Btu/hr} was selected because it was in the medijum-to-
high range of most heaters and yet not far from the maximum value of the
least powerful heater. In the case of the liquid fuel models, the heat
- 10 -
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setting (high - medium - low) was adjusted until a value close to (1,008
kcal/hr, 4,000 Btu) was obtained.
For the Phase II testing, each of the 16 custom-built pads was mounted
in a conventional propane unit that had been modified to accept the various
pad thicknesses. After an initial break-in period of 2 hours, each pad was
warmed up for 1 hour and subsequently run and sampled at four different fuel
rates in the range of 500 to 850 scc/min (655'toll08 kcal/hr, 2,600 to 4,400
input Btu/hrl.
Probe Design
Since many of the heaters were of different sizes and physical configura-
tions, it was necessary to construct a probe of special design that would
incorporate no bias in sampling. A single-point differential probe, while
extremely functional for evaluating inhomogeneities characteristic of specific
pads, was not satisfactory for a program of this scope. Figure 2 illustrates
the first probe which was utilized in the testing. The six prongs welded
shut at the ends were made long enough to accommodate the largest heater.
Several small holes drilled in the sides of tubes facing the heaters were
opened depending upon the size of the pad being tested. In actual practice
this probe design was not satisfactory; it was not possible to size the holes
correctly to ensure uniform sampling over the wide variety of pads encountered.
Figure 3 shows the probe used to obtain all the results reported herein.
The eight prongs of this probe are virtually all of the same length and each
has one 90-degree bend before entering the sample line. In addition, by
loosening the retaining nuts on the "cross" type fittings and adjusting the
prongs, the area covered by the eight points can be greatly reduced or
- 11 -
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BOTTOM
TOP
Figure 2. Original probe.
-12-
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Figure 3. Integral sampling probe.
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enlarged without affecting the pressure drop (and therefore the flow rate)
of the individual lines. The authors believe this design to.be far more
uniform in sampling characteristics than any other encountered to date.
During sampling, the probe was placed 0.376 cm (1/8-inch) above the pad
surface, minimizing dilution of the samples with room air.
Analytical Procedures
With the exception of the probe design just discussed, the sampling
and analytical procedures were identical to those employed in earlier studies
by the Combustion Research Section: paramagnetic oxygen analysis, flame
ionization detection for unburned hydrocarbons, and nondispersive infrared
analysis of CO, C02, and NO^. All sampling was done on a continuous basis,
and the gaseous hydrocarbons were calculated as propane. Traditional
sequential smoke sampling, particulate collection, and SO? analysis were
omitted due to the negligible ash and sulfur content of the fuels. The
details of the entire sampling system are in Appendix D.
- 14 -
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ANALYSIS OF RESULTS
Phase I—Commercial Units
Introductory Note: The purpose of this program was to evaluate cataly-
tic combustion as a new concept in residential heating, not to perform a con-
sumer-type evaluation of presently available units. Therefore, the results
contained herein may be used neither as a basis for any legal action against
any party, nor for sales promotion of any of the products. Also, since most
of the testing occurred during the summer of 1971, new models have undoubtedly
come on the market. It is hoped, however, that the program will provide in-
sight for future work in the field. In addition, it should be noted that all
of the heaters tested were assumed to be representative of their particular
brand; however, the possibility that one or more of the units could have been
defective should not be ignored.
Table 1 shows a complete listing of each of the commercially available
units tested and the emission levels measured at the "full-out" condition.
All pollutant concentrations are reduced to zero percent excess air; i.e.,
air-free. (Appendix E is a detailed explanation of the air-free concept.)
As the table indicates, the operating characteristics of the various units
were significantly different. CO and unburned HC emissions from the liquid
units are considerably higher than from most of the propane units. NO
A
emissions are extremely low from nearly all the heaters. Appendix F is a
complete listing of all the results, as well as specific comments about each
heater.
Table 2 shows both the rated and the measured heating values for the
same heaters under "full-out" operation. It is interesting to note that the
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Table 1. POLLUTANT EMISSIONS FROM COMMERCIAL
UNITS AT MAXIMUM HEAT OUTPUT41
Heater
LPG MODELS
Bernzomatic
Cargo Safe
Coleman
Impala
McGinnis
Primus
Turner (LP7)
Turner (LP27)
Zebco
White Gas Models
Coleman (513A-700)
Coleman (513A-708)
Coleman (515-700)
Coleman (515A-704)
Thermos
C0b
46
124
313
174
20
1560
27
36
1079
665
478
2350
198
1280
HCb
2550
8650
29,000
4050
1000
10,250
1110
1335
5800
7500
8315
19,000
5335
18,000
N0xb
2
16
62
8
6
12
0
4
0
8
Not measured
13
Not measured
32
Fuel control valves set on "high
Reported as ppm at 0% excess air
- 16 -
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Table 2. PERFORMANCE CHARACTERISTICS OF COMMERCIAL
UNITS AT MAXIMUM HEAT OUTPUT3
__ Heater
Coleman (515-700)
Cargo Safe
Coleman (513A-708)
McGinnis
Coleman (513A-700)
Coleman (515A-704)
Primus
Impala
Thermos
Bernzomatic
Turner (LP27)
Coleman
Zebco
Turner (LP7)
Euel
White Gas
LPG
White Gas
LPG
White Gas
White Gas
LPG
LPG
White Gas
LPG
LPG
LPG
LPG
LPG
Rated
Heating
Values
8000
6000
5000
8000
5000
8000
8000
8000
7000
7000
7000
5000
7000
7000
Measured
Heati nq
Valueb
8440
5970
4970
7785
4750
7080
6365
5970
4915 ,
4800
4200
3200
8330
3375
Performance
FactorC
1.06
1.00
0.99
0.97
0.95
0.89
0.80
0.75
0.70
0.69
0.60
0.64
0.55
0.48
Fuel control valves set on "high"
3Btu/hr based on inlet fuel rate (These values do not include a correction
for the fuel lost through the escaping unburned hydrocarbons.)
"Measured heating value/rated heating value
- 17 -
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ratio of the actual heat output to the Tnanufacturer's rated values range
from 0.5 to values slightly in excess of 1.0.
Although all 14 heaters have about the same heat output rating, they
vary rather widely in retail cost and in emissions per actual heat unit.
Table 3 shows the manufacturer's suggested retail cost of each unit; i.e.,
the list price. The table also lists a value index and a pollution index.
Ideally, the consumer would like to maximize-the heat he gets for his dollar
and minimize the pollution. Unfortunately, no one heater does both.
It was decided that the experimental data obtained by operating the
heaters at an equivalent flow rate of 770 scc/min 0>008 kcal/hr, 4,000
Btu/hr) did not provide a fair basis for comparison. The larger heaters
performed very poorly at this reduced rate, probably because it allowed
the catalyst pad to cool below the optimum operating temperature, thus con-
Q
firming the work of other investigators .
- 18 -
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Table 3. COMPARISON OF COMMERCIALLY AVAILABLE UNITS
Heater
McGinnis
Turner (LP7)
Turner (LP27)
Bernzomatic
Cargo Safe
Coleman (515A-704)
Impala
Coleman (513A-708)
Coleman
Coleman (513A-700)
"Primus
Thermos
Coleman (515-700)
Zebco
Fuel
LPG
LPG
LPG
LPG
LPG
White Gas
LPG
White Gas
LPG
White Gas
LPG
White Gas
White Gas
LPG
Pri cea
(Dollars)
110.00
45.00
45.00
45.00
73.00
64.00
50.00
46.00
47.50
28.00
30.00
34.00
40.00
40.00
Cost/
Effectiveness
Indexb
14.13
13.33
10.71
9.38
12.23
9.04
8.38
9.25
14.85
5.89
4.71
6.92
4.74
10.44
Pollution
IndexC
3
8
9
10
21
28
29
96
98
140
245
260
278
282
aBased on best available information regarding manufacturer's suggested
retail price (net cost) in 1971.
I
bRetail cost (dollars)/252 x 103 cal ($/1000 Btu)
cppm CO (air free)/252 x 103 cal Cppm/1000 Btu
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Phase II—CarTtrolied,Testing
Th.e Phase II work was undertaken in an effort to clarify why certain
of the commercially available units performed so much better than others.
The first step was an analysis of the combustion homogeneity across the pad
surface. This was accomplished by taking differential, point-wise emission
measurements. The old style Turner (propane) and the Thermos (liquid fuel)
Were chosen for the tests primarily because each has a grill which makes
probe location simple. Figure 4 shows a similar grid pattern with the results
of the Turner profiling. Due to time limitations, each grid point was not
measured; Figure 4 is based on four carefully selected traverses. The major
non-uniformity occurs at the pad edge (see Figure 4) as was expected. The
poorer combustion region in the center of the pad is apparently due to the
fuel distribution system's blocking the axial flow at this point (see Figure
5). In general, the emissions are reasonably uniform: except for points at
the very edge, the standard deviation in the data is less than 83 ppm; approx-
imately 80 percent of the data points are within 10 percent of the sample
me.an. That fuel distribution problems cannot account for the poor perform-
ance of some heaters is a conclusion confirmed by the Thermos profile data.
The major portion of the effort in Phase II was directed toward evaluat-
ing the effects of substrate thickness, catalyst type and concentration, and
fuel rate on pollutant emissions. Because of the virtually negligible amount
of NO-x produced by all the pads, CO and gaseous HC were chosen as the per-
formance parameters to be used for comparison.
Each of the catalyst treatments was examined on substrates of four dif-
ferent thicknesses (0.95, 1.27, 1.05, and 2.54 cnv, 3/8, 1/2, 3/4, and 1 inch).
- 20 -
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2100
1430
1280
850
677
785
685
670
590
666
619
603
630
616
666
783
850
781
TOP
1010
674
617
646
675
823
747
837
766
849
783
1 /D£
675
623
866
735
762
762
774
664
665
809
727
772
674
903
721
-
972
804
1050
914
BOTTOM
Figure 4. Emission profile (all values are gaseous hydrocarbon in ppm).
-21-
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Figure 5. Cutaway of typical propane unit.
- 22 -
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Figures 6 and 7 show the effects of substrate thickness variation on HC and
CO emissions, respectively, for a sample case. In general, the data from all
16 pads indicate that pad thickness has little, if any, effect.
Figures 8 and 9 show the effects of catalyst composition on HC and CO
emissions, respectively. The data on these graphs ara the result of average
ing the four pad thicknesses with each given .catalyst treatment. Figure 8
Indicates that doubling the platinum concentration causes a slight but dis-
tinct decrease in the HC emissions, especially at the higher fuel rates.
figure 9 suggests that increasing the platinum increases the CO emissions by
about 10 ppm. This may be a real effect or it may be an analytical problem
due to the extremely low levels of CO.
figures 8 and 9 also illustrate that under similar operating conditions,
the addition of 1.0 percent manganese to the catalyst treatment, while appar-
ently having no effect on CO, did show a slight but distinct decrease in HC
emissions. Due to the slight decrease, the 0.25 percent manganese pads were
not tested; however, it does appear that further testing at higher concentra-
tions might be in order since manganese is considerably cheaper than platinum.
By far, the most important parameter encountered throughout the entire
study was fuel rate, especially with regard to HC emissions (see Figure 8).
Indeed, every pad tested produced a parabolic emission curve; interestingly
enough, the minimum vertices of the curves fall consistently in the 625-675
sec/rain range. Further, a fuel rate variation in either direction of as
little as 150 sec/min results in a two- to three-fold increase in unburned
HC emissions. The effect was not as pronounced for CO emissions; however,
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1200
1000 —
o
CO
ce
-------
so
50
40
Q
X
o
o 30
o
oo
ce
•*?.•- ^.r.-a«. —— i
<>3/8-|nch....9.,35
•••••••••••••*••»•••*••*
1-inch -/...
2.54 cm
I
500
550
600 650, 700 750
FUEL RATE, scc/min PROPANE
800
850
Figure 7. Typical case of carbon monoxide emissions for different pad thicknesses.
- 25 -
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1000
900
800
700
600
O
ts>
O
m
DC
<£
O
O
500
>: 400
300
200
500
DOUBLE-PLATINUM
LOADING
STANDARD WITH v
1.0% MANGANESE "
550
600 650 700 750
FUEL RATE, sec/rain PROPANE
850
Figure 8. Comparison of pad types versus hydrocarbon emissions.
-26-
-------
60
50
I
to
X
o
o
CO
ce
30
20
10
DOUBLE-PLATINUM LOADING
STANDARD PAD
STANDARD WITH 1'* MANGANESE
500 550 600 650 700 750
FUEL RATE, sec min PROPANE
800 850
Figure 9. Comparison of pad types versus carbon monoxide emissions.
-------
the reader should keep in mind that the CO levels from all the pads were
extremely low compared to many of the commercial heaters.
The parabolic nature of the curve is probably due to competition be-
tween pad temperature and mass transfer effects. If the fuel rate is too
low, the pad fails to achieve and sustain the temperatures needed for ef-
ficient catalyst performance.
On the other hand, as the flow rate is increased beyond a certain point,
temperature effects become small and the reaction becomes mass-transfer-
limited, specifically by the rate of diffusion of oxygen to the catalytic
surface. From the catalyst geometry, fuel flow, and temperature of each
unit it was possible to compute diffusional rates of oxygen to the surface
of the pad. Using these, with the measured fuel rate data, air-fuel ratios
14
at the surface were then calculated . The results of these calculations
for both the commercial units and the custom pads are shown in Figures 10
and 11. In general, the high emission cases are at conditions computed as
fuel rich; i.e.,where the superficial propane velocity through the pad ex-
ceeds the rate at which stoichiometrtc amounts of oxygen can diffuse to the
pad surface. Quantitatively, this appears to occur when the superficial
propane velocity through the pad exceeds about 0.0244 cm/sec (0.0008 ft/sec).
- 28 -
-------
12,000
10,000
8,000
§ 6,000
=i
o
o
4,C
2,000 —
BO
60
A PRIMUS
B ZEBCO
C TURNER (LP 27)
D TURNER (LP 7)
E CARGO SAFE
F IMPALA
G BERNZOMATIC
H MCGINNIS
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2
Figure 10. Hydrocarbon emissions versus surface stoichiometric ratio (propane).
- 29 -
-------
1600
1400
1200
100Q
a
I 800
o
o
CD
Cd
e£
o
600
400
200
0
AO
A PRIMUS
B ZEBCO
C TURNER (LP 27)
D TURNER (LP 7)
E CARGO SAFE
F IMPALA
G BERNZOMATIC
H MCGINNIS
J COLEMAN
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 24 2.2
(AIR/FUEL)/(AIR/FUEL)STQ|eH
Figure 11. Carbon monoxide emissions versus surface stoichiometric ratio.
- 30 -
-------
Toxicology
Before any final conclusions can be formulated it is necessary to con-
sider the relative importance of the resultant emissions. In general, such
aliphatic HC emissions as propane are biologically and chemically inert; i.e.,
they produce no detectable functional or subclinical alternations. Avail-
able evidence indicates that these gases are rapidly eliminated from the
lungs in an unchanged state. Thus propane gas can be tolerated in relatively
high concentrations in inspired air without producing systemic effects. If
the concentration is high enough to dilute or exclude the oxygen normally pre-
sent in air, the effects produced will be due strictly to oxygen deprivation
or asphyxia. For instance, a concentration of 100,000 ppra ('10 percent),
though not noticeably irritating to eyes, nose, or respiratory tract, will
produce dizziness within a matter of minutes. But more realistically, ex-
posures to 10,000 ppm (1 percent) cause no symptoms in man. Even odor is
not detectable below 20,000 ppm (2 percent).
Only one of the LPG heaters tested produced enough gaseous HC to war-
rant consideration relative to HC toxicity presuming a continuous supply of
fresh air is provided. One Coleman unit produced 29,000 ppm; the others
ranged from 1,000 to 10,000 ppm. Of the units burning white gasoline, both
the Coleroan 515-700 and the Thermos produced greater than 10,000 ppm. CO
is a specific chemical asphyxiant which'combines with the hemoglobin in the
blood to exclude oxygen. The U. S. standard for gas-fired room heaters
states, "A room heater shall produce no carbon monoxide. This provision
shall be deemed met when a concentration of carbon monoxide not in excess of
0.02 percent (200 ppra). is present in an air-free sample of the products of
- 31 -
-------
combustion, when the heater is tested in a room with approximately a normal
oxygen supply." All of the liquid fuel units and at least two of the LP
heaters operating at maximum heat output produced CO close to or in excess
of this limit; tn some cases as much as two orders of magnitude higher. On
the other hand, four of the units averaged less than 50 ppm, suggesting that
h.i.gh. emissions are not necessary. (The authors realize that the units tested
are not strictly "room heaters" as such, but.the normal applications (e.g.,
tents, campers, boats, and garages) put them in virtually the same category.)
Domestic Applications
The value of the catalytic combustion concept is that it operates at a
low temperature, which considerably limits the formation of NO and the chance
of fire. In addition, a few of the commercial units and the work of Phase II
have shown that it is possible to operate at relatively low CO and NO levels.
Table 4 compares the catalytic heating emissions measured in Phase II with
those reported previously for a typical home oil burner. Although the two
are not directly comparable for many reasons, they show that the HC emissions
from catalytic units are several orders of magnitude greater than from units
now being used. Since these emissions considerably enhance the formation of
photochemical smog, catalytic heating cannot even be considered as a viable
domestic heating alternative until this problem is overcome. Note that this
conclusion does not apply to sportsman-type uses because of the relatively
number of units of that type in operation.
- 32 -
-------
Table 4. COMPARISON OF CATALYTIC HEATING EMISSIONS
WITH A DOMESTIC OIL BURNER
Emission
CO
NOX
HC
Catalytic
Combustion3
0.36
<0.04
14.0
Classical
Combustion3
0.40
0.72
0.05
gms of pollutant per kg of fuel burned
- 33 -
-------
CONCLUSIONS
1. Commercially available catalytic combustion units vary widely in both
actual heat output (for the same rated value) and in pollutant emissions
produced. At least four of the heaters examined produced CO levels which
are not acceptable and, compared to other units of comparable price, not
necessary.
2. Controlled tests reveal that fuel rate is the most critical variable
for a given pad size. Pad thickness and platinum concentration have
lesser effects on performance.
3, By optimizing the pad thickness, catalyst treatment, and fuel rate it
is possible to limit CO emissions to a level approaching that currently
possible with conventional domestic heating units. In addition, NOV
J\
formation is essentially zero.
4. For domestic applications the biggest obstacle from the pollution stand-
point is that of excessive HC emissions. Further work must be done in
this, area if the concept is to receive widespread usage.
- 35 -
-------
RECOMMENDATIONS
1. Before any further consideration is given to use of catalytic heating
for domestic applications, it must be shown that present hydrocarbon
levels, can be substantially reduced.
2. Manufacturers' warnings regarding ventilation requirements should be
strengthened,
3, Manufacturers should make a concentrated effort to improve performance
because data shows that some units operate much better than other units
of equivalent price.
4. Safety standards for catalytic heaters are needed to protect the public
from the health hazards of inferior quality units.
- 37 -
-------
BIBLIOGRAPHY
1. Wai den Research Corp., Systematic Study of Air Pollution from
Intermediate-Size Fossil-Fuel Combustion Equipment, EPA, APTD 0924
(NTIS No. PB 207-110), July 1971.
2. Martin, G. B. Status Report on Study of Effects of Fuel Oil Additives
on Emissions from an Oil-Fired Test Furnace, EPA, Office of Air Programs,
June 1970.
3. Howekamp, D. P. et al. Effects of Combustion-Improving Devices on Air
Pollution Emissions from Residentail Oil-Fired Furnaces, EPA, Office of
Air Programs, September 1969.
4. Martin, G. B. Use of Fuel Additives and Combustion Improving Devices to
Reduce Air Pollution Emissions from Domestic Oil Furnaces, EPA, Office
of Air Programs, September 1970.
5. Webster, M. E., assignor to Otto Bernz Co., Automobile Heater, U. S.
Patent No. 3,029,802, Ser. No. 767,407, April 17, 1962.
6. Weiss, G., assignor to American Thermocatalytic Corporation, Radiant
Gas Burner, U. S. Patent No. 3,191,659, Ser. No. 726,720, June 29, 1965.
7. Chinitz, W. and T. Baurer. An Analysis of Non-Equilibrium Hydrocarbon-
Air Combustion, Paper 65-19, Western States Section, Fall 1965, Comb.
Inst. Meeting.
8. Satterfield, C. N. et al. Mass Transfer Characteristics of Woven-Wire
Screen Catalysts, Ind. Eng. Chem., Fundam. 9:613-620, November 1970.
9. Investigation of Catalytic Combustion of Impurities in Air, Phototech Co.,
Div. of Bolt, Beranek & Newman, Inc., June 1967.
10. Benvegno, G. J. (Colonial Metals, Inc., Triumph Industrial Complex,
Elkton, Maryland), Private Communication, September 1971.
11. Keith, C. D. et al., assignor to Engelhard Industries, Inc., Catalytic
Oxidation Unit and Radiant Gas Burner, U. S. Patent No. 3,198,240, Ser.
No. 221,234, August 3, 1965.
12. Berchtold, D. V. et al., assignor to The Coleman Company, Inc., Catalytic
Heater, U. S. Patent No. 3,343,586, Ser. No. 450,710, September 26, 1967.
13. Martin, G. B., D. W. Pershing, and E. E. Berkau. Effects of Fuel
Additives on Air Pollutant Emissions from Distillate-Oil-Fired Furnaces,
EPA, AP-87 (GPO No. EP 4.9:87), June 1971.
14. Moyer, C. B., (Aerotherm Division, Mountain View, California), Private
Communication, October 5, 1972.
- 39 -
-------
15. Air Quality Criteria for Hydrocarbons, EPA, AP-64 (NTIS No. PB 190-489).
16. Gerarde, H. The Aliphatic [Open Chain, Acyclic) Hydrocarbons, Industrial
Hygiene and Toxicology, Second Edition, Volume II — Toxicology 1963.
17. U.S.A. Standard for Gas-Fired. RooiihHeaters, Volume II, Unvented 'Room
Heaters.American Gas Association, Inc., Fifteenth Edition. November 1967.
- 40 -
-------
APPENDICES
Page.
A. List of Commercial Catalytic Heaters Used in 43
Test Program
B. List of Manufacturers of Catalytic Heaters Used 45
i.n Test Program
C. Description of Custom Catalytic Pads 46
D. Sampling System and Instrumentation 47
E. Explanation of Air-Free Concept 49
F. Specific Results and Comments 50
- 41-
-------
Appendix A. LIST OF COMMERCIAL CATALYTIC HEATERS USED IN TEST PROGRAM
CO
I
Brand
LPG Fi
Bernzomatic
Cargo Safe
Impala
McGinn is
Primus
Turner 0-P7)
Turner (LP27)
Zebco
Coleman
Model
red
TX950
Master- Port
8000-36- LP
C4G
Gas Pre-Heat
Duo- Flow 8
LP7
LP27
Traveler
7000
5445-708
Heat rating, Cal (Btu)
252x1 O3 - 1 764x1 O3
(1000 - 7000)
1512xl03 cal/g
(6000)
2016xl03
(8000)
201 6x1 O3
(8000)
504x1 03-201 6x1 O3
(2000 - 8000)
1764xl03
(7000)
1 764x1 O3
(7000)
504x103x1 764x1 03
(2000 - 7000)
504xl03-1260xl03
(2000 - 5000)
Pad configuration
19.05 cm diameter
(round)
25.08x29.8 cm
vertical rectangle
22.8x28.6 cm
vertical rectangle
53.3x27.3 cm
horizontal rectangle
36.8x14 cm
angled double-face
horizontal rectangle
18x26.7 cm
vertical rectangle
26.7x18 cm
horizontal rectangle
27.3x17.8 cm
horizontal rectangle
26.7x16.5 cm
vertical rectangle
Retail
cost, $
44.95
73.20
50.00
110.00
29,99
44.95
44.95
39.95
47.50
-------
Appendix A (Continued). LIST OF COMMERCIAL CATALYTIC HEATERS USED IN TEST PROGRAM
Brand
: Model
Heat rating, Cal (Btu)
Pad configuration
Retail
cost, $
Liquid Fired
Coleman (515-700)
Di
Coleman (513A-700
Di
Thermos
Coleman (513A-708)
Coleman (515A-704)
515-700
al Temp. Adj.
p 5ISA-700
'al Temp. Adj.
8512
512A-J08
515A-704
1260x103-2016x1O3
(5000 - 8000)
756xl03-1260xl03
(3000 - 5000)
1764x1O3
(7000)
756x103-1260x1O3
(3000 - 5000)
1260x103x2016x1O3
C5000 - 8000)
26.7 cm diameter
hemisphere
18.4 cm diameter
hemisphere
19.5 cm diameter
hemisphere
18.4 cm diameter
hemisphere
26.7 cm diameter
hemisphere
39.98
27.98
34.00
45.95
63.95
-------
Appendix B. LIST OF MANUFACTURERS OF CATALYTIC HEATERS USED IN TEST PROGRAM
Bernzomatic
740 Driving Place
Rochester, New York 14613
Phone: 716/458-7076
Impala Industries
1106 East 37th Street
Wichita, Kansas 67204
Phone: 316/838-1486
Primus-Sievert
354 Sackett Point Road
New Haven, Connecticut 06473
Phone: 203/239-2554
Cargo Safe
9918 Atlantic Avenue
South Gate, California 90280
Phone: 213/564-2733
King Seely Thermos Company
Thermos Division
Norwich, Connecticut 06360
Phone: 203/887-1671
Turner Corporation
821 Park Avenue
Sycamore, Illinois 60178
Phone: 815/895-4545
Coleman Company, Inc.
250 North Street Francis Avenue
Wichita, Kansas 67201
McGinnis Marine, Inc.
5320 28th Street, N.W.
Seattle, Washington 98107
Zebco-Brunswick Corporation
P. 0. Box 270
Tulsa, Oklahoma 74101
Phone: 316/267-3211
Phone: 206/782-5777
Phone: 918/836-5581
-------
Appendix C. DESCRIPTION OF CUSTOM CATALYTIC PADS
1. Standard Cataheat "P" cover top surface.
2. Standard Cataheat "P" with twice platinum loading cover top surface
only.
3. Standard pad and platinum loading with 0.25 percent manganese in
excess top surface covering.
4. Standard pad and platinum loading with 1.0 percent manganese in ex-
cess top surface loading.
All pads were 18 cm (7-1/8 inches) wide x 26.7 cm (10-1/2 inches) high and
were mounted vertically.
- 46 -
-------
Appendix D. SAMPLING SYSTEM AND INSTRUMENTATION
Automatic instrumentation was used to continuously record the
concentrations of CC>2, C^, CO, NOX and gaseous HC in the exhaust
gases, as described below:
Parameter
Instrument Brand & Model
Type
CO,
CO
NO
HC
Beckman 315 A
Beckman F3M3
Beckman 315 A
Beckman 315 Al
Beckman 400
Non-dispersive infrared
Paramagnetic
Non-dispersive infrared
(with C00 filter)
Non-dispersive infrared
Flame ionization
(calibrated as propane)
All sampling was done at a rate of 1 liter per minute. The sample
lines were all constructed of'635 cm l.D. 316 stainless steel tubing
except for the NOX NDIR where 635 cm l.D. Teflon tubing was used
(see Figure D-l).
- 47 -
-------
TEFLON
LINE
HEATED
MOLECULAR
, SIEVE
(3A , CLAY BASE)
INTEGRAL
SAMPLING
PROBE
/
oo
i
£
V
9
V
SILICA
GEL TRAP
NDIR
NO
ANALYZER
PARA-
MAGNETIC 02
ANALYZER
-L:
h
FUEL
LINE
\WATER
GLASS-FIBER TRAP
INDUSTRIAL
FILTER
SILICA GEL
TRAP
HEATER
GLASS
WOOL
FILTER
o
FLAME-
IONIZATION
HC
ANALYZER
NDIR
C02
ANALYZER
ANALYZER
Figure D-l. Analytical system.
-------
Appendix E. EXPLANATION OF AIR-FREE CONCEPT
Rased on the composition of fuel burned, it is possible from stoicbio-
.metry to calculate the quantity of C02 produced by burning a given mass of
tliat fuel. At the conditions in which the volume of air consumed is exactly
the same as the amount necessary for complete combustion of the fuel (i.e.,
Stoichtoraetric}, the Q£ concentration in the flue gas is zero. With any
excess air, the C02 concentration is decreased, and the Q£ concentration
ts increased, by dilution with air. From the COp and 62 concentrations,
it i.s possible to calculate the actual volume of flue gas produced. For
pollutants (NO, CO, etc.) the concentrations can be normalized to a basis
Of comparison independent of excess air by multiplying the measured con-
centration by the ratio of actual volume of flue gas to the volume of flue
gas at stoichioraetric conditions. In this manner, the pollutant emissions
from a device operating at various excess airs can be compared on a common
basis, termed "air-free."
- 49 _
-------
Appendix F. SPECIFIC RESULTS AND COMMENTS
Heater
Bernzomatic
Cargo Safe
Impala
i
>
McGinn is
Primus
Turner (LP7)
Sample
configuration
Entire face
Entire face
L/R average
Bottom 1/2
Top 1/2
Bottom 1/2
Top 1/2
Bottom 1/2
Top 1/3
Bottom 1/2
Top 1/2
L/M/R average
Average on "LOW"
L/R average
L/R average
T/B average
Entire face
Kcal/Hr (Btu/hrb)
1209 (4800)
1007 (4000)
1675 (6650)
1504 (5970)
1504 (5970)
1007 (4000)
1007 (4000)
1504 (5970)
1504 (5970)
1007 (4000)
1007 (4000)
1961 (7785)
1915 (7600)
1603 (6365)
1007 (4000)
850 (3375)
1007 (4000)
COC
46
6'
46
115
133
16
22
65
290
60
125
20
22
1560
1280
27
12
HC°
2550
2670
355
5400
11900
550
440
1350
6300
28000
15000
1000
1500
10260
3000+
1100
340
NOXC
2
12
1
14
20
7
7
6
10
7
2
6
3
12
7
0
4
Heat rate basis
Natural draw
1007 cal kg/hr
(4000 Btu/hr)
Natural draw
1007 cal kg/hr
(4000 Btu/hr)
Natural draw
1007 cal kg/hr
(4000 Btu/hr)
Natural draw HIGH
Natural draw LOW
Natural draw
1007 cal kg/hr
(4000 Btu/hr)
Natural draw
1007 cal kg/hr
(4000 Btu/hr)
-------
Appendix F (Continued). SPECIFIC RESULTS AND COMMENTS
Heater
Turner (LP27)
Zebco
Coleman (515-700)
Coleman (513A-700)
Coleman (513A-708)
Coleman (515A-704)
Coleman (LPG)
Thermos
Sample
configuration
" ' i
Entire face
Entire face
Entire face
Entire face on HIGH
Entire face on HIGH
Entire face on HIGH
Entire face on LOW
Entire face on HIGH
Entire face on HIGH
Entire face on HIGH
Entire face
Kcal/Hr (Btu/hrb)
1058 (4200)
1007 (4000)
965 (3830)
2126 (8440)
2126 (8440)
1197 (4750)
873 (3465)
1252 (4970)
1783 (7080)
806 (3200)
1238 (4915)
COC
36
12
1079
L
r
2300
2400
665
80
478
198
313
1280
HCC
1335
688
5800
2000+
1700+
7500
995
8315
5335
29000
18000
NOXC
2
4
Not
measured
13
52
8
6
Not
measured
Not
measured
Not
measured
32
Heat rate basis
Natural draw
1007 Cal kg/hr
(4000 Btu/hr)
Natural draw
Natural draw
Same but with
probe raised
Natural draw
Natural draw
Natural draw
Natural draw
Natural draw
Natural draw
(no control )
L/R - average of left half and right
L/M/R - average of left third, middle third, and right third
T/B - average of top half and bottom half
Calculated values based on fuel rate
'Reported as ppm air-free
-------
BIBLIOGRAPHIC DATA
SHEET
1. Report No.
EPA-650/2-73-018
rTitle and Subtitle
Catalytic Combustion, a Pollution-Free Means of
Energy Conversion?
3. Recipient's Accession No. j
5. Report Date [
August 1973 |
6.
Author(s)
R. E'. Thompson, D. W. Pershing, and E. E. Berkau
8. Performing Organization Rept.
No.
). Performing Organization Name and Address
EPA, Office of Research and Development
NERC-RTP, Control Systems Laboratory
Research Triangle Park, North Carolina 27711
10. Project/Task/Work Unit No.
1A2014
11. Contract/Grant No.
12. Sponsoring Organization Name and Address
13. Type of Report & Period
Covered
Final
14.
15. Supplementary Notes
6. Abstracts The report gives results of a study of the potential of catalytic
combustion for pollution-free domestic heating applications. Nine of
the 14 commercially available catalytic heaters tested operated on
propane; the other five, on lead-free gasoline. Substrate thickness,
catalyst type and concentration, and fuel rate were examined. HC
emissions could not be reduced to levels now possible with conventional
domestic heating units; however.- NOx emissions were very low from nearly
all heaters. In the controlled testing, substrate thickness and catalyst
treatment had little effect on HC emissions. Some units produced very
high levels of CO which the performance of other units and controlled
testing showed to be preventable. Because of the high HC emissions,
more research is necessary before catalytic heating can be considered a
17. Key words and Document Analysis. i7o. ivscript.rs jviable domestic heating alternative.
Air Pollution
Catalysis
Hydrocarbons
Nitrogen Oxides
Carbon Monoxide
>s Identifiers/Open-Ended Terms
*ir Pollution Control
Stationary Sources
Catalytic Combustion
Domestic Heaters
, COSATI Field/Group 13B, 2IB
8. Availability Statement
Unlimited
19.. Security Class (This
Report)
UNCLASSIFIED
20. Security Class (This
UNCLASSIFIED
21- No. of Pages
59
22. Price
I JMTIS-35 (REV. 3-72)
USCOMM-DC 14BS2-P72
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