TEMPERATURE AND EMISSIONS MEASUREMENTS FOR A GAS
BURNER
Ighodalo Osagie, Amunega Ibrahim, Lawani Monday, Onaghinor Sidney,
And Ogboi Terry.
Mechanical Engineering Department,
Ambrose Alli University, Ekpoma.
oighodalo@yahoo.com
Abstract
Emissions for combustion systems continue to pose major environmental and health challenges,
hence the need to regulate these emissions.Temperature and emissions measurements were
carried for a gas burner so as to determine the level of emissions. The burner which was designed
and constructed for furnace firing is a forced draught, pre-mix type and has a power rating of
162.7kW. The experiment was carried out on a burner test-rig which was also designed and
constructed. Temperature readings for five points along the flame length in the combustion
chamber were taken using k-type thermocouples while an exhaust gas analyzer was employed
for the emissions measurements from the chimney. The gas flow rates for the burner were varied
for the test. The maximum temperature obtained from the closed test was 1273OC at full gas
valve opening. The emissions measurements obtained were compared with some established
standards and the levels of emissions were found to be close to the established standard. An
optimum operating condition at ½ gas valve opening was also established for the burner based on
the comparisons made.
Keywords: Burner, emissions, temperature, test-rig, gas analyzer.
Corresponding Author: Dr. O. Ighodalo
Introduction
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Burners are employed for a variety of purposes in the metal melting and other industries. A
burner is a device used for the combustion of fuel with an oxidizer which converts chemical
energy in the fuel to thermal energy (Baukal, 2004). An Emission is the release of gases (CO2,
NOx and CO) from the exhaust after fuel and air is mixed and is being combusted in the burner
(Stern, 1987). These Emissions, when released into the environment have negative
environmental impact and contribute to health challenges. CO emissions are generally an
indication of too little air, poor mixing or insufficient Furnace temperature. The gas is poisonous
and can lead to death when inhaled especially in enclosures. CO2 and H2O are normal products
of fuel combustion but the former is a greenhouse gas which is contributing to global warming.
NOx contributes to ground-level ozone which can be a severe problem to persons with
respiratory diseases, NOx formation is influenced by very high temperatures (The environmental
impact of vehicle emissions, 2007). Other concerns generated by these pollutant emissions
include accumulation of fine particles in the atmosphere, development of acid rain, the
acidification of aquatic systems, visibility limitations (Oland, 2002). The increasing problems
posed by pollutant emissions have led to the stipulation of emission standards in many advanced
countries. Emission standards are requirement that set specific limits to the amount of pollutants
that can be released into the environment. Many emissions standards focus on regulating
pollutants released by burners and other powdered vehicles, but they can also regulate emissions
from industry power plants and diesel generators (Wikipedia, 2012).
Burner testing provides an opportunity to gather and verify valuable information such as
operating parameters, pollutant emissions, heat flux profile etc (Baukal, 2004). Such information
is relevant in order to meet set regulatory standards, customer specifications, operational,
research and developmental efforts at optimizing burner performance to improve emissions and
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other parameter. The temperature and emissions measurements carried out for a gas burner are
here presented in this paper.
MATERIALS AND METHODS
Burner specification
The burner tested was designed and constructed for firing furnaces and is a forced draught, premix type with a power rating of 162.7kW. The burner is fitted with linked valves for
simultaneous adjustment of gas and air flow. The burner specification is given in Table 1 and
Fig. 1 shows the burner schematic diagram.
Table 1. Burner specifications
Length of the nozzle tip = 5cm
Length of the mixing tube = 5cm
Length of the throat = 19cm
Length of the divergent zone = 8cm
Length of the convergent zone = 4.3cm
Diameter of the convergent zone = 5cm
Diameter of the divergent zone = 4cm
Diameter of the nozzle tip = 3.6cm
Diameter of the throat = 3.4cm
Inner diameter of burner D1 = 28cm
Outterside diameter of burner Do = 36cm
Total length of the burner = 397cm
Knowing that the blower was designed to a speed N = 2500rpm
Pressure of air delivered P = 10N/m2
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mixing tube
Gas inlet
air inlet
butterfly valve
nozzle tip
convergent zone
throat
divergent zone
Fig.1. Schematic diagram of the burner
The burner was tested on a burner test-rig. The test-rig has a burner stand, combustion chamber
with five holes for thermocouple probes for temperature measurements aligned along the central
axis of the flame issuing from the burner. The holes were positioned at distances of 10cm, 20cm,
30cm, 40cm and 50cm from the combustion chamber inlet. The outlet of the combustion
chamber has an attached chimney which has a hole for exhaust gas temperature measurements.
The emission from the exhaust was measured using an SV-5Q Automobile Exhaust Gas
Analyzer. The five gases measured by the exhaust gas analyzers are: HC, CO, CO2, O2, and NO.
The exhaust gas analyzer specifications are given in Table 2. The burner test-rig arrangement is
shown in Fig. 2. The burner and burner test- rig were designed and constructed in the Faculty of
Engineering and Technology workshop of the Ambrose Alli University, Ekpoma-Nigeria. The
measurements were also carried out in the same workshop.
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Combustion
chamber
Thermocouple
Hole
Burner
Outlet exhaust
gas hole
.. . .. ... ..
.. . .
. . ..
. ..
. . .. ..
. .. .. .
... . ...
Air cooled
inculcator
Inlet
exhaust
gas hole
Stand
Blower
Seal
Blower pipe
Valve
Fig. 2. Burner test-rig arrangement used for the measurements
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Table 3. Exhaust gas analyzer specifications
1. Measurement range
HC :
0  10000 10-6 (ppm) vol
CO:
0  10.0 10-2 (%) vol
CO2:
0  20.0 10-2 (%) vol
O2:
0  25.0 10-2 (%) vol
NOx:
0  5000 10-6 (%) vol
Speed:
0  10000 rpm
2. Resolution:
CO:
0.01(%) vol
HC:
1 ppm vol
CO2:
0.01(%)vol
O2:
0.01(%) vol
NO:
1 ppm
Speed:
1 rpm
Emissions standards
Emission standards are available for the regulation of different combustion systems; Table 3
shows the U.K emission standard of 2002 for landfill gas flaring, European standard EN 676 of
1998 for automatic forced draught burners for gaseous fuels ( Hubner and Boos, 1998) and
typical emission for gas burners provided by TESTO AG (2011).
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Table 3. Emission standards
TESTO AG
CO
U.K.(2002)
EUROPEAN(1998)
Typical values mg/m3
mg/kWh
80-100ppm
100(93.1ppm)
100(80ppm)
NOx 50-100ppm
150(73.3ppm) 170(96.73ppm)
HC
<50ppm
10(9.23ppm)
-
CO2
8-10%
-
-
O2
2-6%
-
-
TEST PROCEDURE
The following procedure was followed during the testing of the burner on the burner test-rig.
1. The air supply hose from the blower and the gas supply hose from the gas cylinder were
connected to the burner and the burner mounted on a support with nozzle projecting into the
combustion chamber.
2. Thermocouple probes were inserted into the various probe holes on the combustion chamber
and the outlet of the chimney and their terminals connected to the digital display. The
exhaust gas analyzer probe was also inserted into the chimney.
3. The burner air valve and gas valve were set to full opening, the burner was ignited and
temperature and emission readings were taken and recorded after 5 minutes when conditions
had stabilized.
4. The procedure was repeated for gas and air valve openings at three quarter, half and one
quarter respectively.
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RESULTS AND DISCUSSION
The gas and air flow rates corresponding to the valve openings used in the tests are shown in
Table 4.
Table 4. Flow rate at various opening
VOLUMETRIC FLOW RATE M3/S
VALVE OPENING
GAS
AIR
Full
3.33 x 10-6
1.123 x 10-1
¾ full
2.498 x 10-6
8.43 x 10-2
Half
1.67 x 10-6
5.62 x 10-2
¼ full
8.33 x 10-7
2.81 x 10-2
The temperature readings obtained for the combustion chamber are shown in table 5
while that for exhaust temperatures is shown in Table 5. A graph of temperature versus distance
has been plotted as shown in Figure 3.
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Table 5. Temperature versus distance measurements for various valve openings
Distance cm
Temperature
Temperature
Temperature
Temperature
at full opening at ¾ opening at ½ opening at ¼ opening
oc
oc
oc
oc
10
1273
998
1094
592
20
1180
1161
830
630
30
1060
1102
620
828
40
804
946
435
790
50
790
804
278
615
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Table 6. Exhaust gas temperature measurements for various valve opening
Temperature
at Temperature at ¾ Temperature at ½ Temperature
full opening oc
opening oc
opening oc
at¼ opening oc
633
554
436
430
RESULTS OF EMISSION OF GASES
The readings for the emissions at various opening are as shown in Table 7. The plots for
emissions versus gas valve openings are shown in Figures 4 and 5.
Table 7. Exhaust gas emissions
Gases
Emission
at Emission at ¾ Emission at ½ Emission at ¼
full opening
opening
opening
opening
CO
10.75%
7.91%
5.92%
2.80%
CO2
8.50%
5.03%
5.74%
3.64%
HC
90.67ppm
75.6ppm
0ppm
0ppm
O2
2.85%
10.9%
11.93%
11.97%
NO
28ppm
15ppm
8ppm
7ppm
10
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DISCUSSION OF RESULTS
It was observed from Table 5 and graph of Fig. 3 that the maximum temperature
obtained was 1273oc at full valve opening at a distance of 10cm from the nozzle tip. The
maximum temperature was observed to increase with increase in gas valve opening. Also in all
cases the measured temperatures decreased as you move away from the burner nozzle tip.
Table 4 also shows that the exhaust gas temperatures increased as the gas valve opening was
increased.
Table 7 and Fig. 4 and Fig. 5 shows that, CO, CO2, and NO emissions increased with
increase in valve opening, while O2 showed a decrease. The presence of CO indicates an
incomplete combustion due to insufficient supply of air (rich mixture). NO emission is known to
increase at high combustion temperatures.
The level of HC is zero at ½ and ¼ valve openings;
hence no unburned fuel is escaping with the exhaust gases. The HC level is highest at full valve
opening. The level of emissions released therefore depends on the amount of fuel used and the
condition of combustion of the fuel.
A comparison of the emissions produced by the burner was made with the established
standards in Table 2. The emissions produced by the burner were observed to fall within the
range given by Testo AG (2011) for all operating conditions except for CO emission which gave
higher concentrations. A comparison with the U.K and European standards shows that the NOx
emission for the burner meets the set standards for all operating conditions. The HC emissions at
full valve and ¾ valve openings for the burner exceeds the U.K value, while the ½ and ¼ meets
the standard.
An optimum operating condition for the burner may therefore be specified as half valve
opening since the temperature attained is over 1000OC, the HC value is zero and all other
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emissions are also very low. The emission measurements have also shown that the burner is
environmentally friendly.
CONCLUSION
The tests conducted on the premixed, forced draught burner shows that high flame temperatures
were obtained depending on the rate of firing or gas valve opening. The level of emissions
released also depended on the amount of fuel used and the condition of combustion of the fuel.
The emissions released are low and within permissible standards especially for the ½ valve
opening operation which is therefore specified as the optimum operating condition for the
burner.
REFERENCES
Baukal, C.E. Jr. 2004. Industrial Burner Handbook. 790pp. CRC press, Florida, U.S.A.
Hubner, C., and Boos, R.1998. Emissions of oil and Gas appliances and requirements in
European standards .Retrieved April 2012 from.
http://www.verbraucherrat.at/download/gasoil.pdf
Oland, C.B. 2002. Guide to lower emission Boiler and Combustion equipment selection.
ORNL/TM-2002/19 report, Office of Industrial technologies, U.S.A. Retrieved
October 23,2012 from
www1.eere.energy.gov/industry/.../pdfs/guide_low_emission.pdf
Stern, A.M. 1987. Engineering Control of Pollution. 3rd Edition, 620pp. Pergamon press, Oxford.
Testo AG. 2011. Practical handbook Heating Measurement Technology, 3rd Edition.
Retrieved 10th April 2011from http:// www.raeco.com.
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The environmental impact of vehicle emissions. 2007. Retrieved April 19, 2012 from
http://www.engr.uconn.edu/~garrick/ce320/2007/
The U.K. emission standard for landfill gas flaring. 2002. Retrieved January 28, 2012 from
http://www.scribd.com/doc/78309076/30/The-UK-emission-standard
Wikipedia. 2012. Emission standard. Wikipedia the free encyclopedia. Retrieved October
23, 2012 from en.wikipedia.org/wiki/Emission_standard
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