วารสารวิชาการพระจอมเกล้าพระนครเหนือ ปีท่ี 12 ฉบับที่ 2 เม.ย. - มิ.ย. 2545
The Journal of KMITNB., Vol. 12, No. 2, Apr. - Jun. 2002
Correlation between Excess Oxygen Level and Secondary Combustion
Chamber Temperature on the Combustion Efficiency from the
Incineration of Real Infectious Waste in A Controlled-Air Incinerator
Woranuch Jangsawang* and Somrat Kerdsuwan**
Abstract
results of the experimental investigation shown that
The prime objective of this study is to study
the secondary air supplies influence on the
the correlation between the excess oxygen level and
combustion efficiency of gaseous exit from primary
secondary combustion chamber temperature.
chamber. The combustion with higher secondary air
According to the amount of secondary air supply
supply achieves lower CO concentration and higher
influence on both the temperature distribution in
O2 level. Moreover the results shown NO and SO2
secondary chamber and the oxygen level exiting
were not evident on the adjusting of secondary air
secondary chamber. Proper air supply is key to the
supply. The real infectious waste has the
achievement of high combustion efficiency and
disconsistency with respect to heating values and
reduction of pollutant emissions. Experiments, using
moisture contents. These effects result on the
a prototype 50 kg/hr controlled-air incinerator with
variety of combustion behavior and combustion
two combustion chamber, were performed to
efficiency. So, the optimum way to optimize the
investigate the influence of secondary air supply
secondary air supply in a controlled-air incinerator
rate on the combustion efficiency of real infectious
for burning the disconsistency waste should be
waste. The effective preheating primary chamber
add the oxygen regulator system to get the optimum
temperature and feeding waste is 700 °C with 5 kg
secondary air supply by using the information from
feeding waste. These results are used as the
this study.
starting point to optimize the operating conditions
for the real infectious waste. By adjusting the
Keywords : Secondary air supply rate, Infectious
secondary air supply rate and studied its effect on
waste, Optimization, Disconsistency,
the combustion efficiency which is the correlation
Incineration
between the excess oxygen level and secondary
chamber temperature. Specifically, under the constant
1. Rational
conditions (e.g., preheating primary and secondary
The formation and generation of the gaseous
chamber temperature, feeding waste and primary air
emissions from incineration are dependent on either
supply), the combustion gas temperatures and
the availability of certain materials in the waste feed
concentration of gaseous emissions were measured
or on the efficiency of the combustion process [1].
under various secondary air supplies. The significant
There are two strategies that are used to control
*
The Joint Graduate School of Energy & Environment, King Mongkut’s University of Technology Thonburi.
**
The Waste Incineration Research Center (WIRC), Department of Mechanical Engineering, Faculty of
Engineering, King Mongkut’s Institute of Technology North Bangok.
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วารสารวิชาการพระจอมเกล้าพระนครเหนือ ปีท่ี 12 ฉบับที่ 2 เม.ย. - มิ.ย. 2545
The Journal of KMITNB., Vol. 12, No. 2, Apr. - Jun. 2002
gaseous pollutants from incineration [2]. The first
al.,[8] .The results shown that the real infectious
strategy uses the air pollution control systems to
waste has the disconsistency in the components,
control the gaseous pollutant at downstream through
and to achieve high combustion efficiency, the
wet scrubbers, fabric filters or dry scrubbers. The
secondary air supply should be introduced by
second strategy uses the combustion control to
adjusting the secondary air supply along with the
control the gaseous pollutant at upstream through
waste being burnt. Moreover they recommended
the optimum operating condition. The controlling at
that the optimum way to optimize the secondary air
upstream is a challenge way to minimize the gaseous
supply should be controlled by using the automatic
pollutants from combustion process.
oxygen regulator to sensor the oxygen level in the
The present study is the continuing study
off-gases. The primary interest of this study is to
from the previous study. The previous study studied
study the effects of secondary air supply and
the influence of primary chamber temperature on
present the correlation between excess oxygen level
the generation of gaseous emissions [5-6]. The
and secondary chamber temperature on the
previous study used the strategy to control the
combustion efficiency as a basis information to
volume of gaseous pollutants exiting primary chamber
control the secondary combustion air supply.
by obtaining the experiments to determine the
2. Experimental Facilities
effective condition in primary chamber such as
preheating primary chamber and feeding waste. The
The incinerator that be used in this study is
present study aims to determine the effective
the 50 kg/hr infectious waste controlled-air incinerator
condition in secondary chamber to complete the
which installed at the Samphran Hospital,
combustion gases initiated from primary chamber.
Nakhornphatom Province. This incinerator is the
The parameters that control the combustion
prototype infectious waste incinerator that be
conditions in secondary chamber such as secondary
designed and constructed to solve the problem of
chamber temperature, oxygen level and degree of
black smoke and bad odor during the operations of
mixing of the combustion gas and air [7]. These
the traditional infectious waste incinerators [10].
three parameters were introduced by regulate the
The working principle of this prototype infectious
secondary air supply. The proper amount of
waste incinerator is intermittent controlled-air [11].
secondary air supply is required to sustain the
The process diagram of this plant is shown in
sufficient secondary chamber temperature, the proper
Figure 1. The incinerator composes of two
oxygen level and degree of good mixing of the
combustion chambers with automatic feeding machine
combustion gas and air.
and an air pollution control unit. The waste will be
With the aim of gaining more fundamental
put in the hopper and pushed in the primary
knowledge of effects of secondary air supply rate
chamber. The combustion environment in primary
on the combustion processes, the experiments were
chamber is controlled to obtain starved air condition.
conducted to provide data for determining the
The incomplete combustion products will flow to
proper amount of secondary air supply. The
secondary chamber and reburn again with the
experiments were conducted with the real infectious
additional of secondary air supplies. An air blower
waste by using the starting conditions that be
is installed on the top of secondary combustion
obtained from the experiments with simulated
chamber for supply air to primary and secondary
infectious waste [5]. The real infectious waste
chamber. The burners are installed within of
combustion has been studied by W. Jangsawang et
combustion chambers to ignite the waste and maintain
22
วารสารวิชาการพระจอมเกล้าพระนครเหนือ ปีท่ี 12 ฉบับที่ 2 เม.ย. - มิ.ย. 2545
The Journal of KMITNB., Vol. 12, No. 2, Apr. - Jun. 2002
Stack
Secondary Chamber
Feeding Machine
Air Pollution Control System
Primary Chamber
Combustion Air
Figure 1 Experimental Facilities
Table 1 Experimental Program
Parameter
Unit
Condition
Condition
Condition
Preheating Primary Chamber Temperature
Degree C
700
700
700
Feeding Waste
kg/batch
5
5
5
Preheating Secondary Chamber Temperature
Degree C
900
900
900
Primary Air Supply
% Open
0
0
0
Secondary Air Supply
% Open
10
20
30
the desired temperature. The total two K-type
be obtained from the experimental results of simulated
thermocouple temperature sensors are installed in
infectious waste. The effective condition is at the
primary and secondary chamber. They are installed
preheating primary chamber temperature 700 °C with
near the exit of the combustion chamber to provide
5 kg feeding waste. By doing the experiments under
a representative temperature reading away from the
these
flame zone. Gas samples were taken at secondary
secondary air supply rate, the optimum condition
combustion chamber exit. For each test, flue gas
for the real infectious waste can be obtained. The
samples including CO, O2, NO and SO2 were monitored
combustion efficiency of this study depends on the
and recorded continuously.
secondary air supply rate to sustain high sufficient
effective
conditions
and adjusting the
secondary chamber temperature and to clean the
3. Test Conditions and Procedures
combustion gases exiting primary chamber. The
This research aims to study the effect of
secondary air supply is set to be varied by open
secondary air supply rate on the combustion
the secondary air valve at 10, 20 and 30 percents
efficiency and determine the optimum secondary air
of total secondary air supply (as the experimental
supply rate of a 50kg/hr infectious waste controlled-
program in Table 1). The results from the previous
air incinerator. By using the starting condition that
study shown the primary chamber temperature
23
วารสารวิชาการพระจอมเกล้าพระนครเหนือ ปีท่ี 12 ฉบับที่ 2 เม.ย. - มิ.ย. 2545
The Journal of KMITNB., Vol. 12, No. 2, Apr. - Jun. 2002
940
Secon
dary
Cham
ber
Temp
eratur
e (C)
935
930
925
920
915
910
905
Waste Type 1
900
Waste Type 2
895
Waste Type 3
890
0
10
20
30
40
Secondary Air Supply (%)
Figure 2 The effect of secondary air supply rate on the temperature distribution in secondary chamber
strongly effect on the combustion efficiency [5-6].
simulated infectious waste. The proportional of wet
According to the condition in primary chamber is
cotton: syringe: rubber glove in the waste type1 is
set to be constant for all trials so the concentration
8:1:1 by weight. The waste type 2 and 3 compose
of off-gases from primary chamber effects from the
of higher combustible matters than the simulated
disconsistency in the components of waste input.
infectious waste. The proportional of wet cotton:
The disconsistency in the components result on
syringe: rubber glove in the waste type 2 is 7:1:2 by
the variety in heating values and moisture content
weight. The proportional of wet cotton: syringe:
in each of red bag. These causes affect on the
rubber glove in the waste type 3 is 6:1:3 by weight.
combustion behavior and combustion efficiency of
The experiments will conduct with the three types
the burning waste. In practical way to burn the
of waste under the various secondary air supply to
infectious waste normally used the charging by
study its effect and correlation between oxygen
random input. So, to study the effect of secondary
level and secondary chamber temperature on the
air supply rates on the combustion efficiency, it
combustion efficiency and presented respectively.
needs to know the components of what is burning
in the combustion chamber. The experiments will
4. Results and Discussions
conduct with the real infectious waste that be
4.1 Correlation between Oxygen Level and Secondary
known the compositions before charging in the
Chamber Temperature
chamber. According to a charge of waste that
The amount of secondary air supply influence
composes of high amount of combustible matters
on both the temperature distribution in secondary
such as rubber gloves produce high rate of gasify
chamber and the excess oxygen level in off-gases.
in the chamber, resulting on the emission of black
The secondary chamber temperature depending upon
smoke from incinerator [8]. So, the waste that be
the initiated combustion gases from primary chamber
used in this study will consider on the basis of the
and the amount of secondary air supply. The effect
amount of combustible matters in that waste. The
of secondary air supply rate on the temperature
waste will be categorized in to three types in which
distribution in secondary chamber temperature
compose of; low, medium and high combustible
shown in Figure 2. From the experimental results in
matter. The waste type 1 has low combustible
burning the three types of infectious waste shown
matter that has the compositions similar as the
the amount of the secondary air supply influence
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วารสารวิชาการพระจอมเกล้าพระนครเหนือ ปีท่ี 12 ฉบับที่ 2 เม.ย. - มิ.ย. 2545
The Journal of KMITNB., Vol. 12, No. 2, Apr. - Jun. 2002
12
11
O2 Level (%)
10
9
W a s te Type 1
8
W a s te Type 2
7
W a s te Type 3
6
5
0
10
20
30
40
Secondary Air supply (%)
Figure 3 The effect of secondary air supply rate on the oxygen level.
on the temperature distribution in secondary chamber.
creates significant mixing. The large volumes of off
The secondary chamber temperature decreases as
gases in a fixed size of secondary chamber require
increases the secondary air supply. The possible
high secondary air supply for good mixing.
reason is as increase secondary air supply requires
Consequently, increase secondary air supplies
more heat to combust the combustion air. And the
decrease O2 level.
results shown that for burning the wastes that
The secondary air supply influence on both
compose of high combustible matters, the average
the secondary chamber temperature and the oxygen
secondary chamber temperature was higher than the
level as the results shown in Figure 2 and 3.
another trials. That is because the combustion of the
Consequently, the oxygen level and secondary
waste that compose of higher combustible matter
chamber temperature are related. The correlation
produce the combustion gas at higher temperature
between oxygen level and secondary chamber
from the primary chamber exit.
temperature was shown in Figure 4. The result
The level of excess oxygen in the off-gases
shown the oxygen level exiting secondary chamber
plays an important role in combustion control and
related on secondary chamber temperature. The
variations in the gas temperature. The effect of
oxygen level increase as temperature decrease. The
secondary air supply rate on the oxygen level
oxygen level as a function of secondary chamber in
exiting secondary chamber will be presented as in
equation O2 = -56.58 (lnT2)+394.7
Figure 3. The result shown the secondary air supply
rate affects on O2 level. The O2 level exiting the
4.2 Correlation between CO Concentration and O2
secondary chamber for burning the waste that
Level
composes of low combustible matter is higher than
The concentration of CO in the exhaust gas
burning the higher one. That is because the rate of
stream is an indicator of the combustion efficiency.
devolatilization is not high for burning the waste
The formation of CO is dictated by a number of
that composes of low combustible matters, so it
factors such as the oxygen level in secondary
requires low excess O2 for complete combustion.
chamber, the degree of mixing of the combustion
But for burning the waste type 3, the trend of O2
gas and air, the secondary chamber temperature, and
level is slowly decrease. The reasonable reason is
the volume of combustion gas direct to secondary
increasing the amount of secondary air supply
chamber. The volume of combustion gas exit from
25
วารสารวิชาการพระจอมเกล้าพระนครเหนือ ปีท่ี 12 ฉบับที่ 2 เม.ย. - มิ.ย. 2545
The Journal of KMITNB., Vol. 12, No. 2, Apr. - Jun. 2002
12
10
Oxygen Level (%)
8
Oxyge
n
Level
(%)
6
y = -56.579Ln(x) + 394.7
4
2
0
89
90
90
91
91
92
92
93
93
Secondary Chamber Temperature (C)
Figure 4 Correlation between O2 level and T2
600
500
CO Concentration (ppm)
400
300
Waste Type1
200
Waste Type 2
100
Waste Type 3
0
0
10
20
30
40
Secondary Air Supply (%)
Figure 5 The effect of secondary air supply rate on CO concentration
primary chamber is primary effect that resulting
3). As increase secondary air supply, decrease CO
from the waste input. The generation of volatile
concentration. That is because increasing more
combustion gases depends on the characteristic of
secondary air supply results on the combustion
waste input. If the waste has high combustible
gases combust more completely. But the results on
matter, it will burn rapidly and produce a large
the combustion of the waste type1 shown that the
volume of flue gas entering the secondary chamber.
amount of secondary air supply weakly effect on
This rapid rise in off-gases volume in a fixed size
the reduction in CO. That is because the waste
secondary
type1 has low combustible matters, the waste will
chamber
can
lead
to
incomplete
combustion.
burn slowly and produce a little volume of off-gases
Figure 5 shown the effect of the secondary air
exit the primary chamber. So it requires small amount
supply on CO concentration. The results shown the
of secondary air supply to complete the combustion
secondary air supply strongly effect on the CO
gases from this waste type.
concentration for burning the waste that compose
The CO concentration and the oxygen level
of high combustible matter (as in waste type 2 and
exiting secondary chamber are related. The
26
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The Journal of KMITNB., Vol. 12, No. 2, Apr. - Jun. 2002
12
Oxygen
O x y g e n Level
L e v e l (%)
(%
10
8
y = -0.5585Ln(x) + 11.509
6
4
2
0
0
100
200
300
CO
400
500
600
C o n c e n t ra t i o n (ppm)
Figure 6 Correlation between O2 level and CO concentration
112
110
C o n c e n t r ation (ppm)
(ppm)
NoN OConcentration
108
106
104
102
Waste Type 1
100
Waste Type 2
98
Waste Type 3
96
94
0
10
20
30
40
Secondary Air Supply (%)
Figure 7 The effect of secondary air supply rate on NO emission
correlation between O2 level and CO concentration
NO)[12]. The relative importance of these three
was shown in Figure 6. The oxygen level increase as
sources of nitrogen oxide depends on the operating
CO concentration decrease. The correlation between
conditions and the type of the fuel. Thermal NO is
O2 & CO as in equation O2 = -0.558ln (CO)+11.51
very temperature-dependent whereas the conversion
of fuel nitrogen to NO is not strongly temperature-
4.3 Correlation between O2 Level and NO
dependent [13]. Therefore, the NOx derived from
Concentration
nitrogen in the air can be minimized by lowering the
Nitrogen oxides are one of the major air
flame temperature and decreasing the oxygen content
pollutants emitted by stationary combustion sources.
in combustion systems. The factors which affect the
Nitrogen oxides produced during incineration are
emissions of nitrogen oxides during combustion may
oxidation of molecular nitrogen in the post flame
be divided into combustion conditions and nitrogen
zone (thermal NO), formation of NO in the flame
content in the waste. The combustion condition
zone (prompt NO), and oxidation of nitrogen-
that be studied in this research is secondary air
containing compounds in the fuel (fuel-bound
supply rate.
27
วารสารวิชาการพระจอมเกล้าพระนครเหนือ ปีท่ี 12 ฉบับที่ 2 เม.ย. - มิ.ย. 2545
The Journal of KMITNB., Vol. 12, No. 2, Apr. - Jun. 2002
1 2
O xyg e n L e ve l (%
Oxygen Level (%)
1 0
8
y = 3.6127Ln(x) - 7.8371
6
4
2
0
9 6
9 8
100
102
104
106
108
110
112
N O C oncentration (ppm)
Figure 8 Correlation between O2 level and NO concentration
80
70
SO2 Concentratio
SO2 Concentrationtration
60
50
40
W as te Type1
30
Waste Type 2
20
Waste Type 3
10
0
0
10
20
30
40
S e c o n d a r y Air Supply (%)
Figure 9 The effect of secondary air supply on SO2 emissions
The effect of secondary air supply rate on NO
4.4 Correlation between O2 Level and SO2
production was shown in Figure 7. The results shown
Concentration
the influence of the amount of secondary air supply
Sulfur, which is chemically bound within the
on NO production is not evident. For burning all the
materials making up hospital waste, is oxidizes
three waste types studied shown that increasing
during the combustion process to form SO2 [7].
the amount of secondary air results on increasing
Sulfur dioxide produce from the combustion process
NO production slowly. The NO production from
comes from the sulfur content in the fuel. The
burning the same waste type is almost equal.
combustion condition has little or no effect on
The correlation between O2 level and NO
emission of SO2 [7,11].
concentration shown in Figure 8. The result shown
The effect of secondary air supply rate on SO2
the oxygen level and NO concentration exiting
production was shown in Figure 9. The results very
secondary chamber is not significant change. The
clearly shown that the SO2 production from burning
correlation as in equation O2 = 3.163ln (NO)-7.84
the same waste type are almost the same. This
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วารสารวิชาการพระจอมเกล้าพระนครเหนือ ปีท่ี 12 ฉบับที่ 2 เม.ย. - มิ.ย. 2545
The Journal of KMITNB., Vol. 12, No. 2, Apr. - Jun. 2002
12
Oxygen Level (%
10
8
y = -1.0384Ln(x) + 12.002
6
4
2
0
0
10
20
30
40
50
60
70
80
SO2 Concentration (ppm)
Figure 10 Correlation between O2 level and SO2 concentration
result implies that the SO2 production depending
is not evident on the secondary air supply rate.
upon the sulfur contents in the waste being burnt.
From the results shown in the burning the
The increasing in secondary air supply is not
waste that has the disconsistency in the composition
evident on SO2 production for all trials. And the
as the real infectious waste, the secondary air
wastes that compose of higher amount of rubber
supply should be varied to optimize the combustion
gloves produce more SO2 than the lower one.
processes. In case of burning the waste that
The correlation between O2 level and SO2
compose of high amounts of combustible matters,
concentration was shown in Figure 10. The
the high burning rate will occur and produce high
production of SO2 is not significant relate on the
volume of combustion gases, more secondary air
oxygen level exiting secondary chamber.
supply is required. For the waste that compose a little
of combustible matters, increase more combustible
matters resulting on temperature drop and more fuel
5. Conclusions
The test results indicate that secondary air
consumption. So to optimize the operating condition
supply rate is related to the temperature distribution
by adjusting the secondary air supply should be done
and the concentration of gaseous emissions. As
by using the automatically oxygen regulator to
increase the secondary air supply, decrease the
sensor the amount of oxygen in the secondary
primary and secondary chamber temperature. The
chamber by using information from this study.
CO concentration and excess oxygen level are
6. Acknowledgement
strongly effect on secondary air supply rate. The
The
CO concentrations decrease as increase secondary
authors
would like to express their
air supply. The excess oxygen level directly related
grateful to the Joint Graduate School of Energy and
on secondary air supply rate. As increase secondary
Environment for
air supply rate, increase excess oxygen level in the
Waste Incineration Research Center, Department of
off-gases exiting the secondary chamber. Moreover,
Mechanical Engineering, Faculty of Engineering, King
the experiments found the good mixing in combustion
Mongkut’s Institute of Technology North Bangkok
gas and air achieved high combustion efficiency.
for facilities support so that this task can be
And also the result shown, NO and SO2 production
successfully completed.
29
his funding support and the
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The Journal of KMITNB., Vol. 12, No. 2, Apr. - Jun. 2002
8.
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