Energy and Power Engineering, 2010, 2, 175-181
doi:10.4236/epe.2010.23026 Published Online August 2010 (http://www.SciRP.org/journal/epe)
A Burning Experiment Study of an Integral Medical
Waste Incinerator
Rong Xie1, Jidong Lu1, Jie Li1, Jiaqiang Yin2
1State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, Wuhan, China
2Huangshi Zhong You Environmental Protection Corporation, Huangshi, China
Received May 6, 2010; revised June 12, 2010; accepted July 15, 2010
Abstract
Mass burning of the medical waste is becoming attractive in China because Chinese government has banned
landfilling of medical waste. Many advantages can be found in this method, such as reduction in waste vol-
ume, destruction of pathogens and transformation of waste into the form of ash. However, the medical waste
with high moisture in China is not suitable to be treated in the present direct mass burning incinerators. In
this paper, a novel integral incinerator is developed with combining a feeder, a rotary grate, a primary com-
bustion chamber (PCC) and a “coaxial” secondary combustion chamber (SCC) into a unique unit. Its capa-
bility is 10 ton/day. As the air excess level in the PCC was only 40% stoichiometric ratio, the PCC acted as a
gasifier. The 1.0 excess air ratios in the SCC preserved the purpose of full combustion of flue gas. Tempera-
ture and pollutants concentration in the SCC were measured to understand the combustion behavior of vola-
tile organics. Emission concentrations of pollutants before stack were also tested and compared with the
China National Incineration Emission Standard.
Keywords: Medical Waste, Incineration, Mass Burning, Emission Pollutants
1. Introduction
With high-rate economic growth and urbanization in
China, the amount of medical waste increased continu-
ously at the rate of 8.98% since 1980s [1,2]. The citizens
and governor have to face the inevitable challenge of the
medical waste treatment. As the hazardous waste landfill
standard took effect in 2001, the sanitary landfill of me-
dical waste was banned in China [3]. Not only because
the medical waste contained a great quantity of bacteria
and viruses and threaten the surroundings of the landfill,
but also the available area for landfill has become scarce.
Incineration of medical waste and disposal of the resul-
tant ash by landfill is now accepted as an environmentally
friendly disposal method. Its advantages are the destruc-
tion of pathogens, reduction in the volume and transform
of waste in the form of ash [4].
The mass burning medical waste incinerators in-
cludes three basic types: 1) the modular incinerator, 2)
the conventional grate-fired incinerator, 3) the rotary
kiln incinerator.
Among them, modular medical waste incinerators are
the largest number among mass burn installations [5].
The modular incinerator is a compact furnace in the form
of a cube with multiple internal baffles. Each modular
chamber normally has one or two burners to maintain its
required operating temperature. The excess air level is
well above stoichiometric, typically 150%-200% excess
air. This kind of incinerator is not easily adaptable for
continuous operation [6].
The grate-fired medical waste incinerator can be di-
vided into: 1) fixed grate incinerator, 2) moving grate
incinerator. Moving grate incinerators are mainly in use
today, as medical waste can be stirred and ash removal
can be automated. The moving grate incinerator in-
cludes one chamber, where medical wastes go through
heating, drying, pyrolysis, ignition and burning on the
grate. The total injected air is about 120%-160% of the
stoichiometric air requirement. However, experiences
and trials in South Africa show that the moving grate-
fired incinerators are unsuitable to treat medical for its
high emission loads [7].
The rotary kiln system is widely used to treat hazard-
ous waste. The raw medical waste can be fed directly to
the kiln. All reactions such as organic thermal decompo-
sition and char oxidation reactions occur within the ro-
tary reactor. The rotary kiln can produce intensive turbu-
lence and mix air and solid phases completely [8]. But

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176
the high combustion efficiency is still depended on high
auxiliary fuel consumption. Gas sealing of kiln and fixed
parts is also a difficult problem.
The three types of incinerators mentioned above pre-
sented good performance in the mass burning of solid
waste with high heat value (more than 2000 kcal/kg).
However, in China little experience is available of these
incinerators to treat medical waste of high moisture.
In this paper, an integral medical waste incinerator is
developed from the following consideration: 1) Achieve
flue gas emission limits. 2) Reduce heat loss of the incin-
erator. 3) Make full use of medical waste’s heat value. The
integral medical waste incinerator combines a feeder, a
rotary grate, a primary chamber and a “coaxial” secondary
combustion chamber into a unique unit. The incineration
feeding system continuously feeds medical waste into the
incinerator. Heating, drying, pyrolysis of medical waste
and char oxidation occur in the primary chamber, while
gas phase oxidation reactions occur in the secondary
chamber. As there is no similar structure of incinerator to
our knowledge, the objective of this study are to introduce
its novelty, investigate its performance and measure the
combustion pollutants.
2. Incinerator System Description
The diagrammatic sketch of incineration system and waste
treatment process is shown in Figure 1. The basic com-
ponents in the incineration system are the waste feed
system, the combustion system and the air quality control
system. The ash disposal and heat recovery are taken as a
supplemental process. The details are described as fol-
lowing.
2.1. Feeding System
The special bin storing medical waste is weighed and
loaded by the automatic crane, which charges waste into
a 2-meter high chute (C in Figure 2). Two steel clap-
boards are installed in the chute to maintain good seal (B
and E in Figure 2). So the chute can not only prevent air
flowing into the primary chamber, but also prevent fire
from the combustion chamber entering the feeding sys-
tem. A reciprocating propeller (D in Figure 2) installed
in the chute feeds the waste into the primary combustion
chamber.
2.2. Primary Combustion Chamber
The primary combustion chamber (PCC) consists of a
1.2-meter diameter cylinder and a rotary grate. The grate
is installed at the bottom of the PCC. The rotary grate is
made up of three discs fixed on the central bearing body
and one cone fixed on the top disc. Medical waste, pyro-
lysates and bottom ashes are tumbled slowly with the
rotation of the grate. Many small holes (5-cm diameter)
Figure 1. Schematic diagram of incineration system.

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177
A. charge hopper
B. first access slide board
C. vertical bin
D. reciprocating propeller
E. secondary access
slide board
F. combustion chamber
Figure 2. Schematic diagram of the feeding system.
distribute symmetrically on each disc. So the holes with
the space between discs can distribute air homogene-
ously.
In the PCC, The raw medical waste is distributed unif-
ormly onto the waste bed by the feeding system and
forms about 1.5 meters waste bed on the surface of the
rotary grate. Continuous feeding and slagging make the
waste bed maintained at a fixed height. The raw medical
waste undergoes heating and drying process on the the
waste bed as soon as the raw medical waste enters. This
process removes the moisture in the raw medical waste.
When the temperature of medical waste rises up to a
level, the pyrolysis and volatilization of the solid medical
waste start. After pyrolysis and volatilization process, the
remained solid char is further oxidized and forms hot
slag.
The air for the solid char combustion is drawn from
the bottom entrance of the PCC at the room temperature
by a forced draft fan. The “cold” air runs through the hot
slag layer on the surface of the rotary grate. So the air is
heated up while the hot slag is cooled down. The cooled
slag forms a protective layer on the surface of the rotary
grate, which isolates the grate from the high temperature
combustion region. The grate is free from heat transfigu-
ration during the combustion process.
The heated air is then transferred into the combustion
area-solid carbon oxidation layer. The char can be oxi-
dized completely under full excess air and produce lots
of hot flue gases. These hot flue gases pass through the
pyrolysis layer and upwards into the heating and drying
layer. The heat in the hot gases can supply enough en-
ergy for pyrolysis and drying process of the raw medical
waste.
2.3. Secondary Combustion Chamber
The secondary combustion chamber (SCC) has a distinct
cylinder configuration. We call it “coaxial” structure, as
it surrounds the PCC with the same vertical axis. This
design significantly decreases the PCC and the SCC
outer jacket’s contact area with the environment. No
pipeline is needed for connection between the PCC and
the SCC, so the heat loss in pipeline occurring in tradi-
tional multi-chamber incinerator is eliminated. The baf-
fles are installed in the SCC to guide the combustion gases
through 180˚ turn in vertical directions. This “U” shape
combustion channels can significant increase gas turbu-
lence in the high temperature region. In case of the same
volume of the combustion chamber, the length of flue gas
channel is increased relatively, so the residence time of
flue gas at temperatures exceeding 800℃ is ensured for at
least 2 seconds. Secondary air is preheated by a heat ex-
changer and supplied at the top of the secondary combus-
tion chamber. The secondary air injector is fixed in tan-
gential direction to achieve well mixed effect.
Manipulation of combustion in the SCC includes ‘3Ts’
combustion control (temperature, time and turbulence) in
order to maximize system efficiency and minimize envi-
ronmental adverse effect of the incineration. If the com-
bustion temperature is below 800℃ the ignition equip-
ment will start automatically and auxiliary fuel is in-
jected to maintain the temperature. In fact the fuel injec-
tion is necessary when the mass burning starts. When
combustion is stable, the heat release from oxidation
reactions can keep temperature exceeding 800℃.
2.4. Flue Gas Purification System
After incineration, the flue gases pass through the pipe
and enters the into the flue gas purification system. In
order to prevent the erosion by acidic flue gas and flush-
ing by the entrained particles, a thin layer of silicon car-
bide is coated on the surfaced of the pipe. The flue gas is
then induced into semidry scrubbing system. Lime slurry
is injected by a spry nozzle in the scrubber. It has high
and stable removal efficiency for HCl and SOX. No waste-
water treatment equipment is required. After that, flue
gas goes through the demister tower. Activated carbon is
injected into the flue gas to absorb the dioxins and furans
formed in the post combustion process before it enters
the baghouse. Finally the purified flue gases are induced
into the stack by diversion fun.
3. Medical Waste Incineration Experiments
and Results
3.1. Waste Characteristics
The typical medical waste was sampled from the same
batch by random sampling method. First typical medical
waste sample was sterilization by high temperature steam.
Secondly, the large pieces of hard objects removed from

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the sample. Finally sample was grinded for proximate
analysis and then dried for ultimate and energy analysis.
The ultimate analysis of typical medical waste is show in
Table 1. The ultimate analysis of a waste component
typically involves the determination of the percent of
carbon (C), hydrogen (H), oxygen (O), nitrogen (N) and
sulfur(S). Table 1 gives the average chemical composi-
tion of combustible component of medical waste. The
energy content of the medical waste is determined by a
laboratory bomb calorimeter. Typical energy content of
medical waste is also estimated and showed in Table 1.
3.2. Air Supply
The air supply in the PCC is only about 40% of the stoi-
chiometric requirement, equal to 1/3-1/4 of the recom-
mended air levels (140-200%) for traditional mass burn
system [9]. In the lower part of the PCC, this air is en-
sured to burn out the solid char. However, in the upper
zone, the PCC is acting as a gasifier. Pyrolysis is the
dominant mechanism in this zone for the production of
volatiles from medical waste in the absence of oxygen.
The produced volatiles have been identified as CO, CO2,
H2O, CH4 and other light hydrocarbons.
The air supply in the SCC is 100% of the stoichiomet-
ric requirement for complete waste combustion, so the
volatiles from PCC can be decomposed completely.
3.3. Incineration Temperature
Armored thermocouples were installed in PCC and SCC
outlet as measurement equipment of temperature. The
detection accuracy of the thermocouples is 1℃. Varia-
tion of temperature with time in the PCC and SCC is
shown in Figure 3. The temperature of PCC is around
640℃. However the value varied significantly with time.
Because materials of medical waste range from food
products to pathological waste, there is large variation in
the properties of medical wastes. These variations have a
dramatic impact on the performance of medical waste
incinerator.
Although the combustion and pyrolysis mechanisms in
PCC are complex, it is demonstrated that the pyrolysis
production of volatiles and char can be regulated by tem-
perature [10]. The decomposition of the organic matter is
normally total at these high temperatures. When the py-
rolysis temperature is much lower, the production of CO
is much decreased. The low temperature may slow down
the pyrolysis process and lead to delay the time of raw
waste ignition. When the pyrolysis temperature is much
higher, the self-combustion process became unstable.
Because high temperature present in the PCC may lead
to excessive burning of the pyrolysate. It will decrease
the quantity of combustive pyrolysate in the SCC. Con-
sequently the auxiliary fuel has to be consumed to main-
tain the temperature in the SCC. After several testing
before operation, the optimal running temperature for the
PCC was set at 660℃. It can be found in Figure 3 that
the actual operating temperature is close to the setting
temperature.
The combustion temperature in the SCC is higher than
850℃, and the temperature varied slightly with time ex-
cept the heavy disturbing effect from the PCC. This in-
dicates combustion process in SCC is more stable than
the process in PCC. The novel coaxial chamber design
decreases 40% outer contact area of the SCC with the
environment. Heat losses are much reduced. It is easy for
SCC to achieve high temperature and remain stable op-
eration.
3.4. Pollutants and Oxygen in the SCC
In actual operation, whether volatiles are combusted com-
pletely in the SCC is an important performance indicator
of the incinerator. Gas pollutants at different positions of
the SCC were tested by portable infrared flue gas ana-
lyzer. Several verification tests of the gas analyzer were
carried out before the experiment to avoid measurement
errors. As illustrated in Figure 4, five sample points (la-
beled as 1-5) were set symmetrically along the axial di-
rection. Point “1” is near the PCC exit and point “5” is
near the SCC outlet. In the stable operation conditions,
each sample point is tested for three times.
Table 1. Medical waste component.
Proximate analysis (wt.%)
Mar Vd Ad
LHV
(MJ/kg)
64.1 75.3 23.4 25.63
Ultimate analysis (wt.%)
C H N S O
47.54 7.99 2.02 0.5 18.54
Figure 3. Variation of temperature in the PCC and the
SCC.

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179
Concentration profiles of pollutants (CO, CO2, NOX, and
SO2) and oxygen are shown in Figure 5 to Figure 9. It
can be seen from Figure 5 that the CO concentration
decreases intensely from sample point “1” to “5”. This
indicates that CO formed in the PCC is mostly destroyed
in the SCC. The destruction efficiency of CO is round
99.95%. It can be found from Figure 5 that CO2 is
mainly formed in the SCC. The comparison between
Figure 5 and Figure 6 can further explain that CO
Inlet
1
2
3
4
5
Outlet
Figure 4. Sampling points distribution in the SCC.
Figure 5. CO concentration.
Figure 6. CO2 concentration.
mostly translated into CO2 in the SCC. As is illustrated
in Figure 7, concentration of oxygen is gradually decre-
ased with the oxidation reaction going-on. Generally
speaking, the concentration of oxygen in the SCC outlet
is higher than 10%, which meets the demand of Medical
Waste Incineration Standard [11]. From Figure 8 and
Figure 9, we can find that concentration of NOX and SO2
are lower than 30 ppm and 10 ppm, respectively. These
may be due to medical waste containing little N and S
elements. However NOX and SO2 mainly formed in the
pyrolysis process decrease little in the SCC. Conclusions
can be made that combustion in the SCC has no effect on
production of NOX and SO2.
3.5. Pollutant Concentrations in the Stack
Concentrations of NOX, SOX, HCl and particles in the
Figure 7. O2 concentration.
Figure 8. SO2 concentration.

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180
Figure 9. NOX concentration.
exhaust were measured respectively according to the Ch-
ina National Standards [11]. Concentration of CO, CO2,
O2 were also measured by a Combustion Efficiency Mea-
surement Instrument.
The maximum air pollutant concentrations in the inlet
of the stack are summarized in Table 2. National Incin-
eration Emission Standard for each component is also
listed in the Table 2. As shown in Table 2, the measured
pollutants belong generally to the concentration range set
by China National Standards. As Table 2 shows, the
experimental value of particulates in the stack is much
lower than the limit. In addition to the well operated bag-
filter, the low air level in the PCC is an important reason.
Compared with the traditional mass burning system, star-
ved-air combustion in the PCC produces less solid parti-
cles in the gas stream. Researchers have demonstrated
that the dioxin formation from carbon particulates is one
of the potential mechanisms for PCDD/F formation in
the post combustion zone [12,13]. The reduced fly ash
entrainment in flue gas is helpful to control the dioxins.
The concentration of acid gases such as HCl and SO2 are
also lower than the limit. This demonstrates that gas
scrubber is in good working condition.
4. Conclusions
The integral medical waste incinerator combines a feeder,
a rotary grate, a primary chamber and a “coaxial” secon-
dary combustion chamber into a unique unit. The tempe-
rature of the PCC varied significantly with time because
of the intermittent feed and the heterogeneous character-
istics of the raw medical waste, however, due to the co-
axial SCC design, the combustion temperature in the
SCC varied slightly with time. The temperature has great
effect during the formation of pyrolysis gas such as CO.
The low air level (40%) in the PCC well controlled the
Table 2. Emission concentration of pollutants in the flue gas.
Pollutants Experimental values Standard
CO, mg/m3 34.8 80
NOX, mg/m3 15.1 400
SO2, mg/m3 24.2 260
HCl, mg/m3 48.7 75
O2, mg/m3 16.3 6-11
Particulates, mg/m3 32 80
Blackness 0.8 1
chamber’s temperature. The actual operating temperature
in the PCC (640℃) is close to the setting temperature
(660℃). Consequently, char combustion is also kept sta-
ble and complete. Concentrations of pollutants in the
SCC were measured on different sample points. In these
data, CO level represented the best available estimate of
environmentally satisfactory operation for the incinerat-
ion process. The destruction efficiency of total CO in the
SCC is round 99.95%. Emission concentrations of pollu-
tants in the stack were also measured and met the de-
mand of the China National Incineration Emission Stan-
dard.
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