Influences of Injection Positions of Pyrolytic Wastewater on No
x
Emission of Semi-coke
Xueting Yang
1,2
, Guoliang Song
1,2,3,*
, Yuan Xiao
1,2
, Zengcai Ji
1,2
and Chao Wang
1,4
1
Institute of Engineering Thermalphysics, Chinese Academy of Sciences, Beijing 100190, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
3
Dalian National Laboratory for Clean Energy, Dalian 116023, China
4
University of Science & Technology of China, Hefei 230026, China
*Corresponding author
Keywords:
Pyrolytic Wastewater, Semi-Coke, No
x
Emission, CFB.
Abstract:
The amount of pyrolytic wastewater produced by coking plant was huge and it was difficult to deal with,
there were many defects in conventional pyrolytic wastewater treatment methods. Incineration method
could remove most of the organics and harmful substances in pyrolytic wastewater, and generate CO
2
and
H
2
O, it truly realized zero discharge of pyrolytic wastewater, but its effects on the combustion and pollutant
emissions of semi-coke was not clear, so experiments were carried out in a 0.1 MW circulating fluidized
bed test platform to investigate the influences of injection positions of pyrolytic wastewater on the
combustion temperature and NO
x
emission of semi-coke. The results showed that the NO
x
emission was cut
down by 13.81 %and 22.58 % when pyrolytic wastewater was injected into furnace and tail flue,
respectively. It indicated that pyrolytic wastewater realized zero discharge when burning with semi-coke,
the NO
x
emission of semi-coke was cut down as well, and it was more appropriate for pyrolytic wastewater
to reduce NO
x
emission in tail flue compared to the furnace.
1 INTRODUCTION
A large amount of pyrolytic wastewater is produced
every year in the coking plants, the composition of
pyrolytic wastewater is complex, containing
aromatic and long-chain hydrocarbon organic
matters, benzene, volatile phenol, ammonia nitrogen
and oil (Ji, 2016, Wang, 2017), so it has
characteristics such as high chemical oxygen
demand (COD), high chromaticity and poor
biodegradability, it is difficult to degrade and
recycle (Li, 2017, Wang 2014). The conventional
methods are to degrade or flocculate pyrolytic
wastewater by microorganism, chemical reagent and
physical methods. The processes of conventional
methods are complex, which are greatly affected by
temperature and the composition of pyrolytic
wastewater, so that the treatment capacity of
conventional methods is limited. An easy, clean and
efficient treatment method desperately needs to be
found out. Incineration method is not affected by the
temperature and quality of wastewater, and can
destroy the molecular structure of harmful
substances through controllable high-temperature
chemical reaction. It can remove most of the
organics and harmful substances in pyrolytic
wastewater and generate CO
2
and H
2
O, truly
realizing zero discharge of pyrolytic wastewater
(Xiao, 2012).
Literatures about the incineration of coal
pyrolytic wastewater are few, Li XF et al. (Li, 2018)
found through simulation that the temperature of the
furnace reduced when the pyrolytic wastewater
enters the circulating fluidized bed furnace for
incineration, and the power generation was cut down
by about 1.5 % when the coal supply of the system
kept stable.
Alar Konist et al. (Konist, 2018) incinerated
pyrolytic wastewater from shale oil plants in a 60
kW
th
circulating fluidized bed combustor, the NO
x
emission was increased by up to 1.8 times when the
flow rate of pyrolytic wastewater was 4.6 kg/h. Alar
Konist et al.( Konist, 2019) also carried out
experiments in an oil shale fired 250 MW
th
circulating fluidized bed boiler, and found that the
incineration of pyrolytic wastewater increased the
48
Yang, X., Song, G., Xiao, Y., Ji, Z. and Wang, C.
Influences of Injection Positions of Pyrolytic Wastewater on Nox Emission of Semi-coke.
DOI: 10.5220/0011179400003443
In Proceedings of the 4th International Conference on Biomedical Engineering and Bioinformatics (ICBEB 2022), pages 48-52
ISBN: 978-989-758-595-1
Copyright
c
2022 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
NO
x
emission by 27 % and increased oil shale
consumption by up to 6 % when the flow rate of
pyrolytic wastewater was 13 t/h.
To deal with pyrolytic wastewater in CFB
boilers, the appropriate position for incineration and
its influences on the operation and pollutant
emission of CFB boilers should be investigated. In
the experiments of literature (Konist, 2018), the
pyrolytic wastewater was incinerated in the lower
part of furnace which near the feed position of oil
shale, the pyrolytic wastewater was sent to the
furnace together with oil shale in literature (Konist,
2019). To figure out the influences of injection
positions of coal pyrolytic wastewater on NO
x
emissions of semi-coke, some experiments were
carried out in this paper, the injection positions
included furnace and tail flue, and it was vital for the
clean and efficient treatment of coal pyrolytic
wastewater.
2 EXPERIMENTAL SECTION
2.1 Fuel Characteristics
The proximate and ultimate analysis of semi-coke
used during experiments were shown in Table 1,
subscript “ar” represents the as received basis. The
particle diameter of semi-coke was 0-1 mm. The
pyrolytic wastewater used in experiments came from
a coking plant in Shanxi Province, China, and its
components were shown in Table 2.
Table 1: Proximate and ultimate analysis of semi-coke.
Proximate Analysis (wt%) Ultimate Analysis (wt%, ar)
Lower calorific value
M
ar
A
ar
V
ar
FC
ar
C
ar
H
ar
O
ar
N
ar
S
ar
Q
ar,net
(MJ/kg)
4.78 7.06 6.2 81.96 82.54 0.84 3.59 0.82 0.37 28.62
Table 2: Components of pyrolytic wastewater (mg/L).
PH Volatile phenol
Ammonia
nitrogen
COD Oils Salts sulfide
9.02 2.84×10
3
37.2 3.08×10
4
203 6.99×10
4
<0.005
2.2 Test Platform
Experiments were carried out in a 0.1 MW CFB test
platform to investigate the effects of pyrolytic
wastewater on the combustion and emission
characteristics of semi-coke when pyrolytic
wastewater was injected from different positions. As
shown in Fig.1, the 0.1 MW CFB test platform was
consist of furnace, cyclone, loop seal, tail flue, flue
gas cooler, bag filters and induced draft fan. The
inner diameter of furnace was 150 mm, there were
six thermal couples along the axis of furnace, the
inner diameter of tail flue was 150 mm, along which
there were eight thermal couples as shown in Fig.1.
Pyrolytic wastewater was injected into the furnace
and tail flue from the positions near T3 and t2,
respectively, the mass of injected wastewater was
about 10 % of semi-coke.
The excess air ratio was controlled around 1.15,
the temperature in furnace was around 935℃,
pyrolytic wastewater was injected into the furnace in
the position near T3, and was injected into tail flue
in the position near t2 when the temperature was
appropriate. The flue gas was filtered, dried then
analyzed by Testo 350 measuring system. In the
following discussion, the NO
x
emission had
normalized to dry flue gas with an oxygen
concentration of 6 %.
Influences of Injection Positions of Pyrolytic Wastewater on Nox Emission of Semi-coke
49
1- Screw feeder; 2- CFB furnace; 3- Cyclone; 4- Loop seal; 5- Post-combustion chamber; 6- Flue gas cooler; 7- Bag filters;
8- Induced draft fan
Figure 1: Schematic diagram of 0.1MW CFB test platform.
3 RESULTS AND DISCUSSIONS
Compared to the temperature distributions without
pyrolytic wastewater, the temperature of tail flue
was stable when pyrolytic wastewater was injected
into furnace, and the temperature of furnace was
stable when pyrolytic wastewater was injected into
the tail flue. Fig.2 and Fig.3 showed the temperature
distributions of furnace and tail flue in different
conditions, respectively.
T1 T2 T3 T4 T5 T6
820
840
860
880
900
920
940
847
865
932
875
904
896
847
860
925
871
896
887
Combustion without PW
PW was injected into furnace
Temperature (℃)
Sample point in furnace
Figure 2: Temperature distribution of furnace.
“PW” represented pyrolytic wastewater. The
temperature in furnace decreased slightly when
pyrolytic wastewater was injected into T3, the
temperature of T2, T3, T4, T5 and T6 dropped 5 to 9
degrees, while the temperature of T1 did not change
due to the heat storage of bed material. It indicated
that there was little effect on the temperature of
furnace when deal with pyrolytic wastewater in the
furnace.
As shown in Fig.3, the temperature of t2
decreased sharply when pyrolytic wastewater was
injected into the tail flue, the temperature of t3, t4,
t5, t6, t7 and t8 all decreased in varying degrees, and
all above 15℃. It could indicate that the temperature
change of tail flue was more obvious than that of the
furnace when the same percentage of pyrolytic
wastewater was injected into furnace and tail flue,
respectively.
t1 t2 t3 t4 t5 t6 t7 t8
100
200
300
400
500
600
700
800
900
857
756
809
793
776
773
767
758
857
184
782
772
759
756
752
742
Combustion without PW
PW was injected into tail flue
Temperature (℃)
Sample point in tail flue
Figure 3: Temperature distribution of tail flue.
ICBEB 2022 - The International Conference on Biomedical Engineering and Bioinformatics
50
There were lots of semi-coke and bed material
particles circulating through the furnace, cyclone
and loop seal, the heat loss caused by pyrolytic
wastewater was soon supplemented, while there
were few combustible particles in the tail flue, so
that the injection of pyrolytic wastewater led to
larger decrease of temperature. Sample point t2 was
the nearest point from where pyrolytic wastewater
was injected into, much heat was absorbed to
evaporate the water when flue gas and fly ash flow
by the injection position.
Fig.4 showed the pollutant concentration in flue
gas of three cases, respectively, “None” represented
no pyrolytic wastewater was injected, and its NO
x
emission concentration was 439.67 mg/m
3
. It was
obviously that the NO
x
emission decreased when
pyrolytic wastewater was injected into furnace or
tail flue, the NO
x
emission were cut down by
13.81 %and 22.58 % when pyrolytic wastewater was
injected into furnace and tail flue, respectively.
Compared to being injected into the furnace, the
NO
x
emission was lower when pyrolytic wastewater
was injected into tail flue. It indicated that it was
more appropriate for pyrolytic wastewater to reduce
NO
x
emission in tail flue.
When pyrolytic wastewater was injected into
furnace, the semi-coke particles were in the state of
incomplete combustion in the position where
pyrolytic wastewater was injected into, part of
nitrogen in semi-coke was released, and NH
3
in
pyrolytic wastewater reacted with NO
x
through the
following reaction (R1), and the organic matters and
residual NH
3
(if there was) in pyrolytic wastewater
would be oxidized by air.
4NH
3
+6NO→5N
2
+6H
2
O (R1)
None Furnace Tail flue
0
100
200
300
400
500
Injection position
CO
NO
x
CO(ppm)
NO
x
（
mg/m
3
）
Figure 4: Pollutant concentration in flue gas.
The particles in flue tail were almost burned out,
and the NO
x
concentration in the flue gas was high,
the organic matters in pyrolytic wastewater such as
hydrocarbons would not be oxidized due to low
temperature in the position of t2 when pyrolytic
wastewater was injected into tail flue, the CO
emission increased as well due to the drop of
temperature. Hydrocarbons and NH
3
reacted with
NO
x
, so the NO
x
emission was the lowest when
pyrolytic wastewater was injected into tail flue.
The incineration of pyrolytic wastewater
together with semi-coke could not only realize zero
discharge of pyrolytic wastewater, the NO
x
emission
of semi-coke was reduced as well. However, the
residence time of pyrolytic wastewater was short
when it was injected into tail flue, so there was no
guarantee of sufficient residence time for the organic
matters to decompose.
4 CONCLUSIONS
Experiments were carried out to explore the effects
of injection positions of pyrolytic wastewater on
combustion temperature and pollutant emissions of
semi-coke. The main conclusions were as follows:
(1) The temperature change of tail flue was more
obvious than furnace when the same percentage of
pyrolytic wastewater was injected into furnace and
tail flue, respectively.
(2) The NO
x
emission was cut down by
13.81 %and 22.58 % when pyrolytic wastewater was
injected into furnace and tail flue, respectively.
(3) It was more appropriate for pyrolytic
wastewater to reduce NO
x
emission in tail flue
compared to the furnace, but there was no guarantee
of sufficient residence time for organic matters to
decompose.
ACKNOWLEDGEMENTS
This work was financially supported by the National
Key Research & Development Program of China,
grant NO. 2018YFB0605002.
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