Subscriber access provided by UNIVERSITY OF ADELAIDE LIBRARIES
Article
Comparison of the reburning chemistry in O2/N2, O2/CO2 and O2/H2O atmospheres Yizhuo He, Jianghui Luo, Yangguang Li, Huiqiao Jia, Feng Wang, Chun Zou, and Chuguang Zheng Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b01797 • Publication Date (Web): 01 Sep 2017 Downloaded from http://pubs.acs.org on September 2, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 33
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
1
Comparison of the reburning chemistry in
2
O2/N2, O2/CO2 and O2/H2O atmospheres
3
Yizhuo He, Jianghui Luo, Yangguang Li, Huiqiao Jia, Feng Wang, Chun Zou*,
4
Chuguang Zheng
5
State Key Laboratory of Coal Combustion, Huazhong University of Science and
6
Technology, Wuhan, 430074, P. R. China
7
*Corresponding author. Tel.: +86 87542417-8314; fax: +86 87545526.
8
E-mail address:
[email protected] (C. Zou)
9 10
Abstract: The reburning chemistry in oxy-fuel and oxy-steam combustion of methane
11
was investigated both experimentally and numerically. Comparison experiments in
12
O2/N2, O2/CO2 and O2/H2O atmospheres were performed in a flow reactor at
13
atmospheric pressure with equivalence ratio ranging from fuel-rich to fuel-lean and
14
temperature from 973 K to 1773 K. Experimental results showed that compared with
15
N2 and CO2 atmospheres NO reduction observed in H2O atmosphere is the lowest
16
under fuel-rich and stoichiometric condition, while it is the highest under fuel-lean
17
condition. The NO reduction intensity in CO2 atmosphere lies between N2 and H2O
18
atmosphere under fuel-rich and fuel-lean condition, however, it is the highest under
19
stoichiometric conditions. A chemical kinetic mechanism, which was hierarchically
20
structured and updated in our previous work, captured the main characteristics and
21
quantity of CO and NO formation satisfactorily even under fuel-lean conditions.
22
According to the analysis from a chemical kinetic point of view, CO2 and H2O exert
23
significant impacts on altering the radical pool structure to OH dominant subsequently
24
varying the availability of hydrocarbon radical as a reducing agent, which is the 1
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
25
primary reason for the different degrees of NO reduction under fuel-rich,
26
stoichiometric and fuel-lean conditions. In addition, CO2 and H2O also impact the NO
27
reduction by nitrogen-containing radicals. For CO2 atmosphere, NCO radical always
28
occupies an overwhelmingly dominant position in NO reduction due to HCN →
29
CH3CN → CH2CN → CN → NCO and HNCO → NCO channel is amplified
30
substantially. For H2O atmosphere, under fuel-rich and stoichiometric conditions, NH2
31
and NH radical are dominant due to the enhancement of NCO → HNCO → NH2 →
32
NH channel. Under fuel-lean conditions, NCO radical is dominant due to the strength
33
of HNCO → NCO channel.
34 35
Keywords: Oxy-fuel combustion; Oxy-steam combustion; Reburning chemistry;
36
Plug-flow reactor; NO
37 38
1． ．Introduction
39
The climate change synthesis report of Intergovernmental Panel on Climate
40
Change (IPCC) indicated that carbon dioxide (CO2) emission from fossil fuel
41
combustion is the primary reason for global warming.1 In response to environmental
42
crisis, oxy-fuel combustion has been comprehensively considered as one of the most
43
promising options for CO2 capture and sequestration, due to its feasibility to produce
44
sequestration-ready exhaust gas and flexibility of being implemented in existing
45
equipment with modification.2-7
46
In oxy-fuel combustion, fuel combustion occurs in mixtures of oxygen and
47
recycled flue gas instead of air, ensuring that the CO2 volume concentration exceeds
48
90% in the exhaust gas, which is almost sequestration-ready. Carlos8 and Seepana9
49
proposed oxy-steam combustion technology, in which steam, instead of recycled flue 2
ACS Paragon Plus Environment
Page 2 of 33
Page 3 of 33
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
50
gas, is used to moderate the high temperature generated by fuel combustion with
51
oxygen. Due to its advantages, such as a compact system, ease of operation, small
52
geometric size, low emissions, and energy savings, oxy-steam combustion technology
53
is regarded to be an alternative for the next-generation oxy-fuel combustion
54
technology.
55
Due to the absence of nitrogen, fuel-N is the main source of NO formation
56
during oxy-fuel and oxy-steam combustion. Hence, many researchers have paid
57
attentions to the mechanism of fuel-N evolution. Investigations on NO emission for
58
solid fuels10-15 in oxy-fuel combustion have indicated that NO emission can be
59
reduced during oxy-fuel combustion compared with conventional air combustion.
60
Despite gas-phase chemistry, heterogeneous reaction and mixing should be comprised
61
in a complete combustion process for solid fuel, gas-phase chemistry plays a critical
62
role in NO formation and reduction. Hence, it is indispensable to investigate
63
gas-phase chemistry separately to provide theoretical foundation for the underlying
64
mechanisms. Giménez-López et al.16 studied the oxidation of HCN in O2/CO2
65
atmospheres in a flow reactor both experimentally and numerically. They indicated
66
that the inhibition of HCN oxidation is due to the impact of CO2 on radical pool
67
structure. In the experimental and numerical investigations of ammonia oxidation
68
during oxy-fuel combustion, both Mendiara et al.17 and Watanabe et al.18 indicated
69
that the increased OH/H ratio and high CO levels increase the probability of forming
70
N2 instead of NO. He et al.19 experimentally studied the oxidation of ammonia during
71
oxy-steam combustion and they hierarchically structured a detailed chemical kinetic
72
mechanism, which captures the experimental data satisfactorily.
73
In spite of the advantage of oxy-fuel combustion in NOx emission, a NOx
74
reduction technology is still essential in practical combustion equipment to implement 3
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
75
a further reduction. The NOx-control technologies in oxy-fuel process have been
76
reviewed by Normann et al.,20 they indicated that fuel-staging (reburning) technology
77
is a promising option for both conventional air and oxy-fuel combustion system
78
among the primary measures. Hence, many investigations have focused on gas-phase
79
reburning chemistry to reveal the underlying mechanism. Extensive studies have been
80
carried out on reburning mechanism in air combustion,21-29 typically, Glarborg and
81
Miller27,28 updated and structured a detailed chemical kinetic modeling, which
82
predicts the experimental very well in flow reactors, to reveal the reburning
83
mechanism for C1 and C2 hydrocarbon. Dagaut et al.29 further investigated the kinetics
84
of C1 to C4 hydrocarbon/NO interactions in relation with reburning mechanism. There
85
are also recent studies for reburning mechanism in oxy-fuel combustion. Watanabe et
86
al.30 compared NO reduction mechanisms between staged O2/CO2 combustion and air
87
combustion, results showed that a significant reduction in NO emission could be
88
achieved by staged combustion in O2/CO2 combustion. Giménez-López et al.31
89
experimentally examined the NO reduction by reburning under oxy-fuel conditions in
90
a flow reactor and they provided a wide amount of experimental data on reburning.
91
Normann et al.32 numerically investigated reburning reduction of NO in oxy-fuel
92
combustion using a plug-flow reactor and they demonstrated that CO2 changes the
93
radial pool altering the nitrogen chemistry by impacting the formation and oxidation
94
of hydrocarbon radicals. An experimental and numerical study on reburning chemistry
95
in oxy-fuel combustion of methane was carried out by Mendiara and Glarborg33 in a
96
flow reactor and they structured a detailed chemistry kinetic mechanism, but there
97
were obvious defects in predicting NO reduction under fuel-lean conditions. In
98
addition, little information is available for the reburning chemistry in oxy-steam
99
combustion. 4
ACS Paragon Plus Environment
Page 4 of 33
Page 5 of 33
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
100
The objective of this work is to reveal the reburning mechanism in oxy-steam
101
combustion. In the present work, a systematic experimental study of the gas-phase
102
NO reduction by methane in O2/N2, O2/CO2, O2/H2O atmospheres at 1 atm, over a
103
wide range of equivalence ratios (i.e., 0.2, 1.0, 1.6), and within the temperature range
104
of 973–1773 K was performed. The study was conducted in a laboratory plug flow
105
reactor. A chemical kinetic model with 170 species and 1208 reactions, which was
106
hierarchically structured and updated, was adopted and new experimental data are
107
analyzed in terms of this model to evaluate the detailed reburning mechanism of NO
108
interaction with methane in oxy-fuel and oxy-steam atmosphere.
109 110
2. Experimental and Modeling
111
Fig. 1 schematically demonstrates the experimental apparatus used in the present
112
work. The apparatus comprise a gas supplying system, a steam producing system, a
113
flow reactor, and a gas composition test system.
114
The flow reactor with an internal diameter of 12 mm and a length of 1100 mm
115
was constructed according to Skjøth-Rasmussen et al.34 for homogeneous gas-phase
116
reactions. Alumina was chosen as the material of the flow reactor in order to avoid the
117
catalytic effect on experiments. The flow reactor was heated using molybdenum bars
118
in a five-zone temperature controlled electrically heated oven, which allows the
119
maximum temperature up to 1800 K. The temperature profiles within the reactor were
120
measured using a type S thermocouple under inert conditions (1 L/min CO2). The
121
measurement error for the temperature is ±4 K. Typical temperature profiles are
122
demonstrated in Fig. 2, which implies that the length of isothermal reaction zone is
123
approximately 700 mm. The temperature of the isothermal zone is referred to as the
124
reaction temperature in this work. 5
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
125
High-purity gases (99.99%) were separately supplied from gas cylinders and the
126
flow rates were controlled precisely by mass flow controllers. Distilled water was
127
supplied into the homothermal evaporation chamber at 473 K employing a
128
high-accuracy syringe pump. This predefined steam flow was preliminarily blended
129
with the oxygen in the evaporation chamber. Then the total flow was premixed
130
sufficiently with methane in the mixer prior to entering the reactor. In order to avoid
131
steam condensation, the heating tapes were used to heat the pipeline connecting the
132
homothermal chamber, the mixer, and the reactor to maintain the temperature at a
133
constant of 423 K.
134
A water cooler was installed at the outlet of the reactor to cool down the product
135
gas rapidly. In the case of steam addition, argon (Ar) of equal volume to steam was
136
fed into the product gas to compensate for volume loss due to steam condensation.
137
The concentrations of CO and NO in the product gas were measured on-line using
138
Fourier transform infrared spectroscopy (GASMET-DX4000) with a resolution of 8
139
cm−1 and scanning speed of 10 scans per second. The measurement error is estimated
140
as ±1%.
141
In order to minimize the axial dispersion of the reactants and comply with a
142
reasonable plug-flow approximation, the total flow rate for all experiments was kept
143
constant at 1 L/min (Standard Temperature and Pressure), which has been
144
investigated and validated by Skjøth-Rasmussen34 and Mendiara et.al.17 Also, the
145
reactants were highly diluted in nitrogen, carbon dioxide or steam to minimize the
146
influence of temperature rise due to chemical reaction. The methane concentration
147
was about 2500 ppm, the nitric oxide concentration was approximately 1000 ppm, and
148
the oxygen concentration was calculated according to the defined equivalence ratios.
149
Three equivalence ratios, i.e. 0.2, 1.0, and 1.6, were chosen on behalf of fuel-lean, 6
ACS Paragon Plus Environment
Page 6 of 33
Page 7 of 33
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
150
stoichiometric, and fuel-rich conditions, respectively. Experiments were carried out in
151
the temperature range of 973–1773 K at intervals of 20 K. Detailed experimental inlet
152
parameters are listed in Table 1.
153
Numerical predictions adopting full experimental temperature profiles within the
154
flow reactor were performed using the plug flow reactor (PFR) module in conjunction
155
with CHEMKIN-PRO. The mechanism adopted in this work was hierarchically
156
established in our previous study,19 containing the comprehensive oxidation
157
mechanism for hydrogen, C1–C2 hydrocarbons, nitrogen-containing species (HCN,
158
NH3) and the interactions of these compositions. The mechanism contained 170
159
species and 1208 reactions. The more details and validations of this mechanism can
160
be found elsewhere.19
161 162
3． ．Results and Discussion
163
Fig. 3 shows the comparisons between the experimental and numerical results of
164
the CO and NO profiles for CH4 oxidation in the presence of NO as a function of
165
reaction temperature in diverse atmospheres (N2 or CO2 or H2O) and equivalence
166
ratios (fuel-rich, stoichiometric, and fuel-lean conditions). Solid symbols and solid
167
lines represent experimental and numerical results in N2, half solid symbols and grey
168
lines represent those in CO2, whereas open symbols and dashed lines represent those
169
in H2O.
170
Under fuel-rich conditions, as displayed in Fig. 3a, the CO formation in N2 case
171
occurs below 973 K, increases to peak (1617 ppm) at 1293 K, and then nearly
172
stabilizes. The peak of CO formation is accompanied by a sharp increase of NO
173
reduction to 435 ppm and then the NO concentration nearly keeps steady at 450 ppm.
174
In CO2, CO formation also initiates below 973 K, goes up to a higher peak (4435 ppm) 7
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
175
at 1373 K, and then increases gradually with temperature above 1453 K. NO
176
reduction initiates at 1173 K, increases significantly at 1393 K with a NO value of
177
381 ppm and then the NO concentration increases gradually up to 622 ppm at 1773 K.
178
In H2O, CO formation exhibits a maximum value of 566 ppm at 1313 K and then
179
keeps unchanged at a value of 20 ppm. NO reduction reaches a peak (665 ppm) and
180
then weakens to a constant value of 830 ppm.
181
Under stoichiometric conditions exhibited in Fig. 3b, the CO concentration in N2
182
initiates below 973 K, goes up to maximum (485 ppm) at 1233 K, and then reaches a
183
plateau at 85 ppm. The peak of CO concentration is in consistence with a sharp
184
increase of NO reduction to 659 ppm and then the NO concentration increases slowly
185
to a steady value of 776 ppm. In CO2, the maximum CO concentration is 2814 ppm at
186
1333 K, and then CO formation increases gradually with temperature up to 3536 ppm
187
at 1773 K. NO concentration starts to drop at 1133 K, goes down to a minimum value
188
of 500 ppm at 1353 K and then increases gradually to stabilize at 740 ppm at 1653 K.
189
In H2O, CO formation demonstrates a peak value of 460 ppm at 1253 K and then
190
remains unchanged at a value of 12 ppm. NO concentration reaches a bottom (741
191
ppm) at 1273 K and then goes up to a constant value of 900 ppm.
192
Under fuel-lean conditions, as shown in Fig. 3c, the CO formation exhibits a
193
value of 516 ppm at 973 K and the decreases to zero above 1273 K. NO concentration
194
is 924 ppm at 973 K and then increase to a steady level of 971 ppm in N2 cases. In
195
CO2, CO concentration starts at 660 ppm, goes down to 2 ppm and then increases up
196
to 242 ppm at 1773 K. NO concentration remains nearly unchanged at 932 ppm. In
197
H2O, CO concentration initiates at 423 ppm, declines to zero at 1113 K and then
198
cannot be detected again. NO concentration at 973 K is 857 ppm and it increases to
199
stabilize at a value of 915 ppm. 8
ACS Paragon Plus Environment
Page 8 of 33
Page 9 of 33
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
200
Synthesizing the comparisons of the experimental results observed in N2, CO2
201
and H2O atmospheres, there are common phenomena that the temperature of CO
202
concentration peak is in consistence with a vast increase of NO reduction; the onset
203
temperature of NO reduction is N2, H2O and CO2 atmosphere in an ascending
204
sequence; and this temperature is lowered by an increasing O2 concentration for all
205
the three atmospheres. Besides, compared with N2 and CO2 atmospheres, NO
206
reduction observed in H2O atmosphere is the lowest under fuel-rich and
207
stoichiometric conditions, while it is the highest under fuel-lean conditions. The NO
208
reduction intensity in CO2 atmosphere lies between N2 and H2O atmospheres under
209
fuel-rich and fuel-lean conditions, however, it is highest under stoichiometric
210
conditions.
211
It can be seen from Fig. 3 that the chemical kinetic model satisfactorily
212
reproduces the main features of CO and NO formation measured in experiments in N2,
213
CO2 and H2O atmospheres, although tolerant deviations exist especially under
214
fuel-lean conditions. Hence, the mechanism proposed previously is appropriate for
215
revealing the NO reduction mechanisms for N2, CO2 and H2O atmospheres in the
216
chemical kinetic point of view.
217
In the process of fuel oxidation and reduction the radical pool has been generally
218
considered as a critical participant, hence, it is always indispensable to analyze the
219
radical pool structure at first. Fig. 4 compares the H, O, and OH mole fractions
220
profiles in N2, CO2 and H2O atmospheres under fuel-rich, stoichiometric, and
221
fuel-lean conditions at 1673 K. As displayed in Fig. 4, for CO2 atmosphere, OH
222
radicals are dominant in the radical pools under all three equivalent ratios. It can be
223
attributed to that R33 (H + CO2 = CO + OH) competes for H radicals with the main
224
chain branching reaction R1 (H + O2 = O +OH), leading to the dominant position of 9
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 10 of 33
225
OH radicals. For H2O atmosphere, OH radicals are overwhelmingly predominant in
226
the radical pools under all three equivalent ratios. This high production is caused by
227
that the presence of H2O substantially enhances the reactions R30 (H + H2O = OH +
228
H2) and R14 (O + H2O = OH +OH), yielding a large amount of OH radicals and
229
simultaneously consuming large amounts of H and O radicals. In regard to the effect
230
of equivalence ratio on radical pool structure, it can be found that the effect of
231
equivalence ratio is strong in N2 atmosphere, while limited in CO2 and H2O
232
atmospheres. This can be attributed to that from fuel-rich to fuel-lean conditions the
233
increasing O2 concentration enhances R1 (H + O2 = O + OH), leading to a gradual
234
increase of the O and OH radicals. Hence, the concentrations of O and OH radicals
235
increase up to be higher than that of H radical in N2 atmosphere under fuel-lean
236
conditions. However, for CO2 atmosphere, although R1 (H + O2 = O + OH) is
237
enhanced by the increasing O2 concentration, the contribution of R33 (H + CO2 = CO
238
+ OH) to OH production is still dominant in radical pool. As for H2O atmosphere, the
239
impact of the equivalence ratio on the radical pool structure is extremely restricted
240
due to the overwhelming contribution of R14 (O + H2O = OH +OH) and R30 (H +
241
H2O = OH + H2) to OH radicals.
242 243 244
In order to clarify the NO conversion intuitively, the OPR, which is short for the overall production rate, is introduced and defined as follows: l
OPRi , j = ∫ ωi , j dx
(1)
0
245
where i denotes species, j denotes elementary reaction, ωi,j means the mole
246
production rate of species i through elementary reaction j and l is the length of
247
reaction zone.
248
Fig.5 compares the pathways of NO conversion in methane oxidation in N2, CO2
249
and H2O atmosphere by synthesizing the OPRis of all the corresponding elementary 10
ACS Paragon Plus Environment
Page 11 of 33
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
250
reactions along the pathways, taking the fuel-lean conditions as a typical case. As
251
shown in Fig.5, the pathways of nitric oxide reburn chemistry are quite sophisticated.
252
Nitric oxide is reduced through the reducing reactions of NO with hydrocarbon
253
radical, NCO or amine radical. Although all these reactions occur simultaneously
254
during the reburn chemistry, it can be divided into two sections artificially in the
255
pathway point of view throughout this article in order to make the discussions concise
256
and incisive. First, hydrocarbon radicals react with NO generating to HCN, which is
257
the dominant intermediate nitrogen species during NO reduction, and then HCN
258
converts to four critical nitrogen-containing radicals including NCO, NH2, NH and N
259
through a series of chemical reactions. Second, the critical nitrogen-containing
260
radicals interact with NO reduced to N2 ultimately.
261
Fig. 6 demonstrates the OPRNOs of critical reactions between nitric oxide and
262
hydrocarbon radicals in the N2, CO2 and H2O atmospheres for fuel-rich,
263
stoichiometric and fuel-lean conditions at 1673 K. In order to demonstrate a
264
convincing elucidation, the evolution path of hydrocarbon radicals during methane
265
oxidation in N2, CO2 and H2O atmosphere are compared in Fig. 7. It can be seen from
266
Fig.6 that the total amount of NO reduction in different atmospheres through reactions
267
between nitric oxide and hydrocarbon radicals are in well agreement with the NO
268
reduction observed in experiments, however, the importantly contributing reactions
269
vary with diverse atmospheres and equivalence ratios. Under fuel-rich conditions, the
270
reactions between NO and hydrocarbon radicals are all quite strong in N2 atmosphere
271
especially R1145 (HCCO + NO = HCNO + CO). As for CO2 atmosphere, OPRNO of
272
R1104 (CH3 + NO = HCN + H2O) and R1105 (CH3 + NO = H2CN + OH) are higher,
273
while OPRNO of R1145 (HCCO + NO = HCNO + CO) is lower than that in N2
274
atmosphere. These can be attributed to the change of radical pool structure in CO2 11
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
275
atmosphere. Because C2 branch relies more on H and O radicals than C1 branch, C2
276
branch is suppressed in CO2 atmosphere as shown in Fig. 7. Subsequently, the
277
availability of CH3, which is the initial radical for C1 branch, is strengthened as a
278
reducing agent. However, the positive effect of CH3 radical cannot compensate the
279
negative effect of C2 branch under fuel-rich conditions, leading to the smaller
280
magnitude of total NO reduction by hydrocarbon radicals. Regarding to H2O
281
atmosphere, the ultrahigh concentration of OH radical enhances the oxidation of
282
hydrocarbon radicals to CH2OH, CH2O and CO as shown in Fig. 7, suppressing their
283
availability for NO reduction dramatically. Consequently, all the corresponding
284
reactions shown in Fig. 6 are much weaker in comparisons with those in N2 and CO2
285
atmospheres.
286
Under stoichiometric conditions, the reactions between NO and hydrocarbon
287
radicals are still strong in N2 atmosphere, but they are evidently weakened compared
288
to those under fuel-rich conditions. In N2 atmosphere, the increasing O2 concentration
289
promotes the formation of O radical as mentioned above. Then the higher O radical
290
and O2 levels facilitate the oxidation of hydrocarbon radicals mainly through CH3 →
291
CH2O shown in Fig. 7 weakening their removal of NO. For CO2 atmosphere, R33 (H
292
+ CO2 = CO + OH) competes with R1 (H + O2 = O + OH) ensuring the stability of the
293
radical pool structure. This suppresses the production of O radical and subsequently
294
the CH3 → CH2O maintaining the availability of hydrocarbon radical. Hence, the
295
OPRNO values of corresponding reactions are nearly unchanged in comparison with
296
those under fuel-rich conditions. In this case, the positive effect of CH3 radical
297
surpasses the negative effect of C2 branch resulting in the highest value of total NO
298
reduction by hydrocarbon radicals among the three atmospheres. With respect to the
299
H2O atmosphere, similar to CO2 atmosphere but R14 (O + H2O = OH + OH) and R30 12
ACS Paragon Plus Environment
Page 12 of 33
Page 13 of 33
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
300
(H + H2O = OH + H2) maintain the structure of radical pool mightily holding the
301
OPRNO values of corresponding reactions steady, which are still much lower in
302
comparisons with those in N2 and CO2 atmospheres.
303
Under fuel-lean conditions, the higher O2 levels exert further influence on
304
promoting the formation of O radical and the oxidation of hydrocarbon radicals
305
inhibiting the NO reduction. This impact is so strong in N2 atmosphere that the O
306
radical is dominant in the radical pool as discussed above, causing a vast decline of
307
the reactions between NO and hydrocarbon radicals. Hence, the NO reduction by
308
hydrocarbon radicals is weakest in N2 atmosphere under fuel-lean conditions. As for
309
CO2 atmosphere, although R33 (H + CO2 = CO + OH) is not strong enough to inhibit
310
the evident rise of O radical, it ensures the leading position of OH radical in the
311
radical pool. Hence, OPRNO values of corresponding reactions are a little higher than
312
those in N2 atmosphere. In regard to H2O atmosphere, R30 (H + H2O = OH + H2)
313
competes with R1 (H + O2 = O + OH) suppressing the production of O radical,
314
simultaneously, R14 (O + H2O = OH +OH) converts the O radical generated through
315
R1 to OH radical. Therefore, these two reactions can maintain the overwhelmingly
316
predominant status of OH radical in the radical in despite of the sufficient O2
317
concentration. Consequently, the availability of hydrocarbon radicals influenced by
318
O2 concentration is diminished to minimum in H2O atmosphere and the OPRNO values
319
of corresponding reactions are superior to those in N2 and CO2 atmospheres.
320
It can be seen from Fig. 6 that nitric oxide interacts with hydrocarbon radicals
321
generating HCN, HCNO and H2CN. According to the numerical prediction, both
322
HCNO and H2CN are almost completely converted to HCN. Then HCN is ultimately
323
converted to four critical nitrogen-containing radicals including NCO, NH2, NH and
324
N through a series of complicated pathways, as displayed in Fig. 5. This implies that 13
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
325
the total amount of NCO, NH2, NH and N are directly determined by the amount of
326
NO reduced by hydrocarbon radicals. These four critical nitrogen-containing radicals
327
react with NO converted to N2, N2O and NNH, and N2O and NNH are almost totally
328
converted to N2 through R812 (N2O + M = N2 + O + M), R814 (N2O + H N2 +
329
OH), R860 (NNH = N2 + H) and R861 (NNH + H = N2 + H2). Hence, the reactions
330
between the four nitrogen-containing radicals and nitric oxide can be considered as
331
another key point for NO reduction, where further insight should be given to in the
332
following section.
333
Fig. 8 exhibits the OPRNOs of critical reactions between nitric oxide and
334
nitrogen-containing radicals in the N2, CO2 and H2O atmospheres for fuel-rich,
335
stoichiometric and fuel-lean conditions at 1673 K. As seen from Fig. 8, the total
336
amount of NO reduction in different atmospheres through reactions between nitric
337
oxide and nitrogen-containing radicals are in consistence with the amount of NO
338
reduction observed in experiments, however, the importantly contributing reactions to
339
NO reduction are different at diverse atmospheres and equivalence ratios. Under
340
fuel-rich conditions, N and NH radicals exhibit overwhelming dominance in NO
341
reduction in N2 atmosphere through R859 (N + NO = N2 + O) and R853 (NH + NO =
342
N2O + H). This can be attributed to that the high H radical concentration promotes
343
NCO → NH → N channel shown in Fig. 5a by enhancing R1004 (NCO + H = CO +
344
NH) and R844 (NH + H = N + H2). For CO2 atmosphere, NCO radical occupies an
345
overwhelmingly dominant position in NO reduction through R1010 (NCO + NO =
346
N2O + CO) and R1011 (NCO + NO = N2 + CO2). This is because that the lack of H
347
radical suppresses the NCO → NH → N channel dramatically. And the HCN →
348
CH3CN → CH2CN → CN → NCO channel is amplified substantially by sufficient
349
OH radical and the promotion of R1083 (CN + CO2 = NCO + CO). Meanwhile, R983 14
ACS Paragon Plus Environment
Page 14 of 33
Page 15 of 33
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
350
(HNCO + OH = NCO + H2O) is strengthened by the sufficient OH radical leading to
351
the promotion of HNCO converting to NCO. Hence, the availability of NCO radical
352
for NO reduction is superior in CO2 atmosphere. Regarding H2O atmosphere, NH2
353
and NH radical are dominant, which can be attributed to the enhancement of NCO →
354
HNCO channel. The presence of high H2O concentration facilitates R983 (NCO +
355
H2O = HNCO + OH), which is responsible for the enhancement of NCO → HNCO
356
channel. Therefore, more NCO radical is converted to NH2 and NH radical through
357
NCO → HNCO → NH2 → NH channel.
358
Under stoichiometric conditions, N and NH radicals are still dominant in NO
359
reduction in N2 atmosphere, but R859 (N + NO = N2 + O) and R853 (NH + NO =
360
N2O + H) are weakened dramatically in comparison with those under fuel-rich
361
conditions. On one side, the reactions between NO and hydrocarbon radicals are
362
evidently
363
nitrogen-containing radicals. On the other side, the decreasing H radical composition
364
in radical pool is adverse to NCO → NH → N channel through R1004 (NCO + H =
365
CO + NH) and R844 (NH + H = N + H2). For CO2 and H2O atmospheres, the stability
366
of the radical pool structure results in the steady OPRNO values of corresponding
367
reactions in comparison with those under fuel-rich conditions.
weakened
as
discussed
above
shrinking
the
total
amount
of
368
Under fuel-lean conditions, it is quite different from fuel-rich and stoichiometric
369
conditions that NCO radical is predominant in NO reduction for all the three
370
atmospheres as shown in Fig. 8c. As discussed above, the NCO → NH → N and
371
HNCO → NH2 → NH channels are positively sensitive to H radical, and the HNCO
372
→ NCO channel is positively sensitive to OH radical, therefore, the radical pool
373
structure under fuel-lean conditions is beneficial to the accumulation of NCO radical.
374
Especially, it is worth emphasizing that the ultrahigh OH radical in H2O atmosphere 15
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
375
composition reverses R983 (NCO + H2O= HNCO + OH) subsequently the NCO →
376
HNCO channel, which is responsible for the dominant position of NCO radical under
377
fuel-lean conditions. In addition, the total amount of nitrogen-containing radicals is
378
determined by the total amount of NO reduced by hydrocarbon radicals, hence, the
379
total amount of NO reduced by nitrogen-containing radicals is H2O, CO2 and N2
380
atmosphere in a descending order.
381
In addition, in order to give a further insight into reburning chemistry under
382
reducing conditions, it is necessary to discuss the effect of equivalence ratio on
383
reburning chemistry. Fig. 9 shows the comparisons between the experimental and
384
numerical results of the CO and NO profiles as a function of equivalence ratio at 1673
385
K in the N2, CO2 and H2O atmospheres. As displayed in Fig. 9, the prediction results
386
are in good agreements with the experiments data, which offers a further validation
387
for the applicability of the present mechanism. It can been found from Fig.9 that NO
388
reduction intensity observed in H2O and CO2 atmosphere increase slightly with the
389
increasing equivalence ratio, much slower than the increase in N2 atmosphere, which
390
means the equivalence ratio exerts limited effect on NO reduction in H2O and CO2
391
atmosphere while evident effect on that in N2 atmosphere under reducing conditions.
392
NO reduction in H2O atmosphere is always the lowest under reducing conditions. The
393
NO reduction intensity in CO2 atmosphere is the highest at first (1.0-1.2), then it lies
394
between N2 and H2O atmospheres. These imply H2O alters the radical pool structure
395
shrinking the availability of hydrocarbon radical as a reducing agent dramatically,
396
which is hardly affected by O2 concentration. However, this shrink effect of CO2
397
depends on O2 concentration. When the O2 is sufficient enough even under reducing
398
conditions, the suppression effect of CO2 on O radical production and subsequently
399
CH3 → CH2O channel is more dominant than the shrink effect, which is responsible 16
ACS Paragon Plus Environment
Page 16 of 33
Page 17 of 33
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
400
for the highest NO reduction (equivalence ratio 1.0-1.2) in CO2 atmosphere.
401 402
5. Conclusions
403
The reburning chemistry in oxy-fuel and oxy-steam combustion of methane was
404
investigated both experimentally and numerically. Comparison experiments in O2/N2,
405
O2/CO2 and O2/H2O atmospheres were performed in a flow reactor at atmospheric
406
pressure with equivalence ratio ranging from fuel-rich to fuel-lean and temperature
407
from 973 K to 1773 K.
408
Experimental results showed that the onset temperature of NO reduction is N2,
409
H2O and CO2 atmosphere in an ascending sequence, the temperature of CO
410
concentration peak is in consistence with a vast increase of NO reduction. Compared
411
with N2 and CO2 atmospheres, NO reduction observed in H2O atmosphere is the
412
lowest under fuel-rich and stoichiometric condition, while it is the highest under
413
fuel-lean condition. The NO reduction intensity in CO2 atmosphere lies between N2
414
and H2O atmosphere under fuel-rich and fuel-lean conditions, however, it is the
415
highest under stoichiometric conditions.
416
The numerical results using the detailed chemical kinetic mechanism captured
417
the main characteristics and quantity of CO and NO formation satisfactorily even
418
under fuel-lean conditions. The numerical results showed that CO2 and H2O exert
419
significant impacts on altering the radical pool structure to OH dominant and the
420
impact of H2O is much stronger than that of CO2. Under fuel-rich conditions, the
421
alteration of the radical pool structure shrinks the availability of hydrocarbon radical
422
as a reducing agent in both CO2 and H2O atmospheres. Meanwhile, the shrink is far
423
more remarkable in H2O atmosphere. Under stoichiometric conditions, the presence
424
of CO2 suppresses the production of O radical, which is responsible for the 17
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
425
enhancement of NO reduction in CO2 atmosphere. For H2O atmosphere, the ultrahigh
426
OH radical results in that the availability of hydrocarbon radical as a reducing agent
427
still much lower in comparisons with those in N2 and CO2 atmospheres.
428
Meanwhile, regarding the nitrogen-containing radicals under both fuel-rich and
429
stoichiometric conditions, in CO2 atmosphere, NCO radical occupies an
430
overwhelmingly dominant position in NO reduction due to HCN → CH3CN →
431
CH2CN → CN → NCO and HNCO → NCO channel is amplified substantially. In
432
H2O atmosphere, NH2 and NH radical are dominant due to the enhancement of NCO
433
→ HNCO → NH2 → NH channel.
434
Under fuel-lean conditions, the higher O2 levels exert further influence on
435
promoting the formation of O radical and the oxidation of hydrocarbon radicals
436
inhibiting the NO reduction. CO2 and H2O alter the radical pool structure diminishing
437
the influence of high O2 levels. Likewise, the diminishment by H2O is much stronger
438
than that by CO2. In this case, NCO radical occupies an overwhelmingly dominant
439
position in NO reduction in both CO2 and H2O atmosphere due to the strength of
440
HNCO → NCO channel.
441 442
Acknowledgments
443
This work was supported by the National Key Research & Development Special
444
Project (No. 2016YFB0600801) of the National Natural Science Foundation of China.
445 446
References
447
(1) Solomon, S.; Qin, D.; Manning, M.; Chen, Z.; Marquis, M.; Averyt, K.; Tignor,
448
M.; Miller, H. IPCC, Climate change 2007: the physical science basis. Contribution of
449
working group I to the fourth assessment report of the intergovernmental panel on 18
ACS Paragon Plus Environment
Page 18 of 33
Page 19 of 33
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
450
climate change. Cambridge University Press, Cambridge, United Kingdom and New
451
York, NY, USA: 2007.
452
(2) Wall, T.; Liu, Y.; Spero, C.; Elliott, L.; Khare, S.; Rathnam, R.; Zeenathal, F.;
453
Moghtaderi, B.; Buhre, B.; Sheng, C.; Gupta, R.; Yamada, T.; Makino, K.; Yu, J., An
454
overview on oxyfuel coal combustion—State of the art research and technology
455
development. Chemical Engineering Research and Design 2009, 87, (8), 1003-1016.
456
(3) Wall, T. F., Combustion processes for carbon capture. Proceedings of the
457
Combustion Institute 2007, 31, (1), 31-47.
458
(4) Buhre, B.; Elliott, L.; Sheng, C.; Gupta, R.; Wall, T., Oxy-fuel combustion
459
technology for coal-fired power generation. Progress in energy and combustion
460
science 2005, 31, (4), 283-307.
461
(5) Scheffknecht, G.; Al-Makhadmeh, L.; Schnell, U.; Maier, J., Oxy-fuel coal
462
combustion—A review of the current state-of-the-art. International Journal of
463
Greenhouse Gas Control 2011, 5, Supplement 1, (0), S16-S35.
464
(6) Chen, L.; Yong, S. Z.; Ghoniem, A. F., Oxy-fuel combustion of pulverized coal:
465
Characterization, fundamentals, stabilization and CFD modeling. Progress in Energy
466
and Combustion Science 2012, 38, (2), 156-214.
467
(7) Toftegaard, M. B.; Brix, J.; Jensen, P. A.; Glarborg, P.; Jensen, A. D., Oxy-fuel
468
combustion of solid fuels. Progress in Energy and Combustion Science 2010, 36, (5),
469
581-625.
470
(8) Carlos, S., Modeling design and pilot-scale experiments of CANMET’S advanced
471
oxy-fuel/steam burner. International Oxy-combustion research network, USA 2007.
472
(9) Seepana, S.; Jayanti, S., Steam-moderated oxy-fuel combustion. Energy
473
Conversion and Management 2010, 51, (10), 1981-1988.
474
(10) Andersson, K.; Normann, F.; Johnsson, F.; Leckner, B., NO emission during 19
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
475
oxy-fuel combustion of lignite. Industrial & Engineering Chemistry Research 2008,
476
47, (6), 1835-1845.
477
(11) Czakiert, T.; Bis, Z.; Muskala, W.; Nowak, W., Fuel conversion from oxy-fuel
478
combustion in a circulating fluidized bed. Fuel Processing Technology 2006, 87, (6),
479
531-538.
480
(12) Lupiáñez, C.; Guedea, I.; Bolea, I.; Díez, L. I.; Romeo, L. M., Experimental study
481
of SO2 and NOx emissions in fluidized bed oxy-fuel combustion. Fuel Processing
482
Technology 2013, 106, 587-594.
483
(13) Wang, G.; Zander, R.; Costa, M., Oxy-fuel combustion characteristics of
484
pulverized-coal in a drop tube furnace. Fuel 2014, 115, 452-460.
485
(14) Shaddix, C. R.; Molina, A., Fundamental investigation of NOx formation during
486
oxy-fuel combustion of pulverized coal. Proceedings of the Combustion Institute 2011,
487
33, (2), 1723-1730.
488
(15) Jia, L.; Tan, Y.; Anthony, E., Emissions of SO2 and NOx during Oxy−Fuel CFB
489
Combustion Tests in a Mini-Circulating Fluidized Bed Combustion Reactor. Energy
490
& Fuels 2009, 24, (2), 910-915.
491
(16) Giménez-López, J.; Millera, A.; Bilbao, R.; Alzueta, M. U., HCN oxidation in an
492
O2/CO2 atmosphere: An experimental and kinetic modeling study. Combustion and
493
Flame 2010, 157, (2), 267-276.
494
(17) Mendiara, T.; Glarborg, P., Ammonia chemistry in oxy-fuel combustion of
495
methane. Combustion and Flame 2009, 156, (10), 1937-1949.
496
(18) Watanabe, H.; Marumo, T.; Okazaki, K., Effect of CO2 Reactivity on NOx
497
Formation and Reduction Mechanisms in O2/CO2 Combustion. Energy & Fuels 2012,
498
26, (2), 938-951.
499
(19) He, Y.; Zou, C.; Song, Y.; Chen, W.; Jia, H.; Zheng, C., Experimental and 20
ACS Paragon Plus Environment
Page 20 of 33
Page 21 of 33
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
500
Numerical Study of the Effect of High Steam Concentration on the Oxidation of
501
Methane and Ammonia during Oxy-Steam Combustion. Energy & Fuels 2016, 30, (8),
502
6799-6807.
503
(20) Normann, F.; Andersson, K.; Leckner, B.; Johnsson, F., Emission control of
504
nitrogen oxides in the oxy-fuel process. Progress in Energy and Combustion Science
505
2009, 35, (5), 385-397.
506
(21) Kilpinen, P.; Glarborg, P.; Hupa, M., Reburning chemistry: a kinetic modeling
507
study. Industrial & engineering chemistry research 1992, 31, (6), 1477-1490.
508
(22) Bilbao, R.; Millera, A.; Alzueta, M. U., Influence of the temperature and oxygen
509
concentration on NOx reduction in the natural gas reburning process. Industrial &
510
engineering chemistry research 1994, 33, (11), 2846-2852.
511
(23) Bilbao, R.; Alzueta, M. U.; Millera, A., Experimental study of the influence of
512
the operating variables on natural gas reburning efficiency. Industrial & engineering
513
chemistry research 1995, 34, (12), 4531-4539.
514
(24) Bilbao, R.; Alzueta, M. U.; Millera, A.; Duarte, M., Simplified kinetic model of
515
the chemistry in the reburning zone using natural gas. Industrial & engineering
516
chemistry research 1995, 34, (12), 4540-4548.
517
(25) Alzueta, M. U.; Glarborg, P.; Dam-Johansen, K., Low temperature interactions
518
between hydrocarbons and nitric oxide: an experimental study. Combustion and flame
519
1997, 109, (1), 25-36.
520
(26) Dagaut, P.; Lecomte, F.; Chevailler, S.; Cathonnet, M., Experimental and detailed
521
kinetic modeling of nitric oxide reduction by a natural gas blend in simulated
522
reburning conditions. Combustion science and technology 1998, 139, (1), 329-363.
523
(27) Prada, L.; Miller, J., Reburning using several hydrocarbon fuels: a kinetic
524
modeling study. Combustion science and technology 1998, 132, (1-6), 225-250. 21
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
525
(28) Glarborg, P.; Alzueta, M. U.; Dam-Johansen, K.; Miller, J. A., Kinetic modeling
526
of hydrocarbon/nitric oxide interactions in a flow reactor. Combustion and flame 1998,
527
115, (1), 1-27.
528
(29) Dagaut, P.; Luche, J.; Cathonnet, M., The kinetics of C1 to C4 hydrocarbons/NO
529
interactions in relation with reburning. Proceedings of the Combustion Institute 2000,
530
28, (2), 2459-2465.
531
(30) Watanabe, H.; Yamamoto, J.-i.; Okazaki, K., NOx formation and reduction
532
mechanisms in staged O2/CO2 combustion. Combustion and flame 2011, 158, (7),
533
1255-1263.
534
(31) Giménez-López, J.; Aranda, V.; Millera, A.; Bilbao, R.; Alzueta, M., An
535
experimental parametric study of gas reburning under conditions of interest for
536
oxy-fuel combustion. Fuel Processing Technology 2011, 92, (3), 582-589.
537
(32) Normann, F.; Andersson, K.; Johnsson, F.; Leckner, B., Reburning in oxy-fuel
538
combustion: a parametric study of the combustion chemistry. Industrial &
539
Engineering Chemistry Research 2010, 49, (19), 9088-9094.
540
(33) Mendiara, T.; Glarborg, P., Reburn chemistry in oxy-fuel combustion of methane.
541
Energy & Fuels 2009, 23, (7), 3565-3572.
542
(34) Skjøth-Rasmussen, M. S.; Glarborg, P.; Østberg, M.; Johannessen, J.; Livbjerg,
543
H.; Jensen, A.; Christensen, T., Formation of polycyclic aromatic hydrocarbons and
544
soot in fuel-rich oxidation of methane in a laminar flow reactor. Combustion and
545
Flame 2004, 136, (1), 91-128.
546 547 548 549 22
ACS Paragon Plus Environment
Page 22 of 33
Page 23 of 33
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
550
Figure captions
551
Fig. 1. Schematic diagram of the experimental apparatus.
552
Fig. 2. Typical temperature profiles within the reactor.
553
Fig. 3. Experimental data and numerical predictions for different equivalence ratios
554
(fuel-rich (a), stoichiometric (b), and fuel-lean (c) conditions) as functions of reaction
555
temperature.
556
Fig. 4. Comparisons of H, O, and OH mole fraction profiles in the N2, CO2 and H2O
557
atmospheres for fuel-rich (a), stoichiometric (b) and fuel-lean (c) conditions at 1673
558
K.
559
Fig. 5. Comparison of the NO conversion pathways in N2 (a), CO2 (b) and H2O (c)
560
atmospheres for fuel-rich condition at 1673 K.
561
Fig. 6. OPRNO of critical reactions between nitric oxide and hydrocarbon in the N2,
562
CO2 and H2O atmospheres for fuel-rich (a), stoichiometric (b) and fuel-lean (c)
563
conditions at 1673 K.
564
Fig. 7. Comparison of the methane oxidation pathways in the N2 (a), CO2 (b) and H2O
565
(c) atmospheres for stoichiometric condition at 1673 K.
566
Fig. 8. OPRNO of critical reactions between nitric oxide and nitrogen-containing
567
radicals in the N2, CO2 and H2O atmospheres for fuel-rich (a), stoichiometric (b) and
568
fuel-lean (c) conditions at 1673 K.
569
Fig. 9. Experimental data and numerical predictions as functions of equivalence ratio
570
at 1673 K in the N2, CO2 and H2O atmospheres.
571 572
Table captions
573
Table 1. Experimental conditions in the present work.
574 23
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
575
Fig. 1. Schematic diagram of the experimental apparatus. 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 24
ACS Paragon Plus Environment
Page 24 of 33
Page 25 of 33
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
Fig. 2. Typical temperature profiles within the reactor. 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 25
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
a
b
c
Fig. 3. Experimental data and numerical predictions for different equivalence ratios (fuel-rich (a), stoichiometric (b), and fuel-lean (c) conditions) as functions of reaction temperature. 622 623 624 625 626 26
ACS Paragon Plus Environment
Page 26 of 33
Page 27 of 33
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
a
b
c
Fig. 4. Comparisons of H, O, and OH mole fraction profiles in the N2, CO2 and H2O atmospheres for fuel-rich (a), stoichiometric (b) and fuel-lean (c) conditions at 1673 K. 627 628 629 630 631 632 633 27
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
a
b
c
Fig. 5. Comparison of the NO conversion pathways in N2 (a), CO2 (b) and H2O (c) atmospheres for fuel-rich condition at 1673 K. 634 635 636 637 638 639 640
28
ACS Paragon Plus Environment
Page 28 of 33
Page 29 of 33
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
a
b
c
Fig. 6. OPRNO of critical reactions between nitric oxide and hydrocarbon in the N2, CO2 and H2O atmospheres for fuel-rich (a), stoichiometric (b) and fuel-lean (c) conditions at 1673 K. 641 642 643 644 645 646 647 648 649 650 29
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
a
Page 30 of 33
b
c
Fig. 7. Comparison of the methane oxidation pathways in the N2 (a), CO2 (b) and H2O (c) atmospheres for stoichiometric condition at 1673 K. 651 652 653 654 655 656
30
ACS Paragon Plus Environment
Page 31 of 33
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
a
b
c
Fig. 8. OPRNO of critical reactions between nitric oxide and nitrogen-containing radicals in the N2, CO2 and H2O atmospheres for fuel-rich (a), stoichiometric (b) and fuel-lean (c) conditions at 1673 K. 657 658 659 660 661 662 663 664 665 666 31
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Fig. 9. Experimental data and numerical predictions as functions of equivalence ratio at 1673 K in the N2, CO2 and H2O atmospheres. 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687
32
ACS Paragon Plus Environment
Page 32 of 33
Page 33 of 33
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
688 689
φ 1.6 1.0 0.2
CH4/ppm 2511 2505 2499
Table 1. Experimental conditions in the present work. NO/ppm O2/ppm N2 or CO2 or H2O(g)/% Residence time/s 1006 3147 99.34 2038/T(K) 1003 5062 99.15 2038/T(K) 998 24977 97.15 2038/T(K)
690
33
ACS Paragon Plus Environment
