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Detailed kinetic modeling of H2S formation during fuel-rich combustion of pulverized coal
Fuel Processing Technology 199 (2020) 106276
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Research article
Detailed kinetic modeling of H2S formation during fuel-rich combustion of pulverized coal
T
Honghe Maa, , Sichen Lva, Lu Zhoua, Jia Wei Chewb,c, , Jun Zhaod ⁎
⁎⁎
a
Department of Thermal Engineering, Taiyuan University of Technology, Taiyuan, Shanxi 030024, China School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459, Singapore c Singapore Membrane Technology Center, Nanyang Environment and Water Research Institute, Nanyang Technological University, Singapore 639798, Singapore d School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China b
ARTICLE INFO
ABSTRACT
Keywords: Detailed kinetic modeling H2S formation Fuel-rich combustion Pulverized coal Sensitivity analysis Rate of production analysis
The paper presents a detailed kinetic study on H2S formation during fuel-rich combustion of pulverized coal via tube furnace experiment and kinetic analysis with Chemkin. A new detailed kinetic model involving 34 species and 115 reactions was developed, with emphasis on CS2 as a source for H2S. The novel model was validated using experimental data with respect to the concentration distributions of H2, CO, H2O, CO2, SO2, H2S, COS and CS2. Sensitivity analysis shows that H2S concentration was very sensitive to reactions (2) H2S + H = SH + H2, (89) SO2 + CO = SO + CO2, (104) COS + H2O = H2S + CO2, (62) HOSO (+M) = H + SO2 (+M), (103) CS2 + H2O = H2S + COS, etc. Also, SH, S, and SO were the key free radicals for H2S production. Rate of production analysis (ROP) were also performed, which indicate that SH was the most important precursor of H2S. Based on the detailed kinetic model and ROP analysis, the simplified reaction path of H2S formation was constructed. Finally, the new model was compared with the Leeds University sulfur chemistry model. The two models have the same key free radicals and four major elementary reactions. The main difference is that CS2 was a notable source for H2S in our model targeted for coal combustion, and should be given special attention.
1. Introduction Various low-NOx combustion technologies, such as air-staged [1], fuel-staged [2] and low-NOx burners [3], are currently widely employed as primary methods to meet strict NOx emission regulations in coal-fired boilers. These technologies create fuel-rich zones and form a strong reducing atmosphere (e.g., H2, CO) in the region between the burners and the over-fire-air ports [4]. Thereby, high concentration of H2S is produced in this reducing atmosphere [5], causing sulfidation corrosion of the boiler water-wall [6]. For safe boiler operation, it is very important to accurately predict and control H2S distribution [7,8]. Therefore, it is of huge significance to understand the reaction mechanism of H2S formation during fuel-rich combustion of coal. Generally, the reaction mechanism is studied on three scales, namely, global reaction mechanism, detailed reaction mechanism and reduced reaction mechanism. The global mechanism model focuses on explaining the reaction process at the molecular level. To date, the global reactions for H2S generation during coal combustion have been extensively investigated. The involved sulfur species are SO2, H2S, COS,
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and CS2, and the reactants likely include H2, CO, H2O, CO2, etc. [9,10]. Zhang et al. [11] and Monaghan et al. [12] found that high concentration of H2S resulted from the reactions between the reductive gases (e.g. CO and H2) with SO2. Shirai et al. [13,14] studied the sulfur species distribution in a coal-fired furnace and proposed the global reaction of SO2 + 3H2 = H2S + 2H2O. Frigge et al. [15] proposed the reaction of COS + H2 = H2S + CO, and Abián et al. [16] further established the reaction between H2O and COS, as well as H2O and CS2, to produce H2S. These studies mainly directed attention on the reaction formulas between a single reductive gas and one sulfur gas. However, the actual process of H2S formation during coal combustion is very complex with simultaneous reactions of SO2, H2S, COS, CS2, CO, H2, H2O, CO2, etc. [17]. To improve this, Zhang et al. [18] developed a global sulfur species gas-phase reaction model that simultaneously considers the sulfur species of SO2, H2S, and COS, giving the mean error between the experimental and predicated results of approximately 25%. Ma et al. [19] further considered the presence of CS2 and built a comprehensive global mechanism model for H2S production, wherein the maximum error was reduced to within 20%. These models lay an
Corresponding author. Correspondence to: J. W. Chew, School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459, Singapore. E-mail addresses: [email protected] (H. Ma), [email protected] (J.W. Chew).
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https://doi.org/10.1016/j.fuproc.2019.106276 Received 9 September 2019; Received in revised form 23 October 2019; Accepted 5 November 2019 0378-3820/ © 2019 Elsevier B.V. All rights reserved.
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important foundation for further development of detailed mechanism models. In particular, the global mechanism model does not consider the influence of various intermediate radicals (e.g. SH, S, SO, HSO, etc.), and is not able to simulate the H2S formation over an adequate range with desired accuracy [20]. Thus, it is necessary to reveal the H2S formation from the level of detailed mechanism [21]. Unfortunately, up to now, no detailed kinetic model for H2S production in coal combustion has been built. Nevertheless, some detailed kinetic models in other combustion conditions (e.g. methane) have been proposed in past research. Among these models, the Leeds University sulfur mechanism greatly improved the understanding of the H2S formation process and is the most widely cited [18]. However, it does not consider the presence of CS2. As is well known, CS2 is released in the whole coal combustion process of volatile pyrolysis and char combustion, and its concentration ranges from tens to 200 ppm in fuel-rich condition [22]. Moreover, it can be easily converted into H2S [23]. Nevertheless, the critical H2S concentration for causing high-temperature-corrosion in the coal-fired boiler is only 100 ppm [24]. This means that the participation of CS2 has a great influence on H2S concentration and thus the high-temperature-corrosion. Therefore, the presence of CS2 should be taken into account in the detailed mechanism of H2S formation. Motivated by these issues, this work is undertaken to develop a new detailed chemical kinetic model for H2S formation during fuel-rich combustion of pulverized coal. Firstly, the effect of reaction temperature on H2S formation is investigated by kinetic simulation. Subsequently, sensitivity analysis and rate of production (ROP) analysis are performed to study the major production paths of H2S and several key radicals. Then, a simplified reaction path for H2S production is derived from the detailed mechanism. Finally, the comparison between the new detailed kinetic model and the Leeds University sulfur chemistry model is carried out. The new detailed kinetic model is expected to function as the benchmark for the development of the reduced kinetic model for H2S formation in coal combustion.
University sulfur chemistry model [18], and the elementary reactions involving CS2 and the parameters of third-bodies (M) also partially supplemented our new kinetics model [16]. Besides, the pre-factors of reactions of (6), (62) and (64) were updated to fit the experimental data of sulfur species distribution. During pulverized combustion, a large number of free radicals containing C, H or O were produced, and reacted with sulfur species. To account for these radicals, GRI-MECH 3.0 was chosen as the sub-mechanism for the C-H-O combustion system, because it has been validated by various experimental conditions (e.g. methane combustion, coal combustion, etc.). 3.2. Model description In this work, the new detailed chemical reaction mechanism was firstly used to give predictions for H2S formation during fuel-rich combustion of pulverized coal by CHEMKIN-PRO. In this work, the furnace was a tube flow reactor with a large length to diameter ratio, and the viscosity of the flue gas is as low as 4.6 × 10−6 Pa·s. Thus, the flue flow in the furnace can be treated as plug flow. This means there was no mixing in the axial direction but perfect mixing in the direction transverse to this, and the laminar and/or turbulent mass diffusion was neglected. Moreover, in the direction perpendicular to flue gas flow, it was assumed that there was no gradient in velocity, temperature, pressure, or composition, and both physical and chemical properties were very uniform. When tube flow reactors are carried out in steadystate and continuous flow condition, the plug flow reactor (PFR) model in the software is efficient in working out the related problems [25]. So, the PFR model was adopted for the calculation in this work. The calculation domain was determined according to the real experimental geometric configuration and reaction conditions. All major species and sulfur species were considered as ideal gas and frictionless, and the viscous terms in the conservation equations for pressure and velocity were ignored [26]. The reactor wall was treated as non-catalytic. All chemistry processes were assumed to be homogeneous, with surface reaction completely eliminated in the system. The mass continuity and energy continuity equations can be written as follows. Mass continuity equation:
2. Experimental section Fig. 1 shows the schematic diagram of an 18 kW electrically heated pulverized coal-fired entrained flow furnace (2200 mm in length and 150 mm in inner diameter), with Z referring to the axial distance from the low-NOx burner exit. The detailed information of the furnace and procedure is described in our previous work [19]. To avoid repetition, it is not described here. Experimental results show that sulfur release just finished at Z = 450 mm for Daheng coal above 1373 K. Therefore, in this work, the flue gas composition of Z = 450 mm was assumed as the starting point of the gas-phase reactions, and the tests and simulations were executed only in the region from Z = 450 mm to Z = 2200 mm. The reaction conditions are summarized as in Table 1, and the experimental data are listed in Appendix A. In this work, O2, CO, CO2, and H2 were detected by a gas chromatography system with thermal conductivity detectors (SP 3420A), and SO2, H2S, COS and CS2 were measured by another gas chromatography system (Agilent 3000A Micro GC). The lower detection limits of all species were approximately 1 ppm. The axial position was determined according to the insertion depth of the sampling pipe. Considering installation error, the uncertainties in axial location Z was about ± 5 mm, which was assumed to be sufficiently little for this study.
u
d dA du + A + uA =0 dx dx dx
(1)
where ρ, u, and A are respectively the mass density, axial velocity of the flue gas, and cross-sectional area. Energy continuity equation: kg
uA
hk k=1
dYk dT du + Cp +u = ae Qe dx dx dx
(2)
where hk is the specific enthalpy of species k; Yk refers to the mass fraction of species k; Cp represents the mean heat capacity per unit mass of the flue gas; T is the absolute flue gas temperature; Qe refers to the heat flux from the surroundings outer tube wall; and ae represents the surface area per unit length. 3.3. Model validation The predicted data were compared to experimental results in the entrained flow furnace to validate the numerical method. Fig. 2 presents the predicted and measured concentration profiles of CO, H2, CO2, and H2O along the furnace axis. Because GRI-MECH 3.0 was adopted for the C-H-O combustion system in both our and Leeds University models, the predicated results of the major species by the two models were almost the same with each other. Thus, only the predicted data by our model were illustrated in Fig. 2. Clearly, both experimental and calculated results on the axial variation of the major species agree well. The maximum relative error was less than 8%, which indicates that
3. Numerical approach 3.1. Reaction mechanism As listed in Appendix B, a new detailed kinetic mechanism was developed including 34 species and 115 elementary reactions in CHEMKIN format to describe the H2S formation during fuel-rich combustion of pulverized coal. Our new model was based on the Leeds 2
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Fig. 1. The schematic diagram of electrically heated pulverized coal-fired entrained flow furnace. Table 1 Reaction conditions. Inlet gas composition N2 CH4, % CO, % H2, % H2O, % CO2, % NO, ppm SO2, ppm H2S, ppm COS, ppm CS2, ppm Mass rate of flue gas, kg·h−1 Pressure, kPa Reaction temperature, K
Balance gas 2.13 5.20 3.26 7.74 16.68 448 876 132 108 71 3.32 91.92 1373–1673
GRI-MECH 3.0 can provide accurate predictions for the fuel-rich combustion of pulverized coal. The measured and calculated concentration profiles of sulfur species along the furnace axis are shown in Fig. 3. It can be seen that both measured result and predicated result by our model on the axial variation of sulfur species agree well. Most relative errors between predicted by our model and measured values were within 5%, and the maximum relative error was less than 15%. Therefore, the detailed
Fig. 2. Comparison between the predicted and experimental results of major species at 1473 K.
modeling method in this work was validated, and shown to provide accurate predictions for gas-phase reactions of sulfur species during fuel-rich combustion. Additionally, the calculated results by Leeds University model are also presented in Fig. 3. The predicated data shows a similar change trend with the experimental values. Even 3
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Fig. 3. Comparison between the predicted and experimental results of sulfur species at 1473 K.
though not involved in any reactions, CS2 was still treated as a reactant with the same initial concentration as that in our model. That is why its concentration nearly kept constant. The calculated H2S concentration was significantly lower than the measured data with the maximal error was as large as 32%. Therefore, the updating of Leeds University model is necessary and the participation of CS2 should not be ignored during coal combustion. 4. Results and discussion 4.1. Effect of reaction temperature on H2S concentration The influence of temperature on the H2S distribution is shown in Fig. 4. The H2S concentrations were similar initially regardless of temperature, but subsequently increased faster at higher temperatures. This is because that H2S release from coal just finished, and the gasphase reaction started. Further away from the burner, the H2S concentration became relatively unchanged with Z. In brief, the formation of H2S was obviously affected by the temperature in the range of calculation. The higher temperature significantly promoted the formation of H2S, not only the final value of H2S concentration but also the rate of increase. This result agrees well with the experiments [19]. The reason may be attributed to the reactions (R2), (R4), (R14), and (R17), etc. [27,28]. Reactions (R2), (R4) and (R14) are exothermic, and reaction (R17) is endothermic. With an increase of temperature, the equilibriums of reactions (R2), (R4) and (R14) shifted to the left, and that of reaction (R17) to the right. Therefore, more H2S was directly produced via reactions (R2) and (R4). Furthermore, more S, another important source of H2S [29], was also generated by reactions (R14) and (R17), and thus promoted the formation of H2S [30]. The S concentration was very low with the maximum of less than 0.05 ppm. In fact, the concentration was so low that it could be determined only by numerical method. It indicates that S was an important intermediate, and its consumption rate was nearly equal to the formation rate.
H2 S + H = SH + H2
(R2)
H2 S + OH = SH + H2 O
(R4)
S + OH = H + SO
(R14)
S2 + M = S + S + M
(R17)
Fig. 4. Concentrations of H2S, S, CS2 versus axial distance at various temperatures.
concentration was up to 60 ppm, which could produce significant impact on high-temperature-corrosion. Therefore, the presence of CS2 should be taken into account during coal combustion. 4.2. Sensitivity analysis Sensitivity analysis was performed on the kinetic model using the SENKIN code in Chemkin-Pro software. This code produces the ranking of all reactions in our new detailed mechanism, from the most sensitive to the least sensitive, to provide the valuable information on the principal pathways in H2S formation during fuel-rich combustion of pulverized coal. The protocol and principle employed is detailed elsewhere [31]. The definition of sensitivity coefficients is written as Eq. (3),
S=
kj ci = ci kj
ln ci ln kj
(3)
where S is the sensitivity coefficient; kj represents the reaction rate constant of the jth elementary reaction; ci represents the H2S concentration of the special axial position. When the sensitivity coefficient is positive, it means that an increase in the forward reaction rate increases the H2S concentration, thereby promoting reactivity. Conversely, a negative sensitivity coefficient implies a decrease in H2S concentration. As shown in Fig. 5(a), the H2S concentration was sensitive to reactions (2), (89), (104), (62), (103), (74), and (57) at 1373 K, but the functions of the elementary reactions changed with the axial distance Z. H2S concentration was sensitive to reaction (2) within Z = 550 mm, and to reactions (89), (104), (62), (103), (74), and (57) after Z = 550 mm. The sensitivity of these reactions was considerably higher
Additionally, as a new specie in our kinetic model, CS2 is also an interesting sulfur specie. Fig. 4 shows that CS2 concentration remained at the level of no more than 100 ppm along the axis of the furnace within the scope of calculation in this work. That is because the initial value was only 71 ppm. However, the largest change range of CS2 4
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Fig. 5. H2S sensitivity versus axial distance from the burner, where (a) at 1373 K; (b) at 1473 K; (c) at 1573 K; (d) at 1673 K.
than that of reactions of (71), (64) and (111), which only had a weak influence on H2S concentration [32]. This indicates that when the high temperature and reducing atmosphere prevail, radicals SH, S and SO were the key intermediate radicals for H2S production. Also, the functions of elementary reactions changed with reaction temperature, as demonstrated in Fig. 5(b), (c) and (d). When the temperature increased, the positive sensitivity of reaction (89) to H2S formation increased, while that to reactions of (103), (104) and (64) decreased. This is because reaction (89) is endothermic, and reactions of (103), (104) and (64) are exothermic. As the temperature elevated above 1473 K, reaction (7) had a dominant role in H2S consumption within Z = 1100 mm. This may be attributed to the rapid consumption of S for an instant before the triggering of the production of H2S from SH. Beyond Z = 1100 mm, reaction (7) nearly showed no influence on H2S concentration. Additionally, the H2S concentration always showed obvious sensitivity to reaction (103) when the temperature increased from 1373 K to 1673 K, and Z from 450 mm to 2200 mm. This implies that CS2 was a notable sulfur species for H2S formation, and should be taken into account for sulfur evolution during coal combustion.
target species to be studied via ROP analysis. The ROP profiles are presented in Fig. 5. Not all relevant elementary reactions are shown. If the production rate of a reaction for interesting specie was distinctly lower than that of the main contribution reactions, this reaction was not exhibited. Therefore, the number of related elementary reactions varied for different target species. As demonstrated in Fig. 6(a), representative reactions were plotted with respect to their contributions to the production rate of H2S. Reaction (2) was the most important path for H2S production, and reactions (4), (5), (103) and (104) played a secondary role. This indicates that the SH radical played a vital and active role in H2S production. Moreover, it again suggests that CS2 exhibited a considerable role in H2S formation. Meanwhile, the consumption of H2S occurred mainly via the reaction (1) [34], while the collision of S and H2 could reproduce H2S [35]. Therefore, the S radical was an important intermediate during H2S decomposition or production [36]. The ROP analysis of SH is clearly displayed in Fig. 6(b). It clearly indicates that the reaction between S and H2 was the paramount path to SH production (i.e., reaction (7)). Additionally, HSOH was also a source of SH, and the reaction is presented as (47). For SH consumption, reactions (2) and (5) were the major paths, and reaction (4) was also considerable [37]. It is worth noting that the key product of all the three reactions was H2S. This again indicates that SH was the most important precursor of H2S. As shown in Fig. 6(c), S production was originated from decomposition of H2S via reaction (1) and the collision of SH [34]. Additionally, the decomposition of SO via reaction (71) was a minor route to generate S. On the other hand, S consumption took place mainly through reaction (7) to produce SH [38]. Apart from this, the conversion of S to HSOH was also a possible path for S consumption.
4.3. Rate-of-production analysis ROP analysis is useful in understanding the contribution of each elementary reaction to the net production or consumption of the species of interest. A positive production rate value indicates this reaction contributes to the formation of the target species [33]. Conversely, a negative production rate means the reaction contributes to the consumption of the target species. Since radicals S, SH, and SO were the key intermediate radicals for H2S formation, they were chosen as the 5
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Fig. 6. Rate of production of target species versus axial distance under 1473 K.
Fig. 6(d) suggests that SO2 and HOSO were the major sources for SO formation, and the corresponding path were reactions (89) and (74), respectively. Besides that, the decomposition of HOSHO was also an important way for SO production (cf. reaction (58)). Instead, SO consumption mainly occurred via reaction (71) to produce S, and reaction (14) was also an alternative path. Thus, SO was a key intermediate radical [39]. Thus, under fuel-rich condition, SO2 dissociated to SO, and further reduced to form SH and H2S, while SO2 was reproduced for SO oxidation in an oxygen-rich atmosphere [40]. 4.4. Reaction path diagram As shown in Fig. 7, the H2S formation path during fuel-rich combustion of pulverized coal was constructed based on our new detailed reaction mechanism in Appendix B, sensitivity analysis and ROP analysis. The path clearly presented the interactions among the elements in the flue gas. The reactions with the widest red arrows had the fastest reaction rate. The moderately thick blue arrows represent the reactions with fast reaction rate other than those with red arrows. SO, S and SH were the key free radicals for H2S formation. After SO2 converted into S, H2S production followed two major paths. First, S reacted with H2 to generate SH, and then the collision of two SH produced H2S. Second, S was converted into HSOH by H2O attack, and further formed SH. Subsequently, H2S was formed from the reaction between SH and H2. Apart from that, H2S could also be produced from CS2 and COS respectively by reactions (103) and (104), which had a considerable reaction rate (with moderate thick blue arrows). Therefore, the participation of CS2 had notable influence on H2S distribution, and thus CS2 should not be ignored in the sulfur mechanism during fuel-rich combustion of coal.
Fig. 7. Simplified reaction path diagram of formation of H2S.
4.5. Comparison with the Leeds University sulfur chemistry model A comparison was conducted between our new model and the Leeds University sulfur chemistry model at the same reaction conditions, as listed in Table 2. Since our model was established based on the Leeds University model, the two models had some distinctly similar characteristics. First of all, they have the same key free radicals, namely, SH, S, and SO. Furthermore, the four major elementary reactions in the two models also have high levels of consistency. This again demonstrates that the Leeds University sulfur chemistry model has extensive applicability, and is suitable to be adopted as benchmark for development of other sulfur species reaction mechanism models. 6
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the key free radicals for H2S production. ROP analysis shows that the SH radical played a vital and active role in H2S production, and CS2 exhibited a considerable role for H2S formation. SH was the most important precursor of H2S. Reaction (7) S + H2 = SH + H was the paramount path to SH production, and SH consumption was mainly via reactions (2) H2S + H = SH + H2 and (5) H2S + S = SH + SH. S production originated from the decomposition of H2S and the collision of two SH radicals, while S consumption took place mainly through reaction (7) S + H2 = SH + H. SO was the key intermediate radical for SO2 converted into S. SO2 and HOSO were the major sources for SO formation, while reaction (71) SO + M = S + O + M dominated SO consumption to generate S. Compared with the Leeds University sulfur chemistry model, our model had the same key free radicals (e.g. SH, S, and SO) and four major elementary reactions. On the other hand, some differences exist between the two models. In our model, CS2 was a notable source of H2S, which is specific for coal combustion. Moreover, the hydrocarbon functional groups (CH3, CH4) played a greater role in the Leeds University sulfur chemistry model. The development of detailed mechanism is a fundamental and significant step in understanding and predicting gas-phase reaction process for H2S formation in coal combustion. In the next work, our detailed kinetic model will be reduced and combined with a computational fluid dynamic model to investigate the whole sulfur evolution during coal combustion.
Table 2 Comparison between our H2S formation model and Leeds University sulfur chemistry model. Our new detailed model
Leeds University model
Key free radicals The same major elementary reactions
S, SH, SO 1. H2S + M = S + H2 + M 2. H2S + H=SH + H2 7. S + H2 = SH + H 89. SO2 + CO=SO+CO2
Different major elementary reactions
62. HOSO(+M) = H + SO2(+M) 71. SO+M = S + O + M 74. SO+OH(+M) = HOSO(+M) 103. CS2 + H2O=H2S + COS 104. COS + H2O=H2S + CO2 111. SO2 + 3CO=COS + 2CO2
S, SH, SO L1. H2S + M = S + H2 + M L2. H2S + H=SH + H2 L7. S + H2 = SH + H L27. SO2 + CO=SO+CO2 L4. H2S + OH=SH + H2O L5. H2S + S=SH + SH L33. 2SO=SO2 + S L49. HSOH=SH + OH L50. HSOH=S + H2O L76. S + CH4 = SH + CH3 L77. H2S + CH3 = CH4 + SH
On the other hand, there exists some differences between the two models. In our model, CS2 was taken into account, which, as well as COS, was indeed a considerable source of H2S (cf. reactions (103) and (104)). This is the advance made in our model for use in coal-fired boilers. Additionally, the hydrocarbon functional groups (CH3, CH4) played a greater role in the Leeds University sulfur chemistry model (cf. reactions L76 and L77). This may be because the Leeds university model was built in methane combustion condition, but methane concentration is relatively lower during coal combustion.
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
5. Conclusion A detailed kinetic model for the H2S formation during fuel-rich combustion of pulverized coal was developed. The validity of the model was verified by experimental data. The effect of reaction temperature on H2S production was also investigated, with results showing that the production of H2S was significantly elevated with temperature. Sensitivity analysis indicates that H2S concentration showed high sensitivity to reactions (2) H2S + H = SH + H2, (89) SO2 + CO = SO + CO2, (104) COS + H2O = H2S + CO2, (62) HOSO (+M) = H + SO2 (+M), (103) CS2 + H2O = H2S + COS, etc. Also, S, SH, and SO were
Acknowledgements The work was supported by the National Natural Science Foundation of China (Grant No. 51706151); Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi (STIP) (Grant No. 2019L0147); and Major Special Projects for the Innovative Demonstration Zone Construction of National Sustainable Development Agenda in Taiyuan.
Appendix A. Measured species distribution along the axis of the furnace Z, mm
CO, %
H2, %
CO2, %
450 550 750 900 1200 1600 2100
T = 1373 K 5.20 5.26 5.47 5.58 5.74 5.91 6.05
3.26 3.34 3.65 3.77 3.92 4.06 4.13
16.68 16.63 16.31 16.29 16.02 15.84 15.67
450 550 750 900 1200 1600 2100
T = 1473 K 5.20 6.12 6.88 6.94 7.08 7.16 7.21
3.26 3.64 3.91 4.18 4.53 4.62 4.68
450 550 750 900 1200
T = 1573 K 5.20 6.96 7.91 8.32 8.79
3.26 4.94 4.92 4.89 4.87
H2O, %
SO2, ppm
H2S, ppm
COS, ppm
CS2, ppm
7.74 7.79 7.98 8.13 8.24 8.40 8.54
876 849 778 723 715 684 680
132 140 149 171 241 248 254
108 112 120 132 151 170 191
71 93 86 72 67 65 60
16.68 15.38 15.96 16.26 16.21 16.06 15.82
7.74 7.87 7.78 7.69 7.61 7.56 7.49
876 795 728 664 637 630 626
132 189 223 267 286 308 318
108 125 146 168 180 189 201
71 77 86 87 88 56 42
16.68 14.58 13.54 13.17 12.76
7.74 9.20 9.96 10.32 10.63
876 755 688 664 607
132 197 288 359 456
108 110 123 131 167
71 75 60 57 51
7
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9.16 9.45 T = 1673 K 5.20 8.77 9.94 10.43 7.08 7.16 7.21
4.88 4.93
12.35 12.17
10.84 11.06
504 396
463 478
205 235
46 39
3.26 5.15 5.03 5.08 4.53 4.62 4.68
16.68 12.76 11.62 11.34 16.21 16.06 15.82
7.74 10.53 11.34 11.48 7.61 7.56 7.49
876 714 593 504 389 267 210
132 244 377 464 556 579 586
108 113 125 141 167 184 190
71 72 55 50 44 38 32
Appendix B. Detailed reaction mechanism for H2S formation during fuel-rich combustion of coal k = A Tb exp(-E/RT) Reactions 1.
H2S+M=S+H2+M
2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19 20. 21. 22. 23.
H2S+H=SH+H2 H2S+O=SH+OH H2S+OH=SH+H2O H2S+S=SH+SH H2S+S=HS2+H S+H2=SH+H SH+O=H+SO SH+OH=S+H2O SH+HO2=HSO+OH SH+O2=HSO+O SH+O2=SO+OH SH+O=S+OH S+OH=H+SO SH+SH=S2+H2 SH+S=S2+H S2+M=S+S+M S2+H+M=HS2+M HS2+H=S2+H2 HS2+O=S2+OH HS2+OH=S2+H2O HS2+S=S2+SH HS2+H+M=H2S2+M
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.
H2S2+H=HS2+H2 H2S2+O=HS2+OH H2S2+OH=HS2+H2O H2S2+S=HS2+SH HSO+H=HSOH HSO+H=SH+OH HSO+H=S+H2O HSO+H=H2SO HSO+H=H2S+O HSO+H=SO+H2 HSO+O+M=HSO2+M HSO+O=SO2+H HSO+O+M=HOSO+M HSO+O=O+HOS HSO+O=OH+SO HSO+OH=HOSHO HSO+OH=HOSO+H HSO+OH=SO+H2O HSO+O2=SO2+OH HSO2+OH=SO2+H2O HSO2+H=SO2+H2 HSO2+O2=HO2+SO2 H2SO=H2S+O HSOH=SH+OH HSOH=S+H2O HSOH=H2S+O HOSO2=HOSO+O HOSO2=SO3+H HOSO2+H=SO2+H2O HOSO2+O=SO3+OH HOSO2+OH=SO3+H2O
A 1.60E+24 N2 enhanced by 1.500E+00 SO2 enhanced by 1.000E+01 H2O enhanced by 1.000E+01 1.20E+07 7.50E+07 2.70E+12 8.30E+13 7.00E+11 1.40E+14 1.00E+14 1.00E+13 1.00E+12 1.90E+13 1.00E+12 6.30E+11 4.00E+13 9.10E+10 2.13E+13 2.47E+17 3.50E+11 1.20E+00 2.46E+06 2.90E+09 2.15E+08 1.00E+16 N2 enhanced by 1.500E+00 SO2 enhanced by 1.000E+01 H2O enhanced by 1.000E+01 1.20E+07 7.50E+07 2.70E+12 8.30E+13 2.50E+20 4.90E+19 1.60E+09 1.80E+17 1.10E+06 1.00E+13 1.10E+19 4.50E+14 6.90E+19 4.80E+08 1.40E+13 5.20E+28 5.30E+07 1.70E+09 1.00E+12 1.00E+13 3.00E+13 1.10E+03 4.90E+28 2.80E+39 5.80E+29 9.80E+16 5.40E+18 1.40E+18 1.00E+12 5.00E+12 1.00E+12
8
b
E
-2.6
44800
2.1 1.8 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5 0.0 0.0 0.0 0.0 0.0 2.0 1.8 0.0 0.0 0.0
350 1460 0 3700 3723.8 9700 0 0 0 9000 5032.5 4030.6 0 0 0 77000 0 700.0 2900 0 7400 0
2.1 1.8 0.0 0.0 -3.1 -1.9 1.4 -2.5 1.0 0.0 -1.7 -0.4 -1.6 1.0 0.1 -5.4 1.6 1.0 0.0 0.0 0.0 0.0 -6.7 -8.8 -5.6 -3.4 -2.3 -2.9 0.0 0.0 0.0
360 1460 0 3700 460 785 -170 25 5230 0 -25 0 800 2700 150 1600 1900 235 5000 0 0 0 71700 37800 27400 43500 53500 27600 0 0 0
Fuel Processing Technology 199 (2020) 106276
H. Ma, et al. 55. 56. 57. 58. 59. 60. 61. 62.
HOSO2+O2=HO2+SO3 HOSO2+H=SO3+H2 HOSHO=HOSO+H HOSHO=SO+H2O HOSHO+H=HOSO+H2 HOSHO+O=HOSO+OH HOSHO+OH=HOSO+H2O HOSO(+M)=H+SO2(+M)
63. 64. 65. 66. 67. 68.
HOSO+O2=SO2+HO2 HOSO+H=SO2+H2 HOSO+H=SO+H2O HOSO+M=O+HOS+M HOSO+OH=SO2+H2O HOSO(+M)=HSO2(+M)
69. 70. 71.
SO2+OH=HOSO+O SO3+SO=2SO2 SO+M=S+O+M
72. 73. 74.
S+O2=SO+O S2+O=SO+S SO+OH(+M)=HOSO(+M)
75.
SO+O(+M)=SO2(+M)
76. 77.
SO+O2=SO2+O SO2+O(+M)=SO3(+M)
78.
SO2+O(+N2)=SO3(+N2)
79. 80.
SO2+OH=SO3+H SO+H+M=HSO+M
81. 82. 83.
SO3+O=SO2+O2 SO3+OH=SO2+HO2 SO2+OH(+M)=HOSO2(+M)
84. 85. 86. 87. 88. 89 90. 91. 92. 93. 94. 95. 96. 97.
SO3+S=SO+SO2 SO3+H2O=H2SO4 SO3+H=HOSO+O 2SO=SO2+S C+SO2=CO+SO SO2+CO=SO+CO2 CO+SO=CO2+S SO+HO2=SO2+OH SO+OH=SO2+H O+CS2=CS+SO O+CS=CO+S O+CS2=CO+S2 O+CS2=COS+S S+CS2=CS+S2
7.80E+11 0.0 1.00E+12 0.0 6.40E+30 -5.9 1.20E+24 -3.6 1.00E+12 0.0 5.00E+12 0.0 1.00E+12 0.0 1.95E+10 0.8 Low pressure limit: 0.15000E+32 -0.45300E+01 0.49178E+05 TROE centering: 0.30000E+00 0.10000E-29 0.10000E+31 N2 enhanced by 1.000E+00 SO2 enhanced by 1.000E+01 H2O enhanced by 1.000E+01 1.00E+12 0.0 2.08E+13 0.0 6.30E-10 6.3 2.50E+30 -4.8 1.00E+12 0.0 1.00E+09 1.0 Low pressure limit: 0.17000E+36 -0.56400E+01 0.55400E+05 TROE centering: 0.40000E+00 0.10000E-29 0.10000E+31 N2 enhanced by 1.000E+00 SO2 enhanced by 1.000E+01 H2O enhanced by 1.000E+01 3.90E+08 1.9 1.00E+12 0.0 4.00E+14 0.0 N2 enhanced by 1.500E+00 SO2 enhanced by 1.000E+01 H2O enhanced by 1.000E+01 5.20E+06 1.8 1.00E+13 0.0 1.60E+12 0.5 Low pressure limit: 0.95000E+28 -0.34800E+01 0.97000E+03 N2 enhanced by 1.500E+00 SO2 enhanced by 1.000E+01 H2O enhanced by 1.000E+01 3.20E+13 0.0 Low pressure limit: 0.12000E+22 -0.15400E+01 0.00000E+00 TROE centering: 0.55000E+00 0.10000E-29 0.10000E+31 N2 enhanced by 1.500E+00 SO2 enhanced by 1.000E+01 H2O enhanced by 1.000E+01 7.60E+03 2.4 9.20E+10 0.0 Low pressure limit: 0.24000E+28 -0.36000E+01 0.51860E+04 TROE centering: 0.44200E+00 0.31600E+03 0.74420E+04 SO2 enhanced by 1.000E+01 H2O enhanced by 1.000E+01 N2 enhanced by 0.000E+00 3.70E+11 0.0 Low pressure limit: 0.29000E+28 -0.35800E+01 0.52060E+04 TROE centering: 0.43000E+00 0.37100E+03 0.74420E+04 4.90E+02 2.7 5.00E+15 0.0 N2 enhanced by 1.500E+00 SO2 enhanced by 1.000E+01 H2O enhanced by 1.000E+01 2.00E+12 0.0 4.80E+04 2.5 5.70E+12 -0.3 Low pressure limit: 0.17000E+28 -0.40900E+01 0.00000E+00 TROE centering: 0.10000E+01 0.10000E-29 0.41200E+03 N2 enhanced by 1.000E+00 SO2 enhanced by 5.000E+00 H2O enhanced by 5.000E+00 5.12E+11 0.0 7.23E+08 0.0 2.50E+05 2.9 2.00E+12 0.0 4.16E+13 0.0 2.70E+12 0.0 5.10E+13 0.0 3.70E+03 2.4 1.08E+17 -1.4 3.60E+13 0.0 1.63E+14 0.0 1.70E+12 0.0 7.10E+12 0.0 2.40E+12 0.0
9
330 0 37100 30000 0 0 0 46933
500.0 0 -960 60000 0 50000
38200 5000 54000
-600 0 -400
0
1500 1200
1689 12000 0
10000 27225 0
0 0 25300 2000 0 24300 53400 7660 0 1696 760.2 1194 2102 4060
Fuel Processing Technology 199 (2020) 106276
H. Ma, et al. 98. 99. 100. 101. 102. 103. 104. 105. 106. 107. 108. 109.
CS2+O2=CS+SO2 CS+O2=COS+O CS+O2=CO+SO CS2+OH=COS+SH COS+OH=CO2+SH CS2+H2O=H2S+COS COS+H2O=H2S+CO2 CS2+SO=COS+S2 CO+SH=COS+H COS+S=CO+S2 COS+M=CO+S+M CS+S(+M)=CS2(+M)
110. 111. 112. 113. 114. 115.
CS+SH=CS2+H SO2+3CO=COS+2CO2 C+H2S=CH+SH O+COS=CO+SO O+COS=CO2+S CH+SO=CO+SH
1.00E+12 0.0 6.10E+12 0.0 6.10E+12 0.0 5.79E+08 0.0 7.90E+08 0.0 1.74E+11 0.0 1.71E+10 0.0 6.90E+05 0.0 2.87E+07 0.0 3.14E+00 2.6 6.88E+06 0.0 1.90E+26 -4.3 Low pressure limit: 0.62000E+24 -0.24200E+01 0.00000E+00 1.20E+13 0.0 8.60E+12 0.0 1.20E+14 0.0 1.93E+13 0.0 5.00E+13 0.0 1.00E+13 0.0
31050 16500 16500 -1174 0 41497 35299 -6339 15200 2345 30700 0 0 87700 4450.3 2328.6 5530.4 0
Units: mol, cm, s, K, cal.
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Research article
Detailed kinetic modeling of H2S formation during fuel-rich combustion of pulverized coal
T
Honghe Maa, , Sichen Lva, Lu Zhoua, Jia Wei Chewb,c, , Jun Zhaod ⁎
⁎⁎
a
Department of Thermal Engineering, Taiyuan University of Technology, Taiyuan, Shanxi 030024, China School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459, Singapore c Singapore Membrane Technology Center, Nanyang Environment and Water Research Institute, Nanyang Technological University, Singapore 639798, Singapore d School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China b
ARTICLE INFO
ABSTRACT
Keywords: Detailed kinetic modeling H2S formation Fuel-rich combustion Pulverized coal Sensitivity analysis Rate of production analysis
The paper presents a detailed kinetic study on H2S formation during fuel-rich combustion of pulverized coal via tube furnace experiment and kinetic analysis with Chemkin. A new detailed kinetic model involving 34 species and 115 reactions was developed, with emphasis on CS2 as a source for H2S. The novel model was validated using experimental data with respect to the concentration distributions of H2, CO, H2O, CO2, SO2, H2S, COS and CS2. Sensitivity analysis shows that H2S concentration was very sensitive to reactions (2) H2S + H = SH + H2, (89) SO2 + CO = SO + CO2, (104) COS + H2O = H2S + CO2, (62) HOSO (+M) = H + SO2 (+M), (103) CS2 + H2O = H2S + COS, etc. Also, SH, S, and SO were the key free radicals for H2S production. Rate of production analysis (ROP) were also performed, which indicate that SH was the most important precursor of H2S. Based on the detailed kinetic model and ROP analysis, the simplified reaction path of H2S formation was constructed. Finally, the new model was compared with the Leeds University sulfur chemistry model. The two models have the same key free radicals and four major elementary reactions. The main difference is that CS2 was a notable source for H2S in our model targeted for coal combustion, and should be given special attention.
1. Introduction Various low-NOx combustion technologies, such as air-staged [1], fuel-staged [2] and low-NOx burners [3], are currently widely employed as primary methods to meet strict NOx emission regulations in coal-fired boilers. These technologies create fuel-rich zones and form a strong reducing atmosphere (e.g., H2, CO) in the region between the burners and the over-fire-air ports [4]. Thereby, high concentration of H2S is produced in this reducing atmosphere [5], causing sulfidation corrosion of the boiler water-wall [6]. For safe boiler operation, it is very important to accurately predict and control H2S distribution [7,8]. Therefore, it is of huge significance to understand the reaction mechanism of H2S formation during fuel-rich combustion of coal. Generally, the reaction mechanism is studied on three scales, namely, global reaction mechanism, detailed reaction mechanism and reduced reaction mechanism. The global mechanism model focuses on explaining the reaction process at the molecular level. To date, the global reactions for H2S generation during coal combustion have been extensively investigated. The involved sulfur species are SO2, H2S, COS,
⁎
and CS2, and the reactants likely include H2, CO, H2O, CO2, etc. [9,10]. Zhang et al. [11] and Monaghan et al. [12] found that high concentration of H2S resulted from the reactions between the reductive gases (e.g. CO and H2) with SO2. Shirai et al. [13,14] studied the sulfur species distribution in a coal-fired furnace and proposed the global reaction of SO2 + 3H2 = H2S + 2H2O. Frigge et al. [15] proposed the reaction of COS + H2 = H2S + CO, and Abián et al. [16] further established the reaction between H2O and COS, as well as H2O and CS2, to produce H2S. These studies mainly directed attention on the reaction formulas between a single reductive gas and one sulfur gas. However, the actual process of H2S formation during coal combustion is very complex with simultaneous reactions of SO2, H2S, COS, CS2, CO, H2, H2O, CO2, etc. [17]. To improve this, Zhang et al. [18] developed a global sulfur species gas-phase reaction model that simultaneously considers the sulfur species of SO2, H2S, and COS, giving the mean error between the experimental and predicated results of approximately 25%. Ma et al. [19] further considered the presence of CS2 and built a comprehensive global mechanism model for H2S production, wherein the maximum error was reduced to within 20%. These models lay an
Corresponding author. Correspondence to: J. W. Chew, School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637459, Singapore. E-mail addresses: [email protected] (H. Ma), [email protected] (J.W. Chew).
⁎⁎
https://doi.org/10.1016/j.fuproc.2019.106276 Received 9 September 2019; Received in revised form 23 October 2019; Accepted 5 November 2019 0378-3820/ © 2019 Elsevier B.V. All rights reserved.
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H. Ma, et al.
important foundation for further development of detailed mechanism models. In particular, the global mechanism model does not consider the influence of various intermediate radicals (e.g. SH, S, SO, HSO, etc.), and is not able to simulate the H2S formation over an adequate range with desired accuracy [20]. Thus, it is necessary to reveal the H2S formation from the level of detailed mechanism [21]. Unfortunately, up to now, no detailed kinetic model for H2S production in coal combustion has been built. Nevertheless, some detailed kinetic models in other combustion conditions (e.g. methane) have been proposed in past research. Among these models, the Leeds University sulfur mechanism greatly improved the understanding of the H2S formation process and is the most widely cited [18]. However, it does not consider the presence of CS2. As is well known, CS2 is released in the whole coal combustion process of volatile pyrolysis and char combustion, and its concentration ranges from tens to 200 ppm in fuel-rich condition [22]. Moreover, it can be easily converted into H2S [23]. Nevertheless, the critical H2S concentration for causing high-temperature-corrosion in the coal-fired boiler is only 100 ppm [24]. This means that the participation of CS2 has a great influence on H2S concentration and thus the high-temperature-corrosion. Therefore, the presence of CS2 should be taken into account in the detailed mechanism of H2S formation. Motivated by these issues, this work is undertaken to develop a new detailed chemical kinetic model for H2S formation during fuel-rich combustion of pulverized coal. Firstly, the effect of reaction temperature on H2S formation is investigated by kinetic simulation. Subsequently, sensitivity analysis and rate of production (ROP) analysis are performed to study the major production paths of H2S and several key radicals. Then, a simplified reaction path for H2S production is derived from the detailed mechanism. Finally, the comparison between the new detailed kinetic model and the Leeds University sulfur chemistry model is carried out. The new detailed kinetic model is expected to function as the benchmark for the development of the reduced kinetic model for H2S formation in coal combustion.
University sulfur chemistry model [18], and the elementary reactions involving CS2 and the parameters of third-bodies (M) also partially supplemented our new kinetics model [16]. Besides, the pre-factors of reactions of (6), (62) and (64) were updated to fit the experimental data of sulfur species distribution. During pulverized combustion, a large number of free radicals containing C, H or O were produced, and reacted with sulfur species. To account for these radicals, GRI-MECH 3.0 was chosen as the sub-mechanism for the C-H-O combustion system, because it has been validated by various experimental conditions (e.g. methane combustion, coal combustion, etc.). 3.2. Model description In this work, the new detailed chemical reaction mechanism was firstly used to give predictions for H2S formation during fuel-rich combustion of pulverized coal by CHEMKIN-PRO. In this work, the furnace was a tube flow reactor with a large length to diameter ratio, and the viscosity of the flue gas is as low as 4.6 × 10−6 Pa·s. Thus, the flue flow in the furnace can be treated as plug flow. This means there was no mixing in the axial direction but perfect mixing in the direction transverse to this, and the laminar and/or turbulent mass diffusion was neglected. Moreover, in the direction perpendicular to flue gas flow, it was assumed that there was no gradient in velocity, temperature, pressure, or composition, and both physical and chemical properties were very uniform. When tube flow reactors are carried out in steadystate and continuous flow condition, the plug flow reactor (PFR) model in the software is efficient in working out the related problems [25]. So, the PFR model was adopted for the calculation in this work. The calculation domain was determined according to the real experimental geometric configuration and reaction conditions. All major species and sulfur species were considered as ideal gas and frictionless, and the viscous terms in the conservation equations for pressure and velocity were ignored [26]. The reactor wall was treated as non-catalytic. All chemistry processes were assumed to be homogeneous, with surface reaction completely eliminated in the system. The mass continuity and energy continuity equations can be written as follows. Mass continuity equation:
2. Experimental section Fig. 1 shows the schematic diagram of an 18 kW electrically heated pulverized coal-fired entrained flow furnace (2200 mm in length and 150 mm in inner diameter), with Z referring to the axial distance from the low-NOx burner exit. The detailed information of the furnace and procedure is described in our previous work [19]. To avoid repetition, it is not described here. Experimental results show that sulfur release just finished at Z = 450 mm for Daheng coal above 1373 K. Therefore, in this work, the flue gas composition of Z = 450 mm was assumed as the starting point of the gas-phase reactions, and the tests and simulations were executed only in the region from Z = 450 mm to Z = 2200 mm. The reaction conditions are summarized as in Table 1, and the experimental data are listed in Appendix A. In this work, O2, CO, CO2, and H2 were detected by a gas chromatography system with thermal conductivity detectors (SP 3420A), and SO2, H2S, COS and CS2 were measured by another gas chromatography system (Agilent 3000A Micro GC). The lower detection limits of all species were approximately 1 ppm. The axial position was determined according to the insertion depth of the sampling pipe. Considering installation error, the uncertainties in axial location Z was about ± 5 mm, which was assumed to be sufficiently little for this study.
u
d dA du + A + uA =0 dx dx dx
(1)
where ρ, u, and A are respectively the mass density, axial velocity of the flue gas, and cross-sectional area. Energy continuity equation: kg
uA
hk k=1
dYk dT du + Cp +u = ae Qe dx dx dx
(2)
where hk is the specific enthalpy of species k; Yk refers to the mass fraction of species k; Cp represents the mean heat capacity per unit mass of the flue gas; T is the absolute flue gas temperature; Qe refers to the heat flux from the surroundings outer tube wall; and ae represents the surface area per unit length. 3.3. Model validation The predicted data were compared to experimental results in the entrained flow furnace to validate the numerical method. Fig. 2 presents the predicted and measured concentration profiles of CO, H2, CO2, and H2O along the furnace axis. Because GRI-MECH 3.0 was adopted for the C-H-O combustion system in both our and Leeds University models, the predicated results of the major species by the two models were almost the same with each other. Thus, only the predicted data by our model were illustrated in Fig. 2. Clearly, both experimental and calculated results on the axial variation of the major species agree well. The maximum relative error was less than 8%, which indicates that
3. Numerical approach 3.1. Reaction mechanism As listed in Appendix B, a new detailed kinetic mechanism was developed including 34 species and 115 elementary reactions in CHEMKIN format to describe the H2S formation during fuel-rich combustion of pulverized coal. Our new model was based on the Leeds 2
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Fig. 1. The schematic diagram of electrically heated pulverized coal-fired entrained flow furnace. Table 1 Reaction conditions. Inlet gas composition N2 CH4, % CO, % H2, % H2O, % CO2, % NO, ppm SO2, ppm H2S, ppm COS, ppm CS2, ppm Mass rate of flue gas, kg·h−1 Pressure, kPa Reaction temperature, K
Balance gas 2.13 5.20 3.26 7.74 16.68 448 876 132 108 71 3.32 91.92 1373–1673
GRI-MECH 3.0 can provide accurate predictions for the fuel-rich combustion of pulverized coal. The measured and calculated concentration profiles of sulfur species along the furnace axis are shown in Fig. 3. It can be seen that both measured result and predicated result by our model on the axial variation of sulfur species agree well. Most relative errors between predicted by our model and measured values were within 5%, and the maximum relative error was less than 15%. Therefore, the detailed
Fig. 2. Comparison between the predicted and experimental results of major species at 1473 K.
modeling method in this work was validated, and shown to provide accurate predictions for gas-phase reactions of sulfur species during fuel-rich combustion. Additionally, the calculated results by Leeds University model are also presented in Fig. 3. The predicated data shows a similar change trend with the experimental values. Even 3
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Fig. 3. Comparison between the predicted and experimental results of sulfur species at 1473 K.
though not involved in any reactions, CS2 was still treated as a reactant with the same initial concentration as that in our model. That is why its concentration nearly kept constant. The calculated H2S concentration was significantly lower than the measured data with the maximal error was as large as 32%. Therefore, the updating of Leeds University model is necessary and the participation of CS2 should not be ignored during coal combustion. 4. Results and discussion 4.1. Effect of reaction temperature on H2S concentration The influence of temperature on the H2S distribution is shown in Fig. 4. The H2S concentrations were similar initially regardless of temperature, but subsequently increased faster at higher temperatures. This is because that H2S release from coal just finished, and the gasphase reaction started. Further away from the burner, the H2S concentration became relatively unchanged with Z. In brief, the formation of H2S was obviously affected by the temperature in the range of calculation. The higher temperature significantly promoted the formation of H2S, not only the final value of H2S concentration but also the rate of increase. This result agrees well with the experiments [19]. The reason may be attributed to the reactions (R2), (R4), (R14), and (R17), etc. [27,28]. Reactions (R2), (R4) and (R14) are exothermic, and reaction (R17) is endothermic. With an increase of temperature, the equilibriums of reactions (R2), (R4) and (R14) shifted to the left, and that of reaction (R17) to the right. Therefore, more H2S was directly produced via reactions (R2) and (R4). Furthermore, more S, another important source of H2S [29], was also generated by reactions (R14) and (R17), and thus promoted the formation of H2S [30]. The S concentration was very low with the maximum of less than 0.05 ppm. In fact, the concentration was so low that it could be determined only by numerical method. It indicates that S was an important intermediate, and its consumption rate was nearly equal to the formation rate.
H2 S + H = SH + H2
(R2)
H2 S + OH = SH + H2 O
(R4)
S + OH = H + SO
(R14)
S2 + M = S + S + M
(R17)
Fig. 4. Concentrations of H2S, S, CS2 versus axial distance at various temperatures.
concentration was up to 60 ppm, which could produce significant impact on high-temperature-corrosion. Therefore, the presence of CS2 should be taken into account during coal combustion. 4.2. Sensitivity analysis Sensitivity analysis was performed on the kinetic model using the SENKIN code in Chemkin-Pro software. This code produces the ranking of all reactions in our new detailed mechanism, from the most sensitive to the least sensitive, to provide the valuable information on the principal pathways in H2S formation during fuel-rich combustion of pulverized coal. The protocol and principle employed is detailed elsewhere [31]. The definition of sensitivity coefficients is written as Eq. (3),
S=
kj ci = ci kj
ln ci ln kj
(3)
where S is the sensitivity coefficient; kj represents the reaction rate constant of the jth elementary reaction; ci represents the H2S concentration of the special axial position. When the sensitivity coefficient is positive, it means that an increase in the forward reaction rate increases the H2S concentration, thereby promoting reactivity. Conversely, a negative sensitivity coefficient implies a decrease in H2S concentration. As shown in Fig. 5(a), the H2S concentration was sensitive to reactions (2), (89), (104), (62), (103), (74), and (57) at 1373 K, but the functions of the elementary reactions changed with the axial distance Z. H2S concentration was sensitive to reaction (2) within Z = 550 mm, and to reactions (89), (104), (62), (103), (74), and (57) after Z = 550 mm. The sensitivity of these reactions was considerably higher
Additionally, as a new specie in our kinetic model, CS2 is also an interesting sulfur specie. Fig. 4 shows that CS2 concentration remained at the level of no more than 100 ppm along the axis of the furnace within the scope of calculation in this work. That is because the initial value was only 71 ppm. However, the largest change range of CS2 4
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Fig. 5. H2S sensitivity versus axial distance from the burner, where (a) at 1373 K; (b) at 1473 K; (c) at 1573 K; (d) at 1673 K.
than that of reactions of (71), (64) and (111), which only had a weak influence on H2S concentration [32]. This indicates that when the high temperature and reducing atmosphere prevail, radicals SH, S and SO were the key intermediate radicals for H2S production. Also, the functions of elementary reactions changed with reaction temperature, as demonstrated in Fig. 5(b), (c) and (d). When the temperature increased, the positive sensitivity of reaction (89) to H2S formation increased, while that to reactions of (103), (104) and (64) decreased. This is because reaction (89) is endothermic, and reactions of (103), (104) and (64) are exothermic. As the temperature elevated above 1473 K, reaction (7) had a dominant role in H2S consumption within Z = 1100 mm. This may be attributed to the rapid consumption of S for an instant before the triggering of the production of H2S from SH. Beyond Z = 1100 mm, reaction (7) nearly showed no influence on H2S concentration. Additionally, the H2S concentration always showed obvious sensitivity to reaction (103) when the temperature increased from 1373 K to 1673 K, and Z from 450 mm to 2200 mm. This implies that CS2 was a notable sulfur species for H2S formation, and should be taken into account for sulfur evolution during coal combustion.
target species to be studied via ROP analysis. The ROP profiles are presented in Fig. 5. Not all relevant elementary reactions are shown. If the production rate of a reaction for interesting specie was distinctly lower than that of the main contribution reactions, this reaction was not exhibited. Therefore, the number of related elementary reactions varied for different target species. As demonstrated in Fig. 6(a), representative reactions were plotted with respect to their contributions to the production rate of H2S. Reaction (2) was the most important path for H2S production, and reactions (4), (5), (103) and (104) played a secondary role. This indicates that the SH radical played a vital and active role in H2S production. Moreover, it again suggests that CS2 exhibited a considerable role in H2S formation. Meanwhile, the consumption of H2S occurred mainly via the reaction (1) [34], while the collision of S and H2 could reproduce H2S [35]. Therefore, the S radical was an important intermediate during H2S decomposition or production [36]. The ROP analysis of SH is clearly displayed in Fig. 6(b). It clearly indicates that the reaction between S and H2 was the paramount path to SH production (i.e., reaction (7)). Additionally, HSOH was also a source of SH, and the reaction is presented as (47). For SH consumption, reactions (2) and (5) were the major paths, and reaction (4) was also considerable [37]. It is worth noting that the key product of all the three reactions was H2S. This again indicates that SH was the most important precursor of H2S. As shown in Fig. 6(c), S production was originated from decomposition of H2S via reaction (1) and the collision of SH [34]. Additionally, the decomposition of SO via reaction (71) was a minor route to generate S. On the other hand, S consumption took place mainly through reaction (7) to produce SH [38]. Apart from this, the conversion of S to HSOH was also a possible path for S consumption.
4.3. Rate-of-production analysis ROP analysis is useful in understanding the contribution of each elementary reaction to the net production or consumption of the species of interest. A positive production rate value indicates this reaction contributes to the formation of the target species [33]. Conversely, a negative production rate means the reaction contributes to the consumption of the target species. Since radicals S, SH, and SO were the key intermediate radicals for H2S formation, they were chosen as the 5
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Fig. 6. Rate of production of target species versus axial distance under 1473 K.
Fig. 6(d) suggests that SO2 and HOSO were the major sources for SO formation, and the corresponding path were reactions (89) and (74), respectively. Besides that, the decomposition of HOSHO was also an important way for SO production (cf. reaction (58)). Instead, SO consumption mainly occurred via reaction (71) to produce S, and reaction (14) was also an alternative path. Thus, SO was a key intermediate radical [39]. Thus, under fuel-rich condition, SO2 dissociated to SO, and further reduced to form SH and H2S, while SO2 was reproduced for SO oxidation in an oxygen-rich atmosphere [40]. 4.4. Reaction path diagram As shown in Fig. 7, the H2S formation path during fuel-rich combustion of pulverized coal was constructed based on our new detailed reaction mechanism in Appendix B, sensitivity analysis and ROP analysis. The path clearly presented the interactions among the elements in the flue gas. The reactions with the widest red arrows had the fastest reaction rate. The moderately thick blue arrows represent the reactions with fast reaction rate other than those with red arrows. SO, S and SH were the key free radicals for H2S formation. After SO2 converted into S, H2S production followed two major paths. First, S reacted with H2 to generate SH, and then the collision of two SH produced H2S. Second, S was converted into HSOH by H2O attack, and further formed SH. Subsequently, H2S was formed from the reaction between SH and H2. Apart from that, H2S could also be produced from CS2 and COS respectively by reactions (103) and (104), which had a considerable reaction rate (with moderate thick blue arrows). Therefore, the participation of CS2 had notable influence on H2S distribution, and thus CS2 should not be ignored in the sulfur mechanism during fuel-rich combustion of coal.
Fig. 7. Simplified reaction path diagram of formation of H2S.
4.5. Comparison with the Leeds University sulfur chemistry model A comparison was conducted between our new model and the Leeds University sulfur chemistry model at the same reaction conditions, as listed in Table 2. Since our model was established based on the Leeds University model, the two models had some distinctly similar characteristics. First of all, they have the same key free radicals, namely, SH, S, and SO. Furthermore, the four major elementary reactions in the two models also have high levels of consistency. This again demonstrates that the Leeds University sulfur chemistry model has extensive applicability, and is suitable to be adopted as benchmark for development of other sulfur species reaction mechanism models. 6
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the key free radicals for H2S production. ROP analysis shows that the SH radical played a vital and active role in H2S production, and CS2 exhibited a considerable role for H2S formation. SH was the most important precursor of H2S. Reaction (7) S + H2 = SH + H was the paramount path to SH production, and SH consumption was mainly via reactions (2) H2S + H = SH + H2 and (5) H2S + S = SH + SH. S production originated from the decomposition of H2S and the collision of two SH radicals, while S consumption took place mainly through reaction (7) S + H2 = SH + H. SO was the key intermediate radical for SO2 converted into S. SO2 and HOSO were the major sources for SO formation, while reaction (71) SO + M = S + O + M dominated SO consumption to generate S. Compared with the Leeds University sulfur chemistry model, our model had the same key free radicals (e.g. SH, S, and SO) and four major elementary reactions. On the other hand, some differences exist between the two models. In our model, CS2 was a notable source of H2S, which is specific for coal combustion. Moreover, the hydrocarbon functional groups (CH3, CH4) played a greater role in the Leeds University sulfur chemistry model. The development of detailed mechanism is a fundamental and significant step in understanding and predicting gas-phase reaction process for H2S formation in coal combustion. In the next work, our detailed kinetic model will be reduced and combined with a computational fluid dynamic model to investigate the whole sulfur evolution during coal combustion.
Table 2 Comparison between our H2S formation model and Leeds University sulfur chemistry model. Our new detailed model
Leeds University model
Key free radicals The same major elementary reactions
S, SH, SO 1. H2S + M = S + H2 + M 2. H2S + H=SH + H2 7. S + H2 = SH + H 89. SO2 + CO=SO+CO2
Different major elementary reactions
62. HOSO(+M) = H + SO2(+M) 71. SO+M = S + O + M 74. SO+OH(+M) = HOSO(+M) 103. CS2 + H2O=H2S + COS 104. COS + H2O=H2S + CO2 111. SO2 + 3CO=COS + 2CO2
S, SH, SO L1. H2S + M = S + H2 + M L2. H2S + H=SH + H2 L7. S + H2 = SH + H L27. SO2 + CO=SO+CO2 L4. H2S + OH=SH + H2O L5. H2S + S=SH + SH L33. 2SO=SO2 + S L49. HSOH=SH + OH L50. HSOH=S + H2O L76. S + CH4 = SH + CH3 L77. H2S + CH3 = CH4 + SH
On the other hand, there exists some differences between the two models. In our model, CS2 was taken into account, which, as well as COS, was indeed a considerable source of H2S (cf. reactions (103) and (104)). This is the advance made in our model for use in coal-fired boilers. Additionally, the hydrocarbon functional groups (CH3, CH4) played a greater role in the Leeds University sulfur chemistry model (cf. reactions L76 and L77). This may be because the Leeds university model was built in methane combustion condition, but methane concentration is relatively lower during coal combustion.
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
5. Conclusion A detailed kinetic model for the H2S formation during fuel-rich combustion of pulverized coal was developed. The validity of the model was verified by experimental data. The effect of reaction temperature on H2S production was also investigated, with results showing that the production of H2S was significantly elevated with temperature. Sensitivity analysis indicates that H2S concentration showed high sensitivity to reactions (2) H2S + H = SH + H2, (89) SO2 + CO = SO + CO2, (104) COS + H2O = H2S + CO2, (62) HOSO (+M) = H + SO2 (+M), (103) CS2 + H2O = H2S + COS, etc. Also, S, SH, and SO were
Acknowledgements The work was supported by the National Natural Science Foundation of China (Grant No. 51706151); Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi (STIP) (Grant No. 2019L0147); and Major Special Projects for the Innovative Demonstration Zone Construction of National Sustainable Development Agenda in Taiyuan.
Appendix A. Measured species distribution along the axis of the furnace Z, mm
CO, %
H2, %
CO2, %
450 550 750 900 1200 1600 2100
T = 1373 K 5.20 5.26 5.47 5.58 5.74 5.91 6.05
3.26 3.34 3.65 3.77 3.92 4.06 4.13
16.68 16.63 16.31 16.29 16.02 15.84 15.67
450 550 750 900 1200 1600 2100
T = 1473 K 5.20 6.12 6.88 6.94 7.08 7.16 7.21
3.26 3.64 3.91 4.18 4.53 4.62 4.68
450 550 750 900 1200
T = 1573 K 5.20 6.96 7.91 8.32 8.79
3.26 4.94 4.92 4.89 4.87
H2O, %
SO2, ppm
H2S, ppm
COS, ppm
CS2, ppm
7.74 7.79 7.98 8.13 8.24 8.40 8.54
876 849 778 723 715 684 680
132 140 149 171 241 248 254
108 112 120 132 151 170 191
71 93 86 72 67 65 60
16.68 15.38 15.96 16.26 16.21 16.06 15.82
7.74 7.87 7.78 7.69 7.61 7.56 7.49
876 795 728 664 637 630 626
132 189 223 267 286 308 318
108 125 146 168 180 189 201
71 77 86 87 88 56 42
16.68 14.58 13.54 13.17 12.76
7.74 9.20 9.96 10.32 10.63
876 755 688 664 607
132 197 288 359 456
108 110 123 131 167
71 75 60 57 51
7
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9.16 9.45 T = 1673 K 5.20 8.77 9.94 10.43 7.08 7.16 7.21
4.88 4.93
12.35 12.17
10.84 11.06
504 396
463 478
205 235
46 39
3.26 5.15 5.03 5.08 4.53 4.62 4.68
16.68 12.76 11.62 11.34 16.21 16.06 15.82
7.74 10.53 11.34 11.48 7.61 7.56 7.49
876 714 593 504 389 267 210
132 244 377 464 556 579 586
108 113 125 141 167 184 190
71 72 55 50 44 38 32
Appendix B. Detailed reaction mechanism for H2S formation during fuel-rich combustion of coal k = A Tb exp(-E/RT) Reactions 1.
H2S+M=S+H2+M
2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19 20. 21. 22. 23.
H2S+H=SH+H2 H2S+O=SH+OH H2S+OH=SH+H2O H2S+S=SH+SH H2S+S=HS2+H S+H2=SH+H SH+O=H+SO SH+OH=S+H2O SH+HO2=HSO+OH SH+O2=HSO+O SH+O2=SO+OH SH+O=S+OH S+OH=H+SO SH+SH=S2+H2 SH+S=S2+H S2+M=S+S+M S2+H+M=HS2+M HS2+H=S2+H2 HS2+O=S2+OH HS2+OH=S2+H2O HS2+S=S2+SH HS2+H+M=H2S2+M
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.
H2S2+H=HS2+H2 H2S2+O=HS2+OH H2S2+OH=HS2+H2O H2S2+S=HS2+SH HSO+H=HSOH HSO+H=SH+OH HSO+H=S+H2O HSO+H=H2SO HSO+H=H2S+O HSO+H=SO+H2 HSO+O+M=HSO2+M HSO+O=SO2+H HSO+O+M=HOSO+M HSO+O=O+HOS HSO+O=OH+SO HSO+OH=HOSHO HSO+OH=HOSO+H HSO+OH=SO+H2O HSO+O2=SO2+OH HSO2+OH=SO2+H2O HSO2+H=SO2+H2 HSO2+O2=HO2+SO2 H2SO=H2S+O HSOH=SH+OH HSOH=S+H2O HSOH=H2S+O HOSO2=HOSO+O HOSO2=SO3+H HOSO2+H=SO2+H2O HOSO2+O=SO3+OH HOSO2+OH=SO3+H2O
A 1.60E+24 N2 enhanced by 1.500E+00 SO2 enhanced by 1.000E+01 H2O enhanced by 1.000E+01 1.20E+07 7.50E+07 2.70E+12 8.30E+13 7.00E+11 1.40E+14 1.00E+14 1.00E+13 1.00E+12 1.90E+13 1.00E+12 6.30E+11 4.00E+13 9.10E+10 2.13E+13 2.47E+17 3.50E+11 1.20E+00 2.46E+06 2.90E+09 2.15E+08 1.00E+16 N2 enhanced by 1.500E+00 SO2 enhanced by 1.000E+01 H2O enhanced by 1.000E+01 1.20E+07 7.50E+07 2.70E+12 8.30E+13 2.50E+20 4.90E+19 1.60E+09 1.80E+17 1.10E+06 1.00E+13 1.10E+19 4.50E+14 6.90E+19 4.80E+08 1.40E+13 5.20E+28 5.30E+07 1.70E+09 1.00E+12 1.00E+13 3.00E+13 1.10E+03 4.90E+28 2.80E+39 5.80E+29 9.80E+16 5.40E+18 1.40E+18 1.00E+12 5.00E+12 1.00E+12
8
b
E
-2.6
44800
2.1 1.8 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5 0.0 0.0 0.0 0.0 0.0 2.0 1.8 0.0 0.0 0.0
350 1460 0 3700 3723.8 9700 0 0 0 9000 5032.5 4030.6 0 0 0 77000 0 700.0 2900 0 7400 0
2.1 1.8 0.0 0.0 -3.1 -1.9 1.4 -2.5 1.0 0.0 -1.7 -0.4 -1.6 1.0 0.1 -5.4 1.6 1.0 0.0 0.0 0.0 0.0 -6.7 -8.8 -5.6 -3.4 -2.3 -2.9 0.0 0.0 0.0
360 1460 0 3700 460 785 -170 25 5230 0 -25 0 800 2700 150 1600 1900 235 5000 0 0 0 71700 37800 27400 43500 53500 27600 0 0 0
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HOSO2+O2=HO2+SO3 HOSO2+H=SO3+H2 HOSHO=HOSO+H HOSHO=SO+H2O HOSHO+H=HOSO+H2 HOSHO+O=HOSO+OH HOSHO+OH=HOSO+H2O HOSO(+M)=H+SO2(+M)
63. 64. 65. 66. 67. 68.
HOSO+O2=SO2+HO2 HOSO+H=SO2+H2 HOSO+H=SO+H2O HOSO+M=O+HOS+M HOSO+OH=SO2+H2O HOSO(+M)=HSO2(+M)
69. 70. 71.
SO2+OH=HOSO+O SO3+SO=2SO2 SO+M=S+O+M
72. 73. 74.
S+O2=SO+O S2+O=SO+S SO+OH(+M)=HOSO(+M)
75.
SO+O(+M)=SO2(+M)
76. 77.
SO+O2=SO2+O SO2+O(+M)=SO3(+M)
78.
SO2+O(+N2)=SO3(+N2)
79. 80.
SO2+OH=SO3+H SO+H+M=HSO+M
81. 82. 83.
SO3+O=SO2+O2 SO3+OH=SO2+HO2 SO2+OH(+M)=HOSO2(+M)
84. 85. 86. 87. 88. 89 90. 91. 92. 93. 94. 95. 96. 97.
SO3+S=SO+SO2 SO3+H2O=H2SO4 SO3+H=HOSO+O 2SO=SO2+S C+SO2=CO+SO SO2+CO=SO+CO2 CO+SO=CO2+S SO+HO2=SO2+OH SO+OH=SO2+H O+CS2=CS+SO O+CS=CO+S O+CS2=CO+S2 O+CS2=COS+S S+CS2=CS+S2
7.80E+11 0.0 1.00E+12 0.0 6.40E+30 -5.9 1.20E+24 -3.6 1.00E+12 0.0 5.00E+12 0.0 1.00E+12 0.0 1.95E+10 0.8 Low pressure limit: 0.15000E+32 -0.45300E+01 0.49178E+05 TROE centering: 0.30000E+00 0.10000E-29 0.10000E+31 N2 enhanced by 1.000E+00 SO2 enhanced by 1.000E+01 H2O enhanced by 1.000E+01 1.00E+12 0.0 2.08E+13 0.0 6.30E-10 6.3 2.50E+30 -4.8 1.00E+12 0.0 1.00E+09 1.0 Low pressure limit: 0.17000E+36 -0.56400E+01 0.55400E+05 TROE centering: 0.40000E+00 0.10000E-29 0.10000E+31 N2 enhanced by 1.000E+00 SO2 enhanced by 1.000E+01 H2O enhanced by 1.000E+01 3.90E+08 1.9 1.00E+12 0.0 4.00E+14 0.0 N2 enhanced by 1.500E+00 SO2 enhanced by 1.000E+01 H2O enhanced by 1.000E+01 5.20E+06 1.8 1.00E+13 0.0 1.60E+12 0.5 Low pressure limit: 0.95000E+28 -0.34800E+01 0.97000E+03 N2 enhanced by 1.500E+00 SO2 enhanced by 1.000E+01 H2O enhanced by 1.000E+01 3.20E+13 0.0 Low pressure limit: 0.12000E+22 -0.15400E+01 0.00000E+00 TROE centering: 0.55000E+00 0.10000E-29 0.10000E+31 N2 enhanced by 1.500E+00 SO2 enhanced by 1.000E+01 H2O enhanced by 1.000E+01 7.60E+03 2.4 9.20E+10 0.0 Low pressure limit: 0.24000E+28 -0.36000E+01 0.51860E+04 TROE centering: 0.44200E+00 0.31600E+03 0.74420E+04 SO2 enhanced by 1.000E+01 H2O enhanced by 1.000E+01 N2 enhanced by 0.000E+00 3.70E+11 0.0 Low pressure limit: 0.29000E+28 -0.35800E+01 0.52060E+04 TROE centering: 0.43000E+00 0.37100E+03 0.74420E+04 4.90E+02 2.7 5.00E+15 0.0 N2 enhanced by 1.500E+00 SO2 enhanced by 1.000E+01 H2O enhanced by 1.000E+01 2.00E+12 0.0 4.80E+04 2.5 5.70E+12 -0.3 Low pressure limit: 0.17000E+28 -0.40900E+01 0.00000E+00 TROE centering: 0.10000E+01 0.10000E-29 0.41200E+03 N2 enhanced by 1.000E+00 SO2 enhanced by 5.000E+00 H2O enhanced by 5.000E+00 5.12E+11 0.0 7.23E+08 0.0 2.50E+05 2.9 2.00E+12 0.0 4.16E+13 0.0 2.70E+12 0.0 5.10E+13 0.0 3.70E+03 2.4 1.08E+17 -1.4 3.60E+13 0.0 1.63E+14 0.0 1.70E+12 0.0 7.10E+12 0.0 2.40E+12 0.0
9
330 0 37100 30000 0 0 0 46933
500.0 0 -960 60000 0 50000
38200 5000 54000
-600 0 -400
0
1500 1200
1689 12000 0
10000 27225 0
0 0 25300 2000 0 24300 53400 7660 0 1696 760.2 1194 2102 4060
Fuel Processing Technology 199 (2020) 106276
H. Ma, et al. 98. 99. 100. 101. 102. 103. 104. 105. 106. 107. 108. 109.
CS2+O2=CS+SO2 CS+O2=COS+O CS+O2=CO+SO CS2+OH=COS+SH COS+OH=CO2+SH CS2+H2O=H2S+COS COS+H2O=H2S+CO2 CS2+SO=COS+S2 CO+SH=COS+H COS+S=CO+S2 COS+M=CO+S+M CS+S(+M)=CS2(+M)
110. 111. 112. 113. 114. 115.
CS+SH=CS2+H SO2+3CO=COS+2CO2 C+H2S=CH+SH O+COS=CO+SO O+COS=CO2+S CH+SO=CO+SH
1.00E+12 0.0 6.10E+12 0.0 6.10E+12 0.0 5.79E+08 0.0 7.90E+08 0.0 1.74E+11 0.0 1.71E+10 0.0 6.90E+05 0.0 2.87E+07 0.0 3.14E+00 2.6 6.88E+06 0.0 1.90E+26 -4.3 Low pressure limit: 0.62000E+24 -0.24200E+01 0.00000E+00 1.20E+13 0.0 8.60E+12 0.0 1.20E+14 0.0 1.93E+13 0.0 5.00E+13 0.0 1.00E+13 0.0
31050 16500 16500 -1174 0 41497 35299 -6339 15200 2345 30700 0 0 87700 4450.3 2328.6 5530.4 0
Units: mol, cm, s, K, cal.
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