- Email: [email protected]
red-mud composite powders with core-shell structure
Accepted Manuscript Title: Methane explosion suppression characteristics based on the NaHCO3 /red-mud composite powders with core-shell structure Authors: Yan Wang, Yi-shen Cheng, Ming-gao Yu, Yao Li, Jian-liang Cao, Li-gang Zheng, Hong-wei Yi PII: DOI: Reference:
S0304-3894(17)30273-X http://dx.doi.org/doi:10.1016/j.jhazmat.2017.04.031 HAZMAT 18514
To appear in:
Journal of Hazardous Materials
Received date: Revised date: Accepted date:
23-12-2016 22-3-2017 10-4-2017
Please cite this article as: Yan Wang, Yi-shen Cheng, Ming-gao Yu, Yao Li, Jianliang Cao, Li-gang Zheng, Hong-wei Yi, Methane explosion suppression characteristics based on the NaHCO3/red-mud composite powders with core-shell structure, Journal of Hazardous Materialshttp://dx.doi.org/10.1016/j.jhazmat.2017.04.031 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Methane explosion suppression characteristics based on the NaHCO3/red-mud composite powders with core-shell structure Yan Wanga,c, Yi-shen Chenga,c, Ming-gao Yub, Yao Lia,c, Jian-liang Caoa,c, Li-gang Zhenga,c Hong-wei Yia,c, a
State Key Laboratory Cultivation Bases Gas Geology and Gas Control (Henan Polytechnic
University), Jiaozuo, Henan 454000, PR China b
State Key Laboratory of coal mine disaster dynamics and control, Chongqing University,
Chongqing 400044, PR China c
The Collaboration Innovation Center of Coal Safety Production of Henan Province, Jiaozuo,
Henan 454000, PR China
Abstract The NaHCO3/red-mud (RM) composite powders were successfully prepared by the solvent-anti-solvent method for methane explosion suppression. The RM was used as a carrier, and the NaHCO3 was used as a loaded inhibitor. The NaHCO3/RM composite powders showed a special core-shell structure and excellent endothermic performance. The suppression properties of NaHCO3/RM composite for 9.5% CH4 explosion were tested in a 20 L spherical explosion vessel and a 5 L Perspex duct. The results showed that the NaHCO3/RM composite powders displayed a much better suppression property than the pure RM or NaHCO3 powders. The loading amount of NaHCO3 has an intensive influence on the inhibition property of NaHCO3/RM composite powders. The best loaded content of NaHCO3 is 35%. It exhibited significant inhibitory effect that the explosion max-pressure declined 44.9%, the max-pressure rise rate declined 96.3% and the pressure peak time delayed 366.7%, respectively. Keywords: NaHCO3/red-mud composite; methane; explosion suppression; core-shell structure
Corresponding author. Tel./fax: +86 13333910808 E-mail address:[email protected] (M. Yu) 1
1. Introduction Mine gas explosion is one of the major disasters in coal mine production, which seriously affects the safety production of coal industry. The main component of mine gas is methane that a flammable and explosive gas. Inhibitor of the methane explosion is considered to be the key for explosion suppression in coal industry. In recent years, some studies of various inhibitors have been made great progress on the methane explosion suppression. Cao et al. [1-4] researched on explosion suppression property of the ultrafine water mist, which can influence on the flame structure during the propagation process and presented good inhibition performances. Brinkmann.C et al. [5-8] studied on the suppression property of inert gas, which can decrease the explosion limits and maximum overpressure significantly. Nie et al. [9-11] researched on porous materials inhibitors which can contribute to quench the gas explosion flame and suppress the explosion shock wave. As an excellent explosion suppression material, powder material owing the advantages of easy storage, low cost, high efficiency and environmentally benign, has attracted the many attentions and has been applied in the field of methane explosion suppression. According to previous reports, CaCO3, SiO2, NaHCO3, Al(OH)3, (NH4)2SO4, NaCl, diatomite and bauxite all have certain inhibitory effect on methane explosion [12-17]. At present, the development trend of the fire/explosion suppression powders can be concluded as following: 1) Economic, efficient and environmental benign new 2
materials [18-19]. For example, Cheng and co-works selected the natural mineral powder as the explosion suppression material and found that diatomite powder has an inhibitory effect on the gas explosion, which is better than the quartz powder [20]. Kordylewsy et al. studied the explosion suppression material NaHCO3, which exhibits higher efficiency and better suppression performance than that of CaCO3 [21]. 2) Micro/nano ultrafine powder materials [22-23]. For example, Zhou et al. reported that the micro/nano grade ultrafine powder has better extinguishing effect [24]. The research of preventing the formation of detonation shows that the smaller inert particles have strong affection [25]. 3 ） Composite or modification explosion suppression material [26-28]. For instance, using the technology of synergistic, Zuo and co-workers selected Al(OH)3, ammonium polyphosphate and nanostructure diatomite as monomer and synthesized a complex substance for coal dust suppressant [29]. Liao and Ni using porous zeolite as the carrier fabricate a series of core shell structure extinguishing composite materials, which all presented excellent efficiency on extinguishment [30-33]. Likewise, Rosser et al. used zeolite and NaHCO3 to fabricate a new composite extinguishing agent [34]. These experimental results proved that the composite suppressant has better explosion suppression property due to the synergistic inhibition effect. Red mud (RM) is a by-product of the Bayer process in aluminum industry, which primarily composed of Fe2O3, Al2O3, SiO2, CaO and Na2O etc. 1 kg of alumina approximately generates 0.3-0.2 kg of RM as the by-products. If no proper disposal was done, serious pollution can be caused by the MP for its high alkalinity. However, as a very fine material, RM has evenly distributed components which average size is all bellow 10μm. Nowadays, RM is used as catalyst carrier and pollution control materials for its high added value [35-38]. Based on industrial modified treatment, the as-obtained ultrafine RM with abundant micropores and larger surface area exhibits a great application prospect when used as gas explosion suppression powder material [39]. NaHCO3 is also a typical suppressant for gas explosion, which can combine with other power material to create a new type of powder explosion suppressant and fire extinguishing agent. 3
In this work, the NaHCO3/RM composite powders were successfully prepared using the industrial solid waste RM as the base materials, and adopting the solvent-anti-solvent method to load NaHCO3 particles. Moreover, their characteristics of methane explosion suppression were further studied. 2. Experimental section 2.1. Preparation of NaHCO3/RM composite powders The NaHCO3/RM composite powders were prepared with modified RM powders and NaHCO3 crystals. The raw RM was collected from Henan Zhongmei Aluminum Corporation, China. All of the other chemical reagents were analytical grade without further purification. The modified RM powders were preparation according to the method reported by Yu [39]. The NaHCO3/RM composite powders with different amount NaHCO3 were prepared by the solvent-anti-solvent method. The preparation process was as following. Firstly, 8 groups of NaHCO3 saturated solution were prepared with different weight percentage (5%, 10%, 15%, 10%, 25%, 30%, 35% and 40%). Then, 10g modified RM powders were dispersed in ethanol with stirring to become suspension solution, which was prepared 8 parallel groups for further using. Under magnetic stirring, the as-prepared 8 groups of suspension solution was poured into the above 8 groups’ saturated NaHCO3 solution, respectively. The as-obtained 8 groups of mixture continued stirring 2h, aging 4 h, ultrasonication for 30 min, and then filtered out the precipitated and dried in vacuum for 12h. Finally, different NaHCO3/RM composite powders were obtained.c 2.2. Characterization X-ray diffraction (XRD) analysis was carried out on a Philiphs X’Pert Super diffractometer with Cu Kα radiation (λ= 1.54178 Å). The morphology of the products was examined by field emission scanning electron microscope (FE-SEM, JMS-6390LV). The pyrolysis characteristic of the composite powders was characterized by Thermogravimetry-Differential Scanning Calorimetry (TG-DSC) method using the STA449C model synchronization thermal analyzer. Nitrogen absorption/desorption isotherms were recorded using an automatic physical/chemical adsorption analyzer (Quantachrome Instruments U.S.) via conventional volumetric 4
technique at 20ºC. The specific surface area (SBET) was calculated by the Brunauere-Emmette-Teller (BET) method. The total pore volume (Vtotal) was estimated from the amount of nitrogen adsorbed at p/p0 ~0.99. 2.3. Explosion experiment In present work, the maximum explosion pressure (Pm) and maximum rate of pressure rise (dP/dt)max were performed in a standard 20 L stainless steel spherical vessel. Before each testing, 2g composite powders were placed in a powder container (volume: 0.6 L). Then the centrally mounted electrical pulse igniter was connected with the ignition leads, and the explosion chamber was closed safely. In the experiments, 9.5% methane-air mixtures were formulated by the partial pressure ratio method. In the preparation process of explosive gas mixtures, it should be ensured that the internal pressure of explosion chamber was 0.06 MPa and the dispersing air pressure was set to 2 MPa. After the solenoid valve between the powder container and the test chamber was triggered, the high pressure air and the powders were dispersed into the explosion chamber through the rebound type nozzle installed at the bottom of the chamber. The injection process lasted 50 ms. Then after a 60 ms time delay, the electrical pulse igniter was energized, and the discharge time lasted 0.5s. Synchronously, the explosion pressure evolutions were measured by the pressure sensor installed in the vessel wall and recorded by a data acquisition system. The flame propagation rate was tested in another tubular instrument in the report. The experiments were performed in a 5 L Perspex duct with a cross-section of 100 100mm2 and height of 500 mm. The bottom end of the duct was fully closed by a steel plate, and the open end was sealed with a thin PVC membrane to contain the premixed flammable mixture. The detailed experimental procedure was as follows. Firstly, composite powders were evenly sprinkled around the bottom of the bowl-shape powder container. Then the premixed 9.5% methane-air mixtures entered the duct through an inlet at the bottom steel plate. At last, the solenoid valve controlled by synchronous controller was triggered, and the 0.3 MPa premixed 9.5% methane-air mixtures flowed through the nozzle and hence, dispersed the powders into the duct. The injection process lasted 50 ms, then after a 60 ms delay, the 5
methane-air mixtures in the duct were ignited automatically by the electrical pulse igniter, and the discharge time lasted 0.5s. Meanwhile, the flame propagation images were captured by a “LaVision 4G” high-speed camera, which could achieve acquisition rate at a speed of 2000 frames/s with an array of 1024 1024 pixels. 3. Results and discussion 3.1. Materials analysis
Fig. 1. XRD patterns of 35%-NaHCO3/RM composite, RM and NaHCO3.
Fig. 1 shows the XRD patterns of the as-prepared 35%-NaHCO3/RM composite, RM and NaHCO3, respectively. As can be seen from Fig. 1, the characteristic diffraction peaks of 35%-NaHCO3/RM composite and RM are basically the same. However, 35%-NaHCO3/RM also appeared the characteristic diffraction peaks attributed to NaHCO3 crystal phase at 15.3, 18.5, and 40.8 (2θ), indicating that the NaHCO3 crystal particles were successfully loaded on the RM surface. The results showed that the as-prepared 35%-NaHCO3/RM composite is composed by NaHCO3 and RM. Fig. 2 displayed the SEM images of NaHCO3 particles, RM particles and 35%-NaHCO3/RM composite powders. Fig. 2a showed that NaHCO3 crystals consisted of quasi-sphere particles with the size of about 1-2 μm. Fig. 2b indicated that the RM had relatively smooth surface with layered structure, and RM particles were accumulated with micropore structure. However, as is shown in Fig. 3c, when 6
the RM was loaded with NaHCO3, the surface became rough. The surface of the composite powders is covered with a lot of tiny quasi-sphere particles with the size about 1-2 μm, which is NaHCO3 crystals dispersed on the surface of RM and forming a core-shell structure. The solvent-anti-solvent method not only made the RM particles dispersed more evenly, but also made RM and NaHCO3 composite successfully.
Fig. 2. SEM images of NaHCO3 particles (a), RM particles (b) and 35%-NaHCO3/RM composite powders (c).
Fig. 3 presented the TG-DSC curves of the RM and composite, respectively. As shown in the Fig. 3 the TG curve of RM declined smoothly that was due to the decomposition of partial hydroxides, and the weight loss was 28.2%. In contrast, the 35%-NaHCO3/RM composite was stepped with three stages. The first stage from 25 to 125 ºC with the weight loss of 19.5% should be ascribed to the lost of adsorbed and intercalated moisture.The second stage from 125 to 700 ºC with weight loss of 18.5% should attribute to the decomposition of partial hydroxides. The third stage around 700 ºC only with weight loss of 0.8% indicated that the composite powder became stable after 700 ºC. Therefore, the total weight loss of the 35%-NaHCO3/RM composite was 38.4%, which should ascribe to the loaded of NaHCO3 forming a 7
core-shell structure. The corresponding endothermic processes were also shown in DSC curves. As can be seen, the RM exhibited three endothermic peaks, and the 35%-NaHCO3/RM composite presented five endothermic peaks in the range from room temperature to 800 ºC. According to integrating the area of the endothermic peaks on DSC curves, the total endothermic quantity of the RM was 430.57 J/g, and the total endothermic quantity of 35%-NaHCO3/RM composite was 697.9 J/g, which indicated the composite had a better heat absorption performance. 1.5
RM
── 35%-NaHCO3/RM composite
Mass/%
90
d
1.0
b
0.5
80
0.0
a -0.5
70
c
DSC/(mW/mg)
---
100
-1.0
60 100
200
300 400 500 Temperature/
600
700
-1.5 800
Fig. 3.TG-DSC curves of the RM and composite powders: TG (a) and DSC (b) curves of RM, TG (c) and DSC (d) curves of 35%-NaHCO3/RM composite.
Fig. 4 shows N2 adsorption-desorption isotherms and the corresponding pore size distributions curves (PSDs) of RM and 35%-NaHCO3/RM composite powders. As shown in Fig. 4a, the RM and 35%-NaHCO3/RM composite powders all showed typical type IV isotherms with obvious hysteresis loops [40]. However, the 35%-NaHCO3/RM composite powder exhibited a much lower N2 adsorption amount than that of RM, because part of the space in RM was filled with NaHCO3 particles after successful loading. The corresponding PSDs of RM and 35%-NaHCO3/RM composite powders were showed in Fig. 4b, all exhibiting peaks centered at about 2-5 nm without obvious shape change, which means that the loading process of NaHCO3 did not change the pore size of original RM carrier. Therefore, a conclusion can be obtained that the NaHCO3 particles organically combined with RM forming NaHCO3/RM composite powders and maintained basic distribution characteristics of the RM carrier at the same time. 8
RM 35% -NaHCO3/RM
Volume adsorbed（ cc/g）
120
0.10
a
RM 35% -NaHCO3/RM
0.08
dV/dD (cc/nm/g)
100
b
0.06
80 60
0.04
40
0.02
20
0.00 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Relative pressure（ P/P0）
0
5
10
15
20
25
30
35
40
Pore diamater(nm)
Fig. 4. N2 adsorption-desorption isotherms (a) and the pore size distribution (b) of the RM and the 35%-NaHCO3/RM composite powders.
The specific surface area and pore volume of RM and the 35%-NaHCO3/RM composite powders were summarized in Table 1. The specific surface area and pore volume of RM decreased with the NaHCO3 loaded. The RM exhibited a specific surface area of 128.16 m2·g-1 as well as the pore volume of 0.158 cm3·g-1, which all higher than that of the 35%-NaHCO3/RM composite powders (SBET = 65.77 m2·g-1, Vtotal = 0.090 cm3·g-1), meaning that NaHCO3 particles were successfully loaded on the RM carrier. Table 1 Specific surface area and pore volume of RM and the 35%-NaHCO3/RM composite powder. Samples
SBETa（m2·g-1）
Vtotalb（cm3·g-1）
RM
128.16
0.158
35%-NaHCO3/RM
65.77
0.090
a
SBET specific surface area calculated by the Brunauere-Emmette-Teller (BET) method. Vtotal pore volume at p/p0 ~ 0.99.
b
3.2. Explosion suppression tests The explosion pressure parameters were performed on a 20 L spherical vessel. In the situation of 9.5% methane-air premixed gas explosion, the explosion inhibitory properties of the pure NaHCO3, RM and NaHCO3/RM composite powders were tested all with the same concentration of 0.1 g/L. The experimental results are presented in Fig. 5. 9
a
0.8
30%
0.4
5%composite
15%composite
25%composite
0.412MPa(44.9%↓)
40%composite
0.1
0.2
0.3 Time/s
0.4
0.5
C
45 41.15MPa/s
35 30 25 (48.9%↓)
15 (74.7%↓) (82.6%↓) (80.8%↓) (84.4%↓)
0.0
0.6
(94.1%↓) (95.8%↓) (88.9%↓) (93.2%↓) (96.3%↓)
0
The time of pressure peak arriving/s
0.0
The maximum rate of pressure rise/(Mpa/s)
0.446Mpa(40.4%↓)
35%composite
0.0
5
0.479Mpa(35.9%↓)
30%composite
0.1
10
0.525MPa(29.8%↓) 0.498MPa(33.4%↓)
20%composite
0.2
20
0.544Mpa(27.3%↓)
35%
0.3
40
0.569MPa(23.9%↓)
10%composite
40%
b
0.457MPa(38.9%↓)
NaHCO3 5% 10% NaHCO3 15% 20% 25%
0.5
0.748MPa
0.651MPa(12.9%↓)
RM
RM
0.6
Pressure/MPa
no powder
no powders
0.7
0.456Mpa(39.1%↓)
0.1
0.2
0.3 0.4 0.5 0.6 Pressure/MPa
0.7
0.8
0.50 508.8%
0.45
0.9
d
0.40 366.7%
0.35 0.30
284%
292%
0.25
183.2%
0.20
132%
0.15 104%
0.10
161.6%
180%
47.2%
0.05 0.075s 0.00
NP RM NaHCO3 5% 10% 15%20% 25% 30% 35%40%
NP RM NaHCO35% 10% 15%20%25% 30% 35% 40%
Fig. 5. The inhibition effect of different inhibitors: the explosion pressure curves (a), the maximum pressure peak (b), the maximum rate of pressure rise (c), the time of the pressure peak arrival (d).
Fig. 5a presents the explosion pressure curves with pure RM, NaHCO3 and NaHCO3/RM composite loading different amount of NaHCO3 (weight percentage of 5%, 10%, 15%, 20%, 25%, 30%, 35% and 40%). We can see from Fig. 5a, that when RM loading with NaHCO3, the maximum explosion pressure is decreased, and the explosion delay time is increased. With the loading amount of NaHCO3 increased, correspondingly, the inhibitory efficiency of explosion for composite powder suppressant increased. When the loading amount of NaHCO3 reached 35%, the explosion pressure exhibited the most significant inhibition effect with the composite powders. The max-pressure, the maximum rate of pressure rise and the time of the pressure peak arrival were exhibited in Fig. 5b, c and d, respectively. As can be seen clearly, the 35-%NaHCO3/RM composite powders exhibited significant inhibitory effect that the explosion max-pressure declined 44.9%, the max-pressure rise rate declined 96.3% and the pressure peak time delayed 366.7%, respectively. Therefore, the 35%-NaHCO3/RM composite powder possesses the best efficiency on explosion 10
suppression. The inhibitory of flame propagation rate was tested in a 5 L Perspex duct. As is shown in Fig. 6, the explosion flame propagation rate had been effectively retarded after adding suppressants, especially the adding of the 35%-NaHCO3/RM composite
Flame propagation rate (m/s)
powders.
60
no powders
50 40
RM NaHCO3
30 20 10 0
35%-NaHCO3/RM composite
0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10
Time/s
Fig. 6. The flame propagation rate with different inhibitors
Fig. 7. The photographs of explosion flame in different conditions: no powders (a), RM (b), NaHCO3 (c) and the 35%-NaHCO3/RM composite powder (d).
As presented in Fig. 7, the explosion flame photographs were captured by a high 11
speed camera. If no suppressants added, the flame propagation rate increased sharply (Fig. 7a). However, when the suppressants added, the flame propagation rate tend to be increased steadily (Fig. 7b and c), which led to the delay of explosion flame propagation process. It is noteworthy that the 35%-NaHCO3/RM composite powders exhibited the best inhibition performance of flame propagation rate (Fig. 7d), which is consistent with the 20 L spherical explosive device testing results. The 35%-NaHCO3/RM composite powders possess much better suppression property than pure RM and NaHCO3. 3.3. Mechanism of gas explosion suppression discussion The explosion suppression experimental results show that the core-shell NaHCO3/RM composite powders have significant inhibitory effect on methane explosion, which can be mainly manifested in the following two aspects.
Fig. 8. The inhibition mechanism diagrammatic sketch of the NaHCO3/RM composite powders
1) Physical synergistic inhibition effect. The composite powders have a special core-shell structure, which exhibit a significant synergistic inhibition effect in the explosion process. The inhibition mechanism diagrammatic sketch of the NaHCO3/RM composite powders was illustrated in Fig. 8. Under high temperature, the outer NaHCO3 particles detached from NaHCO3/RM composite, and fully dispersed in the explosion space. The NaHCO3 pyrogenic decomposed and react with the free radicals, which generated by CH4 explosion. On the other side, because the outer layer NaHCO3 departed from the RM base materials, the RM particles, which have larger surface area and lots of pores, 12
were fully exposed and contact the free radicals of CH4 explosion. The above two factors simultaneously play the role of explosion suppression, thus forming a synergistic inhibition effect. 2) Chemical synergistic inhibition effect. As generally known, the mechanism of methane combustion is as the following key chain reactions (1) - (6) [41]. CH4 → CH3· + H·
(1)
CH4 + O2 → CH 3· + OH·
(2)
CH4 + OH· → CH3· + H2O
(3)
H· + O2 → OH· + O·
(4)
CH 3· + O2 → HCO· + H2O
(5)
HCO· + OH· → CO + H2O
(6)
The composite powders are composed by the core part of RM and the outer layer of NaHCO3. As the temperature increase, the decomposition process of NaHCO3 is as show in equation (7) - (11). 2NaHCO3 → Na2CO3 + H2O + CO2↑
(7)
Na2CO3 → Na2O↑ + CO2 ↑
(8)
Na2O + H2O → 2NaOH
(9)
NaOH + H· → Na· + H2O
(10)
NaOH+ OH· → Na2O· + H2O
(11)
The Na· and Na2O· free radicals react with the OH· and H· free radical generated by CH4 explosion (12) - (13), which can interrupt the chain reaction and suppress the explosion. On the other hand, the CO2 that generated by the decomposition of NaHCO3, plays an important role in decreasing the concentration of reactants. Na· + OH· → NaOH
(12)
Na2O· + H· → NaOH + Na·
(13)
The dispersed RM core had numerous of pores, which can grab more free radicals to retard the explosion chain reaction. The main ingredients of modified RM are SiO2, Fe(OH)3 and Al(OH)3. During the explosion, SiO2 is not involved in the reaction; only has a physical effect of absorb explosion heat. The Fe(OH)3 and 13
Al(OH)3 decompose and produce the corresponding oxides of Fe2O3 , Al2O3, and H2O (8-9). At high temperature, the as-formed H2O absorbs the heat and immediately endothermic vaporization, thus effectively reducing the methane explosion intensity. 2Al(OH)3 → Al2O3 + 3H2O↑
(8)
2Fe(OH)3 → Fe2O3 + 3H2O↑
(9)
In summary, the different constituents and unique structure of the NaHCO3/RM composite powders play an important role in the process of explosion suppression. The RM base materials have a good combination with the NaHCO3 loading component, which give full play to the synergistic explosion suppression, and achieve a better inhibitory effect. 4. Conclusion (1) NaHCO3/RM composite powders are successfully prepared by a solvent-anti-solvent method. The XRD analyses exhibited typical peaks of NaHCO3 and RM, which proved that those components are contained in the composite powders. From the SEM testing, a unique core-shell structure can be clearly observed. The comprehensive thermal analysis results showed that the as-obtained NaHCO3/RM composite powders have excellent heat absorption characteristic. (2) The explosion suppression testing indicated that the core-shell NaHCO3/RM composite powders with core-shell structure possess an excellent synergistic effect on explosion suppression. After loading NaHCO3, RM exhibited an increased suppression on the explosion. As the loading of NaHCO3 reached 35%, the composite powders exhibited a much better explosion inhibition effect than that of single NaHCO3. When the 35%-NaHCO3/RM was used as gas explosion suppression powder material, the explosion max-pressure declined 44.9%, the maximum rate of pressure rise declined 96.3% and the time of the pressure peak arrival delayed 366.7%, respectively. (3) By using cheap industrial waste RM as the carrier, the high efficiency gas explosion suppressant composite powders were successfully prepared. For the consideration of costing and effect of explosion suppression, the RM is a desirable 14
raw material for the preparation of new kind chemical powder inhibitor. The use of RM powder provided an economical new way for the explosion suppression.
Notes The authors declare no competing financial interests.
Acknowledgment This work was supported by the National Natural Science Foundation of China (51504083, 51404097, 51674104, U1361205, 51574111), China Postdoctoral Science Foundation funded project (2016M592290), the Fundamental Research Funds for the Universities of Henan Province (NSFRF1606), Program for Science & Technology Innovation Talents in Universities of Henan Province (17HASTIT029), Program for Innovative Research Team in University of Ministry of Education of China (IRT-16R22), Foundation for Distinguished Young Scientists of Henan Polytechnic University (J2016-2, J2017-3).
References [1] X. Cao, J. Ren, M. Bi, Y. Zhou, Y. Li, Experimental research on the characteristics of methane/air explosion affected by ultrafine water mist, J. Hazard. Mater. 324 (2017) 489-497. [2] B. Nie, X. He, R. Zhang, W. Chen, J. Zhang, The roles of foam ceramics in suppression of gas explosion overpressure and quenching of flame propagation, J. Hazard. Mater. 192 (2011) 741-747. [3] X. Cao, J. Ren, Y. Zhou, Q. Wang, X. Gao, M. Bi, Suppression of methane/air explosion by ultrafine water mist containing sodium chloride additive, J. Hazard. Mater. 285 (2015) 311-318. [4] Á. Ramírez, J. Garcíatorrent, P. J. Aguado, Determination of parameters used to prevent ignition of stored materials and to protect against explosions in food industries, J. Hazard. Mater. 168 (2009) 115-120. [5] L.G. Zheng, K. Zheng, R.K. Pan, M.G. Yu, H. You, S.Y. Hou, Inhibition of the 15
premixed CH4/air deflagration by powdered extinguishing agents, Procedia Eng. 71 (2014) 230-237. [6] J.J.L.D. Plessis, Active explosion barrier performance against methane and coal dust explosions, Int. J. Coal Sci. Technol. 2 (2015) 261-268. [7] H. Shao, S. Jiang, Z. Wu, W. Zhang, K. Wang, Influence of diaphragm thickness on gas explosion suppression by vacuum chamber, Powder Technol. 295 (2016) 245-253. [8] M. Yu, S. Wan, Y. Xu, K, Zheng, D. Liang, The influence of the charge-to-mass ratio of the charged water mist on a methane explosion, J. Loss Prev. Process Ind. 41 (2016) 68-76. [9] X. Kang, R.J. Gollan, P.A. Jacobs, A. Veeraragavan, Suppression of instabilities in a premixed methane-air flame in a narrow channel via hydrogen/carbon monoxide addition, Combust. Flame 173 (2016) 266-275. [10] J. H. Sun, Q. U. Zheng, C. R. Wei，S. T. Wang, J. P. Zhang, Experimental and mechanism study on gas explosion flame suppressed by foam metal, J. Min Saf. Eng. 30 (2013) 463-467. [11] A. E Dahoe，R. S Cant，B. Scarlett, On the decay of turbulence in the 20-Liter explosion sphere, Flow Turbul Combust. 67 (2001) 159-184. [12] B. Jiang, Z. Liu, M. Tang, K. Yang, P. Lv, B. Lin, Active suppression of premixed methane/air explosion propagation by non-premixed suppressant with nitrogen and ABC powder in a semi-confined duct, J. Nat. Gas. Sci. Eng. 29 (2016) 141-149. [13] M. G. Yu, T. Wang, H. You, A. An, Study on the effect of thermal property of powder on the gas explosion suppression, Procedia Eng. 26 (2011) 1035-1042. [14] Z. Luo, T. Wang, Z. Tian, F. Cheng, J. Deng, Y. Zhang, Experimental study on the suppression of gas explosion using the gas–solid suppressant of CO2 /ABC powder, J. Loss Prev. Process Ind. 30 (2014) 61-67. [15] D. Huang, X. Wang, J. Yang, Influence of particle size and heating rate on decomposition of BC dry chemical fire extinguishing powders, Part. Sci. Technol. 33 (2015) 488-493. 16
[16] Y. Zhang, J.L. Zhang, B.M. Zhang, J.J. Wang, A Study on explosion suppression effect of No. 92 gasoline vapor-air mixture using ABC and BC dry powders, China. Safe Sci. J. 23 (2013) 53-58. [17] Z.M. Luo, F.M. Cheng, T. Wang, J. Deng, C.M. Shu, Suppressive effects of silicon dioxide and diatomite powder aerosols on coal mine gas explosions in highlands, Aerosol. Air. Qual. Res. 16 (2016) 2119-2128. [18] Q. Liu, Y. Hu, C. Bai, M. Chen, Methane/coal dust/air explosions and their suppression by solid particle suppressing agents in a large-scale experimental tube, J. Loss Prev. Process Ind. 26 (2013) 310-316. [19] M. Krasnyansky, Prevention and suppression of explosions in gas-air and dust-air mixtures using powder aerosol-inhibitor, J. Loss Prev. Process Ind. 19 (2006) 729-735. [20] F.M. Cheng, J. Deng, H. Wen, Z.M. Luo, S.R. Li, Experiment study on SiO2 nanometer powder to restrain gas explosion, Coal Sci. Technol. 38 (2010) 73-75. [21] W. Kordylewski, J. Amrogowicz, Comparison of NaHCO3 and NH4H2PO4 effectiveness as dust explosion suppressants, Combust. Flame. 90 (1992) 344-345. [22] Q. H. Wang, J. Deng, Z. M. Luo, Y. Xiao, Research on effects of methane explosion suppression by ultrafine magnesium hydroxide powder, China. Saf. Sci. J. 24 (2014) 33-37. [23] H. Wen, Q. H. Wang, J. Deng, Z. M. Luo, Effect of the concentration of Al(OH)3 ultrafine powder on the pressure of methane explosion, J. China. Coal. Soc. 34 (2009) 1479-1482. [24] X. M. Zhou, L. Z. Jiang, T. Chen, Surface characteristics and fire-extinguishing ability of superfine-powder fire-extinguishing agent, J. Combust. Sci. Technol. 15 (2009) 214-218. [25] A. V. Fedorov, P. A. Fomin, D. A. Tropin, Z. R. Chen, Parameters, limits, attenuation, and suppression of detonation in mixtures of an explosive gas with chemically inert microparticles, J. Eng. Phys. Thermophys. 85 (2012) 368-381. [26] X. Wang, T. Wang, H. Xu, J. Yang, P. Wolanski, Modification of commercial BC 17
dry chemical powder suppressant and experiments on suppression of methane-air explosion, Ciesc. J. 66 (2015) 5172-5177. [27] X. M. Ni, X. Wang, S. Zhang, M. Zhao, Experimental study on the performance of transition metal ions modified zeolite particles in suppressing methane/air coflowing flame on cup burner, J. Fire. Sci. 32 (2014) 417-430. [28] Z. Z. Zhang, N. Gu, J. F. Zhang, The application of aqueous span 80 composite material in methane absorption and explosion suppression, Mater. Sci. Forum. 610-613 (2009) 125-129. [29] Q. M. Zuo, W. M. Cheng, G. G. Zou, J. X. Tang, Applied experiments on coal dust inhibitor based on the theory of synergistic effect. J. Chongqing. Univ. 35 (2012) 105-356. [30] X. M. Ni, K. Q. Kuang, D. L. Yang, X. Jin, G. X. Liao, A new type of fire suppressant powder of NaHCO3/zeolite nanocomposites with core-shell structure. Fire. Safety. J. 44 (2009) 968-975. [31] X. M. Ni, Z. Zheng, X. Wang, S. Zhang, M. Zhao, Fabrication of hierarchical zeolite
4A
microspheres
with
improved
adsorption
capacity
to
bromofluoropropene and their fire suppression performance, J. Alloys. Compd. 592 (2014) 135-139. [32] X. M. Ni, K.Q. Kuang, D.L. Yang, G.X. Liao, Experimental study on the suppression of methane/air diffusion flame by iron-modified zeolite powders, China. Safety. Sci. J. 22 (2012) 53-57. [33] M. Zhao，X. M. Ni, S. Zhang, W. Cao, Y Guan, C. Liang, X. Wang, H. Zhang, Improving the performance of fluoroprotein foam in extinguishing gasoline pool fires with addition of bromofluoropropene, Fire. Mater. 40 (2016) 261-272. [34] W. A. Rosser, J. S. H. Inami, H. Wise, The effect of metal salts on premixed hydrocarbon-air flames, Combust. Flame. 7 (1963) 107-119. [35] Y. Huang, G. Han, J. Liu, W. Wang, A facile disposal of Bayer red mud based on selective flocculation desliming with organic humics, J. Hazard. Mater. 301 (2016) 46-55. [36] B. Xu, F. Qi, J. Zhang, H. Li, D. Sun, D. Robert, Z. L. Chen, Cobalt modified red 18
mud catalytic ozonation for the degradation of bezafibrate in water: Catalyst surface properties characterization and reaction mechanism, Chem. Eng. J. 284 (2016) 942-952. [37] H. Metecan, T. Karayildirim, J. Yanik, M. Saglam, M. Yuksel, The effect of sulfur-promoted red mud catalysts on hydroliquefaction of oil shale, Oil Shale. 20 (2003) 69-79. [38] Y. J. Liu, R. Naidu, H. Ming, Red mud as an amendment for pollutants in solid and liquid phases, Geoderma.163 (2011) 1-12. [39] M. G. Yu, J. Kong, Y. Wang, K. Zheng, L. G. Zheng, Experimental research on gas explosion suppression by modified red mud, J. Coal. Soc. 39 (2014) 1289-1295. [40] W. Kutner, J. Wang, M. L’her, R. P. Buck, Analytical aspects of chemically modified electrodes: Classification, critical evaluation and recommendations (IUPAC Recommendations 1998), Pure. Appl. Chem. 70 (2009) 1301-1318. [41]C. T. Bowman, D. J. Seery. Investigation of No Formation Kinetics in Combustion Processes: the Methane-Oxygen-Nitrogen Reaction. [M] Emissions from Continuous Combustion Systems. Springer US, (1972) 123-139.
19
S0304-3894(17)30273-X http://dx.doi.org/doi:10.1016/j.jhazmat.2017.04.031 HAZMAT 18514
To appear in:
Journal of Hazardous Materials
Received date: Revised date: Accepted date:
23-12-2016 22-3-2017 10-4-2017
Please cite this article as: Yan Wang, Yi-shen Cheng, Ming-gao Yu, Yao Li, Jianliang Cao, Li-gang Zheng, Hong-wei Yi, Methane explosion suppression characteristics based on the NaHCO3/red-mud composite powders with core-shell structure, Journal of Hazardous Materialshttp://dx.doi.org/10.1016/j.jhazmat.2017.04.031 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Methane explosion suppression characteristics based on the NaHCO3/red-mud composite powders with core-shell structure Yan Wanga,c, Yi-shen Chenga,c, Ming-gao Yub, Yao Lia,c, Jian-liang Caoa,c, Li-gang Zhenga,c Hong-wei Yia,c, a
State Key Laboratory Cultivation Bases Gas Geology and Gas Control (Henan Polytechnic
University), Jiaozuo, Henan 454000, PR China b
State Key Laboratory of coal mine disaster dynamics and control, Chongqing University,
Chongqing 400044, PR China c
The Collaboration Innovation Center of Coal Safety Production of Henan Province, Jiaozuo,
Henan 454000, PR China
Abstract The NaHCO3/red-mud (RM) composite powders were successfully prepared by the solvent-anti-solvent method for methane explosion suppression. The RM was used as a carrier, and the NaHCO3 was used as a loaded inhibitor. The NaHCO3/RM composite powders showed a special core-shell structure and excellent endothermic performance. The suppression properties of NaHCO3/RM composite for 9.5% CH4 explosion were tested in a 20 L spherical explosion vessel and a 5 L Perspex duct. The results showed that the NaHCO3/RM composite powders displayed a much better suppression property than the pure RM or NaHCO3 powders. The loading amount of NaHCO3 has an intensive influence on the inhibition property of NaHCO3/RM composite powders. The best loaded content of NaHCO3 is 35%. It exhibited significant inhibitory effect that the explosion max-pressure declined 44.9%, the max-pressure rise rate declined 96.3% and the pressure peak time delayed 366.7%, respectively. Keywords: NaHCO3/red-mud composite; methane; explosion suppression; core-shell structure
Corresponding author. Tel./fax: +86 13333910808 E-mail address:[email protected] (M. Yu) 1
1. Introduction Mine gas explosion is one of the major disasters in coal mine production, which seriously affects the safety production of coal industry. The main component of mine gas is methane that a flammable and explosive gas. Inhibitor of the methane explosion is considered to be the key for explosion suppression in coal industry. In recent years, some studies of various inhibitors have been made great progress on the methane explosion suppression. Cao et al. [1-4] researched on explosion suppression property of the ultrafine water mist, which can influence on the flame structure during the propagation process and presented good inhibition performances. Brinkmann.C et al. [5-8] studied on the suppression property of inert gas, which can decrease the explosion limits and maximum overpressure significantly. Nie et al. [9-11] researched on porous materials inhibitors which can contribute to quench the gas explosion flame and suppress the explosion shock wave. As an excellent explosion suppression material, powder material owing the advantages of easy storage, low cost, high efficiency and environmentally benign, has attracted the many attentions and has been applied in the field of methane explosion suppression. According to previous reports, CaCO3, SiO2, NaHCO3, Al(OH)3, (NH4)2SO4, NaCl, diatomite and bauxite all have certain inhibitory effect on methane explosion [12-17]. At present, the development trend of the fire/explosion suppression powders can be concluded as following: 1) Economic, efficient and environmental benign new 2
materials [18-19]. For example, Cheng and co-works selected the natural mineral powder as the explosion suppression material and found that diatomite powder has an inhibitory effect on the gas explosion, which is better than the quartz powder [20]. Kordylewsy et al. studied the explosion suppression material NaHCO3, which exhibits higher efficiency and better suppression performance than that of CaCO3 [21]. 2) Micro/nano ultrafine powder materials [22-23]. For example, Zhou et al. reported that the micro/nano grade ultrafine powder has better extinguishing effect [24]. The research of preventing the formation of detonation shows that the smaller inert particles have strong affection [25]. 3 ） Composite or modification explosion suppression material [26-28]. For instance, using the technology of synergistic, Zuo and co-workers selected Al(OH)3, ammonium polyphosphate and nanostructure diatomite as monomer and synthesized a complex substance for coal dust suppressant [29]. Liao and Ni using porous zeolite as the carrier fabricate a series of core shell structure extinguishing composite materials, which all presented excellent efficiency on extinguishment [30-33]. Likewise, Rosser et al. used zeolite and NaHCO3 to fabricate a new composite extinguishing agent [34]. These experimental results proved that the composite suppressant has better explosion suppression property due to the synergistic inhibition effect. Red mud (RM) is a by-product of the Bayer process in aluminum industry, which primarily composed of Fe2O3, Al2O3, SiO2, CaO and Na2O etc. 1 kg of alumina approximately generates 0.3-0.2 kg of RM as the by-products. If no proper disposal was done, serious pollution can be caused by the MP for its high alkalinity. However, as a very fine material, RM has evenly distributed components which average size is all bellow 10μm. Nowadays, RM is used as catalyst carrier and pollution control materials for its high added value [35-38]. Based on industrial modified treatment, the as-obtained ultrafine RM with abundant micropores and larger surface area exhibits a great application prospect when used as gas explosion suppression powder material [39]. NaHCO3 is also a typical suppressant for gas explosion, which can combine with other power material to create a new type of powder explosion suppressant and fire extinguishing agent. 3
In this work, the NaHCO3/RM composite powders were successfully prepared using the industrial solid waste RM as the base materials, and adopting the solvent-anti-solvent method to load NaHCO3 particles. Moreover, their characteristics of methane explosion suppression were further studied. 2. Experimental section 2.1. Preparation of NaHCO3/RM composite powders The NaHCO3/RM composite powders were prepared with modified RM powders and NaHCO3 crystals. The raw RM was collected from Henan Zhongmei Aluminum Corporation, China. All of the other chemical reagents were analytical grade without further purification. The modified RM powders were preparation according to the method reported by Yu [39]. The NaHCO3/RM composite powders with different amount NaHCO3 were prepared by the solvent-anti-solvent method. The preparation process was as following. Firstly, 8 groups of NaHCO3 saturated solution were prepared with different weight percentage (5%, 10%, 15%, 10%, 25%, 30%, 35% and 40%). Then, 10g modified RM powders were dispersed in ethanol with stirring to become suspension solution, which was prepared 8 parallel groups for further using. Under magnetic stirring, the as-prepared 8 groups of suspension solution was poured into the above 8 groups’ saturated NaHCO3 solution, respectively. The as-obtained 8 groups of mixture continued stirring 2h, aging 4 h, ultrasonication for 30 min, and then filtered out the precipitated and dried in vacuum for 12h. Finally, different NaHCO3/RM composite powders were obtained.c 2.2. Characterization X-ray diffraction (XRD) analysis was carried out on a Philiphs X’Pert Super diffractometer with Cu Kα radiation (λ= 1.54178 Å). The morphology of the products was examined by field emission scanning electron microscope (FE-SEM, JMS-6390LV). The pyrolysis characteristic of the composite powders was characterized by Thermogravimetry-Differential Scanning Calorimetry (TG-DSC) method using the STA449C model synchronization thermal analyzer. Nitrogen absorption/desorption isotherms were recorded using an automatic physical/chemical adsorption analyzer (Quantachrome Instruments U.S.) via conventional volumetric 4
technique at 20ºC. The specific surface area (SBET) was calculated by the Brunauere-Emmette-Teller (BET) method. The total pore volume (Vtotal) was estimated from the amount of nitrogen adsorbed at p/p0 ~0.99. 2.3. Explosion experiment In present work, the maximum explosion pressure (Pm) and maximum rate of pressure rise (dP/dt)max were performed in a standard 20 L stainless steel spherical vessel. Before each testing, 2g composite powders were placed in a powder container (volume: 0.6 L). Then the centrally mounted electrical pulse igniter was connected with the ignition leads, and the explosion chamber was closed safely. In the experiments, 9.5% methane-air mixtures were formulated by the partial pressure ratio method. In the preparation process of explosive gas mixtures, it should be ensured that the internal pressure of explosion chamber was 0.06 MPa and the dispersing air pressure was set to 2 MPa. After the solenoid valve between the powder container and the test chamber was triggered, the high pressure air and the powders were dispersed into the explosion chamber through the rebound type nozzle installed at the bottom of the chamber. The injection process lasted 50 ms. Then after a 60 ms time delay, the electrical pulse igniter was energized, and the discharge time lasted 0.5s. Synchronously, the explosion pressure evolutions were measured by the pressure sensor installed in the vessel wall and recorded by a data acquisition system. The flame propagation rate was tested in another tubular instrument in the report. The experiments were performed in a 5 L Perspex duct with a cross-section of 100 100mm2 and height of 500 mm. The bottom end of the duct was fully closed by a steel plate, and the open end was sealed with a thin PVC membrane to contain the premixed flammable mixture. The detailed experimental procedure was as follows. Firstly, composite powders were evenly sprinkled around the bottom of the bowl-shape powder container. Then the premixed 9.5% methane-air mixtures entered the duct through an inlet at the bottom steel plate. At last, the solenoid valve controlled by synchronous controller was triggered, and the 0.3 MPa premixed 9.5% methane-air mixtures flowed through the nozzle and hence, dispersed the powders into the duct. The injection process lasted 50 ms, then after a 60 ms delay, the 5
methane-air mixtures in the duct were ignited automatically by the electrical pulse igniter, and the discharge time lasted 0.5s. Meanwhile, the flame propagation images were captured by a “LaVision 4G” high-speed camera, which could achieve acquisition rate at a speed of 2000 frames/s with an array of 1024 1024 pixels. 3. Results and discussion 3.1. Materials analysis
Fig. 1. XRD patterns of 35%-NaHCO3/RM composite, RM and NaHCO3.
Fig. 1 shows the XRD patterns of the as-prepared 35%-NaHCO3/RM composite, RM and NaHCO3, respectively. As can be seen from Fig. 1, the characteristic diffraction peaks of 35%-NaHCO3/RM composite and RM are basically the same. However, 35%-NaHCO3/RM also appeared the characteristic diffraction peaks attributed to NaHCO3 crystal phase at 15.3, 18.5, and 40.8 (2θ), indicating that the NaHCO3 crystal particles were successfully loaded on the RM surface. The results showed that the as-prepared 35%-NaHCO3/RM composite is composed by NaHCO3 and RM. Fig. 2 displayed the SEM images of NaHCO3 particles, RM particles and 35%-NaHCO3/RM composite powders. Fig. 2a showed that NaHCO3 crystals consisted of quasi-sphere particles with the size of about 1-2 μm. Fig. 2b indicated that the RM had relatively smooth surface with layered structure, and RM particles were accumulated with micropore structure. However, as is shown in Fig. 3c, when 6
the RM was loaded with NaHCO3, the surface became rough. The surface of the composite powders is covered with a lot of tiny quasi-sphere particles with the size about 1-2 μm, which is NaHCO3 crystals dispersed on the surface of RM and forming a core-shell structure. The solvent-anti-solvent method not only made the RM particles dispersed more evenly, but also made RM and NaHCO3 composite successfully.
Fig. 2. SEM images of NaHCO3 particles (a), RM particles (b) and 35%-NaHCO3/RM composite powders (c).
Fig. 3 presented the TG-DSC curves of the RM and composite, respectively. As shown in the Fig. 3 the TG curve of RM declined smoothly that was due to the decomposition of partial hydroxides, and the weight loss was 28.2%. In contrast, the 35%-NaHCO3/RM composite was stepped with three stages. The first stage from 25 to 125 ºC with the weight loss of 19.5% should be ascribed to the lost of adsorbed and intercalated moisture.The second stage from 125 to 700 ºC with weight loss of 18.5% should attribute to the decomposition of partial hydroxides. The third stage around 700 ºC only with weight loss of 0.8% indicated that the composite powder became stable after 700 ºC. Therefore, the total weight loss of the 35%-NaHCO3/RM composite was 38.4%, which should ascribe to the loaded of NaHCO3 forming a 7
core-shell structure. The corresponding endothermic processes were also shown in DSC curves. As can be seen, the RM exhibited three endothermic peaks, and the 35%-NaHCO3/RM composite presented five endothermic peaks in the range from room temperature to 800 ºC. According to integrating the area of the endothermic peaks on DSC curves, the total endothermic quantity of the RM was 430.57 J/g, and the total endothermic quantity of 35%-NaHCO3/RM composite was 697.9 J/g, which indicated the composite had a better heat absorption performance. 1.5
RM
── 35%-NaHCO3/RM composite
Mass/%
90
d
1.0
b
0.5
80
0.0
a -0.5
70
c
DSC/(mW/mg)
---
100
-1.0
60 100
200
300 400 500 Temperature/
600
700
-1.5 800
Fig. 3.TG-DSC curves of the RM and composite powders: TG (a) and DSC (b) curves of RM, TG (c) and DSC (d) curves of 35%-NaHCO3/RM composite.
Fig. 4 shows N2 adsorption-desorption isotherms and the corresponding pore size distributions curves (PSDs) of RM and 35%-NaHCO3/RM composite powders. As shown in Fig. 4a, the RM and 35%-NaHCO3/RM composite powders all showed typical type IV isotherms with obvious hysteresis loops [40]. However, the 35%-NaHCO3/RM composite powder exhibited a much lower N2 adsorption amount than that of RM, because part of the space in RM was filled with NaHCO3 particles after successful loading. The corresponding PSDs of RM and 35%-NaHCO3/RM composite powders were showed in Fig. 4b, all exhibiting peaks centered at about 2-5 nm without obvious shape change, which means that the loading process of NaHCO3 did not change the pore size of original RM carrier. Therefore, a conclusion can be obtained that the NaHCO3 particles organically combined with RM forming NaHCO3/RM composite powders and maintained basic distribution characteristics of the RM carrier at the same time. 8
RM 35% -NaHCO3/RM
Volume adsorbed（ cc/g）
120
0.10
a
RM 35% -NaHCO3/RM
0.08
dV/dD (cc/nm/g)
100
b
0.06
80 60
0.04
40
0.02
20
0.00 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Relative pressure（ P/P0）
0
5
10
15
20
25
30
35
40
Pore diamater(nm)
Fig. 4. N2 adsorption-desorption isotherms (a) and the pore size distribution (b) of the RM and the 35%-NaHCO3/RM composite powders.
The specific surface area and pore volume of RM and the 35%-NaHCO3/RM composite powders were summarized in Table 1. The specific surface area and pore volume of RM decreased with the NaHCO3 loaded. The RM exhibited a specific surface area of 128.16 m2·g-1 as well as the pore volume of 0.158 cm3·g-1, which all higher than that of the 35%-NaHCO3/RM composite powders (SBET = 65.77 m2·g-1, Vtotal = 0.090 cm3·g-1), meaning that NaHCO3 particles were successfully loaded on the RM carrier. Table 1 Specific surface area and pore volume of RM and the 35%-NaHCO3/RM composite powder. Samples
SBETa（m2·g-1）
Vtotalb（cm3·g-1）
RM
128.16
0.158
35%-NaHCO3/RM
65.77
0.090
a
SBET specific surface area calculated by the Brunauere-Emmette-Teller (BET) method. Vtotal pore volume at p/p0 ~ 0.99.
b
3.2. Explosion suppression tests The explosion pressure parameters were performed on a 20 L spherical vessel. In the situation of 9.5% methane-air premixed gas explosion, the explosion inhibitory properties of the pure NaHCO3, RM and NaHCO3/RM composite powders were tested all with the same concentration of 0.1 g/L. The experimental results are presented in Fig. 5. 9
a
0.8
30%
0.4
5%composite
15%composite
25%composite
0.412MPa(44.9%↓)
40%composite
0.1
0.2
0.3 Time/s
0.4
0.5
C
45 41.15MPa/s
35 30 25 (48.9%↓)
15 (74.7%↓) (82.6%↓) (80.8%↓) (84.4%↓)
0.0
0.6
(94.1%↓) (95.8%↓) (88.9%↓) (93.2%↓) (96.3%↓)
0
The time of pressure peak arriving/s
0.0
The maximum rate of pressure rise/(Mpa/s)
0.446Mpa(40.4%↓)
35%composite
0.0
5
0.479Mpa(35.9%↓)
30%composite
0.1
10
0.525MPa(29.8%↓) 0.498MPa(33.4%↓)
20%composite
0.2
20
0.544Mpa(27.3%↓)
35%
0.3
40
0.569MPa(23.9%↓)
10%composite
40%
b
0.457MPa(38.9%↓)
NaHCO3 5% 10% NaHCO3 15% 20% 25%
0.5
0.748MPa
0.651MPa(12.9%↓)
RM
RM
0.6
Pressure/MPa
no powder
no powders
0.7
0.456Mpa(39.1%↓)
0.1
0.2
0.3 0.4 0.5 0.6 Pressure/MPa
0.7
0.8
0.50 508.8%
0.45
0.9
d
0.40 366.7%
0.35 0.30
284%
292%
0.25
183.2%
0.20
132%
0.15 104%
0.10
161.6%
180%
47.2%
0.05 0.075s 0.00
NP RM NaHCO3 5% 10% 15%20% 25% 30% 35%40%
NP RM NaHCO35% 10% 15%20%25% 30% 35% 40%
Fig. 5. The inhibition effect of different inhibitors: the explosion pressure curves (a), the maximum pressure peak (b), the maximum rate of pressure rise (c), the time of the pressure peak arrival (d).
Fig. 5a presents the explosion pressure curves with pure RM, NaHCO3 and NaHCO3/RM composite loading different amount of NaHCO3 (weight percentage of 5%, 10%, 15%, 20%, 25%, 30%, 35% and 40%). We can see from Fig. 5a, that when RM loading with NaHCO3, the maximum explosion pressure is decreased, and the explosion delay time is increased. With the loading amount of NaHCO3 increased, correspondingly, the inhibitory efficiency of explosion for composite powder suppressant increased. When the loading amount of NaHCO3 reached 35%, the explosion pressure exhibited the most significant inhibition effect with the composite powders. The max-pressure, the maximum rate of pressure rise and the time of the pressure peak arrival were exhibited in Fig. 5b, c and d, respectively. As can be seen clearly, the 35-%NaHCO3/RM composite powders exhibited significant inhibitory effect that the explosion max-pressure declined 44.9%, the max-pressure rise rate declined 96.3% and the pressure peak time delayed 366.7%, respectively. Therefore, the 35%-NaHCO3/RM composite powder possesses the best efficiency on explosion 10
suppression. The inhibitory of flame propagation rate was tested in a 5 L Perspex duct. As is shown in Fig. 6, the explosion flame propagation rate had been effectively retarded after adding suppressants, especially the adding of the 35%-NaHCO3/RM composite
Flame propagation rate (m/s)
powders.
60
no powders
50 40
RM NaHCO3
30 20 10 0
35%-NaHCO3/RM composite
0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10
Time/s
Fig. 6. The flame propagation rate with different inhibitors
Fig. 7. The photographs of explosion flame in different conditions: no powders (a), RM (b), NaHCO3 (c) and the 35%-NaHCO3/RM composite powder (d).
As presented in Fig. 7, the explosion flame photographs were captured by a high 11
speed camera. If no suppressants added, the flame propagation rate increased sharply (Fig. 7a). However, when the suppressants added, the flame propagation rate tend to be increased steadily (Fig. 7b and c), which led to the delay of explosion flame propagation process. It is noteworthy that the 35%-NaHCO3/RM composite powders exhibited the best inhibition performance of flame propagation rate (Fig. 7d), which is consistent with the 20 L spherical explosive device testing results. The 35%-NaHCO3/RM composite powders possess much better suppression property than pure RM and NaHCO3. 3.3. Mechanism of gas explosion suppression discussion The explosion suppression experimental results show that the core-shell NaHCO3/RM composite powders have significant inhibitory effect on methane explosion, which can be mainly manifested in the following two aspects.
Fig. 8. The inhibition mechanism diagrammatic sketch of the NaHCO3/RM composite powders
1) Physical synergistic inhibition effect. The composite powders have a special core-shell structure, which exhibit a significant synergistic inhibition effect in the explosion process. The inhibition mechanism diagrammatic sketch of the NaHCO3/RM composite powders was illustrated in Fig. 8. Under high temperature, the outer NaHCO3 particles detached from NaHCO3/RM composite, and fully dispersed in the explosion space. The NaHCO3 pyrogenic decomposed and react with the free radicals, which generated by CH4 explosion. On the other side, because the outer layer NaHCO3 departed from the RM base materials, the RM particles, which have larger surface area and lots of pores, 12
were fully exposed and contact the free radicals of CH4 explosion. The above two factors simultaneously play the role of explosion suppression, thus forming a synergistic inhibition effect. 2) Chemical synergistic inhibition effect. As generally known, the mechanism of methane combustion is as the following key chain reactions (1) - (6) [41]. CH4 → CH3· + H·
(1)
CH4 + O2 → CH 3· + OH·
(2)
CH4 + OH· → CH3· + H2O
(3)
H· + O2 → OH· + O·
(4)
CH 3· + O2 → HCO· + H2O
(5)
HCO· + OH· → CO + H2O
(6)
The composite powders are composed by the core part of RM and the outer layer of NaHCO3. As the temperature increase, the decomposition process of NaHCO3 is as show in equation (7) - (11). 2NaHCO3 → Na2CO3 + H2O + CO2↑
(7)
Na2CO3 → Na2O↑ + CO2 ↑
(8)
Na2O + H2O → 2NaOH
(9)
NaOH + H· → Na· + H2O
(10)
NaOH+ OH· → Na2O· + H2O
(11)
The Na· and Na2O· free radicals react with the OH· and H· free radical generated by CH4 explosion (12) - (13), which can interrupt the chain reaction and suppress the explosion. On the other hand, the CO2 that generated by the decomposition of NaHCO3, plays an important role in decreasing the concentration of reactants. Na· + OH· → NaOH
(12)
Na2O· + H· → NaOH + Na·
(13)
The dispersed RM core had numerous of pores, which can grab more free radicals to retard the explosion chain reaction. The main ingredients of modified RM are SiO2, Fe(OH)3 and Al(OH)3. During the explosion, SiO2 is not involved in the reaction; only has a physical effect of absorb explosion heat. The Fe(OH)3 and 13
Al(OH)3 decompose and produce the corresponding oxides of Fe2O3 , Al2O3, and H2O (8-9). At high temperature, the as-formed H2O absorbs the heat and immediately endothermic vaporization, thus effectively reducing the methane explosion intensity. 2Al(OH)3 → Al2O3 + 3H2O↑
(8)
2Fe(OH)3 → Fe2O3 + 3H2O↑
(9)
In summary, the different constituents and unique structure of the NaHCO3/RM composite powders play an important role in the process of explosion suppression. The RM base materials have a good combination with the NaHCO3 loading component, which give full play to the synergistic explosion suppression, and achieve a better inhibitory effect. 4. Conclusion (1) NaHCO3/RM composite powders are successfully prepared by a solvent-anti-solvent method. The XRD analyses exhibited typical peaks of NaHCO3 and RM, which proved that those components are contained in the composite powders. From the SEM testing, a unique core-shell structure can be clearly observed. The comprehensive thermal analysis results showed that the as-obtained NaHCO3/RM composite powders have excellent heat absorption characteristic. (2) The explosion suppression testing indicated that the core-shell NaHCO3/RM composite powders with core-shell structure possess an excellent synergistic effect on explosion suppression. After loading NaHCO3, RM exhibited an increased suppression on the explosion. As the loading of NaHCO3 reached 35%, the composite powders exhibited a much better explosion inhibition effect than that of single NaHCO3. When the 35%-NaHCO3/RM was used as gas explosion suppression powder material, the explosion max-pressure declined 44.9%, the maximum rate of pressure rise declined 96.3% and the time of the pressure peak arrival delayed 366.7%, respectively. (3) By using cheap industrial waste RM as the carrier, the high efficiency gas explosion suppressant composite powders were successfully prepared. For the consideration of costing and effect of explosion suppression, the RM is a desirable 14
raw material for the preparation of new kind chemical powder inhibitor. The use of RM powder provided an economical new way for the explosion suppression.
Notes The authors declare no competing financial interests.
Acknowledgment This work was supported by the National Natural Science Foundation of China (51504083, 51404097, 51674104, U1361205, 51574111), China Postdoctoral Science Foundation funded project (2016M592290), the Fundamental Research Funds for the Universities of Henan Province (NSFRF1606), Program for Science & Technology Innovation Talents in Universities of Henan Province (17HASTIT029), Program for Innovative Research Team in University of Ministry of Education of China (IRT-16R22), Foundation for Distinguished Young Scientists of Henan Polytechnic University (J2016-2, J2017-3).
References [1] X. Cao, J. Ren, M. Bi, Y. Zhou, Y. Li, Experimental research on the characteristics of methane/air explosion affected by ultrafine water mist, J. Hazard. Mater. 324 (2017) 489-497. [2] B. Nie, X. He, R. Zhang, W. Chen, J. Zhang, The roles of foam ceramics in suppression of gas explosion overpressure and quenching of flame propagation, J. Hazard. Mater. 192 (2011) 741-747. [3] X. Cao, J. Ren, Y. Zhou, Q. Wang, X. Gao, M. Bi, Suppression of methane/air explosion by ultrafine water mist containing sodium chloride additive, J. Hazard. Mater. 285 (2015) 311-318. [4] Á. Ramírez, J. Garcíatorrent, P. J. Aguado, Determination of parameters used to prevent ignition of stored materials and to protect against explosions in food industries, J. Hazard. Mater. 168 (2009) 115-120. [5] L.G. Zheng, K. Zheng, R.K. Pan, M.G. Yu, H. You, S.Y. Hou, Inhibition of the 15
premixed CH4/air deflagration by powdered extinguishing agents, Procedia Eng. 71 (2014) 230-237. [6] J.J.L.D. Plessis, Active explosion barrier performance against methane and coal dust explosions, Int. J. Coal Sci. Technol. 2 (2015) 261-268. [7] H. Shao, S. Jiang, Z. Wu, W. Zhang, K. Wang, Influence of diaphragm thickness on gas explosion suppression by vacuum chamber, Powder Technol. 295 (2016) 245-253. [8] M. Yu, S. Wan, Y. Xu, K, Zheng, D. Liang, The influence of the charge-to-mass ratio of the charged water mist on a methane explosion, J. Loss Prev. Process Ind. 41 (2016) 68-76. [9] X. Kang, R.J. Gollan, P.A. Jacobs, A. Veeraragavan, Suppression of instabilities in a premixed methane-air flame in a narrow channel via hydrogen/carbon monoxide addition, Combust. Flame 173 (2016) 266-275. [10] J. H. Sun, Q. U. Zheng, C. R. Wei，S. T. Wang, J. P. Zhang, Experimental and mechanism study on gas explosion flame suppressed by foam metal, J. Min Saf. Eng. 30 (2013) 463-467. [11] A. E Dahoe，R. S Cant，B. Scarlett, On the decay of turbulence in the 20-Liter explosion sphere, Flow Turbul Combust. 67 (2001) 159-184. [12] B. Jiang, Z. Liu, M. Tang, K. Yang, P. Lv, B. Lin, Active suppression of premixed methane/air explosion propagation by non-premixed suppressant with nitrogen and ABC powder in a semi-confined duct, J. Nat. Gas. Sci. Eng. 29 (2016) 141-149. [13] M. G. Yu, T. Wang, H. You, A. An, Study on the effect of thermal property of powder on the gas explosion suppression, Procedia Eng. 26 (2011) 1035-1042. [14] Z. Luo, T. Wang, Z. Tian, F. Cheng, J. Deng, Y. Zhang, Experimental study on the suppression of gas explosion using the gas–solid suppressant of CO2 /ABC powder, J. Loss Prev. Process Ind. 30 (2014) 61-67. [15] D. Huang, X. Wang, J. Yang, Influence of particle size and heating rate on decomposition of BC dry chemical fire extinguishing powders, Part. Sci. Technol. 33 (2015) 488-493. 16
[16] Y. Zhang, J.L. Zhang, B.M. Zhang, J.J. Wang, A Study on explosion suppression effect of No. 92 gasoline vapor-air mixture using ABC and BC dry powders, China. Safe Sci. J. 23 (2013) 53-58. [17] Z.M. Luo, F.M. Cheng, T. Wang, J. Deng, C.M. Shu, Suppressive effects of silicon dioxide and diatomite powder aerosols on coal mine gas explosions in highlands, Aerosol. Air. Qual. Res. 16 (2016) 2119-2128. [18] Q. Liu, Y. Hu, C. Bai, M. Chen, Methane/coal dust/air explosions and their suppression by solid particle suppressing agents in a large-scale experimental tube, J. Loss Prev. Process Ind. 26 (2013) 310-316. [19] M. Krasnyansky, Prevention and suppression of explosions in gas-air and dust-air mixtures using powder aerosol-inhibitor, J. Loss Prev. Process Ind. 19 (2006) 729-735. [20] F.M. Cheng, J. Deng, H. Wen, Z.M. Luo, S.R. Li, Experiment study on SiO2 nanometer powder to restrain gas explosion, Coal Sci. Technol. 38 (2010) 73-75. [21] W. Kordylewski, J. Amrogowicz, Comparison of NaHCO3 and NH4H2PO4 effectiveness as dust explosion suppressants, Combust. Flame. 90 (1992) 344-345. [22] Q. H. Wang, J. Deng, Z. M. Luo, Y. Xiao, Research on effects of methane explosion suppression by ultrafine magnesium hydroxide powder, China. Saf. Sci. J. 24 (2014) 33-37. [23] H. Wen, Q. H. Wang, J. Deng, Z. M. Luo, Effect of the concentration of Al(OH)3 ultrafine powder on the pressure of methane explosion, J. China. Coal. Soc. 34 (2009) 1479-1482. [24] X. M. Zhou, L. Z. Jiang, T. Chen, Surface characteristics and fire-extinguishing ability of superfine-powder fire-extinguishing agent, J. Combust. Sci. Technol. 15 (2009) 214-218. [25] A. V. Fedorov, P. A. Fomin, D. A. Tropin, Z. R. Chen, Parameters, limits, attenuation, and suppression of detonation in mixtures of an explosive gas with chemically inert microparticles, J. Eng. Phys. Thermophys. 85 (2012) 368-381. [26] X. Wang, T. Wang, H. Xu, J. Yang, P. Wolanski, Modification of commercial BC 17
dry chemical powder suppressant and experiments on suppression of methane-air explosion, Ciesc. J. 66 (2015) 5172-5177. [27] X. M. Ni, X. Wang, S. Zhang, M. Zhao, Experimental study on the performance of transition metal ions modified zeolite particles in suppressing methane/air coflowing flame on cup burner, J. Fire. Sci. 32 (2014) 417-430. [28] Z. Z. Zhang, N. Gu, J. F. Zhang, The application of aqueous span 80 composite material in methane absorption and explosion suppression, Mater. Sci. Forum. 610-613 (2009) 125-129. [29] Q. M. Zuo, W. M. Cheng, G. G. Zou, J. X. Tang, Applied experiments on coal dust inhibitor based on the theory of synergistic effect. J. Chongqing. Univ. 35 (2012) 105-356. [30] X. M. Ni, K. Q. Kuang, D. L. Yang, X. Jin, G. X. Liao, A new type of fire suppressant powder of NaHCO3/zeolite nanocomposites with core-shell structure. Fire. Safety. J. 44 (2009) 968-975. [31] X. M. Ni, Z. Zheng, X. Wang, S. Zhang, M. Zhao, Fabrication of hierarchical zeolite
4A
microspheres
with
improved
adsorption
capacity
to
bromofluoropropene and their fire suppression performance, J. Alloys. Compd. 592 (2014) 135-139. [32] X. M. Ni, K.Q. Kuang, D.L. Yang, G.X. Liao, Experimental study on the suppression of methane/air diffusion flame by iron-modified zeolite powders, China. Safety. Sci. J. 22 (2012) 53-57. [33] M. Zhao，X. M. Ni, S. Zhang, W. Cao, Y Guan, C. Liang, X. Wang, H. Zhang, Improving the performance of fluoroprotein foam in extinguishing gasoline pool fires with addition of bromofluoropropene, Fire. Mater. 40 (2016) 261-272. [34] W. A. Rosser, J. S. H. Inami, H. Wise, The effect of metal salts on premixed hydrocarbon-air flames, Combust. Flame. 7 (1963) 107-119. [35] Y. Huang, G. Han, J. Liu, W. Wang, A facile disposal of Bayer red mud based on selective flocculation desliming with organic humics, J. Hazard. Mater. 301 (2016) 46-55. [36] B. Xu, F. Qi, J. Zhang, H. Li, D. Sun, D. Robert, Z. L. Chen, Cobalt modified red 18
mud catalytic ozonation for the degradation of bezafibrate in water: Catalyst surface properties characterization and reaction mechanism, Chem. Eng. J. 284 (2016) 942-952. [37] H. Metecan, T. Karayildirim, J. Yanik, M. Saglam, M. Yuksel, The effect of sulfur-promoted red mud catalysts on hydroliquefaction of oil shale, Oil Shale. 20 (2003) 69-79. [38] Y. J. Liu, R. Naidu, H. Ming, Red mud as an amendment for pollutants in solid and liquid phases, Geoderma.163 (2011) 1-12. [39] M. G. Yu, J. Kong, Y. Wang, K. Zheng, L. G. Zheng, Experimental research on gas explosion suppression by modified red mud, J. Coal. Soc. 39 (2014) 1289-1295. [40] W. Kutner, J. Wang, M. L’her, R. P. Buck, Analytical aspects of chemically modified electrodes: Classification, critical evaluation and recommendations (IUPAC Recommendations 1998), Pure. Appl. Chem. 70 (2009) 1301-1318. [41]C. T. Bowman, D. J. Seery. Investigation of No Formation Kinetics in Combustion Processes: the Methane-Oxygen-Nitrogen Reaction. [M] Emissions from Continuous Combustion Systems. Springer US, (1972) 123-139.
19