Influence of Mechanical Grinding on Particle Characteristics of Coal Gasification Slag
Abstract
:1. Introduction
2. Materials and Methods
2.1. Raw Materials
2.2. Test Methods
2.3. Mathematical Model
2.3.1. Kinetic Equation of CGS Powder
2.3.2. RRB Model
3. Results and Discussion
3.1. PSD and Microstructure of CGS with Different Grinding Time
3.1.1. PSD Characteristics
3.1.2. Microstructure Characteristics
- (1)
- Particle stress refinement stage: Due to the high-speed operation of the grinding ball in the ball mill, the CGS particles are subjected to the collision stress of the grinding ball, and the particles are cracked and refined under impact. At this stage, the SSA of the CGS is linear with the grinding time. Since the whole process belongs to sealed grinding, a large amount of internal energy is generated during the operation of the system, which leads to the decline of the crystallization degree of the CGS particle crystal, the decrease in the bond energy of the internal chemical bond and the gradual increase in the surface-free energy in the system.
- (2)
- Stable stage: In this stage, the CGS gradually tends to the grinding limit, and the crystallization degree, chemical bond energy and surface free energy of CGS particles gradually tend to be stable.
- (3)
- Agglomeration stage: At this stage, due to the high surface free energy of CGS particles, they are more active and absorb a certain amount of water from the surrounding environment, forming a hydroxyl layer on the surface. The formation of hydroxyl layer reduces the electrostatic repulsion effect due to the relaxation phenomenon on the particle surface, and the formation of van der Waals force and hydrogen bond between hydroxyl groups leads to the agglomeration of CGS particles. After that, continuing the mechanical grinding of CGS leads the particle state gradually into reversible equilibrium.
3.2. Grinding Kinetics and RRB Model of CGS
3.3. Characteristic Particle Size and SSA of CGS with Different Grinding Time
3.4. Particle Size Fractal Dimension of CGS with Different Grinding Time
3.5. Strength Activity Index of CGS with Different Grinding Time
4. Conclusions
- (1)
- The results of PSD and microstructure of CGS by mechanical grinding show that with the increase in grinding time, the PSD of CGS is gradually concentrated, and the internal Si–O bond and water molecular structure are gradually destroyed. When the grinding time is more than 75 min, the hydroxyl layer will be formed on the surface of CGS particles. Van der Waals force and the hydrogen bond between hydroxyl groups will lead to “agglomeration phenomenon” of particles.
- (2)
- The mechanical grinding process of CGS can be quantitatively described by Divas–Aliavden grinding kinetics. The grinding efficiency of coarse particles is relatively high, and with the increase in grinding time, the grinding efficiency of coarse and fine particles gradually decreases and tends to zero. The PSD of CGS has a strong correlation with RRB model. With the increase in grinding time, the parameter particle size d* decreases and the distribution index n increases, indicating that the PSD of CGS tends to be concentrated.
- (3)
- With the increase in grinding time, the characteristic particle size of CGS gradually decreases, and the SSA gradually increases. Moreover, the characteristic particle size and SSA of CGS have a good linear relationship with the double logarithm and logarithm of the grinding time, respectively.
- (4)
- The PSD of CGS has obvious fractal characteristics. With the increase in grinding time, the fractal dimension of CGS particles increases gradually, which increases the difficulty of grinding. The fractal dimension has a good linear positive correlation with D50 and a good linear negative correlation with SSA.
- (5)
- The grinding time has a linear positive correlation with the strength activity index at different curing ages, which mainly affects the later strength activity index. The number of CGS particles at 20–30 μm and 10–20 μm has the greatest impact on the early and late strength activity indexes, respectively. Therefore, considering the economic and technical aspects, it is recommended that the optimal mechanical grinding time of CGS is 75 min.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
Abbreviations
References
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Testing Material | Chemical Composition (%) | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
SiO2 | Al2O3 | Fe2O3 | Na2O | CaO | SrO | SO3 | K2O | MgO | TiO2 | Other | |
ISO standard sand | +96 | - | - | - | - | - | - | - | - | - | −4 |
CGS | 30.94 | 11.01 | 23.22 | 5.58 | 17.19 | 3.28 | 2.02 | 0.78 | 0.83 | 0.61 | 4.54 |
Cement | 19.19 | 4.50 | 3.33 | 0.18 | 64.13 | 0.03 | 2.40 | 0.40 | 1.82 | 0.20 | 3.82 |
Representative Particle Size | 15 min | 30 min | 45 min | 60 min | 75 min |
---|---|---|---|---|---|
181.97 μm | 40.93 | 16.1 | 9.27 | 4.55 | 0.33 |
104.71 μm | 61.97 | 36.02 | 32.29 | 22.06 | 14.74 |
60.26 μm | 74.94 | 69.94 | 56.83 | 49.58 | 45.03 |
22.91 μm | 89.48 | 83.45 | 79.18 | 76.01 | 73.16 |
13.18 μm | 92.39 | 89.53 | 87.71 | 85.37 | 83.59 |
4.37 μm | 98.22 | 96.49 | 95.44 | 94.76 | 94.23 |
Representative Particle Size/μm | Kinetic Equation | R2 |
---|---|---|
181.97 | 0.98463 | |
104.71 | 0.96857 | |
60.26 | 0.89987 | |
22.91 | 0.98981 | |
13.18 | 0.96745 | |
4.37 | 0.99988 |
Grinding Time/min | n | d*/μm | ||
---|---|---|---|---|
Fitting Values | Measured Values | Error/% | ||
15 | 1.08 | 191.31 | 199.49 | 4.1 |
30 | 1.11 | 143.77 | 147.51 | 2.5 |
45 | 1.12 | 107.26 | 109.66 | 2.2 |
60 | 1.15 | 77.04 | 78.88 | 2.3 |
75 | 1.17 | 51.73 | 53.12 | 2.6 |
Characteristic Particle Size | 15 min | 30 min | 45 min | 60 min | 75 min |
---|---|---|---|---|---|
D10/μm | 18.72 | 15.31 | 11.52 | 8.76 | 5.78 |
D25/μm | 59.99 | 47.44 | 35.77 | 26.08 | 16.45 |
D50/μm | 147.37 | 110.38 | 82.12 | 59.72 | 39.87 |
D75/μm | 257.99 | 188.92 | 140.86 | 100.85 | 68.39 |
D90/μm | 373.61 | 279.84 | 207.71 | 147.37 | 100.62 |
SSA/m2·g−1 | 2.0973 | 2.7501 | 3.2548 | 3.9356 | 4.4874 |
Curing Age/Day | Particle Size Range/μm | |||||
---|---|---|---|---|---|---|
0–3 | 3–10 | 10–20 | 20–30 | 30–60 | +60 | |
3 | 0.597 | 0.578 | 0.603 | 0.622 | 0.546 | 0.576 |
7 | 0.606 | 0.587 | 0.614 | 0.632 | 0.555 | 0.587 |
28 | 0.632 | 0.660 | 0.706 | 0.680 | 0.630 | 0.503 |
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Zhu, M.; Xie, G.; Liu, L.; Yang, P.; Qu, H.; Zhang, C. Influence of Mechanical Grinding on Particle Characteristics of Coal Gasification Slag. Materials 2022, 15, 6033. https://doi.org/10.3390/ma15176033
Zhu M, Xie G, Liu L, Yang P, Qu H, Zhang C. Influence of Mechanical Grinding on Particle Characteristics of Coal Gasification Slag. Materials. 2022; 15(17):6033. https://doi.org/10.3390/ma15176033
Chicago/Turabian StyleZhu, Mengbo, Geng Xie, Lang Liu, Pan Yang, Huisheng Qu, and Caixin Zhang. 2022. "Influence of Mechanical Grinding on Particle Characteristics of Coal Gasification Slag" Materials 15, no. 17: 6033. https://doi.org/10.3390/ma15176033