After coal seam mining, the residual coal is soaked with the accumulated water in goaf, and its spontaneous combustion characteristics were changed after air-dried. To study the reoxidation characteristics of soaked and air-dried coal, temperature-programmed experiments were carried out, and the cross point temperatures and index gases were investigated. Results showed that the cross point temperature of raw coal (146.3 °C) was reduced to 137.1 °C after it was pre-oxidized at 90 °C. The cross point temperature of water-soaked, and air-dried coal (96 h) was 122.5 °C, while the cross point temperature of water-soaked, air-dried (96 h) and pre-oxidized (90 °C) coal was 111.5 °C. Although CO was produced in the initial slow oxidation phase, it was found that C2H4 and C3H8 were not generated. In the rapid oxidation stage, different pretreatments affected the gas generation and the overall oxidative degree was consistent with the cross point temperature. The generation temperature and the concentration of C2H4 and C3H8 were decreased after the coal was water-soaked, air-dried, and pre-oxidized. Furthermore, the high-energy chemicals and functional groups were studied, which could be used to explain the physical experiment oxidation characteristics of different coals.
In this report, the influence of pre-oxidation degree and ventilation flow on the parameters of spontaneous combustion of coal (temperature, gas concentration, and exothermic intensity) was studied in six sets of programed temperature experiments. The experimental results showed that the pre-oxidation exerted a positive effect on the spontaneous combustion parameters of coal in the early stage of coal-oxygen recombination reaction, but exerted an inhibitory effect in the later stage of coal-oxygen oxidation reaction. Air supply rate had a positive correlation with the initial oxidation of coal samples and 90 °C pre-oxidation spontaneous combustion parameters. Air supply rate had negative correlation with 140 °C pre-oxidation of coal samples. Meanwhile, secondary oxidation significantly reduced the characteristic temperature of coal. The critical temperature of each coal sample was 83.7 °C (coal sample 1-Y), 68.3 °C (coal sample 1-L), 69.6 °C (coal sample 1-G), 82.1 °C (Coal sample 2-Y), 70.4 °C (coal sample 2-L), and 70.0 °C (coal sample 2-G), and dry cracking temperature was 142.6 °C (coal sample 1-Y), 134.8 °C (coal sample 1-L), 136.2 °C (coal sample 1-G), 147.2 °C (coal sample 2-Y), 136.5 °C (coal sample 2-L), and 134.4 °C (coal sample 2-G). The curves of the characteristic parameters of primary and secondary oxidized coal showed exponential growth. And the oxidation process can be divided into three stages, the first stage (30 °C ∼ critical temperature), the second stage (critical temperature ∼ dry cracking temperature), and the third stage (over the dry temperature).
Various applications of the Internet of Things assisted by deep learning such as autonomous driving and smart furniture have gradually penetrated people’s social life. These applications not only provide people with great convenience but also promote the progress and development of society. However, how to ensure that the important personal privacy information in the big data of the Internet of Things will not be leaked when it is stored and shared on the cloud is a challenging issue. The main challenges include (1) the changes in access rights caused by the flow of manufacturers or company personnel while sharing and (2) the lack of limitation on time and frequency. We propose a data privacy protection scheme based on time and decryption frequency limitation that can be applied in the Internet of Things. Legitimate users can obtain the original data, while users without a homomorphic encryption key can perform operation training on the homomorphic ciphertext. On the one hand, this scheme does not affect the training of the neural network model, on the other hand, it improves the confidentiality of data. Besides that, this scheme introduces a secure two-party agreement to improve security while generating keys. While revoking, each attribute is specified for the validity period in advance. Once the validity period expires, the attribute will be revoked. By using storage lists and setting tokens to limit the number of user accesses, it effectively solves the problem of data leakage that may be caused by multiple accesses in a long time. The theoretical analysis demonstrates that the proposed scheme can not only ensure safety but also improve efficiency.
Abstract:The low-temperature oxidation law of coal and rock mass is the basis to study spontaneous combustion in goafs. In this paper, the low-temperature oxidation laws of coal, oil shale, and mixtures of coal and oil shale were studied by using laboratory programmed heating experiments combined with a field beam tube monitoring system. The results from the programmed heating experiments showed that the heat released from oil shale was less than that from coal. Coal had a lower carbon monoxide (CO)-producing temperature than oil shale, and the mixture showed obvious inhibiting effects on CO production with an average CO concentration of about 38% of that for coal. Index gases were selected in different stages to determine the critical turning point temperature for each stage. The field beam tube monitoring system showed that the temperature field of the 1105 co-mining face of coal and oil shale in the goaf of the Liangjia Coal Mine presented a ladder-like distribution, and CO concentration was the highest for coal and lower for the mixture of coal and oil shale, indicating that the mixture of coal with oil shale had an inhibiting effect on CO production, consistent with the results from the programmed heating experiments.
To improve the borehole sealing effect of coal seam water infusion, especially that of coal seam with low permeability and high rigidity, this study investigated the performance test optimization of two cement-based sealing materials. e borehole sealing effect of this coal seam requires high-pressure water infusion. Result shows that when the water-cement ratio is 0.4 and the amount of fiber expansive agent is 10%, the new borehole sealing material displays microexpansion. In addition, the 1-day compressive strength reaches 16 MPa. is result satisfies the material compressive strength requirement under 30 MPa high-pressure water infusion. e sealing performance is also excellent. According to the scanning electron microscopy analysis of new borehole and traditional borehole sealing materials, the surface of new borehole sealing material shows no holes and possesses compactness. e sealing effect is superior to that of other traditional sealing materials. is effect can satisfy the sealing requirement of coal seam water infusion. e new borehole sealing material is considerably significant for the improvement of the water infusion effect.
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