Ignition temperature and explosion pressure of suspended coal dust clouds
Minimum ignition temperature of suspended coal dust cloud under different conditions
The particle size of the coal samples used in the experiment is less than 75 μm. The minimum ignition temperature of coal dust cloud under the condition of spraying dust pressure of 20 kPa is 983 K, as shown in Table 3. In the confined space of the experimental equipment, at a temperature of 983 K, suspended coal dust clouds are ignited, which is the critical temperature at which coal dust clouds can be ignited. Below this temperature, coal dust clouds cannot be ignited. This test data can provide a basis for understanding the combustion and explosion characteristics of coal dust.
On this basis, the minimum ignition temperature of coal dust clouds can be tested under different spray pressure conditions. The test results are shown in Fig. 5. It can be obtained that when the dust spray pressure is greater than 20 kPa, the minimum ignition temperature of the suspended coal dust cloud increases. When the dust spray pressure is 60 kPa, the minimum ignition temperature is 1123 K. When the dust spray pressure is less than 20 kPa, the minimum ignition temperature of the suspended coal dust cloud increases. When the dust spray pressure is 5 kPa, the minimum ignition temperature is 1133 K. These results indicate that the optimal dust spray pressure is 20 kPa. Under this condition, coal dust clouds are more likely to ignite.
Minimum ignition temperature under different dust spray pressure conditions.
As shown in Fig. 6, the effect of dust spray pressure on the diffusion of coal dust cloud particles in the ignition space is presented. In the experimental equipment, when the dust spray pressure is 20 kPa, the coal dust cloud diffuses more evenly, and more coal dust particles move into the ignition space, forming a suspended coal dust cloud. Due to the heat exchange and transfer between coal dust particles, the coal dust cloud under this condition is more easily ignited. If the spraying pressure is less than 20 kPa, the driving force obtained by coal dust particles is significantly insufficient, and the number of coal dust particles that can enter the ignition space is greatly reduced. The particles are concentrated in the upper part of the space, which weakens the heat exchange between particles. To be ignited, higher temperatures are required. If the spraying pressure is greater than 20 kPa, the power to drive coal dust particles into the ignition space is relatively high. Under the action of gravity, more coal dust will be concentrated below the interior of the ignition space, which is not conducive to the release and exchange of heat from coal dust particles, and the temperature required for ignition will be higher.
Effect of dust spray pressure on ignition of suspended coal dust clouds.
Explosion pressure of suspended coal dust clouds under different conditions
In the explosion pressure test experiment, the dust spray pressure is 2 MPa, the ignition delay time is 0.1 s, and the ignition energy is 10 kJ. According to the experimental results, the maximum pressure of suspended coal dust cloud explosion is 0.78 MPa, and the maximum pressure rise rate is 73.27 MPa s−1, the results are shown in Table 4. Under normal circumstances, the standard atmospheric pressure is 0.1 MPa, and an explosion produces a maximum pressure of 0.78 MPa. The required coal dust is only 10 g. This explosion has a great power, and the concentration of coal dust clouds in the explosion space can reach 500 g m−3. This concentration condition is very favorable for the development of the explosion.
In the explosion pressure experiment mentioned above, the mass of coal dust used is 10 g. The change in coal dust quality will affect the concentration of suspended coal dust clouds in the explosion space. The concentration of coal dust clouds can have a significant impact on explosion pressure. Therefore, in order to study the effect of coal dust cloud concentration on explosion pressure, experiments can be conducted continuously by changing the amount of coal dust used. The relationship between the mass concentration of coal dust cloud obtained from the test and the explosion pressure is shown in Fig. 7. It can be clearly seen that when the mass concentration of coal dust cloud is 500 g m−3, the maximum pressure and maximum pressure rise rate are both the highest, with values of 0.78 MPa and 73.27 MPa s−1, respectively. When the mass concentration of coal dust cloud is less than or greater than 500 g m−3, the maximum…
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