Improvement and Evaluation on Binary Mixing Method of Methane and Air in Large-Scale Confined Space
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摘要: 气体混合过程在工业生产和科学研究领域是一个值得关注的课题。以大尺寸爆炸罐内的气体爆炸研究为背景，基于已有的10 m3爆炸罐的基本结构，设计并建立了适用于爆炸罐结构的进气装置，并以此为基础，研究了甲烷和空气在大尺寸密闭空间内的混合过程。根据气体混合效果的评判标准，通过实验确定了适用于爆炸罐的进气装置的具体尺寸参数及相关进气条件，并与未改进前的气体混合过程进行对比。结果表明：采用直管螺旋开孔的进气装置后，当开孔孔径为1.5 mm、孔间距为100 mm时，气体混合效果最好；当进气速率保持在8 m3/h、进气前罐体内外压差为0.04 MPa时，气体混合效果可以进一步优化。经改进之后，爆炸罐内的气体混合时间缩短为原来的1/12，且罐体内气体混合物的均匀度更高，满足气体爆炸实验的要求。此结果亦可为其他大尺寸密闭容器或空间的气体混合过程提供参考数据。Abstract: Gas mixing is an interesting topic in industrial and scientific research fields.Based on the basic structure of an blasting vessel with a volume of 10 m3, this work designed an applicable gas-intake device and theoretically improved the gas intake technology.Then a series of experiments on the whole mixing process of methane and air were carried out in different conditions.According to the evaluation criteria on the gas mixing effect, specific sizes of the gas-intake device and relevant gas-intake conditions were determined.Results indicate that, when the hole diameter of gas-intake device is 1.5 mm and the separation distance is 100 mm, the gas mixing effect reach the optimal condition; and when the gas-intake velocity is fixed at 8 m3/h, and the pressure difference inside and outside the vessel is chosen as 0.04 MPa, the gas mixing effect are further optimized.After being compared with the original binary mixing result, the new system can shorten the mixing time by eleven times and make the mixing more homogeneous.The results in this study provide experimental data and basis for further study on gas mixing in a large scale confined vessel or space.
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Key words:
- large scale /
- confined space /
- methane /
- binary mixing
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图 1 爆炸罐结构图
Figure 1. Structural sketch of the blasting vessel
1. Blasting vessel; 2.Measuring holes; 3.Door; 4.Ignition pole; 5.Observation windows; 6.Dust spraying system; 7.Data measuring system; 8.Controlling system; 9.Ignition device; 10.Gas supply system; 11.Ventilating system; 12.Vacuum pump; 13.High pressure gas pump
图 3 中心采样点气体浓度随时间变化曲线图
Figure 3. Gas concentration versus time of central observation point
图 4 改进前后混气效果的对比
Figure 4. Comparison of mixing effects in initial and optimal conditions
表 1 不同开孔直径条件下的混气效果(孔间距100 mm)
Table 1. Mixing effect of different hole diameters (separation distance:100 mm)
Diameter/(mm) Final mixing duration/(min) Maximum concentration difference/(%) Dead zone proportion/(%) Rich zone proportion/(%) Mixing ratio/(%) 1.5 - 45 25.0 0 4.25 2.0 - 43 25.0 0 3.67 2.5 - 80 25.0 37.5 11.60 3.0 - 67 37.5 12.5 8.71 3.5 - 100 25.0 62.5 23.45 
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表 2 不同开孔间距条件下的混气效果(孔径1.5 mm)
Table 2. Mixing effect of different separation distances (hole diameter:1.5 mm)
Separationdistance/(mm) Final mixing duration/(min) Maximum concentration difference/(%) Dead zone proportion/(%) Rich zone proportion/(%) Mixing ratio/(%) 50 - 50 12.5 75.0 6.75 100 - 22 12.5 0 1.36 150 - 22 0 62.5 5.88 200 - 40 0 62.5 3.97 250 - 40 0 87.5 12.32
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表 3 不同进气速度下的混气效果(真空度0.04 MPa)
Table 3. Mixing effect of different gas-intake velocities (vacuum:0.04 MPa)
Velocity/(m3/h) Final mixing duration/(min) Maximum concentration difference/(%) Dead zone proportion/(%) Rich zone proportion/(%) Mixing ratio/(%) 2 - 31 0 75 6.65 4 - 18 37.5 0 4.46 6 - 20 25.0 0 2.36 8 42 22 12.5 0 1.36 10 40 20 0 0 1.00
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表 4 不同初始真空度下的混气效果(进气速率8 m3/h)
Table 4. Mixing effect of different vacuums (gas-intake velocity:8 m3/h)
Vacuum/(MPa) Final mixing duration/(min) Maximum concentration difference/(%) Dead zone proportion/(%) Rich zone proportion/(%) Mixing ratio/(%) 0.02 31 20 0 0 0.74 0.03 - 18 0 0 0.67 0.04 27 22 0 0 0.73 0.05 - 32 12.5 0 2.07 0.06 - 20 37.5 0 2.72
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