论文中文题名: | LN2/CO2文丘里混合制备浆液降温特性与防灭火数值模拟 |
姓名: | |
学号: | 21204228094 |
保密级别: | 公开 |
论文语种: | chi |
学科代码: | 085900 |
学科名称: | 工学 - 工程 - 土木水利 |
学生类型: | 硕士 |
学位级别: | 工程硕士 |
学位年度: | 2024 |
培养单位: | 西安科技大学 |
院系: | |
专业: | |
研究方向: | 可再生能源利用 |
第一导师姓名: | |
第一导师单位: | |
论文提交日期: | 2024-06-13 |
论文答辩日期: | 2024-06-09 |
论文外文题名: | Slurry cooling characteristics and fire prevention numerical simulation of LN2/CO2 venturi mixed slurry preparation |
论文中文关键词: | |
论文外文关键词: | LN2/CO2 ; Venturi jet injector ; Three-phase state ; Cryogenic slurry ; Fire prevention and extinguishing |
论文中文摘要: |
煤炭在我国能源结构中具有极其重要的地位,但我国许多地区受到煤自燃的威胁,这一现象既造成了煤炭资源的无谓浪费,同时也对环境和人类健康带来了显著的负面影响。在众多煤自燃防灭火技术中,液氮和二氧化碳(LN2/CO2)惰气浆液防灭火技术兼具LN2和CO2防灭火的优点,惰化效果显著。然而,在现有的LN2/CO2制备浆液的工艺中,干冰生成量并不理想,本文利用具有节流效应的文丘里射流器促进干冰的生成,通过惰气节流效应的理论分析、惰气浆液制备的实验测试、文丘里射流器内部流域的数值模拟,以及惰气浆液对采空区降氧效果的数值模拟等多种手段,深入研究LN2/CO2文丘里混合制深冷浆液的防灭火技术,为煤自燃有效防控提供科学依据。主要研究内容如下: (1)基于焦耳-汤姆逊效应分析CO2节流过程中的冷却效应。结果表明,CO2的微分节流效应系数 (2)对LN2与CO2注输比分别2:1、3:1、4:1的三种不同注输比,从支管注输LN2、从主管注输LN2两种不同注输口,利用不同规格的两种双喉混合室文丘里射流器进行深冷惰气浆液制备实验。结果表明,注输口与混合装置不变,注输比增大,温度降低速率随之增大,总压也会相应增大,至最高点后,会出现小幅下降与上下波动;注输比与注输口不变,采用620 mm文丘里射流器所生成的干冰量最多;注输比与混合装置不变,LN2从主管注输时易造成堵管现象。故使用规格为620 mm的文丘里射流器,LN2与CO2的注输比3:1,且LN2从支管注输这一工况为最佳工况。 (3)在不同注输比和不同注输口条件下,对620 mm双喉文丘里射流器内部流体的压力场、速度场、温度场、干冰生成体积分数以及湍流动能分布进行了研究。结果表明,文丘里射流器内流体随着注输比的增大,整体流速增加,流体在收缩段经加速后,于喉管段速度达到最高值,最高可达282.37 m/s,进入扩散段后流速逐渐减少;且流体负压区主要集中在喉管段与扩散段前段,在注输比为3:1时压力最低可达-699 kPa,且随着注输比的增大,负压段也向外扩展;干冰的体积分数在混合室的主管注输口附近与扩散段靠近重力方向管壁处含量最高,在不同注输口情况下的模拟对比发现,当LN2从主管注入时的干冰体积分数要大于LN2从支管注入时的干冰体积分数,但更易造成堵管现象,与实验结果相一致。 (4)通过对采空区注混合浆液在不同注输比和不同注输位置条件下进行数值模拟。结果表明,注入LN2/CO2惰气浆液可有效降低采空区内部氧气浓度,减小三带宽度,降低采空区遗煤自燃可能性;改变LN2/CO2注输比,采空区内氧气浓度随LN2/CO2增加而减小,三带宽度减小,采空区内低温区域分布范围增加,进一步降低采空区自燃风险;改变LN2/CO2注入位置,发现距进风侧40 m处采空区氧浓度最低,分布最小,三带宽度最窄,为最佳注入位置。 |
论文外文摘要: |
Coal plays an extremely important role in China 's energy structure, but many areas in China are threatened by coal spontaneous combustion. This phenomenon not only causes unnecessary waste of coal resources, but also has a significant negative impact on the environment and human health. Among many coal spontaneous combustion fire prevention and extinguishing technologies, liquid nitrogen and carbon dioxide (LN2/CO2) inert gas slurry fire prevention and extinguishing technology has the advantages of LN2 and CO2 fire prevention and extinguishing, and the inerting effect is remarkable. However, in the existing LN2/CO2 slurry preparation process, the amount of dry ice generated is not ideal. In this paper, the venturi jet with throttling effect is used to promote the formation of dry ice. Through the theoretical analysis of the throttling effect of inert gas, the experimental test of inert gas slurry preparation, the numerical simulation of the internal flow field of the venturi jet, and the numerical simulation of the oxygen reduction effect of the inert gas slurry on the goaf, the fire prevention and extinguishing technology of LN2/CO2 venturi mixed cryogenic slurry is studied in depth, which provides a scientific basis for the effective prevention and control of coal spontaneous combustion. The main research contents are as follows : (1) Based on the Joule-Thomson effect, the cooling effect of CO2 throttling process is analyzed. The results show that the differential throttling effect coefficient of CO2 is 1.30 > 0, that is, the expansion temperature of CO2 is reduced by throttling. Dry ice yield can be calculated by adiabatic isenthalpic throttling model or thermodynamic diagram. In addition, through the throttling expansion principle of the venturi tube, two kinds of dual-throat mixing chamber venturi jets that are most suitable for generating dry ice mixed slurry are selected from four different types of venturi jets. The specifications are : 620 mm venturi jet with outlet throat diameter of 20 mm, contraction tube angle of 10.6°, diffusion tube angle of 7.1° and 1390 mm venturi jet with outlet throat diameter of 37 mm, contraction tube angle of 22.3°, diffusion tube angle of 3.1°. (2) The cryogenic inert gas slurry preparation experiments were carried out by using two kinds of double throat mixing chamber venturi jets with different specifications for three different injection-production ratios of LN2 and CO2 injection-production ratios of 2:1, 3:1 and 4 : 1, respectively, and two different injection-production ports of LN2 injection from branch pipe and LN2 injection from main pipe. The results show that when the injection port and the mixing device are unchanged, the injection ratio increases, the temperature reduction rate increases, and the total pressure increases accordingly. After reaching the highest point, there will be a slight decrease and fluctuation. The injection-output ratio and the injection-output port are unchanged, and the amount of dry ice generated by the 620 mm Venturi jet is the largest. When LN2 is injected from the main pipe, it is easy to cause blockage when the injection ratio and mixing device are unchanged. Therefore, using a Venturi jet with a specification of 620 mm, the injection ratio of LN2 to CO2 is 3 : 1, and the injection of LN2 from the branch pipe is the best working condition. (3)The pressure field, velocity field, temperature field, dry ice volume fraction and turbulent kinetic energy distribution of the fluid inside the 620 mm double throat Venturi jet were studied under different injection-output ratios and different injection-output conditions. The results show that the overall velocity of the fluid in the Venturi jet increases with the increase of the injection ratio. After the fluid is accelerated in the contraction section, the velocity reaches the highest value in the throat section, up to 282.37 m/s, and the velocity gradually decreases after entering the diffusion section. The negative pressure area of the fluid is mainly concentrated in the throat section and the front section of the diffusion section. When the injection ratio is 3:1, the minimum pressure can reach -699 kPa, and with the increase of the injection ratio, the negative pressure section also expands outward. The volume fraction of dry ice is the highest near the main pipe injection port and the diffusion section near the wall of the gravity direction in the mixing chamber. The simulation comparison under different injection port conditions shows that the volume fraction of dry ice when LN2 is injected from the main pipe is greater than that when LN2 is injected from the branch pipe, but it is more likely to cause blockage, which is consistent with the experimental results. (4) Through the numerical simulation of the mixed slurry injection in the goaf under the conditions of different injection ratios and different injection positions. The results show that the injection of LN2/CO2 inert gas slurry can effectively reduce the oxygen concentration in the goaf, reduce the width of the three zones, and reduce the possibility of spontaneous combustion of residual coal in the goaf. Changing the LN2/CO2 injection-output ratio, the oxygen concentration in the goaf decreases with the increase of LN2/CO2, the width of the three zones decreases, and the distribution range of the low temperature area in the goaf increases, which further reduces the risk of spontaneous combustion in the goaf. By changing the injection position of LN2/CO2, it is found that the oxygen concentration in the goaf at 40 m from the inlet side is the lowest, the distribution is the smallest, and the width of the three zones is the narrowest, which is the best injection position. |
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中图分类号: | TD752 |
开放日期: | 2024-06-13 |