【作者】 凌忠钱；

【导师】 岑可法； 周昊；

【作者基本信息】 浙江大学 ， 工程热物理， 2008， 博士

【摘要】 随着我国经济社会的快速发展,能源与环境问题日益凸现。与传统的预混燃烧相比,多孔介质内预混燃烧由于多孔介质大的比表面积、良好的蓄热性能,能够提高燃烧热效率、燃烧低热值燃料废气、扩展可燃极限、降低污染物排放,是比较先进的燃烧方式。本文在国家自然科学基金（20307007）的资助下采用试验研究和数值模拟的方法,对多孔介质内预混燃烧特性进行了研究,利用多孔介质能够实现超绝热燃烧的优点来处理硫化氢这种强污染性气体同时获得氢气和硫磺,实现资源综合利用。首先,利用自行设计建造的多孔燃烧反应器对多孔介质内的火焰传播特性进行了详细的试验研究,发现预混气体能够在多孔介质形成稳定传播的燃烧波,较高的化学当量比和较大的孔隙率条件下的燃烧波传播速度也较快,燃烧波的传播速度为10^-3cm/s的数量级。多孔介质内的超绝热燃烧只可能在燃烧波传播方向和气流方向一致时发生,否则只能发生亚绝热燃烧。贫燃条件下发生超绝热燃烧的化学当量比的下限和上限分别为0.4和0.7,富燃条件下发生超绝热燃烧的下限为1.5。超绝热燃烧时NOx排放量很低,基本保持在10ppm的量级。其次,采用了计算流体力学与详细化学反应机理相结合的方法模拟了多孔介质内的甲烷超绝热燃烧,并在甲烷富余的情况下裂解制取氢气。通过大量的数值试验,获得了直径为3mmAl₂O₃小球堆积而成的多孔介质有效导热系数。模拟结果与试验结果对比吻合良好,在Φ=1.5时没能发生超绝热燃烧,模拟温度比绝热燃烧温度低140K左右,而其他三个工况中的模拟温度超过了绝热燃烧温度,在Φ=2.0时超过绝热燃烧温度100K,在Φ=2.2时竟然超过绝热燃烧温度有360K之多,形成了超绝热燃烧。H₂和CO的总摩尔浓度可达23%,试验测量结果与数值模拟结果相比偏低。论文通过试验和动力学研究,研究了硫化氢在不同停留时间、不同反应温度下的裂解转化率。研究发现,硫化氢的热分解需要很高的温度环境,在温度低于850℃时,硫化氢几乎不发生热分解。温度越高、停留时间越长和初始硫化氢的体积浓度越低,硫化氢能够获得转化率就越高。此外,通过硫化氢超绝热部分氧化制氢热力学模拟,发现在一定的化学当量比下,低浓度的硫化氢/空气的混和气组合,比高浓度的硫化氢/氧气的混和气组合更容易达到超绝热燃烧,氧化剂中氧气的含量对其最终分解平衡极限没有影响,氢气的产出率随着氧气浓度的提高其变化也并不是很明显,选用氧化剂时空气的效果比氧气更好。在化学当量比特别是在Φ＞6时,可以得到较多的H₂和较低的SO₂排放。最后,论文试验和数值模拟研究了利用多孔介质内超绝热燃烧,实现硫化氢高温裂解制取氢气。研究发现,氢气的产量在化学当量比为2.5时最大,为2.08%。多孔介质超绝热燃烧能够为硫化氢高温裂解提供高温环境。数值模拟利用CFD所得的稳定温度场作为初始温度输入,采用CHEMKIN的PREMIX软件包并且考虑了管内H₂S燃烧和裂解的复杂化学反应机理,来模拟硫化氢的裂解制氢,模拟结果和试验比较吻合良好。为进一步实现多孔介质超绝热燃烧的应用打下了很好的基础。更多还原

【Abstract】 With the rapid development of Chinese economics, the problem of Energy and environment come up to surface. Premixed combustion in porous media has been proved to be an advanced combustion technology over conventional premixed combustion in which the premixed fuel and air burn as a free flame. Premixed combustion in porous media has many advantages such as reduced emissions of pollutants, wider domain of flammability, much higher thermal efficiency and radiant heat outputs, saving energy because of its highly developed inner solid surface and excellent property of heat transfer and heat accumulation. With the support of the National Nature Science Foundation of China （20307007）, the characteristics of premixed combustion in porous media were investigated by the methods of experiment and numerical simulation. Hydrogen can be produced from sulfide hydrogen based on advantages of super-adiabatic combustion.First, detailed experimental investigation has been done with wave propagation in porous media of a porous combustion reactor. The Experimental results show that self-propagation reactions of premixed mixture of methane/air combustion are possible at a very low velocity, and the wave velocity is determined by equivalence ratio and size of pores of porous media, larger equivalence ratio has a larger combustion wave velocity, porous media which consist of 6mm diameter spheres have larger combustion wave velocity than which consist of 3mm diameter spheres. Downstream propagation of combustion wave can produce super-adiabatic combustion; otherwise under-adiabatic combustion happens. The emissions of NOx are less than 10ppm under super-adiabatic combustion.Computational fluid dynamics （CFD） combined with detailed chemical kinetics was employed to model the filtration combustion of methane/air in a packed bed of uniform 3 mm diameter alumina spherical particles. The standard k-εturbulence model and a methane oxidation mechanism with 23 species and 39 elemental reactions were used. Various equivalence ratios （1.5, 2.0, 2.2, and 2.5） were studied. The numerical results showed good agreement with the experimental data. For ultra-rich mixtures, the combustion temperature exceeds the adiabatic value by hundreds of centigrade degrees. Syn-gas （hydrogen and carbon monoxide） can be obtained up to a mole fraction of 23%. The numerical results also showed that the combination of CFD with detailed chemical kinetics gives good performance for modeling the pseudo-homogeneous flames of methane in porous media.The experimental study and kinetics investigation on the thermal decomposition of hydrogen sulfide was carried out. The decomposition efficiency of hydrogen sulfide under various temperature and residual time was studied and verified by the experimental data. The simulating results show that the reacting mechanism developed in this work can express the thermal decomposition of hydrogen sulfide accurately. The thermal decomposition of hydrogen sulfide relies on the reacting temperature, only the high temperature conditions lead to the high hydrogen generating efficiency. When the temperature is low, the residual time is the key factor influencing the thermal decomposition. The initial hydrogen sulfide concentration has great influence on the thermal decomposition efficiency, lower hydrogen sulfide concentration results in higher thermal decomposition efficiency. A thermodynamic model was used to study numerically by varying H₂S and oxidizer feed compositions. The results show that the adiabatic temperature is lower in low equivalence ratio, the increase of hydrogen sulfide and oxygen concentrations shifts the super-adiabatic partial oxidation combustion zone to high equivalence ratio; The thermal decomposition of hydrogen sulfide greatly relies on the super-adiabatic combustion temperature, and under higher super-adiabatic combustion temperature the higher hydrogen generating efficiency can be achieved. The results of thermodynamic simulation also suggest that the rage of optimal operation of a super-adiabatic partial oxidation unit is above an equivalence ratio of 6, where the hydrogen output is maximized and SO₂ generation is minimized. Under the same combustion temperature lower hydrogen sulfide concentration results in higher thermal decomposition efficiency.Finally, investigation of hydrogen producing based on super-adiabatic combustion has been done through experiments and numerical simulation. The results show that super-adiabatic combustion could offer the high-temperature environment for the decomposition of hydrogen sulfide to produce hydrogen and sulfur and hydrogen concentration was 2.08% atΦ=2.5. The combination of computational fluid dynamics and chemical kinetics investigation was employed to model the filtration combustion of hydrogen sulfide a 17-species, 57-elemental reaction mechanism. The results of the simulation show good agreement with experimental data.更多还原