秸秆燃气增氧燃烧特性的数值模拟

采用ANSYS Fluent软件对秸秆燃气增氧燃烧特性进行二维数值模拟,对燃烧室进行模型设计以及模型假设,运用网格生成软件ANSYS ICEM对燃烧室进行网格划分,结合实际工况以及理论计算值,设置较合理的边界条件,利用Fluent软件对燃烧模型进行仿真求解。针对4种不同入口氧气体积分数(21%,24%,27%,30%)工况下秸秆燃气燃烧室内的温度分布、速度分布及各烟气组分体积分数和污染物NOx生成情况,得出以下结论。增氧燃烧通过提高入口氧气体积分数,减少了加热助燃空气中氮气所需的热量,提升燃烧温度,促进燃烧完全。此燃烧室最适合入口氧气体积分数等于30%的秸秆燃气增氧燃烧。增氧燃烧中,随着入口氧气体积分数的提高,燃烧室最高当地速度和出口平均速度均增加。增氧燃烧中,随着入口氧气体积分数的增加,生成的烟气中H2O、CO2的体积分数均提高,N2的体积分数降低,在入口氧气体积分数为30%时,H2O和CO2这两种辐射能力较强的气体体积分数达到23.7%,增强了燃烧过程的辐射换热。增氧燃烧中,温度对于污染物NOx的影响较大。在燃烧室的局部高温区,NOx质量分数较高,说明热力型NOx占据污染物NOx的大部分,温度的上升导致NOx生成量明显增大。入口体积分数大于等于27%时,NOx排放体积分数明显高于相关标准限定值,所以在追求增氧高温燃烧的同时,要注意烟气的降硝处理,从而满足氮氧化物低排放标准的要求。

Numerical Simulation of Oxygen-enriched Combustion Characteristics of Straw Gas

ANSYS Fluent software was used to conduct two-dimensional numerical simulation of the oxygen-enriched combustion characteristics of straw gas. The combustion chamber model was designed and assumed. The grid generation software ANSYS ICEM was used to grid the combustion chamber. Combined with the actual working conditions and theoretical calculation values,reasonable boundary conditions were set,and Fluent software was used to simulate and solve the combustion model. Based on the temperature distribution,velocity distribution,volume fraction of each flue gas component and NOxgeneration in the combustion chamber of straw gas under four different inlet oxygen volume fractions( 21%,24%,27% and 30%),the following conclusions are drawn: By increasing the inlet oxygen volume fraction,the oxygen-enriched combustion reduces the amount of heat needed to heat nitrogen in combustion supporting air,increases combustion temperature and promotes combustion completion.The combustion chamber is most suitable for oxygenenriched combustion of straw gas with an inlet oxygen volume fraction equal to 30%. In oxygen-enriched combustion,the maximum local velocity and average outlet velocity of the combustion chamber both increase with the increase of the inlet oxygen volume fraction.In oxygen-enriched combustion,as the inlet oxygen volume fraction increases,the volume fractions of H2O and CO2 in the generated flue gas both increase,and the volume fraction of N2 decreases. When the inlet oxygen volume fraction is 30%,the volume fractions of H2O and CO2,which have strong radiating ability,reaches 23. 7%,which enhances the radiation heat transfer in the combustion process. In oxygen-enriched combustion,temperature has a greater impact on NOx.In the local high temperature zone of the combustion chamber,the mass fraction of NOxis relatively high,indicating that most of NOxis thermal NOx,and the increase of temperature leads to a significant increase in NOxgeneration. When the inlet oxygen volume fraction is greater than or equal to 27%,the NOxemission volume fraction is significantly higher than the relevant standard limit value. Therefore,while pursuing oxygen-enhanced high-temperature combustion,attention should be paid to the reduction treatment of nitrate in flue gas to meet the requirements of low nitrogen oxide emission standards.