多源低热值燃气无焰燃烧的数值模拟研究

Numerical simulation of flameless combustion of multi-source low calorific value gas

生物质、生活垃圾、低品位煤等原料通过厌氧发酵、热解气化等技术可制备燃气。这既能处理固体废弃物、清洁利用煤,又能产生可利用的燃气,具有能源和环保的双重效益。但制得的燃气热值低、组成复杂、不可燃组分多,且组成受原料、工艺影响变化较大,采用传统燃烧方式存在点火困难、燃烧不稳定、污染物不易控制等问题。无焰燃烧是一种低氧条件下的温和燃烧模式,污染物排放量低、燃烧效率高,有助于解决这些问题。因此,采用详细化学反应机理GRI Mech 3.0和涡耗散概念(EDC)模型,通过湍流与化学反应的耦合计算,对3种低热值燃气无焰燃烧过程进行数值模拟研究。实验数据验证该方法能够准确地模拟实际燃烧器中的无焰燃烧。随后对沼气、生物质气化气、煤气化气进行无焰燃烧数值模拟研究,包括温度场、组分场、OH自由基分布和污染物排放等,并通过对燃烧器的改进成功实现了生物质气化气和煤气化气的无焰燃烧。结果表明,生物质气化气、煤气化气在进行无焰燃烧时温度分布比天然气、沼气的温度分布更加均匀、反应区结构更大,且NO_(x)接近“零排放”;CO_(2)的稀释对于无焰燃烧有促进作用;CH_(4)成分的存在会改变反应区及OH分布,使温度分布更加趋于不均匀。将3种低热值燃气无焰燃烧横向对比发现,即便输入功率一样,燃气热值越低,炉膛整体温度越低,但烟气量更大,因此应加强烟气的余热利用,增大系统的热效率。

Fuel can be produced from biomass,municipal solid waste,low-grade coal and other raw materials through anaerobic fermentation,pyrolysis gasification and other technologies.It can not only deal with solid waste,and make coal clean to use,but also generate utilizable gas,which has the dual benefits of energy and environmental protection.However,the produced gas has low calorific value,complex composition,more non-combustible components,and the composition changes greatly under the influence of raw materials and processes.There are some problems such as ignition difficulty,combustion instability,and difficult control of pollutants under traditional combustion.Flameless combustion is a mild combustion mode under low oxygen condition with low pollutant emission and high combustion efficiency,which helps to solve these problems.In this study,a detailed mechanism GRI Mech 3.0 and the eddy dissipation concept(EDC)model were used to simulate the flameless combustion process of three low caloric value gas by coupling the turbulent flow with the chemical reaction.The experimental data verify that the simulation method in this study can accurately simulate the flameless combustion in the actual burner.Subsequently,the numerical simulation of flameless combustion of biogas,biomass gasified gas and coal gasified gas was carried out,including temperature field,species,OH radical distribution and pollutant emission.The flameless combustion of biomass gasified gas and coal gasified gas was successfully realized by improving the burner.The results show that the temperature distribution of biomass gasified gas and coal gasified gas in flameless combustion is more uniform than that of natural gas and biogas,the reaction zone structure is larger,and NO_(x)is close to"zero emission".The dilution of CO_(2)can promote flameless combustion,and CH_(4)will change the reaction zone and OH distribution,making the temperature distribution nonuniform.The horizontal comparison of flameless combustion of three low calorific value gas shows that even if the input power is the same,the lower the calorific value of gas,the lower the overall furnace temperature.However,the amount of flue gas is larger,so it is necessary to strengthen the heat utilization of flue gas to increase the thermal efficiency of the system.