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燃用烟煤中心给粉旋流燃烧器流动及燃烧特性研究

Studies on Flow and Combustion Characteristics of Central-fuel-rich Swirl Coal Combustion Burner Burning Bituminous

【作者】 靖剑平

【导师】 李争起;

【作者基本信息】 哈尔滨工业大学 , 热能工程, 2010, 博士

【摘要】 随着环境问题的日益严峻,采用旋流煤粉燃烧技术的锅炉机组,降低NO_x排放量、提高煤种适应性、防止锅炉结渣及保证锅炉机组的安全稳定运行越来越重要。鉴于此,本文对燃用烟煤的中心给粉旋流煤粉燃烧器和日本石川岛播磨(IHI)公司生产的双旋流煤粉燃烧器进行了研究。通过实验室单相试验、示踪试验、两相试验和数值模拟方法对中心给粉旋流煤粉燃烧器和IHI双旋流燃烧器进行了研究,揭示了两种燃烧器的机理,并分别通过工业试验对两种燃烧器的燃烧特性和NO_x排放性能进行了研究。利用IFA300恒温热线热膜流速计对中心给粉燃烧器和IHI双旋流煤粉燃烧器出口气流的流动特性进行了试验研究,研究了不同结构和运行参数下两种燃烧器出口气流的流动特性和湍流强度分布。分别利用热质比拟和可视化研究的方法对中心给粉旋流煤粉燃烧器一、二次风混合特性进行了研究,得到了不同结构及参数下中心给粉燃烧器的一、二次风的混合特性及一次风边界的分形维数同湍流强度的对应关系。利用三维激光相位多普勒测速仪(PDA)研究了不同二次风风量、外二次风叶片角度和内、外二次风风量比例下中心给粉旋流燃烧器的气、固两相流动特性。中心给粉燃烧器在燃烧器中心区域存在较高的颗粒体积流量和颗粒相对数密度,同时具有较大的粒径。利用三维PDA研究了外二次风叶片角度对IHI双旋流燃烧器气、固两相流动特性的影响规律。IHI双旋流燃烧器具有较小的环形回流区,并且在二次风流动区域和边壁区域存在两个颗粒体积流量峰值和颗粒相对数密度峰值,同时燃烧器中心区域的粒径较小。参照PDA试验条件和试验参数,利用Realizable k-ε模型和拉格朗日颗粒随机轨道模型对中心给粉旋流煤粉燃烧器出口区域气、固流动特性进行了数值模拟,并将模拟结果与试验数据进行了对比,表明模拟与试验结果吻合较好。对一台下层8只采用中心给粉旋流煤粉燃烧器燃用烟煤的1025t/h锅炉上进行了冷、热态试验。测量了燃烧器区域的烟气温度、烟气成分及碳燃尽率。采用巴威强化点火双调风燃烧器时,煤的燃烧效率为96.73% ,NO_x排放量为843.55mg/m~3(O2=6%),锅炉最低不投油稳定运行负荷为180MWe,而采用中心给粉燃烧器后,煤的燃烧效率为97.09%,NO_x排放量为727.67mg/m~3(O2=6%),锅炉最低不投油稳定运行负荷为110MWe。在一台采用IHI双旋流煤粉燃烧器燃用烟煤的670t/h锅炉上进行了热态试验。分别测量了不同锅炉负荷、燃尽风挡板开度及外二次风叶片角度下燃烧器区域的烟气温度、烟气成分和碳燃尽率,同时还对整个炉膛温度分布、热流密度分布、NO_x排放量及锅炉效率进行了测量。

【Abstract】 With the increasingly serious environmental problems, it is becoming more important to reduce NO_x emissions, enhance the adaptability of coal variety, and prevent slagging in furnace to ensure the safety and stability of boiler units adopting swirl coal combustion techniques. In view of this, studies are conducted on central-fuel-rich swirl coal combustion burner with bituminous and double-swirl flow burner designed by Ishikawajima-Harima Heavy Industries (IHI) Co., Ltd in Japanese. The mechanisms of two swirl burners are revealed through Single phase experiments, smog tracer tests, gas-particle two phase experiments and numerical simulation, while industrial tests are carried out simultaneously to study the characteristics of combustion and NO_x emissions of them.An IFA300 constant-temperature hot-film anemometer system is used to study flow characteristics at the nozzle region of central-fuel-rich and IHI double-swirl flow burner. The three-dimension flow field and turbulence intensity distribution at the nozzle region are investigated concerning with different structures and operational parameters.Through thermal transfer analogy and visualization used for the research on mixing characteristics of primary air and secondary air of central-fuel-rich burner, we obtain the mixing characteristics and the correlations between fractal dimension and turbulence intensity at the boundary of the primary air in different structures and operation parameters.A three-dimensional particle-dynamics anemometer (PDA) system is used to study gas-particle flow characteristics of central-fuel-rich burner with different secondary air flux, tangential vane angles and ratios of inner/outer secondary air. The particle diameter, altoge ther with volume flux and relative number concentration, are comparatively large in the central region outside the burner nozzle.The influence of outer secondary air vane angles on the gas-particle flow characteristics of IHI double-swirl flow burner are investigated by the three-dimensional PDA system. The IHI double-swirl flow burner has a small ring recirculation zone near the burner nozzle. And there are two peak values of particle volume flux and particle relative number concentration in the secondary air region and near-wall region while the particles in the center of burner are small.As to the conditions and parameters of the PDA experiments, Realizable k-εmodel and Lagrangian stochastic trajectory model are used in the numerical simulation of gas-particle flow characteristics at the nozzle region of central-fuel-rich burner. The simulation results and experiments data coincide well.Both cold air flow experiments and industrial tests are conducted in a 1025 t/h, bituminous fired boiler before and after 8 burners at the bottom row are retrofitted to the central-fuel-rich burners. Gas temperature, gas composition and char burnout are measured in the burner region. For the boiler with enhanced ignition-dual register burners before the retrofit, coal combustion efficiency is 96.73% and the NO_x emission is 843.55mg/m~3 (O2=6%) while the lowest load without auxiliary oil is 180 MWe under the condition of stable operation. After central-fuel-rich burners are adopted, coal combustion efficiency increases to 97.09% and the NO_x emission decreases to 727.67mg/m~3 (O2=6%) , while the boiler could be operated stably at a load of 110 MWe without auxiliary oil.Industrial tests are also conducted in a 670 t/h, bituminous fired boiler which adopts the IHI double-swirl flow burners. Gas temperature, gas composition and char burnout in the burning region are measured under different loads, over-fire air damper openings and outer secondary air vane angles, as well as the furnace temperature distribution, heat flux distribution, NO_x emission and boiler efficiency.

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