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利用循环流化床内气-固两相流动等基础方面的研究成果,根据本文床内气固浓-淡流动模型,建立适用不同结构参数的循环流化床燃烧模型,考虑了床内气体、固体颗粒的返混、循环过程,以及煤燃烧、NO的生成和分解、颗粒磨损等因素。在循环流化床燃烧试验台上进行实验研究,模型仿真结果和实验数据吻合良好,表明气固两相浓-淡流动模型所建立的循环流化床燃烧系统模型可以正确地模拟循环流化床的燃烧过程。 相似文献
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燃烧高水分低热值燃料的内旋流流化床燃烧技术研究 总被引:7,自引:2,他引:7
内旋流型流化床炉利用非均匀布风产生高温气-固两相旋流,使燃料在炉内运动、相互碰撞、干燥、破碎、燃烧,并可通过改变布风控制燃料加热与挥发份析出速率、燃烧温度与热负荷,适合多种高水分劣质煤及城市垃圾的洁净燃烧,是一种高效低污染流化床燃烧技术。本文研究该型燃烧器床内空气运动、燃烧、传热及排放规律,发展新型清洁燃烧技术。 相似文献
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作者在一台蒸发量20吨/时的低倍率循环流化床锅炉上进行了燃烧三种不同粒度分布的福建Ⅱ类无烟煤的工业实验,得到给煤颗粒平均粒径与悬浮段颗粒浓度、飞灰含碳量、炉膛各段温度、以及悬浮段颗粒浓度与温度等关系曲线,热态实验表明:低倍率循环流化床锅炉更适合燃烧粗颗粒的福建省无烟煤,它不仅解决因飞灰量过大造成的环境污染问题,而且还提高了锅炉的热效率。 相似文献
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对于循环流化床锅炉,通常是将总风量分为一次风和二次风来控制燃烧过程的进行,而大型循环流化床锅炉又进一步将二次风沿炉膛高度方向分为若干层并分布在燃烧室四面墙上来加强对燃烧过程的控制.首先介绍了横向二次风射流对促进循环流化床锅炉气固混合及煤燃烧的作用.在一台燃烧低挥发分煤的循环流化床锅炉上进行的实验,分析炉内流场对该锅炉不同供风模式下二次风在炉内分布情况的影响.在此基础上考察二次风在炉内不同的分配方式对煤的燃尽和炉内温度场的影响.实验结果表明,通过二次风优化可以加强炉内气固混合,促进气体和燃料的扩散,提高燃烧低挥发份煤的CFB锅炉燃烧效率. 相似文献
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循环流化床锅炉与煤粉锅炉相比,没有那种复杂的制粉系统,节省了大量投资。与普通流化床锅炉相比,循环流化床通过分离回送机构,将没燃尽的细物料送回沸腾床循环燃烧,使机械不完全燃烧损失大大低于普通流化床锅炉。其锅炉效率可与同类煤粉炉相比。同时流化床锅炉因其分离器所处位置不同分为外循环流化床锅炉和内循环流化床锅炉; 相似文献
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以旋涡流化床悬浮空浮空间喷入二次风形成一强放流场和气固悬浮流动为物理模型,试验研究了床面夹带到悬浮空间颗粒群的运动行为及气固两相浓度场的匹配,指出在气相强旋湍流的作用下,在近壁区形成一稳定的高浓度的颗粒悬浮层,颗粒在炉内的平均停留时间延长,气固滑移速度增大,两相混合强并充分接触,良好的空气动力结构对提高炭粒在悬浮空间的燃尽度,降低场析可燃物质损失十分有利,本文研究结果,对降低常规鼓泡床及抛煤机链条炉内的飞灰可燃物损失,提高悬浮空间的气流横向混合速率有重要参考价值。 相似文献
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本文数值模拟了煤粉旋流火焰燃烧过程,燃烧数值计算包括理论物理模型建立,数值方法两个大部分,计算模型处理了气相湍流与燃烧、气固两相流动、煤颗粒燃烧过程和辐射传热等物理化学过程,以k-ε模型模拟湍流流动;PDF法模拟气相扩散火焰燃烧;颗粒运动计算颗粒运动少颗粒湍流浓度方程模拟颗粒湍流扩散;通量法计算火焰辐射传热,煤粉颗粒复杂燃烧模型计算了颗粒尺寸、形状变化和颗粒孔隙内部燃烧、表面平度对整个颗粒的燃烧过程影响。计算获得了气相速度分布场、气相k和ε分布场、气相温度场、气相组份场和颗粒浓度场及运动过程,揭示了煤粉复合旋流燃烧特性。 相似文献
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某厂燃用褐煤六角切圆670t/h炉为降低NOx排放,进行了如下改造:将原有燃烧器全部改造为水平浓淡风煤粉燃烧器,由于水平浓淡两股一次风煤粉气流各自远离燃料的化学当量比,可有效减少NOx的生成;在燃烧器顶部增设燃尽风喷口,使下部主燃烧区域处于氧浓度较低的气氛,可有效减少NOx的生成;将上、中层燃烧器的下二次风射流轴线向水冷壁偏转一定角度,加大上排燃烧器的二次风切圆直径,推迟二次风与一次风风粉混合物的混合,减少着火阶段的供氧量,可有效减少NOx的生成。试验结果证明,额定负荷下NOx排放量显著降低到315.4mg/m^3(O2=6%,干烟气),远低于排放标准,锅炉效率可达91.85%,比原设计值高1.32%。 相似文献
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Low NOx burner and air staged combustion are widely applied to control NOx emission in coal-fired power plants. The gas-solid two-phase flow, pulverized coal combustion and NOx emission characteristics of a single low NOx swirl burner in an existing coal-fired boiler was numerically simulated to analyze the mechanisms of flame stability and in-flame NOx reduction. And the detailed NOx formation and reduction model under fuel rich conditions was employed to optimize NOx emissions for the low NOx burner with air staged combustion of different burner stoichiometric ratios. The results show that the specially-designed swirl burner structures including the pulverized coal concentrator, flame stabilizing ring and baffle plate create an ignition region of high gas temperature, proper oxygen concentration and high pulverized coal concentration near the annular recirculation zone at the burner outlet for flame stability. At the same time, the annular recirculation zone is generated between the primary and secondary air jets to promote the rapid ignition and combustion of pulverized coal particles to consume oxygen, and then a reducing region is formed as fuel-rich environment to contribute to in-flame NOX reduction. Moreover, the NOx concentration at the outlet of the combustion chamber is greatly reduced when the deep air staged combustion with the burner stoichiometric ratio of 0.75 is adopted, and the CO concentration at the outlet of the combustion chamber can be maintained simultaneously at a low level through the over-fired air injection of high velocity to enhance the mixing of the fresh air with the flue gas, which can provide the optimal solution for lower NOx emission in the existing coal-fired boilers. 相似文献
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《International Journal of Heat and Mass Transfer》2006,49(1-2):421-426
To develop low-pollution burners, the effect of a coal concentrator on NO formation in swirling coal combustion is studied using both numerical simulation and experiments. The isothermal gas–particle two-phase velocities and particle concentration in a cold model of swirl burners with and without coal concentrators were measured using the phase Doppler particle anemometer (PDPA). A full two-fluid model of reacting gas–particle flows and coal combustion with an algebraic unified second-order moment (AUSM) turbulence-chemistry model for the turbulent reaction rate of NO formation are used to simulate swirling coal combustion and NO formation with different coal concentrators. The results give the turbulent kinetic energy, particle concentration, temperature and NO concentration in cases of with and without coal concentrators. The predicted results for cold two-phase flows are in good agreement with the PDPA measurement results, showing that the coal concentrator increases the turbulence and particle concentration in the recirculation zone. The combustion modeling results indicate that although the coal concentrator increases the turbulence and combustion temperature, but still can remarkably reduce the NO formation due to creating high coal concentration in the recirculation zone. 相似文献
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Srdjan Belosevic Miroslav Sijercic Predrag Stefanovic 《International Journal of Heat and Mass Transfer》2008,51(7-8):1970-1978
Paper presents selected results of numerical simulation of processes in air–coal dust mixture duct of pulverized coal utility boiler furnace with plasma-system for pulverized coal ignition and combustion stabilization. Application of the system in utility boiler furnaces promises to achieve important savings compared with the use of heavy oil burners. Plasma torches are built in air–coal dust mixture ducts between coal mills and burners. Calculations have been performed for one of rectangular air–coal dust mixture ducts with two opposite plasma torches, used in 210 MWe utility boiler firing pulverized Serbian lignite. The simulations are based on a three-dimensional mathematical model of mass, momentum and heat transfer in reacting turbulent gas-particle flow, specially developed for the purpose. Characteristics of processes in the duct are analyzed in the paper, with respect to the numerical results. The plasma-system thermal effect is discussed as well, regarding corresponding savings of liquid fuel. It has been emphasized that numerical simulation of the processes can be applied in optimization of pulverized coal ignition and combustion stabilization and enables efficient and cost-effective scaling-up procedure from laboratory to industrial scale. 相似文献