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Combustion characteristics of different parts of corn straw and NO formation in a fixed bed Abstract Experiments with five samples of corn straw were carried out on a one-dimensional bench combustion test rig. The bed temperature distribution and the mass loss of fuel and gas components such as O2, CO, CO2 and NO were measured in the bed. The combustion of corn straw occurred in two stages, ignition front propagation and char oxidation. The average burning rate increased with an increase in the primary air flow until a critical point was reached, beyond which a further increase in the primary air flow resulted in a decreased burning rate. The mean concentration of NO reached a minimum value and then increased with increased primary air flow. The time taken for the drying front to reach the bottom of the bed was 800 s, 700 s, and 500 s; the temperatures in the high bed temperature zones were 900–935 ℃, 800–850 ℃ and 700–743 ℃; and the maximum concentrations of NO were 725 ppmv, 1287 ppmv, and 2730 ppmv, for whole corn stalks, hollow corn stalks and flaked corn stalks, respectively. The maximum concentrations of CO and NO were quite different between samples. There was only one peak in the distribution of NO concentration for sample B, but there were two peaks for whole corn stalks and sample A. Combustion kinetics of coal chars in oxygen-enriched environments Abstract Oxygen-enhanced and oxygen-fired pulverized coal combustion is actively being investigated to achieve emission reductions and reductions in flue gas cleanup costs, as well as for coal-bed methane and enhanced oil recovery applications. To fully understand the results of pilot scale tests and to accurately predict scale-up performance through CFD modeling, accurate rate expressions are needed to describe coal char combustion under these unconventional combustion conditions. In the work reported here, the combustion rates of two pulverized coal chars have been measured in both conventional and oxygen-enriched atmospheres. A combustion-driven entrained flow reactor equipped with an optical particle-sizing pyrometry diagnostic and a rapid-quench sampling probe has been used for this investigation. Highvale subbituminous coal and a high-volatile eastern United States bituminous coal have been investigated, over oxygen concentrations ranging from 6 to 36 mol% and gas temperatures of 1320–1800 K. The results from these experiments demonstrate that pulverized coal char particles burn under increasing kinetic control in elevated oxygen environments, despite their higher burning rates in these environments. Empirical fits to the data have been successfully performed over the entire range of oxygen concentrations using a single-film oxidation model. Both a simple nth-order Arrhenius expression and an nth-order Langmuir–Hinshelwood kinetic equation provide good fits to the data. Local fits of the nth-order Arrhenius expression to the oxygen-enriched and oxygen-depleted data produce lower residuals in comparison to fits of the entire dataset. These fits demonstrate that the apparent reaction order varies from 0.1 under near-diffusion-limit oxygen-depleted conditions to 0.5 under oxygen-enriched conditions. Burnout predictions show good agreement with measurements. Predicted char particle temperatures tend to be low for combustion in oxygen-depleted environments. |
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dulisikao(金币+40,VIP+0):谢谢 4-3 01:05
qingfeng877680(金币-20,VIP+0):马甲行为，请做出解释。 4-3 12:12
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在一维燃烧实验装置上，考察了5种不同的玉米秸秆样品的燃烧特性。本文考察了固定床的床层温度分布，样品的质量损失，还有气体组成（如O2, CO, CO2 ，NO）。玉米秸秆的燃烧分为两步，着火前的扩散和随后的碳氧化燃烧。在空气流量达到临界点前，平均燃烧速度随着空气流量的增加而增加，之后随着空气流通速率的进一步增加，燃烧速度降低。NO的平均浓度先到达一个最低值，然后随空气流通速率的增加而增加。整个玉米秸秆，空心玉米秸秆和片状玉米秸秆，干燥到固定床底部温度的时间分别是800 s ， 700 s ，和500秒;在固定床高温区的温度分别是900-935 ℃ ， 800-850 ℃和700-743 ℃ ; NO的最高浓度分别是725 ppmv ， 1287 ppmv ，和2730 ppmv。CO和NO的最高浓度对不同样本来说有相当的差异。对样品B来说，NO浓度的分布只有一个一个极大值，而对整个玉米秸秆和样品A则有2个极大值。 为了减少CO2排放量和减少废气净化费用，煤粉在富氧或纯氧中燃烧正受到广泛的研究，煤层甲烷气体和油回收利用技术也得到广泛研究。为了充分掌握实验室规模试验的结论以及通过CFD模型准确预测放大后的试验情况，需要知道在富氧或纯氧条件下的精确的煤焦燃烧速率方程式。在本论文里，分别对两份粉煤在常规和富氧空气里的燃烧速率进行了研究。这里使用的试带有光学测温元件和快速淬火取样探针的气流床反应器。对亚烟煤和高挥发份美国东部烟煤已进行研究，氧气浓度范围从6％至36％（mol）和气化温度从1320k至1800 k.实验结果表明，随着氧气浓度的增加粉煤煤焦颗粒燃烧越来越多的受到动力学控制，尽管其燃烧速率也在增加。通过单膜氧化模型，在全部氧气浓度范围内，得到了与经验一致的实验数据。一个简单的n阶的Arrhenius表达式及一个n阶的Langmuir - hinshelwood动力学方程，与数据有良好的匹配。与全部的数据相比，局部的数据在与对富氧和氧气耗尽的n阶Arrhenius表达式拟合的时候有较低的残差。这些拟合结论表明，该表观反应级数从扩散控制即在氧气浓度很少的时候的0.1增加到富氧条件下的0.5。烧尽现象的预测与测量结果吻合良好。预测的煤焦粒子的温度趋向于比氧气耗尽的情况下燃烧的温度低。 |
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