褐煤燃烧过程的Aspen数值模拟研究

利用Aspen Plus软件对某褐煤的预干燥及燃烧过程进行模拟分析,研究干燥介质种类、干燥介质温度和干燥介质流量对干燥特性的影响,过量空气系数、空气预热温度和过氧系数对有害燃烧产物产率的影响。结果表明,提高干燥介质温度和增加干燥介质流量都利于褐煤的干燥,而干燥温度的影响更加明显。提高空气预热温度会使燃烧产物中的NO和NO_2产量增大;过量空气系数大于1时,过量空气系数增大会明显降低燃烧产物中NO和CO的产量;过氧系数大于1时,过氧系数增大会明显降低燃烧产物中CO的产量,而NO的产量会增加。褐煤燃烧过程有害燃烧产物的Aspen Plus数值模拟将对褐煤的高效清洁利用提供参考数据。     

预混燃烧室的NOx与未燃碳氢化合物排放性能研究

建立了一套预混燃烧装置,进行了不同过量空气系数a下的燃烧实验,研究了不同的燃料-空气预混过量空气系数对燃烧尾气中污染物NOx与UHC(未燃碳氢化合物)浓度的影响。结果表明,当过量空气系数a>1.1时NOx与UHC排放均呈下降趋势;     

燃气锅炉过量空气系数对锅炉热效率的影响研究

燃气锅炉以天然气为燃料,燃烧产生热量生产饱和蒸汽或过热蒸汽。以某天然气净化厂CG-75/3.82-Q型燃气锅炉为例,分析了该锅炉生产运行中过量空气系数对锅炉热效率的影响,理论计算了不同炉膛烟气出口氧含量下的锅炉热效率及锅炉过量空气系数的合适区间,为燃气锅炉的配风操作提供了理论依据和技术支撑,可为同类研究提供思路。     

在役锅炉运行参数对其热效率影响的研究

探讨了在役锅炉热效率测试的重要性,并建立了锅炉运行工况热效率简单测试的数学模型。对锅炉的实例测试结果进行了数据分析,研究了排烟温度、排烟处过量空气系数以及入炉冷空气温度在不同数值范围内对锅炉运行工况热效率的影响程度,可为锅炉能效测试提供参考。     

煤层气燃烧器流动及NO_x生成特性数值研究

针对煤层气热值低的特点,设计了一台煤层气旋流燃烧器,采用数值模拟方法研究了不同热负荷及过量空气系数对燃烧性能的影响,并计算了燃烧污染物的生成.结果表明,在燃烧区域存在逆压梯度,加强了烟气的扰动,有利于形成稳定的高温区,提高燃烧效率.燃烧器负荷调节范围大,低负荷时仍能保持较高的燃烧温度和燃烧效率.过量空气系数为1.05时燃烧温度最高,此时NOx生成最多,仅为25.1 mg/m3.     

配风方式对部分预混燃烧系统燃烧振荡的影响

部分预混燃烧系统是燃气热水器的常用燃烧系统,研究这种燃烧系统中配风方式和燃烧工况的关系十分重要。通过搭建实验台,研究了一个具有三次风的部分预混燃烧系统在不同过量空气系数下的燃烧振荡区域。发现该系统存在一个介于两正常工作区域之间的燃烧振荡区域,该区域的界限随着配风方式的变化发生偏移,减小一次风量时其正常工作范围扩大。通过分析,认为其燃烧振荡范围与一次过量空气系数值有直接关系,该范围具有一个上限,对应一次过量空气系数为0.80～0.95;具有一个下限,一次过量空气系数为0.40～0.50,此范围内发生燃烧振荡的概率较大。     

催化燃烧蒸发器热态流场分布研究

为了改善催化燃烧蒸发器中反应和蒸发的耦合行为,提高蒸发器的热效率,文章对催化燃烧蒸发器进行了热态实验研究和数值模拟,确定燃料完全燃烧需要的过氧系数随着空速的增加而降低;同时,通过对催化燃烧蒸发器内初始浓度场和温度场的分析比较,说明当放热反应速率较快时,燃烧腔内温度场的空间分布主要受初始浓度场分布决定。实验和模拟结果的很好吻合,说明建立的多孔介质模型能够很好地预测燃烧腔内的流场分布。     

焦炉结焦过程立火道NO_x生成特性研究

以6m燃高炉煤气的焦炉单对立火道为研究对象,采用CFD数值模拟方法对焦炉加热过程中热力型NO_x的生成规律和影响因素进行研究。研究结果表明,过量空气系数对NO_x生成有很大影响,随过量空气系数增加,NO_x浓度呈现先增加后减小的趋势;立火道对外热流密度对NO_x生成也有很大影响,热流密度减小,燃烧最高温度增加,NO_x生成量也增加;对不同的热流密度,过量空气系数对立火道内温度分布和NO_x浓度分布的影响程度不同。     

注汽锅炉最佳燃烧工况的实现

通过研究某公司的注汽锅炉,发现实际燃烧工况与最佳燃烧工况之间差距较大。分析发现影响锅炉热效率的最主要因素就是过剩空气系数是否达标。因此对锅炉加装热效率监控仪,以及时调整锅炉过剩空气系数,使之达到最佳燃烧工况,实现节能、环保的目的。     

多孔介质燃烧器研究及应用进展

与自由空间燃烧相比,多孔介质燃烧具有功率调节范围大、燃烧稳定性好、燃烧强度和燃烧效率高、污染物排放低等优点。笔者介绍了多孔介质燃烧在居住空间加热、涂料和油漆干燥、食品加工、发动机等民用、工业领域的应用,并对多孔介质燃烧的研究方向和应用前景作了展望。     

Experimental study on effects of operating conditions and fuel quality on thermal efficiency and emission performance of a 300-MW boiler unit firing Thai lignite

This paper presents the results of an experimental study on a 300-MW boiler unit fired with Thai lignite. Effects of operating conditions (excess air ratio and unit load) and fuel quality on the boiler heat losses and thermal efficiency as well as on the gaseous (CO₂, CO, NO_x and SO₂) and particulate matter (PM) emissions from the boiler unit are discussed. The boiler thermal efficiency was weakly affected by the excess air ratio, unit load and fuel lower heating value, varying from 90.3 to 92.3% for wide ranges of the above variables. In all the tests, the NO_x, SO₂ and PM emissions were below the national emission standards for these pollutants. Quite low level of the SO₂ emission was secured by the high-efficiency flue gas desulphurization system. The CO emissions of rather small values were detected only at extremely low excess air ratios. The emission rate and specific emission (i.e. per MWh of electricity produced) for NO_x, SO₂ and CO were quantified using experimental emission concentrations of the pollutants. Meanwhile, the emission characteristics for CO₂ were determined with the use of fuel-C and fuel consumption by the boiler. In addition, the emission rate and specific emission for PM were estimated by taking into account the actual fuel-ash content and fuel consumption by the boiler, as well as the effects of SO₂ adsorption by fly ash in the boiler gas ducts and overall ash-collecting efficiency of the electrostatic precipitators and flue gas desulphurization system. Elevated CO₂ and NO_x emissions from the 300-MW boiler units firing Thai lignite are of great concern.     

陶瓷隧道窑热量消耗分析

本文根据陶瓷隧道热工测定结果,分析了匣钵和瓷重比值、窑车和瓷重比值、漏风量、窑炉单位体积的产量、窑顶外表温度、窑体外表面温度、烧成温度、烧成带温差、加热带长度、窑道利用率对热量消耗的影响。     

影响裂解炉热效率的因素分析及优化措施

热效率是衡量裂解炉先进性的一个重要指标,它关系着装置能耗的高低,文章分析了影响裂解炉热效率的因素,从裂解炉炉衬、过剩空气系数、排烟温度等方面介绍了提高裂解炉热效率的优化措施。     

Coal combustion characteristics in a fluidized bed combustor with a draft tube

The effects of gas velocity to draft tube (3–6 U_m), bed temperature (800–900°C) and excess air ratio (0–30%) on the total entrainment rate, overall combustion efficiency and heat transfer coefficient have been determined in an internally circulating fluidized bed combustor with a draft tube. The total entrainment rate increases with an increase in gas velocity to draft tube, but decreases with increasing bed temperature and excess air ratio. The overall combustion efficiency increases with increasing excess air ratio, but decreases with increasing gas velocity to draft tube. The overall combustion efficiency obtained in internally circulating fluidized beds was found to be somewhat higher than that in a bubbling fluidized bed combustor.     

Analysis of combustion efficiency in CFB coal combustors

Fluidized bed technology is well known for its high combustion efficiency and is widely used in coal combustion. In this study, the combustor efficiency has been defined and investigated for CFB coal combustor based on the losses using a dynamic 2D model. The model is shown to agree well with the published data. The effect of operating parameters such as excess air ratio, bed operational velocity, coal particle diameter and combustor load and the effect of design variables such as bed height and bed diameter on the mean bed temperature, the overall CO emission and the combustion efficiency are analyzed for the small-scale of CFBC in the presently developed model. As a result of this analysis, it is observed that the combustion efficiency decreases with increasing excess air value. The combustion efficiency increases with the bed operational velocity. Increasing coal particle size results in higher combustion efficiency values. The coal feed rate has negative effect on the combustion efficiency. The combustor efficiency considerably increases with increasing combustor height and diameter if other parameters are kept unchanged.     

The study of the effect of operating parameters on the PAH formation during the combustion of coconut shell in a fluidised bed

The effect of combustion parameters on the PAH formation from coconut shell combustion in a FBC was investigated. Among the combustion parameters studied which included temperature, excess air, fuel particle size, and fuel moisture content, only excess air proved to have significant influence on the PAH formation. At 750 °C, an increase of excess air from 20 to 80% resulted in a twelfth fold reduction of PAH emission. At high excess air levels, the combustion temperature had small influence on PAH emission level. In addition to above mentioned combustion parameters, the addition of secondary air to the freeboard was investigated. Due to the relatively low temperature, the addition of secondary air resulted in higher PAH emission. A strong correlation between the combustion efficiency and the PAH emission was observed. According to the results, the CO concentration can be employed as an indicator of PAH level in the exhaust gas.     

Effects of operational parameters on emission performance and combustion efficiency in small-scale CFBCs

A well-designed CFBC can burn coal with high efficiency and within acceptable levels of gaseous emissions. In this theoretical study effects of operational parameters on combustion efficiency and the pollutants emitted have been estimated using a developed dynamic 2D (two-dimensional) model for CFBCs. Model simulations have been carried out to examine the effect of different operational parameters such as excess air and gas inlet pressure and coal particle size on bed temperature, the overall CO, NO_x and SO₂ emissions and combustion efficiency from a small-scale CFBC. It has been observed that increasing excess air ratio causes fluidized bed temperature decrease and CO emission increase. Coal particle size has more significant effect on CO emissions than the gas inlet pressure at the entrance to fluidized bed. Increasing excess air ratio leads to decreasing SO₂ and NO_x emissions. The gas inlet pressure at the entrance to fluidized bed has a more significant effect on NO_x emission than the coal particle size. Increasing excess air causes decreasing combustion efficiency. The gas inlet pressure has more pronounced effect on combustion efficiency than the coal particle size, particularly at higher excess air ratios. The developed model is also validated in terms of combustion efficiency with experimental literature data obtained from 300 kW laboratory scale test unit. The present theoretical study also confirms that CFB combustion allows clean and efficient combustion of coal.     

The efficiency of short airlift pumps operating at low submergence ratios

An airlift pump operating at submergence ratios between 0.2 and 0.6 and using water as the pumping liquid, has been investigated. Circular pipes of constant short length of 1 m and inner diameters of 3 and 5 cm were used as riser tubes. The water flow rate measurements for various air flow rates allowed the study of the pumping efficiency as a function of the air flow rate, submergence ratio and certain geometrical parameters (riser tube diameter and injector design). The efficiency curves start from a zero efficiency at a minimum air flow rate, then increase rapidly with the air flow rate up to an efficiency maximum. For higher air flow rates, the efficiency decreases exponentially. Diagrams showing the influence of the riser tube diameter and injector design, are presented. Additionally, based on the experimental data, two equations are presented, which allow the prediction of the maximum efficiency and the corresponding water and air flow rates inside the experimental range.     

城市污泥流化床中低温空气气化及重金属迁移特性

利用自行搭建的流化床热态实验装置，系统研究了污泥的中低温气化及重金属迁移特性。研究表明，对冷煤气效率和碳转化率影响最大的是气化温度，其次是空气当量比，而一二次风配比和流化数影响较弱。污泥中低温气化的焦油产率较之高温气化明显增加。随着二次风占比和空气当量比的提高，焦油产率单调下降。气化温度由600℃升至850℃，冷煤气效率和碳转化率均呈升高趋势；空气当量比由0.2升至0.4，冷煤气效率呈先升高后下降的趋势，在0.3时达到最大值，而碳转化率则呈单调升高趋势。随着气化温度的升高，污泥中重金属转移至产气、焦油及飞灰的迁移率升高。随着空气当量比的升高，Ni、Cu的迁移率降低，Cr升高，Cd、Zn、As和Pb等其他重金属的迁移率几乎不变。