打捆秸秆的燃烧特性和影响因素分析

利用自主设计的实验台研究生物质秸秆打捆燃料的燃烧特性和影响因素。实验结果表明:生物质秸秆打捆燃料的燃烧是由外向内进行的,燃烧过程经历水分蒸发、热解、燃烧和燃尽4个阶段;当给风量为70 m~3/h时,玉米秸秆打捆燃料着火锋面向下传播的速度比向上传播的速度快,内层传播的速度比外层传播的速度快,燃烧完全所需的时间较长;随着风量的增加,在给风量为90、110 m~3/h条件下,着火锋面向上传播的速度超过向下传播的速度,外层传播的速度超过内层传播的速度,着火锋面温度随着风量的增加而增大;继续增大风量,当给风量为130 m~3/h时,燃烧完全所需的时间最短,但着火锋面温度峰值有所下降;同在给风量90 m~3/h下,小麦秸秆打捆燃料由于内部较松散,其向上、向下、内层着火锋面传播速率和着火锋面温度均高于玉米秸秆打捆燃料。     

煤粉与生物质混燃的低温着火特性

利用自制的管式炉恒温热重测量实验台研究了掺混比、温度、煤种以及生物质种类等因素对煤粉与生物质混燃时低温着火特性的影响,并对煤粉与生物质混燃时的低温着火活化能进行了计算.结果表明:随着掺混比的增大,混合物的燃烧速率加快且燃尽程度提高;温度升高能改善煤粉与生物质混合物的燃烧特性;掺混生物质对难燃煤的着火特性影响比对易燃煤更明显;对于某一煤种,掺混水分和挥发分含量高的生物质,燃烧初期的失重速率加快;掺混灰分含量越多的生物质,在燃烧后期对煤粉的促燃作用越差;燃烧反应活化能随着生物质掺混比和温度区间的增大而减小.     

生物质层燃实验台的设计与实验

研究小型层燃炉燃烧实验系统,设计并搭建了生物质多功能实验台,可进行层燃燃烧、室燃燃烧及配风等实验的模拟.同时对水稻秸秆和玉米芯燃料层燃燃烧过程进行了研究,分析了风量对生物质燃料层燃燃烧的影响.研究表明:对床层内部分布的热电偶的温度和整个燃烧过程中床层上方的气体浓度变化进行分析,燃烧过程的温度变化曲线与床层上方气体浓度变...     

生物质成型燃料层燃NO排放特性研究

在层燃单元体炉上研究了生物质成型燃料的NO排放特性,采用热电偶和烟气分析仪对生物质成型燃料层燃过程中床层温度和表面气氛进行监测,分析了生物质成型燃料的燃烧特性和NO排放特性。试验结果表明,生物质成型燃料层燃分为火焰传播段和焦炭燃尽段。NO主要在火焰传播段生成,而在焦炭燃尽段,由于焦炭的还原作用,NO排放量逐渐降低,此外,NO排放总量随着一次风量的增加先减小后变大。     

生物质与煤掺烧燃烧特性的实验研究

利用热重分析仪,在不同条件下,对单一生物质、煤及其混合物的燃烧特性进行分析,研究了木屑、稻壳、稻草及耒阳白沙煤的着火温度、燃烧最大速率温度和燃烬温度等燃烧特性参数。实验结果表明,生物质的着火温度比白沙煤低,生物质在燃烧过程中有两个明显的失重阶段,而煤只有一个明显的失重阶段。通过掺烧可以使生物质与煤的混合物着火温度降低,着火时间缩短,延长了整个燃烧的温度区间,使煤能更好地燃尽,使燃料的燃烧特性得到了优化。随着生物质掺混比例的提高,掺混样品着火点温度降低得更加明显;且生物质颗粒尺寸由R90变为R200时,同样的掺混比例下,尺寸R200的掺混样品着火温度更低。     

半焦粒子着火与燃烧过程实验研究

实验研究了半焦粒子着火与燃烧过程,测定了几种尺寸的半焦粒子在不同环境温度下的着火温度、着火滞燃期、燃尽时间和燃烧过程中的粒子温度等与燃烧过程相关的参数变化,对影响半焦粒子燃烧的因素进行分析讨论,并将实验结果与理论计算结果进行了对比分析,两者在一定范围内有较好的一致。     

柠条燃烧特性及燃烧动力学研究

应用热分析仪对柠条生物质燃料的燃烧过程进行分析,研究颗粒度、升温速率和风量对燃烧特性与动力学参数的影响。结果表明:(1)颗粒度为0.16 mm试样在升温速率为20 K/min,风量为40 mL/min的工况下,着火温度为221.1℃,最大燃烧速率温度为336.2℃,燃尽温度为559.4℃,最大燃烧速率0.6 mg/min,平均燃烧速率为0.129mg/min,相对于10 K/min和30 K/min升温速率,20 K/min工况下的燃料动力学参数最优,活化能为39.094 kJ/mol,频率因子为2.175×10~7L/min;(2)升温速率的增大会使平均燃烧速率和燃烧特性指数增大,着火温度降低;风量对燃烧速率无影响,但较大风量不利于挥发分析出和燃烧稳定性;颗粒度对挥发分析出有显著影响,颗粒度较大时需较高升温速率和风量才可充分燃烧,而颗粒度较小时即使风量较小也能充分燃烧。     

几种生物质的TG-DTG分析及其燃烧动力学特性研究

采用热重分析技术对木屑、麦秆、玉米秆和玉米芯4种生物质的燃烧特性进行了研究,考察了其着火、燃尽特性和综合燃烧特性,研究了升温速率对生物质燃烧特性的影响,同时在热天平上对其进行了动力学试验研究.研究表明:生物质燃烧过程大致可以分为3个阶段,即水分析出阶段、挥发分析出燃烧阶段、固定碳燃烧与燃尽阶段:生物质具有着火温度低、燃尽温度低、燃尽率高等优点;随着升温速率的提高,着火温度、各试样挥发分最大释放速率、燃尽温度均呈升高趋势,燃烧特性随升温速率的提高而变好.采用一级反应动力学模型和积分法对生物质燃烧动力学参数的研究表明,生物质具有较低的活化能,有利于点燃.     

甲烷火焰中氢气对着火与燃尽的影响

利用化学反应动力学机理研究了甲烷－空气预混火焰添加H2的着火和燃尽特性。通过分析计算,讨论了氢气对甲烷燃烧过程及着火温度、燃烧速率、燃尽时间的影响。结果表明,甲烷火焰中少量氢气的存在不仅可以降低甲烷的着火温度,而且可以显著增大燃烧速率,缩短燃尽时间,这些结果与已有的实验结果吻合。     

固体燃料层燃过程中着火特性的实验研究

为评估燃料在层燃锅炉中的着火特性,设计搭建了单元体炉实验台模拟层燃反应过程,对不同挥发分含量的生物质成型燃料、烟煤、贫煤和无烟煤开展了研究。结果表明,随着燃料挥发分的增大,着火温度逐渐降低。生物质成型燃料的着火温度在280℃左右,而煤的着火温度则在500℃左右。通过与热重实验结果的对比,发现两种方法获得的着火温度具有较强的对应关系,因此,可以利用热重分析仪快速预测层燃过程中燃料的着火温度,为层燃锅炉的设计和运行提供参考依据。     

生物质与炉渣混燃循环流化床锅炉设计构想

目前生物质工业锅炉多采用层燃方式,生物质燃料灰熔点较低,灰成分碱金属含量高,结渣、受热面积灰、腐蚀等情况比较严重,制约层燃生物质锅炉的发展。另外在工业锅炉占很大份额的燃煤层燃炉炉渣含碳量普遍高于20%,造成能源浪费。本文根据生物质燃料以及层燃炉渣的特点,提出燃用生物质与层燃炉渣混合燃料循环流化床锅炉的设计构想。通过合理的燃料配比提高生物质燃料灰熔点,稳定流化床循环物料,采取一定措施减少碱金属的升华和尾部受热面积灰、腐蚀。并对其在小型工业锅炉应用的"节能减排"效果进行了预测。     

生物质链条炉床层燃烧建模及一次风影响分析

基于多孔介质非热平衡的方法,考虑了床层高度的变化及颗粒内部温度梯度的影响,建立了一维非稳态燃烧模型来模拟炉排上移动床层的生物质燃烧。模拟计算结果与实验值对比分析表明,总体上数值计算结果与实验数据吻合较好。通过对不同一次风参数下床层燃烧的模拟结果分析得到,随着一次风风量的增加,床层剩余质量先减小后增大;在燃烧前期,床层出口气体温度上升速度减慢,挥发分析出速率降低,焦炭燃烧速率增大;在燃烧中期,床层出口气体温度先上升后下降,焦炭燃烧速率下降。一次风风温相比于一次风风量对床层燃烧影响较小,增大一次风风温可以提高挥发分析出速率,降低床层出口气体温度和床层剩余质量。     

Investigation of factors affecting channelling in fixed-bed solid fuel combustion using CFD

Channelling is an undesirable phenomenon in fixed-bed combustion. It is characterised by an uneven air distribution, and thus fuel conversion, throughout the fuel bed. To investigate factors that influence channelling, an unsteady, two-dimensional numerical model capable of predicting solid fuel combustion under fixed-bed conditions is presented. Biomass is the focus of this study, but the model can be readily applied to other solid fuels, such as coal and municipal solid waste. The model includes drying, pyrolysis, and heterogeneous char reactions, and incorporates bed shrinkage processes comprised of both continuous shrinkage and abrupt collapses. It is also capable of representing spatial non-uniformities which may occur throughout a bed, arising from irregular packing and non-homogeneous fuel composition. The overall model is validated by means of two different data sources: the first for ignition rates and the second for species profiles through a biomass fuel bed. The validated model is then applied to investigate factors affecting channelling in a randomly packed bed containing a high-porosity passage. The influence of flow resistance through the grate and bed height are compared with previous observations. Additional factors investigated include flue gas recirculation and initial moisture content of the fuel. Predictions show that increasing the flow resistance of the grate improves the gas distribution and reduces channelling because it inhibits flow from deviating towards the relatively porous passage. For deeper beds, however, the effectiveness of grate resistance is diminished because the gas then has more residence time within the bed to track towards the passage. Increasing the initial moisture content from 0% to 30% has a weak influence; nonetheless, wetter fuels show a propensity to amplify channelling. The impact of flue gas recirculation on channelling appears to be insignificant, although its benefits, such as reduced peak temperature, are apparent.     

Grate-firing of biomass for heat and power production

As a renewable and environmentally friendly energy source, biomass (i.e., any organic non-fossil fuel) and its utilization are gaining an increasingly important role worldwide. Grate-firing is one of the main competing technologies in biomass combustion for heat and power production, because it can fire a wide range of fuels of varying moisture content, and requires less fuel preparation and handling. The basic objective of this paper is to review the state-of-the-art knowledge on grate-fired boilers burning biomass: the key elements in the firing system and the development, the important combustion mechanism, the recent breakthrough in the technology, the most pressing issues, the current research and development activities, and the critical future problems to be resolved. The grate assembly (the most characteristic element in grate-fired boilers), the key combustion mechanism in the fuel bed on the grate, and the advanced secondary air supply (a real breakthrough in this technology) are highlighted for grate-firing systems. Amongst all the issues or problems associated with grate-fired boilers burning biomass, primary pollutant formation and control, deposition formation and corrosion, modelling and computational fluid dynamics (CFD) simulations are discussed in detail. The literature survey and discussions are primarily pertaining to grate-fired boilers burning biomass, though these issues are more or less general. Other technologies (e.g., fluidized bed combustion or suspension combustion) are also mentioned or discussed, to some extent, mainly for comparison and to better illustrate the special characteristics of grate-firing of biomass. Based on these, some critical problems, which may not be sufficiently resolved by the existing efforts and have to be addressed by future research and development, are outlined.     

Development of a novel updraft multifuel biomass gasifier

The paper reports the development of a novel multifuel biomass reactor for direct heating applications such as water heating, air heating or steam generation. Studies were conducted on the reactor to maximize its heat release rate by evaluation of the sensitivities of the fuel and charging parameters to firing rate. Maximum firing rates measured for the different fuels were in the range of 8–43 kg/h for the natural draft mode and 45–130 kg/h for the forced draft mode. It is observed that the heat release rate is enhanced by up to 360% by preheating of the charge, increase of the surface-area/volume ratio of the fuel charge, decrease of the charge per feed, and adoption of forced draft mode. For wood, a fuel preheat to 80°C, a surface-area/volume ratio of 600 m^?1 and a charge per feed of 0.5–1.0 kg give a higher heat release and minimize gas temperature fluctuations.     

Some aspects of the formation of nitric oxide during the combustion of biomass fuels in a laboratory furnace

The influence of bed-region stoichiometric ratio and fuel nitrogen content on the formation of gaseous species formed during grate combustion of biomass fuels is reported based on gas measurements made within the fuel bed. Three fuels were studied: two mixtures of pelletized bark and wood chips and one of pelletized straw. Experiments were performed in a vertical, cylindrical, laboratory-scale grate-furnace with 0.245 m i.d. and 1.8 m height. Primary air was supplied through a grate consisting of a steel plate with 340 holes of 3.7 mm diameter. Secondary air was supplied 0.66 m above the grate. Gas analysis was performed for O₂, CO₂, CO, H₂ and NO. Results were compared with values calculated using a computer program for thermochemical equilibrium conditions. The measured contents of O₂, CO₂, CO and H₂ show good agreement with calculated equilibrium conditions at all bed region stoichiometries. A higher formation of NO was found for the straw fuel (0.58% fuel nitrogen) than for the bark/wood chip fuels (≈0.25% fuel nitrogen). This is not in accordance with the thermochemical equilibrium calculations indicating that the formation of nitric oxide does not attain thermochemical equilibrium and that the nitrogen content of the fuel has an influence on the amount of NO that is formed. The fuel nitrogen conversion to NO ranged from 3 to 20% at reducing conditions and from 20 to 40% at bed region stoichiometries between 1.00 and 1.25.     

Experimental study on combustion of torrefied palm kernel shell (PKS) in oxy‐fuel environment

Oxy‐combustion of biomass can be a major candidate to achieve negative emission of CO₂ from a pulverized fuel (pf)‐firing power generation plants. Understanding combustion behavior of biomass fuels in oxy‐firing conditions is a key for design of oxy‐combustion retrofit of pulverized fuel power plant. This study aims to investigate a lab‐scale combustion behavior of torrefied palm kernel shell (PKS) in oxy‐combustion environments in comparison with the reference bituminous coal. A 20 kW_th‐scale, down‐firing furnace was used to conduct the experiments using both air (conventional) and O₂/CO₂ (30 vol% for O₂) as an oxidant. A bituminous coal (Sebuku coal) was also combusted in both air‐ and oxy‐firing condition with the same conditions of oxidizers and thermal heat inputs. Distributions of gas temperature, unburned carbon, and NO_x concentration were measured through sampling of gases and particles along axial directions. Moreover, the concentrations of SO_x and HCl were measured at the exit of the furnace. Experimental results showed that burnout rate was enhanced during oxy‐fuel combustion. The unburnt carbon in the flue gas was reduced considerably (~75%) during combustion of torrefied PKS in oxy‐fuel environment as compared with air‐firing condition. In addition, NO emission was reduced by 16.5% during combustion of PKS in oxy‐fuel environment as compared with air‐firing condition.     

气体燃料再燃对NOx还原的影响

气体燃料再燃是研究较多的降低烟气中ＮＯｘ含量最有效的方法之一。本文以典型的一次燃烧区烟气成分为模拟烟气,研究了不同的气体燃料（ＣＨ４,Ｃ２Ｈ２和Ｃ２Ｈ４）作为再为燃烧料时,再燃区燃烧工况（空气过量系数和再燃温度）对ＮＯｘ再燃过程和ＮＯｘ还原率的影响。通过计算发现,不同组分的气体燃料、再燃区空气过量系数及再燃区对ＮＯｘ的再燃过程和ＮＯｘ还原率都有重要的影响。     

煤和生物质床层燃烧氮氧化物生成规律的对比研究

为揭示和评估燃料特性对床层燃烧过程中氮氧化物生成规律的影响,选取了燃煤与生物质成型颗粒这两种代表性燃料,在单元体炉试验台上模拟层燃反应过程,并测定了床层表面和内部的温度及气氛.结果表明:无论燃煤还是生物质,床层内部的氮氧化物浓度峰值都显著高于床层表面,证实了炭层对氮氧化物优良的还原作用.生物质与燃煤相比火焰锋面处的氮氧...     

火花点火式发动机燃烧过程中缸内气流运动研究

通常在发动机倒拖工况下测量和研究缸内气流运动,对于燃烧过程中缸内流动规律的测量和研究还很少。在一台单缸四气门火花点火式发动机上,用激光多普勒测速仪分别在发动机着火和倒拖条件下测量和分析了燃烧室气流运动的规律。研究结果表明,在燃烧和排气阶段,缸内气流的平均速度与倒拖时有较大差别,而且燃烧速度越快,燃烧过程中气流运动速度的变化越剧烈。