煤粉加压燃烧过程中氧气可达比表面积的实验研究

针对煤粉燃烧SCT模型中的氧气可达比表面积,进行了不同煤种的加压热重分析(PTGA)和不同燃尽度下煤焦N2/BET比表面积的测试,研究表明:煤粉加压燃烧过程中,当平均孔径大于2 nm时,累积比表面积和氧气可达比表面积均随燃尽度的增加而增加,说明该孔径以上的比表面积与燃尽度有很好的相关性;常压下TGA中不同燃尽度下煤焦氧气可达比表面积是PTGA下的1.5～2倍,这部分说明了加压反应速率不可能与压力等倍数增加.     

煤粉燃烧过程中灰膜形成比例实验研究

煤焦颗粒燃烧过程中,灰膜形成显著影响其燃烧特性。因此,本文借助高温沉降炉研究了61~75,75~90和90~125μm三种粒径黄陵烟煤在1273和1673 K温度下的燃烧特性与灰膜形成比例;借助扫描电镜(SEM)详细观测空心微珠颗粒内部结构,提出灰膜比例计算公式,并分析温度,粒径和碳转化率对灰膜比例的影响。结果表明,高温下大部分灰分在焦炭烧尽阶段以灰膜形式存在。灰膜比例随温度和碳转化率增加而增加,随煤粉粒径增大而减小。高温下灰分用于形成灰膜比例相对较高,这为煤焦燃尽阶段的低反应性提供了合理的解释。煤焦颗粒动态燃烧过程中灰膜形成比例随燃烧工况变化而变化。该研究为煤焦颗粒燃烧动力学模拟灰膜比例选择提供了关键数据支撑。     

O_2/CO_2气氛燃煤半焦孔隙特性分析

在沉降炉上制备了不同燃烧气氛、不同燃尽程度的半焦,采用低温氮吸附仪和扫描电子显微镜测定了其孔隙结构和表面形态.结果表明,所取的半焦试样均具有完整且连续的孔结构体系;但在相同的操作条件下,O_2/CO_2气氛下半焦试样的孔结构参数及其分形维数均小于相同O_2浓度的O_2/N_2气氛下的情况;两种气氛下煤焦的燃尽过程中,孔隙结构参数(S_(BET)、V_(BJH)和d_(pore))随燃尽率的增加均呈减小趋势;SEM图像的定性分析结果与N_2吸附的定量测量吻合较好.研究结果为深入认识O_2/CO_2气氛下煤粉的孔隙结构与其燃烧特性的关系提供了基础.     

基于循环流化床预热的半焦燃烧试验研究

在一个由循环流化床和下行燃烧室组合试验台上进行神木半焦燃烧试验。本文研究了神木半焦在循环流化床内预热燃烧特性,对预热后气固相产物进行分析,结果表明预热过程中焦炭氮有35%被还原成氮气,这是本工艺能降低NO_x排放的最主要原因。同时通过改变二次风喷口结构,二次风当量比和燃尽风位置来研究燃烧产物中NO_x变化规律。结果表明合理安排二次风喷口结构和燃尽风位置,可以进一步降低NO_x排放。     

天然焦-H2O气化反应特性

在加压热重分析仪上研究了气化温度和催化剂种类对沛城煤矿天然焦-H2O的气化反应特性的影响,用扫描电镜(SEM)观察不同温度下焦样的孔隙结构,并计算了动力学参数.结果表明,气化温度是影响天然焦-H2O气化反应性的一个主要因素,随着温度的升高,天然焦的孔隙越发达,碳转化率明显增大;K基、Ni基、Fe基三种催化剂均能有效地促进气化反应,其中K基催化剂效果最好,其次是Ni基和Fe基催化剂;天然焦的活化能为Eα=147.25 kJ/mol.     

O_2/CO_2气氛下不同密度煤粉燃烧特性研究

本文将大同烟煤分为低(1.4 g/cm~3)、中(1.4～2.0 g/cm~3)、高(2.0 g/cm~3)3个密度段,进行不同密度原煤的工业和元素分析,利用热重分析仪研究了O_2/N_2、O_2/CO_2气氛(不同氧气浓度下)各样品的燃烧特性,并开展了反应动力学分析。结果显示在O_2/CO_2气氛下,随煤粉密度增加,煤粉最大失重速率减小,最大放热速率减小,燃尽温度升高;提高氧气浓度可降低燃尽温度。与O_2/N_2气氛相比,在氧气浓度相同的条件下,各样品在O_2/CO_2气氛下的着火温度、燃尽温度、表观活化能均升高。     

半焦燃烧特性的热重试验研究

针对目前提倡的煤部分气化燃烧系统集成优化联合生产煤气和热能的新概念,在不同温度下制得四种煤的半焦,通过热天平燃烧试验研究了半焦的燃烧特性,考察了煤种和制备温度对半焦燃烧特性的影响.试验结果表明:煤种不同,所制得半焦燃烧特性不同;相同煤种制得半焦,随制备温度升高,半焦着火温度上升,燃烧活化能增加,燃烧反应活性降低.     

O_2/CO_2气氛下污泥与煤混燃特性研究

利用热重分析研究了O_2/CO_2气氛下污泥与煤混燃特性,基于热重(TG)和微商热重(DTG)分析曲线,分析了泥煤比、升温速率和气氛对污泥与煤混燃特性的影响。结果表明;在21%O_2/79%CO_2气氛下,污泥与煤混合物的着火温度随泥煤比的上升而显著降低,最大失重速率随着升温速率的提高而提高。随着氧浓度由21%提高到50%,燃尽温度从708.3℃降低至599.8℃,污泥与煤混合物的燃尽时间也明显缩短。21%O_2/79%N_2气氛下污泥与煤混合物的燃烧特性介于21%O_2/79%CO_2和30%O_2/70%CO_2气氛之间.     

热处理对煤焦气化和燃烧反应性的影响

利用非等温热重法研究了不同温度下制得的褐煤煤焦CO_2气化和燃烧反应动力学,得到了各反应的反应性指数、活化能、反应速率常数等动力学参数。结果表明,煤焦两种反应的反应性指数、活化能均随着热处理温度的升高而增大,即煤焦的反应性随着热处理温度的升高而减小。矿物质对煤焦的两种反应均具有催化作用,该作用随着热处理温度的升高而减小。煤焦两种反应的反应速率常数k随热处理温度升高显示出不同的变化趋势,反映了煤焦物理化学特性对气化和燃烧反应影响的差异和两种反应动力学过程的不同。     

低氧浓度下煤燃烧特性的热重实验研究

煤燃烧的部分过程是在低氧浓度下进行的,本文利用热重实验研究煤在低氧浓度下燃烧特性的变化,重点研究着火特性、燃尽特性和燃烧速率的变化;同时计算分析低氧浓度下,煤燃烧反应动力学参数的变化。实验结果表明,低氧浓度下煤燃烧反应的TG和DTG曲线均向高温区靠近,着火温度基本不变,燃尽温度提高,燃烧速率下降;低氧浓度下燃烧反应的动力学参数活化能E和频率因子k_0之间存在着补偿效应。     

Pressurized oxy-fuel combustion of a char particle in the fluidized bed combustor

Pressurized oxy-fuel combustion of coal in fluidized bed (FB) holds the potential to realize low-cost CO₂ capture. However, the fundamental study in this manner is still rare due to the difficult access to the pressurized oxy-FB combustion tests. In this work, the experimental study of single char combustion was firstly conducted in a visualized pressurized FB combustor under various operating conditions. Then an experimentally verified particle-scale char combustion model was developed to reveal the dependence of char combustion on parameters. Results showed that the char conversion was accelerated with the increase of pressure, mainly due to the high oxygen diffusion and char gasification. The gasification played a non-negligible role in pressurized oxy-fuel combustion, especially under high oxygen concentration and bed temperature. Increasing oxygen concentration and bed temperature not only promotes the char oxidation rate and particle temperature, but also increases the gasification rate and the share of char conversion via gasification, resulting in shortening the burnout time of char. In addition, a higher fluidization number lowered both the burnout time and peak temperature of char particle, due to the simultaneous improvement of mass and heat transfer. The influences of char size and fluidization number on char gasification conversion ratio are very weak. In addition, the quantitative analysis of the influence of different operating parameters on the combustion process was obtained by model sensitivity analysis.     

EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER AND BURNOUT IN CONDITION OF NONUNIFORM MEGAWATT HEAT FLUXES

Burnout is investigated in tubes under nonuniform heating on the perimeter. Data on heat transfer and critical heat flux (q_cht) in the case of water were obtained for ranges of mass velocity pw = 200-3000 kg/m₂ s, pressure p = 0.1-1 MPa, and inlet water temperature T = 25-98°C. The test section was a horizontal copper tube of 21 mm outer diameter, 8 mm inner diameter with a technically smooth surface and heat transfer-intensifying twisted tape and porous sintered coating. The test section was heated by bombardment with electrons. It is established that a redistribution of heat fluxes and an increase of wall temperature fluctuations occur at burnout. The range of regime parameters to prevent burnout of a heat transfer surface is determined.     

麦秆添加大量CaO热解的TG-FTIR实验研究

利用热重-傅里叶变换红外光谱联用方法研究添加CaO对麦秆热解过程和挥发份析出特性的影响.热重和红外光谱分析均表明添加CaO后麦秆热解旱现两个明显的失重和挥发份析出阶段,而纯麦秆热解则只有一个.CaO在第一阶段不但能够吸收CO2,而且能够降低甲苯、苯酚和蚁酸等焦油类物质的产生,使得该阶段失重率和最大失重速率随CaO添加量增加而减小.CaCO3的煅烧分解是添加CaO麦秆热解第二阶段产生的原因,该阶段失重率和最大失重速率随CaO添加量增加而增大.研究结果表明,在采用生物质为原料的零排放系统中添加CaO有利于捕获CO2和减少焦油物质的产生,系统的气化温度应适当降低以防止CaCO3的煅烧分解.     

Output power analyses for the thermodynamic cycles of thermal power plants

Thermal power plant is one of the important thermodynamic devices, which is very common in all kinds of power generation systems. In this paper, we use a new concept, entransy loss, as well as exergy destruction, to analyze the single reheating Rankine cycle unit and the single stage steam extraction regenerative Rankine cycle unit in power plants. This is the first time that the concept of entransy loss is applied to the analysis of the power plant Rankine cycles with reheating and steam extraction regeneration. In order to obtain the maximum output power, the operating conditions under variant vapor mass flow rates are optimized numerically, as well as the combustion temperatures and the off-design flow rates of the flue gas. The relationship between the output power and the exergy destruction rate and that between the output power and the entransy loss rate are discussed. It is found that both the minimum exergy destruction rate and the maximum entransy loss rate lead to the maximum output power when the combustion temperature and heat capacity flow rate of the flue gas are prescribed. Unlike the minimum exergy destruction rate, the maximum entransy loss rate is related to the maximum output power when the highest temperature and heat capacity flow rate of the flue gas are not prescribed.     

造纸污泥在回转窑中热解的试验研究

本文在自行设计的小型外热式回转窑试验装置上进行了污泥热解试验,考察了污泥在不同热解连温下三种形态热解产物的产率,分析了污泥在热解过程中热解气体的成分和热值的变化特性以及热解半焦的品质。采用表观动力学模型对热解气体的试验数据进行计算,结果表明用该模型描述热解气体的析出是合理的。     

生物柴油-生物油乳化油的燃烧排放特性

在一台未作改动的直喷式柴油机上研究了生物油质量分数分别为10%和20%的生物柴油生物油乳化油的燃烧与排放特性。结果表明:与生物柴油相比,燃用乳化油时燃烧始点推迟,预混燃烧放热峰值升高,扩散燃烧放热峰值、最高燃烧压力和燃烧温度降低,燃烧持续期缩短,且随着生物油含量增加以上趋势更明显。燃用含10%生物油的乳化油时燃油经济性较生物柴油略低,与0号柴油相当,而燃用含20%生物油的乳化油时燃油经济性则低于生物柴油和0号柴油。乳化油的NO_x排放明显低于生物柴油,而碳烟排放高于生物柴油,但低于0号柴油。     

煤的热天平燃烧反应动力学特性的研究

采用热天平获得同一种煤在不同升温速率下的TG、DTG曲线,可求出燃烧速率、燃烧温度随燃烬度的变化曲线,根据两个不同升温速率下的数据,可计算出化学动力学参数活化能和指前因子随燃烬度的变化曲线。根据实验数据计算得到四个煤种的反应动力学参数随燃烬度变化的曲线,并预测其中一种煤在第三个升温速率下的燃烧速率随燃烬度的变化曲线,计算结果与实验结果符合较好。用此模型预测了在不同的恒定温度下试验煤种的煤粉燃烧速率随燃烬度的变化趋势。     

吸力面小翼对扩压叶栅间隙泄漏的影响

采用数值模拟方法对利用吸力面小翼方式控制压气机叶栅间隙流动进行研究。结果表明,附加吸力面小翼可以降低叶顶泄漏流速,削弱泄漏涡强度,使得泄漏涡区损失降低。不同宽度吸力面小翼在不同间隙下部可以较好地减少叶尖泄漏,在叶顶间隙为3.3%叶高时,附加相对宽度为0.5的吸力面小翼可使损失降低4.7%。叶顶压差的降低及对泄漏涡结构的改变是吸力面小翼降低泄漏掺混损失的主要原因。     

环形HYLTE喷管耦合段及光腔区流场的数值模拟

参考传热学相关理论,估算燃烧室的传热损耗分数及相应的平衡温度,确定了主喷管的入口参数设置。在此基础上,对环形HYLTE喷管的耦合段及光腔区流场进行3维的数值模拟,给出了F原子质量分数、静温、静压的空间分布,得到了光腔区各支谱线的小信号增益系数变化曲线。将计算结果与实验结果进行比对,光谱测量结果及移动光轴实验证实了计算模型的合理性。     

Effect of unsteady pressure rise on flame propagation and near-cold-wall ignition

Thermodynamic pressure rise during combustion is a key feature in internal combustion engines. Yet, hardly any studies have been conducted to investigate the effects of transient pressure rise on flame propagation as well as on the ignition of the unburned gas. In this study, the effects of unsteady pressure rise were parametrically studied using a one-dimensional reacting flow model in which the thermodynamic pressure variation is an independent variable and thus its rate of rise can be controlled. It was determined that large rates of pressure rise can significantly increase the mass burning flux of a laminar flame and that this modification becomes more pronounced at higher pressure and temperature conditions. Furthermore, it was shown that the development of ignition near a cold wall, for mixtures that exhibit negative temperature coefficient behavior, is very sensitive to rate of change of pressure. The near-wall ignition behavior was found also to be rather sensitive to the prevailing pressures and temperatures whose values control whether ignition will occur in the main-gas or within the thermal boundary layer.