基于非等温热重法的生物质燃烧反应动力学研究

采用非等温热重法对两种麦秆的燃烧反应动力学特性进行了研究。根据燃烧实验所得的TG,DTG及DTA曲线,对两种麦秆的燃烧过程进行了分析,找出了麦秆挥发分和固定碳燃烧反应阶段的起始温度,采用Coats-Redfern积分法建立了麦秆类生物质的反应动力学方程,求出了2个阶段燃烧过程的活化能E,频率因子A,反应级数n,相关系数R等反应动力学参数,并确定了2个阶段的反应动力学方程。麦秆的燃烧符合合适的反应动力学模型,当用麦秆作为燃料时,所计算的动力学参数能够作为一定的参考。     

玉米秸秆燃烧过程及燃烧动力学分析

采用TG-DTA-DTG热分析联用技术对玉米秸秆在不同升温速率下进行了燃烧实验.考察了着火温度、燃烧速率最大时温度、燃尽温度等燃烧特征参数.根据对不同升温速率下玉米秸秆燃烧过程的分析,用双组分分阶段反应模型能够很好的描述玉米秸秆的燃烧过程.建立了玉米秸秆反应动力学方程,得到了在不同温度区间的燃烧动力学方程和表观活化能、频率因子等燃烧动力学参数,并提出了相应的燃烧机理.     

城市生活垃圾热解/燃烧特性的实验研究

对城市生活垃圾中的6种典型单一组分及两两混合组分进行热重特性试验，先通氮气进行热解反应，当温度达到550℃时，再通氧气模拟空气进行燃烧反应。将热解和燃烧反应特性在同一曲线图中表现出来，分阶段求取反应动力学函数方程及动力学参数活化能E、频率因子A，进而为建立热解／燃烧综合模型提供基础依据；验证了混合物质的热解／燃烧特性可以用单组分物质的热解-燃烧特性的叠加来表示，除某些混合试样的组分之间会表现出一些相互影响，但这种影响并不强。     

几种生物质颗粒燃料等温燃烧过程和动力学研究

对4种华北地区生物质颗粒燃料进行等温燃烧失重试验.由试验数据曲线拟合得到了拟合方程,求解出活化能E、反应级数n、频率因子A.结果表明,生物质颗粒燃料在750～950℃温度下等温燃烧过程的反应级数为2～3.     

玉米秸秆成型颗粒快速燃烧特性及反应动力学研究

基于等温热重分析技术,采用化学动力学法拟合燃烧过程中质量损失率与时间的单方程模型,对不同燃烧温度与成型密度下柱状玉米秸秆成型颗粒的快速燃烧特性进行研究。结果表明:玉米秸秆成型颗粒在600℃下成型密度较大,燃尽时间较长,到达热失重速率(DTG)曲线峰值时间较长;相同密度的成型颗粒,随温度的升高,燃尽时间缩短,DTG峰值高度越高,到达峰值的时间越短;在该实验变量控制范围内,成型密度和外部环境温度对燃尽率无明显作用;通过动力学计算得到玉米秸秆成型颗粒的反应级数在0.5~0.7之间。由实验数据曲线拟合得到拟合方程,求解出活化能E及指前因子A。     

高变质无烟煤催化气化动力学及补偿效应

以碳酸钠为催化剂,利用热天平研究了福建建欣高变质无烟煤常压下水蒸气气化反应动力学,在800～950℃测定了碳酸钠加载量从0～18%时该无烟煤气化反应特性,确定了实验条件下碳酸钠催化剂加载饱和浓度,结果表明,加载催化剂后建欣无烟煤气化反应活化能大幅降低.得到了建欣无烟煤与水蒸气气化反应动力学缩芯模型,并给出相应的动力学参数.分析表明,该催化气化反应体系活化能E与频率因子A0之间存在动力学补偿效应,得出其补偿效应方程为ln,A0=8.66×10-5E-0.2827,等动力学温度为1 389 K.     

锅支架高度对燃气灶性能的影响规律

基于组分传输与反应模型,建立了大气式燃气灶燃烧过程数值模型,其中湍流采用Realizable k‐ε模型,辐射采用DO模型,燃烧采用涡耗散模型。对不同工况下燃气灶燃烧过程进行三维数值模拟计算,研究了不同锅支架高度对燃气灶性能的影响规律。结果表明：随着锅支架高度增加,外圈火焰的内焰温度升高、长度变化不大,外圈火焰的外焰温度变化不大、长度增加;内圈火焰的内焰温度下降、长度变短,内圈火焰的外焰温度与长度变化无差异;CO质量分数呈线性下降趋势。内外圈火孔皆存在时,热效率随锅支架高度增加先下降后上升,而后持续下降,最佳锅支架高度为19 mm ,其热效率为62．43％,CO质量分数为2．652×10－4;只存在外圈火孔时,热效率随锅支架高度增加持续下降,最佳锅支架高度为15 mm ,其热效率为63．43％,CO质量分数为2．856×10－4。     

煤颗粒燃烧灰层厚度对燃烧过程的影响

在恒温条件下利用热重分析研究了单颗粒煤焦燃烧过程灰层厚度对反应动力学的影响并建立了模型．分别对福建龙岩煤、福建永安煤以及山东煤3种煤的单个颗粒(颗粒直径3．0-4．5 mm)在900℃热天平中的反应动力学进行了分析,讨论了灰层厚度对单颗粒燃烧过程的影响．单颗粒煤焦燃烧过程产生的灰层在灰层厚度为颗粒半径的一半时对燃烧过程的阻力达到最大．实验分析表明,灰层对煤颗粒燃烧过程的影响很小,3种煤焦的单颗粒燃烧过程灰层的最大阻力(1／kC)max(灰层厚度δ=R0／2-0．8-1．0 mm时)一般都小于10s/m．     

酒糟与无烟煤混合燃烧的热重分析

目前，酒糟的处理方式主要局限在肥料和饲料，对无烟煤与酒糟混合燃烧研究较少。将废弃酒糟与无烟煤按不同比例进行混合燃烧，与其单独燃烧的过程进行对比，通过热重分析法、动力学理论及综合燃烧特性指数对实验结果进行研究。结果显示：酒糟、无烟煤分别单独燃烧时，只有3个燃烧过程，分别是水分的析出、挥发分的燃烧以及固定碳的燃烧；酒糟与无烟煤混合燃烧过程包括水分的析出、挥发分的燃烧以及各自固定碳的燃烧等4个阶段；酒糟与无烟煤混合物中酒糟所占比例越大，其综合燃烧特性指数也越大；增加酒糟比例能够改善无烟煤的燃烧状况，使其燃烧更加充分。根据Coats-Redfern法对二者混合燃烧反应过程的动力学特征进行研究，当反应级数n为2.2时，得到最佳拟合效果，酒糟热解活化能E为42.22 kJ/mol，指前因子A为4.51×10⁵ min^-1。     

基于详细化学动力学正丁醇定容燃烧过程的损失

利用详细化学动力学在绝热均质定容条件下对正丁醇燃烧过程进行了数值模拟,并通过非平衡态热力学熵平衡方程计算了燃烧过程的损失.结果表明:损失率曲线主要有两个峰值,第1个峰值由正丁醇转变为小分子燃料的反应(阶段1)和H_2O_2,loop及支撑反应(阶段2)构成;第2个峰值由CO、H氧化为最终产物反应(阶段3)构成.提高燃烧初始温度或当量比,反应温度上升,阶段1中高温反应路径取代低温反应路径,使损失降低,阶段2和阶段3中主要反应损失持续时间缩短,使损失降低;然而燃烧温度过高致使离解反应发生,导致不完全燃烧.增加燃烧初始压力或降低氧体积分数都可抑制离解反应,减少不完全燃烧.若使用进气加热、增压、稀燃、提高压缩比和废气再循环等发动机技术,可改变燃烧初始条件,使总损失从30.7%,减少至18.7%,.     

Ash-forming elements in four Scandinavian wood species. Part 1: Summer harvest

Woody biomass in Finland and Sweden comprises mainly four wood species: spruce, pine, birch and aspen. To study the ash, which may cause problems for the combustion device, one tree of each species were cut down and prepared for comparisons with fuel samples. Well-defined samples of wood, bark and foliage were analyzed on 11 ash-forming elements: Si, Al, Fe, Ca, Mg, Mn, Na, K, P, S and Cl. The ash content in the wood tissues (0.2–0.7%) was low compared to the ash content in the bark tissues (1.9–6.4%) and the foliage (2.4–7.7%). The woods’ content of ash-forming elements was consequently low; the highest contents were of Ca (410–1340 ppm) and K (200–1310), followed by Mg (70–290), Mn (15–240) and P (0–350). Present in the wood was also Si (50–190), S (50–200) and Cl (30–110). The bark tissues showed much higher element contents; Ca (4800–19,100 ppm) and K (1600–6400) were the dominating elements, followed by Mg (210–2400), P (210–1200), Mn (110–1100) and S (310–750), but the Cl contents (40–330) were only moderately higher in the bark than in the wood. The young foliage (shoots and deciduous leaves) had the highest K (7100–25,000 ppm), P (1600–5300) and S (1100–2600) contents of all tissues, while the shoots of spruce had the highest Cl contents (820–1360) and its needles the highest Si content (5000–11,300). This paper presented a new approach in fuel characterization: the method excludes the presence of impurities, and focus on different categories of plant tissues. This made it possible to discuss the contents of ash element in a wide spectrum of fuel-types, which are of large importance for the energy production in Finland and Sweden.     

NEXT GENERATION ENGINEERED MATERIALS FOR ULTRA SUPERCRITICAL STEAM TURBINES

正1 ABSTRACT To reduce the effect of global warming on our climate,the levels of CO2emissions should be reduced.One way to do this is to increase the efficiency of electricity production from fossil fuels.This will in turn reduce the amount of CO2emissions for a given power output.Using US practice for efficiency calculations,then a move from a typical US plant running at 37%efficiency to a 760℃/38.5 MPa(1 400/5 580 psi)plant running at 48%efficiency would reduce CO2emissions by 170kg/MW.hr or 25%.     

Contents in Volume 23,2014

<正>~~     

Aerodynamic performance effects of leading-edge geometry in gas-turbine blades

The purpose of this paper is to illustrate the advantages of the direct surface-curvature distribution blade-design method, originally proposed by Korakianitis, for the leading-edge design of turbine blades, and by extension for other types of airfoil shapes. The leading edge shape is critical in the blade design process, and it is quite difficult to completely control with inverse, semi-inverse or other direct-design methods. The blade-design method is briefly reviewed, and then the effort is concentrated on smoothly blending the leading edge shape (circle or ellipse, etc.) with the main part of the blade surface, in a manner that avoids leading-edge flow-disturbance and flow-separation regions. Specifically in the leading edge region we return to the second-order (parabolic) construction line coupled with a revised smoothing equation between the leading-edge shape and the main part of the blade. The Hodson–Dominy blade has been used as an example to show the ability of this blade-design method to remove leading-edge separation bubbles in gas turbine blades and other airfoil shapes that have very sharp changes in curvature near the leading edge. An additional gas turbine blade example has been used to illustrate the ability of this method to design leading edge shapes that avoid leading-edge separation bubbles at off-design conditions. This gas turbine blade example has inlet flow angle 0°, outlet flow angle −64.3°, and tangential lift coefficient 1.045, in a region of parameters where the leading edge shape is critical for the overall blade performance. Computed results at incidences of −10°,   −5°,   +5°,   +10° are used to illustrate the complete removal of leading edge flow-disturbance regions, thus minimizing the possibility of leading-edge separation bubbles, while concurrently minimizing the stagnation pressure drop from inlet to outlet. These results using two difficult example cases of leading edge geometries illustrate the superiority and utility of this blade-design method when compared with other direct or inverse blade-design methods.     

Hydrogen production by steam-gasification of carbonaceous materials using concentrated solar energy – V. Reactor modeling,optimization, and scale-up

A chemical reactor for the steam-gasification of carbonaceous particles (e.g. coal, coke) is considered for using concentrated solar radiation as the energy source of high-temperature process heat. A two-phase reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is applied to optimize the reactor geometrical configuration and operational parameters (feedstock's initial particle size, feeding rates, and solar power input) for maximum reaction extent and solar-to-chemical energy conversion efficiency of a 5 kW prototype reactor and its scale-up to 300 kW. For the 300 kW reactor, complete reaction extent is predicted for an initial feedstock particle size up to 35 μm at residence times of less than 10 s and peak temperatures of 1818 K, yielding high-quality syngas with a calorific content that has been solar-upgraded by 19% over that of the petcoke gasified.     

汽轮机数字电液调节系统挂闸异常的技术完善

分析了200MW汽轮机数字电液调节系统在运行中存在的挂闸异常问题,采取了相应的技术处理措施,且运行实践效果良好。     

新型高压共轨ECU升压模块的数字化开发与优化

为了提高喷油器电磁阀的响应速率,提出了一种基于CPLD(复杂可编程逻辑器件)应用于高压共轨ECU的数字升压模块。鉴于该升压电路结构参数多,其升压电压的恢复响应要求高等特征,基于Pspice建立了升压电路的仿真模型,研究了不同电路参数下升压模块的输出特性,全面优化了该升压模块的性能。结果显示,该升压模块的最大转换效率可以达90%以上。在柴油发动机上对ECU的试验表明,升压电压最大波动不超过10%,其恢复时间仅为1.3ms,功率管最大温升仅为41℃,满足整机运行范围内ECU的需求。     

Trace metal chemistry and silicification of microorganisms in geothermal sinter, Taupo Volcanic Zone, New Zealand

As part of a pilot study investigating the role of microorganisms in the immobilisation of As, Sb, B, Tl and Hg, the inorganic geochemistry of seven different active sinter deposits and their contact fluids were characterised. A comprehensive series of sequential extractions for a suite of trace elements was carried out on siliceous sinter and a mixed silica-carbonate sinter. The extractions showed whether metals were loosely exchangeable or bound to carbonate, oxide, organic or crystalline fractions. Hyperthermophilic microbial communities associated with sinters deposited from high temperature (92–94°C) fluids at a variety of geothermal sources were investigated using SEM. The rapidity and style of silicification of the hyperthermophiles can be correlated with the dissolved silica content of the fluid. Although high concentrations of Hg and Tl were found associated with the organic fraction of the sinters, there was no evidence to suggest that any of the heavy metals were associated preferentially with the hyperthermophiles at the high temperature (92–94°C) ends of the terrestrial thermal spring ecosystems studied.     

Assessment methods of material ageing using Sdobyrev''s creep rupture model

The physical aspects of the activation energy, in higher and high temperatures, of the metal creep process were examined. The research results of creep-rupture in a uniaxial stress state and the criterion of creep-rupture in biaxial stress states, at two temperatures, are then presented. For these studies creep-rupture, taking case iron as an example the energy and pseudoenergy activation was determined. For complex stress states the criterion of creep-rupture was taken to be Sdobyrev's, i.e. σ_red = σ₁ β + (1 − β)σ_i, where: σ₁-maximal principal stress, σ_i-stress intensity, β-material constant (at variable temperature β = β(T)). The methods of assessment of the material ageing grade are given in percentages of ageing of new material in the following mechanical properties: 1) creep strength in uniaxial stress state, 2) activation energy in uniaxial stress state, 3) criterion creep strength in complex stress states, 4) activation pseudoenergy in complex stress states. The methods 1) and 3) are the relatively simplest because they result from experimental investigations only at nominal temperature of the structure work, however, for methods 2) and 4) it is necessary to perform the experimental investigations at least at two temperatures.     

Production of hydrogen from sewage biosolids in a continuously fed bioreactor: Effect of hydraulic retention time and sparging

Hydrogen was produced from primary sewage biosolids via mesophilic anaerobic fermentation in a continuously fed bioreactor. Prior to fermentation the sewage biosolids were heated to 70 °C for 1 h to inactivate methanogens and during fermentation a cellulose degrading enzyme was added to improve substrate availability. Hydraulic retention times (HRT) of 18, 24, 36 and 48 h were evaluated for the duration of hydrogen production. Without sparging a hydraulic retention time of 24 h resulted in the longest period of hydrogen production (3 days), during which a hydrogen yield of 21.9 L H₂ kg⁻¹ VS added to the bioreactor was achieved. Methods of preventing the decline of hydrogen production during continuous fermentation were evaluated. Of the techniques evaluated using nitrogen gas to sparge the bioreactor contents proved to be more effective than flushing just the headspace of the bioreactor. Sparging at 0.06 L L min⁻¹ successfully prevented a decline in hydrogen production and resulted in a yield of 27.0  L H₂ kg⁻¹ VS added, over a period of greater than 12 days or 12 HRT. The use of sparging also delayed the build up of acetic acid in the bioreactor, suggesting that it serves to inhibit homoacetogenesis and thus maintain hydrogen production.