微藻热解特性及其动力学分析

通过热重分析手段研究了杜氏盐藻在室温至900℃下的热解行为和特性,采用高纯氮气作保护气,升温速率分别为5℃/min、10℃/min、20℃/min和40℃/min.TG、DTG曲线的分析表明,热解过程随温度升高经历3个不同阶段.此外,随着升温速率增大,热解的初始温度和峰值温度均增大,且总失重增加.采用等转化速率法和主曲线法对盐藻热解过程进行动力学分析.结果表明,表观热解反应遵循单一动力学机理模型,反应动力学过程为简单级数反应机理模型Fn.求得热解反应表观平均活化能Ea为146.3 kJ/mol,指前因子A为4.28×1013s-1,指数n为2.4.     

黑液木质素焦热解动力学分析

在N_2的气氛下,以10℃/min、20℃/min、30℃/min、40℃/min和50℃/min的升温速率分别对黑液木质素焦进行热重实验,研究升温速率对其热解反应的影响。结果表明,黑液木质素焦的热解过程主要分为三个阶段:180～380℃、380～570℃以及570～800℃;TG和DTG曲线随着升温速率增大逐渐向高温侧偏移,高升温速率不利于热解反应进行;采用Coats-Redfern法、Ozawa法和Kissinger法求得活化能分别为93～251 kJ/mol、111～122 kJ/mol和110～134 kJ/mol。     

水华蓝藻热解特性及热解动力学研究

采用热重分析研究了水华蓝藻在不同升温速率(5,10,15,20℃/min)下的热解特性。通过等转化率法计算了蓝藻热解的反应活化能,并利用主曲线法判断得出其热解动力学机理函数。结果表明:蓝藻主要的热解阶段发生在170~530℃,随着升温速率提高,最大失重速率升高,而最大失重峰向高温缓慢偏移。当转化率为0.2~0.7时,反应活化能基本保持不变(平均值为169.71 kJ/mol),说明此阶段热解过程能够用单一的机理模型描述。当n=5.3时,实验曲线与标准曲线拟合的线性相关系数R2=1,说明热解反应级数为5.3,计算得到指前因子为7.24×1021s-1,热解反应可以表示为da/dt=3.62×1020exp(-169.71/RT)·(1-α)5.3。     

微波诱导市政污泥热解实验的热重分析

通过TG-DSC实验,研究微波辐射对污泥热解特性的影响,与污泥-生物质混合热解特性作对比,并利用Coats-Redfern积分法计算出污泥热分解反应的表观活化能、反应级数及指前因子.结果表明,在辐射剂量为10 W/g、20 W/g和25 W/g的条件下,污泥TG实验的失重率分别提高了4.6％、5.7％和1 1.6％;热解反应的活化能分别降低了19.2 kJ/(mol·K)、2.6 kJ/(mol·K)、12.7 kJ/(mol·K),平均降低了24％,反应级数略有变化.在10 K/min升温速率下,添加质量分数为5％的木屑或麦秆,污泥热解失重率分别为4.7％和8.9％.     

玉米秸秆和海藻共热解特性研究

为解决陆地生物质资源短缺,开发水生生物质有效替代部分陆地生物质迫在眉睫。通过热重法研究玉米秸秆和海藻共同热解的特性,重点考察掺混比例和升温速率的影响,并对混合样品的热力学特性和动力学特性进行分析。结果显示,热解分为干燥、挥发分析出及焦炭热解三个阶段。掺配后的混合样品最终失重率与最大失重速率均小于纯秸秆与纯海藻。随着海藻掺配比例的增加,可燃性指数Ca先增大后减小,燃尽特性指数K递减,热解特性指数S先增大后减小。不同升温速率工况下,在热解区间（200～600℃）,随着升温速率的升高,样品的热重曲线右移,失重率越来越大,最大失重速率先减小后增大,30℃/min时最小。Ca在递减,K、S呈增加趋势。动力学研究结果表明,不同掺配比例工况下,混合样品存在明显的协同作用,降低了共热解所需活化能。在不同升温速率工况下,升温速率越大,所需要的活化能越小,样品越容易发生热解。     

升温速率对杨木屑热解特性的影响

将杨木屑在不同升温速率（10℃/min,15℃/min,20℃/min,25℃/min和30℃/min）下进行热解,基于TG和DTG、温度特征值、失重率及热解产物产率分析不同升温速率下杨木屑的热解规律,利用FWO法计算热解动力学参数,对精制后的焦油进行GC-MS检测,分析其主要有机成分及变化规律。实验表明,杨木屑样品主要失重的温度区间为210～400℃。杨木屑的失重率与升温速率成正比,升温速率的提高会导致温度延迟现象加重。由FWO法求得杨木屑样品的热解反应活化能平均值为129.9kJ/mol。热解产物产率表明,升温速率提高,固相和气相产物产率降低,液相产物产率提高。GC-MS检测结果表明,精制后的焦油主要成分为醇类、苯酚类、酯类、醛类、酸类、糖类、吡啶、烯烃类等有机化合物,其中随着升温速率的提高,酚类、酸类、醇类和醛类的相对含量下降但酚类的表现最为明显。     

生物质热解的TGA-FTIR分析

基于TGA-FTIR联用技术,在线分析研究稻壳、稻秆及麦秆3种典型生物质在不同升温速率下的热解特性.分析生物质种类及升温速率对生物质的热解动力学参数及热解产物的影响.研究表明:由于生物质组成不同,其热失重特性也不同,生物质热解反应的活化能较低,为40～60 kJ·mol-1;红外分析表明试验用生物质热解过程中产物的析出规律相似,热解初始阶段先析出游离水,随后发生解聚和脱水反应,生成各种烃类、醇类、醛类和酸类等物质.随后,这些大分子物质又二次降解为一氧化碳为主的气体产物.     

生物质锯末快速高温热解气化研究

在对木质生物质在0～20℃/min这类较低升温速率条件下的热解特性研究基础上,采用热重分析法并结合TG、DTG曲线研究了干燥锯末在3种不同升温速率下的热解及动力学特性。并计算出活化能、频率因子,分析高升温速率(30、45℃/min)与低升温速率(10℃/min)对锯末热解气化影响的区别。研究结果表明:锯末热解时的最大失重速率随升温速率的升高而增大,在升温速率为45℃/min时达到最大为25.41%/min。在半纤维素热解占主导的阶段,热解反应机理为一级随机成核和随后成长过程,反应的活化能及频率因子随着升温速率的提高呈现先增大后减小的趋势;在纤维素和木质素热解占主导的阶段,热解反应机理为三维球形对称扩散过程,上述2个参数随着升温速率的提高呈现减小的趋势,且较高的升温速率能显著促进锯末挥发物质的析出。     

生物质玉米芯热解动力学实验研究

以玉米芯为对象,利用热重-质谱联用技术,以高纯氩气为载气对其进行了详细的热重分析研究。通过对10℃/min和30℃/min升温速率及其不同温度下的失重曲线分析,发现玉米芯的主要失重温度区间为200~400℃,峰值温度为328~345℃。随着升温速率的提高,玉米芯热解的初始温度升高,热解向高温侧移动。同时通过质谱分析获得了温度和升温速率对热解气化产物的影响规律。在此基础上建立了热解动力学模型,并根据实验数据对模型进行了求解,结果表明玉米芯热解在低温段属一级反应而在高温段属三级反应。     

生物油蒸馏残渣热解特性研究

采用TGA Q500热分析仪和傅里叶变换红外光谱仪联用技术,对生物油蒸馏残渣在不同升温速率下的热解动力学特性进行分析研究。结果表明:生物油蒸馏残渣热解可分为小分子物质挥发析出、大分子物质裂解和焦炭产生3个阶段,热解产物主要为水、烷烯烃、CO_2和芳香类物质。在不同升温速率10、20、30℃/min下,热解主要阶段反应级数均为2级,活化能分别为74.19、72.52和69.05 kJ/mol。随着升温速率的增大,热重曲线整体向高温区移动,热解主要阶段活化能逐渐减小。     

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

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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。     

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.     

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.