煤灰熔融行为及其矿物质作用机制的量化研究

选取典型高灰熔点和低灰熔点煤种,利用X射线衍射仪(XRD)和扫描电镜能谱仪(SEMEDX)对高温气化条件下煤灰熔融行为及其矿物质演变规律进行了实验研究与量子化学计算.结果表明:高温下大量莫来石的生成是导致煤灰试样A具有高灰熔融温度的主要原因;煤灰试样B中由于存在较多的硬石膏、钠长石等低熔融矿物质,且CaO与莫来石反应生成钙长石与钙黄长石的化学反应在煤灰试样B熔融过程中起到了关键作用,从而使其具有低的熔融温度.经量子化学计算分析表明,由于莫来石易与电子接受体结合而难与电子给予体结合,在煤灰熔融过程中,莫来石易与煤灰中常见的碱性阳离子(Ca2+、Mg2+、Fe2+、Na+、K+)电子接受体反应生成其他物质,通过添加不同的阳离子可促使莫来石向不同矿物质转变,可以进一步控制煤灰的熔融变化过程及其熔融温度.     

燃煤锅炉灰沉积物形成过程及机理综述

矿物质是引起锅炉受热面灰沉积的根本原因.综述了目前同内外关于煤中矿物质分类、组成、存在形态,以及在煤粉制备过程中的偏析、富集和在炉内燃烧火焰中的行为特征等方面的最新研究成果,着重分析了飞灰的形成、灰粒在炉内高温娴气中的输运和沉积特性.尤其对沾污和结渣的形成过程及机理进行了较为深入的分析,从而对自煤中矿物质到锅炉受热面灰沉积的整个形成过程有一个全面的认识和了解.     

花生壳与煤加压热解和掺烧成灰矿物相演变研究

在不同压力(0.1～6.0 MPa)、不同温度(800～1100℃)的高温高压管式炉中制备花生壳焦、煤焦及其混合灰,并用X射线衍射(XRD)分析样品的矿物相和微晶结构。结果表明:温度对花生壳与煤混合物中矿物相迁移的影响大于压力对矿物相迁移的影响。随着压力的增大,煤焦和花生壳焦的微晶结构更加有序;煤与花生壳的混合会促进钙长石的形成,抑制莫来石的形成。当混合比较高时,压力主要影响花生壳的燃烧和矿物质的转化。当混合比较低时,压力的变化对煤焦和花生壳焦的相对含量有一定影响,但对其矿物相种类影响不大,压力对矿物质行为的影响主要通过影响煤粉的着火方式而实现。     

污泥焚烧循环流化床锅炉受热面沉积特性研究

针对干化污泥与煤在循环流化床锅炉中混烧,锅炉竖井烟道入口高温过热器区域出现受热面沉积,对该区域的典型沉积物进行研究。通过SEM、EDS和XRD分析了沉积物的主要构成,指出Ca SO4是沉积的主要组分。并从形成机理上分析了炉内受热面沉积的形成过程。     

灰特性对燃煤炉内灰沉积行为的影响

为了解灰特性对燃煤炉内灰沉积行为的影响,以黄陵、神木和新汶3种具有不同灰特性的燃煤为研究对象,通过自制灰污热流探针和SiC结渣棒,分别模拟了正常情况及存在烟气冲墙贴壁情况下的锅炉受热面灰沉积行为,比较了灰渣外形、化学成分、熔融温度和热流变化率等特性参数,并通过对灰渣样晶的X-射线衍射、扫描电镜及能谱分析,获得了3种燃煤灰沉积物的元素组成、矿物相及微观结构和形貌特征.结果表明,由于Ca、Fe的协同作用,黄陵煤的灰沉积特性强于神木和新汶煤,Ca、Fe是引起这类煤灰沉积的主要矿物元素,硬石膏、钙长石和赤铁矿是灰沉积物中的主要矿物相;当存在烟气冲墙贴壁时,灰沉积物中Fe含量很高.使熔融温度大大降低,从而加剧受热面的灰沉积过程,在工程实际中应采取相应措施,避免出现这种情况.     

气化条件下压力影响灰熔融特性的实验研究

利用加压热天平结合X衍射分析仪来研究压力对煤灰熔融特性的影响。受加压热天平温度的限制,只研究1100℃以下压力的影响。利用X衍射分析仪分析不同压力、不同温度下煤灰中的矿物质成分,根据X射线衍射图谱分析矿物质对灰熔融特性的影响,以及在不同压力和不同气氛下矿物质的变化和新生成矿物质对灰熔融性的影响。结果显示:CO2气氛下压力对煤灰矿物质的生成影响不大;N2及H2O气氛下压力具有促进煤灰低温矿物质向高温矿物质转化的作用。     

采用添加剂抑制生物质锅炉受热面沉积的探索与实践

针对生物质燃烧锅炉中的沉积问题,尝试采用添加惰性物质来抑制结焦的可能性,在CFB生物质锅炉的高温过热器、低温过热器区域采集沉积样品,研成粉状后分别添加一定比例抑制剂后在马弗炉中灼烧,通过扫描电镜(SEM)、X-射线衍射(XRD)等分析手段研究添加抑制剂后沉积物的微观结构、组成成分等,并在实际运行的CFB锅炉中添加该抑制剂以观察其对结焦的抑制效果,结果表明,在实验室内样品中添加惰性抑制剂对弱化结焦有比较明显的效果,但在实际运行的锅炉中添加该抑制剂后没有达到之前预期的效果.     

煤中矿物质在标准制灰过程中的演变

选择六种典型的煤,通过低温灰与815℃灰中矿物成分的对比,发现煤中主要矿物质的转变,然后通过热重分析和原位X射线衍射的方法研究煤中主要矿物质在国标法制灰过程中的演变过程。研究发现,煤中的主要矿物质为石膏、烧石膏、方解石、高岭石、石英、黄铁矿、菱铁矿和白云母。这些矿物质的转变过程各有特点,其中方解石的转变对灰熔融特性的影响最为关键。     

镁基助熔剂对高灰熔点煤灰熔融影响的机理

通过向高灰熔点淮南煤灰中添加不同质量分数的镁基助熔剂,研究镁基助熔剂对高灰熔点煤灰熔融特性的影响及其机理.结果表明:对于淮南煤灰,镁基助熔剂的理想添加质量分数为5%,能使煤灰熔点降低到1 350℃以下;通过XRD分析和SEM验证得知,耐熔矿物质莫来石是导致淮南煤灰熔点较高的原因;Mg2+与莫来石发生反应,生成了堇青石和尖晶橄榄石等易熔矿物质,导致灰熔点降低;通过研究莫来石的稳定性推断出,作为电子给予体的Mg2+易于从活性较大的O(7)和O(13)进入莫来石晶体,造成化学稳定性较弱的Al(1)—O(13)和Al(8)—O(13)共价键的断裂,引起硅酸盐网络中2个Si原子之间的距离增大,促使莫来石晶体晶格重组.     

Na掺入制备不锈钢衬底CIGS太阳电池

以轻质柔性不锈钢材料为衬底,利用共蒸发法制备较高质量的四元化合物Cu(In,Ga)Se2薄膜,在沉积CIGS薄膜前沉积一定厚度的NaF预置层,使得所制备的CIGS薄膜含有适量浓度的Na,并获得了10.06%的转换效率.利用X射线衍射仪和X射线荧光光谱仪分别测量了所制备薄膜的晶相和组分,利用扫描电子显微镜分析了不锈钢衬底CIGS太阳电池的断面形貌,最后分析了NaF的掺入对CIGS太阳电池的影响.     

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%.     

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.     

Contents in Volume 23,2014

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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.