用可调卫燃带改善燃煤锅炉低负荷燃烧效率

分析了现有燃煤锅炉低负荷运行时燃烧效率偏低的原因,提出了可调卫燃带的概念及模型。指出在低负荷运行时可调卫燃带提高燃烧效率的机理在于能在炉内构建一合理的温度场;介绍了低负荷运行时可调卫燃带对炉内温度场及燃烧率影响的模拟试验结果,试验表明：可调卫燃带对改善锅炉低负荷时炉内温度分布及提高燃烧效率具有十分明显的效果,图8参6     

可调卫燃带及其可行性试验研究

介绍了可调卫燃带的研究进展及在130t/h煤粉炉上进行试验研究用的可调卫燃带的结构.在130t/h煤粉炉上对可调卫燃带进行了试验测试,在1025t/h煤粉炉中有、无卫燃带时,对炉内温度场进行对比试验研究.结果表明,可调卫燃带可在炉内高温环境下安全可靠运行,负荷变化时,可在燃烧器区域维持准恒温工况.     

一次风速度对煤颗粒群着火特性影响的实验研究

利用Hencken型平面携带流反应器,研究了一次风速度对两种高挥发分褐煤和一种贫煤射流着火特性的影响.实验结果表明,低雷诺数(Re=878)条件下,贫煤煤粉气流先后发生外层单颗粒着火燃烧和内层颗粒群着火燃烧,煤粉颗粒着火和燃烧轨迹十分规则.但在高雷诺数(Re=4,392)条件下,贫煤煤粉气流更难形成群燃火焰,呈现出暗红色火焰.随着一次风速度的增加,尽管煤粉颗粒的停留时间减小,但湍流强度的增加使颗粒加热速率以及挥发分析出的强化作用占主导,使得煤粉气流的着火距离减小.此外,群燃火焰在挥发分聚集到一定程度后产生,是颗粒群燃烧的特有现象,而煤种挥发分含量的增加和有效聚集有利于群燃火焰的出现.     

集富型直流燃烧器可节省燃油

煤粉炉在低负荷时往往要投入燃油才能稳定燃烧,集富型直流燃烧器可维持一定程度的低负荷,从而节省燃油．扬州发电厂６７０ｔ／ｈ锅炉,燃用Ｖａｄ１３％ＧＱａｍｅｒ１９．８２ＭＪ／ｋｇ的混煤,改用集富型直流燃烧器后,负荷降至４７．５％时,仍可不投油且能燃烧稳定。因此该厂每年能节约低负荷用油５００ｔ。淮北发电厂６７０ｔ／ｈ炉和盐城发电厂７５ｔ／ｈ炉也改成集富型直流燃烧器,都收到了类似的效益。集富型燃烧器节能机理：煤粉火焰的着火和稳燃主要决定于着火前的预热阶段,即将带煤粉的气流加热,使水分蒸发和挥发物完全析出…     

调峰型低NO_x浓淡燃烧技术的研究与应用

根据作者提出的“充分发挥向火侧一次风着火优势,形成稳定着火源”的燃烧稳定性原理,研制了一种适用于四角燃烧煤粉锅炉的新型燃烧器──调峰型低NOx可调水平浓淡燃烧器。该燃烧器的煤粉浓缩机构及煤粉浓度调节机构简单、可靠。向火侧与背火侧浓度比在1～4的大范围内可调节,保证了锅炉在变负荷工况下实现最佳浓淡比燃烧。工业应用证明：该燃烧器在燃用陕西贫煤时,机组负荷≥50％时不需投油助燃而能稳定燃烧。     

高浓度稳定煤粉火焰的理论研究与计算

本文以煤粉浓淡燃烧理论为基础，就粉煤浓度对着火温度、着火热、着火时间、着火距离、火焰传播速度等的影响进行了理论分析和计算，以此为基础得出煤粉浓度在一定范围内提高有利于火焰燃烧，尤其是目前国内大部分电厂实用煤粉浓度远小于各种煤种的最佳浓度。同时，通过本文的研究和计算，为可调粉浓度稳燃装置的设计提供了理论依据。     

高碱煤在低负荷时的着火稳燃特性研究

建立炉膛热平衡简化模型,从进入炉膛的风粉气流着火热计算着手,研究了煤粉燃烧产生的热量不同的去向,认为只要炉膛输入热量大于其他部分利用的热量之和,低负荷下炉膛的稳燃就能得到保证,基于此,结合某330 MW机组锅炉在低负荷运行时进行了研究。结果表明,在6个不同的低负荷运行下,风粉气流的着火热能得到保障,着火热在90.85 MW时为18 395.6 kW,此时炉膛输入热量扣去其他部分的利用热量之后,还剩余10 470.8 kW,在实际机组运行中的运行数据也显示该机组在不到30%负荷下能正常运行,本文的研究具有一定的工程参考借鉴作用。     

组合式一次风管对锅炉运行的影响分析

为了解决锅炉低负荷运行时一次风气流中煤粉浓度较低、燃烧不稳定的问题,提出了组合式一次风管的设计。运用Fluent数值模拟软件,采用煤粉燃烧综合模型和污染物排放模型,对某660 MW锅炉分别进行改造前后40%THA工况(THA表示额定工况)和30%THA工况的燃烧模拟和NO_x摩尔分数模拟。对比分析了采用组合式一次风管对锅炉空气动力场、着火稳燃情况和NOx摩尔分数的影响。结果表明:采用组合式一次风管时,只要燃烧器喷口改造合理,对空气动力场的影响较小;炉膛整体温度提高,特别是燃烧器区域,着火燃烧稳定性提高;大大降低锅炉低负荷运行时炉膛出口NO_x摩尔分数,提高了锅炉低负荷运行的安全性和经济性。     

褐煤煤粉火焰着火的稳定性

着火稳定性现今对大容量蒸汽机组的基本要求是: ——增大调节范围,降低最低负荷线; ——燃烧含灰量不断增大的燃料。对此,为了保证固体燃料及时着火和稳定燃烧,常用油助燃。着火的稳定性是煤粉燃烧要求的基本条件。当火焰接近燃烧器口、着火前沿保持在稳定的位置和所有运行条件都尽可能只出现微小的变化时,煤粉火焰是稳定的。     

分流式驻涡煤粉燃烧器的试验研究

本文从煤粉燃烧理论出发，采用试验的方法，研究了分流式驻涡煤粉燃烧器的气流结构、煤粉分布特征及燃烧机理。经过分流板和驻涡稳燃器的双重作用，在燃烧器出口处形成了一个高浓度煤粉和高温区，该区域内同时存在着最大的速度梯度、煤粉浓度梯度和温度梯度，从而使煤粉迅速着火，燃烧稳定。实际应用证明，这种燃烧器在提高锅炉的低负荷稳燃能力，节省燃油等方面具有显著作用。     

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.