燃煤超细颗粒物形成机理及其控制的研究进展

对燃烧过程超细颗粒物形成机理及其控制技术的国内外研究现状进行了综述,介绍了国内外开展的有关超细颗粒物形成的影响因素、形态分析、元素分析和排放控制等几方面的研究成果,阐明了燃烧过程中超细颗粒物形成机理:在燃烧过程中,煤中无机物首先汽化,然后均相成核或者冷凝在已有的细颗粒物上.预测了超细颗粒物形成机理研究、采样和分析方法及其控制技术的发展趋势,提出目前我们应该开展超细颗粒物研究的重点和方向.     

燃煤过程可吸入颗粒物生成及控制措施的分析

燃料燃烧过程是大气中可吸入颗粒物的主要来源之一。从燃煤过程中颗粒物的来源及一次颗粒物的生成途径进行分析,相应提出了控制燃煤过程可吸入颗粒物的燃烧前控制、燃烧中控制和燃烧后控制。燃烧前控制包括了煤种选择和煤粒加工;燃烧中控制措施有调整燃烧工况和使用添加剂;燃烧后控制是通过使细颗粒物凝并、团聚为较大颗粒物后再利用除尘设备加以脱除。     

典型厨余垃圾燃烧超细颗粒物生成演化规律

采用平焰燃烧器研究典型厨余垃圾燃烧过程中超细颗粒物的生成及演化规律．挥发分燃烧阶段,火焰前侧以焦油热解裂解生成的碳烟颗粒为主,后侧则以矿物气化-凝结形成4.6～8.7 nm的硅酸盐颗粒为主,且颗粒平均粒径随着采样高度增加呈现先减小再增大的变化规律,体现出超细颗粒物生成过程中成核和聚并行为的竞争．在焦炭燃烧阶段,出现了大量10 nm级别固态方形颗粒,EDS结果显示颗粒为碱金属氯化物．由于蒸发以及硅酸化反应作用,此类颗粒平均粒径随着采样高度的提升不断减小．基于上述发现,揭示了典型厨余垃圾燃烧过程,以及碳烟演化、矿物气化-凝结及气流吹携等多种机制在内的超细颗粒物生成途径．     

高效洁净燃煤发电基础研究

正开展燃煤高参数超700℃超超临界发电整体热力系统优化、材料体系、燃烧、传热和污染特性等基础研究;以近零排放IGCC为目标的富氢燃烧和富氢燃机的材料和制造技术基础研究;节能型、超低排放循环流化床新型流场模拟研究;燃煤火电机组超细颗粒物过程控制技术基础研究;煤基活性吸附剂制备及再生关键技术基础。     

添加剂对五彩湾煤燃烧过程中钠析出的影响

对五彩湾原煤及加入胶体添加剂后的混合煤样进行燃烧实验,并分别检测了原煤和煤灰中钠元素的含量,确定了五彩湾煤中钠在燃烧过程中的析出规律以及胶体添加剂对其的影响。并且对部分煤灰采用XRD(X射线衍射仪)进行分析。研究结果表明,在原煤燃烧过程中,钠的析出量随着温度的升高而增大,在1 100℃时达到最大值。XRD分析结果表明:适量硅溶胶的添加可将五彩湾煤中可挥发性钠转化成硅铝酸钠等高熔点含钠化合物,从而减少了五彩湾煤中钠的析出;在800℃燃烧温度下,适量铝溶胶的添加也可将可挥发性钠转化为不可挥发性钠,从而减少钠的析出;而在1 000℃燃烧温度下,添加铝溶胶后所对应的灰样中并没有生成硅铝酸钠等高熔点含钠化合物,而是生成了高岭石等物质。     

煤粉燃烧过程中破碎生成PM10的实验研究

以粒径在0~6mm范围的煤颗粒作为研究对象,温度取流化床炉燃烧温度段700~900℃作为实验温度,通过改变燃烧工况,对收集到的燃烧产物可吸入颗粒物进行粒度分析,烟煤颗粒燃烧过程中由于燃烧工况不同,对产生的亚微米颗粒物PM10进行实验分析研究并得出各个燃烧工况对结果的影响程度和趋势。实验结果表明,实验条件范围内,随着燃烧时间的增大,煤颗粒产生的PM10量呈二次多项式y=c+bx-ax2分布,先逐渐增大,当达到最大值后,又开始缓慢减小。烟煤燃烧生成PM10量的多少与原煤粒径的关系是由于煤粒破碎与内在矿物质及焦炭重新凝聚相互竞争的结果,与煤种的结焦性特点有关。由于烟煤颗粒燃烧后产生的细颗粒物的量的多少和粒径分布不仅受单一因素影响,而是同时受多个因素共同作用导致的结果。     

氧化反应温度对柴油机颗粒物表面官能团演变的影响

采用原位红外光谱仪并结合热重分析仪和程序升温氧化-质谱联用仪的测量结果对国Ⅳ柴油机颗粒物表面官能团在颗粒物氧化反应过程中的演变规律进行半定量分析.结果表明,起燃温度(450,℃)前,随反应温度升高,柴油机颗粒物表面碳氢官能团迅速减少、碳氧官能团不断生成,而从程序升温氧化反应曲线可以看到反应气氛中的O2通过化学吸附参与表面官能团的转化,这和碳氧官能团增加的规律相一致;反应温度超过450,℃时,随温度升高,碳氧表面官能团减少,颗粒物氧化燃烧,两个反应具有同步性;在50~425,℃范围内,氧化反应温度对微粒中脂肪烃的支链化程度影响不大;反应温度低于450,℃时,在绝大多数温度段,C=O结构相对含量与C—O结构相对含量的变化趋势相反,表明低温氧化反应中两类官能团间存在相互转化.     

添加CaO对煤粉燃烧后一次颗粒物特性影响的研究

研究煤粉添加CaO3％（wt）与否对燃烧后一次颗粒物特性的影响。以沉降炉作为燃烧设备,燃烧温度1100℃、氧化气氛下,用8级安德森粒子撞击器分离并收集燃烧后的颗粒物样品。从颗粒粒度分布来看,煤粉添加CaO减少了一次颗粒物中细粒子的相对量。以Rosin-Ranunler分布函数对粒度分布曲线进行拟合,得到了很好的拟合性质。从排放特性来看,添加CaO降低了PM10、PM25、PM1的排放量。SEM图像也显示,添加CaO后生成的颗粒物有凝并聚结的颗粒聚团。ICP—AES分析结果表明,Cr、Cu、Ni、Pb、Zn等重金属元素的含量随颗粒粒径减小而增大;而且煤粉添加CaO燃烧后,颗粒物中重金属元素的含量有所降低。     

乙醇柴油添加剂对柴油机颗粒排放及其挥发氧化特性影响

研究了乙醇柴油及燃油添加剂对柴油机颗粒排放及其挥发氧化特性的影响。采用热重分析法分析柴油机燃用不同燃料时排气颗粒物的可溶性有机物挥发性、碳烟样品和颗粒物氧化特性。研究结果表明:含添加剂的乙醇柴油颗粒物排放远低于0#柴油的颗粒物排放,降幅在50%以上。颗粒在热失重过程中经历颗粒失水干燥、可溶性物质氧化和烟煤基元发生氧化反应三个阶段。与0#柴油相比,乙醇柴油及柴油添加剂能降低颗粒物中的可挥发部分质量份额,且乙醇柴油的效果最佳。乙醇及柴油添加剂有助于降低碳烟起燃温度和最大氧化速率对应的温度;与0#柴油相比、N5E10、N5E10XY0.1%和N5E10CN0.3%的碳烟最大氧化速率对应的温度依次降低了39、92、146℃。     

超细煤粉在燃料分级燃烧技术中的应用

超细煤粉分级燃烧是当今较有发展前途的低NOx燃烧技术之一,通过试验研究的方法,探讨了超细煤粉分级燃烧技术中部分因素对NOx排放的影响,研究结果表明,对于不同煤种的主燃料,超细煤粉分级燃烧均能起到显著降低NOx排放的作用;高挥发分的褐煤、烟煤是较好的再燃燃料;煤粉越细,对NOx的还原性越强,同常规粒度煤粉再燃相比,以超细煤粉作为再燃燃料,NOx脱除率显著增加,可达到70％,最佳再燃燃料粒度为20μm;温度低于1200℃时,再燃区内温度越高,NOx的脱除率也越高。     

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.