双区燃烧技术应用于降低NO_x的数值模拟研究

双区燃烧是降低Nox排放,防止炉内结渣的一项新技术.利用CFD软件平台,采用数值模拟方法对其某电厂200 mm四角切圆锅炉改造前后炉内燃烧过程进行研究.计算结果表明:采用双区燃烧技术使炉膛中形成了温度,组分和颗粒相参数显著不同的中心区和近壁区.由于附壁射流的作用,使得高温区集中在炉膛中部,有效的防止了锅炉结渣;改造后炉内有比常规燃烧方式锅炉更大的还原气氛区域,抑制了Nox的产生,使其排放降低34.6 %.     

锅炉燃烧调整对NOx排放和锅炉效率影响的试验研究

在2台典型的1025 t/h锅炉上进行了燃烧调整降低NOx排放浓度的试验研究,通过改变过量空气系数、辅助风配风方式、运行负荷和制粉系统运行方式等,测定了锅炉尾部烟道NOx排放浓度,分析了锅炉运行工况、运行方式对NOx排放的影响.结果表明:降低过量空气系数,烟煤锅炉NOx减排效果比贫煤锅炉好得多;降低负荷,烟煤锅炉的NOx排放量降低值较大;缩腰式配风的NOx排放浓度比均匀配风方式约降低10%,制粉系统的运行方式影响炉内燃料的燃烧状态和温度分布,也影响NOx的生成和排放.在不降低锅炉效率的前提下,调整燃烧工况,可降低锅炉排放NOx浓度1O%～20%.     

某200 MW四角切圆锅炉燃烧器改造降低NOx数值模拟

针对国内某电厂200MW四角切圆锅炉NOx排放量较高,结渣严重的问题,利用CFD软件平台,采用数值模拟方法对其改造前后炉内燃烧过程进行研究。计算结果表明:由于附壁射流的作用,使得高温区集中在炉膛中部,有效地防止了锅炉结渣;改造后炉内有比常规燃烧方式锅炉更大的还原气氛区域,抑制了NOx的产生,使其排放降低34.6%。改造后的计算结果与试验相符的较好,所以此次数值模拟为锅炉设计、改造和运行提供理论依据。     

630MW对冲旋流燃烧锅炉低氮燃烧系统优化改造

针对某电厂1台630 MW前后墙对冲旋流燃烧锅炉NOx排放质量浓度高的问题,对燃烧系统进行了改造,采用Aire JetTM燃烧器替代原低NOx轴向旋流燃烧器(LNASB)。改造后测试结果表明:在600 MW、500MW和400 MW电负荷工况下,锅炉NOx排放质量浓度分别为352 mg/m3、327 mg/m3和238 mg/m3,相比于改造前,降幅达到50%以上;锅炉热效率分别为93.90%、93.93%和94.05%,略低于改造前测试值。改造后飞灰含碳质量分数略有上升,炉内结渣较改造前明显减轻。     

燃煤电站锅炉空气分段低NOx燃烧影响因素的数值模拟

空气分段低Nox燃烧技术目前已逐渐用于现役燃煤电站锅炉的改造和锅炉设计中,通过CFD软件平台,使用数值计算的方法对空气分段燃烧技术进行研究.研究了影响燃煤电站锅炉Nox排放的因素,讨论了影响空气分段燃烧生成Nox的因素.计算结果表明,分段风喷口高度是影响最终Nox排放浓度的重要因素之一.在一定有效范围内,Nox排放浓度随着分段风喷口高度的变化并不大;分段风抽风量也是影响Nox生成的重要因素,Nox排放浓度随着分段风抽风量增大而降低.另外还需综合考虑实际锅炉的运行情况、经济效益和环境效益等各方面因素,进行合理的优化选择最佳运行参数.     

300MW四角切圆锅炉低氮改造关键技术研究与工程实践

针对某电厂1号、2号锅炉NOx排放浓度高的现状,进行了低NOx改造。系统分析了该电厂低氮改造方案,同时对该电厂低氮改造后效果进行了评价。低氮改造采用分隔SOFA(燃尽风)的空气分级方案,具有较高的改造效果;部分二次风采用偏转风技术进行改进,防止水冷壁结渣和高温腐蚀事故的发生,同时有利于防止水冷壁管超温爆管;改造后满负荷下,空预器入口NOx浓度降低了47%,锅炉排烟温度降低了31.8℃,改造取得了圆满的效果。     

防结渣技术在360t/h锅炉上的应用

介绍锅炉结渣的机理以及控制炉内结渣过程的主要因素,用数值模拟方法对某电厂360t/h锅炉结渣问题进行分析,并提出了改造该锅炉切实可行的措施.通过对该锅炉第二次改造后运行实践的检验,得出了与防结渣技术相关的一些结论.     

旋流燃烧器低氮改造后的燃烧优化调整

大修期间,某电厂对2号锅炉进行了低NOx燃烧系统改造,为了将锅炉调整到最佳的运行状态,进行了改造后的优化调整试验。结果表明:燃烧优化调整后,燃用印尼煤种、额定负荷下的NOx排放浓度为347mg/m3,与改造前相比,降幅达50.4%,达到了改造的预期目标;同时,烟气中CO排放浓度大幅降低,有效地减缓了炉内还原性腐蚀和结焦,锅炉热效率提高了约0.74个百分点,燃烧优化调整工作取得了显著的成效。     

公共烟道系统在小型热电厂中的应用

为了减少电站网尘排放的环境污染问题，兖矿集团兴隆庄煤泥热电厂在进行电厂除尘器改造后中，设计建造了公共烟道系统，采用该方法既避免了配套锅炉的停运问题，又提高了平时电站系统运行的灵活性，介绍了电站锅炉除尘器系统的改造方案，在改造后系统运行过程的实际经验，以及项目实施所得到的经济效益，结果表明，设立公共烟道的方法在具有多台机组的小电厂中值得推广使用。     

低NO_x燃烧器改造后飞灰可燃物高原因分析及优化调整

大修期间,某电厂对2号锅炉进行低NOx燃烧系统改造,为了将锅炉调整到最佳的运行状态,进行了改造后的优化调整试验。试验结果表明,燃烧器改造后,320 MW负荷下,不同磨煤机组合运行方式下,NOx排放浓度降低至306～355 mg/m3,相比于改造前,降幅达58.7%,改造效果明显;但由于改造后火焰中心上移,煤粉颗粒在炉内的停留时间缩短,煤粉颗粒未完全燃烧即进入尾部烟气通道,导致飞灰可燃物含量较高,约10%;针对这一问题,进行了燃烧系统的优化调整,调整后飞灰可燃物含量降至4%左右。     

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。     

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.