燃气轮机余热锅炉过渡烟道的优化设计

针对余热锅炉过渡烟道内烟气流通截面的形式,给出了改变烟道上面板仰角和在烟道内加装导流板两种优化方案,并且通过对优化方案的模拟计算,得出了烟气速度在烟道出口截面上的分布情况。在对模拟结果的分析讨论后,得出两个优化方案的最佳选择。计算结果表明,加装导流板能够明显改善烟道出口截面的烟气速度分布,平均速度由11.13m/s增加到11.51m/s,速度的均方差由12.33m/s降为4.02m/s。将所得结论应用于实际工程中,取得了良好效果。     

燃煤锅炉SCR烟气脱硝系统流场优化的数值模拟

对某600 MW超临界燃煤机组SCR系统进行反应器内烟气流动均匀性和飞灰沉积的数值模拟.通过对比进入上层催化剂层烟气速度分布不均匀性,加入飞灰颗粒离散相后,开展烟道内导流板布置形式和导流板结构对SCR反应器内流场以及飞灰沉积的影响研究.结果表明:当SCR反应器入口导流板数目为13时,烟气通过上层催化剂层速度分布较其他3种工况均匀;导流板的弧形板后加装一段竖直直板可进一步引导烟气流动,减小回流作用,烟气进入上层催化剂层时速度更加均匀,综合考虑,弧-直型导流板为最优结构;数目13块的弧-直型导流板结构有利于改善SCR反应器壁面飞灰沉积情况;飞灰颗粒对SCR反应器内流场有一定影响,但改变较小,在实际运行中应进行相应吹灰处理.     

导流板对脱硫塔除雾器前烟气流场的优化模拟

以湿法烟气脱硫塔为研究对象,对脱硫塔整体结构进行合理的建模和简化。基于Fluent软件平台,在烟道出口处采用几种不同的导流板布置方案,并对各方案脱硫塔内流场进行数值模拟,分析比较不同方案下流场均匀性和压降。结果表明:烟道出口前设置导流板能显著改善出口截面的流场分布及压力分布,不同出口导流板结构对出口流场分布影响程度不同,为选择最优导流板布置形式提供了理论指导。     

300MW机组锅炉低省改造后烟道流场特性数值模拟

为优化300 MW机组锅炉低省改造后除尘器区烟道流场特性,基于Fluent 14.0软件,对除尘器前烟道内流场进行三维数值研究,提出了相应的改造方案。研究结果表明:低省改造后烟道内流场存在着强烈的不均匀现象,局部存在的高速区造成烟道磨损;加装导流板能够有效优化烟道内流场分布,降低烟道内速度偏差;进入除尘器前气流分布均匀,导流板具有良好均流效果。此结果可为工程技术改造提供参考。     

SCR系统优化运行数值模拟研究及试验验证

对600 MW燃煤电站SCR系统流场进行优化并试验验证,首先诊断基于原导流板方案下系统喷氨格栅及首层催化剂入口截面内的速度、浓度分布标准偏差,根据诊断结果进行导流板优化方案设计,并研究导流板优化后系统运行特性,最后设计冷模试验进行对比验证。结果表明:导流板优化方案能够有效改善流场、浓度场分布均匀性,AIG截面内流场均匀性相对改善量达54.08%,首层催化剂入口截面内速度、浓度均匀性相对改善量分别为71.79%和61.17%,冷模试验结果与数值模拟结果吻合良好,最大偏差仅为4.44%,合理的导流板优化布置有助于提升SCR系统的运行性能。     

生物质锅炉SCR外置烟道导流板设计仿真研究

为优化SCR外置烟道内的烟气流场,开展了导流板设计的仿真研究。计算结果表明,初始设计方案下脱硝反应器入口的速度不均匀系数高达93.7%。基于数值仿真结果与理论分析,确定了合理的导流板布置方案。优化后,SCR外置烟道阻力为69.4 Pa,脱硝反应器入口速度不均匀系数下降至14.7%。给出的SCR外置烟道的导流板优化方案,可为流场优化的工程设计提供技术指导。     

基于CFD的选择性催化还原烟气脱硝流场优化

SCR反应器内流场的均匀性直接影响还原剂与NO_x的混合效果,从而影响脱硝效率。喷氨格栅(AIG)上游截面和首层催化剂入口截面的标准速度偏差是衡量SCR反应器内流场均匀性的重要指标。应用Fluent18.0软件对某660MW超临界燃煤机组的SCR反应器内烟气流动情况进行模拟,采用不同形状的导流板对SCR反应器内弯头和变截面处的"低速三角区、高速冲刷区和低速回流区"进行优化。优化结果表明,采用不同形状的导流板可以有效抑制烟道弯头和变截面处速度分离的现象。空塔时,AIG上游标准速度偏差57.91%,催化剂入口标准速度偏差为90.45%;优化后,AIG上游标准速度偏差为9.48%,催化剂入口标准速度偏差为8.74%。     

湿式电除尘器进口烟道导流装置数值模拟流场优化设计

Fluent是一款常用计算流体动力学流场模拟软件.在湿式电除尘器进口异形扩张烟道中增设导流板,采用软件模拟不同导流板和均布格栅设置方案优化湿式电除尘器进口处烟气流场分布.通过比较4种不同方案,烟道90° 弯头处设置导流板,扩大口截面设置1层均布格栅,在右侧两片导流板上端分别增加500 mm长不同角度的导流板时出口流场分...     

导流板影响SCR脱硝烟道气动性能数值研究

为研究300MW电厂SCR脱硝烟道内部气动流场,采用数值模拟方法,在获得原始流场烟气分布规律的基础上,分析了入口段扩张流道导流板对速度场的影响。结果表明:导流板可以很好的改善扩张流道内烟气的流动性能,一定程度上均化了催化剂前的速度分布,随着导流板数量的增加,扩张流道出口的速度偏差系数逐渐减小,而催化剂前的逐渐增大,其中在减小反应器中间高速区方面,最佳方案为Case 2。     

“V”型直接空冷凝汽器单元内部导流的数值研究

针对某直接空冷单元温度分布极不均匀的现象,运用FLUENT软件,在考虑环境风的情况下,对"V"型空冷单元风机出口加装不同数量的平直导流板进行数值研究。结果表明,风机出口加装平直导流板确能改善冷却空气流场和温度场,使翅片管束出口温度分布更均匀,且最高温度明显降低,改善了凝汽器的换热性能,在加装4块导流板时,翅片管束出口温度分布达到最佳,最高温度降到最低。     

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%.     

Performance assessment of some ice TES systems

In this paper, a performance assessment of four main types of ice storage techniques for space cooling purposes, namely ice slurry systems, ice-on-coil systems (both internal and external melt), and encapsulated ice systems is conducted. A detailed analysis, coupled with a case study based on the literature data, follows. The ice making techniques are compared on the basis of energy and exergy performance criteria including charging, discharging and storage efficiencies, which make up the ice storage and retrieval process. Losses due to heat leakage and irreversibilities from entropy generation are included. A vapor-compression refrigeration cycle with R134a as the working fluid provides the cooling load, while the analysis is performed in both a full storage and partial storage process, with comparisons between these two. In the case of full storage, the energy efficiencies associated with the charging and discharging processes are well over 98% in all cases, while the exergy efficiencies ranged from 46% to 76% for the charging cycle and 18% to 24% for the discharging cycle. For the partial storage systems, all energy and exergy efficiencies were slightly less than that for full storage, due to the increasing effect wall heat leakage has on the decreased storage volume and load. The results show that energy analyses alone do not provide much useful insight into system behavior, since the vast majority of losses in all processes are a result of entropy generation which results from system irreversibilities.     

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.     

Effect of co-cultivation of Chlamydomonas reinhardtii with Azotobacter chroococcum on hydrogen production

Chlamydomonas reinhardtii cc124 and Azotobacter chroococcum bacteria were co-cultured with a series of volume ratios and under a variety of light densities to determine the optimal culture conditions and to investigate the mechanism by which co-cultivation improves H₂ yield. The results demonstrated that the optimal culture conditions for the highest H₂ production of the combined system were a 1:40 vol ratio of bacterial cultures to algal cultures under 200 μE m^?2 s^?1. Under these conditions, the maximal H₂ yield was 255 μmol mg^?1 Chl, which was approximately 15.9-fold of the control. The reasons for the improvement in H₂ yield included decreased O₂ content, enhanced algal growth, and increased H₂ase activity and starch content of the combined system.     

Natural-gas fueled spark-ignition (SI) and compression-ignition (CI) engine performance and emissions

Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NO_x) emissions, while producing lower emissions of carbon dioxide (CO₂), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fueled engines because of the convergence of one or more of three factors: a reduction in volumetric efficiency due to natural-gas injection in the intake manifold; the lower stoichiometric fuel/air ratio of natural gas compared to gasoline; and the lower equivalence ratio at which these engines may be run in order to reduce NO_x emissions. High NO_x emissions, especially at high loads, reduce with exhaust gas recirculation (EGR). However, EGR rates above a maximum value result in misfire and erratic engine operation. Hydrogen gas addition increases this EGR threshold significantly. In addition, hydrogen increases the flame speed of the natural gas-hydrogen mixture. Power levels can be increased with supercharging or turbocharging and intercooling. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fueled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. At the same time, lower NO_x and CO₂ emissions, as well as higher HC and CO emissions compared with normal CI-engine operation at low and intermediate loads are recorded. These trends are caused by the low charge temperature and increased ignition delay, resulting in low combustion temperatures. Another factor is insufficient penetration and distribution of the pilot fuel in the charge, resulting in a lack of ignition centers. EGR admission at low and intermediate loads increases combustion temperatures, lowering unburned HC and CO emissions. Larger pilot fuel quantities at these load levels and hydrogen gas addition can also help increase combustion efficiency. Power output is lower at certain conditions than diesel-fueled engines, for reasons similar to those affecting power output of SI engines. In both cases the power output can be maintained with direct injection. Overall, natural gas can be used in both engine types; however further refinement and optimization of engines and fuel-injection systems is needed.     

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.     

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.     

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。