煤种对超细煤粉再燃脱硝效率影响的数值研究

应用CFD计算软件FLUENT6.1,对全尺寸四角切圆锅炉超细煤粉再燃烧过程进行了三维数值模拟。以5种煤质差异较大的超细煤粉作为再燃燃料,研究其NOx排放随再燃区长度、再燃燃料投射位置、再燃区过量空气系数及再燃量的变化规律。结果表明,对于不同煤种的再燃燃料,再燃燃料投射位置存在同一最佳值;煤种挥发分越大,再燃效果越显著;NOx的脱除率随着再燃区长度的增加而增大,随着再燃量的提高亦增大。再燃区过量空气系数对NOx脱除率有重要影响,通过分析计算结果,得到了描述再燃煤粉干燥基挥发分含量Vd和再燃区过量空气系数最佳值αop关系的经验公式,为燃烧参数的优化提供了便利的途径。     

超细煤粉燃烧氮氧化物释放特性的研究

通过试验和数值模拟，对超细煤粉在一维热态煤粉炉内燃烧时煤粉粒度、炉膛温度、过量空气系数、煤种等因素对NOx释放特性的影响规律进行了研究。研究结果表明：超细煤粉NOx的排放浓度低于常规粒度煤粉；NOx的排放浓度，随过量空气系数的增加而明显增加；煤种不同，NOx释放规律不同，煤粉超细化后，龙口褐煤的排放量明显减少，晋城无烟煤则变化不大；NOx的排放浓度随温度的升高而升高，但温度升高到一定值后，NOx的排放浓度却呈现下降趋势。以超细煤粉作为再燃燃料，NOx的还原率将比常规粒度煤粉再燃有所提高，褐煤作为再燃燃料时，效果更明显。模拟计算与试验结果较为吻合。图6表2参2     

超细煤粉再燃低NOx燃烧技术的数值模拟

为了验证超细煤粉作为再燃燃料的有效性,使用FLUENT软件对元宝山褐煤在燃烧试验研究装置中的进行了4个工况的数值模拟;1 个为常规燃烧,3 个为超细粉再燃工况。计算结果表明:超细粉再燃可以有效的降低NOx 排放,与常规燃烧相比,脱除率为58.2%~72.5%;再燃区过量空气系数越小,越有利于NOx 的还原;超细粉再燃工况中出口NOx 排放量不仅与再燃区NOx 的还原率有关,而且还与燃尽区新的NOx 生成有关。图5表3参7     

再燃燃料超细煤粉燃尽特性的实验研究

超细煤粉作为燃料分级燃烧技术中的再燃燃料具有可行性,可有效降低NOx的排放,由于再燃区和燃尽区的反应比较复杂,存在再燃燃料燃尽效果不稳定的现象.从煤种、粒度、过量空气系数、氧浓度、炉膛温度等几个因素分析,认为针对不同的煤种,合适的空气流量和燃尽区炉膛温度是提高再燃燃料燃尽的必要条件.     

抛煤机锅炉炉内再燃还原NOx的实验研究

工业锅炉燃烧的NOx处于无控制排放.利用燃料再燃技术在工业锅炉上控制NOx的排放,以抛煤机锅炉为背景,对在抛煤机炉内应用再燃技术脱除NOx进行了研究.其结果为:采用气体燃料再燃,可以将再燃喷嘴设计在前拱中,用废气作为再燃燃料,亦可以用飞灰回燃超细煤粉再燃形成还原性气氛,从理论和实验证明抛煤机炉内再燃可以还原NOx40%以上.     

超细煤粉还原NO_x的试验研究

摘要：超细煤粉再燃技术脱氮效率高而运行费用低,易于实现。通过试验方法,研究了超细煤粉再燃技术中主要因素对N0x还原率的影响。研究结果表明：再燃燃料粒度越细,对N0x的还原性越强,最佳再燃燃料平均粒径为20μm;最佳再燃燃料的比例。对于龙口褐煤为加％,对于神府烟煤为25％;再燃燃料投射位置存在最佳值,一般煤阶越高,距主燃料喷口距离越远;最佳再燃区内的停留时间,龙口褐煤为0．63s,神府烟煤为0．75s。     

温度对超细煤粉再燃降低NO排放的影响

超细煤粉再燃技术是控制燃煤电站NOx排放的有效方法之一。以3种煤的超细煤粉作为再燃燃料,用N2、O2、CO2、NO配制模拟烟气,在立式管携带炉中,研究了温度对再燃降低NO排放的影响。结果表明,在实验温度范围内,随着再燃区温度的增加,再燃还原NO的效果增大;对于挥发份含量较高的超细煤粉,再燃还原NO的效果受温度的影响更大;对于同一煤种,再燃还原NO的效果受温度的影响随再燃料比增加而增大。采用化学动力学理论对这种影响机制进行了分析。图2表1参6     

电站锅炉高效超低NOx排放控制技术

对电站锅炉低NOx燃烧技术进行了重新分类,然后分析其应用中存在的问题,再结合国外NOx排放控制技术的最新科研成果,提出了电站锅炉高效超低NOx排放控制的双分级再还原方法.该方法采用空气分级,煤粉、燃气或生物质进行再燃,同时使用选择性非催化还原NOx技术,而且添加碱金属盐以增效.双分级再还原低NOx燃烧用技术使用约10%的再燃燃料可以达到85%以上的脱硝率.     

四角切圆燃烧锅炉改造工况数值模拟

煤粉再燃是降低NOx排放的一项新技术.借助FLUENT6.1软件平台,采用数值模拟方法对一台容量为35 t/h的四角切圆燃烧锅炉改造前后炉内燃烧过程进行研究.改造前为空气分级燃烧,改造后为超细煤粉再燃燃烧.计算结果表明:改造后在最上面一层一次风喷口的高度区域,形成一个相对低温,低氧的还原性气氛区域一再燃区.再燃降低NOx18.8%,并且与改造前的燃尽效果相当.煤粉颗粒在炉内运动具有很大的随机性,停留时间差异很大.平均而言,煤粉喷入位置越高,停留时间也越短.     

煤粉再燃降低NOx燃烧技术

社会的可持续性发展,使得对环境的要求达到一个新的高度。减少氮氧化物的排放是一个亟待解决的问题,燃料再燃技术是解决此问题的一个十分可行的方法。文章分析了燃料再燃技术的原理,论述了超细煤粉再燃NOx的排放在中试试验炉上的试验和数值模拟结果,中间储仓式热风送粉系统采用三次风再燃技术降低NOx的排放,结果表明这两种燃料再燃技术都可有效降低氮氧化物的排放。     

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.     

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.     

Exergetic evaluation of 5 biowastes-to-biofuels routes via gasification

This paper presents the exergy analysis results for the production of several biofuels, i.e., SNG (synthetic natural gas), methanol, Fischer–Tropsch fuels, hydrogen, as well as heat and electricity, from several biowastes generated in the Dutch province of Friesland, selected as one of the typical European regions. Biowastes have been classified in 5 virtual streams according to their ultimate and proximate analysis. All production chains have been modeled in Aspen Plus in order to analyze their technical performance. The common steps for all the production chains are: pre-treatment, gasification, gas cleaning, water–gas-shift reactions, catalytic reactors, final gas separation and upgrading. Optionally a gas turbine and steam turbines are used to produce heat and electricity from unconverted gas and heat removal, respectively. The results show that, in terms of mass conversion, methanol production seems to be the most efficient process for all the biowastes. SNG synthesis is preferred when exergetic efficiency is the objective parameter, but hydrogen process is more efficient when the performance is analyzed by means of the 1st Law of Thermodynamics. The main exergy losses account for the gasification section, except in the electricity and heat production chain, where the combined cycle is less efficient.     

Decomposition of limestone in a solar reactor

The thermal decomposition of limestone has been selected as a model reaction for developing and testing an atmospheric open solar reactor. The reactor consists of a cyclone gas/particle separator which has been modified to let the concentrated solar energy enter through a windowless aperture. The reacting particles are directly exposed to the solar irradiation. Experimentation with a 60 kW reactor prototype was conducted at PSI's 90m² parabolic solar concentrator, in a continuous mode of operation. A counter-current flow heat exchanger was employed to preheat the reactants. Eighty five percent degree of calcination was obtained for cement raw material and 15% of the solar input was converted into chemical energy (enthalpy).The technical feasibility of the solar thermal decomposition of limestone was experimentally demonstrated. The use of solar energy as a source for high-temperature process heat offers the potential of reducing significantly the CO₂ emissions from lime producing plants. Such a solar thermochemical process can find application in sunny rural areas for avoiding deforestation.