某电厂SCR脱硝催化剂严重磨损原因分析

针对某电厂SCR(先择性催化还原)脱硝催化剂发生严重磨损的现象,采用自行设计的催化剂活性测量装置对其进行性能评价,测量了NO脱除率、SO2/SO3转化率、比表面积,分析其微观形貌、晶型和元素组成。研究结果表明:催化剂磨损严重的主要原因是由于反应器的严重堵塞,堵塞面积约占催化剂总面积的1/4—1/3,且各反应器下层催化剂坍塌较严重。由于催化剂严重磨损导致脱硝系统脱硝率明显下降。     

电站锅炉脱硝系统催化剂磨损数值模拟

国内某660 MW超超临界直流锅炉脱硝系统SCR催化剂出现严重磨损导致脱硝装置失效,统计得知磨损区域集中于催化剂的近锅炉侧。利用数值模拟,分析了磨损形成的机理,数值模拟计算的磨损位置与实际吻合,催化剂磨损的主要原因是由飞灰颗粒场的不均匀分布所导致,提出了6种改造方案并加以计算。通过对比分析,选择一最佳改造方案,通过加装导流撞击装置,使催化剂上部的飞灰颗粒向催化剂的远锅炉侧移动,从而改善SCR烟道内流场及飞灰颗粒场的不均匀性。数值模拟结果证明最佳改造方案能有效解决SCR催化剂磨损问题,显著提高脱硝系统运行的可靠性,且具有施工简单、经济可靠的特点。     

脱硝催化剂堵塞磨损问题工程案例分析探究

以某350MW超临界锅炉脱硝催化运行中出现堵塞磨损问题为工程案例,通过现场运行数据整理,分别从煤质特点、流场分布、吹灰运行、催化剂自身性能等方面,逐项分析引起催化剂堵塞磨损问题的可能因素,分析认为煤质条件和烟气流场是问题主要因素,吹灰运行等其他因素起到促进作用,通过数值模拟对脱硝装置流场情况进行了拟合验证,同时提出运行优化建议。     

烟气飞灰对SCR脱硝催化剂的磨损性能试验研究

利用自制的冷态飞灰磨损试验台,进行了飞灰对SCR脱硝催化剂磨损性能影响的试验研究。结果表明:催化剂磨损主要发生在端面,烟气流速是催化剂磨损的主要因素,催化剂磨损率以速度指数基本为4的规律变化,且速度指数随飞灰粒径的增大而减小;飞灰粒径和飞灰质量浓度是催化剂磨损的次要因素,粒径指数在1附近变化,且随烟气流速的增大而减小,催化剂磨损率正比于飞灰质量浓度;在实际运行过程中,应尽可能保证流场均匀,避免局部高速,以减轻催化剂磨损,保证脱硝系统经济安全地运行。     

SCR脱硝反应塔流场数值模拟研究

选择性催化还原烟气脱硝（Selective Catalytic Reduction,SCR）技术是目前应用最为广泛的烟气脱硝技术,但由于进入催化剂层的烟气气流分布不均匀而导致价格高昂的催化剂得不到充分利用,增加了运行成本.因此,改善SCR脱硝反应塔内的气流分布均匀性,提高催化剂的利用效率,具有很大的现实意义和市场价值.文中通过数值模拟研究了SCR脱硝反应塔内导流板的结构布置对气流分布均匀性、喷氨后的混合效果、压力损失的影响,提出4种导流板加装方案,并确定了最优方案.     

某300MW燃煤机组SCR脱硝催化剂磨损问题分析

简述催化剂磨损机理,结合某300MW燃煤机组脱硝催化剂磨损工程实例,总结分析催化剂磨损原因,并提出相应的优化建议以提高SCR脱硝装置运行的安全稳定性。     

我国SCR脱硝催化剂服役过程中运行规律的研究

针对某电厂SCR脱硝催化剂服役过程中的运行规律进行了现场试验研究,自行设计了催化剂活性测量装置,并利用先进的测试手段研究了催化剂失活的原因.结果表明:催化剂失活主要是由于催化剂磨损造成的活性组分流失及飞灰表面沉积共同作用所致,而在飞灰表面沉积作用中,以碱金属和CaSO4的影响为主.     

SCR脱硝系统催化剂防磨措施的探讨

本文就某电厂已运行两年的SCR脱硝装置催化剂磨损情况描述,并进行分析。对于反应器截面、吹灰方式与催化剂选型的匹配等方面,给出改进建议,为SCR脱硝装置设计改进提供参考。     

660MW机组SCR喷氨策略的模拟研究

本研究利用Fluent软件耦合详细反应机理的方法建立了某660 MW燃煤机组三维SCR反应器模型。通过模型研究了不同喷氨方式以及催化剂比表面积对脱硝反应的影响,结果表明:对于刚投运的催化剂,脱硝反应主要在第一层催化剂内完成,第二层催化剂主要起到吸收氨逃逸的作用,30区喷氨与10区喷氨获得的脱硝效果相同。当投运一段时间后,首层催化剂发生堵塞磨损等问题,导致脱硝效率降低,出口氨逃逸增大,此时30区喷氨效果略优于10区喷氨。     

SCR脱硝催化剂磨损关键因素分析

采用CFD数值模拟软件,对内蒙古某电厂600 MW机组脱硝反应器流场进行数值模拟。通过热态流场测试数据对模拟结果进行验证,并基于Tabakoff磨损理论,研究烟气速度分布对SCR脱硝催化剂磨损情况的影响。结果表明,通过烟气流场的数值计算并结合磨损理论,判断反应器内催化剂磨损的分布情况效果明显。催化剂磨损速率与烟气流速、速度攻击角大小均存在一定关系,当攻击角处于30°～60°,磨损效果最为明显。当烟气流速绝对值保持不变时,其水平方向分量与数值方向分量越接近磨损效果越明显,可通过烟气流速水平方向分量大小直观判断各区域磨损情况。     

Contents in Volume 23,2014

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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.     

Controls on the Karaha–Telaga Bodas geothermal reservoir,Indonesia

Karaha–Telaga Bodas is a partially vapor-dominated, fracture-controlled geothermal system located adjacent to Galunggung Volcano in western Java, Indonesia. The geothermal system consists of: (1) a caprock, ranging from several hundred to 1600 m in thickness, and characterized by a steep, conductive temperature gradient and low permeability; (2) an underlying vapor-dominated zone that extends below sea level; and (3) a deep liquid-dominated zone with measured temperatures up to 353 °C. Heat is provided by a tabular granodiorite stock encountered at about 3 km depth. A structural analysis of the geothermal system shows that the effective base of the reservoir is controlled either by the boundary between brittle and ductile deformational regimes or by the closure and collapse of fractures within volcanic rocks located above the brittle/ductile transition. The base of the caprock is determined by the distribution of initially low-permeability lithologies above the reservoir; the extent of pervasive clay alteration that has significantly reduced primary rock permeabilities; the distribution of secondary minerals deposited by descending waters; and, locally, by a downward change from a strike-slip to an extensional stress regime. Fluid-producing zones are controlled by both matrix and fracture permeabilities. High matrix permeabilities are associated with lacustrine, pyroclastic, and epiclastic deposits. Productive fractures are those showing the greatest tendency to slip and dilate under the present-day stress conditions. Although the reservoir appears to be in pressure communication across its length, fluid, and gas chemistries vary laterally, suggesting the presence of isolated convection cells.     

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.