富氧燃烧条件下煤灰的沾污沉积特性研究

O_2/CO_2富氧燃烧发电技术被认为是未来最具潜力的燃煤低碳电力技术,近年来国内外都得到了快速发展。由于O_2/CO_2富氧燃烧条件下锅炉烟气组份发生了很大变化(以CO_2+H_2O为主),煤灰在富氧燃烧锅炉炉内的沾污、沉积行为也将发生较大变化。为此,在3 MWth煤燃烧热态试验平台上对比研究了煤在空气燃烧和O_2/CO_2富氧燃烧条件下灰的沾污沉积特性。研究结果表明:煤在空气燃烧和O_2/CO_2富氧燃烧条件下各受热面沉积灰样的化学组成并没有显著变化,富氧燃烧条件下沉积灰样中SO_3和Fe_2O_3发生了富集,而Si_2O和Al_2O_3的含量相对偏低,O_2/CO_2富氧燃烧条件下沉积灰样的煤灰熔融温度其在比空气燃烧条件下的煤灰熔融温度约低200℃。     

过渡金属氧化物(MnO_x-CeO_2)改性铜基催化剂的低温SCR脱硝性能研究

利用溶胶凝胶法,将过渡金属氧化物(MnO_x-CeO_2)掺杂到铜基催化剂CuO/γ-Al_2O_3上,制备了不同配比的CuO-MnO_x-CeO_2/γ-Al_2O_3催化剂颗粒,采用程序升温方法在催化反应效能评价系统里测试了其在模拟烟气条件下的低温SCR脱硝性能。利用比表面积测试仪(BET)、X射线衍射仪(XRD)和扫描电子显微镜(SEM)对催化剂进行表征分析,分析了MnO_x-CeO_2改性铜基催化剂低温SCR脱硝的反应机理。结果表明:6%CuO-5%MnO_x-10%CeO_2/γ-Al2O3的催化剂颗粒在100~200℃内的脱硝效率保持在80%以上;SO_2和H_2O对SCR脱硝反应均有抑制作用;O_2是SCR反应持续进行的必要条件。     

吡咯类氮富氧燃烧的分子动力学研究

采用基于ReaxFF反应力场的分子动力学模拟方法研究了不同燃烧温度和氧浓度条件下吡咯在O_2/CO_2和O_2/N_2气氛下燃烧的反应速率和自由基、中间产物及最终产物的分子数变化规律,从微观上探索吡咯在O_2/CO_2气氛下的燃烧机理。研究表明:吡咯富氧燃烧的主要产物包括HCN、NO、N_2、CO_2、CO和H_2O等,主要的中间体和自由基包括C_4H_4N、NCO、HNCO、C_4H_4ON、CHO_2、CN、H、OH、O和HO_2等;随着燃烧温度的升高,O_2/CO_2和O_2/N_2气氛下NO的生成量都随之增加;随着氧气浓度的升高,更多的HCN、NCO、HNCO及其它含氮中间产物转化为NOx,从而使其生成量增加;在燃料与氧气的化学当量比Φ=0.5和1时,O_2/CO_2气氛中NO的生成量比O_2/N_2气氛中的NO的生成量高,在Φ=2时两种气氛中生成的NO量相当。     

基于碳氧原子比空间的富氧燃烧火焰结构及碳黑初生分析

针对富氧C_2H_4/O_2/N_2和C_2H_4/O_2/CO_2对冲火焰,采用详细的化学反应机理进行了数值模拟,在碳氧原子比(C/O)空间下分析了火焰结构和碳黑颗粒初生以及CO_2代替空气中的N_2对碳黑初生的影响.结果表明:在O_2/N2和O_2/CO_2气氛下,随着化学计量混合分数(Zst)的增加,C/O空间下对冲火焰的火焰面位置不变,对应的C/O_原子比值分别为0.50、0.53.在C/O_空间下,两种气氛下,随着Zst的增加火焰中C_6H_6出现的位置不变,C/O原子比值都为0.47左右.当用CO_2代替空气中的N_2时,火焰温度降低,同时使CO_+OH■CO_2+H的逆反应增强,导致火焰中的C_2H_2、H的摩尔分数减少,OH的摩尔分数增加,抑制碳黑的初生.     

600MW亚临界锅炉富氧改造热力学性能及?分析

利用锅炉热力计算和?分析的方法对某600 MW燃煤锅炉在不同O_2/CO_2气氛下进行锅炉热力特性和?效率计算,并与空气气氛下锅炉热力特性和?进行比较。结果显示:在富氧燃烧条件下,锅炉排烟量和排烟热损失有所减少,锅炉效率有所增加,同时锅炉的辐射和半辐射受热面的烟气侧换热系数增加。O_2/CO_2中氧气分压处于25%～30%之间时,锅炉的理论燃烧温度和炉膛出口温度与空气气氛相似。富氧条件下锅炉?效率提高1%左右,且?损失大部分发生在传热和燃烧过程中。     

典型煤种O_2/CO_2/H_2O气氛下中高温燃烧时NO的生成特性

利用自制恒温热分析系统研究了大同烟煤和阳泉无烟煤在O_2/CO_2/H_2O气氛下中高温燃烧时NO的释放行为,并与O_2/N_2和O_2/CO_2气氛下的情况进行了对比分析.结果表明:当氧气体积分数为5%时,大同烟煤在O_2/CO_2和O_2/N_2气氛下燃烧时只有一个NO体积分数峰,而在O_2/CO_2/H_2O气氛下却变成一前一后2个峰;当氧气体积分数升高到21%后,大同烟煤在O_2/CO_2/H_2O气氛中的NO释放过程又变为一个体积分数峰;阳泉无烟煤的NO释放过程与大同烟煤类似;大同烟煤在O_2/CO_2气氛中的NO排放量始终低于O_2/N_2气氛中;由于低氧气体积分数下H_2O气化反应的影响,大同烟煤在O_2/CO_2/H_2O气氛中的NO排放量在高温下高于O_2/CO_2气氛中;氧气体积分数升高后,大同烟煤在O_2/CO_2/H_2O气氛中的NO排放量又低于O_2/CO_2气氛中;阳泉无烟煤的NO排放量高于大同烟煤,但其不同气氛下的变化趋势与大同烟煤一致.     

O_2/CO_2气氛下煤粉燃烧特性及动力学分析

采用热重实验系统进行了煤粉在O_2/N_2和O_2/CO_2气氛下的燃烧实验,研究了氧体积分数和粒径对燃烧特性的影响.实验结果表明,氧体积分数越高、粒径越小,煤粉的燃烧特性越好.在氧体积分数较高时,煤粉在O_2/CO_2气氛下的反应比在O_2/N_2气氛下进行得慢;而氧体积分数较低时,煤粉在O_2/CO_2气氛下的反应比在O_2/N_2气氛下进行得快.此外,采用Coats-Redfern积分法、Flynn-Wall-Ozawa积分法和Kissinger-Akahira-Sunose积分法对煤粉在程序升温过程中的燃烧反应做了相应的动力学分析.结果表明,O_2/N_2和O_2/CO_2气氛下不同氧体积分数时的煤粉燃烧反应动力学参数表观活化能E和指前因子A之间具有动力学补偿效应.煤粉燃烧过程中在同一转化率下的表观活化能E随其粒径的减小而降低.     

富氧燃烧锅炉炉膛内烟气辐射特性计算

用指统计窄带模型结合Mie氏散射理论计算了带有颗粒物的富氧燃烧锅炉炉膛内烟气的黑度,与逐线计算的富氧燃烧气体的黑度以及空燃时烟气黑度结果的比较表明,此方法可以准确地计算富氧燃烧条件下烟气的黑度,并计算了常规燃煤时颗粒物浓度下不同射线行程、不同烟气循环比、不同温度下富氧燃烧烟气的黑度。结果表明:颗粒物对烟气黑度的计算有较大影响;同时,由于富氧燃烧中CO_2和H_2O比例的增大,气体成分对燃烧产物的黑度也存在较大影响。本研究可为富氧燃烧锅炉的设计提供依据。     

喷氨格栅处烟气速度场对高效SCR均流与还原剂混合性能的影响

随着SCR脱硝效率的上升,喷氨格栅(AIG)处烟气速度场在SCR均流与混合技术中变得越来越重要.以某高效电站SCR为研究对象,利用经冷态模型校验过的SCR数值模型,分析AIG处烟气速度场10种典型变化对电站SCR系统内均流与还原剂混合性能的影响.结果显示,对高脱硝效率的SCR系统,AIG处烟气速度场变化对催化剂入口界面上氨氮比分布影响很大,对入口界面上速度场也有一定影响.设计中控制AIG处烟气流速不均匀性可以提高SCR内均流与混合的品质.在AIG处流速不均匀性控制得较好的高效SCR中,随着AIG处流速不均匀性上升,催化剂入口界面上氨氮比不均匀性增大;AIG处速度场与催化剂处速度场具有相似性.     

O_2/CO_2气氛下碳烟氧化的反应动力学研究

利用热重分析对典型碳烟在O_2/CO_2气氛下氧化的动力学特性进行研究,对比了其与O_2/N_2气氛下的差异,并重点考虑了O_2体积分数的影响,建立了富氧燃烧条件下碳烟氧化反应的表观活化能E和频率因子A与O_2体积分数的定量关联机制.结果表明:与O_2/N_2气氛相比,O_2/CO_2气氛下碳烟氧化的起始和结束温度均较高,综合反应指数降低;O_2/CO_2气氛下,随着O_2体积分数增大,碳烟氧化的TG-DTG曲线向低温区移动,起始和结束温度均降低,最大失重速率增加,综合反应指数显著提高;碳烟氧化反应的E与A之间总是存在显著的"动力学补偿效应",当O_2体积分数低于20%时,E和ln A均与O_2体积分数呈正相关,而当O_2体积分数高于20%时,E与A随O_2体积分数的变化不显著.     

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.     

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.     

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.     

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.     

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.     

液压系统常见的故障诊断及处理

任何工程机械式液压设备使用时出现故障是不可避免的。但是怎样确定故障的原因及找到好的解决方法，这是使用者最关心的问题。讲述了液压系统常见的故障及其排除方法。     

Biohydrogen production by Anabaena sp. PCC 7120 wild-type and mutants under different conditions: Light, nickel, propane, carbon dioxide and nitrogen

Increasing awareness of environmental problems caused by the current use of fossil fuel-based energy, has led to the search for alternatives. Hydrogen is a good alternative and the cyanobacterium Anabaena sp. PCC 7120 is naturally able to produce molecular hydrogen, photosynthetically from water and light. However, this H₂ is rapidly consumed by the uptake hydrogenase.This study evaluated the hydrogen production of Anabaena sp. PCC 7120 wild-type and mutants: hupL⁻ (deficient in the uptake hydrogenase), hoxH⁻ (deficient in the bidirectional hydrogenase) and hupL⁻/hoxH⁻ (deficient in both hydrogenases) on several experimental conditions, such as gas atmosphere (argon and propane with or without N₂ and/or CO₂ addition), light intensity (54 and 152 ??Em⁻²s⁻¹), light regime (continuous and light/dark cycles 16 h/8 h) and nickel concentrations in the culture medium.In every assay, the hupL⁻ and hupL⁻/hoxH⁻ mutants stood out over wild-type cells and the hoxH⁻ mutant. Nevertheless, the hupL⁻ mutant showed the best hydrogen production except in an argon atmosphere under 16 h light/8 h dark cycles at 54 ??Em⁻²s⁻¹ in the light period, with 1 ??M of NiCl₂ supplementation in the culture medium, and under a propane atmosphere.In all strains, higher light intensity leads to higher hydrogen production and if there is a daily 1% of CO₂ addition in the gas atmosphere, hydrogen production could increase 5.8 times, related to the great increase in heterocysts differentiation (5 times more, approximately), whereas nickel supplementation in the culture medium was not shown to increase hydrogen production. The daily incorporation of 1% of CO₂ plus 1% of N₂ did not affect positively hydrogen production rate.     

Economie d'énergie en trigénération

Trigeneration is defined as the production of three useful forms of energy—heat, cold and power—from a primary source of energy such as natural gas or oil. For instance, trigeneration systems typically produce electrical power via a reciprocating engine or gas turbine and recover a large percentage of the heat energy retained in the lubricating oil, exhaust gas and coolant water systems to maximize the utilization of the primary fuel. The heat produced can be totally or partially used to fuel absorption refrigerators. Therefore, trigeneration systems enjoy an inherently high efficiency and have the potential to significantly reduce the energy-related operation costs of facilities. In this paper, we describe a model of characterization of trigeneration systems trough the condition of primary energy saving and the quality index, compared to the separate production of heat, cold and power. The study highlights the importance of the choice of the separate production reference system on the level of primary energy saving and emissions reduction.     

Investigation of the thermodynamic and kinetic properties of La–Fe–B system hydrogen-storage alloys

La–Fe–B hydrogen-storage alloys were prepared using a vacuum induction-quenching furnace with a rotating copper wheel. The thermodynamic and kinetic properties of the La–Fe–B hydrogen-storage alloys were investigated in this work. The P–C–I curves of the La–Fe–B alloys were measured over a H₂ pressure range of 10⁻³ MPa to 2.0 MPa at temperatures of 313, 328, 343 and 353 K. The P–C–I curves revealed that the maximum hydrogen-storage capacity of the alloys exceeded 1.23 wt% at a pressure of approximately 1.0 MPa and temperature of 313 K. The standard enthalpy of formation ΔH and standard entropy of formation ΔS for the alloys' hydrides, obtained according to the van't Hoff equation, were consistent with their application as anode materials in alkaline media. The alloys also exhibited good absorption/desorption kinetics at room temperature.     

Mineralogical characterization of the intraseam layers of Lofoi lignite deposits in Florina basin (western Makedonia,northwest Greece)

The mineralogical composition of intraseam layers from Lofoi lignite deposits (northwest Greece) is the subject of the present study. The samples were examined by means of X-ray diffraction (XRD), thermo-gravimetric (TG/DTG) and differential thermal analysis (DTA), and Fourier transform infrared (FT-IR) spectrometry. The clay minerals prevail in most samples, with illite-muscovite being the dominant phase, and kaolinite and chlorite being the other major clay components. No smectite was found. Quartz and feldspars, dominate in two cases. The studied materials are characterized as clays to clayey sands, showing significant similarities with the intraseam layers of the adjacent Achlada lignite deposits.