采用石灰浆液荷电雾化的脱硫机理试验研究

采用环形电极、机械雾化喷嘴等组成的荷电雾化装置,通过测试石灰浆液的荷质比、喷浆脱硫前后烟气中二氧化硫浓度的变化,探讨和分析了不同流量时的荷质比变化规律,首次对不同荷电电压、荷质比与脱硫效率的关系进行研究.结果表明:雾滴的荷电效果与浆液流量有关,且对于同一喷嘴存在荷电效果最佳的流量值;在相同钙硫比条件下,浆液荷电相对于非荷电时脱硫率明显提高;在不同钙硫比情况下,浆液荷电与非荷电的脱硫率变化趋势基本相同.     

石灰浆液荷电雾化脱硫的化学反应动力学研究

运用烟气分析仪和PH计进行化学反应动力学试验,得到石灰浆液荷电雾化吸收SO2的反应级数、速率常数和反应速率方程,进而计算出在不同Ca/S摩尔比、SO2浓度以及荷电电压下的反应速率,并与石灰浆液荷电雾化脱硫的试验脱硫效率进行比较.结果表明:随着Ca/S摩尔比和充电电压的增大,反应速率增大,脱硫效率提高,且反应速率增大和脱硫效率提高的趋势基本一致;从微观的化学机制角度分析,雾滴荷电后确实可以增大化学反应速率,提高石灰浆液的脱硫效率,同时认为荷电对反应速率产生增益作用的原因主要是增大了单位容积内活化分子的百分数、单位接触面积上活化分子的有效碰撞次数和雾滴与烟气的接触几率.     

气液双流程烟气脱硫塔内脱硫效率与传质性能的研究

实验采用电石渣做为脱硫剂,对气液双流程液幕式脱硫塔的脱硫性能以及传质特性进行了相关的实验研究。通过实验测试,提出了烟气流量、浆液循环量、液气比值等主要影响参数对液幕式脱硫塔的脱硫性能的影响。同时本研究提出了一个相关气液双流程脱硫塔的传质模型,其形式如:Sh=16.226Reg0.863Rel-1.64和Sh=27.126Reg-0.77(L/G)-1.64。基于气液传质模型,双流塔内浆液与烟气间复杂的气液传质过程可以通过烟气雷诺数,浆液雷诺数以及液气比描述的经验关系式进行定量计算。这些参数的影响规律为研究液幕式湿法烟气脱硫系统中二氧化硫的反应特性及实际工程的应用提供了重要的指导数据。实验发现,浆液循环量增加时,总的脱硫效率相应会提高,液气比增加时,总的脱硫效率也相应会提高。而烟气流量增加时,相应的脱硫效率却随之降低。通过实验研究发现:当液气比大于20L/m3时,脱硫率可达90%以上;然而pH值对传质的影响作用很小。     

液幕式双流程烟气脱硫塔内气液流动与脱硫传质性能的研究

对液幕式双流程脱硫塔的气液流动性能以及脱硫传质特性进行相关的实验研究.通过实验测试,提出烟气流量、浆液循环量、液气比值等主要参数对液幕式脱硫塔内的气液流动特性和脱硫效率性能的影响.实验发现,随着液气比增加,射流高度和气液两相流阻力系数相应增加;气相雷诺数增加时,射流高度相应增加而气液两相流阻力系数相应减小.浆液循环量和...     

液幕式脱硫吸收塔中气液传质特性的实验研究

对液幕式吸收塔脱硫性能进行了实验研究,分析了烟气流量、循环浆液量、浆液pH值等参数对脱硫性能的影响,合理选择装置结构和运行参数时,脱硫效率可达95%;提出了液幕式吸收塔中传质面积的计算方法,建立了液幕式吸收塔的传质模型,发现传质系数在pH=5～10之间变化不明显,得到了液幕式吸收塔的传质系数关于气相和液相雷诺数的经验关系式.     

槽型芯湿法烟气脱硫的实验研究

湿法烟气脱硫是一个化学反应和传质同时进行的过程，其影响因素众多，如液体浓度、液体流动状况、气体流动状况、液气比、浆液pH值等。本文提出一种横向冲刷槽形芯湿法脱硫技术，通过试验的方法，研究了影响脱硫效率的诸多因素并进行了分析。     

柴油荷电雾滴薄片剥离式破碎模型研究

燃油静电喷雾技术可以提高柴油的雾化性能,并能降低废气的排放。通过理论分析研究了柴油荷电雾滴薄片剥离式静电破碎,并采用已有试验结果进行验证。在考虑韦伯数和雷诺数影响下,通过瑞利极限分析了影响柴油雾滴破碎的主要影响因素,并计算了雾滴静电薄片剥离式破碎的临界荷质比,其临界荷质比的数量级约为10-6~10-5 C/g,而在试验室获得的雾滴粒径范围内其荷质比式验值数量级为10-6 C/g。研究结果表明:在静电场作用下雾滴带有净电荷或者极化电荷,柴油雾滴以薄片剥离式破碎发生了瑞利破碎与泰勒破碎,试验数据与理论分析值较为接近,为柴油雾滴在低压下的静电破碎提供了有力依据。同时,柴油荷电雾滴发生破碎后其数密度大量增加,雾滴间产生聚并趋势,雾滴容易结并因而索太尔平均直径出现峰值,使雾滴粒径与荷电电压呈现非单调性曲线关系。     

石灰石_石膏湿法烟气脱硫过程的试验研究

利用所建立的并流有序降膜式湿法脱硫装置,对石灰石-石膏湿法烟气脱硫过程进行了试验研究。试验结果表明:沿烟气行程上,脱硫率上升趋势逐步减弱,脱硫率较高时,再提高脱硫率,吸收段高度或液气比要大幅增加,火电厂机组在确定脱硫系统脱硫率时,应有适当选择;脱硫浆液pH值下降,且在吸收塔入口至0.5 m范围内,浆液pH值下降迅速,而后下降变缓;浆液中石灰石含量下降趋势逐步增强;同时浆液中Ca2 、六价硫S6 及四价硫S4 浓度均增加,Ca2 、S6 浓度增加使得石膏过饱和度有所增加。     

氧化镁湿法烟气脱硫优化试验研究

基于氧化镁湿法烟气脱硫工艺应用中存在的问题,对影响氧化镁湿法脱硫率及可用率的关键参数如SO2浓度、烟气量、循环吸收液PH值、液气比、曝气量等进行了一系列单因素调整试验研究,得出各参数对脱硫效率的影响趋势;对不同含硫量的燃煤,应采用不同的液气比和吸收剂浆液的PH值,吸收剂浆液PH值控制在5.8比较合理;增强循环槽浆液的曝...     

液气比对石灰石-石膏湿法烟气脱硫过程的影响

石灰石-石膏湿法烟气脱硫系统中,液气比是影响系统脱硫性能及经济性的重要参数.利用所建立的并流有序降膜式湿法脱硫装置,进行了液气比对石灰石-石膏湿法脱硫过程影响的试验研究.结果表明:脱硫率随液气比增加而增加;当液气比小于8 L/m3时,增加液气比能更有效地提高脱硫率;液气比增加,吸收塔吸收段出入口的浆液中石灰石浓度差降低,吸收段内浆液中石灰石溶解量增加,浆液中石灰石浓度增加.     

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.     

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.     

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%.     

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.     

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.     

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.     

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.     

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.