水轮机冷却塔可行性分析

冷却塔在钢铁、冶金、化工等循环水系统中有着广泛的应用,其风机一般采用电机驱动;水轮机冷却塔是利用循环水系统的富余能量带动水轮机作功,以取代风机电机实现节能的目的。     

水轮机节能技术在石化行业循环水冷却塔中的应用

水轮机利用循环水泵的富余扬程带动风机运转,以取代风机电机,实现节能的目的。以高效反击混流式水轮机在青岛石化循环水冷却塔中的应用为例,通过监测单开水轮机风机或电动风机时循环水的温降程度,来对比两种风机的运行效果,并在维持系统管网压力、流量不变的条件下,监测水轮机风机正常运行、转速减半、停运至系统稳定,以及重开风机系统、恢复稳定状态下的运行数据,测试水轮机风机运行对循环水系统的影响,从而验证水轮机节能技术的应用效果及经济效益。结果证明,循环水系统存在富余能量,水轮机利用该富裕能量带动风机运转,不增加循环水系统新的能耗;且水轮机风机降温效果与电动风机相当,可替代电机风机运行,满足精细化操作需要。采用水轮机运转风机,可优化循环水系统配置,减少维护保养费用,经济效益较高,具有较好的推广价值。     

冷却塔水轮机与风机匹配解决方案

在冷却塔的节能改造中,水轮机替代电机直接驱动风机的模式已经得到了越来越广泛的应用。但是由于循环水系统的余能并不能简单确定,同时水轮机-风机机组与常规的水轮发电机组运行特性有很大的不同,在工程应用中,由于缺乏科学分析和技术指导而盲目上马造成改造失败的情况时有发生。为了确保达到要求的性能指标,在改造之前全面分析循环水系统的特征以及水轮机、风机特性,进行水轮机-风机联动关系的计算,并进行水轮机的合理选型并与风机进行最佳匹配,进而精确预算出机组的运行工况,得到改造后机组的转速以及系统流量、压力等关键参数,这样便提前预知了机组运行的效果,避免改造失败带来的经济损失和社会影响。     

新型喷雾推进冷却塔利用循环水余压的应用

新型喷雾推进冷却塔利用循环水的余压,通过雾化装置使冷却水雾化并推动风机旋转。该新型喷雾装置的应用表明,该装置冷却效果和热力性能优于传统的机械通风冷却塔,而且节能效果显著,值得大力推广应用。     

水动风机冷却塔的应用及节能分析

水动风机冷却塔利用水轮机代替电机驱动风机,对水动风机冷却塔在地铁工程中的应用实例进行了分析,该塔和传统的电机冷却塔相比,其冷却能力、外形尺寸、噪声等均满足要求,当冷却泵的富余扬程可以满足水轮机驱动需要时,节能效果较为明显。     

循环水场冷却塔风机节能改造

水轮风机是近年来发展起来的一种利用循环水回水富余动能的设备,使用该设备可以在工程改造量很小的基础上实现对循环水回水富余扬程的利用,从而达到节能的目的。惠州炼化第一循环水场为了最大限度地挖掘节能能力,对2号、3号、4号、5号冷却塔风机进行节能技术改造,即用HLW-4000型水轮机取代LF92型轴流风机电机作为动力源,带动风叶旋转,满足冷却塔抽风降温需求。介绍了技术改造内容及投资概况,并结合不同工况下的实际运行数据,分析了实施改造的可行性以及所能达到的冷却效果。实施改造后,循环水冷却塔按照每年工作8400h计,则每年节约用电462×104kW·h,每年节约电费约277.2万元;实际生产中,水轮风机运行平稳,循环水温差及流量均能满足实际生产需要。利用水轮风机可以降低运行成本,节能效果明显,可在炼化企业推广应用。     

钢铁厂循环水系统节电改造

针对梅山钢铁冷轧循环水系统运行时存在节流损失及能量浪费等问题的分析,提出了改造措施,对泵进行了高效化改造,采用水轮机驱动替换电机驱动风机,应用智慧阀门,从而确保了系统的运行稳定,从改造效果看,节电效果显著,不仅降低了能耗,而且提高了循环水系统效率。     

凉水塔节能技术改造实践

凉水塔是石油炼化行业设备中的一个基本单元,同时也是公用工程中的主要耗能设备之一。为了降低循环水系统的能耗,经过分析调研和对循环水系统的能量核算,最终选择将凉水塔风扇的驱动电机改为水轮机,利用循环水系统的富裕压头来驱动水轮机,以达到节电目的。     

水轮机在循环冷却水系统的节能改造应用

在循环冷却水装置运行过程中,传统模式一般采用减速器加传动轴的电机驱动风机对循环水回水进行冷却,随着新技术的不断开发,水轮机技术应用到循环水系统中,可充分利用循环水系统富余回水位差势能,采用混流式可调速水轮机代替传统的电动机带动风机转动,取代了电机等设备,不需电量消耗,适用水头范围广、结构简单、运行可靠,在保证冷却效果、确保平稳生产的同时,达到了良好的节能效果。     

冷却塔内小型混流式水轮机的设计及数值模拟

为减少冷却塔内小型混流式水轮机生产工艺过程的复杂性和较高的制造成本,以水动风机冷却塔内流量为3 000 t/h的小型混流式水轮机为研究对象进行结构设计。通过CFD对设计后的水轮机模型进行全流道三维定常湍流数值模拟,数值模拟中采用单方程Spalart-Allmars湍流模型,假定水流为不可压缩流体,不考虑能量方程,仅将质量守恒和动量守恒作为控制方程。结果表明,所设计的小型混流式水轮机整体流态较好,水力性能稳定,在设计转速149 r/min时,流量和出力均达到了驱动冷却塔内风机的要求,且水轮机效率较高。     

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.