基于改进超螺旋算法的过热汽温滑模控制

针对火电机组过热汽温被控对象的大惯性、大迟延及动态模型随负荷变化而变化等特性,将滑模变结构控制应用到串级过热汽温系统中。为了减小外部扰动带来的稳态误差和减弱滑模存在的抖振现象,引入积分环节,并采用改进超螺旋算法来代替切换控制,设计了一种新型滑模控制方法。同时在Simulink仿真工具下对过热汽温系统的高阶模型进行阶跃响应、模型参数失配和鲁棒性仿真试验。结果表明:与一般串级PID控制相比,本文方法的控制动态性能效果更好,调节时间和超调量得到显著改善,鲁棒性更强。     

基于神经网络的超临界机组过热汽温设定值优化补偿

基于历史运行数据对过热器喷水减温系统特性进行神经网络建模,在不改变机组原过热汽温控制逻辑和PID参数的前提下,采用基于预测模型的前馈补偿和反馈补偿相结合的策略,在控制回路的顶层对过热汽温设定值进行实时优化补偿,以改善过热汽温控制效果,并借助600 MW超临界机组仿真机进行仿真试验研究.结果表明:采用设定值优化补偿方案可明显提升过热汽温的控制品质,验证了优化方案的有效性.     

基于机理模型的汽温控制系统优化及应用

针对火电机组过热汽温控制的难点和要求，常规串级控制系统无法达到良好控制效果，尤其在大范围变负荷过程中很难控制汽温动态偏差在要求范围内。分析了基于机理模型的双回路汽温控制原理和控制参数整定方法，并对控制方案进行优化。应用于某300 MW CFB机组过热汽温控制，结果表明其稳态和动态控制品质良好，并能适应机组大范围变负荷需要。由于控制方案能够灵活配置汽温控制中惰性区传递函数时间常数和对控制器参数进行增益调整，因此在工程应用中具有很好的推广作用。     

超临界火电机组主蒸汽温度控制算法研究

针对火电机组主蒸汽温度控制系统的大惯性和大时滞特性,将线性自抗扰控制、经典串级PID控制、微分先行控制策略、史密斯(Smith)预估控制等几种温度控制方案的控制效果进行仿真对比。仿真结果表明:经典串级PID控制策略的控制效果差;微分先行(D-PI)控制策略的响应速度快,但鲁棒性差;Smith预估算法能够小幅改善主控制器的控制效果,但效果不够好;线性自抗扰控制策略的控制效果较好、抗干扰能力较强、鲁棒性较强。在面对主蒸汽温度控制问题时,线性自抗扰控制是一种能够替代传统控制策略的合理、有效的选择。     

一种设计模糊-PID复合控制器的新方法及其在电厂控制中的应用

为提高大型火电机组过热蒸汽温度串级控制的性能，提出了一种新型模糊-PID复合控制器的设计方法。该方法可实现在偏离工作点较远的区域模糊控制中起主要控制作用，在工作点附近则主要实施PID控制，实现了两种控制的优势互补，同时还为模糊控制器提供了一种系统化设计方法。实际工业应用结果表明：采用该方法设计的过热蒸汽温度串级控制系统比常规方法设计的系统具有更强的适应能力和良好的控制品质。图9表1参6     

过热汽温系统无记忆状态反馈H_∞鲁棒预测控制

针对火电厂过热汽温大延迟、大惯性和模型不确定等特性,提出了一种多包不确定离散系统的无记忆状态反馈H_∞鲁棒预测控制(HRPC)方法.该方法将鲁棒预测控制、预测控制滚动优化的优点和无记忆反馈控制结合在一起,采用多步控制策略,推导出无记忆状态反馈HRPC的控制律,在不同负荷下对某600 MW机组进行了过热汽温串级控制的仿真实验,并对串级HRPC控制(HRPC-P)与串级PID控制(PID-P)、动态矩阵串级控制(DMC-P)进行比较.结果表明:HRPC-P控制器具有良好的跟踪性能,比PID-P控制器和DMC-P控制器具有更强的鲁棒性,而且减少了控制器优化参数的数量,对工程应用具有一定的参考价值.     

超(超)临界火电机组乘数型协调预测函数优化控制研究及应用

为了提高超(超)临界火电机组协调控制系统控制性能,提出了一种乘数型预测函数控制方法,设计了带扰动信号的乘数型预测函数最优控制律,并将预测函数控制系统与优化控制方法应用于超超临界机组主汽压力与过热汽温控制回路。将汽轮机调门指令和给煤量指令作为主汽压力预测系统的一种扰动信号进行控制,计算出给水优化指令,叠加前馈信号后作用于整个系统;将给水量指令作为过热汽温预测系统的一种扰动信号进行控制,计算出给煤量优化指令,叠加前馈信号后作用于整个系统。结果表明:对于三输入三输出的超临界机组来说,该方法有效地解决了系统的耦合问题,工程实践证明了其良好的应用前景。     

过热汽温多模型预测函数控制策略的研究

过热汽温系统是典型的大时延、大惯性对象,尤其当机组负荷变化时,参数表现出明显的时变特性,大大降低了传统PID串级控制的品质。基于此点,提出先进的多模型切换的过热汽温预测函数控制策略。使用带有Smith预估补偿思想的一阶时滞对象预测函数控制算法,来有效克服对象的大时延、大惯性;并通过建立若干典型工况的固定模型,在线计算其模型匹配度确定控制权重,从而得到控制器的输出的方法,能适应参数的时变。与PID串级控制和单一模型控制的仿真结果对比,证实了本控制策略的有效性。图3表1参8     

面向对象的火电厂主汽温控制方法

大型火电机组主汽温对象具有明显的滞后性、非线性、时变性的特点,采用常规PID串级控制主汽温效果欠佳,提出了面向对象的主汽温控制策略,及汽温对象由扰动通道类、调节通道类及任务处理类三大类子对象组成.以工程实例证明了任务处理类子对象算法对汽温变化的可控性.实践表明:新型控制算法具有较好的控制品质和鲁棒性,且有较强的抗干扰能力,实现了控制过程的零手动、零超温和高品质.     

基于TD—PLS模型预测前馈的垃圾焚烧锅炉脱酸自动控制策略研究与应用

针对垃圾焚烧锅炉半干法脱酸系统自动控制投运率低、控制效果差的问题,在分析脱酸系统运行特性的基础上,设计了一种以PID控制和模型预测前馈相结合的HCl-SO₂协同控制策略。采用以HCl排放浓度作为主要控制目标,SO₂排放浓度作为次要目标的串级PID协同控制策略。在串级PID控制的基础上,基于时间差分偏最小二乘法(TD—PLS)建立HCl排放浓度预测模型作为控制前馈。该控制策略应用于某500 t/d垃圾焚烧机组脱酸系统,实际应用效果表明：脱酸控制投入前,HCl排放浓度波动变化较大,小时排放均值范围20～40 mg/m³,小时排放均值浓度相对标准偏差(RSD)为15.95%。脱酸自动控制投入后,HCl小时排放均值范围在25～30 mg/m³,小时排放均值浓度RSD为6.22%。在协同控制作用下,HCl小时排放均值波动显著减小,单位锅炉蒸发量的石灰浆液消耗量由0.034 m³/t降低到0.027 m³/t,相比投运前降低了21%,在保证出口HCl和SO_2...     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

The Solar Office in context

The goal of sustainability in buildings can only hope to be realised if buildings are designed to both conserve and generate energy. The Solar Office at Doxford International is designed to minimise the use of energy while its external fabric is designed to replace such energy that is used. The recently completed building is now subject of a comprehensive monitoring programme. The programme covers both the performance of the 73 kW_p photovoltaic installation and the environmental conditions within the building as a whole. Hour by hour findings are posted on a dedicated web site. Photovoltaics could have the same impact on building form and layout as the invention of the passenger lift at the end of the last century.     

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。     

Hydrogen recovery from the photovoltaic electroflocculation-flotation process for harvesting Chlorella pyrenoidosa microalgae

In this paper, an integrated process using photovoltaic power to harvest microalgae by electro-flocculation (EF) and hydrogen recovery is presented. It is mainly favorable in regions with high solar radiation. The electro-flocculation efficiency (EFE) of Chlorella pyrenoidosa microalgae was investigated using various types of electrodes (aluminum, iron, zinc, copper and a non-sacrificial electrode of carbon). The best results regarding the EFE, and biomass contamination were achieved with aluminum and carbon electrodes where the electrical energy demand of the process for harvesting 1 kg of algae biomass was 0.28 and 0.34 kWh, respectively, while the energy yield of harvested hydrogen was 0.052 and 0.005 kWh kg^?1, respectively. The highest harvesting efficiency of 95.83 ± 0.87% was obtained with the aluminum electrode.The experimental hydrogen yields obtained were comparable with those calculated from theory. With a low net energy demand, microalgae EF may be a useful and low-cost technology.