基于分支限界法的火电机组负荷分配研究

针对大规模新能源并网调峰问题,提出不同调峰阶段火电机组负荷分配方法：分析火电机组调峰能力、调峰成本及二者之间的关系;以总煤耗成本、机组启停成本之和最小为目标,建立不同调峰阶段火电机组负荷分配优化模型;根据火电机组爬坡率、滑坡率,提出参与负荷分配机组的组合策略,并使用分支限界法对负荷分配优化模型求解。算例表明,随着火电机组调峰深度的增加,机组煤耗成本和启停成本减少,深度调峰运行下附加煤耗成本和机组损耗成本增加。     

600MW火电机组低负荷调峰的经济运行方式分析

随着电网峰谷差的日益增大,600MW火电机组调峰是其必然趋势。提高调峰机组低负荷运行的经济性,是目前亟待解决的问题。从最优化的角度出发,对600MW汽轮机低负荷调峰运行中火电机组之间负荷的优化分配、汽轮机循环水系统运行方式的优化和配汽方式的优化方法进行分析,给出了通过改变运行方式指导调峰机组低负荷经济运行的具体方法。     

大型火电机组优化运行技术的研究

提出了大型火电机组负荷优化分配技术和运行优化技术。介绍了大型火电机组的负荷优化分配的数学模型、求解技术以及大型火电机组运行优化的关键技术，给出了黄台发电厂的应用实例。     

基于飞蛾火焰优化算法的火电调峰负荷分配研究

在分析火电调峰成本的基础上,以调峰成本最小化为目标构建了火电调峰负荷分配模型,引入飞蛾火焰算法作为模型求解方法,以重庆电网为例,共设定3种负荷分配场景,同时以粒子群算法和蚁群算法求解效果与飞蛾火焰算法对比,验证了模型及求解算法的高效性和合理性。结果表明：3种场景下,随着调峰需求的增加,优化过程中需要部分机组进行深度调峰和启停调峰才能满足调峰需求,优化后系统调峰总成本分别达到了1 976万元、2 645万元和3 287万元;3种算法求解过程中,飞蛾火焰优化算法收敛速度更快,求解效率更高,且经飞蛾火焰优化后的系统调峰总成本最低,相比传统优化算法具有更强的规避局部最优解能力。     

330 MW火电机组深度调峰下AGC控制及优化

通过对火电机组实际运行情况的综合分析,得知深度调峰模式下火电机组会频繁出现负荷指令变化等问题,且负荷变化波动大。由于传统PID控制回路响应能力较差,无法满足深度调峰模式下宽负荷段响应需求,导致单元机组协调控制系统各种弊端逐渐显现,如滞后大、多变量等。文章提出一种基于330 MW火电机组深度调峰下的AGC控制及优化方案,根据机组所涵盖各控制系统的动态特征,再利用多变量模型辨识技术,搭建机组动态特性模型,获取最佳运行参数,为优化火电机组重要控制系统提供参考依据,以增强整个火电机组响应能力,实现AGC长期稳定运行。     

考虑需求响应与火蓄调峰的优化调度模型研究

为了应对风电等可再生能源接入引起的系统调峰压力增大且影响系统经济运行的问题,进一步挖掘新型调节电源、传统调节电源和负荷侧协同调峰的潜力,综合利用负荷侧的需求响应和电源侧的抽水蓄能、火电三种调峰措施联合调峰,构建考虑需求响应和火蓄参与深度调峰的电力系统两阶段优化调度模型。第一阶段优化模型中引入负荷侧的需求响应,以最小化负荷与风电差值的平方之和为目标,优化负荷曲线,降低系统峰谷差;第二阶段优化模型利用电源侧的抽水蓄能和火电深度调峰,计及火电深度调峰电量损失成本、抽蓄调峰成本和弃风成本,以系统总运行成本最小为目标,在第一阶段模型的基础上优化各机组出力,增加风电上网空间。以改进的IEEE30节点系统进行算例分析和两阶段优化模型有效性验证,结果 表明,所建模型可提高调峰能力,促进风电消纳,并降低系统总运行成本。火电机组进一步降低出力,积极参与深度调峰,能够有效促进系统风电消纳。三种调峰方式有机结合联合参与调峰,降低了负荷的峰谷差,不仅有效降低了弃风率,还减轻了系统的调峰压力,缩短了火电深调时段。     

燃气-蒸汽联合循环调峰电厂的运行优化改造

在发电机组之间合理分配发电负荷能够提高电厂运行的经济性,从上海某调峰电厂发电机组的配置现状出发,建立机组负荷优化分配的数学模型,继而建立负荷优化分配的动态规划求解模型及求解策略,可获得不同中调发电量下发电机组最佳的负荷分配方案。利用该调峰电厂发电机组的负荷效率特性曲线,采用动态规划优化方法对其原有机组负荷分配方案进行优化,改造后机组的实际运行效果表明：该方法能够获得最佳的发电负荷分配方案,使得该调峰电厂的综合发电效率得到提升,达到运行优化和节能的目的。     

火电厂调峰机组运行经济性研究

本文分析了低负荷运行方式电厂调峰机组间负荷优化分配原理,给出了负荷优化分配通用计算程序。对负荷经济调度出现的问题作了讨论,并以诧城电厂为例,进行了具体计算,给出了低负荷运行调峰时其负荷优化分配曲线。     

1000MW超超临界机组变负荷关键参数性能分析及优化

随着我国新能源的快速发展,火电机组参与深度调峰成为常态化,然而机组低负荷运行时往往会偏离最优运行工况,因此研究低负荷下多参数热力耦合特性以及控制策略优化能有效地改善火电机组的经济性能。本文分析研究了低负荷下汽轮机关键热力参数对机组的效率、热耗率以及节能量等多个变量的影响,优化了机组滑压运行曲线并确定了控制策略优化方案,提高了机组经济性能,具有很重要的学术意义和工程实用价值。     

大型燃煤火力发电机组调峰优化控制技术

调峰优化控制可以使得电网的源荷供需处于平衡状态,对提高火力发电机组调峰的稳定性至关重要。为此,提出一种大型燃煤火力发电机组调峰优化控制技术。构建爬坡压力缓解的目标函数,通过对火电机组、失负荷、储能以及光伏发电进行约束,以缓解爬坡压力。构建火力发电机组调峰优化控制的目标函数,结合火力发电机组在运行功率、功率平衡、启停机时间等方面的约束,实现了大型燃煤火力发电机组的调峰优化控制。实验结果表明,文中技术能够缓解大型燃煤火力发电机组的爬坡压力,优化了响应速度。通过所提技术的调峰优化实现了火力发电稳定运行,顺利完成调峰任务。     

Matching of a DC motor to a photovoltaic generator using a step-upconverter with a current-locked loop

A photovoltaic (PV) generator is a nonlinear device having insolation-dependent volt-ampere characteristics. Because of its relatively high cost, the system designer is interested in optimum matching of the motor and its mechanical load to the PV generator so that maximum power is obtained during the entire operating period. However, since the maximum-power point varies with solar insolation, it is difficult to achieve an optimum matching that is valid for all insolation levels. In this paper it is shown that for maximum power, the generator current must be directly proportional to insolation. This remarkable property is utilized to achieve insolation-independent optimum matching. A shunt DC motor driving a centrifugal water pump is supplied from a PV generator via a step-up converter whose duty ratio is controlled using a current-locked feedback loop     

Studies on a two-staged micro-combustor for a micro-reformer integrated with a micro-evaporator

A new micro-combustor configuration for a micro fuel-cell reformer integrated with a micro-evaporator is studied experimentally and computationally. The micro-combustor as a heat source is designed for a 10–15 W micro-reformer using the steam reforming method. In order to satisfy the primary requirements for designing a micro-combustor integrated with a micro-evaporator, i.e., stable burning in a small confinement and maximum heat transfer through a wall, the present micro-combustor is a simply cylinder, which is easy to fabricate, but is two-staged (expanding downstream) to control ignition and stable burning. The aspect ratio and wall thickness of the micro-combustor substantially affect ignition and thermal characteristics. For optimized design conditions, a pre-mixed micro-flame is easily ignited in the expanded second-stage combustor, moves into the smaller first-stage combustor, and finally is stabilized therein. The measured and predicted temperature distributions across the micro-combustor walls indicate that heat generated in the micro-combustor is well transferred. Thus, the present micro-combustor configuration can be applied to practical micro-reformers integrated with a micro-evaporator for use with fuel cells.     

Using a fin with a parabolic concentrator

The consequences of using a fin collector in focusing solar collectors is examined and is found to have merits.     

Natural convection of a non-Newtonian fluid about a horizontal cylinder and a sphere in a porous medium

The problem of natural convection of a non-Newtonian fluid about a horizontal isothermal cylinder and an isothermal sphere in the porous medium is considered. The present study is based on the boundary layer approximation and only suitable for a high Rayleigh number. Similarity solutions are obtained by using the fourth order Runge-Kutta method. The effects of the wall temperature T_W and the new power-law index n on the characteristics of heat transfer are discussed.     

Bioconvection in a squeezing flow of a micropolar fluid in a horizontal channel

The bioconvection flow of an incompressible micropolar fluid containing microorganisms between two infinite stretchable parallel plates is considered. A mathematical model, with a fully coupled nonlinear system of equations describing the total mass, momentum, thermal energy, mass diffusion, and microorganisms is presented. The governing equations are reduced to a set of nonlinear ordinary differential equations with the help of suitable transformations. The resulting nonlinear ordinary differential equations are linearized using successive linearization method, and the resulting system of linear equations is solved using the Chebyshev collocation method. The detailed analysis illustrating the influences of various physical parameters, such as the micropolar coupling number, squeezing parameter, the bioconvection Schmidt number, Prandtl numbers, Lewis number, and bioconvection Peclet number on the velocity, microrotation, temperature, concentration and motile microorganism distributions, skin friction coefficient, Nusselt number, Sherwood number, and density number of motile microorganism, is examined. The influence of the squeezing parameter is to increase the dimensionless velocities and temperature and to decrease the local Nusselt number and local Sherwood number. The density number of motile microorganism is decreasing with squeezing parameter, bioconvection Lewis number, bioconvection Peclet number, and bioconvection Schmidt number.     

Coupling a two-temperature model and a one-temperature model at a fluid-porous interface

We study a convective heat transfer problem in a fluid-porous domain in the case of the local thermal non-equilibrium assumption (LTNE). The issue of this study is to determine appropriate boundary conditions to model heat transfer, while using models with a different number of equations: a two-temperature model in the homogeneous porous region versus a one-temperature model in the free region. To proceed, a two-step up-scaling approach is used, which has the particularity to provide closed jump relations depending on intrinsic characteristic of the interface. Thus, the use of jump or continuity conditions depend only on the interface location inside the fluid-porous transition region. The pertinence of the approach is illustrated on a 2D convective heat transfer problem considering a solid heat source in the porous medium.     

Comparative analysis of a Sisko nanofluid over a stretching cylinder through a porous medium

The present article examines the Sisko nanofluid flow and heat transfer through a porous medium due to a stretching cylinder using Buongiorno's model for nanofluids. Suitable similarity transformations are used to transform the governing boundary layer equations of fluid flow into nonlinear ordinary differential equations. The finite difference method is used to solve coupled nonlinear differential equations with MATLAB software. The impact of different parameters viz., the Sisko material parameter, porosity parameter, curvature parameter, thermophoresis parameter, and Brownian diffusion parameter on the velocity and temperature distribution are presented graphically. Moreover, the effect of the involved parameters on the heat transfer rate is also studied and presented through table values. It is noticed from the numerical values that the porosity parameter reduces the velocity while enhancing the temperature. The curvature parameter enhances the velocity throughout the fluid regime and reduces the temperature near the surface while enhancing the temperature far away from the surface. The study reveals that the thermophoresis and Brownian diffusion parameters that characterize the nanofluid flow reduce the wall heat transfer rate, while the curvature parameter enhances it. This investigation of wall heating/cooling has essential applications in solar porous water absorber systems, chemical engineering, metallurgy, material processing, and so forth.     

Exploration of heat transfer effect in a magnetohydrodynamics flow of a micropolar fluid between a porous and a nonporous disk

An analysis is carried out for the flow characteristics of a conducting micropolar fluid. The fluid was passed in between two parallel disks of infinite radii. The novelty of the study is to consider one of the disks as porous and the other one as nonporous, and the external magnetic field is applied along the transverse direction of the flow. The flow phenomena for the polar fluid characterized by the magnetic effect in conjunction with the temperature equation reduce to a set of coupled nonlinear ordinary differential equations using the requisite transformations and nondimensionalization. An analytical approach such as the variation parameter method is employed to tackle the system efficiently. To emphasize the effect of various physical parameters contributing to the flow phenomena, that is, non-zero tangential slip, Reynolds number, Prandtl number, magnetic parameter, and material parameter on the flow profiles of axial and radial velocities, the microrotation and temperature profiles are presented graphically. To validate the simulated results, a comparison with established results is made, and it is concluded that both are in good correlation.     

Evaporating characteristics of a microlayer under a bubble

Using the Hallinan‐Ervin model, the flow and evaporation in a bubble microlayer were theoretically analyzed, and the dryout characteristics and Staub's criterion were discussed in detail. It was revealed that the critical dryout radius is associated with the wettability of the heated surface, and that the dominant role for microlayer evaporation is disjoining pressure, not surface tension gradient. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(6): 456–462, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10052