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《锅炉技术》2015,(6)
通过研究燃煤电站深度余热利用系统的变工况特性,以探究深度余热利用系统在变工况条件下节能效果的变化规律和原因。以某典型超超临界机组为案例,通过热力学计算与分析,定量分析机组节能效果及其变化情况,详细分析各因素对节能效果的影响。研究结果表明:从节能效果规律上看,深度余热利用系统在各负荷下均呈现较为理想的节能效果,并且在较高负荷时节能效果更稳定,在较低负荷下,随着负荷降低,节能效果呈现缓慢下降趋势。以案例机组为例,设计工况下节能效果达到3.27 g/(kW·h),随着负荷降低至90%、75%和50%,节能效果分别降至3.26 g/(kW·h)、2.94 g/(kW·h)和2.62 g/(kW·h)。进一步分析表明产生这种变化的主要原因在于低负荷时单位燃料的回收余热量和烟气流量均出现大幅下降,导致旁路烟道内烟气流量和烟气温度出现较大下降,进而导致深度余热利用系统最终节能效果出现明显下降的趋势。 相似文献
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为了探讨0号高压加热器和外置蒸汽冷却器在不同布置方式、不同负荷和不同外置蒸汽冷却器给水质量流量下的节能效果,利用Ebsilon软件对某660 MW机组进行分析。结果表明:当系统增设0号高压加热器时,75%THA和50%THA负荷下,给水温度分别提高23.2 K和21 K,热耗分别降低约31.2 kJ/(kW·h)和35.8 kJ/(kW·h);当利用三抽蒸汽过热度加热给水时,进入省煤器的给水温度可提升约3.2 K,100%THA、75%THA和50%THA负荷下的热耗分别降低10.7 kJ/(kW·h)、10.8 kJ/(kW·h)和13.7 kJ/(kW·h);同时增设0号高压加热器和外置蒸汽冷却器时,在75%THA和50%THA负荷下,热耗分别降低约40.6 kJ/(kW·h)和48.2 kJ/(kW·h),机组在低负荷下经济性有所提高。 相似文献
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为进一步降低尿素热解SCR脱硝系统能耗,提高机组效率,以满足我国电力生产过程中的节能环保要求。基于常规脱硝系统的基础上,提出一种新型尿素热解SCR脱硝系统,该系统在烟道中设置分割烟道,增设高温一次风加热器与省煤器并联,通过烟气加热的方式取代了常规的电加热和蒸汽加热一次风的方式。结合国内某1 000 MW机组,从热力学角度分析了系统节能降耗特性。结果表明:与现有的尿素热解SCR脱硝系统中的电加热和蒸汽加热相比,标准煤耗分别降低0.43g/(kW·h)和0.13g/(kW·h),脱硝系统年折算成本分别降低127.4万元和37.4万元,节能效果和经济效益显著。 相似文献
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《动力工程学报》2017,(4):321-328
以某600MW超超临界燃烟煤机组为对比机组,对常规低温省煤器、低温省煤器前移和旁通烟道3种锅炉尾部烟气余热利用系统进行了热经济性与技术经济性比较.结果表明:回收锅炉排烟由122℃降温至90℃的余热,3种系统可使机组供电标准煤耗分别减小1.51g/(kW·h)、1.71g/(kW·h)和2.81g/(kW·h),需分别投资1 125万元、1 940万元和1 685万元,动态投资回收期分别为4.42a、8.66a和3.29a;低温省煤器前移对机组供电效率的提高不明显,但因应用水媒式空气预热器,受热面投资显著增大,因而技术经济性欠佳;由于节能效果显著,旁通烟道表现出最优的热经济性和技术经济性,建议对其进一步研究和推广应用. 相似文献
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烟气余热回收是提高燃煤电站运行效率的有效手段。本文建立了某600 MW机组烟气余热回收系统的变工况计算模型,获得了环境温度、设计参数和运行参数对系统变工况运行特性的影响规律,提出了运行参数优化与构型在线调整相结合的优化策略:在环境温度较高时采用系统构型自适应策略,在环境温度较低时采用系统构型自适应结合参数调控策略。研究结果表明:优化后,系统在运行范围内的平均节煤率达到了2.72 g/(kW·h),相比原系统平均节煤率仅降低了0.3 g/(kW·h),安全运行的环境温度下限由24℃扩展至-10℃。 相似文献
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以某发电厂2台600 MW燃煤纯凝亚临界机组为例,阐述了燃煤电厂CO_2排放量的测算方法,并测算出2010年至2104年全厂CO_2排放量。通过碳氧化率、脱硫效率等因素的研究,分析了碳减排的可能性。研究发现,2010年至2014年该厂燃煤CO_2排放量占全厂CO_2排放量98%以上,飞灰含碳量是影响机组供电煤耗的关键因素。全厂飞灰含碳量提高0.76%~52.7%时,供电煤耗提高0.44 g/(kW·h)~2.29 g/(kW·h)。当以飞灰含碳量降低幅度最小为例,供电量接近时,全厂1年CO_2减排量可达到约8 000 t。 相似文献
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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 相似文献
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A. d’Hueppe M. Chandesris D. Jamet B. Goyeau 《International Journal of Heat and Mass Transfer》2012,55(9-10):2510-2523
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. 相似文献
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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. 相似文献
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The consequences of using a fin collector in focusing solar collectors is examined and is found to have merits. 相似文献
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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. 相似文献
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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. 相似文献
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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. 相似文献
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A simulation study on the possibility of the utilization of cyclohexane as a vector for hydrogen storage in transport vehicles equipped with hydrogen engine has been carried out. The results of this study for the Pd/Al2O3 catalyst indicate that a dehydrogenation multi-tube reactor for cyclohexane is feasible. Nevertheless, a good heat transfer, which is a limiting factor of the process, has to be assured. To heat this reactor, part of the hydrogen combustion energy normally wasted by the engine cooling system can be used. A system of heat pipes was proposed to transfer the waste heat from the wall of engine cylinders to the wall of the dehydrogenation reactor. 相似文献