【作者】 周新平；

【导师】 杨家宽； 肖波；

【作者基本信息】 华中科技大学 ， 环境工程， 2008， 博士

【摘要】 太阳能烟囱发电技术是一种适宜大规模发电的热气流发电技术。我国特别是人烟稀少的西部地区具有发展大规模太阳能发电系统的优势:广袤的荒地、巨大的山体高差、丰富的太阳能资源和日较差资源。太阳能烟囱热气流利用系统在西部地区有极大的应用潜力。然而,太阳能烟囱发电技术能量转换效率低、投资大、安全可靠性难以保证,至今仍未建成商业性电站,其基础研究及应用模式都有待深入研究。因此,研究和开发综合成本低、运行维护方便、适合西部地域特征的太阳能热气流发电系统服务于西部能源与生态环境的改造具有巨大潜力和现实意义。本文主要研究了基于西部特征的太阳能烟囱发电技术,重点开展了以下两方面的研究。(1)建造了国内第一套小型太阳能烟囱发电实验原型,并展开了相应的实验及数值模拟的基础研究。设计并建造了一套集热棚直径10 m,烟囱高8 m的小型太阳能烟囱发电实验原型,并开展了实验研究。实验结果表明:在集热棚内,从入口向中部汇集过程中,空气温度逐渐升高,速度先减后增,在烟囱内,随着高度增加,空气温度略有降低;不同天气条件下,棚内空气温度较高,晴天、阴天温升可达到20 K和10 K以上,集热棚有较好的温室效应;在早上,烟囱口附近出现逆温层,而且逆温层持续时间随太阳辐射增强而变短,逆温层的出现将使得太阳能烟囱发电系统运行较为困难。太阳能烟囱热气流发电系统中的流动和换热模型解析以及模型应用尚待明确的问题主要集中在空气可压缩性问题、集热棚内对流换热系数确定、涡轮处压降因子确定、涡轮发电机组模拟及效率问题、商业化CFD软件自带浮升力模型模拟问题等。针对以上问题,本论文开展了三类太阳能烟囱发电系统的数值模拟方法。编写了SIMPLE类算法三维数值模型,用于对发电系统进行三维模拟,方便研究者自行调节。通过编写UDF定义流体密度和精确的浮升力项,对Fluent软件进行了二次开发,构建一套三维可压缩流浮升力模型,成功地克服了因商业化CFD软件自带浮升力模型假设过多的缺点而引起解的偏差较大的问题。编写了“1+1”维可压缩流数值模型,通过联合热网方程求解。该模型包括了主要的流动阻力、涡轮处的压降和温降、随高度而变的大气压力和温度、集热棚内空气的混合流(自然对流和强迫对流)等。该模型假设较少,基本上解决了现有模型应用中尚需明确的问题。通过将以上模型模拟的结果与实验数据或权威模型的计算结果比较,分别验证了以上模型。这些模型为后续的研究创造了条件。讨论了采用商业化CFD软件自带的浮升力模型——Boussinesq近似浮升力模型和全浮升力模型模拟大规模太阳能烟囱发电系统的准确性。结果表明:以高1500 m、直径160 m的大型烟囱为例,全浮升力模型和Boussinesq近似浮升力模型造成的发电量的偏差分别达到42%倍和33%倍。通过利用“1+1”维可压缩流数值模型进行计算,探讨了太阳辐射强度、结构参数对太阳能烟囱系统性能的影响规律。结果表明:太阳能烟囱系统的发电功率随太阳辐射强度、烟囱高度或棚直径的增加而增加。(2)基于分析西部地域特征,提出了几种不同的太阳能烟囱热气流利用模式,并对大规模漂浮烟囱的经济性进行了分析,探讨了大型太阳能烟囱对局部气候的影响。结合我国西部地域特点,提出了不同的太阳能热气流利用模式。首次提出了太阳能烟囱直接抽取地下水的概念,设计了太阳能烟囱直接抽取地下水模型,分析了在我国西北边远地区,利用中小规模太阳能烟囱热气流系统抽取地下水提供生活用水和农业灌溉用水的可行性和经济性,结果表明:中小规模太阳能烟囱热气流系统在电网输入困难且风力资源贫乏的偏远山区有很大的应用潜力。讨论了太阳能烟囱热气流抽水装置的额定驱动功率与服务人口规模和地下水源的关系。介绍了三类结合山体的复合式太阳能烟囱发电系统的特性,从效率、建造难度、成本、安全等方面研究和评价了这三类山体复合式烟囱发电系统。和同纬度的传统竖直烟囱系统相比,斜坡集热棚式系统的效率最高,45°倾角的斜坡集热棚式系统的效率提高了近40%,建造在15°倾角山脚上斜烟囱式和山洞烟囱式系统的效率提高了近20%。与高大山体结合的三类复合式发电系统可行性大、“烟囱”高、安全性好、投资较低,有效地解决了超高竖直烟囱带来的安全问题以及投资太大等问题。对大气风力作用下的漂浮烟囱进行了受力平衡分析,讨论了大气风力和净浮力对发电功率的影响规律。结果表明:大气风力越大或净浮力越小,烟囱偏角将越大,发电功率将越小。漂浮烟囱更适用于大风不频繁的地区,地面主风均速在3.5 m/s以下是比较适宜的条件。构建了一套经济学模型,估算了大规模漂浮烟囱发电系统的最低销售价格,表明了在考虑温室气体的减排效益且获得低利率贷款情况下,200 MW以上大规模漂浮烟囱发电系统的电力最低销售价格低于0.58元/kW·h,可与火力发电水平相当。对大型太阳能烟囱出口暖湿气流在高空冷大气中的对流和换热过程进行了数值模拟研究。首次提出了大型太阳能烟囱可能影响局部气候。进一步探讨了降水的可能性和降水强度随着烟囱结构参数、气象条件的变化规律,并讨论了降水机会增加而产生的环境、经济效益。结果表明:烟囱越高,相对湿度越大,或大气风速越小,降水的可能性和降水强度越大;水汽冷凝过程中释放出的潜热促进来流继续上升,从而增大降水面积。本论文的研究成果为太阳能烟囱电站在我国西部地区的实际建立和优化设计提供了一定的理论上的依据和指导。更多还原

【Abstract】 Solar chimney power system (SCPS) is a thermal system that is suitable for large-scale power generation. There are vast desertified regions, high-fall mountains, abundant available solar radiation, and large diurnal temperature in Western China where SCPS has large potential of application. However, the energy conversation efficiency of SCPS is low, its investment is large, and its safety is not good. By now, any commercial power plant has been not built up. Further study on fundamental problems and application of SCPS can be performed. It is significant to develop cost-effectiveness SCPS adapting to the local topography in Western China to supply energy.The dissertation is studying SCPS and its application in Western China and divided into the following two sections.The first section: A testing prototype of SCPS is built and the experimental and theoretical investigations of SCPS are performed.A testing prototype of SCPS is designed and built in China, which has a collector 10 m in diameter and a chimney 8 m high. Experimental investigation of SCPS is performed. The results show that the temperature of air increases along a radius from the inlet to the outlet, the velocity of air firstly decreases and then increases, the temperature of air decreases with heights in the chimney, the temperature rise in the collector reaches more than 20 K in a sunny day and 10 K in a cloudy day, a temperature inversion occurs around the chimney outlet in the morning and its duration decreases with higher solar radiation, and temperature inversion will block the operation of SCPS.The problems of the models modeling the flow and heat transfer in SCPS include compressibility, convective heat transfer between the flow and the ground, pressure drop coefficient, turbine efficiency, simulation using commercial computational fluid dynamics (CFD) software. As for the above problems, three numerical simulation models are developed to simulate the flow and heat transfer in SCPS. A 3D code is written in C based on SIMPLE algorithm. This code written can be free adjusted by the researcher. The CFD programme Fluent is re-developed by introducing functions of accurate density and buoyancy, which improves the inaccuracy of simulation using the buoyancy models automatically included in CFD programmes where some crucial assumptions are made. A‘1+1’dimensional compressible flow code is written by Matlab. In the model, natural and forced convection effects is considered for convection between the air flow and the ground and that between the air flow and the collector roof, flow resistance in the collector and chimney, and the pressure drop and temperature drop at the turbines are included, the ambient pressure and temperature changes with heights. This model has few assumptions and is more realistic, which solves the above problems of other models modeling the flow and heat transfer in SCPS.All the modes are validated by the comparisons of the simulation and the measurements or the calculation using the authoritative model. The deviation of the simulated results using the re-developed buoyancy model and the results using the buoyancy models (i.e. Full buoyancy model and Boussinesq model) automatically included in CFD programmes in a proposed 1500 m high solar chimney is estimated. The results show that Full buoyancy model and Boussinesq model give 42% and 33% times more power respectively than our model. Then, the influence of different solar radiations and dimensions on the power output are analyzed by using the‘1+1’dimensional compressible flow code, respectively. The results show that the power capacity of SCPS increases with the increase in solar radiation, chimney height, or collector diameter.The second section: Adapting to the special topography in Western China, various solar chimney thermal systems are proposed, economic analysis of large scale SCPS and its influence on local climate are performed, respectively.A concept of solar chimney groundwater pumping is first proposed and the solar chimney groundwater pumping system (SCGPS) is designed. The feasibility and economics of the use of small and mediumsmall scale SCGPS for driving to pump groundwater for drinking and agricultural use are discussed. The results show that the small and mediumsmall scale SCGPS has large potential at the remote villages where grid electricity is not reached and wind is plain. The relation of driving power capacity of SCGPS and its service scope and the depth of groundwater is investigated. The performances of three combined power systems with mountains are investigated. The performances of the three combined power systems with high mountains are analyzed by comparing their efficiency, building difficulty, investment, safety and the likes. The efficiency of the sloped collector system is the highest. The efficiency of the sloped collector system with 45°inclination mountain-side is about 40% more than, and the efficiencies of the sloped chimney system and tunnel chimney system with 15°inclination mountain foot are about 20% more than the classical system at the same latitude. It’s concluded that compared to the classical reinforced concrete SCPS, the three combined power systems with high mountains are more available and has potential of reaching high height for‘chimney’, good safety and low investment..Force equilibrium of floating solar chimney is established. The influence of wind velocity and net buoyancy of chimney on the power capacity of large scale floating solar chimney power system (FSCPS) are discussed. The analyses show that the optimal condition for floating solar chimney power system is that annual wind velocity is below 3.5 m/s at the ground level. Economic analyses of FSCPS are performed by using the developed economic model including the carbon credits. The results show that the minimum electricity price of more than 200 MW FSCPS under financial incentive of soft loan is less than 0.58 yuan/kWh, which is competitive with coal-fired plant.Flow and heat transfer of the plume from the gigantic chimney in the cross-section atmosphere are simulated. Viewpoint that the gigantic solar chimney is likely to affect the local climate is presented. The influences of chimney height, relative humidity, and wind velocity on the potential precipitation area and precipitation strength are analyzed. Environmental and economic benefits of increasing chance of precipitation around the large scale FSCPS are analyzed. It is concluded that higher chimney, bigger relative humidity of atmosphere, bigger velocity of wind increased the potential precipitation area and precipitation strength. In addition, latent heat produced in condensation process helps rise of plume by heating the plume.The investigation in this dissertation would provide the theoretical basis for the design and construction of solar chimney power plant in Western China, to some extent.更多还原