基于分段式吸热器的塔式太阳能发电性能研究

发布时间：2018-07-02 07:46

本文选题：DSG塔式太阳能 + 分段式吸热器　；参考：《华北电力大学(北京)》2017年博士论文

【摘要】：近年来,随着可再生能源技术在世界范围内的快速发展与推广,直接蒸汽式(Direct steam generation,DSG)塔式太阳能热发电技术由于低成本、高效率的优势在我国受到广泛关注。针对DSG塔式电站定日镜场聚光模式复杂和电站启机耗时过长的问题,本论文根据水/蒸汽传热流体蒸发和过热过程的传热特性,提出一种由外置式吸热器(蒸发段)和腔式吸热器(过热段)所组成的分段式吸热器,并基于该分段式吸热器的独特结构展开电站系统集成设计与热经济性仿真研究。基于分段式吸热器结构建立定日镜场聚光模型并分析其聚光特性。通过聚光热流分配与迭代计算,得到位于西班牙塞维利亚10MWe DSG塔式电站定日镜场最佳设计方案,此时定日镜场整体效率为72.17%,指向蒸发段和过热段的定日镜数量分别为442个和182个,该定日镜场分配方案不仅保证了分段式吸热器表面热流值不超过安全范围,同时可提供蒸发段和过热段各自所需的热量。经计算,年运行工况下,定日镜场效率不完全随着太阳高度角的增加而增加,但全年内分段式吸热器表面最大热流值往往发生在夏至12:00,因此在进行定日镜场和分段式吸热器设计时,需对该时刻下分段式吸热器表面热流进行校验以确保工程安全性。建立分段式吸热器热力模型以揭示其运行特性。设计工况下10MWe DSG塔式电站分段式吸热器的热效率为86.55%。通过与双外置式吸热器进行对比,得到分段式吸热器热效率提高了3.2%,对应发电效率提高了0.88%。不同运行时刻下,尽管蒸发段采用外置式吸热器,但由于其表面温度远低于过热段,蒸发段热效率大于过热段约5%-9%;通过动态分配蒸发段和过热段所分别对应的定日镜数量,可维持分段式吸热器出口蒸汽温度为额定值。不同管外径下,减少蒸发段管外径对提高蒸发段热效率几乎没有影响,原因在于管壁导热热阻为主要热阻;而减少过热段管外径能大大提高过热段热效率,原因在于对流换热热阻为主要热阻,综合考虑管内对流和泵功消耗,过热段管外径存在最优值。基于分段式吸热器建立DSG塔式电站系统集成模型并对其热经济性进行讨论。在额定发电功率固定为50MWe而土地占用面积可改变的情况下,当太阳倍数和储热时长分别为2.7和9h时,电站标准发电成本(Levelised cost of electric energy,LCOE)最低,为21.4c/k Whe;通过改变电站地理位置可使得年太阳能法向直射辐射强度(Direct Normal Irradiance,DNI)提高55%,电站年发电量提高20.4%,电站最低LCOE降低30.1%,相应的最优太阳倍数降低至2.0;通过逐步改变电站各子系统投资成本进行敏感性分析后得到,最低LCOE受定日镜场和分段式吸热器投资成本变化的影响最大,且最优太阳倍数和储热时长仅随着定日镜场和储热系统投资成本的降低而增加。在土地占用面积固定为4.8km2而额定发电功率可改变的情况下,电站最低LCOE为21.77c/k Whe,对应的太阳倍数为1.7,储热时长为3h;通过改变电站地理位置或电站各子系统投资成本时得到的结论与固定额定发电功率时基本类似,由此可得与电站位置和成本敏感性分析相关的结论通用性较强,受限制域影响不大;通过将固定的土地占用面积由2.15km2逐渐增加至8.11km2时,电站最低LCOE由24.53c/k Whe降低至20.92c/k Whe,但其降低速率在不断减缓,最优太阳倍数和储热时长因电站年发电量和总投资成本变化趋势相对稳定而保持不变。为进一步降低DSG塔式太阳能电站储热系统的投资成本,采用“一步法”制备出比热更高且适用于大规模工程应用的纳米盐复合储热材料。当Cu O纳米颗粒浓度为0.5wt%时,相对于纯二元硝酸盐,纳米盐复合物在液态状态下比热提高率可达到11.48%,其终止熔化温度提高约3℃,因此该纳米盐复合物更适合作为显热储热材料,但在作为显热储热材料时应注意时刻保持其工作温度高于终止熔点,从而防止出现储热材料凝固等安全事故。基于扫描电子显微镜(Scanning Electron Microscope,SEM)图像,推测低浓度Cu O纳米颗粒表面针状纳米结构的半固体层是纳米盐复合物比热提高的原因。通过对该半固体层假设一个合适的比热值,结合修正后的混合物模型,可较为精确地预测低浓度Cu O纳米盐复合物的比热。
[Abstract]:In recent years, with the rapid development and popularization of renewable energy technology worldwide, the direct steam (Direct steam generation, DSG) tower type solar thermal power generation technology has been widely concerned in China because of low cost and high efficiency. In the DSG tower type power station, the light gathering mode of the day mirror field is complex and the power station start time is too long. In this paper, based on the heat transfer characteristics of water / steam heat transfer fluid evaporation and overheating process, a subsection type heat exchanger composed of external heat exchanger (evaporation section) and cavity type heat exchanger (superheated section) is proposed. Based on the unique structure of the segmented type heat exchanger, the integrated design of electric station system and thermal economic simulation study are carried out. The optimum design scheme of the daily mirror field of the 10MWe DSG tower type power station in Seville, Spain, is obtained by the heat flux distribution and iterative calculation. The overall efficiency of the daily mirror field is 72.17%, and the number of the daily mirrors in the evaporation and superheated segments is 442, respectively. And 182, the fixed day mirror field distribution scheme not only ensures that the heat flow value of the subsection heat exchanger does not exceed the safety range, but also provides the heat required for the evaporation section and the overheating section. The maximum heat flow value often occurs at 12:00 in the summer solstice. Therefore, when designing the daily mirror field and the segmented type heat exchanger, it is necessary to check the heat flow of the surface of the subsection type heat exchanger at this time in order to ensure the safety of the project. The thermal model of the segmented type heat exchanger is established to reveal its operating characteristics. The sectional suction of the 10MWe DSG tower type power station under the design condition is designed. The thermal efficiency of the heater is 86.55%. by comparing with the double external heat exchanger, the heat efficiency of the segmented type heat exchanger is increased by 3.2%. The corresponding generation efficiency increases at different time of 0.88%. operation, although the evaporation section uses an external heat exchanger, but because its surface temperature is far below the overheated section, the thermal efficiency of the evaporation section is greater than about 5%-9% of the superheated section. By dynamically assigning the number of the daily mirrors corresponding to the evaporation and superheating segments, the steam temperature of the sectional type heat exchanger can be maintained as the rated value. Under the external diameter of the tube, the reduction of the outer diameter of the evaporation section has little effect on the increase of the thermal efficiency of the evaporation section. The reason is that the heat resistance of the tube wall is the main thermal resistance, and the outer diameter of the tube of the superheated section can be reduced greatly. The heat efficiency of the superheated section is greatly improved because the convection heat transfer resistance is the main thermal resistance, considering the convection and pump power consumption in the tube, the outer diameter of the superheated section has the best value. Based on the subsection type heat exchanger, the DSG tower type power station system integrated model is established and its thermal economy is discussed. The rated power generation power is fixed to 50MWe and the land occupancy surface is fixed. When the product can be changed, the standard generation cost (Levelised cost of electric energy, LCOE) is the lowest when the solar power and the heat storage time are 2.7 and 9h respectively, which is 21.4c/k Whe. By changing the location of the power station, the annual solar method can increase the direct radiation intensity (Direct Normal Irradiance) by 55%, and the annual power generation capacity of the power station is raised. The lowest LCOE of the power station is 30.1%, and the optimal solar power is reduced to 2. The lowest LCOE is affected by the sensitivity analysis of the investment cost of each subsystem of the power station, and the lowest investment cost change of the daily mirror field and the segmental type heat exchanger is the most, and the optimal solar multiple and the heat storage time are only with the setting mirror field and storage. When the land occupied area is fixed to 4.8km2 and the rated power generation power can be changed, the minimum LCOE of the power station is 21.77c/k Whe, the corresponding solar multiple is 1.7 and the heat storage is 3H; the conclusion and the fixed rated power generation by changing the location of the power station or the investment cost of the power stations of the power station are fixed with the fixed rated power generation. When power is basically similar, the conclusion associated with the station location and cost sensitivity analysis is more versatile and less affected by the restricted area. By increasing the fixed land occupancy area from 2.15km2 to 8.11km2, the minimum LCOE of the power station is reduced from 24.53c/k Whe to 20.92c /k Whe, but its reduction rate is slowing down and the optimum is too much. In order to further reduce the investment cost of the DSG tower type solar power plant heat storage system, the "one step method" is used to prepare the nano salt composite heat storage materials with higher specific heat and suitable for large-scale engineering applications. When the Cu O nanoparticle is used. When the concentration is 0.5wt%, compared to the pure two element nitrate, the nano salt complex can increase the ratio of specific heat to 11.48% in liquid state, and its termination melting temperature is about 3 degrees C. Therefore, the nano salt complex is more suitable to be used as a sensible heat storage material, but it should be kept at a time when the temperature is higher than the terminating melting point when it is used as a sensible heat storage material. In order to prevent the occurrence of a safety accident, such as the solidification of the heat storage materials. Based on the scanning electron microscope (Scanning Electron Microscope, SEM) image, it is assumed that the semisolid layer of the needle like nanostructure of the low concentration Cu O nanoparticles is the cause of the increase of the specific heat of the nano salt complex. The mixture model can predict the specific heat of low concentration Cu O nano salt complex more accurately.
【学位授予单位】：华北电力大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TM615

【参考文献】