本文選題：DSG塔式太陽能 + 分段式吸熱器�。� 參考：《華北電力大學(xué)(北京)》2017年博士論文

【摘要】：近年來,隨著可再生能源技術(shù)在世界范圍內(nèi)的快速發(fā)展與推廣,直接蒸汽式(Direct steam generation,DSG)塔式太陽能熱發(fā)電技術(shù)由于低成本、高效率的優(yōu)勢在我國受到廣泛關(guān)注。針對DSG塔式電站定日鏡場聚光模式復(fù)雜和電站啟機(jī)耗時過長的問題,本論文根據(jù)水/蒸汽傳熱流體蒸發(fā)和過熱過程的傳熱特性,提出一種由外置式吸熱器(蒸發(fā)段)和腔式吸熱器(過熱段)所組成的分段式吸熱器,并基于該分段式吸熱器的獨特結(jié)構(gòu)展開電站系統(tǒng)集成設(shè)計與熱經(jīng)濟(jì)性仿真研究。基于分段式吸熱器結(jié)構(gòu)建立定日鏡場聚光模型并分析其聚光特性。通過聚光熱流分配與迭代計算,得到位于西班牙塞維利亞10MWe DSG塔式電站定日鏡場最佳設(shè)計方案,此時定日鏡場整體效率為72.17%,指向蒸發(fā)段和過熱段的定日鏡數(shù)量分別為442個和182個,該定日鏡場分配方案不僅保證了分段式吸熱器表面熱流值不超過安全范圍,同時可提供蒸發(fā)段和過熱段各自所需的熱量。經(jīng)計算,年運(yùn)行工況下,定日鏡場效率不完全隨著太陽高度角的增加而增加,但全年內(nèi)分段式吸熱器表面最大熱流值往往發(fā)生在夏至12:00,因此在進(jìn)行定日鏡場和分段式吸熱器設(shè)計時,需對該時刻下分段式吸熱器表面熱流進(jìn)行校驗以確保工程安全性。建立分段式吸熱器熱力模型以揭示其運(yùn)行特性。設(shè)計工況下10MWe DSG塔式電站分段式吸熱器的熱效率為86.55%。通過與雙外置式吸熱器進(jìn)行對比,得到分段式吸熱器熱效率提高了3.2%,對應(yīng)發(fā)電效率提高了0.88%。不同運(yùn)行時刻下,盡管蒸發(fā)段采用外置式吸熱器,但由于其表面溫度遠(yuǎn)低于過熱段,蒸發(fā)段熱效率大于過熱段約5%-9%;通過動態(tài)分配蒸發(fā)段和過熱段所分別對應(yīng)的定日鏡數(shù)量,可維持分段式吸熱器出口蒸汽溫度為額定值。不同管外徑下,減少蒸發(fā)段管外徑對提高蒸發(fā)段熱效率幾乎沒有影響,原因在于管壁導(dǎo)熱熱阻為主要熱阻;而減少過熱段管外徑能大大提高過熱段熱效率,原因在于對流換熱熱阻為主要熱阻,綜合考慮管內(nèi)對流和泵功消耗,過熱段管外徑存在最優(yōu)值�；诜侄问轿鼰崞鹘SG塔式電站系統(tǒng)集成模型并對其熱經(jīng)濟(jì)性進(jìn)行討論。在額定發(fā)電功率固定為50MWe而土地占用面積可改變的情況下,當(dāng)太陽倍數(shù)和儲熱時長分別為2.7和9h時,電站標(biāo)準(zhǔn)發(fā)電成本(Levelised cost of electric energy,LCOE)最低,為21.4c/k Whe;通過改變電站地理位置可使得年太陽能法向直射輻射強(qiáng)度(Direct Normal Irradiance,DNI)提高55%,電站年發(fā)電量提高20.4%,電站最低LCOE降低30.1%,相應(yīng)的最優(yōu)太陽倍數(shù)降低至2.0;通過逐步改變電站各子系統(tǒng)投資成本進(jìn)行敏感性分析后得到,最低LCOE受定日鏡場和分段式吸熱器投資成本變化的影響最大,且最優(yōu)太陽倍數(shù)和儲熱時長僅隨著定日鏡場和儲熱系統(tǒng)投資成本的降低而增加。在土地占用面積固定為4.8km2而額定發(fā)電功率可改變的情況下,電站最低LCOE為21.77c/k Whe,對應(yīng)的太陽倍數(shù)為1.7,儲熱時長為3h;通過改變電站地理位置或電站各子系統(tǒng)投資成本時得到的結(jié)論與固定額定發(fā)電功率時基本類似,由此可得與電站位置和成本敏感性分析相關(guān)的結(jié)論通用性較強(qiáng),受限制域影響不大;通過將固定的土地占用面積由2.15km2逐漸增加至8.11km2時,電站最低LCOE由24.53c/k Whe降低至20.92c/k Whe,但其降低速率在不斷減緩,最優(yōu)太陽倍數(shù)和儲熱時長因電站年發(fā)電量和總投資成本變化趨勢相對穩(wěn)定而保持不變。為進(jìn)一步降低DSG塔式太陽能電站儲熱系統(tǒng)的投資成本,采用“一步法”制備出比熱更高且適用于大規(guī)模工程應(yīng)用的納米鹽復(fù)合儲熱材料。當(dāng)Cu O納米顆粒濃度為0.5wt%時,相對于純二元硝酸鹽,納米鹽復(fù)合物在液態(tài)狀態(tài)下比熱提高率可達(dá)到11.48%,其終止熔化溫度提高約3℃,因此該納米鹽復(fù)合物更適合作為顯熱儲熱材料,但在作為顯熱儲熱材料時應(yīng)注意時刻保持其工作溫度高于終止熔點,從而防止出現(xiàn)儲熱材料凝固等安全事故。基于掃描電子顯微鏡(Scanning Electron Microscope,SEM)圖像,推測低濃度Cu O納米顆粒表面針狀納米結(jié)構(gòu)的半固體層是納米鹽復(fù)合物比熱提高的原因。通過對該半固體層假設(shè)一個合適的比熱值,結(jié)合修正后的混合物模型,可較為精確地預(yù)測低濃度Cu O納米鹽復(fù)合物的比熱。
[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.
【學(xué)位授予單位】：華北電力大學(xué)(北京)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：TM615

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