核电厂低品位余热发电技术研究
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Research on Power Generation Technologies for Low-Grade Waste Heat in Nuclear Power Plants
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收稿日期: 2025-02-17 修回日期: 2025-04-05
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Received: 2025-02-17 Revised: 2025-04-05
作者简介 About authors
目的 针对核电厂低品位余热直接排放造成的海洋热污染问题,亟需探索高效解决方案以降低排海热负荷。为此,对不同类型余热源特性及其发电潜力进行了系统评估,为核电厂余热利用提供热经济性数据依据。 方法 总结了核电厂中各类低品位余热的特点,并分析了余热的不同利用方式及其发展现状;介绍了3种适用于该余热的发电技术,并结合实际案例对比分析了不同发电技术的热经济性能及不同余热源的回收潜力。 结果 核电厂二回路凝结饱和水的能质系数最高,发电利用潜力最大。此外,有机朗肯循环(organic Rankine cycle,ORC)是热经济性能最佳的余热发电方案,其平准化度电成本最低,为0.037 6美元/(kW⋅h),相对于喷射式有机闪蒸循环和卡琳娜循环分别降低了84%和78%;ORC发电功率为462.2 kW,具有较好的可行性;在回收低压缸乏汽余热场景下,ORC的可减排热负荷为360.3 MW,环保效益显著。 结论 ORC等余热发电技术可大幅降低排海热负荷,为我国核电厂的低品位余热利用与降低排海热负荷提供重要参考。
关键词:
Objectives To address the issue of marine thermal pollution caused by the direct discharge of low-grade waste heat from nuclear power plants, it is imperative to explore efficient solutions to reduce thermal discharge loads. Therefore, by the characteristics of different types of waste heat sources and their potential of power generation are systematically evaluating to provide thermo-economic data basis for waste heat utilization in nuclear power plants. Methods The characteristics of different types of low-grade waste heat in nuclear power plants are summarized, and different utilization methods of waste heat and their current development status are analyzed. Three types of power generation technologies suitable for this waste heat are introduced, and their thermo-economic performance and the recovery potential of different waste heat sources are comparatively analyzed through actual case studies. Results The energy quality coefficient of the secondary loop condensate saturated water in nuclear power plants is the highest, showing the greatest potential for power generation utilization. Moreover, the organic Rankine cycle (ORC) demonstrates optimal thermo-economic performance as a waste heat power generation solution, achieving the lowest levelized cost of electricity at $0.037 6/(kW⋅h), which is 84% and 78% lower than that of the ejector organic flash cycle and the Kalina cycle, respectively. ORC achieves a generation capacity of 462.2 kW, demonstrating good feasibility. In the scenario of recovering waste heat from the low-pressure turbine exhaust, the ORC can reduce thermal discharge by 360.3 MW, showing significant environmental benefits. Conclusions Waste heat power generation technologies such as the ORC can significantly reduce thermal discharge loads into the sea, providing important references for low-grade waste heat utilization and thermal pollution reduction in China’s nuclear power plants.
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本文引用格式
赵雅卓, 张文杰, 廖颖慧, 林晋磊, 张荣勇, 段远源.
ZHAO Yazhuo, ZHANG Wenjie, LIAO Yinghui, LIN Jinlei, ZHANG Rongyong, DUAN Yuanyuan.
0 引言
为弥补上述不足,本文围绕核电厂低品位余热的利用问题,总结了核电厂余热特点,对比了各种余热利用方式,并进一步开展了典型低品位余热发电技术应用可行性研究。
1 核电厂低品位余热特点
表1 核电厂低品位余热的主要来源及其特点
Tab. 1
| 余热来源 | 状态 | 温度/℃ | 压力/kPa | 流量/(kg/s) | 干度 |
|---|---|---|---|---|---|
| 低压缸乏汽 | 气液共存 | 41.7 | 8.10 | 828.30 | 0.911 4 |
| 凝结饱和水 | 液态 | 96.7 | 90.04 | 79.50 | 0 |
| 温排水 | 液态 | 29.6 | 101.33 | 60 624.55 | 0 |
图1
图1
核电厂不同来源低品位余热的可利用潜力
Fig. 1
Utilization potential of low-grade waste heat from different sources in nuclear power plants
2 核电厂余热利用方式及发展现状
在农业种植与水产养殖方面,日本利用核电厂温排水进行商业养殖,显著提升了渔业产量[13]。在市政与工业供热方面,清华大学1989年成功研发5 MW低温核供热试验堆,开创了我国低温核供热技术领域的先河[29];山东烟台的“暖核一号”工程在政府支持下,供热面积从一期的70万m2上升到三期的630万m2,惠及20余万人,每年替代原煤23万t,减排二氧化碳42万t,成为国内首个跨区域核能供暖项目[17-19];瑞士贝兹瑙核电厂采取热电联产技术进行区域供热,每年节省燃油约1.2万t,减排二氧化碳约4.5万t[25]。在海水淡化方面,清华大学以低温核供热技术为基础在摩洛哥首次实现低温核供热堆与海水淡化技术的耦合,建成核能海水淡化厂[30];日本迄今为止,已有近10个核能海水淡化耦合装置,可实现市政管网的大面积供水[31]。表2为上述余热利用方式适用的余热源及其优缺点。
表2 不同余热利用方式适用的余热源及其优缺点
Tab. 2
由表2可以看出,直接热利用方式普遍存在占地面积大、季节性强、消耗量有限、额外耗能多等弊端。相比之下,余热发电技术通过热电转化不仅有效提高了核电厂的能源综合利用效率,还可全年持续稳定运行,这降低了排海热负荷,减轻了对海洋生态环境的热污染,因此成为核电厂低品位余热资源消纳的首选方案。
3 潜在的低品位余热发电技术
3.1 有机朗肯循环
图2
图2
简单ORC系统结构及其T-s图
1—7均为系统工质状态点。
Fig. 2
Simple ORC system structure and its T-s diagram
3.2 喷射式有机闪蒸循环
图3
3.3 卡琳娜循环
图4
4 余热发电技术可行性分析
4.1 问题描述
表3 系统功率设备的效率
Tab. 3
| 参数 | 数值 |
|---|---|
| 工质泵等熵效率ηpump | 0.8 |
| 膨胀机等熵效率ηtur | 0.8 |
| 电动机效率ηmotor | 0.98 |
| 发电机效率ηgen | 0.98 |
为简化分析,采用如下假设:1)系统处于稳态运行;2)忽略设备和连接件的散热和流动压降损失;3)忽略工质泵进、出口处工质重力势能和动能的变化,假设工质为不可压缩流体。
4.2 热力学模型
为评估ORC、EOFC和KC三种发电技术在核电厂低品位余热回收场景应用的热力学可行性,对3种低品位热能发电技术建立热力学模型。这3种发电系统吸热量Qeva的计算式均为
式中:
对于ORC,膨胀机的输出功率
式中:htur,out,s为工质经过等熵膨胀后在膨胀机出口处的焓值;
对于EOFC,膨胀机输出功需额外考虑蒸汽干度x;对于KC,富氨蒸气进入膨胀机做功。
系统中工质泵的耗电功率
式中:
系统的净发电功率Wnet计算式为
系统的热效率
4.3 经济性能模型
本文进一步对ORC、DFC、KC三种技术应用于核电厂低品位余热回收的经济可行性进行对比分析。
4.3.1 换热器成本
换热器部件单位面积成本数据采用中国核电工程有限公司数据的1 300元/m2(178.49美元/m2),单个换热器部件成本为
式中:
换热器总成本CBM,he的计算模型如
式中
4.3.2 功率设备成本
采用化工设备成本估算经验公式计算功率设备成本
式中
膨胀机和工质泵的成本
式中:Cbasic为设备的基础成本;FB为考虑材料、压力和温度等影响因素的成本修正因子[56]。
考虑通货膨胀影响,采用化工成本指数(chemical engineering plant cost index,CEPCI)对成本进行修正,计算式为
式中:
低品位余热发电系统的总投资成本Ctot计算式为
进一步引入净现值(net present value,NPV)CNPV和平准化度电成本(levelized cost of electricity,LCOE)CLCOE 2个指标评价低品位余热发电系统的经济性能,其表达式分别如下:
式中:Eyr为系统年发电总量,根据系统净输出功率计算,年运行时长取7 000 h;J为售电价格,取0.045美元/(kW⋅h)(即0.325 57元/(kW⋅h));COM为年运行维护成本,取总投资成本的1.5%;CDEP为年折旧金额,采用线性折旧方法计算;ηtax为税率,取17%;r为折现率,取5%;Cresidual为运行期末的净资产残值,取0;t为机组运行时长,年;tLT为机组运行年限,取25年。
4.4 技术/经济可行性分析结果
4.4.1 技术可行性
在3种典型余热源场景下,ORC均具有最高的发电效率,如图5所示。对于低压缸乏汽余热利用,ORC的发电效率为3.3%,吸热功率高达360.3 MW,可以显著降低排海热负荷,此外,其发电功率远高于EOFC与KC。对于凝结饱和水余热利用,EOFC具有最大的吸热功率和发电功率,分别高达22.5 MW和1.12 MW,其原因在于,通过闪蒸技术有效提升了热源与循环之间的匹配度;而对于低压缸乏气和温排水,EOFC并没有展现其性能优势。因此,EOFC更适用于余热温度高且供电需求多的应用场景。对于温排水余热利用,ORC与EOFC虽然发电效率极低(低于0.3%),但仍可吸收大量余热(分别为172.4 MW与10.9 MW),有助于达成降低排海热负荷的目标;而KC由于热源温度较低,无法实现发电。
图 5
图 5
不同发电技术在3种典型余热源场景下的热力性能
Fig. 5
Thermal performance of different power generation technologies under three typical waste heat source scenarios
综上,对于核电厂的不同余热源,ORC通常展现出更高的发电效率和发电功率,尤其是在低压缸乏汽和温排水余热利用场景下,而EOFC在凝结饱和水余热利用场景下表现更好:因此,从技术可行性角度看,ORC与EOFC均展现出较高的适配性,具有较好的应用潜力。
4.4.2 经济可行性
图6展示了不同发电技术在3种典型余热源场景下的经济性能。从净现值角度看,不同发电技术在3种典型余热源场景下均无法实现盈利。ORC在3种典型余热源场景下均具有最低的平准化度电成本,结合ORC技术的热力性能优势,具有较好的应用潜力。特别是在回收二回路凝结饱和水余热时,ORC凭借其11.1%的发电效率和0.037 6 美元/(kW⋅h)的平准化度电成本,在经济性方面表现卓越,其平准化度电成本相对EOFC和KC分别降低了84%和78%,成为该热源条件下的首选技术。在回收低压缸出口乏汽余热场景下,ORC同样表现出较高的发电效率(3.3%)和相对较低的平准化度电成本(0.107 2美元/(kW⋅h)),尽管净现值为负,但其较高的技术成熟度和较大的排海热负荷减少量使其在大规模应用中仍具有重要潜力。在回收温排水余热场景下,由于热源温度极低,ORC的发电效率和经济性受到大幅限制,但其在减少排海热负荷方面具有显著的环保效益。相比之下,EOFC和KC在回收低压缸出口乏汽和温排水余热场景下的经济性表现欠佳,这是因为其高投资成本和低发电效率限制了其实际应用。
图 6
图 6
不同发电技术在3种典型余热源场景下的经济性能
Fig. 6
Economic performance of different power generation technologies under three typical waste heat source scenarios
5 结论
聚焦核电厂的低品位余热发电利用,得出以下主要结论:
1)核电厂低品位余热来源广泛、热量丰富,但回收难度不一,现有的直接热利用方式虽具有一定效益,但普遍受季节性、用热不稳定和利用规模限制。相比之下,余热发电技术具备热电转化效率高、运行稳定、全年可用等优势,可有效提升核能综合利用水平,降低排海热负荷,是实现核电厂低品位余热高效利用的优选路径。
2)在回收二回路凝结饱和水余热场景下,ORC是热经济性能最佳的技术方案,其平准化度电成本最低,为0.037 6美元/(kW⋅h),相对于EOFC和KC分别降低了84%和78%;同时其发电功率为462.2 kW,规模较大,具有较好的可行性。
3)通过余热发电技术回收核电厂低品位余热,在当前技术经济条件下虽难以实现直接经济收益,但在降低排海热负荷方面效果显著(如低压缸乏汽余热回收可减排360.3 MW)。因其环保效益与潜在经济效益的协同性,使其具有推广价值。随着制造工艺升级带来的成本下降,部分余热源场景将显现盈利潜力。此外,余热利用可通过农业种植、市政供暖等间接效益实现价值转化。
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Multi-criteria optimization of a biomass-fired proton exchange membrane fuel cell integrated with organic Rankine cycle/thermoelectric generator using different gasification agents
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Working fluid selection of organic Rankine cycle for low-temperature industrial waste heat utilization
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Optimal choice of working fluids of organic Rankine cycle for industrial waste heat recovery
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中低温工业余热ORC回收装置的工质发展与应用
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Advances in research and application of working fluids for ORC waste heat recovery apparatus
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Comparison of the organic flash cycle (OFC) to other advanced vapor cycles for intermediate and high temperature waste heat reclamation and solar thermal energy
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Performance assessment of a low grade waste heat driven organic flash cycle (OFC) with ejector
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Assessment of different configurations of solar energy driven organic flash cycles (OFCs) via exergy and exergoeconomic methodologies
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Technical and economic analysis of organic flash regenerative cycles (OFRCs) for low temperature waste heat recovery
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Analysis and assessment of a novel organic flash Rankine cycle (OFRC) system for low-temperature heat recovery
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Increased power production through enhancements to the organic flash cycle (OFC)
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Synergetic mechanism of organic Rankine flash cycle with ejector for geothermal power generation enhancement
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基于朗肯循环和卡琳娜循环的中低温余热动力循环分析
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Power cycle analysis for mid-low temperature waste heat resource based on rankin cycle and kalina cycle
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不同工质对有机朗肯循环低温余热发电系统性能的影响研究
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Influence of different working fluids on performance of organic Rankine cycle low temperature waste heat power generation system
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Influences of climatic environment on the geothermal power generation potential
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2023 CEPCI annual average value decreases from previous year:Chemical Engineering Page 1
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