燃煤sCO2布雷顿循环及其工质传热特性研究进展

超临界二氧化碳(supercritical carbon dioxide,sCO2)布雷顿循环作为动力循环的主要优势是效率高、结构简单、系统紧凑、热源适应性广,有望在下一代核反应堆、燃煤电站、余热回收及可再生能源(太阳能、地热能等)领域得到大规模应用。作为新型动力循环工质的sCO2具有温和的临界点条件(31.1℃/7.38 MPa),同时在临界点附近物性变化剧烈。鉴于我国以煤为主的能源结构及严峻气候挑战,sCO2动力循环与富氧燃烧、流化床锅炉、煤气化等技术结合为实现煤炭的清洁高效低碳利用提供了新的思路。笔者分析了sCO2工质的性质,介绍了间接加热式和直接加热式两类sCO2布雷顿循环的基本原理,总结了sCO2动力循环应用于燃煤电站的研究进展。sCO2循环燃煤电站的发展可分为以下2条路径:①间接加热式sCO2循环取代蒸汽朗肯循环应用于燃煤电站,可与煤粉锅炉、循环流化床锅炉、富氧燃烧等技术相结合;②发展更加高效且固有碳捕捉能力的直接加热式sCO2循环燃煤电站技术,与带有碳捕捉(carbon capture and storage,CCS)的整体煤气化联合循环(IGCC)电站竞争。分析了sCO2动力循环与燃煤电站结合的多种技术方案,讨论不同方案的优势、技术挑战与发展方向。在此基础上,重点阐述了sCO2作为工质在常规管径圆管、细管道圆管、微细管道圆管及印刷电路板式换热器(printed circuit heat exchanger,PCHE)中的传热试验研究和传热特性,总结了sCO2工质在圆管内和PCHE内流动传热经验关联式并进行分析比较,同时介绍了sCO2工质流动传热的数值模拟研究。最后,从基础理论、系统设计、设备研发层面指出了现有研究的不足和对未来研究的展望。CO2减排在未来几十年将是燃煤发电的主要研究方向,具有更大效率优势和固有碳捕捉能力的直接加热式sCO2循环燃煤发电技术将引起更多关注。在我国将sCO2布雷顿循环应用于燃煤电站更具现实意义,目前我国关于sCO2循环发电技术的研究与国外仍存在相当差距,应依托超超临界燃煤发电机组和IGCC电站的技术积累,快速推动燃煤sCO2循环发电技术的研发进展。

Research progress on supercritical CO2 Brayton cycle and its working fluid heat transfer characteristics for coal-fired power generation

The main advantages of the supercritical carbon dioxide( sCO2) Brayton cycle as a power cycle are high efficiency,simple structure,compact system and wide heat source adaptability,which is expected to be widely used in the next generation of nuclear reactors,coal-fired power plants,waste heat recovery and renewable energy( solar energy,geothermal energy,etc.) fields. As a new type of power cycle working fluid,sCO2 has mild critical point conditions( 31. 1 ℃/7. 38 MPa),and its physical properties change sharply near the critical point. In view of the coal-based energy structure and severe climate challenges in China,the combination of sCO2 power cycle with oxy-fuel combustion,fluidized bed boilers,coal gasification and other technologies provides new solutions to achieve clean,efficient and low-carbon utilization of coal. In this paper,the properties of sCO2 were firstly analyzed,then the basic principles of two types of indirect-fired and direct-fired sCO2 Brayton cycles were introduced,and then the research progress of sCO2 power cycle applied to coal-fired power stations was summarized. The development of sCO2 cycle coal-fired power plant can be divided into the following two paths: ① the indirect-fired sCO2 cycle instead of steam Rankine cycle,which is used in coal-fired power stations,and is combined with technologies such as pulverized coal boilers,circulating fluidized bed boilers,and oxy-fuel combustion;② the direct-fired sCO2 cycle coal-fired power station has higher efficiency and inherent carbon capture,which can compete with the IGCC power station with carbon capture and storage( CCS) system. And then a variety of technical solutions of sCO2 power cycle applied to coal-fired power station were analyzed,including the advantages,technical challenges and development directions of different types. Next,the experimental research and heat transfer characteristics of sCO2 in conventional round pipe,thin round pipe,micro round pipe,and printed circuit heat exchanger( PCHE) were elaborated. Also,the empirical correlations of sCO2 flow and heat transfer in circular tubes and PCHE were summarized and analyzed. At the same time,the numerical simulation methods of sCO2 heat transfer were presented. Finally,from the basic theory,system study and equipment development,the shortcomings of the existing research and prospects for future research were pointed out,which had reference significance for the future development of coal-fired sCO2 cycle power station technology. The CO2 emission reduction will be the main research direction of coal-fired power station in the next few decades. The direct-fired sCO2 cycle coal-fired power generation technology with higher efficiency and inherent carbon capture will attract more attention from academics and industry. In China,it is more practical to apply the sCO2 Brayton cycle to coal-fired power plants. At present,there is a considerable gap between China with foreign countries on the research of sCO2 cycle power station technology. We should rely on the technology accumulation of ultra supercritical coal-fired power plants and IGCC power plants to rapidly promote the research and development of the technology of coal-fired sCO2 cycle power station in China.