重力储能发电现状、技术构想及关键问题

目前,以风能和太阳能为主的波动性电源快速增长,导致电力不平衡矛盾突出,亟需发展储能技术。抽水蓄能是目前为止规模最大、技术最成熟的储能方式,已成为电网储能的主力军。国外相关资料报道,把储能介质“水体”换成其他固体重物的重力储能发电可实现与抽水蓄能电站类似的功效,但国内还缺少系统研讨。本文分析了重力储能发电的现状,类比抽水蓄能技术提出构想方案,引入“重力轮机”“上仓”与“下仓”等概念;阐明了重力储能、发电基本过程及其原理,从理论上推导了重力发电的出力公式;通过科学构想、对比分析初估认为,重力储能发电净高差约100 m,单机容量最大达到10 MW级别,可采用“分布式”规划站点实现灵活的规模化储能;通过开展探讨性剖析,提出4个技术构想及关键问题:1)重物势能转化旋转机械能的重力轮机。研发与水轮机作用类似的重力轮机,最大运行规模按每秒投入约十多吨重物,目标效率可设定为80%。重力轮机是重力储能发电的核心设备,需要在机械工程应用领域开展系统深入的研究。2)适宜的上下仓布置形式。结合实际地理条件,灵活布置上仓与下仓,利用上下仓之间的空间存放重物可减少占地。上下仓布置形式影响重力轮机及输送系统的研发方向,可以统筹研讨、论证。3)重物高效输送系统,包括下仓重物吊运至上仓和仓内输送。降低重物输送能耗,提高系统综合效率,直接关系到重力储能发电的商业价值,故需要开展广泛调研和技术攻关,探寻安全、高效、切实可行的输送方案。4)合理选用重物。采用混凝土为重物的主材较为合适,尽量利用建筑垃圾或就地取材等,以降低对环境的不利影响;宜采用规格相同的标准重物,并能长时间循环使用。重力储能发电具备环境友好、布置灵活、安全度高、寿命长、无自放电等显著优势,研发价值突出,应用前景广阔,目前还处于探索阶段,有待更深入的探究,以推动先期预研、方案规划及技术研发,为新能源长远发展提供后备支撑。

Overall efficiency optimization of controllable mechanical turbo-compounding system for heavy duty diesel engines

A controllable mechanical turbo-compounding(CMTC) system including continuously variable transmission(CVT) and power turbine bypass valve is proposed to recover waste heat from engine exhaust. The combined matching principle considering swallowing capacity of both charging turbine and power turbine, main gear ratio is investigated at first based on the analysis of individual influence. Then the effects and strategies of CVT and power turbine bypass valve are studied for better performance under off-design conditions. At last, the transient response of intake pressure of engine with CMTC system is researched and the fuel saving potential is tested under driving cycle conditions. The results indicate that the overall fuel efficiency elevates at the off-design conditions if CVT is adopted due to the improvement of power turbine operating efficiency by speed modulation. The diversion of exhaust through power turbine bypass valve under the low load condition is necessary. The back pressure of the charging turbine infuences the transient response of intake pressure for a fixed CMTC configuration. A method featured by the assistance of power turbine bypass valve is tested to improve the transient response of the intake pressure. The fuel consumption reduces by 2% and 3.4% under highway fuel economy test(HWFET) and Tianjin 503(TJ503) driving cycles respectively.