不可凝气体对大扁管空冷凝汽器性能的影响分析

Effect of Non-condensable Gas on Performance of Air-cooled Condensers in Power Plants

为了研究不可凝气体(non-condensable gases, NCG)对火电与光热发电机组上广泛使用的大扁管空冷凝汽器性能的影响,以工程机组凝汽器上普遍应用的通流面积220 mm×20 mm的大扁管为研究对象,针对汽轮机典型工况下的实际蒸汽流量,基于Lee相变方程、VOF方法以及组分扩散模型,对蒸汽与NCG混合气体管内两相流凝结换热进行数学建模与数值计算。结果表明:由于大扁管的狭窄通流几何结构与高蒸汽流量,NCG对管内蒸汽凝结的抑制效果要远低于预期;当入口空气质量分数按2%增加时,凝结管凝结换热系数仅下降2%左右,这与NCG导致低流量圆管凝结性能急剧下降的结论不同;空气正常泄漏不会导致空冷凝汽器性能下降而影响发电机组效率。

In order to study the effect of non-condensable gases(NCG)on the heat transfer performance of air-cooled condensers with flat finned tube widely used in fossil and photothermal power plants,taking a large flat tube with flow area of 220 mm×20 mm commonly applied on the engineering unit condenser as the research object,aiming at the actual steam flow under typical operational modes of steam turbines,based on the Lee phase change equation,VOF method and diffusion layer model,the mathematical modeling and numerical calculations for the two-phase flow condensation heat transfer in the tube of the steam/NCG mixed gases were carried out.The results show that the inhibition effect of NCG on steam condensation in tube is not serious as expected,due to the geometric construction of narrow channel and high steam flow rate of the large flat tube.The condensation heat transfer coefficient(HTC)of condenser tube only reduces approximately by 2%when the inlet air mass fraction increases by 2%,which disagrees with the early conclusionthat NCG causes the sharp decline of condensation performance of a circular tube in a relatively low mass flux.The study frees the worry on the leaking air inhibiting the heat transfer performance of air-cooled condensers and impacting the efficiency of generator unit.