板翅式换热器物流分配对天然气液化性能的影响

摘要

板翅式换热器入口物流分配不均是造成换热效能降低的主要因素之一,对天然气液化装置稳定和高效的运行产生不利的影响.针对氮气膨胀和混合制冷剂两种天然气液化工艺,分别研究原料气、氮气制冷剂和混合制冷剂物流分配不均对换热器参数和液化工艺性能的影响,得到换热器入口物流分配不均匀度STD(standard deviation,均方差)的临界值,为换热器的选型和天然气液化工艺的设计提供依据.结果表明:相同STD值下,天然气液化性能受不同物流分配不均影响程度大小依次为氮气制冷剂、混合制冷剂和原料气;倾斜严重影响混合制冷剂的分配及换热效果,倾斜角度由0°增加至20°时,液相STD值由1.3增至3.9,天然气液化率从92.8%降至69.4%;为满足天然气液化率在90%以上,原料气、氮气制冷剂及混合制冷剂物流分配的临界STD值分别为8.3、2.8、4.5(液相),混合制冷剂倾斜工况临界STD值为1.5(液相),对应倾斜角度为1.6°.%One of the main factors that reducing the heat transfer performance are the inlet flow maldistribution of plate fin heat exchanger, and which would result in an adverse effect on the stable and efficient operation of natural gas liquefaction plant.According to nitrogen expansion and mixed refrigerant natural gas liquefaction process, the effects of feed gas, nitrogen refrigerant and mixed refrigerant flow maldistribution on heat exchangers and liquefaction process performance parameters were studied, in order to get the critical value of the heat exchanger inlet flow distribution unevenness STD (standard deviation), which provides the basis for heat exchanger selection and natural gas liquefaction process design.The results show that: under the same STD value, the order of the influence of flow maldistribution on nature gas liquefaction process performance is: nitrogen refrigerant, mixed refrigerant and the naturel gas;the mixed refrigerant distribution and heat transfer are affected seriously by tilt, as the tilt angle increases from 0° to 20°, the liquid STD value increased from 1.3 to 3.9, and the liquefaction rate decreased to 69.4% from 92.8%;in order to maintain the natural gas liquefaction rate of 90%, the critical value of flow distribution unevenness STD of feed gas, nitrogen refrigerant and mixed refrigerant are 8.3,2.8,4.5 (liquid phase), in title condition, the mixed refrigerant STD is 1.5 (liquid phase), corresponding to the title angle of 1.6°.