化工原理课件蒸馏-201203-5(精品·公开课件).ppt

回流比对精馏过程的影响及其选择 特殊平衡关系下的Rmin 水蒸气直接加热的蒸馏计算 直接加热与间接蒸汽加热比较 当xD，D，R,xF,q相同时， 由于直接蒸汽加热，冷凝液与釜液的混合作用，xW下降， 所需理论板数增加 当 xD和 xW 相同时， 直接加热所需理论板数、回收率、采出量D均有所降低。 回收塔的理论板数计算过程 Enriching-column distillation浓缩塔 多股进料的精馏操作线图示 F　yF B,xB D,xD the feed enters the bottom as a vapor The liquid bottoms is the feed If the feed is saturated vapor.q=0 V’= F Equation of operating line of the rectifying section 逐板计算法 由xD始，依次反复应用平衡关系与操作关系，直至 xn≤xw为止。 平衡关系： 对第n块板： αn—第n块板A组分对B组分的相对挥发度。 操作关系： 逐板计算 当塔顶为全凝器时： 板序号 平衡关系 操作关系 1 2 ………………………………………………… n 整理得： 达到规定的分离要求时 对双组分： —— Fenske 方程 School of Chemistry and Chemical Engineering, SCUT , Yang dongjie Minimum reflux ratio the intersection of this line and the stripping line with the q line moves closer to the equilibrium line the number of steps required to give a fixed xD and xW increases the two operating lines touch the equilibrium line, a pinch point at y and x occurs School of Chemistry and Chemical Engineering, SCUT , Yang dongjie How to obtain Rm Graphic method y’ x’ （x’,y’) School of Chemistry and Chemical Engineering, SCUT , Yang dongjie analytical method R=Rm （x’,y’),Rm School of Chemistry and Chemical Engineering, SCUT , Yang dongjie Pinch point xW xf x’ xD y’ the equilibrium line has an inflection School of Chemistry and Chemical Engineering, SCUT , Yang dongjie All actual columns operates at a reflux ratio between the minimum and infinity. School of Chemistry and Chemical Engineering, SCUT , Yang dongjie Operating and optimum reflux ratio Effect of reflux ratio on rectify and choice of R These are the two limits in operation of the tower. School of Chemistry and Chemical Engineering, SCUT , Yang dongjie Total cost=Operating cost＋fixed cost =minimum Operating cost ：rectifying section V=L+D=(R+1)Dstripping section V’=V’+(q-1)F R↑→V↑, V’↑→heating ↑，cooling↑→ Operating cost ↑ fixed cost=NT or Z