流率为0.014kmol/(s·m2)的空气-氨混合气中含氨体积分数为2% 拟用逆流吸收以回收其中95%的氨。塔顶淋入摩尔分
流率为0.014kmol/(s·m2)的空气-氨混合气中含氨体积分数为2%,拟用逆流吸收以回收其中95%的氨。塔顶淋入摩尔分数为0.0004的稀氨水溶液,设计采用的液气比为最小液气比的1.5倍,操作范围内物系服从亨利定律y=1.2x,所用填料的总传质系数Kya=0.052kmol/(s·m3)。试求:
(1)液体在塔底的摩尔分数x1;
(2)全塔的平均推动力Δym;
(3)所需填料层高度m
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解:据题意,知:G=0.018kmol/(s·㎡), y1=3%=0.03, x2=0.00005, (L/G)=1.8(L/G)min, ye=1.2x, ky·a=0.055kmol/(s·m3) y2= y1(1-η)=0.03×(1-95%)=0.0015,x1e=y1/m=0.03/1.2=0.025
(1) (L/G)min=(y1-y2)/( x1e-x2)
=(0.03-0.0015)/(0.025-0.00005)=1.1423
(L/G)=1.8(L/G)min=1.8×1.1423=2.05614 (L/G)=(y1-y2)/( x1-x2)
x1=x2+(y1-y2)/(L/G)=0.00005+(0.03-0.0015)/2.05614=0.01391
(2) Δy1=y1-m.x1=0.03-1.2×0.01391=0.013307
Δy2=y2-m.x2=0.0015-1.2×0.00005=0.00144
Δym=(Δy1-Δy2)/ln(Δy1/Δy2)
=(0.013307-0.00144)/ln(0.013307/0.00144) =0.011867/ln11.672807=0.011867/2.22365 =0.005337
(3) HOG=G/ ky·a=0.018/0.055=0.3273mNOG=(y1-y2)/Δym=(0.03-0.0015)/0.005337=0.0285/0.005337=5.34 H= HOG×NOG=0.3273×5.34=1.75m
答:通过计算知:(1)液体在塔底的摩尔分数x1为0.014; (2)全塔的平均推动力Δym为0.005337;(3)所需填料层高度为1.75m。
