Page 200 - Process Equipment and Plant Design Principles and Practices by Subhabrata Ray Gargi Das

198 Chapter 6 Evaporators

BPE table for NaOH.

X, 0 0.1 0.2 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7
fraction,
w/w

BPE, C 0 2.2 7.8 13.9 19.4 26.1 36.1 41.7 48.9 55.6 66.7 76.7

T steam ¼ 120 C; U 1 ¼ 3000; U 2 ¼ 2000; U 3 ¼ 1250; P steam ¼ Saturation pressure corresponding
2
to (T steam ¼ 120 C) ¼ 0.9926 kg/cm (g)

T con,4 ¼ Saturation temperature of steam at pressure P 3 ¼ 38.4 C
L 3 ¼ Fx F /x 3 ¼ 2.1; V total ¼ F L 3 ¼ 3.9
Trial 1: V 1 ,V 2 ,V 3 are assumed equal to one third of V total
V 1 ¼V total /3 ¼ 3.9/3 ¼ 1.3; V 2 ¼ 1.3; V 3 ¼ 1.3;
Step - A
L 1 ¼ F eV 1 ¼ 6 e 1.3 ¼ 4.7; L 2 ¼ L 1 e V 2 ¼ 4.7 e1.3 ¼ 3.4; x 1 ¼ Fx F /L 1 ¼ 0.1787;
x 2 ¼ Fx F /L 2 ¼ 6(0.14/3.4) ¼ 0.2471; Estimating BPE corresponding to x 1 , x 2 and x 3 in the

effects from BPE table, in C: 6.49, 10.4 and 26.1.
Total BPE ¼ 42.99

Total DT av ¼ 120e38.4 ¼ 81.6 C

DT eff,total ¼ 81.6 e42.99 ¼ 38.61 C
Estimating individual contribution by assuming same q and A i in all effects
DT eff,1 ¼ 38.61 (1/3000)/(1/3000 þ 1/2000 þ 1/1250) ¼7.89
DT eff,2 ¼ 38.61 (1/2000)/(1/3000 þ 1/2000 þ 1/1250) ¼ 11.82
DT eff,3 ¼ 38.61 e 7.89 11.82 ¼ 18.9
T 3 ¼ T con,4 þ BPE 3 ¼ 38.4 þ 26.1 ¼ 64.5
T con , 3 ¼ 64.5 þ 18.9 ¼ 83.4
T 2 ¼ T con,3 þ BPE 2 ¼ 83.4 þ 10.4 ¼ 93.8
T con,2 ¼ 93.8 þ 11.82 ¼ 105.62
T 1 ¼ T con,2 þ BPE 1 ¼ 105.62 þ 6.49 ¼ 112.11

T con,1 ¼ saturation temperature of steam ¼ 120 C
Estimation of effect pressure (g)
2

P 1 ¼ saturation pressure corresponding to 105.62 C ¼ 0.2263 kg/cm (g)
2
P 2 ¼ saturation pressure corresponding to 83.4 C ¼ L0.4792 kg/cm (g)