Question

a sieve plate column operating at atmospheric pressure is to produce nearly pure methanol from an aqueous feed containing 40 percent methanol. The distillate product rate is 5800 kg/h.

1. For a reflux ratio of 3.5 and a plate spacing of 18 in, calculate the allowable vapour velocity and the column diameter.

Answer 1

Ans:- Given Let x be the reflux ratio = 3.5

distilled product rate P =5800kg/hr=1.5m³/s

Molar mass of methanol = 32g

density of liquid methanol = 792kg/m³

Now density of vapour methanol = mass /volume at STP

                                                    =32/22.4

                                                     =1.42kg/m³

At 18 inch spacing k=0.29

Now allowable vapour velocity

                                                 =0.29(792-1.42/1.42)^1/2

                                                 =2.084m²/s

Now vapour flow rate = P(x+1)

                               =1.5(3.5+1)

                                 = 6.75m³/s

Now column diameter =(4xvapour flow rate / allowable vapour velocity x )^1/2

                                 =(4x6.75/2.08x3.14)^1/2

                                 =2.033m