he system. The vapor velocity is converted to mass flow rate by employing the column diameter according the Equation (7):m = VAr(7)where: m = mass flow rate (kg/s)V = vapor velocity (m/s)A = cross sectional area of the column (m2)r = density of the fluid (kg/m3)Equation (6) can be used to find the heat duty for the condenser and then Equation (5) can be used to determine the cooling water flow rate. To calculate the condenser area, the following equation is used:Qc = UADTlm(8)where: Qc = heat duty of the condenser (J/s)U = overall heat transfer coefficient (BTU/ft2*hr*F)A = area of heat exchange (m2)DTlm = logarithmic mean temperature differenceThe final step in this design process is to determine the height of packing in the column. In order to accomplish this, the actual number of stages must be determined using McCabe Thiele analysis. To use McCabe Thiele to determine actual number of stages, the following conditions must be identified. 1.Distillate and bottoms compositions2.Minimum and actual reflux ratio (L/D)3.Feed temperature and slope of the feed lineThe slope of the feed line is dependent on the feed temperature. To find the slope of the feed line, the following equations were used (1, 138): q = (L' - L) / F(9)L' = L + F + c(10)c = (Cp * DT * F) / l(11)slope = q / (q-1)(12)where: F = feed flow rateL = liquid flow rate above feed stageL' = liquid flow rate below feed stageDT = degrees of superheat or subcooling (K)l = latent heatTo find the minimum reflux ratio, a pinch point is used. The slope of the line from the destillate composition on the x = y line to the point where the feed line touches the equilibrium curve is the minimum (L/V) value. Using this value, the minimum reflux ratio can be determined using Equation (13).(L/V) = (L/D) y [(L/D) +1)]where: (L/V) = slope of top operating line(L/D) = reflux ratioThe actual reflux ratio can then be determined, and the actual slope of the top operating line can be foun...
