on of more volatile componentxB,Dist = distillate mole fraction of less volatile componentxA,Bot = bottoms mole fraction of more volatile componentxB,Bot = bottoms mole fraction of less volatile componentTo complete the vapor velocity vs. HETP relationship, vapor velocity must be found. With the assumption of an adiabatic column, the vapor velocity can be determine by using an overall system balance or through a condenser balance. The overall and condenser balances give a heat duty. This heat duty can then be used to determine vapor velocity. The system contained three electrical heaters, therefore, the heat duty was determined through and electrical power equation:P = V2 / R(4)where: P = power input or heat duty (J/s)V = voltage input (volts)R = resistance of the heater (W)To accomplish the condenser balance the cooling water flow rate and temperature drop across the condenser must be known. Once these values are found, the following energy balance can be applied:Q = mCpDT(5)where: Q = heat duty (J/s)m = cooling water flow rate Cp = heat capacity of cooling waterDT = temperature increase on water side of condenserEither of these heat duties can be used to find the vapor velocity. The vapor velocity is found using a system energy balance. The result of this balance is shown in the following equation:Q = S V(xi)dist(DHvap,i)(6)where: Q = heat duty (J/s)V = vapor velocity (m/s)xi,dist = mole fraction of component I in the distillateDHvap,i = heat of vaporization of component IAfter the vapor velocity vs. HETP graph is plotted, the flooding point can be determined. The flooding point is the point at which vapor entrainment occurs. On the vapor velocity vs. HETP graph, flooding is shown at the point where the plot changes from a linear relationship to an exponential plot. Once the design vapor velocity is determined, the column scale up may take place. The appropriate velocity is used to design the condenser and reboiler for t...
