D4

D5 — V5*

*To be considered as an inert gas.

above their critical temperatures when they are at the temperature of the tray under study. Thus, like the steam, they behave as noncondensibles and lower the boiling point of the product in accordance with Dal-ton's Law of partial pressures. Since the product vapor which is to be removed at the next higher draw tray will be near its critical temperature as it leaves this lower draw tray, it is assumed to have no effect on the partial pressure, and for this reason, its presence is neglected.

6. Calculate the hydrocarbon product partial pressure in the total vapor leaving the draw tray and convert the atmospheric bubble point of the unstripped liquid product on the tray to this partial pressure. The vapor pressure data in Maxwell, Section 4, is recommended for this conversion. If this temperature does not check the value which was originally assumed, repeat the procedure for a new assumed temperature.

7. Calculate and tabulate the external heat quantities to the base of Tray (D1 + 1). This will include the heat input to the system by the steam to the product stripper and the heat output from the system in the product liquid Dl. For steam strippers in atmospheric towers, a temperature drop of 30 degrees F for the liquid from the draw tray to the stripper outlet is assumed arbitrarily.

For reboiled strippers, a liquid temperature rise of 30 degrees F is assumed from the draw tray to the stripper outlet. The temperature of the stripout returning to the atmospheric tower is assumed to be 10 de-

env.ez:

AQ'D4

ENV.m

EQUATIONS FOR ENVELOPE m

(1) HEAT BALANCE

(2) HYDROCARBON PARTIAL PRESSURE ABOVE TRAY N P'hc =1PTN)[U*+D5l/(ir +D5+SW +S))]

(3) INDUCED REFLUX ON TRAY N

(Ri)N""(L«)[jhtn —hn )/(H tn_j -htN )]