The overhead reflux drum for a vacuum column in an oil refinery operates at 25 mmHg. The overhead temperature is 120°F, and the composition and flowrate of the vapor in the vent gas (not including any air leaks) is

The vacuum tower and associated equipment and pipes have an approximate volume of 21,000 ft³.

Answer the following:

1. Estimate the air leak into this (“tight”) system.

2. Determine how many stages would be required for a steam ejector to remove the vent gas plus the air leak into the system and deliver it to a vent gas handling system operating at 1.2 bar.

3. Estimate the amount of low-pressure steam (70 psig saturated) required by each stage of ejector assuming there is no intermediate condensation.

4. If cooling water is available at 86°F and must be returned to the cooling tower at 104°F, determine if a partial condenser could be employed and where it should be placed. Also determine if more than one condenser could be employed.

5. Determine the amount of steam required if a single partial condenser is used. You should assume that the condenser is placed between the last two stages of the ejector and a temperature approach of 10°F is used.

Transcribed Image Text:

H₂ = 1.2 lb/h CH4 = 20 lb/h C₂H6 = 45 lb/h C3H8 = 25 lb/h