5.2 Technical questions

1. What is the most important aspect of main column in the CDU ?

Ans: The column hydraulics with a good distribution of liquid and vapor in the CDU is the most important aspect. The entire concept of live steam at various sections, top and bottom pump arounds, over-flash is centered around this designed basic feature.

2. What similarities are there for the CDU with vacuum distillation unit ?

Ans: Both crude and vacuum distillation units have similar architecture of the main and secondary columns i.e., both have complex stream circuitries with pump arounds, heat exchanger networks and utilization of steam. Only basic difference is that while we operate the VDU at lower pressure (30 – 40 mm Hg), the operating temperatures will be lower than those in the CDU. Otherwise, the basic principles remain the same.

3. What primary disadvantage exists by using live steam in the CDU columns ?

Ans:

- Live steam once it enters the column does not condense anywhere, as we don't want any condensation to happen.

- When live steam is used, vapor load increases significantly in the column

- This increases the diameter of the column at various sections. There will be ofcourse a section that has maximum vapor load and this section will have the maximum diameter.

 

References:

1. Gary J.H. ,   Handwerk G.E., Petroleum Refining: Technology and Economics, Taylor & Francis, 2005

2. Jones D.S.J., Elements of Petroleum Processing, John Wiley & Sons, 1995