Initial crude oil fractionation units

Question 1

What are the important equipements before the atmospheric distillation column ?

Answer 1

• Heat exchangers for pre-heating
• Desalter to remove mineral salts
• Furnace to finish heating the feed

Question 2

What is usually the operating pressure in the atmospheric distillation column ?

Answer 2

Between 2 and 5 bara

Question 3

What are the two important design specificities of the atmospheric column (one at the top, one at the bottom) ?

Answer 3

• Smaller diameter at the top (change at kerosene draw off) wherewe expect less liquid traffic
• No reboiler (the feed is close to the bottom and act as one)

Question 4

What are the pump arounds ?

Answer 4

We take material form the draw off and use it to heat the feed. It gets cooled down and is sent back to the column where it acts as a reflux

Question 5

Why are there stripper on the side of the atmospheric distillation column ?

Answer 5

The strippers are there to removelight materialsfrom the draw ofs and send them back to the column

Question 6

What is the specificity of the kerosene draw off splitter ?

Answer 6

It’s a reboiler stripper and not a steam stripper to avoid water contamination in the kerosene cut

Question 7

What is injected at the bottom of the distillation column and why ?

Answer 7

We inject steam :

• vapor traffic in the bottom part
• move the materials to avoid coking

Question 8

What is the usual height of the atmospheric distillation column ?

Answer 8

Around 50 m high

Question 9

What is the usual feed temperature of the atmospheric distillation column ?

Answer 9

360 to 380°C : roughly the final boiling point of the gas oil cut

Question 10

What is the usual vaporization rate of the feed of the atmospheric distillation column ?

Answer 10

> 60%

Question 11

What is the ratio between the heat give by the preheat train and the atmospheric furnace ?

Answer 11

• HX trains : 50-70%

- Furnace : 50-30%

Question 12

What is the purpose of the desalter ?

Answer 12

To remove mineral salts form the crude

Question 13

Which separation principle is used in the desalter ?

Answer 13

Decantation

Question 14

What are the three steps occuring in the desalter ?

Answer 14

• Mixing water and crude to create an emulsion
• Enlarging water droplets withe electrocoalescence
• Decantation (water at the bottom and desalted crude at the top)

Question 15

What are the operating conditions in the desalter ?

Answer 15

• 100 < T < 150 °C (depending on the crude)
• 9 < P < 12 bar
• 20 < residence time < 40 min
• Efficiency : 95%
• Water injection : 3-8% of vol

Question 16

What is the main type of mineral salts in the crude oil ?

Answer 16

Mostly chloride mineral salts

Question 17

How many trays are there usually in the strippers around the atmospheric distillation column ?

Answer 17

4 to 10 trays (strippers, more than is useless)

Question 18

What is the usual pressure in the vaccum distillation column (top and bottom) ?

Answer 18

Top : 60 mbar

Bottom : 90 mbar

Question 19

What is the feed temperature of the vacuum distillation column ?

Answer 19

390°C

Question 20

What kind of internals are used in the vacuum dist. column ?

Answer 20

Packing to ensure a good vacuum in the whole column

Question 21

What is the overflash in the vacuum distillation column ?

Answer 21

We inject part of the last draw-off at the bottom of the column to control the liquid level and to add light component at the bottom and increase vapor traffic in that zone

Question 22

Why do we inject steam at the bottom of the vacuum distillation column ?

Answer 22

• Increase vapor traffic at the bottom of the column

- Create movement and avoid coking

Question 23

What are the streams injected at the bottom of the vacuum distillation column ?

Answer 23

• Steam

- Overflash

Question 24

How many columns are there in the gas plant ?

Answer 24

5

Question 25

What are the columns in the gas plant ?

Answer 25

• Debutanizer
• Deethanizer
• Depropanizer
• Naphtha splitter
• Deisopentanizer