Hydrotreatments Flashcards
In what form are the impurities extracted in HDT units ?
- H2S
- H2O
- NH3
- Metals trapped in catalyst
- Unsaturated compounds are hydrogenated
Under what form is sulfur found in light and intermediate cuts ?
Mainly mercaptants (RSH), sulfides (RSR) and thiophenic compounds (S in unsaturated cycle)
Under what form is sulfur found in gasoil and residue ?
Mainlybenzothiophenic and dibenzothiophenic compounds (S in unsaturated cycle with one or two other aromatic cycles)
Why don’t we like sulfur ?
- It produces pollutants SO2 and SO3
- It’s a source of corrosion
- It smells bad
- It’s a poison for catalyst
Why don’t we like nitrogen in crude ?
- It’s a basic compound that can poison catalysts (with acidic function)
- It’s more difficult to extract than S
In which cuts are metals mostly present ?
Vaccum residue (asphaltenes)
How are residues treated to remove impurities ?
Hydrodemetallization
Why is hydrodemetallization a complex and costly process ?
- Very high pressure (200 bar)
- Large amount of catalyst (because we trap the metal in the catalyst)
- We need new technologies to remove the catalyst when it’s saturated with metal
Which conditions promote hydrotreatment reactions ?
- Increase of T
- Increase of P
What is the range of T for HDT units in a refinery ?
From 300°C (light cuts) to 400 (heavy cuts)
What is the range of P for HDT units in a refinery ?
From 20 bar (light cuts) up to 200 bar (residue)
What characterizes hydrotreatment reactions ?
- ExoT
- H2 consumers
- Induce coke formation
- Can increase cetane of 3 to 4 points
What are the two typical combination of metals in HDT catalyst ?
- Cobalt/Molybdene for S
- Nickel/Molybdene for N and hydrogenation
What is the typical amount of catalyst needed depending on the cut (for 100 t/h of feed) ?
- Light cut : 30 t
- Gasoil : 75 t
- VGO : 200 t
- Vaccuum residue : 300 t
Why do we need more catalyst for heavy feeds ?
The heavier the feed, the harder it is to treat, the more residence time we need and therefore the bigger the reactor and the more catalyst we need
What kind of HDT for fuel gas, LPG and naphtha ?
HDT to remove S, N and olefins
What kind of HDT for kerosene ?
Sweetening to remove mercaptants
What kind of HDT for gasoil ?
HDS
What kind of HDT for VGO ?
HDT to remove sulfur and hydrogenation of aromatics
What kind of HDT for vacuum residue ?
HDM + HDT to remove sulfur
What can we do to limit exoT in gasoli HDS ?
Quench with cold H2 in the reactor to limit exoT to 15°C
What arethe typical T and P in a gasoil HDS ?
T = 360 and P = 60 bar
What are the separation units after an HDS unit ?
- HP separator to remove H2 (55 bar)
- LP separator to remove H2S (10 bar)
- Gasoil stripper to recover wild naphtha
- Vacuum dryer after stripper to recover Gasoil
What are the two kinds of loading in HDS ?
Sock vs Dense loading
How much do we gain with dense loading ?
We can have 15 to 20% more catalyst
