Microsoft Word master thesis report fina doc

1.4.2. Separation section 
The function of this section is to split the full range naphtha into light naphtha, to feed the 
isomerization unit, and heavy naphtha, to feed the reforming unit.
1.4.3. Influents / effluents scheme 
The following scheme represents simply what enters and what goes out the battery limit 
during normal operations.

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Figure B-1-2: Influents/effluents scheme for naphtha hydrotreating unit in normal operations 
1.5. Intermittent operations 
1.5.1. Catalyst sulfiding 
 
The metals of catalysts used in this process are in the oxide form. They must undergo a 
treatment to recover the active sulfide form. If sulfiding is not complete, it could lead to metal 
sintering resulting in poor activity of the catalyst and heavy coke deposits. This operation is 
achieved by injection of the sulfiding agent (dimethyl disulfide (DMDS)) in a circulation of 
hydrogen and raw feed. The required amount of DMDS is determined from the decomposition 
of DMDS into H
2
S. 
Figure B-1-3: Influents/effluents scheme for naphtha hydrotreating unit during catalyst 
sulfiding 
1.5.2. Catalyst regeneration 
When catalysts activity becomes too low, they must be regenerated. This regeneration can be 
in-situ or ex-situ. 
If the regeneration is in-situ, the procedure includes: 
Naphtha 
Hydrotreating Unit 
Catalysts sulfiding 
Inert naphtha 
H
2
DMDS 
H
2
O 
Water saturated with H
2
S 
Butane 
Fugitive emissions 
FG / FO 
Combustion gas 
Naphtha 
Hydrotreating Unit 
Naphthas 
H
2
H
2
O 
Hydrotreated naphtas 
Sour water 
Off-gas 
Fugitive emissions 
Gas relieves 
FG / FO 
Combustion gas 

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- Commissioning of ammonia injection lines and caustic soda injection lines to the circuit. 
- A first coke combustion step with 0.5% vol. oxygen in the reactor inlet gas. 
- A second coke combustion step with 1% vol. oxygen in the reactor inlet gas. 
- A finishing phase with 1% vol. oxygen. 
- The shut-off of ammonia injection and caustic scrubbing. 
- Cooling down of the reactor temperature using the recycle gas circulation to prepare the unit 
for the new start-up. 
Chemical reactions occurring during catalysts regeneration are: 
- Coke combustion to produce carbon dioxide and water. 
- Oxidation of the metallic sulfides on the catalyst to produce sulfur oxides. 
- Neutralization reactions. 
SO
3
+ 2 NH
3
+ H
2
O → (NH
4
)SO
4 
CO
2
+ 2 NaOH → Na
2
CO
3
+ H
2
O 
SO
2
+ 2 NaOH → Na
2
SO
3
+ H
2
O