7 replies to this topic

[sheiko]

Dear refiners,

There is something I don't understand with my diesel HDS unit.

I have the following situation:

- The reactor is loaded with Co-Mo catalyst.
- The hydrodesulfurization reaction is taking place in the reactor.
- This reaction is exothermic.

However, I observe that the reactor outlet is colder than the inlet by 5-10°C
(I actually have noticed the same with the Kerosene HDS and Naphtha HDT).

I suspect endothermic reactions to take place (namely the ring opening of molecules such as thiophenes is endothermic).
I have also thought of heat losses...

Is it a typical situation? May I know your experiences or theories about it?

Edited by sheiko, 03 July 2012 - 05:57 PM.

[Technical Bard]

Are you injecting quench gas between the beds of the reactor? Is it possible the quench gas rates are too high, particularly before the last bed? How does your outlet temperature compare to the WABT of the last bed (this may indicate an instrument problem)?

I know that in diesel HDS units it is desirable to keep the last bed temperature down to reduce recombination reactions, but having an effluent colder than the inlet seems odd.

[Modesty Blaise]

sheiko,

Where is the location of TI which measures the outlet temperature?

Regards,

Edited by Modesty Blaise, 04 July 2012 - 09:17 AM.

[Himanshu Sharma]

Sir,

Please let us know the Feed inlet Temperature,WABT across each bed,Reactor outlet Temperature.

Additionally,please sample catalyst for coke formation.

[Padmakar Katre]

Sir,

Please let us know the Feed inlet Temperature,WABT across each bed,Reactor outlet Temperature.

Additionally,please sample catalyst for coke formation.

Hi,
How the sampling of catalyst will help analyzing the issue of endotherm.

[Himanshu Sharma]

Hi Padamakar !

Glad to hear from you.

Formation of coke is an endothermic reaction,generally its not that predominant in Hydro crackers but a Hydrotreater catalyst at low pressure could be vulnerable to coke formation.

[sheiko]

Are you injecting quench gas between the beds of the reactor? Is it possible the quench gas rates are too high, particularly before the last bed? How does your outlet temperature compare to the WABT of the last bed (this may indicate an instrument problem)?

I know that in diesel HDS units it is desirable to keep the last bed temperature down to reduce recombination reactions, but having an effluent colder than the inlet seems odd.

The reactor is rather small and has a single bed, so there is no quench.

Edited by sheiko, 06 July 2012 - 09:12 PM.

[Qalander (Chem)]

I also suspect that

• some endothermic reactions of the kind of heterogeneous ring opening are always associated
• depending upon crude types and origin and its Nitrogen, Sulphur compounds etc. impurities contents