7 replies to this topic

[Venkat @89]

In Hydrotreaters for Stripping of H2S from Hydrocarbon stream, Naphtha Hydrotreater unit uses simple steam reboiler at the bottom of the stripper, whereas Diesel and Vacuum Gas Oil hydrotreaters uses direct steam injection in strippers. why?

Why can't we use reboiler system in Diesel and Vacuum gas Oil hydrotreaters strippers instead of direct steam injection?

How does required Quantity of steam to strippers are finalized?? Stripper column operated at 11kgf/cm2g. HP steam of 34kgf/cm2g is used for stripping.

Edited by Venkat1989, 18 January 2023 - 09:30 PM.

[Pilesar]

In general, fractionating heavier crude components at high temperatures can result in unwanted thermal cracking. Vacuum columns allow lower boiling temperatures. Direct steam heating reduces the partial pressure of the hydrocarbons which also reduces boiling temperature. Reboiling columns instead of using direct steam reduces the vapor traffic and allows smaller diameter columns. The refinery design was chosen based on a perceived economical optimum. If you would like to compare options yourself, a good steady state simulation software will allow redesign without spending capital. An accurate computer model can identify the effect of varying steam flow.

[Venkat @89]

@ Pilesar sir

Thank you very much for your inputs, it's true especially for fractionation of heavier feeds, direct steam heating helps.

Our Diesel Hydrotreater, Diesel feed Initial boiling point is 160degC and final boiling point is 360degC.

Our stripper main intention is to get rid of H2S from the feed hydrocarbon coming from Hydrotreater reactor outlet, ideally to get rid of h2s and strip out some naphtha from stripper feed. My stripper feed inlet temperature is 265degC, with stripper pressure being at 11kgf/cm2g.

If I have to use reboiler instead of steam stripping, what should be my reboiler outlet temperature? What is the basis for it?

Kindly guide me.

Sorry to say, I am not aware of using any softwares.

 

Is there any general thumb rule for steam quantity to stripper w.r.t stripper feed flow? 

Edited by Venkat1989, 18 January 2023 - 09:24 PM.

[Pilesar]

I do not know of any rules of thumb which might provide you with a reasonable answer. If you do not model this system with a first-principles model, a literature search might find relevant results from some previously published similar comparison study.

[PingPong]

@Venkat1989

 

To get a rough idea you should read about the "Stripping Factor", which is K*V/L.

Google it or consult a proper textbook about distillation/absorption/stripping.

 

You will then also come across the "Absorption Factor" [ = L/(K*V) ], which is the reciprocal of the "Stripping Factor".

 

The GPSA book Chapter 19 would be useful. Chapter 25 gives you a graph for K-value of H2S.

 

For more accurate calculations a simulator is required. If you don't have access to a professional simulator like Hysys or Aspen+ or Pro/II or Chemcad then you could use freeware like DWSim.

[Venkat @89]

@Venkat1989

 

To get a rough idea you should read about the "Stripping Factor", which is K*V/L.

Google it or consult a proper textbook about distillation/absorption/stripping.

 

You will then also come across the "Absorption Factor" [ = L/(K*V) ], which is the reciprocal of the "Stripping Factor".

 

The GPSA book Chapter 19 would be useful. Chapter 25 gives you a graph for K-value of H2S.

 

For more accurate calculations a simulator is required. If you don't have access to a professional simulator like Hysys or Aspen+ or Pro/II or Chemcad then you could use freeware like DWSim.

Thanks for your inputs, shall go through them. 

 

May I know GPSA full form here?

 

Can you please give your inputs on this too?

 

Our stripper main intention is to get rid of H2S from the feed hydrocarbon coming from Hydrotreater reactor outlet, ideally to get rid of h2s and strip out some naphtha from stripper feed. My stripper feed inlet temperature is 265degC, with stripper pressure being at 11kgf/cm2g, using superheated HP steam at 34kf/cm2g.

If I have to use reboiler instead of steam stripping, what should be my reboiler outlet temperature? What is the basis for it?

Kindly guide me.

[PingPong]

Why did you change your user name? By using your email you invoke spam at that email adress.

 

You need to read about "Stripping Factor". You can google it, or use the GPSA book, or any textbook on distillation/absorption/stripping that you have.

 

Using a reboiler would mean using a fired heater. That is costly and moreover consumes fuel. I have seen it in the past but that stripper operated at a considerably lower pressure than your 11 kgf/cm2g. Nevertheless on request of that refinery we redesigned that stripper to use stripping steam instead of reboiling.

 

I don't think you can reboil a gasoil stripper at 11 kgf/cm2g as that would require about 400 oC or maybe more (boiling point of your gasoil at 11 kgf/cm2g) which may produce offspec diesel product, so don't even think about it.

[Venkat @89]

Thanks for the update, username got changed unintentionally. Thought of changing to previous one. But, as per the update from system, it said, can't change for 24hrs.