5 replies to this topic

[processengbd]

1. In determination of crude column top pressure and temperature. I have converted the TVP curve to EFV curve. The efv curve that has been produced is in at atmospheric pressure. So now I need to convert the EFV curve to column pressure. But I cannot find the procedure to convert it to a different pressure. Is it possible to convert the flash curve to a different pressure through phase envelope? How can I? Please direct me to a reference. 

 

2. Is there any reference regarding crude oil distillation where steam is not being used as energy input to the column (conventional reboiler).

 

For info: I am trying to learn crude distillation. I have couple of small plant example design.

 

Have access to HYSYS and Pro II, (More accustomed to HYSYS.)

and following study materials

 

1. Petroleum Refinery Engineering by W. L. Nelson, 4th edition, McGraw-Hill, 1958
2. Petroleum Refinery Distillation by R. N. Watkins, 2nd edition, Gulf, 1979 

3. Refinery Process Design (Lecture Notes) Dr. Ramgopal Uppaluri, IIT Guwahati

4. Data Book On Hydrocarbons Application To Process Engineering J. B. Maxwell

5. Handbook of Petroleum Processing David S. J. Jones, Peter R. Pujado 2006

6. How to Design Crude Distillation Watkins Hydrocarbon Processing-1969

 

I would appreciate any suggestion.

 

Best Regards

processengbd

Edited by processengbd, 07 January 2015 - 02:16 AM.

[colt16]

(1) I may be wrong but if stripping steam is used then the column top temperature is simply at a temperature greater than dew point so that water may appear as vapour at the top and be removed in the reflux drum. 

 

(2) What other types of heating medium are being suggested?

[processengbd]

Thank you tanykiat

Yes you are correct, that is one of the criteria. But as per my limited understanding column top conditions depends on the top distillate desired quality (TBP range & ASTM GAP required from next product i.e. Kerosene). 

 

So as I said need to know key procedure "to convert the EFV curve from atmospheric pressure to at column pressure" 

 

​I have couple of example plant documents where in one they have used direct fired heater as a reboiler. Another one used indirect thermal oil heater is heater. ( Because in both cases crude (Gas Condensate) were very light so requirement of heating the reboiler was within 300 deg C).

 

Regards

processengbd

[Himanshu Sharma]

Dear Processengbd

 

I have used both HYSYS and PRO-II for Crude Unit simulations and  my experience with PRO-II has been better in terms of handling wide HC range as in Crude Oil.

 

If you want to believe me ,TBP distillation of Crude along with component wise input upto C6 as an Input works best with commercial simulators.It is best to have a Crude Assay in form of TBP distillation,the conversions and inter-conversions introduces lots of conversion misfit errors in the system.

 

There are actually no re-boilers in the Crude Tower ,the feed is typically heated through a Fired Heater and flashed in the tower.

Stripping steam helps by lowering vapor pressure and improving distillation but in terms of heat transfer it actually quenches Crude Tower bottoms at typical Crude Tower temperature of 360~380 Deg C.

 

Thanks and Regards

Himanshu

[processengbd]

Dear Processengbd

 

I have used both HYSYS and PRO-II for Crude Unit simulations and  my experience with PRO-II has been better in terms of handling wide HC range as in Crude Oil.

 

If you want to believe me ,TBP distillation of Crude along with component wise input upto C6 as an Input works best with commercial simulators.It is best to have a Crude Assay in form of TBP distillation,the conversions and inter-conversions introduces lots of conversion misfit errors in the system.

 

There are actually no re-boilers in the Crude Tower ,the feed is typically heated through a Fired Heater and flashed in the tower.

Stripping steam helps by lowering vapor pressure and improving distillation but in terms of heat transfer it actually quenches Crude Tower bottoms at typical Crude Tower temperature of 360~380 Deg C.

 

Thanks and Regards

Himanshu

 

Dear Mr. Sharma

 

Thank you very much for taking the time to reply to the post.

 

Yes I agree (after reading all the post in the forum praising Pro II) that Pro II will be the ultimate simulator in which I would do my final simulation. 

 

But I am now in a stage where I need to decide very basic criteria such as (No of stages, reflux ratio, Column pressure profile, Feed temperature & Pressure, etc) before going into simulations. Now I am stuck in determining column top conditions (pressure- temperature). Which I presume will be available from EFV curve at column pressure.

 

Regarding of C1 to C6 input: Yes I totally agree, even a slight diversion of IBP, results totally different product in simulation.

 

Regarding Reboiler: Yes I agree that crude distillation does not require a reboiler. But the case that I am studying is too light and FBP 328 deg C. And the capacity is very small 3200 BBL/day. So that is why I am guessing that they have chosen to use reboiler.

 

Best Regards

processengbd

Edited by processengbd, 09 January 2015 - 10:20 AM.

[PingPong]

Forget about EFV. That is completely useless.

 

Column top temperature is calculated by the simulator, not set by you. Condensor outlet temperature is set by you depending on temperature of available cooling media (cooling water, aircooling, crude preheat, .... whatever).

 

Condensor outlet pressure then depends on the distillate condition you want to obtain. For example: if you want the distillate to be all liquid, then the condensor outlet pressure is the bubble point pressure (vapor pressure) of the distillate.

But you also need to look at the bubble point temperature of the bottoms product: the higher the condersor outlet pressure you choose (to minimise vapor distillate production) the higher the column bottoms pressure, and therefor the higher the column bottoms temperature (bubble point temperature, boiling point) that needs to be achieved by the reboiling medium. So you also need to look at the reboiler media available: HP steam, hot oil, or otherwise you need a fired heater. If a fired heater is not desired, then the maximum (withj steam or hot oil) achievable column bottoms temperature sets the maximum allowable condensor outlet pressure.

 

So the first thing you need to do is estimate, from the TBP data of the crude feed, what the distillate composition and the bottoms product composition are going to be, and for each: what their bubble point temperature (boiling point) is as function of pressure.