15 replies to this topic

[paulinaote]

x

Edited by paulinaote, 19 August 2015 - 01:38 AM.

[Zauberberg]

Hi Paulina,

 

It is a bit hard to follow through your post - I didn't understand where the problem is actually. Are you having issues with determining the HGO product draw-off rate (flow) from the column, or the problem is to calculate the cut point of HGO based on available crude assay and given product specification?

 

If you want to reduce end point of HGO, you have to reduce the draw-off rate of HGO, or MGO, or Kerosene. Reducing the draw-off rate of HGO or side products which are above HGO, you are effectively increasing the internal reflux in the column, thus making the products lighter.

 

I can suggest you the books "Petroleum Refinery Distillation" by R.N.Watkins or "Handbook of Petroleum Processing" by D.Jones, where you can find extensive information about these subjects.

[PingPong]

It is not clear to me what exactly you are doing, and the spreadsheets are not clear for outsiders either.

 

You should however realise that you can not simply demand a certain TBP 50% temperature (or any other property) without adjusting the quantities of one or more products.

 

Apart from  that I have great difficulty to believe that a 39.7 API crude has a TBP end point of only 397 ^oC. That seems very very low.

Exactly which crude are you talking about?

[Zauberberg]

To reduce the 50% point of HGO (as well as the end point) without affecting product yields - for which I assume Naphtha, Kerosene, and Diesel - you can do one of the following:

 

• - Increase the heater outlet temperature but without changing draw-off rates of any product;
• - Decrease the draw-off rate of HGO, for constant heater outlet temperature as in the original case;
• - Increase the stripping steam in the main column (this works only up to a certain limit - then you get a flat rate of product recovery, no matter how much more steam you introduce in the column)
• - A combination of the three from above, depending on heater and crude oil limitations.

 

These are your handles. If you can't do anything from this list, then change the crude.

[PingPong]

I don't know what kind of crude comes out of the ground in Patagonia, but I am sure that a 39.7 ^oAPI crude does not have a FBP of only 397 ^oC. That crude TBP table in column E of your spreadsheet has unrealistically low temperatures, especially the second half of it.

 

You need to find a proper crude assay of that crude. Without a proper TBP curve/table you cannot do a useful simulation.

 

For case 1, the current situation get the following production plant.
CASE 1
Nafta -> 492 m3 / d
Kerosene -> 380 m3 / d
Diesel -> 594 m3 / d
Reduced crude -> 929 m3

Are those flowrates measured in the actual operation, or are they from your simulation?

 

On the other hand, I determined curve HGO with the "Probaility chart" uniting the end point and the temperature of 90% .....

When you have a converged simulation with an HGO drawoff, the simulation output will give you the TBP as well as the ASTM D86 curves (tables) of the HGO. No need to use astrology to invent them.
 

I must increase the yield intermediate (kerosene + diesel) so I design a lateral extraction of a new product between diesel and reduced crude, what I call HGO.

Where did you get the idea that adding an HGO drawoff will increase the yield of kerosene + diesel?

 

I don't understand how many theoretical stages you are using, you mention only 13 ? That is way too low for the whole column.

 

Also I don't understand your fixation with the 50% TBP of the HGO. Normally such HGO would have a 90% or 95% ASTM D86 specification, and a max pour point or max cloud point, and sometimes a max viscosity and/or a max density.

Edited by PingPong, 10 March 2015 - 10:07 AM.

[PingPong]

The method of calculation yields Perry is 13-84. It uses 50% TBP.

What do you mean by Perry 13-84 ? Does that 13-84 refer to a page number or a figure number? What edition of Perry?

 

- The ASTM oil was made by laboratory, I doubt that were wrong.

I doubt that that ASTM was D86. Maybe it was D1160 but then you need to know at what pressure it was determined.

But the best is to get the official name of that crude and look for a proper crude assay.

 

Until now I was under the impression that you want to withdraw that new HGO somewhere between the diesel drawoff and the column feed nozzle, but as you have only 3 real dishes there, I am not sure that I understand what you have in mind.

 

Can you make a simple hand sketch of the column, showing tray numbers, drawoffs, pumparound, et cetera, both for the existing situation, and for the future situation with the HGO drawoff?

[Zauberberg]

Paulina,

 

You can post sketches, simulation files, etc. by using the "More Reply Options" button which is below the last post in each thread.

[PingPong]

extraction of HGO, my idea is to design this draw-up the "stripping crudo red".

You want to draw the HGO from one of the reduced crude (atmospheric residue) stripping trays?

That is not a good idea, because what you will draw is then not HGO, but simply residue, and therefor to heavy to be of any use.

 

The column drawing is not very clear. Text is almost unreadable. Therefor I can't see at which nozzles the kero and the diesel are withdrawn. Is the diesel drawoff a total drawoff, or a partial? I can't see the pumparound drawoff and return nozzles. I can't see whether there are sidestrippers for kero and/or diesel and where the vapors of those enter the crude column.

 

And you should clearly define what the purpose of that new HGO drawoff is. What is it to be used for, and therefor what are its product specificitions.

Earlier you wrote:

I must increase the yield intermediate (kerosene + diesel) so I design a lateral extraction of a new product between diesel and reduced crude, what I call HGO.

but you still have not explained why you think that an HGO drawoff would increase kerosene+diesel yield. Who came up with that idea? The refinery? It seems nonsens to me.

If the purpose of your thesis work is to increase kerosene+diesel yield then I suggest you focus on that and forget about this rather useless HGO drawoff.

 

This topping column is a very short column, so the refinery can not expect miracles from it.

Is this in the Plaza Huincul Refinery?

 

Is this 39.7 API crude oil in fact a shale oil? Vaca Muerta?

In any case: ask for a crude assay of the oil. With what you have now you can not do any serious simulations.

 

ASTM D86 is normally not done on crude oil because it is not suited for high temperatures that cause cracking of the heavies in the oil. Maybe that is what happened in the lab, and therefor the temperatures hardly increase above 60 %, making that part of the TBP useless.

[PingPong]

- The extraction of HGO's is diesel under the dishes, not in the stripping crud zone.

What is the number of the dish that you intend to draw the HGO from?

 

If you want to increase the Intermediate Yield then you first have to increase the feed heater outlet temperature.

Then increase diesel draw rate. In the present design however the kerosene and diesel are condensed by the overhead condensor of the topping column. If the column top and condensor can not handle that, you could consider increasing the pumparound and take an HGO draw from that pumparound and see whether that can be mixed with the diesel while still meeting the diesel specifications.

 

I am not going to repeat my comments on that crude TBP again and again, but you should realise that it is your thesis that is at stake here.

[PingPong]

From the previous drawing I was under the impression that the diesel product was withdrawn above the PA, but now I see that the diesel is drawn from the same tray as the PA. That makes a separate HGO draw even more useless. Just increase the PA and draw more diesel. Forget about a separate HGO draw.

 

Moreover: what you intend to do is draw the HGO from the tray just above the flash zone. That liquid is not only too heavy to be mixed with diesel, but is moreover contaminated with entrained residue from the flash zone. It is a dirty brown liquid that is not good for anything but mixing with the reduced crude. So forget about it.

 

I don't have a crude assay of Tierra del Fuego and I don't see anything useful on the internet either. If the refinery does not have an assay either (which I find very strange however) a "reconstitution of crude" is your only option. But I advise you to have a good look at the resulting reconsitution TBP before using it in a column simulation. You probably need to smooth the reconsitution TBP curve by hand first.

[PingPong]

What I meant was: you probably get a reconstition TBP that looks like:

 

 reconstition TBP.jpg   8.07KB   3 downloads

 

So you need to make a smooth curve of that, without maxima and minima.

 

Can't you change the subject of your thesis?

Or is this sidedraw an idea from one of the refinery engineers? In that case you should ask him how that is supposed to yield a usable gasoil. In my opinion such HGO will be to dirty and too heavy for anything but fuel oil.

[PingPong]

I would have to think about that.

 

In the mean time you should concentrate on obtaining a useable TBP of that Tierra del Fuego crude.

[Zauberberg]

It is not uncommon to have Diesel pumparound and Diesel product draw-off at the same tray. I have seen this more than once and it worked OK.

 

Pulling HGO from Atmospheric column is an "adverse necessity" - otherwise the ejector system in downstream Vacuum Distillation Unit will suffer and lose a good fraction of its capacity. If you don't pull HGO, a lot of Diesel fractions will end up in atmospheric residue. Essentially, the column will operate with huge overflash which is a waste of energy.

 

HGO is never a real product anyway - depending on the regime it can be used partially for Diesel blending, some portion goes to FCC together with VGO, and something ends up in Fuel Oil pool.

[PingPong]

I never said that it is uncommon to have Diesel pumparound and Diesel product draw-off at the same tray. Of course it will work. But from the first drawing and the associated listing of number of trays I got the impression that it was not from the same tray here. From the good drawing however it is clear that it was.

 

It is however not necessary to pull HGO from the atmospheric column when there is a downstream vacuum unit, to the contrary. In new designs it is common nowadays to have a vacuum distillate top product in the VDU that is blended with the atmospheric gasoil to make diesel. The quality of such vacuum distillate is better than the quality of an HGO from the atmospheric column.

 

In this case the topping column is so short that there is no room for an additional HGO draw between diesel and feed inlet. Making more diesel can however just as well be done by drawing more diesel. No need for an additional HGO draw. Except that the subject of the thesis is to have an additional product draw, so there must be one. Stupid reason really, but that's life....

Edited by PingPong, 12 March 2015 - 04:37 AM.

[PingPong]

Obviously, to a side extraction should add more dishes

The wash section (between diesel drae and flash zone) does not have dishes (trays) but structured packing, only 1.5 meters high. There is no room to make an additinal HGO sidedraw there. You would need to cut the column and insert a new piece of shell, complete with a new drawoff tray (chimney tray), new liquid distributor and new section of packing.

 

1. In Refinery Gregorio occurs MGO diesel fuel used for marine vessels. Depending on whether it is summer or winter, the specification for cold product properties vary. In the first case (less stringent requirements) is feasible to produce a greater amount of diesel MGO, while in winter the extraction is less and over is "lost" as Reduced Crude, primer and less valuable.

This makes it much more clear what it is really about. Wish you expained us this from the start.

 

So in winter you have to separate the heavy end of the diesel MGO and produce that heavy end as a new HGO product.

What are the summer and winter product specifications (cold flow properties, ASTM 95%, et cetera) for the diesel MGO ?

What is the new HGO going to be used for? And consequently what are its product specifications?

 

The numbers on the flow scheme you posted earlier are unreadable. What is the pressure and temperature in the preflash drum?

Edited by PingPong, 13 March 2015 - 08:25 AM.

[PingPong]

MGO Diesel specifications are in excel, these are direct data topping then mixed with heavy naphtha to improve the pour point and sell the product.

Is the diesel pour point in the excel sheets before or after the addition of heavy naphtha?

 

Can you guide the plane went above and data from excel?

I have no idea what you mean.

 

Distillation curves that went: crude oil - kerosene - diesel MGO - Reduced crude, are of February 11, 2015.

Which distillation curves do you mean? I don't see any distillation curves in the excel sheets.

 

There is no flash drum pressure in the excel sheets. They only give the flash drum temperature. Could you find out what the pressure is?