31 replies to this topic

[ziron]

 

- overflash (1 tray above the feed tray) of 1134 m3/d.

 

crudo_in: 2650 m3/d

overflash: 1134 m3/d

% overflash: 1134/2650*100 = 42.8%. 

 

 

 

Hello Paulinaote,

 

Just a quick question when you say 2650 m3/d do you refer to it at operating conditions or at standard condition, at which conditions is the overflash? because when I looked at your print screens of hysys I saw in the Crudo_in table Std Ideal liquid flow = 2650 m3/d.

 

You should use Actual Volume flow from my point of view.

 

LE: I would specify the Condenser temperature around 40-45 degC, you have 81degC and from my point of view is too high (not the Off-Gas flow).

      The top PA should be around 60 degC from my point of view.

       I would of specify the Naphtha flow instead of the  column Top Temperature.

 

This is just an opinion at the first view. I'll read all the post to make a better idea of your problem.

 

 

Regards.

Edited by ziron, 14 May 2015 - 07:50 AM.

[PingPong]

Ziron,

 

The problem here is that there is no crude assay available for the Tierra del Fuego crude mix that is being processed in this refinery.

Paulina is trying to determine the crude TBP based on the limited operating data available, and use that crude TBP curve to reproduce the present operating conditions in a Hysys simulation. So far with little result because the main problem is that there is no ASTM distillation available for the Reduced Crude.

 

Therefore what matters for the material balance are the standard volumes and specific (or API) gravities of crude and products. The actual volumes are irrelevant as we are not interested in pipe velocities or pressure drops.

 

The Topping column does not have a top PA.

 

The condensor temperature of 81 ^oC in the simulation may be the dewpoint of the distillate as there are no data on light ends in the crude, but at this point in time its value does not really matter, as it does not influence the quest for the TBP curve.

Edited by PingPong, 15 May 2015 - 10:17 AM.

[PingPong]

The top temperature is the same that T of stream To ejectors?

The overhead vapor from the SVF goes to a precondensor where most of the steam and slop oil is condensed, and the remaining vapor (leak air plus some steam and hydrocarbons) goes to the first ejector. The precondensor is usually part of the ejector package.

 

But I assume Ziron was talking about the Topping Condensor temperature of 81 ^oC in your Hysys screenprint, which is unrealistically high. But at this point in time it does not really matter as it does not influence the Topping bottoms temperature.

 

 

 

I looked in more detail at your crude oil TBP compared to that of the naphtha, kero and diesel, and now think it is too heavy in the part between 30 and 70 v%. That may be the reason that in your simulation of the Topping unit the temperatures of heater outlet, column inlet and column bottoms are much higher than actual operation.

 

I will come back on this in more detail when I have more time.

[PingPong]

Paulina,

I had a close look at the operating data that you posted over the past weeks and compared those with the crude TBP curve that you made using Hysys (I assume that's what you used).

I specifically looked at the April 2015 data because those are the most complete. Data are only useful if they contain both the material balance, and the ASTM D86 data and gravities of the products.

Also the data of 11 Februari 2015 were useful.

 

Using the average result of API1987 and API1994 conversion methods, I converted the products D86 data into TBP data and plotted those in the same graph as your Hysys crude TBP curve:

 

 Hysys Crude TBP and Products TBP.png   327.64KB   1 downloads

 

As you can see your Hysys Crude TBP (HCT) curve is too high to match especially the diesel TBP data. But that part of the TBP has a big impact on the required heater outlet temperature, and on the design of the new SVF.

I prepared an Alternative Crude TBP (ACT) curve that matches the product TBP's much better.:

 

 Alternative Crude TBP and Products TBP.png   320.64KB   1 downloads

 

This ACT curve and the specific gravities of its pseudofractions were prepared taking into account the gravity of the total crude as well as the gravities of naphtha, kero and diesel.

Based on the april 2015 material balances and product specific gravities it can be calculated that the crude gravity is approximately 39.4 API, and so is the gravity of the ACT.
The pseudofractions of the ACT are listed in this file:

 

 Alternative Crude TBP pseudofractions.xls   22.5KB   10 downloads

Using these ACT pseudofractions in your Topping simulation will reproduce the operating data much closer than your HCT.

When you simulate the Topping Unit you must always use consistent data, so dat from the same day.

For example: I notice that in your last Topping simulation you used three stripping steam quantities that exactly correspond to the average of Februari 2015, but you used a crude flowrate that is 10 % higher than the Februari average.

I suggest you base your Topping simulation on the data of 7 April or 8 April 2015. These days operated on 2650 m³/d and moreover the sum of the products flowrates is very close to the crude flowrate. That is important. You can select the data from another day provided that the material balance of that day is not off by more than 1 %.

In the Topping simulation spec the product flowrates of reduced crude, diesel and kero (naphtha is automatically the balance). Do not spec ASTM temperatures, or other properties, of the products.

[PingPong]

I don't understand several things:

 

1) According to your Simulation.xlsx file you simulate the material balance of 8 April 2015.

However the material balance that you now use is very different from the 8 April 2015 material balance that you posted in the past, which were:

naphtha: 496 m3/d, instead of 580

kero:       463 m3/d, instead of 440

diesel:     519 m3/d, instead of  500

RC:        1156 m3/d, instead of 1130

 

What day are you really simulating?

 

2) That large amount of offgas that your simulation now produces. That is not possible with the ACT that I made. It seems that Hysys "modified" the TBP that you entered by adding Lights. Or did you add those Lights yourself? The reduced crude that you simulated contains some C2/C3/C4 now, so they must be present in the crude feed that Hysys uses.

And who knows what else Hysys modified in that TBP. The NBP's of the pseudofractions are different than in the ACT, and what did Hysys do with the gravities of the pseudofractions?

You should have a close look at the crude TBP and the Lights and Pseudofractions that Hysys actually uses now.

 

Does the reflux drum produce offgas in actual operation at 35 ^oC ?

 

3) As I wrote before: you have to use consistent data for the material balance, operating conditions and product properties (D86, gravity, pour point). So best use all data of one particular day, and compare product properties with the real properties of that day, not with product properties of another day when the column operated on somewhat other TBP cutpoints.

However you use the material balance of one day, and compare the results with actual D86 data of several other days (24April for naphtha, 11Feb for kero,10 and 22Apr for diesel). That is not correct, because the D86 data (and gravities, and pour points) are affected by the TBP cutpoints between products, which again depend on the amounts of the products that you spec in the simulation.

 

 

 

In both cases D86 90% Naphta is 146 °C.  Should be 136 °C.

Not surprising if you produce much more naphtha than in real. That moves up the TBP cutpoint between naphtha and kero, and consequently the D86 90 % goes up as well.

 

 

You must work more accurately, and think before you do something, because otherwise you keep wasting time.

And I can't keep going through all your numbers again and again, because my time is also limited.

Edited by PingPong, 20 May 2015 - 05:12 AM.

[PingPong]

The naphta thay I spec weeks ago (496 m3/d) is not directly produced from the topping. It is a mix of heavy naphta and light naphta downstream  of splitter from naphta topping. I realized this recently. The naphta Topping it is always in the range 580 - 590 m3/d.

(11) Does that mean that the material balances that you posted in the past are not really those of the Topping column, but after blending some of the heavy naphtha in kero and in diesel?

 

(12) But what does this mean for the naphtha, kero and diesel properties such as gravity, D86 and pour point?

For example: in the past you posted data for April 2015:

 

 Operating Data April 2015.jpg   359.46KB   1 downloads

 

According to what you say now, the naphtha flow of 8 April there is too low and the kero and diesel flows are too high. The same for the other days. But on what flowrates are the gravities, pour points and D86 in that table based on: before or after blending of part of the heavy naphtha into kero and diesel?

 

I have a two D86 Diesel topping (pure diesel) both in plant process condition: WINTER. One its for the day april 10 and the other its april 22.

(14) Are those D86 for diesel directly from sidestripper, or for diesel after blending with heavy naphtha?

 

I have one D86 Crude thats feed the plant. It is for the day april 10

(15) A D86 is not much help, as oil starts cracking above 300 ^oC or even lower. That cracking produces lighter molecules that boil at lower temperatures than the larger molecules they were formed from. As crude oil contains a lot of material boiling above 300 ^oC that will crack, a crude oil D86 is of little use.

But anyway, you can post it here.

 

(16) That cracking also has an impact on diesel D86 temperatures above 250 oC, especially above 300 oC. So when the lab reports a diesel D86 90 % or EP above 300 oC it is really higher than that. Remember that when you compare a simulation with reality.

 

 

I wish to know how calculated ACT to not disturb with different balance.

(17) Due to the limited amount of info, making the ACT requires a lot of hand work, base on experience. I am not going to publish how I arrived at that particular ACT. You can use it, or you can use your HCT, which is however clearly off in the diesel and heavier range, or you can produce something else that you feel comfortable with.

 

What matters is whether the ACT reproduces the actual operation, not how it was made.

You do not know how Hysys fiddles with the numbers, but you do not question Aspen to find out. They probably would not tell you anyway. Nowadays everybody with little or no experience uses Hysys, without really knowing what they are doing. When it comes out of Hysys they will believe everything.

 

(18) Moreover the ACT that I posted before was based on the assumption that the excel sheets with material balances that you posted in the past weeks were for the Topping column, before blending of heavy naphtha into kero and diesel. If that is not the case then my ACT is somewhat off.

 

(19) Once again: it is important that you understand that for your work, a D86 is of no value without the associated material balance. And a material balance is of no value without the associated gravities and D86's of all products.

 

(20) Also it is important that the material balance of a selected day has no more than 1 % difference between crude flow and sum of products. 1% may not seem much but it can affect cutpoints between products by about 5 ^oC and consequently affects D86 10 % and 90 % by almost the same 5 degrees. You must realise that when you compare simulated D86 with actual D86 of that day.

For example: earlier you found that simulated naphtha D86 90% was 146 instead of 136 ^oC, but you were producing 75 m³/d (= 3% on crude) more naphtha than the ACT is based on, so no wonder that the D86 90% was 10 degrees too high

[PingPong]

(21) I don't understand what you are doing.

You mix crudes with naphtha, kero and diesel? That does not sound realistic, as the mix is then short of reduced crude.

 

(22) The material balance of 10 April 2015 that you published before (see my remark (12) above) was:

Crude feed:                 2650 m³/d

 

Product Naphtha           503 m³/d   

Product Kero                 450 m³/d

Product Diesel               506 m³/d

Product Red Crude      1120 m³/d 

--------------------------------------------

Total Products               2579 m³/d

 

Material balance error: 2650 - 2579 = 71 m³/d = ~ 3 % on crude.

As I wrote several times: that error is too big to use the data of that particular day.

Why? Because it is impossible to know to which product(s) that 71 m³/d should be added, or whether it should be subtracted from the crude, or a combination of both.

 

(23) In view of your latest statements I now assume that those product flowrates are after mixing heavy naphtha into kero and diesel.

According to the April table in my remark (12) the heavy naphtha blended into kero and diesel was 17.5 and 35.93 m³/d respectively.

Therefor the topping products, before blending of heavy naphtha, must have been:

 

Topping naphtha = 503 + 17.5 + 35.93 =  556 m³/d       while you now use 580

Topping kero       = 450 - 17.5               =  433 m³/d       while you now use 450

Topping diesel     = 506 - 35.93             =  470 m³/d       while you now use 500

Reduced crude                                      =  1120 m³/d     and you also use 1120

------------------------------------------------------------------     -------------------------------

Total Products                                            2579 m³/d                                 2650

 

Apparently the refinery, or you, distributed the 71 m³/d material balance error over the light products only.

 

 

(24) In the past 10 weeks you have not answered most of my questions.

A lot of what I advised was also ignored.

And now again you did not even answer one question from my previous post.

 

We are going around in circles for 10 weeks now and I am getting dizzy and starting to loose my patience. Therefor I will no longer respond to this topic.

 

Good luck with your thesis.