4 replies to this topic

[Dtan76]

Hello Gen

Any ideal to estimate "realistic" consumption to blanket Hot Oil Circulation system with N2 gas?
I have work out the N2 needed during normal operation, steady-state. The N2 losses from blanketinge quipments is very minor. See below:

Nitrohen Bottle Design Pressure 200 Bar g
Minimum Pressure in the Bottle 5 Bar g
Nitrogen Bottle capacity 50 Liter
Total Nitrogen weight available per bottle:

N2 need at maximum pressure: Mf = Volume x density(N2)
Density(N2) = (Pb x MW)/ (R x T) r = 209.17 Kg/m3
Mass = 10.46 Kg

N2 need at minimum pressure: Me= Volume x density(N2)
Density(N2) = (Pmin x MW)/ (R x T)
r = 5.21Kg/m3
Mass= 0.26Kg
Net Volume of N2 per Bottle
Ma = M2 - M1
= 10.20 kg
So, the Net Vol per bottle is about 10.2Kg

N2 FOR BLANKETING (maximum expected daily consumption)
Blanketed equipment: a) HTF Storage Tank 170 m3
Drain Tank 14 m3
c) Expansion Tank 45.4 m3

Expansion Tank:
Hot oil volume, Vo 45.4 m3
Density@10°C/Density@200°C 0.01
dV = Vo x 0.01 0.454
T (N2) 160 °C
P(N2) 2+1 Barg
density(N2) 2.343Kg/m3
For 2 discharges /day
Mb3 Nitorgen required = 2 x density(N2) x dV 2.13Kg/day

Total N2 required for Blanketing
Mreq= Mb1+Mb2+Mb3 15.12 Kg/day
Assuming 2 weeks of hold-up & refilling: 211.66 Kg

No of Bottles required for Blanketing: 212/10.2 = 21 Bottles (Approximate)

Suppose we only need to provide 21 bottles to blanket Expansion Tank, 45m3 for (2) weeks.
This true for normal operation. I do not know what is the actual consumption during FIRST FILLING, I mean FIRST START-UP the Hot Oil Circulation system. According to my vendor, for FIRST FILLING N2 consumption is about 382 kg/hr (Norm) Blanketing - Expansion vessel;134 Kg/hr (Norm) Blanketing - Storage Tank;87Kg/hr (Norm) Blanketing - Drain Tank.

I doubt we need such huge N2 volumetric flow to blanket above equipments. Imagine let say 382 Kg/hr equivalent to 38 Bottles (=382/10.2) every hour cosntantly to blanket expansion vessel. One day we need 38 x 24 = 912 Bottles for Expansion Tank!!

Not way we can sourcing the numbers of N2 bottles in the our construction site. I can understand my vendor advise me it is huge N2 because N2 gase need to purge the air subject to the stability of crude flow and crude temp, varation during First Filling.

You can check my calc at here:

Attached Files

•  SIZING_N2_Consumption_1stOil.pdf   22.32KB   155 downloads

[Art Montemayor]

Dtan:

I don’t get the same results that you claim. Perhaps it’s because I can’t make out part of what you are stating and calculating. Your calculations are very bad quality and your explanations are deficient.

A professional engineer shouldn’t have to struggle to try to understand what another engineer has calculated. Engineering calculations should be accompanied by at least a sketch, a drawing, or a detailed scope of work and explanation of what is proposed. Your work doesn’t show any of this and, as a consequence, I (& probably everyone else) have to start assuming and guessing what it is that you propose and what is basically your problem. Please refer to my attached calculations and you will get an idea of what I mean by professional engineering calculations.

Do not assume that all engineers are supposed to know what “HTF”, “expansion tank”, and your nomenclature mean. I don’t know what you call “Mb1”, “Mb2”, etc., etc. You, as the calculations’ originator, should spell out all the nomenclature in detail. I believe I know what kind of basic Heated Thermal Fluid (HTF) system you have. But that’s only because I’ve been around the engineering block for 45 years. I wouldn’t expect the majority of engineers reading this to also have that amount of years in experience. You should describe your problem as detailed as required so that everyone can accurately know what it is that you are talking about. An engineering sketch is always a big help for starters.

Note how simply I calculate the amount of HP N2 cylinders you require to fill your system – and I also give you the exact source where you can confirm the data I employ. (Also note that you have failed to mention that there is a heater and all the associated piping that have to be initially inerted.) I would add 25% to the 26 cylinders calculated to arrive at a realistic estimate.

I simply can’t understand your ramblings about the amount of N2 expected to be consumed by the circulating HTF. There is no consumption of N2 in the expansion tank. Additionally, under ideal operating conditions, there is no consumption of N2 during operation – if the system is well designed, there are no leaks, process upsets, inventory changes, and multiple shut-downs and start-ups. However, in the real world there are the previous things that I’ve mentioned. And you are the only one who can estimate with reasonable accuracy the expected N2 consumption – simply because you are in control of the design and the operation. We don’t even have an accurate sketch of the system from you, so we can’t even begin to estimate the hourly or daily consumption of N2 in your system. The only thing any other engineer can say is that depending on how well you designed, built, and operate the system, you will have some N2 consumption. If you did a good job on all the items mentioned, then I would expect a token N2 consumption of a cylinder of N2 a week. If you did a bad job, then prepare yourself for consuming a lot of cylinders.

I hope this helps to clear up the picture you tried to describe and that it also helps you get an idea of what you require to make your system work correctly.

 N2_Purge___Inert.zip   60.81KB   205 downloads

[Dtan76]

Hello Art Montemayor

Thanks for promtly reply. Sorry i forgot attached the Engineering Sketch PFD. Please find below PFD and also my engineering calc.xls format. i forgot to estimate Hot Oil Circulation piping circuit but according to my last calc done (2) months ago, the piping circuit(pipes, fittings) approximate 15m3 volume Max. The Hot Oil Heat Exchanger - (2) operate and (1) standby - 4.2m3 net volume each.

Also, in my latest calc.xls I incorporate (2) circulation pumps consumption, In the P&ID's, itindicate 62.5liter/hr (Norm) consumption. Please see attached BORNO recommended consumption list for FIRST FILLING ONLY.

Many thanks
Young Jedi, DTan76

[Art Montemayor]

Dtan:

Thanks for the belated PFD and the revised calculations. However, your data is still not clear. Note in the Borno Utility Consumption List that Crude Oil and HTF (hot oil?) are listed as “consumptions”. I may be in error, but I don’t think you are consuming crude oil and HTF at the rates shown. This is a basic fault and mis-employment of logic. What, precisely, do you label as “consumption”? The improper use of the term (in any language) can be very confusing. What you are furnishing are consumption rates (used for pipe sizing) – not absolute consumptions.

The Expansion Tank is shown in the PFD as having 45 m3 of capacity. However, in the Utility Consumption List, under Note 1, it is stated “'the consumption indicated (for the expansion tank) is relevant to the first filling when the expansion vessel contains the hot oil at minimum level (~16m3) and the remaining part (~ 50 m3) shall be filled with nitrogen (at operating pressure) in about 30 minutes”. This description therefore states that the expansion tank has (16 + 50) = 66 m3 – far in excess of what the PFD cites. Which is correct?

A 45 ft3 capacity expansion tank is, in my opinion, an exaggerated size for your application. Even if you combine the needs of surge capacity, level control, and expansion all in the same vessel, it seems far too large for your needs. In reality, I think it also fulfills the need of having storage capacity also within the circulation loop. My point here is that I consider the Bono “consumption” estimates to be misleading and I also fail to understand what is meant by your calculation of N2 “consumption”. As you probably know, the N2 is applied to your HTF circulating system as a static, constant inert atmosphere. During normal, leak-proof, spill-proof, and goof-proof operation there should be NO N2 consumption. The same applies to your Storage Tank and more-so to your “drain tank”. Granted, we all know there will be leaks, spills, and inventory changes which lead to a need to add N2 to the system. But these should be minor quantities if the system is designed and operated well as it should be. The true N2 consumption is furnished by the proposed N2 cylinders. The initial N2 fill of the system is not a consumption – it is a “fill”. To express it as an hourly rate leads to confusion and misunderstandings.

One bad engineering detail I see in your PFD is that the fuel, air, and process lines entering and leaving the HTF heater are not shown independently. The heater is depicted as resembling a plate heat exchanger and, as a result, we can’t tell where the make-up HTF is injected and whether the heater is a direct-fired coil or radiant type. There are many other faults with the PFD, but they do not infringe on the question of N2 blanketing.

You haven’t asked for any more information and I still question the need to make so much calculation about the amount of N2 in the system. I agree you should be concerned about the amount of N2 you will consume in making up the daily losses but only you, I repeat, can make that estimate based on the quality of the design and the unit’s operation. Do not fail to calculate the N2 velocity in the supply lines. Most, if not all, of your N2 lines will be subjected to possible “choked” flow if you are not careful. I would use a minimum of 2-stage regulation of the N2 pressure and I presume you will be manifolding several banks of cylinders.

Hope this response helps and you are secure in estimating your N2 cylinder needs.

[Dtan76]

Hello Art Monte

Sorry becoz I forgot to attached you the PFD and indicate blanket equipments max operating pressure. For instant, the HTF Storage Tank set point is 0.15 Barg, drain tank set pressure is 0.99Barg and Hot Oil Expansion Vessel set pressure at 5 Barg. We will initially fill in the hot oil at 25C without heating up.

In the vendor consumption list, it recommend to fill in the Hot oil with minimum 16m3 and blanket 50m3 with N2 at pressure of 4 Barg.

The necessary nitrogen to fill 50m3 at 4 bar is explained here below:
((4x28)/0.0821)/303 = 4.50 Kg/m3 (Nitrogen Density)
4.50 x 50 =225.11 Kg
225.11 / 10.2 =22.03 Nitrogen bottles.
You need 22 nitrogen bottles to fill 50m3 @ 4bar.

Once reached the operating temperature of Hot Oil, the pressure inside the expansion vessel will be increased. The balance between this new pressure and the vessel operating pressure of 7 barg should be reached adding further nitrogen. The nitrogen bottles necessary to reach 7 barg cannot be evaluated at this moment. Surely, if you repeat the calculations made at above considering 7barg=8bar instead of 4bar you will get 44 bottles; it is the maximum numbers of nitrogen bottles we could needed, but if I do this during the hot oil heating I will loose the excess of nitrogen due to the pressure increasing.

Same calculation procedure repeating for Drain Tank and HTF storage tank, first filling fo rboth tank is very small and 1 bottle is more than enough.

Regards
DTan76

Attached Files

•  FromDTan.zip   47.47KB   115 downloads