Fuel Oil Pipeline Design - What to do when finished loading

[khardy]

I am designing a pipeline to transport #6 fuel oil from an off-shore mooring to a terminal. Distance from the terminal to the shore is 5-miles and the line will be buried for the entire run. The distance from the shore to the mooring is 1.5-miles. The product is #6F.O. with a 400cSt viscosity at 120F. Deliveries will be made every four months or so. The site is in the Caribbean where the temperatures rarely get below 75F. The product will be received heated to 120F. What is the best way to leave the line after the delivery to ensure we can receive product the next time?

1) Leave it in the line. Pros: easiest. Cons: product could solidify to the point the ship can’t pump the slug out on the next delivery.

2) Fill the line with sea water. Pros: cheap. Cons: corrosion, environmental.

3) Fill the line with air. Pros: no corrosion or slug. Cons: compressor expense, don’t know how easy this will be operationally, fire hazard of fuel / vapor mixture.

4) Fill the line with fresh water with corrosion inhibitor and re-use the same water each time. Pros: no corrosion or slug. Cons: expense of water storage tank & pump.

5) Steam trace. Pros: common. Cons: Expense

6) Other ideas?

I’m hoping somebody with operational experience can help with this.

 

[BigInch]

jmw,

I don't see where khardy mentions any beach/shoreline facilities. The only facilities he mentions are
1.) Terminal and 2.) Offshore Mooring, which I assume is an SPM or similar off-loading buoy. The terminal is 5 miles from shoreline and the mooring is 1.5 miles into the sea.

For getting a proper choice of realistic pipeline options, let's go back to the original problem,

The manifold pressure will be 150-psi which is a condition
of the contract. No booster pumps are envisioned. Lines will be sized for heated product.
*The pipeline can hold some 275,000-gal of fuel.
36 hrs to unload 60,000 bbls @ 120ºF
low ambient temp 75ºF

Therein lies the problem. They will allow the product TO cool off in the pipeline, but the pipeline diameter sizing condition is 120ºF. (how rediculuous is that? let's see.)

With a visc at 120F of 400 => 16" D => dP = 77 PSI
With a visc at 60F of 1200 => 20" D => dP = 91 PSI

With such a small difference in pipeline diameters between hot and cold product cases, it is totally obvious that the savings of the smaller diameter are quickly offset.

If recirculation is the solution, a second pipeline, shore pumps, tank, valves and more complicated operational proceedures are needed.

If leaving water in the pipeline is the solution, shore pumps, tank, valves are needed. Additionally, the pipeline is exposed to possible corrosion from salt water (I'm sure they'll use inhibitor every time), or they will have to pay for diesel or other diluent, and the operations are more complicated.

As Al Gore says, "What kind of choice is that?"
I think its definitely a no-brainer.

http://virtualpipeline.spaces.msn.com

 

[owg]

What is the flash point of the No. 6 Fuel Oil?

HAZOP at

http://www.curryhydrocarbons.ca

 

[BigInch]

I take it this is a new thread?

150ºF

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[khardy]

I was happily away from my computer this weekend.

My original post was based on assumed lengths. I now have the actual lengths.

Marine hose: 80-ft 12”
Marine line: 1.5-miles 12”*
Shore line: 4.2-miles 16”*

*Based on 120F

Biginch: By ridiculous you mean why not just use a larger diameter pipeline that can handle FO at 60F? I would agree if your numbers made sense to me. With the lengths stated above, the total head loss is roughly 125-psi for 400cSt, SG 1.0, HFO flowing at 2,000-bbl. (not including elevation changes) The viscosity of 400-cSt is at the reference temperature of 122-F. I don’t have another reference viscosity but a typical 400-cSt @ 122-F HFO would have a viscosity of 7,000-cSt when cooled to 60F. Besides, even if the choice was between 16” or 20” the cost difference between the two sizes would be $580K not including freight or installation.

I’m inclined to pack the line with a light oil. (cutter, mgo, or similar.) I’m checking to see of the ship can launch a batching pig between the light oil and the HFO. As it does so the LO will be stored at the terminal in a tank built for that purpose. When the loading is completed the terminal will displace the HFO by pumping the LO down the line with a batching pig in between.

 

[jmw]

Er, does $580k include the cost of the additional fuel/distillate left in the pipeline if it is increased from 16" to 20"?

BigInch,
You are right, Khardy doesn't mention these facilities on the beach but in suggesting ways and means I'd suggest they become necessary due to my assumption that HFO would have to be purged to the terminal not the vessel due to (a) demurage and (b) what to do with the 275,000 gallons of fuel purged back to the vessel.

It seems from Khardy's last post that utilising the tankers pump is indeed one of the options being considered.
But we are back to the tanker purging the line and now maybe pigging it.

That would mean either the option of providing a cutter stock source to the tanker and connecting to the inlet of the tankers pump or the tanker carrying 275,000galls of cutter as part of the cargo (easier to pump seawater, no extra fixed installation).
But if the tanker provides the cutter stock, over time this would mean accumulating cutter at the terminal, another 275,000 galls each time the tanker calls.

Either way I can't see any use of the tanker being as simple as investing in some beach plant and letting the tanker depart the moment it has fully unloaded.

Since this is a purge at leisure, I suspect the pipeline and beach installation need not be that expensive.

I am sure pumping water or diesel down the line from the tanker or pigging (most unusual wouldn't you think?) would incur a capital cost, even if they could/would use their pumps but probably some modifications would be required which I doubt they would want to do as it would mean committing the same tanker every time.

Of course, the demurage or charges for special services by the tanker would be a recurrent cost as against a capital cost for a fixed installation managing the pipe line flush.

Incidentally, based on a 390cst fuel (at 50C) I suggest the actual viscosities will higher than 1200cst at 60F; the viscosities are likely to be:
at 10C: 14,100cst
at 15C: 7,900cst
at 20C: 4,650cst
based on ASTM D341 calculations for a G, H or K35 fuel (35cst at 100C).
What would that do to the pipe sizing?


JMW

http://www.ViscoAnalyser.com

 

[BigInch]

I think you need to know the viscosity without question, before you start making any decisions.

My info shows 830 cP at 60, so to be a bit on the safer side I used 1200 cP at 60F. I did use 1166 gpm, so I had the flowrate wrong.

With the new length and correct flowrate, I get a 20" D, if cP <= 1200 then dP <= 115 psi, no elevation change from sea level to tank, but you've got 45 psi left at the inlet, so that's enough to measure and fill a tank for a cheap bunch of operators.

No ship is going to launch a batching pig and they're a waste of time anyway. You're not going to make less interface in 5.7 miles, possibly more.

You've still got no way to pump LO into the subsea pipeline out to the mooring point? It is full of #6 when the ship leaves.

The standard way to do this is with a larger line diameter, or in some cases a recirculation line can be used, but probably not for #6, heavy heavy crudes maybe yes. Both pipelines would be one-way to the beach when pumping #6 from the ship, then changing to LO out in one line, #6 in on the other line until both are full of LO.

How much do you think you'll have to pay for a pump, valves, control system, taking a tank out of service, the extra operation hassle, the power cost, the maintenance cost, for the next 50 years????? One larger line diameter, looks like a bargin when compared to all that or to $ 580 K for a larger line.

Oh I forgot, its the cost of leaving some unused fuel in the pipeline that the client has a problem with. Back to the water.

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[owg]

BigInch: I was just checking on the safety of using air to fill the line while out of service. I see that has been considered. Air compressors are cheap, portable, and available on many sites.

HAZOP at

http://www.curryhydrocarbons.ca

 

[BigInch]

Vapor handling?

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[khardy]

Biginch: I know the viscosity: 400-cSt @ 122F. This has been given to us by the fuel supplier. As JMW points out this, this grade of fuel will have a viscosity of some 7,000-cSt when cooled to 60-F. (Actually, I doubt it would cool below 75F, but even at this temperature the viscosity would be around 3,000-cSt.)

JMW: I do not intend to have any facilities on the beach besides a small valve pit for an isolation valve. My intention is to store the LO (or water) up at the terminal. After the HFO was discharged, a pump at the terminal would push the LO all the way back to the ship. When the next ship arrives it would use HFO to push the LO back to the terminal’s LO storage tank.

 

[BigInch]

OK just check with the fuel supplier what the viscosity is at 60 F, to keep me happy, please. If the viscosity is too high for one reasonably sized pipeline, I would definitely use a recirculation system. You can make two smaller diameter pipelines and flow inbound with the heavy fuel oil, then reverse one to circulate diesel or light oil or even water to get the leftover heavy fuel in the pipeline to the terminal.

Half my work experience (and the hardest of it all) was educating clients, so I really do feel your pain there. Use water if you have to, but use a recirculating system of some kind.

With one pipeline, I still don't understand how the light oil is supposed to get to the ship so they can pump it into the pipeline and force the leftover heavy fuel oil in there to go to the terminal, unless they will accept the backflow of the heavy fuel oil as you fill the pipeline with something else.

http://virtualpipeline.spaces.msn.com

 

[khardy]

“With one pipeline, I still don't understand how the light oil is supposed to get to the ship so they can pump it into the pipeline and force the leftover heavy fuel oil in there to go to the terminal, unless they will accept the backflow of the heavy fuel oil as you fill the pipeline with something else.”

Now I understand the confusion. I expect the ship to accept the heavy fuel oil displaced from the line as the terminal pumps LO. I assume they won’t mind since it’s the same fuel that just came from their boat anyway. I will confirm this.

If the ship will accept the “back flow” the cheapest option is to use a single 16” as opposed to two smaller lines. To equal the cross-sectional area of a 16” line (or flow capacity) the possible combinations of dual lines are 14” & 8” or 12” & 12”. Both combinations weigh more (and therefore cost more) than a single 16” line.

I’m with you completely on using LO instead of water. And I’m pretty sure I’ll be able to sell it to the client.

 

[BigInch]

OK! Finally. I originally suggested you might be able to push it back to them, but nobody seemed to like the idea and I assumed we wrote that option off. If you can make that work, good stuff. Chavez could seend it on to Cuba or something.

Right. Nothing messier than water and oil. Have you ever seen Orimulsion?

http://virtualpipeline.spaces.msn.com

 

[khardy]

Nope, but i've built a pipeline and four tanks intended for it. They changed their minds before we finished and went with fuel oil.

Or should i say Chavez chainged thier minds.

 

[BigInch]

Mr. Price changed their minds. He's a very influential guy.

http://virtualpipeline.spaces.msn.com

 

[jmw]

BigInch,
it was me who kept on about the question of whether Khardy was going to push back or not, and he did not prejudice us by saying one way or another nor if he had intentions for a beach installation.

I considered, whether rightly or wrongly, that changing environmental regulations might not make what should be a simple option no longer feasible, if not now, then in the near future. The secondary consideration is demurage... the added time to pump out the line to the tanker from the terminal. Most usually tankers arrive, discharge and go.

As I said, I just got through visiting a fuel barge, not a tanker, where they have already had to change their practise of returning with some fuel left in the vessel, to a complete pump out because MARPOL Annex VI requires that all fuels are maintained segregated. A fuel barge delivers fuels to ships, but otherwise has much in common with tankers, I'd assume.

This might not be a problem at the terminal and it might not be a problem for tankers only delivering fuel to power stations not affected by MARPOL.

If the tanker is used for other duties such as Marine fuel oil deliveries, then this should be anticipated.

If the tanker operator has no problem with this then sure, a single tank in the terminal is easily the best way to go.
If not and it is a liquid flush that is required, then it could start to get more complex.

But, whatever else, these are enjoyable questions.





JMW

http://www.ViscoAnalyser.com

 

[BigInch]

It was YOU! I thought I was to blame. OK, I don't remember now. True, it is another complication, so not ideal, but if they're willing to take off with excess oil, why not. Wonder if there's a price increase or reduction. I don't know how to evaluate that in relation to building two pipelines or the larger diameter options. Fortunately, I don't have to.

khardy, good luck. Let us know what the final decision is.

http://virtualpipeline.spaces.msn.com