Fuel Oil Pipeline Design - What to do when finished loading

Interesting problem.
I can’t give you a gospel answer, just some thoughts about how I’d tackle it and what factors I’d consider.
You will need to get the ideas from the other forum mebmers and some comment on my thoughts.

Questions:
[ul][li]how do you measure the quantity delivered?[/li]
[li]how do you check the quality?[/li]
[li]6.5 miles total pipeline will contain how much stranded fuel?[/li]
[li]what type of pump or pumps are you using?[/li]
[li]will they have to blow out the lines at the mooring anyway or are these self sealing or otherwise sealed connections when separated?[/li]
[li] what is the nature of the terrain under which the pipe will be run?[/li][/ul]

I’d say you have several different aspects to consider:
Environmental, commercial and security plus capital costs.

If you are within reach of the EPA and I’d guess this is a power station, take note of what happened to PREPA (Puerto Rico) who settled out of court on a range of pollution offences. I’d hate to think what they would have paid if they had gone to trial. If not, then you must still have some serious environmental concerns to consider. One would be how to prevent some leakage from a 6.5 mil pipe full of heavy fuel oil that is unused and untended for long periods. How do you know it won’t leak under ground? If it is only used for unloading then the scope for harm is less.

Secondly, however much fuel the pipeline will hold, if you leave the fuel in the pipe it becomes stranded asset and at $386 a ton for 380cst (Houston price) work out just how much extra cost is invested in this pipeline. Now you might be paying that sort of price but you might be getting it from Hugo Chavez at whatever knock down price it is today, but if someone can tap into your pipeline, it is the market price that controls what they can sell it for. Now this has had some disastrous consequences in some parts of the world but don’t think it just happens in Africa. I know of a paper mill in the UK where they piped high pressure steam to the next mill a couple of miles away. People in “gypsy camps” would regularly tap into the line and pirate the steam. They’d also tap into the electric lines.

Now consider quality and quantity. Both can be suspect when delivered and any opportunity for the issue to become clouded will be exploited in a dispute.
There isn’t much argument about fault when you find dry cleaning solvents in your fuel but there are a great many other problems for which plausible “accidents” can be claimed. These include entrained air (cappuccino effect which messes up tank dipping) and air bowing (at the end of batch which messes up flow meters and can also disturb tank dipping to an extent) plus air will cause false density and viscosity readings if you do an offline test. Now air just affects the quantity invoiced.
Water is the other most common problem, fresh or salt. I’ve visited power stations where the fuel delivered was so full of water it couldn’t be used but they didn’t find out till too late. Was it an accident or deliberate? If you provide water or air to the pipeline, you may create an opportunity for them to be introduced into your fuel rather than just into the pipe.
OK, you can see that I lean toward leaving the pipe line empty after unloading but how to do it? That depends on how you are pumping the fuel? One big PD pump at the mooring pushing it all the way on its own? Or a sequence of pumps sharing the load along the pipeline?
If a sequence then are you using centrifugal pumps? Fuel barges prefer centrifugal pumps to bunker vessels because they are cheaper and all that happens is that if the fuel gets too cold the delivery rate drops.

If centrifugals then I’d think about once the unloading is complete just keep pumping and as the air reaches each pump, shut it down. When starting up, just switch them on as the fuel reaches each pump.
If these are PD pumps then you’ll need to vent air into the lines at each pump discharge when finished unloading so that as you shut down each pump you don’t close the suction to the next, and conversely, when starting up you’ll need to vent the pump inlets to purge the air out of the line ahead of the fuel. Alternatively, just shutdown and bypass each pump until you need it. That way you jiust shunt the air and fuel around dormant pumps.


JMW

Use an inert generator(makeing 95% N2) to push the oil out.

-Continuous circulation
-Use a Diesel flush

Thank you all for your comments.

JMW:

*The product is measured by sounding the tank at the terminal before and after loading.
*Not sure how they check the quality. I would think it’s sampled by the client & customs on the ship prior to receiving.
*The product will be pumped via ship pumps which I am sure are vertical turbine. 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.
*I do not believe they blow out the hoses but I’m not sure.
*Terrain: Gentle grade from the beach to the terminal. Mostly loose soil.


I’ve designed and installed several lines both for fuel oil and lighter products such as gas and diesel. I’ve built diesel lines longer and F.O. lines shorter but no FO lines that are this long and will sit idle for so long between receiving product. I’ve got a good handle on the security, environmental, and capitol cost considerations. The only problem I’m not comfortable with is the possibility of product solidifying to the point it can’t be pumped quickly enough so as not to incur demurrage charges from the ship. (The contract stipulates 36-hr to unload 60,000-bbl.)

Dcasto:
I will look into this but it seem expensive and overly complicated. (I am a firm believer in the KISS approach.)

JLSeagull:
This was my first idea. Client shot it down because of the cost of the diesel needed to pack the line which would be in the range of $275K.

General:
Client want’s to use fresh water between batches with corrosion inhibitor. It would be recovered and re-used. I am concerned about contamination but I know of several clients who fill their lines with seawater and don’t have problems. It’s probably a mater of tight operations to ensure contamination doesn’t happen.

The nitech inert generators are just packed beds, 100% automated, a lot more simple than water and corrosion inhibitor and a lot more environmentally friendly.

Fill it with diesel or a lighter crude.

I can't hardly believe they are complaining about the 275,000 to fill with diesel. MG, what do they think happens when you initially fill a 1750 mile long 42" diameter. "That oil" stays in there for the next 50 years at least. Just tell them its a one time cost, and oil is only going to get more expensive. By the time they take it out of there it'll be worth $ 10,000,000. That'll get them thinking!

Yes, but whether diesel or water it isn't just putting it into the line, you have to have some pump-out storage for it. Now assume this is at the mooring end so it pushes the HFO ahead of it. Now, when the next tanker arrives, you have to think where you want this diesel (or water).
Do you pump it back to storage at the mooring end and, and if so, how? You need a pump and what do you pump it out.
You could have a return main from the terminal like a railway siding (and because of the lower viscosity it could be smaller diameter).
So you can use the next HFO delivery to push it out of the main pipeline into the side pipe flowing back to the Mooring end diesel/water reservoir.
Once the HFO reaches the entry to the side pipe at the terminal you change the diverter valve over so the HFO now goes to storage at the Terminal.
Now if the Client won't spend on Diesel, this would work with water, fresh or salt. All you have to be able to do is use a low pressure pump to get it from the mooring end to the tankers pump inlet. The tankers pump will determine if you can use salt or fresh water.
This would give as near a closed system as you could get because the water or diesel only flows from the mooring end storage via the taker into the main pipe and back via the side pipe. The side pipe is always full of water/diesel.
I'd guess the most secure way to control the diverter valve would be with some form of interface detection, e.g. density probe.
The question is, at 1cst (water), and with a 150psig pump, what pipe diameter could the side pipe be? The difference in viscosity between water and diesel might result in a smaller diameter side pipe.

JMW

1 Tank (SI) placed in Temporary interface duty, 1 existing pipeline, 270,000 + gal Light Crude, pump, 2 valves and a volume totalizer. (take it out of the $ 10,000,000)

Light Crude Storage-Interface (SI) tank in beach tankfarm.
Tanker pulls up and starts unloading HC, pushing (LC) left standing in the pipeline ahead of it into the temporary duty Storage-Interface tank.

LC/HC interface arrives at tank farm and is pushed into SI.
SI tank valve closes and HC tank valve opens when flow totalizer reads 275,000 gal + a bit. Maybe some HC/LC interface goes into the SI tank.

HC flows into HC tank.
HC tank loads.
HC tank valve closes.

SI tank valve opens, SI tank Pump starts, pushing 275,000 gal HC back to tanker ahead of the LC.

When 275,000 gal is pumped, pump stops, valves close.

Tanker leaves with 275,000 gal of HC
Pipeline stands with LC inside.

The SI tank is now empty and can be switched back to normal duty.

If LC is used, there should not be any concern about product quality and pumping water back into the tanker or mixing with any batches on the beach. A little LC can almost always be added to an HC tank w/o problems. Not so for water/salt water.

Better to put the LC?HC interface into the HC storage, the amount will be insignificant in the HC gievn the amount of HC delivered.

I visited a fuel barge operation last week and they said that under the MARPOL regulations fuel delivery vessels are now pumped dry instead of leaving a residual amount behind. (This also means that they will pump air briefly when the change compartments.) Same for tankers I guess, when used to deliver fuels for marine use and I'd guess the tanker must also do this (if anyone knows, I'd appreciate learning).
If that is the case then any fuel pumped back to the Tanker must be re-blended and analysed or off-loaded as it could find use as a marine fuel. (this about accounting for SOX based on fuel sulphur content).
Now MARPOL is applied to marine fuels so it may not apply here and BigInch could be right that it's OK to send some back on the tanker.
I'm not sure how the land based pollution regs stand on fuel segregation.

JMW

What goes back to the tanker is simply the same product that the tanker had just pumped out. When the light crude (LC) gets to the buoy they stop pumping and lines are closed, so no LC should ever get to the tanker (provided the volume totalizer is accurate and actual temperature & pressure compensated volumes are measured. If there's any problem, its not with the method above, but perhaps there could be some with the paperwork. I'll leave that for the bean counters to work out.

Well actually in the original post it is No6 fuel oil and I assume this is a power station.
It may well be the same as has just been unloaded but it won't be the same as will be loaded next time and if next time it is marine fuel oil cargo then they have to do something with what has been left over.
But, using your original proposal, we can modify it slightly.
Let us start with a new tanker load arriving and the line flooded with diesel.
The terminal temporary diesel storage is empty.
The vessel pumps heavy fuel into the line and when the HFO/diesel interface reaches the terminal the valve diverts the no 6 fuel to HFO storage.
At the end of unloading diesel from the mooring side tank is piped to the tanker pump inlet and pumped into the line until the interface reaches the diverter valve.
The diverter valve changes over and the supply from the mooring diesel tank to the tankers pump is closed.
The diesel in temporary storage at the terminal is now pumped back into the pipeline. The diesel flows back into the moorings storage. Once the terminal storage is empty the pump shuts down.
This pump is only handling diesel with the lines flooded only with diesel.

JMW

"Terminal" usually means bulk storage terminal, but that could also be at a power station, no matter.

You lost me with this,

At the end of unloading diesel from the mooring side tank is piped to the tanker pump inlet and pumped into the line until the interface reaches the diverter valve.
(what? "tank is piped to the tanker pump" ?? What's being pumped?)

The diverter valve changes over and the supply from the mooring diesel tank to the tankers pump is closed. (what is in the pipeline now?)

The diesel in temporary storage at the terminal is now pumped back into the pipeline.
(where does the HC in the tanker to terminal pipeline go?)

The diesel flows back into the moorings storage.
(Where?)

Once the terminal storage is empty the pump shuts down.
This pump is only handling diesel with the lines flooded only with diesel.
(I get that last part)

Click to expand...

OK, if pumping back to the main tanker isn't cool, then pump the 275,000 gal into a small shuttle tanker and haul it back to the docks, or build a return pipeline.

Wait. Step back a minute. What's the minimum water temperature? Evaluate the possibility of solidifying. Sounds like you haven't done that yet. I don't think it will solidify in the warmer waters you have there. Make the line piggable.

6 miles of steam tracing doesn't sound feasible.
Hot water in an insulated annular jacket, maybe.

You could build two smaller diameter bundled lines to the PLEM, both one way when pumping HFO from the tanker; after the ship finishes unloading, circulate diesel or some light oil until all the HFO is displaced from the two pipeines on to shore.

Sorry BigInch,
KHardy says he'll use the tankers pumps to pump the flush fluid into the line. Diesel, fresh or salt water or whatever.
That means that wherever the storage of the flush (diesel) is at the mooring end, we run a connection to the tanker pump inlet.

Now:
Now the next tanker arives.
It pumps HFO and pushes the diesel out of the line into the terminal temporary diesel storage which is empty at the start.
When the interface reaches the terminal the HFO is pumped to storage.
So, when finished pumping HFO, they make the diesel connection to the tanker pump inlet and the pump flushes the line with diesel pushing the remaining HFO in the line ahead of it into HFO storage and when the HFO/diesel interface reaches the diverter valve in the terminal the tanker stops pumping, disconnects and departs completely empty.
Now the pump in the terminal diesel storage pumps its diesel back into the pipeline and reverse flows the diesel into the diesel storage at the mooring end of the pipeline and continues to pump until the terminal diesel storage is empty.
The line is now left flooded with diesel.
The terminal diesel store is empty and the mooring end diesel terminal is at maximum.

It is OK to run the interface into the HFO tanks as the very small amount involved will not normally affect the HFO. But if we run HFO into the diesel we will progressively degrade the diesel, which is not consumed.
If you use water, again the amounts involved in the interface are probably going to be insignificant and HFo usually contains an amount of water anyway. For marine fuels this is now down to a max of 0.5% but what the allowable limit is for burners I don't know. If it is a problem, then it may be necessary to use centrifuges just as are used for engine fuel supplies.

Anyway, this way we don't end up with excess diesel at the terminal and a shortage at the mooring end.




JMW

By the way, I guess we don't need to use a fuel grade of diesel, we could use one of the low cost low grade low viscosity products normally used as cutter stocks. I don't know what the cheapest of these is that would be suitable but probably a lot less than MDO or MGO or similar fuel grades.

JMW

"So, when finished pumping HFO, they make the diesel connection to the tanker pump inlet and the pump flushes the line with diesel pushing the remaining HFO in the line ahead of it into HFO storage and when the HFO/diesel interface reaches the diverter valve in the terminal the tanker stops pumping, disconnects and departs completely empty. "

"the diesel connection to the tanker pump inlet", tanker pump, I assume is a pump on the tanker, so how does the diesel get out there?

BignInch, you are right, I assumed something from khardy's 2nd post he did not say.

Let us note Khardy's comment about demurage charges and that these will most certainly apply if the tanker has to stand around while the lines are purged.
Let us also assume that we will need to flush the pipe from the beach to the mooring of HFO both for environmental risk reasons and so as to avoid this being a part of the demurage charge risk avoidance.

I initially proposed a second pipeline for the diesel from the terminal to a diesel tank at the mooring end of the line, but your suggestion of tanks and pumps at either is better even if simply because the return pipeline I proposed would have imposed a bigger pumping burden on the tanker (twice the pipe to pump at the beginning ect.)

So I think we will need a pipe line dedicated to supplying diesel to the mooring point but not onto the tanker , only to the diverter valve in the fixed installation.

BUT NOW:
When the tanker arrives, it couples up and starts pumping. The first pert of the description is fine; it pushes the diesel out into the terminal storage tank as described.

Now, however, once the tanker has finished pumping it doesn't wait around for my approach; using the tankers pumps to flush the line, nor your approach, waiting while the line is purged back into the tanker. Instead, it just disconnects and goes.
No demurage.

The line is left full of HFO at this point.

Now the diverter valve at the mooring point switches over to admit diesel from the beach storage and the beach pump starts pushing the HFO out of the pipe all the way to the terminal.
When the HFO/Diesel interface reaches the terminal the beach pump stops and is bypassed to allow the terminal diesel storage pump to pump the terminal tank back out to the Beach tank. Once the terminal tank is empty, it stops. The line is left with diesel ready for the next delivery.

With this approach we have no time constraints.
This means that the the diesel pumps at either end and the 1.5 mile beach to mooring diesel pipe can be much more modestly sized.... take as long as you like to complete this operation.

For diesel, read water with corrosion inhibitor, if that is what the client wants.
The water will be practically in a sealed system as it goes nowhere but back and forth along the pipeline.
If there is concern about contaminating the fuel storage with water then interface detection at each diverter valve is a small add on cost compared to the overall installation cost. Multi-product pipelines usually use density meters which can also be used to monitor the quality of the water. Or viscometers which will monitor the water and the oil quality.
For example, in the UK the pipeline connecting the refineries and airports etc. has, I believe, a simple primary detector some way out that alerts the operators to the approach of an interface and a more sophisticate measurement to synchronise the valve switching when the interface reaches the valves.

JMW