Jet Fuel Bulk Storage 6

[FredGarvin]

I was wondering if anyone here has experience with jet fuels and bulk storage of them.

I have a engine performance gremlin that I have been trying to track down for some time. One theory has been presented that involves stratification of JET-A in our storage tanks. Some people here have taken to the idea that JET-A stratifies in both our above ground and below ground tanks because we do not stir them and the resulting light ends seperating from the heavies is causing problems.

I personally am not convinced that this can happen as quickly as it is being presented, if at all. However, I am anything but a chemist.

Can anyone shed a little light on the possibilities of this "problem" or know of anyone I can contact?

Thanks for the help!

S.H.

 

[MaNaTMoS]

Hmm, it reminds me of similar problem we have had just a few months ago.

Check for microbial growth and water content (emulsified + dissolved); compare the IFT values before and after "stratification".

 

[FredGarvin]

Thanks for the tip. I will do that.

 

[jmw]

You don't say how many engines are using fuel from the same source.

Aviation fuel is blended for certain characteristics and the other parameters are pretty much a consequence of what refinery processes are running. There is no control over density or viscosity, for example.

Aviation fuels are usually bridged into segregated storage because the density from one batch to another, even sequenctial batches from the same refiner, can show significant variation (the key to interface detection). Of course, the main concern is the fuelled up weight of the aircraft and with many more fuelling bowsers equipped with density meters to correct the volumetric flowmeters this is probably not the problem it once was. Even so, co-mingling batches may lead to stratification.
But will it affect the fuels combustion properties?

Viscosity can also vary measureably. Viscosity affects the spray pattern and it is also affected by temperature. Significantly so? I doubt it, though when testing diesel engines fuel density and viscosity are required for the SAE J??? power factor correction, but i think this as much relates to engines tested cold as to anything else.

In any event, it should not be a problem to take top middle and bottom samples from storage and to take samples from the fuel lines to the engine under test, both when there is a problem and when not, and have an analysis done. This will confirm the fuel meets it specification. But apart from that, unless specific tests are called for, contaminants will not be discovered.

One thing more that can e done is to review any recent maintenance operations that occured at around the time the problems where noticed and to focus on the engine and any installation unique to the engine with a problem. For example, if someone has fitted the wrong seal material or gasket etc then this could be contaminating the fuel locally.
If there are several engines and only one has the problem, if possible exchange it with an engine in another installation and see if the problem moves with the engine or stays with the installation.

It sthe old story, once you have eleiminated what it isn't, what it is, should be easier to track down.

JMW

http://www.viscoanalyser.com

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[rmw]

Moisture as well as microbiological growth would be exacerbated in your above ground tanks, if you are in an ambient where the atmosphere goes below the dew point on a regular basis.

The tanks heat up during the day time sun, breath out, and cool down at night, breathing in the most moisture laden air of the daily cycle.

Do you feed from above ground tanks to the underground tanks?, and do you sample your tanks, for moisture collection in the bottoms, and/or drain regularily??

Do you test and take fuel from the tanks immediately after a fuel delivery. All the stuff in the bottom of the tank, the free moisture, and the slime caused by micro growth gets stirred up, and can be picked up and be transported to your filters, plugging them, and affecting engine performance.

If it were possible to keep the above ground tanks as full as possible as long as possible, in order to minimize the vapor space above the liquid level for atmospheric air to breath into and out of (leaving behind its moisture load when the tank wall is below dew point) you could minimize the breathing problems. If you ever come out on a cool morning and see the above ground tanks "sweating", know that the inside of the tank is just as "sweaty," if there is any moisture inside. And, of course, the condensation of this moisture creates a vacuum, drawing in more wet air to replace the volume change of the vapor to liquid.

Do you have breather valves on the vents, or are they just open vented to the atmosphere. Breather valves will reduce the amount of diffusion of air into and out of the vapor spaces, as well as lessen losses of product vapors.

Your tanks are no different than every gasoline station and/or diesel trucker out there. Attention to breathing problems is essential. Some of this problem is mitigated, the lighter the fraction gets, the reason that gasoline car owners don't have the same problems as diesel owners, the vapor pressure of the gasoline is higher than diesel, so the gasoline vapors tends to fill the space above the liquid, while diesel does not have this benefit.

I am not going to to look it up, but I suspect Jet-A is more similar to diesel than gasoline in that regard. If I am wrong, someone will post a correction, I am sure.

And, in the case of diesel, for long term bulk storage, certain additives are recommend to fight bugs and slime from growing in the fuel, as well as to coalesce the water so that it can be brought to collection points, traps, and filters, and removed before the engines 'eat' it.

Good luck,

rmw

 

[jmw]

Re RMWs comment "I suspect Jet-A is more similar to diesel than gasoline in that regard" prompts me to wonder about fuel degradation with time.Somewhere in one of these threads I posted a link to an article about diesel fuel breakdown with time. Perhaps this is a possibility here also?

JMW

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[rmw]

One excellent link on the topic was in thread483-90990 titled "Bunker C" in a post I did on March 27, 2004 from Power Engineering Mag, and I think that is where your (JMW) comments on the subject were as well.

rmw

 

[jmw]

Ah!
Yes, RMW posted the original link, but that did not stop me cribbing it and posting it elsewhere!
Here is RMW's link again:

http://pepei.pennnet.com/Articles/A...ion=CURRI&ARTICLE_ID=200233&VERSION_NUM=1&p=6

JMW

http://www.viscoanalyser.com

Eng-Tips: Pro bono publico, by engineers, for engineers.

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[rmw]

JMW,

Besides being too lazy to copy and paste the link again, I posted the thread number, so that the readers could see your remarks in that thread as well, which I thought were excellent, and especially since you had brought it back to my attention. Your memory is better than mine.

I hope SH or FredGarvin finds some useful information there.

rmw

 

[jmw]

Just to satisfy anyones curiosity, the standard i was thinking of is SAE J1995. I think. (there are plenty to choose from on the

http://www.SAE.org

web site and all I recall is several years ago commissioning an inline digital viscometer to measure the base density and viscosity so they could ease up on the intensive lab work in a diesel engine plant somewhere in the south, NC I think.

Anyway, the standard applies to IC and SI engines excluding aero and marine versions and jets, and though i guess there may be some similar standard, I didn't look to far for it.

http://www.sae.org/servlets/productDetail?PROD_TYP=STD&PROD_CD=J1995_199506

JMW

http://www.viscoanalyser.com

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[jmw]

PS kind words about my "rant", thanks RMW. Let's hope that interested parties will take the time to look at several of these threads.

JMW

http://www.viscoanalyser.com

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[FredGarvin]

Thanks for the input all.

To get a bit more specific, we are a jet engine designer/manufacturer. The variation we see is in two places. The first is in one of our test facilities that draws off of the bottom of above ground tanks that are 300 gal. The second place we see it is in our production ATP test cell that draws off of a float system on an underground 10,000 gal tank. Each tank has one engine running at any time. We do test every load we get, but we wait for 24 hours before doing so to allow for settling. When we see our variation in performance we always retake our fuel samples as well as a full engineering analysis of the engine in question. To date, we have not been able to find a smoking gun.

I can readily see issues with the small above ground tanks. Especially with the temperature swings we see. The one fact that I see that helps us here is that our turn over rate on the fuel in them is pretty high. That fuel does not stay put for long periods.

We monitor all of our fuels' net heat of combustion as well as other parameters. Over the years we have seen an approximate 3% variation in API gravity and an even less variation in net heat of combustion. Always the fuel must, and does, meet specs set forth in ASTM D 1665. RMW, your assumption about jet fuel being closer to deisel is a correct one. They are not too terribly different. We do include inhibitors and and an anti-icing additive.

Our below ground tanks are indeed vented and do not have breather valves. That is definitely something I will look into.

The big thing I was hoping to get a feel for is the rate at which a tank can stratify. We have some people quoting time spans that I have no idea are possible or not. Does anyone have an idea of what kind of ballpark time it should take for a large tank to stratify? Are we talking hours, days, weeks?

Thanks again for all of the info and the links.

 

[jmw]

About all i can do is suggest a logical "truth table" type structured investigation to isolate what the most probable causes and focus the investigation on these.

Unless you are buying very special fuel or your installation and storage follow unique design and operation, one would suspect that a detailed investigation of these aspects is not yet warranted.

For example, can we conclude that more than one engine uses the same fuel but not all engines exhibit the problem?
If so, one would tend to believe the fuel in storage is OK. As a check, when there is a problem, possibly you have the means to supply fuel to the problem engine from a different source, i.e. fuel that does not, apparently, cause a problem with other engines when used in other test beds. Maybe you can even tanker some fuel from one facility to the facility in question. (You don't say how these tanks are filled or if the smaller tanks are direct filled from the fuel supplier or a fuelled from your own bulk storage).

You say you see the problem in two places. Is it always the same two places? Does it effect several different engines tested in these places? Some of them or all of them? One type of engine or any type? Have you been able to move a problem engine from to a trouble free test bed to see if the problem persists?

If the problem is localised, I would suspect one possibility is something in the installation unique to each of these two places. Presumably these are installation where there has been a history of good performance, i.e. the problem is not with the system design but may be due to a change in the system e.g. new component or something done during maintenance or service, or a change in the way the system is operated.

It is at this point I would start to look at anything that could provide localised contamination. You did not sy if you test fuel samples taken from the problem locations. If you do, it may be worth having a more extensive investigation made. You would be looking for a rogue contaminant and possibly a transient contaminant i.e. not always present if not all engines are effected.

JMW

http://www.viscoanalyser.com

Eng-Tips: Pro bono publico, by engineers, for engineers.

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[FredGarvin]

We are indeed in the middle of a very similar process. This thought on stratification in our tanks was simply a question that makes up the rest of the investigation.

Thanks again.

 

[oxilume]

SH,

First, I will state a few of my qualifications:
(1) Certified DOD/GSA Fuels Inspector
(2) 1 patent for increasing octane via catalyst enhancement
(3) 1 patent for removing sulfur from diesel/mineral spirits cut (jet fuel)
(4) 1 patent for preventing oxidation of Jet Fuel in storage tanks!!!
(5) Test Cell Engineer for variety of Gas Turbine Engines
(6) Sold bulk fuel additives, such as anti-oxidants, biocides, etc.

You stated you have engine performance gremlins! Let's start at your test cell;
(1) Are you using the same fuel pump on every class of gas turbine?
(2) Do you have any type of filter system prior to the fuel pump?
(3) Do you have a fuel preheater?
(4) What is the material of construction for the fuel storage tanks?
(5) What chemicals are you adding to your fuel?
(6) Who is the fuel supplier and what are the additives?
(7) Have you changed bulk fuel supplier within the past 6 to 12 months?
(8) Do you conduct visual inspection of fuel as part of check list prior to running each and every engine?
(9) What is BS&W of fuel in tanks?
(10) Do you have a fuel quality program in place?

Todd







Todd

http://www.oxilume.com

 

[tkequipments]

Are your tanks equipped with floating suction lines, which would avoid to pump out all the bottom sediments and water that we usualy find here???
An other solution to avoid moisture comming inside the product is to install an internal floating cover (for the aboveground only, of course!!!)

try this :

http://www.larco.fr

 

[25362]

Are the additives throughly mixed ? Additives in small dosages don't alter the main fuel properties, however they show sometimes adverse effects such as on water-separating properties. This is one other item for checking.

 

[Fizzhead]

FredGarvin:

I have built several jet fuel reception, storage, treatment and distribution systems for airports and have never encountered a problem with short term stratification of fuels. We follow guidelines that prohibit usage of fuel that has sat in storage (in-pipe or in-tank) over 30 days without pump around to thoroughly remix the fuel and then retest for specific gravity, color and particulate contamination. Note that all tanks are sumped daily for removal of bottom solids and water. Fresh fuel is accepted, settled for 24 hours and then tested for the parameters listed above. IF a tank should sit for over 30 days, part of the recertification process is to compare current test results to initial results. In the case of pipes which have not been used over 30 days, the pipes are flushed with a minimum of three pipe volumes of fresh fuel and then tested for particulate until samples meet specifications. This procedure detects corrosion products from the piping/tankage that might be a problem as well as biological problems. All flushed fuel is recycled within the system (i.e., passed through a filter/separator for particulate/water removal) and retested. If it meets spec, it's added back into a tank of already accepted fuel. If not, it goes into the slop fuel system for disposal.

Have you taken a close look at the above ground tank pumpout configuration for bottoms removal? Make sure it is removing all the condensed water. Bottom product draw tanks are the worst problem for this because the water drawoff may be offset in favor of a centered product drawoff, thus hindering the effectiveness of sumping activities. I also must agree with jmw, check and see if any recent maintenance activities have resulted in the use of gaskets, etc. which are not Jet A compatible. Finally, I would have to agree with 25362 that the mixing of the additives should be checked as inadequate mixing could result in the types of problems you describe.

 

[FredGarvin]

Thanks to everyone who has replied. I am going to need some time to digest all of the information and links given here.
Some very quick answers are:

1. We have used the same carrier for years. We have not changed.

2. We use float systems in the tanks which draw approx. 12" below the fuel level.

3. We monitor for water and contamination, both through the level monitoring system we use and weekly visual inspection.

4. Our only additive to Jet A is PRIST.

5. The engines we see the gremlins on are brand new engines, during their initial performance evaluations and only during a very small timeframe during the year (it has repeated and we noticed the trend).

6. All of our facilities use the same type of fuel pump, but in differing capacities depending on engine type.

7. We filter after the main pump.

8. We do not use preheat from the fuel farm, however the engine itself has a liquid to liquid cooler.

9. All fuel is inspected prior to offloading for water and contamination. We analyze for SG only on every load. Our suppliers are responsible for maintaining conformity to ASTM specifications.

Fizzhead: We have a similar program in place for our fuel storage. That is why I have a hard time believing the proponents for the fuel stratification theory.

Thanks to everyone again. I appreciate the assistance.

SH

 

[25362]

Fizzhead merits a star for his useful post.