API 13 Fuel Oil Viscosity vs Temperature 3

[coachk]

Help!!

I have spent a lot of time searching for information regarding the viscosity of API 13 fuel oil at various temperatures. I have searched through various links given in answers to numerous threads, but keep coming up empty-handed.

Thanks for your help!

 

[jmw]

What information do you have?
Do you know the viscosity and/or density at any temperatures?

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.

 

[25362]

Can you tell us the grade of fuel oil according to ASTM D396-02a ?

 

[jmw]

The closest I have come to finding anything on API 13 is from a search of

http://www.api.org:

Publ 1571
Diesel FuelÑQuestions and Answers for Highway and Off-highway Use
Provides answers to some of the frequent questions asked about diesel fuel.
Included are explanations of the quality features of diesel fuel and their significance;
descriptions of diesel fuel classifications; discussions of additives
normally used and their purposes; and explanations of factors that can affect
performance. Pages: 20
4th Edition / January 1996
Product Number: F15714 / Price: Pack of 25 for $57.00

Which i don't have but possibly your engineering standards library has this available.

Diesel is usually blended for a specific energy content based on the cetane index. This means that deifferent batchs od diesel, and for aviation fuels, the density and viscosity can vary according to the conditions at the refinery.

Density can vary significantly (especially critical in aviation fuels where different batches are sepearately stored). A common practise appears to be to refer to the API specific gravity measured for the batch.

I wonder if this is the description that you have (though API 13 sounds low, those that i have found are in the API 20-30 range).

Viscosity is no less variable but because, for light diesels, the viscosity is quite low, it is often disregarded (except for power factor correction; injector performance testing etec.) i.e. there is no compensation for viscosity in engine management.

On the other hand, intermediate fuels and above are blended for their viscosity because viscosity is significant in the efficiency of operation and is controlled through fuel heating.

If you can add some further information to help us understand your question, please do so.


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.

 

[coachk]

Thanks for the quick responses. It is no. 6 fuel oil for a power plant. The closest that I was able to find is that API 14.5 has a min & max viscosity of 150 - 480 cST @ 50C (122F). The API 13 fuel oil is typically delivered at a temperature of 140F, but can cool to close to 90F. I would like to be able to know the viscosity in that temp range.

 

[jmw]

Ah!
I imagine you need to determine your heater control temperatures.

download spreadsheet ASTM D341 from here:

http://www.viscoanalyser.com/downloads.html

It is already pre-programmed with a number of heavy fuel oils.

For your oil, you should have at least one defined viscosity at the reference temperature, which you quote (150 - 480 cST @ 50C). Some specifications also suggest the approx viscosity at 100[°]C(which is the second temperature in the pre-programmed oils) and this works very well.

For your specific oil, you may need to tweak the second temperature until you get the appropriate "A" & "B" values (proportionately the same at the second temperature as at the first). Then you can read of the viscosity at any other temperature from the table (you can adjust these temperatures).

You will also note that it includes provision for you to enter the density, if known, but this is only really used for engines where they want the ignition index.

Also included is the heater control temperature to achieve the optimum injection viscosity. All you do in this column is enter your target viscosity e.g. 15cSt and it returns the equivalent temperature for each of the oils.

In burner applications it is more usual to measure the viscosity at one temperature in the lab, use a table such as this or a chart to predict the nozzle temperature and adjust the heater control set-point accordingly i.e. control the heaters by temperature.

This was necessary because most viscometers did not work on heavy fuel oil to burners (though they do to engines).
The downside is that because fuel quality is very variable, you need to re-assess the heater control temperature on a routine basis (this is repeated on a very regular basis even for a single fuel grade, because fuel quality is vary variable; your data suggests you will be using different fuel grades), perform flame inspections and, probably, run excess oygen to around 4.5% or so.

All very expensive.

Some modern viscometers for heater control will work on any fuel in power stations for burners and even on very dirty fuels.

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.

 

[jmw]

PS You could also approach any major oil comapny marine fuels HQ and ask for a free copy of the fuel calculator programs.

Shell and Exxon have them, you can also obtain them from DNV PS and online, from

http://www.steamesteem.com,

all of which have routines for making these calculations.

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.

 

[25362]

In addition to what has been said in this and other threads concerning the viscosity effects that residual fuels have on pumpability, on burners', on spray nozzles' and atomizers' performance, it is worth to note that at temperatures in the region of 100 deg F some residual fuels tend to deposit wax from solution.

This complicates the determination of viscosity and exerts an adverse effect on the accuracy of the results because the fuel oil doesn't behave as a Newtonian fluid, in which the rate of shear is proportional to the shearing stress applied.

For this reason there is some opinion in favour of replacing the reference temperature of 122 deg F (50 deg C) by adopting a higher temperature level, for example, 180 deg F as some British experts propose, when handling more waxy (e.g., North African) crudes, thus avoiding possible anomalous viscosities by causing all wax to remain in solution.

 

[jmw]

Ah, some good points 25362.
Heavy fuels oils traditionaly are blended based on the 100[°]C viscosity and blended at between 90 and 130[°] in refineries.

However, it is only the refineries that they blend at these temperatures; in terminals, on barges, on ships and in power stations the storage temperature and transfer temperatures are often much lower. Even as low as 20[°]C.

In all these places the reference temperature is 50[°]C.
CIMAC working bodies have now decided that for many reasons the reference temperature used throughout will be 50[°]
The CIMAC fuel standard is based on the ISO 8127 standard.

It now has fewer grades but many more rules regarding "inclusions".

Over 65% of heavy fuel oils are now blended residuals and low grade cutter stock, and not straight run.

When dealing with crudes, especially in pipelines, wax is a definite problem that must be managed.
In these applications the viscosity required is usually the pipeline temperature apparent viscosity i.e. a behavioural measurement.

So whatever flows past the meter and is measured is what is wanted. Same for heater controls. Of course, when handling heavy fuels at low temperatures and where handling is important, 25362 is right, you cannot depend on the viscosity temperature chart for temperatures below the wax ppoint if waxes are present. I don't recall, off hand, if waxes are normally tested for and hence appear on the fuel certificate.

One normally expects waxes to have been removed during the refinery processes as wax is a valuable product. Residual oils are not.

So, in many crude oil applications, the viscosity is measured online and under flowing conditions.

In fuel oil heating it is also measured on line and at flowing conditions. Only analytical measurements aadmit or require determination of the viscosity at another (reference) temperature. The use of calculation to interpolate the viscosity at one temperature when measured at another, is risky if the temperatures are extreme and widely different to the process temperature.

Incidentally, the change to 50[deg;] reference temperature will cause some problems for refineries that use process measurement set up for 100[°]C as the heat exchangers will need to be re-sized.

Terminals, barges and ships, for so long without any form of quality meaurement of viscosity, actally have it much easier now since they don't need any heat exchangers or special conditioning equipment as their measurement temperature is very close to the reference temperature.
Blending and quality checking require analytical measurements and this requires referal so it is also the temperature viscosity relationship that is a problem as the wax behaviour will complicate the issue, if the process measurement is made at low temperatures.

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.

 

[coachk]

I very much appreciate the responses, as this is a new area for me, and I am learning a lot about the subject.

From what I have been reading through this thread and other areas on the net, it is apparent that the low temperature should be modified from the 90 deg F. It appears that 100 F should be the lowest to maintain flow.

I have since found that the types of fuel for this application could range from API 10 - 13.5. As the standard temperature utilized is 122 F, where might I find the typical viscosity range for these fuels? The folks at API (at least the ones that I have talked to) have no idea.

Thanks again!

 

[jmw]

Try one of the oil companies.
They may be able to help.
Or ask your supplier. He could give you the equivalent grades if necesary i.e. the equivalent ISO 8127 grades.

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.

 

[25362]

From my relatively old sources, No.6 fuel oils have viscosities in cSt (=mm²/s), per ASTM D 445-04 or IP 71 methods, as follows:


at 122 F at 212 F

min 92.0 (approx.) 15.0
max 638 " 50.0

Same sources also indicate other porperties such as water and sediment % vol, max., and flash point, min.

 

[jmw]

Thanks 25362, I don't have that data but it fits nicely with the CIMAC/ISO 8217 standards, which is already programmed into the spreadsheet I referred to.

Intermediate fuel oils have viscosities from 10-25cSt at 100[°]C and Residual fuels from 35-55cSt at 100[°]C

I would suggest that a very useful program to acquire is BunkerMaster 2 (version2.3) supplied by DNV PS (Det Norske Veritas Petroleum Services) which is free, or similar programs from Shell Marine Fuels, Exxon Mobil Marine Fuels or from any other marine fuel oil company.

These programs all contain fuel specifications and calculations including for the specific energy of the fuel. They are primarily for blending fuels (65% or all fuels are blended and the % is increasing). You should also approach your fuel supplier for any information they can give.

Itis useful to acquire these programs and to ask the supplier for the orginal certificates on the resid and cutter stocks that make up your fuel.

With this data and with a fuel calulator you can verify that the blended fuel you receive has fuel qualities consistent with the raw components. All to often it proves difficult for suppliers to precisely blend the grade you want if the fuel is not a refinery blend.

Also, some fuels, even refinery blends, that come to you through third parties or during shippment, can "become contaminated" e.g with chemical wastes, excess water, used mpotor oils etc.
The new Standard recommende by CIMAC does addres these issues because contamination (accidental, incidental or deliberate adulteration) is a fact of life even for engine applications where the fuel quality is far more critical than for burners. i.e. what you order and what leaves the suppliers tanks may not be what you get.
Unless you run a good quality checking procedure which should include sampling during transfer and from storage with the samples sent to suitable laboratories for an analysis, you may be parting with good money for bad fuel.

You could visit sites such as

http://www.ibia.net

for information, or

http://www.viswalab.com

for much discussion on fuel quality. Viswalab, Lintech, DNV PS and others provide fuel testing services.

Even without contaminants, because of the difficulties of precision in blending, fuel quality is a variable. Some burner fuel pruchasors e.g. power stations, have attempted to improve the consistency of the delivered quality by changing suppliers. This can mean buyoing refinery blends. The alternative is to know what you receive and to know the quality as it is being burned and impliment suitable controls.

PS the DNV PS program has useful information and recomendations on storage and handling and they say (which compliments what 25362 says)

When in colder sea temperatures heating coils should be used to avoid formation of wax crystals and allow ease of transfer to settling tanks (additionally heating in storage will promote settlement of water and sediments).

.

You will notice that they are all primarily concerned with engine fuel and with marine operations. I am sorry to say that the inseinsitivity of burner operations to many of the things engines are sensitive to means there does not seem to be the same attention to quality or management in the burner industry so you are very much on your own in many cases.

Of course, burner nozzls are easily and cheaply replaced and I think this is usually the main equipment concern. Fuels for engines are managed very differently as the delivered fuel is settled, filtered and centrifuged to clean it up, eliminate excess water, fines, sediments etc. i.e. anything that may damage the engine.

I don't know if this means that burner operators are discriminated against when it comes to quality. I do know that the problems with fuel heater control have been more difficult; viscometers that work with these grades of fuel, work. When used for burner fuels they mainly do not and heaters are still, mainly, controlled by temperature. The difference may be treatment of the fuel between storage and the engines.

In the EPA regulated areas they have been getting tough. On power generator with burners was required to find and fit reliable viscometers which they successfully did using the digital viscometers designed especially for fuel oil heater control duty.

http://www.prepa.com/aire.asp

(see bullet point three; there was a lot of effort behind this).

The problems do not end there. Compatability and stability are two other fatcors that have to be considered. e.g.

http://www.bre.com/technicalpapers/technicalpaper.asp?articlenumber=33

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.

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

 

[jmw]

Finally, this link will let you calculate the specific energy and cost:

http://www.dan-bunkering.dk/Valuecalc.htm

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.