Fuel Oil Level tank fluctuations
Fuel Oil Level tank fluctuations
(OP)
Hello,
We have a fuel oil tank that is approximately half full (300,000) litres.
This tank is only there for use as a standby, should our gas supply become interupted.
The tank is measureing the level using 3 rosemount level level transmitters. Looking at PI trends over a period of ten days (any ten days) the level measurements 'change' by a few thousand litres.
The trends show peak high levels at approximately 4pm each afternoon, and peak low levels at approximately 4am each morning.
can anyone help explain this please?
http:/ /img266.im ageshack.u s/img266/8 184/fueloi llevel.jpg
We have a fuel oil tank that is approximately half full (300,000) litres.
This tank is only there for use as a standby, should our gas supply become interupted.
The tank is measureing the level using 3 rosemount level level transmitters. Looking at PI trends over a period of ten days (any ten days) the level measurements 'change' by a few thousand litres.
The trends show peak high levels at approximately 4pm each afternoon, and peak low levels at approximately 4am each morning.
can anyone help explain this please?
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RE: Fuel Oil Level tank fluctuations
And how does this track with temperature changes and corresponding density changes?
Do you have warm days and cold nights? How does this change seasonally?
You could get something close to 1% for a 10-15C swing.
What is the accuracy of the level transmitters and the effect of temperature on their accuracy?
(see www.viscoanalyser.com downloads for a temperature density calculation, density 12mf.xls)
JMW
www.ViscoAnalyser.com
RE: Fuel Oil Level tank fluctuations
RE: Fuel Oil Level tank fluctuations
RE: Fuel Oil Level tank fluctuations
0.0008 1/C * 300,000 Liters * 10 C diurnal temperature change
is 2667 liter change in oil volume.
"The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward X-CEO BP
http://www.youtube.com/watch?v=hpiIWMWWVco
"Being GREEN isn't easy." Kermit
http://virtualpipeline.spaces.live.com
RE: Fuel Oil Level tank fluctuations
JMW
www.ViscoAnalyser.com
RE: Fuel Oil Level tank fluctuations
"The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward X-CEO BP
http://www.youtube.com/watch?v=hpiIWMWWVco
"Being GREEN isn't easy." Kermit
http://virtualpipeline.spaces.live.com
RE: Fuel Oil Level tank fluctuations
P = ρ.g.h
Even if the tank level (i.e. h in the above equation) does vary with temperature, the pressure gauge will not "see" it because the product of ρ and h will remain constant.
The cause is more likely to be the effect of temperature on the filled capillary between the sensor diaphragm and the actual pressure transmitter. If the filler oil and the capillary material do not have exactly the same thermal expansion characteristics the pressure in the capillary will change with temperature and you effectively have a wandering zero on your level gauge.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Fuel Oil Level tank fluctuations
Yes, it is clear that this is the temperature effects on the capilliaries causing the change. The scale of the graph threw me slightly, however when you work it out it is only a 0.9% change from high to low.
I have a question for BigInch
In your calculation, what is the 0.0008? is it a density coeffecient per degree for fuel oil?
RE: Fuel Oil Level tank fluctuations
In the way BigInch presented it, it appears to me that 0,0008/oC is a cubic thermal expansion coefficient.
RE: Fuel Oil Level tank fluctuations
"The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward X-CEO BP
http://www.youtube.com/watch?v=hpiIWMWWVco
"Being GREEN isn't easy." Kermit
http://virtualpipeline.spaces.live.com
RE: Fuel Oil Level tank fluctuations
JMW
www.ViscoAnalyser.com
RE: Fuel Oil Level tank fluctuations
At 2pm today (Monday) I fixed a hosepipe to the capiliaries of the transmitters and doused them with water, and continued to do so for an hour. You can see a clear difference in the drop of level on the PI graph (http://img186.imageshack.us/f/dieseltanks2.jpg/) (Please ignore the yellow line, i have no idea why is shoots up?!)
To work out the difference in levels during the day the following formula is used:
Difference in volume = Coefficient of thermal expansion * difference in temperature * quantity in tank
If you take at a rough guess the highs and lows of the level being 293k litres and 287k litres respectively, then you can say that the daily average is 290k litres.
(I had to work this out in Fahrenheit, as I could only find the coefficient of thermal expansion of diesel in F and not C)
10 degrees C = 50 degrees F
25 degrees C = 77 degrees F (These are rough estimates at the ambient during day and night)
Coefficient of thermal expansion for diesel = 0.00046 per degree Fahrenheit
Put all this in to the equation
Difference in volume = Coefficient of thermal expansion * difference in temperature * quantity in tank
= 0.00046 * 27 degrees F * 290,000
=3601.8 litres
From this, you can say the measure levels due to the changes in ambient conditions will swing +/- 3601.8 litres. If you look at PI, this proves this theory.
http://img186.imageshack.us/f/dieseltanks2.jpg/
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But one final thing, is this the whole volume of liquid expanding in the tank, or just the small amount in the capilliaries
ie. there is less liquid to heat and cool in the capillaries and so this is why you get this kind of fluctuation in level readings?? Ideally if this was a critical system you would have temperature compensation and density compensation, however the process is not that important to plant availability
RE: Fuel Oil Level tank fluctuations
"The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward X-CEO BP
http://www.youtube.com/watch?v=hpiIWMWWVco
"Being GREEN isn't easy." Kermit
http://virtualpipeline.spaces.live.com
RE: Fuel Oil Level tank fluctuations
Your system can tell you about changes in volume but how accurate is its measurement of total volume?
Tank level is the first step in volume calculation.
You need your tank shape tables and then you need to know how the tank volume changes with temperature, as has already been indicated, and with actual fill - how much does the tank distort due to the mass of fuel in it and how does this affect volume.
The easy bit would seem to be noting the fact that volume changes with temperature because your volume measurement changes with temperature.
I'd suggest looking up the history of the sensor. Manufacturer's data, any relevant calibration certs etc. Chances are it hasn't been calibrated in a while.
How long has this fuel been sitting there. Has it stratified in the tank? has it begun to break down? got too much water in it?
What could happen to it?
It can be pilfered is one thing. It can degrade for another.
There ought to be a routine of taking top middle and bottom samples to look at quality. These samples should give you the analysis of the oil which should give you the density at 15C or 60F some where.
(by the way, if you have a 60F value, you can enter the data into the spreadsheet in degF, calculate the base density for 15deg C from that and then use the spreadsheet for your calculations. It isn't necessarily kosher, but it will do what you want.)
JMW
www.ViscoAnalyser.com
RE: Fuel Oil Level tank fluctuations
"The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward X-CEO BP
http://www.youtube.com/watch?v=hpiIWMWWVco
"Being GREEN isn't easy." Kermit
http://virtualpipeline.spaces.live.com
RE: Fuel Oil Level tank fluctuations
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com