Water settlement in heavy fuel oil&diesel tanks

[uzairsahmed]

I would like to know what is the approximate percentage of water settlement in a heavy fuel oil (HFO)and high speed diesel (HSD) storage tank. we need to design and provide a provision for removing this quantity of water from this tank?

Appreciate all the help

 

[jmw]

It begins with how much water you can expect to find in the fuel. For marine fuels this ought to be less than 0.5% these days.
The problem is that the fuel quality certificate is rarely exact to begin with and between the original fuel testing and the time it ends up in your tanks, a lot can go wrong. Sometimes it is accidental but a lot is fraud. It is quite common to offload part of the fuel consignment and replace it with water. In marine fuel scenarios that can be clean water or sea water.
The first step is to test fuel quality before it gets into your tanks. Once in there all sorts of problems will arise like "The fuel we delivered was spot on but you had water in your tanks already." It gets messy.
Sometimes it isn't water but chemical wastes. Used dry cleaning fluids, tank washing chemicals, you name it and heavy fuel oil is a great sink. Quality checks are rare, it is a thick black dirty fuel that can hide all sorts of things including used lubricating oils....
So the amount of water to manage could be whatever can get past your QA system, and that can overwhelm any calculation of condensation and original content.
I 'd suggest you need to consider very specific quality checks that verify that the fuel you receive is the fuel declared on the suppliers quality statement otherwise your calculation may become meaningless.
I was at a power plant in Portugal where they had so much water in the fuel "you could shower in it" as the German commissioning engineers said. They had to dump the entire store of fuel.

JMW

http://www.ViscoAnalyser.com

 

[MJCronin]

Isn't it common practice to take samples of large petrochemical bulk purchases ?

Couldn't you evaluate test results of the amount of water entrained an extrapolate from there ?

Bulk petrol tanks are specifically designed with sumps and low point drains to facilitate periodic water drainage. Water accumulates due to daily breathing when temperatures swing.

Where are you located ?

Were these tanks originally designed for another purpose ?

Why was there no evaluation of water contained when the liquids were purchased ?

-MJC

 

[jmw]

Heavy fuel oil density can vary but maximum values are set which allow separation at temperature.
It can vary either side of the water density from 950 (A10)to 1010kg/m3 (K55) at 15degC.
Now factor in storage temperature....
In fuel flow to engines, centrifuges are used to separate the water, the temperature is typically 98degC at the centrifugre where the oil density range is then 892 to 953kg/m3. Water density at 98degC is 958kg/m3 i.e. just enough difference to be separated.
Somewhere near 40degC, the density of water and the heaviest fuel oils are very similar and below this the water is the least dense.

It is recommended to take samples and check the quality. There are off line test kits which enable some basic properties, including water content, to be tested on site during delivery. (see

http://www.kittiwake.com)

but then we come up against the various tricks some suppliers are adept at to defeat such testing.
It is usual to use an inline drip sampler to collect a sample progressively as the fuel is delivered and which is then sent for lab analysis. Spot samples for off line testing are easier to take but easy enough to defeat.
Once the fuel is received, it is not always easy to have it taken away again and there is plenty of opportunity to obscure the issue.... what was in the tank originally? and so on....
One reason for this uncertainty is that HFO is (was) cheap and no one would ever pay for instrumentation.
If online instruments were used and the supplier obliged to provide an actual lab analysis with the fuel (rather than a typical set of values) then most of the problems would be managed.
(see

http://viscoanalyser.com/page35a.html

for examples of how bad fuel oil quality can be ... partly due to a lack of fuel management and partly because, without online instruments, the opportunities for fraud are rife and see

http://viscoanalyser.com/page29a.html

for a method to use density and viscosity measurement as a fuel quality assurance system to validate the suppliers fuel quality certificate.... some engine manufacturers use this approach to checking fuel quality as received in stationary power station applications... the marine industry would rather not just at the moment because the range of fuel management issues that would be revealed by any online instruments would necessitate significant investment ... and who would pay for that?)

JMW

http://www.ViscoAnalyser.com

 

[tickle]

The BP website used to have some fact sheets about diesel contaminants and the installation of diesel storage tanks. I have not looked for a while so cannot confirm if they are still there.

From memory, diesel will deposit sludge and water, whether from what was originally there, or condensed atmospheric water. Horizontal tanks should be installed with a slope towards a water removal point.