Black sticky mud from diesel tank bottom 1

[CostasV]

A few weeks ago, we found that in the bottom of the backup diesel generator diesel tank (5000 lit), there was about 2cm of dark brown (almost black) sticky sediment, with viscosity like toothpaste, maybe even thicker.
The diesel was inside the tank for about 4 years, no new fuel added. It had 7% biodiesel. We tested the diesel for fungus and bacteria, and the result was negative.

We cleaned the tank (a man inside the tank mechanically removed the sediment from the bottom and the verticall surfaces) and kept this black thick mud in two buckets. Half of the bucket was the mud and above it was black diesel up to 3/4. The next day, when we tried to pour the liquid and to leave only the "solid" mud, we found that the mud had turned into black diesel, leaving only about 2-3cm of the nud in the bottom of the bucket.

Any thoughts of what this sticky mud is? If it was asphaltene, is it expected to be disolved so easily into liquid?
As the bacteria test resulted negative, I guess the bacteria produced mud is ruled out, no?
I am curious if this mud is going to be produced again (after 1-2 years), or if we have removed the most of it.

Has anyone seen something similar?

 

[EmmanuelTop]

Does it look like this?

Black sludge (asphaltenes) are quite common in diesel tanks - especially if diesel has been sitting in the tank for a long time. There are plenty of potential culprits: aging, addition of incompatible chemicals, mixing of two or more diesel products from different crude oils, etc.

This is an extract from diesel fuel contamination article at Marine engineering:

"Asphaltenes, the most polar and heaviest compounds of oil, associate themselves in solution to form complex colloidal structures. Asphaltenes causes serious problems in diesel engines, fuel systems, oil recovery, oil-carrying pipelines, and refinery operations, and many of them being related to the presence of aggregates in the heavy fraction.

Asphaltene agglomerations cause sludge build-up. Flocculation of asphaltenes occurs, not only from the natural oxidation and aging of the fuel, but also as the result of mixing oils from different crude sources. This can occur when blending fuels or mixing into a storage tank that contains fuel.

Asphaltene solubility is also affected by the aromaticity and the type (and concentration) of resins in the blend components. When the fuel blend components are mixed, the asphaltenes may precipitate and form sludge."

Dejan IVANOVIC
Process Engineer, MSChE

 

[CostasV]

Thank you for the information.
Our mud looked rather different. See the photos.

http://files.engineering.com/getfil...a43b-487a-a27e-61a9edca1222&file=DSC_0329.jpg

http://files.engineering.com/getfil...68a9-488b-9a7c-ad340d5fc908&file=DSC_0330.jpg

 

[EmmanuelTop]

Both samples look very much similar to me, with the exception that the filter sample is liquid-free.

For diesel sitting 4 years in a tank, degradation seems to be the primary suspect for sludge deposition - especially if it has been in contact with atmospheric air. Diesel tanks in refineries are usually blanketed with Nitrogen, for the same reason: avoid degradation.

Nowadays is quite easy to determine asphaltene content in petroleum products. You can get in touch with any decently quipped laboratory and submit a sample for analysis. This will clear all your doubts.

Dejan IVANOVIC
Process Engineer, MSChE

 

[MikeHalloran]

You got the good stuff...

The last time I handled Diesel, in translucent acid carboys, it appeared to be about ten percent water, and five percent dirt.



Mike Halloran
Pembroke Pines, FL, USA

 

[arunmrao]

Last month, I got the diesel storage tank about 10000Litres capacity cleaned as the contaminated diesel ( sludge about 12inches thick in the tank) was clogging the filters of 2x 1250kva D.G sets. We have now installed a filtration system , from the tanker to the main storage tanks and several filters along the distribution line. This was a big investment, and we shall assess the benefits soon.


"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[Artisi]

Back in my early pump days, we use to hire heavy duty self-priming pumps to a particular company in Australia who specialised in cleaning the oil refinery tanks of this accumulated "sludge" -- extremely hard heavy work on the guys manhandling the hoses inside the tanks vacuuming this stuff and the clean-up of the pumps at completion of the job. The hire only terminated once we gave the OK for "clean" pumps to be removed from site.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[CostasV]

Thank you for your comments!. I am sending a sample for analysis. I'll keep you informed.