Using centrifuge for de-watering

[Carrington]

People have been asking if you can use a centrifuge as a aid to de-watering and up util now I've been of the opinion that its no real use but I know think that I've been wrong in my assumption.
My fuge's are set up over a pair of s/sinks so I can take samples from the out flow and from there they outlet through the plug hole's to a tank with a submersible pump.
Something I have noticed on closer inspection is that as the fuge's are running the bio dance's across the sink bottom giving me a good visual indication as to the cleanliness of the bio but when I have run a batch through them of 3k litre's and the wind them down I start to get water dropping out and sitting on the bottom of the sink.
So now I'm thinking that fuge's do work in de-watering but its only possible if you can separate the flow at the end of the run or install some form of absorbent linner to hold onto the water once the cycle has finished.
I think the best way to use the fuge to de-water is to run the product into a bowl where the outlet is higher than the bottom of the bowl so during the cycle you could stop the fuge so as to let it drain and any water wouldn't contaminate the finished fuel.

If this is of any  interest then I will do some more  test with the fuel before and after  using calcium hydride to come up with some proper results

Paul

[Julian]

I built a centrifuge a few years back.  It was based on the US bowl design.  It performed well and seemed to do a good job of wringing good oil out of whites.

This from the VOD ...

I had a bash at a centrifuge some time back. Mostly made out of sheet aluminium, it worked well but had an extremely slow through put. Cost was minimal, 3000 rpm double ended motor, ex old main frame computer cooling fan - free, legs from a scrap bath - free, aluminium sheet ... can't remember but couldn't have been more than 20 quid and some rather wonderful aluminium "brazing rod" ...again, can't remember but I'd guess another 20 quid plus some odd bits of scrap alli. and steel. So they can be made quite cheaply but perhaps not particularly safely!

The design was a shameless copy of one offered for sale in the States http://www.simplecentrifuge.com/gallery.cfm?id=25 As far as I can gather my unit produced circa 718g. Had it have not been so slow, the plan was to mount a pump on the second out put shaft underneath so it would be "self feeding". In the end it was quicker and a lot less hassle to filter under gravity but the project was quite absorbing, great fun and produced a great deal of adrenalin when first testing an unbalanced rotor "stuck" together with something I'd never used before!












What design of centrifuge are you using to have trouble seperating the water ... have you looked at milk centrifuges?  They seem to offer continious operation and continious seperatioin of light and heavy liquids ...



Discussion on the VOD here ... http://www.vegetableoildiesel.co.uk/forum/viewthread.php?tid=14854 but ebay links long gone.

[Carrington]

Hi Julian
The fuge's I have been using are a couple of Nathan robos and the question has been asked by many people as to will they de-water.
Looking at the milk separator that looks like something I need in a different part of my process. Time to look for auction's in the dairy industry ( not sure I can build something to the drawing supplied ).

[photoman290]

 hi paul,
think that milk centrifuge is called something else. looks like one the reckless engineer posted over on VOD  recently. think he said its called a clarifier? not sure though. he seems to know his stuff concerning this subject. might be worth dropping him a u2u.

[therecklessengineer]

I'd call the above a purifier, and a clarifier similar, but with no discharge for separated milk. It would essentially just remove sludge rather than sludge/water.

And yes, I run two purifiers in my day job. One removes water/sludge from lube oil for two very large diesels. The other removes water/sludge from fuel oil before being stored in tanks which then feed the above engines.

In both cases, the product (lube oil/fuel oil) is heated to about 70 degrees to increase the density difference between water/product and aid separation.

Water is removed continuously from the equivalent of the 'separated milk' outlet on the diagram above, whilst the separated product comes from the cream outlet.

After a certain interval, the bowl opens to dispel all sludge/water down a sludge outlet.

A good explanation is here: http://www.marineengineering.org.uk/. It won't let me post a direct link so you'll have to scroll down on the left bar to Utilities/Fuel Treatment/Purifiers.

Next time I've got one in bits I'll get some photos if you're interested.


Edit: The act of purifying the lube oil on the diesels is that it essentially makes it last indefinitely. As I'm sure you'll appreciate, if you're talking 3000 litres of lube oil, it's kinda expensive to do an oil change! The sludge and water is removed from suspension in the oil which maintains the oils performance. The only thing that we need to watch the the total base number - this will decrease when running on high sulphur fuels due to the formation of sulphuric acid as part of the combustion process.

However, due to the trend towards low sulphur fuels this means our oil is lasting longer and longer. I've personally seen about 6000 hours on these engines which is rapidly approaching the equivalent of about 500,000 miles - and no oil change yet.

[greasemonkey]

Interesting. Looking at it that way, it could well be justifiable to use that process on vehicle engine oil. Depends a bit on the cost of the equipment to do it, and how much oil the sump takes, but wouldn't be to difficult to work out how long till it pays off.

[Julian]

From the little time I spent in the Marine industry, think he's talking about bits of kit that cost very many times the price of a new car!

[1958steveflying]

From the little time I spent in the Marine industry, think he's talking about bits of kit that cost very many times the price of a new car!

But in essence just doing the same job that one of Nathans would for our car engine oil.  Not that I would go to the bother.

[Tony]

Fascinating post about marine diesels   Who'd have thought that oil could be preserved so long?

What about carbon deposits, are they fuged out of the oil as well?

[greasemonkey]

And, I was under the impression that the pressures in the engine could start degrading the structure of the oil molecules, reducing their lubricating properties. Could be wrong there though.

[therecklessengineer]

Not so much pressures, but temperatures. Particularly turbos can cause reactions in engine oil. Some marine diesels (not the ones I'm currently looking after) actually have their own oil system for the turbo.

The above is slightly inaccurate - we do check the oil regularly for correct performance and change it if necessary. Although in my case this hasn't proved necessary yet. Another problem I didn't mention above is fuel contamination of lube oil - a purifier cannot help in this case. Normal procedure when we find a problem would be to change enough to bring the oil back in spec - not necessarily the whole lot.

I probably should have defined 'sludge'. It's particulate matter - in the case of lube oil it's mostly carbon deposits. By the time it's captured in the bowl it's a sludgy horrible gunky mess. So yes Tony - carbon deposits too.

Automotive versions do exist. Certainly the LR Td5 engine has a smaller version of one of these as part of the oil filtration system. It's driven by a turbine type arrangement on lube oil pressure. How similar it is I'm not sure - I've never had one in bits, but it's certainly the same principle.