Bio-methanation at the Agricultural College of Obernai

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Flytox
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by Flytox » 03/09/14, 21:33

Did67 wrote:It is stainless steel.


There are stainless steel and stainless steel. In certain very specific environments, certain stainless steel grades do not hold up even though they are capable of withstanding other "very difficult conditions" of corrosion. The anecdote, a local craftsman who uses submerged stainless steel cables for special boats has no problem in the Atlantic Ocean .... these same cables do not hold for the same use in the Pacific. : Shock: : Mrgreen: He had to change the shade of stainless steel so that it always works whatever the ocean / sea.
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by Did67 » 04/09/14, 07:45

There, the environment is so corrosive that there is no choice.

But I also wondered if there was really "hard" stainless steel, like hardened steel ??? All stainless steel that I know is rather "soft" ...
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by chatelot16 » 04/09/14, 09:44

stainless steel is not that stainless: there is often corrosion where it remains very dirty for a long time ... and a methanization tank is indeed a concentrate of dirt

in the manufacturer's doc that you mentioned stainless steel is not the only material used: we also see high resistance steel, but what shade?

I would think of hadfield steel which is a little stainless but which is above all very resistant to wear: they are made into truck bodies, hoppers and other equipment in quarries and mines to resist wear

this steel is less resistant to corrosion but would perhaps be a better compromise, if the wear is so rapid

see also that hardness is not the only way to resist wear: in certain systems where abrasive materials are used, steel parts are protected by sticking rubber to them: even if it is softer it wears less
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by Janic » 04/09/14, 09:53

Hello
tefloning is also a solution against wear.
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by Did67 » 04/09/14, 10:28

As stated, it is a commercial model of the SUMA brand.

I suppose she has studied this question, as an expert on the subject.

But we will surely have contacts, I will not fail to ask the questions you ask!

We'll see if there are answers!
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by chatelot16 » 04/09/14, 10:34

another material both hard and stainless: stellite: it is a very hard alloy, and stainless

we made it a very used cutting tool before tungsten carbide: it is still used for band saw teeth

it is used in chemistry to make taps: we appreciate both its hardness to make taps that do not wear out, and its chemical resistance

alas it would certainly be much too expensive to make whole propellers

the stellites are easy to deposit with a torch to reload a part just where it wears out, and the reloaded part becomes stronger than the original part
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by Flytox » 04/09/14, 20:43

There is also the cavitation trail. When the phenomenon is violent and / or permanent, it causes craters on the surface of the blades / vanes several mm deep and ends with accelerated wear of the parts. Example Froude brake rotor stator.
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by chatelot16 » 04/09/14, 21:07

cavitation is a problem of high speed propeller type outboard: we should be far in the mixing of a methanizer where it must be quite slow

in addition, the bacteria should not be destroyed: a fast propeller with cavitation would kill everything that passes in the zone at zero pressure
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by Did67 » 04/09/14, 22:42

Some explanations :

- there are "hardened steel" propellers
- the client (it was a call for tenders of the "design-build" type) had chosen the model with "normal" propellers: there were objectives in terms of efficiency once the nominal power had been reached, a budget to keep, but no clause on the guarantee of the life of wear parts (we did not think about it! Our main fear being that the station does not produce enough gas, that the engine does not run at fund and that the sales are insufficient to repay the credits; therefore all the guarantees were focused on these elements!)
- from the agitator manufacturer (SUMA), these have a lifespan of 1 to 3 years; we are right in the middle; it is not an anomaly
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by Cuicui » 07/09/14, 15:02

Did67 wrote:- from the agitator manufacturer (SUMA), these have a lifespan of 1 to 3 years; we are right in the middle; it is not an anomaly
Do these propellers rotate continuously? If so, that's about 12 hours in 700 years, it's not that bad already. There is certainly a way to do even better with a better suited material.
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