Resurrection of a CFEI 100 KVA Induction Furnace

[awemawson]

Pete yes that’s my fear !

John, I’d not thought of fire as it’s a bit close to the goose fence , but I had considered my Karcher MPDS battlefield decontamination unit, as it’s a steam cleaner on steroids but it’s rather deeply buried at the back of the shed.

As I’ve solved the not starting issue with my small Chinese pressure washer (*) I’ll have a go with it this morning. After all it was a sensible suggestion from Pete some time ago to try and flush out the gap with a pressure washer.


(* why would it not start? Oil sensor switch saying low oil when dip stick says full! Importers suggestion: fill the oil until it runs out of the dip stick hole! I think they’ve had this issue before. It’s a copy of a Honda engine mounted in a wheeled frame and I suspect that it sits rather more tilted than the engine designer intended)

[awemawson]

So with the finest (so highest pressure) nozzle fitted I gave the manhole cover an intensive session with the pressure washer. It was obviously doing 'something' as every now and again a great spurt of brown rusty water would came back at me in the face !

I blasted it vigorously for quite some time, then gave it more violence from the sledge hammer before again an intensive session with the pressure washer. Not easy to see what it's done with all the water about so I blew it off with an air gun.

As you can see from the pictures below the 'gap' is much more pronounced in some places but still totally jammed full in others - it MUST have helped I tell myself 
 

[Sea.dog]

How about another approach, Andrew? If you have plasticine or similar, plug the elongated holes around the edge, build a dam around the periphery and flood the whole area with a concentrated solution of vinegar/citric acid/phosphoric acid and put a lid on it to prevent evaporation?

[awemawson]

Another good suggestion Graham that I will put on the list to try.

I have a recently retired and recently divorced Fireman who got stuck in isolation on the farm in his caravan by the virus when his arranged site closed and he'd already left his other half. This morning he's seen what I'm doing (from the prescribed 2 metres!) and is taking it as a personal challenge that he cannot open it.

Who am I to deny him his entertainment - it has to be better than just polishing his caravan, he'll have no paint left 

[AdeV]

it has to be better than just polishing his caravan

Hmm, I've never heard it called that before! 

Can you get a pry bar into the slots at the edge? Maybe you could see some movement?

[awemawson]

I've been swinging my not inconsiderable mass on the end of a 6 foot pry bar this morning, and no movement what so ever!

This afternoons job is to make a slightly more substantial slide hammer !

[hermetic]

This may sound daft, but have you tried putting a couple of manhole keys in the slots, then putting a bar between them and trying to turn the manhole lid inside the frame, it occurs to me that those two prying slots could also be the holes for a couple of tabs to come out if the manhole cover is a bayonet type fitting, and locks down to the frame.
  I like the fire idea, but then, anything to do with fires.......... my late aunt used to say "the smell of smoke follows naughty boys"
Phil

[awemawson]

Phil, There is a location tab that stops it rotating and ensures correct alignment.

But never mind:

We Have A Borehole

I made up my more substantial slide hammer, and even using it like a maniac for quite some time had no effect. In places I could get a hacksaw blade into the gap the full two inches of cover thickness, but elsewhere it would not go in at all - managed to clear a bit of debris using it but nothing substantial.

So I decided to use the slide hammer as an attachment and do a tentative lift with the Fork Lift to put tension on the cover - no lid movement what so ever, and continuing the entire massive concrete structure started lifting 

Clearing the turf away from round it, (to stop it falling into my nice water source!) I carried on lifting until a gap appeared showing WATER - lots of water !

Getting my cable drawing fibreglass duct rod, I tried pushing it down - there was a definite circular 'thing' in the centre under water - presumably a pipe, and I was able to push at least 20 maybe 25 metres down the hole before feeling any resistance. All this was at an odd angle as the concrete structure was balancing on one key (my slide hammer) off the fork lift.

Common sense told me to lower it back before there were any accidents 

So now I need to work out what's next 

[Sea.dog]

What a result 

Things are definitely looking good for the future of this project 

[hermetic]

that manhole cover is REALLY stuck, but no matter, you have a supply of cool water! onward!!
Phil

[awemawson]

Thanks for the encouragement chaps . . . .

. . . .  you do know that it's DANGEROUS to encourage me don't you 


So who knows about the maths of heat exchangers? It would be nice to pump cold water from the borehole though a simple heat exchanger the other side of which carries the 'furnace water' that needs 40 kW removing

... lot of variables (too many!) - no idea of which / what heat exchanger - make one / buy one / beg one / steal one

[charadam]

Hey! I was in the shower when you took the lid off!

Most unpleasant experience and my solicitors will be in touch.

[chipenter]

Standard domestic indirect hot water cylinder , with the coil to furnace and cold circulating in the tank will shift a lot of heat .

[AdeV]

SO.... drill hole in manhole cover - lower pipe, job's a good 'un! 

[awemawson]

Standard domestic indirect hot water cylinder , with the coil to furnace and cold circulating in the tank will shift a lot of heat .

I used that system as a 'cold store' at my last place but got the impression that actually it was limiting the cooling due to the relatively low heat transfer - may be the tank I used was furred up !

I'm now looking at 'welded plate' stainless heat exchangers - they are remarkably compact for their capacity - the bit I'm not too sure of is their effectiveness at the  temperatures involved. My 'bore water' will be nice and cold out of the ground - probably 14 C max. My circulating water round the furnace and furnace driver electronics I want to keep to less than 30 C - so the differential of 15/16 degrees is not what for instance you would get with a domestic set up.

[awemawson]

SO.... drill hole in manhole cover - lower pipe, job's a good 'un! 

Yes Ade, that's the idea, but I'd still like to be able to remove the man hole cover.

I've been tapping a 3" long strip of 1.2 mm  steel 15 mm wide gently into the gap - if you start where the gap is full depth (2") and work against the 'wall' of the next bit you can crumble bits of the rust / clay / mud until eventually you get another full depth bit, but by heck it's as tedious job. If only the Grand Children could come and stay - ideal pocket  money earner except for our current virus lock down !

Drilling the cover will be a last resort - most bore hole pumps seem to be 3" diameter - also I have absolutely no idea if the  lining pipe is in the centre of the circular lid, or well to one side, and it would be a shame to miss.

Remember that the underside of these covers are webbed like the under side of a surface plate so random holes can end up in unfortunate places un-knowingly 

[awemawson]

Matthew (who lives in France) kindly got in touch with CFEI on my behalf to find out about back up batteries and what they retain. Not really unexpectedly they have little information to reveal other than 'change the battery with power on' which is the same for most systems.

The lithium battery in 'half AA' size 3.6 volts is fortunately a standard RS item so one should be delivered tomorrow, plague, tempests and viruses permitting.

Thank you Matthew for that.

[David Jupp]

Plate heat exchangers are good - but for welded ones make sure the water is clean and soft, as you can't get them apart to clean.

The fluid velocity is important to get the heat transfer coefficient up. A single coil in tank won't be great, as the velocity around the coil will be modest at best.

[awemawson]

Good point about not being able to dismantle for cleaning. Would plumbing arranged for an occasional reverse flush be sensible?

The water circulating in the furnace / furnace driver loop can be closely controlled as it is always the same. This cannot be said of water from the bore hole. Historically bore holes round here ceased to be used for public supply due to high iron content. Not sure how much filtering and settling it is practical to apply.


Assembled gasketed bolted together plate heat exchangers are far less available than brazed / welded ones.

[David Jupp]

Not convinced that reverse flush will help much - deposits tend to be uniformly across the plates.  On a plant where I worked, we used to swap plate exchangers over weekly, strip and wash down the plates with a 'steam gun'.  That was though in a location where we needed particularly good cooling, and part of the system was open to atmosphere so 'bugs' could get in - other exchangers were cleaned far less frequently.  Welded plate exchangers are found in most combi boilers and seem to last quite well...

Spiral plate exchangers can have a door on the end for cleaning, but I bet they cost more.  Shell & tube likely to be quite good, though larger.  I guess a lot will depend on what you can find and price.

A simple pipe in pipe exchanger is good if you don't need  lot of cooling - or they tend to get large and unwieldy.

[Sea.dog]

How about  having a side tank with pump, which is valved off from the cooling circuit until required,  and filled with something nice such as concentrated phosphoric acid? Heat it, too, and it'll shift any residue very effectively.

[awemawson]

I may be doing a re-think here !

The original chiller cost about £2 per hour in electricity to run

I am being charged about  £1.80 per cubic metre of treated drinking water. So if I can get adequate cooing in the heat exchanger using my tap water realistically it's no more expensive than using the original (and now) defunct chiller. It will eliminate the need for expensive bore hole pumps, trenching etc.

This would mean that the heat exchanger cold side would have filtered treated water of course.

So this morning I need to measure how fast my local internal water distribution system can deliver water to the foundry, then somehow work out if that is an adequate source of cooling for the heat exchanger 

[Sea.dog]

If only you had a hydrant somewhere     

[awemawson]

And the answer is 3 gallons in 55 seconds at 10 degrees C

Or 14.8 litres / minute.

But how the heck does 14.8 litre / min at 10 degrees C through a heat exchanger translate into energy extracted from the primary?

There must be some sort of 'transfer function' for the H.E. that varies with the temperature differential, and the cooling water is going to be raised in temperature by a certain amount. And that volume of warmed water in (say) an hour translates into a certain amount of energy but now I'm getting on very shaky ground.

[awemawson]

If only you had a hydrant somewhere     

It's a long way away and that would be naughty !