As mentioned by another poster, at 5kW and assuming $0.06 per kWh (as it is
here in Vancouver), that would translate to about $0.30 per hour (yes that's
30 cents per hour). I'm not sure which system the 250k number is based on
but I know that it takes almost nothing to run this small furnace - there
are customers that run these machines in two 8 hour shifts every day in the
Melting cast iron with my induction furnace I recently used 3.8 kWh to
melt a 3Kg ingot - having fitted a re-settable kWh meter to my 100kVA
diesel generator I make a habit of resetting it before each melt.
Obviously s/s will be more as the melting point is higher, although
the latent heat of liquifaction may be a bit less.
OK, here is a quote from a recent posting of mine in the electrocast
group, that breaks down the figures:
Having fitted a digital resettable three phase kWh meter to my
kVA generator, I thought it would be amusing to see what sort of
overall efficiency I'm running at in terms of electricity input
molten iron output.
A few assumptions:
1/ I melted approx 3kgs of white iron
2/ Ambient temperature was 13 deg C
3/ The iron melted at 1535 deg C
4/ It was super heated to 1635 deg C
5/ Specific heat of iron is 0.449 J/g degK
6/ Latent heat of liquifation of white iron is 138 KJ/Kg
(suprising difference with grey iron at 95 KJ/Kg)
There are three phases:
a/ Raise iron from room temp to melting point
b/ Stuff in enough energy to melt it overcoming the latent heat
c/ Super heat by a further 100 deg C
By my calculations (but please check them)
a/ uses 0.569 Kwh
b/ uses 0.115 Kwh
c/ uses 0.012 Kwh
Thus a total at 100% efficiency should be 0.696 kWh
I measured usage of 3.8 kWh so:
Now of course heat is lost in the electronics, in the walls of
crucible, and in the various cables, but 18.3% is pretty
low I reckon, especially as it takes no account of the energy
piled into my water cooling plant, nor the 1 hp coolant
If I did the same calculations from the diesel in the generator
to molten iron, and allowed for the other factors mentioned
well I reckon I'd be down into single figures of efficiency !!!!
Wed May 9, 2007 7:45 pm
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