John
As a follow up to my previous post...
I forgot to mention to C side of things. For the size of bloom I
described (4kg raw), I would expect to use 50-60kg charcoal in the
smelt and probably 60-80kg in the smithing to 1kg bar iron. With
larger furnaces the smelting may get a bit more fuel efficient - one
set of experiments (Sauder & Williams) achieve a total charcoal
consumption of 82kg per kg bar iron (smelting and smithing), when
bloom size is up around 13kg.
Now for some more speculative thoughts...
If iron-making continued for 400 years they clearly would not have
deforested large areas if they wanted to survive. The problem lies in
the large areas of managed woodland required. To play with your
figures a little:
11 million tonnes of slag = 780,000 tonnes bar iron
over 400 years = 1,950 tonnes per year
requires approximately 250,000 tonnes of charcoal per year
in UK managed woodlands charcoal can be made at 6 tonnes per
acre of coppice (= approx 15t / hectare)
so your production requires some 15,000 hectares of coppice
woodland per year. If the coppice cycle was 16 yrs (typical UK
cycle) , then you need 240,000 hectares of woodland (ie 2400 sq
km). Elba has an area of only 220 sq km - so even if completely
wooded, could not have supported even one tenth of that industry.
These figures are based on UK rather than Mediterranean yields
and coppice cycles - so may be rather out, but ought to give some
idea of the nature of the fuel problem!
Hope my ramblings help!
Tim
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Dr Tim Young
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