On 27 Oct, 22:15, Rod wrote:

the coal consumed was two hundredweight".

"Coal" in that period was commonly used to refer to any of the black,
lumpy fuels. You have to check carefully as to which was used. Even
charcoal is sometimes described as "coals" in the 16th century. "Pit
coal" or "sea coal" is the sort that we commonly know as coal.

Much of Trevithick's work took place in the Welsh valleys at Pen-y-
darren, but although this was a coal-mining area it was also an
ironmaking town and he had ready access to the coke that was being
used in the furnaces.