The refinery was a separate hearth used to convert grey cast iron into white cast iron prior to its conversion to wrought iron in the finery and chafery.
With the introduction of the coke fired blast furnace the silicon content of cast iron increased. This resulted in the production of grey cast iron rather than white, as was normally the case with the charcoal-fired blast furnace. Grey cast iron was more difficult to refine, because the silicon had to be oxidized before the carbon could be removed. The carbon in grey cast iron was in the form of graphite was more difficult to oxidize than when it was combined with iron in the form of cementite, as in white cast iron. To solve this problem, an additional step in the fining process was added, in which the grey cast iron was heated under oxidizing conditions until the silicon was removed and the metal was converted to white cast iron.