Going on memory.
Blast furnaces produce a LOT of carbon monoxide which must be burnt to carbon dioxide to avoid poisoning the workers around - generally this is done in an associated power station.
Highest priority use is providing air for the blast furnace (the blast bit).
There is generally more than enough power for a complete steelworks and considerable export but initial rolling of slabs can be tricky re phase etc so better to have the power station connected to a larger grid. Other high loadings are starting big electric motors eg fan motors for blast, sinter plant suction etc.