"coke for its ovens"
Coke is the solid product from the distillation of coal in an oven which is mostly carbon and which is in turn burned as a fuel -- in the past, to drive steam trains and ships and to heat large buildings; more recently, as a fuel in metallurgy to reduce metallic oxides to metals. Mr. Halloway is probably speaking of it as a fuel for a steam engine, and metaphorically for the operation of the entire evil carnival.