The article leaves some points out. But the energy to turn the coal into "coke" will have to come from somewhere... Prolly bu burning thermal coal at some stage.
"The industrial production of coke from coal is called coking. The coal is baked in an airless kiln, a "coke furnace" or "coking oven" at temperatures as high as 2,000 °C (3,600 °F) but usually around 1,000–1,100 °C (1,800–2,000 °F).[17] This process vaporizes or decomposes organic substances in the coal, driving off volatile products, including water, in the form of coal-gas and coal-tar. The non-volatile residue of the decomposition is mostly carbon, in the form of a hard somewhat glassy solid that cements together the original coal particles and minerals."
