Spatial variation of coke quality in the non-recovery beehive coke ovens

Abstract

More than 50% of hot metal production worldwide takes place in blast furnaces. Coke is the most expensive raw material in the blast furnace. It acts as the burden support as well as heat source and reductant in the blast furnace. As technology advances, supplementary fuels can supply heat and reduce the iron oxides, but coke would always be needed as burden support. Blast furnaces have been using coke for the past century and will continue to use coke for the next few decades. The price of coke is determined by its quality. Strict environmental laws and regulations in the USA pushed coke-making technology since the early 1990s towards the beehive type of oven. Gas collected during the coke cycle is used to supply heat to the process. The aim of this study is to investigate the spatial variation and coke quality in the non-recovery ovens and provide an explanation for it. The original coal was tested and samples of the coke were obtained from the top, bottom and sides of a coke oven. The samples were prepared and submitted for image analysis to determine the porosity, cell wall thickness and pore diameter. The samples were also submitted for a microscopical point counting to determine the micro textures of the coke. The coke was further submitted for the coke strength after reaction testing (CSR). The results show clear variation in the coke and a model of the behavior of the gas inside the coke oven during the carbonization process was developed based on the results of the tests. The model shows the flow of gas from the bottom of the oven up along the sidewalls to escape from the coke charge through the top. The flow of gas enriched the coke on the side of the oven by deposition of pyrolitic carbon to create an ultra-high grade of coke that could physically be separated from the rest of the coke and be sold separately at a higher price.