1.2.1.1 Cokemaking
Blending of coals with different plastic properties is extensively carried out prior to cokemaking. The blend must fuse at moderate temperatures and resolidify to form cohesive semi-coke. The development of strong, lump coke is completed by heating to high temperature, typically between 1000°C and 1100°C.
Coke is the critical fuel of integrated iron and steel plants It must possess certain properties in order that blast furnaces operate effectively. It must comprise large well graded lumps with few fines. High resistance to breakage during handling and passage down the blast furnace is important. Irregular shapes give high voidage (hence permeability) to coke in layers. It must also have a high internal porosity (about 50%) and possess low to moderate reactivity to gases (principally CO2) in the blast furnace.
The concept of a coke plant with direct combustion of the raw gas would omit the entire gas treatment plant and produce only coke and power. Aside from these achievements with conventional coke oven batteries, the non-recovery technology has also found acceptance. Coke plants of this type are in operation in the USA, Australia and India. One plant in the USA is a heat- recovery coke plant that produces power from the waste gas. Further improvements in plant efficiency and coke quality are achieved with stamping of the coal charge, which is now developed for non-recovery ovens, too.
Coke production is mainly carried out in conventional slot-ovens. 
In a conventional slot oven coking converts the coal to a higher carbon content solid which contains all feed minerals.  Some of the volatile components (gases, vapours and liquids) are used to heat the coke oven while the remainder are recovered as tars for by- products and coke oven gas use within the steelworks as a fuel.  Conventional coke ovens (slot type ovens) with raw gas recovery have reached dimensions of more than 8 m height and 90 m 3 useful oven volume, boosting the capacity of a single battery to 1.3 Mt/y and the production of a single coke plant with one operating team to 2.6 Mt/y. At the same time, the emissions from batteries and gas treatment facilities have been reduced to the lowest amounts ever. A further increase in energy efficiency and environmental protection for conventional coke batteries is expected from the combustion of the hot raw gas with subsequent generation of electricity. The energy balance of a conventional coke oven is shown below.  The yield, size distribution and strength of wharf coke can be estimated from the properties of the charged coal blend.
graphic

The need to improve environmental controls for existing cokemaking facilities and to find more cost- effective methods of producing high quality metallurgical coke has prompted several new and emerging technologies, for example:
  • The European Jumbo Coking Reactor has reconfigured batteries for larger individual batch process ovens. Recent studies have indicated that capital costs for the technology, also referred to as the Single Chamber System, were significantly greater than conventional technology, and therefore, interest in utilizing the technology is minimal.
  • Non-recovery cokemaking is a proven technology derived from the Jewell- Thompson beehive oven design. Beehive ovens operate under negative pressure, eliminating by- products by incinerating the off-gases. The technology also includes waste heat boilers, which transfer heat from the walte products of combustion to high-pressure steam for plant use and for conversion into electricity.
  • The Coal Technology Corporation is using a formcoke process that produces coke briquettes from noncoking coals, etc.. The process is currently referred to as the Antaeus Continuous CokeTM process, named for the Australian company which purchased the patent rights.
  • The Japanese SCOPE21 project, still in its early stages of development, is using a formcoke process that combines banqueted formcoke and improvements in existing batteries. With this technology, cokemaking is performed in three sections: coal pretreatment, carbonization, and coke upgrading. The project is being developed as part of an eight-year research program.
Nicol & Durie review recent changes in cokemaking and blast furnace steelmaking.
The Chair of Iron and Steel Metallurgy of the Department of Ferrous Metallurgy (IEHK) at the RWTH Aachen University offers learning units and lessons of the course "Ironmaking" online, these lesson include a lecture on coke properties.