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.
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
- 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.