Petroleum coke is a carbon-rich byproduct of crude oil refining. The solid coal-like material has low levels of sulfur and trace elements, making it suitable for a wide range of industrial uses. Coke coming directly from the coker, or "unprocessed petroleum coal" (UPC), is called green coke. UPC must be further processed in a rotating kiln, also known as calcination. This is done to prepare it for aluminum production. The hydrocarbons are removed and the anode coal is converted into primary aluminum.
The calcined petroleum coke can also be used to make graphite electrodes in electric arc furnaces, and it is also a good cathode for nickel melting. Demand for calcined petroleum coke will grow quickly due to increased demand from developing countries and the iron and steel industry, as well as favorable government initiatives relating to green energy.
Optimizing calcined coke production is a critical step in the overall smelting and graphite processes. The ability to control the reactivity of the coke with the slag binder, as well as the oxidation resistance of the anode, is critical to maximizing aluminum production and yield. In addition, the calcined coal is a key raw material in producing titanium dioxide. This is used for a variety of purposes, such as paints and plastics.
The calcining process is a multistage one. Initially, the coke is loaded into a rotary kiln and subjected to heat from the combustion of volatile matter (VM) and fine coke particles. This heat is transferred to a waste heat recovery system that can either be sold to nearby power plants or used to produce steam for a boiler-driven turbine generator.
This supplementary energy source improves the economics of calcination by reducing fuel costs and by providing additional revenue from the sale of electricity. Moreover, the system also provides substantial thermal energy savings from reusing the flue gases that would otherwise be vented to atmosphere.
The invention has direct applications in the growing industrial energy-intensive calcined coke market, with significant benefits for U.S. manufacturers. The technology enables smelters to meet strict environmental and quality requirements while simultaneously achieving high aluminum production and yield. The technology also reduces the energy consumption as well as the emission of NOx, SO2, and CO by using the heat generated during the calcination to power a steam generator or waste gas scrubber.
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