The aluminum smelting industry has increased its demand for anode-grade calcined coke. This is due to increasing investment in infrastructural development and urbanization by countries such as India, China, and Singapore. In addition, government initiatives such as "Smart Cities" and "Housing for All" are expected to drive the growth of this industry over the forecast period.
The production process of calcined petrocoke involves the conversion from crude oil to heavy fuel in delayed coking unit. Below is an image of a typical flow chart: The residual oil from the crude oil is pumped in a drum for calcination, and then carbonization. This produces coke often referred by the names green coke and anode grade (low sulfur and metals). The calcined petcoke is then used in the melting process to produce graphite electrodes or directly for the steel production.
Different calcination procedures are available, depending on the desired coke quality. These include a fluidized calciner system, an electrothermal calciner and an advanced CHP system. The advanced CHP technology utilizes solid fuels such as petcoke, coal, and alternative fuels to provide heat for the calcination process. The reduced energy consumption and emissions improve the economics of calcined coke production.
A typical CHP unit consists a gas turbine, exhaust gas recycling, a heat recovery boiler, and a coal degasser. The waste heat from the combustion process of solid fuels provides an important portion of the required heat for calcining the coke inside the rotary oven. Additionally, exhaust gas recirculation helps reduce NOx and Sox emissions during the calcination. In addition, the waste-heat utilization system produces electricity from hot flue-gases of the rotary furnace by running it through steam turbines and generating electricty.
Emissions of SO2 and NOx from the calcination of the coke are significantly reduced by the use of these technologies. However, the emission levels of a calcined petroleum coke are still considerably higher compared to those of natural gas. This is due the fact that combustion of solids fuels in a process of calcination produces much more NOx and SOx than natural gas combustion.
Blending systems have been installed in refineries to further reduce emissions from calcined oil coke. These systems are designed for a blend of low and high S and V coke, along with anode grade coal, to be fed to the aluminium smelting processes. This allows smelters a better economics and to meet the historical V specifications. The cost to install a coke blend system is low and can pay off within the first operating year. The coke blending system also improves consistency in the smelter's feedstock. This is important for maintaining a stable production and consistent product quality.
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