A byproduct of petroleum refining, petcoke is a carbon-rich solid. Its use in steelmaking primarily involves blending with coal in coking ovens to make metallurgical coke, which improves its performance.
The calcined petroleum coke produced in this process is known as fuel grade or anode grade coke. It is typically stockpiled or sent to a refiner for conversion to liquid fuels.
The raw coke that exits from the delayed coker is typically known as green petroleum coke (GPC). GPC must be further processed through calcining to drive out volatile matter (VM) and increase its carbon content, prior to baking in an anode oven for use in steelmaking.
VM removal is accomplished by heating the GPC to high temperatures in a rotary kiln or shaft calciner. The kilns are lined with refractory brick to withstand the extremely high heat levels required for calcination. The kilns are sloped and rotate slowly to move the coke through the calcination process. The counter current of hot combustion gases from the kiln’s flue gasses drives off VM and burns it in the calcination process.
Smelters are increasingly using a combination of shaft and rotary kiln/rotary hearth CPC. Mixing different quality cokes allows smelters to source the lowest cost and highest S and V-free, low impurity GPC possible for anode production. This can avoid large pitch level and anode density variation in fraction preparation and ensure consistent anode performance.
The calcination process heats the coke to burn off volatile materials and reduce its ash content. The fuel grade petcoke that results from this process is a versatile energy source. It can be burned directly in refinery boilers to generate steam and hot water, which can help offset some of the energy costs associated with the refining process.
The fuel grade coke can also be used as a substitute for coal in steel and aluminum smelters. This can lower the emissions of both sulfur and nitrogen oxides that are associated with burning fossil fuels.
The calcination process generates particulate and gaseous pollutants that can cause respiratory health problems. This risk characterization evaluates the ambient concentrations of particulate matter and gases from petroleum coke calcining facilities to ensure they comply with standards that are protective of public health. The characterization also identifies opportunities for further emission reductions. These include the use of an advanced Combined Heat and Power (CHP) system that utilizes process waste off-gases as opportunity fuels to provide additional energy savings.
Over the past decade, the majority of new refineries have been configured to process heavier crude oils that offer a discount over light sweet crudes. This has resulted in a reduced supply of low sulfur (category A) GPC. As a result, prices for this coke have increased.
GPC must undergo calcination to remove volatile material and purify it for use as anode carbon. Calcination transforms the GPC’s disordered, electrically non-conductive structure into a more ordered form that has an acceptable level of reactivity.
For smelters that use a combination of shaft and rotary kiln/rotary hearth CPC, blending is increasingly important because these cokes have different porosities and bulk densities. Large variations in these properties can lead to substantial pitch level and anode density fluctuations. In addition, a trend toward increasing sulfur levels in CPC and tighter SO2 emissions limits are driving more calciners to add SO2 scrubbing. This technology is expected to increase smelter profitability and reduce environmental risk.
Several air pollutants are produced during the handling and calcining of raw petroleum coke. Particulate matter and gaseous emissions can pose passive health risks to nearby communities. CII Carbon utilizes advanced technology in its coke calcining process to minimize these impacts.
Coke is the byproduct of petroleum refining and comes from the bottom end of the refinery distillation process, or coker unit. The coke can be fuel grade (high sulfur and trace metals) or anode grade (low sulfur and low metallic impurities).
Fuel grade petcoke is burned in refinery boilers to generate heat and steam. This energy source is a cost-effective alternative to natural gas.
Anode grade petroleum coke is used to produce carbon anodes for aluminum smelters. Its sponge-like structure allows binding material to penetrate into the coke particles to form a solid carbon block through which aluminum smelters conduct electricity into their smelting pots. There is no commercially viable substitute for calcined coke in aluminum smelter anode production.
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