The green coke to calcined coke process is a significant step in the aluminum industry. It also serves carbon raiser applications in iron and steel metallurgy.
The invention provides a method for processing green petroleum coke by heating it in a cylindric rotary kiln at a slow rate to allow structural rearrangement and the release of volatile matter without excessive shrinkage.
Green petroleum coke is a solid carbon material that must be heated in order to drive off moisture, volatile matter and impurities. The calcined coke thus obtained is used as recarburizer in the primary aluminum industry.
It is dried in an indirect green coke dryer 1 and then calcined in a cylindric rotary kiln 2. The dryer is equipped with a heat recovery steam generator for exploiting the energy of the lean calcination gas.
The kiln is rotated at different speeds by means of a hydrostatic drive, permitting to vary the residence time. The kiln is also equipped with an adsorption-based off-gas treatment system. This enables to satisfy the increasingly high demands regarding the quality of the calcinate and to comply with the ever-stricter environmental protection regulations.
The devolatilization process removes volatiles and moisture from the coke, and converts some of it into carbon black, resulting in a denser, more electrically conductive product. This step is required to meet the quality limits set by the primary aluminum industry.
It also enables the production of graphite, electrodes and metal carburizers to be processed using petroleum coke as feedstock. Additionally, fuel nitrogen (NO) released during devolatilization and char oxidation is converted to NO2 in the gas phase.
In this project, an advanced CHP system was designed to utilize by-product and waste heat of the calcination process and opportunity fuels to reduce energy and carbon intensity. This technology is being commercialized within Superior Graphite Company. Other calciners have already begun evaluating the proposed technology concept.
The coke that comes directly out of the coker is referred to as green coke. Green coke needs to be further processed (calcined) in a rotary kiln to produce calcined petroleum coke or anode grade coke for the Aluminum (Al) and Steel industry.
In order to achieve the desired calcined coke properties it is necessary to heat the coke very slowly. This allows structural rearrangement of the carbon molecules to take place without a disruptive release of volatile matter.
This project developed an advanced CHP system concept to best utilize process waste off-gas as opportunity fuels to provide an energy efficient calcination process. The technology will dramatically reduce the overall carbon footprint of the calcination process while achieving predicted energy savings. This is an exciting opportunity for the nation’s coal industry.
The process involves heating the green coke/coal tar pitch slowly to facilitate structural rearrangement of carbon molecules without disruptive release of volatile matter. This is accomplished through the use of a preheater and controlled air addition.
The spherical shape of the calcined coke improves packing density and increases mechanical strength. This helps to improve anode baking density, which is critical for the aluminum (Al) and steel smelting industry.
Many rotary kilns are equipped with waste heat energy recovery systems to capture the thermal energy generated by combusting VM in the coke bed and fine coal tar pitch carried over from the calcination process. This thermal energy can be used to produce steam for the smelting industry or to generate electricity with a steam turbine generator.
In addition to being used as an alternative source of fuel in the production of electricity, green petroleum coke can be processed to produce carbon products and asphalts. It also can be used as a raw material in the production of chemicals such as methanol, formaldehyde, and acetic acid.
Rotary kilns are large diameter, sloped, refractory lined steel-shelled cylinders that rotate during operation. Green coke is fed continuously at one end and calcined coke is discharged from the other.
The technology involves the energy-efficient process of petroleum coke calcination in an electrothermal fluidized bed kiln integrated with waste heat utilization. The pro- posed technology is expected to significantly improve the flexibility of utilizing different quality green petroleum cokes for producing a calcined coke with the desired properties.
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