A carbon fuel that resembles coal, petroleum coke is produced by the final cracking process of crude oil refining. Once cooled, it can be used as anode material in aluminum, steel and titanium smelting.
The calcining of petcoke produces air pollutants that can impact human health. This project modeled and measured exposure concentrations of particulate and gaseous pollutants to ensure they are below standards that protect public health.
Petroleum green coke (PGC) is a key raw material in the production of carbon anodes for Hall-Heroult aluminum smelting. Its low impurity levels and ready availability make it a preferred raw material to other non-refined carbon sources such as coal or natural gas.
In order to be used in the smelting process, PGC must be calcined or heat-treated (also known as devolatization). The calcining of petroleum green coke is accomplished in large rotary kilns where volatile materials are driven off through heating under an oxygen deficient atmosphere.
PGC is a relatively incombustible material, and its physical properties can be improved through calcining. The calcination process changes the molecular structure of the material, making it electrically conductive and less porous.
Vibrated bulk density (VBD) is an important measurement in the aluminum industry to evaluate the quality of calcined petroleum coke. However, the current ASTM International (ASTM) method D4292 generates a wide range of VBD data due to varying crushing equipment, gross sample preparation and apparatus set up.
The rotary kiln (RK) is the equipment that performs the calcination of petroleum coke in a coke-calcining plant. The coke, which is the byproduct of oil refinery coker units and known as green coke, undergoes a high temperature calcination process to yield calcined coke or anode grade coke for use in aluminum reduction cells.
The RK has an inner cylinder that is surrounded by a steel shell that is lined with high-temperature refractory brick. The RK rotates and the coke moves through a series of different zones that de-moisturises, devolatalises, and resolidifies the material. This is done under controlled operating conditions to impart the required crystalline structure, density, and electrical conductivity properties to the coke.
The rotational motion of the kiln also creates an airflow that cools the coke as it passes through the calcination process. The rotational speed and temperature of the kiln can be adjusted to match the desired calcination and cooling characteristics of the coke.
Coke calcining plants can be located in oil refineries, captive plants at aluminum smelters or merchant plant locations. Sized petroleum green coke is fed into a rotary kiln where it undergoes high temperature calcination (heat treatment) to drive out volatile material and oxidize coke structure. The resulting calcined petroleum coke is an electrical nonconductor with a low reactivity to oxygen and carbon dioxide.
After the calcination process is complete, the resulting calcined petroleum coke (CPC) is transported in an enclosed conveyor system to storage buildings or docks for loading onto barges, ships or land based transportation loading facilities. The motors powering the conveyor belt, rollers, limited space for personnel movement and access within the conveyor structure all present potential physical and electrical hazards that must be included in the Job Safety Analysis for production and maintenance tasks performed by workers.
A drainage system is used to extract the drained coke from the coking chambers through a draining metal belt conveyor with drilled openings arranged on its outer housing. The drained CPC is collected in a hopper that also functions as a bin to allow the drainage of the slurry.
The calcined petroleum coke (CPC) market is expanding. This is due to growing infrastructural development activities and population growth in APAC region. In addition, favourable government initiatives on the green environment are expected to support the market over the forecast period.
The project technology is designed to reduce energy consumption and greenhouse gas emissions in the industrial energy-intensive CPC calcination process. It is also suited to other high-heat applications that require efficient combustion technologies, such as in steel production and power generation.
Vibrated bulk density (VBD) is a critical measurement in the aluminum industry to evaluate the porosity and bulk density of calcined coke used in the production of carbon anodes for aluminum reduction smelting. Oxbow Calcining investigated the reproducibility of the current ASTM International VBD procedure - D4292. The results led to a revision of the method. This has increased the reliability of VBD measurements, which is critical to the success of smelters using rotary and shaft CPC.
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