Petroleum coke calcining
Petroleum coke calcining is taking anode grade green coke from the oil refining process and converting it to almost pure carbon, with a defined structure. The calcined coke is used to produce carbon anodes for the aluminum industry.
Metso is the world’s leading supplier of coke calcining systems and equipment, having furnished 50 plants representing approximately 70 percent of the world’s coke calcining capacity. These plants range in capacity from 50,000 STPY to over 400,000 TPY.
Coke kilns are suitable for:
- Petrochemical, Independent coke producers
Customers of calcined coke (Anod & Needle) are:
- Metallurgical, chemical
Main benefits of Metso systems are:
- Year of experience with coke calcining systems (Feed, kiln, cooler, afterburner)
- Control systems for entire facility
- Capable of installation anywhere in world
- True understanding of process conditions
- In house engineering for custom fit applications
Most plants are located in oil refineries with a coking system. The petroleum green coke is feed directly into a rotary kiln where the volatiles are driven off during the calcining process. Once discharged from kiln the coke is feed into a rotary cooler. A waste gas combustor is used to burn the volatiles created in the kiln. This heat normally creates steam for other parts of the plant.
Basic calcining process:
Petroleum coke calcining is a process whereby green or raw petroleum coke is thermally upgraded to remove associated moisture and volatile combustion matter (VCM) and to otherwise improve critical physical properties, eg., electrical conductivity, real density and oxidation characteristics. The calcining process is essentially a time-temperature function with the most important control variables being heating rate, VCM/air ratio and final calcinations temperature. To obtain the calcined coke properties required by the carbon and graphite industries, the coke must be subjected to temperatures of 1200-1350 Deg C or higher to refine its crystalline structure. The final quality of the calcined coke is directly related to the specific characteristics and quality of the green coke fed to the calciner. While calcinations cannot improve upon certain quality limits inherent in the green coke, potential quality can be lost by improper calcining.
When the hot calcined coke leaves the kiln, it is transferred to a rotary cooler. This cooler consist of a steel cylinder, usually at least partially refractory lined at the feed end, that is slightly inclined to induce downward travel of the coke as it is rotated. In the cooler, the hot coke is quenched by water sprayed from a number of nozzles. The exit temperature is controlled at approximately 150 degrees C to assure a moisture-free product. Some installations employ indirect cooling equipment which assures a moisture-free product; however, the design of these indirect coolers is often quite complicated, requiring large amounts of recalculating cooling water with high maintenance costs.
Flexibility in operations
Metso rotary kilns can handle a wide range of green coke feeds including needle, sponge, shot, fluid or tar pitch green cokes. The rotary kiln is also able to optimize the coke calcining operating parameters, be it residence time, temperature gradient, and heat up rate, all of which impact product quality.
Coke kilns can be fueled with: Gas, heavy oil, oil, refinery gas, and waste oil.