Retort calciner and rotary kiln are the two main types for petroleum coke calcination. Rotary kiln is widely used in Europe and the United States, while retort calciner is used earlier and more in China. There are great differences between the two in calcination process principle, yield, capacity, calcination quality, floor area, construction investment, energy consumption, operation cost, labor productivity, automation, waste heat utilization and working environment, etc:
Compared with the rotary kiln, the investment per unit capacity of the retort calciner is 15 % – 20 % higher, but the operation cost is low, and the comprehensive technical and economic indexes are better. The retort calciner calcines petroleum coke as indirect heating, the volatile matter burns in the flame path and generates heat, and then indirectly transfers heat to petroleum coke through firebricks. As the heating is indirect, petroleum coke is hardly oxidized, while the volatile matter of the rotary kiln burns directly on the surface of petroleum coke, and the loss of oxidation is relatively large, usually around 8 %. If improper operation results in a large coefficient of excess air, the loss of oxidation will be greater, which is one of the main advantages of the retort calciner.
The retort calciner has low output and poor adaptability to changes in volatile matter of raw materials, especially petroleum coke with high sulfur content cannot be calcined for a long time, because the silicon brick of the furnace body is easily eroded by sulfur content, and in addition, the retort calciner has low labor productivity and is suitable for decentralized production.However, if the quality of raw petroleum coke is poor and dispersed in the supply, the anode plant will use retort calciner for centralized production, with obvious effects of energy conservation, emission reduction, quality improvement and consumption reduction, it will easily have a competitive advantage
The rotary kiln system has large output, strong adaptability to raw materials, good operating conditions, high degree of automation and easy environmental protection, but the calcined coke has poor quality and low yield and is suitable for centralized production in the coke producing area.In addition, if a large amount of steam in a large rotary kiln has no users, it is better to use waste heat to generate electricity.
In terms of calcination quality, the true density, specific resistance, compacted packing density, air reactivity and CO2 reactivity of the calcined coke are closely related to anode consumption. The volatile matter has natural advantages over the rotary kiln. On the one hand, the heating time of the retort calciner is usually 72 hours, so that the petroleum coke is relatively slow in release rate of volatile matter and its corresponding calcined petroleum coke particles have relatively few pores, and the particle stability and volume density are relatively good, which is conducive to improving the density and strength of the carbon anode and reducing the consumption of the carbon anode. At the same time, the residence time of the petroleum coke in the high-temperature phase of the retort calciner is also long and the calcination is more complete and uniform.However, the heating time of rotary kiln is usually 1 – 1.5 hours. Due to the limitation of time conditions, the performance of calcined petroleum coke in rotary kiln is difficult to compare with that in retort calciner.
Both retort calciner and rotary kiln need to be further optimized in design and process operation.Improving the hourly production capacity of retort calciner, the automation level of process production and improving the process operating environment are the main directions for the development of petroleum coke calcination technology in retort calciner.
The development direction of rotary kiln technology is to improve the yield and operation rate of rotary kiln, reduce material consumption and energy consumption, improve calcination quality and make full use of waste heat.