Simulation of Combustion and Thermal-Flow Inside a Petroleum Coke Rotary Calcining Kiln—Part II: Analysis of Effects of Tertiary Airflow and Rotation

Abstract

A computational model is established to simulate the combustion and thermal-flow behavior inside a petcoke rotary calcining kiln. The results show that peak temperature is located at the tertiary air zone and a cold region that exists between the natural gas combustion zone and the tertiary air zone causes the coke bed to lose heat to the gas stream. The cold tertiary air injections reduce the gas temperature inside the kiln, so preheating the tertiary air using extracted gas or other waste energy is essential to saving energy. The devolatilization rate and location have a pronounced effect on the simulated temperature distribution. As the calcining kiln rotates, the tertiary air injection nozzles will move relative to the coke bed and exert cyclic air-bed interactions. At zero angular position, the air injection nozzles are diametrically located away from the bed so the interactions between the tertiary air jets and the coke bed are minimal. As the kiln rotates to a 180 deg position, the stem of the air injection nozzles are actually buried inside the coke bed with the nozzles protruding outward from the bed. At this position, the tertiary air jets will provide a fresh layer of air just above the coke bed, and the interaction between the air flow and the coke bed becomes strong. The 45 deg rotational angle case shows a better calcination with a 100 K higher bed surface temperature at the discharge end compared with the rest of rotational angles. Without including the coke fines combustion and the coke bed, the lumped gas temperature for the rotational cases shows a peak temperature of 1400 K at Z/D=2, which is due to natural gas combustion; the lowest temperature is around 1075 K at two locations, Z/D=4 and 8. The exhaust gas temperature is approximately 1100 K. The insight gained from this study will be used to design innovative means to reduce natural gas consumption.