The temperature variation effect to the AISI 316L corrosion rate of the rotary dryer off-gas line in the nickel smelting plant

Burning of coal will produce exhaust gases containing SOx compounds as well as NOx which can form acidic compounds such as H2SO4. When there is a decreasing in temperature as an effect of coal burning to reach the dew point so that will lead to corrosion, especially in the off gas line. This research was conducted to determine the effect of temperature to the corrosion rate of off-gas line material. The tested material was AISI SS 316L steel with temperature variation at 60ºC, 70ºC, 80ºC, 90ºC and 100ºC. The corrosion rate tests were performed by weight loss method where the corrosive medium used to soak the steel was 3.5% NaCl solution of 500 ml and flowed by SO2 gas for 3 hours. From this corrosion rate testing, it was found that the corrosion rate increased along with the temperature increment where the highest corrosion rate was at the temperature of 100ºC which is equal to 7,767,96950 mm/yr and included in very bad corrosion resistance level, beside that the steel sample color was also changed into black after immersion. The corrosion rate obtained at 80ºC and 90ºC showed poor corrosion resistance, while the corrosion rate at temperatures 60ºC and 70ºC are at very good and good level. This result was also shown by samples that were not change in color as well as at temperatures of 80ºC, 90ºC and 100ºC. This research was also conducted to find out the temperature distribution model in off gas line by simulation in ANSYS software. From the simulation it was found that the decreasing in temperature began to occur in the ducting before the Electrostatic Precipitator (ESP) and continued to decrease down to the stack outlet.