Study on the migration characteristics of nitrogen and sulfur during co-combustion of oil sludge char and microalgae residue

Integrated thermal treatment (coupled pyrolysis and combustion) has great potential to be a clean and effective method for massive oil sludge (OS) utilization. Produced OS pyrolysis char (OS char) can be effectively utilized through fluidized bed incinerator with auxiliary fuels. A study on co-combustion of OS char and microalgae extraction residue (MR) were conducted with a coupled thermogravimetric-mass spectroscopy system (TG-MS), and a fluidized bed reactor system. Co-combustion process of OS char and MR could be divided into three stages, including water evaporation, volatiles release and combustion, fixed carbon combustion and minerals decomposition. SO2 emissions decreased with the increase of MR ratio and NOx emissions initially decreased followed by an increase until the MR ratio exceeded 50%. Both NOx and SO2 emissions initially increased before a decrease with combustion temperature raised. Higher excessive air ratio (alpha) promoted the pollutants emission. Pyrrole (N-5) content increased with the increase of MR ratio and more N-5 and pyridine (N-6) could be converted to oxidized nitrogen (N-X) in the bottom ash under a higher temperature during OS combustion. Besides, the temperature range (900-1000 degrees C) was conductive to SO2 release, and S4+ formation.