Copyrolysis and Cocombustion Performance of Karamay Oily Sludge and Zhundong Subbituminous Coal

Karamay oily sludge (KOS), Zhundong subbituminous coal (ZSBC), and their equal mass mixture (M _KOS/ZSBC) were selected as the research samples, and composition characteristics and pyrolysis performance of KOS, ZSBC, and its mixture were investigated by means of various analytical methods. Results showed that yields of fixed carbon and volatile matter from ZSBC are higher than those from KOS, and the content of moisture in ZSBC is also higher; most of the components in KOS are inorganic minerals, with the ash yield of 71.4%, and the fixed carbon yield of nearly 0. According to Fourier transform infrared spectrometer (FTIR) analysis, the types of functional groups in KOS and ZSBC are basically the same, while the contents of which are different. Thermogravimetry-differential thermogravimetry (TG-DTG) analysis indicated that the mass loss of ZSBC, KOS, and M _KOS/ZSBC are 41.1%, 25.7%, and 32.8% with a heating temperature up to 990 °C, respectively. By analyzing the theoretical pyrolysis and combustion TG-DTG profiles of M _KOS/ZSBC and the measured composition of the flue gas produced during the tested processes, it is found that the mixture of oily sludge and coal helps generate remarkable combustible gases with significantly reduced CO₂, indicating that there is an effective "synergistic effect" between KOS and ZSBC. Based on the Coats-Redfern (CR) model, in the main pyrolysis temperature range, when the reaction order is selected as 1, the kinetic fitting effect of pyrolysis and combustion profiles for ZSBC is better, with the correlation coefficient R ² > 0.98. While for KOS and M _KOS/ZSBC, in N₂ atmosphere, the fitting effect is satisfactory as the reaction order is set to 5, in air atmosphere, the better fitting effect is considered that reaction order is selected as 1.