Thermal characteristics and kinetics of refining and chemicals wastewater, lignite and their blends during combustion

• Wastewater was mixed with lignite and the co-combustion behaviors were studied.
• Effects of blending ratio and heating rate on the combustion process were evaluated.
• The interactions between RS and HL were inhibitive effects during main combustion.
• Surface morphology and minerals of residues were separately detected by SEM and XRD.
• The activation energies were calculated by using the KAS and FWO method.

Co-combustion characteristics of refining and chemicals wastewater solid (RS) and Huolinhe lignite (HL) were studied through thermogravimetric analysis (TGA). The combustion behaviors of the blends at various RS to HL ratios were compared with those of the individual samples. Co-combustion experiments showed that the combustion performance of the blends would be improved with the percentage of RS rising. The interactions between RS and HL during the co-combustion could be divided into four phases, and there were no interactions below 120 °C (PH 1) and beyond 700 °C (PH 4), inhibitive effects at the temperature range of 120–700 °C (PH 2 and PH 3). The results of SEM and XRD indicated that the sintering and fusion degree of residues after combustion became more severe with the percentage of RS increasing. The iso-conversional methods, Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO), were used for the kinetic analysis of the combustion process. The results showed that the activation energy of RS was higher than that of HL, and the minimum value was obtained at 75HL/25RS.