Hazardous waste alternative fuels to novel ecological energy: Combustion characteristics and effects on clinker's environmental safety

Due to their detrimental and persistent impacts on the environment, it is imperative to manage and dispose of hazardous wastes (HW) in a secure manner. This study investigates the combustion characteristics and environmental impacts of using HW as alternative fuels in clinker production. The HW categories analyzed include industrial hazardous waste (IHW), medical hazardous waste (MHW), and household hazardous waste (HHW). Specifically, IHW consists mainly of waste mineral oils, waste organic solvents, organic resin wastes, waste residues, and waste coatings. MHW primarily consists of medical plastic products. HHW mainly includes packaging from waste pharmaceuticals, waste pesticides, disinfectants, and waste paints. Compared to traditional pulverized coal, hazardous waste alternative fuel (HWAF) exhibits a lower fixed carbon content, with its heat generation primarily dependent on volatile substances, and a higher ash content, chemically similar to coal ash. The combustion process of HWAF involves three stages: moisture evaporation (0 °C–150 °C), volatile matter combustion (150°C–400 °C), and fixed carbon combustion (400 °C–550 °C). The primary emissions from this process include CO₂, CO, trace amounts of SO₂, NO₂, H₂O, and various complex organic compounds such as carboxylic acids, alcohols, ketones, and aldehydes. While HWAF ignites more readily than pulverized coal, it burns more slowly and less completely. The incorporation of combustion by-products into the cement clinker formulation does not interfere with the clinker's hydration processes or reactions. HWAF ensures a reduced heavy metal input rate in the firing system without significantly impacting the heavy metal content in the clinker. Mortar samples produced with this clinker meet the heavy metal leaching standards, affirming the environmental safety of the cement product. Increasing the proportion of HWAF results in a reduction in standard coal consumption and an increase in CO₂ reduction, achieving a maximum coal saving of 3.67 kgce/t.cl and a CO₂ emission reduction of 10.11 kg/t.cl. This study presents a clean production model for the co-processing of HWAF, effectively transforming waste into valuable resources by using hazardous waste materials as alternative fuels.