Oxidation kinetics of the combustible fraction of construction and demolition wastes

Proper disposal of construction and demolition wastes (CDW) has received wide attention recently due to significantly large quantities of waste streams collected from razed or retrofitted buildings in many metropolitan regions. Burning the combustible fractions of CDW (CCDW) and possibly recovering part of the heat content for economic uses could be valuable for energy conservation. This paper explores the oxidation kinetics of CCDW associated with its ash characterization. Kinetic parameters for the oxidation of CCDW were numerically calculated using thermal gravimetric analysis (TGA) and the resultant rate equations were therefore developed for illustrating the oxidation processes of CCDW simultaneously. Based on three designated heating rates, each of the oxidation processes can be featured distinctively with five different stages according to the rate of weight change at the temperature between 300 K and 923 K. In addition, Fourier transform infrared (FTIR) spectroscopy was employed, associated with a lab-scale fixed-bed incinerator for monitoring the composition of flue gas. Carbon dioxide (CO₂) was found as a major component in the flue gas. The fuel analysis also included an ash composition analysis via the use of X-ray powder diffraction (XRD), atomic absorption (AA) spectroscopy, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDX). The ash streams were identified as nonhazardous materials based on the toxicity characteristic leaching procedure (TCLP). Overall, the scientific findings gained in this study will be helpful for supporting a sound engineering design of real-world CCDW incineration systems.