Integration of Time Domain Reflectometry in a smouldering reactor

Self-sustaining smouldering is a novel technology that has been efficiently applied for soil remediation and the treatment of waste at very high moisture content. During smouldering, combustion of an organic phase occurs within an inert porous matrix. Simultaneously, processes such as evaporation, condensation and further migration of water take place. Due to the dynamics of the smouldering, all these processes are interconnected. Water evaporation and re-condensation is one of the main mechanisms responsible for smouldering quenching. The understanding of water migration within the porous medium is crucial for the design and development of self-sustaining smouldering reaction systems. This paper introduces the first smouldering reactor performing Time Domain Reflectometry (TDR) measurements during smouldering combustion experiments, aiming to measure water content distributions within the porous matrix. An existing smouldering reactor is transformed into a coaxial transmission line designed for the propagation of electromagnetic signals. Wet artificial faeces mixed with sand were used for the tests, as its behaviour in smouldering was extensively studied. TDR signals and temperatures at different positions along the reactor were recorded simultaneously. This allows for the determination of the temporal changes of the water content distribution within the smouldering reactor. This development is the first step towards the determination of moisture content profiles during waste smouldering treatment applications.