Experimental Investigation of Pyrolysis and Char Burnout Kinetics in a Plug Flow Reactor with Focus on the Ignition and Early Char Burnout Phase
The reliable design of technical oxy-fuel combustion systems requires quantitative data about the kinetic rates of volatile release and char burnout. While the devolatilization is important for the fuel ignition, the char burnout is the time determining scale of the combustion process. The main factors of influence are coal rank, temperature, heating rate as well as composition of the gas phase.
The aims of this project are the development of new and the optimization of existing reaction models to predict first the pyrolysis and second the char burnout. Due to different approaches in measurement methods two test rings have been constructed: a laminar plug flow reactor with a gas analyzing system to investigate pyrolysis and a laminar flow reactor with optical access, applying an imaging two color pyrometry system for particle size and temperature measurements. Both facilities work at heating rates typical for pulverized fuel boilers (105 K/s).
While in the first reactor the devolatilization is measured through gas emissions and char sampling, the second reactor is used to measure particle temperature and diameter to close the energy balance around burning char particles to determine reaction rate parameters.
The focus of measurement and model development lies on:
- The influence of elevated CO2 concentration in oxy-fuel systems, leading to increased gasification rates and thermal boundary conditions
- Changes of surface reactions through competition of dissociative absorption of CO2/O2
- Alteration of the order of reaction and validity of global kinetics approaches in an oxy-fuel atmosphere