Measurement of the Emissivity of Fuel Particles in oxy-fuel Atmospheres
In this sub-project, the surface emissivity of burning char particles is measured. Due to the high temperature level of oxy-fuel-combustion, heat transfer is dominated by radiation. The emissivity is one of the key-parameters to determine the heat transfer between particles and their surroundings, which strongly affects the thermal balance in oxy-fuel boilers. In this project it is approached to measure the temperature und thermal radiation emitted from burning char particles in-flight. This is a novel technique compared to all present methods of emissivity-determination char particles and will help to deliver a sound model of oxy-fuel combustion.
A test rig consisting of a laminar flow burner and an optical setup combining visual and NIR sensors for radiation measurements is used for the experiments. The burner provides typical pulverized-fuel conditions, i.e. gas temperature and gas composition, which supports a particle burnout comparable to large scale boilers. The detector setup has to provide contact-free measurement of the particle temperature and diameter. Simultaneously, the thermal radiation emitted by single burning particles is measured in the wave length range between 0.9-5 µm. From these measurements, the emissivity is calculated.
Parameters which will be tested for their influence on the emissivity are:
· Coal rank
· Coal minerals
· Degree of conversion (burnout)
· Atmospheric influence