Rotational-vibrational O2–CO2 coherent anti-Stokes Raman spectroscopy for determination of thermochemical states in oxy-fuel biomass combustion

Proceedings of the Combustion Institute, vol. 40, pp. 105457

Abstract

This study focuses on the development and application of an in-situ and non-intrusive measurement technique to determine the thermochemical states in pulverized oxy-fuel combustion in the absence of N2. This is a challenging task in such harsh environments and has not been achieved for oxy-fuel combustion. Coherent anti-Stokes Raman spectroscopy (CARS) using the probe molecules O2 and CO2 was chosen to access the thermochemical states in all flame regions. Experimental validation of the developed O2-CO2-CARS setup showed relative accuracies below 3% and relative precisions around 5% for the determination of gas temperatures up to 2100 K. The mole fractions of O2 and CO2 could be estimated with relative accuracies below 6% when both species were present in the gas mixture with mole fractions greater than 0.2. For small amounts of O2, CO2 mole fractions showed relative accuracies around 5% and relative precisions around 10%. The O2-CO2-CARS setup was applied to a solid fuel combustor operating swirled gas-assisted pulverized fuel flames under oxy-fuel conditions up to 70 kWth. First, the gas flame was investigated solely, showing maximum temperatures close to the maximum adiabatic flame temperatures and consistency with the flow field investigated in a previous study. The subsequent investigation of gas-assisted pulverized fuel combustion using walnut shell particles as a biomass representative demonstrated the applicability of the developed O2-CO2-CARS setup in particle-laden reactive flows. A strong influence of the solid fuel particles on the inner recirculation zone of the swirl flame was observed. The thermochemical state within the inner recirculation zone was found to be almost spatially homogeneous, while broad distributions were found within the mixing zone of the main flow and the outer recirculation zone. In this region a linear relationship between O2 mole fractions and gas temperature was observed with decreasing O2 mole fractions with increasing temperature.

Authors 5

1. Henrik Schneider corresponding

   Technische Universität Darmstadt

   Affiliation as printed

   Technical University of Darmstadt, Department of Mechanical Engineering, Reactive Flows and Diagnostics, Otto-Berndt-Str. 3, Darmstadt 64287, Germany

2. Janik Hebel

   Technische Universität Darmstadt

   Affiliation as printed

   Technical University of Darmstadt, Department of Mechanical Engineering, Reactive Flows and Diagnostics, Otto-Berndt-Str. 3, Darmstadt 64287, Germany

3. Benjamin Böhm

   Technische Universität Darmstadt

   Affiliation as printed

   Technical University of Darmstadt, Department of Mechanical Engineering, Reactive Flows and Diagnostics, Otto-Berndt-Str. 3, Darmstadt 64287, Germany

4. Reinhold Kneer Aachen Faculty of Mechanical Engineering Institute of Heat and Mass Transfer

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University, Faculty of Mechanical Engineering, Institute of Heat and Mass Transfer, Augustinerbach 6, Aachen 52062, Germany

5. Andreas M. Dreizler

   Technische Universität Darmstadt

   Affiliation as printed

   Technical University of Darmstadt, Department of Mechanical Engineering, Reactive Flows and Diagnostics, Otto-Berndt-Str. 3, Darmstadt 64287, Germany