Oxyfuel-combustion of coal in 210kWth test rig - aspects of burner design and process control
At the Institute for Energy Systems at TUM a 210 kWth test rig is used to investigate the combustionbehaviour of lignite under oxyfuel conditions. The combustion chamber has an inner diameter of 700mm, the inner height is 4000 mm. A number of radially arranged measurement ports are used formeasurements with a suction pyrometer, flue gas analysis, video surveillance and radiation measurements.Flue gas treatment incorporates particle removal with cyclone/ torch filter, cooling using agas/gas heat exchanger and drying in a water cooled condenser. The flue gas train is equipped witha system of valves allowing for wet and dry recirculation.The research focus is to investigate non-stoichiometrical burner operation as a means to controlthe temperature distribution and heat exchange with low recirculation rates and thus to lower theadditional energetic and tangible expenditure of oxyfuel operation compared to the retrofit case withits higher flue gas recirculation rates. Non-stoichiometical burner operation leads to gradual release ofcombustion enthalpie and thus to lower (adiabatic) flame temperatures. In order to achieve an overallstoichiometry between = 1:0 1:15 and low oxygen concentrations at the combustion chamberoutlet a multiburner arrangement of up to three vertically aligned burner will be investigated.Based on experiences with staged natural gas oxyfuel combustion and thermodynamic simulationsa first coal burner design was developed and investigated under non-stoichiometrical single burnerconditions. The data obtained was then used to modify models for CFD-based burner optimizationwith respect to aerodynamical behaviour. Currently a second-generation burner is investigated. Simultaniouslythe test rig is being equipped with the components necessary for multiburner operation.First results show that the flame temperature profile obtained by increasing the stoichiometry fitswell to the calculated adiabatic reference case. The maximum flame temperature is shifted to higherstoichiometries, though, probably due to inhomogenities in the oxygen distribution and effects of thecombustion process. A clear trend of increased NOx formation at higher stoechiometries could beobserved. Radial gas profile analyses for flame characterization have shown a clear distinction betweenflame core (low oxygen and NOx concentration ) and outer combustion zone (high oxygen and NOxconcentration). Radial gas profiles taken below the flame nevertheless show a rather constant trendindicating an almost completed burnout. The NOx reduction potential of the subsequent flame levelis subject to further investigations.