97/03079 Strengthen flame stability during the furnace's load decrease

Abstract

The major objective of the work is to take detailed measurements of flow field and gas properties in the quarl zone of a pulverized coal flame and assess the role of flow field computations in predicting the combustion rates. The measurements have been carried out in a semi-industrial scale furnace fired by a 2.5 MW, swirl-stabilized, pulverized coal burner. A Laser Doppler technique has been used to measure both axial and tangential velocities. A special water-cooled probe was designed to accommodate the fiber and transmitting and receiving optics. Signal processing was performed with a fast Fourier transform processor. The effect of particle slip relative to the gas phase has been discussed. It is concluded that inside the swirl-induced recirculation zone (IRZ) the measured particle velocities represent the gas phase velocity. Within the fuel jet, in the burner vicinity, the LDV measurements indicated substantial slip between gas and particle velocities. Gas temperatures, O2, CO, CO2, NOx, HCN, NH3, N2O and char burnout were measured using sampling probes.The paper contains unique measurements of the IRZ properties. At the burner quarl outlet, around 6% of the total air flow was recirculated back and the reverse flow sensible enthalpy was 4% of the total thermal input. Chemical composition of the quarl zone has been measured in detail.The measured flame has been computed using a previously developed mathematical model. It was concluded that the overall flow pattern and velocities were reasonably well predicted. The main deficiencies of the model were related to over-predictions of the gas phase temperature of the quarl zone.