LATERAL GAS MIXING IN THE FREEBOARD ZONE OF A CFB BOILER

摘要

Lateral gas mixing was experimentally studied in the freeboard zones of 3 cold CFB test rigs with different sections of 0.19m ID, 0.3m 0.3m, 0.25m 　and0.5m respectively and with the same net furnace height of 4m. Sands were used as the bed material and CO2 was used as the tracer gas. The influences of operational condition such as superficial velocity, suspension solid density, shape and size of the riser on gas mixing were studied. It was found that with particles present in the bed the lateral gas dispersion will decrease and the highest lateral dispersion exists in a particle-free bed. The addition of solid particles will first weaken the dispersion and then as the particle load is high than a critical value, the further addition of particles may enhance gas dispersion. In this study the solid density at the transition point is about 8-10kg/m3, varying with the suspension velocity. It is believed that such a transition is mainly caused by the transition of flow pattern in the riser. The superficial velocity has only minor influence on the gas dispersion in the range of which is used in an industrial CFB boiler. The effect of riser diameter on the lateral mixing coefficient is stronger than that of solid suspension density and superficial velocity. In this study and previous studies Dr increases liner with the riser’s equivalent diameter.