Research On Two-dimensional Concentration Distribution And Particle Heat Transfer Characteristic Of Circulating Fluidized Bed Boile

Faced with the increasingly serious environmental and resource problems,China’s circulating fluidized bed boiler technologydevelops rapidly and the national installed capacity continues to expandin recent years, putting forward higher requirements to improve the stable operation of the boiler level.Therefore, the study of circulating fluidized bed boiler in gas solid flow, heat transfer and combustion is of great significance for improving boiler combustion efficiency andefficient operation of boiler.According to the test of pressure drop in the dense phase region of 300 MW CFB Boiler with breeches-leg with different loads, this paper got changes of average particle concentration in the dense phase zone with the load, and analyzed the impact of air velocity and bed material quantity on the particle concentration distribution,thereby obtaining the datas of porosity and pressure drop in the dense phase zone to provide parameters for secondary air momentum and flow model.Simulation of gas solid flow and heat transfer in dilute phase zone of circulating fluidized bed boiler is studied. This paper took the particle size distribution from first broken test of coal samples as datas of wide screeningmodel,and established the flow model of the ring core structure and the heat transfer model of the particle mass updating model. According to the furnace temperature measuring points, we modified the bed temperature of model,and calculated under different loads the share of particle cluster covering on the walls, convective heat transfer coefficient, radiation heat transfer coefficient and the total heat transfer coefficient distribution along furnace height.At the same time, the factors affecting the furnace heat transfer were discussed.According to bed temperature, a secondary air ratio, the percentage of oxygen and circulation rates obtained by Soft measurement method,the variations of heat transfer coefficient under different loads were studied.Carbon content in fly ash is an important indicator reflecting the combustion conditions.The factors influencing carbon content in fly ash of circulating fluidized bed boiler were studied. Under different stable conditions,in the aspects of the particle size distribution, bed temperature, primary and secondary air ratio, economizer outlet flue gas oxygen content, secondary air momentum, test and analysis on the influence of carbon content in fly ash were carried out.The test and simulation results show that when the boiler is running under a higher load, the impact of the load fluctuation on the particle surface coverage is smaller, and then the convective heat transfer in the furnace is less. The deviation of the temperature along the bed in the furnace is slightly decreased with the increase of the load, and the influence of the radiation heat transfer islarger than that of the convective heat transfer.Primary and secondary air ratio is negatively correlated with heat transfer coefficient.Bed temperature is positively correlated with heat transfer coefficient.To make the best heat transfer conditions, you need a reasonable control of the secondary air ratio and bed temperature, so that the economizer outlet oxygen content at an optimum value,while the circulation rate should be controlled in the optimal range. Primary and secondary air ratio is positively correlated with fly ash carbon content,economizer outlet flue gas containing oxygen, secondary air momentum and bed temperature are negatively correlated with fly ash carbon content. The influence of secondary air momentum and primary and secondary air ratio on the fly ash carbon content is bigger, economizer outlet oxygen and bed temperature relatively small.