Cold Model Experimental On Circulating Fluidized Bed Based On Two-stage Separation-return

Circulating fluidized bed coal gasification technology has the advantages of environmental friendliness,wide adaptability of coal types,low investment and operation costs,and is one of the important development directions for clean and efficient utilization of coal.However,due to the moderate reaction temperature,there is a problem that the fly ash content is large and the carbon content of fly ash is high,which leads to low carbon conversion rate of the system.Therefore,it is necessary to develop a new circulating fluidized bed process with the aim of improving carbon conversion rate.This thesis proposes a two-stage separation return circulating fluidized bed process that combines a two-stage loop with a Venturi return device to return to the top of the furnace.Using cold state experimental research methods,the influence of hierarchical separation structural parameters and main operating parameters on the system operating characteristics was studied,A study was conducted on the influence of Venturi return nozzle on gas-solid mixing in the upper part of the furnace,providing basic data for the design and application of hot state reactors.The experiment research results on the impact of hierarchical separation structural parameters on system performance indicate that the two-stage separation return circulating fluidized bed proposed in this thesis can achieve stable operation.Compared to the structure where the secondary return point returns to the primary circuit,the structure of the second level return point returning to the top of the furnace has a higher internal circulation and a larger axial particle concentration in the riser,resulting in an increase in particle concentration in the dilute phase zone of the upper riser;The change of the inlet mode of the primary separator structure from radial to tangential can significantly improve the efficiency of the primary separator,the proportion of materials in the primary circuit,and the particle concentration in the dense phase zone of the riser;When the Venturi return nozzle is put into operation,the circulating flow rate of the secondary circuit increases,and the particle concentration in the dilute phase zone at the top of the riser increases.The Venturi return device effectively shares the reverse pressure difference that the secondary return device needs to overcome.The experiment results of the influence of main operating parameters on the system performance show that the particle concentration in the dense phase zone of the riser axial furnace increases significantly when polystyrene resin is used as the bed material compared with quartz sand;The proportion of primary materials in the two-level circuit material allocation relationship increases,while the proportion of secondary materials decreases.The experiment results of the influence of Venturi return nozzle on the gas-solid mixing in the upper part of the furnace show that the jet air of Venturi return nozzle is conducive to improving the uniformity of the solid particles in the upper part of the furnace along the radial distribution function;The radial distribution function of gas is uniform;Within the operating range of 20 m/s to 30 m/s involved in this experiment,the gas-solid mixing effect is better when the nozzle operates at a gas velocity of 20 m/s to 25 m/s;When the nozzle is changed from single channel structure to dual channel structure,the radial distribution function uniformity of solid particles is greatly improved.