Study On The Flow Characteristics Of The Ende Pulverized Coal Gasifier

Ende pulverized coal gasifier as a fluidized bed gasifier with the advantages of wide coal adaptability,synthetic gas without phenolic and tar,low price and operating costs and others play an important role In the small and medium-sized chemical enterprises.In order to study the flow characteristics of the gasifier,As the domestic and foreign less research on the gasifier and in order to further study its flow characteristics,In this paper,a single-phase cold-state model test bench was designed according to the similarity criteria for an ende pulverized coal gasifier with a gas production of 40,000Nm3 / h in a chemical plant.The aerodynamic field of the gasifier was measured by constant temperature hot wire anemometer,and the gas-solid two-phase flow in the original gasifier was simulated by Fluent software.This paper is the basic research on the flow characteristics of the gasifier and the aim is to lay a foundation for the gas-solid two-phase cold test and industrial test and provide some theoretical guidance for the actual operation.According to the gasifier in the actual operation of the variable load to change the amount of gasifier supply and the emergence of nozzle failure need to close the case of individual nozzles,single-phase test conditions to change the nozzle jet velocity and close the different locations of the nozzle.When the nozzle jet velocity increases from40m/s to 80m/s,the change of the flow field is mainly manifested in the increasing axial velocity of the middle area and the growth rate gradually decreases,and the return area appears near the edge of the gasifier with its position almost unchanged.The process of nozzle jet convergence causes the axial velocity of the radial distribution to change from "hump" to "single peak" with the height until it approaches the straight section of it.When close the single or adjacent position nozzles,the gasifier aerodynamic field occurs serious skewed situation;When the nozzle of separated position is closed,the edge of the gasifier produced an upward flow of irregular counterclockwise rotation,and the formation of negative pressure in the middle area makes the axial velocity small or even negative.In the actual operation,it won't inevitably make the central area normal fluid and it will increase the carbon content of the bottom ash;When the relative position nozzle is closed,the experimental results show that the degree of deflection of the flow field is small,which is close to the distribution of the aerodynamic field in the gasifier during normal operation.Therefore,when the nozzle fails,it is considered that closing the relative position nozzle can improve the flow field in the gasifier.The gas-solid two-phase numerical simulation was performed using a two-fluid model so that the initial fluidization process and the gas-solid two-phase flowcharacteristics are analyzed in detail and the optimum static bed height and the best nozzle jet velocity are obtained according to consider the internal stability of the gasifier.Under the design conditions,six nozzle jets converge to form three strands with an angled angle.The solid phase is mainly concentrated in the side wall and center of the gasifier.Different from the random flow pattern in the fluidized bed,the gasifier forms a stable circulation mechanism and has a flow area similar to the spouted bed.Therefore,this paper think that the ende pulverized coal gasifier is a multi-nozzle spouted fluidized bed.In the design case with changing that the initial bed height exceeds 1000 mm and the nozzle jet velocity is less than 80 m / s,more than 120 m / s,according to observe the pressure drop fluctuation curve,pressure drop standard deviation and solid content distribution map,it founds that the stability of the gasifier is deteriorated,and the three strands becomes large bubbles or a serious deflection.In this case,the stable flow mechanism is destroyed and is not conducive to the mixing of the gas and solid phases in the gasifier.Therefore,in the design case,the best static bed height should not exceed1000 mm and the best nozzle jet velocity is between 80m/s to 120m/s.