| Fixed bed and fluidized bed gasifiers are widely adopted by the coal chemical industries in China.Unfortunately,the operating temperature of these units is low at about 1000?,such that the outgoing syngas contains a large amount of fly ash with a high combustible content(20%-40%).The fly ash can be used as secondary fuel,but is difficult to be utilized effectively.There will be serious fuel waste and enormous economic losses.The fly ash entrained-flow gasifier,where the high-temperature raw syngas carrying the fly ash is treated using the entrained-flow gasification,has been developed.It combines the removal and utilization processes of fly ash.During the trial operation,there were problems of slagging at the burner outlet and the base of this novel entrained-flow gasifier.In order to solve the above problems,the fully mixed gasification method of raw syngas and gasifying agent as well as counter-biased burner arrangement are proposed.Meanwhile,researches on the gas/particle flow and gasification characteristics at the burner outlet and gasification chamber are needed.An 80,000Nm~3/h fly ash entrained-flow gasifier was put into trial operation.The gas species concentration and carbon content of the raw syngas at the inlet and those of the purified syngas at the outlet of the gasifier,as well as t he gas temperature near the wall were obtained from the in situ experiments.Based on the above trial operation results,a calculation method was proposed to get the outlet temperature of the entrained-flow gasifier whose wall was made of firebricks.The calculated value of the outlet temperature in the fly ash entrained-flow gasifier was1438.5?and higher than the ash fusion temperature.As this gasifier could discharge liquid slag,it was feasible to use fly ash entrained-flow gasification to treat the raw syngas from Ende fluidized bed gasifier.A 1:2.5 scale single-phase cold test was conducted using the temperature tracing method to study the mixing characteristics in the near-burner region of a single parallel two-channel burner and the fully mixed burner.The effectiveness of the fully mixed gasification method on enhancing the mixing between the raw syngas with the external gasifying agent was proved.The burner outlet temperature field under different injection angles,nozzle diameters,injection distances,and the mass ratios of external gasifying agent from the fully mixed burner were measured.And the effects of the above parameters on the dimensionless penetration depth,area-averaged residual temperature,maximum mixing rate,jet width,critical combustion area ratio and other mixing characteristics were comprehensively studied.The optimal injection angle,nozzle diameter,injection distance and the mass ratio of external gasifying agent were 70°and 80°,13mm,13mm,and 50%,respectively.A 1:8-scaled gas/particle two-phase modeling test facility of the fly ash entrained-flow gasifier was used to investigate the impact of six burners being co-biased,opposed and counter-biased on the air/particle flow field by using a3D-phase Doppler Particle Anemometer(PDA).The results showed that,on the horizontal cross-section passing through burner centerlines with co-biased burners,opposed burners and counter-biased burners,the dimensionless radiuses of mixing zone were 0.196,0.160 and 0.174;meanwhile,the ratios of total particle volume flux in the near-wall region to the total particle volume flux in the measurement zone were 76.5%,26.1%and 57.8%,respectively.On the vertical cross-section above burner outlet,the dimensionless radius of the central recirculation zone with co-biased burners remains to expand to 0.88,while that with counter-biased burners gradually shrunk to 0.19.At the same time,the influence of the burner centerline angle on the gas/particle flow characteristics in the fly ash gasifier adopting the counter-biased burner arrangement was studied.Further,a novel method was provided to quantify the air-particle mixture extent with dimensionless difference of particle volume concentration.As the burner centerline angle decreased from 75°to69°,the dimensionless radius of the mixing zone reduced from 0.275 to 0.174.And the dimensionless difference of particle volume concentration in the same cross-sections of the mixing zone decreased,demonstrating that reducing the burner centerline angle improved the air-particle mixture extent.The three-dimensional numerical model was developed for a fly ash entrained-flow gasifier.The effect of the injection angle and the mass ratio of external gasifying agent for the fully mixed burners on the flow field,temperature,syngas concentration was studied.The optimal injection angles of external gasifying agent for the full-mix burner were recommended to be 70°and 80°,and the optimal mass ratio of external gasifying agent of 50%was recommended.On this basis,a comparative study of the heat flow field and gasification characteristics in the fly ash gasifier using the parallel two-channel burners and the fully mixed burner was conducted.Meanwhile,the influence of the burner arrangement of the fully mixed burners on the fly ash gasification characteristics was researched.The effectiveness of the fully mixed gasification method and counter-biased burner arrangement was therefore discussed.Compared with the parallel two-channel burners,the whole raw syngas from the full-mix burner adopting the above optimization parameters was rapidly heated to 1550?,which led the temperature of the near-burner wall and bottom outlet to exceed 1500?and 1600?,respectively.The continuous and stable operation of the fly ash gasifier was achieved.Compared with the co-biased and opposed arrangement of full-mix burners,the temperature distribution in the gasification chamber with the counter-biased burners was more uniform because the mixing between the burner jets was more complete.In this way,the combustible content of fly ash and the carbon conversion rate at the gasifier outlet were 4.5%and89.4%,respectively,which indicated that the utilization rate of the fly ash was the highest. |
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