| Coal has always been the main energy source in China,accounting for60%-70%of China's energy consumption composition,and this trend will not change in a short period of time.Every year,about 84%of China's coal burns directly,causing serious air pollution and greenhouse effect.Circulating fluidized bed coal gasification technology is to convert solid coal into clean gas fuel,which has great advantages in reducing pollutant emission and improving the environment.Ende gasifier is a kind of circulating fluidized bed gasifier.It has the advantages:it can use low rank coal(such as lignite)for gasification;stable and reliable operation;high gasification intensity;low operating cost;simple gas purification process,no tar and phenol generation.The fly ash of Ende gasifier has a high combustible content(20%-40%),and the discharged fly ash cannot be fully reused,causing serious energy waste.In order to reduce combustible content,this thesis proposes an End gasifier fly ash circulating gasification technology.The gas-solid flow characteristics in the Ende gasifier are studied by experiment and numerical simulation,the gasification characteristics of the circulating materials are given,and the industrial experiment is carried out on a 45000 Nm3/h Ende gasifier.According a 45000 Nm3/h Ende gasifier,a 1:15 gas-solid two-phase test bench was established to study the solid flow characteristics in the furnace under different,down jetting agent speed and nozzle structure arrangement using a reflective fiber particle concentration velocity measuring instrument.The results show that with the increasing of down jetting agent speed,the velocity of particles in the spout zone increases gradually,and the velocity in the reflux zone decreases gradually.On the whole cross-section,the concentration of particles gradually decreased.Under tangential arrangement,the velocity of particle velocity in the central spout zone is lower than that of opposed arrangement,and the concentration is higher than that of opposed arrangement.Although the opposed of concentration distribution of particles in furnace is better than that in tangential arrangement,the circulation rate of the particles under tangential arrangement is higher,and the fluctuation is smaller,and the system runs stably.The solid flow characteristics of different ejector working medium pressure,upper jetting agent speed,material layer height and different materials were studied.The results show that:As the ejector working medium pressure increases,the particle velocity in the central spout zone decreases,the particle concentration increases,and the particle cycle rate increases.When the ejector working medium pressure is 0.06 MPa,the velocity fluctuation of solid particles in the return conduit is small,and the mass flow rate of working medium accounts for 1.6%of the primary air,which has little effect on the flow characteristics of solid particles in the furnace.The velocity of yellow rice particles in different furnace height is smaller than that of millet in the spout zone,and the concentration of the particles is higher than that of millet.With the increase of upper jetting agent speed,the velocity of particles in the spout zone gradually decreases and the concentration increases gradually;in the reflux zone,the absolute velocity decreases and the concentration decreases gradually.When the secondary wind velocity is 25 m/s,the circulation rate of the particles reaches the highest value of 0.51 kg/h,which have little effect on the flow behavior of the particles inside the gasifier.By means of numerical calculation,the cold state numerical simulation studied the gas-solid flow characteristics in the furnace under different ejector working medium pressure.When the working medium pressure is less than 0.06MPa,because of the low working medium pressure,it is impossible to overcome the reverse airflow in the furnace,which leads to its inability to enter into the furnace interior.When working medium pressure is greater than or equal to 0.06 MPa,working medium flow gradually approached the furnace as the working medium pressure increased.At the height of the fixed furnace section,the slip velocity in the radial direction of the furnace is basically three peaks.At the middle and upper part of the furnace,the gas-solid slip velocity in the central spout zone gradually decreases with the gradual increase of working medium pressure.In the temperature range of 0?-1250?,the non-isothermal weight method was studied for gas production 45000 Nm3/h Hailar circulating materials,Hailaer coal and gas production 20000 Nm3/h Shenhua circulating materials,respectively.The results showed that:When the temperature is lower than 840?,the circulating materials of Hailaer circulating soids and Shenhua circulating soids are easier to gasify than Hailaer coke.Increasing circulation rate of the particles and increasing the operating temperature of the gasifier are beneficial to increase the gasification rate.When the temperature reaches 946?,the mass loss rate of Hailaer coal is higher than that of Hailaer circulating soids and Shenhua circulating soids.When the temperature further increased to 1050?,the mass loss of Hailaer circulating soids and Hailaer coal has increased significantly.Industrial test results show that:When the ejector pressure barrier increased from 200 to 1100 Pa,the pressure difference between the ejector outlet and bottom of the gasifier gradually increased from-0.9 k Pa to 2.29 k Pa.The combustible content in fly ash decreased from 26.92%to 15.32%.When the pressure barrier reaches 800 Pa,steam mass flow rate is 0.17 kg/h,which can effectively prevent the flue gas from flowing from the bottom of the gasifier to the cyclone separator through the return conduit,the effective gas composition(CO,H2)in the synthetic gas reaches 74.5%,which is 1.24%higher than the transformation,and the combustible content in fly ash decreases from 26.92%to 19.91%.The causes of nozzle damage of ejector are analyzed by combining SEM,EDS and CFD simulation.The results show that:the surface of nozzle is obviously washed by solid particles,and the precipitation of?-Cr phase at high temperature which leads to nozzle damage.Through the numerical simulation of the gas-solid flow characteristics in the ejector under different steam jet pressures:When the steam jet pressure is 35 k Pa,it can effectively prevent the solid particles from scouring the outer wall of the nozzle,and the temperature of the outer wall of the nozzle is about657?747?.The industrial experiment was carried out after the ejector was equipped with steam jet device,and the nozzle did not appear wear failure for 2years of operation,and the amount of steam jet accounted for about 1.78%of the steam quantity of gasifier gasification agent,which had little effect on the gasifier. |
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