Experimental And Simulation On Atmospheric Pulverized Coal Entrained-Flow Gasification Technology With Strongly Swirling Flow

In Chinese coal-to-chemicals industry,atmospheric fixed bed gasification technology is widely used among small and medium-sized enterprises.However,some disadvantges including outdated production capacities and high pollutant emissions exist.Although pressurized coal gasification technology is becoming increasingly mature,the high capital,operational and maintenance costs greatly limit its wide application.Characterised by low capital costs,high efficiency and low pollutant emissions,the atmospheric pulverized coal entrained-flow gasification technology is therefore the best fit for small and medium-sized chemical companies.This paper proposed a novel atmospheric pulverized coal entrained-flow gasification technology(involving a strong swirling flow)and the main units with gas production of 30,000 Nm3/h in this technology were designed.The single-phase and gas-solid two-phase tests,numerical simulations and industrial-scale experiments were respectively conducted to study the gas/soild flow and gasification characteristics in the gasifier.The thermal stress of the slag layer was also analyzed.On basis of these results,an optimized gasification technology was presented.This optimized system has already been installed and the hot performance optimizing will be carried out in the near future.The thermegravimetry experiments were firstly conducted to measure the gasification reaction kinetics of design coal from Sanxing region.On the basis of equilibrium modeling and calculations of the radiative heat transfer in the gasifier,a method for calculating the thermal characteristics of the entrained-flow coal gasifier was developed.By using this approach,an atmospheric pulverized coal entrained-flow gasifier with strongly swirling flow capable of generating gas at 30,000 Nm3/h was designed.The ribbon and water film tracing tests as well as the gas/solid two-phase measurements by phase Doppler anemometry were conducted to study the flow characteristics in the gasifier.The effects of gasification agent ratios on the flow characteristics in various gasifier furnaces were determined.The results indicated that,a stable central recirculation zone appeared in the furnace,with the appearacne location deviated from the furnace center.On reducing the gasification agent ratio,the area of central recirculation zone at different horizontal sections decreased,and simultaneously,the air trajectory in the near-wall region significantly shortened.The high-velocity swirling airflow mainly concentrated in the near-wall region.At the sections in the central and lower regions of the gasification agent nozzle,the particle volume flux peaked in the near-wall region,and reached a minimum value in the central recirculation zone.The combustion and gasification characteristics at different mass ratios of oxygen to coal were studied by numerical simulations.The numerical results indicated that,the overall temperature distribution was characterized by a high temperature in the near-wall zone and a low temperature in the central zone.The maximum temperature of approximately 3000 K appeared in the region of gasification agent nozzle.The coal combustion process mainly occurred in the furnace upper region,and the gasification reaction primarily existed in the high-temperature boundary region.Industrial experiments were performed on an atmospheric pulverized-coal entrained-flow gasifier which was capable of generating gas capacity of 30,000 Nm3/h.The experimental results were summrized in three aspects.First,the gasifier was found to discharge slag smoothly,and a large ratio of effective gas existed in the synthesis gas.However,the temperatures in the furnace upper region is too high,thus casusing the burning damage of the SiC layer and studs.Secondly,the main operating parameters of the waste heat boiler were close to the design values.The boiler kept stable operation and no slagging and desposit were observed in the furnace.Thirdly,some undesired problems happened including the designs of coal bunker,lock hopper and feed tank,as well as the selection of rotary valves.The numerical simulations were also employed to study the thermal stress in the slag layer.The results demonstrated that the equivalent thermal stress was gradually increased as the temperature decreased,and was continuously distributed in the slagging layer.During the cooling process,the slagging layer was influenced by the tensile stress.Near the intial liquid-solid interface,the principal stress distribution curve showed a peak value of 72 MPa,indicating that cracks were most likely to occur at this location.According to the industrial test results,the optimization schemes for the pulverized coal pressurization,conveying,gasifier and waste heat boiler units were proposed.The cold single-phase experiments and numerical simulations were also carried out to study the optimized gasier.These cold single-phase experiments indicated that the flow field in the gasifier could be divided into six regions of upper backmixing,upper refraction,horizontal jet,central cutting circle,lower refraction and lower backmixing zones.The numerical simulation results showed that the reactions between the pulverized coal and gasification agent primarily occurred at the boundary of jet stream,and the high temperature area mainly concentrated in the cutting circle zone formed by the upper jets in the gasifier.The temperature at the exit was 1602 K,which met the requirements for liquid slag discharge,while the effective gas(CO+H2)concentration reached a maximum of 89.1%.