| The Shell Coal Gasification Process(SCGP)has lots of advantages,and obtain the widely promotion and the application.But there are also many problems,especially the problem of ash deposition in syngas cooler.It causes corrosion of the water wall surface and reduction of heat transfer efficiency of the cooler,finally leads to safety hazard to process.Among the variety of ash removal methods,mechanical rapping-off-ash method can adapt to the complex environment of high temperature and high pressure,and have a higher ash removal efficiency.In this paper,the mechanical rapping-off-ash method was taken as the research background,the mechanism and process of coal ash particles falling from the wall in cold state was explored on experimental and numerical calculation method.It provided a research way of thinking and method for the subsequent hot state drop test or the microscopic study of the falling-off of fly ash,and a theoretical basis to design of rapping-off-ash device.Firstly,the stress situation of coal ash particles in the furnace was analyzed,including the force of the coal ash particles in the flow field,the force between the coal ash particles and the force between the wall with the coal ash particles.The mechanism of the rapping-off-ash was introduced,the coal ash particles adsorbed on the surface of the wall can be detached from the wall to meet the two conditions: the coal ash particles were subjected to an external force by the vibration which was greater than the normal adsorption force or the tangential force was greater than the friction force of the coal ash particles.Based on the above,the mechanical model of the coal ash falling was established.Secondly,independently,a set of experimental testing system for rapping-off-ash which comprised an impact unit,an ash layer model unit and a measuring unit were designed.The phenomenon of coal ash falling off was observed and summarized.The influence of different sizes of impact force and the thickness of different coal ash layers on the crush and separate of the coal ash were also explored.The results show that,under the action of small impact force,the coal ash falling presented the "Stratification phenomenon" and "phased phenomenon",and the greater the impactforce,the more blurred the boundaries between the phases,but the phenomenon was not obvious under the impact of the large impact force;in addition,the greater the impact force,the quality of the falling coal ash particles off more close to the previous impact;under the same impact force,the thickness of coal ash layer was larger,and the quality of falling coal ash was more concentrated in the previous several times;the minimum effective impact force and the maximum impact vibration force were all decreased with the increase of the thickness of coal ash.Finally,numerical calculation of structural response of metal plate and coal ash layer structure under impact force loading was carried out,and then,the effect of coal ash layer characteristics and rapping mode on the coal ash falling was analyzed.Calculation results show that structural response was the superposition of longitudinal and transverse vibrations.When the load frequency were 10 Hz,68Hz,86 Hz and172Hz,the response of the structure was larger,which was the maximum when the frequency was 68 Hz,and most beneficial to the coal ash falling.The maximum displacement response,maximum velocity and maximum acceleration of the structure are decreased when the thickness of the coal ash layer was increased;When the impact time increases,the maximum displacement response of the structure increases,but the maximum velocity and maximum acceleration are both reduced;in addition,when the impact time increases,the maximum displacement response of the structure increases,but the maximum velocity and maximum acceleration are both reduced.Among them,the impact time on the structural response was of the greatest impact to coal ash falling,followed by the thickness of the coal ash layer,and last the density of coal ash was. |
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