| The resource structure in China determines that coal is the main source of energy consumption for a long period.With the requirement of carbon peak and carbon neutral,the clean,efficient,and low-carbon utilization of coal will be a difficult task in the energy field in the future.Entrained flow gasification is a clean,efficient and widelyused coal utilization technology.The radiant syngas cooler(RSC)of entrained flow gasifier could recover sensible heat and improve energy utilization efficiency.The slag deposited on the wall tubes of RSC reduces the heat transfer.During the operation of the RSC,the sootblowing and rapping-off-ash methods are effective methods to remove slag deposits,which could destroy and fall off the slag attached to the wall tubes.The mechanical properties of slag are the key parameters affecting the fracture of slag deposits.However,the researches on the mechanical and fracture properties of slag in the RSC were rare.Given the above problems,this paper carried out a series of research.Based on the experimental research results of mechanical parameters of slag from the RSC,the numerical calculation of sootblowing process was carried out,the dynamic characteristics of deposit fracture were deeply analyzed,and the rapping layout analysis and impact response simulation of the RSC model were investigated.Firstly,slag from the RSC and the sintered slag were investigated experimentally,including the chemical composition,microstructure,ash fusion temperature,and mechanical properties.The results showed that the difference between ash fusion temperature and composition affected the enrichment position of slag in the RSC.The elastic modulus(E)and the compressive strength(σ)of the slag on the wall tubes were between 550～750 MPa and 20～22 MPa,respectively,which were much larger than the elastic modulus(7～54 MPa)and the compressive strength(1.2～3MPa)of the slag on the RSC bottom and the sintered slag.The results indicated that the differences in local slag forming temperature would change the porosity,melting,and adhesion of slag,which were the key factors affecting the mechanical properties of slag.Then,the mechanical model of slag was established based on the cohesive zone method(CZM).The simulation parameters were determined by verifying the simulation results with the experimental results.The fracture phenomenon of the slag sample was closed to the experimental results,and the trend of the stress-strain curve was consistent.The fracture process of the slag sample under compression was analyzed.The results showed that the crack first initiated and gradually expanded in the slag sample,and the edges and centers were the most severely damaged areas of the slag.Then,a 3D numerical sootblowing model was developed that combined the CZM and coupled Eulerian-Lagrangian(CEL)analysis in ABAQUS.Two kinds of sootblowing conditions were taken as the research objects: syngas sootblowing in the RSC and steam sootblowing in the boiler,and the whole dynamic processes of jet impact,slag deposit fracture,and stress wave propagation were displayed,and the effects of the operating pressure of RSC and the steam sootblowing pressure of boiler on sootblowing efficiency were quantitatively studied.The sootblowing simulation results in the RSC showed that the damage rate of the slag deposits on the wall tube propagated faster on the vertical direction than on the horizontal direction.Higher operating pressure led to longer sootblowing time and more sootblowing syngas consumption,resulting in lower sootblowing efficiency.The sootblowing simulation results in the boiler showed that the direct impact of the jet on the slag and the propagation of stress waves were the main factors for the fracture of the slag layer.Increasing the sootblowing pressure could improve the sootblowing efficiency,decrease the sootblowing time and reduce the steam consumption.However,it would increase the stress on the wall tube and affect the wall tube’s lifetime.The sootblowing pressure of 1.2 MPa was suitable for boiler operation.Because of the lack of research on rapping-off-ash removal of wall tubes of the RSC,the modal analysis theory was applied to the research of rapping-off-ash removal.Modal parameters of wall tubes composed of three single tubes and fins were experimentally determined through the modal test analysis and FEA simulation under both empty and water-filled conditions.The results showed that the water in the tube slightly reduced the structure’s natural frequency,but the modal shapes remained the same as that of the empty condition.The first five natural modes ranged from 14 to 154 Hz.When the external excitation frequency was the same as the first,second,fourth,and fifth natural frequencies,the maximum vibration occurred at the 1/2 height position of the wall tube structure.The experimental and simulation results showed that the modal shapes were the same,and the relative error of the natural frequency of the forward mode was less than 10%,which proved the reliability of the simulation method.Finally,the acoustic-solid coupling model of the RSC was established in ABAQUS,and the model was analyzed by modal analysis and harmonic response analysis method to guide the layout of rapping-off-ash devices.The results showed that the change of natural frequency presented symmetry related to the structure of the wall tubes.When the sweep frequency reached 2.75 Hz and 15.37 Hz,the responses of fin wall tubes and cylindrical wall tube reached the peak,respectively,and fluctuated wildly between 14～17 Hz.The rapping devices were arranged at a 1/2 height position of the cylindrical wall tube,with an interval angle of 60°.When the frequency of excitation force was 16 Hz,the structure’s vibration and sound pressure response reached a total maximum.The instantaneous impact analysis of the model under the conditions of different vibration points,single-point impact,and the circumferential multi-points sequential impact were carried out.The results showed that when the wall tubes were impacted at different heights,1/2 height position had a continuous maximum displacement response.The wall tube had multiple stress regions on the horizontal direction.The displacement response was faster on the vertical direction.The impact energy led to the change of sound pressure in the RSC,and the vibration phenomenon of wall tubes occurred under the combined action of rapping and sound force.The shorter the rapping interval,the greater the cumulative deformation of the wall tubes,the longer the response time of sound pressure oscillation,and the better the slag removal effect. |
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