Research On Fatigue Behavior And Vibration Damage Of Calcium Hexaluminate Castable For Catalytic Gasifier

Coal catalytic gasifier has more advantages than traditional gasifier.During the service of gasifier,the lining refractories often suffer from the impact of the cyclic loading such as the production cycle,fluctuation of process parameters,thermal loads,and furnace vibration,which leads to fatigue failure of refractories.Hence,understanding the mechanical behavior of materials under cyclic loading is very important to the prediction of furnace lining life and the selection of suitable materials.As lining of coal catalytic gasifier,calcium hexaluminate is not sensitive to the reducing atmosphere,chemical stability in the alkaline conditions or the lower wettability of the molten metal and slag.In this paper,the effect of different particle size of calcium hexaluminate on the properties of corundum castable was investigated,and the fatigue resistance of calcium hexaluminate castable was optimized by using SiO₂ powder.Finally,the fatigue behavior of lining and the vibration fatigue performance of gasifier were studied by numerical simulation method.The anti-vibration fatigue performance of gasifier was improved by material and structure optimization.The main conclusions are as follows:?1?Refractory castable was damaged by fatigue,the curve of the fatigue strain against the number of cycles has a classical sigmoid shape with three phases:firstly,the strain rate decreased;secondly,it remained unchanged;thirdly,it increased significantly.The corundum based castable where 3¹ mm tabular alumina particles were replaced by the same size of calcium hexaluminate particles had better grain-matrix interface,which led to the optimum fatigue resistance.When the SiO₂ powder content was 1.5 wt%,the flexural strength and compressive strength of calcium hexaluminate castable sintered at1100°C could reach at 31.3 MPa and 190 MPa.With the increased of SiO₂ powder content,the fatigue resistance of calcium hexaluminate first increased and then decreased.When SiO₂ powder content was 3.0 wt%,microcracks were produced in the castable to achieve the effect of toughening,so the fatigue resistance of calcium hexaluminate castable was better.?2?Compared with the experimental results,the deviation of the numerical calculation results under monotonic loading at room temperature was less than 10%.Based on the fatigue damage mechanics,a three-point bending fatigue model of refractories at room temperature was established.The calculation results showed that the fatigue resistance of calcium hexaluminate castable was better than that of corundum castable under the same stress level.Based on the room temperature model,the high temperature fatigue model of lining materials was established.The fatigue life equation"lg?=-0.2399lgN+2.5839"of lining materials for coal catalytic gasifier was obtained,which can describe the fatigue life of lining materials at high temperature.?3?The vibration fatigue damage model of coal catalytic gasifier was established.The anti-vibration fatigue performance of gasifier was described by the natural frequency and vibration displacement of gasifier.Calcium hexaluminate castable as gasifier working layer can better enhance its vibration fatigue stability.The change of natural frequency of gasifier was less than 5%when the medium flow was coupled in the gasifier,so the medium flow in the gasifier had little effect on its vibration resistance.When the working temperature was 750°C,the first-order natural frequency of the gasifier was reduced by 50.3%,which increased the probability of resonance at high temperatures,and the lining materials were prone to vibration fatigue damage.Setting U-shaped tube plates in gasifier can optimize the structure of the gasifier,which improved its vibration resistance and reduced the impact of the damage of the lining materials by vibration.