Numerical Simulation Of Transient Temperature Field-stress Field And Corrosion Characteristics Of Refractory Lining Of Coal Water Slurry Gasifier

Coal water slurry gasification technology plays a vital role in the efficient and clean utilization of coal resources.Refractory lining is a key component of coal water slurry gasifier.When the gasifier is start-up,shutdown or the operating conditions are unstable,the drastic temperature changes will cause the refractory lining to produce a large transient thermal stress,which will cause cracks on the surface of the brick and the cracks will gradually expand.The slag and strong reducing atmosphere in the gasifier will further accelerate the damage of the refractory lining through cracks,which will affect the normal operation of the gasifier and cause unpredictable losses.Therefore,the transient temperature field and stress field distribution and corrosion characteristics of the refractory lining under different operating conditions of the coal-water slurry gasifier are deeply studied.It is important to improve the service life of the refractory lining and prevent damage to the gasifier in actual production.This paper focuses on the following aspects:In the first part,a three-dimensional transient finite element calculation model of the refractory lining at the K brick part of an actual coal-water slurry gasifier was established.The transient temperature field and stress field of the refractory lining during the refractory preheating,start-up and shutdown stage are analyzed and discussed using heat transfer and finite element methods.The results show that during the refractory preheating process of the gasifier,the heat is gradually transferred from the hot face brick to the steel shell.Due to the hysteresis of heat transfer,the temperature field distribution of the refractory lining can be consistent with the temperature distribution in the steady state analysis after a period of time.After reaching the steady state,the temperature of the outer surface of the shell was 212.3? which was basically the same as the temperature measured by the infrared thermometer.The temperature gradient at the top bend of the hot face brick is the largest,so the stress value there is also the largest,which is 4.12×10⁹ Pa.The transient stress field in the refractory lining is consistent with the trend of the temperature field,indicating that the thermal stress caused by the temperature gradient plays a decisive role in the strength of the refractoiy lining.The tensile stress generated during the cooling down process of the gasifier is the direct reason of the cracks in the refractory lining.During the frequent startup and shutdown of the gasifier,the refractory lining is constantly subjected to the interaction of tensile and compressive stress,which is the fundamental cause of its fracture.In the second part,the finite element model of refractory lining with cracks is established based on the location of cracks on the surface of refractory bricks in practical use.Effects of crack length,depth and crack deflection angle on the stress intensity factor K₁ and J-integral distribution was analyzed,and the annual growth of cracks with different sizes was calculated according to the fatigue crack propagation formula.The fracture failure behavior of the refractory lining of the coal water slurry gasifier under different working conditions was explored.The results demonstrated that for surface cracks,the variation laws of K₁ and J-integral numerical distribution are the same.The maximum value of K₁ and J-integral occurred near the two endpoints of the crack(?=0°,180°),while the minimum value of K₁ and J-integral occurred near the deepest crack front(?=90°).The crack is easy to expand from the two endpoints.For cracks with the same ratio of crack depth to length a/c,the K₁ and J-integral increased with the increasing of the crack depth a/t and decreases with increasing crack angle.The J-integral results indicate that excessive crack depth is likely to lead to destabilizing cracks growth.The greater the K₁ and the J-integral,the easier the cracks will propagate and the more likely the refractory lining will break.The annual crack growth is the smallest during the refractory preheating process and the largest during the shutdown process.The maximum annual crack growth is 9.06 mm,and the longer the initial crack length,the greater the annual crack growth.In the third part,based on the industrial Opposed-Multi Burner(OMB)coal-water slurry gasifier of the National Energy Group Ningxia Coal Industry Co.,Ltd.,the microstructure and chemical composition changes of the high chromium bricks after service at the top of the gasifier are analyzed.The mechanism of the refractory bricks at the top of the arch of the OMB coal-water slurry gasifier being damaged by slag corrosion is revealed.The results show that the high chromium brick at the top of the arch of the OMB coal-water slurry gasifier is the weak part of the gasifier for normal operation and the corrosion rate reaches 22.5%after 12181 h of operation.A dense slag layer was formed on the surface of the high-chromium brick,and the surface impact marks were obvious.At the working face of the high chromium brick after service,Fe₂O₃ and MgO in the slag react with Cr₂O₃ and Al₂O₃ in the high chromium brick to form a dense protective layer of(Mg,Fe²⁺)(Cr5Fe)₂O₄ composite spinel,which can slow down the corrosion rate to a certain extent.The SiO₂ and CaO in the coal slag penetrate into the high chromium brick through the pores,resulting in a thick metamorphic layer on the brick,which is the direct cause of the corrosion of the slag.