Stress Analysis Of Ethylene Cracking Furnace Pipe System With Environmental Factors

The production of Ethylene plays an extremely important role in the petrochemical industry.The Ethylene cracking furnace is the core equipment in the process of Ethylene production,where the furnace tube of radiant section in Ethylene pyrolyzer which is one of the most important fittings of steam cracker is one of the main factors restricting the long-term safety operation of ethylene plant.The service condition of cracking furnace tube is very complicated,and the requirement of withstanding high temperature about 1150? for the outer wall of the furnace tube should be satisfied since that the way of heat transfer is through convective heat transfer between the inner wall of furnace tube and the cracking medium with high carbon potential and low oxygen pressure.The combined effects of carburization,coking and thermal fatigue causes the damage of furnace tube,affecting the long-term safety operation of ethylene cracking furnace tube.Many researchers at home and abroad have also studied the influence on the performance of ethylene cracking furnace tube by carburization,coking and thermal fatigue.On the basis of these studies,the evaluation methods of residual life for furnace tube in various damage conditions are developed to ensure the long-term safety operation of ethylene cracking furnace tube.However,there are few reports about the high temperature behavior under the influence of environmental factors and the effect of environmental factors on the relationship stress of the furnace tube under the high temperature environment of more than 1000? at home and abroad.In this paper,two kinds of centrifugally cast austenitic heat-resistant alloys Cr35Ni45 Nb and Cr25Ni35 Nb were tested for single oxidation,single carburization and pre-oxidation+carburization under the influence of temperature and oxidation.Thermal expansion test and small punch experiment were carried out to obtain mechanical properties such as elastic modulus,linear expansion coefficient,yield strength and tensile strength.In the process of analysis,the influence of heat source arrangement and furnace tube installation restraint on pipe system stress is considered.Finally,the thermal stress analysis of fluid-solid thermal sequential coupling is carried out on the WORKBENCH simulation platform under ANSYS.The effects of heat source arrangement,on-site installation restraint and Carburization on the stress of furnace pipe system are considered in the analysis process.The results show that with the increase of carburizing layer thickness,the performance of ethylene cracking furnace tubes shows a deteriorating trend,and high temperature pre-oxidation will accelerate carburizing behavior.The yield strength and tensile strength of Cr35Ni45 Nb material are higher than that of Cr25Ni35 Nb material is obtained by small punch experiment.Combined heating of bottom and side wall of burner is found by the numerical simulation of the temperature distribution in the tube based on heat source arrangement,and the parallel heating of the side wall makes better temperature distribution in pipe can be concluded.By the numerical simulation of the influence of tube bundle layout on stress of furnace tube system,it is found that the upward and downward movement and bottom rotation of the furnace tube can offset part of the stress by deformation.The furnace tube has been broken in the case which the maximum stress of the furnace tube reaches 1455 MPa and the maximum displacement is 697.5 mm when the bottom is stuck.The numerical simulation of the effect of carbonization on the stress of furnace tube indicates that the values of mises stress,hoop stress,and axial stress of Cr35Ni45 Nb material are all lower than Cr25Ni35 Nb material.Besides,the stress of furnace tube increases with the increasing the thickness of carburized layer and radial stress can be neglected because of the very small value.