Fracture Features Of Mullite Ceramic Regenerative Material Under Thermal Shock Conditions

Mines in China give out a huge amount of ventilation air methane emission per year, which not only wastes resources but also pollutes the environment The counterflow oxidation technology is the only technology that could recycle ventilation air methane at a relatively low cost at the present stage. Honeycomb ceramic regenerator is the core component of the processor for coal mine ventilation oxidation whose normal and stable operation is the guarantee for the high efficiency and energy saving of counterflow oxidation. However, in the process of actual application, when the honeycomb ceramic regenerator works, there often emerge a series of problems such as the breakage, dislocation and jam of the honeycomb holes, which not only affects the heat transfer effect of the oxidation unit but also reduces the gas utilization efficiency. Besides, in severe cases, it could influence the normal operation of the equipment and bring serious burdens to production maintenance. Therefore, this paper firstly studied the thermal shock and fracture characteristics and rule of the mullite-based ceramics commonly used in regenerators and then analyzed the fracture failure of the honeycomb regenerators from the perspective of structure. Finally, it predicted the service life of the honeycombs based on the experimental data and numerical stimulation results.The research in this paper is conducted as follows:1) According to the heat charge and discharge of the regenerators, the heating and cooling method was selected to simulate the hot working environment of the regenerators. Then thermal shock experiment was designed to make the thermal shock test and thermal fatigue test on the mullite renegerative materials. In the thermal shock test, the single edge notched beam method and the three point bending method were employed to study how the post-peak flexural strength and fracture toughness of the mullite ceramics changed with different thermal shock parameters such as temperature and medium. The thermal fatigue test studied how post-peak flexural strength at different thermal shock temperatures changed with the thermal shock cycle times so as to provide related experimental data to predict the thermal life of the subsequent materials.2) From the viewpoint of energy, work of fracture was indirectly employed to calculate the fracture energy of mullite ceramic materials. It studied how it changed with the thermal shock temperature difference and the crack depth and made a co MParative analysis between it and the energy release calculated from the linear-elastic fracture mechanics.3) Indirect coupling method was employed to make thermal stress coupling analysis on the simplified regenerator model so as to get the temperature field and stress filed during the heat transfer of the regenerators. By analyzing the changing rule of the temperature field and the stress field, the failed peril points during the heat transfer of regenerators were discovered to judge the method by which the peril point got fractured.4)Based on the thermal fatigue life theory of ceramics, the thermal fatigue life under the high temperature differences of the mullite samples was obtained through tests. Then based on thermal fatigue experiment data and strength attenuation curve, the thermal shock damage equations of the materials were established. By combining with the numerical simulation result, it predicted the service life of the regenerators. The research in this paper provides useful references for mullite ceramic materials in the engineering design, fracture assessment, service life prediction and reliability evaluation of the regenerators. Besides, it could promote the development and application of the counterblow oxidation technology in the mine ventilation recycling.