Study On Stress Accumulation And Weakening Of Metal Hydride Reactor During Hydrogen Absorption/Desorption

The storage and transportation process is the key to efficient utilization of hydrogen energy.Solid metal hydrogen storage has significant advantages such as high mass density ratio,large hydrogen storage volume ratio,good safety,high hydrogen purity,and good reversible cycling.It is expected to play an important role in the future hydrogen economy.The reactor is the core equipment for hydrogen storage alloys to achieve heat and mass transfer and stability.However,the periodic expansion and contraction of metal in the process of cyclic hydrogen absorption and discharge will cause stress accumulation,which will gradually attenuate the metal hydrogen storage capacity and lead to the plastic failure of the reactor in serious cases.Currently,there is relatively little research on the characteristics of hydrogen storage alloys in terms of hydrogen absorption,desorption,and pulverization,as well as the stress accumulation and distribution characteristics caused by them.In this paper,the stress accumulation effect in the process of hydrogen absorption and release cycle in the solid hydrogen storage alloy reactor is studied,the online feedback and real-time monitoring system of the strain of the hydrogen storage alloy reactor is designed and built,the core and key factors affecting the strain response and reliability of the hydrogen storage reactor are analyzed,and a new idea of ultra-low speed rotation,low strain and high filling rate of the hydrogen storage alloy reactor is proposed.The stress accumulation of conventional vertical reactor is effectively alleviated,and the strain response characteristics of the reactor are obviously improved.With the help of real-time strain measurement and analysis system and biaxial resistance strain gauge,the strain distribution characteristics of the bed during the process of cyclic hydrogen absorption and discharge in the reactor were studied,and the influence of the bed wall thickness,alloy type,placement state and other factors were discussed.Under the multiple effects of environmental hydrogen pressure,swelling and shrinking effect,compression effect and gravity settlement effect,the apparent strain of the bed wall during a single hydrogen absorption and discharge cycle can be divided into five stages:the stage of rapid strain increase,the stage of hydrogen absorption and expansion strain growth,the stage of alloy self-adjusting strain stabilization,the stage of hydrogen release strain decline and the stage of alloy strain gradual reduction.The variation of radial strain and axial strain of the reactor is significantly different.For the traditional vertical reactor,the maximum strain or failure generating region is relatively similar,and strengthening the strength of this region is one of the effective mitigation measures.The particle size and local density or porosity of the hydrogen storage alloy have a significant effect on the strain characteristics of the bed,and the lattice expansion and shrinkage of the alloy during the hydrogen absorption and desorption process is gradually transformed into the macroscopic particle size,surface morphology,wall strain and other changes.Under the action of gravity,the powder alloy gradually moves and deposits to the lower region of the bed,which makes the particle size,porosity and accumulation degree of the alloy in the lower region of the reactor change obviously,and the local filling ratio and stress increase rapidly,and the stress accumulation phenomenon occurs.A new low-speed rotating reaction device was designed to alleviate the stress accumulation characteristics generated during the hydrogen absorption and desorption process of alloys in conventional vertical reactors.Under the same wall thickness of the bed,the placing state and rotation frequency of the bed were changed,and the comparative tests of cyclic hydrogen absorption and desorption were carried out under the same conditions,and the and differences of strain responses of different types of reactors were analyzed.The results of fixed-point circumference measurement and DIC deformation analysis system monitoring show that the stress accumulation position of the new reaction bed is shifted from the bottom to the hydrogen inlet side,which significantly weakens the risk of single downward deposition of the pulverized alloy,makes the pulverized alloy achieve a relatively ideal diffuse distribution in the new reaction bed,the alloy packing density is uniform,the powder compaction phenomenon is improved,the plastic failure caused by excessive local stress of the bed is greatly alleviated,and the service life of the reaction bed is prolonged.