Heat Storage And Heat Supply Performance Of Zeolite-MgSO₄ Composites

Compared with sensible heat storage and latent heat storage,thermochemical heat storage has the characteristics of high heat storage density,large heat release power,and suitable for long-term storage of thermal energy.Adsorption heat storage,as a kind of thermochemical heat storage,realizes heat energy release through adsorption reaction,and the reaction product can be recycled after desorption.Industrial waste heat and solar energy can be used as energy sources for desorption reaction.As a low-polluting and high-efficiency energy storage technology,the application of adsorption heat storage in building heating is still very limited.The combination of building heating and adsorption heat storage technology is of great value to building energy conservation and emission reduction,industrial waste heat recovery and energy cleaning.are of great value.In this paper,the adsorption heat storage system of inorganic salt and water vapor is used,and the heat storage salt is combined with the carrier to prepare the composite heat storage material.In this paper,composite heat storage materials were prepared by infiltration method,MgSO₄was used as heat storage salt,and five zeolites such as 3A,4A,5A,10X,13X were used as carrier materials,and MgSO₄solutions with mass fractions of10wt%and 20wt%were used.A total of 10 composite materials were prepared after soaking different zeolites.The water vapor adsorption performance,microscopic morphology,MgSO₄content and theoretical storage capacity of each group of materials were tested by constant temperature and humidity chamber,scanning electron microscope（SEM）,energy dispersive analyzer（EDS）,differential scanning calorimeter（DSC）,the group with the best performance is used for water vapor adsorption heating in the pipeline test bench.The heating performance of the composite material varies greatly under different experimental conditions,and the cycle performance test of the best group is carried out.Finally,the thermal energy utilization rate of the composite material is tested through the constructed foam concrete box to simulate the residential space.The main research contents and experimental conclusions are as follows:（1）The temperature and humidity of the constant temperature and humidity chamber were set to 25°C and 60%RH,and the composite material was placed in it for 24h water vapor adsorption test.Experiments show that 3A zeolite and 13X zeolite soaked in 10%MgSO₄solution and 3A zeolite soaked in 20%MgSO₄solution have the highest water vapor adsorption capacity,which are 6.14g,6.32g and 6.18g respectively.The temperature was kept at 25°C,and the humidity gradient was set to60%RH,70%RH,80%RH,and 90%RH.Repeated experiments found that 90%RH was the optimum adsorption humidity.The humidity was 60%RH,and the temperature gradient was set to 25°C,35°C,45°C,and 55°C.Repeated experiments found that 45°C was the optimal adsorption temperature.The samples were observed under a scanning electron microscope（SEM）with a magnification of 10,000 times and 20,000 times.The electron microscope pictures showed that each group of materials had a rough and porous microscopic morphology.The energy dispersive analysis（EDS）results show that the 3A and 5A zeolites soaked in 20%MgSO₄solution have the highest Mg content,and their Mg atom content is 4.675%and4.940%,respectively.The material was placed in a differential scanning calorimeter to test the heat storage density.The results showed that the 3A zeolite soaked in 20%MgSO₄solution had the highest heat storage density,reaching 539.0J/g.（2）The 3A zeolite soaked in 20wt%MgSO₄solution was used as the experimental material for the pipeline adsorption heating experiment,and the humidity and flow rate of the gas entering the reactor were controlled and tested.According to the calculated experimental conditions,when the gas humidity is90%RH and the flow rate is 14Nm³/h,the composite material exerts the maximum heat supply density of 474.2J/g.Compared with the DSC test result of 539.0J/g,the thermal energy utilization rate is about 88.0%.Keeping the experimental conditions unchanged,three sets of cycle experiments were carried out on the composite material.The average heat supply density was calculated to be 479.4J/g,and the material did not show obvious thermal performance decay and had good cycle characteristics.（3）Selecting suitable raw materials,including cement,fly ash and foaming agent,etc.,poured several foam concrete slabs under the conditions of dry density grade A07 and water-binder ratio of 0.50.Using epoxy resin and curing agent to bond the partition into a box to simulate a residential space.The existing pipeline adsorption experimental bench is correspondingly modified,so that the dry and hot air in the reactor can be normally transmitted to the inside of the box for heating.The composite material was taken in the reactor for water vapor adsorption.The experimental conditions were that the gas humidity was 90%RH and the flow rate was 14Nm³/h.The generated dry hot air was passed into the interior of the foam concrete box to measure the heat obtained in the box space.After three cycle experiments,the average heat supply density of the composite material for heating the simulated residential space is 289.6J/g.Compared with the result 539.0J/g of DSC test,its thermal energy utilization rate is 54%.