| Adsorption heat pump technology provides an effective solution for industrial low-grade waste heat recovery.Direct contact heat exchange method is employed in an adsorption heat pump system to generate high-temperature steam?>200°C?from low-grade heat source?70°C hot water and 130°C dry gas?with zeolite 13X-water working pair.However,the amount of free water content in the porous zeolite adsorbent is still considerable,which results in the decrease in system performance.In this thesis,zeolite13X was functionalized by silane coupling agent KH-570??-methacryloxypropyl trimethoxy silane?to reduce the free water content inside and outside the particles.High-temperature steam generation process was then enhanced;thus,system performance was remarkably improved.Results and conclusions are summarized as follows:?1?XS-5,XS-15 and XS-25?XS-5 represents zeolites 13X was functionalized by of the silane with 5%concentration?zeolite samples were functionalized by using the grafting modification method.Then various properties of modified zeolite were tested and analyzed.The static water adsorption capacity of the functionalized zeolite with low concentration silane solution was not significantly different from that of the original 13X zeolite.The water adsorption capacity of the functionalized zeolite with a slightly higher silane solution concentration was decreased slightly,7.9%lower than the original zeolite.The adsorption heat of the three functionalized zeolites has not decreased.The contact angle test found that the functionalized zeolite could be hydrophobic with a 99°contact angle obtaining in XS-25 zeolite.The free water content of the functionalized zeolite was decreased by 5.4%,6.1%and 20.7%,respectively.The alkyl?C-Hx?vibration peaks at 2850 cm-1 and 2950 cm-1 were observed by FT-IR spectrogram,which confirmed that the silane group was successfully grafted to the zeolite surface.TG analysis confirmed that the organic components of the functionalized zeolite could remain stable up to 300°C.The free water content in the zeolite particles is decreased thanks to surface hydrophobic functionalization.The adsorption heat and static water adsorption capacity is slightly decreased,nevertheless the functionalized zeolites can remain stable at high temperature environment.?2?Dynamic thermal response based on different types of modified zeolite packed bed during generation and regeneration processes were elaborated and analyzed.The duration of the steam generation process in the XS-25 zeolite packed bed was reduced by 14.9%.At the same time,the maximum temperature of steam was increased with functionalized zeolite as adsorbent.In the XS-25 zeolite experiment,the maximum steam temperature reached 207.2°C,and the system temperature rose to 106.2°C.The results of multiple experimental cycles show that the final generated steam mass in functionalized zeolite experiments is consistent with that in 13X zeolite experiment.The time consumed in the removal of free water inside zeolite above 2/3 height in XS-25 zeolite packed bed was reduced by 53.7%.However,the time consumed for the desorption of adsorb water has not decreased.Compared with the 13X zeolite regeneration experiment,the energy input to remove free water in functionalized zeolite experiment was reduced by up to 20.6%.The water migration pattern on zeolite surface has been changed by functionalization.Overall thermal response of the bed was accelerated and the conversion of adsorption heat to steam heat was promoted.Meanwhile the free water content was also decreased significantly leading to a quick regeneration process.?3?The improvement of system performance by the functionalized zeolite was evaluated from multiple perspectives.Firstly,compared with 13X zeolite experiment,the mass ratio of steam and inlet water in XS-25 zeolite experiment was improved by29.8%.Secondly,GTL?gross temperature lift?was increased by up to 8.38%with three different functionalized zeolites.Finally,COPh?heating coefficient of performance?and SHPs?specific heating power for steam generation?were increased by 23.6%and5.7%,respectively.The input of low-temperature heat sources was saved to some extent during the generation process by functionalized zeolite.In addition,the system's ability to upgrade of waste heat source was enhanced and the adsorption/desorption processes were intensified.Thus,the overall performance of the heat pump was improved consequently. |
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