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High-temperature steam generation from low-grade waste heat from an adsorptive heat transformer with composite zeolite-13X/CaCl2
- Xue, Bing, Ye, Song, Zhang, Linsheng, Wei, Xinli, Nakaso, Koichi, Fukai, Jun
- Energy conversion and management 2019 v.186 pp. 93-102
- X-ray fluorescence spectroscopy, adsorbents, adsorption, calcium chloride, exergy, heat, models, scanning electron microscopes, steam, temperature, water uptake, zeolites
- High-temperature adsorptive heat transformer for steam generation has been experimentally investigated by introducing composite zeolite/CaCl2-water working pair based on a direct contact method. Composite adsorbents are prepared by immersing zeolite into different mass concentrations of CaCl2 solutions. SEM (Scanning Electron Microscope) is used to observe the surface structure of the composite zeolite. XRF (X-Ray Fluorescence) is selected to analyze the element mass ratios in adsorbents. BET (Brunauer-Emmett-Teller models) is employed to calculate the pore characteristic of pores inside zeolite. Characterization results confirm the success of preparation for composite zeolite. Adsorption properties including equilibrium water uptake and integral adsorption heat are measured for basic evaluation. Overall volumetric adsorption heat is increased by 13.1% for CA40% (immersion of zeolite in CaCl2 solution concentration at 40%) compared with that for 13X. Cyclic experiments are conducted to test the design of system. Superheated steam above 200 °C is generated for 13X and different composite zeolites from hot water below 80 °C. Dry gas at 130 °C is used for regeneration. Gross temperature lift is more than 100 °C for single stage zeolite adsorptive heat transformer. Dynamic steam generation on interface between water and zeolite is enhanced with more heat released by using composite zeolite. Subsequently, adsorption equilibrium is easier to be achieved inside the whole range of the packed bed. Effective time ratio for steam generation is elevated by 18.6% for CA40% compared with that for 13X. Mass of generated steam is raised by 12.9% simultaneously. Both the time and mass of generated steam have been obviously promoted with the increase of CaCl2 impregnated in zeolite. COPex (Exergy Coefficient of Performance) is kept constant while SHP (Specific Heating Power for steam generation) is increased by 12.6%.