Investigation on the rotary regenerative adsorption wheel in a new strategy for CO2 enrichment in greenhouse

Abstract

• A new greenhouse CO 2 enrichment system with air carbon-capture was proposed. • A local thermal and mass non-equilibrium model was developed for the analysis. • The RAWs with different adsorbent materials were comparatively researched. • The effects of adsorbent materials and operating conditions were analyzed. The optimal concentrations of CO 2 for plant growth in greenhouses are commonly higher than that in the atmosphere. A new strategy using direct air carbon-capture was developed to increase CO 2 concentration in the greenhouse. A rotary regenerative adsorption wheel (RAW) for the temperature swing adsorption process was utilized as the critical equipment in the CO 2 enrichment system to achieve continuous CO 2 capture. To investigate the heat and mass transfer characteristics of RAWs, a 3D thermal and mass non-equilibrium modeling of the temperature swing adsorption process in a bi-sectional RAW was first developed. The RAWs with activated carbon, zeolite 13X and Mg-MOF-74 were comparatively researched. Three dimensional distributions of temperature and mass parameters in the RAW are obtained and analyzed. Air streams with different CO 2 concentrations can be obtained by suitably arranging the airflow channels at outlets. The increased rotating speed will cause small temperature swings and lead to poor CO 2 enrichment performance. The increased air flowrate will reduce adsorbent mass per air flowrate and weaken the CO 2 enrichment performance. The RAWs with Mg-MOF-74 and zeolite 13X have very close performance and are much higher than that with activated carbon. Although Mg-MOF-74 is theoretically better than zeolite 13X on the CO 2 adsorption performance, the difference between the two is not obvious due to the small temperature swings between adsorption and desorption sectors in this study. Improving the overall mass transfer coefficient is critical for promoting the CO 2 enrichment performance of the RAW when the overall mass transfer coefficient is less than 0.002 s −1 .