Solar greenhouses can be promising candidate for CO2 capture and utilization: mathematical modeling

Int J Energy Environ Eng (2015) 6:295–308 DOI 10.1007/s40095-015-0175-z ORIGINAL RESEARCH Solar greenhouses can be promising candidate for CO2 capture and utilization: mathematical modeling Mohammed B. Effat1 • Hamdy M. Shafey1 • A. M. Nassib1 Received: 15 December 2014 / Accepted: 29 April 2015 / Published online: 14 May 2015 Ó The Author(s) 2015. This article is published with open access at Springerlink.com Abstract Solar greenhouses can be considered as efficient places for biological CO2 capture and utilization if CO2 enrichment becomes a common practice there. As CO2 enrichment is applied only when greenhouses are closed, ventilated greenhouses––which represent a large percentage of greenhouses all over the world––cannot be considered for this practice. Consequently, ventilated greenhouses cannot be considered for CO2 capture and utilization. The aim of this paper is to show––through modeling and simulation–– that these ventilated greenhouses can be activated for serving as efficient CO2 capture and utilization places if they are kept closed (to apply CO2 enrichment) and used microclimate control methods alternative to ventilation. The paper introduces a realistic mathematical model in which all the processes and phenomena associated with the biological CO2 capture and utilization by photosynthesis inside greenhouses are considered. The model validity and accuracy were ensured through the good agreement of its numerical predictions with the available experimental results in the literature. The effect of different environmental and planting conditions on the CO2 capturing process (the photosynthesis process) is investigated. A case study was chosen to investigate the effects of the cooling method, cooling temperature, planting conditions, and CO2 concentration level on the cumulative amount of captured CO2 which represents the greenhouse capturing performance. Electronic supplementary material The online version of this article (doi:10.1007/s40095-015-0175-z) contains supplementary material, which is available to authorized users. & Mohammed B. Effat 1 Mechanical Engineering Department, Assiut University, Assiut 71516, Egypt The results show that the capturing performance of greenhouse can be enhanced from value as low as 1.0 g CO2/ m2 day for ventilated greenhouses with low planting density to a value as high as 140 g CO2/m2 day for high planting density when alternative microclimate control methods and CO2 enrichment are applied, considering the appropriate plant type. Additional benefits besides CO2 capture are also discussed for the possible increase of the plant productivity and possible lowering of water consumption by plants. Keywords Carbon capture and utilization  Solar greenhouses  Mathematical model  Biofixation Nomenclature An Net assimilation specific rate, lmol CO2/m2/s1 Ax Surface area of greenhouse component x, m2 C CO2 concentration inside the greenhouse air, lmol/mol air Cd, Cw Drag coefficient and wind coefficient, respectively Cx Specific heat of greenhouse component x other than air, J/kg K G CO2 injection specific rate for enrichment, lmol CO2/m2/s1 H Greenhouse height, m hfg Latent heat of vaporization, J/kg hg Enthalpy of saturated water vapor, J/kg k Thermal conductivity, W/m K L Greenhouse length, m LAI Leaf Area Index l Depth of the greenhouse soil, m Mair Molecular weight of the greenhouse air, kg/mole 00 m Mass transfer specific rate, kg/m2 s n00CO2 ;vent Molar specific rate accounting for the loss of CO2 by ventilation, lmol/m2/s1 123 296 Int J Energy Environ Eng (2015) 6:295–308 Pair-dry P0 q00solidfluid q00cool Rd;vis=NIR Rdf;vis=NIR Rsx Rxy R0;vis=NIR Tx t u, ug Vcmax0 W Dry air pressure, kPa Atmospheric air pressure at sea level, kPa Convective heat specific rate between the humid air and the cover inner surface, W/m2 Energy specific rate accounting for cooling of the greenhouse by ventilation or other alternative cooling method, W/m2 Direct visible and near infrared solar radiation fluxes, respectively, W/m2 Diffuse visible and near infrared solar radiation fluxes, respectively, W/m2 Solar radiation specific rate absorbed by the greenhouse component x, W/m2 Net thermal radiation energy specific rate exchanged between surface x and surface y of the greenhouse, W/m2 Extraterrestrial visible and near infrared solar radiation fluxes, respectively, W/m2 Temperature of the greenhouse x component, K Time, s Specific internal energy of the greenhouse air and dry saturated water vapor J/kg, respectively Biochemical capacity of the plant (carboxylation specific rate), lmol/m2 s Greenhouse width, m Greek symbols q Material density, kg/m3 x Humidity ratio of the greenhouse air, kg H2O/kg air Subscripts air Greenhouse air atm Atmosphere base Base of the greenhouse soil cov Greenhouse cover can Canopy cond Condensation cool Cooling dehumid Dehumidification floor Greenhouse floor leaf Leaf sky Sky soil Soil tran Transpiration Introduction Carbon dioxide is strongly blamed for being the major contributor to the global warming problem. The increase in burning fossil fuels increases CO2 concentration in the atmosphere and increases the effect of global warming. 123 Therefore, solutions to reduce CO2 emissions to the atmosphere are necessary. In recent years, a new technology called carbon capture and storage (CCS) had been introduced to reduce CO2 emissions to the atmosphere [1]. In these technologies, CO2 is separated from the exhaust gas streams, compressed, and then treated for clean environment. This treatment can be either by permanently storing CO2 (e.g. geological reservoir) or by utilizing it in any beneficial application (food industry, water treatment, agriculture sector). Biofixation is considered as one of the promising CO2 utilization applications in which terrestrial plants can capture and utilize considerable amounts of CO2 through the process of photosynthesis. The common application of biofixation is the increase of forestation to lower the CO2 concentration in the atmosphere [2–4]. Another possible application of biofixation, that is not receiving much attention, is the CO2 enrichment inside commercial greenhouses. Carbon dioxide enrichment is a process performed in some greenhouses in which pure CO2 is introduced to the vegetated crops at high concentration levels. This process leads to increasing the productivity of the crops inside the greenhouse as the photosynthesis rate of enriched plants is much higher than that of plants subjected to ambient CO2 concentration [5]. Considering this practice, if the pure CO2 supplied to plants inside the greenhouse is provided from the CO2 that was separated previously from a CO2 capturing process, this will allow the plants inside the greenhouse to utilize it at high rates instead of just burying it underground. Furthermore, greenhouses are currently occupying large areas all over the world and as these areas will continuously increase [6, 7], commercial greenho (...truncated)