Εργαστήριο Εναλλακτικών Καυσίμων & Περιβαλλοντικής Κατάλυσης
Title: An experimental investigation of sodium acetate trihydrate on the thermal stratification in solar water tank [view paper]
Journal: Renewable Energy 134 (2019) 862-874.
Authors: Wang Z.a, Zhang H.a,*, Huang H.a, Dou B.a, Huang X.a, Goula M.A.b
Affiliations:
aSchool of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai, 200093, China
bDepartment of Environmental Engineering, Western Macedonia University of Applied Sciences, Koila, Kozani, 50100, Greece
Abstract
Thermal storage technology is an important approach to improve the efficiency of solar energy utilisation. To analyse the thermal stratification in a hot water storage tank at an initial temperature of 80 oC and at an inlet temperature of 5 C, this study thoroughly analysed the impact of the position of PCM balls on the thermal stratification for various flow rates (1, 3, 5, 7, and 9 L/min) under different position. Performance parameters, including the Richardson number, MIX number, and exergy efficiency, were involved in the evaluation. The study was further extended to explore the applicability of Fill Efficiency (FE) as a performance parameter of thermal stratification within a storage tank. The experimental results indicated that, for the same inlet flow rate, an improved thermal stratification of the tank was achieved as the positions of the balls became closer are to the inlet, and the balls with a small diameter also showed remarkable potential for improving the thermal stratification of the water tank. When the flow rate increased, the cold and hot water mixing intensified, and the thermocline thickness in the tank increased. Thus, the thermal stratification weakened. Furthermore, when the water-release process progressed, the mixing of the hot and cold water in the water tank tended to be stable, and formed a stable thermocline. Finally, when the inlet flow rate was less than 7 L/min, the thermal stratification of the water tank exceeded that of the PCM water tank, while for an inlet flow rate in excess of 7 L/min, the thermal stratification of the PCM water tanks was superior to that of the water tank in the case when the balls was on the fourth layer.
Reforming of Glycerol
Biodiesel production has grown, between 2005 and 2015, at almost 25% per annum (reaching approximately 32 billion liters), leading to a seven-fold expansion of the sector. Although biodiesel is thought of as a renewable, biodegradable, environmentally-friendly fuel, there are concerns over the production of glycerol, the main by product of the transesterification reaction (it accounts for 10% of the volume of oil undergoing the reaction).
An innovative option is the energetic utilization of glycerol via steam reforming (SR), as every mole of glycerol fed to the reactor can theoretically produce seven moles of hydrogen. At LAFEC we have devoted our efforts towards the design of appropriate catalysts based on transition metals that can be used in the GSR. In some of our previous works, we reported on the performance of different transition metals (Ni, Co, Cu) on silica [BioResources 11 (2016) 10173-89] and alumina [Fuel Process Technol 152 (2016) 156-75], of Ni catalysts based on alumina, zirconia, silica [Top Catal 60 (2017) 1226-50] and apatite-type lanthanum silicates supports [RSC Adv 6 (2016) 78954-8], the influence of the synthesis method on Ni/Al catalysts [Chinese J Catal 37 (2016) 1949-65], the effect of the addition of lanthana on Ni/Al catalysts [Int J Hydrogen Energ 42 (2017) 13039-60], the effect of the addition of CaO-MgO on Ni/Al catalysts [Int J Hydrogen Energ 44 (2019) 256-273], the use of AlCeO3 as supporting material for a Ni catalyst [Catalysts 9 (2019) 411], the effect of the addition of silica [Top Catal 60 (2017) 1226-1250] or yttria [Int J Hydrogen Enrg, In press] on Ni/ZrO2 catalysts. We have also tested Ce-Sm-xCu [Sust Energ Fuels 3 (2019) 673-691] and Ni/Ce-Sm-xCu [Nanomaterials 8 (2018) 931] catalysts. A comprehensive literature review with particular focus on the main catalysts and support systems under development has also been carried out [Surf Coat Technol 352 (2018) 92-111].
Moreover, we have also examined glycerol reforming via chemical looping using Ni/ZrO2 nano-composite oxygen carriers [Int J Hydrogen Energ 43 (2018) 13200-11].
CO2 Utilization - Biogas Dry Reforming
It is well understood that human activities, emanating from current practices relating to the production and consumption of fossil based energy have an unequivocal impact upon the global climate. A promising technology is the Dry Reforming of Biogas, as the process makes use of the main greenhouse gases (CH4 and CO2), and can provide a renewable resource with a potential zero carbon footprint. The product of this process is syngas, a key chemical feedstock for the synthesis of oxygenated chemicals and hydrocarbons from Fisher – Tropsch synthesis.
At LAFEC we have examined the performance of nickel catalysts based on alumina modified with ceria, lanthana [J Nat Gas Sci Eng 31 (2016) 164-83 & Catal Today 195 (2012) 93-100], magnesia or calcium [Waste Biomass Valori 7 (2016) 725-36]. A theoretical investigation of Ni-Al2O3 and Ni/CeO2-Al2O3 has also been performed [Int J Hydrogen Energ 35 (2010) 9818-27].
We have also devoted effort in investigating the performance of Nickel catalysts based on zirconia modified with ceria, lanthana [Int J Hydrogen Energ 42 (2017) 13724-40] and tugsten [Front Environ Sci 5 (2017) 66]. Moreover, we have examined different synthesis techniques in an effort to maximize the dispersion of active phase and optimize the active species [Catal Today 46, 175-83; Int J Hydrogen Energ 40 (2015) 9183-00].
Finally, we have committed ourselves at investigating the carbonaceous species formed during the reaction [J Catal 161, 626-40; Adv Mater Proc 2 (2017) 807-12; Mater Today: Proc. 5 (2018) 27607-27616; Int J Hydrogen Energ 43 (2018) 18955-18976; Appl Surf Sci 474 (2019) 42-56], as it is one of the main reasons for catalyst deactivation.
NOx and SO2 abatement
Nitrogen and sulphur oxide abatement is a subject of major environmental importance, as Nitric (NOx) and Sulphur (SOx) oxides are recognized as important precursors of acid rain, contributors to the formation of photochemical smog and to the destruction of the ozone layer. Recently, a lot of academic and policy attention has focused on N2O emissions control. Nitrous oxide (N2O) is listed as one of the most harmful greenhouse gases with a strong global warming potential (310 times higher than that of CO2), that severely contributes to the stratospheric ozone layer depletion.
At LAFEC, we were the first to investigate the lean NOx reduction by propene, H2 as well as by propene + H2 over supported (on γ-Al2O3), low loading (0.5 wt%), Pt, Pd and Ir catalysts [J Environ Chem Eng 4 (2016) 1629-41]. In addition, we have examined the impact of alkali promoters (K) on the physicochemical properties and catalytic performance of Ir/Al2O3 catalysts towards the N2O decomposition [Top Catal 59 (2016) 1020-7]. Finally, we have examined the deactivation and regeneration procedures of copper oxide catalysts/sorbents that are supported on Al2O3, SiO2, CeO2-Al2O3, in the presence of SO2 and identified the appropriate conditions for the simultaneous removal of NO and SO2 [Global Nest J 14 (2012) 166-74].
Selective deoxygenation (SDO) of natural triglycerides
There are two main drawbacks associated with the production of biodiesel through the transesterification reaction: (a) The unsuitability of plant oils with relatively high acidity for transesterification catalyzed by basic solutions, and (b) the increasing accumulation of glycerol, the main sub-product of the process.
However, natural triglycerides can be upgraded using selective deoxygenation (SDO), which is realized by hydrotreatment via decarboxylation (deCO2), decarbonylation (deCO) and hydrodeoxygenation (HDO), to hydrocarbons in the range of petro-diesel (green or renewable diesel).
At LAFEC we have set up appropriate experimental procedures and are investigating the: (i) effect of supports, metal loading and promoters on catalytic performance, (ii) SDO pathways over transition metallic catalysts, and (iii) effect of preparation method on catalytic performance.
We have recently published a comprehensive literature review on the topic [Energies 12 (2019) 809].