Release of Hydrogen from Nanoconfined Hydrides by Application of Microwaves

The release of hydrogen from solid hydrides by thermolysis can be improved by nanoconfinement of the hydride in a suitable micro/mesoporous support, but the slow heat transfer by conduction through the support can be a limitation. In this work, a C/SiO2 mesoporous material has been synthesized and employed as matrix for nanoconfinement of hydrides. The matrix showed high surface area and pore volume (386 m²/g and 1.41 cm³/g), which enabled the confinement of high concentrations of hydride. Furthermore, by modification of the proportion between C and SiO2, the dielectric properties of the complex could be modified, making it susceptible to microwave heating. As with this heating method the entire sample is heated simultaneously, the heat transfer resistances associated to conduction were eliminated. To demonstrate this possibility, ethane 1,2-diaminoborane (EDAB) was embedded on the C/SiO2 matrix at concentrations ranging from 11 to 31%wt using a wet impregnation method, and a device appropriate for hydrogen release from this material by application of microwaves was designed with the aid of a numerical simulation. Hydrogen liberation tests by conventional heating and microwaves were compared, showing that by microwave heating hydrogen release can be initiated and stopped in shorter times.2019-04-0

Evaluation of the Flexural Strength, Sorption, Rheological and Thermal Properties of Corncob Plastic Composites

Plastic composites were made from corncobs and high density polyethylene (HDPE) by extrusion and evaluated. The composites were manufactured using two different screened corncob particle size fractions

Briquetting and torrefaction of agricultural residues for energy production

Ph. D. ThesisAgricultural residues are a potential feedstock for renewable energy because they are abundant and CO2 neutral. Due to their low energy density and heterogeneity, there are key challenges in handling, storage, transportation and utilization, therefore pre-treatment is required. The aim of this study was to evaluate a range of pre-treatment options of agricultural residues for energy applications. The effect of moisture content (7.14-16.94%), particle size (˂2.36-˂4.00mm), compression temperature (20-80oC), pressure (100-250MPa), and type of agricultural residues (corn cob and bean straw) on briquette properties i.e. density, impact resistant and compressive strength was studied. Torrefaction of corn cob and bean straw were also investigated over a range of temperatures (200-300oC) and holding times (0-90 min) to study the impact of operating conditions on yields and properties of torrefaction products (char, liquid and gas). The results showed that density, impact resistance, and compressive strength significantly increased with increasing compacting temperature (20-80oC) and compacting pressure (100-250MPa) but decreased with increasing moisture content and particle size. Briquettes that satisfied the German Standard DIN 51731(density >1000kg m-3) and European Standard Committee CEN/TC 335 (durability >95%) standards for solid fuels were obtained with particle size ˂4 mm, compression temperature of 80oC and (i) moisture content of 10-12% with pressure of 100-250MPa for bean straw and (ii) low moisture content (<10 %) and high pressure (200-250 MPa) for maize cob. Briquettes derived from a bean straw:maize cob blend had high density and strength at low pressure and temperature compared to those derived from maize cobs due to enhanced bonding via mechanical interlocking, thereby reducing the costs of production. Torrefied solid products obtained at 300oC had properties comparable to coal with energy yields of 74.84-79.47% for maize cob and 90.08-92.93% for bean straw. The gaseous product (3.25-17.41% yield) was predominantly CO2 due to decomposition of hemicellulose within the temperature range studied. Briquettes that met the above certified standards were studied for pyrolysis and combustion in a fixed-bed reactor. The effects of pyrolysis temperature (410-650oC), heating rate (10-20oC min-1), carrier gas flow rate (40-60 cm3 min-1) and briquetting conditions (temperature (20-80oC), pressure (150-200MPa) and blend ratio) on the yields and properties of pyrolysis products from maize cob iv and bean straw briquettes were investigated. It was found that bio-oil and gas yields increased while, char yields from both biomass feedstocks decreased with increasing pyrolysis temperature due to an increase in decomposition of lignocellulosic components and secondary decomposition of primary char. Briquetting conditions, heating rate and carrier gas flow rate had negligible effect on product yields and properties. Increasing maize cob content in briquettes resulted in an increase in the yield of bio-oil from 48 to 51% at the expense of char yield, due to the low ash and fixed carbon content of the maize cob. Combustion and pyrolysis of raw/untreated and torrefied maize cob and bean straw in a thermogravimetric analyzer occurred through moisture release, devolatilization and char degradation. The kinetic study of raw maize cob and bean straw combustion/pyrolysis revealed that the average activation energies of maize cob and bean straw were 202.26 kJ mol-1 and 165.64 kJ mol-1 for combustion and 214.15 kJ mol-1 and 252.09 kJ mol-1 for pyrolysis. Modelled data of pyrolysis and combustion of bean straw and maize cob using the obtained kinetic parameters agreed well with the experimental data, which will be useful in reactor design for energy generation via pyrolysis and combustion from agricultural residues. The findings of this study could help in promoting the use of agricultural residues for energy generation which will potentially lessen the impacts of global warming, diversify and decentralize the energy supply through the improved management/utilisation of agricultural wastes. Briquette production, torrefaction and pyrolysis could provide opportunities for the local population to increase employment and income in rural areas. This study will also provide a reference for future research on densification and utilisation of agricultural residues for energy generation.Commonwealth Scholarship Commissio

Release of Hydrogen from Nanoconfined Hydrides by Application of Microwaves

The release of hydrogen from solid hydrides by thermolysis can be improved by nanoconfinement of the hydride in a suitable micro/mesoporous support, but the slow heat transfer by conduction through the support can be a limitation. In this work, a C/SiO2 mesoporous material has been synthesized and employed as matrix for nanoconfinement of hydrides. The matrix showed high surface area and pore volume (386 m²/g and 1.41 cm³/g), which enabled the confinement of high concentrations of hydride. Furthermore, by modification of the proportion between C and SiO2, the dielectric properties of the complex could be modified, making it susceptible to microwave heating. As with this heating method the entire sample is heated simultaneously, the heat transfer resistances associated to conduction were eliminated. To demonstrate this possibility, ethane 1,2-diaminoborane (EDAB) was embedded on the C/SiO2 matrix at concentrations ranging from 11 to 31%wt using a wet impregnation method, and a device appropriate for hydrogen release from this material by application of microwaves was designed with the aid of a numerical simulation. Hydrogen liberation tests by conventional heating and microwaves were compared, showing that by microwave heating hydrogen release can be initiated and stopped in shorter times.2019-04-0

Study of the Thermal Behavior of Almond Shells and Acorn Cups for Production of Fuel Briquettes

Because of the importance of his field, its neutrality in terms of pollution, biomass sector is an attractive way for the promotion of renewable energies, the fight against deforestation and the protection of our environment. In Morocco, almond shells and acorn cups  are still rejected as a  solid waste, while they can be a source of renewable energy and provide a continuous supply of solid liquid and gas fuels, through a thermochemical conversion. The conversion of acorn cups and almond shells to energy by thermochemical conversion processes requires a fundamental understanding of their thermal properties. The purpose of this research is to investigate the thermal behavior of these wastes, its energy recovery by the production of fuel briquettes from roasted fine and to study combustion behavior of these briquettes. The results of thermogravimetry (TGA), derivate thermogravimetry (DTG) and differential thermal (DTA) analysis allowed us to determine the stages of thermal decomposition of acorns cups and almond shells and associated phenomena. Characterization of briquettes showed us that the particle size and residence time during roasting are the determinants factors of their quality. Keywords: Renewable energy, fuel briquettes, almond shells, acorn cups

Effect of Particle Size and Starch Gelatinization on the Mechanical and Metallurgical Performance of Jarosite Plus Blast Furnace Sludge Self-Reducing Briquettes

Jarosite and blast furnace sludge (BFS) are two of the main wastes from hydrometallurgical zinc production and iron production by blast furnace, respectively. Jarosite is a hazardous material that can, however, be reused in the steel industry after the recovering of the iron contained within it through carbothermal reduction in which BFS is exploited as a reducing agent. Yet, both wastes have a powdery nature that makes it necessary to agglomerate them for industrial use. On the other hand, despite the advantages of producing a self-reducing product, the particle size of the starting powders and the level of gelatinization of the binder could play a crucial role on the mechanical and metallurgical performance and, consequently, on the industrial applicability of the briquettes. Accordingly, two powder particle sizes (very fine sand vs. coarse silt) and three degree of corn starch binder retrogradation (10%, 30% and non-gelatinized starch) were used to produce briquettes, and their influence was studied by experimental and statistical investigation. The results showed that gelatinization plays the main role on the mechanical properties of briquettes, while particle size affects both density and reduction behavior; in particular, although all the mixtures were able to recover iron at 950 °C the most optimal mixture were obtained by using a granulometry of 63–125 μm for jarosite and less than 63 μm for BFS, while the local maximum of mechanical performance was obtained for a 30% starch retrogradation level

Converting Arabica Coffee Parchment into value added products: Technical and Economic Assessment

The coffee processing industry is experiencing a continuous rise in residues due to increased coffee-cherry production. However, the utilization of coffee parchment, which contains toxic compounds, remains limited and requires further investigation. This study aims to convert coffee parchment into biochar for potential use as a raw material for porous carbon material. The research was conducted using a purpose-built pilot-scale reactor. The goal was to address challenges related to operational cost, simplicity in operation, and maintenance, utilizing the Net Present Value (NPV) approach. Results indicated that coffee parchment comprised 34.5% biochar, 42.15% bio-oil, and balanced un-condensable-gas. Additionally, biochar products consisted of 42.02% fixed carbon and 38.63% volatile matter. The pyrolysis equipment designed for coffee parchment showcased economic viability, considering optimized annual operating days and scalability for production. Key words: Biochar; Economic analysis; Hydrogen storage; Pyrolysis

Biomass–Coal Hybrid Fuel: A Route to Net-Zero Iron Ore Sintering

The global steel industry uses fossil fuels to produce millions of tonnes of iron ore sinter each year. Sintering is an energy-intensive process that fuses iron ore and flux to produce material that balances a high mechanical strength at a sufficient particle size to ensure a macroporous burden in the blast furnace to enable rapid gas flow. As significant CO2 greenhouse emissions are emitted, the defossilisation of these CO2 emissions is vital to net-zero carbon targets. Two iterations of a new biomass–coal hybrid fuel (ecoke®(A) and ecoke®(B)) were compared with coke breeze and an anthracite coal using oxygen bomb calorimetry, simultaneous thermal analysis (STA) combining thermogravimetry and differential scanning calorimetry, and isoconversional kinetic modelling and pyrolysis–GCMS to study the volatile matter. The calorific values of both ecoke®(A) and (B) were marginally higher than that of the coke breeze: 27.9 MJ/kg and 27.8 MJ/kg, respectively, compared with 26.5 MJ/kg for the coke breeze. A proximate analysis revealed both ecoke® samples to have higher volatile matter contents (ca. 12–13%) than the coke breeze (7.4%), but less than the anthracite coal (ca. 14%). The thermogravimetric analysis of the burnout kinetics of the fuels heated up to 1000 °C, at heating rates from 5 to 25 °C/min, showed that that the coke breeze and anthracite coal had higher ignition and burnout temperatures than the ecoke® samples. Kinetic analysis using the Freidman and Ozawa methods found that the ecoke® samples showed comparable maximum mass loss rates to the coke breeze but lower activation energies. From these results, both ecoke® samples have the potential to replace some of the coke breeze in the sintering process or EAF processes to help achieve net zero by offsetting up to 30% of the CO2 emissions

Comparative analyses of three olive mill solid residues from different countries and processes for energy recovery by gasification

International audienceBiomass is a renewable energy source which may provide a significant contribution to the reduction of fossil fuels consumption and the associated environmental impacts. The use of agricultural or agro-industrial waste such as solid residues from olive oil production is particularly relevant since it may combine several benefits. Gasification is a promising waste-to-energy technique for this type of lignocellulosic residues. The technology however is adapted to a relatively limited panel of solid waste fuels of defined specifications, which must therefore be characterized properly to assess their adaptation. The purpose of this research was to analyze and compare three different olive mill solid residues by complementary techniques such as Fourier transform infrared spectroscopy (FTIR) and thermochemical methods, in order to characterize these residues as potential fuels for gasification. The results obtained underlined the complex nature of the residues and indicated that they were mainly organic, with very little mineral matter. In addition to the major organic components (cellulose, hemicelluloses and lignin), the presence of several minor organic constituents was shown by thermogravimetry coupled to differential scanning calorimetry and FTIR. The gas produced from pyrolysis was analyzed by gas chromatography and mass spectrometry. It was found to contain several degradation products from lignocellulosic material and olive oil, such as hydroxyacetone, furfural and methoxyphenols. The influence of the olive oil extraction process (two-phase or three-phase) was also demonstrated. It was shown that the thermochemical degradation of olive mill residues followed a complex pathway but the composition of the residues met the requirements for gasification for most parameters