Comparative performance analysis of solar powered supercritical-transcritical CO2 based systems for hydrogen production and multigeneration

CO₂ based power and refrigeration cycles have been developed and analyzed in different existing studies. However, the development of a CO₂ based comprehensive energy system and its performance analysis have not been considered. In this study, the integration of a CO₂ based solar parabolic trough collector system, a supercritical CO₂ power cycle, a transcritical CO₂ power cycle, and a CO₂ based cascade refrigeration system for hydrogen production and multigeneration purpose is analyzed thermodynamically. This study aims to analyze and compare the difference in the thermodynamic performance of comprehensive energy systems when CO₂ is used as the working fluid in all the cycles with a system that uses other working fluids. Therefore, two comprehensive energy systems with the same number of subsystems are designed to justify the comparison. The second comprehensive energy system uses liquid potassium instead of CO₂ as a working fluid in the solar parabolic trough collector and a steam cycle is used to replace the transcritical CO₂ power cycle. Results of the energy and exergy performance analysis of two comprehensive energy systems showed that the two systems can be used for the multigeneration purpose. However, the use of a steam cycle and potassium-based solar parabolic trough collector increases the comprehensive energy systems’ overall energy and exergy efficiency by 41.9% and 26.7% respectively. Also, the use of liquid potassium as working fluid in the parabolic trough collectors increases the absorbed solar energy input by 419 kW and 2100 kW thereby resulting in a 23% and 90.7% increase in energetic and exergetic efficiency respectively. The carbon emission reduction potential of the two comprehensive energy systems modelled in this study is also analyzed.     

From cassava to gari: mapping of quality characteristics and end-user preferences in Cameroon and Nigeria

User’s preferences of cassava and cassava products along the value chain are supported by specific root quality characteristics that can be linked to root traits. Therefore, providing an evidence base of user preferred characteristics along the value chain can help in the functional choice of cassava varieties. In this respect, the present paper presents the results from focus group discussions and individual interviews on user preferred quality characteristics of raw cassava roots and the derived product, gari, – one of the major cassava products in Sub-Saharan Africa – in major production and consumption areas of Cameroon and Nigeria. Choice of cassava varieties for farming is mainly determined by the multiple end uses of the roots, their agricultural yield and the processing determinants of roots that support their major high-quality characteristics: size, density, low water content, maturity, colour and safety. Processing of cassava roots into gari goes through different technological variants leading to a gari whose high-quality characteristics are dryness, colour, shiny/attractive appearance, uniform granules and taste. Eba, the major consumption form of gari in Cameroon and Nigeria, is mainly characterised by its textural properties: smoothness, firmness, stickiness, elasticity and mouldability. Recommendations are made, suggesting that breeding will have to start evaluating cassava clones for brightness/shininess, as well as textural properties such as mouldability and elasticity of cassava food products, for the purpose of supporting decision-making by breeders and the development of high-throughput selection methods of cassava varieties. Women are identified as important beneficiaries of such initiatives giving their disadvantaged position and their prominent role in cassava processing and marketing of gari.     

Why a global decarbonisation agenda needs input from well-informed millennials

The recent and growing momentum surrounding climate change and renewable-energy push especially among millennials, although encouraging, does call for concerned caution. While increased interest in low-carbon energy transitions by millennials should be acknowledged and encouraged, well researched facts devoid of emotion and politics must guide the agitation by millennials for global decarbonisation. Drawing extensively from literature and facts from the public scene, this perspective evidences that millennials are being denied significant roles in shaping their future energy-wise.     

Simultaneous Reaction-Deactivation Kinetics in N-octane and Methylcyclopentane Reforming Reactions on Platinum-Containing Catalysts

The deactivation data obtained from the multiple regeneration of platinum-containing catalysts were utilized to explore the efficiency of reforming catalyst utilization. The data were collected in a CSTR at a total pressure of 101.325 kPa and W/F values up to 0.33 g min/cm³. The reactive system investigated was the re-forming and coking of n-octane and methylcyclopentane on the monometallic Pt/Al₂O₃ and the bimetallic Pt-Re/Al₂O₃ catalysts. The deactivation models combined the kinetic equation with the coking equation; both of these equations were derived from mechanistic models. The kinetic expressions were based on the models of Susu et al. for n-octane reaction and Dartingues et al. for methylcyclopentane reaction. The coking mechanism of Corella and Asua was used for the coking reaction. The coupling of the two models resulted in a dynamic expression, and the parameter estimates were carried out without decoupling the main reaction from the coking reaction. The model formulation affords the estimation of the level of residual activity by the incorporation of a factor, f, representing incomplete deactivation. A high value of f was obtained for all deactivation-kinetic data indicating high utilization efficiency for the catalysts for the two reactants, regardless of the large difference in the coking ability of the hydrocarbon species.     

Understanding cassava varietal preferences through pairwise ranking of gari-eba and fufu prepared by local farmer–processors

Within communities in Osun and Imo States of Nigeria, farmer–processors grew and processed a diverse set of improved and landrace cassava varieties into the locally popular foods, gari, eba and fufu. Local and 15 main varieties were grown in a ‘mother and baby trials’ design in each state. Mother trials with three replications were processed by farmer–processors renown in their community for their processing skills. Baby trials were managed and processed by other farmer–processors. The objective was to identify food quality criteria to inform demand-led breeding to benefit users, especially women, given their key roles in processing. Farmer–processors evaluated the overall quality of fresh roots and derived food products through pairwise comparisons. Improved varieties had higher fresh and dry root yield. Overall, landraces ranked first for quality of gari and eba, but several improved varieties were also appreciated for good quality. Landraces in Osun had higher gari yield and a higher swelling power compared to improved varieties. Colour (browning), bulk density, swelling power, solubility and water absorption capacity were the criteria most related to food product ranking by farmer–processors. Evaluation of varieties under farmer–processors’ conditions is crucial for providing guidance to breeders on critical selection criteria.     

Biochemical properties,nutritional quality,colour profile and techno-functional properties of whole grain sourdough and malted cowpea and quinoa flours

The particular interest in biomodifications of underutilised but nutritionally distinct whole grains is vital to promote diet diversity, nutrition transition and food security. This study investigated the use of short-term solid-state fermentation and germination to ease processability and improve the quality characteristics of whole grain (WG) cowpea and quinoa flours. The fermented and germinated WG flours were prepared at 28 °C for 48 h. The biochemical, nutritional quality and techno-functional properties of the obtained flours were determined. The macromolecules’ biomodification by microbial metabolism and endogenous enzymes activation influenced quality variations in the biomodified flours. The cowpea sourdough flour (CSF) presented lower acidity (pH 4.72), higher total flavonoid (29.63 mg QE/g), total phenolic (8.21 mg GAE/g) and antioxidant activity. The flour also showed high contents of fibre (5.30%), ash (4.42%), calcium (864.49 mg/kg), potassium (12848.64 mg/kg), zinc (33.83 mg/kg), good protein (21.43%) and a moderate fat level (2.65%). Higher oil absorption and water solubility indices were also noted for CSF. In contrast, malted quinoa flour (MQF) exhibited higher swelling power, increased dispersibility and improved final, peak and trough viscosities. The CSF displayed higher redness and browning index, whereas MQF had greater lightness. The results suggest that CSF and MQF had the best complementary quality attributes. Their formulation as gluten-free, whole and multigrain ingredients may promote healthy choices for individualised growing dietary needs.