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.     

Synthetic Chain Terminators Off‐Load Intermediates from a Type I Polyketide Synthase

Modular biocatalysis is responsible for the generation of countless bioactive products and its mining remains a major focus for drug discovery purposes. One of the enduring hurdles is the isolation of biosynthetic intermediates in a readily‐analysed form. We prepared a series of nonhydrolysable pantetheine and N‐acetyl cysteamine mimics of the natural (methyl)malonyl extender units recruited for polyketide formation. Using these analogues as competitive substrates, we were able to trap and off‐load diketide and triketide species directly from an in vitro reconstituted type I polyketide synthase, the 6‐deoxyerythronolide B synthase 3 (DEBS3). The putative intermediates, which were extracted in organic solvent and characterised by LC‐HR‐ESI‐MS, are the first of their kind and prove that small‐molecule chain terminators can be used as convenient probes of the biosynthetic process.     

Dielectric properties of polymer-derived ceramic reinforced with boron nitride nanotubes

The electrical and dielectric properties of boron nitride nanotubes (BNNTs) reinforced ceramic composites using the polymer-derived ceramic (PDC) processing route were investigated in this work. The electrical resistivity of the pristine PDC increases from 10⁶ to 10⁸ Ω m after the addition of BNNTs. When the BNNT loading was increased to 5 wt%, the average real relative permittivity of the PDC decreased from 2.94 to 2.80, while the quality factor (Q) of the PDC increased from 134.40 to 176.77. The BNNTs can increase the Q factor of the PDC due to the reduction in the porosity cause by the introduction of the BNNTs. Further increasing the BNNT content decreases the real relative permittivity of the nanocomposites and increases the Q factor at high frequency. The average real relative permittivity decreases to 2.29, while the average Q factor increases to 208.60 when the BNNT content is increased to 30 wt%. The dielectric loss after the addition of high fraction of BNNTs can be explained by the Lorentz resonance relaxation process. Results of this work showed that PDC-BNNT nanocomposites are satisfactory electromagnetic transparent materials when the BNNT fraction is less than 10 wt%.     

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.     

Population dynamics of yeasts inhabiting bioethanol production with cell recycling

Seeking to understand the dynamics of the yeast population in a bioethanol fermentation process that uses cell recycling, the yeast inhabiting the fermentation tanks throughout the production season were monitored. A total of 26 yeasts were isolated from tanks in a Brazilian bioethanol distillery plant during six different periods of the season. These yeasts were evaluated with regard to fermentative capacity and all yeasts were qualified to be used for bioethanol production. Based on the numerical taxonomy, it was possible to say that they were all representative of Saccharomyces sensu stricto. A total of 10 different banding patterns were obtained from the 16 strains isolated. This work has shown that the yeast introduced at the beginning of the season was quickly replaced by one or more native yeast strains. It was also shown that the replacement of these strains is not always harmful to the process and isolating such yeasts found in the fermentation tanks could be an interesting strategy for new strain selection. Copyright © 2015 The Institute of Brewing & Distilling