Michael Lubwama

Using hydrogen gas for iron ore reduction offers carbon‐neutral ironmaking, but scaling up faces safety and energy challenges. Ammonia is a safer carbon‐free hydrogen carrier with higher energy density and ease of liquefaction. This study investigates the characteristics of ammonia‐based direct reduction (AmDR) of natural iron oxide using thermodynamic modeling and thermogravimetric analysis (TGA) combined with quadrupole mass spectrometry (QMS). Particle sizes of 6, 10, and 14 mm in diameter were reduced at 650–850 °C, for 4–6 h in ammonia‐flow (180 mL min ⁻¹ ). AmDR characterization process utilized X‐ray diffraction (XRD), energy‐dispersive X‐ray spectroscopy (EDS), and light/electron microscopy (LOM/SEM). Temperature and particle size significantly influence reaction kinetics and apparent reduction degree (Rd _a ). At 850 °C, all particle sizes reached >92% Rd _a . Larger particles (10 and 14 mm) reduce slowly due to internal diffusion limitations. Gas evolution profiles indicate temperature‐dependent ammonia dissociation, hydrogen generation, and transient nitrogen‐oxide formation. Microstructural analyses reveal that AmDR produced porous metallic iron containing locally interconnected pore features and surface cracking. Cross‐sectional analyses of partially reduced particles revealed progressive growth of the product layer and inward advancement of the reaction front. Kinetic analysis shows agreement with contracting‐sphere (R3) and Ginstling–Brounshtein (D4) models ( R ² > 0.97), with R3 fitting best, indicating predominant interfacial chemical‐reaction control for AmDR.

Grass is an abundant and renewable source of cellulose, which makes it a sustainable and cost‐effective source for producing cellulose nanocrystals. Moreover, the extraction of cellulose nanocrystals from grass provides a value‐added product from an otherwise low‐value agricultural waste material, which can contribute to the development of a circular economy. In this study, cellulose nanocrystals (CNCs) were extracted from Hyparrhenia filipendula via citric acid hydrolysis. The Hyparrhenia filipendula stems were pre‐processed through mechanical size reduction and Soxhlet extraction. The extractive‐free stems were fractionated using two solvents: 10 wt% (w/v) sodium hydroxide (NaOH) and deep eutectic solvent of ethylene glycol:citric acid (1:2 molar ratio). The fractionated samples were bleached with acidified sodium chlorite and hydrolyzed with 80 wt% citric acid for 4 h at 120°C in a Parr reactor. The samples obtained at each treatment stage were characterized using standard scientific procedures for chemical composition, morphology, elemental composition, crystallinity, and thermal stability. The results show that CNCs were successfully extracted from Hyparrhenia filipendula via citric acid hydrolysis. The surface morphology of alkali fractionated CNCs was needle‐like, whereas the surface morphology of DES fractionated CNCs was rod‐like. The alkali fractionated and hydrolyzed sample, NaCNC, had the highest cellulose purity (91%), as well as the highest thermal stability. The FTIR analysis proved the removal of non‐cellulosic components in the CNCs, except for the unbleached CNCs that had significant quantities of hemicellulose and lignin. The XRD analysis revealed the presence of characteristic cellulose Iβ in the CNCs, with the UNNaCNC sample (NaOH fractionated, unbleached, acid hydrolyzed sample) having the highest crystallinity index of 81% and the largest crystallite size of 4.20 nm. The properties of the CNCs obtained in this study are comparable to CNCs derived from previously reported lignocellulosic materials. The CNCs from Hyparrhenia filipendula therefore have a wide range of potential applications.

Uganda’s heavy reliance on traditional bioenergy, mainly firewood and charcoal, has led to rapid forest degradation and significant health and labor burdens, especially for women and children. However, the long-term, system-wide impacts of clean energy interventions advanced to address those challenges remain insufficiently understood. This study developed and applied a system dynamics (SD) model, using nationally calibrated time-series data and stakeholder-informed parameters, to evaluate the effectiveness of clean cooking policy strategies through 2050. The model captures endogenous feedbacks within Uganda’s firewood and charcoal value chains and assesses the effects of three core interventions: household energy diversification, adoption of efficient charcoal kilns, and uptake of modern cookstoves. Five policy scenarios were simulated: Business as Usual (BAU), Efficient Charcoal Production (ECP), Efficient Cookstoves (EC), Fuel Substitution (FS), and a Comprehensive Transition (CT) combining all three interventions. Results show that under BAU, woody biomass harvest exceeds sustainable supply levels by the early 2030s. While individual interventions reduced harvest by an average of 55% by 2050, the CT scenario stands out with an 84% reduction and a 150% improvement in cost-efficiency relative to BAU. Notably, both CT and EC scenarios transition from net costs to net savings before 2050, driven by avoided health burdens, time savings, and carbon credit revenues. These findings underscore the nonlinear, synergistic benefits of integrated policy approaches and the importance of including indirect socio-economic costs in planning. The model offers transferable insights for other biomass-dependent economies seeking to design equitable, cost-effective clean energy transitions.

Biomass briquettes are still important to communities in developing nations because they are cheap, sustainable, and generated from solid waste that can be utilized to produce energy. However, the low quality of the briquettes when compared to traditional cooking fuels hampers their widespread adoption; yet, there is an opportunity for expanding the briquette market due to the rise in charcoal prices, increasing scarcity of forest resources, and more environmental awareness among consumers. The main objective of this study was to develop a bio-based briquette with improved combustion characteristics through the use of an innovative binder. A novel nanocomposite briquette (biochar/cellulose nanocrystals (CNC)/polyvinyl alcohol (PVA) was produced using the solution casting method, with CNC/PVA nanocomposite as a binder. A total of five (5) nanocomposite briquettes having biochar-to-binder ratios of; 90:10, 80:20, 70:30, 60:40, and 50:50 and designated as BCP (9/1), BCP (8/2), BCP (7/3), BCP (6/4) and BCP (5/5), respectively were developed. The nanocomposite briquette samples were characterized for thermal stability, mechanical properties, elemental composition, surface morphology, proximate composition, and combustion characteristics using established methods. The produced briquettes had a very low ash content of less than 2% and a low average moisture content of 8%. The surface morphology of the briquettes revealed a rough and porous structure that can enhance combustion. The BCP (9/1) briquette had the highest calorific value of 27 MJ/kg, followed by BCP (8/2) and BCP (7/3) which had a calorific value of 26 MJ/kg. The BCP (7/3) nanocomposite briquette was the most thermally stable, with the lowest onset degradation temperature (220 °C), highest peak temperature (514 °C), least char residue, and the most compressive strength of 11 MPa. The BCP (9/1), BCP (8/2), and BCP (7/3) nanocomposite briquettes also satisfied the combustion indices criteria, demonstrating their potential to replace coal in industrial applications. The thermal degradation and kinetics of the nanocomposites were studied using TGA-DTG techniques at three different heating rates; 5 °C/min, 10 °C/min, 20 °C/min in an oxygen environment. The kinetic parameters, that is, the activation energy and pre-exponential factor were calculated using the Coats-Redfern method. The combustion of the briquettes happened in three distinct phases with a higher activation energy required at higher heating rates to initiate the first stage of combustion. Also, up to 40% of the binder can be added without affecting the ignition, combustion, and burn-out properties of the briquette. This study, therefore, demonstrates that Biochar-PVA-CNC nanocomposite briquettes are a potential biofuel for industrial and household applications.