Michael Owen

Solar Aided Power Generation (SAPG) provides a pathway to leverage existing coal-fired infrastructure while enhancing Renewable Energy penetration in a cost-effective manner. By integrating Concentrated Solar Thermal (CST) energy into coal power cycles, SAPG enables reduced coal consumption for the same output, or increased generation for the same fuel use. Countries with high Direct Normal Irradiation (DNI) and strong reliance on coal are well suited for this hybrid approach. This study provides a preliminary evaluation of the techno-economics of SAPG within a South African context. A Parabolic Trough Concentrating Solar Power (CSP) system was modelled in the System Advisory Model (SAM), while a coal-fired Rankine Cycle was simulated in Python using mass and energy balance calculations. Solar heat was extracted from the CSP model and integrated into the coal plant via a feedwater heater at the boiler inlet, enabling either power boosting (displacing turbine extraction steam to the feedwater heaters) or fuel saving (reducing coal feed rate). Results show that SAPG increased net power output in boosting mode and can decrease specific coal consumption in saving mode. The Levelized Cost of Energy (LCOE) of the hybrid system is lower than that of a standalone CSP plant of equal size, demonstrating economic competitiveness. This study concludes that SAPG represents a promising transitional solution for South Africa, supporting decarbonization while maintaining grid reliability.

Supercritical carbon dioxide (sCO₂) Brayton cycles are increasingly investigated for concentrating solar power (CSP) applications due to their compactness, high efficiency, and ability to operate at elevated turbine inlet temperatures. This study presents the design and simulation of a Natural Draught Direct Hybrid Cooling Tower (NDDHCT) for heat rejection in an sCO₂ Brayton recompression cycle. The recompression configuration was selected for its high efficiency potential, with the cooling system aimed at providing reliable, low-maintenance, and low-cost operation while maintaining sCO₂ outlet temperatures of 30–35°C. Site-specific atmospheric conditions were obtained from System Advisor Model (SAM) Typical Meteorological Year (TMY) data, and cooling loads were estimated to inform design specifications. A mathematical framework was developed, and simulations were performed in FLOWNEX SE under dry, wet and hybrid operating modes. Results indicate that the NDDHCT can meet cooling requirements for approximately 75.5% annually under dry mode, 89.3% of annual operation, and up to 99.5% when only night-time conditions are considered. However, the penalty for make-up water was found to be a major constraint. The water consumption was estimated to 1103 kg/MWh for full day operation and 120 kg/MWh for night-time only. The NDDHCT simulations recorded an annual 6% improvement on its heat rejection potential. These findings highlight the potential benefit of using the hybrid natural draught cooling to enhance efficiency and sustainability of sCO₂ CSP systems in water-scarce regions.

This study investigates the integration of a natural-draft direct hybrid cooling tower (NDDHCT) with a 20 MWe supercritical carbon dioxide (sCO₂) Brayton recompression cycle (BRC) for concentrated solar power (CSP) applications. An existing thermodynamic model of the BRC was implemented in the Flownex Simulation Environment and directly coupled with the NDDHCT model to assess system performance under dry, wet and hybrid cooling modes. Annual transient simulations were conducted using typical meteorological year (TMY) data for Upington, South Africa, while maintaining a prescribed turbine inlet temperature (TIT) through automatic adjustment of cycle heat input. The results show that hybrid cooling maintained the main compressor inlet temperature (CIT) between 30 and 35°C for approximately 60% of the simulated year, below 30°C for 27%, and above 35°C for 13%. Compared with dry cooling, hybrid operation increased annual electricity production by 2.09 GWh (1%) and improved average cycle thermal efficiency by 3%. Annual water consumption was approximately 0.529 m³/MWh of electricity generated, representing a 73% reduction relative to wet cooling. These findings demonstrate the potential of integrating a dry-led NDDHCT with an sCO₂ BRC to balance power-cycle performance and water consumption in water-scarce CSP regions. The direct coupling of the cooling system and power cycle captures the influence of weather-dependent cooling performance on cycle operation and provides a basis for developing coordinated cooling and power-cycle control strategies.

The industrial sector dominates global energy usage, accounting for approximately 50% of total energy demand, with process heat representing two-thirds of this consumption. Although renewable energy technologies have become increasingly cost-competitive, industrial users have been hesitant to replace fossil fuels to meet heat generation requirements. This study presents a practical framework for industrial energy transition, proposing a phased approach toward sustainable manufacturing practices, processes, and energy technologies. The framework emphasises that while energy efficiency measures form the foundation, strategic technological investment priorities should target the replacement of fossil fuels with sustainable and renewable energy technologies. The formulation of the three-phased energy technology advancement framework is informed by techno-economic analyses across a range of technical interventions available to plant operators, namely beverage manufacturers. For South African conditions, cost–benefit analyses suggest that the industry will prioritise investments in photovoltaic and battery energy storage systems, driven by attractive returns on investment, which are expected to improve. However, sustainability plans and efforts must extend beyond immediate financial returns, particularly in terms of future space requirements and capital allocation. This more holistic approach will ensure long-term sustainability while meeting increasingly stringent environmental commitments.

Actuator-disk rotor models are important simulation tools for cost-effective industrial axial fan system analysis. Actuator-disk fan model performance, however, is constrained by the conventional use of two-dimensional airfoil coefficient input data, which limits the accuracy of the models to a narrow operating range free from significant radial blade flow. Radial blade flow is characteristic of off-design fan operation, which is often unavoidable within typical industrial fan system environments, so the enhancement of actuator-disk model performance for these conditions is desired. This paper accordingly presents a new means of robustly determining actuator-disk model coefficient inputs that are suitable for a wide range of fan operating conditions. The proposed augmented actuator-disk method (AADM) capitalizes on new insights into the unique aerodynamic behavior of low-pressure axial fan rotors. The performance of the AADM is evaluated for two different industrial cooling fans and is shown to outperform existing actuator-disk coefficient formulations through computational fluid dynamics simulations. The AADM is shown to better predict key fan performance metrics, spanwise blade force distributions, and to produce flow fields that are more physically representative (an important feature for industrial heat exchanger studies where the AADM is anticipated to be commonly applied). The AADM has been developed to be easily adopted in generic industrial fan analyses and is expected to serve as a valuable springboard for future actuator-disk fan model developments.

To decarbonise industry, which accounts for half of the total energy demand, renewable and sustainable energy solutions must be embraced. Not only to meet electricity requirements but, more importantly, to substitute fossil fuels used to generate process heat. This research assesses the cost-benefits of renewable and sustainable energy solutions for the South African beverage sector, representing an estimated 3020 GWh in annual energy demand, and provides a framework for the broader adoption of these technologies. For South African beverage producers, the study concludes that investments in photovoltaic and battery energy storage systems will continue to take priority, given the favourable 17–21 % Year-1 return on capital. However, given spatial and capital constraints, the judicious planning of solar thermal energy system requirements is advocated, to address the in-situ nature of process heat generation.

Implicit axial flow fan models are commonly used for the numerical analysis of industrial heat exchanger systems. However, these fan models perform poorly within the often complex off-design flow environments characteristic of these systems, as their low-order formulations lose applicability under highly 3D flow conditions. At off-design flow conditions, rotation and blade solidity effects cause physical fan blade behavior to deviate from the anticipated 2D behavior characterized by the implicit models. Physical fan blade behavior at off-design flow conditions, however, remains uncertain and the specific effects of rotation and solidity are not yet widely understood. This study investigates off-design fan blade behavior by presenting explicit 3D computations of two low-pressure axial flow fans. The effects of rotation and blade solidity are then identified through a side-by-side comparison of the computed 3D fan blade data against isolated 2D airfoil data. The rotating fan blade lift characteristics are shown to be distinct from the comparative 2D airfoil trends. At low-flow (off-design) operating conditions, rotation establishes large radial flow movements, and the high blade solidities cause standing vortices to develop within the rotating blade passages. The radial outflow energizes the blades' boundary layers, and the vortices inhibit the flow from separating from the blades' surfaces. Consequently, blade stall is avoided and high lift coefficient values are realized. The presented fan blade lift characteristics are unique relative to literature on other turbomachines of lower blade solidity, highlighting the importance of considering solidity effects in implicit rotor model developments.