• Energy Research

Abstract In the present study, a mathematical approach is utilized so as to modeling the flame structure of organic dust particle and air through a two-phase mixture consisting in a counterflow configuration where heat loss is taken into account. Lycopodium is considered as the organic fuel in our research. In order to simulate combustion of organic dust particles, a three-zone flame structure has been considered; preheat-vaporization zone, reaction and post flame zones. The variations of the gaseous phase mass fraction and fuel particle mass fraction as a function of the distance from the stagnation plate are obtained. Subsequently, flame temperature and flame velocity in terms of strain rate are studied. Finally, the effect of heat loss on the non-dimensionalized temperature at different heat loss coefficients is investigated.

Abstract In the present study, a mathematical approach is utilized so as to modeling the flame structure of organic dust particle and air through a two-phase mixture consisting in a counterflow configuration where heat loss is taken into account. Lycopodium is considered as the organic fuel in our research. In order to simulate combustion of organic dust particles, a three-zone flame structure has been considered; preheat-vaporization zone, reaction and post flame zones. The variations of the gaseous phase mass fraction and fuel particle mass fraction as a function of the distance from the stagnation plate are obtained. Subsequently, flame temperature and flame velocity in terms of strain rate are studied. Finally, the effect of heat loss on the non-dimensionalized temperature at different heat loss coefficients is investigated.

This article presents the structure of laminar, one-dimensional, and steady-state flame propagation in uniformly premixed wood particles. In order to predict the effect of radiation and particle size on the pyrolysis of biomass particles, the flame structure is divided into three regions: a preheat vaporization zone where the rate of the gas-phase chemical reaction is small; a narrow reaction zone composed of three zones (gas, tar, and char combustion) where convection and the rate of vaporization of the fuel particles are small; and finally a convection zone where diffusive terms in the conservation equation are small. In this model, it is assumed that fuel particles vaporize first to yield a gaseous fuel of known chemical structure. The analysis is performed in the asymptotic limit, where the value of the characteristic Zeldovich number is large and the equivalence ratio is larger than unity (i.e. ϕu≥1). The overall investigation of this study leads to a novel non-linear burning velocity correlation. Consequently, the impacts of radiation and particle size as determining factors on the combustion properties of biomass particles are declared in this research.

This article presents the structure of laminar, one-dimensional, and steady-state flame propagation in uniformly premixed wood particles. In order to predict the effect of radiation and particle size on the pyrolysis of biomass particles, the flame structure is divided into three regions: a preheat vaporization zone where the rate of the gas-phase chemical reaction is small; a narrow reaction zone composed of three zones (gas, tar, and char combustion) where convection and the rate of vaporization of the fuel particles are small; and finally a convection zone where diffusive terms in the conservation equation are small. In this model, it is assumed that fuel particles vaporize first to yield a gaseous fuel of known chemical structure. The analysis is performed in the asymptotic limit, where the value of the characteristic Zeldovich number is large and the equivalence ratio is larger than unity (i.e. ϕu≥1). The overall investigation of this study leads to a novel non-linear burning velocity correlation. Consequently, the impacts of radiation and particle size as determining factors on the combustion properties of biomass particles are declared in this research.

Abstract Solar supercritical water gasification (SCWG) of biomass has attractive advantages for liquid fuel production, but only very few system-level concepts have so far been investigated. Here, a solar SCWG reactor is integrated with a downstream solar reforming reactor and a supplementary hydrogen supply (assumed from photovoltaic-powered electrolysis), to produce syngas at the H2:CO ratio required for liquid fuels synthesis. Three alternative reforming reactor options are considered. The overall process, excluding the liquid synthesis, is modelled as a steady-state process in Aspen Plus, with detailed heat transfer modelling for most process units. Reactors are modelled as idealised equilibrium reactors, due to the absence of kinetics data in the case of SCWG. Optimal process parameters are determined through parameter studies: algae concentration should be high (25% by mass, at the limit of pumping), as should the SCWG reactor temperature (605 °C, within pipework material limits, at 24 MPa pressure) and reformer temperature (1050 °C in the case of steam methane reforming). Overall exergy efficiency declines strongly at reduced algae concentrations, since lower concentrations necessitate greater recirculation of water, and cause consequently higher exergy destruction in heat exchangers and separators. Char production is another factor that greatly affects process efficiency, and the lack of good models and data mean that further work is required to understand and control this factor. Alternative reformer options (steam methane reforming, autothermal reforming and partial oxidation/dry reforming) had negligible affect on the overall process carbon, exergy or energy efficiency (88%, 71% and 45%, respectively, at the optimal design point), but greatly affected the amount of H2 required from the supplementary photovoltaic-electrolysis system. This tradeoff offers interesting design choices for hybridised solar-thermal/photovoltaic solar-fuel systems, which should be the topic of future technoeconomic analysis.

Abstract Solar supercritical water gasification (SCWG) of biomass has attractive advantages for liquid fuel production, but only very few system-level concepts have so far been investigated. Here, a solar SCWG reactor is integrated with a downstream solar reforming reactor and a supplementary hydrogen supply (assumed from photovoltaic-powered electrolysis), to produce syngas at the H2:CO ratio required for liquid fuels synthesis. Three alternative reforming reactor options are considered. The overall process, excluding the liquid synthesis, is modelled as a steady-state process in Aspen Plus, with detailed heat transfer modelling for most process units. Reactors are modelled as idealised equilibrium reactors, due to the absence of kinetics data in the case of SCWG. Optimal process parameters are determined through parameter studies: algae concentration should be high (25% by mass, at the limit of pumping), as should the SCWG reactor temperature (605 °C, within pipework material limits, at 24 MPa pressure) and reformer temperature (1050 °C in the case of steam methane reforming). Overall exergy efficiency declines strongly at reduced algae concentrations, since lower concentrations necessitate greater recirculation of water, and cause consequently higher exergy destruction in heat exchangers and separators. Char production is another factor that greatly affects process efficiency, and the lack of good models and data mean that further work is required to understand and control this factor. Alternative reformer options (steam methane reforming, autothermal reforming and partial oxidation/dry reforming) had negligible affect on the overall process carbon, exergy or energy efficiency (88%, 71% and 45%, respectively, at the optimal design point), but greatly affected the amount of H2 required from the supplementary photovoltaic-electrolysis system. This tradeoff offers interesting design choices for hybridised solar-thermal/photovoltaic solar-fuel systems, which should be the topic of future technoeconomic analysis.

This paper focuses on how the low-cost renewable H2 can change a process design configuration in solar fuel plant. As a case study, an industrial process is considered in detail at ANU to convert the algal biomass into Fischer–Tropsch liquid fuels via solar-powered supercritical water gasification (SCWG). The yield gases from the gasifier mainly contain methane, which is then converted into the suitable composition of syngas in the steam methane reforming (SMR) process. Two scenarios are evaluated here to balance the H2:CO ratio for the downstream process: (i) dumping a fraction of carbon in the form of CO2, (ii) supplying make-up H2 from PV-driven electrolysis unit. A detailed steady-state model of the SCWG-SMR and FT plants is developed in Aspen Plus software. The performance curves of gasification/FT units at design and off-design points together with a set of control logics is used to form an energy-based system-level dynamic model in OpenModelica. The levelised cost of fuel (LCOF) as a key parameter for system optimisation is calculated for the considered scenarios. It is revealed that the preferred process design choice of the whole plant is highly affected by the H2 price from a techno-economic standpoint. If the H2 cost falls by 42% (i.e. 5.6 AUD/kg), the SMR-H2 configuration is more economically feasible as compared to the SMR-dumping scenario.