• Energy Research

This work studies a fluidization system through cold experiments by using a mixture of rice husk and sand to investigate three parameters: type of bed distributor (perforated plate and plate with Tuyere-type injectors), sand granulometry (mean diameters of 324 µm and 647 µm) and rice husk mass ratio (from 1% to 10% of rice husk). The results reveal that the perforated distributor plate achieved a lower minimum fluidization velocity. However, the plate with Tuyere injectors generated better mixing, thus reducing possible stagnation points. An increase in the mean diameter of the sand raises the minimum fluidization velocity but also facilitates the formation of preferential channels. As for the rice husk mass ratio, values of over 5% cause stagnation points and preferential channels. It was also found that the relation between minimum fluidization velocity and rice husk ratio follows an exponential behavior, and an equation was developed to better describe their relation.

Brazil has set a goal to reduce greenhouse gas (GHG) emissions, which is a significant opportunity to leverage calcium looping (CaL) technology for energy generation in natural gas power plants. CaL is a promising technology, due to sorbent low cost and availability, but its industrial implementation performance decay is a major challenge to face. While evaluating carbon-capture technologies, net emissions perspective is essential, and optimizing CaL capture through a partial carbonation cycle is a promising approach, both to reduce net emissions and improve the number of cycles before deactivation. In this context, a Brazilian dolomite was characterized and evaluated, to be used as sorbent in a CaL process employed in natural gas power plants. For such a purpose, a novel methodology has been proposed to evaluate the mass ratio of CO2 captured, to assess the energy consumed in the process. A rotatable central composite design (RCCD) model was used to identify the optimal temperature and residence time conditions in the carbonation stage of the CaL process, focusing on achieving energy efficiency. The five most promising conditions were then tested across 10 calcination–carbonation cycles, to examine the impact of partial carbonation in capture efficiency over extended cycles. The results indicate that temperature plays a critical role in the process, particularly in terms of capture efficiency, while residence time significantly affects energy consumption. The conditions that demonstrated optimal performance for both the single and the multi-cycle tests were 580 °C for 7.5 min and 550 °C for 10 min, given that index of capture efficiency (IEC10,c) values of 1.34 and 1.20 were found, respectively—up to 40% higher than at 475 °C. There was lower energy expenditure at 580 °C (Esp) (33.48 kJ), 550 °C (Esp = 37.97 kJ), CO2 mass captured (CO2cap = 9.80 mg), and the samples exhibited a more preserved surface, thus making it the most suitable option for scale-up applications.

Abstract Biomass and coal have different physicochemical properties and thermal behavior. During the co-combustion of coal-biomass mixtures, their thermal behavior varies according to the percentage of each fuel in the mixture. Thereby, this research aims to characterize the thermal behavior of mixtures of coal, sugarcane bagasse, and biomass sorghum bagasse as biomass in simulated combustion (O2/N2) and oxy-fuel combustion (O2/CO2) environments. Experiments have been performed in duplicate on a thermogravimetric analyzer at heating rate of 10 °C/min. A uniform granulometry was considered for all materials (63 μm) in order to ensure a homogeneous mixture. Four biomass percentages in the mixture (10, 25, 50 and 75%) have been studied. Based on thermogravimetric (TG) and thermogravimetric (DTG) analyses, parameters such as combustion index, synergism, and activation energy have been determined, as well as the combustion environment influence on these parameters. The results indicate that, although sugarcane bagasse has the lowest activation energy, the thermal behavior of both types of biomass is similar. Thus, biomass sorghum bagasse can be used as an alternative biomass to supply the power required during sugarcane off-season. For both mixtures, optimal results were obtained at 25% of biomass. By analyzing the environment influence on combustion behavior, the results indicate that when N2 is replaced with CO2, it is observed an increase in reaction reactivity, a higher oxidation rate of materials and an improvement in evaluated parameters.

Abstract Ignition experiments with two bituminous coals were carried out in an atmospheric bubbling fluidized bed combustor (FBC) and a thermogravimetric analyzer (TGA). In the FBC tests, the rapid increase in O2, CO2, and SO2 concentrations is an indication of the coal ignition. In the TGA technique, the ignition temperature was determined by the evaluation of the TGA curves in both combustion and pyrolysis processes. Model-Free Kinetics was applied and the coal ignition temperatures were associated with changes in the activation energy values during the combustion process. The results show the coal with the lowest activation energy also showed the lowest ignition temperature, highest values of volatile content and a higher heating value. The application of two different ignition criteria (TGA and FBC) resulted in similar ignition temperatures. The FBC curves indicated the high volatile coal ignites in the freeboard, i.e. during the feeding in the reactor, whereas the low volatile coal ignites in the bed. Finally, the physicochemical characteristics of the investigated coal types were correlated with their reactivities for the prediction of the ignition temperatures behaviors under different operating conditions as those in FBC.

Abstract A fixed bed reactor has been used to assess the influence of slow pyrolysis process parameters on biochar yield from rice husk. Taguchi's method (L9) was used for such a purpose, which four parameters varied according to three different levels: heating rate (β) of 5, 10 and 20 °C/min; temperature (T) of 300, 400, and 500 °C; residence time (t) of 3600, 5400 and 7200 s; rice husk mass (m) of 125, 250, and 500 g. ANOVA were utilized to verify the statistical significance of process parameters. Different physical-chemistry techniques have been performed to assess the energy potential of processing rice husk through thermochemical processes. The results showed that the highest biochar yield (37.71 %wt) was achieved through the following experimental conditions: 500 g of biomass, β = 20 °C/min, T = 300 °C, and t = 5400 s. However, the highest heating value (HHV = 23.41 MJ/kg) was obtained by using 125 g of biomass, β = 10 °C/min, T = 500 °C, and t = 5400 s. However, optimal conditions for higher fixed carbon content (60.10 %wt) were 500 g of biomass, β = 5 °C/min, T = 500 °C, and t = 7200 s. It was 49.05% higher than HHV found for raw rice husk. ANOVA results have revealed that temperature is the most significant parameter for the slow pyrolysis process. Furthermore, Taguchi's method was applied to define the levels of experimental conditions and optimize the process. Energy ratio assessment yielded values ranging between 0.38 and 1.77, which indicates that it is technically feasible to obtain energy gains through the slow pyrolysis of rice husk.

In view of the increasing demand for clean energy and the growing awareness of environmental sustainability, a bibliometric study examines the various facets of renewable natural gas (biomethane). Sustainable fuels are gaining importance as an alternative to fossil fuels because they are renewable and can reduce greenhouse gas emissions. In addition, an overview of the use of biomethane was compiled for Brazil. The country was chosen because it is the authors’ home country. These emerging energy sources have the potential to play a critical role in the transition to a cleaner, more sustainable and cost-effective energy landscape, thereby reducing environmental impact and strengthening the resilience of our energy future.

Mineral carbonation incurs high operating costs, as large amounts of chemicals and energy must be used in the process. Its implementation on an industrial scale requires reducing expenditures on chemicals and energy consumption. Thus, this work aimed to investigate the significant factors involved in pH-swing mineral carbonation and their effects on CO2 capture efficiency. A central composite rotatable design (CCRD) was employed for optimizing the operational parameters of the acid dissolution of serpentinite. The results showed that temperature exerts a significant effect on magnesium dissolution. By adjusting the reaction temperature to 100 °C and setting the hydrochloric acid concentration to 2.5 molar, 96% magnesium extraction was achieved within 120 min of the reaction and 91% within 30 min of the reaction. The optimal efficiency of carbon dioxide capture was 40–50%, at higher values than those found in literature, and 90% at 150 bar and high pressures. It was found that it is technically possible to reduce the reaction time to 30 min and maintain magnesium extraction levels above 90% through the present carbonation experiments.