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Simulation and modeling of thermal recuperative incinerators may play an important role in enhancing efficiency and ensuring compliance with environmental regulations. In this context, the primary objective of this study is to simulate and comprehensively understand the operation of a geometrically complex thermal recuperative incinerator with an integrated preheater featuring varying levels of heat recovery. To achieve this objective, a simple yet effective 0D model was developed. This modeling approach allows for a holistic evaluation of the performance of the incinerator, enabling the assessment of key parameters, such as temperatures and heat transfer rates, under varying operating conditions. Successful validation of the model is established by comparing its results with measurements from an industrial thermal recuperative incinerator in operation at a vehicle assembly plant, with maximum relative differences of around 9%. Simulations for different percentages of flue gases bypassing the preheater were conducted, indicating a good compromise between heat transfer and pressure drop and a 22% heat recovery at around 50%. The model presented in this paper provides a robust foundation for comprehensively assessing and optimizing the performance of thermal recuperative incinerators and systems that comprise thermal recuperative incinerators, with implications for waste management and sustainable energy recovery systems.

Porous baffles can be used to enhance heat transfer in various engineering applications, including electronic cooling, gas turbine blades, and chemical reactors. Also, the backward-facing step is a widely used configuration in fluid dynamics studies due to its simplicity and relevance to real-world geometries. This study examines heat transfer and flow characteristics in a backward-facing step channel featuring a heated bottom wall and two porous baffles. A computational fluid dynamics model, validated against prior research, is used to investigate flow and temperature fields. The innovation of this work lies in the application of multi-objective optimisation to search for a set of solutions that establish a trade-off between the average Nusselt number and the pressure drop. The optimisation specifically considers various parameters of the porous baffles, including height, width, distance from the step, and Darcy number, to identify optimal design configurations. Results show that porous baffles significantly improve heat transfer compared to a backward-facing step channel without them, despite an increase in pressure drop due to their presence. This work offers valuable insights into the trade-off between heat transfer performance and pressure drop, crucial for designing efficient heat transfer systems. By exploring the Pareto-Frontier, which represents various optimal design solutions, the study provides practical guidance when seeking to optimise heat transfer in backward-facing step channels with porous baffles. The findings contribute to advancing the understanding of heat transfer enhancement, highlighting the potential of porous baffles as a viable solution for improving thermal management in engineering systems.

Studies that quantify forest bioenergy potentials hardly address the questions of site quality, proportion and type of residues removed from the stands, and environmental impacts of those removals. However, those factors are important for energy-potential results and forest sustainability. This study compares, in terms of residual biomass availability for energy production and of sustainability, different locations, site indices, and forest management strategies in Eucalyptus globulus stands for pulp and paper in northern and central Portugal. A growth and production simulator was used to calculate the availability of residues and the area needed to supply a biomass-fired power plant under a variety of scenarios. Regions with more rainfall generate more residues, but site index and quantity and type of residues harvested are the most important factors. Under the different scenarios analyzed, the amount of residues potentially harvested range from 0.7 to 4.3 Mg ha−1 a−1, the upper bound corresponding to a scenario where stumps are valorized. The maximization of residue removal maximizes the bioenergy produced but has to be considered prudently. Studies indicate that stump removal has limited effect on Eucalyptus globulus stand productivity, diversity, and system sustainability, but impacts of residue removals increase with a decrease in site index.

Wastewater treatment plants (WWTP) located in regions far from a high-pressure grid can produce renewable biomethane, which can partially substitute the natural gas locally consumed. However, the economic viability of implementing biomethane plants in WWTP has to be guaranteed. This paper uses the discount cash flow method to analyze the economic viability of producing biomethane in a WWTP located in Évora (Portugal). The results show that, under the current conditions, it is unprofitable to produce biomethane in this WWTP. Since selling the CO2 separated from biogas may result in an additional income, this option was also considered. In this case, a price of 46 EUR/t CO2 has to be paid to make the project viable. Finally, the impact of potential government incentives in the form of feed-in premia was investigated. Without selling CO2 , the project would only be profitable for feed-in premia above 55.5 EUR/MWh. If all the CO2 produced was sold at 30 EUR/t CO2 , a premium price of 20 EUR/MWh would make the project profitable. This study shows that the economic attractiveness of producing biomethane in small WWTP is only secured through sufficient financial incentives, which are vital for developing the biomethane market with all its associated advantages.

Since black carbon concentrations are useful to reveal changes in anthropogenic activities, measurements taken from 2007 to 2015 in a Portuguese city are used to assess to which extent the ambient air was impacted by the economic crisis. The average black carbon concentrations are representative of an urban area of small size (1.3 ± 1.3 μg m −3 ). The highest concentrations are observed in the heating season, being biomass combustion one of the causes for the high values. The daily cycle of black carbon concentrations presents both morning and evening peaks, mainly due to road traffic and, in the heating season, to domestic heating as well. The yearly averaged black carbon mass concentrations decreased 33 % from 2007 to 2015, possibly due to a combination of the economic recession and environmental legislation. The reduction in road traffic led to a decrease in the daily morning peak from 2007 to 2015. This reduction was not followed by a decrease in the evening peak, explained by an increase in biomass burning. Biomass is the cheapest heating fuel in Portugal, and its consumption increased in the aftermath of the economic crisis. The use of bioenergy is an alternative to fossil fuels and presents many advantages. However, energy policies should discourage inefficient biomass burning and promote better ways of exploiting the available energy resources and emission air pollution mitigation strategies.

In 2014, Portugal was the seventh largest pellets producer in the World. Since the shortage of raw material is one of the major obstacles that the Portuguese pellets market faces, the need for a good assessment of biomass availability for energy purposes at both country and regional levels is reinforced. This work uses a Geographical Information System environment and remote sensing data to assess the availability and sustainability of forest biomass residues in a management unit with around 940 ha of maritime pine forest. The period considered goes from 2004 to 2015. The study area is located in Southwestern Portugal, close to a pellets factory; therefore the potential contribution of the residual biomass generated in the management unit to the production of pellets is evaluated. An allometric function is used for the estimation of maritime pine above ground biomass. With this estimate, and considering several forest operations, the residual biomass available was assessed, according to stand composition and structure. This study shows that, when maritime pine forests are managed to produce wood, the amount of residues available for energy production is small (an average of 0.37 t ha-1 year-1 were generated in the study area between 2004 and 2015). As a contribution to the sustainability of the Portuguese pellets industries, new management models for maritime pine forests may be developed. The effect of the pinewood nematode on the availability of residual biomass can be clearly seen in this study. In the management unit considered, cuts were made to prevent dissemination of the disease. This contributes to a higher availability of forest residues in a specific period of time, but, in the medium term, they lead to a decrease in the amount of residues that can be used for energy purposes.

Inlet and outlet pressure drop effects can contribute significantly to the total pressure drop in porous media if thin solid matrices are used. However, these effects are usually ignored and few are the studies that focus on this topic. This paper uses a numerical simulation approach to determine the importance of the inlet and outlet pressure drop effects on the total pressure drop in a staggered arrangement of square cylinders with equal sizes, dc. The Navier-Stokes equations are solved at the pore level for several matrix lengths (from dc to 34dc) and for several Reynolds numbers based on dc and maximum velocity of the velocity inlet profile (from 36 to 120). Accurate results of the velocity and pressure fields are obtained through the use of the immersed boundary method in combination with the finite differences method, 4th-order compact schemes for spatial discretization and 4th-order Runge-Kutta temporal discretization. The results presented in this paper confirm that the classical models (e.g., Hazen-Dupuit-Darcy model) are only valid when the solid matrix has a length above a certain value, called the critical length. For shorter porous media, the pressure drop does not vary linearly with the matrix length. The deviations to the model that occur at the shortest porous media are explained by the entrance and exit contributions to the total pressure drop that, in these cases, are not negligible when compared to the bulk pressure drop. For the staggered array of square cylinders and range of Reynolds numbers considered, the critical porous medium length is 16dc. A practical outcome of the present study is the quantification of the influence of the pressure tap locations on the measurements of pressure drop in porous media. When the matrix is short when compared to the particle diameter, care must be taken with the pressure taps placement: they should be located outside the porous matrix and not too close to its inlet and outlet sections. If the matrix is thick enough when compared to the particle diameter, the taps can be placed either inside or outside the matrix. Also, if the influence of the side walls on the total pressure drop is not high (i.e., the walls are at a relative large distance when compared to the particle diameter), there is no practical need to correct the measured pressure values to account for the influence of the walls. This correction should be considered for the shortest matrices though.