Search

In this study, thermodynamic strategies are determined for the energy conversion of Municipal Solid Wastes (MSW) in incineration plants under sub-stoichiometric conditions. Energy generation from MSW is an alternative to mitigate the environmental impacts derived by their final disposal, being the production rate of MSW in Medellin city (Colombia) of about 1800 ton/day. The analysis is conducted by means of a thermochemical equilibrium model of the gasification process, where the effect of moisture content and fuelair equivalence ratio on the thermochemical process is studied. The energy potential of MSW from the city is between 28 and 44 MWe. The thermodynamic strategies for energy recovery from MSW in incineration plants at sub-stoichiometric conditions, under auto-thermal regimens and avoiding ash fusion, establish that the process must be carried out with a fuel-air equivalence ratio between 1.5 and 3.3, regardless of the moisture content of the MSW. [ABSTRACT FROM AUTHOR]

The biomass gasification process in fixed bed was studied by means of computational fluid dynamics (CFD) numerical analysis. The aim was to evaluate the effect of the biomass packing factor on the thermochemical process. The fuel-wood used was Jacaranda Copaia in various shapes: chips, cylinders, and cubes with packing factors (PF) of 0.38, 0.48, and 0.59, respectively. The mathematical model is a transient 2D CFD model, which was developed through the implementation of User Defined Functions in ANSYS-Fluent. The model was extended to simulate the gasification process by expanding the chemical kinetic mechanism and by adapting the stages of pyrolysis, oxidation, and reduction. The model was validated with experimental data. The average relative error between experimental and numerical data was 5.45%. By means of the sensitivity analysis, it was found that with an increase in the packing factor from 0.38 to 0.59, the absorption of radiative heat transfer increases by 27% leading to increase the solid temperature in the reaction front, but due to a lower penetration of radiation, the drying and pyrolysis reaction rates decrease. But nevertheless, the higher solid temperature with packing factor favors the convective solid-gas heat transfer in the drying stage. [ABSTRACT FROM AUTHOR]

Thermodynamic criteria as a feedstock selection tool for decentralised downdraft gasifiers coupled to spark-ignition engines are presented in this work. The methodology consists of an energy and exergy analysis of gasification process. The analysis is carried out by computational modelling of the gasification process as a function of biomass type (ultimate analysis, moisture content and heating value) and fuel/air ratio. Considering a system operating with different wood species, analysed parameters are gas heating value, energy and exergy efficiencies and engine fuel quality (EFQ). With a fixed fuel/air ratio (2.6) and moisture content (20%wt), it is highlighted that as the carbon-oxygen molar ratio of wood decreases from 2.0 to 1.78 as model input, reaction temperature increases by 9%, energy and exergy efficiencies diminish by 1.8% and 4.2%, respectively, while EFQ increases by 3.2%. Therefore, for decentralised power plants, biomass should be selected to produce higher EFQ. [ABSTRACT FROM AUTHOR]

The effect of composition and heating value of torrefied biomass under an oxidizing atmosphere at different conditions (180, 210, and 240 °C during 30, 75, and 120 minutes) was studied relative to downdraft gasification performance. An extended model for gasification in thermochemical equilibrium was used to evaluate the effect of pretreated biomasses, fuel to- air equivalence ratio, and char byproduct production on the producer gas composition, reaction temperature, cold gas efficiency (CGE), and the engine fuel quality (EFQ). The model was validated with experimental data, reaching a global relative error of 8.5%. For raw or torrefied biomasses, with regard to char production, the CGE decreases if char increases; this is due to the fact that the process tends to combustion regimes when a lower amount of carbon is involved in the gasification reaction. Otherwise, the CGE and EFQ increase (up to 80% and 2.5 MJ/kg, respectively) if fuel-to-air ratio increases. With regard to the torrefied biomass, it is highlighted that CGE and EFQ increase from 77% to 82% and from 2.2 MJ/kg to 2.5 MJ/kg, respectively, when the torrefaction conditions (temperature and/or time) increase. This behavior is related to the increase of the autothermal zones in the gasification process and due to the higher heating value of torrefied biomass. [ABSTRACT FROM AUTHOR]

• Reaction-front of oil sludge and palm kernel shell mixtures was assessed. • Higher values of flame front velocity were obtained as airflow increased. • Reactor operation tended to combustion regime as the equivalence ratio was raised. • Adsorption/desorption curves of char obtained were performed. • Char pore structure was composed mainly of micropore and mesopores. A reaction-front assessment and char characterization of a mixture of oil sludge and palm kernel shell in a fixed-bed reverse-downdraft gasifier using air as the oxidizing agent has been performed. The investigation was focused on assessing the effect of airflow (from 30 up to 60 L/min) on the reaction front as well as on the characterization of char derived from the thermochemical treatment. The thermochemical conversion process was described by output parameters such as fuel consumption rate, flame front velocity (V ff), maximum process temperature (T max), air–fuel equivalence ratio, and char yield. The char was characterized regarding its surface structure by determining Brunauer, Emmett, and Teller (BET) surface area, pore volume, and pore size distribution. The results demonstrated that as the airflow rate increased from 30 to 60 L/min, V ff and T max augmented from 4.36 to 6.49 mm/min, and from 967 to 1090 °C, respectively, as the process approached a combustion regime. In parallel, the char yield decreased from 13.4 to 4.5 % for the same airflow range due to the higher temperatures, which favors oxidation reactions. The char characterization showed that the BET surface area reached a maximum value of 269.8 m2/g at 50 L/min and subsequently decreased, which was attributed to the thermal deformation of the pore structure as the process temperature increased. Furthermore, pore size distribution showed that the char was mainly composed of micropores. Besides providing useful information related to the operation of gasifiers and char production, this analysis is particularly relevant for solutions aimed at mitigating environmental impacts, as it involves renewable sources and energy recovery. [ABSTRACT FROM AUTHOR]

Socioeconomic conditions and the main firewood species used for cooking in three Colombian regions are studied in this work. The species collected were Cordia alliodora, Guazuma ulmifolia, Eucalyptus grandis, and Pinus patula. The used patterns of biomass and socioeconomic conditions of the selected regions were defined by means of secondary information. Firewood was physicochemically characterized and the species are compared with fossil fuels with regard to emissions of CO2, energy density, and costs. The studied regions require solutions to use firewood in eco-efficient systems, since in these rural regions people use biomass as an energy source. Studied firewood species are suitable to be gasified in fixed bed reactors due to their high volatile matter content (>80%) and low ash content (<1.8%). Pinus patula is the one with the highest fuel value index, mainly due to its low ash content (0.4%). The firewood consumption in advanced stoves has environmental advantages resulting from its low CO2 emissions: a cubic meter of Eucalyptus could replace 113 liters of kerosene or 120 m3 of natural gas for cooking applications. [ABSTRACT FROM AUTHOR]

The objective of this work was to study the effect of torrefaction temperature on properties of patula pine (Pinus patula) wood that could be of interest for further thermochemical processing. Torrefaction temperature was varied from 200 to 300 °C for 30 minutes using a batch spoon type reactor. Raw and torrefied materials were characterized for proximate and ultimate analyses, thermogravimetry, and pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). Results showed that torrefied pine has greater higher heating value and chemical exergy due to the reduction of O/C and H/C ratios. Compared with raw biomass, the material torrefied at 200 and 250 °C did not present significant changes in chemical composition and thermal behavior. Conversely, material torrefied at 300 °C did show important changes in both chemical composition and thermal behavior. Py-GC/MS results suggested that the main constituents of biomass, i.e., hemicellulose, cellulose and lignin, suffer a progressive thermal degradation with increase in torrefaction temperature. [ABSTRACT FROM AUTHOR]

In this work is studied the effect of biomass packing factor (PF) and oxygen enriched air as gasifying agent (GA) on fixed bed biomass gasification. Oxygen concentrations in GA are 21, 24 and 29% vol. The biomass used as fuel is Jacaranda Copaia wood with three defined particle forms: square prism, cylindrical and chips. Flame front velocity and biomass consumption rate increase with oxygen concentration in the GA. These results are due to smaller amount of nitrogen involved in the process, which leads to decrease thermal energy losses by nitrogen heating. Moreover, lower convective cooling effect of gas over solid phase and lower radiation attenuation in the solid are reached with less nitrogen concentration in GA. The efficiency slightly increases when PF increases, this is due to less radiation penetration from the oxidation zone to drying and pyrolysis stages, thereby biomass consumption rate decreases. [ABSTRACT FROM AUTHOR]

A detailed sensitivity analysis is performed on a one-dimensional fixed bed downdraft biomass gasification model. The aim of this work is to analyze how the heat transfer mechanisms and rates are affected as reaction front progresses along the bed with its main reactive stages (drying, pyrolysis, combustion and reduction) under auto-thermal conditions. To this end, a batch type fixed-bed gasifier was simulated and used to study process propagation velocity of biomass gasification. The previously proposed model was validated with experimental data as a function of particle size. The model was capable of predicting coherently the physicochemical processes of gasification allowing an agreement between experimental and calculated data with an average error of 8%. Model sensitivity to parametric changes in several model and process parameters was evaluated by analyzing their effect on heat transfer mechanisms of reaction front (solid–gas, bed–wall and radiative in the solid phase) and key response variables (temperature field, maximum solid and gas temperatures inside the bed, flame front velocity, biomass consumption and fuel/air ratio). The model coefficients analyzed were the solid–gas heat transfer, radiation absorption, bed–wall heat transfer, pyrolysis kinetic rates and reactor-environment heat transfer. On the other hand, particle size, bed void fraction, air intake temperature, gasifying agent composition and gasifier wall material were analyzed as process parameters. The solid–gas heat transfer coefficient (0.02 < correction factor < 1.0) and particle size (4 < diameter < 30 mm) were the most significant parameters affecting process behavior. They led to variations of 88% and 68% in process velocity, respectively. [ABSTRACT FROM AUTHOR]

In this work is presented a repeatability study applied to a cookstove based on wood pellets gasification (19.03 MJ/kg). The analysis is carried out under a modified water boiling test (WBT 4.2.3). The repeatability of the gasification-based cookstove was assessed by means of two methodologies, such as the variation coefficient (CV, %) and the analysis of variance (ANOVA). The answer variables evaluated under repeatability were the efficiency (η, %), power (P, kW), fuel consumption (FC, g/min), fuel specific consumption (SFC, g/L), energy specific consumption (SFEC, kJ/L), and energy specific consumption per unit time (SFCT, kJ/L-min). By the CV analysis, the global average CV was 4.69% ± 0.87%. Therefore, as CV ≤ 5%, it is concluded that the gasification based cookstove is statistically repeatable. Concerning the ANOVA, the P-values of the variables studied were higher than 0.05 (P>0.05), thereby, it is stated that the improved cookstove is repeatable with a confidence level of 95%. Consequently, it is highlighted that the average thermal efficiency reached by the cookstove is ~29% ± 2.25%, with a confidence level of 95%. This thermal efficiency value is comparable with other biomass cookstoves based on gasification reported in the literature with values between 16 and 38%. The methodology and the results of this work constitute a theoretical foundation for assessing future developments of biomass cookstoves since the results reliability found in the prototypes tested at the laboratory level can be quantified and analyzed. [ABSTRACT FROM AUTHOR]

The technical, energy, social and environmental benefits of the integration of commercial forest crops in Colombia under biorefinery concepts are evaluated. This concept is part of various programs use of biomass as an alternative source to the silvicultural potential of the country. In this paper we review some specific processes that can be evaluated as integration strategies with high potential to use the wood planted in Colombia under biorefinery concepts. The processes considered are low-middle power gasification, industrial scale gasification to high quality biofuel production, wood pretreatment to improve the solid biofuel and alternative methods for biochar production. Finally, we also review the value-added wood products market. To conclude we highlight the potential of Colombian forest in this industry, Through strategic alliances between universities, research centers and the forestry sector, more efficient and innovative development of new valueadded products should be sought, taking advantage of the unexplored market opportunities in Colombia for bioenergy and bioproducts. This review aims to advance knowledge on the features and possible uses of forest species to produce bioenergy, biofuels, and bioproducts sustainably. [ABSTRACT FROM AUTHOR]

SUMMARY This study aimed at presenting a model to simulate downdraft biomass gasification under steady-state or unsteady-state conditions. The model takes into account several processes that are relevant to the transformation of solid biomass into fuel gas, such as drying; devolatilization; oxidation; CO2, H2O, and H2 reduction with char, pressure losses, solid and gas temperature, particle diameter, and bed void fraction evolution; and heat transfer by several mechanisms such as solid-gas convection, bed-wall convection, and radiation in the solid phase. Model validation is carried out by performing experiments in two lab-scale downdraft fixed bed reactors (unsteady-state conditions) and in a novel industrial pilot plant of 400 kWth-100 kWe (steady-state conditions). The capability of the model to predict the effect of several factors (reactor diameter, air superficial velocity, and particle size and biomass moisture) on key response variables (temperature field, maximum temperature inside the bed, flame front velocity, biomass consumption rate, and composition and calorific value of the producer gas) is evaluated. For most response variables, a good agreement between experimental and estimated values is attained, and the model is able to reproduce the trend of variation of the experimental results. In general terms, the process performance improves with higher reactor diameter and lesser air superficial velocity, particle size, and moisture content of biomass. The steady-state simulation appears to be a versatile tool for simulating different reactor configurations (preheating systems, variable geometry, and different materials). Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The main objective of this paper is to study the effect of operating and design parameters, mainly reactor geometry, air superficial velocity, biomass moisture content, particle size and biomass type (pine bark and sewage sludge), on the performance of the gasification/combustion process of waste biomass in fixed bed downdraft reactors. This experimental approach allows optimizing the dynamic behavior of the thermochemical process. Emphasis was put on interactions between the mentioned parameters with output or response variables, such as biomass consumption rate, fuel/air equivalence ratio, producer gas heating value and composition, tars concentration, and flame front velocity. The effect of the operating and design parameters on response variables was studied by means of multifactorial experimental designs. The statistical R 2 obtained through the data fitting of the multifactorial experimental designs indicated that the factors taken into account explained between 80.8% and 98.8% of the variability of the response variables. For the particular experiments carried out, the optimal gasification conditions were obtained with the following set of inlet conditions: air superficial velocity of 0.06m/s, biomass particle size between 2 and 6mm, and biomass moisture content of 10.62%. The corresponding response variables were: flame front velocity=11mm/min, fuel air equivalence ratio=3.2, biomass consumption rate=125kg/h/m2, lower heating value of the producer gas=2965.6kJ/Nm3, tar concentration=7.73g/Nm3, and an average composition of the producer gas of 8.0% H2, 13.0% CO, 1.4% CH4, 14.9% CO2, and 62.7% N2. [Copyright &y& Elsevier]

We consider M/G/1-type Markov chains where a transition that decreases the value of the level triggers the phase to a small subset of the phase space. We show how this structure—referred to as restricted downward transitions—can be exploited to speed up the computation of the stationary probability vector of the chain. To this end we define a new M/G/1-type Markov chain with a smaller block size, the G matrix of which is used to find the original chain's G matrix. This approach is then used to analyze the BMAP/PH/1 queue and the BMAP[2]/PH[2]/1 preemptive priority queue, yielding significant reductions in computation time. [ABSTRACT FROM AUTHOR]

Abstract: This article discusses a mathematical model for the thermochemical processes in a downdraft biomass gasifier. The model combines the chemical equilibrium and the thermodynamic equilibrium of the global reaction, predicting the final composition of the producer gas as well as its reaction temperature. Once the composition of the producer gas is obtained, a range of parameters can be derived, such as the cold gas efficiency of the gasifier, the amount of dissociated water in the process and the heating value and engine fuel quality of the gas. The model has been validated experimentally. This work includes a parametric study of the influence of the gasifying relative fuel/air ratio and the moisture content of the biomass on the characteristics of the process and the producer gas composition. The model helps to predict the behaviour of different biomass types and is a useful tool for optimizing the design and operation of downdraft biomass gasifiers. [Copyright &y& Elsevier]

Visual analytics (VA) is a paradigm for insight generation by using visual analysis techniques and automated reasoning by transforming data into hypotheses and visualization to extract new insights. The insights are fed back into the data to enhance it until the desired insight is found. Many applications use this principle to provide meaningful mechanisms to assist decision-makers in achieving their goals. This process can be affected by various uncertainties that can interfere with the user decision-making process. Currently, there are no methodical description and handling tool to include uncertainty in VA systematically. We provide a unified workflow to transform the classic VA cycle into an uncertainty-aware visual analytics (UAVA) cycle consisting of five steps. To prove its usability, three real-world applications represent examples of the UAVA cycle implementation and the described workflow. [ABSTRACT FROM AUTHOR]

Biochar (BC) is a solid byproduct of gasification and could be valorized looking for contributing to the feasibility of gasification projects. In this study, the effect of airflow during fixed-bed gasification of pelletized fallen leaves to BC was evaluated at 0.075 and 0.150 kg/s/m2. The influence of glycerol in the leaf feedstock was also studied, and the gasification products were characterized. BC formation under gasification conditions was simulated using a two-dimensional (2D) unsteady computational fluid dynamics (CFD) model. When airflow was increased, convective heat transfer from the gas to the solid phase increased by 250%, and absorption of radiative heat transfer in the solid phase increased by 59%. This was ascribed to the increase in the process temperature, which also promoted the release of volatile matter. The H:C and O:C ratios in the feedstocks were reduced by 80% and 92%, respectively. The surface areas and pore volumes of the samples increased by up to 50%. The BC with the largest surface area (68.63 m2/g) also had the highest total organic carbon content (21.3%) and the highest water retention capacity (408.13%). The pH of the BCs obtained in the study ranged from 8.7 to 10, making them suitable for acid soils. • Gasification's cold gas efficiency of fallen leaves pellets (FLP) is up to 60%. • Convective and radiative heat transfer affect physicochemical properties of biochar. • If glycerol increases, biochar (BC) density decreases and BC temperature increases. • FLP's BC as a byproduct of fixed-bed gasification is suitable for acid soils. • FLP's BC is not suitable as a solid fuel due to its high ash content (∼58 wt%). [ABSTRACT FROM AUTHOR]

Biochar is the product from the decomposition of biomass, whose physicochemical characteristics are associated with its origin and the combustion method used. Among these properties, the surface area, the formation of macro and micropores, and the presence of functional groups are highlighted. Due to these characteristics, biochar becomes an alternative material with a high adsorption capacity for toxic compounds contained in polluted wastewater. This work provides information on the biochar generation mechanisms and how they interfere with its physicochemical characteristics. Likewise, the parameters involved in the pollutant removal processes are described, and the treatments under which the biochar can be subjected for its adsorption capacity to be improved are mentioned. Finally, the possible uses or the suitable final disposition that the biochar must have in order to contribute to the circular economy strategy are indicated. [ABSTRACT FROM AUTHOR]

The gardens from the University of Antioquia main campus (Colombia) produce ∼2.8 tons of fallen leaves (FL) per month on a dry weight basis. A sample of this garden waste was pelletized (fallen leaves pellets, FLP). Accordingly, the physical and thermochemical properties of FLP were characterized for use as solid biofuel. The densification of FL was carried out with varying moisture (10, 15 and 20 wt%) and the glycerol contents (0, 5, and 10 wt%) as binders following a multifactorial statistical experimental design. In particular, the significant effect of the glycerol content on physical properties of FLP is noteworthy, as its increase influenced bulk density, which decreased from 524 to 380 kg/m3. Furthermore, it was found that with the simultaneous increase of moisture and glycerol contents, tensile strength decreased by 10%, but the elastic behavior of pellets was elevated, leading to increases in their deformation capacity from 0.75 mm to 2.35 mm. This behavior can also be checked with superficial hardness of FLP, which decreased by up to 70% when the glycerol content increased. The fuel value index of FLP diminished by 15% with the glycerol content, while the volatile matter increased, leading to improve the reactivity of the pellets. Image 1 • A physical and thermochemical analysis of fallen leaf pellets is presented. • If moisture and glycerol content increase in pellets, densities decrease. • If glycerol content increase, tensile strength decreases, and deformation increases. • Volatile matter of pellets increases with low moisture and high glycerol contents. • The glycerol addition in low concentrations improves energy properties of pellets. [ABSTRACT FROM AUTHOR]

Microalgal biomass has been widely investigated as a source of renewable energy, but currently, some alternatives are not economically competitive. Thermochemical conversion of biomass is an alternative way to transform their organic compounds into liquid and gaseous fuels. The aim of this work is twofold; first, the pyrolytic process of the microalga Botryococcus braunii (BB) by thermogravimetric analysis, as well as the relevant reaction kinetic constants and related activation energies, is assessed. Secondly, a sensitivity analysis of the biomass gasification process with air using a thermochemical model was conducted to predict the composition of a syngas as a function of the biomass moisture content and the biomass/air ratio. The results showed that BB biomass is composed mainly of carbon (62.4 wt.%) with volatile solids of 84 wt.%, while the fixed carbon represents around 7 wt.%. Additionally, observed values for heating (27.86 MJ kg−1) and activation energy (~ 110 kJ mol−1) were different from other algal feedstocks due to the capacity of accumulation of liquid hydrocarbons of this. On the other side, the gasification process showed it was found that the moisture content in the biomass and biomass/air ratio variables are key parameters for reaction temperature and producer gas composition. Accordingly, with a suitable combination of these variables, it is possible to obtain a syngas composed of gaseous species with high energy content (CO, 18 vol.%; H2, 17 vol.%; and CH4, 2 vol.%.), which can be transformed through processes such as Fisher-Tropsch process into liquid biofuels such as kerosene or gasoline. [ABSTRACT FROM AUTHOR]

Highlights • A biomass downdraft gasification model with particle size distribution is presented. • The char gasification byproduct is related to the bed pressure drop. • The model results are accuracy with particle size distributions of 16 different sizes. • The gasification efficiency decreases if the target electric power increases. Abstract A one-dimensional model of a downdraft biomass gasifier is presented to investigate the effect of operating parameters on the performance of a power plant. The approach considers the biomass fed to the reactor by employing discrete particle size distribution (DPSD) to simulate the real operational conditions of a gasification power plant (120 kW e /400 kW th). Char production (byproduct) and producer gas (PG) flow are the targets of the model; the model has been validated using data from an industrial power plant (biomass consumption, pressure drop, and PG composition) with an average relative error of 1.8%. The model achieved stable and reliable results using DPSD for 16 different particle sizes. The increase in the mean biomass particle diameter (15–60 mm) diminished the PG power (363.8–285.3 kW) and the cold gas efficiency (CGE) (63.2–54.36%) because of low particle surface/volume ratio. When biomass moisture content increased (5–25 wt%), the PG power decreased (364.14–318.75 kW) because of low gasification temperature. Moreover, when the number of driven engines was increased from 2 to 5 (electric power), the CGE decreased (68.17–59.17%) due to the low residence time of the solid and gas phases, which inhibited the gasification reactions, in the reactor. [ABSTRACT FROM AUTHOR]

In this paper the effects of the tax incentives of the Law 1715 of 2014 (Colombian law of renewable energies) on the levelized cost of electricity (LCOE) of cogeneration plants using forest biomass in the Antioquia Department are analyzed. Generation technologies such as Gasification, Combustion and Rankine Organic Cycle (ORC) were considered based on the energy potential of the forest biomass crops. Three study cases were carried out: 1) LCOE without tax incentives, 2) LCOE with tax incentives, and 3) LCOE with tax incentives considering ten years for assets depreciation. On the other hand, a sensitivity analysis was carried out to evaluate how the LCOE is affected due to changes in the forest biomass cost, the technology cost, the minimum acceptable return rate and the grace period on credits to finance the cogeneration plants. Finally, the results show that the LCOE with the ORC (13,2 ¢U$/kWeh) is the case with the greatest reduction (11,2%), when the incentives of Law 1715 of 2014 with assets depreciation at 10 years, financing the 50% of the initial investment and grace period for 5 years are considered. [ABSTRACT FROM AUTHOR]

In this work, chemical properties and structure of patula pine wood chips torrefied under air atmosphere are studied. Oxidative conditions instead of inert environment are an interesting way to reduce torrefaction operating costs. In this way, the torrefaction process was carried out in a batch rotary kiln by varying temperature (180, 210, and 240 °C) and residence time (30, 75 and 120 min). Sample amount (∼50 g), heating rate (10 °C/min), airflow (1 slpm), and particle size (between 10 and 20 mm) were fixed. Proximate, ultimate, and heating value analyses, as well as the contents of hemicellulose, cellulose and lignin of raw and torrefied biomasses were determined. Similarly, changes in thermal behavior by DTG, chemical structure by FTIR, surface area by BET, and cell-wall structure by SEM were analyzed. A severe degradation of both hemicellulose and cellulose was found at 240 °C, and a char-like material rich in lignin with high LHV is obtained. At this temperature, oxidation reactions are favored leading to highest specific surface area (174.95 m 2 /g) at 75 min. In addition, the reactivity of torrefied biomasses were higher than the raw material; particularly, those produced at 180 and 210 °C. Likewise, their structure exhibited a higher aromaticity with torrefaction severity. Therefore, torrefaction under air conditions upgrades the quality of patula pine wood as a solid biofuel for further thermochemical processing such as combustion or gasification. [ABSTRACT FROM AUTHOR]

The effects of torrefaction under an oxidizing atmosphere on the physicochemical properties of patula pine wood chips were studied. Raw and torrefied pine were characterized to evaluate the effect of temperature and residence time on biofuel properties, such as bulk density, equivalent Hardgrove grindability index (HGIeq), ultimate and proximate analyses, heating value, and fuel value index (FVI). In contrast, the torrefaction process was characterized by mass and energy yields, and by the energymass co-benefit index (EMCI). Torrefaction was performed in a rotary kiln at temperatures between 180 °C and 240 °C during residence times between 30 min and 120 min. The torrefaction process under an oxidizing atmosphere tended to increase the fixed carbon/volatile matter ratio (from 0.19 to 2.5), while the H/C and O/C atomic ratios decreased 73% and 55%, respectively. The best properties of wood reached in the experimental plan were obtained at 210 °C during 75 min. For this torrefaction condition, energy yield, FVI, and EMCI were 85.91%, 1.91 MJ/cm3, and 4.41%, respectively. Additionally, the lower heating value for torrefied pine (18.65 MJ/kg) was higher than for the raw material (17.76 MJ/kg), and the HGIeq was 17% greater, which resulted in a better grindability behavior. [ABSTRACT FROM AUTHOR]

We are interested in the potential risk of short-term load imbalance in hydro-thermal power systems under high integration of renewable energy sources, including wind, solar, and biomass. Toward this end, the short-term load balance across the system is formulated as a joint chance constraint. Due to non-convexity issues and the lack of information about the joint probability distribution of the renewable energy resources, we analyze a distribution-free robust relaxation and a p -efficiency approximation of the joint chance constraint. Our proposal is embedded within the widespread SDDP algorithm, and compared with the popular CVaR scheme on a simplified version of the Colombian power system. • An extension of the SDDP framework is presented for power system management. • The load balance requirement is formulated as a chance constraint. • The chance constraints are efficiently approximated. • The proposals prove efficient compared with the CVaR scheme. [ABSTRACT FROM AUTHOR]

The production of synthetic or substitute natural gas (SNG) from coal is a process of interest in Colombia where the reserves-toproduction ratio (R/P) for natural gas is expected to be between 7 and 10 years, while the R/P for coal is forecasted to be around 90 years. In this work, the process to produce SNG by means of coal-entrained flow gasifiers is modeled under thermochemical equilibriumwith the Gibbs free energy approach. The model was developed using a complete and comprehensive Aspen Plusmodel. Two typical technologies used in entrained flow gasifiers such as coal dry and coal slurry are modeled and simulated. Emphasis is put on interactions between the fuel feeding technology and selected energy output parameters of coal-SNG process, that is, energy efficiencies, power, and SNG quality. It was found that coal rank does not significantly affect energy indicators such as cold gas, process, and global efficiencies. However, feeding technology clearly has an effect on the process due to the gasifying agent. Simulations results are compared against available technical data with good accuracy. Thus, the proposed model is considered as a versatile and useful computational tool to study and optimize the coal to SNG process. [ABSTRACT FROM AUTHOR]

Abstract: A one-dimensional stationary model of biomass gasification in a fixed bed downdraft gasifier is presented in this paper. The model is based on the mass and energy conservation equations and includes the energy exchange between solid and gaseous phases, and the heat transfer by radiation from the solid particles. Different gasification sub-processes are incorporated: biomass drying, pyrolysis, oxidation of char and volatile matter, chemical reduction of H2, CO2 and H2O by char, and hydrocarbon reforming. The model was validated experimentally in a small-scale gasifier by comparing the experimental temperature fields, biomass burning rates and fuel/air equivalence ratios with predicted results. A good agreement between experimental and estimated results was achieved. The model can be used as a tool to study the influence of process parameters, such as biomass particle mean diameter, air flow velocity, gasifier geometry, composition and inlet temperature of the gasifying agent and biomass type, on the process propagation velocity (flame front velocity) and its efficiency. The maximum efficiency was obtained with the smaller particle size and lower air velocity. It was a consequence of the higher fuel/air ratio in the gasifier and so the production of a gas with a higher calorific value. [Copyright &y& Elsevier]

• As moisture of MSW increases, unit exergy cost increases and efficiency decreases. • The plasma gasifier and gas turbine have the largest exergy destruction ratio. • The unit exergoeconomic cost of electricity varied from 11.7 up to 15.6 ¢US$/kWh. • IPGCC plant feasibility depends on origin, amount, and disposal fee of waste. • The minimum waste disposal fee for a competitive local plant was 57.6 US$/t. This work studies how different scenarios of the municipal solid waste (MSW) management, moisture content, origin, and production rate affect the exergoeconomic performance of an integrated plasma gasification combined cycle (IPGCC) power plant. Several parameters associated with MSW management are considered as input for the exergy assessment of an IPGCC power plant simulated in Aspen Plus. The feedstock considered is waste from residential (1121 t/day), institutional (75 t/day), commercial (168 t/day), and industrial (104 t/day) sectors, as well as the mixture between them. Thus, for this analysis, several plant scenarios were formulated, according to the amount and moisture content (MC) of the MSW from different origins. Regarding the exergy analysis, the plasma gasifier (PG) and the gas turbine (GT) exhibited the largest exergy destruction ratio, with an average contribution of 36.2% and 40.3%, respectively. Furthermore, as MC increased from 26.6% to 57.9% (according to each waste type), the exergy destruction ratio of the PG increased by 23.5%, leading to a decrease in energy and exergy efficiencies of the IPGCC plant by 23.7% on average. The exergy cost of electricity ranged from 11.7 to 15 ¢US$/kWh. Therefore, the plants with a processing capacity from 100 to 1000 t/day require a MSW treatment fee between 96 and 57.6 US$/t to match the price of hydro-electricity in the Colombian energy market (6.92 ¢US$/kWh). [ABSTRACT FROM AUTHOR]

• Biochars (BCs) from main biomass commodities traded worldwide are characterized. • Gasification temperature of wood pellets (WP) is higher than that of chips (WCH). • High density and temperature lead to increase the gasification efficiency by ∼41 %. • As BC from WP has 367.33 m2/g and 29.25 MJ/kg, it is a suitable solid biofuel. • WP as compared to WCH is a better feedstock to co-produce producer gas and BC. Wood pellets (WP) and chips (WCH) are the most frequently sold products worldwide to produce bioenergy under thermochemical processes. The effects of the bulk density of patula pine (Pinus patula) WP (555.97 kg/m3) and WCH (151.29 kg/m3), and their gasification conditions were studied on the properties of the produced biochars (BCs). The aim of this study was to generate a good-quality gas fuel (producer gas), as well as a BC with properties that would enable it to be used as a solid biofuel instead of being considered as a byproduct or waste. An atmospheric reverse-downdraft gasifier was used, setting the air flow at 0.12 kg/m2/s for the samples of biomasses studied. With regard to the gasification performance, the temperature inside the reactor was found to increase by 70 % for WP, obtaining a higher cold gas efficiency (51.6 %) in comparison with the efficiency achieved for WCH (36.7 %). Concerning the properties of the BCs, the highest gasification temperature allowed to reach a pellet-derived biochar (WP-BC) with a surface area (BET) larger than that one obtained for the chip-derived biochar (WCH-BC), with 367.33 m2/g and 233.56 m2/g, respectively. Furthermore, the WP-BC heating value was found to be 29.25 MJ/kg, while this parameter for the WCH-BC was 28.36 MJ/kg. It is highlighted the low probability of corrosion and ash fusion occurrence within the reactor when using these biofuels (raw and BCs). Additionally, regarding the pyrolysis kinetics of the raw biomasses, WCH showed a higher reactivity with an activation energy (E α) of 80.84 kJ/mol in comparison with the E α value obtained for WP (124.38 kJ/mol). [ABSTRACT FROM AUTHOR]

In Latin America, one of the key tasks of Community and Liberation Psychology has been to recover the memories of marginalized and excluded communities that have experienced multiple pasts marked by political violence. In Chile, researchers have focused on poor urban neighborhoods, where the question of how memories are transmitted in areas where conflicts and violence are still present has been overlooked. In this context, the following article aims to analyze the ways in which memories are transmitted in a neighborhood that has a long organizational history in the struggle against social inequalities; while at the same time being classified as a critical area by the state due to its current levels of violence and social conflict. The researchers led a 3‐year case study from an ethnographic perspective, and applied a collaborative methodology that brought together the research team and the members of a territorial organization. The analysis is based on 72 interviews, 5 conversation groups and ethnographic observation. The data was analyzed using discourse analysis. The results revealed that the main form of memory transmission is not based on intergenerational narratives of the past, but rather on joint action; namely, dialogical practices among neighborhood residents that generate an ethos; a common way of life. [ABSTRACT FROM AUTHOR]

• We propose a methodology for the management of hydrodominated power systems coupled with wind energy and energy storage. • The methodology enables leveraging the reliability of the system against the short-term volatility of wind power. • The risk profile of the decision maker is taken into account in the operating cost and the load balance constraints. • The proposal is applied to the Colombian power system under different likely wind integration scenarios. Operation planning models for hydro-dominated power systems usually use low temporal resolutions due to the excessive computational burden, thus ignoring short-term characteristics of such systems. As a result, in systems coupled with wind energy, such models may fail to accurately capture wind variability, and may not appropriately take into account potential consequences of uncertainty on the system operation. This paper addresses this drawback by (i) "controlling" the cost associated with the operation of a hydro-dominated power system equipped with wind power and batteries via a risk-measure and (ii) formulating the short-term load balance as probabilistic constraints in order to hedge against potential extreme wind power scenarios. The risk-averse scheme is embedded in the stochastic dual dynamic programming framework. Simulation results for a case study on a real industrial setting show that hedging the system against the short-term volatility of wind power contributes to mitigating the risk of excessive operations costs or load curtailments, and that the consideration of the decision maker risk profile contributes to decreasing the variability of the solutions. In addition, the results of the application also illustrate the potential of the scheme to assess the energy situation of a country or a region under the penetration of wind energy and batteries deployment. [ABSTRACT FROM AUTHOR]

This article evaluates the efficiency of Colombian banking using nonparametric border models. The results indicate that there has been a gradual increase in efficiency and that the global financial crisis of 2008 affected this trend. Since 2009 there has been a rapid recovery of efficiency measures, except for cost efficiency. This suggests that, in the face of external shocks, the adjustment costs of banks are greater. Mergers and acquisitions contribute to the increase in banking efficiency. [ABSTRACT FROM AUTHOR]

The aim of this research was to evaluate four different cacao ( Theobroma cacao L.) fermentation conditions and their effect on fermented bean quality, in order to be able to recommend the most suitable condition to producers in the municipality of Huimanguillo, Tabasco, Mexico. Fermentations were carried out in square wooden boxes with capacity for 1000, 300, and 100 kg of fresh beans, as well as a rotary drum with capacity for 500 kg thereof. The fermentation process was carried out for 7 days, and the response variables measured were mass temperature, total soluble solids ( TSS), pH, and acidity. The TSS were totally depleted after 2 days, during which time the yeasts transformed them into ethanol at temperatures of 25-35°C. The most notable temperature increase in the four treatments was 49°C on the third day, corresponding to a decrease in pH from 6.31 ± 0.40 to 4.76 ± 0.03 and an increase in acidity from 0.38 ± 0.04 to 1.17 ± 0.25 g kg−1, due to the formation of organic acids. There were no significant differences among the four treatments (Tukey α = 0.05). The cut test showed that fermentation in 300- and 100-kg boxes and in the 500-kg rotary drum produced the same effect on fermentation quality, but the 1000-kg boxes exhibited lower quality (Tukey α = 0.05). [ABSTRACT FROM AUTHOR]