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The present work develops a novel mathematical model for coal char activation with CO2, steam, and a CO2/steam mixture. The main assumption is that CO2 and steam react with distinct active sites, considered by attributing a unique char structure effect to each gasifying agent; the CO2-char reaction increases the pore length, whereas the steam-char reaction increases the pore radius. Additionally, pore overlapping effect was taken into account and the radial pore growth was computed by means of a population balance equation. Model predictions of both the pore size distribution and specific surface area changes were compared with experimental data, resulting in an outstanding fit. This supports the model main assumption, which reconciles discrepancies between various authors regarding the overall reaction rate during activation of coal chars with CO2/steam mixtures. Finally, the maximum specific surface area occurs under chemically-controlled conditions, where all particle zones reach their maximum surface areas simultaneously, while for activation with diffusional limitations each particle zone attains its maximum specific surface area at a different time.
Juan C. Maya, Robert Macías, Carlos A. Gómez and Farid Chejne
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https://www.sciencedirect.com/science/article/pii/S0008622319312217
This work proposes a novel population-balance based model for a bubbling fluidized bed reactor. This model considers two continuum phases: bubble and emulsion. The evolution of the bubble size distribution was modeled using a population balance, considering both axial and radial motion. This sub-model involves a new mathematical form for the aggregation frequency, which predicts the migration of bubbles from the reactor wall toward the reactor center. Additionally, reacting particles were considered as a Lagrangian phase, which exchanges mass with emulsion phases. For each particle, the variation of the pore size distribution was also considered. The model presented here accurately predicted the experimental data for biochar gasification in a lab-scale bubbling fluidized bed reactor. Finally, the aggregation frequency is shown to serve as a scaling parameter.
Robert J. Macías, Juan C. Maya, Farid Chejne, Z. Afailal, and J. Arauzo.
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https://aiche.onlinelibrary.wiley.com/doi/full/10.1002/aic.17199
Thermal energy changes the chemical composition of cocoa, which is related to its quality, during roasting. The effect of the heating rate on the physicochemical changes of cocoa, and the dynamics of generation and degradation of volatile compounds during heating are still unknown. Therefore, the weight loss of cocoa and the chemical composition of the released gases released at temperatures from 40 to 350 °C were identified in using a μ-reactor (PTV-GC-MS) with heating rates of 2 (β1), 4 (β2), and 8 °C sec−1 (β3). The thermal process was divided into three stages (raw ‒ dry, dry – roasted, and roasted – over-roasted). Higher heating rates cause lower volatilization at the same temperature due to shorter residence times. Likewise, more compounds were identified in the gas-fraction at β1 than at β2 and β3 with the same temperatures. Also, a 2D phenomenological model coupled to kinetics was made to predict phenomena such as thermal differentials, water and gas content, solid fractions, conversion, pressure, and gas outlet rate.
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https://www.sciencedirect.com/science/article/pii/S026087742200156X
This paper presents the results of co-gasification of Sub-bituminous coal type A (SubbA coal) with palm kernel shell (PKS) in a fluidized bed gasifier to meet the energy requirements for baking 300 tons/day of bricks in a tunnel kiln. Standardized operation of the co-gasification process of the SubbA coal – PKS 90/10 wt.% mixture was confirmed for a 24 h run. The reactor has the capacity to process up to 700 kg/h of the mixture, using air and an air/steam as the gasifying agent at 800°C, with an equivalent ratio of air/fuel (ER) between 0.5 and 0.7 and a steam/fuel ratio of 0.2. The product syngas had a HHV of 5.0 MJ/Nm3 that efficiently substitutes and the traditional use of pulverized coal by means of carbojets into the tunnel kiln without affecting the production process, while using a much cleaner gas to cook the bricks with lower emissions. This demonstrating the synergy existing in this coupling. Positive results of these experiments can enhance figure use of coal in a clean manner. This technology is mature enough to be implemented as a continuous energy supply to industrial processes that currently use traditional combustion for heat.
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https://www.sciencedirect.com/science/article/pii/S1359431116312170
In this work, a mathematical model that serves as a design tool for constructive systems with thermally efficient microencapsulated phase change materials (MPCM) incorporated in mortar was developed. The model allows quantifying how is influenced room internal temperature due to design variables, such as % wt. MPCM in the mortar mix, mortar and brick wall thickness, calculate the walls of the room that must have mortar with MPCM incorporated, application of mortar in the external or internal layer of the room, and consumption of electrical energy. This was done by taking into account the integration of two scales: microcapsules and wall. MPCM was incorporated as a source term that considers melting and solidification time, a solid-liquid interface while the phase change is happening, and energy storage by latent heat. Furthermore, the particle size distribution for the microcapsules was included by means of a Gaussian function. The results highlight that a suitable MPCM dosage in mortar is 15% wt. MPCM/mortar external application can reduce the internal room temperature up to 9 °C without consuming electrical energy, while the internal application allows the room to be kept at approximately a uniform temperature of 23 °C. Therefore, both implementations gave positive results; the choice will depend on the environment where the designed MPCM/mortar system will be applied. In conclusion, by incorporating 15% wt. MPCM in the mortar mixture on two walls of the room with a mortar wall thickness of 7 cm, HVAC demand would be reduced by up to 80%. Finally, this model was endorsed with experimental data taken from the literature. Additionally, the fact that the mechanical behavior was also evaluated experimentally for the obtained mortar dosage is highlighted, a relevant aspect in the final design of the construction system.
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https://www.sciencedirect.com/science/article/pii/S2352152X22001384
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