RESUMEN
Numerical simulations of a 600 t/day waste incinerator was carried out using the fluid dynamic incinerator code and Fluent to evaluate the effect of biomass blending on furnace temperature, pollutant generation, and selective noncatalytic-reduction (SNCR) denitrification when treating low calorific-value waste. The results show that as the biomass blending ratio increases, the water content gradually decreases, the calorific value increases, and the maximum temperature of the incinerator gradually increases from 1227 to 1408 K, while the content of exported NOx increases from 579 to 793 mg/Nm3; during the combustion of low-quality waste, the residence time of the flue gas in the high-temperature region (above 1123 K) is 1.62 s. When the biomass blending ratio exceeds 20%, the residence time of the flue gas in the high-temperature region is more than 2 s, which can effectively curb the generation of dioxin. When the biomass blending ratio is 20%, and the normalized stoichiometric ratio (2nurea/nNO) of urea injected into the SNCR is 1.1, the NOx concentration at the outlet is 230.08 mg/Nm3, which satisfies the NOx emission standard of less than 250 mg/Nm3.
RESUMEN
To accurately predict the life-cycle carbon reduction benefits of replacing a diesel heavy-duty truck with an electric one, taking a single heavy-duty truck as the object, the variation trend in electric and diesel carbon emission factors from 2023 to 2050 were predicted; coupled with the life spans and life-cycle mileage of the two types of heavy-duty trucks, a dynamic carbon emission model for the heavy-duty trucks was constructed in stages. The carbon footprints of the trucks under the "Net Zero Emissions by 2050 Scenario (NZE)", "Announced Pledges Scenario (APS)", and "Stated Policies Scenario (STEPS)" were analyzed. In addition, the carbon reduction and carbon reduction rate were calculated. The results showed that battery manufacturing and battery recycling were the main factors to impair the improvement of carbon reduction in the production and recycling stages of electric heavy-duty trucks, respectively. For every 1 g·(kW·h)-1 reduction in the electricity carbon emission factor (CO2), an electric heavy-duty truck could reduce 1.74 t of carbon emissions over its life cycle. Under the three scenarios, the carbon emissions during the operation stage of both types of heavy trucks accounted for more than 90% of the total life-cycle carbon emissions. Carbon reduction benefits from the highest to the lowest were NZE, APS, and STEPS, and their corresponding life-cycle carbon emission reductions were 1054.68, 1021.78, and 1007.97 t, with carbon reduction rates of 54.38%, 52.68%, and 51.97%, respectively.
RESUMEN
The solid surface with several cavities containing gas strongly influences the bubble's dynamical behaviors. To reveal the underlying physical mechanism of the cavitation bubble near a rigid boundary with a gas-entrapping hole, a fully compressible three-phase model, accounting for the three-phase volume transport equation, was implemented in OpenFOAM. The predicted bubble shape was validated with the corresponding experimental photos, and good agreement was achieved. The bubble's primary physical features (e.g., the expanding shock wave, upward and downward liquid jet, and high-pressure region) are well reproduced, which helps understand the underlying mechanisms. The numerical results show that the solid wall with a gas-entrapping hole could affect the morphology of both the bubble and liquid jet, as well as shortens the bubble's first oscillation period in comparison to an intact rigid wall. The relationship among the prolongation factor, the standoff distance, and the relative size ratio is analyzed. It is found the prolongation factor increases as the relative size ratio decrease. As the standoff distance decreases, the gas entrapping hole plays a significant role in the oscillation period of the bubble. The current model can be further extended to reveal the microscopic mechanism of aeration avoiding cavitation damage and investigate the interaction between air bubbles and cavitation bubbles, which is of great interest to practical applications.