Effects of pressure drop and superficial velocity on the bubbling fluidized bed incinerator.

Since performance and operational conditions, such as superficial velocity, pressure drop, particles viodage, and terminal velocity, are difficult to measure on an incinerator, this study used computational fluid dynamics (CFD) to determine numerical solutions. The effects of pressure drop and superficial velocity on a bubbling fluidized bed incinerator (BFBI) were evaluated. Analytical results indicated that simulation models were able to effectively predict the relationship between superficial velocity and pressure drop over bed height in the BFBI. Second, the models in BFBI were simplified to simulate scale-up beds without excessive computation time. Moreover, simulation and experimental results showed that minimum fluidization velocity of the BFBI must be controlled in at 0.188-3.684 m/s and pressure drop was mainly caused by bed particles.

Three-dimensional modeling of air flow and pollutant dispersion in an urban street canyon with thermal effects.

Effects of excess ground and building temperatures on airflow and dispersion of pollutants in an urban street canyon with an aspect ratio of 0.8 and a length-to-width ratio of 3 were investigated numerically. Three-dimensional governing equations of mass, momentum, energy, and species were modeled using the RNG k-epsilon turbulence model and Boussinesq approximation, which were solved using the finite volume method. Vehicle emissions were estimated from the measured traffic flow rates and modeled as banded line sources, with a street length and bandwidths equal to typical vehicle widths. Both measurements and simulations reveal that pollutant concentrations typically follow the traffic flow rate; they decline as the height increases and are higher on the leeward side than on the windward side. Three-dimensional simulations reveal that the vortex line, joining the centers of cross-sectional vortexes of the street canyon, meanders between street buildings and shifts toward the windward side when heating strength is increased. Thermal boundary layers are very thin. Entrainment of outside air increases, and pollutant concentration decreases with increasing heating condition. Also, traffic-produced turbulence enhances the turbulent kinetic energy and the mixing of temperature and admixtures in the canyon. Factors affecting the inaccuracy of the simulations are addressed.

Numerical simulation of gas flow around a passive vent in a sanitary landfill.

A numerical model, based on the Darcy law, was used to simulate the two-dimensional gas flow around a passive vent in a sanitary landfill. We follow Findikakis and Leckie [ASCE J. Environ. Eng. 105 (1979) 927] in modeling the biodegradation of the solid waste and assume the first-order biodegradation kinetics. The numerical results from the Fresh Kills landfill, New York, show that the well's ability in extracting the landfill gas by the passive vent decays quickly with the increase of the radial distance from the well. The influence radius of the well is generally less than 20 m. The effects from the final soil thickness, well depth, and other parameters on the gas flow are also discussed.

Emissions of submicron particles from a direct injection diesel engine by using biodiesel.

Small airborne particles less than 1 microm in diameter have a high probability to deposit deeply in the respiratory tract and cause respiratory diseases such as lung cancer. In this study, emission characteristics of submicron particles from a direct injection diesel engine using biodiesel (provided by the American Soybean Association) and petroleum-diesel fuels were measured under different operation conditions. The results show that the emitted particle sizes for both fuels are about the same. But when fueled with biodiesel, the diesel engine can substantially reduce 24-42% emission of the total number concentration, and 40-49% of the total mass concentration of submicron particles, which indicates that the emission of submicron particles can be effectively approved.