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[en] The advantages of using fluidized bed heat recovery units with diesel engines are well documented. Two of those are: significantly less tube fouling and heat transfer coefficient four to five time higher than that of conventional shell and tube heat exchangers. The high concentration of soot in the exhaust gases of diesel engines make fouling a major concern in design of any kind of heat recovery unit. In the experiment a conventional fluidized bed heat exchanger was connected to the exhaust of a diesel engine mounted on a dynamometer. With this arrangement it was possible to test the heat recovery unit under a wide range of operating conditions. The main objective of this experiment was the determination of the performance characteristics of the heat recovery unit, especially with reference to its heat transfer and fouling characteristics. (author)
[en] Highlights: • Regenerative temperature field of cordierite ceramic filter was measured. • Different idle speeds were tested for DPF regeneration during drop to idle process. • Idle-up strategy was provided to decrease the peak temperature and temperature gradient under drop to idle process. The idle-up strategy of diesel particulate filter (DPF) regeneration during a drop to the idle (DTI) process was investigated in this study. This strategy could control the peak temperature and maximum temperature gradient of a cordierite ceramic filter. Experimental results showed that as the engine working condition dropped to idle speed during regeneration with a DPF soot load of 4 g/L, the peak temperature was reduced from 820 °C to 632 °C when the idle speed was increased to 1100 r/min, a decrease of 22.9%, while the maximum temperature gradient was reduced from 30 °C/cm to 10 °C/cm, a decrease of 66.7%. The peak temperature and temperature gradient of the DPF cordierite ceramic filterwith DTI during regeneration were effectively reduced. The idle speed range for the idle-up strategy to decrease the peak temperature and temperature gradient of a cordierite ceramic filter was discussed. The maximum idle speed of the idle-up strategy should not be higher than the speed of common engine working conditions in order to avoid DTI during a regeneration increase at current engine driving speed.
[en] In order to study the various health influencing parameters related to particulate as well as to gas-phase pollutants emitted by Diesel engine exhaust, there is an urgent need for appropriate sampling devices and methods for cell exposure studies and associated biological and toxicological tests. In a previous paper , a specific concept for a cell culture exposure chamber was introduced to allow the uniform exposure of cell cultures to diesel aerosols. In the present work, this cell culture exposure chamber is evaluated and characterized with state-of-the-art nanoparticles measurement instrumentation to assess the local deposition of soot aggregates on the cell cultures and any losses due to particle deposition on the cell culture exposure chamber walls, and in addition an upgraded Multiculture Exposure Chamber (MEC) for in vitro continuous flow cell exposure tests is introduced with improved, compared to the previous version, features. Analysis and design of the MEC employs CFD and true to geometry representations of soot particle aggregates.
[en] Because of its adaptability over a wide range of environments in North America, the U.S. Department of Energy has chosen switchgrass as a model species for developing herbaceous energy crops. The suitability of energy crops as a feedstock for fuels or power is reflected in their energy content and conversion, and in their ease of handling, which also ultimately determine the type of potential and uses. Analyses indicate that switchgrass is versatile. Its energy content (when the initial moisture content is considered) is similar to wheat straw's and greater than wood's. Early analysis of ethanol production by enzymatic hydrolys/fermentation indicates that it produces high yield with current technology. Earlier reports of its high ash and alkaline contents have increased attention to harvesting, storage, and handling techniques to reduce soil contamination. With proper methods, ash and alkaline can be maintained at a relatively low level, and problems of slagging in conventional combustion systems can be avoided. (au) 18 refs
[en] The Advanced Staged Fluidized-Bed Coal Combustion System (ASC) is a novel clean coal technology for either coal-fired repowering of existing boilers or for incremental power generation using combined-cycle gas turbines. This new technology combines staged combustion for gaseous emission control, in-situ sulfur capture, and an ash agglomeration/vitrification process for the agglomeration/vitrification of ash and spent sorbent, thus rendering solid waste environmentally benign. The market for ASC is expected to be for clean coal-fired repowering of generating units up to 250 MW, especially for units where space is limited. The expected tightening of the environmental requirements on leachable solids residue by-products could considerably increase the marketability for ASC. ASC consists of modular low-pressure vessels in which coal is partially combusted and gasified using stacked fluidized-bed processes to produce low-to-medium-Btu, high-temperature gas. This relatively clean fuel gas is used to repower/refuel existing pulverized-coal, natural gas, or oil-fired boilers using bottom firing and reburning techniques. The benefits of ASC coal-fired repowering include the ability to repower boilers without obtaining additional space while meeting the more stringent environmental requirements of the future. Low NOx, SOx, and particulate levels are expected while a nonleachable solid residue with trace metal encapsulation is produced. ASC also minimizes boiler modification and life-extension expenditures. Repowered efficiencies can be restored to the initial operating plant efficiency, and the existing boiler capacity can be increased by 10%. Preliminary cost estimates indicate that ASC will have up to a $250/kW capital cost advantage over existing coal-fired repowering options. 4 figs., 4 tabs
[en] Rice husk ash (RHA) which contains more than 90 percent silica is proven to be an active silica source in zeolite synthesis. In this study, nano sodalite has been successfully synthesized hydrothermally at 60 degree Celsius using RHA as silica source in alkaline medium at various crystallization times. Commercial fumed silica was used as comparison for the silica source. Analysis by XRD has shown that pure nano sodalite was formed in 3 hours and stable up to more than 24 hours when using RHA as silica source. On the other hand, fumed silica produced pure nano sodalite only at 4 hours while a mixture of zeolites was observed outside this time range. FESEM shows a worm-like morphology of nano sodalite in the size range of 50-100 nm while FTIR shows the formation of aluminosilicates bonds. Analysis on the dissolved silica in the gel reaction mixture demonstrates the decreasing mass of silica after prolong time of crystallization which indicates the consumption of the dissolved silica in crystal growth of nano sodalite. This study shows that RHA is a better silica source in stabilizing the nano sodalite phase in oxide gel reaction mixture as compared to fumed silica. (author)
[en] Solutions are proposed for enhancement of the in-service safety of hydraulicked ash-slag dumps with consideration of their hydrothermal regime. An assessment is given for the minimum dimensions of the settling basins and top surface of ash-slag dumps.
[en] The calculations of the optical characteristics of fractal aggregates find important applications in a wide spectrum of disciplines. Consequently, considerable research efforts have been invested to develop models to predict the scattering properties of aggregates. A comprehensive understanding of the accuracy of these models is highly desirable for the users. Therefore, this study assessed two commonly-used fractal scattering models, in terms of their accuracy for predicting both the integrative scattering properties (e.g., the scattering cross section) and the angular scattering properties (e.g., the elements of the Mueller scattering matrix). The results were organized as contour plots with respect to scattering angle and aggregate size to facilitate the estimation of error introduced by these models in practical applications. Meanwhile, a direct comparison and evaluation of these models was also performed, which can potentially enable a hybrid model for better accuracy. This study was conducted under the context of scattering by soot aggregates; hence, the results are expected to be directly applicable for soot characterization by laser scattering