Theoretical Analysis on the Criteria of MILD Coal Combustion
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MILD combustion is featured with a uniform heat flux and low NOx emission, and is thus a promising technology for clean coal utilization. Establishing the theoretical criteria of coal combustion modes is essential to guide the design and organization of MILD coal combustion. In this work, different coal combustion modes were classified theoretically based on the analysis of time scale, heterogeneous ignition, heat transfer, and flue gas entrainment. The predicted coal combustion modes agreed well with the experimental results from the literature. The effects of the structural and operational parameters on coal combustion modes were also discussed. As the nozzle diameter increases, the critical inlet Reynolds number switching from traditional combustion to MILD combustion increases, while the corresponding jet speed decreases. When the size of the furnace cross section increases, the critical inlet Reynolds number increases. As the coal particle diameter increases, the critical inlet Reynolds number decreases. As the secondary air temperature increases, the critical inlet Reynolds number decreases. The classification method of coal combustion modes was further applied to instruct the organization of MILD coal combustion on a Hencken burner. The experimental results proved that the theoretical analysis is reasonable.Keywords:
Entrainment (biomusicology)
This paper describes a methodology for modeling long-term evolution of multiple inlet systems in southwest and central Florida. The paper discusses the application of this methodology to two inlets within Sarasota Bay system in southwest Florida. The case studies of Longboat Pass and Venice Inlet demonstrate the importance of considering large temporal and spatial scales in multiple inlet systems. The results describe the evolution of Longboat Pass and Venice Inlet from 1880 to present. The analysis begins with natural conditions that existed before dredging or inlet modifications and investigates how inlet evolution can be influenced by navigation improvements or mining of ebb shoals for beach nourishment.
Dredging
Shoal
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This study aims to assess the effects of a new inlet on the hydrodynamics of a semi-permanent tidal inlet and the back-barrier sound. Research on dual-inlet interactions is motivated by the increased vulnerability of barrier islands to breaching during hurricanes, phenomenon that can have important consequences on the hydrodynamics and morphology of a barrier island system with pre-existing inlets. This particular study takes place in the northern Outer Banks of North Carolina, where Oregon Inlet is the main inlet connecting the Atlantic Ocean with the Albemarle-Pamlico Sound. During Hurricane Irene in 2011, Pea Island – the island south of Oregon Inlet – was breached creating a new inlet that remained open until 2013. Dual-inlet interactions between Oregon Inlet and the new inlet in Pea Island are analyzed by means of numerical modeling experiments. Changes in flow velocities, water levels, and the tidal prism of Oregon Inlet due to the new inlet are computed for different wave and water level conditions. In addition to the actual inlet that opened in 2011, the effects of idealized inlets with different geometries and location are also included in this study. Results indicate that the original breach in Pea Island did not modify the dynamics of Oregon Inlet. Instead, its effects were restricted to a 5 km radius that extended mostly into the sound. The relative small size of the breach and its distance from Oregon Inlet are the two main factors that prevented dual-inlet interaction. Exploration of idealized breaching scenarios in Pea Island suggests that inlet spacing and breaching geometry play a major role in multiple inlet stability theory.
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Inlet change along the Virginia barrier islands has been studied on an individual inlet basis. This study evaluated the ten inlets both individually and as a group. Evaluating the inlets as a group allows the discovery of inlet change patterns among the inlets. Inlet width was measured from satellite and aerial images. Width is the straight-line distance from the northernmost fast land to southernmost fast land. Measurements spanned from July 1999 to April 2018 with a frequency of four to eight width measurements per year. Total width change to 2018 was 2 percent to 357 percent. The largest change was to Great Machipongo Inlet. The inlet widened from approximately 800 meters wide in 1999 to 3645 meters wide in 2018. This widening effectively splits the remaining nine inlets into two groups. Inlet widening patterns of the two groups are high rates for the first three or four inlets and a very low rate for the final inlet of the group. Wind direction change also plays a significant role in net inlet widening. Inlet widening has not abated and wider inlets will allow larger waves to affect environmentally and commercially important areas to the west of the barrier island/inlet system.
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This chapter describes sand transport patterns and sand bypassing at seven inlets; five of these are located on the east coast of the USA (Price Inlet, Breach Inlet, Captain Sam's Inlet, Mason Inlet and Wachapreague Inlet), one inlet is located in the Bay of Plenty on the North Island of New Zealand (Katikati Inlet) and another is part of the Dutch Wadden Sea coast (Ameland Inlet). The inlets are selected because they are still in their natural state and have been extensively studied. Emphasis is on the mode of bypassing, location stability and their relationship with the P/M ratio. In judging the results, it should be pointed out that estimates of longshore sand transport have limited accuracy.
Longshore drift
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In Chilka lake a new inlet was formed due to natural coastal processes at Gabakunda in August 2008 at 1 km north of the existing inlet at Sipakuda. Present study deals with 2-D mathematical model (MIKE21) studies with two inlets to assess the hydrodynamic changes and salinity variations due to the formation of new inlet at Chilika lake. Predicted tide, monthly average inflows of the rivers and observed salinity are used for the model studies with a constant width of inlets throughout the simulation period. Newly formed inlet has a dominant role in contributing tidal exchanges over Sipakuda inlet. Decrease in tidal prism with two inlets is observed in comparison with that of single inlet system at Sipakuda, which leads to decrease in salinity of about 10 ppt in all the sectors of the lake. Lake salinity is improved by preserving tidal exchange by maintaining the cross sectional area and depth of the inlets.
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Coal combustion and gasification are an anthropogenic source of mercury emission to the atmosphere. Effectively minimizing the emission and understanding the atmospheric fate and transport of mercury require knowledge of its speciation in flue gases. Hg0(g) is the thermodynamically stable form in the highest temperature regions of combustors and gasifiers. Hg0(g) remains as the dominant form in the relatively reducing conditions of a gasification flue gas, but with decreasing temperature in a combustion flue gas Hg0(g) will react to form Hg2+ compounds. Current mercury speciation analysis results suggest that generally >50% of the Hg0(g) reacts with oxidants in coal combustion flue gases; results for gasification conditions are lacking. Oxidation is beneficial because Hg2+ compounds are generally water-soluble and are therefore more effectively captured by wet scrubber pollution control systems and are more apt to deposit locally or regionally. Conversely, Hg0(g) is difficult to control and is likely to enter the global atmospheric cycle because of its high vapor pressure and low water solubility. The physical and chemical processes governing the interactions of mercury species with flue gas components are poorly known.
Mercury
Wet scrubber
Flue
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The morphologic response of inlets that are part of a multiple inlet system, defined here as two or more coastal inlets connected to the same bay, is a complex problem. It has been thought that one inlet will eventually dominate, and that other inlets will close. Of course, in nature, there is a full range of situations and physical realities that complicate this situation. As more experience and historical information become available, various approaches can be tested. There may be multiple inlet systems serving a bay region that have naturally developed and coexisted for many years in some cases or there maybe newly developed multiple inlet systems whose inlets immediately respond to each other, with the more efficient inlet creating a decline in the size of the other inlet, probably at a varying rate proportional to their efficiencies. An example of this type situation at two inlets on the Guatemalan coast is examined in this paper.
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In the utilization and transformation of lagoon, the measure to reduce the inlet width is often adopted in order to increase the inlet depth. Because of this the desired results have not been achieved. On the contrary, lagoon environment is getting worse. Therefore, the relations among tidal inlet velocity, cross-sectional area, inlet length, phase lag and repletion coefficient as well as the effect of drift sand along the coast on the inlet have to be analyzed. On the basis of self- experience and studies, the proposal of transforming problematic inlet, such as using the method of diversion dike under mean tidal level and double profile of inlet as well as inlet dividing, has been put forward for different types of lagoons.
Dike
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Space velocity
Selective catalytic reduction
Mercury
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