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Flow of particulate materials in a vertical standpipe
(1983) Chen, Ye-Mon; Luss, Dan; Flumerfelt, Raymond W.; Deans, Harry A.; Lienhard, John H.; Kleis, Stanley J.
Standpipes are mechanical devices used to convey particulate solids downwards, usually from a region at lower pressure co a region at higher pressure, with tne aid of gravity. A well known application is the flow of a gas- solid mixture down from a fluidized bed in refinary processes, such as fluid catalytic cracking, fluid hydroforming and fluid coking. Tney are also used in the SASOL synthetic gasoline process and solid fuel processes of coal gasification and liquefaction. Despite the importance of the present applications and the potential of much wider use in the future, the mechanics of standpipe operation is still poorly understood. As a result, most industrial standpipes are still being designed empirically based on past experience. Inis is particularly unfortunate since standpipes are well known to devolop an instability under certain circumstances, causing a transition to a state with inadequate pressure build-up in the pipe. This may lead to operational problems such as loss of circulation and reversed gas flow which have resulted in a reduction of plant throughput or even complete shut-down of the plant. [...]
Single particle and reactor studies on char combustion
(1983) Kumpinsky, Enio; Amundson, Neal R.; Luss, Dan; Richardson, James T.; Wagner, David H.
When coal particles are introduced into a combustor, they experience a rapid temperature rise. As a result, an almost instantaneous evolution of volatiles occxrrs and a solid fuel is generated, called char. This analysis is concerned with the establishment of reliable mathematical models for processes Involving the combustion of char. With this intention, two categories of investigation were conducted, comprising single particle and whole reactor models. Factors such as the distribution of heterogeneous kinetics, competition for active sites, carbon reactivity, carbon-carbon dioxide reaction and particle shape were examined to assess their influence on the pseudosteady-state structure from qualitative and quantitative perspectives. The research on reactor models was initiated with stirred pots, thereby substantiating that the transient path of a single particle burning under fixed conditions is very sensitive to the ambient oxygen concentration in the surroundings. As a natural extension, it was necessary to develop combustor models with diverse degrees of segregation of the gaseous species. This enabled the conventionally employed approach of perfect gas mixing to be evaluated in relation to its suitability for the prediction of actual reactor performance. On the basis of this work, it is recommended that char combustor models take into consideration as much of the detail of internal transport as possible. Indeed, the combustion rates generated by means of distributed models are always larger than those evaluated at the average concentrations in lumped systems, due to considerable changes in the behavior of the ignition-extinction phenomenon.
Modeling of a solar steam reforming reactor
(1983) Alagappan, P.; Richardson, James T.; Balakotaiah, Vemumi; Vant-Hull, Lorin L.
Chemical Energy Transmission Systems (GETS) are based on reversible endothermic and exothermic reactions. One of the essential tasks of a large scale solar energy utilization plant is the transmission of energy from the solar collector to the consumer. This can be accomplished through GETS, with a solar thermal process called SOLTHERM. In this process, the endothermic reaction product can be transported through pipelines to any destination, where the exothermic reverse reaction is made to proceed with the release of energy. The best reaction system for GETS is the endothermic methane-steam reforming reaction and the reverse exothermic methanation reaction. A two-dimensional pseudo-homogeneous model has been developed for a packed-bed methane-steam reforming reactor which uses a heat pipe as a flux transformer to distribute the heat collected by the solar receiver system to the chemically reacting system. This model is capable of obtaining temperature and conversion profiles and mole fractions of various system components at every length within the reactor. Various sensitivity studies are performed for variations in inlet gas temperature and inlet natural gas flow rate, Sensitivities to changes in the available rate equation and heat transfer correlations are evaluated. The effect of variations in the heat pipe temperature and inlet steam-methane ratio are also examined. Calculations are done to evaluate the minimum thermodynamic steam-methane molar ratio above which there is no risk of carbon formation, for various temperatures. This is combined with the predictions of the model to evaluate carbon formation potentials within the reactor for different inlet conditions. Operating conditions are suggested to avoid carbon formation.
Simulation of packed gas absorption columns with first order irreversible reactions
(1983) Chen, Ing-Ray; Henley, Ernest J.; Pollard, Richard; Tucker, Charles T.
Gas absorption in packed towers has been modelled taking into account heat effects and first order irreversible chemical reactions. A theory based on the film factor concept was developed using steady state assumptions. The theory was transformed into a computer program which simulates the start-up procedure of the column dynamically and shows good convergence behavior. The computer program was tested with a pseudo-first order case, NaOH-CO2-Air, and good agreement with experimental data [21] was obtained.
Double-ringed and multiringed basins on the Moon and Mercury : morphologic correlations with size and other parameters
(1982) Williams, Adele Fuller; King, Elbert A., Jr.; Butler, John C.; Mote, Victor L.
Clues to the formation of concentric-ringed basins were sought through examination of Lunar Orbitor and Mariner 10 images. Morphologic type, inner ring subtype, size, ring ratio, location, degree of modification, terrain and crustal thickness were determined and correlated with each other. Increase in size from central peak to double-ringed to multiringed basins is noted. Mercury exhibits a strong clustering of basins around 200 km in diameter while the Moon shows a more uniform size distribution. The larger basins are equatorial on both planetary bodies. On the Moon, the larger basins, with the greater ring ratios, are mainly on the nearside. Most inner rings are approximately one half the diameter of the next outer ring, though the ratio is generally smaller for central peak basins and larger for multiringed basins. No certain relationship was found for inner ring subtype, degree of modification or terrain. A rebound model of formation is preferred because it best conforms to the observations, involves a single main mechanism for all concentric-ringed basins, explains a transition from one type to another with increased energy, and confines the main energy within the basin.