United States Department of Energy

About: United States Department of Energy is a government organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Coal & Catalysis. The organization has 13656 authors who have published 14177 publications receiving 556962 citations. The organization is also known as: DOE & Department of Energy.

Searching for Next Single-Phase High-Entropy Alloy Compositions

Abstract: There has been considerable technological interest in high-entropy alloys (HEAs) since the initial publications on the topic appeared in 2004. However, only several of the alloys investigated are truly single-phase solid solution compositions. These include the FCC alloys CoCrFeNi and CoCrFeMnNi based on 3d transition metals elements and BCC alloys NbMoTaW, NbMoTaVW, and HfNbTaTiZr based on refractory metals. The search for new single-phase HEAs compositions has been hindered by a lack of an effective scientific strategy for alloy design. This report shows that the chemical interactions and atomic diffusivities predicted from ab initio molecular dynamics simulations which are closely related to primary crystallization during solidification can be used to assist in identifying single phase high-entropy solid solution compositions. Further, combining these simulations with phase diagram calculations via the CALPHAD method and inspection of existing phase diagrams is an effective strategy to accelerate the discovery of new single-phase HEAs. This methodology was used to predict new single-phase HEA compositions. These are FCC alloys comprised of CoFeMnNi, CuNiPdPt and CuNiPdPtRh, and HCP alloys of CoOsReRu.

Prediction of hydrogen flux through sulfur-tolerant binary alloy membranes

Abstract: Metal membranes play a vital role in hydrogen purification. Defect-free membranes can exhibit effectively infinite selectivity but must also provide high fluxes, resistance to poisoning, long operational lifetimes, and low cost. Alloying offers one route to improve on membranes based on pure metals such as palladium. We show how ab initio calculations and coarse-grained modeling can accurately predict hydrogen fluxes through binary alloy membranes as functions of alloy composition, temperature, and pressure. Our approach, which requires no experimental input apart from knowledge of bulk crystal structures, is demonstrated for palladium-copper alloys, which show nontrivial behavior due to the existence of face-centered cubic and body-centered cubic crystal structures and have the potential to resist sulfur poisoning. The accuracy of our approach is examined by a comparison with extensive experiments using thick foils at elevated temperatures. Our experiments also demonstrate the ability of these membranes to resist poisoning by hydrogen sulfide.

Overview of combustion and gasification of rice husk in fluidized bed reactors

Abstract: Rice is cultivated in more than 75 countries in the world. The rice husk is the outer cover of the rice and on average it accounts for 20% of the paddy produced, on weight basis. The worldwide annual husk output is about 80 million tonnes with an annual energy potential of 1.210 9 GJ corre- sponding to a heating value of 15 MJ/kg. India alone generates about 22 million tonnes of rice husk per year. If an eAcient method is available, the husk can be converted to a useful form of energy to meet the thermal and mechanical energy requirements of the rice mills themselves. This paper provides an overview of previous works on combustion and gasification of rice husk in atmospheric bubbling fluidized bed reactors and summarizes the state of the art knowledge. As the high ash content, low bulk density, poor flow characteristics and low ash melting point makes the other types of reactors like grate furnaces and downdraft gasifiers either ineAcient or unsuitable for rice husk conversion to energy, the fluidized bed reactor seems to be the promising choice. The overview shows that the reported results are from only small bench or lab scale units. Although a combustion eAciency of about 80% can nor- mally be attained; the reported values in the literature, which are more than 95%, seem to be in higher order. Combustion intensity of about 530 kg/h/m 2 is reported. It is also technically feasible to gasify rice husk in a fluidized bed reactor to yield combustible producer gas, even with suAcient heating value for application in internal combustion engines. A combustible gas with heating value of 4-6 MJ/Nm 3 at a rate of 2.8-4.6 MWth/m 2 seems to be possible. Only very little information is available on the pol- lutant emissions in combustion and tar emissions from gasification. The major conclusion is that the results reported in the literature are limited and vary widely, emphasizing the need for further research to establish suitable and optimum operating conditions for commercial implementations. # 1998 Pub- lished by Elsevier Science Ltd. All rights reserved

Optimization of a Pressure-Swing Adsorption Process Using Zeolite 13X for CO2 Sequestration

Abstract: A pressure-swing adsorption process, which uses zeolite 13X as an adsorbent to recover and sequester carbon dioxide from mixture gas (nitrogen and carbon dioxide), is investigated through dynamic simulation and optimization. The purpose of this paper is to improve the purity of each component by finding optimal values of decision variables with a given power constraint. Langmuir isotherm parameters are calculated from experimental data of zeolite 13X and a general mathematical model consisting of a set of partial differential and algebraic equations and solved in gPROMS. The method of centered finite differences is adopted for the discretization of the spatial domains, and a reduced space SQP method is used for the optimization. As a result, the optimal conditions at cyclic steady state are obtained.