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Miller, D

Publications and source records attributed to Miller, D.

30 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

IMPACT OF SMALL COLUMN ION EXCHANGE STREAMS ON DWPF GLASS FORMULATION MELT RATE STUDIES

This study was undertaken to evaluate the potential impacts of the Small Column Ion Exchange (SCIX) streams - particularly the addition of Monosodium Titanate (MST) and Crystalline Silicotitanate (CST) - on the melt rate of simulated feed for the Defense Waste Processing Facility (DWPF). Additional MST was added to account for contributions from the Salt Waste Processing Facility (SWPF). The Savannah River National Laboratory (SRNL) Melt Rate Furnace (MRF) was used to evaluate four melter feed compositions: two with simulated SCIX and SWPF material and two without. The Slurry-fed Melt Rate Furnace (SMRF) was then used to compare two different feeds: one with and one without bounding concentrations of simulated SCIX and SWPF material. Analyses of the melter feed materials confirmed that they met their targeted compositions. Four feeds were tested in triplicate in the MRF. The linear melt rates were determined by using X-ray computed tomography to measure the height of the glass formed along the bottom of the beakers. The addition of the SCIX and SWPF material reduced the average measured melt rate by about 10% in MRF testing, although there was significant scatter in the data. Two feeds were tested in the SMRF. It was noted that the ground CST alone (ground CST with liquid in a bucket) was extremely difficult to resuspend during preparation of the feed with material from SCIX and SWPF. This feed was also more difficult to pump than the material without MST and CST due to settling occurring in the melter feed line, although the yield stress of both feeds was high relative to the DWPF design basis. Steady state feeding conditions were maintained for about five hours for each feed. There was a reduction in the feed and pour rates of approximately 15% when CST and MST were added to the feed, although there was significant scatter in the data. Analysis of samples collected from the SMRF pour stream showed that the composition of the glass changed as expected when MST and CST were added to the feed. These reductions in melt rate are consistent with previous studies that showed a negative impact of increased TiO{sub 2} concentrations on the rate of melting. The impact of agitating the melt pool via bubbling was not studied as part of this work, but may be of interest for further testing. It is recommended that additional melt rate testing be performed should a potential reduction in melt rate of 10-15% be considered an issue of concern, or should the anticipated composition of the glass with the addition of material from salt waste processing be modified significantly from the current projections, either due to changes in sludge batch preparation or changes in the composition or volume of SCIX and SWPF material.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2011

Modeling of circulating fluised beds for post-combustion carbon capture

A compartment based model for a circulating fluidized bed reactor has been developed based on experimental observations of riser hydrodynamics. The model uses a cluster based approach to describe the two-phase behavior of circulating fluidized beds. Fundamental mass balance equations have been derived to describe the movement of both gas and solids though the system. Additional work is being performed to develop the correlations required to describe the hydrodynamics of the system. Initial testing of the model with experimental data shows promising results and highlights the importance of including end effects within the model.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2011

A model for the adsorption kinetics of CO2 on amine-impregnated mesoporous sorbents in the presence of water

A simple model for the adsorption kinetics carbon dioxide onto an amine-impregnated mesoporous sorbent, NETL-32D, was developed. The model was developed based on the mechanistic pathways believed to be responsible for the uptake of CO2 by the sorbent, including interactions with H2O. The model consists of quasi-ideal expressions to describe the kinetics of three reactions responsible for the uptake of CO2 and H2O by the sorbent. The model was fitted to experimental data obtained from thermogravimetric analysis and found to be a reasonable representation of the observed equilibrium and kinetics. The model is able to predict the increased uptake due to the interaction between CO2 and H2O in the sorbent. The heat of reaction predicted by the model for the uptake of CO2 in dry conditions of -65 kJ/mol compares well to the value of -67 kJ/mol obtained via calorimetry for similar sorbents.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2011

A computational methodology for learning low-complexity surrogate models of process from experiments or simulations. (Paper 679a)

Costly and/or insufficiently robust simulations or experiments can often pose difficulties when their use extends well beyond a single evaluation. This is case with the numerous evaluations of uncertainty quantification, when an algebraic model is needed for optimization, as well as numerous other areas. To overcome these difficulties, we generate an accurate set of algebraic surrogate models of disaggregated process blocks of the experiment or simulation. We developed a method that uses derivative-based and derivative-free optimization alongside machine learning and statistical techniques to generate the set of surrogate models using data sampled from experiments or detailed simulations. Our method begins by building a low-complexity surrogate model for each block from an initial sample set. The model is built using a best subset technique that leverages a mixed-integer linear problem formulation to allow for very large initial basis sets. The models are then tested, exploited, and improved through the use of derivative-free solvers to adaptively sample new simulation or experimental points. The sets of surrogate models from each disaggregated process block are then combined with heat and mass balances around each disaggregated block to generate a full algebraic model of the process. The full model can be used for cheap and accurate evaluations of the original simulation or experiment or combined with design specifications and an objective for nonlinear optimization.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2011

Optimization of carbon capture systems using surrogate models of simulated processes.

With increasing demand placed on power generation plants to reduce carbon dioxide (CO2) emissions, processes to separate and capture CO2 for eventual sequestration are highly sought after. Carbon capture processes impart a parasitic load on the power plants; it is estimated that this would increase the cost of electricity from existing pulverized coal plants anywhere from 71-85 percent [1]. The National Energy and Technology Lab (NETL) is working to lower this to below a 30 percent increase. To reach this goal, work is being done not only to accurately simulate these processes, but also to leverage those accurate and detailed simulations to design optimal carbon capture processes. The major challenges include the lack of accurate algebraic models of the processes, computationally costly simulations, and insufficiently robust simulations. The first challenge bars the use of provable derivative-based optimization algorithms. The latter two can either lead to difficult or impossible direct derivative-free optimization. To overcome these difficulties, we take a more indirect method to solving this problem by, first, generating an accurate set of algebraic surrogate models from the simulation then using derivative-based solvers to optimize the surrogate models. We developed a method that uses derivative-based and derivative-free optimization alongside machine learning and statistical techniques to generate the set of low-complexity surrogate models using data sampled from detailed simulations. The models are validated and improved through the use of derivative-free solvers to adaptively sample new simulation points. The resulting surrogate models can then be used in a superstructure-based process synthesis and solved using derivative-based methods to optimize carbon capture processes.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2011

Development of moving bed simulation model for carbon capture from fossil energy systems.

The capture and separation of carbon dioxide (CO2) has been identified as a high-priority topic to cope with global climate change. Fossil fuels currently supply the most of the world's energy needs, and their utilization is the major source of the anthropogenic CO2 emission [1]. Particularly, the existing coal-fired power plants annually emit about 2 billion tons of CO2 which is equivalent to two-thirds of the total emissions from U.S. power sector [2]. Therefore, it is critical to develop the cost-effective technologies to mitigate this problem. There are three options for capture for capturing CO2 from fossil energy system: post-combustion capture, pre-combustion capture, and oxy-combustion. Among them, post-combustion capture has the greatest near-term potential for reducing CO2 emission, because it can be applied to the existing coal-fired power plant with relative ease through a retrofit. The current commercially available solvent-based processes have advantages of fast kinetics and strong reactions, however only at a significant cost and efficiency penalty. Recently, various solid sorbents are being explored for one of promising CO2 capture technology, which are expected to reduce energy requirement and water usage with the approaches of fluidized or moving bed. However, solids are inherently more difficult to work with than liquids and no large scale system has yet been commercialized. In this study, we developed the rigorous 1-D PDE model for moving beds in Aspen Custom Modeler; the entire system consists of adsorbers, regenerators, and auxiliary equipment. The simulation result will be expected to compare with those of other post-combustion processes. We will deal with not only advantages of lower capital costs and power requirements but also problems associated with pressure drop and heat transfer.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2011

Economic analysis of municipal wastewater utilization for thermoelectric power production

The thermoelectric power industry in the U.S. uses a large amount of freshwater. The large water demand is increasingly a problem, especially for new power plant development, as availability of freshwater for new uses diminishes in the United States. Reusing non-traditional water sources, such as treated municipal wastewater, provides one option to mitigate freshwater usage in the thermoelectric power industry. The amount of freshwater withdrawal that can be displaced with non-traditional water sources at a particular location requires evaluation of the water management and treatment requirements, considering the quality and abundance of the non-traditional water sources. This paper presents the development of an integrated costing model to assess the impact of degraded water treatment, as well as the implications of increased tube scaling in the main condenser. The model developed herein is used to perform case studies of various treatment, condenser cleaning and condenser configurations to provide insight into the ramifications of degraded water use in the cooling loops of thermoelectric power plants. Further, this paper lays the groundwork for the integration of relationships between degraded water quality, scaling characteristics and volatile emission within a recirculating cooling loop model.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2011

Effect of makeup water properties on the condenser fouling in power planr cooling system

The thermoelectric power industry in the U.S. uses a large amount of fresh water. As available freshwater for use in thermoelectric power production becomes increasingly limited, use of nontraditional water sources is of growing interest. Utilization of nontraditional water, in cooling systems increases the potential for mineral precipitation on heat exchanger surfaces. In that regard, predicting the accelerated rate of scaling and fouling in condenser is crucial to evaluate the condenser performance. To achieve this goal, water chemistry should be incorporated in cooling system modeling and simulation. This paper addresses the effects of various makeup water properties on the cooling system, namely pH and aqueous speciation, both of which are important factors affecting the fouling rate in the main condenser. Detailed modeling of the volatile species desorption (i.e. CO{sub 2} and NH{sub 3}), the formation of scale in the recirculating system, and the relationship between water quality and the corresponding fouling rates is presented.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2011

Synthesis of optimal adsorptive carbon capture processes.

Solid sorbent carbon capture systems have the potential to require significantly lower regeneration energy compared to aqueous monoethanol amine (MEA) systems. To date, the majority of work on solid sorbents has focused on developing the sorbent materials themselves. In order to advance these technologies, it is necessary to design systems that can exploit the full potential and unique characteristics of these materials. The Department of Energy (DOE) recently initiated the Carbon Capture Simulation Initiative (CCSI) to develop computational tools to accelerate the commercialization of carbon capture technology. Solid sorbents is the first Industry Challenge Problem considered under this initiative. An early goal of the initiative is to demonstrate a superstructure-based framework to synthesize an optimal solid sorbent carbon capture process. For a given solid sorbent, there are a number of potential reactors and reactor configurations consisting of various fluidized bed reactors, moving bed reactors, and fixed bed reactors. Detailed process models for these reactors have been modeled using Aspen Custom Modeler; however, such models are computationally intractable for large optimization-based process synthesis. Thus, in order to facilitate the use of these models for process synthesis, we have developed an approach for generating simple algebraic surrogate models that can be used in an optimization formulation. This presentation will describe the superstructure formulation which uses these surrogate models to choose among various process alternatives and will describe the resulting optimal process configuration.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2010

{sup 34}P({sup 7}Li,{sup 7}Be+{gamma}) Reaction at 100A MeV in Inverse Kinematics

We report on the first successful extraction of a {beta}{sup +} Gamow-Teller strength distribution from a radioactive isotope in an intermediate-energy charge-exchange experiment in inverse kinematics. The ({sup 7}Li,{sup 7}Be+{gamma}(429 keV)) reaction at 100A MeV was used to measure Gamow-Teller transition strengths from {sup 34}P to states in {sup 34}Si. The results show that little mixing occurs between sd and pf shell configurations for the low-lying 0{sup +} and 2{sup +} states even though {sup 34}Si neighbors the island of inversion and low-lying 2({h_bar}/2{pi}){omega} intruder states exist. Shell-model calculations in the sdpf model space are consistent with these findings.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

MELT RATE TESTING FOR SLUDGE BATCH 6

The Savannah River National Laboratory (SRNL) was requested to provide Savannah River Remediation (SRR) with a recommended frit composition for Sludge Batch 6 (SB6) to optimize processing at the Defense Waste Processing Facility (DWPF). This report discusses the results of a series of melt rate experiments that were completed in support of the frit recommendation and the preparation of the feed used in the testing. The objective of the work was to identify the impact of individual frit component concentrations on melt rate for both SB6 and for DWPF sludge batches in general. The dry fed, Melt Rate Furnace (MRF) was used to compare the relative melt rate performance of several candidate frit compositions. Sludge composition projection changes and variation led to the fabrication and testing of several new frits along with Frit 418, which is currently utilized at the DWPF for Sludge Batch 5 (SB5) processing. The melt rate testing results show that changes in the frit composition, such as increases in B{sub 2}O{sub 3} or Li{sub 2}O concentrations, can provide a faster melt rate for SB6 relative to Frit 418. However, the composition of SB6 as currently projected (February 2010 blended with a 40 inch heel of SB5) does not allow for significant changes in frit composition relative to Frit 418 without compromising the projected operating windows. Only one of the new frits tested, Frit IS7, remains viable for SB6 processing based on the current composition projections. The melt rate results also demonstrated that a low Na{sub 2}O concentration frit (particularly Frit IS7) can provide reasonable melt rates if the concentrations of Li{sub 2}O or B{sub 2}O{sub 3} in the frit are increased. The measured melt rate for Frit IS7 with the simulated SB6 feed was about 15% faster than that for Frit 418. The projected operating windows for Frits 418 and IS7 are very similar with the current SB6 projections. However, waste loadings with Frit IS7 are limited by low viscosity predictions, while waste loadings with Frit 418 are limited by predictions of nepheline crystallization. It is recommended that SRNL reevaluate the final SB6 composition once washing and blending are complete to determine whether a change in frit composition could provide improved operating windows, improved sulfate solubility, and/or increased waste throughput.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗