Denitration of High Nitrate Salts Using Reductants

Smith, H.D.; Jones, E. W.; Schmidt, AJ; Zacher, AH; Brown,; Elmore, Joshua R.; Gano,

doi:10.2172/6226

Cited by 9 publications

(19 citation statements)

References 17 publications

(47 reference statements)

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“…Thus, the DTA-measured exothermic enthalpy will underestimate the cellulose/nitrate reaction enthalpy; this contrasts with the 3.12 ARC's operation where the gas's latent heat is not lost and will be observed by the ARC. For the Smith et al (1999) postulated reaction, the theoretical enthalpy would be -0.84 J/g feed or about 3.5 times that measured by DTA. This significant difference is expected because of the removal of the gases and their latent heat; further calculations would be required to estimate the heat removed with the gases.…”

Section: Thermal Sensitivity Of Cellulose-spiked Es-31f Feed As Measumentioning

confidence: 83%

“…The simulated feed is a mixture of simulated S-109 LAW mixed with cellulose (added on a 0.75:1 carbon to nitrate/nitrite nitrogen basis) and GFMs. The nominal stoichiometry identified by Smith et al (1999) determined the nominal molar stoichiometry for the nitrate-reduction reaction to be 1:1; therefore, the simulated feed is designed to eliminate 75% of the nitrate and nitrite.…”

Section: Experimental Designmentioning

confidence: 99%

“…Cellulose proved to be the best carbon source since it improved dryer operations and was reactive enough to react with nitrates at temperatures below 300°C. Smith et al (1999) postulated that cellulose reacts with nitrate via the reaction C 6 H 10 O 5 + 6 NaNO 3 → 3 Na 2 CO 3 + 3 CO 2 + 5 H 2 O + 2 N 2 + N 2 O + O 2 or at a 1:1 C:N molar ratio. Hrma et al's (2005; laboratory experience has shown that cellulose added at concentrations supplying 0.75 moles of carbon for every mole of nitrogen in the feed effectively reduced the amount of MIS penetration and did not react in 22-liter dryer tests at nominal drying conditions.…”

Section: Introductionmentioning

confidence: 99%

“…As we did in our earlier investigations on the reactivity of sucrose's reactions with nitrate/nitrite in simulated 6-tank composite waste (Kim et al 2005), we used thermogravimetric analysis and differential thermal analysis. We also added 1) accelerating rate calorimetry to determine thermal sensitivity and provide another measure of reaction energies or enthalpies and 2) infrared spectrometry and mass spectroscopy to characterize the residual gases from the ARC experiments.PNNL's thermoanalytical studies of cellulose's reaction with nitrate and nitrite in the ES-31F simulated BV feed found that• the reaction proceeds in three distinct steps beginning at 100°C and ending at 550°C• the principal product gases are those postulated by Smith et al (1999) • only small amounts of the flammable gases hydrogen or methane are present in the residual gases• for 1-to 6-g quantities, the reaction onset temperature for ES-31F feed is near 100°C under adiabatic conditions, which is less than the 50°C rule-of-thumb safety margin recommended by the Center for Chemical Process Safety (CCPS) (Heemskerk et al 1995) for reactive chemical systems with no engineered controls of the expected operational temperature of the dryer• once initiated under adiabatic conditions, the cellulose nitrate reaction or series of reactions will continue until completed with significant gas release• engineering analyses of actual process systems are required to determine if the reaction is capable of sustaining itself under non-adiabatic conditions. Although the DTA analyses suggest that when gases are rapidly exhausted from the chemical system, significant heat is removed, these DTA analyses are not representative of larger chemical systems where the product, heat-bearing gases have an opportunity to significantly interact with residual solids.…”

mentioning

confidence: 99%

“…• the principal product gases are those postulated by Smith et al (1999) • only small amounts of the flammable gases hydrogen or methane are present in the residual gases…”

mentioning

confidence: 99%

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Evaluation of Exothermic Reactions from Bulk-Vitrification Melter Feeds Containing Cellulose

Scheele¹,

McNamara²,

Bagaasen³

et al. 2007

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SummaryThe baseline bulk-vitrification (BV) process (also known as in-container vitrification ICV™) includes a mixer/dryer to convert liquid waste into a dried, blended feed for vitrification. Feed preparation includes blending liquid low-activity waste (LAW) with glass-forming minerals and cellulose and drying the mixture to a suitable dryness, consistency, and particle size for transport to the ICV TM container.This drying process is conducted under vacuum in the temperature range of 60 to 80°C. The nominal melting process starts with a refractory-lined metal box that is partially filled with feed. The refractory lining is referred to as the castable refractory block (CRB). Heat is applied in the form of electrical power through two graphite electrodes. Initially, the electrical current is carried through a graphite starter path, but as the feed is heated, it forms a molten glass that becomes the electrical conductor. The feed subsides as the glass is formed, allowing more feed to be added to the top of the melt in a feed-while-melt operation that continues until the box is filled to the desired level with glass.A full-scale (FS) test (FS-38C) was conducted in CY06 (Witwer et al. 2007), which evaluated using a thick cold cap of feed to condense volatile contaminants and increase the single-pass retention of those contaminants in the BV melt. Using a thick cold cap resulted in high single-pass retentions and significant quantities of molten ionic salt (MIS) outside the CRB panels, which is thought to be related to the thick cold cap.The main problem with MIS outside of the CRB panels is that radionuclides in the LAW are also initially salts and are concentrated in the MIS. If the MIS migrates to cooler regions of the ICV™, the salts either do not decompose, or they partially decompose to form glasses with poor durability. This is undesirable as the unreacted salts and low-durability glasses are susceptible to leaching after disposal. The significant quantities of MIS in the FS-38C test are also thought to be related to the high concentration of lowmelting nitrates in the Tank 241-S-109 simulant (S-109) used for the test.Because Tc is carried into the CRB by MIS, decreasing MIS migration into the CRB would proportionally decrease the concentration of the soluble Tc in the refractory lining. Current activities are exploring several methods for controlling MIS migration but focus mainly on methods to decrease the MIS mobility within the BV feed. These studies find that the MIS mobility is decreased by 1) increasing the specific surface area of solids and 2) adding organic carbon to denitrate the feed and reduce the amount of MIS. Using solids with fine grains or grinding the existing solids (soil) reduces migration by bonding free MIS to solid grains by capillary forces. Adding organic carbon decreases the amount of MIS in the feed by destroying its main components, nitrates and nitrites, at temperatures below 300°C. iv However, because of potential increased reactivity at off-normal conditions, the project pursue...

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Section: Thermal Sensitivity Of Cellulose-spiked Es-31f Feed As Measumentioning

confidence: 83%

Section: Experimental Designmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

“…• the principal product gases are those postulated by Smith et al (1999) • only small amounts of the flammable gases hydrogen or methane are present in the residual gases…”

mentioning

confidence: 99%

See 3 more Smart Citations

Evaluation of Exothermic Reactions from Bulk-Vitrification Melter Feeds Containing Cellulose

Scheele¹,

McNamara²,

Bagaasen³

et al. 2007

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Effect of sucrose on foaming and melting behavior of a low‐activity waste melter feed

et al. 2019

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Reductants, such as sucrose (C12H22O11), are added to nuclear waste melter feeds containing high fractions of nitrates and nitrites to reduce excessive foaming during feed‐to‐glass conversion, decrease sulfate segregation, and increase technetium retention. The effect of sucrose on foaming and melting reactions during the conversion was examined using the feed volume expansion test, thermogravimetric analysis, evolved gas analysis, x‐ray diffraction, and scanning electron microscopy with energy dispersive x‐ray spectrometry. Different amounts of sucrose were added to vary the carbon to nitrogen (C/N) ratio in the melter feed. As the C/N ratio increased, the extent of foaming decreased, and the N2/NO ratio increased in the evolved gas. Significant foam suppression, rapid gas release at approximately 250°C, and reduction in transition metal oxides were observed at C/N > 1.1.

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Initial Laboratory-Scale Melter Test Results for Combined Fission Product Waste

Riley¹,

Crum²,

Buchmiller³

et al. 2009

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SUMMARYPacific Northwest National Laboratory (PNNL) and Savannah River National Laboratory performed a joint study to develop acceptable glasses for the combined alkali and alkaline-earth fission products (CS) + lanthanide fission products (LN) + transition metal fission products (TM) waste streams and CS + LN combined waste streams. Glass CSLNTM-C-2.5 was selected as the baseline glass for the CS + LN + TM waste stream as it had the highest MoO 3 -loaded glass that did not crystallize during slow cooling and it had properties within acceptable tolerances for glass processing and waste form performance (Crum et al., 2009).To obtain an initial understanding on the processability of this selected glass composition, initial smallscale melter tests were performed. This report summarizes the melter feed processing in a 3"-diameter laboratory-scale melter at PNNL as well as techniques that could be employed to improve the efficiency of vitrifying such a waste stream. Two experiments were run (including a shakedown test) in the melter with the same feed, representative of the actual waste stream. Reaction vessel and off-gas line solid condensates were analyzed to perform a mass-balance of the most volatile components -Cs and Mo. The analysis of the condensates showed that volatile components (i.e., Cs, Mo) evolved during the melting process at reasonable concentrations. From these studies, it is apparent that a recuperator for the volatile compounds should be considered. Initial Laboratory-Scale Melter Test Results for Combined Fission Product Waste

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Denitration of High Nitrate Salts Using Reductants

Cited by 9 publications

References 17 publications

Evaluation of Exothermic Reactions from Bulk-Vitrification Melter Feeds Containing Cellulose

Evaluation of Exothermic Reactions from Bulk-Vitrification Melter Feeds Containing Cellulose

Effect of sucrose on foaming and melting behavior of a low‐activity waste melter feed

Initial Laboratory-Scale Melter Test Results for Combined Fission Product Waste

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