Thermal decomposition (pyrolysis) of urea in an open reaction vessel

Schaber, Peter M.; Colson, J. P.; Higgins, Steven R.; Thielen, D.R.; Anspach, B.; Brauer, Jonathan I.

doi:10.1016/j.tca.2004.05.018

Cited by 710 publications

(553 citation statements)

References 7 publications

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“…Melting of urea occurs at around 406 K as reported by Sangster (1999). Schaber et al (2004) reports the vaporization of molten urea at 413 K and direct decomposition into ammonia and isocyanic acid at temperatures above 425 K. The experiments on a single droplet by Wang et al (2009) also show fast depletion of urea at temperatures above 423 K conforming to the observations of Schaber et al (2004). Whereas the experimental data of Emel 'Yanenko et al (2006) and Bernhard et al (2011) suggests urea phase change to gaseous state at temperatures around 406 K. Different numerical approaches have been used to solve this problem.…”

Section: Urea Depletion Thermolysis and Hydrolysismentioning

confidence: 58%

Urea-Water Droplet Phase Change and Reaction Modelling: Multi-Component Evaporation Approach

Shirodkar¹

2016

Frontiers in Heat and Mass Transfer

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Urea-water solution droplet evaporation is modelled using multi-component droplet evaporation approach. The heat and mass transfer process of a multi-component droplet is implemented in the Langrangian framework through a custom code in ANSYS-Fluent R15. The evaporation process is defined by a convection-diffusion controlled model which includes the effect of Stefan flow. A rapid mixing model assumption is used for the droplet internal physics. The code is tested on a single multi-component droplet and the predicted evaporation rates at different ambient temperatures are compared with the experimental data in the literature. The approach is used to model the injection of urea-water solution spray in a duct carrying hot air to predict the urea to ammonia conversion efficiency. Thermolysis reaction of the evaporated urea and the hydrolysis of the byproduct iso-cyanic acid are solved as volumetric reactions in the Eulerian framework using laminar finite rate approach. The spray simulation results are compared with the experimental data and the numerical results of surface reaction based direct thermolysis approach available in the literature.

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Section: Urea Depletion Thermolysis and Hydrolysismentioning

confidence: 58%

Urea-Water Droplet Phase Change and Reaction Modelling: Multi-Component Evaporation Approach

Shirodkar¹

2016

Frontiers in Heat and Mass Transfer

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“…This level is consistent with the observed relative mass just before calcination (79%), which then is the sum of the relative masses of calcium carbonate and stable inorganics. The weight loss in between 112 and 162 • C (5%) may relate to decomposition/combustion of urea, which begins at 130 • C [47]. On the other hand, the decomposition of struvite, yielding magnesium hydrogenphosphate upon releasing ammonia and water, occurs in a single step between~55 and 250 • C [48], and can hardly be separated from the decomposition/combustion of organics.…”

Section: Resultsmentioning

confidence: 99%

Indications that Amorphous Calcium Carbonates Occur in Pathological Mineralisation—A Urinary Stone from a Guinea Pig

et al. 2018

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Abstract:Calcium carbonate is an abundant biomineral that is of great importance in industrial or geological contexts. In recent years, many studies of the precipitation of CaCO 3 have shown that amorphous precursors and intermediates are widespread in the biomineralization processes and can also be exploited in bio-inspired materials chemistry. In this work, the thorough investigation of a urinary stone of a guinea pig suggests that amorphous calcium carbonate (ACC) can play a role in pathological mineralization. Importantly, certain analytical techniques that are often applied in the corresponding analyses are sensitive only to crystalline CaCO 3 and can misleadingly exclude the relevance of calcium carbonate during the formation of urinary stones. Our analyses suggest that ACC is the major constituent of the particular stone studied, which possibly precipitated on struvite nuclei. Minor amounts of urea, other stable inorganics, and minor organic inclusions are observed as well.

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“…The kinetic scheme is shown in Table 1. The kinetic parameters are re-optimized to best match the published experimental data (Schaber et al, 2004).…”

Section: Wall Film Modelmentioning

confidence: 99%

“…Among the four deposit by-products assumed in this study, very little ammelide is produced throughout the temperature range, and urea and biuret are easily decomposed. Consequently, CYA seems to be the most harmful deposit component, since it will not decompose completely unless the temperature is higher than 653 K (Schaber et al, 2004) and is difficult to remove. In our simulation, CYA begins to form from 495 K and becomes the dominant component of deposits at 539 K. This indicates that deposits formed at higher temperatures are more difficult to deal with.…”

Section: Deposit By-products Analysismentioning

confidence: 99%

Quasi 1D modeling of two-phase flow and deposit formation for urea-selective catalytic reduction systems

Gan

Yao

et al. 2016

J. Zhejiang Univ. Sci. A

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A quasi 1D model of two-phase flow for a urea-selective catalytic reduction (SCR) system is developed which can calculate not only the generation of reducing agent but also the formation of deposits in the exhaust pipe. The gas phase flow is solved through Euler method, variables are stored on staggered grids, and the semi-implicit method for pressure-linked equation (SIMPLE) algorithm is applied to decouple the pressure and velocity. The liquid phase is treated in a Lagrangian way, which solves the equations of droplet motion, evaporation, thermolysis, and spray wall interaction. A combination of a direct decomposition model and a kinetic model is implemented to describe the different decomposition behaviors of urea in the droplet phase and wall film, respectively. A new 1D wall film model is proposed, and the equations of wall film motion, evaporation, thermolysis, and species transport are solved. The position, weight, and components of deposits can be simulated following implementation of the semi-detailed kinetic model. The simulation results show that a decrease in the exhaust temperature will increase the wall film region and the weight of deposits. Deposit components are highly dependent on temperature. The urea-water-solution (UWS) injection rate can affect the total mass of wall film and expand the film region, but it has little influence on deposit components. An increase in exhaust mass flow can decrease the total weight of deposits on the pipe wall because of the promotion of the mass and heat transfer process both in the droplets and wall film.

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Thermal decomposition (pyrolysis) of urea in an open reaction vessel

Cited by 710 publications

References 7 publications

Urea-Water Droplet Phase Change and Reaction Modelling: Multi-Component Evaporation Approach

Urea-Water Droplet Phase Change and Reaction Modelling: Multi-Component Evaporation Approach

Indications that Amorphous Calcium Carbonates Occur in Pathological Mineralisation—A Urinary Stone from a Guinea Pig

Quasi 1D modeling of two-phase flow and deposit formation for urea-selective catalytic reduction systems

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