An experimental and modeling study of acetylene-dimethyl ether mixtures oxidation at high-pressure

The oxidation of acetylene (as soot precursor) and dimethyl ether (DME, as a promising fuel additive) mixtures has been analyzed in a tubular flow reactor, under high-pressure conditions (20, 40 and 60 bar), in the 450–1050 K temperature range. The effect of varying the air excess ratio (λ≈0.7, 1 and 20) and the percentage of DME with respect to acetylene (10 and 40%) has been analyzed from both experimental and modeling points of view. The addition of DME modifies the composition of the radical pool, increasing the production of OH radicals which cause a shift in the onset temperature for C2H2 conversion to lower temperatures; the higher the amount of DME, the lower the temperature. The presence of DME favors the oxidation of C2H2 towards products such as CO and CO2, eliminating carbon from the paths that lead to the formation of soot. On the other hand, in the presence of C2H2, DME begins to be consumed at temperatures higher than those required for the high-pressure oxidation of neat DME, around 175–200 K more. Consequently, the negative temperature coefficient (NTC) region characteristic of this compound at low temperatures is not observed under those conditions. However, an additional analysis of the influence of DME inlet concentration (at 20 bar and λ=1) indicates that, if the amount of DME in the mixture is increased to 500 ppm and more (700 or 1000 ppm), the reaction pathways responsible for this high DME reactivity at low temperatures become more relevant and the NTC region can now be observed

A study of dimethyl carbonate conversion and its impact to minimize soot and NO emissions

Fuel reformulation through the use of oxygenated compounds e.g. dimethyl carbonate (DMC) is a potential option both to reduce the harmful soot emissions and to overcome the dependence on fossil fuels since many of them are bio-derived fuels. DMC presents a relative high oxygen content as compared with other additives and suitable characteristics to be used in combustion systems. The different fundamental aspects of the DMC combustion process including its oxidation behavior its tendency to produce soot and the role of the NO presence in the reaction system were studied. Experiments were conducted under well controlled conditions using specifically designed flow reactor systems. Results demonstrated the low tendency of DMC to form soot compared to other oxygenates and its capacity to contribute to NO reduction under specific fuel-rich conditions. Modeling calculations successfully reproduce reasonably well the experimental trends observed and emphasized the sensitivity of the results to the thermodynamic data of DMC and DMC derived species

CO assisted NH3 oxidation

In the present work, experimental results from the literature on the effect of CO on the NH oxidation in the absence and presence of NO are supplemented with novel flow reactor results and interpreted in terms of a detailed chemical kinetic model. The kinetic model provides a satisfactory prediction over a wide range of conditions for oxidation in flow reactors and for flame speeds of CO/NH. With increasing levels of CO, the generation of chain carriers gradually shifts from being controlled by the amine reaction subset to being dominated by the oxidation chemistry of CO, facilitating reaction at lower temperatures. At elevated temperature, presence of CO causes a change in selectivity of NH oxidation from N to NO. The present work provides a thorough evaluation of the amine subset of the reaction mechanism for the investigated conditions and offers a kinetic model that reliably can be used for post-flame oxidation modeling in engines and gas turbines fueled by ammonia with a hydrocarbon or alcohol as co-fuel

Experimental and Modeling Evaluation of Dimethoxymethane as an Additive for High-Pressure Acetylene Oxidation

The high-pressure oxidation of acetylene–dimethoxymethane (C2H2–DMM) mixtures in a tubular flow reactor has been analyzed from both experimental and modeling perspectives. In addition to pressure (20, 40, and 60 bar), the influence of the oxygen availability (by modifying the air excess ratio, λ) and the presence of DMM (two different concentrations have been tested, 70 and 280 ppm, for a given concentration of C2H2 of 700 ppm) have also been analyzed. The chemical kinetic mechanism, progressively built by our research group in the last years, has been updated with recent theoretical calculations for DMM and validated against the present results and literature data. Results indicate that, under fuel-lean conditions, adding DMM enhances C2H2 reactivity by increased radical production through DMM chain branching pathways, more evident for the higher concentration of DMM. H-abstraction reactions with OH radicals as the main abstracting species to form dimethoxymethyl (CH3OCHOCH3) and methoxymethoxymethyl (CH3OCH2OCH2) radicals are the main DMM consumption routes, with the first one being slightly favored. There is a competition between β-scission and O2-addition reactions in the consumption of both radicals that depends on the oxygen availability. As the O2 concentration in the reactant mixture is increased, the O2-addition reactions become more relevant. The effect of the addition of several oxygenates, such as ethanol, dimethyl ether (DME), or DMM, on C2H2 high-pressure oxidation has been compared. Results indicate that ethanol has almost no effect, whereas the addition of an ether, DME or DMM, shifts the conversion of C2H2 to lower temperatures

High-pressure study of methyl formate oxidation and its interaction with NO

An experimental and modeling study of the influence of pressure on the oxidation of methyl formate (MF) has been performed in the 1-60 bar pressure range, in an isothermal tubular quartz flow reactor in the 573-1073 K temperature range. The influence of stoichiometry, temperature, pressure, and presence of NO on the conversion of MF and the formation of the main products (CH2O, CO2, CO, CH4, and H2) has been analyzed. A detailed kinetic mechanism has been used to interpret the experimental results. The results show that the oxidation regime of MF differs significantly from atmospheric to high-pressure conditions. The impact of the NO presence has been considered, and results indicate that no net reduction of NOx is achieved, even though, at high pressure, the NO-NO2 interconversion results in a slightly increased reactivity of MF

NH3 oxidation and NO reduction by NH3 in N2/Ar and CO2 atmospheres

Impact of using CO2 or N2/Ar as bath gas, representative respectively of oxy-fuel or air combustion scenarios, has been evaluated on the oxidation of ammonia under a variety of operating conditions in a combined experimental and simulation study. Variables of relevance as temperature and oxygen stoichiometry have been considered at atmospheric pressure and under carefully controlled experimental conditions. Additionally, the impact of the presence of NO, which can be formed from ammonia oxidation, has also been evaluated. The experimental results obtained have been simulated with significant success with a detailed literature kinetic mechanism, which has been further used to interpret the main experimental observations. The results obtained are of interest in the power and energy industry, and can be used for guiding the co-firing of NH3 and carbon containing fuels

Ethanol as a Fuel Additive: High-Pressure Oxidation of Its Mixtures with Acetylene

An experimental and modeling study of the oxidation of acetylene-ethanol mixtures under high-pressure conditions (10-40 bar) has been carried out in the 575-1075 K temperature range in a plug-flow reactor. The influence on the oxidation process of the oxygen inlet concentration (determined by the air excess ratio, λ) and the amount of ethanol (0-200 ppm) present in the reactant mixture has also been evaluated. In general, the predictions obtained with the proposed model are in satisfactory agreement with the experimental data. For a given pressure, the onset temperature for acetylene conversion is almost the same independent of the oxygen or ethanol concentration in the reactant mixture but is shifted to lower temperatures when the pressure is increased. Under the conditions of this study, the ethanol presence does not modify the main reaction routes for acetylene conversion, with its main effect being the modification of the radical pool composition

Conversion of NH3 and NH3-NO mixtures in a CO2 atmosphere. A parametric study

The present work addresses the oxidation of ammonia and ammonia-nitric oxide mixtures in a CO2 atmosphere, characteristic of oxy-fuel processes and/or biogas combustion, from both experimental and kinetic modelling points of view. A parametric study of NH3 and NH3/NO mixtures oxidation is carried out, evaluating the influence of the temperature (700–1500 K), stoichiometry (from pyrolysis, λ = 0, to significantly oxidizing conditions, λ = 3.3), gas residence time (low values, 195/T(K) s and high values, 3100/T(K) s) and NH3/NO ratio (0.5–2.2), at atmospheric pressure under well-controlled laboratory conditions using two tubular flow reactor setups. Experimental results have been simulated with an updated literature reaction mechanism, which has been used to interpret the experimental observations

Oxidación de mezclas de acetileno y dimetoximetano

En el presente trabajo se ha realizado una serie de experimentos de oxidación del acetileno con concentraciones de DMM distintas (50 y 200 ppm) y en presencia y ausencia de NO. El principal objetivo consiste en determinar cuáles son las mejores condiciones para la eliminación del acetileno y, por tanto, de la materia particulada y NOx. Además de los experimentos, también se ha realizado una simulación con las condiciones de dichos experimentos. Se trabaja a temperatura ambiente, presión atmosférica y en un rango de temperaturas de 500 a 1100 ºC. El reactor utilizado es de flujo pistón en un horno eléctrico abierto. Los mejores resultados se obtienen para 50 ppm de DMM, en condiciones oxidantes y en presencia de NO

Interacción de NH3 y HCN con NO en condiciones de oxi-combustión

En el contexto energético y medioambiental actual, la captura y almacenamiento de CO2 surge como la única manera de seguir produciendo energía a partir de combustibles fósiles sin emitir CO2 a la atmósfera. Entre las distintas opciones de captura, la oxi-combustión es una buena opción debido a que en ella se produce una corriente del 95-98% de CO2. En esta técnica, el combustible se quema con O2 puro en lugar de aire junto con parte de los gases de salida que se recirculan para diluir el oxígeno. Otros contaminantes producidos en los procesos de combustión como por ejemplo los NOx deberán ser eliminados y/o producidos en menor medida antes de que el CO2 sea capturado. El proceso de reburning es una técnica que ha sido empleada desde los años 90 para reducir la cantidad de NOx producidos en combustión tradicional con aire. Una etapa clave en el proceso es la oxidación de HCN y NH3 en presencia de NO en atmósfera de CO2, y dado que apenas existen estudios al respecto, el objetivo del presente PFM es estudiar la oxidación de HCN y NH3 en condiciones de oxi-combustión. El trabajo se ha realizado tanto experimentalmente como mediante simulación con un modelo cinético. El estudio experimental se ha llevado a cabo en un reactor de flujo pistón isotermo a presión atmosférica, estudiándose variables clave como temperatura (600-1.150 °C), concentración de oxígeno (250-3.500 ppm de O2), que representan valores de estequiometría entre ?= 0,2 y 2, y presencia y concentración de NO. Además, en el caso del NH3 se ha estudiado la influencia de la atmósfera (CO2-N2) debido a la ausencia de un estudio similar. Los resultados experimentales se han comparado con un modelo de cinética química utilizando el software de simulación CHEMKIN-PRO. Los resultados obtenidos indican que la oxidación de NH3 sin NO se ve desfavorecida en atmósfera de CO2 con respecto a atmósfera de N2 en todas las estequiometrías estudiadas. La influencia de la concentración de oxígeno es mayor en atmósfera de N2 que en CO2. La formación de NO está favorecida en atmósfera de N2 debido a la reacción N2 + H2O NO + NH2. La presencia de NO acelera la oxidación de NH3 en todas las concentraciones de oxígeno estudiadas. La mayor reducción de NO por NH3 se alcanza para condiciones oxidantes. La presencia de NO inhibe la oxidación de HCN hasta las temperaturas 1.050-1.150 °C para todas las estequiometrías estudiadas. A partir de dicha temperatura, la oxidación de HCN es independiente de la presencia de NO y se obtienen valores similares de conversión de HCN. La reducción de NO es mayor cuanto más oxidantes son las condiciones. En cuanto a la simulación de los experimentos, el modelo es capaz de predecir correctamente tanto la oxidación de HCN y la reducción de NO como la formación de N2O. Sin embargo, el modelo no es capaz de predecir correctamente la oxidación de NH3 en atmósfera de CO2 y/o N2 ni tampoco en ausencia y/o presencia de NO