Importance of Vanadium-Catalyzed Oxidation of SO2 to SO3 in Two-Stroke Marine Diesel Engines

Low-speed marine diesel engines are mostly operated on heavy fuel oils, which have a high content of sulfur and ash, including trace amounts of vanadium, nickel, and aluminum. In particular, vanadium oxides could catalyze in-cylinder oxidation of SO2 to SO3, promoting the formation of sulfuric acid and enhancing problems of corrosion. In the present work, the kinetics of the catalyzed oxidation was studied in a fixed-bed reactor at atmospheric pressure. Vanadium oxide nanoparticles were synthesized by spray flame pyrolysis, i.e., by a mechanism similar to the mechanism leading to the formation of the catalytic species within the engine. Experiments with different particle compositions (vanadium/sodium ratio) and temperatures (300–800 °C) show that both the temperature and sodium content have a major impact on the oxidation rate. Kinetic parameters for the catalyzed reaction are determined, and the proposed kinetic model fits well with the experimental data. The impact of the catalytic reaction is studied with a phenomenological zero-dimensional (0D) engine model, where fuel oxidation and SOx formation is modeled with a comprehensive gas-phase reaction mechanism. Results indicate that the oxidation of SO2 to SO3 in the cylinder is dominated by gas-phase reactions and that the vanadium-catalyzed reaction is at most a very minor pathway

Estudio de la oxidación de SO2 a SO3 con catalizadores basados en vanadio. Aplicación a motores marinos diésel de dos tiempos

Los grandes barcos utilizan generalmente motores diesel de dos tiempos, funcionan con fuelóleo pesado, que contiene grandes cantidades de azufre y vanadio. Por ello, es posible que se de lugar a la formación de ácido sulfúrico y que lleve a la llamada corrosión fría. Este trabajo pretende determinar la influencia de la presencia de vanadio sobre la conversión de SO2 y, por tanto, sobre la corrosió fría

Axial Concentration Profiles and NO Flue Gas in a Pilot-Scale Bubbling Fluidized Bed Coal Combustor

Atmospheric bubbling fluidized bed coal combustion of a bituminous coal and anthracite with particle diameters in the range 500-4000 ím was investigated in a pilot-plant facility. The experiments were conducted at steady-state conditions using three excess air levels (10, 25, and 50%) and bed temperatures in the 750-900 °C range. Combustion air was staged, with primary air accounting for 100, 80, and 60% of total combustion air. For both types of coal, high NO concentrations were found inside the bed. In general, the NO concentration decreased monotonically along the freeboard and toward the exit flue; however, during combustion with high air staging and low to moderate excess air, a significant additional NO formation occurred near the secondary air injection point. The results show that the bed temperature increase does not affect the NO flue gas concentration significantly. There is a positive correlation between excess air and the NO flue gas concentration. The air staging operation is very effective in lowering the NO flue gas, but there is a limit for the first stage stoichiometry below which the NO flue gas starts rising again. This effect could be related with the coal rank

New 0-D methodology for predicting NO formation under continuously varying temperature and mixture composition conditions

The development of new diesel combustion modes characterized by low combustion temperatures, to minimize the NOx emissions, has caused a noticeable change in the diesel spray s structure and in the NOx chemistry, gaining relevance the N2O and the prompt routes in detriment of the thermal mechanism.Therefore, to accurately predict the NOx emissions, the detailed chemistry and physics must be taken into account, with the consequence of increasing the computational cost. The authors propose in the current study a new predictive methodology associated to low computational cost, where detailed chemistry and simplified physics are considered. To diminish even more the computational cost, the chemistry was tabulated as a function of temperature and oxygen excess mass fraction (parameter which effectively couples the equivalence ratio and the EGR rate). This tool has been developed with the objective of being applicable in continuously varying temperature and mixture fraction conditions (the diffusion diesel spray context) and was validated with the Two-Stage Lagrangian model (TSL-model) and with real engine measurements. The results in both validation scenarios reflect a high degree of accuracy making it applicable, at least, to perform qualitative predictions. By extension, it is expected to perform similarly in continuously varying temperature conditions (i.e.: homogenous charge compression ignition diesel combustion modes) which are less demanding computationally speaking.The authors would like to acknowledge the contribution of the Spanish Ministry of Economic and Competitively for the financial support of the present research study associate to the projects TRA 2008-06448 (VELOSOOT) and to Dr. V. Golovitchev for his valuable comments and suggestions.Benajes Calvo, JV.; López Sánchez, JJ.; Molina Alcaide, SA.; Redón Lurbe, P. (2015). New 0-D methodology for predicting NO formation under continuously varying temperature and mixture composition conditions. Energy Conversion and Management. 91:367-376. https://doi.org/10.1016/j.enconman.2014.12.010S3673769

Towards a common C0-C2 mechanism: a critical evaluation of rate constants for syngas combustion kinetics

Since the pioneering studies of Tsang and Hampson [1], and of Baulch and co-workers [2, 3], the knowledge of elementary combustion kinetics has increased, largely due to more accurate theories, advanced computing facilities and progresses in experimental measurements [4]. However, no effort has been devoted to the collection and reinterpretation of this knowledge after the early 2000s. Starting in February 2017, we have collected and interpreted a very large number of direct and indirect rate constant measurements from the literature, as well as every state of the art theo-retical calculation available for 50 elementary reaction steps involved in H2/CO pyrolysis and combustion. A strong need for reconciling rate constant measurements and theory has emerged from this analysis. A significant number of the indirect measurements of rate constants and theoretical determinations seem, in fact, to disagree beyond the expected accuracy of parame-ters in the syngas subset. This is mostly due to the need for reconciliation of data and theory and the reinterpretation of the raw signals of the measurements with more accurate and better constrained models according to a careful iterative procedure. The joint effort of SMARTCAT partners at Politecnico di Milano, NUI Galway, ELTE Buda-pest and Denmark Technical University together with RWTH Aachen University (DE) and Argonne National Laboratory (USA), aims to propose a fundamentally based state of the art mechanism for syngas combustion, to serve as a reference for the entire combustion kinetics community. Due to many different reasons, models for real fuels available in the literature rely on more or less different C0-C2 subsets. These differences often do not have substantial im-pacts on the overall performances as different rates in the core mechanism are often counter-balanced by different rates in the model subset relating to heavier fuels. This leads to very sim-ilar radical distributions and therefore in similar macroscopic behavior. However, the adoption of a fundamentally based common core mechanism will constitute a substantial thrust to in-crease the robustness of higher molecular weight fuel’s kinetics