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In recent years, hydrogen-carrying compounds have accrued interest as an alternative to traditional fossil fuels due to their function as zero-emission fuels. As such, there is interest in investigating hydrogen-carrying compounds to improve understanding of the fuels' characteristics for use in high pressure systems. In the current study, the oxidation of ammonia/natural gas/hydrogen mixtures was carried out to study carbon monoxide (CO) formation profiles as well as the ignition delay times (IDTs) behind reflected shock waves in order to refine chemical kinetic models. Experiments were carried out in the University of Central Florida's shock tube facility by utilizing chemiluminescence to obtain OH* emission and laser absorption spectroscopy to obtain CO profiles over a temperature range between 1200 K and 1800 K with an average pressure of 2.2 atm. Experimental mixtures included both neat and combination natural gas/hydrogen with ammonia addition, with all mixtures except one having an equivalence ratio of 1. Results were then compared with the GRI 3.0 mechanism, as well as the newly developed UCF 2022 mechanism utilizing chemkin-pro software. In general, both models were able to capture the trend in auto-ignition delay times and CO time histories for natural gas and ammonia mixtures. However, for ammonia-hydrogen mixtures, GRI 3.0 failed to predict ignition delay times, whereas the UCF 2022 mechanism was able to capture the IDTs within the uncertainty limits of the experiments. A sensitivity analysis was conducted for different mixtures to understand the important reactions at the experimental conditions. Finally, a reaction pathway analysis was carried out to understand important ammonia decomposition pathways in the presence of hydrogen and natural gas. [ABSTRACT FROM AUTHOR]

Ignition delay times from undiluted mixtures of natural gas (NG)/H2/Air and NG/NH3/Air were measured using a high-pressure shock tube at the University of Central Florida. The combustion temperatures were experimentally tested between 1000 and 1500 K near a constant pressure of 25 bar. As mentioned, mixtures were kept undiluted to replicate the same chemistry pathways seen in gas turbine combustion chambers. Recorded combustion pressures exceeded 200 bar due to the large energy release, hence why these were performed at the high-pressure shock tube facility. The data are compared to the predictions of the NUIGMech 1.1 mechanism for chemical kinetic model validation and refinement. An exceptional agreement was shown for stoichiometric conditions in all cases but strayed at lean and rich equivalence ratios, especially in the lower temperature regime of H2 addition and all temperature ranges of the baseline NG mixture. Hydrogen addition also decreased ignition delay times by nearly 90%, while NH3 fuel addition made no noticeable difference in ignition time. NG/NH3 exhibited similar chemistry to pure NG under the same conditions, which is shown in a sensitivity analysis. The reaction CH3 + O2 = CH3O + O is identified and suggested as a possible modification target to improve model performance. Increasing the robustness of chemical kinetic models via experimental validation will directly aid in designing next-generation combustion chambers for use in gas turbines, which in turn will greatly lower global emissions and reduce greenhouse effects. [ABSTRACT FROM AUTHOR]

An increase in the exploitation of sour reservoirs with a high content of acid gas (mainly H2S and CO2) and the enforcement of stringent emission standards have triggered demand for high sulfur recovery efficiency in sulfur recovery units (SRUs). The high amount of H2O that is present in feed gases to the SRU can act as a diluent in the thermal section of the SRU and can also pose operational difficulties and have substantial chemical effect on the equilibrium-limited reactions of sulfur production and the destruction of impurities. This paper explores the role of H2O (0-12% in the furnace feed) in sulfur recovery and in the fate of undesirable aromatics, COS, and CS2 in the thermal section using a detailed reaction mechanism and industrial SRU operating parameters. An increasing H2O concentration in the feed decreased the sulfur recovery efficiency in the thermal section significantly, as the equilibrium conversion of H2S to sulfur was affected. The higher H2O concentrations increased the concentrations of H2S, H2, and SO2 at the furnace exit because of the production of OH radicals from enhanced chemical decomposition of H2O by active radicals such as SH, O, and H. It also increased the quantity of unwanted aromatics exiting the Claus furnace, but COS and CS2 production declined because of the fall in the decomposition of CO2 and feed hydrocarbons as the furnace temperature decreased. This study provides guidelines to increase sulfur production in the thermal section and reduce the number of catalytic stages to decrease SRU operational cost. [ABSTRACT FROM AUTHOR]