GE Oil and Gas

The oxidation of n-butane at elevated pressures has been investigated by experiments in a laminar flow reactor at 100 bar and temperatures of 450-900 K. The onset temperature for reaction increased from 550 K under oxidizing conditions (& phi; = 0.02) to 625 K under reducing conditions (& phi; = 13). NTC behavior was observed at 600-650 K (& phi; = 0.02) and 625-675 K (& phi; = 1.0). A detailed chemical kinetic model for the oxidation of n-butane was established. The present model and those suggested in literature were evaluated against the present experimental results and literature data at elevated pressures. None of the tested models could accurately reproduce the NTC behavior of n-butane under stoichiometric conditions of the present study, but all evaluated models could reproduce experimental data from literature with different levels of accuracy.

Autoignition delay times of ammonia/dimethyl ether (NH3/DME) mixtures were measured in a rapid compression machine with DME fractions of 0, 2 and 5 and 100% in the fuel. The measurements were performed at equivalence ratios phi=0.5, 1.0 and 2.0 and pressures in the range 10-70 bar; depending on the fuel composition, the temperatures after compression varied from 610 K to 1180 K. Admixture of DME is seen to have a dramatic effect on the ignition delay time, effectively shifting the curves of ignition delay vs. temperature to lower temperatures, up to similar to 250 K compared to pure ammonia. Two-stage ignition is observed at phi=1.0 and 2.0 with 2% and 5% DME in the fuel, despite the pressure being higher than that at which pure DME shows two-stage ignition. At phi= 0.5, a reproducible pre-ignition pressure rise is observed for both DME fractions, which is not observed in the pure fuel components. A novel NH3/DME mechanism was developed, including modifications in the NH3 subset and addition of the NH2+CH3OCH3 reaction, with rate coefficients calculated from ab initio theory. Simulations faithfully reproduce the observed preignition pressure rise. While the mechanism also exhibits two-stage ignition for NH3/DME mixtures, both qualitative and quantitative improvement is recommended. The overall ignition delay times for ammonia/DME mixtures are predicted well, generally being within 50% of the experimental values, although reduced performance is observed for pure ammonia at phi= 2.0. Simulating the ignition process, we observe that the DME is oxidized much more rapidly than ammonia. Analysis of the mechanism indicates that this 'early DME oxidation' generates reactive species that initiate the oxidation of ammonia, which in turn begins heat release that raises the temperature and accelerates the oxidation process towards ignition. The reaction path analysis shows that the low-temperature chain-branching reactions of DME are important in the early oxidation of the fuel, while the sensitivity analysis indicates that several reactions in the oxidation of DME, including cross reactions between DME and NH3 species presented here, are critical to ignition, even at fractions of 2% DME in the fuel. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

The current global consumption of natural gas as a fuel is roughly 4 trillion cubic meters per year. In terms of energy, the demand for natural gas exceeds the global demand for fossil fuels for transportation. Despite this observation, the challenges to natural gas end use that arise when changing the composition of the fuel are largely absent from public, policy, and research agendas, whereas for transportation fuels the issues are more appreciated. Natural gas is delivered via complex networks of interconnected pipelines to end users for direct and indirect heating in household and industrial sectors, and for power generation. This interconnectedness is a crucial aspect of the challenge for introducing new fuels.In this paper we discuss the issues that arise from changing fuel properties for an existing population of end-use equipment. To illustrate the issues, we will consider the changes in (combustion) performance of domestic combustion equipment and gas engines for power generation in response to substituting natural gas by hydrogen or hydrogen/natural gas blends. During the discussion, we shall also indicate methods for characterizing the properties of the fuel and identify the combustion challenges that must be addressed for a successful transition from the current fuel mix to whatever the future mix may be.

Hundreds of offshore platforms are approaching the end of their productive life and will require decommissioning within the next decade. Removal of a large offshore structure is a highly complex exercise that poses significant safety challenges. In this paper, we propose a new concept to remove large and heavy structures with a single lift, utilizing three semi-submerged vessels. Such a twin-lift solution for decommissioning involves an operation of lifting of a topside structure, carried on two semi-submerged vessels, to the third semi-submerged vessel. Although the method appears simple, it requires adequate stability using ballast tank, and synchronized motion of moving vessels, especially under environmental disturbances. In order to ensure efficiency and safety, we perform a wave tank test for such a twin-lift decommissioning solution. Some aspects of an experimental facility set-up for scaled model test with dynamic positioning (DP) system are described. It includes the layout of the experiment and details of the deck mating, DP and monitoring system. Preliminary experimental results are presented, to reveal that a simple controller combined with DP system is able to produce a robust and precise performance.

Measurements of autoignition delay times of NH3 and NH3/H-2 mixtures in a rapid compression machine are reported at pressures from 20-75 bar and temperatures in the range 1040-1210 K. The equivalence ratio, using O-2/N-2 /Ar mixtures as oxidizer, varied for pure NH3 from 0.5 to 3.0; NH3/H-2 mixtures with H-2 fraction between 0 and 10% were examined at equivalence ratios 0.5 and 1.0. In contrast to many hydrocarbon fuels, the results indicate that, for the conditions studied, autoignition of NH3 becomes slower with increasing equivalence ratio. Hydrogen is seen to have a strong ignition-enhancing effect on NH3. The experimental data, which show similar trends to those observed previously by He et al. (2019) [28], were used to evaluate four NH3 oxidation mechanisms: a new version of the mechanism described by Glarborg et al. (2018) , with an updated rate constant for the formation of hydrazine, NH2 + NH2 (+M) = N2H4 (+M), and the literature mechanisms from Klippenstein et al. (2011) [30], Mathieu and Petersen (2015) [25], and Shrestha et al. (2018) [31]. In general, the mechanism from this study has the best performance, yielding satisfactory prediction of ignition delay times both of pure NH3 and NH3/H-2 mixtures at high pressures (40-60 bar). Kinetic analysis based on present mechanism indicates that the ignition enhancing effect of H-2 on NH3 is closely related to the formation and decomposition of H2O2 ; even modest hydrogen addition changes the identity of the major reactions from those involving NHx radicals to those that dominate the H-2/O-2 mechanism. Flux analysis shows that the oxidation path of NH3 is not influenced by H-2 addition. We also indicate the methodological importance of using a non-reactive mixture having the same heat capacity as the reactive mixture for determining the non-reactive volume trace for simulation purposes, as well as that of limiting the variation in temperature after compression, by limiting the uncertainty in the experimentally determined quantities that characterize the state of the mixture. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.