Abstract

Lean premixed swirl stabilized combustion is one of the most successful technologies for NOx reduction in gas turbines. The creation of inherent coherent structures such as recirculation zones is one of the main advantages of these flow-stabilized systems since these zones create regions of low velocity that allow heat transfer improvement between reactants and products while increasing residence time for unburned species. However, these effects can also affect the stability of the flame under lean conditions, with various instabilities that can appear during the combustion stage such as flashback, blowoff, autoignition, etc. These processes are even more complex when new alternative fuels are being used for power generation applications. Synthesis gases (syngas) are some of the most concerning out of the available range of fuels as their heating values, flame speeds, ignition energies, etc. are highly dependent on the combination of species that comprise them. Since new gas turbines need to deal with these new blends for fuel flexibility and current lean premixed swirled stabilized systems seem to be the most cost effective-technical option to keep NOx down, gas turbine designers need more information on how to properly design their equipment to achieve stable flames with low NOx whilst avoiding instabilities.

Therefore, this paper presents a study using numerical and experimental analyses to provide guidance on the use of CH4/H2/CO blends in tangential swirl burners. Methane content was decreased from 50% to 10% (volume) with the remaining amount being split equally between carbon monoxide and hydrogen. Ambient temperature conditions were assessed using a swirl number close to 1.0. Particle Image Velocity was used to experimentally validate numerical predictions and determine features of the coherent structures affecting the flame close to the nozzle. Modelling was carried out employing the k-ω SST turbulence model, providing more information about the impact of these structures and the flame turbulent nature close to blowoff limits. The study emphasizes the analysis of various nozzles with different angles and how these geometrical changes at the outlet of the swirl chamber affect the onset of blowoff. Recommendations on the use of RANS CFD modelling are provided on the basis of blend composition.

The oil and gas sector has a significant impact on sustainable development, making it important for the sector to implement serious changes in the way it does business. Oil and gas operations involve both upstream activities, and downstream activities. Due to the nature of these activities which cause high risks, companies work continuously to reduce the significance of their adverse impacts on the environment and people. Thus, evaluating the sustainable production in this sector is become a necessity. This paper proposes a set of Key Performance Indicators (KPIs) for evaluating the sustainable production believed to be appropriate to the oil and gas sector based on the triple bottom line of sustainability. The Analytical Hierarchy Process (AHP) method is applied to prioritize the performance indicators by summarizing the opinions of experts. It is hoped that the proposed KPIs enables and assists this sector to achieve the higher performance in sustainable production and so as to ensures business sustainability.

Abstract

Swirl stabilized combustion is one of the most successful technologies for flame and nitrogen oxides control in gas turbines. However, complex fluid dynamics and lean conditions pose a problem for stabilization of the flame. The problem is even more acute when alternative fuels are used for flexible operation. Although there is active research on the topic, there are still various gaps in the understanding of how interaction of large coherent structures during the process affect flame stabilization and related phenomena. Thus, this paper approaches the phenomenon of lean premixed swirl combustion of CH4/H2/CO blends to understand the impacts of these fuels on flame blowoff. An atmospheric pressure generic swirl burner was operated at ambient inlet conditions. Different exhaust nozzles were used to alter the Central Recirculation Zone and observe the impacts caused by various fuel blends on the structure and the blowoff phenomenon. Methane content in the fuel was decreased from 50% to 10% (by volume) with the remaining amount split equally between carbon monoxide and hydrogen. Experimental trials were performed using Phase Locked PIV. The Central Recirculation Zone and its velocity profiles were measured and correlated providing details of the structure close to blowoff. The results show how the strength and size of the recirculation zone are highly influenced by the fuel blend, changing stability based on the carbon-hydrogen ratios. Nozzle effects on the shear flow and Re numbers were also observed. Modelling was carried out using the k-ω SST CFD model which provided more information about the impact of the CRZ and the flame nature close to blowoff limit. It was observed that the model under-predicts coherent structure interactions at high methane fuel content, with an over-prediction of pressure decay at low methane content when correlated to the experimental results. Thus, complex interactions between structures need to be included for adequate power prediction when using very fast/slow syngas blends under lean conditions. 

Currently the origin and trajectories of novel traits are emphasised in evolutionary studies, the

role of stabilization is neglected, and interpretations are often post hoc rather than as

hypothesised responses to stated agents of selection. Here we evaluated the impact of

changing environmental conditions on trait evolution and stabilization and their relative

contribution to diversification in a prominent Australian genus, Hakea (Proteaceae). We

assembled a time-based phylogeny for Hakea, reconstructed its ancestral traits for six

attributes and determined their evolutionary trajectories in response to the advent or

increasing presence of fire, seasonality, aridity, nectar-feeding birds and (in)vertebrate

herbivores/granivores. The ancestral Hakea arose 18 million years ago (Ma) and was broad

leaved, non-spinescent, insect-pollinated, had medium-sized, serotinous fruits and resprouted

after fire. Of the 190 diversification events that yielded the 82 extant species analysed, 8−50%

involved evolution, stabilization or re-evolution (reversal) of individual novel traits.

شهوب محممد أمحمد الأحمر, Byron B. Lamont, (10-2017), استراليا: تم اختياره bioRxiv Journal, 1 (10), 1-33