Humidified gas turbine (HGT) is a promising technology with several advantages compared to traditional thermal power plants, such as higher electrical efficiency, lower investment costs, and lower emissions. Using steam diluted, carbon neural bio-syngas as fuel in the HGT cycle leads to distributed wet combustion, often characterised by high Karlovitz number. This kind of combustion may be unstable if a small perturbation of biosyngas fuel composition occurs and it can lead to flame blow-off. Hence, quantifying wet bio-syngas fuel variability effects on the flame physicochemical behaviour is an important step. Using uncertainty quantification, it is found that a 0.75% perturbation of a typical wet bio-syngas composition can lead to 10% fluctuation of the flame speed, 7.5% fluctuation of the flame thickness and 2% fluctuation of flame temperature for stoichiometric combustion of steam diluted reactants at gas turbine conditions. Since near stoichiometric combustion is associated with highly steam-diluted bio-syngas to retain constant thermal efficiency of HGT, ultra-wet combustion has indeed suffered from strong combustion instability led by fuel variability. The main sensitivity study shows that hydrogen variability is responsible for the high fluctuation of flame speed while methane variability is responsible for the fluctuation of thermal efficiency and flame thickness. A high pressure (HP) burner running on a typical wet bio-syngas can suffer from a change of Karlovitz number by 20 (300% by fraction) and Reynolds number by 14,000 (10% by fraction), with potential impact on flame stability and cycle performance due to small perturbation of bio-syngas composition.

Fuel variability effects on physicochemical properties such as adiabatic flame temperature and laminar flame speed of premixed bio-syngas combustion are investigated via polynomial chaos expansion (PCE) based uncertainty quantification (UQ) approach at several equivalence ratios. Questions regarding confidence level of using bio-syngas with varying fuel composition are tackled from a statistical point view. Impacts of unburnt gas temperature and different chemical mechanisms (GMI-Mech 3.0 and San Diego Mechanism) on predicted uncertainties of these combustion properties are discussed. It was found that fluctuation of flame temperature at various equivalence ratios is less affected by bio-syngas fuel variabilities, while flame speed is sensitive to uncertainties in fuel composition. For instance, 1.5% fluctuation of bio-syngas constituent can lead to 14% fluctuation of flame speed for rich combustion, and 3% for lean combustion. Less than 0.8% fluctuation of flame temperature due to variability of bio-syngas fuel composition was observed. UQ of bio-syngas combustion showed that hydrogen variability plays a significant role (70-80% at lean condition) in flame speed variation, while methane variability, although thought to be important, has a negligible impact except for fuel-rich combustion. Overall, the current study has provided a fundamental understanding of the effects of fuel variability on physicochemical properties of bio-syngas combustion. Dominating compositions to variations of biosyngas combustion are provided quantitatively to guide targeted uncertainty reduction from the upstream gasification process.

Fuel variability effects on high hydrogen content syngas combustion physicochemical properties and NOx emission characteristics are investigated invoking polynomial chaos expansion based uncertainty quantification. The focus is put on providing an in-depth understanding of fuel variability effect under very lean conditions, i.e., near lean blowout limit. It is found that leaner combustion of syngas leads to higher flame speed fluctuation. Under 1.5% small fluctuations in species concentration of syngas fuels, a maximum of 5% fluctuation of flame speed is observed at equivalence ratio of 0.45 for H60CO30 (60% H-2 + 30% CO), while the lowest fluctuation is observed near equivalence ratio of 0.8 for the cases considered. Meanwhile, maximum NO concentration fluctuation of 8.3% and NO2 concentration fluctuation of 6.5% are observed at very lean conditions. Uncertainty analyses show that on one hand, hydrogen always has the highest contribution to flame speed variation followed by carbon monoxide, carbon dioxide, and methane. On the other hand, carbon monoxide is found to have the highest contribution to variation of flame temperature, followed by hydrogen, carbon dioxide, and methane. The quantified sensitivity information reported in present study can be used to guide targeted uncertainty reduction from syngas upstream gasification process.

Towards achieving sustainable and decarbonized power, biomass to electricity is an attractive pathway. To that end, the humidified gas turbine cycle is a promising technology. Recirculated steam which contains low-grade heat can be used to replace part of the air flow. This immediately reduces power loss in the compressor and increases specific power output, benefiting higher electrical efficiency compared to dry cycles. With high steam content, wet combustion leads to the so-called flameless combustion (FC) or colorless distributed combustion (CDC) which is presently investigated using large eddy simulation and a detailed finite rate chemistry method. Further insight regarding the coherent structures is obtained. Proper orthogonal decomposition method is applied on both the velocity and the heat release field aiming to explore the in-depth dynamic of flow-flame interaction in a swirl burner. Our results are the first reporting two distinct sets of helical coherent structures. A higher frequency mode or structure at Strouhal number St -0.7 is caused by the vortex shedding, and a lower frequency mode at St -0.1 corresponds to the off-central motion of an intermittently occurring precessing vortex core (PVC). With high steam content (hence very distributed reaction regime), more frequent occurrence of the marginally stable PVC is observed. The wet flame local extinction is evidenced to be an important driver towards the promotion and suppression of the PVC structure. Compared to the very energetic flow-flame interaction in conventional flames, FC or CDC flames undergo less fluctuations.

The present contribution experimentally examined the combined effect of non-thermal plasma and Mn-based composite catalysts on CO2 reforming of toluene as a model compound of tars in synthesis gas production from biomass gasification and pyrolysis. The experimentation was performed using a fixed-bed reactor packed with a catalyst and incorporating a dielectric barrier discharge (DBD) to generate non-thermal plasma in-situ. The effects of specific energy density (SED), catalyst loading, and CO2 concentration on the yields of H-2, CO and light hydrocarbons (such as CH4, C2H6 and C2H2) were systematically studied and a potential synergistic mechanism for the plasma catalytic reforming of toluene by CO2 is proposed. The experimental results indicate that Mn-based catalysts perform similarly well in the plasma catalytic reforming of toluene by CO2 as has previously been observed in the literature using O-2 as the reforming agent.

Towards developing humidified gas turbines (HGT) capable of running at high electrical efficiencies and low emissions, wet/steam-diluted combustion in a premixed swirl burner is investigated using large eddy simulation and a partially stirred reactor method. Chemical explosive mode and extended combustion mode analyses are performed to promote the understanding of wet flame structures. The former identifies the key features of the wet methane oxidation processes, and the latter extends the flame regime classification method to describing the combustion status of fluid parcels using local properties. Three combustion regimes are extensively discussed: the swirl stabilized (SS), colorless distributed (CDC) and non-combustible. Using the combined analyses of the two approaches, it is found that compared to dry flames, wet flames present more fluid parcels defined in the practical CDC regime where local heat release is low and Damkodhler number is smaller than unity. The wet fluid parcels are capable of self-igniting via radical explosion, while dry fluid parcels self-ignite via thermal runaway. The species CH2O and temperature are the first and second highest contributors towards the explosivity of dry flames, while temperature is insignificant to that of wet flames. The species C2H6 is found an important source to the self-ignitability of wet fluid parcels in the practical CDC regime due to the activation of the three-body ethane formation reaction R148: 2CH(3) + M = C2H6 + M in the low O-2% wet combustion environment. Proper use of proposed methods to quantify wet flame behavior guides stable and low emission operation of practical HGT.