Investigation of wet combustion instability due to bio-syngas fuel variability

Abstract

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 bio-syngas 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.