Towards Fast Prediction of Flame Stability and Emissions of mGT Combustion Chambers: a Chemical Reactor Network Approach

Abstract

Hydrogen as energy carrier, in combination with dry, low-NOx micro gas turbines (mGTs), is receiving increasing attention, since it can represent an attractive solution for a low-carbon, highly efficient and decentralized energy restitution system. However, accommodating hydrogen-enriched fuel blends in already existing combustion technologies is not an easy task, due to the increased reactivity of this fuel and the higher associated NOx emission. In this framework, reliable numerical models are needed to assist the industry towards the re-design of existing combustion assets. In particular, predicting thermal efficiency and pollutant emissions is of crucial importance for assessing the performances of a given system, since energy production facilities will have to cope with more stringent regulations. Alternative, physics-based modeling tools, such as Chemical Reactor Networks (CRNs), can represent an appealing solution for fast and reliable predictions of overall combustion efficiency and pollutants emissions. This tool allows to represent complex reactive flow fields as a series of idealized reactor models, thus drastically reducing the computational cost of the simulations. For this reason, detailed kinetic schemes can be employed. Detailed chemistry is crucial for reliable pollutants predictions, especially for NOx and CO, since the formation of those chemical species follows complex chemical pathways. The use of CRNs is quite frequent in literature, especially for performing parametric studies for gas turbines applications. The design of an equivalent CRN for a given combustor is based on the manual observation of the main flow-field features, which can be obtained from experiments or CFD data. The aim of this paper is to construct a highly simplified CRN of a typical mGT, Turbec T100 combustor, in order to perform design exploration studies. The effect of the main operating parameters, such as equivalence ratio, air inlet temperature and fuel composition was studied. Moreover, part load conditions were also simulated. Results highlighted that hydrogen addition does not systematically leads to increased pollutants emissions, since due to its higher reactivity, it offers the possibility to operate in leaner conditions, with respect to natural gas. The obtained results aim at providing useful guidelines for further experimental or detailed numerical design explorations for identified interesting conditions.