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Modelling alkali metal pollutant formation in LES of pulverised-coal combustion

Funding body

The Royal Society

Principal investigator: Jun Xia

Co-investigator: Prof Luc Vervisch, INSA de Rouen, France

 

Project description

Gas-solid and gas-liquid two-phase combustion in a turbulent flow is scientifically challenging and practically important. It dominates the performance of a broad range of important engineering applications, such as fuel spray processes in mobile combustion engines and stationary gas turbines, and turbulent pulverised-coal combustion in industrial coal-fired boilers. Among others, a common key issue in turbulent combustion modelling faced by scientists is to properly predict the formation and dynamics of intermediate and minor species during the burning, which, although little in amount, play a pivotal role in key flame characteristics such as ignition, stability, extinction and pollutant formation. With rapid development of computing capacity, high-fidelity simulation enabled by high-performance computing can now play an important role in exploring complex flow and combustion physics, thereby developing technologies to control and optimise the performance and reduce harmful emissions of the engineering application. In the present project, we aim to achieve a better scientific understanding of the reacting dynamics of alkali metal species, mainly sodium (Na) and also potassium (K), during turbulent pulverised-coal combustion. Large-eddy simulation (LES) will be used, in which large and small flow structures, compared to the computational grids used, are directly resolved and modelled, respectively, with mutual interactions between the large-scale simulation and small-scale modelling. These alkali metal species have been identified to be the key polluting sources for fouling and corrosion of heat transfer surfaces within industrial boilers burning low-rank high-Na coals, jeopardising safe operation of coal-fired power stations. Therefore there is an urgent need to develop effective technologies to suppress and control the release of these alkali metal species during turbulent pulverised-coal combustion, before which an improved scientific understanding is a prerequisite.

We have set up a detailed plan to tackle the challenging research question. A key to the success is to properly model turbulent combustion, especially the reacting dynamics of the minor alkali metal species within low-rank coals, in large-eddy simulation. In view of Prof Vervisch's expertise in this area, especially some recent developments in his group that matches the need of our research, we propose this collaboration to incorporate leading-edge modelling techniques into our simulation framework. These advanced modelling approaches will be validated and improved in LES of turbulent pulverised-coal combustion.

Coal currently produces 25% and 75% of the electricity in the UK and China. In addition, advanced coal burning technologies, including co-firing of coal and biomass, oxy-coal combustion for carbon emission reduction from coal-fired
power stations, have been strongly pushed forward since more and more stringent emission regulations are in place. The proposed research will pave the way for us to tackle these challenging topics. It will also impact on other important research areas such as fuel spray combustion, which shares similar research questions to answer, e.g. how to reduce harmful emissions such as nitrogen oxide emitted from liquid-spray (and solid-coal) combustion. By coping with these important research questions, we will endeavour to contribute to building a healthy and sustainable UK society, together with other scientists and engineers.