Cleaner Coal Combustion Technologies – The Impact on NOx Emissions and Fireside Corrosion

Despite efforts to curb global warming, the use of coal for power generation is projected to increase. The impact of this on global warming could be negated by the proliferation of carbon capture technologies, but their adoption is slow and inhibited by techno-economic challenges. In the meantime, coal combustion is associated with NOx emissions, which cause a plethora of environmental problems, and economic uncertainties caused by ash-related issues. The aim of this thesis is to minimise the negative impacts of coal’s continued consumption, through aiding the development of clean coal power generation. This aim was achieved by investigating two technologies. The first was the use of low-NOx burners during oxy-coal combustion in order to minimise NO formation and maximise destruction of recycled NO via reburning, using a 250 kWth combustion test facility that can be run in air-firing or oxy-firing mode. A range of burner configurations were tested across two oxy-fuel regimes with varying levels of NO recycling. Measurements were taken at the flue, radially in the flame and axially down the centreline of the flame. The profiles showed that burner staging aids in controlling the products of NO reburning. The second technology, an Fe-based additive, was investigated in two parts. The first route was investigating the impact of this additive on selective non-catalytic reduction, using a 100 kWth combustion test facility able to load the fuel with additive. The presence of the Fe-based additive was shown to increase NO reduction due to SNCR. This interaction was then kinetically modelled and analysed for its sensitivity to process conditions. The second route was investigating the impact of the additive on fireside corrosion, using the equilibrium modelling software, FactSage. The investigated coal ash was not corrosive enough to show any trends in FactSage, so three biomass fuel ashes were investigated and the Fe-based additive was compared with two coal ashes and alumina to analyse the extent of any inhibition witnessed. The metrics used for analysis were the formation of various corrosive compounds and by-products. The Fe-based additive could inhibit corrosion but not as well as either of the coal ashes, as it was key to increase the Al and Si content of the deposits. The Fe-based additive should not be used solely to inhibit corrosion but it is a positive side effect if used for other applications.