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Investigating the potential of industrial waste stream ammonia as a fuel for low carbon, gas turbine power generation

Hewlett, Sally 2021. Investigating the potential of industrial waste stream ammonia as a fuel for low carbon, gas turbine power generation. PhD Thesis, Cardiff University.
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Abstract

Ammonia (NH3) is found in many industrial waste streams, including as a component of a concentrated aqueous vapour stream, arising from the cleansing of coke oven gas (COG) on integrated steelworks sites. Anhydrous ammonia (AA) can be recovered from the vapour via the Phosam process. Ammonia has recently gained significant research interest as a carbon-free fuel for use in gas turbines. Major challenges are its comparatively low reactivity and a propensity for high NOx emissions. Numerical simulations in Chemkin-Pro and experimental investigations in a premixed, representative gas turbine combustor (~500 K inlet, ~0.1 MPa) were used to identify the optimal blend of ammonia (both AA and humidified ammonia of 30%vol H2O) with a locally available support fuel, to maximise reactivity whilst minimising pollutant emissions. The findings enabled the development of novel anhydrous and humidified ammonia thermodynamic cycles in Aspen Plus, scaled to 10 tonnes per day NH3, i.e. from a 2 Mt p.a. steelworks. Optimal fuel support was found with 15%vol COG for both AA and humidified ammonia (HA). The AA blend outperformed the HA blend for emissions, achieving a minimum 172, 5 and 1 ppm for NOx, NH3 and CO respectively, for staged combustion (fuel-rich then lean) at 0.11 MPa. Modest experimental pressure elevations of 17% (0.13 MPa) produced ~25% NOx reductions, with kinetic modelling predicting ~70% reduction for typical gas turbine operating pressures, suggesting regulatory compliance is possible. Partial secondary air substitution with nitrogen produced ~10% reductions in NOx. Delaying the second stage (10 cm further downstream) reduced NOx at 0.11 MPa but not 0.13 MPa. Inlet temperature elevations of just 30 K above 500 K significantly increased overall NOx emissions. The Brayton/Rankine cycle with recuperator modelled in Aspen Plus achieved >48% cycle efficiency and generated ~1.2 MWe net power, with >80% greenhouse gas reductions versus natural gas.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: ammonia, gas turbine , combustion , steelworks , waste , NOx
Date of First Compliant Deposit: 21 June 2022
Last Modified: 21 Jun 2022 11:24
URI: https://orca.cardiff.ac.uk/id/eprint/150619

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