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Ammonia cracking with heat transfer improvement technology

Alboshmina, Najlaa 2019. Ammonia cracking with heat transfer improvement technology. PhD Thesis, Cardiiff University.
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Abstract

In recent decades, ammonia has been used as a means of hydrogen storage that, because it is easily dissociated, can be used as a sustainable fuel for, e.g., power generation. Ammonia as a fuel, offers significant advantages in comparison to hydrogen in terms of cost and convenience, its higher density and its easier storage and distribution. However, due to its noticeably low flame speed, green ammonia is very difficult to use directly in conventional internal combustion engines and gas turbines (GTs). However, a limited number of studies have suggested that ammonia combustion can achieve acceptable levels of efficiency if the ammonia is partially cracked into hydrogen and nitrogen, so that the fuel is a mix of ammonia and hydrogen. This thesis reports the design, build and testing of a novel cracker system that employs energy from the combustion process to pre-crack ammonia. A unique geometry has been tested and shown to provide the energy required for the cracking process, and simultaneously establish recirculation regions that improve flame stabilisation. The project has also achieved reduced NOx emission levels by injecting a small percentage of the fuel mix into the region upstream of the cracker and downstream of the burner. Numerical and experimental results demonstrate that a particular configuration, i.e. a hemispherically tipped bluff body, located in the centre of a swirl combustor can enhance flame retention (i.e. better blowoff resistance), generate larger recirculation zones for increased residence time, and the anchoring structures holding the cracker in place can be used to disperse unburned ammonia for NOx control purposes. Thus, it is concluded that the system presented here is viable for use with ammonia as a fuel, and it is expected that the system will mitigate NOx emissions whilst enabling the efficient combustion of ammonia-based blends.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Swirl burners; Ammonia cracking; Gas turbine; Combustion; NOx emissions; Heat transfer.
Date of First Compliant Deposit: 4 November 2019
Last Modified: 04 Nov 2019 13:43
URI: http://orca.cf.ac.uk/id/eprint/126553

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