Ammonia is an excellent hydrogen carrier and a practical means to export carbon-free fuel. It can be made at scale from entirely renewable resources and its combustion emits no carbon oxides, sulfur oxides or particulate matter. However, its combustion characteristics are very different to conventional hydrocarbon fuels.
To use ammonia directly as a carbon-free fuel for combined heat and power generation there are still technical challenges to overcome – it has a slower flame propagation speed in air, a higher ignition energy and high autoignition temperature than hydrocarbon fuels, and as such, the flame stability is poorer and heat release intensity is lower. Combustion efficiency can be poor and there is high potential for nitrogen oxides (NOx) emission.
The fundamental chemistry of ammonia combustion and associated NOx formation must be better understood under practically-relevant conditions to advance its use as a fuel for heat and power generation.
Program 2: Fluidised-bed combustion of ammonia for stationary combined heat and power generation
The overall aim of this project is to advance the science underpinning the development of fluidised-bed combustion systems using ammonia as a fuel for combined heat and power applications.
Fluidised bed reactors provide a stable thermal reservoir that should ensure reliable ammonia ignition, stable combustion and controllable heat release. The inert bed material may also inhibit ammonia oxidation by extinguishing radicals in reaction chains on the solid surface, altering the combustion chemistry and suppressing NOx formation.
Stage 1 of the project is to design and construct a laboratory-scale fluidised-bed reactor to study ammonia combustion and NOx formation mechanisms under practically relevant conditions. The fully-instrumented reactor will enable testing of different bed materials such as quartz, alumina and specific catalysts, and studies of combustion rate, heat release rate and NOx emissions. The effects of bed temperature, fuel/air ratio, bed materials and catalysts on combustion efficiency and NOx generation will be determined and optimised.
Stage 2 of the project is to develop a mathematical model of ammonia combustion incorporating hydrodynamics, reaction kinetics, heat and mass transfer, validated against the experimental measurements and findings in Stage 1. This will allow further investigation of the effect of the reaction temperature, operating pressure, feed composition, particle size and superficial velocity on the combustion rate, heat release rate and NOx emission. This understanding of the ammonia combustion reaction mechanism and kinetic rate equations is necessary for reactor design, process modelling and scaling.
Advancing the science of ammonia combustion and NOx formation and destruction will underpin the development of practical combustion technologies using ammonia as a renewable and carbon-free fuel.
Partners: Shanxi Keteng Environmental Protection Technology Co. Ltd, The University of Western Australia
Project Researchers: Professor Dongke Zhang, Dr Zhezi Zhang, Dr Mingming Zhu, Dr Isabelle Jones
Duration: 3 years