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.
The challenge
Being an excellent hydrogen (H2) carrier and effective and practical means of exporting Australia’s rich renewable energy resources, ammonia (NH3) can be used directly as a carbon-free fuel for transport or combined heat and power (CHP) generation. NH3 combustion emits no carbon oxides, sulphur oxides or particulate matter but the technical challenge is to combust NH3 efficiently with low nitrogen oxides (NOx) emission. The UWA Centre for Energy has conceptualised a fluidised-bed combustion technology using NH3 as a fuel for power generation. This project will advance the science of NH3 combustion in fluidised bed and associated NOx formation that underpin the development and deployment of fluidised-bed combustion systems for power generation using NH3 as a carbon-free fuel.
The solution
The project employed a stepwise experimental approach to investigating and revealing the mechanisms of the complex reaction system in fluidised-bed combustion of ammonia, which involves ammonia dissociation, direction oxidation of ammonia, oxidation of hydrogen, nitrogen oxides formation and destruction and the effect of the presence of bed materials. The experimental techniques included a flow-reactor configuration, a fixed-bed reactor configuration and a fluidised-bed reactor configuration. The experimentation covered a wide range of operating conditions including reactor set temperature, flowrate, equivalence ratio and fuel throughput.
The outcome
This research for the first time obtained the most comprehensive experimental dataset on the complex reaction system in fluidised-bed combustion of ammonia that allowed the complex reaction mechanisms and their interactions with transport processes to be understood. It was revealed that partial dissociation of ammonia often precedes oxidation of ammonia and hydrogen from ammonia dissociation. Furthermore, the endothermicity of ammonia dissociation was found to, surprisingly, have a profound effect of subsequent reactions of ammonia dissociation, oxidation, hydrogen oxidation, NOx formation and reduction of NO by both ammonia and hydrogen. Bed materials, such as silica and quartz, have an appreciable promotion effect on ammonia dissociation and direct oxidation of ammonia and an inhibition effect on NOx formation. The thermal inertia of the bed particles, in either fixed-bed or fluidised-bed configurations were shown to diminish the endothermic effect of ammonia dissociation, promote early ignition, stabilise ammonia combustion, and reduce NOx emissions.
In addition to fluidised-bed combustion of ammonia, the project was expanded to shed new light on porous media stabilised ammonia flame, which, conceptually, extends the outcomes of the present research to embrace ammonia combustion in utility boilers, industrial heaters, high-temperature manufacturing processes (e.g., ceramics, glasses, cement, bricks and metallurgy) and stationary ammonia-fired gas turbines for power generation.
The impact
A world’s first of its kind, this FEnEx CRC project has successfully achieved all original objectives, with a prolific publication record and completion of PhD and other ECR training. For the first time this research revealed the thermal and catalytic effects in the complex reaction system of ammonia combustion involving ammonia dissociation, ammonia oxidation, hydrogen oxidation, NOx formation and destruction, and catalytic effect of presence of solid particles and NO on ammonia oxidation. Scientifically, the research established previously unknown mechanisms of ammonia combustion in fixed-bed and fluidised-bed reactors. Technologically, the project proved the feasibility and laid a solid foundation for fluidised-bed combustion as a means of zero-carbon power generation.
Next steps
Now, possessing with the World’s most advanced knowledge and unique knowhow, the FEnEx CRC’s relevant research team stand ready to assist any industry partners, venture capital investors and institutions who are willing to bring the ammonia combustion technologies to practical fruition in their effort to decarbonise the economy.
Project researchers
- Prof. Dongke Zhang
- Mr Zhezi Zhang
- Ms Yii Leng Chan
- Dr Yiran Liu
- Dr Mingming Zhu
- Dr Chiemeka Okoye
- Dr June Wu
- Dr Isabelle Jones
Project status
Complete
Partners
