Ammonia Combustion: Design Principles and Case Studies
(2024) MVKM05 20241Department of Energy Sciences
- Abstract
- Ammonia combustion in gas turbines is emerging as a carbon-free solution for the power-generation sector. The challenges associated with using ammonia as a fuel include its combustion characteristics, which can lead to instability, and the emission of NOx due to the presence of nitrogen atoms. This study examines the diffusion flames of partially cracked ammonia at low cracking degrees and the air in an SGT750-based burner with an RQL configuration. An LES study is conducted to extract the products from the rich combustion in the primary zone. Then, the product gases are fed into the CRN model with a secondary air stream to calculate NOx emissions at the RQL burner exit. Flame stabilisation is observed with this design; however, NO... (More)
- Ammonia combustion in gas turbines is emerging as a carbon-free solution for the power-generation sector. The challenges associated with using ammonia as a fuel include its combustion characteristics, which can lead to instability, and the emission of NOx due to the presence of nitrogen atoms. This study examines the diffusion flames of partially cracked ammonia at low cracking degrees and the air in an SGT750-based burner with an RQL configuration. An LES study is conducted to extract the products from the rich combustion in the primary zone. Then, the product gases are fed into the CRN model with a secondary air stream to calculate NOx emissions at the RQL burner exit. Flame stabilisation is observed with this design; however, NO relaxation does not reach equilibrium values with this length. When secondary air is mixed, it can either increase the NOx formation for the early injection or maintain zero net production of NOx if the injection is delayed up to a point. For both rich flame in the primary zone and lean flame in the secondary zone, the predominant NO formation pathway is via HNO species, which are the species that link to the decomposition of NH3. For rich flame, the dominant pathway is through the reduction of HNO to NO in the presence of third-body species. On the other hand, in the secondary zone, NO is mainly formed by HNO oxidation. Wall cooling with secondary air does not have significant effects on emissions compared to the deviation in the equivalence ratio. With the design in this study, operating at ϕ_pz = 1.2 and the air injection at 40 ms of residence time or 0.9 m length in the primary zone is suggested to obtain a NOx level around 40 ppm at the burner exit. However, minimum NOx can be obtained when the air is injected at the latest in the richest flames. Future work should include the CFD simulation of the complete RQL burner, case studies on the modifications to the burner and fuel conditions, and the experimental observation of the actual NOx level. (Less)
- Popular Abstract
- In the transition away from fossil fuels, the power generation sector has been seeking a clean fuel for gas turbine combustion. Ammonia (NH3) is a promising alternative fuel that does not produce carbon dioxide (CO2) when it burns. However, burning ammonia is tricky due to its properties. It is not only difficult to keep the flames stable, but the burner should also be modified to control the level of another harmful pollutant, nitrogen oxides (NOx), within the allowed range.
In this study, computer simulations are performed to explore the design of ammonia combustion in gas turbines. Initially, ammonia is partially broken down into hydrogen and nitrogen to adjust the fuel properties and keep the flames stable. This fuel mixture is... (More) - In the transition away from fossil fuels, the power generation sector has been seeking a clean fuel for gas turbine combustion. Ammonia (NH3) is a promising alternative fuel that does not produce carbon dioxide (CO2) when it burns. However, burning ammonia is tricky due to its properties. It is not only difficult to keep the flames stable, but the burner should also be modified to control the level of another harmful pollutant, nitrogen oxides (NOx), within the allowed range.
In this study, computer simulations are performed to explore the design of ammonia combustion in gas turbines. Initially, ammonia is partially broken down into hydrogen and nitrogen to adjust the fuel properties and keep the flames stable. This fuel mixture is burned in a burner that has been modified to satisfy a special burning technique. This technique includes 2 combustion zones, meaning that air enters the burner twice; one is together with the fuel, and another is between the zones. The latter air injection effectively controls the amount of NOx at the burner exit. The question is, where is the optimum point for the secondary air injection?
According to the literature, it is necessary to wait for the first combustion to reach a balanced state before injecting the additional air. This is to avoid chemical reactions that produce more NOx during the second combustion. While this study finds that wall cooling has a small influence on emissions, fuel condition in the first zone is more important. At the balanced state, richer fuel conditions in the first zone can reach lower NOx levels, but it comes with a longer waiting time. However, the burner cannot be infinitely long. With the current design, it is suggested to work in a slightly rich condition so that the first combustion zone stays within a 1-meter length and a NOx level below the regulation limit is reached.
Further details on NOx formation through different chemical pathways are also explained, and future studies should include simulations of the complete burner and experimental observations. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9170534
- author
- Kittiwirayanon, Boonsita LU
- supervisor
- organization
- course
- MVKM05 20241
- year
- 2024
- type
- H2 - Master's Degree (Two Years)
- subject
- keywords
- Ammonia combustion, Carbon-free fuel, Chemical reactor network, Hydrogen carrier, Gas turbine, Large eddy simulation, NOx emission, Rich-burn quick-quench and lean-burn
- report number
- ISRN: LUTMDN/TMHP-24/5597-SE
- ISSN
- 0282-1990
- language
- English
- id
- 9170534
- date added to LUP
- 2024-09-03 10:32:38
- date last changed
- 2024-09-03 10:32:38
@misc{9170534,
abstract = {{Ammonia combustion in gas turbines is emerging as a carbon-free solution for the power-generation sector. The challenges associated with using ammonia as a fuel include its combustion characteristics, which can lead to instability, and the emission of NOx due to the presence of nitrogen atoms. This study examines the diffusion flames of partially cracked ammonia at low cracking degrees and the air in an SGT750-based burner with an RQL configuration. An LES study is conducted to extract the products from the rich combustion in the primary zone. Then, the product gases are fed into the CRN model with a secondary air stream to calculate NOx emissions at the RQL burner exit. Flame stabilisation is observed with this design; however, NO relaxation does not reach equilibrium values with this length. When secondary air is mixed, it can either increase the NOx formation for the early injection or maintain zero net production of NOx if the injection is delayed up to a point. For both rich flame in the primary zone and lean flame in the secondary zone, the predominant NO formation pathway is via HNO species, which are the species that link to the decomposition of NH3. For rich flame, the dominant pathway is through the reduction of HNO to NO in the presence of third-body species. On the other hand, in the secondary zone, NO is mainly formed by HNO oxidation. Wall cooling with secondary air does not have significant effects on emissions compared to the deviation in the equivalence ratio. With the design in this study, operating at ϕ_pz = 1.2 and the air injection at 40 ms of residence time or 0.9 m length in the primary zone is suggested to obtain a NOx level around 40 ppm at the burner exit. However, minimum NOx can be obtained when the air is injected at the latest in the richest flames. Future work should include the CFD simulation of the complete RQL burner, case studies on the modifications to the burner and fuel conditions, and the experimental observation of the actual NOx level.}},
author = {{Kittiwirayanon, Boonsita}},
issn = {{0282-1990}},
language = {{eng}},
note = {{Student Paper}},
title = {{Ammonia Combustion: Design Principles and Case Studies}},
year = {{2024}},
}