Numerical Study on Nitric Oxide Production of Moderate or Intense Low-Oxygen Dilution Combustion Using Ammonia and City Gas

Abstract

Ammonia (NH₃) is attracting attention as a carbon-free fuel that does not emit carbon dioxide, but there is concern that a large amount of nitrogen oxides is emitted during its combustion. The mixtures of NH₃ and city gas are used as fuels, and the effectiveness of Moderate or Intense Low-oxygen Dilution (MILD) combustion to reduce nitric oxide (NO) emissions is investigated through zero-dimensional and three-dimensional numerical simulations for various NH₃ concentrations of the fuels at the lower heating value basis, E_NH3. The zero-dimensional numerical simulations show that NO emissions reach their maximum value for E_NH3 = 20–40%, and that dilution of the fuel and oxidizer by exhaust gas recirculation reduces NO emissions. On the other hand, the three-dimensional numerical simulations of an actual furnace show that MILD combustion is valid for reducing NO emissions for E_NH3 = 0%, 20% and 100%. For burner design, the nozzle diameters used for the oxidizer, D, and the distance between the fuel and the oxidizer nozzles, L, are important parameters. For E_NH3 = 20%, a 0.39-fold reduction in D and a 2.5-fold increase in L make the NO emissions 56% and 74%, respectively.

Additional information

Notes on contributors

Takafumi Honzawa

Takafumi Honzawa is a senior researcher of Fundamental Technology Department, Tokyo Gas Co., Ltd., Japan. He also belongs to Kyoto University as a PhD student. He conducts several research on thermal fluid technology of city gas, especially combustion technology. In his most current research, both numerical simulations and its verification by experiments are conducted. His recent interest is in the reduction of CO₂ and NO_X emission for manufacturing sectors through fuel conversion from oil to natural gas as fuel, combustion of new fuels such as hydrogen, ammonia and biogas and so on.

Makihito Nishioka

Makihito Nishioka is Professor of Department of Engineering Mechanics and Energy, and Dean of School of Science and Engineering, University of Tsukuba, Japan. He conducts research in the field of combustion science. In particular, he has been studying fundamental combustion characteristics of simple-shaped laminar flames that can be treated one-dimensionally, and ultra-lean or ultra-diluted laminar swirling premixed/nonpremixed flame. As simple-shaped quasi 1-D laminar flames, tubular flame, counterflow premixed/nonpremixed flames, and rotating counterflow twin flame have been his research targets. In most of his studies, both experiments and detailed kinetics numerical calculations have been conducted.

Ryoichi Kurose

Ryoichi Kurose is a Professor of Department of Mechanical Engineering and Science, Kyoto University, Japan. He has authored more than 160 publications. He conducts research in the fields of turbulence, momentum/mass/heat transport phenomena, and chemical reactions appearing in industrial and environmental flows. In particular, he is very interested in combusting flows seen in many engineering applications such as energy conversion devices and engines, which includes gas-, liquid-, and solid-fueled combustion and gasification. Their combustion mechanisms and modellings are studied experimentally and numerically. Recently, he is focusing on massively parallel computations for turbulent combustion as a tool for elucidating the combustion mechanism and precisely predicting the combustion characteristics in realistic combustors and engines. He is the chair of the Consortium for Next Generation Combustion System CAE (CNGC), Japan, in which more than 20 universities, research institutes and industries participate.