Emission Characteristics of NO and NO2 in Rich-Lean Combustion of Hydrogen

Abstract

Hydrogen is expected as a clean and renewable alternative to the conventional hydrocarbon fuels. Because the only possible pollutants from the hydrogen combustion are nitrogen oxides (NOx), it is crucial to reduce the NOx emission in the hydrogen utilization. The rich-lean combustion is well known as a technique to reduce the emission of the Zel’dovich NO from the continuous combustion burners for such as gas turbines and boilers. Because the Zel’dovich NO occupies a large part of the total NOx emission, the rich-lean combustion is quite effective to reduce the NOx emission. However, the NOx reduction effect of the rich-lean combustion has not yet been proven for the hydrogen fuel, while the effect has been demonstrated for the hydrocarbon fuels. On the other hand, the prompt NO is emitted from the hydrocarbon combustion especially under the fuel-rich conditions. Though the amount of the prompt NO is quite small for premixed or diffusion combustion, it could be a relatively significant part in the total NO emission from the rich-lean combustion due to the decreased Zel’dovich NO. The authors estimate that hydrogen is more suitable for the rich-lean combustion compared with hydrocarbons, because hydrogen does not emit the prompt NO even under the fuel-rich conditions which necessarily exist in the rich-lean combustion. This research proposes the rich-lean combustion as a method to reduce the NOx emission from hydrogen combustion and experimentally analyzes the characteristics using a coaxial rich-lean burner with varying the mixture conditions.

Reduction of Energy Cost and CO2 Emission for the Boilers in a Full-Scale Refinery Plant by Adding Waste Hydrogen-Rich Fuel Gas

“…This is due to the fact that at the rich combustion zone, hydrocarbons are decomposed into CH radicals, reacting with nitrogen in the air to form HCN. HCN then reacts through the reactions to increase the formation of prompt NO x . ,,,,, When RG is used to replace the natural gas and hence raises the hydrogen concentration in the fuel, both CH and HCN concentrations are lowered and consequently a lesser amount of prompt NO x is yielded. At present, due to the existence of higher carbon in the fuel and the dominance of the prompt mechanism, the contribution of prompt NO to the total NO x formation is considerable for heavy fuel oil combustions.…”

“…Steam boilers are a major source of heat and also serve as gas turbines for electricity generation. However, the boiler consumes a lot of fossil fuels and emits greenhouse gases, which have a serious impact on the environment. , The use of hydrogen in gas turbines and industrial burners can help reduce the emission of pollutants. This eliminates the formation of greenhouse gas CO 2 , CO, unburned hydrocarbons, and particulates such as soot. , However, certain characteristics of hydrogen prevent it from fully replacing fossil fuel as a major energy source, including its high flammability, fast reaction rate, low volumetric energy density, low flash point, and need for highly complicated storage techniques.…”

Optimization of the ammonia coverage ratio references in diesel engine two-can selective catalytic reduction systems via nonlinear model predictive control

“…The chemical reactions inside the engine are complicated, and the formation of NO and the formation of NO 2 are affected by numerous environment factors. 36,37 Moreover, the formation of NO 2 has received relatively less attention because of the low concentration or the low percentage ratio. For the engine-out ratio model, we adopt the work by Hsieh and Wang, 35 in which the engine-out NO 2 has a relation to the total NO x given by…”