Role of OH Radical in Fuel-NOx Formation during Cocombustion of Ammonia with Hydrogen, Methane, Coal, and Biomass

Abstract

Some of the impurities (Br, Cl, Fuel-N, and S) in fuels can reduce the radicals (O, H, and OH) formed in the flames on combustion, thus lowering the radical mole fraction. The variation in the radical mole fraction affects the NO x emissions. In this study, the radical reducing effects caused by these impurities were modeled based on measurements of the radical mole fractions. Linear relationships were obtained between the mole fractions of the impurities in the flames and the reciprocals of the radical mole fractions. The slope of this straight line was defined as the radical reducing effect coefficient (α). The value of α for each radical was determined for fuels containing HBr, CH3Br, HCl, CCl4, CH3NH2, NH3, H2S, and CS2 impurities. The OH radical was the most susceptible to the reducing effects of the fuel-N impurity. However, the calculated radical mole fractions (CH4–NH3 flame) by detailed chemical kinetics did not agree with the experimental results, and the O atom radicals were, in fact, most susceptible to the fuel-N impurities. The calculations overestimated the OH mole fraction and fuel-N conversion to NO x . The α value calculated for the OH radical was 19.4 times smaller than that obtained experimentally. The contributions of OH radicals to fuel-NO x generation for methane–ammonia and hydrogen–ammonia cocombustion were investigated by using a simplified reaction scheme for fuel-NO x . If the OH radical was a controlling factor in fuel-NO x generation, the difference in NO x conversion between experiment and calculation could be explained. On the basis of the results, the reaction scheme was extended to the solid fuel combustion of coal and biomass. The NO x conversion for the cocombustion of coal and ammonia was lower than that for the methane–ammonia cocombustion. The effect of Cl impurities on biomass combustion was also investigated. If the OH radical mole fraction was lowered by the presence of Cl in the biomass fuel, the NO x conversion tended to be low. However, if the OH mole fraction was too low to decompose ammonia in the flame, the NO x conversion tended to be high.

Experimental and Kinetic Study on the Oxidation of Syngas-Ammonia under Both N2 and CO2 Atmospheres in a Jet-Stirred Reactor

“…Syngas is a clean fuel that has been widely used in heating furnaces and gas turbines. , It is produced from coal, biomass, or waste by gasification, pyrolysis, or reforming processes . In actual syngas, there are a certain number of nitrogen-containing components (e.g., NH 3 ) resulted from the syngas production process. − NH 3 is a typical fuel-nitrogen precursor and the control of the fuel-NO x emission is essential for the combustion of ammonia-containing syngas. , The investigation on the oxidation of syngas-ammonia is crucial for suppressing the fuel-NO x emission from the combustion of actual syngas containing initial NH 3 .…”

Pollutant Formation during Utilization of Renewable Natural Gas Containing Trace Ammonia Impurities

“…Recently, NH 3 is being considered as a promising vehicle for hydrogen storage, and there is an increasing number of studies on the use of NH 3 for power generation, both in pure form , but also when co-mixed with fuels such as NG and pulverized coal. − In addition to considerations like power density and efficiency, there are concerns about potential corrosion and damage to equipment, and pollutant emissions, particularly NO x , because of their known negative effects on the environment and since such emissions are strictly regulated in many countries, including the United States. Miller and Bowman and Sullivan et al have reported the main chemical formation routes of NO x from NH 3 during combustion.…”

Oil Palm Wastes Co-firing in an Opposed Firing 500 MW Utility Boiler: A Numerical Analysis

“…Presently, the electricity industry is responsible for about 40% of global carbon dioxide (CO2) emissions, and electricity demand is expected to grow by more than 50% by 2040 [1][2]. Due to the huge reserves and affordability of coal, coal-fired thermal power plants produce a significant share of the world's primary electricity [2][3][4][5][6]. Since coal has a high carbon content, coal-fired thermal power plants generate more CO2 than any other form of power generation [7][8], and they are one of the main anthropogenic CO2 emission sources [2,4,9], contributing for 30.4% of global CO2 emissions in 2018 [10].…”

“…Due to the huge reserves and affordability of coal, coal-fired thermal power plants produce a significant share of the world's primary electricity [2][3][4][5][6]. Since coal has a high carbon content, coal-fired thermal power plants generate more CO2 than any other form of power generation [7][8], and they are one of the main anthropogenic CO2 emission sources [2,4,9], contributing for 30.4% of global CO2 emissions in 2018 [10]. The reduction of greenhouse gas (GHG) emissions is essential for addressing climate change triggered by global warming, and the reduction of CO2 emissions is now a global consensus [7,[9][10][11][12][13].…”