Catalyst-free approach for removal of NOx

Pulsed electron beam to enhance NOx removal at lower capital cost with greater efficiency than other large-scale NOx removal methods

Energy Environmental

Nitrogen oxides (NOx), a combination of nitric oxide (NO) and nitrogen dioxide (NO2), are a concern because of their impact on human health and the environment. The byproducts of NOx reactions in the atmosphere can enter the lungs and strain the respiratory system. These byproducts are composed of nitric acid from reactions with ammonia, water, and other compounds, and ozone from reactions with volatile organic compounds in the presence of sunlight. A second concern for human health is the conversion of NOx to nitrate particulates in the atmosphere. These particulates make up a large proportion of the fine particle pollution in most areas of the United States. A correlation between elevated fine particulate matter and increased incidence of illness and premature mortality has been identified. The health effects of particulate matter smaller than 2.5 microns are increased death, primarily in the elderly and those with heart and lung disease, aggravation of respiratory and cardiovascular illness, decreased lung function, and symptomatic effects. NOx emissions also affect quality of air, soil, and water through acid rains. NOx emissions are notable because of their ability to travel long distance and are known to create smog from generating ozone. Recent environmental concerns led to stringent regulations on the allowable levels of NOx emission from combustion power plants, gas turbines, incinerators, boilers, diesel engines, and other polluting sources. Methods to cost effectively mitigate the NOx emission from the stack in these sources could lower the economic impact of these regulations.

Fig. 1 Schematic of the modified electron beam facility: velvet cathode (1), titanium foil (2) over a 11.7 × 29.6 cm2 aperture, 26.3 liter stainless steel reaction chamber (3), NO inlet (4), NO2 inlet (5), N2 inlet (6), chemiluminescent detector outlet (7), residual gas analyzer outlet (8)

Navy researchers have developed an improved process for removing NOx from exhaust gases produced by combustion-based energy sources. In this process, catalyst-free exhaust gas is directed into one or more ducts. The gas is cooled and then passes through the duct, where the gas flow rate and the electron beam pulse rate are configured to cause each successive volume of gas that flows past the beam window to be subjected to only a single electron beam pulse. A single short, intense electron beam is fired into the exhaust through the window in the reaction chamber as the exhaust flows past the window, with some of the electrons being reflected back into the gas by a reflective plate situated opposite the window. The deposited electron energy causes NOx from the exhaust to be converted into N2 and O2, which are output into the atmosphere with the thus-scrubbed exhaust.

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