Oxides of Nitrogen NOx

For most lime kilns, the emission of oxides of nitrogen is not an issue. 

The concentration of NOx in the exhaust gases reflects the temperatures in the flame and/or in the kiln. In kilns such as rotaries, the flame influences the NOx level, and a low NOx burner may be used to reduce the NOx level [33.5, 33.6]. Further experience is probably required to asses the effects of such burners on other aspects of kiln operation. Production of dead-burned dolomite in rotary kilns requires temperatures of up to 1900 °C. This results in very high NOx levels (Table 33.2). 

In many shaft kilns, the fuel is burned as an ill-defined flame and, in consequence, the gas temperatures within the kiln are generally low. As a result, the NOx levels are well within required emission limits (Table 33.2). Low NOx burner technology may, however, be of some benefit in those shaft kilns which have combustion chambers, and in which there is a well-defined flame. 

If it were necessary to reduce NOx levels by means other than low NOx burners, and lowering kiln temperatures/excess oxygen levels, standard NOx destruction techniques would have to be considered. 

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In addition to carbon monoxide (CO) and unbumed hydrocarbons (UHC), the most significant products of combustion are the oxides of nitrogen (NOx). At high temperatures, free oxygen not consumed during combustion reacts with nitrogen to form NO and NO2 (about 90% and lO /i of total NOx, respectively). 

In April of 1998, the EPA published a final rule for emission of oxides of nitrogen (NOx), hydrocarbons (EIC), carbon monoxide (CO), particulate matter (PM), and smoke opacity for newly manufactured and rcmanufacturcd locomotives. The rulemaking took effect in 2000 and is estimated by the EPA to cost the railroads 80 million per year—about 163 per ton of NOx reduced, according to EPA figures. The emissions standards for the several pollutants will be implemented in three tiers—for locomotives... 

Acid deposition or, acid rain, occurs when SO2 and oxides of nitrogen (NOx) react with water, oxygen, and oxidants to form acidic compounds. It is deposited in dry form (gas, particles) or wet form (rain, snow, fog), and can be carried by wind hundreds of miles across state and national borders. Acid rain harms lakes and streams, damages trees, crops, historic buildings, and monuments. 

Acid precipitation—two relatively easily controllable classes of trace gases— oxides of nitrogen (NOx) and oxides of sulfnr (SOx) with relatively well quantified risks... 

Scientists have discovered that air pollution from the burning of fossil fuels is the major cause of acid rain. Acidic deposition, or acid ram, as it is commonly known, occurs when emissions of sulfur dioxide (SO ) and oxides of nitrogen (NOx) react in the atmosphere with water, oxygen, and oxidants to form various acidic compounds. This mixture forms a mild solution of sulfuric acid and nitric acid. Sunlight increases the rate of most of these reactions. 

Another driver of a shift to hydrogen is concern about urban air pollution. The transportation sector remains one of the largest sources of such pollution—especially (1) the oxides of nitrogen (nox) that are a precursor to ozone smog and (2) particulates—... 

Oxides of nitrogen (NOx) and sulfur (SOx), produced by the combustion of fossil fuels in vehicles and power plants are pollutants and also precursors to acid rain. 

Emissions from Primary Reformer. The primary reformer of feed gas is conventional combustion emission source for oxides of nitrogen (NOx), carbon monoxide (CO), and particulate matter (PM). 

The combustion of hydrogen with air however can also produce oxides of nitrogen (NOx) ... 

The burning of coal in thermal power plants results in major pollutants such as suspended particulate matter (SPM), sulphur dioxide (SO2), oxides of nitrogen (NOx) etc, of vdiich NOx is believed to be a key con nent responsible for several hazards associated with ecology and human health(l). Given the relative abundance of coal in India, coal-based thermal power plants will continue to play a dominant role in the power sector. Therefore NOx abatement through primary and secondary measures assumes great importance. Post combustion techniques such as selective catalytic reduction (SCR) can reduce NOx emissions by >95% (2). 

Exceed DOE s goal of reducing 1998 emission standards by 75% by achieving 99.5% reduction. Carbon monoxide (CO) emissions will be <1 ppm, non-methane hydrocarbon (NMHC) emissions will be <0.05 g/hp-hr, and oxides of nitrogen (NOx) will be <0.15 g/hp-hr. 

Catalytic converters were first installed on US passenger cars in 1975. For several years, their mandate was limited to the reduction of tailpipe concentrations of CO and unbumt hydrocarbon (HCs). Although oxides of nitrogen (NOx) were recognized as health and environmental hazards, the allowable limit was attainable by non-catalytic measures, such as recirculating a portion of the exhaust gas to cool the engine. 

A primary gaseous air pollutant from combustion sources such as power plants is oxides of nitrogen (NOx). Since NOx is a known precursor to ozone formation, the Clean Air Act Amendments of 1990 call for reduction of NOx from certain facilities throughout the United States. 

However, it is not only the production of carbon dioxide from coal that needs to be decreased. The production of pollutants such as sulfur dioxide (SOj) and oxides of nitrogen (NOx, where x = 1 or 2) also needs attention. These gases react with the water in the atmosphere and the result is an acid ... 

Oxides of nitrogen (NOx) The compounds nitric oxide (NO) and nitrogen dioxide (NO2) NOx refers to the combined concentration of the two. 

FIGURE 3 Inventory of national oxides of nitrogen (NOx) emissions by principai source category in the United States for 1997. 

Atmospheric Emissicms [13] - The main emissions to the atmosphere are oxides of nitrogen (NOx) and nitrous oxide (N2O). The concentration of NOx in emissions varies between 75 and 2,000 ppmv. The concentration of NOx depends on final acid concentration, absorption tower pressure and design, temperatures of the cooling tower water, quantity and quality of process water, d degree of tail-gas treatment, if any. 

In the troposphere, the lowest layer of atmosphere, volatile terpenes perform a dual action, depending on the presence of anthropogenic pollutants such as oxides of nitrogen (NOx). When NOx concentrations are low, volatile terpenes react with ozone to reduce the atmospheric concentration of this ph5hotoxic gas. When air is contaminated with NOx formed e.g., by combustion, volatile terpenes participate in reactions which results in formation of tropospheric ozone. 

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