Nitrogen oxides emissions regulations

C.T. Bowman. Control of Combustion-Generated Nitrogen Oxide Emissions Technology Driven by Regulation. Proc. Combust. Inst., 24 859-878,1992. 

Environmental. Stringent environmental laws require that nitrogen oxides (NO ) and sulfur oxides emission from furnaces be drastically reduced. In many parts of the world, regulations require that NO be reduced to 70 vol ppm or lower on a wet basis. Conventional burners usually produce 100 to 120 vol ppm of NO. Many vendors (McGill, John Zink, and North American) are supplying low NO burners. 

Regulated Pollutants The NSPS regulates MWC emissions, and nitrogen oxides (NOJ emissions from individual MWC units larger... 

The new law also includes specific requirements for reducing emissions of nitrogen oxides, based on EPA regulations to be issued not later than mid-1992 for certain boilers and 1997 for all remaining boilers. 

Emissions monitoring is essential in controlling industrial environments and processes to ensure good air quality standards are maintained. It is also required in order that the various regulations and guidelines related to air quality are met. In addition to gaseous emissions, such as sulfur dioxide, carbon monoxide, nitrogen oxides, hydrocarbons, and many others, the emissions of particulate material and heavy metals must also be controlled. 

Power plant emissions result from the comhustion of fossil fuels such as coal, gas, and oil. These emissions include sulfur dioxide (SO,), nitrogen oxides (NO.,), particulate matter, and hazardous air pollutants, all of which are subject to environmental regulations. Another emission is carbon dioxide (CO,), suspected of being responsible for global warming. 

At pulp and paper mills, air emissions from both process and combustion units are regulated under the National Ambient Air Quality Standards (NAAQS) and the State Implementation Plans (SIP) that enforce the standards. States may implement controls to limit emissions of particulate matter (PM), nitrogen oxides (NO ), volatile organic compounds (VOCs), and sulfur dioxide (S02). 

These harmful effects of nitrogen oxides being known from several years, regulations in their emissions have been progressively introduced in most of the countries worldwide. Therefore, new technologies have been introduced to either limit their formation or convert them to N2. Among these technologies, the selective catalytic reduction (SCR) was the one which was most successfully developed. 

Nitric oxide is the primary nitrogen oxide emitted from most combustion sources. The role of nitrogen dioxide in photochemical smog has already been discussed. Stringent emission regulations have made it necessary to examine all possible sources of NO. The presence of N20 under certain circumstances could, as mentioned, lead to the formation of NO. In the following subsections the reaction mechanisms of the three nitrogen oxides of concern are examined. 

As is well-known, sulfur oxides and nitrogen oxides exhausted into air, which can result in acid rain, have caused serious deterioration of the environment. The potential need for regulation of SO and NO gases in combustion emissions is, nowadays, becoming an important research area. 

Normal operation should be well within the environmental regulation limits set by the EPA. Liquid waste is virtually non-existent and can be sent to the normal sewerage drains. Any acid spills should be diluted. Tail-gas emissions are thought to be less than 1000 ppm of nitrogen oxides (about half the current EPA limit). Should tail-gas emissions exceed this figure, then a catalytic combustor would be necessary to reduce nitrogen oxide levels to below 400 ppm. 

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