Most large industrialized urban areas in the United States cannot meet National Air Quality Standards (NAAQS) for ozone. Atmospheric studies have shown that ozone formation is the result of a complex series of chemical reactions involving volatile organic compounds (VOCs) and nitrogen oxides (NOx). These studies show that many urban areas with a VOC / NOx ratio above 15: 1 can only reduce the ozone level in the area by reducing NOx emissions. As a result, many countries are implementing NOx control regulations for incinerators complying with the NAAQS ozone standard.
This article addresses the characterization of NOx emissions from industrial combustion devices. Thereafter, evaluation of the applicable NOx control technologies and the selection of an appropriate control method are advised.
Characterize emissions
Most industrial combustion devices have not been tested for their basic NOx emissions. Instead, the NOx emissions from these devices were simply estimated using a number of factors. However, given the latest regulations, it is imperative that NOx emissions for the units concerned are now known with certainty. This determines the current compliance status of each device and defines the management technologies that apply to the fees for the devices that need to be modified to achieve compliance.
It is therefore important to test each combustion device to check its NOx emission characteristics. The testing process should streamline to provide timely and necessary information to make decisions about the use of NOx control technologies.
The basic approach is to select a unit in a class of units (ie with the same design and size) for the characterization tests (NOx, CO2 and 02). Tests are performed at three charge points representing the unit's normal operating range, with tests to change the excess oxygen at each charge point. Figure 1 shows the typical results of the characterization tests. The remaining devices in the class are tested on a single charging station that is almost fully charged.
The operational data obtained during the tests are used in conjunction with the NOx and CO data to define the compliance status of each device and the NOx control technologies that apply to the devices to be modified. In most cases, this approach tests multiple devices per day and provides the operational data that the engineer needs to properly evaluate potential NOx management technologies.
Basic concepts
The reasonably available regulatory technology regulations (RACT) for NOx emissions are defined in terms of emission limit values, such as 0.2 lb NOx / MMBtu, rather than determining specific NOx control technologies. Depending on the fuel used and the design of the combustion device, a variety of control technologies may be practical options. Before choosing RACT for a particular combustion unit, you must know how NOx emissions are generated so that the appropriate control strategy can be formulated.
The NOx emissions generated during the combustion process are a function of the fuel composition, mode of operation and basic construction of the boiler and the combustion system. Each of these parameters can play an important role in the final NOx emission.
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