NOX

Chen FI Y and Sachtler W M FI 1998 Activity and durability of Fe/ZSM-5 catalysts for lean burn NOx reduction in the presence of water vapor Catal. Today 42 73-83... 

Traa Y, Burger B and Weitkamp J 1999 Zeolite-based materials for the seleotive oatalytio reduotion of NOx with hydrooarbons Microporous Mesoporous Mater. 30 3-41... 

Nocolok 100 Flux NOx contiol Noctal Noctamid n-octanol Nod factois No. 2 fuel oil... 

The most popiilar dry scrubbing systems for incinerators have involved the spray drying of hme slurries, followed by dry coUection in electrostatic precipitators or fabric filters. Moller and Christiansen [Air Poll. Cout. Assoc. 84-9.5 (1984)] published data on early European technology. Moller et al. [U.S. Patent no. 4,889,698 (1989)] describe the newer extension of that technology to include both spray-dryer absorption and dry scrubbing with powdered, activated carbon injection. They claim greatly improved removal of mercury, dioxins, and NOx. 

Gas-Otto-Engine NOx Air/fiiel ratio = 1- and. 3-way catalytic converter... 

If in an ozone nonattainment area, does the toller facility actually emit, or have the potential to emit, VOC or NOx in excess of the threshold limit value ... 

Provide annual estimates of all point and fugitive emission sources (tons per year) of hazardous substances, volatile organic compounds (VOCs), heavy metals and fossil fuel products (for example, NOx and SOx) that are released to the environment. 

Figure 3.6.1 (Berty 1979) is a Sankey (1898) diagram, used in power engineering, where the bandwidth is proportional (here qualitatively only) to the flowing masses. This illustrates the calculation results for a rather extreme case of an NOx reduction problem. The case is extreme because the catalyst particle has a dp=0.2mm, i.e., 200 microns. Flow resistance is very high, therefore an L=1 mm deep bend is used only. Per pass concentration drop is still high, Ci-C=1.2ppm, or Dai=0.11. This was tolerated in this case, since it is between 11.2 and 10.00 ppm concentration, and nothing better could have been achieved.

Cl. Calculation of Operating Conditions and Transport Criteria for NOx Abatement in Air in the Rotoberty ... 

Page 3 gives a summary of the most important result in a figure illustrating in a semi-quantitative way the conditions in the specified CSTR. As can be seen on line 74, Dar is somewhat larger than the critical value but the concentration difference on line 75 is small, so this result can be accepted with some reservations. The Carberry number is also larger than the criteria, therefore these experimental results are marginal for Nox abatement... 

On pages 232-234 is an example in the other extreme, where a high-pressure, fast reaction is studied on an industrial size catalyst. The layout and calculation schemes are the same as in the NOx example, so these are not repeated here. 

A high pressure level results in a higher energy requirement with possibly higher utility eosts. On the other hand, today s striet environmental pollution laws with regard to NOx diseharged into the atmosphere are easier to meet at higher pressures, and oxidation of NO to NO2 is favored by inereased pressure and low temperature. 

The new gas turbines also utilize Low NO eombustors to reduee the NOx emissions, whieh otherwise would be high due to the high firing temperature of about 2300 °F (1260 °C). These low NOx eombustors require eareful ealibration to ensure an even firing temperature in eaeh eombustor. New types of instrumentation sueh as dynamie pressure transdueers have been found to be effeetive in ensuring steady eombustion in eaeh of the eombustors. 

Figure 1-33. Control of gas turbine NOx emissions over the years.

The use of dynamic pressure transducer in the combustor section, especially in the Low NOx Combustors ensures that each combustor can is burning evenly. This is achieved by controlling the flow in each combustor can till the spectrums obtained from each combustor can match. This technique has been used and found to be very effective and ensures smooth operation of the turbine. 

NOx Emissions. The amount NO emissions is very eritieal in most regions where gas turbines are being utilized for power generation. The present eap is about 22 ppm the aim is to go down to as low as 9 ppm. The teehniques offered here all are NOx emission friendly, in that they do not inerease the present levels of NOx, in faet in the ease of the injeetion systems, both steam, and heated and humidified eompressed air will lower the NOx emissions making the plant even more environmentally friendly, espeeially in this eritieal loea-tion. 

It is necessary to modify the edge of the hole in various ways to reduce these stress concentrations. Some methods of modification are priming, plunging, and standard radiusing and polishing methods. In the Dry Low NOx Combustors, especially in the lean pre-mix chambers, pressure fluctuations can set up very high vibrations, which lead to major failures. 

Figure 10-18 shows how in the past 30 years the reduetion of NOx by first the use of steam (Wet Combustors) injeetion in the eombustors, and then in the 1990s, the Dry Low NOx Combustors have greatly redueed the NOx output. New units under development have goals, whieh would reduee NOx levels below 9 ppm. 

Figure 10-19. A typioai oombustor showing the NOx produetion zone.

Advances in combustion technology now make it possible to control the levels of NOx production at source, removing the need for wet controls. This of course opened up the market for the gas turbine to operate in areas with limited supplies of suitable quality water, e.g., deserts or marine platforms. 

Although water injection is still used, dry control combustion technology has become the preferred method for the major players in the industrial power generation market. DLN (Dry Low NOx) was the first acronym to be coined, but with the requirement to control NOx without increasing carbon monoxide and unburned hydrocarbons this has now become DLL (Dry Low Emissions). 

The majority of the NOx produced in the combustion chamber is called thermal NOx. It is produced by a series of chemical reactions between the nitrogen (N2) and the oxygen (O2) in the air that occur at the elevated temperatures and pressures in gas turbine combustors. The reaction rates are highly temperature dependent, and the NOx production rate becomes significant above flame temperatures of about 3300 °F (1815 °C). Figure 10-19 shows schematically, flame temperatures and therefore NOx production... 

The great dependenee of NO formation on temperature reveals the direet effeet of water or steam injeetion on NOx reduetion. Reeent researeh showed an 85% reduetion of NOx by steam or water injeetion with optimizing eombustor aerodynamies. 

Basis for NOx Prevention. Emissions from turbines are a funetion of temperature and thus a funetion of the F/A ratio. Figure 10-20 shows that as the temperature is inereased the amount of NOx emissions are inereased and the CO, and the unburnt hydroearbons are deereased. The prineipal meehanism for NOx formation is the oxidation of nitrogen in air when exposed to high temperatures in the eombustion proeess, the amount of NOx is thus dependent on the temperature of the eombustion gases and also, to a lesser amount on the time the nitrogen is exposed to these high temperatures. 

The challenge in these designs is to lower the NO without degradation in unit stability. In the combustion of fuels that do not contain nitrogen compounds, NOx compounds (primarily NO) are formed by two main mechanisms, thermal mechanism and the prompt mechanism. In the thermal mechanism, NO is formed by the oxidation of molecular nitrogen through the following reactions ... 

NOx is primarily formed through high temperature reaction between Nitrogen and Oxygen from the air. 

The prompt mechanism predominates at low temperatures under fuel-rich conditions, whereas the thermal mechanism becomes important at temperatures above 2732 °F (1500 °C). Due to the onset of the thermal mechanism the formation of NOx in the combustion of fuel/air mixtures increases... 

Figure 10-21. Correlation of adiabatio flame temperature with NOx emissions.

The important parameters in the reduetion of NO as seen in the above equation are the temperature of the flame, the nitrogen and oxygen eontent and the resident time of the gases in the eombustor. Figure 10-21 is a eorrelation between the adiabatie flame temperature and the emission of NOx- Reduetion of any and all these parameters will reduee the amount of NOx emitted from the turbine. 

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