NO+ emission

Fuel switch. The choice of fuel used in furnaces and steam boilers has a major effect on the gaseous utility waste from products of combustion. For example, a switch from coal to natural gas in a steam boiler can lead to a reduction in carbon dioxide emissions of typically 40 percent for the same heat released. This results from the lower carbon content of natural gas. In addition, it is likely that a switch from coal to natural gas also will lead to a considerable reduction in both SO, and NO, emissions, as we shall discuss later. 

Such a fuel switch, while being desirable in reducing emissions, might be expensive. If the problem is SO, and NO, emissions, there are other ways to combat these, which will be dealt with in the next chapter. 

Dealing with NO emissions. There are two main reaction paths for NO,r formation ... 

Fuel-bound NO. is formed at low as well as high temperatures. However, part of the fuel nitrogen is directly reacted to N2. Moreover, N2O and N2O4 are also formed in various reactions and add to the complexity of the formation. It is virtually impossible to calculate a precise value for the NO, emitted by a real combustion device. NO, emissions depend not only on the type of combustion technology but also on its size and the type of fuel used. 

Chemical reduction. The injection of ammonia reduces NO emissions by the reduction of NO , to nitrogen and water. Although it can be used at higher temperatures without a catalyst, the most commonly used method injects the ammonia into the flue gas upstream of a catalyst bed (typically vanadium and/or tin on a silica support). 

A conclusion is that meeting the regulations for NO emissions in industrial combustion practically implies a limit in the nitrogen content of fuel of 3000 ppm. 

No emission during holds was observed but the concentration of events in clusters and the high level of amplitude of events confirmed the results of the proof test. After 20 bars, the bottom of the vessel around the defect became silent and activity is observed in the high part of the vessel near welds. 

Since SO2 and NO2 are criteria pollutants, their emissions are regulated. In addition, for the purposes of abating acid deposition in the United States, the 1990 Clean Air Act Amendments require that nationwide SO2 and NO emissions be reduced by approximately 10 million and 2 million t/yr, respectively, by the year 2000. Reasons for these reductions are based on concerns which include acidification of lakes and streams, acidification of poorly buffered soils, and acid damage to materials. An additional major concern is that acid deposition is contributing to the die-back of forests at high elevations in the eastern United States and in Europe. 

Equation 25 represents the reaction responsible for the removal of uv-B radiation (280—330 nm) that would otherwise reach the earth s surface. There is concern that any process that depletes stratospheric o2one will consequently increase uv-B (in the 293—320 nm region) reaching the surface. Increased uv-B is expected to lead to increased incidence of skin cancer and it could have deleterious effects on certain ecosystems. The first concern over depletion was from NO emissions from a fleet of supersonic transport aircraft that would fly through the stratosphere and cause reactions according to equations 3 and 26 (59) ... 

Control of NO emissions from nitric acid and nitration operations is usually achieved by NO2 reduction to N2 and water using natural gas in a catalytic decomposer (123—126) (see Exhaust control, industrial). NO from nitric acid/nitration operations is also controlled by absorption in water to regenerate nitric acid. Modeling of such absorbers and the complexities of the NO —HNO —H2O system have been discussed (127). Other novel control methods have also been investigated (128—129). Vehicular emission control is treated elsewhere (see Exhaust control, automotive). 

Ethanol blends can also have an effect on NO emissions. Scattered data indicate that NO may increase as oxygenates are added to the fuel. 

Methanol, a clean burning fuel relative to conventional industrial fuels other than natural gas, can be used advantageously in stationary turbines and boilers because of its low flame luminosity and combustion temperature. Low NO emissions and virtually no sulfur or particulate emissions have been observed (83). Methanol is also considered for dual fuel (methanol plus oil or natural gas) combustion power boilers (84) as well as to fuel gas turbines in combined methanol / electric power production plants using coal gasification (85) (see Power generation). 

Fig. 6. Trade-off between cetane number and aromatics for NO emissions (85).

Fig. 8. Transient NO emissions at synthetic wastes nitrogen contents of (D), 1% ( ), 3% and (0)> 10%, where the % of O2 is 2ero. Aniline is used as a nitrogen source and toluene is used to keep the total hydrocarbon weight fixed at 35 g (29).

Fig. 9. Measured coal-fired flow faciUty (CFFF) NO emissions where ( ) represents high sulfur coal, (e) low sulfur coal, (A) low sulfur coal having K2/S = 1.15, and ( ) LMF5-G. A, Illinois No. 6 coal (3% S) B, Montana Rosebud coal (1% S), and the NSPS range is between the dotted lines. To...

The plant is designed to satisfy NSPS requirements. NO emission control is obtained by fuel-rich combustion in the MHD burner and final oxidation of the gas by secondary combustion in the bottoming heat recovery plant. Sulfur removal from MHD combustion gases is combined with seed recovery and necessary processing of recovered seed before recycling. 

New units can be ordered having dry, low NO burners that can reduce NO emissions below 25 ppm on gaseous fuels in many cases, without back-end flue-gas cleanup or front-end controls, such as steam or water injection which can reduce efficiency. Similar in concept to low NO burners used in boilers, dry low NO gas turbine burners aim to reduce peak combustion temperatures through staged combustion and/or improved fuel—air mixing. 

A notable difference between the newer large machines and the somewhat smaller units is the use of multiple, reverse-flow can combustors configured annulady. Because the individual cans are relatively small, they reportedly lend themselves well to laboratory experimentation with various fuel types, including reduced-heat value synfuels (see Fuels, synthetic). A dry, low NO version of the can combustors has been developed for both gas and hquid fuel firing. NO emissions can reportedly be held below 25 ppm when firing gas fuel. By employing water injection, NO emissions can be held below 60 ppm for oil-fired units. 

Because of the necessity to comply with national standards for ground-level ozone, some states are planning another phase of more stringent NO emissions limits which may take place in the eady 2000s. These additional post-RACT reductions may affect plants of all sizes and types, but are likely to focus on major sources. The deadline for compliance in the most extreme areas is 2010. For severe nonattainment areas (O levels 0.181—0.280 ppm), including many coastal areas in the Northeast, from northern Virginia to southern Maine, compliance must be achieved by November 2005 to November 2007. Serious ozone nonattainment areas (O levels 0.161—0.180 ppm) are expected to be in compliance by November 1999. Moderate noncompHance areas must comply by November 1996. 

SO2 and NO Emissions ControlFechnology Comparative Analysis of Options, SPA Pacific Inc., Mountain View, Calif., Sept. 1991, pp. 4.1—4.8. 

Also, wood fuel is low in sulfur, ash, and trace toxic metals. Wood-fired power plants emit about 45% less nitrogen oxides, NO, than coal-fired units. Legislation intended to reduce sulfur oxides, SO, and NO emissions may therefore result in the encouragement of wood-burning or cofiring wood with coal. 

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