NO Emissions Reduction

The PAG system utilizes plasma to oxidize NO to NO2, which then reacts with a suitable reductant over a catalyst. LNC, NSR, and PAG systems have still several challenging tasks to be solved. Gonsequently, all these technologies are not yet appropriate for commercial applications to diesel and lean-burn engine exhausts [47]. 

Emission control from heavy duty diesel engines in vehicles and stationary sources involves the use of ammonium to selectively reduce N O, from the exhaust gas. This NO removal system is called selective catalytic reduction by ammonium (NH3-SGR) and it is additionally used for the catalytic oxidation of GO and HGs.The ammonia primarily reacts in the SGR catalytic converter with NO2 to form nitrogen and water. Excess ammonia is converted to nitrogen and water on reaction with residual oxygen. As ammonia is a toxic substance, the actual reducing agent used in motor vehicle applications is urea. Urea is manufactured commercially and is both ground water compatible and chemically stable under ambient conditions [46]. 

The challenges to be faced in air-purification systems using photocatalysis involve the treatment of relatively large gas flows in devices with low pressure drops, good catalyst irradiation, and efficient reactant species as well as good photocatalyst contacting [51-53]. 

---

Titles I and IV are most relevant to SO, and NO control. Title I establishes a 24-hour average ambient air standard for SO, of 0.14 ppm. The NO provisions require existing major stationaiy sources to apply reasonably available control technologies and new or modified major stationaiy sources to offset their new emissions and install controls representing the lowest achievable emissions rate. Each state with an ozone nonattaininent region must develop a State Implementation Plan (SIP) that includes stationaiy NO emissions reductions. 

The optimal strategy in this case dramatically reduced the deposition at the two sites in Germany which responded least in the first series of optimisations, in the second series their depositions were reduced by 4.9% and 14.0% instead of 2.5% and 5.6%, respectively. However for the other nine sites, except the Netherlands site, the second series gave lower NO, emission reduction requirements compared... 

Paul, P. Maaskant, O. Catalytic NO emission reduction at a cogeneration plant in the food industry, NOXCONF, Paris, France, March 2001. 

Seher DHE et al (2003) Control strategy for NO - emission reduction with SCR, Proceedings of the International Truck Bus Meeting Exhibition... 

Mirvakili, A., Samimi, F., and Jahanmiri, A. (2014) Simultaneous ammonium nitrate decomposition and NO emission reduction in a novel configuration of membrane reactor a simulation study. 

It is significant that the cofiring of dWS to achieve NO, emissions reductions goes beyond the use of this as a water injection technique. Figure 3.5 shows the reduction in urea consumption when cofiring 7.6 1/s (121 gpm) of CWS with NO, reduced to 0.155 kg/GJ... 

Sulfur emission flux (g S m a ) in the United Kingdom in 1995, assuming no emission reductions are implemented. 

Table 2 shows that no emission reductions are required anywhere to reduce deposition on the southwest coast of Norway to 1.5 g S m a . To reduce the deposition to 1.0 g S m a , emission reductions are required in the German Democratic Republic, the United Kingdom, Czechoslovakia, Norway, Denmark and Poland, in order of national percentage of the total European cost of 3.8 billion DM per year. Substantial percentage emission reductions (from unabated 1995 levels) are required in the German Democratic Republic, Denmark, and Norway the last two because of their relative proximity to the receptor site, the first because of the relatively low marginal costs for sulfur emission control there. Note that emissions in Norway are not lowered to the minimum possible value but only by 45% after that point it is more cost-effective to reduce emissions elsewhere. 

Greenhouse gas reduction potential ratings for Scopes 1 2 and Scope 3 3 = highest emission reduction, 0 = no emission reduction. 

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. 

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). 

Large sources of SO2 and NO may also require additional emission reductions because of the 1990 Clean Air Act Amendments. To reduce acid... 

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. 

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). 

In the United States, the reportable quantity of 1-propanol for spills under CERCLA "Superfund" is 100 Ib/d (45.4 kg/d). However, no reportable quantity is assigned for transport (43). The substance is on the list for atmospheric standards, as defined iu 40 CER 60.489 (47). The iatent of these standards is to require all newly constmcted, modified, and reconstmcted manufacturiug units to use the best demonstrated system of continuous emission reduction for equipment leaks of volatile organic compounds (47). 1-Propanol is also on the right-to-know regulations of the states of Connecticut,... 

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. 

Even rain is not pure water. Reports from the U.S. Geological Survey show that it contains 2.3—4.6 ppm of soflds, or a yearly precipitation of 2.5—5 t/km. Recently (ca 1997), work conducted ia the United States and Europe has underscored the rather dangerous results of iacreased use of fossil fuels, where the SO and NO emissions that end up ia the rain lower its pH from 5.6 (slightly acidic) for uncontaminated rain, to acid rains. Such acid rain has serious effects on surface waters (1). About 40 x 10 t of SO and 25 x 10 t of NO were emitted ia the United States ia 1980. There are, however, encouragiag trends the 1970 Clean Air Act has led to a gradual reduction ia these emissions, bringing the SO emissions down from the previous levels cited by 10% by 1990, and the NO emissions down by 6%, with a consequent slight decrease ia rain acidity. A part of the Clean Air Act is also iatended to cap SO emissions from major poiat sources at 13.5 x 10 t (2). Between 1994 and 1995, total SO emissions ia the U.S. decreased remarkably by 13% and total NO emissions by 8%. 

The additive approach to reducing SO emissions can be either detrimental or beneficial toward NO reduction. Early alumina-based SO removal additives actually produced substantial increases in NO content in the flue gas (48). The more recent spinel-based SO removal additives have been reported to reduce NO emission by 30% in one commercial trial (49). 

There has been a growing demand for a lean NO catalyst ia order to decrease the relatively low NO emission of the lean bum engine sufftciendy to meet the future standards. Lean NO catalysts have been developed based on 2eolites (see Molecularsieves). Cu-promoted ZSM-5 2eolite has shown ability to reduce NO ia an exhaust having excess oxygen at an efficiency of 30 to 50% (153). Durability is not proven. Research has revealed that certain hydrocarbons are preferred for the reduction of NO, and that CO and H2 apparentiy do not reduce NO over such lean NO catalysts (154). 

Selective Catalytic Reduction. Selective catalytic reduction (SCR) is widely used in Japan and Europe to control NO emissions (1). SCR converts the NO in an oxygen-containing exhaust stream to molecular N2 and H2O using ammonia as the reducing agent in the presence of a catalyst. 

NO Emission Control It is preferable to minimize NO formation through control of the mixing, combustion, and heat-transfer processes rather than through postcombustion techniques such as selective catalytic reduction. Four techniques for doing so, illustrated in Fig. 27-15, are air staging, fuel staging, flue-gas recirculation, and lean premixing. 

This cycle, as shown in Figure 2-23, is a regenerative cycle with water injection. Theoretically, it has the advantages of both the steam injection and regenerative systems reduction of NO emissions and higher efficiency. The work output of this system is about the same as that achieved in the steam injection cycle, but the thermal efficiency of the system is much higher. 

---