No. removal

In an economic comparison of these three common abatement systems, a 1991 EPA study (58) indicates extended absorption to be the most cost-effective method for NO removal, with selective reduction only matching its performance for small-capacity plants of about 200—250 t/d. Nonselective abatement systems were indicated to be the least cost-effective method of abatement. The results of any comparison depend on the cost of capital versus variable operating costs. A low capital cost for SCR is offset by the ammonia required to remove the NO. Higher tail gas NO... 

These catalysts contained promoters to minimise SO2 oxidation. Second-generation systems are based on a combined oxidation catalyst and particulate trap to remove HC and CO, and to alleviate particulate emissions on a continuous basis. The next phase will be the development of advanced catalysts for NO removal under oxidising conditions. Low or 2ero sulfur diesel fuel will be an advantage in overall system development. 

Wet gas scmbbing, which is highly effective for SO removal, is much less effective for NO removal. Because NO in the flue gas is 90—95% NO and because NO has a relatively low solubiUty in absorbing solutions, Htfle NO is removed (47). 

The oxidation of HC and CO must proceed in balance with the reduction of NO by CO, HC, or H2. For the NO removal reaction, a reductant is required. First NO is adsorbed on the catalyst surface and dissociates forming N2 which leaves the surface, but the O atoms remain. CO is required to remove the O atoms to complete the reaction cycle (53). 

NO removals of 90% are achievable. The primary variable is temperature, which depends on catalyst type (38). The principal components of an SCR... 

The ammonia—air dilution system dilutes the vaporized ammonia by a factor of 20 to 25 with air for better admixing through the AIG and to prevent explosive ammonia—air mixtures. Once the catalyst volume is selected, the NO removal is set by the NH /NO mole ratio at the inlet of the SCR system (39). 

Hardware installation and removal (including support installation but no removal costs)... 

If there were no removable cover on the front end of the exchanger, it would be designated BES." The second nozzle and pass partition in the front end are discretionary depending upon the shell type. Types A and B bolt onto the shell. In type C, the head cannot be unbolted for maintenance. 

Kinetic parameters are deduced from studies of the following 230 equilibria (no removal of water) ... 

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 hexamine cobalt (II) complex is used as a coordinative catalyst, which can coordinate NO to form a nitrosyl ammine cobalt complex, and O2 to form a u -peroxo binuclear bridge complex with an oxidability equal to hydrogen peroxide, thus catalyze oxidation of NO by O2 in ammoniac aqueous solution. Experimental results under typical coal combusted flue gas treatment conditions on a laboratory packed absorber- regenerator setup show a NO removal of more than 85% can be maitained constant. 

In order to confirm the proposed mechanism described above, in which O2 may have a positive effect on NO absorption, the comparative experiments have been carried out. The results are shown in Fig. 1, from which one can see that the presence of O2 will greatly improve the NO removal performance. In the absence of O2, NO coordination occurs according to Eq. (2), a reversible reaction limited by equilibrium, the NO removal decreases from the initial 100% to about 60% in one hour. In the presence of O2 however, contribution of Eq. (2) is little, the most coordination of NO is certainly attributed to the cascade reactions from Eq.(3) to Eq.(6), and the final reaction of Eq. (7), which will not be constrained by the reaction equilibrium, and thus the NO removal can be maintained 100% in 2-3 hours. 

On the other hand, it can be inferred from Fig. 1 that the NO removal efficiency will decrease as the reaction proceeds. The NO removal declines from 100% at the very beginning to 93% after 4 hours with 5.2% O2 present in the gas phase. This phenomenon may be due to the oxidation of Co(NH3)6 into Co(NH3)6 meaning deactivation of the catalyst. 

Figure 1. Effect of on NO removal Figure 2. Effect of activated carbon on reduction (O.OIMCo(AWj)f, 50 C, NO=640ppm)...

High quality (total digestion, no contamination, no removal of unstable compounds)... 

Finally, the abatement of NO pollution by using sorbing catalytic materials [59,60] must also be cited. Several solid sorbents for NO removal (metal oxides, spinels, perovskites, double-layered cuprates, zeolites, carbonaceous materials, heteropolyacids and supported heteropolyacids) have been tested. The results are interesting, but not competitive to actual technologies. To mention that the use of sorbing materials allows... 

In general, several spectroscopic techniques have been applied to the study of NO, removal. X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) are currently used to determine the surface composition of the catalysts, with the aim to identify the cationic active sites, as well as their coordinative environment. 

The SCR of NO by NH3 is actually the best developed and widespread method for the NO removal from stationary sources due to its efficiency and selectivity. The process... 

To finish with another trend for NO removal consisting in NO direct decomposition, we would like to depict the infrared study of NO adsorption and decomposition over basic lanthanum oxide La203 [78], In this case, the basic oxygens are proposed to lead to N02 and N03 spectator species, whereas the active sites for effective NO decomposition are described as anion vacancies, which are often present in transition metal oxides. This last work makes the transition with the study of DeNO, catalysts from the point of view of their ability to transfer electrons, i.e. their redox properties. 

Another way to work in transient conditions is to stop suddenly (or conversely to instantaneously introduce) one of the reactants, in order to destabilize the system and to enhance the concentration of labile species. With this method, for example, Poignant et al. studied the DeNO. reaction mechanism on a H—Cu-ZSM-5 catalyst, using propane or propene as reducing agents. The introduction of 2000 ppm of hydrocarbon in a flow of NO (2000 ppm) + 5% 02 allowed to evidence the formation of acrylonitrile, which behaved as an intermediate. Its reactivity with NO+ species constituted a fundamental point to describe a detailed SCR mechanism for NO removal on zeolitic compounds [137],... 

Operando studies for NO removal from stationary sources... 

The influence of the NO,/NO feed ratio on the NO removal efficiency is depicted in Figure 9.10 for different temperatures [37], Below 300°C, DeNO always increases linearly with increasing N02 fractions up to 50%, for which the highest DeNO was... 

The gas mixture containing the nitrogen oxides is very important as well. Experiments and modeling carried out for N2/NOx mixtures, or with addition of 02, H20, C02 and hydrocarbons will be discussed. Typical hydrocarbon additives investigated are ethane, propene, propane, 2-propene-l-ol, 2-propanol, etc. As compared to the case without hydrocarbons, NO oxidation occurs much faster when hydrocarbons are present. The reaction paths for NO removal change significantly, in fact the chemical mechanism itself is completely different from that of without hydrocarbon additives. Another additive investigated extensively is ammonia, used especially in corona radical shower systems. 

Numerous studies of NO removal in DBD have been carried out [20-36], The effect of electrode shape, discharge gap length, discharge polarity, gas composition and flow rate, and operation temperature on NO conversion will be considered. 

The composition of the carrier gas containing the nitrogen oxides is another very important factor in NO removal. The influence of oxygen content in N2/02/N0 mixtures on the conversion of NO was investigated [26-28], The addition of water vapor [26,27,29-32], carbon dioxide [26,32] and hydrocarbons [27-35] was studied as well. 

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