NOX Control

Under mildly acidic conditions, e.g. pH 3-4, the reaction can take minutes to hours to complete, whereas under highly acidic conditions (pH 1), the reaction is complete in seconds. Where the effluent is to be treated under conditions of elevated temperature or the effluent contains significant levels of transition metals, Caro s acid is the preferred oxidant. 

In the case of a mixed cyanide/nitrite waste stream, it is advisable to treat the effluent first at alkaline pH to remove cyanide before reducing the pH to the acid range for nitrite treatment. This reduces the risk of toxic hydrogen cyanide laden waste streams. 

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FIGURE 7.8 NOx control in combustion by reburning. Addition of hydroearbons (CHn) late in the eombustion process leads to the reduetion of nitrous oxide (NO) to nitrogen gas (N2). 

Wood SC (1994) Select the Right NOx Control Technology, Chem Eng Prog, Jan 32. 

Tennison, P., Lambert, C. and Levin, M. (2004) NOx Control Development with Urea SCR on a Diesel Passenger Car, SAE Technical Paper Series 2004-01-1291. 

Although the gasifier product itself has low levels of NOx, the total systems emissions of this product must be carefully scrutinized. When clean biogas is eventually burned, NOx will be produced, as it is in most combustion systems with all fuels. The use of biogas rather than solid biomass fuels provides the opportunity to better control the combustion process, which can potentially result in lower NOx emissions. As such, gasification offers potential environmental emissions advantages over combustion alternatives. However, NOx may still occur as the gas is burned, and appropriate NOx control technologies may be needed. 

Pitts, J. N., Jr. Air Pollutants and Public Health Old Problems and New Horizons for NOx Control. Statewide Air Pollution Research Center Report No. 2. Riverside University of California, 1975. 31 pp. 

In short, the effectiveness of VOC versus NOx controls depends critically on the VOC/NOx ratio. 

In contrast, at downwind locations where the airshed ozone peaks are more typically encountered, reduction in VOC starting at point B without concurrent NOx control does not lead to the rapid decrease in 03 observed for DTLA indeed, even an 80% reduction in VOC alone is not predicted to reach the U.S. air quality standard of 0.12 ppm 03. In this case, control of NO(. reduces 03 more rapidly than comparable control of VOC. 

While recognizing these limitations, such isopleths are useful, however, in examining the differing responses of various locations within an air basin to control of VOC and NOx. Since the air mass that starts upwind in the morning traverses the air basin during the day, a multidimensional approach to ozone control is clearly needed. Isopleths characteristic of different locations in an air basin such as those in Fig. 16.16 demonstrate that a combination of VOC and NOx control is essential if air quality throughout a major air basin is to improve consistently (although not necessarily by equal amounts) in all locations. 

As expected, then, inclusion of biogenic emissions in models can have a significant effect under some conditions on the predicted effects of VOC versus NOx control. For example, Pierce et al. (1998) show that when increased isoprene emissions are included in the RADM model, ozone formation in many regions of eastern North America is predicted to be more sensitive to reductions in NOx rather than in VOC. 

The TLEV, LEV, and ULEV standards incorporate the concept of reactivity-weighted mass emissions of VOC, concurrent with increasingly strict NOx control. The intent is to regulate based on equal ozone-forming potentials of the VOC emissions rather than simply on their total mass. That is, the emission standards for organics are set in terms of the amount of ozone formed in the atmosphere per mile traveled by a given vehicle/fuel combination rather than in terms of the simple total mass of VOC emitted per mile. 

Utilities using post-combustion SCR-supported ammonia injection for NOx control as well as those using ammonia conditioning to improve electrostatic precipitator performance will produce fly ash that contains ammonia compounds. The ammonia is primarily physically adsorbed onto the fly ash particles as sulphate and bisulphate species. In many cases, the residual ammonia levels are quite low (<50ppm) however, elevated concentrations can occur as the catalyst ages or due to mechanical problems with the ammonia injection system. While elevated ammonia concentrations in fly ash do not negatively impact pozzolanic properties, it can reduce ash marketability due to odour concerns. For this reason, several processes have been developed to remove or reduce the amount of ammonia in fly ash. 

NOx Control. NOx control limitations are described in both Tide 1 and Tide 4 of the CAAA of 1990. Tide 4 requirements affect only coal-fired boilers and take effect at the same time that the boilers are impacted by CAAA S02 requirements. As of 1996, EPA had established Tide 4 NOx limits only for tangentially fired and wall-fired, dry-bottom boilers that would be impacted by Phase I of the CAAA S02 regulations (Tide 4). Limits of 0.22 kg/106 kj (0.5 lb/106 Btu) and 0.19 kg/106 kj (0.45 lb/106 Btu) have been set for wall-fired and tangentially fired units, respectively. The EPA based these levels on what was achievable using low NOx burners. However, plants can employ a number of different front- or back-end emissions controls, including a combination of options, to achieve these levels. EPA plans to announce Tide 4 NO requirements for 300 additional boilers by late 1996 or eady 1997. 

NOx control Noctal Noctamid n-octanol Nod factors No. 2 fuel oil... 

In addition to engine optimisation measures, Euro V NOx control has been achieved by implementation of two alternative configurations - either the use of EGR or the use of SCR. Ligterink et al. [20] described the different performance of... 

Urea is used in Liquid and solid fertilizers, urea-formaldehyde resins that make adhesives and binders mostly for wood products, livestock feeds, melamine for resins, NOx control from boilers and furnaces, and numerous chemical applications113. Urea uses in the United States are listed in Table 11.6230. 

As indicated earlier, incineration plants usually rely on a combination of the above mentioned devices. Enea and Federambiente (2006) found that different combinations are used in Italy, even though dry and semi-dry techniques are preferred for acid gas control and SNCR is favored over SCR for NOx control, with a large use of activated carbon adsorption for removal of micropollutants. 

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