SNOX process

Figure lO.n. Schematic diagram of the SNOX process used to remove both SO2 and NOx from the flue gas. (Courtesy of Haldor Topsoe A/S.)... 

In Denmark the new SNOX process has been developed by Agerholm et al. [153]. Flue gases with a temperature of about 653 K are cleaned from NO by means of selective catalytic reduction. The gas is reheated up to 673 K and introduced to an SO2 converter which is located downstream from the SCR reactor. SO2 is oxidized into SO3 which is converted to sulfuric acid. The ammonia slip from the SCR reactor is oxidized simultaneously. Advantages of the SNOX process are ... 

Some of the advanced techniques used in postcombustion cleaning—such as the use of granular calcium oxide or sodium sulfite solutions—have already been described above. In the SNOX process, cooled flue gases are mixed with ammonia gas to remove the nitric oxide by catalytically reducing it to molecular nitrogen. The resulting gas is reheated and sulfur dioxide is oxidized catalytically to sulfur trioxide, which is subsequently hydrated by water to sulfuric acid, condensed, and removed. 

The SNOX process is also known as the WSA-SNOX process when both SO2 and NO are removed or, if only SO2 is removed, as the WSA process where WSA stands for Wet Sulfuric Acid. This process catalytically reduces both the SO2 and the NO in flue gases by more than 95% and, with integration of the recovered heat from the WSA condenser, is reported to have lower operating costs than conventional technologies. No chemical or additive is required other than ammonia for optional NO reduction. Sulfuric add at 93.2% concentration is produced that is said to meet or exceed U.S. Federal Specifications. The SO2 conversion catalyst can tolerate up to 50% water vapor and several hundred ppm of chlorides. CO and hydrocarbon emissions are said to be low (Collins et al., 1991). 

The SNOX process consists of the following components particulate collector, gas-to-gas heat exchanger, NOx SCR, SO2 converter, sulfuric add condenser, and add conditioning unit. Figure 7-41 shows a typical SNOX process flow diagram for a boiler application. Par-... 

HaUor Tops0e WSA-SNOX. The WSA-SNOX process was developed by Haldor Topspe A/S, Denmark, and is offered in the U.S. by ABB Combustion Engineering, Inc. The process is one of the most highly developed of the combined NOj,/S02 systems. Several industrial systems are in operation in Europe, and a demonstration unit has been operated in the U.S. (Kingston et al., 1990). 

In the WSA-SNOX process, the flue gas passes first through a conventional SCR unit where NO is reduced to N2 by ammonia. The flue gas is then heated slightly and passed through a second catalyst where SO2 is oxidixed to SO3. The SO3 is hydrated to form sulfuric acid and concentrated to 9S wt% acid in an air-cooled falling-film condenser constructed of glass. Ammonia slip from the SCR reactor is oxidized in the SO2 converter, eliminating a problem encountered in conventional SCR processes. A more detailed description of the process is given in Chapter 7 in the section titled SNOX Process. ... 

Kingston, W. H., Cunninghis, S., Evans, R. J., and Speth, C. H 1990, Demonstration of the WSA-SNOX Process Through the CCT Program, paper 90-JPGC/FACT-17 presented at the Joint ASME/IEEE Power Generation Conference, Boston, MA, October 21-25. 

The combined approach of removing both the sulfur and the NOx from the flue gas is called SNOX (Haldor Topsoe A/S) or DESONOX (Degussa). An example of the setup for this process is shown in Fig. 10.11, where 99% of the NOx is converted in the SCR reactor and the SO2 is converted into sulfuric acid. 

SNOX A combined flue-gas desulfurization and denitrification process. The NOx is first removed by the SCR process, and then the S02 is catalytically oxidized to S03 and converted to sulfuric acid by the WSA process. Developed by Haldor Topsoe and first operated at a power station in Denmark in the 1990s. 

WSA [Wet gas sulphuric acid] A process for recovering sulfur from flue-gases and other gaseous effluents in the form of concentrated sulfuric acid. It can be used in conjunction with the SCR process if oxides of nitrogen are present too. The sulfur dioxide is catalytically oxidized to sulfur trioxide, and any ammonia, carbon monoxide, and carbonaceous combustibles are also oxidized. The sulfur trioxide is then hydrolyzed to sulfuric acid under conditions which produce commercial quality 95 percent acid. Developed by Haldor Topsoe 15 units were commissioned between 1980 and 1995. See also SNOX. 

WSA-SNOX A combined flue-gas treatment process which converts the sulfur dioxide to sulfuric acid and the nitrogen oxides to nitrogen. Developed by Snamprogetti and Haldor Topsoe, based on the WSA process. A large demonstration unit was under construction in 1989. 

In this paper, the application of microelectronic processing technology to the fabrication of SnOx and PdAu/SnOx microsensors on silicon wafers is described, sensor responses to various gases in air are presented, and the possible sensing mechanisms are briefly discussed. 

Figure 1. Processing steps for the fabrication of PdAu/SnOx...

To achieve better conversions in less time, several common acid, base and transition metal catalysts were screened for the purpose of lowering the reaction temperature in the glycerin process. The results for each category of catalyst are represented in Figure 6.6. All reactions were performed with crude (neutralized) glycerin. The activity of the catalysts is compared based on a standard reaction time at 180 °C for 4 hours and normalized based on equal equivalents of metal content per moles of acid. The organo-metal catalysts, tetrabutyltitanate (TBT), dibutyltin oxide (DBTO), and tinoxalate (SnOx) were the most efficient catalysts. Overall, while tin compounds are effective catalysts, they can be problematic because of their potential toxicity, unless they can be removed from the product in a cost effective manner. 

Fig. 18. X-ray diffraction patterns and intensity curves for the SnOx films after deposition by magnetron sputtering (pressure of 1 Pa in Ar-Ch mixture) and H-plasma treatment (a), deposition and annealing at 550°C for 1 h (b), the subsequent processing of H-plasma (c) and re-armeahng at 550°C (d).

The phenomena of self-organization of matter in SnOx layers were identified, consisting in the intensive formation of Sn02 crystallites with sizes of 4 nm in the process of film deposition by magnetron sputtering (pressure in the Ar-02 mixture is 2.7 Pa), and Sn02 crystallites with sizes of 3 nm at the deposition of films by the sol-gel technique (concentration of Sn 0.14 mol/L in a solution). 

Other additives to platinum-based electrodes, such as tin-oxide (SnOx) [71], have also been shown to significantly improve the catalytic activity of the oxygen reduction reaction. Using a PPA-Processed w-PBI membrane with a 7 wt% SnO in Pt/Sn02/C catalyst under unhumidified H2/O2 at 180°C, a voltage of 0.58 V under a load of 0.2 A cm was produced. Under the same conditions, a w-PBI MEA using a Pt/C catalyst produced only 0.4 V at 0.2 A cm . ... 

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