Oxidation in flue gas

Takaki, K., Jani, M.A. and Fujiwara, T. (1999) Removal of nitric oxide in flue gases by multi-point to plane dielectric barrier discharge, IEEE Trans. Plasma Sci. 27, 1137—45. 

Mine tailings are a source of both metal and nonmetal contamination. A common material in coal mines is iron pyrite, FeS2. As a contaminant of coal, this compound and similar compounds contribute to the production of sulfur oxides in flue gases when coal is burned. As a material in mine tailings, it contributes both iron and sulfur to water pollution when the sulfide is oxidized in a series of reactions to sulfate and the Fe(II) oxidized to Fe(III) ... 

Suhr H. and Weddigen, G. Reduction of nitric oxide in flue gases by point to plane corona discharge with cataiytical coatings on the plane electrode Combust. Sci. and Techoi. 1990,72,101-115... 

Purer product no contamination or oxidation in flue gases as in conventional dryer... 

Nissinen T, Kukkonen J (2004) Catalytic process for reducing nitrogen oxides in flue gases and reducing agent composition. FI2,004,000,057... 

Metal Oxide - Since metals are less electrophilic than silicon, metal oxide adsorbents show even stronger selectivity for polar molecules than do siliceous materials. The most commonly used metal oxide adsorbent is activated alumina, used primarily for gas drying. Occasionally, metal oxides find applications in specific chemisorption systems. For example, several processes are under development utilizing lime or limestone for removal of sulfur oxides from flue gases. Activated aluminas have surface areas in the range of 200 to 1,000 ftVft Average pore diameters range from about 30 to 80 A. 

CAT-OX [Catalytic oxidation] An adaptation of the Contact process for making sulfuric acid, using the dilute sulfur dioxide in flue-gases. A conventional vanadium pentoxide catalyst is used. Developed by Monsanto Enviro-Chemical Systems, and operated in Pennsylvania and Illinois in the early 1970s. 

DeDiox A process for destroying polychlorinated dioxins and furans in flue-gases by catalytic oxidation with hydrogen peroxide. The catalyst is based on silica and the process is operated at 80 to 100°C. Developed by Degussa from 1994. The business was offered for sale in 1998. 

In flue gases MISiC sensors can be used to either monitor the gas components, such as CO, nitric oxide (NO), and oxygen, or identify different modes of combustion in the boilers of small power plants. In this way, it is possible to optimize the combustion in boilers of about 0.5-5 MW in which optical techniques such as Fourier transform infrared (FTIR) are too expensive and complex. The authors have performed measurements in a 100-MW boiler, which has been used to heat houses and industries and generate electricity in Nykoping, Sweden, and in which there was a natural randomization of the flue gases [59]. Data was collected over several... 

Sulfur oxides (S02 and S03) present in flue gases from upstream combustion operations adsorb onto the catalyst surface and in many cases form inactive metal sulfates. It is the presence of sulfur compounds in petroleum-based fuels that prevent the super-sensitive base metal catalysts (i.e., Cu, Ni, Co, etc.) from being used as the primary catalytic components for many environmental applications. Precious metals are inhibited by sulfur and lose some activity but usually reach a lower but steady state activity. Furthermore the precious metals are reversibly poisoned by sulfur compounds and can be regenerated simply by removing the poison from the gas stream. Heavy metals such as Pb, Hg, As, etc. alloy with precious metals and permanently deactivate them. Basic compounds such as NH3 can deactivate an acidic catalyst such as a zeolite by adsorbing and neutralizing the acid sites. 

Oxidation is extremely important both from a scientific and a practical point of view. Without oxidation life would not exist. In the chemical industry, too, oxidation is probably the most important process. A major example is the combustion of fossil fuels. This process is usually uncatalyzed, but sophisticated catalytic processes do exist. Examples in the inorganic industry are the oxidation of sulphur dioxide and ammonia in the manufacture of sulphuric acid and nitric acid, respectively. In the petrochemical industry many catalytic synthesis processes are carried out, for example the production of ethylene and propene epoxide, phthalic acid anhydride. An example which has recently also become important is the catalytic combustion of hydrocarbons in flue gases. Table 5.2 gives a list of examples of oxidation catalysis in industry [93]. 

C3H7OH, C2HCI3 and CCI4 in Flue Gases Using Silent Discharge Plasmas (SDPs), Enhanced by (V)UV at 172 nm and 253.7 nm,/. Adv. Oxid. Technol. 2 223-238. 

In the environmental sector ammonia is used in various processes for removing S02 from flue gases of fossil-fuel power plants. The resulting ammonium sulfate is sold as fertilizer. In the selective catalytic reduction process (SCR) the NOx in flue gases is reduced in a catalytic reaction of the nitrogen oxides with a stoichiometric amount of ammonia [1427] - [1430]. Also noncatalytic reduction is applied with ammonia or urea solutions. 

The rotational speed and angle at which it is positioned control the residence time of the solid in the kiln. Normally solid waste is converted into CO, particulate matter, or ash. For complete oxidation of flue gases and particulate matter, the kiln is also provided with a secondary combustion chamber. The volatilized combustibles exit the kiln and enter the secondary chamber where a complete oxidation tube is placed. 

Y. Naruse, T. Ogasawara, T. Hata, and H. Kishitaka, "Deactivation of Iron Oxide Catalysts During NOx Reduction with NH3 in Flue Gases", Ind. Eng.. Chem. Prod. Res. Dev.. 1980, 12, 62-65. 

The low-temperature selective catalytic reduction of NO over an active carbon-supported catalyst was studied in order to develop catalysts that are active at temperatures around 150 X as part of a low-temperature process for NO control in flue gases from coal-fired power plants. Reductants studied include acetone, isopropanol, isobutanol, ethyl ether, ethanol, propene, and methanol. Acetone is the most active reductant for the selective reduction of NO over the 5%Cu-2%Ag/C catalyst tested. At 150 C, 35% NO conversion was obtained in the presence of 4% O2 and 8% H2O at 3,000 h space velocity after 5 h on stream. There is some decrease in NO and hydrocarbon conversion with time on stream. It is believed that the oxidation of acetone minimizes the oxidation of carbon in the presence of O2 and promotes the selective reduction of NO. 

Environmental concerns and strict pollution legislation prompted action in the construction of up to date coal-fired boilers and adaptation of existing plants. At the present time, flue gas desulfurization is the only conventional method employed on a commercial scale for reducing sulfur emissions after coal combustion. Over 90% reduction of sulfur dioxide in flue gases can be achieved by this process. Combustion control techniques of the flames will effectively reduce oxides of nitrogen emissions into the atmosphere. 

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