China
Africa
Explore chapters and articles related to this topic
Electric Power Production
Published in J. Lawrence, P.E. Vogt, Electricity Pricing, 2017
The major factors contributing to the creation of plant NOX emissions is the nitrogen content of the fuel and the characteristics of the combustion process, including the amount of excess air and the firing temperature, which are directly related to the boiler’s design and operating characteristics. A common technique for controlling nitrogen oxide emissions is a modification of the combustion process using low-NOX retrofit burners. Several power plants are utilizing a method known as selective catalytic reduction (SCR), which is a post-combustion treatment of the flue gases. With SCR, ammonia (NH3) is injected into the flue gas stream using honeycomb or plate-type catalytic beds thereby creating a reaction with the NOX gases that results in the release of free nitrogen (N2) and water (H2O) in vapor form. Both temperatures and ammonia injection amounts must be carefully controlled in the SCR reactor to ensure effective operation and avoidance of creating undesirable substances, such as ammonium sulfate ((NH4)2SO4) and ammonium bisulfate (NH4HSO4), particularly when burning high sulfur coal. Although possible, a combined process for removing NOX and SO2 together is both complex and more expensive at this time than the application of separate FGD and SCR methods.
Postcombustion NOx Control
Published in David A. Lewandowski, Design of Thermal Oxidation Systems for Volatile Organic Compounds, 2017
As discussed in previous chapters of this book, VOC compounds containing a halogen or sulfur atom can produce acid gases in a thermal oxidation system. Their potentially corrosive effect on refractory and metals has also been described earlier. They can also be problematic with SNCR systems. When sulfur is present, both ammonium sulfate (NH4)2SO4 and ammonium bisulfate (NH4HSO4) can form. Both salts are brownish gray to white in color and soluble in water. Ammonium bisulfate is a sticky substance that can form deposits on lower temperature sections of heat exchangers or waste heat boiler components. It causes rapid corrosion of metals as well as fouling and plugging. Ammonium sulfate is not corrosive, but its formation contributes to fouling and plugging and increased particulate emissions.
*
Published in James P. Lodge, Methods of Air Sampling and Analysis, 2017
As a deterrent to topochemical reactions of H2SO4 with collected particles, (PDA-Br)-impregnated filters were used to stabilize H2SO4(109). Pyrolysis then produced stoichiometric amounts of SO2. Total sulfate was determined by extracting the filter with PDA-Br solution, followed by pyrolysis. Ammonium sulfate (and presumably ammonium bisulfate) were acknowledged to interfere with the method. To determine H2SO4 in the presence of other particulate sulfates, including (NH2)2SO4, Dasgupta et al. (110) heated the sample stream to reduce relative humidity to ∼40% such that (NH4)2SO4 and other particulate sulfates were collected as solid particles and did not react with the (PDA-Br)-impregnated glass fiber filter, as did H2SO4. Treatment with barium acetate solution in methanol-acetone converted the remaining particulate sulfates to BaSO4. Excess PDA-Br was removed by frontal elution chromatography with methanol and the organic sulfate (PDA-Br + H2SO4) reacted with HNO3 to form a colored compound that was measured spectrophotometrically. No attempts were made to differentiate H2SO4 from NH4HSO4; also the method cannot be applied to high volume samplers without major engineering modifications in order to obtain the required 40% r.h.
Selective catalytic reduction of NOx by NH3 at low temperature over manganese oxide catalysts supported on titanate nanotubes
Published in Chemical Engineering Communications, 2018
R. Camposeco, S. Castillo, V. Rodríguez-González, Luz A. García-Serrano, Isidro Mejía-Centeno
It has been proposed (Peña et al., 2004; Lee et al., 2017; Zhang et al. 2017) that SO2, instead of NH3, is adsorbed preferentially on the active sites of the catalysts. SO2 adsorbed can be oxidized to SO3, which in presence of water it can form H2SO4 (Zhang et al., 2017). Sulfuric acid reacts further with ammonia to produce ammonium sulfate and ammonium bisulfate. The deposition of these salts on the surface of the support is the primary cause for the deactivation of the catalysts at low temperature (Zhang et al., 2017).