Flue denitrification

Particle size distribution relating to gas cleaning is well understood in the industry. This section deals with general rules of thumb. Certain important issues not included in this section are flue gas desulfurization, flue gas denitrification, hazardous waste gas cleaning, waste incineration gas cleaning, and removal of CO2 from flue gas. All these topics have special requirements, which must be considered separately in the design process. 

Bioprocesses for the removal of nitrogen oxides from polluted air are an interesting alternative [58], but current reaction rates are still too low for large-scale applications. Advanced biological processes for the removal of NO from flue gases are based on the catalytic activity of either eukaryotes or prokaryotes, e.g. nitrification, denitrification, the use of microalgae and a combined physicochemical and biological process (BioDeNO ). 

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. 

Technical Analyses of a Wet Process for Flue Gas Simultaneous Desulfurization and Denitrification... 

The technical and economic aspects of wet flue gas simultaneous desulfurization and denitrification systems are presented so that their practicality for utilization by utility industry can be assessed. The emphasis is on the kinetics of the systems based on the employment of ferrous chelates to promote the solubility of NO and the reactivity of NO with SO2 in scrubbing liquors. Analytical techniques are developed for characterizing reaction intermediates and products. Alternative approaches and novel ideas that could develop into a more efficient and cost-effective scrubber system employing metal chelate additives are discussed. 

One of the problems in studying the chemistry of wet processes for desulfurization and denitrification of flue gas in order to determine an optimum design and operating condition of scrubbers is the difficulty in quantitatively detecting all important species produced. Specifically, there was no methodology available for the convenient determination of the large number of N-S compounds that can be produced. 

Fig. 7.3. Analogies between adsorptive, membrane and reverse-flow reactors for flue gas denitrification and oxidative catalytic waste gas treatment.

The inherent ability of selective catalytic reduction (SCR) catalysts for stack gas denitrification to store ammonia adsorptively can be exploited with appropriate control algorithms to damp out the influence of fluctuations in the amount of gas and level of nitrogen oxides being treated. Moreover, it also forms the basis of the adsorptive reactor concept for the total denitrification of flue gases without ammonia... 

The suitability of regenerating the adsorbent by reactive means can only be judged on a case-by-case basis. With some adsorptive reactors - for example, for the total denitrification of flue gases or the unsteady-state Deacon process - the reactive regeneration is the object of the exercise. The prerequisite that the adsorbate does not undergo further reaction and is adsorbed in reasonable amounts at moderate temperatures means that the molecules being adsorbed tend to be small and stable, and thus do not lend themselves to reactive regeneration. 

The problem addressed in this chapter concerns the design of a process for NO removal from flue gases to levels below 10 ppm vol. The process will be based on the formation of the l e(II) EDTA-NO2 complex, followed by microbial denitrification. The process should be flexible enough to handle large variations in the fluegas load originating from a 10 MW gas-turbine, with the following characteristics (nominal values in bold) ... 

The selective catalytic reduction (SCR) is the only flue gas denitrification technique so fer that has proven to be very effective. It has been extensively studied, successfiilly commercialised and applied on a large scale [2], Carbon can be used as catalyst in the SCR unit at lower temperatures than those used with conventional SCR catalysts. 

Ion chromatography may also contribute analytically to the monitoring of the flue gas denitrification process. The most important parameter - the concentration ratio between nitrite and nitrate - can be established within five minutes as revealed in Fig. 8-26. 

Fig. 8-26. Analysis of nitrite in a scrubber solution from flue gas denitrification. - Separator column IonPac AS3 eluent 0.0028 mol/L NaHC03 + 0.0022 mol/L Na2C03 flow rate 2.3 mL/min detection suppressed conductivity injection 50 pL sample...

Identification of an efficient metal chelate for optimum absorption of NO requires knowledge of the thermodynamics and kinetics of the coordination of NO to various metal chelates. Knowledge is also needed of the kinetics and mechanisms of the reaction between nitrosyl metal chelates and absorbed SO2 in solution to calculate the regeneration rate of metal chelates and to control the products of reaction by adjusting the scrubber operating conditions. Not much of this information is available in the literature, although several ferrous and cobalt chelates have been used as additives for testing in bench-scale wet flue gas simultaneous desulfurization and denitrification scrubbers. 

Customer Flue gas source Gas flow rate, [NmV ] Inlet SO2 cone, /desulphurizatio n efficiency, [ppm]/[%[ Inlet NOx cone, /denitrification efficiency, [ppm]/[%]... 

Put the flue gas through a denitrification system, into which (pure) ammonia is pumped. The amount of ammonia pumped in is three times as much as would theoretically be needed to use all of the nitrogen dioxide in the flue gas. 

Flue gas purification (SCR) removal of NO ,- with NH3 Ti, W,V mixed oxides as honeycomb bulk catalysts Ti, W,V oxides on inert honeycomb supports hot denitrification (400 °C) cold denitrification (300 °C... 

The pollution control system configuration varies with the application and the process supplier. If the flue gas contains chlorine, a separate chlorine removal step may be required since chlorine inhibits the adsorption of SO2. Separate beds may also be provided for different pollutants. For example, when both SO2 and NO, are to be controlled, it is necessary to first reduce the SO2 concentration in the gas in a separate bed. This minimizes atiunonium sulfate formation which would increase ammonia consumption and prevent effective denitrification. Also, an initial separate bed is sometimes provided for the removal of heavy metals, organic compounds, and fine particulate and a final separate guard bed is sometimes provided as a buffer to remove any remaining trace pollutants. 

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