| Selective catalytic reduction(SCR)with NH3 or urea as reducing agent is the most widely used denitration technology in thermal power plant.The method is mature,high efficiency,reliable operation and easy maintenance and operation.V2O5 catalysts react in the catalytic reduction of NOx and at the same time,also make part of SO2(0.5%-2.0%)in flue gas oxidated into SO3,which reacts with SCR denitration process incomplete reaction of ammonia in a certain condition to produce ammonium bisulfate(ABS),liquid ABS is sticky,easy to deposite on the surface of the catalyst and downstream equipment and piping device,adsorpting a large number of fly ash in flue gas,causing airpreheater resistance increases,reducing the efficiency of heat transfer elements,affecting the normal operation of the heat transfer of air preheater and the unit.Therefore,research on ABS volatilization characteristics and control method become particularly important.In this paper,utilize ABS volatilization test-bed designed by ourselves to research on the rules of volatilization and condensation after volatilization.It is concluded that with the temperature increasing,the evaporation rate increases,while the temperature reached 400?,the volatilization rate of emergence increased sharply;the volatilization rate elevated with the increase of contact area;the finer the particles,the higher the volatilization rate;with increasing doping amount of ABS in fly ash,volatilization rate decreased;using ion chromatography to analyze the condensation products,it is concluded that when the evaporation temperature is lower than 300?,products may be NH4HSO4 and a small amount of H2SO4 in condensing tube condensation,when higher than 350?,the condensation products may be H2SO4 and a small amount of ammonium sulfate(AS).Thermogravimetric analysis showed that the initial volatilization temperature of ABS is 206?,297-390? is rapid evaporation stage,achieving the fastest evaporation rate at 378?;the decomposition process of ABS: first the deamination reaction,then H2SO4 further decomposes into SO3 and H2O;thermogravimetric data of temperature and constant temperature kinetic analysis indicated that the volatilization of ABS is divided into three sections,which are all accord with anti-Jander volatilization kinetics model,that is three dimensional diffusion.Under the condition of high temperature corrosion rate of ABS and AS on carbon steel were decreasing with increasing temperature,changing little above 200?;the corrosion rate of carbon steel ABS faster than AS when the temperature is lower than 200?;the higher the concentration of ABS,the faster the corrosion rate;analysis by SEM/EDS and XRD,it determined that the corrosion products are iron oxides and(NH4)Fe(SO4)2;mechanism for high temperature corrosion: firstly,carbon steel occurs acid corrosion and oxygen corrosion,series of secondary reactions of Fe2+ generated form iron oxides and(NH4)Fe(SO4)2.According to the experimental results,in order to ensure the effect of ABS volatilization and avoiding the corrosion problem at the same time,the temperature of flue gas should be 350? when adopting the method of controlling the temperature of airpreheater to control ABS.DSI technology can achieve better SO3 removal efficiency,effective control of the ABS and lower operation cost.This study provide enterprises theoretical basis to control or reduce the negative influence of ABS in power plants?... |
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