Experimental Study On The Effect Of Bio-oil On Urea DeNO_x Process

Nitrogen oxide is one of the main components of the atmospheric pollutants, which isextremely detrimental to the environment and people’s health. The coal-fired power plantsare the main source of NO_xemissions. To meet the more and more strict environmentalstandards, coal-fired power plants further depth denitration is an inevitable trend. However,while a single denitration technology has failed to meet the emissions requirements recently,the most feasible method is to integrate existing denitration technology. SelectiveNon-Catalytic Reduction (SNCR) system is simple, low cost, and can easily compatiblewith other denitrification technologies to achieve the purpose of deep denitrification.The circulating fluidized bed boiler has been widely used due to its own low emissioncharacteristics, but in order to fit the requirements of the new environmental standards,extra denitration technology is needed to be combined in the circulating fluidized bedboilerin order to achieve further denitrification. The cyclone is a natural SNCR reactionsites, but the temperature window of SNCR reaction is relatively narrow, the temperature incyclone is lower than the floor of temperature window for SNCR reaction, thus thedenitrification efficiency in cyclone is not ideal. So it has great significance to find the rightway to broaden SNCR reaction temperature window and improve denitrification efficiencyin low-temperature zone. Previous studies have shown that oxygenated organic compoundsand other additives can effectively broaden the temperature window and improve thedenitration efficiency in low-temperature section. In this context, considering the cost of theadditive and the use of renewable energy, we selected bio-oil and its main ingredient aceticacid as SNCR additives and investigated its effects on Urea-SNCR process.First, experimental research had been performed to analysis the main influencingfactors on urea SNCR reaction in a laboratory fixed bed reactor. The results showed thatthere was a significant temperature window for SNCR reaction,with a NormalizedStoichiometrc Ratio(NSR) between1.5to2.0. And with the increase of the oxygenconcentration, the denitration efficiency curves moved towards low temperature and hadnarrow temperature window and the maximum denitration efficiency slightly declined, in order to ensure that the SNCR reaction was completed, the residence time needed morethan1s.Then, the secondary pollutant emissions in urea SNCR process was simulated usingchemkin software, in order to make up for the lack of experiments. Through sensitivityanalysis, we identified the main reaction processes which had the most importantinfluence on the denitration efficiency and the secondary pollutant emissions, and analyzedthe role played by each elementary reaction, provided a way to suppress secondarypollutant emissions theoretically.Finally, we studied the effect of bio-oil and acetic acid on the Urea-SNCR process, andcompared with the sodium salt additives. The results showed that, adding a small amount ofacetic acid and bio-oil could broaden the temperature window, and could greatly improvethe efficiency of denitrification in the low temperature zone. The ability comparison ofbroaden the temperature window was: acetate> sodium salt> bio-oil, but the bio-oil couldimprove the maximum denitrification efficiency in a certain degree, while the acetic acidand the sodium salt made the maximum efficiency of the denitration decreased, whereinsodium salt decreased the maximum denitration efficiency maximum. So Urea-SNCRtechnology can be well used in circulating fluidized bed after adding a small amount ofBio-oil.