Research On Decoupling NOx Removal By Carbon Monoxide In Coordination With Air Preheating Technology

Nitrogen oxides(NOx)are important exhaust pollutants and are usually treated with ammonia-based Selective Catalytic Reduction(SCR)technology.Carbon monoxide(CO)is a good reducing agent.It can react with NOx to produce harmless N2 and H2O.It is safer,easier to prepare,and more secure than NH3.However,the reaction is more sensitive to oxygen concentration.Higher oxygen concentrations inhibit the reaction.Based on NOx Storage Reduction(NSR)technology in mobile source,NOx treatment is decomposed into two stages,NOx adsorption and NOx reduction.A rotary NOx removal and air preheating integrated reactor(INA)was designed.First,temperature simulation is performed on the rotary air preheater of the power plant.Based on the model,the heat transfer model of the INA reactor is obtained,and the heat storage process is explored.An air preheater and low temperature CO decoupling and denitration test bench were established.The catalyst was prepared on the test stand to test the NOx removal activity and explore the reaction process.Finally,CuO2/Fe2O3-CeO2 catalyst with better efficiency is used.Using Fourier in-situ infrared spectroscopy to complete the mechanism of the heat storage-reaction process of the entire INA reactor.Three zones are designed in this reactor:a flue gas zone,a reducing gas zone,and an air zone.On the aspect of heat transfer,catalysts in the reactor is heated by flue gas,and then reheated by the hotter reducing gas,and finally cooled down by air.On the aspect of reaction,NOx is adsorbed onto the catalysts in the flue gas zone where oxygen concentration is high and catalyst temperature is low.Then the adsorbed NOx on the catalysts is reduced by CO in the reducing gas zone where oxygen is free and catalyst temperature is higher.It's expected that NOx reduction efficiency could be enhanced by the separated setting of temperature and oxygen.The capital cost of the reactor will be also reduced by integrating two facilities,the deNOx reactor and air preheater.In this paper,heat transfer was investigated for the proposed INA reactor to study its performance of temperature evolution.A heat transfer model was first developed for an air preheater for verification.Energy balance equations were proposed for both gas and matrix phase.The influences of several factors on heat transfer performance were investigated:flow direction of reducing gas,inlet temperature of flue gas,rotating speed of the reactor,inlet temperature and flow rate of reducing gas,and different zone distributions.It was concluded that slower rotating speed was preferred to maintain big temperature different between different zones,which benefited the temperature dependant NOx adsorption-reduction process.For the reducing gas,downward flow direction,higher temperature and flow rates were preferred.The heat transfer performance is not very sensitive to zone distribution,which may be more important for the reaction process.Based on the theoretical research of the IN A reactor,we propose an air preheater and a low-temperature CO decoupling NOx removal experimental bench.It is used to achieve the processes of the INA reactor.We prepared three catalysts,CoO-CeO2/TiO2,MnO2-NiO,and Fe2O3-CoO/ASC.NOx removal performance and sulfur and water resistance were also tested.Experiments show that the MnO2-NiO catalyst has higher NOx removal efficiency in the low,middle and top sections.It could significantly improve the effect of NOx removal if we properly extending the time of the flue gas zone at high temperatures.At the same time,its resistance to SO2 and water is also excellent.The performance of CoO-CeO2/TiO2 is quite mediocre.However,the Fe2O3-CoO/ASC catalyst has a poor NO removal effect.When the reaction temperature is higher than 300?,the catalyst loss is serious.And it has almost no NO removal effect at higher temperatures.Therefore,it is not suitable as an active agent in the INA reactor.CuO2/Fe2O3-CeO2 catalyst has excellent performance for NOx adsorption-reduction performance.We use the heating furnace temperature control device to make the temperature change in the reactor consistent with the INA simulated temperature.The mechanism of NOx removal cycle is studied.Tests on catalyst sulfur and water resistance showed that 10%H2O in the flue gas would reduce NOx removal efficiency by no more than 10%.Adding 10%H2O and 200 ppm SO2 to the flue gas will reduce the NOx removal efficiency by no more than 20%.Reaction mechanism was then proposed base on in situ DRIFT study.NOx is stored in the adsorption zone as nitrate.In the reduction zone,NOx can be rapidly decomposed by high temperature and CO,so that the catalyst is deeply regenerated.Therefore,temperature rise,as well as the CO feeding,is critical for the catalyst regeneration process and is key to the excellent NOx removal performance of the INA reactor.This paper resolves the contradiction between atmosphere and temperature in carbon monoxide denitration.The INA reactor is proposed and designed.It realizes the efficient distribution of NOx adsorption and NOx reduction.At the same time,the waste heat of the flue gas is utilized.The heat transfer/reaction coupling synergy effect of the system is studied,which lays a theoretical foundation for the heat storage/NOx removal process.