the_temperature_window_of_the_ammonia_sncr_reaction_process_calculated_by_chemkin_W

1、题 目Thetemperature windowoftheammonia SNCRreactionprocesscalculatedbyCHEMKIN 课 程低污染燃烧理论与技术 姓 名李源 周明熙 常威 易思阳 宋亚超年 级研一 所在院系能源工程学系 2014-01-10The temperature window of the ammonia SNCR reaction process calculated by CHEMKIN1. IntroductionControlling nitrogen oxides (NOx) emissions is becoming a daunting

2、technical challenge as increasingly strict emission limits are being imposed. The stringent regulations have prompted the innovation and characterization of NOx control technologies suitable for various applications. This paper presents a solution in which CHEMKIN is introduced to calculate the temp

3、erature window of selective non- catalytic reduction (SNCR) technology. This includes initially how SNCR emerged as a technology along with a comparison with other relevant technologies. A review of various features related to selective non-catalytic gas phase injection of ammonia and ammonium salts

4、 (as reducing agent) is presented. The use of CHEMKIN solution as a reducing agent and its performance in laboratory and pilot scale tests as well as large- scale applications is also discussed. Use of cyanuric acid as a potential reducing agent is also presented. The underlying reaction mechanisms

5、have been reviewed for ammonia, urea and cyanuric acid for the explanation of various observations. Computational fluid dynamics (CFD) modeling as applied to SNCR is also presented. Subsequently the use of SNCR coupled with other in-combustion and post- combustion NOx control techniques is elaborate

6、d. Additionally, a two-stage NOx removal strategy to control un-reacted ammonia slip and to improve overall efficiency is discussed 1.2. The theme of our paperSNCR is a method to reduce nitrogen oxide emissions in conventional power plants that burn biomass, waste and coal. The process involves inje

7、cting either ammonia or urea into the firebox of the boiler at a location where the flue gas is between the temperature of 760 and 1,090 degrees to react with the nitrogen oxides formed in the combustion process. The resulting product of the chemical redox reaction is molecular nitrogen (N2) and wat

8、er (H2O).The goal of our group is tocalculate the temperature window using CHEMKIN, there are three significant factors that have great effect on the temperature window 2.Among the various kinds of formation of the NOx, there are 3 kinds of SNCR Processes. The most common is ammonia, which is involv

9、ed in the Thermal DeNOx process. Other compounds that can be used are cyanuric acid and urea. The former is used in the RAPRENOx process while the latter in the NOxOUT one.FOR the reaction requires a sufficient reaction time within a certain temperature range to be effective, typically 760 to 1,090.

10、 At lower temperatures, the NO and the ammonia do not react. Ammonia that has not reacted is called ammonia slip and is undesirable, as the ammonia can react with other combustion species, such as SO3, to form ammonium salts. While, at temperatures above 1093 ammonia decomposes, In that case, NO is

11、created instead of removed.All the simulations discussed in the following have been performed using the PFR Model of CHEMKIN. And this is the detailed kinetic model for NOxOUT process.3. The calculation of CHEMKIN for the temperature window3.1 Basic mechanisms of SNCRThe range of temperature in whic

12、h the reaction takes place causing a net reduction of NO is termed as the temperature window. This is a narrow interval because below 800 the reaction is too slow to give any reduction and most of the injected NH3 remains un-reacted. At higher temperatures (greater than 1200) NH3 tends to oxidize to

13、 form NO rather than to reduce it.The range over which any significant NOx removal rates can be achieved varies from one system to the other depending on the system parameters such as flue gas constituents, flue gas velocity gradients and system geometry which influences the mixing between the reage

14、nt and theflue gas. Table 1 also shows the temperature ranges and peak optimum temperatures reported in the literature for various systems 3.3.2 The effect of the NH3/NO ratioFirst, is about the effect of the ratio of NH3/NO. In this part, compositions of feed mixture used in the CHEMKIN.pro simulat

15、ions are listed as follows. We can see that there is only a change of NSR, which ranges from 0.75 to 1.5. Other parameters we have set are here. The Reactor length is 40 centimeter, the Reactor diameter is 3 millimeter, Residence time is 0.8 second, and the Pressure is 1atm. Then, by changing the te

16、mperature of the reactor, we can obtain the relationship between the temperature and the NO concentration in the outlet of the reactor.NO O2（%） H2O（%） NH3 N2（%） NSR 1 400ppmv 2 20 200ppmv 7794 0.5 2 400ppmv 2 20 400ppmv 7792 1 3 400ppmv 2 20 500ppmv 7791 1.25 4 400ppmv 2 20 600ppmv 7790 1.5 3-1 The

17、effect of the NH3/NO ratio on temperature windowWe defined the denigrations efficiency like this. is equal to the percentage dividing the difference of NO concentration between the inlet and the outlet by the NO concentration in the inlet. Reactor length: 40cm; Reactor diameter: 3mm; Pressure: 1atm;

18、 NH3/NO ratio: 1.00As is denitration in the chart, the maximum denitration efficiency increases with the increase ofthe NH3/NO ratio. The temperature range where the denitration efficiency is larger than 50% is defined as the temperature window in our simulation. A smaller NH3/NO ratio narrow the ra

19、nge of the temperature window. It shows that the optimum denitration temperature decreases with the increase of the NH3/NO ratio.3.3 The effect of the residence timeSecondly, we investigated the effect of the residence time. This time, we set the NH3/NO ratio as 1, and residence times were set as 0.

20、6, 0.8, and 1, respectively. We can see that, The increases of the residence time lead to a more broaden temperature window. It is noticeable that the upper limits are almost in the same level, while the lower limits decrease with longer residence time.NOO2（%）H2O（%）NH3N2（%） 400ppmv2 20 400ppmv 7792

21、time=0.6s time=0.8s time=1.0s1.00.6h8009001000Temperature110012003-2 The effect of the residence time on temperature windowAs is denitration in the chart, the maximum denitration efficiency change a little when the residence time increases. The temperature range where the

22、denitration efficiency is larger than 50% is defined as the temperature window in our simulation.3.4 The effect of the additive (NaOH)Finally, we conducted research about the effect of the additive. In this work, since HCOONa 、CH3COONa 、 NaNO3 、 Na2CO3 have similar influences in DeNOx process, it is

23、 reasonable to assume the sodium salts change into NaOH by reaction in a very short time. Therefore, NaOH is directly regarded as the additive in the simulations.NOO2（%）H2O（%）NH3N2（%）NO 400ppmv220400 ppmv 400ppmv 7792 NaOH=0ppmv NaOH=30ppmv NaOH=50ppmv1.00.6h80090010001100

24、1200Temperature3-3 The effect of the additive (NaOH) on temperature windowCompositions of feed mixture used in the CHEMKIN.pro simulations are listed in the table. Here, we simulated the DeNOX process under 3 kinds of situation the NaOH concentration was set as 0 ppmv, 30 ppmv and 50 ppmv, respectively. And other parameters are listed as above.Well, in this picture, with the additive in DeNOx process, the temperature window is broadened significantly. Because th