Through the sintering pot test, the effects of coke breeze ratio, sinter mixture moisture, sinter mixture basicity and material bed depth on NOx emission were studied. The results show that reducing the ratio of coke breeze is beneficial to reducing NOx emission under the condition of certain sintering time and not affecting the quality of sinter. At the same time, adopting low moisture and deep bed sintering can also achieve the purpose of reducing NOx emission. The basicity of sinter mixture has little effect on NOx emission

Cao, L.

Li, J.

Wang, S. P.

English

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19METALURGIJA 62 (2023) 1, 19-21S. P. WANG, L. CAO, J.LIEXPERIMENTAL STUDY ON INFLUENCING FACTORS OF NOx EMISSION IN IRON ORE SINTERING PROCESSReceived – Primljeno: 2022-04-28Accepted – Prihvaćeno: 2022-07-04Original Scientific Paper – Izvorni znanstveni radThrough the sintering pot test, the effects of coke breeze ratio, sinter mixture moisture, sinter mixture basicity and material bed depth on NOx emission were studied. The results show that reducing the ratio of coke breeze is benefi-cial to reducing NOx emission under the condition of certain sintering time and not affecting the quality of sinter. At the same time, adopting low moisture and deep bed sintering can also achieve the purpose of reducing NOx emis-sion. The basicity of sinter mixture has little effect on NOx emission.Key words: iron ore sintering, NOx emission, coke breeze ratio, basicity, bed depthISSN 0543-5846METABK 62(1) 19-21 (2023)UDC – UDK 669.1.052-622.785:669.786-541.451:662.74:541.454 = 111INTRODUCTIONNOx is the main component of air pollutants, which can not only cause direct harm to human body, but also cause acid rain, ozone hole and photochemical smog pollution. Sintering is the main process of iron and steel production, and also the main source of NOx emissions in the iron and steel industry. The nitrogen oxide emis-sion of sintering process accounts for more than half of the total emission of iron and steel process [1]. The emission concentration of NOx from sintering in China is generally in the range of 200 – 310 mg/m3, up to 700 mg/m3 [2]. In the face of the increasingly serious NOx emission problem, China has formulated stricter emis-sion standards, the latest NOx emission standard is less than 50 mg/m3. Therefore, sintering NOx emission re-duction is imperative.At present, NOx control in sintering process mainly depends on terminal control, and its methods include selective non-catalytic reduction (SNCR), selective cat-alytic reduction (SCR) and activated carbon method, etc. [3-6]. The cost of terminal control is high and it is difficult to reach the standard stably, so it is urgent to upgrade the technology from terminal pollution control to the whole process pollution control.This project started with reducing the emission of NOx in the sintering process, studied the influence of different sintering process parameters on the generation of NOx in the sintering process, and carried out the pro-cess control of the sintering process, so as to achieve the purpose of reducing the emission of NOx from the source of sintering flue gas.S. P. Wang, L. Cao, Hebei Vocational University of industry and Tech-nology, Shijiazhuang, China.J. Li, Baosteel Central Research Institute, Wuhan, China.Corresponding author: L. Cao (cao_lei2008@126.com)EXPERIMENTsThe effects of coke breeze ratio, sintering mixture moisture, the basicity of sintering mixture and the depth of sintering bed on NOx content in sintering flue gas were studied through sintering pot test. From the begin-ning of ignition of the sintering pot, the process param-eters of the sintering pot and the emission data of the flue gas analyzer were recorded every 1 minute. And after the experiments, the data were compared and ana-lyzed. Chemical compositions of raw material used in the experiments are given in Table 1 and the industrial analysis of coke breeze is shown in Table 2.Table 2 Industrial analysis of coke breezeFCd Ad Vd St.d Mad84,40 13,11 1,88 0,74 0,61Table 1 Chemical composition of raw material / wt. %Ore TFe SiO2 Al2O3 CaO MgOSFLA 64,33 5,16 0,80 0,03 0,04Atlas Fines 64,61 4,29 1,74 0,07 0,03Canadian Fines 65,76 4,38 0,20 0,51 0,49SFCJ 66,14 1,46 1,09 0,03 0,04Yandi Fines 56,82 5,77 1,80 0,06 0,08Limestone 0 0,96 0,17 50,99 2,50Dolomite 0 1,16 0,14 31,55 20,42Quicklime 0 0,84 0,16 78,35 3,02RESULTS AND DISCUSSIONIn the experiments, the coke breeze ratio was in-creased from 3,6 % to 3,9 % to investigate the influence of different coke breeze ratio on NOx generation of sin-tering flue gas. Different coke breeze ratio, sintering time and average NOx content in sintering flue gas are 20  METALURGIJA 62 (2023) 1, 19-21S. P. WANG et al.: EXPERIMENTAL STUDY ON INFLUENCING FACTORS OF NOx EMISSION…shown in Table 3. Under the condition of different coke breeze ratio, the variation trend of NOx content in flue gas with sintering time is shown in Figure 1.It can be seen from Table 3 and figure 1 that when the coke breeze ratio is 3,7 %, the NOx content in sinter-ing flue gas is the highest, which is 214 mg/ m3. When the coke breeze ratio is 3,8 % and 3,9 %, the NOx con-tent in the flue gas is the same, both 190 mg/ m3. When the ratio of coke breeze is 3,6 %, the NOx content is the lowest, 180 mg/ m3. It can be concluded that there is no strong correlation between NOx content in flue gas and coke breeze ratio, which may be related to the permea-bility of sintering bed and sintering time at that time. When the permeability of sintering bed is good, the sin-tering speed is fast, and the combustion of coke breeze and oxygen is sufficient, the flue gas emission speed is fast, which is easy to cause the increase of NOx content in flue gas. It can also be seen from table 3 that when the coke breeze ratio is 3,7 %, the sintering speed is the fastest, the sintering time is 33,9 min, and the NOx con-tent in the flue gas is the highest. When the ratio of coke powder is 3,6 %, the sintering time is 38,5 min. Al-though the sintering time is shorter than that of 3,8 % and 3,9 %, the content of NOx in flue gas is slightly lower than that of 3,8 % and 3,9 % because of its low ratio and low N content in fuel.The content of NOx in sintering flue gas is affected by the ratio of coke breeze and sintering time. Under the same sintering time, the higher the ratio of coke breeze, the higher the content of NOx in sintering flue gas. Under the same coke breeze ratio, the shorter the sintering time, the higher the NOx content in the sintering flue gas.The average NOx content in sintering flue gas with different sintering mixture moisture is shown in Table 4. As can be seen from Table 4, when water content is 6,7 %, NOx content is relatively low, which is 157 mg/ m3. When the water content is 6,8 % and 6,9 %, the NOx content is similar, 188 mg/ m3 and 181 mg/ m3, respec-tively. When the water content is 7,1 %, the NOx content was the highest, which is 212 mg/ m3. It can also be seen from Figure 2 that with the increase of water content of sinter mixture, NOx content in the sintering flue gas tends to increase.The sinter basicity was adjusted by adjusting the ra-tio of quicklime, and the influence of different basicity on NOx content of sintering flue gas was studied. NOx content in sintering flue gas with different ratio of quicklime is shown in Table 5, and the variation trend of NOx content in flue gas with sintering time is shown in Figure 3.Table 3  Average NOx content with different coke breeze ratioCoke breeze ratio / % 3,6 3,7 3,8 3,9Sintering time / min 38,5 33,9 41,7 40,2Average NOx content , mg / m3 180 214 190 190 Figure 1 Effect of coke breeze ratio on NOx content in flue gasTable 4 Average NOx content with different water contentWater content of mixture / % 6,7 6,8 6,9 7,1Average NOx content , mg / m3 157 188 181 212 Sintering time / min 41,3 41,7 38,5 40,2Figure 2 Effect of water content on NOx content in flue gasTable 5 Average NOx content with different quicklime ratioQuicklime ratio / % 1,8 2,4 3,0 3,6Average NOx content, mg / m3 188 200 180 178 Figure 3 Effect of quicklime ratio on NOx content in flue gasAs can be seen from Table 5, when the quicklime ratio is 2,4 %, the NOx content in sintering flue gas is the highest, up to 200 mg/ m3. When the quicklime ratio is 1,8 %, the NOx content is slightly lower than that of quicklime ratio of 2,4 %, about 188 mg/ m3. When the ratio of quicklime is increased to 3,0 % and 3,6 %, NOx content decreases to 180 mg/ m3 and 178 mg/ m3, re-spectively, which are equivalent. It can also be seen from Figure 3 that increasing basicity within a certain range has a certain effect on reducing NOx content in sintering flue gas, but the effect is not very obvious.The effects of different sintering bed depth on NOx content in sintering flue gas were investigated. The depth of the test sintering bed was set as 700 mm and 550 mm respectively, and the NOx emission in the flue 21S. P. WANG et al.: EXPERIMENTAL STUDY ON INFLUENCING FACTORS OF NOx EMISSION…METALURGIJA 62 (2023) 1, 19-21gas was observed. The experimental results are shown in Table 6 and Figure 4.It can be seen from Table 6 that when the depth of sintering bed is 700 mm, the NOx content in the flue gas is 188 mg/ m3, and when the depth of sintering bed is 550 mm, the NOx content is 202 mg/ m3. The lower the depth of sintering bed is, the higher the NOx content in flue gas is. This is because the depth of sintering bed is low, the sintering speed is fast, the sintering time is short, and the NOx release rate in the flue gas is fast. It can be seen from Figure 4 that in the early stage of sin-tering, when the depth of sintering bed is 550 mm, the NOx content in the flue gas is significantly higher than that of 700 mm, while in the later stage of sintering, when the depth of sintering bed is 550 mm, the NOx content in the flue gas decreases rapidly. Therefore, in-creasing the depth of sintering bed can reduce the con-tent of NOx in sintering flue gas to a certain extent.CONCLUSIONSThe purpose of this study is to obtain the process parameters for reducing NOx emissions through the sin-Table 6  Average NOx content with different sintering bed depthBed depth / mm 700 550Average NOx content , mg / m3 188 202 Figure 4  Effect of sintering bed depth on NOx content  in flue gastering pot test, so as to achieve the purpose of reducing NOx emissions from the source.In the actual production process, when the sintering time is fixed, in order to reduce NOx emission in the sintering process, the “automatic heat accumulation” principle of deep bed sintering should be used to reduce the ratio of coke breeze, so as to reduce NOx emission. Low moisture sintering shall be carried out without af-fecting the quality of sinter. The basicity of sinter has little effect on NOx emission.AcknowledgmentsThis research was supported by the Doctor Founda-tion of Hebei Vocational University of industry and Technology [No. bz202204].REFERENCES[1]  D. Sh. Li. Analysis on NOx formation mechanism and emission reduction method of sintering flue gas. Metallur-gy and materials 39(2019)5, 24-25.[2]  Y. D. Su, X. W. Li, X. H. Fan. Research progress of NOx reduction technology in sintering process. Sintering and Pelletizing 38(2013)6, 41-44.[3]  S. F. Zhang, J. J. Li, S. Shu. Study on denitration perfor-mance of NH3-SCR over manganese modified magne- tite catalyst. Applied Chemical Industry 50(2021)11, 2913-2918.[4]  W. J. Dong. Progress and application of sintering flue gas denitration technology. China Resources Comprehensive Utilization 35(2017)11, 4-77.[5]  H. L. Zhang, Q. Shi, H. M. Long. Analysis of NO x remo-val process in sintering flue gas. Iron & Steel 52 (2017)5, 100-106.[6]  G. Yang, S. H. Zhang, Y. Sh. Yang. Current Status and Pro-spects of Emission Reduction Technology for Gaseous Pollutants in Sintering Flue Gas. Multipurpose Utilization of Mineral Resources (2021)1, 45-56.Note:  The responsible translator for English language is S. P. Wang, Shijiazhuang, China

Experimental study on influencing factors of NOx emission in iron ore sintering process

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