Influence of blast furnace top gas composition and dust on HCl removal with low temperature Ca-based dechlorination agent
来源期刊:中南大学学报(英文版)2018年第8期
论文作者:滕艾均 胡宾生 贵永亮 薛向欣
文章页码:1920 - 1927
Key words:blast furnace top gas; HCl gas; dechlorination; breakthrough time; penetration chlorine capacity
Abstract: Using fixed-bed reaction method and changing the gas composition and dust content, the influence of blast furnace top gas composition and dust on HCl removal with low temperature Ca-based antichlor was studied. It was found that, when the content of CO2 in blast furnace top gas increased, the dechlorination efficiency was getting worse obviously; when the contents of CO and N2 increased, the dechlorination efficiency was getting better to a certain extent; when the content of H2 changed, the dechlorination efficiency got no significant change; as the content of dust increased, the dechlorination efficiency got better obviously when the content was less than 15 g/m3, but it would be got worse quickly when the content was more than 20 g/m3, and the best content was 15–20 g/m3; the suitable site of the process of dechlorination was after gravity dust collector and before bag dust collector.
Cite this article as: TENG Ai-jun, HU Bin-sheng, GUI Yong-liang, XUE Xiang-xin. Influence of blast furnace top gas composition and dust on HCl removal using low temperature Ca-based dechlorination agent [J]. Journal of Central South University, 2018, 25(8): 1920–1927. DOI: https://doi.org/10.1007/s11771-018-3882-9.
J. Cent. South Univ. (2018) 25: 1920-1927
DOI: https://doi.org/10.1007/s11771-018-3882-9
TENG Ai-jun(滕艾均)1, 3, HU Bin-sheng(胡宾生)2, GUI Yong-liang(贵永亮)2, XUE Xiang-xin(薛向欣)1, 3
1. School of Metallurgy, Northeastern University, Shenyang 110819, China;
2. North China University of Science and Technology, Tangshan 063009, China;
3. Key Laboratory of Liaoning Province for Recycling Science of Metallurgical Resources,Shenyang 110819, China
Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract: Using fixed-bed reaction method and changing the gas composition and dust content, the influence of blast furnace top gas composition and dust on HCl removal with low temperature Ca-based antichlor was studied. It was found that, when the content of CO2 in blast furnace top gas increased, the dechlorination efficiency was getting worse obviously; when the contents of CO and N2 increased, the dechlorination efficiency was getting better to a certain extent; when the content of H2 changed, the dechlorination efficiency got no significant change; as the content of dust increased, the dechlorination efficiency got better obviously when the content was less than 15 g/m3, but it would be got worse quickly when the content was more than 20 g/m3, and the best content was 15–20 g/m3; the suitable site of the process of dechlorination was after gravity dust collector and before bag dust collector.
Key words: blast furnace top gas; HCl gas; dechlorination; breakthrough time; penetration chlorine capacity
Cite this article as: TENG Ai-jun, HU Bin-sheng, GUI Yong-liang, XUE Xiang-xin. Influence of blast furnace top gas composition and dust on HCl removal using low temperature Ca-based dechlorination agent [J]. Journal of Central South University, 2018, 25(8): 1920–1927. DOI: https://doi.org/10.1007/s11771-018-3882-9.
1 Introduction
Dry dust removal technology of blast furnace is widely applied to blast furnace dust removal system of each large steel and iron company, because of its high efficiency of dust collection and purification ability, high utilization rate of the gas sensible heat, less water consumption, etc [1]. But compared with wet dust removal technology, the dry dust removal technology is difficult to solve the problem of chlorine content in the gas, such as the salt corrosion of gas pipeline and TRT operation leaves, and the erosion of hot blast stove regenerator checker brick. All of these problems are caused by the chlorine in the gas and these problems are seriously harmful for the normal production of blast furnace. In addition to the improvement of national emphasis about environmental protection recent years and the quality problems of the low grade iron ores, chlorine brings significant impact on the whole production process and it is receiving more attentions gradually. So, it is necessary to remove the HCl gas before the blast furnace top gas into the gas pipeline.The removal of HCl gas in the gas has been carried out extensive researches in petrochemical industry and coal chemical industry, and the research and development of high temperature gas dechlorination agent are relatively wide and mature. Some typical researches are as follows. KRISHNAN [2] studied the performance of HCl desorption in the coal gas by the baking soda in 525–650 °C using fixed bed reaction device and the result showed that the saturated chlorine capacity can be up to 45%. NURA et al [3] studied the aspects of dynamics of CaO and HCl from the reaction kinetics theory and got activation energy of the gas–solid reaction and the reaction gas diffusion through the product layer respectively. In the air and energy engineering research laboratory of USA, JOZEWICZ et al [4] studied the reaction mechanism of HCl with Ca(OH)2 and CaO and the product structure (CaCl2·2H2O and CaClOH) by using DSC thermogravimetric analyzer and X-ray diffraction. WAN [5] studied the reaction mechanism of removing HCl gas by calcium oxide at 600–800 °C and found that the restriction factor is the gas diffusion in the product layer. It can be seen that these studies about HCl desorption under high temperature conditions only aim at the non-blast furnace gas. However, the gas temperature in the blast furnace gas pipeline is ranged from 100 °C (±20 °C) to 300 °C (±50 °C), and the temperature is 150–200 °C between the gravity dust collector and the gravity dust collector. Therefore, it is necessary for us to study the HCl desorption aiming at the blast furnace gas. Because the study of dechlorination for blast furnace gas is relatively few, this research simulates the blast furnace gas under the condition of laboratory, and learns the effects of gas composition and dust content for the low temperature dechlorination agent from the aspects of basic reaction kinetics.
2 Experimental
2.1 Materials
The dechlorination agent used in this present study was selected the H-L low temperature dechlorination agent from a company in Liaoning Province, China. The sample was chemically analyzed using inductively coupled plasma optical emission spectroscopy (ICP-OES), and the chemical composition of the sample is shown in Table 1. Because the reaction circumstance that we simulated was between the gravity dust collector and the bag dust collector, the dust we used in this experiment was a mixture of the gravity dust and bag dust (the mass ratio of gravity dust to bag dust was 1:1). And the chemical compositions of the mixed dust, gravity dust, and bag dust are listed in Table 2. All the gas such as CO, CO2, N2, H2, HCl were of analytical grade.
2.2 Apparatus and procedure
The main devices of this experiment are three parts including gas supply device, reaction device and gas detection device and the schematic diagram is shown in Figure 1. The gas supplying device consists of CO, CO2, N2, H2 and HCl five kinds of gas supply bottles, powder spraying equipment, mixing bottle and gas heater; the reaction device is a cylindrical fixed bed reactor of which the length is 150 cm and the inner diameter is 20 cm; in the fixed bed the temperature remains constant and the dechlorination agent takes reaction with the HCl gas; the gas detection device is used to detect the concentration of HCl gas real-time monitoring at the export of the fixed bed.
According to the average level of the basic components of the gas in the blast furnace gas-pipeline, the reference gas ratio of this experiment was: CO: CO2: N2: H2=20: 20: 59: 1, and the variation range of each gas was as follows: the content of CO was 18%–24%, the content of CO2 was 16%–22%, the content of N2 was 56%–63%, and the content of H2 was 0.5%–2.5%. According to the fluctuation range of dust content between gravitate dust filter and bag dust filter in blast furnace iron making system, the dust content was kept at 10 g/m3 when studying the effect of gas content variety, and the dust content was kept at 0–55 g/m3 when studying the effect of dust content variety. While, the size of dust used in this study was screened to 44–178 μm. According to the fluctuation range of the gas temperature in the blast furnace gas-pipeline, the test temperature was controlled at 150 °C (±1 °C). The initial concentration of HCl gas in the gas was controlled at 100×10–6 (±0.5×10–6) and the gas flow rate was 5 L/min. The dechlorination agent was screened to 3–5 mm, and a certain amount of dechlorination agent was put into the fixed bed reactor. The dechlorination agent was set as a cylindrical in which the high-diameter ratio is 1:1 (the diameter is 20 cm).
Table 1 Chemical composition of H-L low temperature dechlorination agent (wt%)
Table 2 Results of analysis of BF dust composition (wt%)
Figure 1 Schematic diagram of HCl removal from blast furnace top gas test equipment:
This study used the breakthrough time and the penetration chlorine capacity to evaluate the effect of the dechlorination agent. When the content of HCl gas was greater than 1×10–6 in the gas detection device at the export, it can be seen that the dechlorination agent has been penetrated. The time from the beginning to eject HCl gas to the dechlorination agent penetrated was defined as the breakthrough time, and the chlorine mass percentage of the dechlorination at this time was called the penetration chlorine capacity. The chlorine capacity was analyzed by X-ray fluorescence spectrometer (XRF); the major phases of the dechlorination agent samples were identified by X-ray diffraction (XRD); the surface morphology of the dechlorination agent samples was examined by scanning electron microscopy (SEM).
3 Results and discussion
3.1 Effect of CO2 and CO content
The effects of CO2 content on the breakthrough time and the penetration chlorine capacity of the dechlorination agent are shown in Figure 2. As the CO2 content increased gradually, the breakthrough time and the penetration chlorine capacity of dechlorination agent got reduced. When the concentration of CO2 increased from 16% to 22%, the breakthrough time decreased from 398 min to 345 min, reduced by about 13.32%; meanwhile, the penetration chlorine capacity decreased from 18.33% to 16.16%, reduced by about 11.84%. As shown in Figure 3, with the CO content increased gradually, the breakthrough time and the penetration chlorine capacity of dechlorination agent got increased. When the concentration of CO increased from 18% to 24%, the breakthrough time increased from 345 min to 398 min, increased by about 15.36%; meanwhile, the penetration chlorine capacity increased from 16.16% to 18.33%, increased by about 13.43%.
Figure 2 Effects of CO2 content on dechlorination efficiency of antichlor
Due to the fact that the dechlorination agent used in this test is Ca-based antichlor which contains CaCO3, the main chemical reactions might happen in the reaction process as follows:
Figure 3 Effects of CO content on dechlorination efficiency of antichlor
CaCO3(s)+2HCl(g)=CaCl2(s)+H2O(g)+CO2(g)
CaO(s)+2HCl(g)=CaCl2(s)+H2O(g)
CaCO3(s)=CaO(s)+CO2(g)
The above three chemical reactions are reversible under certain conditions. So from the point of chemical reaction equilibrium, when the concentration of CO2 increased, the forward reaction would be restrained and it could reduce the rate of reaction, made the breakthrough time and the penetration chlorine capacity decrease accordingly. Figure 4 shows the XRD patterns at different CO2 contents. The results show that the CO2 content can be proved to have a negative effect on the dechlorination agent. The specific performance is that the peak intensity of CaClOH at 16% CO2 content is higher than that at 22% CO2 content, while the peak intensities of CaCO3 and CaOH are relatively low.
Because under the normal condition of blast furnace system, the content of CO+CO2 in the blast furnace top gas keeps a fixed value, when the content of CO increases, the CO2 would be reduced accordingly, the time of reaction also would be increased, and the penetration chlorine capacity would be increased accordingly. From the comparison of Figure 2 and Figure 3, it can also be informed that the effects of CO and CO2 on the dechlorination reaction are just opposite.
Figure 4 XRD analysis of antichlor when changing CO2 content
3.2 Effect of N2 content
The effects of N2 content on the breakthrough time and the penetration chlorine capacity of the dechlorination agent are shown in Figure 5. As the N2 content increased gradually, the breakthrough time and the penetration chlorine capacity of dechlorination agent got increased gradually. When the concentration of N2 increased from 53% to 62%, the breakthrough time increased from 343 min to 372 min and it gained about 8.45% increment; meanwhile, the penetration chlorine capacity increased from 15.95% to 17.42%, increased by about 9.22%.
Figure 5 Effects of N2 content on dechlorination efficiency of antichlor
The reason why the increase of N2 can enhance the efficiency of dechlorination is that: when the concentration of N2 increased, the CO2 content would be decreased and it could improve the rate of reaction, and the breakthrough time and the penetration chlorine capacity increased accordingly. Figure 6 shows the XRD patterns at different N2 contents. The results show that the N2 content can be proved to have a positive effect on the dechlorination agent. The specific performance is that the peak intensity of CaClOH at 62% N2 content is higher than that at 53% N2 content, and the peak intensities of CaCO3 and CaOH are relatively low.
Figure 6 XRD analysis of antichlor when changing N2 content
From Figure 4 and Figure 6, it indicates that CaClOH peaks appeared, which can be attributed to the fact that the CaCO3 was converted to CaCl2, then the CaCl2 absorbed H2O and transformed into CaClOH. The crystal transformation relationship of CaCO3, CaCl2 and CaClOH is shown in Figure 7. The crystalline structure of CaCO3 (Figure 7(a)), with space group Pmcn(62), unit cell parameters of a=4.9614 , b= 7.9671 , c=5.7404 , α=β=90° and γ=120°, has the crystal structure of aragonite, strontianite, and witherite. In the initial reaction process, C—O bonds of CaCO3 were broken by HCl, forming the orthorhombic structure of CaCl2. The crystalline structure of CaCl2 (Figure 7(b)), has space group Pbcn(60), unit cell parameters of a=6.268 , b= 7.619 , c=6.923 , α=β=γ=90°. With the development of reaction, the formed CaCl2 got with H2O, the Ca—Cl bonds of CaCl2 was broken by H2O, forming the hexagonal structure of CaClOH. The crystalline structure of CaClOH (Figure 7(c)), has space group P63mc(186), unit cell parameters of a=3.8641 , c=9.9044 , α=β=90°, γ=120°.
3.3 Effect of H2 content
As shown in Figure 8, it can be seen that when the H2 content increased, the breakthrough time and the penetration chlorine capacity of the dechlorination agent kept stable basically. There are two reasons for this phenomenon: one is that the proportion of H2 content in blast furnace top gas is very low and the variety of H2 content has a little effect of dechlorination in the process; the other is that H2 and dechlorination agent can not take any chemical reaction and the variety of H2 content only has a slight influence on the fixed value of CO+CO2. So when changing the content of H2 gas, both the breakthrough time and the penetration chlorine capacity had no obvious change, only fluctuated around a fixed value, which is shown as the breakthrough time remaining for about 360 min and the penetration chlorine capacity remaining at about 16.81%.
3.4 Effect of dust content
The effect of dust content is shown in Figure 9. it can be seen that: when the dust content increased from 0 to 15 g/m3, the breakthrough time gained about 20.97% increment and the penetration chlorine capacity gained as much as 68.26% increment; when the dust content arrived about 20 g/m3, the breakthrough time and the penetration chlorine capacity of the dechlorination agent reached the top; when the dust content increased from 20 g/m3 to 55 g/m3, the breakthrough time reduced about 12.20% and the penetration chlorine capacity decreased as much as 16.97%.
The SEM images of the surface of the dechlorination agent are shown in Figure 10. Figures 10(a) and (b) show the surface characteristics of the dechlorination agent before reaction, indicating that there are a lot of cracks and wrinkles on the surface, which can not only make the gas enter in easily but also enlarge the reaction area. These are two positive factors for the reaction. Figure 10(c) shows the surface features of the dechlorination agent in the reaction at the initial stage of adding dust, showing that many tiny particles are adsorbed on the surface. Figure 10(d) shows the surface features of the dechlorination agent after adding lots of dust. It can be seen clearly that lots of dust are adsorbed on the surface round and round.
Figure 7 Transformation relationship of CaCO3, CaCl2 and CaClOH in reaction process
Figure 8 Effects of H2 content on dechlorination efficiency of antichlor
Figure 9 Effects of dust content on dechlorination efficiency of antichlor
The dust used in this test is the mixture of the gravity dust and the bag dust. From Table 2, it can be known that a certain amount of alkaline substances was produced in the process, and the chemical reaction may be as follows:
Fe+2HCl=FeCl2+H2
2FeO+6HCl=2FeCl3+2H2O+H2
CaO+2HCl=CaCl2+H2O
Al2O3+6HCl=2AlCl3+3H2O
Na2O+2HCl=2NaCl+H2O
MgO+2HCl=MgCl2+H2O
K2O+2HCl=2KCl+H2O
ZnO+2HCl=ZnCl2+H2O
From the above reactions, it can be seen that the dust can consume part of HCl to a certain extent, and the water produced by the reaction can also absorb some HCl, so it causes the chlorine capacity increasing significantly at the initial stage of adding dust. According to JAMES [6] on the catalytic properties of the materials and some researches on the catalytic properties of tiny particles [7–16], some tiny particles can react with HCl in the dust adsorbed on the surface of the dechlorination agent as shown in Figure 10(c). And numerous small levels rapid reaction fields are formed, which promoted the absorption of HCl. So the breakthrough time and the penetration chlorine capacity increased quickly at the initial stage of adding dust. Figure 10(d) shows that lots of tiny particles adsorbed on the surface and filled in the cracks and wrinkles at the later stage of adding dust. Figure 11 shows the gas pipe-path formed on the bed of the dechlorination agent. When the gas contains a lot of dust, parts of large particles dust is easy to settle and block the interlayer pores of the dechlorination agent, and part of tiny particles dust adsorbed on the large particles and dechlorination agent surface tightly. This leads to a phenomenon that some gas pipe-paths form on the bed of the dechlorination agent. These gas pipe-paths can decrease the breakthrough time, and then reduce the whole absorption of the dechlorination agent. This causes the breakthrough time and the penetration chlorine capacity reduced gradually when the dust content was more than 20 g/m3. To sum up, the best dust content of dechlorination is between 15 g/m3 and 20 g/m3, the suitable site of the process of dechlorination is after gravity dust collector and before bag dust collector.
Figure 10 SEM images of antichlor’s surface:
Figure 11 Gas pipe-path formed on bed of dechlorination agent
4 Conclusions
1) As the CO2 content increased, the breakthrough time and the penetration chlorine capacity of the dechlorination agent reduced obviously and the effect of dechlorination became worse.
2) When the CO and N2 content increased, the breakthrough time and the penetration chlorine capacity of the dechlorination agent increased obviously and the effect of dechlorination became better.
3) With the H2 content increased, the breakthrough time and the penetration chlorine capacity of the dechlorination agent had no obvious effect.
4) When the dust content was less than 15 g/m3, the effect of dechlorination became better quickly; when the dust content was more than 20 g/m3, the effect of dechlorination got worse obviously; the best dust content for dechlorination was between 15 g/m3 and 20 g/m3.
References
[1] PAN Bo, ZHANG Chun-xia, XU Hai-chuan. Application and energy-saving analysis of dry dust removal technology in large blast furnace [J]. Energy for Metallurgical Industry, 2009, 28(1): 11–17.
[2] KRISHNAN G N. High temperature coal gas clean up for molten carbonate fuel cell applications [R]. USA.: Morgantown Energy Technology Center, 1991: 133.
[3] NURA G, LALLAI A. On the kinetics of dry reaction between calcium oxide and gas hydrochloric acid [J]. Chem Eng Sci, 1992, 47(9–11): 2407–2411.
[4] JOZEWICZ W, GULLETT B K. Reaction mechanisms of dry Ca-based sorbents with gaseous HCl [J]. Industrial and Engineering Chemistry Research, 1995, 34(2): 607–612.
[5] WAN Dan. The research of calcium oxide to remove hydrogen chloride at high temperatures [D]. Wuhan: Huazhong University of Science and Technology, 2013. (in Chinese)
[6] JAMES G. Speight. Lange’s handbook of chemistey [M]. New York: McGraw-Hill Book Co., 1976.
[7] ZHU Jun-jiang, XIAO Ping, LI Hai-long, CARABINEIRO S A C. Graphitic carbon nitride: Synthesis, properties and applications in catalysis [J]. ACS Applied Materials & Interfaces, 2014, 6(19): 16449–16465.
[8] XING Wei-dong. Reforming catalyst regeneration system about technical improvements of dechlorination [J]. Petroleum Refinery Engineering, 2013, 43(12): 34–37.
[9] LIU Wu-can, ZHANG Jin-ke, SHI Neng-fu, XU Wei-guo. Research progress of hydrogenation dechlorination technology and catalyst [J]. Zhejiang Chemical Industry, 2012, 43(1): 1–6. (in Chinese)
[10] VANDER WAL R L, BERGER G M, TICICH T M. Carbon nanotube synthesis in a flame using laser ablation for in situ catalyst generation [J]. Applied Physics A-Materials Science and Processing, 2003, 77(7): 885–889.
[11] CHANG Zheng, GUO Can-xiong, DUAN Xue, ZHANG Mi-lin. Preparation and characterization of ultrafine magnetic solid acid catalyst SO42––ZrO2/Fe3O4 [J]. Chinese Journal of Catalysis, 2003, 24(1): 47–51. (in Chinese)
[12] YE Qing, ZHAO Jian-sheng, LI Dong-hui, CHENG Shui-yuan, KANG Tian-fang. Au/SnO2 and M-Au (M=Pt, Pd)/SnO2 bimetallic catalysts for the low-temperature catalytic oxidation of CO [J]. Acta Physico-Chimica Sinica, 2011, 27(1): 169–176. (in Chinese)
[13] KONG Fan-hai, QIU Jian-rong, LIU Hao, AI Zhi-hui. Catalytic oxidation of gas-phase elemental mercury by nano-Fe2O3 [J]. Journal of Environmental Sciences, 2011, 23(4): 699–704.
[14] CARLOS E, MIQUEL S. From solid-vacuum to solid-gas and solid-liquid interfaces: In situ studies of structure and dynamics under relevant conditions [J]. Surface Science, 2013, 607(1): 2–9.
[15] HU Bin-sheng, TENG Ai-jun, GUI Yong-liang, HAN Xiao-guang, QIN Rong-huan. Research on blast furnace refractory erosion mechanism caused by HCl in gas [J]. Journal of Materials and Metallurgy, 2014, 13(1): 20–23. (in Chinese)
[16] ZHU Jian-fei, XIAO Qi. Meso-macroporous Fe-doped CuO: Synthesis, characterization, and structurally enhanced adsorption and visible-light photocatalytic activity [J]. Journal of Central South University, 2015, 22(11): 4105– 4111.
(Edited by YANG Hua)
中文导读
高炉炉顶煤气中气体成分和炉尘对常温钙基氯剂脱除HCl的影响
摘要:通过研究高炉炉顶煤气的气体成分和炉尘对低温钙基脱氯剂脱除HCl的影响发现:在高炉炉顶煤气中,随着CO2含量的增加,脱氯效果明显变差;随着CO含量和N2含量的增加,脱氯环境明显改善;H2含量的变化对脱氯效果的影响不大;当炉尘含量处在较低范围时(<15 g/m3),炉尘含量的增加使脱氯效果得到大幅度改善;而当炉尘含量超过一定量(>20 g/m3)后再提高炉尘的含量时,脱氯效果则明显恶化,在含尘量为15~20 g/m3时脱氯效果最佳,脱氯剂的最佳工作位置为重力除尘器之后与布袋除尘器之前。
关键词:高炉炉顶煤气;HCl;脱氯;穿透时间;穿透氯容量
Foundation item: Project(51274080) supported by the National Natural Science Foundation of China; Project(E2013209051) supported by the Hebei Science Foundation and the Steel and Iron Joint Research Foundation Project, China; Project(U1502273) supported by the Joint Funds of the Natural Science Foundation of China and Yunnan Provincial Government; Projects(N150202001, N150203003) supported by the Fundamental Research Funds for the Central Universities, China
Received date: 2017-04-20; Accepted date: 2018-03-11
Corresponding author: TENG Ai-jun, PhD; E-mail: wdtaj2008@163.com; ORCID: 0000-0002-1472-0661