-
我国资源禀赋决定了煤炭在一次能源供给中的主导地位。燃煤排放的二氧化硫 (SO2) 和氮氧化物 (NOx) 等烟气污染物导致环境问题频发[1–3]。目前,国内燃煤电站已全面实施大气污染物超低排放,工业烟气治理重点已转向非电行业。我国中小型锅炉消耗了全国约25%的煤,却排放了高达燃煤总排放量60%的大气污染物[4]。因此,治理中小型燃煤锅炉和工业炉窑烟气污染物迫在眉睫。
常见烟气脱硫技术有石灰石-石膏法[5-6]、钠碱法[7]、氨法[8]、镁法[9-10]、有机胺法[11-12]、海水法[13]等,但这些方法在脱除大气污染物的同时,也带来了液、固的二次污染[14]。典型地,运用最为广泛的湿法石灰石–石膏法脱硫工艺年产含水石膏约9.5×107 t,石膏堆存占地20000 km2,废弃硫资源量1.3~1.66×107 t,而同期我国硫磺进口量却高达1.078×107 t,形成了硫资源废弃与进口的巨大反差;其烟气处理后排放的脱硫废水所含溶解盐对环境亦造成影响。中国工程院将“工业废水脱盐与水回用关键技术”列为2035环境工程科技关键、共性与颠覆性技术指数前十项之一[15]。因此,通过高效脱除技术并耦合区域产业链,将污染物转化为资源加以利用,同步实现生态与经济效益是环境治理追求的目标。
我国磷矿资源储量丰富,位居世界第二,开采量位居世界第一,主要集中在中西部地区。2019年,全国磷矿石产量高达9.33×107 t,其中约85%的磷矿用于湿法磷酸生产[16-17]。如果将磷化工生产的原料磷矿石用作SO2吸收剂,既能将锅炉烟气中污染物SO2脱除,又能将SO2转化为硫酸分解磷矿石。该过程不仅节约了磷矿浮选过程中需要添加的硫酸用量,产生一定的经济效益,而且脱硫后的废弃矿浆直接输送至磷矿浮选阶段用于湿法磷酸生产,无废水和固体废弃物产生,亦是一条绿色、经济、低成本的脱硫技术[18-19]。磷矿石对SO2的吸收容量 (以每克磷矿粉吸收的SO2质量计) 为3.8×10–2 g·g−1,是同体积水吸收容量的264倍、NaOH饱和溶液的42倍[20]。利用磷矿浆脱除湿法磷酸中过量的SO3,可有效降低硫酸消耗 [21]。武春锦等[22]通过中试研究发现液相F–含量随温度、pH上升而下降;F– 仅在液相中,不会逸出到气相;液相中Mg2+含量随温度的升高而增大,但随浆液pH升高而下降。通过正交实验得出,影响脱硫率的因素排序为:循环量>气量>磷矿浆pH;磷矿浆脱硫最佳工艺条件为气量3.5×103 m3·h−1 (气速 1.94 m·s−1) ,循环量为33 m3·h−1,矿浆pH为6.5。吕武华[23]以动力波设备为反应器,研究了矿浆pH、气量、矿浆循环量等因素对脱硫率的影响;当动力波入口的SO2质量浓度为2.8×103 mg·m−3时,仅用单层喷头,脱硫率即可达到78%以上。此外,吴琼[24]研究了磷矿浆脱硫除镁的影响因素,通过正交实验得出镁溶出率的最佳工艺条件为:SO2质量浓度为1×103 mg·m−3、浆液质量分数为30%、温度为50 ℃、pH等于7。
目前,一些企业已开展了磷矿浆脱硫的应用,瓮福化工公司通过高镁磷精矿处理硫酸尾气,但由于磷矿浆脱硫反应机制不清楚及反应器选型等问题,脱硫效率仅为70%~80%,效果不甚理想[25-26]。在本团队前期研究工作中已探明了磷矿浆高效脱硫的反应原理[18]、矿浆中丰富的金属离子催化促进脱硫机制[27]、含磷复合矿浆同时脱硫脱硝过程中硫氮相互作用促进SO2和NOx脱除机制[28],并与中化云龙有限公司合作建成的75 t·h−1燃煤锅炉烟气脱硫装置,其脱硫率高达100%,回收的SO2作为下一工段的原料使用,并产生一定的经济效益 [18, 23]。然而,磷矿浆脱硫过程中各组分变化情况及脱硫率下降原因尚不清楚。基于此,本研究对磷矿浆脱硫过程开展分析,探究磷矿中的关键组分碳酸镁钙和氟磷酸钙对脱硫的影响,旨在揭示脱硫过程中脱硫活性组分及脱硫率下降的原因,以期为磷矿浆技术的发展和应用提供参考。
磷矿关键组分对湿法烟气脱硫技术的影响
The effect of primary components of phosphate rock on wet flue gas desulfurization
-
摘要: 磷矿浆湿法烟气脱硫技术将污染物SO2吸收转化为硫酸原位分解磷矿,失活后的磷矿浆用于生产磷酸,节约了湿法磷酸生产中硫酸用量,无废水废液排放,是一种绿色、经济的技术。通过对磷矿浆及其主要组分开展脱硫实验,确立了磷矿中脱硫的关键活性组分及其对脱硫效果的影响。XRD、IC等实验及表征结果表明,SO2吸收后转化形成的硫酸会优先与磷矿中的活性组分碳酸镁钙反应,待其消耗殆尽再与氟磷酸钙反应。与氟磷酸钙相比,碳酸镁钙呈现出优越的脱硫活性。氟磷酸钙分解过程中产生的H+和PO43–会抑制S(Ⅳ)转化为S(Ⅵ)的速率,导致脱硫率下降。PO43–抑制SO2脱除与温度、pH均有关,当温度高于55 ℃、且pH为4.75~2.61时,其抑制作用最明显。本研究可为磷矿浆湿法烟气脱硫技术的优化提供参考。Abstract: Wet flue gas desulfurization with phosphate rock slurry is a green and economic technology. The pollutant SO2 is absorbed and converted into sulfuric acid to decompose phosphate rock in situ, and then the inactivated phosphate rock slurry is directly transported to the flotation section for producing phosphoric acid, which effectively saves the amount of sulfuric acid. In addition, there is no waste water and liquid waste discharged in the whole process. Herein, the key active components for desulfurization in phosphate rock and their influence on desulfurization effect were established, through the desulfurization experiment with phosphate rock and its main components.The XRD, IC and other experiments and characterization results indicated that CaMg(CO3)2 preferentially reacted with sulfuric acid formed by SO2 conversion. When CaMg(CO3)2 was exhausted, Ca5(PO4)3F began to react with sulfuric acid. Significantly, compared with Ca5(PO4)3F, the CaMg(CO3)2 showed superior desulfurization activity. The H+ and PO43–, produced from the decomposition of Ca5(PO4)3F, would inhibit the conversion of S(Ⅳ) towards S(Ⅵ), which was the key reason for the decrease of desulfurization efficiency. The inhibition effect of PO43– on SO2 removal was related to temperature and pH value. It was most significant when the temperature was higher than 55 ℃ and the pH value was between 4.75 and 2.61. Our research can provide a reference for the optimization of wet flue gas desulfurization technology for phosphate slurry.
-
-
[1] 汤常金, 孙敬方, 董林. 超低温(< 150 ℃)SCR脱硝技术研究进展[J]. 化工学报, 2020, 71(11): 4873-4884. [2] NIE Y X, DAI J F, HOU Y D, et al. An efficient and environmentally friendly process for the reduction of SO2 by using waste phosphate mine tailings as adsorbent[J]. Journal of Hazardous Materials, 2020, 388: 121748. doi: 10.1016/j.jhazmat.2019.121748 [3] LI S, YANG J Q, WANG C, et al. Removal of NOx from flue gas using yellow phosphorus and phosphate slurry as adsorbent[J]. Energy Fuels, 2018, 32: 5279-5288. doi: 10.1021/acs.energyfuels.7b03964 [4] 田恬, 程茜, 赵雪, 等. 2019年脱硫脱硝行业发展评述及展望[J]. 中国环保产业, 2020, 26(2): 23-25. doi: 10.3969/j.issn.1006-5377.2020.02.007 [5] LANCIA A, MUSMARRA D, PRISCIANDARO M, et al. Catalytic oxidation of calcium bisulfite in the wet limestone–gypsum flue gas desulfurization process[J]. Chemical Engineering Science, 1999, 54(15): 3019-3026. [6] LANCIA A, MUSMARRA D. Calcium bisulfite oxidation rate in the wet limestone gypsum flue gas desulfurization process[J]. Environmental Science and Technology, 1999, 33(11): 1931-1935. doi: 10.1021/es9805425 [7] 刘敦禹, TERRY W, ROHAN S. 富氧燃烧烟气冷凝塔钠碱法脱硫过程SO2和CO2共吸收建模与实验研究[J]. 化工学报, 2018, 69(9): 4019-4029. [8] GAO X, DING H L, DU Z, et al. Gas–liquid absorption reaction between (NH4)2SO3 solution and SO2 for ammonia–based wet flue gas desulfurization[J]. Applied Energy, 2010, 87: 2647-2651. doi: 10.1016/j.apenergy.2010.03.023 [9] VALLE R, NIUBO M, FORMOSA J, et al. Synergistic effect of the parameters affecting wet flue gas desulfurization using magnesium oxides by–products[J]. Chemical Engineering Journal, 2015, 262: 268-277. doi: 10.1016/j.cej.2014.09.085 [10] YAN L Y, LU X F, WANG Q H, et al. Recovery of SO2 and MgO from by–products of MgO wet flue gas desulfurization[J]. Environmental Engineering Science, 2014, 31(11): 621-630. doi: 10.1089/ees.2014.0004 [11] HONG Y H, KIM H, KIM Y J, et al. Nitrile–functionalized tertiary amines as highly efficient and reversible SO2 absorbents[J]. Journal of Hazardous Materials, 2014, 264: 136-143. doi: 10.1016/j.jhazmat.2013.11.026 [12] TAILOR R, ABBOUD M, SAVARJ A. Supported polytertiary amines: highly efficient and selective SO2 adsorbents[J]. Environmental Science & Technology, 2014, 48: 2025-2034. [13] DARAKE S, HATAMIPOUR M S, RAHIMI A, et al. SO2 removal by seawater in a spray tower: experimental study and mathematical modeling[J]. Chemical Engineering Research and Design, 2016, 109: 180-189. doi: 10.1016/j.cherd.2015.11.027 [14] 武春锦, 吕武华, 梅毅, 等. 湿法烟气脱硫技术及运行经济性分析[J]. 化工进展, 2015, 34(12): 4368-4374. doi: 10.16085/j.issn.1000-6613.2015.12.039 [15] 但智钢, 史菲菲, 王志增, 等. 中国环境工程科技2035技术预见研究[J]. 中国工程科学, 2017, 19(1): 80-86. [16] 中华人民共和国自然资源部. 中国矿产资源报告[M]. 北京: 地质出版社, 2020. [17] 吴发富, 王建雄, 刘江涛, 等. 磷矿的分布、特征与开发现状[J]. 中国地质, 2021, 48(1): 82-101. doi: 10.12029/gc20210106 [18] NIE Y X, LI S, WU C J, et al. Efficient removal of SO2 from flue gas with phosphate rock slurry and investigation of reaction mechanism[J]. Industrial & Engineering Chemistry Research, 2018, 57: 15138-15146. [19] 杨加强, 梅毅, 王驰, 等. 湿法烟气脱硝技术现状及发展[J]. 化工进展, 2017, 36(2): 695-704. doi: 10.16085/j.issn.1000-6613.2017.02.041 [20] 贾丽娟, 张冬冬, 殷在飞, 等. 磷矿浆脱硫新技术及工业应用[J]. 磷肥与复肥, 2016, 31(3): 39-41. doi: 10.3969/j.issn.1007-6220.2016.03.015 [21] 马克猛, 杨林台. 用磷矿浆脱除湿法磷酸中过量SO3的研究及其应用[J]. 磷肥与复肥, 2012, 27(1): 23-25. doi: 10.3969/j.issn.1007-6220.2012.01.007 [22] 武春锦. 磷矿浆脱除燃煤锅炉烟气中SO2的研究[D]. 昆明: 昆明理工大学, 2015. [23] 吕武华. 动力波洗涤器用于磷矿浆脱除尾气二氧化硫的研究[D]. 昆明: 昆明理工大学, 2016. [24] 吴琼. 磷矿浆脱硫与磷矿脱镁协同机理研究[D]. 昆明: 昆明理工大学, 2018. [25] 李红林, 蒋世国. 磷精矿脱硫工艺在硫酸尾气处理中的应用[J]. 磷肥与复肥, 2016, 31(9): 7-10. doi: 10.3969/j.issn.1007-6220.2016.09.004 [26] 李红林, 刘海, 赵建勇. 磷矿浆脱硫技术的开发及工业应用[J]. 硫酸工业, 2017, 4: 39-42. doi: 10.3969/j.issn.1002-1507.2017.04.013 [27] NIE Y X, LI S, DAI J F, et al. Catalytic effect of Mn2+, Fe3+ and Mg2+ ions on desulfurization using phosphate rock slurry as absorbent[J]. Chemical Engineering Journal, 2020, 390: 124568. doi: 10.1016/j.cej.2020.124568 [28] NIE Y X, WANG X J, DAI J F, et al. Mutual promotion effect of SO2 and NOx during yellow phosphorus and phosphate rock slurry adsorption process[J]. AIChE Journal, 2021, 67(8): e17236. [29] FABIAN R, KOTSIS I, ZIMANY P, et al. Preparation and chemical characterization of high purity fluorapatite[J]. Talanta, 1998, 46: 1273-1277. doi: 10.1016/S0039-9140(97)00391-3 [30] LIU S Y, XIAO W D. Modeling and simulation of a bubbling SO2 absorber with granular limestone slurry and an organic acid additive[J]. Chemical Engineering & Technology, 2006, 29(10): 1167-1173. [31] KARATZA D, PRISCIANDRAO M, LANCIA A, et al. Calcium bisulfite oxidation in the flue gas desulfurization process catalyzed by iron and manganese ions[J]. Industrial & Engineering Chemistry Research, 2004, 43: 4876-4882. [32] MA X X, KANEKO T, TASHIMO T. Use of limestone for SO2 removal from flue gas in the semidry FGD process with a powder–particle spouted bed[J]. Chemical Engineering Science, 2000, 55: 4643-4652. doi: 10.1016/S0009-2509(00)00090-7 [33] LANCIA A, MUSMARRA D, PEPE F. Model of oxygen absorption into calcium sulfite solutions[J]. Chemical Engineering Journal, 1997, 66: 123-129. doi: 10.1016/S1385-8947(96)03168-3