Thermodynamic analysis and engineering practice of high efficiently recycle of fluorine contained in tail gas from wet-process phosphoric acid plant

doi:10.11949/0438-1157.20241192

Abstract

Abstract:

For the extraction-concentration and tail gas washing fluorine release process of wet phosphoric acid, the gas-liquid distribution ratio of fluorine element under thermodynamic equilibrium of H₂SiF₆-H₂O and H₂SiF₆-H₃PO₄-H₂SO₄-H₂O systems was established, and the model prediction error was within 20%. Based on the thermodynamic analysis, reducing the tail gas washing temperature can increase the mass transfer driving force, improve the mass transfer rate of fluorine absorption and produce high concentration fluorosilicic acid solution, but the condensate water increases, which increases the water balance pressure of the system. A 75000 t P₂O₅/a WPA tail gas emission reduction and resource utilization project was designed and implemented. The unit operation of concentrating fluorosilicic acid by flash evaporation without pump was connected in series in the fluorine absorption circulating circuit. The low temperature and high concentration fluorosilicic acid is used to absorb and cool the tail gas below 323 K to make the fluorine-containing tail gas supersaturate and condense, which not only enhances absorption of the tail gas fluoride, but also avoids the loss of fluidity due to the agglomeration of silica particles. The results show that the fluorine content in tail gas is ≤2 mg/m³, the recovery of fluorine in tail gas is ≥99%, the total emission reduction of tail gas is more than 20%, and the H₂SiF₆ is ≥18%(mass) in the fluorosilicic acid product. An engineering example of high efficiently recycle of fluorine contained in tail gas from wet-process phosphoric acid plant is provided.

Key words: wet-process phosphoric acid, fluorine, gas-liquid distribution ratio, tail gas, recycle, engineering practice

摘要：

针对湿法磷酸萃取-浓缩和尾气洗涤氟逸出过程，建立了H₂SiF₆-H₂O与H₂SiF₆-H₃PO₄-H₂SO₄-H₂O体系热力学平衡下的氟元素气液分配比，模型预测误差在20%之内。基于热力学分析，降低尾气洗涤温度，可增加传质推动力，有利于提高氟吸收传质速率和产出高浓度的氟硅酸溶液，但冷凝水增多，加大了系统水平衡压力。在氟吸收循环回路串联无泵循环闪蒸浓缩氟硅酸的单元操作，设计并实施了7.5万吨P₂O₅/年WPA尾气减排与资源化利用项目，用低温、高浓度氟硅酸逆流吸收并冷却尾气低于323 K，使含氟尾气过饱和冷凝，既强化尾气氟化物吸收，又避免硅胶颗粒结块丧失流动性，使尾气氟含量≤2 mg/m³，尾气氟回收率≥99%，尾气总量减排20%以上，氟硅酸产品H₂SiF₆≥18%（质量），提供了一个湿法磷酸含氟尾气高效资源化利用的工程范例。

关键词: 湿法磷酸, 氟, 气液分配比, 尾气, 资源化, 工程实践

CLC Number:

TQ 028.8

Ji LI, Jiacai WANG, Yongqiang MA, Haibin YUAN, Luming JIAN, Jican JIANG, Jiahua ZHU. Thermodynamic analysis and engineering practice of high efficiently recycle of fluorine contained in tail gas from wet-process phosphoric acid plant[J]. CIESC Journal, 2025, 76(4): 1484-1492.

李季, 王佳才, 马永强, 袁海斌, 简路明, 姜基灿, 朱家骅. 湿法磷酸含氟尾气高效资源化利用热力学分析与工程实践[J]. 化工学报, 2025, 76(4): 1484-1492.

Figures/Tables 6

Fig.1 Comparison of model predicted and experimental values of fluorine vapor-liquid equilibrium

Fig.2 Thermodynamic analysis of WPA fluorine emission

Fig.3 Engineering practice of 75000 t P2O5/a WPA tail gas fluorine emission reduction and utilization

Fig.4 Thermodynamic analysis of the defluorination process of tail gas containing fluorine in WPA

Fig.5 Defluorination efficiency and fluorine content of 75000 t P2O5/a WPA tail gas

Table 1 Economic analysis of 75000 t P2O5/a WPA tail gas emission reduction and utilization project

项目	原系统	新系统
氟硅酸产品浓度/%（质量）	≤13	≥18
氟回收率/%	≤70	≥99
循环洗液温度/K	338~343	313~318
清理人数	25	0
尾气氟含量/(mg/m³)	10	≤2
系统清理周期/d	5	7
清理费用/（万元/年）	24.88	0
新增产品收益/（万元/年）	—	20.98

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