Optimized Control On Production Index For Sulphuric Acidusing Smelting Off-gas On A Scale Of 1.60 Mt Annual

With the rapid development of domestic high concentration phosphate fertilizer and phosphate compound fertilizerindustry, the demand on sulfuric acid is increasingly growing. The location of Guangxi Jinchuan(Fangchenggang) project is adjacent to Yunnan Province, Guizhou Province and Sichuan Province which are the concentrated production area of phosphorite, and this is also the area in China which consumes large quantities of sulfuric acid. About 2600 kt/a solid sulfur is imported through Fangchenggang Port and transported to the area mentioned above for sulfuric acid production and local sales.Fangchenggang 400 kt/aelectrolytic copper project constructed by Jinchuan Company in 2013 appliesdouble flash furnaces smelting technique. SO2 content in the off gas from the melting process may reach 30%-35%, which is the effective resource for acid making. As a sub project of copper smelting project, the capacity of the metallurgical acid plant has reached 1600 kt/a.Considering complicated off gas composition and diverse impurity substance in off gas and absorbing experience of metallurgical acid making at home and abroad, this project introduces the latest technologies of high SO2 conversion plus conventional “3+2” conversion, Heat Recovery System, the absorption of tail gas by ionic liquid circulation and so forth. Given part of these technologies are applied for the first time, how to digest and absorbnew process knowledge and how tooperate new equipment and instruments in order to implement process control and optimizeproduction organization have become the primary problems after the construction of project was completed and put into operation. During pilot production, the control of process index was so unstable that actual process index exceeded the standard, which made negative effects on the whole system. Therefore, it is necessary to optimize the control of process index in order to efficiently operate and manage acid making system and to reach the design capacity and standard as early as possible.This paper, after gathering a large quantity of statistics on the process control parameters and operation data as well as combining the theoretical knowledge of the gas cleaning, drying, absorption and heat recovery,aims at studying the optimization of process control parametersand summarizing the best operating value of key process index on this sulfuric acid production system, such as sulfur dioxide recovery rate of the gas cleaning, conversion rate, absorption rate and the SO2 emission. After optimization of process control, the process effect has been obtained as follows:1) The relative impurity substance content in outlet process gas of Stage 2 west electric static precipitator shall be controlled: acid mist≤3mg/Nm3、F≤0.25 mg/Nm3、As≤0.6 mg/Nm3. The rate of qualified product of sulfuric acid shall reach 100%, which increase by 3%compared with that index before optimization.2) Through adjustment of temperature of pre-exchanger, the inlet temperature of exchanger and heat exchange between every exchanger, conversion could be completely controlled more than 99.95% and total absorption≥99.98%. As a result, compared with index before optimization, both conversion and total absorption increase by 0.05%、0.08% respectively.3) The process of tail gas desulphurization applies “absorption of SO2 by ionic liquid circulation” technology. The amount of ionic liquid circulation is 35m3/h, temperature of absorption solution is 45℃, temperature of regeneration is 110℃, rate of desulphurization is more than 95% and SO42- content in absorption solution is 100g/l as tail gas discharge which reaches the requirement of environmental protection. As a result, compared with index before optimization, the amount of SO2 discharge decreases by 50%.It is optimization of process control that makes the relative parameters and index in the leading level nationwide, which plays not only a positive role in promoting this project to reach the design capacity and standard, but also a good model for acid making by the high SO2 concentration off gas from the smelter.