Decomposition Characteristics Of PG And Its Fluidization Decomposition Process For Producing Sulphuric Acid And Lime

The rapid development of phosphorous chemical industry brings about two problems, which are the comprehensive utilization of phosphogypsum(PG) and the quick increase of sulphuric acid demand. Thus, PG fluidization decomposition process for producing sulphuric acid and lime is proposed, which is a good way to solve the two ploblems mentioned above. The research of decomposition characteristics of PG and its fluidization decomposition process is carried out.Firstly, XRD, XRF, laser particle size analyzing and high temperature microscope tests were used to study the basic characteristics of PG. The results showed that the main mineral composition of PG is CaSO4·2H2O, which is more than 90%, and the content (dry basis) of CaO and SO3 is about 30% and 35～45% respectively, which shows it is a high-quality raw materials for sulfuric acid and lime generation. Besides, particles with the size≤0.075mm are more than 91.25%, so the raw material may be directly used to produce acid after being crushed and dried. Also, the results showed that the impurity in PG causes the lowering of melting point to approximately 1280℃, and liquid phase may occur after 1200℃, which differs with the variation of impurity content.Secondly, HSC Chemistry was used to study the reactions in the reductive decomposition of PG. The results of thermodynamic calculation showed that CO and carbon both lower initial decomposition temperature and theoretical heat consumption. However, CaS is easily generated under low temperature conditions. Therefore, the formation of CaS should be avoided in the course of low-temperature pre-heating of PG.Thirdly, thermal analysis was used to study PG decomposition course and phase change law. The results showed that the impurity in PG lowers its initial decomposition temperature and promotes the decomposition. In the nitrogen atmosphere, coke dose has a great influence on the decomposition result of CaSO4. The main product is CaO in the case of C/S=0.5, while CaS becomes the main product in the case of C/S=2. Under the condition of high than1100℃, O2=3%, CaS can be slowly oxidized to CaO, releasing SO2. Fourthly, high-temperature atmosphere furnace tests were used to study the decomposition characteristics of PG in decentralized state. Under the condition of 1000℃～1100℃,3%～5% CO,25%～30% CO2, and 20min of decomposition time, decomposition degree can reach 95% while desulfurization degree can exceed 85%. An Infrared Sulfur Analyzer is set to study PG decomposition. The desulphurization degree of PG can be obtained quickly, conveniently, continuously and accurately with Infrared Sulfur Analyzer. The desulphurization degree equation of PG thermal decomposition isα=Vmax(?), in which, theκvalue is a useful parameter to predict the reaction time of complete decomposition. Under a condition of 1000℃, 3%CO and 15min of decomposition time, desulfurization degree can reach 75%. At 1150～1200℃, the desulfurization degree can quickly exceed 90% if proper amount of O2 is added because of the oxidizing reaction of CaS.The technological requirements of PG fluidization decomposition process for producing sulphuric acid and lime is obtained on basis of decomposition characteristics of PG. Then, the critical process is designed according to the technological requirements. Lastly, the feasibility of this process is analysed.