Thermodynamics Analysis And Simulation Of Roasting Molybdenum Concentrates By Rotary Kiln

The oxidizing roasting process of molybdenum concentrate is of great importance in molybdenum metallurgical process, and inner-heated rotary kiln is widely used in China for roasting at present. A new technology, which is called carbon-free roasting, was first proposed and introduced in detail in this paper to cover the disadvantages of traditional technology, such as low content of MoO3, high energy consumption, a large amount of flue gas, low concentration of SO2in flue gas, etc. Then, exergy balance calculation is adopted for new technology, and the result is compared with that of heat balance calculation. In the end, mathematical model of heat transfer is made for studying heat transfer in rotary kiln.On the basis of technical analysis of traditional roasting process of molybdenum concentrate, the new technology of carbon-free roasting is proposed. The key technology and innovation of it is using heat exchanger for heat transfer, which means that by heat exchanger installed in rotary furnace, air is used as heat carrier to take heat from main reaction zone and then to supply heat for desulfuration, so desulfurization reaction can fully occur. Finally, economic effects and prospect of the new technology is summarized.In order to find out the situation of energy flow in rotary kiln and the direction for energy saving in the future, according to previous heat balance test and analysis, exergy balance test and analysis is adopted for the new technology. Method of calculation for exergy balance in new technology is proposed. The results indicate that chemical exergy, brought into system by molybdenum concentrate, is the major input which accounts for99.85%of total; the output of exergy includes physical exergy of molybdenum oxide, chemical exergy of molybdenum oxide, physical exergy of flue gas, chemical exergy of flue gas, which accounts for5.32%,7.65%,30.96%and34.04%respectively; chemical exergy of flue gas is the largest output. The results of heat balance analysis and that of exergy balance analysis are compared and analyzed so that energy flow in rotary kiln is clarified. This is the theoretical basis to find the direction for energy saving in the future.In order to clarify the heat transfer regulation and the impact of operating parameters in new technology, mathematical model of heat transfer in rotary kiln is made. By the model, heat transfer in rotary kiln is analyzed and regulation of complicated heat transfer process in rotary kiln is clarified. The calculation results indicate that in preheating section, what play a leading role in temperature raising of material is convection heat transfer between gas and material and comprehensive heat transfer between material and covered kiln wall, while the amount of radiation heat exchange between gas and material and that between kiln wall and material is relatively small. The impact of major operating parameters on heat transfer in rotary kiln is discussed, and conclusions include that when mass flow rate of material is increased, temperature of flue gas and that of material both decrease; heat transfer between gas and material and that between kiln wall and material can be obviously enhanced when rotational speed of rotary kiln is properly increased. These work can be helpful to make complete mathematical model of roasting molybdenum concentrate by rotary kiln and to optimize the process.