Process Design And Experimental Study On Preparation Of Magnesium Oxide From Bischofite By Spray Pyrolysis

In this paper, bischofite is used as raw materials to produce magnesium oxide by spray pyrolysis process which is simple, high product purity and environment friendly. According to the thermal decomposition mechanism of bischofite, experimental data and basic operation parameters, process design of the spray pyrolysis process was carried out. Under the condition of processing amount of 10L/h, hot air temperatures were 700℃ before and 300 ℃ after the reaction, results are as follows:the yield of magnesium oxide is 1.82kg/h, the energy consumption is 42389.6 kJ/h and the structure of the reactor with diameter D=0.83m and height H=2.8m. Other parts and equipment of the entire process such as atomizer, fluid transportation machinery, combustion and control system structure, cyclone separator and falling film absorption tower are also designed or selected.Combined with the process design, experimental study on preparation of magnesium oxide from bischofite by spray pyrolysis is also conducted. By changing the temperature, processing amount and other parameters, the particle size distribution of product and temperature distribution within the reactor are obtained. XRD, SEM and other means are used to characterize the product to find the optimal conditions- under the temperature of 730 ℃ at the combustion zone and processing amount of 4L/h, high purity magnesium oxide particles with an average particle size of 100μm are obtained. And some whisker with a length of 30μm are found near the middle zone of the reactor under the temperature of 400 ℃, which proved to be Mg2(OH)3Cl·4H2O, an intermediates.CFD numerical simulation is also used to study the atomization process and the flow and thermal fields within the reactor. The influence of pressure(0.3Mpa,1.5Mpa,5MPa) and fluid properties(water, ethanol, fuel oil) on atomization are conducted, results show that increasing the pressure in a certain range helps atomization and get best under pressure of 1.5Mpa, while the viscosity increase is not conductive to atomization and movement of droplets. Simple flow and thermal field within the reactor is also got. Results shows a good consistency with experiment’s and three zones with an average temperature of 900K,770K,720K (at the inlet temperature of 1200K) along the axis direction. All of these will provide basic models and parameters for nozzle selection, reactor structural optimization and simulation of the entire process with considering of heat and mass transfer, droplet coalescence, collision, etc.