An Investigation Into The Calcination Of Cement Clinker By Coarse Particles Fluidization-Thermo Dynamics Of The Calcination Process

Cement is used in civil engineering in largely quantity,existing cement production technologies consume energy resource excessively in some degree.The energy shortage becomes more and more severe all over the world,so it is necessary to develop new types of cement production technology with low energy consumption and high thermal efficiency.The Coarse-Particle-Fluidized-bed technology,which turns clinker calcinations from stack- to suspending-state,suggested by the Institute of Powder Engineering of Xi'an University of Architecture and Technology.The technology has been explored for many years,and various schemes and facilities have been tested.In the period from June 2007 to May 2008,a new type of fluidization bed of laboratory was designed and built.On the basis of experiments carried out in the previous projects,the author studied the behavior of the meal pellets under high temperature condition,including heating, limestone decomposition,and burning of the coal contents in the meal pellet.In addition, mechanisms of fragmentation of pellets and agglomeration between pellets under high temperature were analyzed,and the measures to circumvent these difficulties were suggested as well.Then the experiment for clinker calcinations under high temperature was carried out by using a high-temperature-fluidized-device of pilot scale.The experimental results indicated that time required for the complete decomposition and combustion of the meal pellet decreased with increasing in gas temperature and velocity and decreasing in pellet size as well.It was found that to prevent pellets from fragmentation in an unaccepted level,the temperature in preheating zone should be lower than 600℃.The retention time of pellets in preheating zone should be about 5 minutes for improving thermal efficiency;in order to reduce the temperature of gas entering preheating zone,the retention time of pellets in decomposition and precalcination zone should be about 7 minutes.The approaches for reducing probability of the pellets agglomeration occurrence include: adopting pellet wrapped,increasing the gas velocity in the fluidized bed under high temperature,optimizing the system configuration.The experiment under high temperature was carried out after improving the experimental facilities.The fluidization of pellets of in the bed was successfully initiated by following steps:●Heating the bed body for 2 hours at about 1000℃;●Feeding pellets followed by increasing gas velocity,then repeating the operation step by step until pellets in the bed was enough.The mass flow rates to each of the sections in the whole height of the device were determined by mass balance.From the experimental results,the optimum operation parameters were recommended for future experiment under high temperature.