A Research And Development Of A New Suspension Process With High Solid-gas Ratio For The Treatment Of Ammonium-sulfate-residue

Ammonium sulfate residue is the processing particulate solids as generated in utilization of phosphogypsum to produce ammonium sulfate.Such particulate solids are small in particles size（about 42μm in mean size）,high in moisture but complex in chemical compositions;how to handle and re-use such complex residue has always been challenging.Based on the high solid-gas ratio suspension preheating&decomposition theory,efforts were made in this thesis to develop an industrial scale production line to produce a high-quality active lime by decomposing Ammonium sulfate residue.This production line can be used as new technology applicable to process different residues such as active Ca O.The main work as carried out in the thesis includes:analysis of raw material and fuel’s effects on decomposition of residue;investigation of equipment structures as required for residue decomposition based on the thermal calculations–a combination of processes with preheating unit,decomposition apparatus and cooling unit were then proposed;comparison of various factors affecting the residue decomposition process–these factors were then optimized as optimum specifications,and adopted as a basis for the equipment design.As a result,a new type of device and technology for ammonium sulfate residue decomposition was developed;an industrial scale production line was built.In addition,general plan and procedures were determined according to condition on the site to conduct complete measurements along the production line in order to verify the design parameters,with which energy consumption in the line was assessed.A technical feasibility was also discussed to apply this newly-developed technology to the conventional lime production industry.The main conclusions from the study are given as follows.（1）The main characteristies of ammonium sulfate residue are close to cement raw materials,which contain lower Ca CO₃ and higher moisture,its moisture content can reach to 25%.These characteristics determine that the active lime roasting system can refer to the cement preheater,and also the structure needs to carry out targeted improvements.（2）Calculation from thermal analysis showed that a production line consisti ng of a two stages high solid-gas ratio suspension preheating unit,a decomposit ion apparatus and a three stages cooling unit can be expected to get optimum o perational conditions.The heat consumption in such system is estimated about 3912.3 k J/kg product;temperature of C1 outlet can be controlled at 170℃,an d the temperature of product can be reduced to 207.2℃.（3）The newly-designed decomposition production line is simple in its design,fulfilling within it a whole process of residue drying,residue decomposition and product cooling to get high activity,high-quality lime products;no extra specific drying equipment or rotatory kiln is required.The production line was stable in operations,and appeared to be advanced in some key aspects:high activity of Ca O,with a Ca CO₃ decomposition rate greater than 97.7%,a mass fraction of effective product Ca O 59%and a low heat consumption of 4402k J/kg product.（4）Assessment based on the on-line measurement and reverse engineering analysis results showed that the design parameter for each single device is appropriate;water evaporation intensity is high and the temperature of product can be less than 100℃.The separation efficiency and heat transfer efficiency between the preheating and cooling unit correlated in optimum.（5）This process can be adopted in limestone industry with some modifications.Such a process can be applied in a large scale to produce highly active Ca O,with a heat consumption as predicted around 4131.7k J/kg product,and it is much more stable as well.