Spouted Bed Reactor Dry Preparation Of Ultrafine Calcium Carbonate Process

The conventional process to manufacture the ultra-fine CaCO3 powder is to introduce carbon dioxide (CO2) gas into calcium hydroxide (Ca(OH)2) slurry to produce CaCO3 by reactive precipitation. The precipitated CaCO3 is then dried, pulverized and classified to produce as final dry powders. Apparently, this process is composed of several operation steps, and the complexity of the process causes difficulty in controlling the operating conditions to be suitable for the powder product. Although carbonation reaction is a fast ion reaction, in fact, the precipitation operation takes a very long time because the reactants were coated by reaction product. Therefore, to develop a new process with less operation steps is very important to the production of the ultra-fine powders.Spouted bed owing to its excellent properties in heat and mass transfer between particles and gas play an important part in the drying and chemical process.In accordance with the characteristics of the carbonation reaction and the spouted bed, a new process to produce the ultra-fine CaCO3 powders was developed by using a powder-particles spouted bed (PPSB). In this process, the powder-particle spouted bed (PPSB) was used as a reactor in which gas involving CO2 was reacted to Ca(OH)2 slurry, and the producted CaCO3 powders were simultaneously dried by the hot gas. This process supplies a method to produce dry fine particles simultaneously. Experiments were carried out in a spouted bed with a 42mm diameter to study the effects of theoperating conditions on conversion of Ca(OH)2 and properties of the powder product. In a two-dimensional spouted bed, using glass bead and millet as experimental materials, we had surveyed the effect operation parameter ( static bed height, spouting velocity ) and the properties of experiment materials on hydrodynamics of two-dimensional spouted bed, which include bed pressure drop, minimum spouting velocity and voidage distribution. The following resulting were obtained:(1) Under the present experiment condition, powder product with average diameter 80 nm, calcium hydroxide conversion over 90% and moisture content below 0.15% had been achieved.(2) Based on the experimental results, a model considering various operating condition was developed for calcium hydroxide conversion in spouted bed.The conversion of Ca(OH)2 calculated from this model agrees well withexperiment data. The equation for carbonation reaction kinetics was obtained:(3) With increases in spouting gas velocity, there are four successive regimes found in the two-dimensional spouted bed, namely: fixed bed regime, beginning spouted bed regime, spouted bed regime and jetting spouted bed regime.(4) By regressing the experimental data, the correlation used to calculate the minimum spouting gas velocity was obtained:...