Study On Some Basic Problems In Chemical Reactor Scale-up

The gasification is the core and the key of the technologies to realize theclean utilization of coal. Two-stage gasifier has many characteristics, such as awide adaptability of coal, low oxygen consumption, high carbon conversion,environmental friendly, and so on. And these make the technology have apromising prospect. However, the two-stage gasifier has not been utilized inindustrialization. That is mainly because of the influence of many factors, suchas the complex gasification reactions. It is necessary to investigate the effects ofvarious factors on the gasifier performance. And it is the guarantee to realize thelong-term and stable operation of gasifier. Compared with the traditional methodof experiment, the model is an effective method to research the gasificationperformance of the two-stage gasifier. Therefore, we investigate the effects ofvarious operational parameters on the gas composition, temperature and gascomposition in different regions. It is of important theoretical value for theoptimization of operating conditions, the regulation of gas composition, and thedesign of industrial reactor.In this paper, based on the hydrodynamics properties, the gasifier is dividedinto different regions, and then the equivalent model is established. By using themodel, we investigate the gasification performances, such as the gascomposition, carbon conversion and so on, under various operating conditions. It is helpful to deepen our understanding of gasification process in the gasifier.The specific conclusions are as follows:1. Based on the hydrodynamics properties, we establish an equivalentmodel of gasifier by introducing the jetting diameter. This method solves theproblem that we usually treat the reactor as a whole. So the model can reflect thechanges of properties of different regions in the gasification process. Manyfactors, including the structure of gasifier, the properties of feed, reactions andso on, are considered in the process of establishing model. So the model canreflect the real process in the gasifier. The simulation results are in goodagreement with the experimental data, which validates the rationality of themodel.2. By using the model, we investigate the effects of the operatingparameters of first-stage, including coal feed rate, oxygen feed rate and steamfeed rate, on the gasifier performance. The results show that the operatingparameters of first-stage have a critical effect on the gasifier performance,especially the coal feed rate and oxygen feed rate, which have great influenceson the temperature, carbon conversion and gas composition. And this is mainlydue to the changes of gas temperature and unreacted carbon content. Therefore,in order to realize the stable operation of the gasifier, we should properly adjustthe operating parameters to ensure the temperature of the gasifier above the ashmelting point, and more attention should be paid to the first-stage in the gasifierscale up.3. The jetting zone is critical to lower the temperature of the product gas.With different operating conditions of second-stage, the heat loss of ash andreactor wall of first-stage changes. When the coal feed rate raises from190kg/hto310kg/h, the temperature of first-stage drops only3.34K，which has littleeffect on the gas composition and carbon conversion of first-stage, and the temperature of second-stage drops37.67K. When the steam feed rate raises from25kg/h to125kg/h, the temperature of second-stage drops64.15K. Temperatureis a key factor to influence the gasifier performance. And observing the changesof temperature of outlet, it can be concluded that the changes of operatingconditions of second-stage have a little influence on the carbon conversion andgas composition. So the thermochemical characteristics are mainly consideredwhen we adjust the parameters.