Experimental Study On Release Characteristics Of Alkali And Alkaline Earth Metals During Biomass Rapid Pyrolysis And Gasification

Biomass is a kind of clean and renewable energy which is abundant in the world. The thermal utilization of clean biomass energy is an important means of energy saving and pollution reduction. It's also an important aspect of the comprehensive utilization of energy and resource in the countries all over the world. The pyrolysis and gasification are two main methods of biomass thermo-chemical utilization. The alkali and alkaline earth metals (AAEMs) play an important role during the utilization of biomass which are rich in AAEMs. Quantitative analysis of the AAEMs is made during the pyrolysis /gasification process of biomass for further understanding the precipitation process of the AAEMs which can provide basic evidence for the solution of the AAEMs problem.The phenomenon of agglomeration, sintering, sedimentation, erosion and so on which caused by the alkali/ alkaline earth metal is discussed in the thesis, as well as the catalysis of the alkali/ alkaline earth metal. At the same time, the detection technologies of the alkali/ alkaline earth metal at present are summarized, and some research results about the precipitation and transportation of the alkali/ alkaline earth metal during the thermo-chemical conversion process are introduced in the thesis. The limitation of the research in this field is analyzed, and on the base of the analysis we put forward the research ideas which are clarified as follows.Four kinds of typical biomass are chosen as the samples for the research, and the basic characteristics of the samples are tested. The samples are pretreated with the low-temperature ashing instrument and then the amount of AAEMs is tested. By comparing the testing results of the original and ashed samples, we find that the amount of AAEMs in ashed samples is a little lower than that of original samples. In order to make the results more exactly, we could test the original samples directly instead of getting pretreated.The rapid pyrolysis and gasification experiments of biomass are taken on the fixed-bed reactor, and the residual chars collected during the progress are tested. The results are shown as follows: As the increase of conversion rate in the rapid pyrolysis progress of biomass, the release of alkali metals terminates at levels of 70-80% in a short period of time, while that of alkaline earth metals terminates at levels of 20-40%. During the gasification of the char in steam, the release of AAEMs is so little which suggests that very significant volatilization of any of the major AAEMs does not occur during the gasification progress.