The Study On Lignite Upgrading And Release Characteristics Of Volatiles During Rapid Pyrolysis

Lignite is one kind of low rank coal, and has the characteristics of high inherent water, high volatile, low heat value, strong chemical activity, poor thermal stability etc. What’s more, lignite is easy to be weathered, fragmented and has a risk of spontaneous combustion. Therefore, lignite is not fit to transport for long distances, and often combusted directly at power plants near the coal mines, thus don’t obtain more effective application for a long time. However, there is a large reserve of lignite in China, with the coal resources is becoming more and more deficient, the efficient utilization of lignite have attracted ever-increasing attentions.First of all, three kinds of lignite were dewatered and upgraded by hydrothermal treatment under high temperature and high pressure conditions and evaporated directly in the tube furnace respectively. Compared with the evaporation dewatering technology, the experimental results show that non-evaporation hydrothermal treatment can effectively decrease the inherent water in coal, volatile and oxygen content, also increase the fixed carbon content and heating value, eventually make lignite rank elevate gradually, thus improve the comprehensive utilization value of lignite substantially.The coal macerals, pore structure, micromorphology etc physical and chemical properties has been performed comprehensive analysis and comparison between the raw lignite and upgraded lignite. The experimental results show that hydrophilic oxygen-containing functional groups reduced constantly, aromatic carbon structure increase gradually after dewatering and upgrading. Compared with the single heating effect of evaporation upgrading technology, the synergistic effect of high temperature and pressure hydrothermal treatment make lignite rank elevate more significantly. Dewatering and upgrading makes the lignite pore size distribution gradually develop towards the microporous direction. And surface area, average pore size and pore volume show different degrees of downward trend respectively. The upgraded lignite whose micromorphology has also changed a lot, for instance, the surface becomes chiseled, the structure becomes more compact, and coal quality becomes dense up. The rapid pyrolysis experiments were performed to investigate respectively the effect of final pyrolysis temperature and upgrading temperature on release characteristics of low molecular volatiles during lignite pyrolysis at5000℃/s. The experimental results show that CO and CO2are both the main components of the pyrolysis gas for law lignite and upgraded lignite, while the contents of H2and CH4are much lower. When the final pyrolysis temperature is1000℃, the low heating value of pyrolysis gas is the highest. For the hydrothermal treatment, the low heating value of pyrolysis gas goes up constantly with an ascent in the final reaction temperature, however, it shows a slight upward trend for the evaporation upgrading technology.Also, the rapid pyrolysis experiments were performed to investigate release characteristics of large molecular volatiles about upgraded lignite at5000℃/s. As the hydrothermal treatment final reaction temperature climbs, it is found that the aliphatic hydrocarbons, acids and phenolic substance content reduces, while the aromatics content increases gradually. The alcohols content of the raw coal pyrolysis products is very low, during dewatering and upgrading its content overall show upward trend, but it is still very low. Moreover, esters show no obvious regularity.