Upgrading of coal tar from fast pyrolysis of Shenmu bituminous coal by nascent char

The tar from the pyrolysis of coal at relatively low temperature can be used to produce liquid fuel or highvalued fine chemicals. One of the key technologies for the industrialization of pyrolysis tar production is improving the tar yield and quality. As one of the main intermediate products of coal pyrolysis reaction system,the char used for improving the tar from coal pyrolysis has attracted wide attention. The volatiles from the fast pyrolysis of Shenmu bituminous coal (SM) in the free fall reaction section of the pyrolysis reactor were upgraded over the nascent char (in-situ char) in the downstream moving bed upgrading reaction section. The effects of char bed temperatures and heights on the tar upgrading at a steady state were studied. The results show that the nascent char reduces the formation of asphaltene obviously and thus improves the quality of tar compared with that without char-volatiles interaction. When the char bed height is 3 cm and the char bed temperature is lower than 610℃,the yield of light tar remains almost unchanged,the contents of phenol and other aromatic O-containing compounds in the light tar decrease and the contents of benzene and naphthalene aromatic hydrocarbons increase. When the char bed temperature is higher than 610℃,the poly-condensation of the gas phase is enhanced,which would adversely affect the tar quality. The yield of asphaltene shows a slightly decrease trend and the light tar yield changes little by further increasing the char bed height. After reacting with the volatiles,the yield of char increases and the specific surface area of the char decreases. The results show that the use of nascent char to modify the coal tar is beneficial to reduce the formation of heavy tar in-situ during pyrolysis,which can effectively delay or restrain the coking and blockage of the equipment in the subsequent treatment process. This work provides a theoretical guidance for the clean and efficient utilization of low rank coal through the pyrolysis at a relatively low temperature,so as to realize the directional conversion to the target products.